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NEAR Sends Back Images of Eros
Ongoing Reports
Eros - December 25/24, 1998 - Despite an aborted engine burn that postponed the January 1999, rendezvous of the NEAR spacecraft with asteroid Eros, mission operations team members were able to quickly upload new commands to the spacecraft, making it possible to obtain valuable information during a December 23, flyby of the asteroid.

Science data, including multicolor images, spectral data, and magnetic field measurements taken during the flyby, are now coming into the Applied Physics Laboratory's NEAR Science Data Center. Doppler navigation data and real-time telemetry were collected that will help determine the mass of the asteroid.

The flyby gave NEAR Mission Operations an opportunity to test tracking and instrument sequences in preparation of a rendezvous event, says Mission Operations Center Manager Mark Holdridge. "The flight recorders, full of Eros science data, are being played back at the present time. The spacecraft is healthy and doing just fine and it has been confirmed that the flyby pointing and instrument command sequence executed flawlessly to completion."

In addition to flyby data processing, team members are also studying data sent by the spacecraft soon after contact with it was reestablished on Dec. 22, following 27 hours of communication blackout to determine the exact nature of the software anomaly that led to the rendezvous burn failure.

NEAR and Eros are now traveling in separate orbits around the sun as plans are being made for a rendezvous sometime between August 1999 and April 2000.

Laurel - Dec 24, 1998 - On Dec. 23, at 1:43 p.m. EST, the NEAR spacecraft made a flyby of Eros designed to provide scientists with detailed data on the asteroid. In a matter of hours, mission operations personnel were able to respond to an aborted scheduled engine burn and program the command sequence that put the spacecraft on a trajectory approximately 2,500 miles (4,100 kilometers) from the surface of the asteroid. Currently (Dec. 23, 3 p.m. EST), the spacecraft is executing the command sequence as planned.

Three instruments onboard the spacecraft, the Multispectral Imager, the Near-Infrared Spectrometer, and the Magnetometer, are operating as expected. More than 1,100 images of the asteroid are anticipated, which will provide scientists with valuable information on the size, shape, and surface characteristics of Eros and whether it has any moons.

The first photographs will be posted on the NEAR Web site on Dec. 24 between 1:00 - 2:30 p.m.

Laurel - Dec 22, 1998 - (6pm EST) NEAR will slip behind 433 Eros at a distance of 4,100 kms at 1.43pm, Wednesday 23. With NEAR safely in a matching solar orbit to Eros the slow dance of orbital mechanics will then deliver NEAR back to Eros in May 2000 for an orbital insertion, described as "much easier than the original plan."

In what could be a year of great mission recoveries, the NEAR team is starting to feel a lot more comfortable than earlier this week when the prospect of loosing a $210 million mission at the frontdoor to Eros loomed high.

The new flight plan will see NEAR slip behind Eros as the asteroid's higher velocity takes it past the small robotic explorer. Over the next 18 months, NEAR and Eros will move around the sun in a relatively close orbit that will eventually bring the two close enough together to enable a shorter main engine burn for NEAR to obtain orbit about Eros. The new plan will also help make up for fuel lost as a result of Sunday's aborted engine burn

As Eros laps NEAR, the spacecraft's magnetometer will be turned on to measures the varying strengths of Eros' complex magnetic field. Matching this data with a limited 30 pixel image scan of the asteroid will give the NEAR team valuable data for planning the orbit insertion in May 2000.

The images to be returned in the next 48 hours, while fuzzy will provide a good indication of the shape and size of Eros, but will not be of the same quality as the Mathailde flyby in 1997.

At this stage there are no plans to conduct a limited main engine burn as the data so far received shows the spacecraft to be in good health, giving confidence to the decision to go for a May 2000 orbit.

Laurel - Dec 23/22, 1998 - (5pm EST) NEAR will make it closest approach to 433 Eros on Wednesday at 1.43pm EST at a distance of 3570 km, with the possibility of attaining orbit by mid-1999 still high, following extensive analysis the past 24 hours.

According to Andy Cheng, Project Scientist at NEAR, "The main engine appears to be OK, with the attitude anomaly caused by a software problem.

"We are currently planning to execute a contingency flyby sequence tomorrow to observe Eros with MSI/NIS as we fly past. The flyby will occur at ~3570 km closest approach distance, tomorrow at 1:43PM.

"We are still analysing and plan to simulate the attitude anomaly so as to prepare for another attempt to execute the biprop burns. At this point we may be able to enter Eros orbit as early as the summer of 1999, or some months later depending on how soon we are ready to do the burns," said Cheng.

NEAR Mission Operations at John Hopkins University were abel to achieve a communications lock on NEAR following extensive efforts by NASA's Deep Space Network. A command was uploaded Tuesday at 10pm EST instructing the spacecraft to download data from the aborted orbital burn.

This data has revealed that the main engine had a "hard start" and exceeded its thrust vector tolerance, causing the burn abort. If the tolerances are adjusted for the next attempt, the main engine should work fine.

The spacecraft maintained attitude for about 40 s after the abort, but then began firing thrusters and put itself into the tumble. The low voltage sense occurred about 4 minutes after the burn, cutting off all instrument power. Instrument power was restored 27 minutes later. Several momentum dumps occurred and about 30 kg of hydrazine was expended, leaving enough fuel remains to accomplish a rendezvous mission if the engine fires correctly next time.

Laurel - Dec 23/22, 1998 - (8.00am EST-US) "At 8 p.m. EST on Dec.21 NASA's Deep Space Network verified a positive lock on a radio signal from the NEAR spacecraft. Throughout the night scientists and engineers at NEAR's Mission Operations Center have been communicating with the spacecraft. At 8 a.m. this morning, Dec. 22, Mission Operations is working to analyze preliminary data as it is transmitted to Earth by the spacecraft." said Helen Worth, Public Affairs Officer at Johns Hopkins University Applied Physics Laboratory.
Laurel - Dec 22/21, 1998 - (11.30pm EST-US)"NASA's Deep Space Network has located NEAR and we will send a command up to it at 2 am EST-US to tell it to download the data collected during the aborted rendezvous burn. By 7-8 am EST-US Tuesday morning we might know what went wrong," said Helen Worth, Public Affairs Officer at Johns Hopkins University Applied Physics Laboratory.

Canberra - Dec 22/21, 1998 - (2pm AEST (10pm EST-US)Operators at the Canberra Deep Space Network station in Australia report that the DSN 70-meter dish has locked onto NEAR and they are waiting for mission control at John Hopkins University to give the go-ahead to attempt a command uplink. NEAR appears to be in a slow role, giving some pause to any early optimism. Canberra DSN will be in contact with NEAR until 5am EST-US.

Washington - December 22, 1998 - After two years of spectacular success in deep space, planetary scientists are facing the prospect of being returned to Earth with a thump, as communication with the Near Earth Asteroid Rendezvous remains offline following an aborted 20 minute rendezvous burn Sunday.

At 5:20 p.m. today, Dec. 21, the NEAR mission team is still trying to reestablish communications with the spacecraft. Communications ceased at about 5:10 p.m. EST, Sunday, Dec. 20, during the first of four rendezvous burns that would put the spacecraft at optimum speed and location for a Jan. 10, 1999, rendezvous with asteroid 433 Eros.

Doppler data collected at about 5:40 p.m. Dec. 20, leads team members to believe that the spacecraft was transmitting at that time. Around-the-clock strategy sessions are being held to correct the problem. If communications are not established by midnight tonight it is highly unlikely that the spacecraft will go into orbit on January 10.

Because of the robust nature of the spacecraft design many alternatives are available to the team to ensure that the mission can weather schedule changes and still yield significant science return. Those alternatives will be reviewed once communications have been reestablished.

Except for brief communication shortly after the scheduled 20-minute burn period, contact with the spacecraft has been lost. Mission Operations is now working to reestablish contact based on expectations that NEAR has entered safe mode after the burn was aborted by the spacecraft.

According to NEAR mission control at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. NEAR was to be boosted by several engine firings to bring into orbit about Eros. A two-minute fuel prep process was completed successfully, but contact was lost during further preparation ahead of the first 18-minute orbital burn.

Brief contact with NEAR was achieved at 5:40 p.m. giving rise to some hope that the craft had not been destroyed, and that some of last minute workaround could salvage the $211 million mission to orbit an asteroid for the first time.

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