AirSpaceMag.com

DARPA's Space Surveillance Telescope in White Sands, New Mexico. Photo courtesy DARPA

At a little after 10:00 EST this morning, a “bus-size” asteroid will give us a little buzz. It isn’t big enough to do damage, even if it were to hit our atmosphere, but its a reminder that there are objects out there that we might want to be worried about, if only we knew where they were.

Now an innovative new telescope is getting into the asteroid hunting game. DARPA’s Space Surveillance Telescope (SST) had its first light early in 2011, and is now officially online and going through its first demonstration, seeking out potentially Earth-threatening asteroids.

It’s not the first asteroid hunter. Among others, NASA’s WISE (Wide-field Infrared Survey Explorer) space telescope found over 33,000 new asteroids during its all-sky survey in 2010 (the team will be publishing their official results this March). There’s also the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) on top of Mount Haleakala in Maui, Hawaii. The team’s goal since they started operations in 2010 is to complete a survey of all asteroids over 1 km wide.

DARPA hopes the SST will fill out that catalog further by seeing even smaller, but still potentially dangerous, asteroids. Commissioned in 2002, the SST is unique in that its “mirrors are some of the steepest aspherical curvatures ever to be polished, and allow the telescope to have the fastest optics of this aperture class.” It’s short focal length and wide field-of-view allow it to be moved rapidly. By seeing smaller objects, it can help protect not just Earth, but satellites in orbit — military satellites, that is, as SST is primarily run by the U.S. Air Force at the White Sands Missile Base in New Mexico.

Scientists unveiled the first full closeup of the asteroid Vesta today. The picture, stitched together from frames taken by the Dawn spacecraft from a distance of 3,200 miles on July 24, shows mysterious parallel grooves around the asteroid’s middle, which may have formed when Vesta contracted, then expanded after a giant impact early in its history. See more Dawn images here. The movie shows the asteroid rotating over a period of 5.3 hours.

The Dawn spacecraft continues to close in on Vesta, one of the last unexplored objects of appreciable size between here and Pluto. Dawn is expected to go into orbit around the asteroid on July 16.

NASA/JPL-Caltech/UCLA/MPS/DLR/PSI

This is how Vesta looked in the navigation camera view as of June 20, when Dawn was 117,000 miles away. And here’s a time-lapse view of the approach so far.

Read more about the Dawn mission in our June/July issue, or listen to this recent talk by project co-investigator Carle Pieters (below), who describes what scientists hope to learn at Vesta.

Today, two asteroids pass the Earth at a fairly snug distance. One, 2010 RX30, went by just before 6:00 a.m. EDT about 154,000 miles above the northern Pacific Ocean. That’s equivalent to three-fifths the distance to the moon. The other one, 2010 RF12, goes by just after 5:00 p.m. EDT, above Antarctica, and offers a slightly closer shave: 49,000 miles, a bit bit more than twice the altitude of a geostationary communications satellite.

Two asteroids do a drive by today, September 8, 2010. Image: NASA/JPL

The first rock was a maximum of 65 feet in diameter, and the second a max of 46 feet. So even if they made a direct hit on the home planet—even though they’d each unleash the force of multiple Hiroshima-size atomic bombs—they’d do so tens of thousands of feet up in the atmosphere. If it happened over land, which covers thirty percent of the planet, it probably wouldn’t come close to the destructive power of the Tunguska Event of 1908. That object might have been a stony asteroid a couple hundred feet in diameter, or a more loosely packed comet a few thousand feet in diameter. Either way, not even that object made it near the ground, and probably exploded three-to-six miles high. Still, Tunguska unleashed a few thousand times the force of a Hiroshima explosion, and flattened 830 square miles of Siberian forest.

Here's a top-down view. Image: NASA/JPL

Astronomers guess that asteroids up to 35 feet in diameter shoot by within the Earth-moon distance of 240,000 miles about once a day, and enter the planet’s atmosphere perhaps once every ten years. Asteroids ten times that size arrive on average every 10,000 years. Both of today’s asteroids are close enough to be visible through amateur telescopes.

Seeing as how this subject has a direct bearing on human survival, it’s a topic we’re interested in at Air & Space. Read our article about meteors.

On the Mayflower, at least you could go out on the deck. (Image: Lockheed Martin)

At first I was excited to read press reports of a Lockheed-Martin concept for a bare-bones human asteroid mission, using a pair of Orion capsules yoked together. Finally, a near-term plan! Because the Orion is mostly built, the first “Plymouth Rock” mission could fly as early as 2016, nine years earlier than NASA’s (extremely) loose target for an asteroid trip.

After skimming a 41-page Lockheed white paper on Plymouth Rock, I’m less excited.

I don’t doubt that motivated astronauts would forgo a certain amount of comfort to make history’s first trip into deep space. And the three-month trip to the asteroid wouldn’t be so bad. Two Orions provide about 10 cubic meters of volume for each of two astronauts—not nearly as roomy as the International Space Station, but bearable. On the way back, though, one of the vehicles would be jettisoned, leaving the pair to squeeze into a single capsule. Now they’d each get four cubic meters. For three months. That’s equivalent, says the white paper, to the volume of a modern American minivan with its seats removed. It’s twice the room the three-man Apollo 7 crew had in 1968, but their mission only lasted 11 days—and they were miserable.

Recognizing that this may be too cramped for even the most gung-ho space adventurer, the authors suggest adding another module, something like the logistics modules attached to the space station. But now the simple plan starts to get more complicated, and more expensive.

Like I said: Less excited.