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78 votes
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Shouldn't space junk fall back to Earth on its own? How long will take for a ~1 cm piece of junk in LEO to fall back to Earth on its own for example?

It depends on the altitude. Here is a chart from ESA and UNOOSA. Basically, anything under 500 km will fall relatively quickly, maybe 25 years. Everything under 800 km should fall within a century or ...
PearsonArtPhoto's user avatar
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77 votes
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Why would a box full of 1cm balls released into LEO be so scary to an engineer supporting the ISS?

Well, gee, this question may as well have my name printed directly on it! Spacecraft protection from the orbital debris threat comes in two flavors: Shield and withstand Detect and avoid To start, ...
Tristan's user avatar
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55 votes
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What caused this bright light from the ground at night seen from the ISS?

Well I confirmed via Google Maps that this is Mecca. As shown in the map and image below the roads align with those lighted in the image. The dark areas in the first image are steep hills to the ...
Josh King's user avatar
  • 2,469
41 votes
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Which LEO satellite lost over 30 km of altitude in the geomagnetic storm of 13-14 March 1989?

This appears to be an error that has propagated from paper to paper over the years. Examining the original paper cited by all these other authors, "Effects of the March 1989 Solar Activity" by Allen ...
Organic Marble's user avatar
33 votes
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How is the altitude of a satellite defined, given that the Earth is not spherical?

update: 6378.137 km is what I use now. By convention the altitude of a spacecraft is the distance to the center of the Earth minus roughly 6378 kilometers, or some reference radius that is ...
uhoh's user avatar
  • 149k
32 votes

Why would a box full of 1cm balls released into LEO be so scary to an engineer supporting the ISS?

There's a few pieces of information that are needed to explain why one might be wary of 1 cm objects: Objects as small as 4 inches (about 10 cm) can be seen by radars or optical telescopes on Earth ...
called2voyage's user avatar
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30 votes

Which LEO satellite lost over 30 km of altitude in the geomagnetic storm of 13-14 March 1989?

update: There has been a new analysis of "catastrophic" altitude drops during solar events. The largest drop cited is about 440 meters. NASA Goddard feature: Solar Superstorms of the Past ...
uhoh's user avatar
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29 votes
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What is the name of the area on Earth which can be observed from a satellite?

What is the name of this line or this area? line A term for the line that's perfectly usable for this purpose is "horizon". The horizon, the line line separating the land from the sky, ...
SE - stop firing the good guys's user avatar
28 votes
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SpaceX's 4,425 satellite constellation - what's the method to the madness?

Nodal precession doesn't matter for a plane of satellites like this, they will rotate around in unison, so the coverage will remain the same. Okay. So, why the unusual dual inclination constellation? ...
PearsonArtPhoto's user avatar
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28 votes
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How was Skylab's orbit inclination chosen?

Skylab's science experiments included Earth surface observations, and the higher inclination orbit allowed more surface to be viewed. Per Living and Working In Space: The NASA History of Skylab: The ...
Russell Borogove's user avatar
28 votes

Shouldn't space junk fall back to Earth on its own? How long will take for a ~1 cm piece of junk in LEO to fall back to Earth on its own for example?

Space debris poses a real risk for spacecraft in LEO. From the Technical Report on Space Debris UN Committee on the Peaceful uses of Outer Space (Table 5), a satellite in orbit can expect to collide ...
Woody's user avatar
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26 votes
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How did two satellites end up in almost the same orbit except moving in opposite directions?

How? Simple, because they launched into those orbits. Why? Well, first, let me explain what their orbits actually are. IRAS (13777) and GGSE-4 (2828) are both in high-inclination orbits, 70° and 99°...
Anton Hengst's user avatar
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23 votes
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Was SpaceX's launch of Formosat-5 more vertical than normal for any particular reason?

FORMOSAT-5 was deployed directly to a 720 km circular orbit, with only a single burn. In order to do a circular orbit so high, one has to have a more vertical ascent then would be typical. Basically, ...
PearsonArtPhoto's user avatar
  • 121k
23 votes

What is the name of the area on Earth which can be observed from a satellite?

What is the name of this line or this area? Typically, the part of the earth's surface that a satellite can view at any moment is known as its footprint, a term frequently used for remote sensing ...
Duncan C's user avatar
  • 347
21 votes

Why use a Mars orbital Earth return vehicle for sample return?

Earth Orbit Rendezvous is a method for applying brute force. Mars Orbit Rendezvous actually improves efficiency, potentially by a lot. A Mars sample return (or, for that matter, a straight-up crewed ...
ikrase's user avatar
  • 8,923
21 votes
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Would the reflected sun's radiation melt ice in LEO?

Would the reflected sun's radiation melt ice in LEO? This is an elegant question and an interesting challenge because though very simple to ask requires a lot of real, practical spaceflight ...
uhoh's user avatar
  • 149k
20 votes
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Why are there no LEO satellites in the earth's equatorial plane?

Uhoh touches one side of the problem: "Why" - the lower the orbit, the less of Earth is covered in a single pass, and the closer to equator the orbit, the less do the passes vary further narrowing the ...
SF.'s user avatar
  • 55.1k
20 votes
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Where did Heinlein say "Once you get to Earth orbit, you're halfway to anywhere in the Solar System"?

This phrase was quoted by Jerry Pournelle in an article entitled "Halfway to Anywhere" first published in the Galaxy Magazine in the April 1974 Issue in his column "A Step Farther Out". This article ...
OON's user avatar
  • 1,684
20 votes
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Aborting a de-orbit maneuver

For the shuttle, technically the deorbit burn could be aborted, but the window to do so was extremely limited. Once the deorbit burn was started, one of the key parameters monitored by the crew was ...
Organic Marble's user avatar
20 votes

Payload capacity of a rocket

The short answer is: Tsiolkovsky rocket equation. You need some velocity to achieve some position (an orbit or a body) in space. Farther a position - more velocity. More velocity - more propellant ...
Peter Nazarenko's user avatar
19 votes
Accepted

Can the Right Ascension and Argument of Perigee of a spacecraft's orbit keep varying by themselves with time?

You are correct to a point that the RA of the ascending node and argument of perigee won't change over time without some external force acting upon the satellite. In a simplified gravitational field, ...
Jack's user avatar
  • 9,966
17 votes
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How to get semi-major axis from TLE?

The TLE gives mean motion ($n$) in $\frac{rev}{day}$. This needs to be converted to $\frac{rad}{s}$ which can be accomplished by multiplying the $n$ TLE value by $\frac{2\pi}{86400}$. Therefore, to go ...
amkas90's user avatar
  • 456
17 votes
Accepted

How much fuel is necessary to cause delta-v?

The Tsiolkovsky rocket equation tells you how much delta-V you get for a given exhaust velocity and full/empty mass ratio per stage. Typically you'll want to divide the total 9400m/s requirement into ...
Russell Borogove's user avatar
17 votes

Payload capacity of a rocket

It perhaps become clearer when stating what rockets do. They change velocity. In space terms, that's delta-v. A rocket stage can only change your velocity some limited amount. Different targets in ...
SE - stop firing the good guys's user avatar
17 votes
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How does a satellite's mass affect its fuel consumption to maintain orbit?

If you re-boost them both at the same time interval, then the lighter satellite's orbit will decay more between re-boosts, it will experience more drag because it falls deeper into the atmosphere, and ...
phil1008's user avatar
  • 7,403
16 votes
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Artificial Shooting Stars - how could this possibly work (economically/technologically)?

Now that I have my comment out of the way, I can't envision sending something up to a relatively high LEO would be either effective or efficient. It would make far more sense to do something on a ...
Tristan's user avatar
  • 17.3k
15 votes

What is the extent of on-orbit refueling experience at the ISS? Which fuels? Which spacecraft?

The propulsion system of the Service Module (public relations name: Zvezda), part of the Russian side of the ISS, is refueled by Russian Progress spacecraft, and formerly by European Automated/Ariane ...
Organic Marble's user avatar
15 votes

What does 'a nudge' mean in the context of rocketry?

"Nudge" is not being used here in the rocketry context, but rather in a marketing context. There's no way to throw a rocket from ground level into orbit without making a significant burn ...
Russell Borogove's user avatar
14 votes
Accepted

Is the Starlink array really visible from Earth?

Yes, the Starlink satellites were visible from earth with your naked eye and have been seen and recorded by several people. See also https://vimeo.com/338361997 and read about it here. Gizmodo: ...
DarkDust's user avatar
  • 12.6k
14 votes
Accepted

I'm building a CubeSat for a short 8-day mission in LEO followed by a fairly quick reentry, what range of orbits to consider?

You want a very low altitude, to maximize drag, to make the object deorbit quickly even if you never manage to establish control from the ground. The constraint is that you don't want to go too low, ...
Ryan C's user avatar
  • 8,022

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