All Questions
7,144
questions
47
votes
8
answers
13k
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What would be the (most difficult) challenge to make a 10,000 year satellite?
Update: Bezos' recent Tweeted update on the 10,000 year clock. Also see The Verge's Construction begins on Jeff Bezos’ $42 million 10,000-year clock
The discussions associated with the question Can ...
- 149k
36
votes
9
answers
14k
views
Why do rocket nozzles flare?
Why do rocket nozzles open wider at the end than, let's say, get narrower?
Let me explain:
A jet engine works by having this amazing thing called a combustion chamber. The combustion chamber ignites ...
- 817
35
votes
3
answers
39k
views
How much power would a spacecraft's magnetic shield require?
I've read over the decades that a magnetic shield might protect a spacecraft from cosmic radiation. Its a fascinating idea that might only be theory or science fiction at the moment. In regards to ...
- 879
20
votes
6
answers
13k
views
What artificial satellite has the farthest orbit around the Earth?
What is the furthest Earth orbiting satellite?
What is its speed and purpose?
- 1
18
votes
3
answers
2k
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How much can the Mars rover Curiosity do autonomously, after four years of operation?
I was under the impression (when asking this question) that over the past four years that experience by ground operators and programmers had lead to a configuration where the Mars rover Curiosity ...
- 149k
11
votes
2
answers
3k
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Why would sub-cooled LOX tanks need to "topped-off" until the last minute or so?
Here is my understanding, let me know if I've got it right or wrong:
Until recently, most cryogenic propellants were at or close to their boiling points. Each unit of heat leaking into the tank would ...
- 149k
10
votes
2
answers
1k
views
If not constrained by underpasses, etc., would Falcon 9 have been less of a flying noodle?
This excellent answer to the question Why is Falcon 9's shape so tall and skinny? mentions California, Florida, Texas and Alabama, within and between-which there must be at least a few limiting ...
- 149k
9
votes
1
answer
1k
views
Have there been any documented mini-moons since 2006 RH120?
The conference call with Bill Bottke (MP3 plus other documents) about "minimoons" presents an alternative to Asteroid Redirect first got me interested in orbital mechanics. The idea is that there are ...
- 149k
9
votes
1
answer
1k
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How does Curiosity know how to point and move it's high gain antenna in real time?
The Curiosity rover has a compact X-band high-gain antenna (HGA) that allows for low data rate communication directly with Earth, but is used though for higher data rates it usually uses UHF to ...
- 149k
7
votes
2
answers
1k
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Would it be possible to build a probe that could operate at about 480 °C (900F degrees) without insulation?
I read a question about cooling a Venus lander, and got to thinking that the problem was in building a probe that has no problem with Earthlike temperatures and pressures, then trying to insulate it ...
- 431
5
votes
2
answers
1k
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How can the two MarCO cubesats remain reliably close to InSight during their six month trip to Mars?
According to the NASA JPL web page Mars Cube One (MarCO) Mission Overview and the YouTube video MarCO: First Interplanetary CubeSat Mission linked there, after the Centaur upper stage deploys InSight, ...
- 149k
5
votes
1
answer
4k
views
Delta-V of Starlink Satellites
The recently launched Starlink satellites are designed to use their HAL Ion thrusters to seek their own independent orbits, evade collisions, and de-orbit at the end of their lives. That's a lot of ...
- 4,894
2
votes
0
answers
411
views
Did DSCOVR travel "along the stable manifold of its future SE L1 Halo orbit" to get there?
I just wrote (and have since removed) the following paragraph in this answer to How many times do you have to circle the Earth to break orbit?:
As can be heard in this video SpaceX's launch of the ...
- 149k
85
votes
7
answers
24k
views
What can the KSP game actually teach about spaceflight and orbital mechanics, and what are its limitations?
I have seen at least several different users mention that they've found Kerbal Space Program helpful to understand issues of spaceflight and orbital mechanics.
According to Wikipedia:
While the game ...
- 149k
39
votes
5
answers
13k
views
Why aren't all satellite-carrying rockets launched from airplanes?
There are several significant advantages to air launching a satellite-carrying rocket:
save fuel/propellant as a horizontal take-off is more energy efficient
fully mobile platform allowing the launch ...
32
votes
2
answers
18k
views
Will the ISS need more docking ports?
Currently the ISS has two basic segments, the Russian and US sides.
The Russian side has 4 docking ports. Usually occupied by 2 Soyuz, 1 or 2 Progress freighters or an ESA ATV vehicle.
You can see ...
- 79.6k
25
votes
4
answers
7k
views
How does the Falcon 9 know where the landing barge/pad is?
The descending Falcon 9 has got to hit (preferably gently) the tiny target of the Autonomous Spaceport Drone Ship (ASDS) in the middle of the ocean. How does the Falcon 9 know where the ASDS is?
...
- 7,119
22
votes
2
answers
1k
views
How far up have satellites used a GNSS for positioning, and how does the precision degrade with altitude?
GNSS satellites (at least GPS ones) are in Medium Earth Orbit (MEO). LEO satellites can use GNSS for positioning. Is this still possible for satellites in elliptical, such as Molniya, orbits? For ...
- 11.6k
18
votes
3
answers
2k
views
What's the largest aperture telescope sent beyond the Earth-Moon system?
The question and answer about telescopes sent to different planets got me wondering. There are so many solar system bodies that have been photographed by deep space spacecraft, planets, dwarf planet(s?...
- 149k
11
votes
2
answers
2k
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Do antennae on the ISS have to constantly move to maintain data links?
In this question and answer pair I see that the ISS can maintain data links to earth through direct access to ground stations as well as through the TDRSS geostationary satellite network.
What kind ...
- 149k
10
votes
6
answers
1k
views
Hijacked space data, notable instances of recovering images or other goodies from someone else's space mission?
These are images taken by a Chinese cubesat in lunar orbit, taken again by a Dutch radio telescope.
The original of this GIF was tweeted here and I've reconstructed it because I don't know how to ...
- 149k
9
votes
3
answers
2k
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Getting state vectors from JPL Horizons ephemerides
I'm simulating the Sun-Earth-Moon system by numerical integration of equation of motion.
I've confused a little bit in JPL Horizons ephemerides.
Could anyone explain (if possible, on pictures), how ...
8
votes
0
answers
3k
views
For the mathematical relationship between J2 (km^5/s^2) and dimensionless J2 - which one is derived from the other?
The term $J_2$ seen in discussions of nodal precession of orbits (e.g. sun-synchronous) appears to come in two flavors. For example, in the Wikipedia article Geopotential model it has a value of $1....
- 149k
5
votes
3
answers
832
views
Are there terms for Earth orbits with rational number multiples of 1 sidereal day?
An Earth orbit with a period of 1 sidereal day (and zero inclination) is a geosynchronous orbit, orbits slightly above and below that are supersynchronous and subsynchronous orbits, and a Molniya ...
- 149k
-6
votes
2
answers
983
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What regulations, agreements, or other forces can help mitigate "PrankSats"? [closed]
comment: I've used a somewhat innocuous abstraction of 'pranks in space' below, but there's no end to the trouble that could be caused and the increasing ease with which a state (nation or otherwise) ...
- 149k
53
votes
2
answers
20k
views
Why is gold used in space technology to protect from heat radiation?
AFAIK, NASA and others are using mainly gold to protect surfaces from heat radiation.
But, as we can see with our own eyes, chrome or silver had probably a much better albedo, because they are white, ...
- 3,288
35
votes
7
answers
12k
views
Why didn't NASA use the shuttle to make a profit?
My understanding is the shuttle was designed as cost-effective workhorse, a space-van to ferry cargo up to the ISS, conduct zero-G experiments and put satellites into orbit.
So why didn't NASA take ...
- 453
32
votes
4
answers
7k
views
Is it possible to track an object as small as the Tesla Roadster around the Solar System
I have heard that we will soon lose track of the Tesla Roadster launched with the Falcon Heavy test launch. Yet, we know where Voyager is out beyond the Solar System and we followed other satellites ...
- 3,551
31
votes
4
answers
10k
views
How small could an orbital rocket be?
To what extent might a booster designed to place an extremely light weight "micro" satellite with radio transmitter, say 100 grams for the sake of argument, be scaled down before factors such as ...
- 341
27
votes
3
answers
2k
views
If I wanted to reconstruct an entire Apollo mission's crewed spacecraft trajectories, what are the key sources of historical data I'd look for?
The last few images in Robert A. Braeunig's Apollo 11's Translunar Trajectory;
and how they avoided the heart of the radiation belts are fascinating and a bit perplexing as discussed in this answer ...
- 149k
21
votes
3
answers
25k
views
Puncturing space suit during EVA. What would happen?
What would happen, if the space suit of a spacewalking crew was punctured during the extravehicular activity (EVA)? What are the chances of this happening? Has this already happened to anyone in the ...
- 351
21
votes
2
answers
4k
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Curiosity is still dirty! How will the ExoMARS Rover keep its solar panels dust-free and collecting sufficient power?
update:
Current events makes this question even more poignant
sols 5183 to 5189, Aug. 23, 2018 - Aug. 29, 2018: Team Continues to Listen for Opportunity
Curiosity selfie has been released just a few ...
- 149k
17
votes
2
answers
6k
views
WHY did Rosetta have to go into hibernation for 2.5 years?
It seems the Rosetta spacecraft was put (put itself) into hibernation 08-June-2011. It spun itself up to stabilize its attitude, then shut down navigation, attitude control, communication systems as ...
- 149k
16
votes
1
answer
5k
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What are the sources of light at L2? How will the James Webb telescope be powered?
The James Webb space telescope will be positioned very close to L2. According to JPL, Webb will have a large solar-array to power itself. I don't understand how this works, since L2 is positioned "...
- 263
14
votes
1
answer
1k
views
Flying fuel tanks! Which deep-space spacecraft had the largest fuel mass fraction?
The Los Angeles Times' Deborah Netburn just wrote a really nice retrospective; ‘OK. Let’s do it!’ An oral history of how NASA’s Cassini mission to Saturn came to be with plenty of photos and quotes ...
- 149k
12
votes
4
answers
893
views
Why was the 100m Green Bank dish needed together with DSN's 70m Goldstone dish to detect Chandrayaan-1 in lunar orbit?
The Phys.org article New NASA radar technique finds lost lunar spacecraft describes the use of radar to relocate two spacecraft that were in orbit around the moon but who's orbit had not been actively ...
- 149k
11
votes
4
answers
2k
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Are large halo orbits around L₁'s and L₂'s preferred over small orbits for reasons other than geometry?
There have been many examples of the placement of satellites in orbits around Lagrange points, most have been sun-earth and earth-moon $L_1$ and $L_2$ due to their proximity to earth. In each case ...
- 149k
10
votes
1
answer
1k
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How are the orientations of the ISS' eight independent solar arrays optimized?
I've noticed that in various photos and videos the orientation of the ISS' eight independent solar arrays are often moving, and usually some are different than others.
0th-order naive thinking would ...
- 149k
10
votes
1
answer
5k
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What is the cause of the blue light from LH2/LOX rocket engines?
Below are some screen shots from circa June 2016 launch (or re-launch) videos by Blue Origin (video link) and SpaceX (video link). The New Shepard burns $\text{H}_2$/$\text{O}_2$, while the Falcon 9 ...
- 149k
9
votes
2
answers
5k
views
In "spacecraft talk" is nadir just a fancy word for "down"?
Assume the approximation that the Earth is spherically symmetric — without higher order gravitational multipoles, and other effects that might be related to gravity from other bodies or the ...
- 149k
9
votes
2
answers
2k
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If there was a non-rotating skyhook in Earth orbit, what would re-entry be like after dropping from its foot?
I have been looking at a space station that orbits Earth at an altitude of 3500 km above the equator, and has tethers that extend from it downwards to 250 km above the surface, and outwards to 6500 km ...
- 21.4k
8
votes
1
answer
837
views
How many nuclear fission reactors have been launched into space? How many are still there?
I remember p@Hobbes's answer to Which countries have built RTGs and used them in Earth orbit and/or beyond? mentioning that the US has put one nuclear fission reactor in space, and that not much was ...
- 149k
8
votes
2
answers
2k
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What are these very large, square panels on Inmarsat 5?
Question: What are these very large square panels on Inmarsat 5's? They seem to each have an extremely reflective mirror-like flat/smooth tiled-appearing side, and a nearly black side with a lot of ...
- 149k
7
votes
1
answer
633
views
Unravelling Cassini's "ball of yarn" orbit around Saturn, tabulation of propulsive maneuvers?
The cool GIF on the NASA JPL Cassini resources page All Orbits (2004-2017): The Ball of Yarn is quite beautiful to look at, but it also hints at some beautiful engineering and orbital mechanics as ...
- 149k
4
votes
1
answer
966
views
Will JAXA try again to launch TRICOM-1 with the "world's smallest orbital rocket" SS-520-4 again?
From the Spaceflight 101 article Experimental Launch of World’s Smallest Orbital Space Rocket ends in Failure:
SS-520-4 lifted off from the Uchinoura Space Center in Japan’s Kagoshima prefecture at 8:...
- 149k
3
votes
2
answers
2k
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What is the analytical closed-form solution of the two-body problem to verify its numerical integration results?
The purpose is to study the motion of two celestial bodies analytically. What is the closed-form of the two-body problem if I was to solve it analytically without using a numerical approximation ...
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113
votes
13
answers
65k
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What are the choices today for orbital mechanics simulation software?
I used to be familiar with the various choices out there for orbital mechanics simulation software. Alas, those days are gone. What are the choices today, preferably sorted by platform?
This ...
67
votes
8
answers
39k
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Why would SpaceX not use parachutes for the final descent of the first stage?
According to what I've read, SpaceX tried to use parachutes to recover the first stage of the Falcon 9, but it did not survive reentry.
Now they plan to use 2 separate rocket burns to land:
Reentry ...
- 5,223
50
votes
14
answers
27k
views
Why are there no spacecraft rotating for artificial gravity?
Spacecraft rotating to generate artificial gravity through "centrifugal force" are commonplace in science fiction but not in reality. Considering the problems in long missions (among others: bone loss,...
- 945
29
votes
3
answers
7k
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How can I intuitively understand gravity assists?
For example:
How should a spacecraft pass the Moon to reach escape velocity from Earth?
How should it pass Venus for a slingshot towards Jupiter orbit?
Conversely, to descend Venus to Mercury?
Is ...
- 55k