There’s a plan A, and then there’s a plan B. Or in the case of NASA’s Asteroid Redirect Mission, there’s a concept, and then there’s an additional concept.
After all, there is more than one way to find, capture and relocate an asteroid from deep space into the Earth-Moon system.
A study is underway to develop an additional mission concept for NASA’s Asteroid Redirect Mission, and Dan Mazanek, a near-Earth object (NEO) expert at NASA’s Langley Research Center in Hampton, Va., is taking the lead. During Langley’s September Colloquium, he discussed concepts for the current and alternate missions.
The current concept for NASA’s Asteroid Redirect Mission involves retrieving a near-Earth asteroid (NEA) that is 7 to 10 meters in diameter. An asteroid that size is considered non-threatening to Earth, even after being relocated to the Earth-Moon system. Though it’s a beast of a rock, with a comparable weight of three to six full-grown male blue whales, it is a pebble in comparison to most of the 10,000-plus asteroids already identified by NASA. There are approximately 30,000 objects that are 100 meters or larger, a size that would be considered a threat to Earth, Mazanek says.
No matter the concept, the first step is finding a suitable asteroid to visit. Size is a major uncertainty when trying to identify NEAs, since their reflectivity (albedo) is typically unknown, and some asteroids are black as coal. According to Mazanek, larger asteroids are typically much easier to detect, track and characterize. However, they are difficult to deflect and disrupt.
The additional mission concept looks at identifying and visiting an asteroid that is 100 meters or larger, and returning a massive boulder from its surface, as opposed to the entire asteroid.
“The boulder would likely be less massive than an entire NEA, maybe up to 40 metric tons, which is the mass of just a single male sperm whale,” Mazanek said. “That might be more sensible for an initial retrieval mission.”
Adding to that, visiting a larger NEA is something that NASA has done twice before, and there are approximately 117 NEA mission candidates 100 meters or larger, where at least 10 metric tons could be returned to lunar vicinity by 2025.
“Approximately 160 metric tons could be returned from the NEO named 2000 SG344, which could be close to 100 meters in size,” Mazanek said. “However, no observations of 2000 SG344 from Earth-based telescopes are possible until the year 2028.”
Mazanek added that our current knowledge of very small NEAs is extremely limited.
During capture, smaller asteroids pose a significant challenge because they tend to rotate faster, sometimes as rapidly as one or two revolutions per minute, Mazanek says, while larger asteroids typically rotate once per hour or slower. The capture mechanism will likely need to match the rotation rate of the asteroid, nulling the relative position and velocity between the spacecraft and the target to nearly zero.
The reference approach to capture an entire NEA utilizes an inflatable strut and bag system, which would essentially swallow up the asteroid and carry it away in a bag. A bag isn’t needed to capture and return a boulder, and additional capture system concepts are being studied. These concepts could utilize manipulator technologies, sparse nets, and possibly microspines, a gripper technology that allows robots to attach to the pits and crevices of a rocky surface.
In the case of the solar electric propulsion technology needed to transport an asteroid, size matters. And there is a big difference between a 10- to 40-ton piece of an asteroid and a 500- to 1,000-ton asteroid, the approximate mass range of an asteroid that is 7 to 10 meters in diameter. To date, the most powerful solar electric propulsion system flown by NASA is the 10 kW power system being used by the Dawn spacecraft on its way to visit Ceres in the main asteroid belt. The current approach for the Asteroid Redirect Mission will require a system approximately five times as powerful (50 kW).
With either concept, “the return mass is orders of magnitude greater than anything we’ve done before,” Mazanek said.
A Request for Information (RFI), released by NASA on June 18, was the first opportunity for industry and other potential partners, including private individuals, to offer ideas on planning for NASA's mission to redirect an asteroid for exploration by astronauts.
More than 400 submissions were received in response to the RFI. From those, NASA will invite individuals and industry representatives from across the nation to attend an RFI workshop Sept. 30 through Oct. 2. There are many items up for discussion: observation and redirection systems, deflection demonstrations and asteroid capture systems, to name a few. The RFI responses and feedback from the workshop will be factored into mission plans moving forward.
According to Mazanek, review of the additional mission concept for NASA’s Asteroid Redirect Mission began in summer and will continue at least through fall.
“We are in the process of refining the mission approach for the overall Asteroid Redirect Mission, in whatever form it takes shape,” Mazanek said.
NASA Langley Research Center