lecture-17 ppt for Cubesat

Micropropulsion for Nanosatellites

Olivia Billett - AA 236A 2006

Mission Statement

Why do we need thrusters for CubeSats?

�Attitude Control

�Camera Pointing

�Formation Flying

�Rendezvous

�Vehicle Inspection

�Orbit Changes

�De-Orbit Capability

�Research and Development

�Because they’re cool

CubeSat Constraints

� Size: < 10 x 10 x 10 cm

� Weight: < 1 kg

� Power: < 1 Watt

� Minimum Ibit ~ 10-4 Ns

� Flight ready ?

� Affordable ?

What’s so hard about adding thrusters?

Previous Missions

What kinds of micropropulsion are currently in use?

Not much. As of 2006:

• 1 CubeSat (UIUC ION), pending launch

• Few nanosats (UW, MTU, U Toronto) but no launches scheduled

In student satellites:

In industry satellites:

Increasing interest from DARPA, AFRL

• SSTL, Northrop Grumman, JPL

(Viable) Types of Micropropulsion

� Electric Propulsion� Pulsed Plasma Thruster (PPT)

� Vacuum Arc Thruster (VAT)

� Micro Resistojet

� Colloid Microthrusters

� Chemical Propulsion� Monopropellant MEMs

� Bipropellant MEMs

� Solid Propellant MEMs

� Cold gas thrusters (micro & MEMs)

. . . more?

Evaluation Criteria

� Primary Propulsion vs Attitude Control?

� Thrust < 1 N vs Ibit ~ 0.1 mNs

� CubeSat constraints:

� 1 kg, including all fuel

� 1 W (average power)

� 10 x 10 x 10 cm

� cheap!










the PPT man

Andy Sadhwani

2006 Thrusters Team Leader

Pulsed Plasma Microthruster

�Thrust: 0.006 mN

�Rotate 90º: 12 min (4,500 pulses)

�Lifetime: Forty 90° rotations (200,000 pulses )

�Input: 5 V at 30 mA

�Output: 1500 V at 1000 A for 10 ns at 6 pps

Specs

�Low Thrust

�EM Interference

�Much R&D Left

�High ISP

�Small

�Low Power

ConsPros

5 VVoltage

Stepper

1500 V Capacitor

0.03 A

1000 A for 10 ns

Teflon Coax

Vacuum Arc Thrusters (VAT)

� Different cathodes vary impulse

� Variable pulsing (width & freq)

� Lighter PPU than PPT

�MVAT – increased thrust?

MTU HuskySat micro-Vacuum Arc

Thruster

� High EMI

� Not tested

� Hard to fit 3 in CubeSat

Alameda Applied Sciences

• Power = 4 W

• Mass = 150 g

• Thrust = 54 uN (90° in 10 min)

• Ibit = 1 uNs

• Size = 4 x 4 x 4 cm

Alameda Applied Sciences

• Power = 4 W

• Mass = 150 g

• Thrust = 54 uN (90° in 10 min)

• Ibit = 1 uNs

• Size = 4 x 4 x 4 cm

Micro Resistojet

UK-DMC Micro-Resistojet, 2003

� Simple system

� Fuel: water, nitrous oxide

� Larger versions used for years

� Low impulse

� Test failed – propellant leak?

� Research discontinued (water)

� Weight of propellant

SSTL [Water]

• Power = 3 W

• Dry Mass = 13 g

• Thrust = 3.3 mN

• Size = 10 cm long

SSTL [Water]

• Power = 3 W

• Dry Mass = 13 g

• Thrust = 3.3 mN

• Size = 10 cm long

� Entire system on silicon chip

� Easy to fit 3 axis system

� Research at: Aerospace Corp, Tshingua U, Indian Institute of Technology

MEMs Resistojet

� Still in research stage

� Thrust not well characterized

IIT

• Power = 1 – 2.4 W

• Thrust = 5 - 120 uN

• Size = 2.5 x 2.5 mm

IIT

• Power = 1 – 2.4 W

• Thrust = 5 - 120 uN

• Size = 2.5 x 2.5 mm

Colloid Microthrusters

� High current � droplets and ions, high ISP

� Low current � droplets only, low ISP

� Tiny arrays of multiple needles with micromachining

� Need external neutralizer

� Operating voltage ~ 15 kV

� Far from flight-ready – still in research stage, unreliable

Busek

• Power = 2 W

• Mass = 80 g

• Thrust = 1 mN

Busek

• Power = 2 W

• Mass = 80 g

• Thrust = 1 mN










Monopropellant MEMs

� High propellant density

� Low power, high Isp

�Wide range of impulse and thrust levels

� Hyrazine (high Isp) and hydrogen peroxide (non-corrosive, easy handling)

� Essentially size of 1U

� High Ibit

Micro Aerospace Solutions

• Wet mass = 175 g

• Ibit = .17 mNs

• Thrust = 50 mN

• Size = 2” diameter tank

• 4 thrusters

• Lifetime = 50,000 firings

• Flight-ready

Micro Aerospace Solutions


• Ibit = .17 mNs

• Thrust = 50 mN

• Size = 2” diameter tank

• 4 thrusters

• Lifetime = 50,000 firings

• Flight-ready

Picture courtesy of Micro Aerospace Solutions websitePicture courtesy of Nasda.go.jp

Bipropellant MEMs

� Very high thrust-to-weight ratio

� High propellant densities

� Low power

� Research at Stanford (Mech Eng)

� Ibit too high for attitude control. Good for primary

propulsion only

� Still in research stage

� More complex system, harder to fabricate

Solid Propellant MEMs

� High propellant densities

� Low power

� No moving parts, feed systems, pumps, leakage

� Tiny arrays of multiple nozzles allow for range of thrust

� One-time-only firing

� Too expensive!

Picture courtesy of Northrop Grumman Picture courtesy of LAAS, France

Cold Gas Thrusters

� Reliable, simple systems with long flight history

� Benign propellants

� Continuous & pulsed operations

� Very low power

� COTS valves available

� High Ibit� Propellant volume

� Leakage

Marotta

• Dry mass = 50 g

• Ibit = 44 mNs

• Thrust = 445 mN

• Power = 0.4 W

• Flight-ready

Marotta

• Dry mass = 50 g

• Ibit = 44 mNs

• Thrust = 445 mN

• Power = 0.4 W

• Flight-ready

Flight history on microsatellites:

NASA ST missions

Picture courtesy of Marotta

Cold Gas MEMs – VACCO MiPS

� Chemically etched valves and system

� Fits all constraints

� Butane propellant – easy handling

� Designed for CubeSats

� Expandable propellant tank

� Not ready/ not for sale?

VACCO


• Ibit = .55 mNs

• Thrust = 55 mN

• Size = 2.5 x 10 x 10 cm

• 5 thrusters � 3-axis control

• Designed for CubeSats

VACCO


• Ibit = .55 mNs

• Thrust = 55 mN

• Size = 2.5 x 10 x 10 cm

• 5 thrusters � 3-axis control

• Designed for CubeSats

Picture courtesy of VACCO Industries

VACCO Piezoelectric Thrusters

Liquid valve

Thruster valve

120 psi

Fuel storage tank10-15 psi

Plenum

2 identical 1” valves controlling flow of iso-butane

10 mN thrust

• 220 ms pulse � 1.5 deg/s rotation rate

• 90 degree turn in 60 seconds

Low power

• To open valve: 200 mW for 20 ms

• No power required to keep valve open

PV=nRT

P

T

Isobutane Self-pressurization

Problem…

Only 2 thrusters donated by VACCO/JPL

. . . can spin up but can never spin down

• Centrifugal effect separates different phases of butane

• Allows complete single-axis control

Gas

Liquid

Inlet tubePerforated baffle plate

Solution: 2-Thruster Design

Tank Location in 2U Assembly

Moment of Inertia

Single Axis

Rotation

Temperature

Protection

Tank Sizing and Characteristics

256320.93

384531.40

769062.79

ManeuversVolume (cm3)

Full Volume = 62.7cm3

Pressure ~ 44 psi @20oC











� Chemical Propulsion� Cold gas thrusters (micro & MEMs)

Questions?

Documents

lecture-17 ppt for Cubesat