Date: Thu, 11 Feb 1999 10:13:04 -0800 From: John L. CALLAS To: MARS-NET@VM.STLAWU.EDU Subject: ATTENTION: UHF from the Mars Climate Orbiter in Deep Space! ATTENTION ATTENTION ATTENTION ATTENTION ATTENTION Dear Radio Amateurs, I know this is short notice. We are planning on performing a deep space test of the UHF system on the Mars Climate Orbiter (MCO) next week. As many of you know, NASA will be using UHF (~400 MHz) extensively for relay communications at Mars between orbiting spacecraft, and landers, rovers and microprobes on the surface of Mars. In preparation, we are scheduling to test the UHF relay system on MCO using the 46-meter antenna at Stanford University. Some of you may remember we did this with MGS. The difference (for you amateurs) this time is the test is much shorter in duration and the signals are much weaker. The MCO spacecraft will be approximately 16 million kilometers away! Here are some details on the test. The UHF system on MCO will be transmitting at approximately 437.101 MHz with right circular polarization. We do not know the exact frequency of the transmission due to the unknown temperature of the transmitter at power on. The signal is frequency shift keyed (FSK) modulated with a modulation index of 2. The modulated bit rate is 8003 bits/s. This means expect two sync functions at +/- 8003 Hz from the center frequency. There is no carrier in this signal. The UHF system will "ping" every 3 seconds. This means for about 166 ms every 3 seconds there will be a modulated signal. The rest of the time there will be nothing. Approximately 1328 bits of data are expect within each ping. The data are actually a fixed pattern of mostly alternating ones and zeros. The transmit power will be around 16 watts but with an EIRP of about 29 dBm. This small number is due to the obstruction from the high-gain X-band antenna blocking the UHF antenna's view of Earth. This number is only a rough estimate and could be much worse. The first test opportunity will begin at approximately 0700 UTC on 1999-02-16 and extending until approximately 1100 UTC. The spacecraft distance at the start of the test is approximately 15,696,800 km. The approximate start and end times depend on the actual spacecraft commanding that will be done in realtime. So the total test time for the first day will be less than 4 hours. If Stanford is unsuccessful on the first day in detecting the signal, a second test may be performed the following day beginning approximately 0700 UTC on 1999-02-17 and extending until approximately 1050 UTC. The spacecraft distance at the start of the second day's test is approximately 15,830,800 km. Here is the latest prediction for the position of MCO during the two opportunities for the UHF Ping Test next week. The data are calculated for geocentric coordinates. The Doppler offset, referenced to geocentric coordinates, is calculated from an assumed frequency of 437101000 Hz. Date Time Range Dec RA Rate Doppler Offset [UTC] [UTC] [km] [deg] [deg] [km/s] [Hz] 990216 070000 1.57E+07 12.39 221.64 1.5639 -2280.2 990216 080000 1.57E+07 12.39 221.63 1.5628 -2278.5 990216 090000 1.57E+07 12.39 221.62 1.5616 -2276.9 990216 100000 1.57E+07 12.39 221.62 1.5605 -2275.2 990216 110000 1.57E+07 12.39 221.61 1.5593 -2273.5 990217 070000 1.58E+07 12.41 221.49 1.5376 -2241.9 990217 080000 1.58E+07 12.41 221.48 1.5366 -2240.3 990217 090000 1.58E+07 12.41 221.48 1.5355 -2238.8 990217 100000 1.58E+07 12.41 221.47 1.5345 -2237.3 990217 110000 1.59E+07 12.41 221.46 1.5335 -2235.8 To assist you in determining the possibility for detection, I have included the link analysis for Stanford: Spacecraft MCO Frequency [Hz] 437101000.0 Wavelength [m] 0.686 Transmit Power [dBm] 42.0 Antenna Gain [dBi] -12.0 Circuit Losses [dB] -1.0 Earth-Spacecraft Range [m] 1.58E+10 Space Losses [dB] -229.2 Receiving Station Stanford Antenna Diameter [m] 45.7 Antenna System Efficiency 0.50 Antenna Gain [dBi] 43.4 Antenna Effective Area [m2] 820.9 Half Power Beam Width [?] 1.2 Polarization Loss [dB] -2.4 Misc Loss [dB] -0.35 Receiving Signal [dBm] -159.6 System Temperature [K] 85 Noise Spectral Density [dBm/Hz] -179.3 Search Bandwidth [Hz] 8003.0 Instantaneous SNR [dB] -19.3 Effective SNR [dB] after 1 ping -3.7 Effective SNR [dB] after 1 min 2.8 Effective SNR [dB] after 4 min 5.8 Effective SNR [dB] after 15 min 8.7 Effective SNR [dB] after 1 hour 11.7 Effective SNR [dB] after 4 hrs 14.7 Unfortunately because of the low signal levels, only the largest amateur antenna operators will have a chance of detecting the signal. In order to have any chance of detection, you will need to integrate for several minutes if not hours. And because of the limited test duration, only those amateurs in the Western Hemisphere will be able to attempt a detection. In any case, we welcome all radio amateurs to listen for the signal. Additionally, we would like to ask all those amateurs in the San Francisco Bay Area to refrain from transmitting near 437.1 MHz during the times of the two test days. RFI is our biggest headache when we attempt these weak signal detections. Your assistance would be greatly appreciated. Please feel free to forward this information on to any other radio amateurs. I will post any updates to this information on the Mars-Net list service. And, of course, I would like to know of any attempts (and successes) of detecting the UHF signal from MCO. I hope you will join us in this adventure of Deep Space Exploration! Sincerely, John Callas ------------------------------------------------------------------------------- John L. Callas Jet Propulsion Laboratory Mail Stop 169-327 1-818-354-9088 (Office) 4800 Oak Grove Drive 1-818-354-1004 (Fax) Pasadena, California 91109 John L. Callas (E-mail) -------------------------------------------------------------------------------