WHEN President Barack Obama announced that the next destination for a US astronaut would be an asteroid, it caught many by surprise. Yet the move is not as sharp a break as it might seem with the Bush-era plan to return astronauts to the moon.
鈥淭he decision to go to an asteroid is not as sharp a break as it might seem with the Bush-era plan for the moon鈥�
Both missions would serve as intermediate steps in the long-term plan to send humans to Mars in search of life. Moon landings would help NASA develop the skills to land on a large celestial object 鈥� and get off it. On the other hand, visiting an asteroid would need a months-long journey through deep space, providing a taste of the challenges to be expected on the two-year round trip to Mars.
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Although Obama鈥檚 plan cancels the expensive rockets and lander NASA was developing to return astronauts to the moon by 2020, it does not rule out trips to the moon at a later time, with more affordable hardware. The decision then is not so much whether to go to the moon or an asteroid, but which to visit first. The problem with the idea of heading to the moon first is that it has failed to inspire Congress or the American public, who find it hard to get excited about repeating what was done more than 40 years ago. In contrast, a mission to an asteroid would be genuinely new. That is important because NASA will need all the public enthusiasm it can get if it is to hold onto its funding.
Still, the public-relations benefit must be weighed against the additional hazards of an asteroid mission (see 鈥淲e鈥檙e flying to an asteroid 鈥� but which one?鈥�). Spending months in deep space would increase the chances of the crew being exposed to a deadly blast of radiation from a solar flare. Much more work is needed to develop better ways to shield astronauts from such outbursts, and from the constant trickle of cosmic rays that can increase an astronaut鈥檚 risk of cancer. Tackling the extra dangers of landing and staying on an asteroid with little gravity could pay back later: we would have a head start if we ever had to deflect or destroy an asteroid hurtling towards Earth.
Despite Obama鈥檚 announcement, there is no real need to decide now whether to head first for an asteroid or the moon. It will take years to develop the heavy-lift rocket, which he also announced, that will be needed for both missions. Until it exists, NASA cannot afford to begin work in earnest on a landing vehicle for a moon mission.
Rather than locking NASA into a hasty decision now, it makes more sense to let the debate continue for a few more years. By that time, robotic missions will probably have taught us more about the risks and potential rewards of visiting each destination, and new technologies for propelling spacecraft and warding off space radiation could tip the balance.