Millions of solar sails to bring down the temperature on Earth ?
– News of September 15, 2019 –
Imagine that in a few decades or perhaps a hundred years, global warming makes the Earth almost unbearable. Humanity is unable to recapture all the carbon emitted during centuries of industrialization. We can then imagine that we will considering extreme solutions, at the risk of playing with our survival. This is one of those solutions that the American astronomer Roger Angel tried to imagine in 2006. The basic principle of his idea is rather simple, it is necessary to cool the Earth by all means. The easiest way is to limit the amount of light that comes to us from the sun.
According to the American astronomer, we should block 1.8% of the light that reaches us to counterbalance the warming due to a doubling of atmospheric CO2. The best way to achieve this would be to deploy millions of small semi-transparent solar sails at the Lagrange L1 point of the Sun-Earth system. This would obviously cost an astronomical sum of money and this would be difficult to maintain in place because of the radiation pressure of the sun. But humanity could have a century or two of respite.
This solution would limit global warming but would not change the chemical effects of the increased presence of CO2 in the atmosphere. So it is a bandage and a risky gamble, because nobody knows exactly what other effects would have a limitation of the arrival of solar light on Earth. This could disrupt a number of climate or biological processes in an uncontrolled manner. The best thing is to never have to make this bet to save humanity.
The LightSail solar sail maneuvers in space without fuel
– News from September 1, 2019 –
The LightSail solar sail is a small CubeSat developed by the Planetary Society. It was launched on June 25, 2019 by a SpaceX Falcon Heavy rocket. Its objective is to demonstrate that maneuvers can be done in orbit only with the strength of the solar wind. On 23 July, the small satellite managed to deploy a 32-square-meter sail using four telescopic masts. It successfully completed maneuvers to modify its orbit during the following month. The goal was to increase its apogee without using fuel.
To achieve this, the solar sail has changed position every half hour. As close as possible to the sun, it exposes its solar sail abreast to have a very small acceleration thanks to the pressure of the sun’s radiation. Once on the other side of the Earth, the solar sail rotates by 90 degrees and it finishes its orbit with a minimal exposure to the pressure of the radiation of the sun. By repeating the operation hundreds of times, LightSail has managed to change its orbit by about two kilometers. It’s not a lot but we have to remember that these maneuvers are done without any engine. It’s essentially a technical demonstration.
Thanks to this success, the solar sails may be interesting for companies and space agencies to keep their satellites in orbit. It is not possible to perform all the maneuvers thanks to them but the fact of not having to spend propellant remains a very attractive argument. LightSail will enter the atmosphere within a year.
Solar sails could be an effective solution for cleaning the geostationary orbit
– News of May 28, 2019 –
Solar sails can be used to maneuver in orbit. We can imagine them to navigate to one or more space debris to capture them. In this situation, the advantage of a solar sail is that its shape allows it to greatly increase its atmospheric drag, which speeds up the process of destruction of the space debris collected. The University of Surrey in the UK is working on a small CubeSat to prove that. This CubeSat will deploy a solar sail of 25 square meters to demonstrate its ability to maneuver without fuel. At the end of the mission, this solar sail will allow the CubeSat to deorbit faster.
Solar sails can also help clean up debris in geostationary orbit. In this case, the Earth’s atmosphere is too far away to allow efficient de-orbiting. Instead, satellites would be put a little higher to free up space in the geostationary belt. A small 50 kg CubeSat equipped with a 800 square meter solar sail should be able to effectively maneuver space debris up to one ton.
The advantage of such a system is that it is reusable many times. The solar radiation pressure can provide a nearly infinite delta V for this type of maneuver. A small amount of solar sails could thus effectively deal with maintenance of the geostationary orbit, which is very important for telecommunications. Space debris is not destroyed, it is placed in a parking orbit. This strategy could be tested quickly.
Image by Andrzej Mirecki [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]