By 
February 19th, 2014
Envisat, an artist’s impression
Credit: ESA/Denmann production
The Robotic Refueling Mission (RRM) module on the International Space Station, as seen in this 2011 photo. The RRM is an International Space Station demonstration that proves the tools, technologies and techniques to refuel and repair satellites in orbit – especially satellites not designed to be serviced.
Credit: NASA
No doubt that the hit movie “Gravity” struck a chord with moviegoers – and made an impact in the public mind about the threat of human-made orbital debris.
A team of University of Leicester students have taken a hard look at the European Space Agency’s (ESA) Envisat that lost contact with Earth in April 2012. Envisat is ESA’s largest Earth observation satellite.
Their appraisal: The huge spacecraft could potentially pose a threat similar to the events which plagued Sandra Bullock in the Oscar-nominated sci-fi/fact thriller.
What’s more, the task of bringing the satellite back to Earth may be too costly and complex to be feasible, according to the final year paper written by the students for the Journal of Physics Special Topics, a peer-reviewed student journal run by the University’s School of Physics and Astronomy.
Congested region
ESA’s Envisat now orbits the Earth out of human control at an altitude of some 490 miles (790 kilometers). That’s where the amount of space debris around the planet is greatest.
This means there is a chance of collision with other satellites and debris during the 150 years it is expected to remain in space, according to a news release from the University of Leicester Press Office.
Each year, two objects are expected to pass Envisat to within about 656 feet (200 meters). Other spacecraft have already had to move out of Envisat’s path.
According to the student research, it is possible — though unlikely — that a collision with Envisat could lead to a chain reaction effect, known as the “Kessler Syndrome.” That’s where fast-moving debris runs into other space junk and creates more clutter.
The result: It could make it difficult for future space missions to pass through the region of Envisat’s altitude, if the region becomes congested with space debris.
Tall order
De-orbiting Envisat, the student study suggests that around 308 pounds (140 kilograms) of fuel would be required to move the satellite to a point where it would naturally return to Earth within 25 years.
This could be quite feasible, according to the students, if two of the craft’s four fuel tanks were replaced.
But actually getting this fuel to the satellite in orbit would be a pretty tall order due to the costs involved of such a mission – which has never been attempted for a satellite which wasn’t designed to be refueled.
De-orbiting Envisat
So although it is unlikely to happen, de-orbiting Envisat is certainly worth considering.
“Unfortunately, it would be very unlikely we could move Envisat to the right altitude due to how much it would cost,” said physics student Katie Raymer, 22, from Whitstable. “Envisat was not designed to be refueled, so another method of de-orbiting Envisat may be a better option.”
The students suggest it may be possible to use NASA’s Robotic Refueling Mission (RRM) which has been designed to refuel and repair non-operational satellites. But that hardware is still in its earliest stages of testing.
Major risk factors
There’s one cosmic caveat to the student research work: The team stressed that the calculations used in the paper should be taken as an estimate, as a full treatment would be very complicated and beyond the scope of a Journal of Physics Special Topics paper.
George Fraser, Director of the University’s Space Research Center, commented:
“The Special Projects paper highlights the huge area and mass of Envisat as the major risk factors for space debris,” Fraser said. “The fact that Envisat is in a near-polar orbit doesn’t help either, since its path intersects most satellites’ orbits nearly at right angles. Imagine driving down the motorway and every so often a large truck cuts right across all four lanes right in front of you!”
Note: The full paper can be found at:
http://physics.le.ac.uk/journals/index.php/pst/article/viewFile/621/424
Posted in Space News
It sounds to me like a great study. Did they look at tethers or other propulsive means like ion engines that could clamp onto the satellite and bring in back to Earth?
The simplest solution for Envisat is to capture it with an EDDE spacecraft, drag it to a less crowded altitude, and maintain control with the EDDE propellantless electrodynamic propulsion system so that Envisat is no longer a danger to operating satellites.
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