NASA Mulls Solar Electric Propulsion for Deep Space Exploration

From Yahoo News:  NASA Mulls Solar Electric Propulsion for Deep Space Exploration

Nathan Strange, a mission formulation systems engineer at NASA's Jet Propulsion Laboratory's Mission Concepts Section, recently gave a telecom presentation about the use of solar electric propulsion to explore the inner Solar System.

The talk was accompanied by a slide presentation.

Electric propulsion

According to a website on the subject by Northwestern University, solar electric propulsion works by generating electric power from solar arrays which is used to give a positive electric charge to atoms inside a chamber which are thrust out by magnets. Because SEP offers low but long-lasting thrust, it can build up a great deal of velocity for spacecraft traveling in deep space. SEP is also called ion propulsion and has been used by a number of space probes, such as Deep Space One and Dawn.

Solar electric propulsion to travel to the moon, asteroids, and Mars

Strange's presentation suggests combining the advantages of solar electric propulsion and chemical propulsion. Essentially, most of a deep spacecraft would be slowly moved to a point in cislunar space, such as a high Earth orbit, lunar orbit or one of the Lagrange points where the gravity of the Earth and moon cancel one another out. Then a crew of astronauts, riding an Orion multi-purpose crew vehicle launched by a Space Launch System, would ride to the deep spacecraft, dock, and board it. Chemical rockets would blast the ship out of the Earth's gravity field and then the solar electric propulsion system would take over to take the spacecraft the rest of the way.

Mission scenarios

Strange presented a number of mission scenarios that could start in the early 2020s. A deep space station would be established at the L2 point to test out exploration systems. Asteroids of increasing size and difficulty to reach could be visited. With the addition of a lunar lander, the lunar surface could be visited. The ultimate goal is a visit to the Martian moons of Deimos and Phobos, to be followed by a landing on the Martian surface.

Power considerations
The technology hurdle, according to Strange, that has to be surmounted is to develop SEP systems that generate power in the hundreds of kilowatts. Thus far 50 kilowatt SEP systems have been tested in the laboratory at NASA's Goddard Research Center. Such could be clustered together to provide the amount of thrust needed to send crewed deep space craft to their destinations.
Launch vehicle advantage

The one great advantage, according to Strange, in using SEP is that the 70 metric ton lift version of the Space Launch System would be sufficient to launch the various parts of the deep spacecraft, including the crew. NASA would not have to wait for the 133 metric ton lift version of the SLS to conduct deep space exploration. With some tweaking, Strange implied that the 53 metric ton lift Falcon Heavy might be used as well. 

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Mark R. Whittington is the author of Children of Apollo and The Last Moonwalker. He has written on space subjects for a variety of periodicals, including The Houston Chronicle, The Washington Post, USA Today, the L.A. Times, and The Weekly Standard.