COMPASS Orion Design Session • Purpose: – a cubesat design for SLS launch opportunity for EM -1 – EM-1 launch (2018) to a lunar free return trajectory. – A small ∆V before

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DAVID: Diminutive Asteroid Visitor with Ion Drive

A Cubesat Asteroid Mission Geoffrey A. Landis

NASA Glenn Research Center

COMPASS Team at NASA Glenn: Steve Oleson, Melissa McGuire, Aloysius Hepp, James Stegeman, Mike Bur, Laura Burke,

Michael Martini, Jim Fittje, Lisa Kohout, James Fincannon, and Tom Packard Collaborating Institutions:

Busek (propulsion); COSMIAC (spacecraft integration); Case Western (Ralph Harvey, Asteroid Science lead); Planetary Science Institute (Asteroid Science)

DAVID visualization

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Background:

• Purpose: – a cubesat design for SLS

launch opportunity for EM-1 – EM-1 launch (2018) to a

lunar free return trajectory. – A small ∆V before lunar fly-by

can adjust the escape trajectory to C3 =0 (co-orbital to Earth)

• Mission: visit an asteroid

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Highly Constrained Project:

• Size constrained: – 6U – about the size of a large shoebox

• Mass constrained – 12 kg total mass – including 1.3 kg assumed growth

• Propulsion constrained – no energetic components

• Cost constrained – $5.6 million dollar cost cap – about $5 million after subtracting

required cost reserves – (does not include launch)

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Choice of Target

• 12874 close approaches by asteroids were analyzed • List narrowed down:

– nearest approach no earlier than 2019 (>1 year after launch date) – Nearest approach no later than 2020.

• 2001 GP2 was chosen as a target. – From visual magnitude, estimate* ~18-meter diameter.

• Fly-by and Rendezvous missions analyzed • From escape, ∆V of ~400 m/s needed for May 2020 fly-by.

• October 2020 fly-by was just outside the window of the solicitation

• ∆V ~2000 m/s needed to achieve a rendezvous.

*depending on asteroid albedo

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Asteroid 2001 GP2 Earth Fly-by

• Closest pass: Oct 3, 2020 • Closest approach at 0.5 to 4.3 time Lunar distance • (~100,000 to 1 million miles)

– Further observations will decrease uncertainty • V relative: 2.37 km/sec

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Near Earth asteroid Eros (viewed by the NEAR spacecraft)

Itokawa: the smallest asteroid ever visited by a spacecraft

viewed by the Hayabusa spacecraft

What makes Asteroid 2001 GP2 Interesting?

• 10-20 meters in diameter – Two orders of magnitude smaller than any other

asteroid ever visited – Typical of “city killer” impact threats (much more

frequent than extinction-level threats)

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Asteroid Itokawa

What makes Asteroid 2001 GP2 Interesting?

• Asteroids this tiny have never been visited by spacecraft – Recent modeling suggests YORP-induced spin-ups

can disaggregate bodies smaller than 150 m in size. – 2001–GP2 sits significantly below this model’s

threshold for stability: • Will it be an Itokawa-like body with a blocks and finer

grained material, or a single cohesive block? • Will it be tumbling chaotically or spinning? • What history is evident or implied?

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Asteroid Itokawa

Representative of a whole class of objects that are numerous and interesting, but have never been observed up close

DAVID (Diminutive Asteroid

Visitor using Ion Drive)

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• 6-U cubesat • Mass limit 12 kg • Design must include

margin on all systems

Size

23.94 cm

36.59 cm

11.28 cm

Planetary Systems Corporation Canisterized Satellite Dispenser

SLS 6U Cubesat Deployed Dimensions

13.86 cm

52.29 cm

33.8 cm

81.46 cm

Arrays Rotated 90 Degrees

32.69 cm

System Schematic

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Propulsion Trade Off

Mission is mass and volume constrained

Electric propulsion systems:

• High Specific Impulse: Low propellant use, high power requirement

– If Isp is too high, the power system mass dominates the system

• Low Specific Impulse: High propellant use, low power requirement • If Isp is too low, the propellant mass dominates the system

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Propulsion Choice

• Trade-off study included many propulsion systems • The Hall thruster has the greatest base of experience in

operation in space, but the cases analyzed exceeded the initial mass allowance of 12 kg, as did the Xe ion thruster.

• A case with two 10-W PUC (Propulsion Unit for Cubesats) electrospray thrusters also exceeded the mass allowance, but a revised case where this was reduced to lower power and a single thruster was run, which met the requirements.

• Single PUC electrospray thruster chosen for baseline design

• Rendezvous case requires higher Isp and larger solar array – ion engine needed

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Electrospray Thruster

Propellant: high density ionic liquid

Busek Electrospray Thruster

• Mechanical Simplicity: No Moving Parts • Small Volume, Mass, and Power • Leverages $20M NASA ST7 Technology Flight

Development • Leverages SBIR Work on Micro-Valves and Power

Management • Non-Volatile Propellant • Multi-Emitter Design • Lisa Pathfinder Flight Heritage • Propellant Stored in Low Pressure Stainless Steel

Bellows Tank • Cold Ion Plume (No Hot Gas) • Self Regulating Feed System • Piezo-Actuated Isolation Micro-Valve

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Busek Electrospray Thruster

Integrated PPU/DCIU (Engineering Model)

LISA Pathfinder Thruster Integration

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2001 GP2 Interplanetary Trajectory 2018 Launch

• Colloid (Electrospray) Thruster Parameters:

– Power to thruster = 9W – Isp = 800s – Efficiency = 31% – Duty Cycle = 90%

• Trajectory Assumptions: – Fly-by of 2001 GP2 – Constant 9W to thruster – SLS Launch Date: 12/17/2018

• 4 days, 10 m/s to correct for worst-case SLS injection

– Spacecraft Wet mass = 12 kg • Trajectory Details:

– Delta-V = 390 m/s – Required Prop Mass = 0.58 kg – TOF = 507 days – Total Thrusting Time = 89 days

2018 Thrust Profile

2001 GP2 Interplanetary Trajectory mid-2018 Launch (Double Fly-by)

• Colloid (Electrospray) Thruster Parameters:

– Power to thruster = 9W – Isp = 800s – Efficiency = 31% – Duty Cycle = 90%

• Trajectory Assumptions: – Double Fly-by of 2001 GP2 – Constant 9W to thruster – SLS Launch Date: 7/31/2018

• 4 days, 10 m/s to correct for worst-case SLS injection

– Spacecraft Wet mass = 12 kg • Trajectory Details:

– Delta-V = 365 m/s – Required Prop Mass = 0.546 kg – TOF = 1037.8 days – Total Thrusting Time = 75 days

2001 GP2 Interplanetary Trajectory

Fly-by 2001 GP2

2001 GP2 Interplanetary Trajectory

Fly-by 2001 GP2

2001 GP2 Interplanetary Trajectory 2018 Launch (October Fly-by)

• Colloid (Electrospray) Thruster Parameters:

– Power to thruster = 9W – Isp = 800s – Efficiency = 31% – Duty Cycle = 90%

• Trajectory Assumptions: – Fly-by of 2001 GP2 – Constant 9W to thruster – SLS Launch Date: 12/17/2018

• 4 days, 10 m/s to correct for worst-case SLS injection

– Spacecraft Wet mass = 12 kg • Trajectory Details:

– Delta-V = 43 m/s – Required Prop Mass = 0.065 kg – TOF = 660 days – Total Thrusting Time = 57 days

2018 Thrust Profile (October Fly-by)

Instruments

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SLS 6U Cubesat External Components

Sun Sensor

Science Camera

Solar Array Wing

X-Band Patch Antenna

Neutralizer

Solar Array Wing Sun Sensors

X-Band Patch Antenna

Electrospray Thruster

Sun Sensor

Solar Array Gimbal Unit

Solar Array Wing

X-Band Omni Antennas

Space Weather Science

Sun Sensor

Star Tracker

Sun Sensor

Status

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• Proposal submitted to SIMPLEX solicitation, but not selected for the EM-1 Mission Opportunity

• Proposal was rated highly, and selected for a one-year technology development study • Asked by program office to focus work on maturing the instrumentation

• Continuing to working on the engineering design • Looking for a launch opportunity to C3=0 in 2019 or

early 2020

Where do we go if we find a launch, but miss the window for the Oct 2020 fly-by?

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• Latest possible launch for 2020 fly-by is ~May 2020 • Asteroid 2011-CL50 has December 24 2020 fly-by

• not quite as good, but almost • only slightly later

• If we miss that, 2010 UE51 has opportunity Dec. 2023 • Tiny asteroid (~10 m class) • Farther away, but much slower fly-by speed • Possibility to do a rendezvous mission

Conclusions

• Asteroid mission is possible with a 6-U cubesat Targeting near earth asteroids that fly close to Earth minimizes the propulsion required for fly-by/rendezvous

• Upcoming Oct 2020 fly-by has VERY low ∆V *assuming you can reach escape

• Rendezvous mission is possible as a stretch goal

– ∆V is very significant for a 6U cubesat: – ~2000 m/s needed for rendezvous with 2001 GP2

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DAVID visualization

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Backup/Slides not used

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Mission Delta-V Summary

• Total propellant in table represents usable propellant • Additional 5% of usable carried as margin in inert mass of vehicle • Isp = 800 s

Reacquiring 2001 GP2

• Asteroid hasn't been seen since its discovery year • Uncertainty in orbit is a million miles!

– we need to refine orbit or else we miss it entirely

• The good news: it makes an Earth close approach in May 2019, at a distance of 0.154 AU • can reacquire asteroid and refine orbit one year before the May 2020

fly-by; 17 months before the Oct 2020 fly-by • plenty of time to fine-tune trajectory • phase angle to sun ~90° (directly ahead of Earth in orbit)

• The bad news: estimated magnitude at this approach is about ~24 – need a big telescope to see object that faint.

• Keck or similar capability ground-based telescope • Hubble space telescope

• February 2020 close approach at 0.124 AU is near opposition – 3 month lead time for May 2020 fly-by, 8 month for Oct 2020 fly-by

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Propulsion System Layout

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Micro Valve Bellows Tank

Electrospray Thruster\l PPU/DCIU Propellantless Cathode

NEXT Style

Gimbal

SLS Cubesat Bus Propulsion (EP Hardware) MEL

• SLS Cubesat Bus Propulsion (EP Hardware) Subsystem MEL

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WBS Description QTYUnit

MassBasic Mass Growth Growth

Total Mass

Number Case #3.5 SLSCubesat 2013 CD-2013-101 (kg) (kg) (%) (kg) (kg)12/3/201306 SLS Cubesat 7.80 16.8% 1.31 9.1106.1 Cubesat Bus 7.80 16.8% 1.31 9.11

06.1.9 Propulsion (EP Hardware) 1.40 10.7% 0.15 1.55

06.1.9.a Primary EP System Hardware 0.72 10.8% 0.08 0.80

06.1.9.a.a EP System Hardware 0.72 10.8% 0.08 0.80

06.1.9.a.a.a Electrospray Thruster 1.00 0.52 0.52 8.0% 0.04 0.56

06.1.9.a.a.b Gimbal 1.00 0.20 0.20 18.0% 0.04 0.24

06.1.9.b Power Processing Unit (PPU) 0.50 8.0% 0.04 0.54

06.1.9.b.a Integrated PPU/DCIU 1.00 0.50 0.50 8.0% 0.04 0.54

06.1.9.c Propellant Management (EP) 0.18 18.0% 0.03 0.21

06.1.9.c.a EP Propellant Tank system 0.18 18.0% 0.03 0.21

06.1.9.c.a.a Custom Tank 1.00 0.13 0.13 18.0% 0.02 0.15

06.1.9.c.a.b Feed System 1.00 0.05 0.05 18.0% 0.01 0.06

SLS Cubesat Bus Propellant (EP) MEL

• SLS Cubesat Bus Propellant (EP) Subsystem MEL

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WBS Description QTYUnit

MassBasic Mass Growth Growth

Total Mass

Number Case #3.5 SLSCubesat 2013 CD-2013-101 (kg) (kg) (%) (kg) (kg)12/3/201306 SLS Cubesat 7.80 16.8% 1.31 9.1106.1 Cubesat Bus 7.80 16.8% 1.31 9.11

06.1.10 Propellant (EP) 0.69 0.0% 0.00 0.69

06.1.10.a Main Propellant (EP) 0.69 0.0% 0.00 0.69

06.1.10.a.a Primary EP Propellant Used 1.00 0.63 0.63 0.0% 0.00 0.63

06.1.10.a.b Primary EP Propellant Residulals (Unused) 1.00 0.03 0.03 0.0% 0.00 0.03

06.1.10.a.c Primary EP Propellant Performance Margin (Unused) 1.00 0.03 0.03 0.0% 0.00 0.03

Communication

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For analysis purposes, a transmission antenna gain of 8 dBi was used for both systems, not taking advantage of the ability of X-band to produce a tighter beam spread. Both S-band and X-band transmission can accomplish the required data rate of 174 bps with either receiving antenna. The encounter data can thus be downlinked in two DSN sessions with the 34-m receiver, or in less than one session, if the 70-m dish can be used.

CMAD Spectrometer

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2001 GP2 Interplanetary Trajectory Rendezvous 2017 Launch

• 3cm RF Ion Thruster Parameters: – Power to thruster = 50W – Isp = 2200s – Efficiency = 27% – Duty Cycle = 90%

• Trajectory Assumptions: – Rendezvous of 2001 GP2 – Constant 50W to thruster – SLS Launch Date: 12/17/2017

• 4 days, 10 m/s to correct for worst-case SLS injection

– Spacecraft Wet mass = 12 kg • Trajectory Details:

– Delta-V = 2088 m/s – Required Prop Mass = 1.11 kg – TOF = 611 days – Total Thrusting Time = 456 days

2001 GP2 Interplanetary Trajectory

Arrive at 2001 GP2

Requires 11,000 hours (456 days) of thrust -ion thruster needs qualification for this duration of operation

Fly-by versus rendezvous summary

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