STARDUST Status Report

June 25, 1999

Earlier this week, flight sequence SC006 started with the STARDUST spacecraft at 1.6 AU from the Sun and 0.7 AU from the Earth, increasing about 0.01 AU per day. All subsystems are performing normally. The spacecraft attitude is off-pointed 20 degrees from the Sun, exposing only 20% of the Max Planck Institute Cometary and Interstellar Dust Analyzer (CIDA) collector to the interstellar dust stream. The collector area of CIDA exposed to the stream has been decreasing as the need to point the solar panels more directly toward the sun has increased as the spacecraft recedes from the sun. During flight sequence SC007, the spacecraft will be pointed directly at the sun to collect sufficient energy to operate the spacecraft and the CIDA collector will be totally blocked by the dust shield from the interstellar dust stream.

The flight team at Lockheed Martin Astronautics completed testing commands to turn on the High Gain Antenna (HGA) for the first time. Currently communications with the spacecraft have been through the Low Gain (LGA) and the Medium Gain Antennae (MGA) which uses Solid State Power Amplifier 1 (SSPA 1). The HGA uses SSPA 2 which will be powered on for the first time in flight along with the HGA. This means that SSPA 1 will be powered off and will be left off until the next communications session using the MGA next Thursday. SSPA 1 has been powered off previously, during safing and to dissipate trapped charges.

SSPA 1 has received attention since its performance has had small, but explained variations during the last few months. The SSPA's have only one commandable gain state, high, which uses about 55 watts of power and draws 1.9 amps of current. Over time, many hours to days, a trapped charge builds raising the temperature of SSPA 1 at which time SSPA 1 protection circuitry drops its current to 1.5 amps, with an associated drop in gain of 2-3 dB. The trapped charge can be dissipated and an annealing process occurs to bring SSPA 1 back to normal operations by powering it off, for many days or more being preferable. It is not known if SSPA 2 will exhibit this same behavior.

The drop in gain in SSPA 1, up until recently, has not been a problem. But as the spacecraft continues to journey far beyond the orbit of Mars and as the distance to Earth increases, every dB of gain counts. During last week's commanding of the Solar Array Switching Unit (SASU) changing from series to parallel connections, we had only a margin of 0.5 dB, dangerously close to losing lock on the downlink signal. This has lead the flight team to consider powering off SSPA 1 between communications sessions to dissipate the trapped charges and then turning it back on just before communications start so that the SSPA will stay in its high gain state through the communications pass and provide an extra few dB of margin.

The STARDUST Outreach made a presentation to NEWMAST, a national group of K-12 teachers, and also to the San Diego Astronomy Association.

For more information on the STARDUST mission - the first ever comet sample return mission - please visit the STARDUST home page: