EE Times Under the Hood - June 23, 2008 - (Page U9)

UTH0623pg4-10.qxd 6/13/08 5:46 PM Page 9 www.eetimes.com • www.techonline.com From bottom left to bottom right: main controller board; Kenwood amateur radio transmitter atop heat sink to maximize black-body radiation; full kit, before shipping to Russia; Orlan spacesuit before launch, showing antenna on very top and switch controller box on helmet; flight engineer and cosmonaut Valeri Tokarev loads up the suit prior to launch. Controller and radio are in the green pouch; the green blocks are the high-capacity, silveroxide batteries. teries, which would be in an unknown state of charge, the team made sure the transmission was easy to listen to and did not require an excess amount of energy. The result was a 30-seconds-off, 30-second-broadcast mission profile. The electronics were assembled at Microchip in June 2005, sent to Russia and transported to the International Space Station on the Progress 19 cargo ship that September. The suit was launched from the space station on Feb. 3, 2006. Lessons learned SuitSat-1 was a clear success, providing two weeks of transmissions before the batteries finally gave out. The suit itself finally burned up in the atmosphere after six months. However, there were a few snafus along the way. “In the postmortem, the transmit signal was not as strong as desired,” said Bible, referring to a signal 20 dB lower than expected. There were a number of theories for this, including transmitter failure, but Bible went over the schematics and could find no point of failure that would cause a reduction in output power. The coax was a possible culprit, but Bible and his team saw the antenna as the more likely problem, combined with the tumbling of the suit. “The antenna was a hand-me-down,” he said. “It wasn’t designed to be used in a helmet, and it went up without a lot of testing.” For SuitSat-2, he said, the antenna will be selfcontained and will likely have a ground plane behind it. That won’t be the only improvement. Seeing that the original suit lasted six months in orbit, the team decided to develop a solar panel power source to extend the operating life of SuitSat-2 to possibly two months. But how do you design a converter that is efficient all the time it’s out there, given that there is no control over the orientation of the suit and its panels? That task fell to John Tray, principal applications engineer at Microchip. Tray came up with a six-panel design in which one panel will always be in full light, while two or three will be in partial light. However, with a 90-minute orbit giving 45 minutes of light and 45 minutes of darkness, Bible said, Tray incorporated a power scheme that “can run the whole system off the panels and recharge the batteries at the same time.” The converter analyzes how much power is coming out of the solar panel, “and it actually maximizes it for a peak detect on power,” Tray said. “A solar panel looks like a constant current source, and often you’ll hook it up to a battery directly and charge it at a constant current, but that’s not taking advantage of the power coming out of the solar panel.” The resultant dc/dc Max Power Point Converter will take the maximum operating point of the solar panel and continually run at that point, even though the conditions change. “It’ll be charging the battery at its maximum rate possible,” Tray said. Power storage is via a supercapacitor. “There’s not a lot of info about this stuff out there,” said Tray, “so we wrote an app on how to do it simply, for extremely low cost.” It will be posted on the company’s site, he said. “Anyone who’s looking at having extended applications run off of solar power in a remote area, where you don’t want to service it, that converter will run excellently.” Other power innovations include two-way communica- extraction, they mounted hot spots, such as the Kenwood radio transmitter, on a large aluminum block that was itself attached to the enclosure. Also, thermal extremes had to be avoided. As it orbited, the suit would be exposed to heat and cold alternately for 45 minutes each. While the suit was designed to keep an active cosmonaut cool, the team had no information on the environment without a human inside. The suit was not going to be actively cooled. As the electronics were placed inside, the engineers banked on it being an insulator against extreme cold and heat. They used a temperature sensor and spoken telemetry to monitor the variations. It stayed at 12°C for the entire mission. While the electronics went inside, the switch box and antenna were bolted externally to the helmet, with the cables running inside, taking care to reduce snagging potential. To maximize life expectancy from the used bat- June 23, 2008 | Electronic Engineering Times, TechOnline 9 http://www.techonline.com http://www.eetimes.com

Table of Contents Feed for the Digital Edition of Under the Hood - June 23, 2008

Under the Hood - June 23, 2008 Extreme Design: SuitSat Pushes Desigers' Limits Evolution of the Smart Phone Mature Devices get Rolly Rocking GPS: Garmin Nuvi 750 vs. HP iPaq 310 Inside the Sony OLED TV Multizone Dgital Audio Flip Ultra Camcorder - An Ode to Clean Design Robot Guitar Tunes Itself E-book is a Sight for Sore Eyes Scientific Calculator Boils Down to Two ICs $100 BOM Eludes First OLPC Laptop 45 nm: What Intel Didn't Tell You Next Step in NAND Flash Evolution Surveillance on a Shoestring Hot 3G Phone Owes Debt to Analog SecurID Fob: Single-Chip Safety Net

Under the Hood - June 23, 2008

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