Exactly one week from today on February 12th, the Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft will end its five-year, two-billion-mile mission, making what scientists hope will be a soft landing on the asteroid 433 Eros (see animation). The spacecraft, which began orbiting Eros on Valentine's Day last year, has collected 10 times more data than originally planned, including about 160,000 images. "We have answered the questions we had when the orbit began," says project scientist Andrew Cheng from the Applied Physics Laboratory (APL). "But we also found many other things we didn't expect to see and have questions we didn't know to ask at the start of the mission. Scientists will be looking at these data for years."
Many researchers are anxiously awaiting the last few photos NEAR Shoemaker will snap next Monday, which will provide them with the closest look yet at a small celestial body. They estimate these pictures could show surface features as small as four inches across. The scientists are also eager to attempt the craft's controlled decent onto Eros' 6-mile wide "saddle" area. "With the spacecraft just about out of fuel and our science objectives met, this is a great way to end a successful mission," says NEAR Mission Director Robert Farquhar of APL. "It's all bonus science. It's never been tried before and it certainly is a complicated set of maneuvers, but at this point the only real risk is not taking one."
The plan is to begin moving NEAR Shoemaker out of its current orbit at about 10:31 a.m., Eastern Standard Time (EST). A series of thruster firings will then slow the spacecraft down from a speed of about 20 miles per hour to 5 miles per hour. It should drift to the surface on its side, aiming its telescopic camera towards the landing site. The estimated arrival time is just after 3 p.m. EST. Mission operators intend to use blurring photos, altitude data from the spacecraft itself, Doppler tracking and eventually, the loss of a signal, to determine when NEAR Shoemaker actually lands.
"The whole sequence of engine burns has to go right, or it might not be a very soft touchdown," Farquhar says. "The unknown nature of the surface makes it hard to predict what will happen to the spacecraft, especially since it wasn't designed to land. The most we can hope for is a beacon from NEAR Shoemaker that says it's still operating."