Transmitting from space
By Robert Cravotta, Technical Editor - April 13, 2006
On Feb 3, 2006, the crew of Expedition 12 released the SuitSat-1 into orbit around the Earth. SuitSat-1 is a Russian Orlan space suit that had reached the end of its life, but the cosmonauts added a radio transmitter and sensors to measure temperature and battery power to support one last four- to nine-day mission. Exceeding expectations, for more than two weeks, the space suit captured the attention of the world by acting as a temporary satellite, transmitting recorded messages and telemetry data that students and ham-radio operators could receive. A few weeks after the suit's final mission began, it re-entered Earth's atmosphere and burned up.
ARISS (Amateur Radio on the International Space Station), AMSAT (The Radio Amateur Satellite Corporation), ARRL (American Radio Relay League), the Russian Space Agency, and NASA co-sponsored the SuitSat-1 project. The final confirmed reception of the Suit’s voice audio was on Saturday, Feb. 18. The final confirmed telemetry recorded that the suit’s 28V power source had dropped to 18.3V before the suit stopped transmitting its message. The transmitted message consisted of recorded greetings in English, French, Japanese, Russian, German, and Spanish. The suit transmitted the 30-second message and telemetry at 145.990 MHz FM, and then it paused for 30 seconds, to extend battery life, before repeating the message.
|The front panel for the switch box provides three independent switches to separate the power from the radio (courtesy Microchip).|
Steven Bible was the project leader of the volunteer team at Microchip that designed, assembled, and tested the controller for the SuitSat-1 project. The design and development of the controller spanned three weeks. The controller team did not have the suit or batteries during its effort; the crew on the station performed the final integration, which consisted of mounting the switch box on the helmet and placing the controller on the suit. The assembly consisted of three boxes rather than a single box to make it easier to handle and to provide flexibility for placement in the suit by the flight team. The controller system consisted of three boxes that housed the helmet mounted switch box, the transmitter box, and the controller box (block diagram ).
The flight team integrated the controller box into the suit and connected it to the switch and transmitter boxes using cables. The controller box provided 12V regulated power from 28V of power to the radio. The controller box housed the EMI filter, the dc/dc converter, and the microcontroller, which read the sensors and managed transmission of the messages and telemetry.
The switch box attached to the helmet by a specially made bracket and connected to the controller box by a cable. The switch box employed three independent safeties to prevent an RF hazard to the deployment team: power, timer 1, and timer 2 switches. The power switch was a latch from the 28V power source to the other two switches that provided a two-pull disconnect from the power source to the radio transmitter. The timer 1 and timer 2 switches enabled a ripple counter that would assert 12V of power to the radio after eight minutes had elapsed; this delay would be enough time for the suit to drift far enough from the station to pose no RF hazard.
|The transmitter box contains an off-the-shelf Kenwood amateur radio transceiver (courtesy Microchip).|
The flight team integrated the transmitter box into the suit and connected it to the controller box using a cable. The transmitter box contained an off-the-shelf Kenwood Corp model TH-K2 amateur-radio transceiver with its battery pack removed. The radio mounted on a block of aluminum that acted as a heat sink. The frequency of the radio was 145.99 MHz, and the power output was 500 mW to extend battery life. The radio acted only as a transmitter, with no capability to receive commands.
Three 28V batteries powered the SuitSat-1 controller box. The controller box conditioned and converted the power for the rest of the system components.
|The controller box houses the EMI filter, DC-DC converter, and the microcontroller PCB (courtesy Microchip).
The development team for the controller built and integrated two flight units that were shipped to NASA in Houston, TX, for further shipping to Russia for final testing and certification. The flight antenna is the same used on the ISS Amateur Radio station, already resided in Russia. Because the Orlan space suit and batteries reside on the ISS (International Space Station), the final integration was performed on the space station. An effort for a SuitSat-2 in 2007 is in the planning stages.
Special thanks to Steven Bible, principal applications engineer and project leader of the volunteer team at Microchip, for sharing the technical information about the Spacesuit Satellite project.