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### Why do we not fly to space with helicopters? What are the practical altitude limits?

People will tell that there is no air, and this is why we cannot. But if I read on the internet, there is air in space, much less, but still something. For example: 100 km: $6\ \cdot 10^{-7}$ times ...
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### How often does ISS require re-boosting to higher orbit?

I know that ISS, being in low Earth orbit, requires regular boosts. But I can't seem to find information on how often does this happen. Is it done during each resupply mission, only during some of ...
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### What is the density of the earth's atmosphere at an altitude of four hundred kilometers?

What is the density of the earth's atmosphere at an altitude of four hundred kilometers? I want to use it to calculate the drag on something in orbit near the ISS. The Jacchia Reference Atmosphere is ...
18k views

### Does the orbit of the ISS decay?

Does the orbit of the ISS decay? I don't know much about the ISS, but I heard some rumors. The rumor I heard was that there is a very, very tiny atmosphere at the ISS orbit.
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### What is the ISS drag?

ISS constantly loses altitude to air drag and other forces (tidal, electromagnetic). While finding that rate in the sources isn't that hard, with orbital mechanics of altitude loss actually increasing ...
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### Why do malfunctioning satellites come back to Earth?

In school, I learned that if a satellite moves at a speed $\sqrt{gR}$ (the square root of the product of the acceleration due to gravity and radius of the Earth), then it will remain in Earth's orbit. ...
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### How strong and "hot" is the wind on the payload after the fairing is deployed at ~110km?

In the question What makes 21st century fairings so valuable that they'd potentially be recovered and re-used? I said: 21st century fairings are much more than passive rooftop boxes to "keep the ...
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### Why does Earth's atmospheric density have a big "knee" around 100 km? Is there a good analytical approximation?

I've used a quick very rough approximation of the drop of atmospheric density with altitude in this answer and in this answer by using a single exponential and scale height parameter, but that's not ...
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824 views

### How much fuel to maintain VLEO for communication satelites?

A recent answer about communication satellites in VLEO (≤350 km) estimates a useful orbital life of about month without fuel. I.e. Once the vehicle is out of fuel to maintain orbit, THEN it has the ...
1k views

### What is the lowest altitude that an ion thruster can be used for station keeping?

What is the lowest altitude that an ion thruster can realistically be used for station keeping before its small amount of thrust is overcome by atmospheric drag? Please state your assumptions such as ...
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437 views

### Could Vostok 1 deorbit on its cold gas thrusters?

Citing the Wikipedia article: The orbit's perigee and apogee had been selected to cause reentry due to orbital decay within 10 days (the limit of the life support system function) in the event of ...
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