78
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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 ...
- 120k
76
votes
Accepted
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, ...
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54
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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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 ...
- 76.1k
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 ...
- 172k
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 ...
- 17.1k
33
votes
Accepted
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 ...
- 149k
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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32
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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
...
- 23.9k
30
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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 ...
- 149k
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, ...
28
votes
Accepted
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 ...
- 120k
28
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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 ...
- 58.2k
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? ...
- 120k
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 ...
- 164k
28
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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?
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 ...
- 14.3k
25
votes
Accepted
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°...
- 10.3k
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 ...
- 19.2k
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, ...
- 120k
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 ...
- 347
22
votes
Accepted
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 ...
- 76.1k
21
votes
Accepted
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 ...
- 15.4k
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 ...
- 8,548
21
votes
Accepted
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 ...
- 149k
20
votes
Accepted
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 ...
- 120k
20
votes
Accepted
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 ...
- 54.1k
20
votes
Accepted
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 ...
- 1,704
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 ...
- 1,173
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, ...
- 9,884
18
votes
Accepted
Do astronauts only perform spacewalks while the ISS is on the night side of the Earth?
No. Most International Space Station (ISS) spacewalks last in the order of several hours, often up to 8 hours during more difficult and time-consuming repairs and installations, and some nearly 9 ...
- 76.1k
Only top scored, non community-wiki answers of a minimum length are eligible