';

Mission Statement

The mission of Main Flight Communications system is to complete the link from the satellite to the ground station. The communications system must transmit telemetry and data from the satellite to the ground station in support of the experiments onboard the MidSTAR satellite.

The Main Flight communications system is intended to be a space-rated, reliable communications system that will allow the satellite to receive commands from the ground station as well as transmit telemetry and data. The MidSTAR communications system is designed to support the MidSTAR line of spacecraft as a general purpose communications system capable supporting a variety of space missions by accommodating a wide variety of experiments and instruments onboard the MidSTAR spacecraft.

Mission Requirements

The Main Flight Communications system onboard the MidSTAR-1 spacecraft must be able to complete the link between MidSTAR-1 and the satellite ground station with sufficient margin as determined by the link budget.

  1. Link margin must be 10.07 dB on the uplink and 10.70 dB on the downlink.
  2. Must have uplink frequency of 1.767 GHz and downlink frequency of 2.20226 GHz.
  3. The bit error rate must be better than 2 x 10-5 to support CFTP.
  4. Data rate must be 64 kbps on the uplink and 100 kbps on the downlink.
  5. The communications system will operate in a GMSK modulation scheme.
  6. Link between satellite and ground station must be completed independent of spacecraft orientation.

The link budget calculations can be found here. Requirements 2,4, 5 and 6 are based on design decisions made at the concept level and passed on to the communications team as requirements.  The communications system must support the the CFTP specifications of bit error rate and the data rate. These specifications imply a bandwidth wide enough to transmit data from the CFTP experiment onboard the satellite to the ground station.

Reliability for the communications system can be accomplished in one of three ways: using parts that have heritage, using parts that are space-rated, or using parts that are both. The SpaceQuest components to be used for the communications system are space-rated components that should provide the reliability desired by STP. The communications system will achieve ground station contact independent of spacecraft orientation by having multiple antennas on opposing ends of the spacecraft. For a schematic of the antenna locations see the Antenna Placement Diagram.

MidSTAR has 200 MB of storage onboard. However, the experiments are only expected to use 2 MB of this memory daily. In order to transmit this data during the 44 minutes of overhead time per day, the data rate must allow all 2 MB to be sent. At 100 kbps, 33 MB of data can be sent in 44 minutes. At 64 kbps, 21.12 MB of data can be sent in 44 minutes.