Turning Up the Power on Solar Electric Propulsion

NASA’s Evolutionary Xenon Thruster (NEXT) ion thruster. /  Image Credit NASA.

After arriving at the dwarf planet Ceres one month ago, NASA’s ion powered Dawn spacecraft entered an initial capture orbit which took it to a maximum altitude of more than 46,000 miles above the icy body. Firing steadily, a 2.6 kw ion engine, one of three on-board, is now gradually reducing the spacecraft’s altitude to an initial science orbit 8,400 miles above the surface.

After completing the initial science phase, Dawn will gradually reduce its orbit even further, ultimately reaching a lower position more suited for high resolution photographs, some of which it is hoped, may solve the mystery of Ceres’ intriguing bright spots.

Dawn’s remarkable odyssey, which included a 14 month stint at the giant asteroid Vesta before breaking orbit and heading to Ceres, has produced a treasure trove of information, much of which can be found on the newly launched Vesta Trek website.

What we have learned of Vesta, and what we will learn of Ceres, is largely due to the history making performance of three 2.6 kw ion engines. While the mission is often described as “futuristic,” and in many ways it is, the engines themselves are dated, having been directly adapted from the single 30 cm NSTAR engine which powered the Deep Space 1 probe launched in 2008.

In the intervening years, electrical propulsion for commercial satellites, initially for station keeping, has gained steadily in popularity, a trend which culminated in the launch earlier this year of two Boeing built all-electrical comsats, which rode to orbit aboard a SpaceX Falcon 9 on March 1st.  With Airbus now booking electrical satellites as well, their future in Earth orbit appears well secured.

It is in applications beyond Earth orbit however, where NASA seems to harbor a great deal of desire, but an unfocused strategy on how best to employ a technology which has the potential of leveraging deep space launch capability.

On March 30th, the agency announced three awards for advanced solar electrical propulsion as part twelve awards granted in its NextSTEP campaign. In this case, the painfully stretched acronym stands for Next Space Technologies for Exploration Partnerships (NextSTEP), the purpose of which is “to advance concept studies and technology development projects in the areas of advanced propulsion, habitation and small satellites.”

The three propulsion awards, which have a range of $400,000 to $3.5 million per year for a period of no more than three years were made to Ad Astra Rocket Company of Webster, Texas, Aeroject Rocketdyne Inc. of Redmond, Washington and MSNW LLC of Redmond, Washington.

These are for ground test articles only, but significantly, they are for a power range of 50 to 300 kilowatts, a level significantly exceeding the 5 kw “state of the art” and the 40 kw range which has been targeted for NASA’s somewhat unpopular Asteroid Redirect Mission. And that is where the questions come in. By tying a significant step in solar electrical propulsion, which in the case of ARM would be used to drive a small boulder from the vicinity of its native asteroid to high lunar orbit, NASA has placed this particular aspect in a precarious place. If Congress, which has no great love for ARM, denies funding, then one of its brighter components will suffer a setback.

If that turns our to be the case, the three three advanced propulsion awards, of which is for Ad Astra Rocket Company’s highly anticipated Variable Specific Impulse Magnetoplasma Rocket, or VASIMIR concept (press release here), will take on added significance.

For NASA, heavily focused on its “Journey to Mars” at the moment, the potential for electrical propulsion as a leveraging technology for cargo delivery to Mars orbit is an element showing up so frequently in the various proposed mission models, that it could be taken for a requirement. Or at least as much as any can for a goal which has a title, but with little else in the way of serious definition.

Regardless of what becomes of ARM, it is not too early for the agency to begin displaying the same enthusiasm for shipping unmanned cargo containers to the Red Planet via solar electrical propulsion (SEP) that its does for using the Space Launch System booster and the Orion spacecraft to send humans. It is after all, the one element of the equation which is likely to make any sort of financial sense.

It is also the key to building on the remarkable legacy of the Dawn spacecraft and opening up the entire inner solar system. If NASA, working with industry, can achieve something on the order of a standardized advanced propulsion package which is tailored to work with newly affordable EELV class boosters, then mission planners could be looking at a wide range of new possibilities.

In the end however, it is the coupling of electrical propulsion with a nuclear power source, a necessity for prolonged operation in the outer planets, which holds the potential for opening up a true golden age of automated planetary exploration. That age may be an unnecessarily long time coming however. NASA’s supply of PU-238, the power source for a number of critical missions such as the Cassini space probe and the Mars Curiosity rover, is perilously low, and in danger of running out.

Posted in: Advanced propulsion

About the Author:

Post a Comment