
Wow!
That's an expensive game of chicken...
The Indian Space Research Organisation revealed late last week that its Chandrayaan-2 moon orbiter has twice maneuvered to avoid potential collisions with similar craft. The Indian craft raised its orbit on September 19 – two weeks before it would have made an uncomfortably close encounter with Korea's Danuri spacecraft, …
I'm sure the shift was to maintain a very large margin of safety, like multiple if not double digit number of kilometers.
The example I like to use is to imagine people driving cars on the surface of the Earth (if it was smooth and had no oceans, etc.) at thousands of kph where the steering wheel is disabled unless you plan and execute a maneuver to change your path around the globe. It would be extremely unlikely you'd set your car in EXACTLY the same path as another to the point it would result in a collision even if you both nominally drive from pole to pole. Even then for a collision to happen would be pretty bad luck since you would on average be separated by some 20,000 kilometers.
And that example is in two dimensions. You take it to three where you can choose to "drive" at various heights above the surface and you can see why the odds of a collision are so small. Now once we have hundreds of thousands of satellites all orbiting the Earth in various "low" orbits, not even accounting for the other bits ranging from specks of paint to pieces of satellites destroyed by anti satellite missile tests, the odds increase by orders of magnitude but started out so long that even if we weren't doing our best to avoid collisions with other known objects in orbit it would be spectacularly bad luck for one to happen in our lifetimes.
There's also a small cloud of debris around many of them, such as combustion byproducts left over from the previous manoeuvre, outgassed material, and flecks of paint and mylar etc that have flaked off.
While encountering those at high speed might not destroy the whole spacecraft, they could easily destroy an instrument and would definitely result in even more flecks of paint and mylar around.
So you leave a large gap.
But ... when the spacecraft manoeuvres, why do you think it takes its cloud with it?
You'd have both dodge, so as to avoid each others clouds.
I will say that's the first time I'd heard that theory, and traces of atmosphere, minute differences in orbit, radiation pressure, and possibly earth and solar magnetic fields might be reasons why.
"It would be spectacularly bad luck for one to happen in our lifetimes."
I don't know how old you are but 2009 is in my lifetime. That was the first genuine satellite-satellite collision. Before that and since, there have been multiple satellite-debris collisions.
"Before that and since, there have been multiple satellite-debris collisions."
There's also been other loss of satellites where the reason is unknown. Just a satellite that can still be tracked on RADAR but is completely uncommunicative. Many Starlink sats have died so they'll just continue to orbit until that orbit finally falls low enough that there's drag enough to start it coming down more rapidly. Just like a car that stops on the motorway, everybody else has to swerve around it.
IIRC Starlink orbits can be between ~350 to 600Km and the highest could take up to 5 years to orbit if the fail and lose communications, ie can't be commanded to de-orbit. There was a story a little while ago about SpaceX de-orbiting about 100 of the earliest sats due to probable design fault that could cause them to die before expected EOL and so are pre-emptively de-orbiting them to avoid them being uncontrolled hazards. But with the size of the planned constellation, not to mention the other planned mega constellations, it's pretty much certain to be a problem. Bezos is planning on competing with Starlink and there 2 or 3 Chinese companies also in the planning stages for similar, so potentially 100's of 1000's of Starlink-like sats up there at any one time.
> Bezos is planning on competing with Starlink and there 2 or 3 Chinese companies also in the planning stages for similar, so potentially 100's of 1000's of Starlink-like sats up there at any one time.
And before we know it we have a Dyson Sphere forming
I'm guessing that the calculations and concerns happen on the ground, not the satellite?
I suspect that an orbit isn't just around the mathematical 'point mass' but that local mass concentrations will move orbits just a little bit - enough to ensure that a satellite might not be quite where it was originally intended to be.
Driving in Turkey was similar to driving in India, but Turkey added another hazard: it was common knowledge then that non-Turkish drivers should drive rather carefully because, if a non-Turkish driver was involved in an accident, they would automatically be at fault on the grounds that the accident would not have happened if they hadn't been in Turkey. I was there and managed to drive the length of the country twice and emerge accident-free both times, but was never mad enough to drive in Istanbul: it was safer to leave one's vehicle in the BP Mocamp and take a bus or taxi inro town.
"I was there and managed to drive the length of the country twice and emerge accident-free both times, but was never mad enough to drive in Istanbul: it was safer to leave one's vehicle in the BP Mocamp and take a bus or taxi inro town."
There are a lot of places like that. The really mad thing is when those people visit a western country and start ignoring stop signs, fail to give way when they should and use whatever lane seems to be the fastest regardless of which side it's on. We all know that use of indicators is an inverse function based on the price of the vehicle. As is parking in handicapped spaces.
Isn't the price of a vehicle parked in a handicapped space without a placard directly correlated with the chance of it being damaged in your country?
Because it definitely is here. Particularly if it's some type of sports car, there's a much better chance of you coming back to key marks and damaged tires for that. Mostly because people assume that the handicapped parking fine won't bother you, but scraped paint and a slashed tire on your expensive car will.
So now I have a question. Does anyone know what the protocol is for lunar orbiters when. Their work is done?
Orbiting the earth they can decay and burn up, but no atmosphere in the moon means if they decay they will just spread debris over the surface, where it will stay forever.
I presume these things don’t have enough fuel to lift themselves out of orbit entirely?
There's no formal protocol
NASA: 2024/09/19 @ 19:45:12 - Moves satellite 1 km higher up in orbit to prevent disaster.
ISRO: 2024/09/19 @ 19:45:14 - Moves satellite 1 km higher up in orbit to prevent disaster.
Everybody goes home happy.
Anyway, so is there nobody that thinks "To avoid collision, I'm going to let my satellite orbit at 100.5 km" and somebody else who thinks "To avoid collision, I'm going to let my satellite orbit at 99.75 km"? Is there something magical about orbiting at 100.00 km?‡ We have computers that can calculate adjustments.
‡ I am not a scientist.
(Yield to the right =======>)
"Is there something magical about orbiting at 100.00 km?"
On the moon, not particularly, but there are orbits where the precise altitude and inclination matter. The most obvious such orbit is geostationary.
But you've just suggested a separation of 750m, which might sound alot, but with the "lumpy" nature of lunar gravity it's not a precise game: I don't think many organisations would be happy with that distance.
"Is there something magical about orbiting at 100.00 km?‡ "
Most observation satellites don't fly a circular orbits, they fly elliptical orbits so there will points there are closer and can take a detailed reading and further out to take a overview reading. So you may find that a satellite is over a particular point on the surface at its lower orbit point (perigee) once every 500 orbits for example. There is a slight issue that all three satellites (and the Chinese) are focusing on southern poles as that is where the ice is likely to be and most likely target for next human landing so you may find they are flying similar orbits on their polar passes.
"focusing on southern poles as that is where the ice is likely to be and most likely target for next human landing so you may find they are flying similar orbits on their polar passes.
A polar landing is pretty aggressive after not landed people for a long period of time anywhere. I'd suggest robotic missions to search for water and human missions to look at some of the cavern entrances that have been photographed (perhaps after a robotic mission to some of those too). We can send water to support some manned missions in the beginning. I feel the same way about reusable landers. Some landers with separate decent and ascent sections could be used to field missions that would construct a landing pad/zone for later fully reusable craft. One of the Apollo missions set down on the engine bell and that could have been curtains for the astronauts if that was their only engine damaged.
"There is money for one system and the public aren't going to buy into timelines that will take decades especially with the Chinese making so much progress."
Who is saying anything about decades? A lot of the Apollo mission lander development is there for the taking. Dust it off, update it and get building. NASA did a tremendous amount of research from Mercury-Apollo that doesn't need to be repeated. One disastrous mission where people die on the moon will likely kill the program for some time. At least to me, it's worth building up to an aggressive plan rather than pushing all the chips into the pile and hoping the other player isn't holding that other Ace. And then doing it again, and again each time.
Most of Apollo mission were only a few steps away from disaster, much like Shuttle program NASA was under pressure to push on. And SpaceX has said they are grateful for the research that has gone on before them. Thing is the objectives are different this time, not looking at doing a couple of days on the surface but weeks and means more capability required which means new designs.
From a quick google,
Apollo could manage around 1.5T (16T for Lunar model of which 10T was decent model and 4.5T for ascent module).
Blue Origin are aiming for around 4T
Starship HLS, who knows. But we do know is that the figure they are aiming for is going to require a more complex design with in orbit refuelling and crew transfers, etc Thing being with the cadence they are hoping to achieve and will need then there is opportunity to do extended testing. Of course there is still a lot of development work to be done but if they can hit even 10 launches next year (they are aiming for 25) that is a lot of testing they could get done. We will see, no more launches this year anyway.
It's quite fascinating how humans can be so smart and yet so dumb. I'm looking forward to the day when a spectacular satellite pileup occurs that destroys a majority of hardware orbiting planet Earth and what with the Russians pre-occupation of cutting the undersea cables we find ourselves transported back to the 1970s.
Now where did I put my flares and Diamond Dogs album.
I will miss satellite navigation though, I will have to practise driving one handed while reading the AtoZ like in the old days.