NASA gets another shot at space target
NASA's asteroid hunter is born again - and once again closing in on its target.
Members of the Near Earth Asteroid Rendezvous mission thought they lost a precious opportunity when a navigation glitch sent the probe whizzing by asteroid 433 Eros in December 1998.
But a little more than a year later, efforts to salvage the mission have again put NEAR on Eros's doorstep. Now, appropriately enough, the craft is set to tryst with the rock named for the Greek god of love on Monday - Valentine's Day.
"That will be a historic first - the first spacecraft to orbit a small body," says mission director John Farquhar at Johns Hopkins Applied Physics Laboratory in Laurel, Md.
A successful rendezvous would help quell increasing criticism of NASA after two Mars missions failed last year. Moreover, it would give Dr. Farquhar and his colleagues a first detailed look at one of the missiles in the galactic shooting gallery where Earth is a potential target.
Indeed, these leftovers from the formation of the solar system not only could offer clues about the creation of the cosmos, but also hold significant amounts of key materials such as titanium and water.
Peanut-shaped Eros measures 21 miles by 8 miles by 8 miles. It barely has enough gravity to hold onto the NEAR craft for the year they are to waltz together.
"We have enough control over the orbit so it won't be too unstable," Farquhar says.
Yet getting into orbit will be tricky. NEAR is creeping up on Eros at a relative speed of 18 m.p.h. It will fire small thrusters at 10:33 a.m. EST Monday to slow down enough for Eros to capture it.
That takes delicate rocket handling. NEAR scientist Peter Thomas at Cornell University in Ithaca, N.Y., says that, compared with the powerful course-correcting blasts made earlier by NEAR's main engine, this is like "having to sneeze to get into orbit - but sneezing in the right direction."
NEAR mission members have acknowledged feeling pressure to do this job right. After its recent Mars failures, NASA needs success. And there's no better hallmark of success than turning what had seemed to be failure into an unexpected bonus.
For more than a day after they lost contact with NEAR on Dec. 20, 1998, controllers feared they had lost the spacecraft. Then, as programmed, the radio woke up. The Eros rendezvous was scratched.
But quick reprogramming set a new course and sent the $125 million spacecraft to within 2,378 miles of Eros on Dec. 23. NEAR captured 222 useful images as it sped by at about 2,200 m.p.h. NEAR then did a U-turn, entered nearly the same solar orbit as Eros, and got on a year-long course for Monday's rendezvous.
Assuming all goes well Monday, NEAR has a busy 12-month schedule. Its instruments will take visible light and infrared images, make radar maps of topography, and analyze minerals on the surface.
NEAR will slowly descend to within 31 miles of the asteroid over the next two months. It then will begin to climb to 311 miles in late August for more comprehensive views. Then, in December, it will drop to within a mile or less of Eros, where its instruments could distinguish mineral composition of rocks as small as a grapefruit, according to NASA.
The $224.1 million mission ends in February 2001. NEAR scientists hope that, at that time, NASA will let them try to have NEAR touch down on the surface and then ascend to image its footprints. This could help determine surface strength and texture. It's a dangerous maneuver NASA has yet to approve.
Launched Dec. 17, 1996, the 1,775-pound spacecraft has already done useful science. It inspected the asteroid Mathilde on June 27, 1997. It made a detailed survey of Antarctica during a subsequent flyby of Earth Jan. 23, 1998. Earth's gravity then sent NEAR on course for Eros. Now, some 240 million miles from Earth, it has finally reached its destination.
(c) Copyright 2000. The Christian Science Publishing Society
