Tug of love proposed

In an earlier post I outlined the danger posed by the near-Earth asteroid Apophis, which it is thought may smash into our blue Earth in the year 2036.

According to a news item this week, NASA is on the case “drawing up a shortlist of ideas to be unveiled early next year for diverting” Apophis from its potentially disastrous course.

“NASA’s plan,” we’re informed, “is to engineer a minor shift in the asteroid’s trajectory that would make it miss Earth by a wider margin on this and all subsequent passes.”

The most favoured option to accomplish this appears to be the deployment of what’s known as a “gravitational tractor”. The principle is outlined in the article from the November/December issue of Australian Sky & Telescope magazine from which I drew for my previous post:

Park a spacecraft in close proximity to the asteroid, cant it’s highly efficient solar- or nuclear-powered ion thrusters to the side so their plumes don’t hit the object, and hover beside it for several months or more with long, continuous thrusting. Due to the spacecraft’s and asteroid’s gravitational attraction on each other, the vehicle effectively tows the rock along with it using gravity as the towline.

If we launched a tugboat to Apophis before the 2029 close approach, we would only need to move the asteroid a few hundred metres to miss the 2036 keyhole, rather than several thousand kilometres to miss the entire planet. The tiny change in the asteroid’s orbit could be accomplished with only a 1-tonne solar-electric-propulsion spacecraft similar to NASA’s low-cost Deep Space 1 mission.

According to this week’s news item,

Lu calculates that a 20-tonne craft gently firing its thrusters could safely deflect a typical 198m asteroid in about a year, assuming there was 20 years of warning to launch and get the blocker into position.

Lu’s approach is far more cautious than that proposed by Hollywood in films such as Deep Impact or Armageddon. In the latter, the character played by Bruce Willis dies leading a team of astronauts who drill into an Earth-bound asteroid to plant a nuclear weapon that destroys it, and him along with it.

Lu and others say such an approach would increase the threat by turning a single piece of rock into smaller chunks that could bombard the planet.

Indeed, let’s hope Lu’s smart ideas win the day over certain ham-fisted mainstream approaches. We must certainly resist the reflex to throw bombs at yet another problem.