Posted on 01/28/2020 10:20:22 AM PST by Red Badger
It’s a two-dimensional problem. The collision cross section is determined by the projection of the respective satellites silhouettes onto the plane perpendicular to direction of their relative velocity at the moment of closest approach.
The third dimension, the dimension in the direction of the velocity doesn’t count because at some point the separation in that dimension *will* go to zero by definition, at exactly the moment of nearest approach. It does not influence whether or not there is a collision, only when. (You can assume that the satellites are not rotating during the duration of the collision event. If the velocity of rotation about its own body center were comparable to the orbital velocity, the centrifugal force would exceed 10,000 g’s and would already have torn the satellite apart.)
You got peanut butter on my chocolate! Hey! Wait a minute....yum.
Sunlight glinting off thousands of metal parts would need no oxygen..................
How about using them as ASAT target practice?
“Even as close as 15 meters the odds of them actually colliding are astronomically against. 15 meters is bigger than either satellite and we are talking about 3 dimensions rather than 2.”
Pointing out that this is the problem that NMD had to solve with hit-to-kill warheads. Executing that last course adjustment to make impact — that’s the trick.
“... and we are talking about 3 dimensions rather than 2.”
We are talking about two dimensions.
"The difference between the almost right word and the right word is really a large matter - 'tis the difference between the lightning-bug and the lightning."
-- Mark Twain
Massive NASA/NSA orgasm...
If the powers that be know a satellite has a finite life span, why do they not build and program it to burn itself up in the atmosphere?
Instead there will be even more space junk floating around.
What happens if the retired space telescope and former spy satellite crash into each other?
you get a bigger telescope on the spy satellite?
Yes, of course. Not to mention gobs and gobs of money.
Sounds like a job for The US Space Force. Shoot those suckers down.
You get a satellite that can see the numbers on your watch....................
They essentially let gravity do it.
Slow, very slow, but sure....................
Per the article, they have a relative velocity of about 32,880 miles per hour. That implies they are in very different orbits. In fact, IRAS in a near polar orbit and GGSE-4 in a highly inclined orbit, their individual velocities of about 16,000 miles per hour can in fact sum up to the cited relative velocity if one is heading northward and the other southward. So if IRAS even catches a tiny bit of a GGSE-4 boom there can be significant debris flying around.
It takes a lot of propellant to lower these satellites’ orbits sufficiently to reenter the atmosphere. Poppy was launched in 1967 and IRAS in 1983. Back then there were relatively few satellites and the collision/debris risk was minimal. Today the rule is that low earth orbit satellites should reenter no more than 25 years after they stop operating.
I take it the 25 year rule relies on physics to pull the satellites into the atmosphere?
It relies on the tiny bit of drag that the satellites experience from the super thin atmosphere up there. As they get lower and lower the atmosphere density increases so the process accelerates gradually toward reentry. Satellites today typically save some fuel to lower their orbit partway at end of service life and then let drag take over from there. Some newer concepts inflate a balloon or other appendage at the end of satellite life to provide a larger drag cross-section and speed up the reentry process.
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