Dragracer to demonstrate the value of tethers for satellite deorbit
A pair of nearly identical cubesats built by Millennium Space Systems could help answer a nagging question. Can deployment of a lengthy tether speed a satellite’s reentry into Earth’s atmosphere? And if so, how does it change the reentry timeline?
Millennium, working with partners TriSept Corp., Tethers Unlimited Inc. (TUI) and Rocket Lab, developed the Dragracer mission to find out. Millennium built two six-unit cubesats called Augury and Alchemy. Alchemy is equipped with a 70-meter TUI’s aluminized Kapton Terminator Tape.
“Aside from the tether, the cubesats have identical stowed mass properties,” said Patrick Kelly, Millennium Dragracer program manager.
TriSept integrated the cubesats in a deployer built by Tyvak Nano-Satellite Systems and booked the Nov. 15 launch from Mahia, New Zealand on a Rocket Lab Electron.
If all goes as planned, Alchemy will unfurl its Terminator Tape about 36 minutes after orbital insertion. Millennium engineers will closely monitor satellite telemetry and compare flight data with predictive deorbit models.
“We’re estimating that the tether unit, Alchemy, will reenter in about 45 days or so,” Kelly said in a Nov. 12 interview. “Whereas Augury, the untethered unit, will remain on orbit for about five to seven years.”
Millennium executives see two important benefits. If the company can prove scientifically that tethers are a valid alternative to onboard propulsion for deorbiting satellites, the technology would benefit customers.
In addition, the density of objects in low Earth orbit is increasing, due in part to the launch of constellations of thousands of satellites. If tethers work as advertised, they could help mitigate the threat posed by orbital debris by moving satellites out of orbit soon after they complete their missions, said Mike Scardera, vice president of advanced concepts at Millennium, a Boeing company.
U.S. government guidelines generally require satellites to move out of orbit 25 years after they complete their missions, although the Federal Communications Commission recently considered rules to tighten that deadline.
Some small satellites in 800- to 1,000-kilometer orbits could perform missions that last six months to two years but then spend a decade or more moving toward atmospheric reentry.
“Having the capability to activate a system like this at the end of mission pulls that reentry timeline down, doesn’t further contribute to the orbital debris problem and gives you the ability to do very capable small satellite missions at those higher orbits that can meet all the regulatory requirements,” said Jason Armstrong, TriSept Launch Integration Services director.
Millennium is encouraging space enthusiasts to help document the descent of the Dragracer satellites, which have LEDs to make them easier to view at night. Alchemy also has a 70-meter reflective tether.
“That should light up the sky if it hits the sun just right,” Kelly said.
Dragracer is not the first satellite to unfurl an electrodynamic tether but it is likely to help settle the debate on their efficacy.
Prox-1, a 71-kilogram technology demonstration cubesat launched in June 2019 on a SpaceX Falcon Heavy rocket, also was equipped with a 70-meter Terminator Tape that deployed 90 days into the mission. Prox-1’s descent sped up at that point, but its altitude is only decreasing by about 1.2 kilometers per year.
“If it stayed that way, that wouldn’t be enough to bring it down within 25 years,” TUI CEO Rob Hoyt said by email. “The important thing to note, however, is that we are currently just past solar minimum. The decay rate of the Terminator Tape is strongly dependent upon the solar conditions, because it relies upon passive interactions with the neutral particles in the upper atmosphere and the ionospheric plasma to generate drag.”
As solar activity increases in the next few years, Hoyt expects Prox-1’s deorbit rate to “accelerate substantially,” bringing the satellite into Earth’s atmosphere within about 10 years.
This article originally appeared in the Nov. 16, 2020 issue of SpaceNews magazine.