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Propulsion for Agile, Resilient Spacecraft


TECHNOLOGY AREA(S): Space Platforms 

OBJECTIVE: To develop innovative propulsion concepts that address the increasing agility requirements of Air Force and DoD spacecraft. 

DESCRIPTION: Future DoD spacecraft will need greater agility to change orbits for mission requirements or to avoid the increasing hazards in crowded orbits. An agile spacecraft is one that can make an orbital change while maximizing propulsive life through propellant conservation. Agility requires, at minimum, propulsion concepts that are able to trade specific impulse (Isp) with thrust over a wide range as mission needs require. Short notice needs would require high thrust at the expense of propellant. Mission needs that have less severe time constraints can use high Isp and conserve propellant. However, a truly agile spacecraft will require both high thrust and high Isp simultaneously, at least for short periods of time. This topic seeks to develop in-space propulsion concepts that can be operated for short periods of time at high Isp and high thrust simultaneously. By high thrust, it is meant that the thrust is higher than a typical Hall thruster but can be less than a typical spacecraft chemical thruster, on the order of a few tens of newtons. By high Isp it is meant that the Isp is much higher than a chemical thruster, on the order of 1000 seconds or higher. By short period of time it is meant that large orbital maneuvers can be made impulsively instead of by spiral changes. It is anticipated that successful SBIR efforts will take advantage of increasingly efficient, low mass batteries or ultra-capacitors while carefully managing system mass so that the spacecraft mass fraction does not become unreasonable. This topic is looking for responsive propulsion giving high delta-V more characteristic of chemical propulsion while using a small fraction of propellant that a chemical thruster would use. Offerors are encouraged to also suggest innovative orbital maneuver strategies that might be enabled from their proposed solution. Current spacecraft propelled by electric thrusters use Hall thrusters that are too low in power to provide true agility. Additionally, current spacecraft do not have the power capability to supply a larger electric thruster. However, current energy storage devices could enable the use of high power electric thrusters using existing spacecraft photovoltaic systems. High thrust enables faster large orbit changes to mission altitudes. Once on orbit, a larger thruster could provide rapid acceleration and large delta-V with the use of energy storage. Current Hall thruster technologies may be a good fit at higher Isp, where many designs are approaching 70% efficiency, close to the limitations of physics. It is not as clear that Hall thrusters are a good solution at an Isp of 1000s or lower as their efficiencies drop off rapidly. Therefore, this topic will allow electric propulsion technologies other than Hall thrusters. Lower Isp allows higher thrust to power which would reduce orbit transfer times, yet be much more efficient in propellant than chemical thrusters. Proposed solutions should also be compatible with typical DoD spacecraft. The possibility of spacecraft system contamination should be addressed. The proposed propulsion concept should not limit spacecraft lifetime, most of which have expected lifetimes of 15 years. No unusual thermal, power, or balance constraints should be placed on the spacecraft by the proposed concept. 

PHASE I: Select propulsion concepts and identify how spacecraft agility could be improved by these concepts. A proof of concept demonstration is desirable. Technical challenges or barriers should be identified. An approach to a phase II effort should be outlined. 

PHASE II: Further develop the Phase I effort by building and testing a prototype thruster or thruster system including a propellant feed system. Government Furnished test facilities and hardware may be available so the proposer should request if desired. Further interaction with Spacecraft Prime Contractors would be desirable. 

PHASE III: Transition the technologies developed under this topic to a demonstration flight and space qualification. 


1. Gulczinski, F. S., et al., “Micropropulsion Research at AFRL,” AIAA-2000-3255, 36th Joint Propulsion Conference, Huntsville, Alabama, 2000.; 2. Hawkins, T.W., Brand, A.J., McKay, M.B., and Ismail, I.M.K., “Characterization of Reduced Toxicity, High Performance Monopropellants at the U.S. Air Force Research Laboratory”, Fourth International Conference on Green Propellants for Space Propulsion, Noordwijk, NL, June 2001.; 3. Koelfgen, Syri, et. Al. “A Plasmoid Thruster for Space Propulsion”, AIAA-2003-4992. Joint Propulsion Conference, 2003.; 4. E.Y. Choueiri and J.K. Ziemer. “Quasi-Steady Magnetoplasmadynamic Thruster Performance Database”. Journal of Propulsion and Power, 17:967–976, 2001. September-October.

KEYWORDS: Electric Propulsion, MagnetoPlasmaDynamics (MPD), Spacecraft Propulsion, Advanced Propulsion, Magneto Hydrodynamics (MHD), Plasma 

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