MEX (SC 41) Mid-Cruise (CR1) BSR Test DSS 43 - Pass 139 18 October 2003 Summary: This pass was scheduled as a second check of the end-to-end function of DSN 70-m systems for Mars Express bistatic radar (the first test was conducted 6 July 2003). It included X-band uplink, X/X and X/S ranging, and various downlink modulation states, as well as the 1-way unmodulated, dual frequency signal needed for bistatic radar. It was the first radio science test in which a systematically generated Sequence of Events and DSN Keyword File were used at JPL/DSN. Organizationally, the test appeared to go well. But three problems would have hindered derivation of science results had this been a real bistatic radar pass: only two (instead of the needed four) closed loop receivers (CLR's) were available the S-LCP channel could not be calibrated for amplitude there was no X-RCP signal at the input to the RSR Overview: The test was divided into five phases: a pre-cal, spacecraft acquisition and 2-way tracking, a simulation of 1-way bistatic radar, additional 2-way (and 3-way) tracking, and a post-cal. RSR data were collected in X-RCP, S-RCP, X- LCP, and S-LCP. Problems: The three problems noted above and their effects were as follows. A few days before the test, the NOPE advised the Radio Science Systems Group that only two closed-loop receivers would be available. Although the primary data from bistatic radar operations are open-loop, continual monitoring of parameters such as system temperature requires that there be one CLR for each channel. We further learned that noise diodes can only be turned on and off through a CLR and that a separate CLR is required to control each diode. We assigned our two receivers to X-RCP and S-RCP, the two channels on which we expected the strongest signals. At the beginning of the 1-way unmodulated part of the test we asked the station to turn on the X-RCP and S-RCP 12K noise diodes for five minutes. Then we asked that they reconfigure the receivers to X-LCP and S-LCP and repeat the noise injections. The receivers were then returned to X-RCP and S-RCP. At one hour intervals the procedure was repeated twice more. The noise diode intervals are thus spread over 10- 15 minutes with the LCP interval about 6-8 minutes later than the RCP interval, depending on the speed at which the reconfigurations took place. The continuous record of system temperature generated through the CLR's is available only on X-RCP and S-RCP and is interrupted for 6-8 minutes every hour. The source of the S-LCP calibration problem is unknown but appears to be associated with inability to connect the ambient load to the front end of that channel. We specifically requested that the ambient load be connected to S-LCP and were told that the mechanism was not working. This means that the S-LCP channel is not calibrated for amplitude, though an estimate of its system temperature may be possible if we can obtain recent calibration records of the noise diode on that channel. At the beginning of the test it was apparent that there was no signal reaching the RSR from the X-RCP feed. We reassigned the channels and asked the station to investigate but there was never any improvement. The station reported that there was signal in the X-RCP CLR chain but operators were not able to determine where it was being lost on the open-loop side. We recorded the X-RCP channel but it shows only internally generated noise and occasional 'birdies' drifting through the spectrum. Microwave Configuration: The briefing message was not specific regarding polarization assignments at the LNA/feed. The SOE and DKF indicated that all receivers should be connected for RCP. DSS 43 requested clarification early in the pre-cal and it was decided that S-RCP would connect to the HEMT and S-LCP would connect to TWM1. RSR Configuration: RSR's were configured for 16-bit samples and for both 2 kHz (subchannel 2) and 25 kHz (subchannel 1) complex sampling rates. The low sampling rates were used when the spacecraft was 2-way; the high sampling rates were used for 1-way, pre-cal, and post-cal data collection. Pre-Cal: For pre-cal measurements (cold sky, noise diode, and ambient load), the following Fgain settings were used at DSS 43 during RSR recording. These were the values recommended based on the test results in July. UWV RSR Fgain ----- --- ----- X-RCP 1A 60 S-RCP 1B 63 X-LCP 2A 60 S-LCP 2B 63 The following Y-factors and ambient load physical temperatures were reported by the station from their pre-cal activities: UWV RSR Y-Factor Ambient Load ----- --- --------- ------------ X-RCP 1A 12.228 dB 16.6 C S-RCP 1B 11.297 dB 20.7 C X-LCP 2A 12.2 dB 16.7 C S-LCP 2B N/A N/A Toward the end of the pre-cal we proposed that the station cycle through the RSR sequence per the briefing message, turning on the X-RCP and S-RCP noise diodes before the ambient load interval, and reconfiguring the CLR's to turn on the X-LCP and S-LCP noise diodes after the ambient loads. About 35 minutes of data were recorded. Details are listed below in the Timeline section. Times are approximate, because the noise diodes have to be switched on and off manually, the RSR has to be started and stopped manually, and we were attempting to diagnose the loss of X-RCP at the same time. Tracking: DSS 43 was about 50 minutes late in beginning the track, due primarily to the time required for the pre-cal activities. Station personnel stated that the Y-factor measurements alone required 30 minutes for all four channels. Calibrating both X- and S-band ranging systems appeared to take a comparable amount of time. The spacecraft came up with X-band downlink ON via the high-gain antenna, COH ON (but no uplink). X-band telemetry ON (modulation index 1.25 and symbol rate 209715.2 sps), and (uplink) command rate set to 2000 bps. The RSR operations were conducted using 2-way predicts (whether generated by RSSG or DSN is unknown). The following looked like good settings for tracking. The carrier drifted a total of about 10 kHz over the four hours of 1-way tracking; the values shown for 'offset' would have been good starting and ending values for FRO. 1-Way (TLM OFF) ----------------- UWV RSR Fgain Offset (dB) (kHz) ----- --- ----- -------- X-RCP 1A N/A N/A S-RCP 1B 63 -2 to +2 X-LCP 2A 60 -5 to +5 S-RCP 2B 53 -2 to +2 Post-Cal: In the post-cal the RSR's were started (step 1) with DSS 43 pointed at zenith (cold sky). After about 5 minutes, the X-RCP and S-RCP noise diodes were turned on (step 2). After another 4 minutes the ambient loads were switched in (step 3a), and a minute later the noise diodes were turned off (step 3b). After 5 minutes the ambient loads were taken out, the CLR's were reconfigured for X-LCP and S-LCP, and the LCP noise diodes were turned on (step 4). After 4 minutes the RSR recordings were stopped. There was no effect on X-RCP in any step. There was no effect on S-LCP in step 3 because the ambient load would not connect. There was no effect on X-LCP in step 4, but the reasons for this problem is unknown. During the pre-cal, injection of noise from the diode on X-LCP produced the expected effect. The station confirmed that the diode was on during step 3 and that its value was 12K. The post-cal recordings were 20 minutes each. Playback: The post-cal data were played back at the conclusion of the test. Each file, repesenting 20 minutes of real-time data, required about 17 minutes to play back. Difficiency Reports (DR's): UNK: late AOS UNK: S-LCP Y-factor and ambient load failure C102917: No X-RCP signal reaching RSR from X-RCP feed. Timeline: 06:40 Begin pre-cal 06:55 RSSG connected to voice net 06:55 DSS 43 told to connect S-RCP to HEMT and S-LCP to maser 07:15 DSS 43 reports it can only turn on/off two noise diodes if it has only two closed loop receivers. 07:45 DSS 43 says ranging calibration for S and X band is time consuming, asks whether delay in BOT is acceptable in order to complete noise diode and Y-factor calibrations (answer is yes) 08:05 MEX mission Operations Center agrees to delay in BOT, but sets 09:00 as limit 08:10 RSR X-LCP histogram indicates connection to ambient load as part of Y-factor measurement. 08:17 DSS 43 reports success in getting only three Y-factors; the value for S-LCP is considered "not good". At this time, the antenna is pointed to cold sky. 08:20 Begin RSR recording. The (noise) signal for X-RCP is very weak. 08:25 The noise diodes for X-RCP and S-RCP are on. 08:30 In order to increase the signal level on X-RCP, the station turns on the 50K diode. There is no apparent change in the X-RCP RSR level. 08:30 DSS 43 notes that obtaining Y-factors does not require receivers; the procedure involves a maintenance tool and future briefing message can be improved by making this change in wording. DSS 43 also notes that 30 minutes was required to complete the Y-factor procedure for all four channels (except that X-LCP was unsuccessful). 08:38 Noise diodes off 08:40 X-LCP is on ambient load 08:41 S-RCP is on ambient load 08:42 RSSG reports no sign that S-LCP has been connected to an ambient load. DSS 43 replies that this is part of their Y-factor problem. 08:45 All ambient loads out (after several false starts). 08:50 Closed loop receivers reconfigured for X-LCP and S-LCP; 12K noise diodes enabled on both. 08:55 DSS 43 going to point 08:58 Telemetry in lock 09:00 Shift change at DSS 43 09:00 X-LCP carrier at -2500 Hz with 1-way predicts 09:18 RSRs recording at 2 ksps 09:50 Stop RSR recordings 09:52 Restart RSR recordings at 25 ksps Fgain settings: X-RCP 20 S-RCP 63 X-LCP 60 S-LCP 63 09:55 S-band FRO's set to -1490 Hz; X-band FRO's set to -5490 Hz these values put the 1-way carrier in the center of the passband 10:00 X-RCP and S-RCP 12K noise diodes on 10:05 X-RCP and S-RCP 12K noise diodes off 10:08 Closed loop receivers reconfigured for X-LCP and S-LCP. Noise diodes enabled, but station notes that X-LCP diode defaulted to 0.25K. Upon request they reset it to 12K. 10:22 DSS 43 confirms that Closed Loop Receivers were reconfigured to X-RCP and S-RCP and notes that 0.25K diodes have been enabled. On request they turned the 0.25K diodes off. 10:43 Spur (birdie) appears at right (high) side of the X-RCP spectrum. It moves slowly, reaching the center (along with two others) at 10:50. This is not the first spur seen on X-RCP; none have been seen on other channels. 11:00 DSS 43 confirms X-RCP and S-RCP noise diodes on. 11:02 DSS 43 reports Y-factors and physical ambient load temperatures from pre-cal: Channel Y-factor Ambient Load Temperature ------- --------- ------------------------ X-RCP 12.228 dB 16.6C S-RCP 11.297 dB 20.7C X-LCP 12.2 dB 16.7C S-LCP N/A N/A 11:08 DSS 43 confirms X-LCP and S-LCP noise diodes on 11:21 Fgain and FRO changes to values as follows (takes about 3 minutes): 1-Way (TLM OFF) ----------------- UWV RSR Fgain Offset (dB) (kHz) ----- --- ----- -------- X-RCP 1A N/A N/A S-RCP 1B 63 0 X-LCP 2A 50 -1000 S-RCP 2B 53 0 11:50 DSS 43 confirms transmitter drive off 12:00 X-RCP and S-RCP noise diodes on. 12:06 X-LCP and S-LCP noise diodes on. 12:25 A small spur at the low end of the X-LCP spectrum moves slowly toward higher frequencies as the carrier drifts. 12:56 X-band telemetry on; carrier drops 8 dB (Px/No = 43 dB) 12:58 X-band FRO's now 4000 Hz, S-band FRO's 1000 Hz 13:10 In response to a question about calibration of noise diodes, station replies that calibration is a maintenance task and is not done by operations personnel. To obtain the latest calibration results, users should contact the day staff. 13:54 DSS 43 confirms start of uplink sweep. 13:57 All RSR recordings stopped; all FRO's set to 0. 14:02 DSS 43 confirms receivers in 2-way lock 14:04 Restart RSR recordings at 2 ksps; all signals centered (except X-RCP, which remains missing) 14:07 Ranging in lock 14:57 S-band LOS 14:59 End RSR recording on S-RCP and S-LCP 15:03 End recording on X-RCP 15:05 DSS 43 transmitter off in preparation for 3-way with NNO uplink 15:15 X-LCP carrier out of 2 ksps passband, but visible near 8 kHz in 25 kHz bandwidth. 15:30 NNO uplink sweep begins 15:38 X-LCP captured by NNO sweep, exits 25 ksps passband, then returns 15:43 X-LCP FRO set to 7600 Hz; carrier returns to center of 2 kHz band 16:00 End of track (30 minutes ahead of schedule) 16:11 DSS 43 pointing at zenith to cold sky 16:11 Restart RSR recordings at 25 ksps 16:16 X-RCP and S-RCP noise diodes on 16:20 Ambient loads in 16:21 Noise diodes off 16:26 Ambient loads out 16:27 Closed loop receivers reconfigured for X-LCP and S-LCP; noise diodes on (no effect seen on X-LCP; station confirms noise diode is on and that value is 12K). 16:31 End RSR recordings 16:34 Begin replay of post-cal data (20 minutes per channel). Each file consists of about 5000 blocks and takes about 17 minutes. This is followed by replay of all 2 ksps data. Items Needed and/or Deliverables 1. RSR data from this pass (can be obtained by query from rsops2) 2. NMC logs 3. 0158-MON data, if available 4. TNF data 5. ODF, Media Calibration, and Meteorology data Conclusions Support was excellent, especially from DSS 43 personnel. Briefing message needs to include polarization assignments Briefing message should refer to Y-factor procedure and equipment rather than to 'receivers'. Need to correct problems with S-LCP Y-factor measurement Need to check noise diode switch for X-LCP noise diode Need to repair broken X-RCP link between feed and RSR Need to reserve four Closed Loop Receivers for bistatic radar experiments Radio Science Participants at JPL: Sami Asmar (RSSG) Aseel Anabtawi (RSSG) Gene Goltz (RSSG) Dick Simpson (Stanford) Dick Simpson 20 October 2003