by Marc D. Rayman
Washington - March 28, 2000 - Operating under the philosophy of "If it isn't impossible, it isn't worth doing," the team controlling Deep Space 1 has been making remarkable progress in developing a new way to operate the spacecraft and control it for the exciting mission that lies ahead.
Testing of phase 1 of new software will begin this week in the DS1 test facility at JPL. This is a simulation of the spacecraft, created using some hardware similar to what is on the real spacecraft and some computer programs that emulate the behavior of other parts of the spacecraft.
The tests and refinements to the software will continue until early May when the final preparations for transmitting it to the distant probe will begin.
In the meantime these reports will be updated less frequently, but your ever-faithful correspondent remains vigilant and will revise this recording if events warrant.
In addition to conducting tests on Earth, the operations team has run some tests on the actual spacecraft because the test facility does not reproduce the spacecraft's performance perfectly.
The camera that will acquire images to aid in determining Deep Space 1's orientation will be called upon to operate in new ways, so after completing certain tests in the test facility that do not require the new software, controllers repeated some of them on the spacecraft itself.
These help answer detailed questions such as how long the camera's exposures should be and what the most reliable instructions are to transfer pictures from the camera to the central computer. These tests are proving extremely valuable in preparing the new software.
In the meantime, the spacecraft waits patiently as the work continues. The last recording, already in the halls of fame on several planets in the Milky Way's neighbor the Small Magellanic Cloud, described the nature of this work.
So the Deep Space 1 mission status information line is pleased to present an encore performance of parts of that informative recording, with updates for March 26...
As Deep Space 1 continues its travels far from Earth, the focus of the control team's work is to write new computer programs for the stalwart little craft.
As faithful listeners of many species know, after having successfully completed its primary mission last year, DS1 accepted a new, bonus assignment.
This extended mission represents NASA's desire to continue to reap as many rewards as possible from the investment made in DS1. But in November the spacecraft's star tracker ceased operating.
During the subsequent two months, the DS1 operations team devised a new method of controlling the spacecraft so that its main antenna could be pointed at Earth even without the sensor that had previously been so important.
Since then, this new and innovative technique, which (as described in detail in a previous recording) involves monitoring the strength of DS1's radio signal to determine exactly where it is pointed, has been used repeatedly to conduct communications with the spacecraft. But a new system is under development that will allow DS1 to point without the aid of mission controllers.
The star tracker, whose creative name is inspired by its function of tracking stars, had been responsible for helping the spacecraft determine how it was oriented in space.
This was not part of the autonomous navigation system, one of the advanced technologies DS1 tested during its primary mission; rather, it was part of what is called the attitude control system.
To reduce the attitude control system's regular reliance on distant Earth, engineers would like to replace the method of observing the radio signal to calculate the spacecraft's orientation.
Of course, all there is to work with is what is already on board; the only new "equipment" that can be provided is computer programs.
So engineers are writing new software that will allow the computer to control the pointing using images from the camera, another one of the 12 technologies that was included so that its innovative design could be tested in deep space.
This new method builds on the autonomous navigation system's capability to analyze the camera's pictures.
The star tracker worked by photographing the stars wherever it was pointed and analyzing the pictures to find familiar patterns. This is similar to how you might orient yourself at night if you knew the constellations.
But the star tracker and the camera have very different designs, including how large a section of the sky they see at one time and how fast they can take a picture and transfer the electronic image to the computer.
Nevertheless, DS1 engineers have devised a very clever new system that should allow the spacecraft to operate without frequent assistance from Earth. In effect, engineers are building a new attitude control system on DS1 from across the solar system.
A tremendous number of complex technical details have been worked out and more have yet to be finalized, as the small team that has accomplished so much is working hard to restore our deep space emissary's capabilities.
The new software will be radioed to the spacecraft in May; then, following a few weeks of tests on board, DS1 will return to thrusting with its ion propulsion system to propel it to an encounter with a comet next year.
When DS1 was launched, controllers had in mind that if the mission were successful and if the spacecraft remained healthy, NASA might extend its flight to conduct an encounter with Comet Borrelly in September 2001.
The mission went so surprisingly well that they were able to plan for it to visit two comets instead of one. But now that the star tracker has stopped, the spacecraft has fallen behind in its schedule of thrusting, so there is not enough time to do the thrusting necessary to keep both appointments. The DS1 science team met in January and concluded that the originally planned target should be kept.
Deep Space 1 is now almost 1.8 times as far from Earth as the Sun is and nearly 700 times as far as the moon. At this distance of more than 266 million kilometers, or over 165 million miles, radio signals, traveling at the universal limit of the speed of light, take longer than 29 and a half minutes to make the round trip.
DEEP SPACE ONE
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