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Deep Space Testbed A Growing Success
JPL - January 12, 1999 - During the past three weeks, Deep Space 1 has exercised its autonomous navigation system, an advanced science instrument that studies space plasma and a radio system that transmits at an unusually high frequency. In addition, the spacecraft has continued to use its ion propulsion system and advanced solar array.

The operations team turned the ion propulsion system off December 18 to turn the spacecraft's helm over to the autonomous navigation system, known as AutoNav. This system, one of the 12 technologies that Deep Space 1 is validating, is designed to find the spacecraft's location in the solar system by taking images of known asteroids and comparing their positions to background stars. Because the autonomous navigation system knows where the asteroids are and where the more distant stars are, it can determine where it is in the solar system when the picture is taken.

AutoNav transitioned into spacecraft control by directing the ion propulsion system to pressurize its xenon tanks for thrusting, commanding the spacecraft's attitude control system to turn the spacecraft to thrust in the direction that AutoNav desired and, finally, starting the thruster.

AutoNav determines how much power to devote to the ion propulsion system, which uses electricity to ionize and accelerate xenon. To do this, AutoNav has knowledge of how much power the advanced solar arrays can produce and how much power the spacecraft consumes apart from the ion propulsion system. The spacecraft will consume more power as it ventures farther from the Sun because it will need to operate its heaters more.

When the ion propulsion system is thrusting, AutoNav updates both the direction and the throttle level for the thrusting every 12 hours in order to follow the flight profile stored on board. So far the AutoNav system has operated flawlessly.

On December 21, thrusting was suspended for a few hours, during which AutoNav commanded the spacecraft to turn to point its camera at asteroids and stars and take images of them. The images taken are allowing AutoNav's designers to improve onboard computer routines for processing such pictures. Previously, all they had was prelaunch predictions of the camera's performance; now, with actual images, the routines can be updated. The successful demonstrations of AutoNav's control over the ion propulsion and attitude control systems and the camera are another step in transferring many of the responsibilities normally fulfilled by human controllers to intelligent spacecraft of the future.

A skeleton team monitored the spacecraft over the holidays, with the ion propulsion system powered on.

On Tuesday, January 5, AutoNav turned off the ion engine, completing the first thrust segment of the Deep Space 1 mission. During that period, the engine accumulated over 850 operating hours and experienced 59 recycles, which are momentary automatic interruptions, or shutoffs, of the system, primarily for the system to protect itself from damage due to drifting particulates. By contrast, in the first 850 hours of ground testing of the flight-spare ion thruster ion engine, approximately 240 recycles were experienced. The lower number of recycles in flight is an indication that in-space operation of an ion thruster is more benign than operation in a vacuum chamber. During the entire thrusting period, the power processor and the xenon propellant storage/control systems have worked just as designed.

On Wednesday, January 6, the Plasma Experiment for Planetary Exploration (PEPE) was turned back on, and new software for the advanced science instrument was tested. On Friday, January 8, it was turned to its highest data rate so that it and a plasma instrument on the Saturn-bound Cassini spacecraft could make simultaneous observations of the solar wind. Those observations continued over the weekend.

On Thursday, January 7, AutoNav again commanded the spacecraft to turn to point its camera at asteroids and stars and take images of them.

On Sunday night, January 10, Deep Space 1 participated with the Deep Space Network in a telecommunications experiment. Deep Space 1 transmitted to the Deep Space Network complex at Goldstone, California, using a very small, lightweight amplifier made by Lockheed-Martin for radio signals at a frequency about four times higher than the current standard frequency used for deep-space missions. This frequency band, called Ka-band, offers the possibility of sending more information with less power, important for future small but capable spacecraft. These tests are helping the Deep Space Network develop the capability to receive Ka-band routinely for future spacecraft.

Deep Space 1 is almost 45 times as far away as the Moon now. At this distance of more than 17 million kilometers (more than 10 million miles), radio signals sent from Earth take nearly one minute to reach the spacecraft.

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