Gerstenmaier Elucidates Asteroid Return Strategy
Bill Gerstenmaier, the head of NASA's human spaceflight program, explained the thinking behind the agency's new plan to bring an asteroid into lunar orbit at two meetings this week. Three clear messages came through about what it is and what it is not.
Fundamentally, the idea is to send a solar electric-powered robotic spacecraft to capture a 5-7 meter diameter, 500-1,000 metric ton asteroid and put it on a course that will place it in a retrograde orbit around the Moon. Using the Space Launch System (SLS) and Orion spacecraft, astronauts would then embark on a 20-22 day mission to visit the asteroid and bring a sample back to Earth. It is all part of the longer term goal to send astronauts to Mars. A number of media sources refer to it as NASA's plan to lasso an asteroid.
Speaking first at a meeting of the Space Transportation Association (STA) and later in the week to a joint meeting of two NASA Advisory Council committees, Gerstenmaier, NASA's Associate Administrator for Human Exploration and Operations, stressed that this is not just a mission or an initiative, but a strategy to align NASA's space science, space technology and human spaceflight activities. Other Administration officials refer to it as an Asteroid Return Mission and/or an Asteroid Return Initiative (or "retrieval" instead of "return"). In response to a question at the STA meeting, Gerstenmaier agreed that it is a mission that is part of an initiative that, in turn, is part of a broader agency strategy with an emphasis on the strategy.
Second, he made clear that he is making no promises to actually capture an asteroid. The agency has a concept of how to accomplish that, but until the robotic spacecraft arrives at whatever target is selected, not enough will be known about the asteroid to ensure capture will succeed. The only way to improve the chances would be to send a precursor mission to study the asteroid in advance, which would add cost and time, undermining the rationale for the project. He suggested that the mission should be considered a success even if no capture is possible because it will have demonstrated, at a minimum, high power (40 kilowatt) solar electric propulsion.
Third, he cautioned that the relationship between this activity and planetary defense (or what he called planetary protection) -- defending Earth from Potentially Hazardous Asteroids (PHAs) that could cause catastrophic damage -- is tangential. Gerstenmaier was directly asked at the STA meeting why NASA is not selling this to the public on the basis that it is "to save your kids" instead of as a step to Mars. He replied: "Because it's not 100% applicable to saving your kids." It will provide relevant information, he said, but may not be "the most efficient and most effective way to get planetary protection" because there is "lots of stuff that we're going to have to understand for planetary protection that is different from this. This will help us. ... It's got a clear piece of planetary protection, but I think it's a little disingenuous to say its sole purpose is planetary protection." PHAs are much larger than the 5-7 meter diameter asteroid envisioned for this activity, which poses no threat to Earth.
President Obama announced three years ago that sending astronauts to an asteroid by 2025 is the next goal for NASA's human spaceflight program. The announcement was very controversial and a December 2012 National Research Council report concluded that it was not widely accepted inside or outside of NASA. At a hearing before the House Science, Space and Technology Committee on Wednesday, the President's science adviser, John Holdren, credited NASA with devising this new "ingenious" method to accomplish President Obama's goal, which he believes is more attractive.
NASA selected a sample asteroid as a test case to demonstrate the concept was feasible from an orbital dynamics perspective. That particular asteroid would reach the retrograde lunar orbit in 2024, but Gerstenmaier stressed that was not the asteroid NASA actually plans to capture. NASA is requesting increased funding to accelerate ongoing effects to search for Near Earth Objects (NEOs, asteroids and comets). To date, that search has been for NEOs 140 meters or more in diameter. The new funding would expand the search to include much smaller asteroids, which will be more difficult to find.
The concept originated in a study by the Keck Institute for Space Studies (KISS) released in 2012. Nonetheless, its inclusion in NASA's FY2014 budget was a bit of a surprise and there is a lot of confusion about what it entails. NASA and other Administration officials use varying terminology to discuss it, which complicates efforts to explain it to stakeholders. For example, Holdren repeatedly referred to "towing" the asteroid into lunar orbit, while Gerstenmaier stressed that it would not be towed at all. That would require significant amounts of propellant. Instead, he explained, they need to find a suitable asteroid in terms of size, spin rate, and composition that is already on a course toward the Earth-moon system. The robotic spacecraft will nudge it, using hydrazine thrusters, over a period of several years into a retrograde lunar orbit.
The way the concept is presented in the President's FY2014 budget request adds more confusion. The Office of Management and Budget (OMB) states that the request includes $78 million for this activity, but NASA usually says it is requesting $105 million. The $105 million includes:
As explained by NASA Chief Financial Officer Beth Robinson at an April 10 budget briefing, the $27 million difference is because the additional $20 million in SMD and the $7 million in STMD for broader hazard mitigation technologies are not part of the "mission," but of the "initiative." The distinction between those terms and the implications of money being in one category or the other are bewildering.
Skeptics point out that, apart from technical challenges, there is no explanation of where the money will come from to execute the mission in future years. It does take advantage of spending already planned for SLS/Orion and solar electric propulsion, but the increase for NEO searches is only for one year and no development funds are identified in future year budgets for the robotic spacecraft. NASA assumes the agency will be flat-funded for the next five years at about $17.7 billion. Finding funds for a new robotic spacecraft equipped with a capture device in a zero-sum budget environment will be difficult. The KISS study estimated the cost of this type of mission at $2.6 billion. NASA said it thinks it might be able to do it for less because some of the work is already underway, but the basis for that optimism is obscure since the agency will not even complete a mission concept study until the end of this summer.
One reason President Obama's plan to send humans to an asteroid by 2025 has not won acceptance is that the target asteroid has not been identified so there is no sense of where the astronauts will be going. Another is that funds are not included in future-year budget projections to pay for additional hardware, like a habitability module for the astronauts, required for the mission. This new concept suffers the same drawbacks.
Gerstenmaier said he wants to launch the robotic spacecraft in 2017, just four years from now. It will be designed and developed in parallel with the search for the target asteroid, so engineers will not know its specific destination. Notionally, it will take about a year and a half to reach the asteroid, three years to nudge it onto the right trajectory to enter a retrograde lunar orbit, and another year to get it into the precise orbit desired, Gerstenmaier told the NAC committees. Also notionally, it would be in place for a visit by astronauts on their first launch aboard SLS/Orion in 2021.
At both meetings, he said that it would almost be better if they could not find an asteroid to be in place by 2021 since that would be "pretty aggressive" to do on the first flight of a new spacecraft. He added that the idea is for the astronauts to make two spacewalks to the asteroid, but they will not be "sophisticated" spacewalks, just an opportunity for the astronauts to "reach out and grab something" wearing slightly modified launch and reentry spacesuits.
One point Gerstenmaier stressed, however, is that this mission would change the paradigm of human spaceflight because once launched the crew would not be able to return to Earth for nine days, breaking the tie with the planet. "That's a different posture for us," he told the NAC committees. With the International Space Station (ISS) and even the Apollo missions, it was possible to return to Earth in relatively short order if an emergency developed, but not in this case. He considers that a vital step to take before committing to missions even further from Earth, like Mars.
Gerstenmaier seemed enthusiastic about the way the strategy aligns NASA's various space activities, as well as the paradigm-changing aspect of testing how astronauts react to breaking the bond with Earth.
All in all, however, the White House and NASA may be exacerbating the challenge of winning support from Congress and other stakeholders. Some officials are using imprecise terminology, there is confusion over the relationship of this mission to protecting Earth from asteroids as well as why about humans are needed to bring back a sample of an asteroid when NASA already is building a robotic probe (OSIRIS-REx) to do that (not to mention that Japan already has done so and is planning a second mission), and the budget is murky in the short term and lacks credibility for the long term.
Rep. Lamar Smith (R-TX), chair of the House Science, Space and Technology Committee, said it seemed to him that the mission was "an afterthought" when the original mission did not win support. NASA and the White House will have their hands full trying to dispel that characterization, but Gerstenmaier's presentations may be a step in the right direction.
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