Solar Electric Propulsion: ARRM an uncertain test for new technology

Michael Cole

Continuing our story about the solar electric propulsion (SEP) program at NASA’s Glenn Research Center and its proposed demonstration on the future Asteroid Redirect Robotic Mission (ARRM), the effort to design and build higher powered systems is a priority at the center. Part of the reason for this urgency is that a high powered SEP engine is needed, most immediately, for the propulsion system of the ARRM and has been a priority at NASA because the direction for it came straight from President Obama, himself.

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In 2010, Obama set a new course for NASA’s manned space program when he canceled the Constellation program, which focused on sending American astronauts back to the Moon. Constellation was revamped and redirected into developing the Orion manned spacecraft and the Space Launch System (SLS) rocket. Orion and SLS would be the crew spacecraft and heavy-lift vehicle in support of future manned missions to deep space destinations and eventually Mars.

“By 2025, we expect new spacecraft designed for long journeys to allow us to begin the first-ever crewed missions beyond the Moon into deep space,” Obama said in September 2010 at the Kennedy Space Center in Florida. “So we’ll start by sending astronauts to an asteroid for the first time in history.”

The plan had merits. Sending astronauts to an asteroid is something humans had never done, and the low gravity of an asteroid makes getting a lander onto and off of its surface a low-energy task.

However, there were problems with the plan from the beginning. Even after more than two years of study, scientists could find no suitable asteroid close enough for astronauts to visit in the proposed Orion spacecraft, a vehicle designed to support its crew for no more than 21 days in deep space.

Eventually, NASA engineers faced the reality that they had neither the hardware nor the budget resources to attempt a manned mission to an asteroid anywhere close to the 2025 date. To accomplish Obama’s goal, NASA crafted a plan that would, essentially, make the asteroid meet the astronauts half way. The solution was ARRM.

ARRM is a mission designed to robotically retrieve a boulder from an asteroid and return it to an orbit around the Moon, where astronauts aboard the Orion spacecraft could examine it and return samples. The proposed unmanned mission was viewed as an excellent dress rehearsal for many of the systems and in-space tasks that would need to be perfected in preparations for missions to Mars.

“ARRM is a partnership between JPL, Glenn, and Goddard,” said JPL chief engineer Brian Muirhead.

The Jet Propulsion Laboratory (JPL) is developing the spacecraft bus while NASA Glenn develops the higher powered SEP engines. Additionally, NASA Goddard is designing and testing the grappling system for grabbing and securing the asteroid boulder.

The NASA centers are currently in the process of awarding private contracts to develop and build this hardware.

“Those design contracts will be done in two phases,” Muirhead said. “There will be a development phase in which we work very closely with the contractor in developing and finalizing the design, for all the test units. We’ll verify and certify the designs. Once we do that, then will come the second part of the design—developing the units for flight. Here at JPL, we’ve started a two-phase contracting process for the selection of the spacecraft contractor, who will then have delivered to them the electric propulsion engines and power processing unit from Glenn to use on the spacecraft.”

But will it get that far?

Those who control the purse strings of NASA in Congress have long been scratching their heads as to how the ARRM mission gets humans closer to the ultimate destination of Mars.

Then, last April, the NASA Advisory Council (NAC) adopted a finding that NASA should cancel the asteroid mission and instead send the spacecraft all the way to Mars and perhaps visit one of the Martian moons, Phobos or Deimos, and return a sample from there.

NAC members are appointed by the NASA administrator. So the current group is made up of people individually picked by current NASA administrator, Charles Bolden, to give him candid feedback and highly informed suggestions and advice about NASA’s programs. The NAC members pointed out that the opinions they deliver are findings, not official recommendations, and that NASA is under no obligation to act on them. But their finding on canceling ARRM and sending the spacecraft to Mars instead was unanimous.

“Certainly, there is a range of opinions about ARRM,” said NASA Glenn senior propulsion engineer Dave Manzella. “Fortunately, in all the conversations that I’ve been privy to, there hasn’t been any debate about the importance of the SEP part of the ARRM mission. There has been some discussion as to whether that mission is the right first application of it. And it is true that the primary reason we are focusing on the asteroid mission is that is the policy that was directed from the [Obama] Administration. That is what they wanted NASA to do.”

Even though ARRM is a kind of “fix” mission for accomplishing the Obama Administration’s goal of getting astronauts to an asteroid, Manzella believes the mission can reap benefits.

“Ultimately the hope is that we can use that technology to do human crewed missions to Mars,” Manzella said. “Would it be better to do a SEP mission to a Martian moon? It is a little bit better. But the difficulty of going to Phobos or Deimos and try to pick up a boulder from its surface […] that’s a more difficult mission than the one that we’re considering, which means that it has [a] higher cost. So one of the challenges of conducting the mission is actually paying for it.” For a mission to either destination, paying for it is always the big challenge. There were some recent indications from NASA that, as the agency moves into Obama’s last year in office, there is weakening support for the ARRM mission. In a Feb. 2, 2016, teleconference with reporters, NASA’s chief financial officer, David Radzanowski, casually announced that the proposed launch date for ARRM had now slipped from 2020 to 2023 or later. And the budget figure requested from Congress for ARRM and the further development of its SEP engine technology was not an impressive figure relative to other agency priorities. “The overall Space Technology request for 2017 for a SEP demonstration, which is for the Asteroid Redirect Robotic Mission, and a capability we need for ongoing future exploration missions beyond low-Earth orbit and on to Mars… is $66.7 million,” Radzanowski said. “I noted that is in [the] formulation. We are looking at a target date in the early to mid-2020s, roughly 2023, but that is just a notional date at this point in time.” The problem is that this notional date plays havoc with the timeline of the mission to the target asteroid, 2008 EV5. ARRM, as planned, will take two years to reach the asteroid. It will perform a number of experiments while on its surface, secure the boulder, then begin the return trip, which will take another three years. A five-year, round-trip mission. The currently proposed launch date would not have the boulder in lunar orbit for Orion to go toward and inspect until 2028. With less than ecstatic enthusiasm for ARRM, and Obama’s remaining months in office nearing single digits, some believe NASA is simply going through the motions of one last budget cycle with ARRM, knowing that another set of priorities are likely to be handed to them in the very near future. The Bottom Line “The bottom line is NASA has continued on a path that the administration has requested which is to go to an asteroid and bring back a large boulder,” said JPL’s Brian Muirhead. “I personally think the NASA Advisory Council’s recommendation was a reasonable one. It really would seem a reasonable second mission for this type of vehicle that we’re developing. The technologies that will prove out with the ARRM could then be applied to a mission to the Mars system, to maybe land on Phobos. Maybe bring back a sample. That’s possible with an ARRM type system. It’s just that that’s much more of a science mission. ARRM is first and foremost a capability demonstration mission both in technology and in crew operations. So, yes, if NASA wanted us to go that way, we could. But that’s a more expensive mission and obviously much more of a science mission.” Last week, a 21-member Formulation Assessment and Support Team (FAST), which was formed in fall 2015 to examine scientific issues involved with ARRM, found no critical scientific problems with the proposed mission, but they suggested that a precursor or “scout” mission to the target asteroid could help ensure the mission’s success. The concern of the FAST team was that current radar observations of asteroid 2008 EV5 indicate hundreds of boulders on the surface in the 2–3-meter size that ARRM is designed to retrieve. But visually confirming their existence would be nice. No detailed images of the asteroid’s surface have been made. A visit by a spacecraft may be the only way to confirm the existence of the boulders. Without it, there is the possibility that ARRM could arrive at the asteroid and be unable to find a suitably sized boulder, thus dooming to failure a mission that never had a chance to succeed. But this possibility seems small, compared to the cost of an additional spacecraft to scout the asteroid. It is yet another decision that remains to be made. In short, the engineers keep working while the priorities and politics of the mission shake themselves out. “I think we all have the anticipation that there is going to be a 50 kW class SEP demonstration mission, in about the time scale that we’re talking about,” Manzella said. “Whether it is the ARRM mission in the way that we’re conceiving it is hard to say.” It is possible that the work they do in the next two years on SEP at NASA Glenn and the work on ARRM at JPL and Goddard may get them close enough to the finish line that the mission will go forward as planned, without any change. For now, they need to work as if it will. “We want to get to a hundreds of kW SEP system, and we know there needs to be an intermediate step. So the expectation is we would use that type of technology in some other kind of demonstration if it is not used in ARRM.” The outcome of ARRM as a demonstration mission for SEP remains to be seen. It may go forward. It may be canceled. Or it may go to Mars instead. Is SEP truly the deep space propulsion method of choice for the near future? “I think there is a clear agreement that for applications where you don’t have crew or big time constraints, that SEP is the propulsion of choice,” Manzella said. “It’s been a sizable change from where we were four or five years ago. The primary focus of almost all the work we had done on SEP in the previous couple of decades was focused toward the robotic science missions. Not really in support of human crewed missions. But in this era after the retirement of the [space shuttle] orbiter, and looking at things we might do as we wind down with ISS, and we looked at all the things we would like to do, and if we did them with the existing technology, it’s really unaffordable.” “We decided to pause and see what kind of technologies we can develop that would make things more affordable in the future,” Manzella concluded. “And that’s what has really brought solar electric propulsion into the forefront.” Video courtesy of NASA