Last year, NASA announced it was seeking proposals for mission concept studies of a high-power solar electric propulsion (SEP) system that could be used in a "space tugboat." Such a ship would be used ferry payloads in low Earth orbit (LEO) into higher energy orbits, including geosynchronous Earth orbit (GEO) and Lagrange point one (L1) - saving on fuel and the use of expensive secondary boosters. NASA also anticipates an SEP system could be used to propel spacecraft into deep space for science missions and for the placement, service, resupply, repositioning and salvaging of space assets by commercial operators.
Following the announcement, NASA awarded five companies four-month study contracts totaling approximately US$3 million, with a maximum individual contract award of $600,000. The selected companies were Analytical Mechanics Associates, Ball Aerospace & Technologies, Boeing, Lockheed Martin, and Northrop Grumman. Each company is tasked with providing a final report that will help identify technology gaps and look at possible solutions using SEP systems. NASA will use the studies to plan and implement a future flight demonstration mission that will test and validate key capabilities and technologies.
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While conventional chemical rockets will still be required to deliver payloads into LEO, NASA says the advantages of using SEP to efficiently transport heavy payloads into higher energy orbits has been shown in multiple studies. High power SEP systems would be used to power ion drives, which create thrust by accelerating ions using either electrostatic or electromagnetic force.
Along with efficiently delivering payloads from LEO to GEO and L1 - the point where the gravitational pull of the Earth and the Moon cancels each other out and is therefore seen as a potential assembly point in space between the Earth and the Moon - NASA says SEP systems could also facilitate missions to near Earth asteroids and other destinations in deep space.
One of the contract beneficiaries, Northrop Grumman, has announced it is working on alternatives to the typical solar array approach and that its concept will be scalable to 300 kW. Its study, along with those of the other four selected companies should be due in a few months.