105 votes
Accepted

Can I produce a true 3D orbit?

There are no known orbits of this kind, but they aren't proven to be impossible. You need to have 3 objects in order to have a 3d orbit, and it's known that the general 3-body problem is chaotic and ...
  • 130k
101 votes
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Can you shoot someone with a bullet... from orbit?

Projectile Atmospheric Entry Simulations I put together a bit of code to compute the trajectory of projectiles as they fall through the Earth's atmosphere. I made the following simplifying ...
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84 votes
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Can two adjacent, life-sustaining planets orbit a star such that they are rarely near each other?

You could put both planets in the habitable zone on horseshoe orbits. Janus and Epimetheus orbit Saturn on this type of orbit. From the point of view of one moon, the other follows a horseshoe shape ...
  • 3,369
77 votes
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How fast could earth orbit the sun without its orbit changing?

About 30km/s; that it to say, the velocity cannot change at all if you wish to maintain the same orbit. Every circular orbit is associated with exactly one orbital velocity. Every general elliptical ...
72 votes

Why would it be unfortunate for a day length to vary in a planet; other than that Java API developers need to work a few hours more?

It really bugs them What you've probably misunderstood is what the term "Java developer" actually denotes. Java developers are a small mammal similar to civet cats in Indonesia both in physical ...
  • 8,589
66 votes
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Is it possible to have a planetary system with planets having perfectly synchronized orbits?

Is it possible for such a system to exist? I'm sorry, but no. At least not according to orbital mechanics as currently understood. Kepler's third law of planetary motion is one of the old workhorses ...
  • 28.7k
59 votes

Is space piracy orbitally practical?

Building on Hariz Rizki's answer, your actual space pirate isn't going to be a swarthy, one legged man in a spacesuit with a parrot on his shoulder, but rather a well dressed functionary at the Deimos ...
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57 votes
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Is it possible to orbit inside a gas giant?

It would lose speed due to drag and fall in. If you're thrusting to maintain speed, just fly like a plane and don't try to orbit. The hypersonic speed of orbital velocity would be conspicuous anyway, ...
  • 68.7k
57 votes

How do you non-catastrophically reduce the mass of the Sun by half?

C. Must not create any phenomena that would have devastating consequences on life on the planets (i.e.: no radiation, excessive heat, energy surges) except for the diminishing of the Sun's current ...
53 votes
Accepted

Can two moons have intersecting orbits yet be guaranteed not to collide?

Ok, so you say 'Harmonic Orbits', but actual Space-Talking-Dudes call that 'orbital resonance', and it's the solution to your problem. We've got an example of something ALMOST exactly like what you'...
52 votes
Accepted

Is it physically possible for a planet to have seasons of different lengths?

Yes and no. This NASA page has a good summary of why we have seasons (emphasis mine): It is true that Earth’s orbit is not a perfect circle. It is a bit lop-sided. During part of the year, Earth is ...
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52 votes
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How could a planet have erratic days?

Binary star. If you have two sources of light, you will have 4 options for night and day: double star day, two single star days, and night. These will be predictable but for a complex orbit the ...
  • 288k
50 votes
Accepted

Could two planets follow the same orbit and never "see" each other?

I assumed, based on the limited knowledge I have on the subject, that all star systems have ellipsoidal orbits (the star being in one of the two focal points) just like our own You are right, this is ...
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47 votes
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Is space piracy orbitally practical?

Just because you can see pirates coming, doesn't mean you can stop them I'm going to make some assumptions about how your spaceships work. The average distance from Earth to Mars is 225 million km, ...
  • 84.5k
43 votes
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Can 3 planets rotate around each other like this?

In theory, yes, this is possible. In practice, it would be a rare thing to encounter, just because the laws of nature can be fickle and somewhat unpredictable. I'm going to call the planet your ...
  • 29.5k
41 votes

Can planetary bodies have a second axis of rotation?

I asked this same question, on the physics stack. The answer is that a body can have only one axis of rotation. Below pasted is the link to the question and the answer I picked. https://physics....
  • 288k
39 votes

Is it possible to orbit inside a gas giant?

Like JDługosz wrote, what will cause problems in the scenario you describe isn't so much your orbit as the fact that you are within the gas giant's atmosphere. I'm going to use Jupiter here to have ...
  • 28.7k
39 votes
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How to create an annual celestial event for a world

Two moons are in orbital resonance You can have your two moons be in a m:n orbital resonance, the way that Io and Jupiter are. That way, at some time period $nT$ where $T$ is the orbital period of ...
  • 84.5k
39 votes

How do you non-catastrophically reduce the mass of the Sun by half?

Wormhole [A,C,D,E,F,G] A traversalable wormhole would be an excellent mechanism to remove mass from the sun. A wormhole is consistent with general relativity while avoiding all of the pitfalls of ...
  • 901
38 votes

Is it possible to have a planetary system with planets having perfectly synchronized orbits?

The only way such an arrangement could exist is having external planet being the heaviest and the others each in L1 point of next outer one. Unfortunately such an arrangement is not stable, so it ...
  • 17.1k
37 votes

How big can a moon be where you can physically jump out of its orbit, to its planet?

No. You can't jump from a moon in stable orbit to the planet. This is because the orbital velocity of the satellite is sufficient to keep the satellite in orbit, the jumper starts with that same ...
36 votes
Accepted

Could two planets be tidally locked to each other so close they share their atmosphere?

The Roche Limit alluded to in other answers may not be a barrier to this. Rigid Approximation For two rigid planets of the same mass M and radius R, both held together by the force of gravity, the ...
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36 votes

Can you shoot someone with a bullet... from orbit?

It couldn't be done, no matter how improbably skilled the sniper, because he would lack information required to do the aiming. Regular snipers have to consider more than the direction their firing, ...
  • 31.1k
36 votes
Accepted

Where is the best place to park your damaged spaceship, longterm?

The orbits of larger moons should be stable and mostly clear of hazards. I'd recommend placing your ship at one of their Trojan points. Just pick the one most convenient. Closer to planet, not already ...
36 votes

What do Martians use for months and weeks?

Please remember that time is an arbitrary concept Without any outside influence, the very first basis of time is the "day" consisting of a period of "light" and a period of "no light" that we ...
  • 97.6k
35 votes

Is it physically possible for a planet to have seasons of different lengths?

I'm surprised no one mentioned Sitnikov planets yet. Image found on Wikipedia. There is a very unlikely constellation in which a planet moves along the axis through the centre of gravity of a binary ...
35 votes

Is space piracy orbitally practical?

Lots of people here, including the OP, are worrying over the capabilities and tactics of space pirates, but the question fundamentally deals not with those particulars, but rather the economical and ...
  • 2,874
35 votes

Can two moons have intersecting orbits yet be guaranteed not to collide?

You should have a look at Janus and Epimetheus. They are two moons of Saturn that exchange orbits approximately every four Earth years. This setup is probably not stable for more than a few billion ...
34 votes

Could two planets follow the same orbit and never "see" each other?

Circular orbits are not practically possible From Astronomy.SE, there are a variety of reasons why orbits are not circular. There is relativity, there is planetary flexing with gravity, there is ...
  • 84.5k
34 votes
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How can I launch a projectile to hit something in orbit, using only geological structures and power sources?

It doesn't seem to be possible using "normal" geology. You'd need a supervolcano to attain the required energies, and "piloting" one with the required precision doesn't look doable. You need to score ...
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Only top scored, non community-wiki answers of a minimum length are eligible