Montage of our solar system

With its technology tests almost complete, NASA's Deep Space 1 mission is about to undertake the closest encounter with an asteroid ever attempted when it flies within 15 kilometers (10 miles) of the newly named asteroid Braille tonight at 9:46 p.m. Pacific time (July 29 at 04:46 Universal Time).

Deep Space 1 will rely on its experimental autonomous navigation system, called AutoNav, to guide the spacecraft past the mysterious space rock at a relative speed of nearly 56,000 kilometers per hour (35,000 mph).

"Deep Space 1's main purpose is to test advanced technologies for the benefit of future missions, so we view the flyby and its science return as a bonus," said Dr. Marc Rayman, Deep Space 1's chief mission engineer and deputy mission manager at NASA's Jet Propulsion Laboratory, Pasadena, CA, where the mission is managed. "This ambitious encounter is a high-risk endeavor, and its success is by no means guaranteed. But should there be significant data return, the findings will be of great interest to the science community."

This morning, the spacecraft experienced a "safing" event at about 1200 UTC (5 a.m. PDT), during which Deep Space 1's flight computer rebooted itself and the spacecraft halted activity to wait for commands from Earth. However, the mission team and spacecraft recovered quickly from the event, which is not expected to impact tonight's flyby significantly. The spacecraft is operating as expected.

Asteroid Braille was previously known as 1992 KD. The new name was announced on Monday, July 26, by the Planetary Society, Pasadena, CA, as the result of a contest that focused on inventor themes and drew more than 500 entries from around the world. The name honors Louis Braille (1809-1852), the blind French educator who developed the system of printing and writing named for him and used extensively by the blind.

The winning entry was submitted by Kerry Babcock of Port Orange, FL. Eleanor Helin, who co-discovered the asteroid with fellow astronomer Kenneth Lawrence, made the final decision on the name. Helin and Lawrence are astronomers at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, which also manages Deep Space 1.

During the encounter, Deep Space 1 will be in the ecliptic plane (the plane in which Earth and most other planets orbit the Sun), moving more slowly than the asteroid, which will be progressing up through the ecliptic plane from below. It may well be more appropriate to say that the asteroid will zoom by Deep Space 1 than the reverse.

The flyby will allow final testing of AutoNav, which enables the spacecraft to use images of distant stars and asteroids within our Solar System to keep track of its location in space and to guide trajectory changes. Deep Space 1 has successfully completed tests of its 11 other new technologies.

The asteroid and the space environment surrounding it make scientifically interesting targets for two advanced science instruments aboard Deep Space 1. During the flyby, a spectrometer and imaging instrument will send back black-and- white photographs and images taken in infrared light, while a second instrument observes the three-dimensional distribution of ions and electrons, or plasma, in the area.

In addition to their value for designing future missions, the images and other data returned from this encounter will greatly assist scientists in understanding the fundamental properties of asteroids. Although scientists believe Braille's diameter is approximately 1 to 5 kilometers (0.6 to 3 miles), they know little else about it. With this flyby, they can learn more about its shape, size, surface composition, mineralogy and terrain.

Launched on Oct. 24, 1998, from Cape Canaveral Air Station, FL, Deep Space 1 marked the first launch of NASA's New Millennium Program, which tests and validates 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 and capable of more independent decision-making so that they rely less on ground controllers.

The mission has exceeded almost all of its technology validation requirements by conducting more extensive tests than had been planned. As one dramatic example, the spacecraft's experimental xenon ion engine, which was required to thrust for a minimum of 200 hours, has been operated for nearly 1,800 hours.

A Deep Space 1 asteroid flyby press kit, along with mission status reports from launch to the present, 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.

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