Huygens Radio Receiver Test
29 May 1998The Huygens off-Sun AGC calibration test was successfully executed on 28 May at 22:04 UTC. The test lasted 33 minutes, including thetwo manoeuvres required to point Cassini's high-gain antenna (HGA) 12 deg away from the Sun and back. The purpose of the test was tocalibrate the automatic gain control (AGC) level of the Huygens receivers in a radio-noise free environment.
The Huygens Probe AGC Test mini-sequence was executed and the first of three data playbacks occurred during the DSN pass over Canberra. This test turned the Orbiter 12 degrees off its normal HGA-to-Sun line for 33 minutes and powered on the Probe electronics for 30 minutes to investigate unexpectedly low AGC values measured across the Probe-to-Orbiter umbilical link during the second inflight Probe checkout in 3/98.
The present hypothesis is that the lower AGC value was caused by higher solar noise during the second inflight checkout relative to the first, perihelion occurring the same day as the second checkout. The injection of noise thru the HGA feed has been demonstrated to cause a reduced Probe AGC value using the Engineering model for test at the Huygens Probe Operations Center (HPOC) in Darmstadt, Germany.
Thursday's test will allow the Solar effect to be demonstrated or ruled out. Huygens Probe reports that the first 7 minutes of the Probe AGC test data were transmitted to Earth during the DSN pass available for the test. The preliminary analysis of this first data set indicates that the Huygens radio receivers perform as expected in a radio noise free environment. The rest of the AGC test data will be transmitted to earth on May 30 and May 31. A full test report will be published when the complete data set will have been analyzed.