Jul 29, 1999

Face-to-face with asteroid Braille

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Using an experimental autopilot system, NASA's exotic Deep Space 1 spacecraft has completed the closest-ever flyby of an asteroid.




Deep Space 1 ion drive. Image credit JPL
July 29, 1999: NASA's Deep Space 1 experimental spacecraft successfully flew closely above the surface of asteroid 9969 Braille at 9:46 p.m. Pacific time Wednesday, July 28, using a sophisticated new space autopilot system, exceeding 100 percent of the mission's objectives.

"This is a dramatic finale to an amazingly successful mission," said Dr. Marc Rayman, chief mission engineer and deputy mission manager. "With AutoNav's successful piloting of the spacecraft, we've completed the testing and validation of the 12 new technologies onboard and possibly acquired important science data, including photos."

Right: Hot blue ions emerge from a prototype ion propulsion drive like the one which now powers Deep Space 1. Although the ion drive on DS1 provides acceleration much smaller than we feel toward Earth, it has gradually given the spacecraft the speed necessary to travel across our Solar System and visit asteroid Braille. The July 29, 1999 flyby of Braille was accomplished while the spacecraft was under the control of AutoNav, a cutting-edge experiment in autonomous navigation. Image Credit: JPL.



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Data from the spacecraft will be analyzed in coming days to determine the actual flyby distance, which at about 15 kilometers (less than 10 miles), was by far the closest flyby of an asteroid ever attempted.

Ten minutes after the flyby, when the spacecraft signals reached Earth after a 10-minute journey, the team burst into spontaneous applause at the news that the spacecraft was turning back to face the asteroid. The turn was indicated by a marked Doppler shift, a clear early indicator of a successful encounter. Like a siren whose pitch changes after passing by, the Doppler shift indicates movement past an object.

Launched Oct. 24, 1998, Deep Space 1 is the first mission under NASA's New Millennium Program, which tests new technologies for future space and Earth-observing missions. The technologies that have been tested on Deep Space 1 will help make future science spacecraft smaller, less expensive, more autonomous and capable of more independent decision-making so that they rely less on tracking and intervention by ground controllers.
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Of the 12 new technologies on board, all but the spacecraft's autonomous navigation system had been completely tested since launch. With the asteroid encounter, AutoNav finished its last five percent of testing.

Making the flyby all the more memorable -- and serving as a testimonial to the team's quick ability to think on its feet -- was the fact that the spacecraft experienced a "safing" event earlier in the day, starting at about 5 a.m. PDT on July 28 and ending at about 11 a.m. PDT. A small software glitch, now fully diagnosed, was detected by Deep Space 1's fault-detection software, which triggered a protective program that causes several events: the spacecraft halts non-critical activity, orients its solar panels toward the Sun, points light and heat- sensitive instruments away from the Sun and reverts to its low- gain antenna while awaiting new commands.
NEAR image of asteroid Mathilde, courtesy APOD
Left: On the way to visiting the near-Earth asteroid 433 Eros, the Near Earth Asteroid Rendezvous (NEAR) spacecraft flew right by another asteroid: 253 Mathilde in June 1997. Shown above is one picture from the encounter. Deep Space 1's flyby of Braille was the closest to date. Pictures of Braille will released at an August 3, 1999 briefing. Credit: Astronomy Picture of the Day [more information about Mathilde]

"This has been by far the most challenging, dramatic and stressful day on the project," said Rayman. "The last 16 hours before the flyby were really, really exciting. We had the safing event, we recovered from it and we managed to squeeze in a trajectory correction maneuver to update Deep Space 1's flight path."

Science results will be downlinked in a series of telemetry sessions over the next several days. During the flyby, a spectrometer and imaging instrument took black-and-white photographs and images taken in infrared light, while a second instrument observed the three-dimensional distribution of ions and electrons, or plasma, in the area.

A science update covering science results is scheduled to take place at NASA's Jet Propulsion Laboratory, Pasadena, Calif., on Tuesday, August 3, at 10 a.m. PDT. It will be broadcast live on NASA TV.

A live videocam view of the Deep Space 1 mission control area is available at

Deep Space 1 is budgeted at $152 million, including design, development, launch and operations. The mission is managed for NASA's Office of Space Science by JPL, a division of the California Institute of Technology.
Web Links

Deep Space 1 - Jet Propulsion Lab's Mission Page
Solar Electric Propulsion on DS1 - JPL
NASA Glenn Provides Critical Technologies for Deep Space 1 Mission - Jet Propulsion Lab's Mission Page
Exotic Technologies Finish Road Test on Cosmic Highway - NASA Headquarters press release
SwRI engineers activate Deep Space One instrument - Southwest Research Institute (SwRI) press release
Ion propulsion now a practical reality - Story on Astra 2A Communications Satellite which uses ion propulsion
Xenon Ion Propulsion - Hughes Space And Communications commercial ion propulsion for satellites.
More Space Science Headlines - NASA research on the web
NASA's Office of Space Science press releases and other news related to NASA and astrophysics

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