Space

Propellantless propulsion system could keep satellites in orbit, reduce space junk

Propellantless propulsion syst...
This system could be useful for satellites orbiting the Earth such as the Sentinel-1
This system could be useful for satellites orbiting the Earth such as the Sentinel-1
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This system could be useful for satellites orbiting the Earth such as the Sentinel-1
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This system could be useful for satellites orbiting the Earth such as the Sentinel-1

One of the main factors limiting the life of satellites is how much propellant they can carry to execute orbital corrections. Now scientists in Spain have come up with a propellantless propulsion system that also doubles as an electric generator. Using the Earth's magnetic field interacting with a 2-km long aluminum tether, the system could be used to dispose of space debris and boost the orbit of the International Space Station (ISS).

The recipient of two Spanish patents, the new propulsion system developed at the Universidad Carlos III de Madrid (UC3M) and the Universidad Politécnica de Madrid is based on the principle of Lorentz drag. That is, using a long conducting tether that is lowered from a satellite and builds up an electrical potential as it passes through the Earth's magnetic field. Put simply, what this does is allow the satellite to convert the spacecraft's orbital momentum into electricity, causing it to lose altitude as its orbit decays. On the other hand, if electricity is pumped into the tether, this generates thrust, causing the satellite to increase in altitude.

The idea isn't a new one. In fact, variants of it have been tested over the past decades, but its application has been limited because the tethers have been complex, expensive, and very prone to contamination even in the vacuum of space. Where the new tether differs in that it consists of an aluminum tape only a few centimeters wide featur what is called a "low work" coating, which has enhanced electron emission properties when exposed to sunlight or heat.

"Space tethers have been investigated for decades and have flown in more than twenty space missions," says Claudio Bombardelli, from the UPM Space Dynamic research group and one of the inventors. "Our contribution to this technology comes from a strikingly simple design in which two lightweight aluminum tape deployed from a satellite without any active electron emitter are able to supply power and/or propulsion to a spacecraft. Besides, to make things more efficient, we thought about exploiting the photoelectric effect of the tapes exposed to sunlight. We believe that this is an extremely important simplification which can boost tether technology."

The researchers see the technology as having a number of applications. Aside from boosting the orbits of satellites and even the ISS, it could also be used as a way of deorbiting satellites when they reach the end of their service lives, or as an onboard power source. They are currently working on extending the existing patents into the European area and building small-scale prototypes.

"The biggest challenge is its manufacturing because the tether should gather very specific optical and electron emission properties," says Gonzalo Sánchez Arriaga, Ramón y Cajal researcher at the Bioengineering and Aerospace Engineering Department at UC3M. "We have been awarded very recently a small research grant by the Ministry of Economy, Industry and Competitiveness of Spain to investigate promising materials. We are also coordinating an international consortium and submitted a FET-OPEN R&D proposal to the European Commission. The FET-OPEN project would be foundational because it considers the manufacturing and characterization of the first low work function tether and the development of a deorbit kit based on this technology to be tested on a future space mission. If funded, it would be a stepping stone to the future of low-work-function tethers in space."

The inventors say that they have also contacts ESA, experts in the United States and Japan, as well as the Spanish company SENER about the new technology.

The video below discusses the new space tether.

Source: UC3M

Nuevo sistema de generación de potencia eléctrica y propulsión para satélites en órbita

3 comments
Bob
I understand the principal of this but am confused as to how it will actually work. Will it be lowered from and below the satellite or trail behind? I understand the magnetic force generated by the electrical current working against the earth's magnetic field to produce drag like the load on an electric motor or even the opposite to make it function like a generator. This will drag the satellite down but the part about using the repelling magnetic force to boost the satellite eludes me. It's like the old joke that pulling a car with a chain is easier than pushing it with a chain. In other words how will the thin ribbon push the satellite or will it move ahead of the satellite and pull it? I suspect it will have to move ahead and pull it but the article didn't mention how it will work. It would seem that the electrical power used to boost the satellite would be a heavy drain on whatever electrical system the satellite used. It would also have to overcome the small extra aerodynamic drag of the long ribbon. In theory this sounds great but executing it in the real world won't be so simple.
Craig Jennings
Bob, I'd say they'd deploy it away from the earth if they were looking to "pull" themselves up when putting juice into it. And if they don't have the juice on it'll fall back towards them.
Ralf Biernacki
There are two tethers: one stretches away from Earth, and is kept taut by the centrifugal effect, because it moves faster than the local orbital speed; the other stretches towards Earth, and is kept taut by gravity, because it moves slower than the orbital speed. The orbital dynamics involved have been best described by Larry Niven in "Integral Trees" (with aerodynamic drag added).