America’s next great leap into space may very well be to a Near Earth Asteroid, or NEO (not to be confused the lead character, Neo, in the Matrix series films, who gets roughly ten times as many Google hits as interplanetary NEOs.)
The scientific payoffs from such a mission include investigating the origins of the solar system, better understanding NEOs that could endanger Earth, and characterizing NEOs as space resources for propellant, life support and construction materials.
This could be done by 2025 according to the Obama administration’s long-term planning for NASA.
But of the tens of thousands of NEOs out there, which ones would be best to visit, optimizing fuel and ease of speeding back to Earth should anything go wrong?
The name of the game in space travel is to minimize fuel requirements and maximize payload capacity. Therefore, the ideal NEO candidate should require a minimal change in the spacecraft’s speed (dubbed “delta-v”) to shuttle to the asteroid’s orbit.
Ideally, the “trans-asteroid” burn should change the spacecraft’s velocity by less than 10,000 miles per hour. (It’s already traveling 64,000 miles an hour simply because that’s Earth’s orbital velocity.)
The manned mission would assemble all components in low Earth orbit (LEO) and then do a transition burn to climb out of Earth’s gravitational field to reach the asteroid several months later. Upon arrival the spacecraft would have a small rocket burn to rendezvous with the asteroid.
At present, only a handful of so-called “ultra-low delta-v” NEOs are known. Some have been suggested, such as an object called 1999 AO10. But The complete population of candidate NEOs must be much larger. Planetary astronomers estimate that 95% of NEOs have yet to be discovered.
What’s needed to find them, says a team of astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) and MIT, is robotic precursor mission that puts a survey telescope near Venus.
Why Venus? It is the best vantage point to see NEOs that might go undetected in Earth-based surveys. A Venus-based telescope could scan a wide swath of Earth’s orbit continuously. NASA’s Wide Infrared Survey Explorer (WISE) only detected a few percent of the ultra-low delta-v population because of its short observing lifespan.
Carried out over five years, a Venus-orbiting optical or infrared survey would find all ultra-low delta-v NEOs with a diameter greater than approximately 500-feet. “If this were carried out by 2020 it would enable timely target selection for the 2025 goal for a first human mission,” writes Martin Elvis of CfA.
The best candidates from the catalog would be scrutinized as to how potentially hazardous the NEOs are to visit. Astronauts maneuvering within dozens of feet of the surface of a rapidly rotating asteroid could smack into skyscraper-high boulders.
Another navigational hazard is that many NEOs wobble, they do not rotate about their center of mass. An orbiting spacecraft would and risk crashing head on into the NEO due to the asteroid’s complex gravitational field.
What’s more, if the NEO candidate is a dead comet nucleus, ices may lie close to the surface and could be uncovered by astronauts trekking around. These might explosively erupt when hit by sunlight.
So our next great leap beyond Earth will require planning every bit as thorough as the preparations for the Apollo landings on the moon. Except the moon was a specific destination. Now we have to do a needle-in-haystack search for our next space-faring port-of-call.
Illustrations courtesy of NASA, Armagh Observatory
