Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace

Interplanetary CubeSat Workshop, Cambridge May 29-30, 2012

Ion Electrospray Thruster Assembly for CubeSats

François Martel, Espace; Paulo Lozano, MIT AeroAstro

• Ion electospray microthrusters, an ideal propulsion technology for CubeSats• High IsP, escape velocity and injection into interplanetary space• Ion electrospray micro-thruster technology• Precision thruster assemblies for CubeSat propulsion and attitude control• One example of CubeSat interplanetary mission application enabled by the ion microthruster technology

1

Ion Electrospray Thruster Assemblies for CubeSats

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace

• Ion electrospray microthrusters are ideal ion propulsion technology for CubeSats:• Miniaturized, very low mass and small volume, high mass/volume thrust density• Very high ISp (2500-5000 sec) hence low volume / mass of propellant• Rugged, no moving parts, no valves, no pressurized tank, non-toxic propellant• Modular: can be mass produced and assembled in multiple configurations and arrays, and miniaturized assemblies• Precision control (acceleration voltage, thrust pulse duration)

2

Ion electrospray microthrusters: advantages and characteristics for CubeSat applications

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace

• The high Isp of the ion microthrusters (2500-5000 sec) minimizes the amount of propellant required to achieve large ΔVs.

• The low propellant requirements and the low-mass thruster assemblies allow 3U CubeSats to reach escape velocity with thruster assemblies using a fraction of a U.

•A 3U Cubesat probe launched in GO as miniature piggy-back payload, can reach an heliocentric orbit with the ion micro-thruster assemblies. The whole assembly will fit in less than1/2U and provide continued attitude control to the platform.

3

High Isp, escape velocity and interplanetary space

Mp

M 0

= 1− exp −ΔVgIsp

⎛

⎝⎜⎞

⎠⎟

propellant mass fraction

In a first approximation for: Isp~ 3000 sec; Mo=3kgm

ΔVe(600km) ~3.12 km/secMp= 320 grams

ΔVe(36000km)~1.27km/secMp= 127 grams

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 4

Microthruster Fabrication Process

Frame

Porous

Bonding

Extractor

Frame fabricated in silicon using plasma

processing

Porous metal substrate bonded to

silicon frame

Porous metal processed to form a 2-D array of ion emitters

Extractor grid is bonded to silicon

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 5

Examples of Etched Micro-Tips

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 6

Alignment of Extractor Grid

• Good alignment is essential for MEMS thruster performance

Detail of extractor/emitter assembly as seen through a microscope

Inspection using a microscope

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 7

Microthruster Performance and Fine Control

Specific impulse: 3000-5000 Thrust density: 0.1 - 0.2 N/m2

Current (and thrust) are a strong function of voltage beyond the extraction potential

High resolution controls of extractor grid potential and pulse durations allow the ion microthrusters to perform as precision actuators for fine thrusting of space platforms

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace

• The Precision Electrospray Thruster Assembly (PETA) is a NASA SBIR development of a flight-worthy, high-resolution, high-voltage source to demonstrate the performance of the miniature ion electrospray thrusters as precision actuators

• An important aspect is the implementation of the PETA assembly in a functionally capable propulsion and attitude control assembly for cubesats to facilitate practical and rapid flight tests of the thruster and assembly performances. (Cubesat form factor (9.5 x 9.5 X 3.3 cm=1/3U), designed to minimize consumption and obtain good power conversion efficiency (70%).

• The PETA cubesat prototype assemblies also provide new capabilities to cubesat missions, with a minimum of 200m/sec ΔV to 3U CubeSat and pitch/yaw/roll control

• Additional ΔV can be added with larger propellant tanks

8

Precision Electrospray Thruster AssemblyDevelopment

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 9

• Several iterations led to 1/3 U configuration for the 3-board assembly (33mm thickness, CubeSat format, based on actual measurements)

• Design based on a total of 20 grams propellant (200 m/sec-3U); 16 bit voltage resolution; 0 to ±1600 V; millisecond switching; 70% power conversion efficiency; pitch, yaw, roll and propulsion

• Possibility of increasing ~ doubling tank size in the same configuration

• Possibility of radical increase in propellant mass by adding one board (increasing thickness to ~ 48mm)

• Flexibility in thruster locations and orientations

Precision Electrospray Thruster AssemblyBaseline configuration

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 10

• Rev 1 HV board (in test) provides ± 800V to ± 1800 V (3600V) with 16 bit resolution, and current and HV feed-back measurements. Rev 3 (in production) provides 0 to ±1600 V, and 70% conversion efficiency.

PETA Rev 1 Tests

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 11

• High Voltage / Control board (Rev. 1) undergoing tests with ion electrospray source at MIT

PETA Rev 1 Tests

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 12

• High voltage steps applied to a single ion electrospray source

• In that case the estimated equivalent thrust is about 6 nanoNewtons, and is brought through three large 25 Volt steps to about 7.5 nanoNewtons, a total of 1.5 nanoNewton modulated through 75 volts

• Prototype assembly can provide at least 1 ma of current, or 100 micro-Newtons of thrust

PETA Rev 1 Tests

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 13

• Two PETA assemblies provide full (propulsion, pitch, yaw, roll) and high resolution control to the three U CubeSat platform

• The assemblies provide a total of about 400 m/sec ΔV

• In this case the thrusters are all oriented “side-way” to leave the 3U extremities to the S-band antenna patches

Example of PETA Cubesat configuration(test mission)

Espace &MIT AeroAstro

iCubeSat Workshop, Cambridge, May 29-30, 2012 P. Lozano, MIT AeroAstro F. Martel, Espace 14

The ion microthruster assemblies facilitates new lower-cost versions of interplanetary mission concepts such as SIRA (R. J. Mac Dowall, N. Gopalswammy et al. 2005). ( HF imaging for Solar science & space weather) An array (~16) of CubeSats in interplanetary space (L1 or other heliocentric orbit) form the elements of a sparse antenna in the HF range. They hover around a Mothership (<100kg) that collects, correlates and compresses CubeSats RF & ranging data and manages ground links.

Mothership and CubeSat “grape/carrier” get to their interplanetary orbits by hitching a ride to GO with a multi-ton GO satellite launch (no dedicated launch). They propel to their heliocentric station with arrays of ion microthrusters.

Example of interplanetary mission concept enabled by the ion-microthruster technology