Electronic Design

Latest Amateur-Radio Satellite Is No Empty Suit

We've all heard references to clueless executives as "empty suits." But the old Russian Orlon spacesuit that crew members tossed out of the International Space Station (ISS) and into freefloating Earth orbit on February 3 was anything but empty. Rather, the event marked the deployment of SuitSat-1, an unusual experiment that has thrilled amateur-radio operators worldwide (Fig. 1).

SuitSat carried an integrated amateur-radio station that transmitted an FM signal on 145.990 MHz. Transmission contents included voice messages recorded by school children from around the world in six languages, a single slow-scan television image, and spoken-English telemetry. The point of the experiment was to give students, teachers, Scouts, amateurradio operators, and the general public an opportunity to track the satellite and participate in this historic event.

The Radio Amateur Satellite Corp. (AMSAT) and the American Radio Relay League (ARRL) sponsored the SuitSat. Lou McFadin, W5DID, and Stan Wood, WA4NFY, led the hardware design team. The station's radio box contained an off-the-shelf Kenwood TH-K2 transceiver. A controller box contained an electromagnetic-interference (EMI) filter, a dc-dc converter to drop the 28-V battery voltage to 12 V, and a controller pc board.

The latter, designed by Steve Bible, N7HPR, contained a Microchip Technology PIC18F8722 MCU, MCP9800 temperature sensor, and MCP6022 op amps (Fig. 2). The MCU was key to assembly of the voice telemetry messages from phrases stored in 8 Mbytes of on-board serial flash memory. A helmet-mounted switch box and 2-m vertical antenna completed the system.

Cosmonaut Valery Tokarev carried out the final assembly of the suit on board the ISS. He and ISS Expedition 12 Commander Bill McArthur, KC5ACR, stuffed some laundry into the Orlon suit to help it hold its shape. Tokarev then released the suit into space.

Station power was drawn from three 28-V cells built into the suit. The system was expected to have a life of about a week. However, amateur stations were still copying SuitSat transmissions more than 13 days after deployment. But although the TH-K2 was set to transmit at 500 mW, actual power output seemed to be less. According to McFadin, this may be due to a less than optimal antenna.

"The antenna is one that was left over from use as a training model for the ISS ham antenna used on the ISS Service module," says McFadin. "In its intended configuration, there's a metal plate on which the antenna is mounted. This plate serves as the ground plane for a 1/4-wave whip antenna. In this application, there is essentially no ground plane. Thus, the VSWR is probably high. This could account for the low signal level."

So, reception of SuitSat signals required high-gain VHF antennas and mast-mounted preamps. It had been hoped that listeners could hear SuitSat's transmissions with handheld 2-m amateur transceivers and general-coverage VHF scanners, but this was not to be. Nonetheless, SuitSat-1 received an official designation by AMSAT as OSCAR 54 (AO-54).

The moral of the story, says McFadin, is that end-to-end testing should always be a priority. "This project was put together in such a hurry that it wasn't possible," says McFadin. Future SuitSat missions are a distinct possibility. To hear samples of SuitSat transmissions, visit www.aj3u.com/blog/.

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