78
votes
Accepted
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 ...
- 121k
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, ...
- 17.2k
54
votes
Accepted
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 ...
- 2,391
41
votes
Accepted
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 ...
- 178k
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 ...
- 17.2k
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
Accepted
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 ...
- 4,350
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
...
- 23.8k
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 ...
- 149k
29
votes
Accepted
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
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 ...
- 58.5k
28
votes
Accepted
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? ...
- 121k
28
votes
Accepted
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 ...
- 167k
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 ...
- 17.5k
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°...
- 10.6k
23
votes
Accepted
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, ...
- 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 ...
- 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 ...
- 8,627
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
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 ...
- 54.9k
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 ...
- 1,694
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, ...
- 9,976
18
votes
Why won't JWST deploy in LEO where it is potentially serviceable?
The James Webb Space Telescope will not be deployed in Low Earth Orbit because there is too great a risk of the optics being damaged by debris.
[T]he environment around the ISS is not suitable for ...
- 23.8k
18
votes
Accepted
What was the distant bright light in the SpaceX webcast of Orbcomm OG2 deployment?
It was the Moon. It was illuminated at roughly 85-86% as seen from low Earth's orbit at the time of deployment, so pretty bright, and roughly directly overhead of the Americas. Deployment camera was ...
- 76.5k
18
votes
Is it possible to covertly put an EMP weapon into an ISS-like orbit by masquerading it as a legitimate launch?
Classified satellites are launched all the time. For example, fourteen KH-11 espionage satellites were launched between 1976 and 2013, and we still have no idea what they look like. So you can launch ...
- 126k
18
votes
Accepted
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 ...
- 178k
17
votes
Accepted
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 ...
- 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 ...
- 167k
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 ...
Only top scored, non community-wiki answers of a minimum length are eligible