I was watching a live stream of the ISS on YouTube when I found this.
https://www.youtube.com/watch?v=kOIyBAcz1yI
Very interesting, but scary I think. There's so many things that can go wrong. I have had nightmares free flowing in space. LOL
One thing I have to wonder. How do they steer the ISS? I mean stay at a certain vector and adjust the height above earth when you veer off a slight bit. Where are those computers?
Lol that crazy hair in space haha. Would be so fun to be up there, but I imagine after about a week it gets long, or maybe not. Would be so surreal maybe you just can't get enough of it. Just the idea of being in a rather confined space with other people and not really have any time to yourself though maybe that would make some go a little crazy.
Think the computers are in the Russian modules. I'd guess they use reaction wheels to keep it steady. It probably has to constantly compensate not only for keeping it "facing" the same direction relative to Earth but every time people move around in it. Come to think of it, not really sure where the boosters are, it does have boosters and it does carry fuel. They have to boost the orbit once in a while as it slowly decays. There's a very tiny amount of atmosphere at that altitude, space dust etc... that slows it down over time.
It's amazing how they can keep track of all that though, like the speed, altitude etc. And not only for the ISS but everything else in space, to ensure there's no collision.
Reaction wheels keep it oriented, small thrusters keep it aligned above the earth and in the correct orbit.
When we are boreing holes through the sky we use a non-propulsive attitude control system based on Control Momentum Gyros so as not to disrupt microG ops.
CMGs are similar to reaction wheels but unlike reaction wheels which spin up and down to provide control torques, CMGs spin at a constant speed. The torque come from physically pointing the CMGs in different directions. (If you ever spun a bicycle wheel while standing on a freely rotating platform at a science museum you'll get the idea.)
The ISS has four CMGS:
During a normal orbit we fly a torque equilibrium attitude. The sum of the torques from gravity gradients, aero forces and what the CMGs can provide average 0 over the orbit. As long as the total torque averages 0 and the torque required by from CMGs stays below their maximum the CMGs can hold attitude indefinitely.
Now sometimes the ISS doesn't fly a TEA because we need to dock or perform a reboost. In those cases we use thrusters. While the Russian service module has thruster we normally use the thrusters attached to the Progress resupply vehicle whenever we can. Saves wear on SM thrusters.
Coordinating a maneuver takes a lot of work by Mission Control in Houston and Moscow. On board it takes coordination between the US guidance computer and command computer and the Russian guidance and control computers. Solar arrays have to be safed, window shutters have to be closed, and communications have to be analyzed.
To figure out what altitude the ISS should maintain takes an entire team on the ground to analyze. An active sun can puff up the atmosphere and cause more drag requiring more frequent reboosts so you might want to keep the ISS higher. A heavily loaded resupply vehicle may be coming in 2 months and doesn't have the performance to reach the ISS if it boosts to high.
Here's the ISS altitude for the first 7 years:
It takes a lot of planning to execute a maneuver with the ISS.
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