UNIVERSITÉ DE LIÈGE UNIVERSITÉ DE LIÈGE UNIVERSITÉ DE LIÈGE UNIVERSITÉ DE LIÈGE APPLIED SCIENCES FACULTY DESIGN AND TESTING DESIGN AND TESTING DESIGN AND TESTING DESIGN AND TESTING OF THE PRESSURE PAYLOADS AND DATA OF THE PRESSURE PAYLOADS AND DATA OF THE PRESSURE PAYLOADS AND DATA OF THE PRESSURE PAYLOADS AND DATA ACQUISITION OF ACQUISITION OF ACQUISITION OF ACQUISITION OF QARMAN QARMAN QARMAN QARMAN CUBESAT CUBESAT CUBESAT CUBESAT Thesis submitted in partial fulfilment of the requirements for the degree of Master in Aerospace Engineering by: Roger TORRAS NADAL Advisor: Prof. Gaëtan Kerschen Jury composed of: Dell'Elce L., Rochus P., Verly J., Broun V. Academic Year 2012/2013
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UNIVERSITÉ DE LIÈGEUNIVERSITÉ DE LIÈGEUNIVERSITÉ DE LIÈGEUNIVERSITÉ DE LIÈGE
APPLIED SCIENCES FACULTY
DESIGN AND TESTINGDESIGN AND TESTINGDESIGN AND TESTINGDESIGN AND TESTING
OF THE PRESSURE PAYLOADS AND DATA OF THE PRESSURE PAYLOADS AND DATA OF THE PRESSURE PAYLOADS AND DATA OF THE PRESSURE PAYLOADS AND DATA
ACQUISITION OF ACQUISITION OF ACQUISITION OF ACQUISITION OF QARMANQARMANQARMANQARMAN CUBESATCUBESATCUBESATCUBESAT
Thesis submitted in partial fulfilment of the requirements
for the degree of Master in Aerospace Engineering by:
First of all, a basic frame of the whole configuration and the data and power connections
between the different units is given in
De-orbiting System) is connected by dashed lines due to it will be only necessary during panel
deployment in Phase 2 (from 330 km to 120 km of altitude).
Figure
2.1.1.2.1.1.2.1.1.2.1.1. Attitude determination and control subsystemAttitude determination and control subsystemAttitude determination and control subsystemAttitude determination and control subsystem
This subsystem is tasked with identifying the location and the orientation of the satellite at all
times during the orbit as well as changing the orientation of the satellite. QARMAN will be
stabilized in orbit using the drag force of the
QARMAN design and payloadQARMAN design and payloadQARMAN design and payloadQARMAN design and payload
The purpose of this section is to be a summary of what QARMAN is. This way, according to the
irements compliancy table for QB50 mission, it has been developed a preliminary design
for the subsystems of this CubeSat, which are going to be described in the following section.
Following a proper spacecraft design and sizing, next step is going to be the definition of the
budgets of mass, power and data. They all will give precious information for the preliminary
design made by QARMAN team, which will be the starting point of an iterative process.
Once the general configuration of the satellite is defined, the set of aerothermodynamic
payload suited in this CubeSat will be also presented. However, the aim of this project is to
specifically design only two of these payloads, which are going to be commented in detail. By
the end of this section, it is expected to understand the basic aspects of QARMAN platform to
properly start with the payload design.
First of all, a basic frame of the whole configuration and the data and power connections
between the different units is given in Figure 3. Note that AeroSDS (Aerodynamic Stabilization
is connected by dashed lines due to it will be only necessary during panel
hase 2 (from 330 km to 120 km of altitude).
Figure 3. System overview with power and data bus [5]
Attitude determination and control subsystemAttitude determination and control subsystemAttitude determination and control subsystemAttitude determination and control subsystem
This subsystem is tasked with identifying the location and the orientation of the satellite at all
orbit as well as changing the orientation of the satellite. QARMAN will be
stabilized in orbit using the drag force of the AeroSDS. By controlling the surface exposed to
9
The purpose of this section is to be a summary of what QARMAN is. This way, according to the
irements compliancy table for QB50 mission, it has been developed a preliminary design
for the subsystems of this CubeSat, which are going to be described in the following section.
he definition of the
budgets of mass, power and data. They all will give precious information for the preliminary
design made by QARMAN team, which will be the starting point of an iterative process.
ned, the set of aerothermodynamic
payload suited in this CubeSat will be also presented. However, the aim of this project is to
specifically design only two of these payloads, which are going to be commented in detail. By
ected to understand the basic aspects of QARMAN platform to
First of all, a basic frame of the whole configuration and the data and power connections
(Aerodynamic Stabilization
is connected by dashed lines due to it will be only necessary during panel
This subsystem is tasked with identifying the location and the orientation of the satellite at all
orbit as well as changing the orientation of the satellite. QARMAN will be
. By controlling the surface exposed to
10
the residual atmosphere, it is possible to change the magnitude of the atmospheric drag
affecting the CubeSat and therefore, it is possible to control the trajectory of the spacecraft.
Thus, AeroSDS aims to be an attitude control method in order to provide the required orbital
conditions at 120 km. This system will be located at the end of the CubeSat structure,
displacing the gravity center downstream and leading to a stabilizing moment.
However, AeroSDS is not going to be the only attitude control system. This way, a set of active
ADCS instruments are included in the subsystem. They can be seen in Table 2. At the early
stages of the mission the active ADCS will only be needed for detumbling4 with little
requirements on the pointing accuracy during mission Phase 0. After this, QARMAN should be
stabilized and pointing into flight direction, getting ready for the deployment of the AeroSDS.
Following deployment the ADCS is only needed for attitude and position determination in-orbit
and during re-entry.
Instrument Quantity Definition
Magnetotorquers 3 It generates a magnetic field which interacts with the ambient magnetic field, providing a torque to change
orientation
Reaction wheels 3 This system change the orientation of the CubeSat
around its center of mass thanks to the torques generated with the rotation of these wheels
Star tracker 1 It is an optical device that measures the position of
stars using a small camera
Gyroscope 1 It senses the rotation in the three-dimensional space
without any observation of external objects
Accelerometer 1 This device measures proper acceleration of the
CubeSat
Magnetometer 1 It measures the magnetic field values at the present
point
GPS receiver 1 This device is able to provide accurate position
determination at any time Table 2. Set of active ADCS instrumentation
2.1.2.2.1.2.2.1.2.2.1.2. Electrical power subsystemElectrical power subsystemElectrical power subsystemElectrical power subsystem
It provides conditioned power to all spacecraft and payload subsystems and components. They
are designed and size for the mission end of life. The critical phase for QARMAN is going to be
the re-entry (from 120 km to 50 km of altitude), where the CubeSat will completely run on
battery power. This phase will last around 600 seconds, but in the worst case solar panels will
stop charging batteries half orbit before arriving at 120 km of altitude due to eclipse. Hence, it
is required to the system to provide power at least during 45 minutes (35 minutes the half
orbit + 10 minutes of re-entry). After a market survey, the proposed EPS is NanoPower P31u
with internal battery pack providing 18.7 Wh and a power margin of 136% during Phase 3 [5].
4 It can be defined as the stabilization of the angular rate right after orbital insertion
11
2.1.3.2.1.3.2.1.3.2.1.3. OnOnOnOn----board computer and onboard computer and onboard computer and onboard computer and on----board data handlingboard data handlingboard data handlingboard data handling
This subsystem can be considered as the heart and the brain of the satellite. It is responsible
for controlling the different modes of operation with the following main functions:
• Data handling
• Computation for other subsystems
• Command execution
• Payload operations
• Error handling and diagnosis
• Communication with Ground stations
In QARMAN case, the On-Board Computer (OBC) will acquire raw data from the payloads and
format them for the telecommunication system (packet format for the Iridium system), but it
is important to note that no onboard data processing will be made except data compression
before transmission. After a market survey, the NanoMind A712C (32-bit ARM7 RISC CPU, 2MB
static RAM, 2x4MB data/code storage, optional 2GB MicroSD extension) has been selected [5].
2.1.4.2.1.4.2.1.4.2.1.4. Telemetry, Tracking and Command SubsystemTelemetry, Tracking and Command SubsystemTelemetry, Tracking and Command SubsystemTelemetry, Tracking and Command Subsystem
The system provides the functional interface between the spacecraft and ground stations and
can is divided into three different elements:
• Tracking, to determine the position of the CubeSat and follow its orbit by means of the
ADCS information.
• Telemetry, to monitor the status of the satellite through the collection, processing and
transmission of data from the other subsystems to the ground.
• Commands, which are received from the ground stations for controlling mission
operations.
The configuration of this subsystem for QARMAN mission needs to be carefully studied due to
it is going to be really challenging. In the early phases of the mission, there should not appear
any problem related to the communications aspects, but during re-entry (Phase 3) a plasma
sheet will be formed in front of the vehicle and at some point of the phase the electron density
located there could be able to block any radio signal, preventing communication with the
ground stations. Additionally, there fact of having a compatible ground station at the location
of re-entry could increase the complexity of data transmission.
Thus, considering these aspects, the solution chosen to properly transmit data during Phase 3
is to do it through an antenna located in the lower electron density region, which will be
situated downstream of the CubeSat. On the other hand, in order to have access to the ground
stations at any time during re-entry, data from the spacecraft will be sent to a network of
communication satellites. For this purpose, Iridium constellation formed by 66 satellites at 780
12
km of altitude and an inclination of 86.4º has been chosen. So far, coverage analysis has been
already done demonstrating that QARMAN will be within the communication range of at least
4 Iridium satellites during the entire trajectory [5].
The market survey performed for the communication system ended with the selection of two
systems: the NanoCom U482C UHF transceiver and the IRIDIUM transceiver IR9602, each one
of them covering a different frequency range. For the preliminary design of QARMAN, it will be
assumed that both communication systems will be integrated, even though it is possible that
Iridium system will be chosen as the only one.
2.1.5.2.1.5.2.1.5.2.1.5. Thermal Protection System Thermal Protection System Thermal Protection System Thermal Protection System
The Thermal Protection System (TPS) is in charge to maintain the skin of the CubeSat within
acceptable temperatures, especially during re-entry, where the aggressive environment
conditions could burn up the spacecraft. Note that during this phase, temperature will rise up
to more than 2000 K at the tip and more than 1000 K at the end of side panels. For this reason,
it has been decided to introduce an ablative TPS to protect the front of QARMAN, which by
erosive processes will allow lowering the heat of the entire CubeSat.
QARMAN TPS will be a passive system designed for the critical altitude of 50 km (end-of-life).
Preliminary designs of the system ended up with a total weight of 577 grams (360 g for the
front part and 217 g for the side panels) including margins. Besides, front thermal protection is
foreseen to have a maximum thickness of 50 mm, property that is going to be of importance
for the design of the payload housed there. Additionally, the thermal status of the entire
CubeSat will be monitored during the entire mission by means of thermistors and payload
The main objective of this payload is to determine the stability of QARMAN during Phase 2 of
the mission. This way, it will be giving attitude information additional to sun sensors
accelerometers and the gyroscopes. It will be composed by two pressure sensors, and it has
been decided that for the preliminary design one of them will be operating in absolute mode
and the other one in differential mode.
The design of the whole measur
preliminary configuration for testing. On the other hand, the sensor housing design is out of
scope of this project due to no CFD has been done for the side panels yet. For this reason, only
basic requirements for the location of the pressure ports and pressure transducers will be
given.
Differential pressure: As the name indicates, it is based on the difference between
pressure values from both pressure intakes. For this reason, differential pressure
two separate pressure ports (see Figure 6). These types of sensors
are able to measure positive and negative pressure differences depending on the
inputs. Differential mode will be implemented on one of both pressu
Figure 6. Principle of differential pressure sensor
XPL02XPL02XPL02XPL02
pressure measurements will be taken at the front TPS of the CubeSat
during Phase 3 of the mission. This payload will be designed in detail throughout this project,
giving a preliminary configuration for the measurement chain, as well as the housing design of
ts will be presented in section 3, but main requirements c
XPL03XPL03XPL03XPL03
The main objective of this payload is to determine the stability of QARMAN during Phase 2 of
the mission. This way, it will be giving attitude information additional to sun sensors
accelerometers and the gyroscopes. It will be composed by two pressure sensors, and it has
been decided that for the preliminary design one of them will be operating in absolute mode
and the other one in differential mode.
The design of the whole measurement chain is contemplated in this thesis and it will be given a
preliminary configuration for testing. On the other hand, the sensor housing design is out of
scope of this project due to no CFD has been done for the side panels yet. For this reason, only
basic requirements for the location of the pressure ports and pressure transducers will be
15
Differential pressure: As the name indicates, it is based on the difference between
pressure values from both pressure intakes. For this reason, differential pressure
). These types of sensors
are able to measure positive and negative pressure differences depending on the
pressure sensors for
pressure measurements will be taken at the front TPS of the CubeSat
esigned in detail throughout this project,
giving a preliminary configuration for the measurement chain, as well as the housing design of
, but main requirements can be seen in
The main objective of this payload is to determine the stability of QARMAN during Phase 2 of
the mission. This way, it will be giving attitude information additional to sun sensors,
accelerometers and the gyroscopes. It will be composed by two pressure sensors, and it has
been decided that for the preliminary design one of them will be operating in absolute mode
ement chain is contemplated in this thesis and it will be given a
preliminary configuration for testing. On the other hand, the sensor housing design is out of
scope of this project due to no CFD has been done for the side panels yet. For this reason, only
basic requirements for the location of the pressure ports and pressure transducers will be
16
Finally, during the development of the project it has been possible to order all components in
order to start with the calibration of the measurement chain of the pressure sensor operating
in differential mode. Thus, in section 4.2 it will be explained in detail the procedure followed
for these tests, the facilities and instruments used and finally, results obtained will be
presented in order to validate the configuration designed. The main requirements for this
payload are presented in APPENDIX 1.
2.2.3.2.2.3.2.2.3.2.2.3. XPL04XPL04XPL04XPL04
This payload aims to monitor laminar to turbulence transition on the side panels, preferably by
shear force measurements. This way, skin friction will be measured by means of four Preston
tubes and it is foreseen that in a preliminary design two of them will be connected in common
with pressure sensors from XPL03. However, it will finally depend on the subject trades of this
payload, considering that one of the pressure sensors from XPL03 will be measuring in
differential mode. The design of this payload is out of scope and will not be dealt with in this
report. However, preliminary design is presented in APPENDIX 1.
2.2.4.2.2.4.2.2.4.2.2.4. XPL05XPL05XPL05XPL05
In this case it is foreseen to record off-stagnation temperature evolution for ground testing method validation purposes. The payload will be composed by ten thermocouples located in the side panels of QARMAN. Its design is out of scope, but a preliminary study is presented in APPENDIX 1.
2.2.5.2.2.5.2.2.5.2.2.5. XPL06XPL06XPL06XPL06
This payload aims to study the species presented during re-entry environment. The embedded
emission spectrometer onboard QARMAN intends to provide the first spectrally resolved data
in the flight regime of from 7.7 km/s at 120 km of altitude and 5 km/s at 50 km, which does not
exist [6]. With information acquired, a better knowledge of the radiation environment will
permit a more accurate sizing of TPS for International Space Station return.
17
2.3.2.3.2.3.2.3. BudgetsBudgetsBudgetsBudgets
Considering the previous configuration for QARMAN, it has been developed the preliminary
budgets for mass (Table 3), power (Table 4) and data (Table 5). By comparing values among all
subsystems requirements, the design of the aerothermodynamic payload is delimited.
2.3.1.2.3.1.2.3.1.2.3.1. Mass budgetMass budgetMass budgetMass budget
In this case, note that the maximum mass expected for the payload sensors is 265 grams. This
way, considering that QARMAN will be housing 33 aerothermodynamic sensors, meeting this
requirement is going to be really challenging. For this reason, measurement chains will need to
be connected between them reducing size and mass.
Subsystem Mass (g) Contingency (g) Mass with
contingency (g) Fraction (%)
Volume
[10cm]
Structural 390 78 468 14.7 n/a
ADCS 250 25 275 8.7 0.20
EPS 225 23 248 7.8 0.33
Solar panels 320 16 336 10.6 n/a
OBC / OBDH 55 6 61 1.9 0.16
GPS (including
antenna) 82 9 91 14.7 0.05
TT&C 239 24 263 8.3 0.46
Heat shield 300 60 360 11.3 0.63
Side panel
therm. Prot. 180 37 217 6.8 n/a
Acquisition
PCB 200 40 240 7.6 0.25
Sensors 265 54 319 10.0 0.25
AeroSDS 250 50 300 9.4 0.50
Total 2827 422 3178 111.9 2.83
Target mass 3000 3
Mass margin
-178 (Target mass–
Total mass with contingency)
-5.93%
(Target mass– Total mass with
contingency) / Target
mass
0.056%
Table 3. Mass budget for QARMAN [5]
18
2.3.2.2.3.2.2.3.2.2.3.2. Power budgetPower budgetPower budgetPower budget
Aerothermodynamic payload of QARMAN will be switched on only during Phase 2 and Phase 3.
Considering Table 4 values, a total power consumption of 4.5771 Watts is foreseen for the
entire mission. Note that during mission 3 no power will be generated, thus power all power
required for the different subsystems will be given by the batteries.
Average Duty Cycle by Mode (%)
Load
Power
consumption
(W)
Safe mode (Phase
1)
Recovery mode
(Phase 0)
Payload ULg
Operation mode
(Phase 1)
In orbit measurements
(Phase 2)
Safe mode (LPM, Phase
2)
Payload VKI
Operation mode
(Phase 3)
OBC 0.2937 100 100 100 100 100 100
UHF/VHF 0.510 10 20 20 20 10 0
S-band Tx (Iridium) 1.25 0 0 0 0 0 100
Attitude
determination 0.5 100 100 100 100 100 100
Attitude control 1.3 0 15 20 0 0 0
GPS 1 100 100 100 100 100 0
EPS 0.250 100 100 100 100 100 100
Aerothermodynamic
payload (Payload
VKI, phase 2)
1.2393 0 0 0 100 0 0
Aerothermodynamic
payload (Payload
VKI, phase 3)
3.3378 0 0 0 0 100
Equivalent number of solar cells
exposed to the sun 5 2.5 2.5 5 5 -
Power consumed (W) 2.09 2.34 2.4 3.47 3.3293 5.6315
Power generated (W) 2.6 2.6 2.7 4.5 4.5 0
Table 4. Power budget for QARMAN [5]
2.3.3.2.3.3.2.3.3.2.3.3. Data budgetData budgetData budgetData budget
The data rate of the active sensors for Phase 2 and 3, have been estimated using the
acquisition frequencies, the amount of sensors and the expected data size of each
measurement according to APPENDIX 1. If required, note that acquisition frequencies of the
3.1.3.1.3.1.3.1. Data Acquisition System designData Acquisition System designData Acquisition System designData Acquisition System design
3.1.1.3.1.1.3.1.1.3.1.1. Stating the Problem and Designing the Payload ObjectivesStating the Problem and Designing the Payload ObjectivesStating the Problem and Designing the Payload ObjectivesStating the Problem and Designing the Payload Objectives
Space vehicles re-entering a planetary atmosphere require the use of a thermal protection
system (TPS) in order to protect them from aerodynamic heating, which is the result of
compression, surface friction with the atmospheric gases and exothermic chemical reactions.
This shield is formed by an ablative material designed to melt and erode away from the vehicle
as it heats up.
There is a great interest to study the properties of these materials (i.e. durability, temperature
capability, thermal conductivity) to improve vehicle performances. So far not much data has
been obtained in a real re-entry flight, mainly because of the high cost to design a dedicated
vehicle for this purpose. For this reason, QARMAN gives engineers a very good opportunity to
help increasing the knowledge of the Earth aerothermodynamic re-entry phenomenon. Hence,
it has been decided to suit a payload formed by two absolute pressure sensors installed into
the TPS (apart from the other two thermocouples). In the following sections there will be
carefully defined the design of this payload and its measurement chain. In the end, a final data
acquisition system will be implemented for testing in VKI facilities.
Taking into account the main requirements for XPL02, which can be consulted in APPENDIX 1,
a list of scientific objectives is developed:
1. Total pressure measurements in the stagnation region.
Considering the previous market survey it can be defined the preliminary configuration for the
measurement chain of XPL02. As it’s been explained, QARMAN will be experimenting pressure
values somewhere between 0 and 20 kPa. This way, it is obviously needed to cover this range
also taking into account the main characteristics of the sensors summarized in Table 9.
Knowing that pressure measurements can be obtained in absolute, gauge and differential (as
seen in section 2.2.2), it has been finally decided to test this payload based on absolute
pressure. The main reason is that its value is not influenced by changes in atmospheric
pressure. In addition, it is zero-referenced against the perfect vacuum, so this kind of sensor
27
will only need one pressure intake in the TPS. With this property defined, the market survey
has been carried out and comparisons between all sensors can be done in order to find the
pressure sensor that fits better to QARMAN.
Regarding the properties defined in Table 9, there can be seen that most of them have the
same response time, operating temperature and cost. This way, the final decision prioritizes
the supply voltage, the operating pressure range and the accuracy. Additionally, amplified
sensors have been dismissed due to they are operating in a range from 0 to 100 kPa (larger
than the required one) with a worst accuracy than the unamplified ones. Furthermore, it is
known that a maximum of 5 Volts will be provided to QARMAN’s platform. It means there
must be ensured that XPL02 can work properly with this voltage supply. For all these reasons,
the pressure sensor proposed for XPL02 is the NPC-1220, which is the one that requires less
voltage supply and it is also operating into an adequate pressure range with a very good
accuracy. See Table 11 for detailed information. Moreover, this sensor is one of the lightest
one, which is also a benefit for the whole CubeSat design. There should be also noticed that
the 101B-a19L pressure sensor has been also considered due to its high accuracy and general
performances, but it has been finally dismissed due to its design. Both pressure sensors are
shown in Figure 8 for a better comparison.
Figure 8. On the left, pressure sensor 101B-a19L; on the right, pressure sensor NPC-1220
Another important part of the chain is the filtering process. According to the datasheet,
pressure sensor chosen will be outputting noise from 10 Hz to 1 kHz, which means that a low
pass filter can be required. This kind of filter is a simple electrical circuit which consists of a
resistor in series with a load, and a capacitor in parallel with the load. If a filter is finally
necessary, the idea is to design this component in the electronics laboratory of VKI. In that
case, the filter would not require energy supply, which agrees with the idea of keeping a
simple vehicle design. Just in case, the market survey is already done to have another
possibility. Following the filter, the measurement chain will include an amplifier. Taking into
account the market survey developed for this component, the most suitable amplifier is the
AD8671 because of its low voltage supply and its high gain, which gives better output signal of
10 Volts. Finally, there is the analog-to-digital conversion. For initial tests of XPL02 in the VKI
facilities, it has been chosen the ADS7828E, which is also the same as the one used in XPL01
[2]. Depending on its performance the A/D converters from Table 10 may or not be in
consideration.
28
With all components for the preliminary DAQS for XPL02 decided, the important
characteristics at each point of the circuit are defined. They are summarized in detail in Table
11. Firstly, the pressure sensor datasheet advises to use a supply voltage of 1.235 V, obviously
lower than the 5 Volts available for the platform. Its range fulfills the required one, and taking
into account the accuracy of the sensor, a pressure error of 0.442 kPa is found. Note that this
should be the maximum pressure error obtained at any pressure value, but its validation needs
to be performed in laboratory. Output voltage range and error for the pressure sensor are also
given in the same table. Another important characteristic is the zero output Voltage, because it
defines the lowest pressure the sensor is able to measure. However, by calibration in
laboratory the pressure range can be adjusted, for example by modifying the gain of the
amplifier.
For the preliminary design, the amplifier chosen is the AD8671. As you can see, the voltage
supply meets the one required (less than 5V). Note that the gain presented in the table is the
maximum one, but it can be modified using a simple potentiometer in order to have the
desired output. Finally, there is the analog-to-digital converter ADS7828E. For this component,
the voltage supply required is also in the limits. It has a very good resolution of only 8.33 Pa,
value that corresponds to an absolute error of 0.0245%. In addition, thanks to the high number
of channels the possibility of connecting other payloads to this converter can be considered.
On the other hand, the sampling frequency exceeds by far the 1Hz frequency required.
NPC-1220-005A-3-S
PRESSURE SENSOR
Measurement type Absolute pressure
Supply Voltage [V] 1.235
Pressure Range [kPa] 0 to 34
Pressure Error [kPa] 0.442
Output Voltage Range [mV] 0 to 50
Output Voltage Error [mV] 0.65
Zero Pressure Output [mV] 2
AD8671
Supply Voltage [V] 4 to 18
Gain [dB] 135.6
Output Voltage [V] ±3.39
Offset Voltage [µV] 125
Output Voltage error [mV] 88.14
ADS7828E
Supply Voltage [V] 2.7 to 5
Voltage resolution [mV] 1.66
Pressure resolution [Pa] 8.33
Resolution [bit] 12
Channels 8
Sampling Rate [kHz] 50
Max. Error in Pressure [kPa] 0.442
Table 11. Preliminary measurement chain for XPL02
29
3.1.6.3.1.6.3.1.6.3.1.6. Final configurFinal configurFinal configurFinal configurationationationation
The preliminary design presented in the previous section has been shared with QARMAN
team. The electronic technicians have carefully read and interpreted the datasheets of each
component forming the measurement chain. This way, taking into account their experience,
compatibility between components is checked in order to define a possible configuration.
Therefore, the preliminary configuration defined in previous section is slightly modified. On
one hand, filters are dismissed because technicians think the noise is going to be pretty low.
However, oscilloscope will be used during tests in order to check it. On the other hand,
pressure sensor and the amplifier already chosen will be finally implemented. Finally, instead
of the analog-to digital converter, technicians decided to use the microcontroller MSP430. This
component has an internal 12-bit ADC module which has a maximum conversion rate of 200
kilo-samples per second and an internal reference voltage generator. There are 16 channels in
total, much more than the 8 channels from the ADC selected for the preliminary design.
However, 4 of these channels are internally connected and they cannot be used to take
external measurements; otherwise, the other 12 channels are accessible via the MSP430’s
pins. These and other characteristics are listed in Table 12.
Component MSP430
Supply Voltage [V] 5
ADC integrated Yes
Kilo-samples per second 200
Channels available 12
Resolution [bit] 12
Memory type Flash
Temperature range [ºC] -40 to 85
Maximum input voltage [V] 3.3
Table 12. MSP430 main characterstics
For this reason, two possible configurations are proposed for testing: Version A and Version B.
Each one of them gives different characteristics to the circuitry and it is intended to test both
of them in VKI facilities.
Even though a final configuration is presented here, due to ordering problems the pressure
sensor measuring absolute pressure was not in stock. It means that this project will not cover
the tests for XPL02, but only the configuration and housing design. Luckily, the same pressure
sensor measuring differential pressure has been acquired, so XPL03 tests have been carried
out during the development of this project and they are described in see section 4.2.
30
3.1.6.1.3.1.6.1.3.1.6.1.3.1.6.1. Version AVersion AVersion AVersion A
NPC 1220 pressure sensor will be used in the design. Since the output of the sensor is quite
low, an amplifier circuitry must be connected to the output of the sensor. AD8671 amplifier
has been chosen for this purpose. Application schematic of the pressure sensor can be seen in
Figure 9.
Figure 9. Pressure sensor circuitry and components
The CSR (current set resistor, see the scheme) is placed between negative input of the OP-AMP
and the ground. Since this amplifier operates with negative feedback, negative input voltage
will be equal to the Vref. It means that current value passing through the pressure sensor bridge
circuit is determined as:
� =�������
On the other hand, the gain of the buffer amplifier (see red box) can be calculated by means of
the resistors there defined:
� =2 · 100�Ω + 3.3�Ω
3.3�= 61.606
In addition, typical sensor output should be 50 mV, so the output voltage of this configuration
can be easily calculated as follows:
�� = 50$� · 61.606 = 3.08�
Note that 3.08 V is the maximum output differential voltage. The sensor should be driven by
certain amount of current and this is achieved using the current set resistor and the current
source structure also defined in Figure 9. At this point, the configuration and pins connection is
defined as it is shown in Figure 10. Three operational amplifiers will be used: the one in the
31
green are used for the current supply; the ones in the red box are amplifying the pressure
sensor output, also illustrated.
Figure 10. Version A configuration and pin connection
3.1.6.2.3.1.6.2.3.1.6.2.3.1.6.2. VerVerVerVersion Bsion Bsion Bsion B
Pressure sensor output voltage is proportional to the bridge resistor values inside the sensor.
According to the datasheet of the sensor, maximum resistor value is 6k Ω. Considering this
configuration, output voltages from negative and positive leads of the sensor (pins 1 and three
of the NPC-1220 shown in Figure 10) exceed 5 Volts, while the differential voltage between
them is still 50 mV at maximum. This way, once these values are amplified by the circuit inside
the red box, the final output will be around 7 V. At that point, maximum differential output will
be around 3.08 Volts, but the microcontroller chosen cannot measure voltages above 3.3 V.
In order to solve this problem, a differential amplifier with gain 1 could be used in order to get
one single output into the required voltage range. However, it means having three OP-AMP to
only measure the output of one single sensor and also more resistors to complete the circuit.
In the end, it leads to a more complex design and also to error amplification. For this reason,
an instrumental amplifier will be used. These devices are widely used for signal conditioning
circuitry for bridge type sensor. It has two inputs and single-ended output. First stage (two OP-
AMPs on the left on Figure 11) is the buffer stage. It isolates the input and the output.
Furthermore it amplifies the incoming signal depending on the Rgain. The most important
characteristic of this stage is that it has very high input impedance. Thanks to this feature, no
current flow through the input which means no current drawn from the sensor. If some
current draws from the bridge circuitry of the sensor, this would distort the balance of the
bridge giving wrong measurements.
Second stage is a differential amplifier. Usually gain of this stage is set to 1. The main purpose
of this stage is to subtract input signals between them giving single-ended output and being
possible to connect this output directly to the microcontroller.
Instrumental amplifiers input signal has two components: the common mode signal (the
average of both input signals) and the differential signal (difference of both sig
important thing here is that only the differential signal has importance for data acquisition.
Common mode signal must be suppressed, so only the differential signal can reach to the
output. IN-AMPs have very good common mode rejection ratio (CM
variations in the common mode signal cannot affect the output signal.
All this characteristics make IN
resistor values inside the IN
produced with very high precision so, if possible, it is advised to use these chips instead of
building a circuit by using 7 resistors and 3 OP
Thanks to the experience of the electronic technicians, the instrumental amplifi
chosen by them. This way, the IN
characteristics listed in Table
AMP that includes two ident
used for supplying constant current to the sensor and the other one has been used for
reference voltage generation for the IN
OP-AMPs are only for current and voltage supply to the circuit, so once verified these values
remain constant their effects to the pressure sensor outputs can be dismissed. As you can see
in Figure 12, the gain of the IN
gain set resistor. To control it, the following equation presented in the instrumental amplifier
datasheet is used:
Figure 11. Typical instrumental amplifier
Instrumental amplifiers input signal has two components: the common mode signal (the
average of both input signals) and the differential signal (difference of both sig
important thing here is that only the differential signal has importance for data acquisition.
Common mode signal must be suppressed, so only the differential signal can reach to the
AMPs have very good common mode rejection ratio (CMRR), what means that
variations in the common mode signal cannot affect the output signal.
All this characteristics make IN-AMPs proper for bridge type sensors. It is very important that
-AMP are precise. Single commercial integrated circuits (IC) are
produced with very high precision so, if possible, it is advised to use these chips instead of
building a circuit by using 7 resistors and 3 OP-AMPs.
Thanks to the experience of the electronic technicians, the instrumental amplifi
chosen by them. This way, the IN-AMP AD8226 is decided to suit Version B with main
Table 13. On the other hand, LMP7718 (inside green box) is a dual OP
AMP that includes two identical and separated operational amplifiers. One of them has been
used for supplying constant current to the sensor and the other one has been used for
reference voltage generation for the IN-AMP (inside red box). However, note that these two
y for current and voltage supply to the circuit, so once verified these values
remain constant their effects to the pressure sensor outputs can be dismissed. As you can see
, the gain of the IN-AMP represented inside red box can be adjusted thanks to the
. To control it, the following equation presented in the instrumental amplifier
�' =49.4�Ω� � 1
32
Instrumental amplifiers input signal has two components: the common mode signal (the
average of both input signals) and the differential signal (difference of both signals). The
important thing here is that only the differential signal has importance for data acquisition.
Common mode signal must be suppressed, so only the differential signal can reach to the
RR), what means that
AMPs proper for bridge type sensors. It is very important that
egrated circuits (IC) are
produced with very high precision so, if possible, it is advised to use these chips instead of
Thanks to the experience of the electronic technicians, the instrumental amplifier has been
AMP AD8226 is decided to suit Version B with main
. On the other hand, LMP7718 (inside green box) is a dual OP-
ical and separated operational amplifiers. One of them has been
used for supplying constant current to the sensor and the other one has been used for
AMP (inside red box). However, note that these two
y for current and voltage supply to the circuit, so once verified these values
remain constant their effects to the pressure sensor outputs can be dismissed. As you can see
djusted thanks to the
. To control it, the following equation presented in the instrumental amplifier
33
Figure 12. Version B configuration and pin connection
In summary, the advantages respect to Version A can be listed as follows:
• A single IN-AMP is used instead of two OP-AMP.
• Efficiency and noise immunity of the IN-AMP is better.
• Only one external resistor is needed.
• Output is single ended (not differential as Version A), so it is easier to read voltages by
the ADC channel of the microntroller.
For all this reasons, it has been decided that Version B is by far the best configuration. This
way, preliminary tests at VKI facilities will be based on this last version of the measurement
chain. However, as it has been explained, it will be only possible to test the differential
pressure sensor from XPL03 during the development of this thesis, due to absolute pressure
sensors were out of stock when the components were ordered.
Component AD8226
Supply Voltage [V] 2.7
Gain [dB] 60 (adjustable)
Output Voltage [V] 3
Settling time to 0.01% [µs] 350
Operating temperature [ºC] -40 to 125
Volume [mm3] 17.24 Table 13. AD8226 main characteristics
3.2.3.2.3.2.3.2. Pressure ports design and sensor housingPressure ports design and sensor housingPressure ports design and sensor housingPressure ports design and sensor housing
3.2.1.3.2.1.3.2.1.3.2.1. Objectives and main considerationsObjectives and main considerationsObjectives and main considerationsObjectives and main considerations
The Thermal Protection System will fit both pressure taps for pressu
this reason, two holes will be drilled through the shield with the objective of connecting the
atmosphere with the pressure sensor transducers. Their design will be mainly driven by two
important properties:
- The diameter of the ho
- The location of pressure taps in the TPS.
On one hand, it must be verified the holes are wide enough to ensure the air flows properly
through them. This way, it is required to know if the size of the particles coming from the
ablation of the TPS can obstruct the pressure taps. The rate of recession must be known in
order to control and optimize the diameter.
On the other hand, the location of the pressure taps in the TPS will also be guided by testing
this shield in Plasmatron. Knowing its ablation evo
will be acquired. So far, some CFD’s have been done, which tell us that with an ideal attitude of
the satellite (perfectly aligned with the velocity vector) the regions near the stagnation point
and the corners of the TPS are the ones which ablate the fastest. The highest temperatures
and pressures are obtained there, as shown in
will change and the CubeSat will be turning
attack different to zero. It will obviously cause differences from the ideal ablation just
mentioned.
It means the design of the holes placed near the borders of the TPS will be a trade
the structure integrity and the pressure distribution of this region. For example, holes drilled
very close to the corners could cause the fracture of this region and, as a result, the loss of the
symmetry and attitude problems.
Figure 13. TPS at 66 km of altitude. a) Pressure distribution; b) Temperature distribution
Pressure ports design and sensor housingPressure ports design and sensor housingPressure ports design and sensor housingPressure ports design and sensor housing
Objectives and main considerationsObjectives and main considerationsObjectives and main considerationsObjectives and main considerations
The Thermal Protection System will fit both pressure taps for pressure data acquisition. For
this reason, two holes will be drilled through the shield with the objective of connecting the
atmosphere with the pressure sensor transducers. Their design will be mainly driven by two
The diameter of the holes.
The location of pressure taps in the TPS.
On one hand, it must be verified the holes are wide enough to ensure the air flows properly
through them. This way, it is required to know if the size of the particles coming from the
bstruct the pressure taps. The rate of recession must be known in
order to control and optimize the diameter.
On the other hand, the location of the pressure taps in the TPS will also be guided by testing
this shield in Plasmatron. Knowing its ablation evolution, precious information for its location
will be acquired. So far, some CFD’s have been done, which tell us that with an ideal attitude of
the satellite (perfectly aligned with the velocity vector) the regions near the stagnation point
of the TPS are the ones which ablate the fastest. The highest temperatures
and pressures are obtained there, as shown in Figure 13. However, in-flight conditions things
will change and the CubeSat will be turning a bit around its velocity vector, having an angle of
attack different to zero. It will obviously cause differences from the ideal ablation just
It means the design of the holes placed near the borders of the TPS will be a trade
structure integrity and the pressure distribution of this region. For example, holes drilled
very close to the corners could cause the fracture of this region and, as a result, the loss of the
symmetry and attitude problems.
TPS at 66 km of altitude. a) Pressure distribution; b) Temperature distribution
34
re data acquisition. For
this reason, two holes will be drilled through the shield with the objective of connecting the
atmosphere with the pressure sensor transducers. Their design will be mainly driven by two
On one hand, it must be verified the holes are wide enough to ensure the air flows properly
through them. This way, it is required to know if the size of the particles coming from the
bstruct the pressure taps. The rate of recession must be known in
On the other hand, the location of the pressure taps in the TPS will also be guided by testing
lution, precious information for its location
will be acquired. So far, some CFD’s have been done, which tell us that with an ideal attitude of
the satellite (perfectly aligned with the velocity vector) the regions near the stagnation point
of the TPS are the ones which ablate the fastest. The highest temperatures
flight conditions things
a bit around its velocity vector, having an angle of
attack different to zero. It will obviously cause differences from the ideal ablation just
It means the design of the holes placed near the borders of the TPS will be a trade-off between
structure integrity and the pressure distribution of this region. For example, holes drilled
very close to the corners could cause the fracture of this region and, as a result, the loss of the
TPS at 66 km of altitude. a) Pressure distribution; b) Temperature distribution
Considering the points already presented for QARMAN, the design of the measurement chain
of XPL02 will be similar to the one implemented for the Mars Entry Atmospheri
Development (MEADS) of the Mars Science Laboratory. It is a series of seven pressure ports, in
the thermal protection system that connect
Its general configuration is presented in
a diameter of 2.54 mm, connecting the atmosphere to the heat shield, which is housing a
spool. In the end, this last element allows a proper connection with the sta
which guides the atmosphere pressure to the pressure transducer. For all this, the TPS bonding
structure of QARMAN will be housing a specific spool. The following sections will be focused
Unlike MEADS design, QARMAN TPS will be housing only two pressure ports. However, before
taking a decision about where to place them, let’s consider the option taken by MEADS and
see if it is compatible for a CubeSat. As may be seen in Figure 15, seven pressure ports are
implemented for Mars Science Laboratory mission. Points P1 and P2 are located in the
n point to provide a nearly direct measurement of the total pressure in the high Mach
regime. Ports P3, P4 and P5 lie on the spherical nose cap and are placed in order to take
advantage of the simple geometry for angle-of-attack measurements. Additionally,
at the geometric center, provides a nearly direct total pressure measurement at the low Mach
regime prior to parachute deployment. The final two ports are located in the horizontal plane
of symmetry, approximately 1 meter from the centerline. The ports P6 and P7 provide the off
axis measurements needed to estimate the angle of sideslip. The pressure ports are connected
to pressure transducers via the stainless steel tube system already illustrated in
35
Considering the points already presented for QARMAN, the design of the measurement chain
of XPL02 will be similar to the one implemented for the Mars Entry Atmospheric Data System
Development (MEADS) of the Mars Science Laboratory. It is a series of seven pressure ports, in
via stainless steel tubing to pressure transducers.
. In this case, the holes drilled in the TPS have
a diameter of 2.54 mm, connecting the atmosphere to the heat shield, which is housing a
spool. In the end, this last element allows a proper connection with the stainless steel tube,
which guides the atmosphere pressure to the pressure transducer. For all this, the TPS bonding
structure of QARMAN will be housing a specific spool. The following sections will be focused
Unlike MEADS design, QARMAN TPS will be housing only two pressure ports. However, before
option taken by MEADS and
, seven pressure ports are
implemented for Mars Science Laboratory mission. Points P1 and P2 are located in the
n point to provide a nearly direct measurement of the total pressure in the high Mach
regime. Ports P3, P4 and P5 lie on the spherical nose cap and are placed in order to take
attack measurements. Additionally, P4, located
at the geometric center, provides a nearly direct total pressure measurement at the low Mach
regime prior to parachute deployment. The final two ports are located in the horizontal plane
The ports P6 and P7 provide the off-
axis measurements needed to estimate the angle of sideslip. The pressure ports are connected
illustrated in Figure 14.
Figure
QARMAN TPS is going to house two thermal plugs and a spectrometer, apart from the two pressure ports of XPL02. On one hand, the spectrometer will be located exactly at thestagnation point of the TPS. On the other hand, both thermocouples will be placed diagonal direction between the stagnation point and the corner.
In addition, the CFD’s done at the altitudes of 66 km, 60 km, 53 km and 50 km show the
pressure distribution around the TPS during re
be observed that regions near the stagnation point have higher pressures than regions near
the corners. For a more detailed press
At this point, taking into account all this information one first decision can be made: the two
pressure ports shall be located at the points of maximum and minimum pressure. This can be
translated into placing them somewhere near the stagnation point and near the corner. It
would allow QARMAN to get data required to accomplish the payload objectives and it would
also give interesting information for further TPS designs by comparing these two points.
Another obvious but important thing is that both pressure ports must be housed diagonally
opposed from the thermocouples, avoiding crowded regions and cabling related problems.
Figure 15. MEADS pressure ports configuration
QARMAN TPS is going to house two thermal plugs and a spectrometer, apart from the two pressure ports of XPL02. On one hand, the spectrometer will be located exactly at thestagnation point of the TPS. On the other hand, both thermocouples will be placed diagonal direction between the stagnation point and the corner.
In addition, the CFD’s done at the altitudes of 66 km, 60 km, 53 km and 50 km show the
ibution around the TPS during re-entry. This can be seen in Figure
be observed that regions near the stagnation point have higher pressures than regions near
the corners. For a more detailed pressure distribution at each altitude, consult
At this point, taking into account all this information one first decision can be made: the two
pressure ports shall be located at the points of maximum and minimum pressure. This can be
o placing them somewhere near the stagnation point and near the corner. It
would allow QARMAN to get data required to accomplish the payload objectives and it would
also give interesting information for further TPS designs by comparing these two points.
other obvious but important thing is that both pressure ports must be housed diagonally
opposed from the thermocouples, avoiding crowded regions and cabling related problems.
36
QARMAN TPS is going to house two thermal plugs and a spectrometer, apart from the two pressure ports of XPL02. On one hand, the spectrometer will be located exactly at the stagnation point of the TPS. On the other hand, both thermocouples will be placed in the
In addition, the CFD’s done at the altitudes of 66 km, 60 km, 53 km and 50 km show the
Figure 16. It can easily
be observed that regions near the stagnation point have higher pressures than regions near
ure distribution at each altitude, consult APPENDIX 2.
At this point, taking into account all this information one first decision can be made: the two
pressure ports shall be located at the points of maximum and minimum pressure. This can be
o placing them somewhere near the stagnation point and near the corner. It
would allow QARMAN to get data required to accomplish the payload objectives and it would
also give interesting information for further TPS designs by comparing these two points.
other obvious but important thing is that both pressure ports must be housed diagonally
opposed from the thermocouples, avoiding crowded regions and cabling related problems.
37
Figure 16. TPS pressure distribution at a) 66 km; b) 60 km; c) 53 km; d) 50 km of altitude
Once the region is decided, it is time to know exactly where to place the pressure ports and
which diameter will they have. From CFD’s at the different four altitudes, the TPS pressure
distribution from the stagnation point to the corner is obtained as a function of axis Z (see axis
in Figure 17). Thus, it can be noticed that at Z=0 m maximum pressure is obtained and near
Z=0.05 m it is reached the minimum one as expected. In addition, it can be seen that as
altitude increases, pressure changes become smoother around the stagnation point. The same
happens near the corner.
For this reason, the first pressure port P1 will be located where pressure starts dropping more
rapidly for the most critical altitude, which is 50 km. This point corresponds to Z=0.015 m.
Represented with the grey vertical line in Figure 17. On the other hand, pressure port P2 is
going to be placed at Z=0.04 m, represented too, which corresponds to a point where pressure
has decreased an important amount at all altitudes and it is far enough from the corner
avoiding structural problems. However, this configuration must be tested in Plasmatron
(facility described in section 4.2.2) to validate the design.
Finally, there is only one thing left: the size of the pressure ports. Taking into account the
diameter of the holes made for MEADS is 2.54 mm, it has been decided to make a preliminary
design with holes 20 % smaller than the previous ones, which corresponds to 2 mm diameter.
38
Figure 17. TPS pressure distribution as a function of altitude
3.2.3.3.2.3.3.2.3.3.2.3. Spool options consideredSpool options consideredSpool options consideredSpool options considered
In order to properly connect the pressure ports from the TPS with the pressure transducers, it
will be designed a specific spool for QARMAN. This element will be similar to the one used in
MEADS (see Figure 14), but different options has been considered for its design. In the end,
taking into account the advantages and disadvantages of each one, a final design will be
proposed for further tests in Plasmatron.
As it has been explained in the previous section, both holes drilled in the TPS for the pressure
ports have a diameter of 2 mm. This way, in-flight air will get in the holes and it will also pass
through the 50 mm of TPS. The thermal shield will be attached to a boundary metallic
structure, which is going to house the spool. So far, neither the material nor the shape of the
metallic structure is defined, just some preliminary and incomplete CATIA designs have been
developed. Hence, it has been decided that the design of the spool will guide the final design
of the TPS boundary structure. Taking this into account, it is intended to create a spool
minimizing the thickness of this structure and therefore the weight of the satellite.
The main objective of the spool is to enable the connection between the pressure ports and
the plastic tube which will end up at the pressure transducer. Thus, the basic requirement is
that the spool shall have an outer section so the tube can be connected, but the global design
can differ in many ways. That is why three different options have been presented in order to
The last of the three preliminary designs, shown in Figure 20, is a mix between the previous
ones. On one hand, it is really optimized in size, due to almost the entire spool remains inside
the boundary structure and the manufacture seems to be the simplest one. On the other hand,
the idea of a thread has been also implemented in this case, but now it connects the metallic
structure with the spool. Again, in order to avoid possible obstructions, the diameter of the
hole is two times the one drilled for the pressure taps. In addition, a new section is added to
the head of the spool, which is housed inside the TPS. This will ensure a perfect connection of
the spool with the pressure ports from the TPS and it will help avoiding relative displacements
between the boundary structure and the thermal shield. The only problem for this design
could be to perfectly suit the spool inside the bonding structure. There is not a solid position
for this element, so the engineers must be really carefully during the assembly. For this reason,
solder could be required. Consult APPENDIX 3 for detailed drawings of this design.
Figure 20. Option 3
42
3.2.4.3.2.4.3.2.4.3.2.4. SpoolSpoolSpoolSpool final design final design final design final design
The design chosen for the preliminary tests in Plasmatron is shown in Figure 21. It can be seen
as the fusion of all three preliminary designs. Firstly, it has been chosen the design from option
one for the body of the spool, which means this element has only one position once suited to
the TPS boundary structure. It helps avoiding problems during assembly. Secondly, it has been
decided to use almost the same kind of thread as the one from option 2. The only difference is
that it has been introduced an improvement due to the new design: the spool will be threaded
with the TPS boundary structure, giving more solidity to the system. Additionally, it will be
included a nut to the design giving two main advantages:
- The configuration allows the assembly and disassembly of the spool if required.
- It is a flexible design considering that the thickness of the TPS boundary structure
could change due to weight or size constraints.
In addition, the nut can be soldered either to the boundary structure or to the thread in order
to ensure both bodies will not separate from each other because of vibrations or other in-flight
forces. For the design of the spool, the VKI engineers will take advantage from the facilities
available there, which allow them to manufacture any kind of shape, regardless of whether or
not it is a commercialized and normalized design. Due to the size of this component, that’s to
say low weight, it has been decided to use stainless steel as a material because of its
mechanical properties such as its high corrosion resistance or its high ultimate tensile strength
(860 MPa versus 400 Mpa for structural steel). Furthermore, see in Figure 21 that the threaded
section of the spool is long enough to allow a proper plastic tube connection to the pressure
transducer. Note that this length can be changed whenever necessary, depending on how
deep the plastic tube needs to be connected.
Figure 21. Spool final design
43
Finally, it has been implemented the idea of including a new upper section to the spool to
connect with the TPS. As commented in 3.2.3.3, it allows an improved assembly between the
TPS and its boundary structure, ensuring a proper air flow throughout the pressure ports.
However, this is a preliminary design for the tests of XPL02, so in the end size can suffer some
changes, even though based on the same idea.
For a better understanding of the whole configuration and the final spool design, the assembly
and final drawings are included in Figure 22 and Figure 23, respectively. Note that for an ISO
metric 6 thread (M6), the pitch must be 1 mm and that the nut designed has a thickness of 3
mm. Taking into account this component will not be subjected to high stresses, these sizes
should be enough. However, remember soldering can be applied to the nut if necessary.
Figure 22. Final assembly between the spool (green) and the nut (purple)
Figure 23. On the left, front and top drawings of the nut; on the right, front and top drawings of the bolt
44
4.4.4.4. XPL03XPL03XPL03XPL03
4.1.4.1.4.1.4.1. Data acquData acquData acquData acquisition system designisition system designisition system designisition system design
4.1.1.4.1.1.4.1.1.4.1.1. Stating the problem and designing the payload objectivesStating the problem and designing the payload objectivesStating the problem and designing the payload objectivesStating the problem and designing the payload objectives
In-flight, QARMAN will be experiencing forces such as gravity, drag or lift that might disturb the
CubeSat from its normal flight path. These attitude changes must be controlled near real time,
checking the orbit is the expected one. For this purpose, components such as sun sensors,
accelerometers and gyroscopes are suited to the CubeSat (see section 2.1 for further
information). This instrumentation will provide basic stability and control instrumentation such
as angular rates, normal and lateral accelerations and pitch and roll attitudes. Additionally, the
set of aerothermodynamic payload for QARMAN will include the XPL03. This one will be
formed by two pressure sensors, aiming to determine the stability of QARMAN during Phase 2
and Phase 3 of the mission. Such as it has been explained in section 1.1, these phases
correspond to a range of altitude from 330 km to about 50 km.
Unlike XPL02, it has been decided that one of the pressure sensors from XPL03 will be working
in differential mode, and the other one in absolute mode. It means that there is going to be
three pressure ports located somewhere in the side panels of QARMAN, at or near the nose of
the vehicle. Differential pressure will be measured in the horizontal or vertical axes, relative to
the CubeSat. The pressure differential is used together with the dynamic pressure to
determine the angle of attack and/or sideslip of the aircraft. For this reason, it is going to be
really important to share data obtained with this payload to total pressure values obtained
from XPL02, which is formed by two absolute pressure sensors. On the other hand, the sensor
measuring absolute pressure will give static pressure measurements to QARMAN, generating
important data to meet more scientific objectives.
Now, taking into account the main requirements for XPL03, which can be consulted in
APPENDIX 1, the list of scientific objectives is developed for this payload:
Similar to XPL02, this payload will be formed by two pressure sensors, but in this case one will
be measuring in absolute pressure and the other one in differential pressure. In Table 14 it is
shown the requirements established for this payload. As you can see, it is foreseen to have a
total mass of 0.06 kg, which is the same than the one for XPL02. The energy consumption for
XPL03 shall be 840 mW·h/sensor at maximum, a value much greater than the 4.16
mW·h/sensor for XPL02, and being the second payload in consumption after the spectrometer.
However, as seen in Table 14, the total acquisition duration of 336 hours is also higher than
the 0.16 hours of XPL02 (even though during Phase 2 power supply will be covered by solar
panels), due to the fact it will be switched on during Phase 2. Remember that Phase 2 goes
from an altitude of 330 km to 120 km, significantly increasing the acquisition time available
respect to Phase 3. For this reason, acquisition frequency can be set to 0.1 Hz, ten times lower
than the 1 Hz defined for XPL02.
Investigated challenge TPS & environment
Parameter to measure Absolute and differential
pressure
Sensor 2 x Pressure sensor
Total mass [kg] (sensor + wiring +
housing) 0.060
Energy consumption/ Piece [mW·h] 840
Data size/ measurement [bit] 10
Phase 2
Total data size [kB/ phase] 302.4
Acquisition frequency [Hz] 0.1
Number of measurements 120960
Total acquisition duration [h] 336
Response time [ms] 0.1
Power [W/piece] 0.250 Table 14. Performance thresholds for XPL03
48
4.1.5.4.1.5.4.1.5.4.1.5. Measurement chain and final configurationMeasurement chain and final configurationMeasurement chain and final configurationMeasurement chain and final configuration
As it has been explained throughout this section, XPL03 will be formed by two pressure
sensors. One of them will be measuring in absolute pressure, thus it will have exactly the same
measurement chain as the one defined for XPL02. The other sensor will work in differential
mode, comparing pressure between two different pressure ports drilled in the side panels.
However, this is going to be the only difference respect to previous payload, so the signal
conditioning will have the same requirements:
• Sensor output voltage amplification.
• It shall include a low pass filter.
• Offset correction.
• Multiplexing the output with other payload output signals to reduce weight and size.
• Analog-to-digital data conversion.
This way, taking previous payload design experience, the final measurement chain
configuration for testing this payload will be exactly the same as Version B from XPL02. In
Table 15 there are listed the most important characteristics of the system. It should be noted
that the theoretical maximum pressure error should be less than 442 Pa and that after testing
the circuit on a breadboard with an oscilloscope, the introduction of a filter into the circuit has
been dismissed due to the low outputting noise. In addition, the microcontroller incorporates
an analog-to-digital converter, so this component is going to be in charge of the data
conversion and it will also incorporate the software to command this payload. It is also
important to notice that maximum input voltage for the microcontroller is 3.3 V, this needs to
be taken into account especially during the testing of XPL03, which are widely described in the
following section.
The detailed configuration and pin connection can be seen in Figure 25. All components
forming the measurement chain are there defined. Current supply for the pressure sensor will
be controlled with the amplifier inside the blue box, which is going to be connected to the
pressure sensor, inside the green box. Finally, the output signal from the sensor is sent the
instrumental amplifier, whose output is the input of the ADC housed in the microcontroller.
Figure 25. XPL03 configuration and pin connection
49
NPC-1220-005A-3-S
PRESSURE SENSOR
Measurement type Absolute pressure
Supply Voltage [V] 1.235
Pressure Range [kPa] 0 to 34
Pressure Error [kPa] 0.442
Output Voltage Range [mV] 0 to 50
Output Voltage Error [mV] 0.65
Zero Pressure Output [mV] 2
AD8226
Supply Voltage [V] 2.7
Gain [dB] 60 (adjustable)
Output Voltage [V] 3
Output Voltage error [mV] 39
Operating temperature [ºC] -40 to 125
MSP430F5438A
(microcontroller)
Component series MSP430
Supply Voltage [V] 5
ADC integrated Yes
Kilo-samples per second 200
Channels available 12
Resolution [bit] 12
Memory type Flash
Temperature operating range [ºC] -40 to 85
Maximum input voltage [V] 3.3
Voltage resolution [mV] 0.73
Pressure resolution [Pa] 8.3
Max. Error in pressure [kPa] 0.442
Table 15. Final measurement chain for XPL03
50
4.2.4.2.4.2.4.2. Ground Testing methodology anGround Testing methodology anGround Testing methodology anGround Testing methodology and Extrapolation to Flightd Extrapolation to Flightd Extrapolation to Flightd Extrapolation to Flight
4.2.1.4.2.1.4.2.1.4.2.1. Motivation and requirementsMotivation and requirementsMotivation and requirementsMotivation and requirements
The goal of the pressure sensors located in the side panels is to measure the static and
differential pressure during atmospheric re-entry. As seen in section 3.1.6, it has been
proposed two different configurations for the data acquisition system of XPL02. However, it
has been decided to implement only Version B for the preliminary design of both
measurement chains. In this section there is going to be tested the differential pressure sensor
from XPL03, which was the only pressure sensor available when ordering. The system will be
tested at the VKI facilities and thus, it will be possible to make some corrections on their
calibration, if required. By the end of these tests, the whole measurement chain for the
differential pressure sensor from XPL03 will be validated, making the necessary changes and
adjustments to fulfill the requirements.
In order to reproduce near vacuum pressure conditions it is foreseen to use the Induction-
Coupled Plasma Minitorch. The facility operates in a range of pressure from 3 kPa to 100 kPa,
which is enough for the pressure sensors that are able to work from 0 to 34 kPa. This way,
note that tests will be covering the 91.2% of the sensors operating range. All differential
pressures will be sampled at a rate of 1 Hz as specified in the requirements. During tests, a
mercury manometer will be used to check pressure differentials inside the vacuum chamber,
taking those values as reference, in order to compare them against the acquired ones with the
DAQS of XPL03. With these results, a calibration of the system will be performed by modifying
either the circuitry or the software. In addition, it must be ensured the electromagnetic field
generated by the facility does not affect the data acquisition. For this reason, it will be
required some kind of protection for testing, which is going to be an aluminum foil.
These tests also aims to generate valuable data for the absolute pressure sensors calibration
included in XPL02 and XPL03. By the end of this section, it will be possible to check the real
specifications of the entire system, comparing them to the expected ones. Even though it is
out of scope, it is expected to test this payload in Plasmatron, a facility able to simulate near
real re-entry conditions. Some of the characteristics of the facilities used for the testing of
XPL03 are defined in the following section.
4.2.2.4.2.2.4.2.2.4.2.2. Facilities and main testing componentsFacilities and main testing componentsFacilities and main testing componentsFacilities and main testing components
• INDUCTION-COUPLED PLASMA MINITORCH
It is a high enthalpy facility able to generate a vertical jet of plasma in a tube shaped chamber
of 0.3 m of diameter and 1.2 m long. The facility, shown in Figure 26, is able to work in a range
of pressure from 30 mbar to atmospheric. The plasma is generated by electrical induction
inside a 3 cm diameter not refrigerated quartz tube, with a power consumption of 15 kW. In
addition, a recirculating water system is used to protect the test chamber from plasma
51
heating, as well as to cool the gas extracted from the test chamber by a 190 m3/h vacuum
pump. The system operates normally in the subsonic regime, but by addition of a cooled Laval
nozzle a supersonic plasma jet at Mach 2.2 can be obtained. Argon, nitrogen, carbon dioxide,
air or other gas mixtures can be used to
generate the plasma.
The instrumentation includes cooled
pressure and heat flux probes, Langmuir
probes, and a laser Doppler velocimeter.
One important advantage is that Minitorch
can use some of the Plasmatron
instrumentation, such as the emission
spectrometer and the two-color pyrometer.
Even though for the current test the facility
is going to be used as a vacuum chamber, it
can also be used for inductively coupled
plasma torch optimization studies or for
comparisons with numerical simulations of
inductively coupled plasma flows.
• PLASMATRON
The Plasmatron, shown in Figure 27, is a high enthalpy facility in which a jet of plasma is
generated in a test chamber kept at sub-atmospheric pressure (between 5 and 200 mbar). The
plasma is generated by heating a gas (argon, N2 , CO2, air or any other gas mixture) to
temperatures up to about 10000 K, using electrical current loops induced inside a plasma
torch. Its Plasma generator offers much better plasma purity compared to classical arcjets, as
there is no pollution from any
vaporized electrode material.
The facility, which is the most
powerful induction-coupled plasma
wind tunnel in the world, has a
power consumption of 1.2 MW. The
plasma generator feeds the single-
turn inductor of an 80 mm or 160
mm diameter plasma torch, which is
mounted on a 1.4 m diameter, 2.5 m
long, water-cooled test chamber.
Hot gas from the test chamber exits
through a group of three rotary-vane
Figure 26. Induction-Coupled Plasma Minitorch
Figure 27. Plasmatron from Von Karman Institute
52
vacuum pumps and a Roots pump, which are capable of extracting 3900 m3/h, with a terminal
vacuum capability of 0.04 mbar.
A 1050 kW cooling system using a closed loop deionized water circuit (2090 litres/min) and
fan-driven air coolers provide cooling to all facility components. Plasmatron is controlled using
two PC's for controlling and monitoring operations. Available instrumentation includes
intrusive cooled pressure and heat flux probes, a one-meter emission spectrometer with CCD
camera and a two-color pyrometer.
• MERCURY MANOMETER
This device uses liquid mercury to
measure the differential pressure
between two points. Particularly, the
manometer from Von Karman Institute
illustrated in Figure 28 has a
measurable span of 700 mmHg and a
pressure resolution of ±0.1 mmHg.
During the testing one pressure tap will
be directly connected to the vacuum
chamber and the other one will be let
free measuring the atmospheric
pressure.
• ELECTROMAGNETIC FIELD PROTECTION
As it has been commented before, the
data acquisition system of XPL03 is going
to be installed near the vacuum chamber
during the testing. For this reason, it has
been decided to place an aluminum foil
between the facility and the circuitry in
order to avoid electromagnetic related
problems as shown in Figure 29.
Figure 28. Mercury manometer
Figure 29. Electromagnetic field protection
53
• DIGITAL ATMOSPHERIC PRESSURE SENSOR
Before starting the tests and right after they have finished, atmospheric pressure has been
noted in order to identify possible variations. The device has a resolution of ±0.1 Pascal and is
illustrated in Figure 30.
Figure 30. Digital atmospheric pressure sensor
• MERCURY THERMOMETER
The same way as atmospheric pressure, atmospheric temperature has been noted before
starting the tests and once they have been finished. It has been used a mercury thermometer
with a resolution of ±0.1ºC and it has been placed next to the measurement chain of XPL03.
• DATA ACQUISITION SYSTEM
The measurement chain for the differential pressure sensor of XPL03 has been implemented
on a breadboard, as you can see in Figure 31. All components are properly connected between
them to meet the configuration of Version B. As you can see, one of the pressure ports was let
free to the atmospheric pressure and the other one, with the transparent silicon tube, has
been directly connected to the vacuum chamber. All data generated by this circuit has been
sent to a laptop incorporating the required software.
Figure 31. DAQS of the differential pressure sensor of XPL03
54
• MULTIMETER
This device is going to be used to get voltage data connecting it to different points of the
circuit in order to check everything is going well during tests. In addition, it will be collected
the voltage outputs from the instrumental amplifier to compare them to the values gathered
with the laptop and identify possible errors in the system.
Design 2 of the spool. On the left, drawing of the bolt; on the right, drawing of the nut:
78
Design 2 of the spool. On the left, drawing of the bolt; on the right, drawing of the nut:
• Drawing for design 3 of the spool:
Drawing for design 3 of the spool:
79
80
APPENDIX 4: APPENDIX 4: APPENDIX 4: APPENDIX 4: Detailed test matrixesDetailed test matrixesDetailed test matrixesDetailed test matrixes
• Test matrix 1Test matrix 1Test matrix 1Test matrix 1 (13:40 h, 10(13:40 h, 10(13:40 h, 10(13:40 h, 10----07070707----2013)2013)2013)2013) Test Name Differential pressure [mmHg] Number of measurements Data Acquisition Frequency [Hz] Vacuum chamber pressure [kPa]