Mission Statement of ICSat

The mission of the ICSat Communications system is to test the feasibility of transmitting and receiving telemetry, data, and commands via TCP/IP as well as complete the link between MidSTAR-1 and the satellite ground station with sufficient margin as determined by the link budget.

The ICSat Communications system is designed to be constructed from off-the-shelf components that will allow the satellite to receive commands from the ground station as well as transmit telemetry data. The integration of the other experiments with the communications system must occur within the constraints of the components of the communications system.

Mission Requirements

The ICSat 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. The communications system must operate within the bandwidth, temperature range, and bit error rate determined by the operating parameters of the ComBlock components and design decisions made early in the project.

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.
4. Data rate must be 1 Mbps on the uplink and downlink.
5. The communications system will operate in a BPSK modulation scheme.
6. Link between satellite and ground station must be completed independent of spacecraft orientation.

The link budget calculations can be found in the ICSat Link Budget document on the MidSTAR Document Archive page. Requirements 2, 3, 4, and 5 are based on design decisions made at the concept level and passed on to the communications team as requirements. Requirement 6 is derived from a design decision at the concept level to have no attitude control on the spacecraft.

MidSTAR has 200 MB of memory onboard. However, the anticipated data collection for experiments is expected to be only 2 MB per day of experimentation. Given the very high data rate of ICSat, there are no anticipated difficulties in transmitting several days’ data in a single transmission. However, the current plan still calls for daily transmissions of experimental data to increase the frequency of data collection at the ground station and minimize the risk of losing data in the event of an anomaly.

The ComBlock receiver must operate at 1.767 GHz in satisfaction of requirement 2.

The ComBlock transmitter must operate at 2.20226 GHz, also in satisfaction of requirement 2. The ComBlock modulator and demodulator satisfy requirement 5, which states that the communications system must operate with BPSK modulation.