The 2006 NASA study didn’t go into detail about what astronauts would do once they reached an asteroid. But results from Japan’s robotic Hayabusa mission, which in 2005 investigated the near-Earth asteroid 25143 Itokawa up close, have led to some intriguing speculations.
“Itokawa was one of the most heavily researched asteroids—radar, visible, infrared,” says Paul Abell, a scientist on contract with NASA from the Planetary Science Institute who participated in the Advanced Projects Office study. “Many countries and collaborators had studied it. But when we got there with Hayabusa we were surprised by what we saw.”
It turned out to be a rubble pile loosely held together by its own gravity. “It’s a sandbox,” Abell says, “about 40 percent porous. Lots of empty space, like you have in a jar full of marbles. That was a really profound discovery.”
The first asteroid to be explored by humans might look a lot like Itokawa. While scientists are reluctant to name a specific target when the mission hasn’t even been approved, two candidates tend to crop up on lists of NEOs that would be reachable in the next two decades. A tiny one called 1991 VG—just 40 by 14 feet, or about one-seventh the size of Itokawa—comes around in the year 2017, but is probably too small to be of interest. A more likely candidate, 1999 AO10, is the size of a football field. It could be reached in 2025, long after Orion starts flying. Both missions would require a round trip of 150 days.
“We really don’t have a ‘best one,’ ” says Abell. “It’s far too early in the time line to select a target.” Besides, scientists find new asteroids all the time. “Hopefully we will have many more [choices], and get to know them a little better than we do now.”
Although Ed Lu has left NASA, he hasn’t gone far, and his Mountain View, California office is just down the road from Korsmeyer’s. Lu took a job last year with an advanced projects group at the headquarters of Google, where the former astronaut is dreaming up technologies that will go beyond Google Maps and Google Earth. He thinks of it as Google’s version of the Lockheed Skunk Works.
Lu says there are two basic ways to reach a NEO. An optimal target would have an orbit similar in breadth to Earth’s, but inclined, so that it would cross the plane of Earth’s orbit at a point not far away. Such an object would come around every six months.
Orion would fly out to meet the asteroid at its first plane crossing, stay with it for half a year, then come home when the asteroid crosses the plane again on the opposite side of the sun.
“You hop on,” says Lu, “and hop off six months later.” The payoff: less fuel required.
The other option—a shorter mission of up to, say, four months—would rendezvous with the asteroid as it approaches Earth, ride it home, then hop off. Or, hop on as it passes Earth, ride it for a few weeks, and hop off in deep space, requiring a return trip of several weeks to a couple months. This type of mission demands more fuel, but would open the field to a greater number of target asteroids.