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Fwd: ATTENTION: UHF from the Mars Climate Orbiter in Deep Space



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Subject:    ATTENTION: UHF from the Mars Climate Orbiter in Deep Space!
Author:   "John L. Callas" <John.L.Callas@JPL.NASA.GOV>
Date:       2/11/99 10:13 AM

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

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 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@jpl.nasa.gov
(E-mail)
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