Orbital Collisions?
Discussion
Whilst reading the thread about the two satellites that collided, I noticed people kept referring to "closing speeds" of orbital collisions as being up to 35,000mph and there or there abouts.
How?
I assumed everything in earth orbit went in the same direction in pretty much "free fall" so where does this kind of speed differential come from?
I await humiliation - serious question btw, no shuttle on a conveyor belt s
t please 
How?
I assumed everything in earth orbit went in the same direction in pretty much "free fall" so where does this kind of speed differential come from?
I await humiliation - serious question btw, no shuttle on a conveyor belt s
t please paddyhasneeds said:
Whilst reading the thread about the two satellites that collided, I noticed people kept referring to "closing speeds" of orbital collisions as being up to 35,000mph and there or there abouts.
How?
I assumed everything in earth orbit went in the same direction in pretty much "free fall" so where does this kind of speed differential come from?
I await humiliation - serious question btw, no shuttle on a conveyor belt st please
SPEED KILLS!!How?
I assumed everything in earth orbit went in the same direction in pretty much "free fall" so where does this kind of speed differential come from?
I await humiliation - serious question btw, no shuttle on a conveyor belt s
t please TheEnd said:
some stuff isn't in geostationary orbit (ie hanging over the same spot)
a good point all the same though
OK so satellite goes up, gets put into geostationary orbit, stays in a relative position over the same spot, understand that.a good point all the same though
Shuttle goes up, goes into an orbit, obviously it builds up sufficient speed to break out of the atmosphere and go into orbit.
Let's just assume it were to take a path right into one of those satellites - what would the relative speed difference actually be?
paddyhasneeds said:
TheEnd said:
some stuff isn't in geostationary orbit (ie hanging over the same spot)
a good point all the same though
OK so satellite goes up, gets put into geostationary orbit, stays in a relative position over the same spot, understand that.a good point all the same though
Shuttle goes up, goes into an orbit, obviously it builds up sufficient speed to break out of the atmosphere and go into orbit.
Let's just assume it were to take a path right into one of those satellites - what would the relative speed difference actually be?
If it did get up to 20,000 miles while in orbit the speed would have to be the same as everything else in that orbit. Any slower and down it comes, any faster and it flies off to meet ET. The point is that satellites at the same altitude and therefore going at the same speed might be going in different directions.
paddyhasneeds said:
Whilst reading the thread about the two satellites that collided, I noticed people kept referring to "closing speeds" of orbital collisions as being up to 35,000mph and there or there abouts.
How?
I assumed everything in earth orbit went in the same direction in pretty much "free fall" so where does this kind of speed differential come from?
I await humiliation - serious question btw, no shuttle on a conveyor belt st please
There's your problem right there. The maths involved will make your brain hurt but not everything in orbit travels in the same direction and at the same speed. It's true Geostationary satellites are pretty much all at the same height and the same bit of the sky and as a result the relative speeds are pretty low. However outside of that there are are a myriad of diffrent orbits and lots of 'dead' unmanoeverable sats up there - surprising it hasn't happened before now.How?
I assumed everything in earth orbit went in the same direction in pretty much "free fall" so where does this kind of speed differential come from?
I await humiliation - serious question btw, no shuttle on a conveyor belt s
t please http://en.wikipedia.org/wiki/List_of_orbits
Given that speeds in a Low Earth Orbit (with a period of about 90 mins) are something like 17,500 mph, the closing speeds could be very large indeed! I don't know if anything would actually go in opposite directions though. It seems more likely they'd converge while going in similar directions. This is all guesswork though, as I know very little about space and tha'.
Up in a GEO the speeds are measured in kilometres a second, which I can't even comprehend.
Up in a GEO the speeds are measured in kilometres a second, which I can't even comprehend.
Satellites travel around the earth in a myriad of directions and at a large selection of altitudes above the surface of the earth. Their altitudes can range from just over 100 miles to tens of thousands of miles. Some orbits are almost circular and some orbits are very elongated (elliptical).
So, not all satellites are travelling in parallel tracks around the earth. They are whizzing about from north to south, east to west, west to east and all variations in between - so, although an absolute head-on collision might not be very likely, a collision at 90 degrees or 127 degrees or 45 degrees (and other "odd" amounts )angles of impact are defintely possible. Low eartb orbit satellites orbit at a speed relative to the ground of 17,500 mph. Obviously, meeting a satellite in a similar orbit but travelling in the opposite direction would result in a 35,000 mph impact. Even though this is not likely to happen, impact speeds of over 20,000 mph are genuinely possible.
So, not all satellites are travelling in parallel tracks around the earth. They are whizzing about from north to south, east to west, west to east and all variations in between - so, although an absolute head-on collision might not be very likely, a collision at 90 degrees or 127 degrees or 45 degrees (and other "odd" amounts )angles of impact are defintely possible. Low eartb orbit satellites orbit at a speed relative to the ground of 17,500 mph. Obviously, meeting a satellite in a similar orbit but travelling in the opposite direction would result in a 35,000 mph impact. Even though this is not likely to happen, impact speeds of over 20,000 mph are genuinely possible.
Edited by Eric Mc on Saturday 14th February 10:29
I too wondered about that, thinking that things in the same orbit travelled at the same speed (or possibly not, depending on weight I suppose, the heavier object having to go faster to maintain the same height orbit. Then after a few seconds it dawned on me that they didn't all go in the same direction!
Simpo Two said:
I too wondered about that, thinking that things in the same orbit travelled at the same speed (or possibly not, depending on weight I suppose, the heavier object having to go faster to maintain the same height orbit. Then after a few seconds it dawned on me that they didn't all go in the same direction!
Weight isn't an issue. An object maintains its particular orbit purely because of the speed it carries. If an astronaut loses a spanner whilst out on a spacewalk, the spanner will, more or less maintain the same orbit as the astronaut and the spacecraft from which the spacewalk was being conducted. If the astronaut somehow "batted" the item away from him/her, it will have a slightly different velocity to the astronaut so will gradually drift away in a very slightly different orbit.A classic example of this is the toolbox lost by the female astronaut during the last Shuttle mission. The space walk was carried out whilst the Shuttle was attached to the International Space Station. Therefore, all the objects (Shuttle/ISS/Astronaut) had the same orbits and orbital velocity. The tool bag was knocked away from the astronaut and given an ever so slightly greater orbital velocity impetus. Currently, it is in roughly the same orbit as the ISS but would now be a few kilometers ahead or behind the ISS itself. Even though it is much, much lighter than the ISS, it is still in roughly the same orbit.
The debris from the the destroyed satellites will, even though the individual pieces are much smaller and lighter than the original two satellites, will mostly maintain the same orbits of the original object.However, some of the bits will have changed direction because of the impact energies involved. Currently, NORAD is tracking two clouds of debris containing roughly 600 pieces down to a size of a few centimetres. Their radars can't make out smaller pices - of which there must be thousands.
Edited by Eric Mc on Saturday 14th February 10:17
There are many misconceptions out there concerning how and why spacecraft and satellites orbit.
The most common one being that the aim of a space launch is to ensure that the satellite somehow "gets outside the atmopshere". Getting outside the atmosphere is necessary to prevent the object from being pulled back down to earth by atmospherically induced aerodynamic drag but it is not the core aim of a space launch. The aim of a space launch is to ensure that the object being placed into orbit:
i) achieves the velocity necessary to maintain the orbital altitude required (anything from 100 miles to tens of thousands of miles)
ii) is pointed in the right direction so that it orbits the earth at the desired angle in relation to the equator (called the "orbital inclination").
Objects being launched from an airless world, like the moon, have no atmosphere to worry about and could orbit as low as they need to go -0with maybe just enough clearance to miss the highest peaks of the lunar mountains. Orbiting at 30,000 feet above the moon would be some ride. The Apollo spacecraft orbited the moon at an altitude of around 60 miles above the lunar surface.
Now and then, a spacecraft is given enough velocity to break completely free of the earth's gravitational pull (escape velocity - 7 miles per second) and enter its own orbit around the sun. In effect, it becomes, for a while at least, a man made planet. These spacecraft may just need to orbit the sun - for instance, if they are on a mission to observe the sun. More likely, they are on their way somewhere else, like another planet. In these situations, the orbit around the sun takes them out to a rendevous point with the target planet where they will use some technique to slow down (retro rockets or aerodynamic braking in the planet's atmosphere) to enter into orbit around the planet.
If the spacecraft is not going to enter orbit around the planet but just "fly-by", then the spoacecraft may be given a huge amount of initial speed as it leaves earth which allows it to break free of the sun's gravitational pull completely. It will then move outwards from the sun forever and, eventually, enter interstellar space and travel out to the stars. Pioneers 10 and 11 and Voyagers 1 and 2 are doing just that right now.
The most common one being that the aim of a space launch is to ensure that the satellite somehow "gets outside the atmopshere". Getting outside the atmosphere is necessary to prevent the object from being pulled back down to earth by atmospherically induced aerodynamic drag but it is not the core aim of a space launch. The aim of a space launch is to ensure that the object being placed into orbit:
i) achieves the velocity necessary to maintain the orbital altitude required (anything from 100 miles to tens of thousands of miles)
ii) is pointed in the right direction so that it orbits the earth at the desired angle in relation to the equator (called the "orbital inclination").
Objects being launched from an airless world, like the moon, have no atmosphere to worry about and could orbit as low as they need to go -0with maybe just enough clearance to miss the highest peaks of the lunar mountains. Orbiting at 30,000 feet above the moon would be some ride. The Apollo spacecraft orbited the moon at an altitude of around 60 miles above the lunar surface.
Now and then, a spacecraft is given enough velocity to break completely free of the earth's gravitational pull (escape velocity - 7 miles per second) and enter its own orbit around the sun. In effect, it becomes, for a while at least, a man made planet. These spacecraft may just need to orbit the sun - for instance, if they are on a mission to observe the sun. More likely, they are on their way somewhere else, like another planet. In these situations, the orbit around the sun takes them out to a rendevous point with the target planet where they will use some technique to slow down (retro rockets or aerodynamic braking in the planet's atmosphere) to enter into orbit around the planet.
If the spacecraft is not going to enter orbit around the planet but just "fly-by", then the spoacecraft may be given a huge amount of initial speed as it leaves earth which allows it to break free of the sun's gravitational pull completely. It will then move outwards from the sun forever and, eventually, enter interstellar space and travel out to the stars. Pioneers 10 and 11 and Voyagers 1 and 2 are doing just that right now.
Edited by Eric Mc on Saturday 14th February 10:46
Eric, you may be able to educate me on something I was trying to remember recently. When studying spacecraft systems briefly, I remember learning about some trade-off involved with launch profiles. I seem to remember one side of it was that if the craft accelerated directly upward to start with, it would get into thinner air more quickly, before pitching to adopt an orbital path. However, I can't remember what the other option was or what the pros and cons of each were. Sound familiar?
. I'll dig my notes out next time i'm at home to satisfy my wonderings.Eric Mc said:
Currently, it is in roughly the same orbit as the ISS but would now be a few kilometers ahead or behind the ISS itself. Even though it is much, much lighter than the ISS, it is still in roughly the same orbit.
Given enough time, does that mean it will eventually orbit "all the way round" and eventually return back the ISS?Possibly ,although I wouldn't know how long before it would catch up.
The ISS orbits low enough that so it gradually loses velocity due to aerodynamic drag with the upper atmosphere. Every couple of months it is boosted back up to a higher altitude to prevent orbital degradation and re-entry.
I reckon the tool bag will re-enter and burn up way before it ever catches up with the ISS.
On a similar vein, if an astronaut was standing on a low gravity body, such as the surface of a small asteroid or a comet, and he pitched a cricket ball at the orbital velicity required for the asteroid/comet (perhaps less than 100 mph), if he stayed still for an hour or so, the cricket ball would perform one orbit and smack the astronaut in the back of the head.
The ISS orbits low enough that so it gradually loses velocity due to aerodynamic drag with the upper atmosphere. Every couple of months it is boosted back up to a higher altitude to prevent orbital degradation and re-entry.
I reckon the tool bag will re-enter and burn up way before it ever catches up with the ISS.
On a similar vein, if an astronaut was standing on a low gravity body, such as the surface of a small asteroid or a comet, and he pitched a cricket ball at the orbital velicity required for the asteroid/comet (perhaps less than 100 mph), if he stayed still for an hour or so, the cricket ball would perform one orbit and smack the astronaut in the back of the head.
Edited by Eric Mc on Sunday 15th February 17:15
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