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### Tiangong-1 reentry impact place probabilities

Following all the news concerning Tiangong-1, I have seen the following plot made by the Aerospace Corporation where Blue area: null probability of impact Yellow area: high probability of impact ...
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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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### What does “supersonic large amplitude ID maneuver PTI” mean, and what does a tumble motor do?

In this question I linked to a YouTube video of the Ares X-1 launch. You can start listening at 02:00 for the point where these are mentioned: "Supersonic large ...
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### Have spacecraft ever dipped below the Karman line and then safely continued spaceflight?

The item in Science Alert's A Harvard Astrophysicist Says Outer Space Is Actually Closer Than We Think (see also Science; Outer space may have just gotten a bit closer) talks about the recent Acta ...
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### 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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### Why are deorbited satellites allowed a slow orbit decay instead of burning them up rapidly?

In "What are the conditions for re-entry of an object in a (highly) elliptical orbit?" Eerie asks about orbital mechanics of orbital decay of decommissioned satellite: starting with extremely ...
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### How do I calculate re-entry velocity when decaying from a circular orbit?

I am trying to find the velocity of an object during re-entry so that I can calculate the peak heat flux but I'm a bit stuck. I know how to find the velocity of the original, circular orbit (300km) ...
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### North Korean objects 41332 and 41333; how fast are they losing altitude?

I cited objects 41332 and 41333 launched in early 2016 as counterexamples to this answer on my highly down voted and closed but otherwise "perfect" question What regulations, agreements, or other ...
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### PSLV-C39/IRNSS-1H TLE accuracy

The TLEs accuracy for PSLV-C39/IRNSS-1H seems low when compared to that of the other LEO satellites (ISS, HST, Tiangong, Sfera 2, ...). Look, for example, at the following graph that shows the radius ...
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### How did Venus Express' periapsis decay so quickly?

ESA's Venus Express ran out of propellant in late 2014 and has probably decayed out of orbit since then. A timeline of events from my research for my answer to Are there currently any spacecraft in ...
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1 vote