The Design and Characterization of a Porous-emitter Electrospray Thruster (PET-100) for Interplanetary CubeSats Chengyu Ma 1 , Charlie Ryan 2 1 PhD Candidate, University of Southampton [email protected]2 Lecturer in Astronautics, University of Southampton [email protected]+44 023 8059 3881
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The Design and Characterization of a Porous-emitter
Electrospray Thruster (PET-100) for Interplanetary CubeSats
Klesh, A., & Krajewski, J. (2015). MarCO: CubeSats to Mars in 2016. In Proceedings of the 29th Annual AIAA/USU Conference on Small Satellites. Logan, Utah.
RJ Peukert, M., & Wollenhaupt, B. (2014). OHB-System ‘ s View on Electric Propulsion Needs. In Proceedings of the EPIC Workshop 2014. Brussels.
Enpulsion. (2018). IFM Nano Thruster Product Overview. Retrieved May 18, 2018, from https://enpulsion.com/uploads/a/admin/ENP_-_IFM_Nano_Thruster_-_Product_Overview.pdf
Micro-propulsion for CubeSats
Miniaturized Hall Effect thruster
Miniaturized ion thruster
Micro-resistojet thruster
Helicon plasma thruster
Pulsed plasma thruster (PPT)
Field emission electric propulsion (FEEP)
Micro-electrospray thruster
ELECTROSPRAY THRUSTERS
• Liquid propellant: generally Room Temperature Ionic Liquids
• Electrostatic force v.s. surface tension
▪ Remain high performance when scaled
• High efficiency (>70%)
• Scalable thrust: 0.1 µN to 100s mN (limited by power)
• High specific impulse (>4000 s)
▪ Compact configuration
• Light weight
• Passive propellant feeding based on capillary action
• Pressure-free propellant storage
A suitable candidate for micro/nanosatellite maneuvers.
Emitter
Extractor
AIM OF THIS RESEARCH
To develop a low-cost electrospray thruster with high-Isp and high thrust for interplanetary CubeSats.
Test and characterization the thruster performance.
Understand the physics behind and improve the thruster performance.
DESIGNS OF
POROUS-EMITTER ELECTROSPRAY THRUSTERS (PET)
MAX thrust per emitter:
2.2 µN to 7 µN
MAX specific impulse:
4500 s to 8200 s
PET-proto PET-25 PET-100
PET-1
40 mm
1. Ma, C., Bull, T., & Ryan, C. (2017). Feasibility Study of a Micro-Electrospray Thruster Based on a Porous Glass Emitter Substrate. In Proceedings of the 35th International Electric Propulsion
Conference. Atlanta, Georgia: Electric Rocket Propulsion Society.
2. Ma, C., & Ryan, C. N. (2018). Characterization of a Micro-electrospray Thruster with a Porous Glass Emitter Array. Proceedings of the Space Propulsion Conference 2018, (SP2018-260).
3. Ma, C., & Ryan, C. (2018). A Miniature Electrospray Thruster for Precise Attitude Control of a Nanosatellite. Proceedings of 4th IAA Conference on Dynamics and Control of Space Systems,
(AA-AAS-DyCoSS4-3-7).
TESTING THRUSTER (PET-100) DESIGN
CNC machined emitter
Ionic liquid propellant EMI-BF4
High surface tension
High electrical conductivity
Purely Ionic emission
high specific impulse (>4000 s)
Porous reservoir
Passive propellant transport
3D printed casing
Water-jet cut extractor
Distal electrode - Porous Ni sheet
40 mm
Miniature & low-cost !
EXPERIMENTAL SET UP - THE DAVID FEARN ELECTRIC PROPULSION LABORATORY
2 m in diameter, 6 m in length
Base pressure 9.8 x 10-7 mbar
I-V CHARACTERISTICS OF PET-100
▪ Onset voltage:
▪ ±2200 V with ±2.5 µA
▪ MAX voltage:
▪ +2970 V with +3.19 mA
▪ -2890 V with -4.75 mA
▪ MAX current per emitter
▪ +31.9 µA
▪ -47.5 µA
I_emitter
I_extractor
I_emission
PLUME HITTING EXTRACTOR
Emission current / emitter current
Excessive plume accumulated
▪ Post-test extractor
REDUCE PLUME HITTING
10%-35% 5%
-3.5
-2.5
-1.5
-0.5
0.5
1.5
2.5
3.5
-3000 -2000 -1000 0 1000 2000 3000
Cu
rren
t (m
A)
Thruster voltage (V)
Emitter currentExtractor current
0
20
40
60
80
100
-3000 -2000 -1000 0 1000 2000 3000
I_em
issi
on
/ I_
emit
ter
(%)
Thruster voltage (V)
-3.5
-2.5
-1.5
-0.5
0.5
1.5
2.5
3.5
-3000 -2000 -1000 0 1000 2000 3000
Emis
sio
n c
urr
ent
(mA
)
Thruster voltage (V)
TIME-OF-FLIGHT CHARACTERIZATION OF PET-100
ToF collector size : 37 cm x 37 cm
ToF distance = 90 cm
No secondary electron emission (SEE) suppression grid was used.
Φ is the emitter voltage
𝐿 is length of flight
𝑡 is the time of flight
𝐼(𝑡) is the current variation on ToF trace
𝑔0 is the Earth gravitational acceleration
Thrust on the ToF collector
Specific impulse
Mass flow rate
TOF CHARACTERIZATION OF PET-100
At positive voltages: +1997 V, +2465 V, +2711 V and +2970 V.
At +2970 V
Thrust = 223 µN
Thrust per emitter = 2.23 µN
Specific impulse = 7527 s
Power efficiency = 62.1%
Emission of nearly pure monomer ions (EMI+)
Minor fragmentation effects
Secondary electron emission (SEE) – to be confirmed
TOF CHARACTERIZATION OF PET-100
Possible reasons:
▪ Droplets in emission: to further limit flow rate by using
emitters with smaller pores
▪ Secondary electron emission (SEE) – to be confirmed
At negative voltages: -1997 V, -2447 V, -2686 V and -3067 V.
ESTIMATION OF PERFORMANCE RANGE
Thrust
Pure monomer
Pure dimer
Specific impulse
Pure dimer
Pure monomer
6000 s to 8500 s5 µN to 223 µN
INITIAL PLUME ANGLE MEASUREMENT
At +2000 V
Plume half angle = 17 degrees
PROBLEMS: ELECTROCHEMICAL EFFECTS
A main life-time limiting factor
Tested for 30 mins
MAX test time of single emitters:
5 hours
A long life-time test is needed.
Emitter before test Emitter post-test: degradation