The older board shown below is relatively large and heavy, especially when used on the balloon. Fortunately, the Internet of Things is driving the cost and mass of radio capable devices down rapidly. Leveraging this technology, the balloon should be able to include a high speed and low mass radio system.
I recently purchased such an IOT device, the ESP32 DevKit C. The specs for this are summarized under the processor tab and will not be repeated here. The goal for the design is to use off the shelf hardware as much as possible. For testing purposes the ESP32 can stand in for a more customized but comparable device that is able to execute communications protocols necessary to communicate with the current or future orbiters. Modifications to the ESP32 board needed to add this function should not dramatically increase the mass or size of the board.
For testing purposes, the DevkitC should allow the use of standard WiFi (TCP/IP) tools for data transfer such as http, ftp, etc. These tools will allow for some testing of the upload of images and other data wirelessly to a base station that is some distance away.
This is an image of the board, compare to the older FPGA based system shown lower:
The radio hardware for the balloon would likely be a descendant of the electra radios used on the current Mars missions. Per NASA, the electra radios are software defined radios (SDR). Electra light is on the Mars Science Laboratory rover. This radio is still far too large, heavy, and power hungry for our balloon however.
A very good bit of work was documented on this website: https://eceproxy.engg.ksu.edu/research/mars/
They say this about the board “The Mars Mictrotransceiver Evaluation Board above includes the fully-integrated 100 mW RFIC transceiver (center), an optional 1-Watt RF power amplifier (left), an FPGA for digital modem functions (right), and voltage regulators (top). Total size of the evaluation board is 9cm x 5.5 cm x 1 cm, and can be reduced to less than half this dimension as required.”
Here is a bit more from their one paper “| A low-volume low-mass low-power ultra-highfrequency radio transceiver for future planetary missions is described. The project targets a volume of less than 10 cm3, mass of less than 50 grams, and power consumption of 50 mW on receive and 100 mW, 300 mW, or 3 W on transmit (for 10 mW, 100 mW, and 1 W output options). The transmitter design supports convolutionally coded binary phase-shift keying (BPSK), RC-BPSK, and quadrature phase-shift keying transmission from 1 to 256 kbps. Command/control instructions can be received at 2 or 8 kbps, with a sensitivity of better than 120 dBm. In addition to its low volume/mass/ power features, temperature compensation to 100 C and radiation tolerance to 100 krad allow operation outside of thermally controlled, shielded enclosures, further reducing the mass and complexity of exploration vehicles. The design is described in a top-down format, beginning with system requirements and proceeding through digital modem algorithm development, discussion of the silicon-on-sapphire CMOS process used and elaboration of key blocks in the radio-frequency (RF) integrated circuit design. Techniques to address coupling between high-sensitivity RF and on-chip digital circuits are also presented, and test results are given for prototypes of all major functions. Although designed for the Martian environment, the transceiver is expected to be useful in other proximity links where a small low-power radio compatible with Prox-1 space-link protocols is desired.”
This work seems to have been done a few years ago. For the balloon, we need a much higher speed connection (256k is the speed that Odyssey uses and would seriously impact our image transmission.) Still this indicates that a modem could be built and gives an idea of how to update the project.
For more information visit the link above or read their paper below: