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NASA Launches Micro Solar Sail
greyarea67 writes with news that NASA has successfully used a "microsatellite" (a term given to satellites weighing between 10kg and 100kg) to deploy a "nanosatellite" (a term given to satellites weighing between 1kg and 10kg). The deployed object, the first of six in the microsatellite's payload, was the NanoSail-D flight unit. NanoSail-D masses 4kg and is "about the size of a loaf of bread" until it deploys its solar sail.
"...when the NanoSail-D sail is deployed it will use its large sail made of thin polymer material, a material much thinner than a single human hair, to significantly decrease the time to de-orbit the small satellite without the use of propellants as most traditional satellites use. The NanoSail-D flight results will help to mature this technology so it could be used on future large spacecraft missions to aid in de-orbiting space debris created by decommissioned satellites without using valuable mission propellants."
Someone else will probably beat me to this short bout of pedanticism questioning how micro and nano are applied in this situation (micro-ton?) and highlighting the fact that there are three orders of magnitude separating the micro and nano scale.
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I had to dig long and hard to find the answer to this one...
"The NanoSail-D flight results will help to mature this technology so it could be used on future large spacecraft missions to aid in de-orbiting space debris created by decommissioned satellites without using valuable mission propellants."
It appears that it might have something to do with not wanting to waster mission propellants. My keen insight into human psychology tells me that since the satellite is dead, colliding with it is someone else's problem so the cost/benefit ratio is nearly infinity. Free markets are wonderful things, but externalities tend to get ignored and our government lacks the nuts to correct these situations.
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"about the size of a loaf of bread", "much thinner than a single human hair". How many football fields will this satellite travel? How many Statue of Liberties high will this thing orbit?
Does this qualify as a "solar sail"? It seems more like it's a fractional atmosphere parachute. Solar sails are intended to interact with solar wind particles, but it would seem to be almost useless in an orbital situation, half the orbit you'd be head into the solar wind, half you'd have it at your back accellerating you. In either case, the solar wind is an exceedingly small force, which is why solar sails are proposed on the scale of square miles+. The solar wind would be dwarfed by stray atmospheric particles in earth orbit.
This seems like they're using the term "solar sail" when they mean something completely different.
It all depends on the orbit of the satellite, and the purpose of the mission.
A low-Earth orbit satellite will naturally de-orbit due to atmospheric drag, and can be de-orbited in a controlled manner with a very low fuel cost since it just means bringing your perigee down ever so slightly so it burns up. This is good because LEO is the most crowded region you'll find, and the most likely place to encounter an accidental collision.
However, when you start to get up middle altitudes, such as those used by GPS satellites, those things will stay up forever if you don't do anything about them. They're also a lot more expensive to de-orbit, in terms of fuel usage, and even if you do have fuel you plan to use for that, if you lose communications with the satellite you can't do anything about it anyway. Fortunately its much less crowded up there, so a collision is not a very large risk.
Finally, geostationary orbits are interesting, because it gets a lot more crowded again. The costs of truly de-orbiting those is also extremely high, so its not done. Instead, you have what are called graveyard orbits that GEO birds are put into at their end-of-life. This works well enough, but there is an issue of what happens when you have a vehicle die before it can be moved to its graveyard orbit -- this gives you the aptly named zombie satellites that are a significant danger to geostationary spacecraft.
So yes, satellite engineers foresee the problems, but its damned hard to design something that will behave perfectly for years and decades with no capability to go out and make physical repairs. A device to make satellites in high-orbits have the same self-deorbiting properties as LEO satellites would be quite handy.
OK, it might be easier to test a solar sail by de-orbiting something faster, and it's important to not contribute further to orbital debris. But the interesting direction is UP! Get the thing from low-orbit to a higher orbit with the solar sail, like the Japanese have started to do with the IKAROS satellite. Can we get from LEO to geostationary with a solar sail? Can we use it to maintain an orbit without propellant? That means less mass for delta-V to lift out of the atmosphere, and thus less cost but maybe a long time to achieve the final orbit.
Bruce Perens.
"Are there still dead satellites in orbit because of malfunction,..."
Over 11000 dead satellites (or pieces thereof) are tracked by space command.
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This topic begs the question why were satellites designed so that they would still remain in orbit after "death."
Generally, they're not. When large satellites reach end of life, they are either purposely deorbited, or they are boosted way above geosynchronous orbit where they can sit for centuries.
These sails are meant for small satellites; small enough to not have any station keeping thrusters on board. They'd generally deorbit in a few months anyways, but the sail would hasten the process.
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