Dead sat walkin'... er, fallin'
Whew! Been a while since I've posted. Gotta vacuum some dust off this page.
Anyway, I saw a bit o' spacey news today that I thought was kinda cool.
Maybe you saw the news a month or so ago that a big-ass broken spy satellite was falling, and would probably crash sometime in March. In case you missed it, it's a 2.5-ton satellite whose main computer totally crapped out shortly after it got into orbit. Since the computer's toast, it's just a big flying piece of scrap metal. Since it can't be guided at all, the orbit's been decaying ever since.
That decaying-orbit thing happens to all satellites, 'cuz even way up in orbit there's an eentsy little bit of atmosphere. Just enough to very gradually slow things down. That's why satellites have small "station-keeping" thrusters, so they can get a little boost every now and then and stay where they belong. More on this in a minute, 'cuz it's kinda important to this story.
A falling satellite of this size poses two problems. One, it's BIG. Big enough that it's not going to all burn up on re-entry. That means some bits will hit the ground, and potentially cause damage or injuries. This USUALLY isn't an issue with big satellites, because if they're still "alive" they can be steered so that they hit the ocean and thusly don't conk anyone on the noggin. This sat, though, is totally uncontrolled, so nobody knows where it's gonna come down. It'll PROBABLY land in the ocean (about 75% of the surface under its flight path is water), but no promises.
The second problem is from those thrusters that I mentioned before. Most satellite thrusters use a fuel called hydrazine. It's a really good rocket fuel for satellites, but it's hella-nasty stuff health-wise. Not like nerve-gas nasty, but you definitely don't want to be playing with it. Most re-entering satellites don't have much hydrazine left in the tanks by the time they're brought down, and what IS left burns up and/or dissipates pretty high up so it doesn't do any harm.
This particular problem-child sat, though, crapped out right after it got up there, so its fuel tanks are pretty much full. There's about a half-ton of the stuff in there. And to make matters worse, it's most likely frozen! Hydrazine freezes at around 36 degrees F, and space is A LOT colder than that. Without the satellite's on-board heaters (no computer = no heaters), the stuff is probably a big rocket fuel popsicle... a big enough popsicle that much of it is likely to survive re-entry and cause problems on the ground.
So, what to do about this mess? SHOOT THE SUCKER DOWN! :-) The Navy is modifying three SM-3 missiles, one on each of three ships, to try to shoot down the wayward satellite in a week or so, once it gets a little lower. If the missiles can hit it (the guidance software as-is is designed to track and hit ballistic missiles, not falling satellites), the hope is that the great big satellite will be broken up into small enough pieces that pretty much everything will burn up. If things go REALLY well, they'll hit the fuel tank and break up the big toxic ice cube. It should be interesting.
And I'm sure that, even though the intercept will be at a much lower altitude than satellites typically operate, and the SM-3 missile can't actually reach practical orbital altitudes (probably), I'm sure that the Navy's more than happy for the extra target practice. :-)
Anyway, I saw a bit o' spacey news today that I thought was kinda cool.
Maybe you saw the news a month or so ago that a big-ass broken spy satellite was falling, and would probably crash sometime in March. In case you missed it, it's a 2.5-ton satellite whose main computer totally crapped out shortly after it got into orbit. Since the computer's toast, it's just a big flying piece of scrap metal. Since it can't be guided at all, the orbit's been decaying ever since.
That decaying-orbit thing happens to all satellites, 'cuz even way up in orbit there's an eentsy little bit of atmosphere. Just enough to very gradually slow things down. That's why satellites have small "station-keeping" thrusters, so they can get a little boost every now and then and stay where they belong. More on this in a minute, 'cuz it's kinda important to this story.
A falling satellite of this size poses two problems. One, it's BIG. Big enough that it's not going to all burn up on re-entry. That means some bits will hit the ground, and potentially cause damage or injuries. This USUALLY isn't an issue with big satellites, because if they're still "alive" they can be steered so that they hit the ocean and thusly don't conk anyone on the noggin. This sat, though, is totally uncontrolled, so nobody knows where it's gonna come down. It'll PROBABLY land in the ocean (about 75% of the surface under its flight path is water), but no promises.
The second problem is from those thrusters that I mentioned before. Most satellite thrusters use a fuel called hydrazine. It's a really good rocket fuel for satellites, but it's hella-nasty stuff health-wise. Not like nerve-gas nasty, but you definitely don't want to be playing with it. Most re-entering satellites don't have much hydrazine left in the tanks by the time they're brought down, and what IS left burns up and/or dissipates pretty high up so it doesn't do any harm.
This particular problem-child sat, though, crapped out right after it got up there, so its fuel tanks are pretty much full. There's about a half-ton of the stuff in there. And to make matters worse, it's most likely frozen! Hydrazine freezes at around 36 degrees F, and space is A LOT colder than that. Without the satellite's on-board heaters (no computer = no heaters), the stuff is probably a big rocket fuel popsicle... a big enough popsicle that much of it is likely to survive re-entry and cause problems on the ground.
So, what to do about this mess? SHOOT THE SUCKER DOWN! :-) The Navy is modifying three SM-3 missiles, one on each of three ships, to try to shoot down the wayward satellite in a week or so, once it gets a little lower. If the missiles can hit it (the guidance software as-is is designed to track and hit ballistic missiles, not falling satellites), the hope is that the great big satellite will be broken up into small enough pieces that pretty much everything will burn up. If things go REALLY well, they'll hit the fuel tank and break up the big toxic ice cube. It should be interesting.
And I'm sure that, even though the intercept will be at a much lower altitude than satellites typically operate, and the SM-3 missile can't actually reach practical orbital altitudes (probably), I'm sure that the Navy's more than happy for the extra target practice. :-)