The Design and Characterization of a Porous-emitter

Electrospray Thruster (PET-100) for Interplanetary CubeSats

Chengyu Ma1, Charlie Ryan2

1 PhD Candidate,

University of Southampton

cm4f15@soton.ac.uk

2 Lecturer in Astronautics,

University of Southampton

c.n.ryan@soton.ac.uk

+44 023 8059 3881

OUTLINE

The design of a miniature electrospray thruster

The testing performance of the thruster

Issues found and solutions

Work to be done in the future

ADVANCED MICRO/NANO SATELLITE MISSIONS ON TREND

Formation flying

QB 50

Constellations

Planet (Labs)

OneWeb

Starlink

Higher orbit & deep space missions

MarCo

Lunar IceCube

Propulsion system need

High specific impulse

Relatively high thrust

Compact size

High efficiency

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.

MarCo

Lunar IceCube

TYPICAL PERFORMANCE COMPARISON OF VARIOUS

ELECTRIC PROPULSION SYSTEMS

10

20

40

80

160

320

640

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Thru

st p

er

po

we

r (m

N/k

W)

Specific impulse (s)

η=100%

η=80%

η=60%

η=40%

η=20%

η=10%

ResistoJet

FEEP

HET

Colloid

Hydrogen Arcjets

Arcjets

SF-MPD

PPT

GIT

AF-MPD

IFM-Nano-FEEP

HEMPT

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

APPLYING PET-100 ON CUBESATS

1 thruster

MAX thrust = 223 µN

MAX power = 13.85 W

4 thrusters

MAX thrust = 892 µN

MAX power = 55.4 W

8 thrusters

MAX thrust = 1.784 mN

MAX power = 110.8 W

MAX Isp = 7527 s

Power efficiency = 62.7%

6 U3 U

TYPICAL PERFORMANCE COMPARISON OF

VARIOUS ELECTRIC PROPULSION SYSTEMS

10

20

40

80

160

320

640

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Thru

st p

er

po

we

r (m

N/k

W)

Specific impulse (s)

η=100%

η=80%

η=60%

η=40%

η=20%

η=10%

ResistoJet

FEEP

HET

Colloid

Hydrogen Arcjets

Arcjets

SF-MPD

PPT

GIT

AF-MPD

IFM-Nano-FEEP

HEMPT

PET

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

SPECIFIC IMPULSE AND FUEL EFFICIENCY

PET-100: Isp = 7500 s

Full mass proportion at ΔV=1km/s: 1.3%

Full mass proportion at ΔV =10 km/s: 12.7%

CONCLUSIONS

▪ PET-100 manufacturing and test:

▪ CNC machining is a low-cost but rather promising method for manufacturing porous glass electrospray emitter arrays

▪ Extractor current of PET-100 is controllable

▪ Propulsive performance:

▪ The PET-100 achieved a (relatively) high thrust up to 223 µN and a high specific impulse of 7527 s at 3,000 V

▪ Can enable interplanetary CubeSat transfer with reasonable fuel cost

▪ Future work:

▪ Main lifetime limiting issue: electrochemical effects

▪ Improve emitter geometric property

▪ On-board power process unit

▪ Complete measurement system (RPA, Faraday Cup)

▪ PET-1600

MICRO/NANOSATELLITE HIGH ΔV APPLICATIONS

PET-1600

▪ To be manufactured

▪ An emitter array of 40 x 40

▪ Estimated performance

▪ Thrust: 3.5 to 11 mN

▪ Specific impulse: 7500 s

▪ Power: 150 W

ION BEAM SHEPHERD USING PET

▪ To be investigated

▪ Targets: space debris and small asteroids

▪ Bidirectional emission

▪ Deployable structure

▪ Scalable thrust and power

▪ 30 mN & 7500 s:

▪ 100 x 100 emitter array with 20 cm x 20 cm, 1.5 kW

▪ 300 mN & 7500 s:

▪ 316 x 316 emitter array with 63 x 63 cm, 15 kW

▪ 3 N & 7500 s:

▪ 1000 x 1000 emitter array with 2 x 2 m, 150 kW

CS CS

Solar panel

Emitter

panel

Asteroid

https://www.esa.int/gsp/ACT/doc/ARI/ARI%20Study%20Report/ACT-RPT-MAD-ARI-10-6411c-1107-FR-Ariadna-Ion_Beam_Shepherd_Madrid_4000101447.pdf

Thank you!

Any questions?