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98 votes

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

Given a pair of objects that are gravitationally bound to each other, they will orbit around their common barycenter (center of mass of the system). The object to be most logically deemed the moon ...
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98 votes

Does it make any scientific sense that a comet coming to crush Earth would appear "sideways" from a telescope and on the sky (from Earth)?

The comet's tail always points away from the Sun. Yes, even when the comet is heading back into the outer solar system. This is because the tail isn't a 'trail' of where the comet has been, like a ...
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81 votes
Accepted

Why don't the Space Shuttle's tires explode in the vacuum of space?

Standard atmospheric pressure at sea-level Earth is just 14.696 psi. Compare that to 340 or 300 psi (23.14 and 20.42 amt, respectively). The difference in internal tire pressure in Earth's atmosphere ...
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74 votes

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

Gravity isn't just about mass, but about distance, too. Our moon has a surface gravity of about 1/6th of Earth, because it is small and less dense than the Earth is. Surface gravity of a body is ...
60 votes

Could a spacecraft spin so fast that it spontaneously deconstructs?

Did it really happen? Yes. The investigation of Japanese Hitomi spacecraft's failure found that it was spinning too fast due to attitude control error. As a result, the spacecraft spun so fast that ...
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59 votes
Accepted

Could a spacecraft spin so fast that it spontaneously deconstructs?

To parallel @Heopps answer: Did it really happen? Yes. In spectacular fashion! In 1965 NASA launched a boilerplate Apollo command module on a Little Joe II rocket to test the Launch Escape System (...
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56 votes
Accepted

If an astronaut threw a cup of coffee into space, would it freeze, or boil off into gas?

This was tested nearly sixty years ago. Using a very large cup filled with 95 tons of water. An empty second stage of a Saturn I under test was used. Only the first stage should be tested but with ...
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54 votes
Accepted

Could a space colony 1g from the sun work?

Interesting but no, it wouldn't work for the same reason that astronauts in the International Space Station, other space stations, or orbiting shuttles or capsules do not "feel" gravity with respect ...
  • 148k
46 votes
Accepted

Do you need 0 km/s velocity to crash into the sun?

Wouldn't i inevitably spiral to sun surface even if i was faster than 0km/s ? No. On reasonable timescales, an orbit will have a fixed distance of closest approach, called "periapsis." (These ...
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45 votes
Accepted

Why can solid rockets be both the skinniest and most spherical launch vehicles while liquid fuel rockets have a more limited range of aspect ratios?

The squat end of the spectrum has little to do with solids versus liquids and everything to do with aerodynamics. Spherical tankage is most weight-efficient, so you'd expect squat stages in cases ...
44 votes
Accepted

If I drop a feather from orbit, would it burn up or "hit" the ground?

Throwing it down at 5 m/s will do basically nothing. That will simply cause it to advance in its orbit a bit. To deorbit, you need to throw it backwards, not down. However in this case, since the ...
44 votes
Accepted

Can/should you swim in zero G?

Two major problems present themselves right away. As the human body is almost neutrally bouyant with water, one might think that there are no issues with the actual movement in water. But this is only ...
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40 votes
Accepted

Could a complex system of reaction wheels be used to propel a spacecraft?

Previously posted comments are correct: in free space (assumed free of any other bodies' gravity fields) there is no way to convert the reaction wheels' angular motion to translational motion. There ...
  • 18.1k
40 votes

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

As far as I know, there has not been a space mission that would have been impossible without a theory of relativistic physics. It is true that the relativistic effects are clearly visible in GPS ...
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39 votes

Is Quantum Entanglement technology possible for interplanetary communication in future to achieve low real-time latency?

He replied that we actually received the signals in just 1-2 seconds with the help of MarCO CubeSats. Later on followed up with confusion from other users with his statement and asked for ...
36 votes
Accepted

Would a grinding machine be a simple and workable propulsion system for an interplanetary spacecraft?

The main engineering challenge in implementing your proposal is that in order to be competitive with a chemical rocket engine, the grinding wheel must rotate at an extremely high velocity. A typical ...
  • 476
36 votes

What is the "pendulum rocket fallacy" as it relates to analogizing a pencil balanced on a finger to maintaining attitude of a hovering rocket?

The pendulum fallacy is the belief that rockets would be passively stable with engines at the top, with the rocket "hanging" from them. The error lies in expecting gravity to pull the body ...
34 votes

When burns are made during inefficient parts of the orbit, where does the lost energy go?

After writing my comments, I started writing a new answer. That got long, so here's a shorter one. The "energy of an orbit" may be poorly defined and depending on the definition, is not ...
  • 10.2k
31 votes

If an astronaut threw a cup of coffee into space, would it freeze, or boil off into gas?

It would not freeze into a block. It would quickly expand and boil, but not in a rolling boil. Without pressure, bubbles would form throughout the coffee and expand rapidly, causing it to spray out of ...
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30 votes
Accepted

Teleporting an object into geosynchronous orbit

I'm afraid you are incorrect. An object on the equator of Earth has a velocity of ~460 m/s. A satellite in geosynchronous orbit has a velocity of ~3000 m/s. You may be confused by the fact that both ...
29 votes
Accepted

How best to maneuver inside a large room within a space station using only arm and leg motion?

It turns out that yes, there are things you can do, but they depend on things other than the astronaut's body, and they will take a long time. Physics tells us that an object's translational momentum ...
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28 votes
Accepted

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

Was standard Newtonian mechanics sufficient or were relativistic effects included? Relativistic effects didn't have to be modeled; other sources of error would have swamped the effects of relativity,...
28 votes

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

Yes, it is possible. As James K observed in a comment, the surface gravity of Uranus is slightly less than that of Earth, but its mass is 14 times larger. If Earth were orbiting Uranus, it would be a ...
  • 7,804
27 votes
Accepted

Why do some meteors explode in air?

The Chelyabinsk meteor was travelling at over 65,000 km/h when it hit the brunt of the atmosphere 23 km high in the air. This is 60 times the speed on sound! NASA estimates that the meteor's mass at ...
26 votes
Accepted

Is Quantum Entanglement technology possible for interplanetary communication in future to achieve low real-time latency?

Apparently not: I like this Quora answer. Here's part of it, the rest is worth reading as well: No experiment conducted using entangled photons has ever demonstrated faster than light communication! ...
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25 votes
Accepted

What would be necessary in order for us to achieve a single stage to orbit, reusable rocket?

I am referring to rockets capable of taking supplies and humans to other planets. For an interplanetary single-stage rocket with tens to hundreds of tons of payload capability, no existing propulsion ...
25 votes

How best to maneuver inside a large room within a space station using only arm and leg motion?

Fortunately, it turns out humans come with a nitrogen/CO₂ thruster built in... Assuming the room is filled with air, I reckon the best method is to use your breath. What you should do is, point your ...
24 votes
Accepted

Why don't we use catapults to get to space?

I'm leaning toward option 2, that you "have something terribly wrong in [your] thought process". Here's at least some arguments why; I by no means claim this to be an exhaustive list: Mach 3 (which ...
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