Use an Asteroid to Get to Mars

31May13

Instead of trying to build spacecraft to travel to Mars, maybe we should be (1) learning to steer asteroids and (2) building spacecraft that could hitch rides on asteroids.

The steering concept builds on what we already do with spacecraft.  The craft that we send off to explore parts of the solar system sometimes use the gravity of one planet or another to steer or catapult themselves on to the next stage of their mission.  In the case of an asteroid, a single- or multi-phase effort might begin by identifying an asteroid whose trajectory could be bent so that it would pass Earth and then, later, Mars.  In another post, I proposed using similar technology to terraform Venus; practice for that mission could lay a foundation, at a relatively safe distance, for work with asteroids closer to Earth.

If such an asteroid could be steered once, perhaps it could be reused.  The same rocket system that would be used to steer it, in the vicinity of Earth, might also steer it around Mars, so that it would return toward Earth.  Ideally, the asteroid itself could then become a sort of space station, housing some infrastructure that would not have to be recreated for each mission.

One advantage of such an approach would be its potential payload.  Through multiple launches from Earth during the asteroid’s single pass, or on successive Earth passes over a period of years, the asteroid could be loaded up with a collection of materials useful for a Mars exploration.  It would not be necessary to affix a Mars-capable rocket system to each individual item being transshipped.  At the far end, astronauts might have some busy hours, as they set up those various payload items to be jettisoned from the asteroid for their Mars landings.

A variation on the theme might seek a way to collect space junk, meteors, and other detritus into a larger body that, again, could provide a platform onto which materials could be loaded from Earth and unloaded at Mars (or, eventually, vice versa).  Such an enterprise would avoid the cost of lifting bulky materials into orbit.  It would require containers, welds, or adhesives to hold those scrap materials together in a single unit, as well as technologies to catch and assemble the constituent pieces in Earth orbit.  Assuming such a unit could be assembled, it would have the advantage of being easier to load than a speeding asteroid, but the disadvantage of being harder to propel away from Earth.

Another option would be to compose the artificial asteroid of the items being transshipped — to bolt them together into one interplanetary barge, and to send them off to languish in Mars orbit until the astronauts arrive.  In this scenario, the item shuttling back and forth between Earth and Mars would be the tugboat — the large nuclear rocket system that could propel a large payload between planets.

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One Response to “Use an Asteroid to Get to Mars”

  1. The problem is that the reaction mass (fuel) required to move something as massive as an asteroid is prohibitive. The amount of energy required to move something is directly proportional to its mass. That’s one reason why we hope that early detection of large asteroids might give us a chance to apply lots of thrust early so as to deflect it just enough so it misses the Earth. Discover a big one too late, and there probably isn’t enough fuel on Earth to change its path.

    These asteroids are moving at very high velocities. Inertial is the product of mass and velocity. For a large-ish asteroid, both mass and velocity are significant, so the total inertia is enormous! There is probably no practical way to use them effectively as spacecraft.

    Find useful ones early enough, and you can over time deflect their orbit enough to bring them closer for mining or whatever. But using them as spacecraft is a non-starter, I’d think.


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