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From The "JPL Universe"
July 23, 1999

Deep Space 1 set to make close flyby

Craft will pass within 15 km of asteroid 1992 KD
By JOHN G. WATSON

Deep Space 1 has been remarkably successful with a complicated mission. Now the 44- member operations team, busy working out of mission control facilities on the second floor of historic Building 230, is preparing to undertake a still more challenging assignment: the spacecraft is poised to encounter asteroid 1992 KD on Wednesday, July 28, at 9:46 p.m. Pacific time, marking the closest flyby of an asteroid ever attempted.

"Busy" may be an understatement. Unlike missions of yore, when flyby activities were solidified long in advance, at press time the small team continued to test and make modifications to the flyby sequence. With an overall compression of the development timeline, the encounter has proven to be challenging indeed in more ways than one.

The spacecraft's new autonomous navigation system, or AutoNav, will attempt to guide Deep Space 1 to just under 15 kilometers (9.3 miles) of the asteroid's surface. During the encounter, the spacecraft will fly past the asteroid at a relative velocity of about 56,000 kilometers per hour (35,000 miles per hour). The encounter will provide an opportunity to complete the final 5 percent of testing of AutoNav, through which the spacecraft keeps track of its location in space and makes trajectory changes to remain on course.

Deep Space 1 has completed validation of its 11 other new technologies. Since testing of these technologies is at the heart of the mission, the flyby and its science return is a bonus. The ambitious encounter is a high-risk endeavor whose success is by no means guaranteed but whose findings, should there be significant data return, will be of great interest to the science community.

The asteroid and the space environment surrounding it make scientifically interesting targets for two advanced, highly integrated science instruments. During the flyby, an integrated spectrometer and imaging instrument is scheduled to send back images taken in infrared and visible light while an instrument that studies the three-dimensional distribution of ions and electrons, or plasma, will conduct several investigations.

Asteroid 1992 KD, which was discovered in May 1992, by astronomers Eleanor Helin and Kenneth Lawrence of JPL, was chosen from more than 100 flyby possibilities.

In addition to their value for engineering future space missions, images and other data returned from this encounter will greatly assist scientists in their understanding of the fundamental properties of asteroids. Asteroid 1992 KD was chosen from more than 100 flyby possibilities. Its elliptical orbit curves within and outside Mars' orbit of the Sun, at its most distant extending more than three times farther from the Sun than Earth. Although scientists believe its diameter is approximately 1 to 5 kilometers (0.6 to 3 miles), they know little else about the object. With this flyby, they can learn more about its shape, size, surface composition, mineralogy and terrain.

The diminutive Deep Space 1 spacecraft, reaching just 2.5 meters (8.2 feet) in height, was launched on October 24, 1998, onboard a Delta II rocket from Cape Canaveral Air Station, Fla. It marked the first launch of NASA's New Millennium Program, testing and validating new technologies in a series of deep space and Earth-observing missions. This is one of the first-ever deep space NASA missions to have technology, rather than science, as its key focus.

The technologies that have been tested on Deep Space 1 generally fall into two categories: those concerned with making future spacecraft smaller and less expensive, and those concerned with making spacecraft more autonomous. Many of the technologies are designed to make spacecraft smaller, less expensive and capable of more independent decision-making so that they rely less on tracking and intervention by 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 ion engine, which was required to thrust for a minimum of 200 hours, has in fact been operated for nearly 1,800 hours to date.

Deep Space 1 has also tested the feasibility of compressing mission preparation periods to as short as 39 months from initial concept through launch and of reducing mission budgets to substantially less than that of other recent NASA missions. Deep Space 1 is budgeted at $152 million, including design, development, launch and operations.

Xenon, the same gas that fills photo flash tubes and glows brightly in many lighthouse bulbs, is the propellant for the ion propulsion system. Although this type of engine has been tested in labs and on Earth-orbiting satellites, only now has it been flight-tested as the primary propulsion source on a deep space mission. Having been proven in flight, ion drives are likely to be used on many future deep space and Earth-orbiting missions that would otherwise be impractical or unaffordable with conventional propulsion systems. The mission also features three key experiments that give the spacecraft more autonomy in navigating and general decision-making. Autonomous navigation, when combined with ion propulsion, "is like having one's car find its own way from Los Angeles to Washington, D.C., arrive in a designated parking space, and do it all while getting 300 miles to the gallon," said Dr. Marc Rayman, Deep Space 1's chief mission engineer and deputy mission manager.

JPL manages the Deep Space 1 mission for NASA's Office of Space Science.

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