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CubeSat Status 5/2/03

CubeSat Status 5/2/03. Review Previous State Modifications Current Status & Issues. Review of requirements. Hardware Budget = 80g GPS mass closer to 65g Power Consumption Operation = 270mA (board) + 6mA (antenna) Memory = 24uA up to 320uA Software:

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CubeSat Status 5/2/03

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  1. CubeSat Status 5/2/03 Review Previous State Modifications Current Status & Issues

  2. Review of requirements • Hardware Budget = 80g • GPS mass closer to 65g • Power Consumption • Operation = 270mA (board) + 6mA (antenna) • Memory = 24uA up to 320uA • Software: • Cold Start < 10 mins; Warm start < 3 mins • Accept Propagator input • Sample SNR at 50Hz • Produce a data product output (nav soln and snr data)

  3. New Modifications • Old SNR compression scheme. Example SNR=1687 1. 1687/100 = 16 2. 16+100 = 116 (char)  t 3. 1687%100 = 87 4. 87+100 = 187 (char)  ╗ 1687 normally requires 4 ascii codes, where each code is 8-bit. This scheme minimizes it down to 2 ascii codes, or 16-bits.

  4. New Modifications • New SNR compression scheme Motivation: Since memory onboard is limited, we want data storage to be as efficient as possible without loss of accuracy. Try to compress SNR to a single char (8-bits). What if we could round off the SNR values to the nearest multiple of 12? Why 12? SNR values range from 500 – 3000  2501 numbers Ascii codes 32 and below MUST be reserved, leaving us codes 33 – 255  223 codes. 2501 #’s / 223 codes  11.21 #’s / code

  5. New Modifications diff=10; k=-1; while(abs(diff)>=6 && (500+12*k)<(SNRtemp+15)) { k+=1; diff=SNRtemp-(500+(12*k)); } if(k==-1) k=0; sprintf(buff,"%c",(char)(33+k));

  6. New Modifications • Example: SNR = 1836 500+12*110 = 1820 500+12*111 = 1832 500+12*112 = 1844 print ascii code 33+111 = 144  É

  7. New Modifications • Old Compression Scheme for Nav Soln Since satellite altitude is ~400 – 600km, we will allow the ECEF coordinates to be 8 digits long (including one decimal place) ex: ECEF x = 321526.1 m 1. Multiply coordinate by 10  3215261 2. Parse into groups of two, starting from the right 03 21 52 61 3. Add 100 to each group, and transmit as a ascii char Uses 32-bits total, versus the original 64-bits

  8. New Modifications • Scheme is confusing. • Loss of some accuracy. • Solution Proposed • C&DH rather receive the raw format of the navigation solution. • This will ease data reading when updating the propagator • C&DH will deal with compressing the navigation solution

  9. Current status & issues • We have successfully burned and tested chips in the prototype board. • Prototype is able to obtain navigation solution and track satellites • Communication between computer and board successful • Tests with GPS and C&DH boards • C&DH is able to receive and decode GPS output • GPS board unable to recognize C&DH inputs • Suspect incorrect protocol formats from C&DH

  10. Current Status & Issues • Comm. Board is not operational. • Board layout was re-done. • New layout caused connectors to interfere with GPS antenna connector • Solution: Reorient GPS board in the satellite • Ground Station Testing • Currently, no commands sent up to GPS board

  11. Current Status & Issues • ADCS – Tape Measure issues • Switched to thicker width tapes • Required changing positions – solar cell issue • Solution: They devised a flap that would flip up with an extra solar cell • Moved GPS antenna to the corner on the top wall panel

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