Electrospray Propulsion Systems for Small Satellites Douglas Spence, Eric Ehrbar, Nate Rosenblad, Nate Demmons, Tom Roy, Samuel Hoffman, Dan Williams, Vlad Hruby Busek Co. Inc. 11 Tech Circle, Natick, MA 01760; 508-655-5565 Chris Tocci ALFA, LLC 87 Plymouth St., Halifax, MA 02338 www.busek.com 2013 Busek Co. Inc. All Rights Reserved.
Overview and Outline Propulsion systems for small spacecraft are not simple reductions in SWAP and propulsion capability from larger spacecraft. New ways of looking at the complete spacecraft system must be employed. Busek developed heuristic for evaluating capability of propulsion systems for spacecraft at the CubeSat level Examples of selected propulsion technologies are presented for illustration and Busek s different propulsion solutions for CubeSatscale spacecraft Brief overview of the DARPA Phoenix objectives and how the rocket equation heuristic, plus additional system considerations, led to selection of electrospray propulsion for Phase 1 development
Heuristic for evaluating propulsion systems Challenge for very small spacecraft is not delta V but available mass and volume Mass ratio (initial mass/final mass) has much greater influence than the specific impulse. V = I sp g 0 ln m f m i Propulsion engineers are in love with I sp. Provides a simple basis of comparison for various propulsion technologies but how does this help select a useful propulsion system? Illustration of effect of mass ratio (initial mass/final mass) and Isp upon ΔV
Busek s Propulsion System offerings For small satellites Busek spans the spectrum: Electrospray (Pressure feed and Passive feed) Micro pulsed plasma (for ACS and translation) Microresistojet (MRJ) RF Ion Miniature green monopropellant chemical rocket All are capable of (or nearly) a mass of 1kg and size 1000cm3, with some already at 500g and 500cm 3, and may soon reach 100g and 100cm 3 Consider the following Busek thrusters:
Busek Electrospray Thruster Ionizes and accelerates droplets and/or ions from a liquid surface using strong electric field Very high thrust/power and low absolute power requirements Greatest V potential capability of any propulsion technology for small spacecraft due to small thruster size Electronics (PPU, DCIU, HSKP) advancing rapidly requiring only two 9 x 9 cm boards First space qualified units delivered to NASA/JPL/ESA for ST-7 LISA Pathfinder DARPA Phoenix Project Phase I
1.25cm Electrosprays of the future Unpressurized (wicking feed) electrospray thruster. Unit shown is 7.5 x 6.5 x 1cm. Heater PPU/DCIU Board Next-generation 100g/100cm3 with 100µN, 180N-s Impulse
Micro-PPT (Pulsed Plasma Thruster) Operates by discharging an arc across the surface of Teflon at end of stick No tank or feed system, only electronics and propellant rods Small and easily distributed within a small volume envelope and at various thrust vectors for ACS or bundled for translation. Exceptionally efficient propellant loading Low efficiency but low power little as 2W Low-cost and easy-to-integrate propulsion system Selected for AFRL FalconSat - 3 mission launched in 2007 and still operational
Microresistojet (MRJ) Operates by heating a gas 1U system with primary propulsion and 8x cold gas ACS thrusters 2X Valves
RF Ion and Green MonoProp 1 cm RF Ion thruster (thruster head only, also 3 and 7 cm) Green monopropellant thruster. app. 1 dia. x 4 long
Busek s Propulsion System offerings For small satellites Busek spans the spectrum - Producing V s (sec) (for 4kg SC) Electrospray (Pressure feed and Passive feed) 151, 76 Micro pulsed plasma (for ACS and translation) 65, 63 Microresistojet (MRJ) 60 RF Ion 244 Miniature green monopropellant chemical rocket 130 A comparison technique which includes mass (as a minimum) is required
Total Impulse (N-s) Comparison of Propulsion Systems 2000 1800 1600 1400 1200 1000 800 600 400 200 0 Comparison of Propulsion Systems by Total Impulse vs. Wet Mass 0 500 1000 1500 2000 Wet Mass (g) Electrospray (current 0.7 mn) Electrospray Next Generation (100 µn) µppt (current) µppt (next generation) RF Ion (100 µn) Mini Cold-Gas (10-50mN) Get over love affair with I sp. Wet Mass will be about the same as the Dry Mass. The comparison of Total Impulse vs. wet mass (initial mass) is instructive for selection.
DARPA Phoenix Program Phase I The goal of the Phoenix program is to develop and demonstrate technologies to cooperatively harvest and re-use valuable components from retired, nonworking satellites in GEO and demonstrate the ability to create new space systems at greatly reduced cost. Phoenix seeks to demonstrate robotically removing and re-using GEObased space apertures and antennas from de-commissioned satellites in the graveyard or disposal orbit. The Phoenix program envisions developing a new class of very small satlets, similar to nano satellites, which could be sent to the GEO region more economically as a ride along on a commercial satellite launch, and then attached to the antenna of a non-functional cooperating satellite robotically, essentially creating a new space system.. Source: http://www.darpa.mil/our_work/tto/programs/phoenix.aspx
Servicer/tender Robot installing Satlets Busek initial proposed propulsion configuration De-commissioned Satellite Satlet = Cellularized Satellite
Busek contribution to Phoenix Phase 1 Radiation-tolerant 0-10kV 10W Electrospray PPU Ø2.5 Thruster/ Feedsystem +Propellant Proposed autonomous electrospray propulsion satlet, with reduced propellant loading but greater flexibility.
Conclusions Very different considerations must be applied to small spacecraft propulsion systems. Systems must be optimized for efficiency not simple reductions in SWAP. This implies new ways of looking at the complete spacecraft system where the initial mass is close to final mass. A Busek developed heuristic can be applied for evaluating propulsion systems based on Total Impulse / kg. Demonstrated Busek s extensive work in small satellite propulsion technologies and Busek s different propulsion solutions for CubeSatscale spacecraft. Electrospray thrusters may be the solution for the DARPA Phoenix mission to repurpose an antenna.