Asteroids Could Be 'Stepping Stones' to Mars

One of President Obama's key space policy objectives is the Asteroid Redirect Mission (ARM), which aims to nudge an asteroid into lunar orbit for accessible study. But according to MIT planetary scientist Richard Binzel, missions that use asteroids as interplanetary "stepping stones" pack a more powerful scientific punch than ARM, not to mention the fact they could enable a manned Martian mission.

"I am advocating for something called the 'Flexible Path' that was most clearly defined in a 2009 Presidential report," Binzel told me. The Flexible Path idea was to gradually develop heavy rocket and deep space infrastructure with progressively more ambitious manned missions—from lunar orbits, to Lagrangian points, and finally to asteroids. "That idea was lost when ARM was proposed," said Binzel.

Binzel outlined for returning to this mission structurein a comment piece called "Find asteroids to get to Mars," published today in Nature. The plan's first priority is revamping asteroid survey networks like NASA's Near-Earth Objects program, which was recently revealed to be seriously behind schedule in cataloguing near-Earth asteroids.

Surveys "will find targets and destinations that are available for all concepts whether it is retrieval, human exploration, hazard assessment, or eventual future resources," Binzel said, calling them "a win-win-win for all aspects."

The development of a more comprehensive catalogue of near-Earth asteroids would make asteroid retrieval plans somewhat redundant. As Binzel writes, "Why retrieve an asteroid when we can wait for one to come near us?" He also notes that the asteroids that are optimal for exploration are often the same ones that may pose an impact threat, so it's well worth knowing where they are regardless.

The exploration of these asteroids would be cumulative, beginning with one target candidate that would allow space agencies to gain a foothold with other nearby objects. "I view a series of missions that go to one asteroid and come back," Binzel told me.

"Each mission is a little farther, a little longer," he said. "Then, we know that Mars is in our grasp."

These missions could be initially robotic, then eventually evolve into manned exploration. But either way, they would require significantly less complicated hardware than lunar or Martian exploration, given that no landing gear would be necessary.

"The minuscule gravity of an asteroid effectively means an asteroid is 'zero g,'" explained Binzel. "You can't land, only float alongside, kind of like a scuba diver floats above the ocean floor as they swim above."

"Zero gravity means that it takes no extra fuel to depart and head home," he added. "That makes asteroids very easy destinations in terms of how much rocket fuel you need."

If the 'flexible paths' idea was sufficiently supported, Binzel thinks the first explorers could be launched in the 2020s, with a budget comparable to NASA's New Frontiers program (under $800 million per mission). The most exciting objective would be to map out a trail of asteroid-sized breadcrumbs leading to Mars. But the missions could also learn how to deflect hazardous objects from impacting Earth, or develop mining technology to extract their resources.

That last point has huge implications for the future of manned spaceflight. "Speaking of 2050 and beyond," said Binzel, "if we begin to learn how to extract water from these asteroids and use them to support astronauts in space, then we can have much longer sustained spaceflights that become less dependent on Earth."

The idea of following a trail of asteroids to another planet is undeniably enticing, and harkens back to the early days of oceanic travel, when remote islands and archipelagos sustained expeditions to new continents. Maybe the key to planning humanity's first Martian journey is to find some choice rest stops along the road.