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Questions tagged [orbital-mechanics]

Orbital mechanics (also called astrodynamics) is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft on an orbital or escape trajectory. For the movements of celestial bodies, use [celestial-mechanics], not this.

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115 votes
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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 ...
85 votes
7 answers
23k 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 ...
uhoh's user avatar
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73 votes
5 answers
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Why is it easier to escape the solar system than get to Mercury or the Sun?

It has been mentioned several times on this site that it is "easier" (less delta-v, and hence less fuel) to reach the escape velocity of the solar system, than to reach the planet Mercury or ...
DrSheldon's user avatar
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61 votes
6 answers
11k views

When was Newton "not good enough" for spaceflight; first use and first absolute requirement for relativistic corrections?

Concepts in Special Relativity (1905) and of General relativity (first developed between 1907 and 1915) substantially predated spaceflight; they were well known and had been tested well before objects ...
uhoh's user avatar
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51 votes
6 answers
16k views

Is it possible for a moon to have a higher surface gravity than the planet it is attached to?

Is it possible that a moon has a higher surface gravity than its planet? I guess it would mean that the moon has a higher mass, but then it would be the planet gravitating around the moon and the ...
Lucile Bellamy's user avatar
51 votes
10 answers
13k views

Game for teaching basics of orbital mechanics

I am looking for a game that would be suitable for teaching basic orbital mechanics concepts to primary school students (grades 6-8). Contrary to most of the questions here asking about spaceflight ...
ben's user avatar
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51 votes
7 answers
9k views

Can you tack against the sun using a solar sail?

Solar sails are a great, inexpensive way to move out from the sun, if you’re not in a hurry. Ocean going ships are able to tack against the wind, and to move up wind. Could a solar sail gain inbound (...
James Jenkins's user avatar
48 votes
1 answer
38k views

How often does ISS require re-boosting to higher orbit?

I know that ISS, being in low Earth orbit, requires regular boosts. But I can't seem to find information on how often does this happen. Is it done during each resupply mission, only during some of ...
Viniter's user avatar
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46 votes
7 answers
10k views

Why did Saturn V not head straight to the moon?

This may seem a naive question, but as I understand it one of the reasons for the enormous energy expended by rockets is the extremely high speed (around 28,000kph) you need to achieve a stable orbit ...
Party Ark's user avatar
  • 549
45 votes
3 answers
44k views

How realistic is Kerbal Space Program?

Kerbal Space Program is an independent spaceflight simulation game, which has become quickly popular due to being (kind of) precise at simulating actual spaceflights. But how precisely? How close is ...
Zoltán Schmidt's user avatar
45 votes
2 answers
5k views

Without the accident, would Apollo 13 still have been the farthest crewed mission from the Earth?

This answer notes that the Apollo 13 crew holds the record for the distance that humans have traveled beyond Earth. Had the mission exactly followed the flight plan, would they still have been the ...
DrSheldon's user avatar
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44 votes
10 answers
29k views

Which is closer to Mars, Earth or the Moon?

Which is closer to Mars, Earth or the Moon? I'm writing a novel and I'm so grateful for the wealth of information. The only answers I find refer to Phobos and Demos Mars moons.
T. Constantine's user avatar
40 votes
6 answers
20k views

Does a satellite naturally turn in phase with its orbit, always facing Earth?

Assume you want a satellite to constantly point its radio dish towards Earth while orbiting it, or its solar panels towards the Sun if it is instead orbiting it. Is any of the following true about ...
LocalFluff's user avatar
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39 votes
4 answers
7k views

What uses would the Aldrin-Cycler have?

An Aldrin-Cycler is a vessel on an orbit on which it passes both Earth and Mars every few years without expending much fuel. At first glance this seems like a great thing for a permanent ...
Philipp's user avatar
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39 votes
1 answer
7k views

Does it require less energy to reach the Sun from Pluto's orbit than from Earth's orbit?

Somewhat inspired by this question and its answers, does it require less delta-v for an object to fall into the Sun the further away it is from the Sun? It makes sense that an object has to shed its ...
TipTap's user avatar
  • 533
38 votes
5 answers
7k views

Did Sputnik 1 tell us more than "beep"? What science was improved by information gained from its orbiting the Earth?

Sputnik 1 was the first artificial satellite launched by humans to orbit the Earth. This answer begins: Sputnik had just one single job: Prove its existence by sending a simple "beep" ...
uhoh's user avatar
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38 votes
5 answers
5k views

How did theorists determine that the atmosphere attenuates enough to support unpowered orbits?

Before getting rockets into space were scientists certain that the density of the earth's atmosphere would decrease with height enough to permit low earth orbits? If so how was that determined? (If ...
Lysander's user avatar
  • 497
38 votes
3 answers
10k views

Why should the James Webb Space telescope stay in the unstable L2?

We all know that James Webb Space telescope is planned to be launched in 2018. It has been decided that the orbit of JWST will be elliptical around the Lagrange point L2, which has been declared as ...
Waffle's Crazy Peanut's user avatar
37 votes
3 answers
6k views

Is the "airship to orbit" mission profile feasible?

By one of those weird coincidences, I had been on JP Aerospace's site mere hours before reading this question about space dirigibles here. Their mission plan seems too good to be true. They are ...
Jerard Puckett's user avatar
36 votes
5 answers
10k views

The dreaded apocalyptic asteroid approaches Earth but lands safely on the Moon at zero relative velocity

An asteroid approaches and the Moon 'catches' it in the same way that a sports player catches a ball - that is to say by matching the velocity of the hand to that of the ball. Could a lucky slingshot ...
chasly - supports Monica's user avatar
36 votes
3 answers
54k views

How to programmatically calculate orbital elements using position/velocity vectors?

I would like to build some orbital mechanical software from scratch. I feel that this would be a great way to learn the steps required to calculate different Kepler orbital elements of an object, plot ...
Stu's user avatar
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35 votes
6 answers
8k views

Why should space probes have to orbit the Earth before being launched at other planets?

I'm curious to know why any satellites that need to be sent to other planets should be moving around the Earth rather than directly going towards their destination? Today, India launched one satellite ...
SpringLearner's user avatar
34 votes
3 answers
21k views

How did the Lunar Module dock with the rest of Apollo 11 and what is the "CSM"?

I'd like to ask if anyone can, in layman's terms, describe the procedure by which the Apollo 11 astronauts were able to get back to their ship? I ask because the most accessible literature on this ...
Rob Truxal's user avatar
33 votes
7 answers
10k views

Is there any reason why a spacecraft would not be able to turn around without a gravity assist?

Let's say you have a spaceship on its way to Mars; halfway there you decide you need to come back to Earth instead. Is there any reason a spacecraft would be unable to do this? Let's assume it began ...
Rick Austinson's user avatar
33 votes
3 answers
17k views

Is there a lot of space trash at the Earth-Moon Lagrange points?

Lagrange points are the points in a multi-body gravitational system in which the gravitational force and centrifugal force sum to zero. The image below from this Wikipedia article shows the 5 ...
Chris Mueller's user avatar
33 votes
2 answers
5k views

Why does this plot show Starman's speed relative to the Sun fluctuating so often?

After the launch of Starman, during the inaugural flight of SpaceX's heavy lift vehicle, the Falcon Heavy, PearsonArtPhoto set up a website to track various stats about Starman and his Roadster. A ...
Edlothiad's user avatar
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33 votes
3 answers
3k views

Could a partial space elevator be practical and useful?

Would it be technologically and economically practical to build and operate a space elevator that only provided transport between lower and higher orbital paths? Such a mechanism would only avoid some ...
Paul A. Clayton's user avatar
32 votes
3 answers
33k views

Determining orbital position at a future point in time

This might come of as a millionth-time award winner beginner question, but since I'm not familiar with either correct terms or designations, I'll put this question in my own language, since I'm not ...
Henrik's user avatar
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31 votes
5 answers
10k views

How could an object barely exceeding escape velocity from the Moon eventually reach the Earth?

Since NASA is once again targetting low-cost missions to the Moon, I was thinking about low-cost methods of getting stuff from the Moon back to Earth. Although it seems reasonable to assume that ...
user avatar
31 votes
5 answers
6k views

Do any launches bypass LEO?

If sending a payload to GEO (geosynchronous orbit) or any other high orbit, you could start off launching to LEO (low Earth orbit), and then use a Hohmann transfer to raise the height of the orbit. I ...
AlanSE's user avatar
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31 votes
3 answers
5k views

Orbiting Earth before heading to Moon

Each of the lunar Apollo missions (Apollo 8-17) entered Earth orbit immediately after launch. Each mission then left Earth after a few orbits by burning the S-IVB engine, and headed off to the Moon. (...
Sam Hallerman's user avatar
30 votes
8 answers
23k views

Why is geosynchronous orbit an altitude, rather than a velocity?

When people talk about geosynchronous orbit--an orbit in which the satellite continuously remains "directly overhead" for the same ground position on Earth--they talk about it being at a specific ...
Mason Wheeler's user avatar
30 votes
3 answers
6k views

Why is delta-v the most useful quantity for planning space travel?

Many of the questions and answers on this site make use of the concept of delta-v. Is there an easy to understand the reason why delta-v, the magnitude of the change of the velocity, $|\mathbf{v}|$, ...
WaterMolecule's user avatar
29 votes
3 answers
6k views

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 ...
SF.'s user avatar
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29 votes
4 answers
12k views

How is the altitude of a satellite defined, given that the Earth is not spherical?

The altitude of a satellite is the distance between the Earth's surface and the satellite, but the Earth itself is not spherical. At the equator the Earth's radius is 21 km more than at the poles, and ...
Sumit Agrawal's user avatar
29 votes
2 answers
14k views

How long does a CubeSat last?

If I were to launch a CubeSat, how long would it last before falling out of orbit and burning up in the atmosphere?
berry120's user avatar
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28 votes
7 answers
4k views

The Martian: Does it really take a supercomputer to calculate spaceflight maneuvers?

My preemptive apologies for asking a question about a movie, and the spoilers within said question, but considering the widespread support for its scientific plausibility, I'm hoping you'll let it ...
TheEnvironmentalist's user avatar
28 votes
4 answers
12k views

Could the sun be used as a gravity assist outside the solar system (with current tech)?

I think I might have understood what this XKCD comic is trying to do. The diagram is proposing to use the Oberth effect at closest approach to the sun to escape the solar system! (image license: CC ...
AlanSE's user avatar
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28 votes
1 answer
51k views

How many active or inactive artificial satellites are in Mars orbit?

I just read in the BBC news that four nations have placed satellites in Mars orbit. How many active or inactive artificial satellites are there in orbit around Mars (2014)?
James Jenkins's user avatar
27 votes
3 answers
3k views

Why is the ribbon of decommissioned geosynchronous satellites skewed?

I was looking at this 3D map of satellites orbiting earth and noticed something interesting. Around the green ring of active geosynchronous satellites, there is a ribbon of what I assume are obsolete ...
EagleV_Attnam's user avatar
27 votes
3 answers
4k views

Is it possible to have an orbit around the earth and the moon

I was just wondering if it were possible to A) Orbit the moon and earth B) To orbit any two celestial bodies really?
Josh R's user avatar
  • 373
27 votes
2 answers
4k views

Why was InSight planned to launch from Vandenberg?

Why does the InSight Mars lander mission intend to launch from Vandenberg, which does not allow for prograde launches? Will it launch into polar or retrograde orbit? Why? It will do an interplanetary ...
Hans's user avatar
  • 3,372
27 votes
2 answers
11k views

How complex was the math and physics necessary to place Apollo 11 on the moon?

Specifically, I'm interested in how closely the models used to calculate the various burns and course corrections represented reality. Was standard Newtonian mechanics sufficient or were relativistic ...
Sam Anderson's user avatar
27 votes
1 answer
4k views

SpaceX's 4,425 satellite constellation - what's the method to the madness?

The BBC article SpaceX aims to launch internet from space discusses the SpaceX proposal for a dense array of over 4,000 LEO satellites for global internet coverage, and links to SpaceX non-...
uhoh's user avatar
  • 149k
26 votes
7 answers
12k views

Could we wait for Mars to come to us?

This may be a stupid question but I didn't find much information online about it. The concept is simple, could we launch a vehicle into space from Earth, stop right on Mars trajectory and wait for the ...
Wyglaf's user avatar
  • 405
26 votes
6 answers
15k views

Why does the ISS track appear to be sinusoidal?

Okay, time for a stupid question, but it keeps me up at night trying to figure it out. The ISS 'route' appears on paper as such: I am imagining it has to do with a combination of its orbit and the ...
Mikey's user avatar
  • 2,911
26 votes
4 answers
7k views

How many petaflops does it take to land on the moon? What does Artemis need with an Aitken?

All of the top five answers to The Martian: Does it really take a supercomputer to calculate spaceflight maneuvers? are essentially "no, orbital mechanics isn't rocket science". Okay I have ...
uhoh's user avatar
  • 149k
26 votes
4 answers
11k views

Does the International Space Station get TV?

For obvious reasons the ISS cannot get cable TV. Can the ISS get the new digital air TV or satellite TV using an issued dish and receiver like a house? How would that be done compared to how it is ...
Muze's user avatar
  • 1
26 votes
3 answers
6k views

What is the "mass" of a Lagrange point?

Of the five Lagrange points, L4 and L5, as stable points, can be orbited by asteroids, satellites, and any other useful or interesting object. Assuming two-body motion however, calculating orbits with ...
TheEnvironmentalist's user avatar
26 votes
2 answers
4k views

How do we ensure an orbit of a satellite doesn’t interfere with existing ones?

How do we ensure a new orbit/route of a LEO satellite or even a swarm of LEO satellites doesn’t collide with currently existing ones when planning a mission? I’ve thought about running a simulation ...
Andy Tso's user avatar
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