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 ...
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  • 119k
74 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? - (Updated)

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, ...
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53 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 ...
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  • 2,211
43 votes
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How often does ISS require re-boosting to higher orbit?

The easiest to see ISS orbital reboosts is by checking Height of the ISS (where with height they mean orbital altitude above mean sea-level) over at Heavens Above. For example, for the last year, this ...
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  • 75.6k
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 ...
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35 votes
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Minimum Orbit Altitude

The answer varies with atmospheric density (due to varying solar activity), with satellite geometry and mass, and with attitude. But for a typical 3U cubesat, the minimum altitude for a circular ...
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35 votes

Why does the ISS rotate exactly once per orbit?

ISS orbits most of its time in what is called a Torque Equilibrium Attitude (TEA). Since gravitational acceleration varies depending on distance from the Earth, non-symmetric objects of any ...
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  • 16.9k
32 votes
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Could the shuttle's SRB alone reach orbit?

No, a quick calculation yields a $\Delta v$ of about 4.6 km/s and you need about 9 km/s to get to low-Earth orbit. You'll lose a lot of that velocity to aerodynamic drag as well as the vertical ...
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  • 4,320
32 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 ...
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  • 148k
31 votes

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

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 ...
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30 votes
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What is the total mass sent into orbit over all history?

Using the links in Erik's answer and comments, I threw this together. ...
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  • 6,553
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 ...
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  • 148k
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, ...
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28 votes

Why won't JWST deploy in LEO where it is potentially serviceable?

JWST is being launched on an Ariane V with a cryogenic upper stage. That upper stage has to be used immediately to launch it on a trajectory to the Sun-Earth L2. The stage operates on batteries, and ...
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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 ...
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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 ...
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  • 6,758
27 votes
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Is it possible to reach space using home-made rocket?

First of all, LEO isn't just reaching 160 km, it's reaching there and moving at a very fast speed. In fact, 160 km would be a really poor orbit, you really need something more like 350 km to get ...
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  • 119k
26 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? ...
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25 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°...
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  • 10.1k
23 votes
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Could the Hubble HST be saved by docking with the ISS?

The altitude difference is minor compared to the plane change. Even 23 degrees of plane change would require a prohibitively large change in velocity 2 * 7.5 km/s * sin(23 degrees / 2) = 3.0 km/s ...
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23 votes
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How does a spacecraft such as Soyuz detect when it's on collision course with an object?

Spacecraft rely on information from earth to avoid space debris, they don't have instruments for scanning and detecting debris. There's a few reasons for this: Power: most spacecraft don't have ...
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  • 18.9k
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, ...
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  • 119k
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 ...
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  • 347
22 votes
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How are EVA's in LEO affected by being at the night side of Earth?

Spacesuit designers and extravehicular activity (EVA) planners would probably prefer if spacewalks only took part in the Earth's shadow. From the spacesuit design perspective, one of the biggest ...
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  • 75.6k
21 votes
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How long will a 500 km altitude satellite spend in Earth - shade per orbit

In this pic the angle $\phi$ is asin(6378/6878) or about 68º. It stays in the shade over 2 * 68º or about 136º. That's about 38% of the period. That's 2145 seconds or about 36 minutes. This is what ...
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  • 15.2k
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 ...
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  • 8,401
20 votes
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How often does the ISS orbit align with the day/night terminator?

The short answer: 2-4 times per year the ISS enters a "full sun" period. Right before this happens, the ISS will line up near the terminator at the beginning and the end of this period. Full answer: ...
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  • 119k
20 votes
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Is the Hubble's orbit larger than that of the moon?

No, Hubble is in low Earth orbit, much lower than the Moon. The shuttle delivered it to orbit, and the Shuttle can't get near the Moon. The image you reference is very similar to one that came from ...
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  • 119k
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 ...
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  • 52.6k
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 ...
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