An Asteroid Boulder Will Be A Stepping Stone on the Journey to Mars

NASA announces details in its plan to capture an asteroid and bring it into lunar orbit

Asteroid Redirect Vehicle
The Asteroid Redirect Vehicle gets ready to push off from the asteroid after grabbing a boulder in this artist’s interpretation NASA

NASA’s plan to snag an asteroid and bring it into orbit around the moon for astronauts to explore just took another step toward reality. For a while now, the agency had been considering two options for its Asteroid Redirect Mission (ARM): One that would grab an entire small asteroid and tow it back and another that would land on a larger asteroid, scoop up a smaller, boulder-sized chunk and cart that back. 

Today, NASA associate administrator Robert Lightfoot announced in a press briefing that the mission will go with the second option. After extensive review, so-called option B would be less expensive and offer a better chance for success. 

If the mission chose to grab a small asteroid, they would need to choose a final target year before launch. Going for a boulder essentially offers several choices at once. From past missions, NASA has learned that the surfaces of larger asteroids are strewn with boulders. With option B, the team can identify several likely targets and send spacecraft with the ability to take measurements on all of them before grabbing one. "We will make an educated choice on which to pull," Lightfoot said.

NASA also laid out a planned timeline for the mission. The ARM robotic spacecraft will launch in December 2020 and cruise on solar electric propulsion toward the chosen asteroid. NASA has announced that it is eying three candidates: Itokawa, Bennu and 2008 EV5. In the press briefing, Lightfoot focused on 2008 EV5, "one we think we have fairly well characterized," though other candidates may present themselves in the coming years.

After about two years flight, the ARM spacecraft will sidle up to the asteroid, make a soft landing and start sampling a few boulders. Once the selection is make, the spacecraft will take its bounty into a "halo orbit" around the large asteroid. Spacecraft and boulder together will be a small mass compared to the asteroid, but it will be enough to gradually nudge the larger body’s movement. "We are talking about a small deflection," Lightfoot said, but one that can be measured from Earth. This part of the mission will prove that NASA has the capability to move an asteroid — a vital part of the ARM mission is to test whether Earth would be able to avert an asteroid headed for impact. 

The spacecraft will hang out in halo orbit for 215 to 400 days, depending on how successful that nudge is. Then with asteroid boulder secured, it will make its way back toward an orbit around the moon. 

The plan is for the boulder and spacecraft to be in place, stably orbiting the Moon and ready for astronauts to visit and study by 2025.

The Orion spacecraft, carrying a two-man crew, will be able to dock with the ARM spacecraft. A NASA press statement offers more details:

This crewed mission will further test many capabilities needed to advance human spaceflight for deep space missions to Mars and elsewhere, including new sensor technologies and a docking system that will connect Orion to the robotic spacecraft carrying the asteroid mass. Astronauts will conduct spacewalks outside Orion to study and collect samples of the asteroid boulder wearing new spacesuits designed for deep space missions.

Collecting these samples will help astronauts and mission managers determine how best to secure and safely return samples from future Mars missions. And, because asteroids are made of remnants from the formation of the solar system, the returned samples could provide valuable data for scientific research or commercial entities interested in asteroid mining as a future resources.

The mission will also be a critical demonstration of the capabilities of the solar electric propulsion system, which converts the Sun’s energy into power that then sends charged atoms streaming behind the spacecraft, propelling it forward. "Future SEP-powered spacecraft could pre-position cargo or vehicles for future human missions into deep space, either awaiting crews at Mars or staged around the moon as a waypoint for expeditions to the Red Planet," NASA writes.

It might not be a whole asteroid, but the plan is no less impressive for the choice to retrieve a boulder. NASA plans to keep the cost of the whole mission at $1.25 billon. Next, the agency will assess whether it will develop the propulsion system in-house or contract out. Meanwhile, we all get a little closer to an exciting new era of human spaceflight and exploration. 

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