Communications Design Review

1. Communications Design Review Morehead State University Morehead, KY Prof. Bob Twiggs RJTwiggs@gmail.com SSE-122

2. Design Review How are you going to transmit data up/down? How often will you be over a single ground station with a LEO orbit? How much time will you have to transmit during passes? Will your link margin allow you to communicate horizon to horizon? What do you do if you get errors in your communication data? How much of the contact time will you need to use for commanding satellite? 2 SSE-122

3. Design Review How are you going to transmit data up/down? How often will you be over a single ground station with a LEO orbit? What do you need to know to determine this? How much time will you have to transmit during passes? Will your link margin allow you to communicate horizon to horizon? What do you do if you get errors in your communication data? 3 SSE-122

4. Design Review How much of the contact time will you need to use for commanding satellite? If you can not get all of the data down with a single ground station and you can not add any more stations, what are your options? How will your down loading data have an impact on the power system? What kind of analysis do you need to do now with the EPS? 4 SSE-122

5. Design Review Will this operational scenario affect the thermal system? Where is the heat coming from? What about the charging and discharging of the battery? 5 SSE-122

6. Design Review Do a Comm System Design 6 SSE-122

7. Design Review Make some assumptions – verify my assumptions and recalculate Orbit: 600 km, circular - 6 passes/day - get ~ 13 minutes view time horiz. to horiz. on zenith pass. - get ~ two passes with 6 minutes, one before and one after zenith. - this pattern will occur twice a day. Link margin: - assume you must take one minute to connect on each pass and one minute to terminate comm at end of each pass. 7 SSE-122

8. Design Review More assumptions – verify my assumptions and recalculate Data volume: - assume you have a 20% overhead required to correct errors. - if you use FEC you must have a 100% overhead. Data conversion: analog - digital Resolution needed: Temperatures, voltages: accuracy 5% Currents: battery: accuracy 10% Currents: solar panel accuracy – 5% Currents: subsystem accuracy – 3% All others: - 10% 8 SSE-122

9. Design Review More assumptions – verify my assumptions and recalculate Discrete bits to monitor: 25 discrete bits for states in satellite bus Duty cycle: You decide as a bus engineer what you need to diagnoses anomalies. 9 SSE-122

10. Design Review Analysis: From data collection, find total data collected each 12 hours. Assume you have 1 watt on satellite with a -3dBi gain antenna. Transmitter line loss is 0.3dB. You are operating at 435MHz. Your ground antenna has a gain of 18dBi. Your ground antenna line has a loss of 1.5 dB You have an average 2 degree pointing error. 10 SSE-122

11. Design Review Continued Analysis: The BER must be 10-5 or better. Can you get all of the data down for the contact time given? If not, what can you change to get data down that is reasonable? Maybe you need to reduce the amount of data collected. Change duty cycle? 11 SSE-122

12. Design Review Continued Analysis: Change sample frequency? Change resolution? Change BER? 12 SSE-122

13. Design Review Got all the information you need here to do this analysis? 13 SSE-122