Dr. Marc Rayman's Mission Log
 



  January 23, 1999

Mission Update:


Thank you for visiting the Deep Space 1 mission status information site, now beginning its fourth month on the list of most frequently visited sites in the solar system for information on this technology validation mission. This message was logged in at 10:30 am Pacific Time on Saturday, January 23.

Deep Space 1 accomplished experiments with 7 of its advanced technologies this week. With all these impressive achievements to hear about, settle in for a long entry!

The autonomous navigation system, known to its close friends as AutoNav, has demonstrated its ability to conduct optical navigation imaging sessions each week. The activity consists of AutoNav commanding the spacecraft to turn to point its new technology camera at asteroids and stars and take images of them. The apparent position of an asteroid relative to the much more distant stars will allow AutoNav later in the mission to estimate where it is in the solar system. This is based on parallax and is the same phenomenon you observe if you hold a finger in front of your face and view it through each eye separately. The apparent position of your finger shifts as you switch from one eye to the other. As an example of how this is applied, suppose that distant trees are visible through a window in your house. If I took a picture from inside your house and showed it to you, you could find exactly where I had been standing when I took the picture by lining up the edge of the window with the distant trees. Similarly, 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. The images taken this month are being used by AutoNav's designers to improve on-board computer routines for processing the pictures. Previously, all they had were prelaunch predictions of the camera's performance; now, with actual images, the routines can be tested on the ground and updated as needed. The successful demonstrations of AutoNav's control over important spacecraft systems are another step in preparing NASA for an exciting future in which many of the responsibilities normally fulfilled by human controllers will be transferred to intelligent spacecraft.

Another of DS1's new technologies is the plasma experiment for planetary exploration, affectionately known as PEPE. This device measures charged particles in space, both electrons and charged atoms, or ions. It combines several functions into a unit of lower mass and lower power consumption than on traditional science missions. PEPE was developed by the Southwest Research Institute in San Antonio and the Los Alamos National Laboratory and was verified to work during several days of testing on DS1 last month. The testing of PEPE on DS1 is another step toward NASA's use of smaller, less expensive missions to explore the solar system. It and a related instrument on another spacecraft have conducted simultaneous observations of the solar wind, the stream of charged particles flowing from the Sun. Cassini, an exciting mission on its way to explore the ringed planet Saturn and its environment, carries an instrument that makes measurements similar to the ones PEPE can make. PEPE, with its advanced design, weighs one third and consumes half the power of the instrument on Cassini, but it is nearly as capable. With the two instruments observing the solar wind from different locations, scientists will gain valuable insight into its complex flow through the solar system. Yesterday the ion propulsion system was turned on for about 45 minutes. Part of the objective was to test new software for PEPE that was supposed to allow it to operate in the presence of the xenon ions produced by the advanced propulsion system. With PEPE designed to observe the more tenuous solar wind, it could be overwhelmed by the xenon, but yesterday's results show that this versatile instrument can be adjusted to accommodate the ion propulsion system.

Friday's firing of the ion propulsion system, the first since AutoNav correctly turned it off on January 5, also was used to gain more information about DS1's advanced solar array. The innovative array uses 720 lenses to focus sunlight onto 3600 solar cells, each converting the light into electricity. To test exactly how much power the array could generate, the operations team needed to find a way to draw as much power from the array as it could deliver. The ion propulsion system is the largest consumer of power on the spacecraft, so it was powered on and raised to a high throttle level. The data that were generated contribute to understanding the detailed performance of this advanced solar array. BMDO provided the array to NASA for testing on DS1. It was developed by AEC-Able Engineering, Entech, and NASA's Lewis Research Center. The solar cells on the array were manufactured by Tecstar.

DS1 has been collaborating with the Deep Space Network in a number of telecommunications experiments. NASA has antennas in Madrid, Spain, near Canberra, Australia, and near Goldstone, California for communicating with probes in deep space, but only certain antennas at Goldstone are capable of receiving special signals that DS1 can send, so the tests occur when the spacecraft is within view of that location on Earth. In December, DS1 validated a very small, lightweight amplifier made by Lockheed-Martin for radio signals at a frequency about 4 times higher than the current standard frequency used for deep-space missions. This frequency band, meaninglessly called Ka-band, is like another channel in the radio spectrum and offers the possibility of sending more information with less power, important for future small but capable spacecraft. The tests conducted this month are helping the Deep Space Network develop the capability to receive Ka-band routinely for future spacecraft. DS1 also put the heart of its radio system through a test, and it continued to operate as planned. That unit, built by Motorola and known by the inspiring appellation Small Deep Space Transponder or SDST, combines many functions normally performed by separate elements into one low mass unit. Most of the tests of that device were completed in December, but a final test was conducted this week, and it passed with flying colors.

Last week the SDST was used in a successful preliminary test of another of DS1's autonomy technologies, the beacon monitor experiment. When beacon monitor is used, it will summarize the overall health of the spacecraft. Then it will select one of 4 radio tones to send to Earth to indicate how urgently it needs contact with the large antennas of the Deep Space Network. These tones are easily detected with low cost receivers and small antennas, so monitoring a spacecraft that uses this technology will free up the precious resources of the Deep Space Network. Each tone is like a single note on a musical instrument. One tone might mean that the spacecraft is fine, and it does not need contact with human operators. Another might mean that contact is needed sometime with a month, while a third could mean that contact should be established within a week. The last is a virtual red alert, indicating the spacecraft and, therefore, the mission, are in jeopardy. In this first test, the small deep space transponder was used to transmit 4 different beacon signals to verify predictions of how well experimental instruments could detect them. The new detectors worked as planned, paving the way for future tests -- and use -- of this technology.

Over the coming weeks, DS1 will continue to exercise its technologies, providing still more useful data for designers of future science missions on the performance of these powerful systems.

Deep Space 1 is almost 60 times as far away as the moon now. At this distance of nearly 23 million kilometers, or more than 14 million miles, it takes radio signals 2 and a half minutes to make a round trip.





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