WASHINGTON — NASA has selected an option for its Asteroid Redirect Mission (ARM) where a robotic spacecraft will grab a boulder from the surface of a larger asteroid, agency officials announced March 25.
NASA Associate Administrator Robert Lightfoot told reporters in a teleconference that he selected what the agency had been calling Option B for the robotic element of ARM in large part because it offered more choices in what object to bring back to lunar orbit to be visited by astronauts.
“From what we know of the asteroids we’ve been to, they have boulders on the surface,” allowing a visiting spacecraft to choose which one to grab, he said. “I’m going to have multiple targets when I get there. That’s what it boils down to.”
Under Option B, a robotic spacecraft will travel to an asteroid several hundred meters in diameter and grab a boulder up to four meters across from its surface. The robotic spacecraft would then return the asteroid into a distant retrograde lunar orbit. An Orion spacecraft, with two astronauts on board, would then fly to the asteroid to collect samples for return to Earth.
Option B won out over the original ARM concept, known as Option A, where a robotic spacecraft would redirect an entire asteroid no more than ten meters across into a lunar orbit. NASA had planned to select between the two options last December, but postponed the decision in order to perform additional studies on the concepts.
Lightfoot said that in addition to the greater choice in targets, Option B also offered more technologies that could be applied to future exploration missions, including the ability to perform a soft landing on the asteroid and mechanisms for grappling the boulder. “Those are the kinds of things we know we need when we go to another planetary body,” he said.
Lightfoot added that it was harder to identify and characterize targets for Option A, given the difficulty in finding asteroids that small. “It gave us a little pause,” he said. “It was the risk of having a target that I was comfortable with that we would be able to get to. It’s a one-shot deal.”
Option B costs about $100 million more than Option A, Lightfoot said, the same cost difference that he announced in December. However, he added that Option B was still able, at least in this early planning phase, to fit with a cost cap of $1.25 billion, excluding launch vehicle, for the robotic part of ARM.
NASA has yet to select a target for ARM, but is currently using for planning purposes a near Earth asteroid named 2008 EV5. That asteroid, about 400 meters across, has been previously proposed as a target for robotic asteroid sample returns, including a concept called MarcoPolo-R that was a finalist in the European Space Agency’s Cosmic Vision M3 competition in 2014, losing to an exoplanet science mission.
The notional schedule for ARM calls for launching the robotic mission in December 2020, arriving at the target asteroid about two years later. Lightfoot said the decision on the target asteroid could be deferred to as late as 2019, allowing NASA’s near Earth object search program additional time to find alternative targets.
Once at the asteroid, the spacecraft would spend as long as 400 days in the vicinity of the asteroid, grabbing a boulder and performing other studies. That includes tests of a technique called a “gravity tractor,” where the spacecraft’s gravity adjusts the trajectory of the asteroid slightly, a technique that has been proposed as a way of deflecting potentially hazardous asteroids.
The robotic spacecraft would then leave the asteroid, returning the boulder to lunar orbit by late 2025. A crewed expedition to the boulder would follow on a mission some time after Exploration Mission 2 (EM-2), the first crewed Space Launch System/Orion mission currently planned for 2021. EM-2, Lightfoot said, would serve as practice for that later asteroid mission, flying to that same distant retrograde orbit.
With ARM having completed its mission concept review, it now moves into a planning phase known as Phase A in NASA program management parlance. “It’s really a refinement phase,” he said. That work will include development of better estimates of the cost and schedule for the mission.
Phase A work also includes an acquisition strategy meeting in July to decide how to procure key elements of the mission. “That’s the next big milestone coming up,” Lightfoot said. He noted that there appeared to be more commercial interest, in the form of supplying spacecraft components and technologies, in Option B.
Lightfoot emphasized that ARM, which to date has enjoyed only lukewarm support, at best, from the space community, is intended to be a key step in the agency’s long-term plans to send humans to Mars. “It’s bringing together the best of NASA’s human exploration, science portfolio, and technology portfolio,” he said. “It really gives an opportunity to demonstrate the capabilities we’re going to need for future human missions beyond low Earth orbit and ultimately to Mars.”