2017-11-24 07:04:55


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Mars Orbiter Mission

Page: Sats.MarsOrbiter - Last Modified : Fri, 28 Nov 14
S-band downlink parameters
  
Frequency:2293 MHz
Modulation:PM + BPSK 2000Bd on 64000Hz subcarrier
Frame:3640bits = 64bit sync (CCSDS 1/2 Turbo 0x034776C7272895B0) + 3576 coded bits (Turbo codeword, scrambled)
 Turbo coding according to CCSDS (taps G0=10011 G1=11011, G1 punctured for 1/2)
 CRC-16 at the end of frame for error checking
Data frame:223 bytes, CCSDS v1, S/C ID 0x29A (matches SANA registry), VC2
  
  

S-band downlink spectrum screenshots (click for full size image):

 

Signals as appeared when dish was moved to correct position
    
Nice signal with clear sidebands
 
 

Signal when it reappeared
    
Unlock of Madrid ground station
 
 

Decoded CCSDS frames structure (click image for full resolution)

Comments:

  1. Orbiter was 262,570,622km away. Not bad signal for that range on S-band, but then receiving on 10m dish helps a bit.
  2. First two screenshots are taken just before it flew behind the Mars. Signal was noticeably stronger before and weaker when it appeared again, about hour later.
  3. When signal reappeared, Madrid ground station transmitted to MOM, swept the downlink and locked it to uplink signal. On last screenshot, unlock can be seen with typical frequency shift. Sideband signal level increased little bit when uplink was locked and decreased again on unlock.
  4. Signal looked weak, but thanks to the Turbo coding, it took just 1-2 iterations to get perfect copy! So 10m dish is more than enough for correct demodulation and decoding of MOM telemetry.

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