Thanks to quick actions of NEAR ground teams, a make-up maneuver placed the spacecraft on a trajectory that would swing it back Eros' way. On February 14, Valentine's Day, and 13 months later than planned, NEAR is on track to experience its own second coming.
"NEAR is like nothing else in deep space. This is the first time in history that a spacecraft has attempted to go into orbit around a small body, such as an asteroid or a comet nucleus."
As for figuring out why NEAR didn't steer itself into Eros orbit on December 20, 1998, the APL issued a NEAR Anomaly Review Board report last month. The report, which was obtained by space.com, found that hardware and software specialists have been unsuccessful in piecing together what specifically took place that day far from Earth.
"The investigation established a good understanding of the events during approximately the first 47 minutes after the abort, but no explanation for the failure of on-board autonomy to quickly correct the problem," the report says. "The Board is unable to establish a complete explanation for the rendezvous burn events."
"We just couldn't put our finger on what precisely happened," said APL's Eric Hoffman, who chaired the study into the spacecraft's past woes. More than 128 simulations were done on a NEAR ground simulator to help track down the spacecraft's actions, but to no avail. "It was frustrating," he said.
Hoffman said there were valuable lessons learned from the report's work, with future spacecraft designers already benefiting from the research into NEAR's abnormalities.
The report did find that NEAR ran into problems shortly after the first and largest of a series of Eros rendezvous burns had begun. When the spacecraft's main engine ignited, the burn aborted after a fraction of a second, then went into safe mode. At that point, communications with the spacecraft were lost for 27 hours.
During that blackout period, the report found, NEAR had turned wildly. The probe fired its thrusters thousands of times, exhausting huge quantities of precious fuel in the process.
A casualty resulting from the fuel loss is NEAR's Multi-spectral Imager, built to help discern the overall composition of Eros. Propellant spewing from the craft has contaminated and degraded the imager, the report said.
However, re-calibration of the camera and ground processing can partly overcome this problem, minimizing the impact on mission science.
Another fuel loss issue addressed in the report: "The remaining fuel is sufficient to carry out the original NEAR mission, but with little or no margin."
Lofted from Earth in February 1996, NEAR is the first NASA planetary mission to be carried out by a non-NASA space center. APL engineering teams developed the spacecraft over a fast-paced 26-month period at a cost of a little more than $108 million.
APL management points with pride to the fact that $3.6 million was shaved off NEAR's original estimated price tag of $112 million, epitomizing the faster, better, cheaper way of doing space business.
"NEAR is like nothing else in deep space," explained APL's Robert Farquhar, the spacecraft's mission manager. "This is the first time in history that a spacecraft has attempted to go into orbit around a small body, such as an asteroid or a comet nucleus. It has never been done before," he said.
Farquhar also noted that a simulation of flight events for the spacecraft's upcoming re-encounter with Eros is to be done at APL's mission control on January 19. "If that works, then everything should be okay," he said.
If all continues as planned, ground operators will fire the spacecraft's set of thrusters on February 2 and again on February 14. Although NEAR's main engine could be used to brake into Eros orbit, it has been decided not to use this large motor.
The spacecraft's less powerful thrusters will nudge it into orbit around Eros, an elongated asteroid whose dimensions -- 21 miles by 8 miles by 8 miles (34 kilometers by 13 kilometers by 13 kilometers) -- give it the look of a giant shoe.
NEAR is to circuit Eros for a year, zipping over the asteroid's surface in closer and closer flybys.
As the mission draws to a close, scientists would like to finesse the craft into hover mode over select spots on Eros. If given a go-ahead by NASA, the probe may even attempt a landing on the asteroid.
"We have a very comprehensive science payload on NEAR. We're not just taking a snapshot of Eros. We're going to do a long term investigation," Farquhar said.
As for NEAR's problems in trying to settle into Eros orbit the second time around, Farquhar is sure next month's thruster firings will take place without problems. "I'm very confident that we're going to pull off those burns," he said.
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