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 ...
- 17.6k
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 ...
- 6,511
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 ...
- 8,188
63
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 ...
- 9,121
60
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 (...
- 18.4k
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 ...
- 49.5k
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 ...
- 151k
47
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 ...
- 15.4k
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 ...
- 172k
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 ...
- 2,486
41
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 ...
- 3,328
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 ...
- 18.4k
39
votes
Accepted
Person falling from space
Your question is under-specified (you don't give the size or posture of your subject), so I'm assuming an average-sized woman falling in the classic face-down skydiver posture. I'm also modeling this ...
- 15.9k
38
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 ...
- 172k
37
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 ...
- 486
37
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 ...
- 10.9k
35
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 ...
- 11.2k
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 ...
- 11.6k
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 ...
- 189k
29
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,...
- 172k
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 ...
- 18.4k
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 ...
- 11.6k
27
votes
Would it take less thrust overall to put an object into higher orbit?
A slower orbital speed does not mean less energy. It means that a smaller fraction of the total energy is in kinetic form, but the sum of the kinetic and potential energy is greater.
Consider a ...
- 8,649
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 ...
- 172k
25
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!
...
- 151k
24
votes
Could a human jump off Mimas without return?
tl;dr: No chance, not even close!
The escape velocity from the surface of a round (spherically symmetric) body is given by
$$v_{esc} = \sqrt{\left(\frac{2 GM}{r_0} \right)}, $$
showing that it is ...
- 151k
24
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 ...
- 3,771
24
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?
In the inverted pendulum problem:
gravity exerts a vertical force on the pendulum, at the center of gravity
the support of the pendulum (like the finger under the pencil) exerts a vertical force on ...
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Only top scored, non community-wiki answers of a minimum length are eligible