Goals for the EQUiSat Communications System
- Downlink satellite health data and sensor data to ground stations in order to determine the attitude and track the location
- Provide a means of disabling the system from a ground station via uplink
What is EQUiSat’s Communication System
EQUiSat will include an antenna that will deploy after launch and a small BeeLine radio transmitter that can communicate both with simple HAM radios and more complex ground stations. Registered ground stations, including the primary ground station for EQUiSat at Brown University, will have a special shutdown code, which can switch off the communications system when necessary, as required by the International Amateur Radio Union (IARU).
EQUiSat will include an XDL Micro Transceiver from Pacific Crest Communications because it is well-documented and tested for thermal and vibrational standards.
- External Power Required: Regulated 3.6 VDC +/- 10%
- Power Required during RX:0.45 W nominal @ 3.6 VDC
- Power Required during TX:2.9 W @ 0.5 RF Output
- Dimensions: 69 mm L x 46.6 mm x 11.2 mm H
- Weight: 40 g
- Operating Temperature: -40ºC – +65ºC
- Shock and Vibration: MIL-STD-810 F
- Modulation/Link Rate: GMSK 4800 bps
- Frequency Band: 403-773 MHz
- Frequency Control: Synthesized 12.5 kHz tuning resolution
- Sensitivity: -110 dBm BER 10-5
We will use a low bi-rate (4800 bps) with built-in forward error correction.
The radio will transmit and receive signals in the 435-438 MHz band. The transmission will include EQUiSat’s registered call sign as well as data automatically generated by the microprocessor to give updated reports of battery, solar panel, and LED health, as well as sensor data that will help determine the attitude. The micro controller will be able to adjust the quantity and length of transmissions, preventing the radio from draining the batteries to unsafe levels. Additionally, a duty cycle of less than 5% will be imposed in order to minimize the amount of power required to operate the radio. The transmissions will be frequent enough to ensure reception of full messages via ground stations during any 2-minute pass, even at low angles to the horizon.
When in receiver mode, the transceiver will listen for a shutdown code, as required by the IARU. This code will be available only to our registered ground stations.
Because the antenna’s two poles (13 cm) must be longer than the side of EQUiSat (10 cm), the antenna will be launched coiled on the top of the satellite and tied down with nylon fishing line. The fishing line is intersected by a thin piece of nichrome heating element that is heated electronically once in space to melt the nylon and deploy the antenna. The antenna is made from highly elastic nickel-titanium, so it easily springs into position when released, much like measuring tape.
The primary ground station for EQUiSat will consist of a receiving antenna and recorder device located at Brown University. This ground station is in development and will be able to continuously monitor EQUiSat’s transmissions when it is in range.
EQUiSat is designed so that HAM radio operators will also be able to receive signals. Any HAM radio receiver will be able to receive transmission if it is tuned correctly. This will be tested using the Arrowhead Arrow II Antenna connected to the FUNCube Dongle. This combination has been successfully used by ITUPSat, which is currently flying the same BeeLine radio transmitter that EQUiSat will use.