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Satellite Made on the Cheap Closing in on 2 Years in Orbit and Still Ticking

07/08/2015

At just a few months shy of turning 2 years old, the $50SAT Amateur Radio “PocketQube” microsatellite — also known as Eagle 2 (MO-76) — is still operating, although it’s not entirely well either. The satellite, which transmits on 437.505 MHz at a power of 100 mW, may be heard using a handheld transceiver, but it does not include a transponder.

Launched in late 2013 from Russia, $50SAT is a collaborative education project of Prof Bob Twiggs, KE6QMD, of Kentucky’s Morehead State University, and three other radio amateurs — Howie DeFelice, AB2S; Michael Kirkhart, KD8QBA, and Stuart Robinson, GW7HPW. Formerly of Stanford University, Twiggs and Jordi Puig-Suari of Cal Poly are the co-inventors of the CubeSat model. $50SAT’s stated purpose was to evaluate if the PocketQube form factor offered a cost-effective means for engineering and science students to use in developing real-world skills. The “$50” is a bit of a misnomer. The tiny satellite actually was constructed from about $250 worth of parts. Kirkhart recently offered an update on $50SAT, which measures just 5 × 5 × 7.5 cm and weights 210 grams.

“The good news is [that] it is still operating. The bad news is the power situation has been degrading, with an apparent step change on or near May 12, 2015, followed by another on June 23, 2015,” he said.

Kirkhart, who lives in Michigan, said his last full telemetry capture was on May 27, and the last time he heard $50SAT was on June 6. “I continued to attempt to listen for it for another week or so, and heard nothing,” he said. $50SAT transmissions repeat about every 75 seconds, starting with an FM slow Morse code call sign beacon, data at 60 WPM Morse, and FSK RTTY data and digital data telemetry.

Since then, Kirkhart has been monitoring the satellite via the WebSDR site of Anton Janovsky, ZR6AIC, as $50SAT makes daytime passes over South Africa — which happens in the early morning hours in Michigan.

“This is tough, as I am not a morning person,” Kirkhart said. “During these passes, where it has already spent a significant amount of time in sunlight, the battery voltage is below 3400 mV.”

Kirkhart said that while it’s possible that the battery has suffered some loss of charge capacity, it’s merely a storage vessel for the solar power system, and he has pondered whether the real problem could be a degradation in solar power generation.

Kirkhart said he noticed in May that current solar power readings were typically less than 10 mA, “much lower than it should be.” He said current flowing in the solar power system and the battery voltage are both “significantly lower this year that during the same period last year.” He speculated that while loss of battery capacity is likely, “it appears the low battery voltage is due to low solar power output.”

He said this could be a result of solar cell damage; since there was no protective covering on the solar cells, the impact of high-energy particles could have damaged the solar cells, resulting in a drop in output. He also said the solar cells could have been damaged through thermal cycling, as the satellite passes in and out of periods of dark and light. A short circuit is another possibility, but, Kirkhart said that, because of the limited amount of telemetry gathered, “it may not be possible to determine the exact cause.”

He said that if the solar output continues to drop, the battery voltage may never get above the 3300 mV threshold needed to enable the transmitter, “at which point we will lose the ability to monitor its status.”

“Even if this does happen,” Kirkhart continued, “we never really thought it would last this long.  We would have been happy if it just worked, and really happy if it lasted a month or two.” — Thanks to AMSAT News Service and Southgate ARC

 



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