Getting Old Rocket Upper Stages and Satellites Down

Tough choice tonight.  I find myself with two paths in front of me.  One is to go down the path of the color revolution against the US that is apparently in process right now.   Down that path, I really don't know much.  Not enough to write authoritatively.  I've been listening to people talk about it but I'm not where I could write authoritatively about it.  I'd recommend you read that linked article, but that's about it for now.

Or I could go down the path of a novel little story about space technology I ran into from Microwaves & RF magazine's website.  Since that's a decidedly techy story about space, two of my main labels, I'll go that way.

Researchers at Perdue have been working on a way to get dead satellites and rocket upper stages out of orbit.  This is a drag sail, sort of a parachute that will be deployed at the end of life.  Even as high as 400 miles, there's a minuscule amount of atmospheric drag; the drag sail uses it to bleed velocity off the satellite or upper stage, getting it to eventually re-enter the atmosphere, over “months or years.”

“High-value orbits around Earth are getting congested,” said David Spencer, a Purdue adjunct associate professor of aeronautics and astronautics and the mission manager for the Mars Sample Return Campaign at NASA’s Jet Propulsion Laboratory (JPL). “If we don’t get satellites or other launch vehicle components out of orbit, then eventually highly utilized orbits are going to become unusable for other space systems,” he said. “Drag sail technology is designed to launch with a host spacecraft or launch vehicle and deploy at the end of the host vehicle’s mission. The drag provided by the Earth’s atmosphere will accelerate the vehicle’s deorbit.”

Dirt simple concept.  The trick is the drag sail is going to be a tightly packed until it's needed to drag the satellite down, so it needs to survive being packed tightly and work after a long time in the hostile environment we call low earth orbit.  Lots of missions, especially deep space missions to other planets, have requirements like that.  

The drag sail, called “Spinnaker 3,” is named after its 3-m-long booms. It is not the first drag sail to be launched into space, but it is the first to be large enough to deorbit the upper stage of a launch vehicle. The Alpha rocket launch for Firefly Aerospace is being planned for an orbiting altitude of about 200 miles. The Spinnaker3 drag sail is capable of deorbiting rockets and launch vehicles at altitudes of 400 miles or more above the Earth. Spinnaker3 (see the figure) employs 3-m-long carbon fiber booms that pull out a sail with an area of 194 ft.² The sail employs a fluorinated polyimide material called CP-1, produced by the company NeXolve Materials and designed to withstand any deterioration effects of monatomic oxygen in low Earth orbit.

The drag sail self deploying.  Purdue photo. 194 square feet is 13.9 feet on a side, which goes nicely with each of those four “arms” being 3m long.  As usual, more at the Purdue site linked there than the Microwaves & RF excerpt of it. 

The options for getting something down from a densely populated Low Earth Orbit are pretty much something like this or some sort of thrusters.  The idea of getting upper stages down have centered on having enough fuel left over to de-orbit the upper stage.  As the article points out, that's pounds of fuel instead of payload and rocket makers don't like that trade.  A bigger drag sail on something like the upper stages of vehicles that put satellites up higher might have its place, too.  Or a combination of some sort of thruster to bring the satellite down from its service orbit to a lower altitude where the drag sail could bring it down the rest of the way. 

As the article points out, it's getting crowded out there, especially in the “high-value orbits.”  The easy and cheap access to orbit that has been developing for the last decade will only increase that crowding.  It's getting to be past the time to pay attention to reducing the amount of stuff in orbit.