Budget satellite drag sail shows space junk how to gracefully exit orbit

A prototype satellite built to test a deployable drag sail to de-orbit satellites appears to have fulfilled its purpose, burning up on re-entry earlier this month after spending just 445 days in orbit.

SBUDNIC, an acronym chosen to be a play on "Sputnik," was put together by students at Brown University, Rhode Island, using low-cost off-the-shelf commercial components. The CubeSat design featured a drag sail made from Kapton polyimide film, and with structural supports of thin aluminum tubing, which deployed once the satellite was in orbit.

The project was intended to demonstrate a potential solution to the problem of low Earth orbit becoming a graveyard for more and more defunct satellites that have reached the end of their life, as The Register detailed previously. If proved successful, the idea is that future satellites could incorporate a similar mechanism to help de-orbit them at the end of their life span.

SBUDNIC was sent up aboard the SpaceX Transporter 5 launch in May last year as part of a payload comprising a number of other small satellites. Its sail "popped open like an umbrella" at a height of about 520 kilometers above the Earth's surface, according to the project team, to create drag and cause its orbit to decay.

The project appears to have been successful in this respect, according to tracking data the team obtained from US Space Command. It indicated that SBUDNIC was about 470 kilometers (292 miles) above the Earth in early March, while other comparably sized satellites deployed to a similar orbit as part of the same mission were still at altitudes of 500 kilometers (310 miles) or more.

The decay of the CubeSat's orbit accelerated as it dropped lower, such that its last known altitude was just 146 kilometers (90 miles) on August 8, shortly after which it is assumed to have been destroyed by burning up in the atmosphere.

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Previous predictions had suggested that the drag device would reduce the orbital lifetime of SBUDNIC from over 20 years to as few as 6.5 years, but in reality it was brought down in about a year and a quarter.

"We were trying to prove that there are ways of de-orbiting space junk after mission life has ended that are not super costly," said Selia Jindal, one of the project leads who graduated from Brown University this year. "This showed that we can do that. We were successfully able to de-orbit our satellite so that it's no longer taking up space in Earth's orbit."

The sail concept is orders of magnitude less costly than rival ideas for tackling orbital junk such as space tow trucks or nets to capture the junk and pull it out of orbit, according to Dheraj Ganjikunta, SBUDNIC's lead program manager who graduated last year.

"Rather than taking junk out of space after it becomes a problem, we have this $30 drag device you can just throw onto satellites and radically reduce how long they're in space," Ganjikunta said.

Of course, this requires future satellites to be designed to have a similar mechanism built in, and so does not help to address existing space junk, but every little presumably helps.

SBUDNIC was a 3U CubeSat, meaning it was effectively the size of three 10cm cubes combined. It was based around a $10 Arduino system plus 65 AA lithium batteries and included a variety of 3D-printed parts produced with consumer-grade printers. ®