Can We Use Special Sails To Bring Old Satellites Back Down To Earth?

The growing problem of space debris in LEO (Low-Earth Orbit) is garnering more and more attention. With thousands of satellites in orbit, and thousands more on the way, our appetite for satellites seems boundless. But every satellite has a shelf-life. What do we do with them when they’ve outlived their usefulness and devolve into simple, troublesome space debris?

In the next five years alone, it’s expected that we will launch up to 2600 more nanosatellites and cubesats. There are already almost 5,000 satellites orbiting Earth, and many of them are non-functioning space debris now, clogging up orbital paths for newer satellites. In fact, according to the United Nations Office for Outer Space Affairs (UNOOSA), we launched a total of 382 objects into space in 2018 alone, an unsustainable number.

There’s no shortage of potential solutions to this problem. Some exotic-sounding solutions involve harpoons, nets, magnets, even lasers. Now NASA has Purdue University-related startup Vestigo Aerospace money for a six month study that looks at using drag sails to de-orbit space junk, including satellites, spent rocket boosters, and other debris, safely.

Artist’s impression of a laser removing orbital debris, based on NASA pictures. Credit: Fulvio314/NASA/Wikipedia Commons

Vestigo Aerospace was started by David Spencer, an associate professor in Purdue’s College of Engineering. “Through the six-month study, we will advance drag sail technology for the deorbit of small satellites and launch vehicle stages,” Spencer said in a press release. “The safe disposal of space objects upon mission completion is necessary to preserve the utility of high-value orbits.”

Drag sails are a bit different than other methods. While the harpoons, lasers, and nets proposed by various agencies are meant to deal with the space junk that’s already accumulated, drag sails are designed to be built into a satellite and deployed at the end of their useful life.

Drag sails can be used to de-orbit old satellites. Image Credit: Purdue University/David Spencer

“Vestigo Aerospace is developing a product line of drag sails to address the need for deorbit capability as an alternative to conventional propulsion systems,” said Spencer, who worked for 17 years at the Jet Propulsion Laboratory before joining the Purdue faculty. “The team will also investigate the use of drag sails for targeted reentry of space objects, to reduce the uncertainty in atmospheric reentry corridors and debris impact zones.”

The sails would be deployed at the end of a satellite’s life. Once deployed, they would reduce an object’s velocity and then help it deorbit safely. Currently, satellites deorbit more or less on their own terms, and it’s difficult to calculate where they may strike Earth, if they’re too large to burn up on re-entry.

A key design feature of Vestigo Aerospace’s system is scalability. In an email exchange with Universe Today, David Spencer said, “… we are designing the system to be scalable, so that it can be used to deorbit host satellites ranging from 1 kg CubeSats to 450 kg smallsats, or 1,000 kg launch vehicle upper stages.”

Their system also provides what’s called “passive aerodynamic stability.” According to Spencer, “This allows the system to naturally trim to the maximum drag orientation.”  

Vestigo Aerospace aren’t the first to investigate and develop drag sails. The CanX-7 (Canadian Advanced Nanospace eXperiment-7) was a 2017 demonstration mission that looked at deorbiting nanosatellites with drag sails. It was primarily aimed at Cubesats, where it would be attached to the exterior so as not to interfere with electronics.

CanX-7 with Drag Sails Deployed in SFL Clean Room. Image Credit: Space Flight Laboratory.

CanX-7 used four sails to deorbit its 3.5 kg (7.7 pounds) of mass. In only one week after deployment, it succeeded in changing its orbital rate of decay significantly. Eventually, it stabilized itself with all four sails to the rear of the satellite, which increased orbital decay even more.

 CanX-7’s early deorbiting progress. In blue, CanX-7’s altitude, covering the period immediately before drag sail deployment and one week after. In red, the BSTAR component of the two-line elements from NORAD showing increased drag on the satellite. Image Credit: Space Flight Laboratory.

Guidelines have been in place since 2007, stating that the orbital life of a nanosatellite should not exceed 25 years. Those guidelines come from the IADC (Inter-Agency Space Debris Coordination Committee). While it could be up to the more exotic methods to deal with accumulated debris in orbit, drag sails offer an affordable, and potentially easy-to-develop method to ensure future satellites don’t outlive their usefulness.

Sources:

Evan Gough

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