Much of the activity in the intervening week has revolved around validation of the engine's "throttle levels." The data that are being returned are extremely valuable, and this is an important step in Deep Space 1's charter of evaluating high-risk technologies critical for NASA's future space science missions.

This system can be throttled, with higher throttle levels drawing more electrical power and delivering more thrust. With Deep Space 1's design, the minimum throttle level is 0 and the maximum is 111, although it has never been planned that the highest throttle levels would be reached.

The spacecraft does not have enough electrical power to drive the ion engine at the highest levels, but for this technology validation mission, the highest levels are unnecessary. When the thruster started last week, it was at level 6. On Wednesday, November 24, the operations team brought the ion propulsion system to level 27 and then later to level 48. The thruster operated extremely well and the team decided to try to let the system continue thrusting at throttle level 27 during the four-day holiday weekend.

On Monday morning, November 30, the operations team raised the throttle level to 48 again to collect data to determine whether there are any changes in its performance from when it was operated at that level 5 days earlier. Following that, the thruster was commanded to throttle levels 69, then 83, and finally 90, with data being collected on its behavior at each level. The spacecraft and the ion propulsion system continued to work extremely well. At throttle level 90, it appeared that the spacecraft was near its limit for providing power to the ion propulsion system, so it was throttled back to level 83 and was left there overnight. At throttle level 90, the sytem drew approximately 2.4 kilowatts of power.

As of 1 p.m. Pacific time today, the system has thrusted continuously for approximately 190 hours. The team has now operated the thruster for a longer uninterrupted time than had been planned during the entire mission; with the original plan, the thruster would have been turned off for at least 15 hours every week to allow other spacecraft activities to be conducted.

Deep Space 1 has now operated its thruster for a much longer uninterrupted time than any deep space probe using any other propulsion system.

The ion propulsion system can be turned on without necessarily thrusting by keeping the xenon ions in the plasma chamber instead of accelerating them, which can be useful for testing and diagnostics. However, the system has in fact been thrusting for all 190 hours.

In the process of going to high throttle levels with the ion propulsion system, the team gathered additional validation data on the twin solar arrays, which provide the electrical power to operate the ion propulsion system and the rest of the spacecraft. They use 720 lenses to focus sunlight onto high efficiency solar cells to generate electricity. This was the first opportunity that the arrays had to provide high power, because the propulsion system has the greatest power requirements of any unit on board.

While the spacecraft was thrusting on Monday, the team opened the partially transparent cover on the combination camera/imaging spectrometer. This maneuver was intentionally delayed until several weeks after launch to allow time for any residual gases left over from launch to dissipate. Some images have already been collected from this advanced technology for preliminary engineering analysis, and opening the protective cover cleared the way for later tests. The cover will remain open for the rest of the mission.

Deep Space 1 is now more than 15 times as far away from Earth as the moon is. Radio signals, traveling at the universal limit of the speed of light, take about 40 seconds to make the round trip.

The ion propulsion system is one of 12 advanced technologies being validated on Deep Space 1. The system is a product of the NASA NSTAR program, a cooperative effort between JPL and the Lewis Research Center. The industrial participants are Hughes Electron Dynamics Division; Moog Inc.; Spectrum Astro Inc.; and Physical Science Inc. The solar arrays were provided to NASA by BMDO and were developed by AEC-Able Engineering, Tecstar, Entech, and NASA's Lewis Research Center.