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Questions tagged [physics]

How physics applies to a particular activity in space or to getting to and from space.

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77 votes
3 answers
45k views

What will be the effect if we stand on Jupiter?

As we all know Jupiter is a gaseous gas giant and it has a large mass, almost twice the sum of all other planets in the Solar system. So, if it happens that we go to Jupiter, and, as we know it does ...
SpringLearner's user avatar
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
2 answers
22k views

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

According to this NASA article the tires are inflated to 340 psi (main gear) and 300 psi (nose gear). At landing, there is significant strain, but what about in space? Are the tires exposed to vacuum ...
James Jenkins's user avatar
49 votes
6 answers
11k views

Can/should you swim in zero G?

Inspired by Are there types of animals that can't make the trip to space? (physiologically) and related to but not a duplicate of Can you swim in space? Swimming on the Moon / in low gravity looks ...
Baldrickk's user avatar
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40 votes
8 answers
12k views

Could a spacecraft spin so fast that it spontaneously deconstructs?

I have to admit, first and foremost, that this was inspired by Kerbal Space Program. During a launch I decided to hold the "E" key and spin my rocket to the fastest rotation speed possible. At some ...
Magic Octopus Urn's user avatar
38 votes
10 answers
15k views

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

Stupid question obviously. But did you ever had an idea which sounded so brilliant, but you know it is totally stupid? So, lets hear my idea: Do you know how we launch jet fighters from navy ships? ...
Pavel Janicek's user avatar
37 votes
4 answers
12k views

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

If an astronaut threw a cup of coffee into space somehow, would it freeze into a block, or boil off into gas due to the zero pressure?
James from NZ's user avatar
34 votes
1 answer
7k views

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

I know that capsules typically require heat shields to survive reentry from orbit. I'm wondering how an object's size, density and aerodynamic profile affects this. For more specificity: The feather ...
neelsg's user avatar
  • 5,223
31 votes
3 answers
7k views

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)? [closed]

In multiple different movies and fiction, there's the threat of a burning space comet heading for Earth, threatening to kill everyone and destroy the planet. One example is the animated Comet in ...
Snusmumriken's user avatar
29 votes
8 answers
7k views

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

I am wondering if any space agency has ever considered using a grinding machine as a propulsion system for an interplanetary spacecraft. This system would not be used to lift the spacecraft off of a ...
user avatar
27 votes
2 answers
12k 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
23 votes
2 answers
4k views

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

Any Kerbal Space Program player will know that burns prograde and retrograde to the velocity vector are most efficient closest to the body being orbited, while burns normal and anti-normal are most ...
TheEnvironmentalist's user avatar
22 votes
7 answers
10k views

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

I was reading a popular thread about the delta-v required to escape the solar system compared to the delta-v required to crash into the sun. I get it: the earth itself already has a high speed (29.7km/...
ker2x's user avatar
  • 331
22 votes
4 answers
9k views

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

There is a small debate over the comment session in NASA Lands InSight on Mars video uploaded by JPL. The 1 minute and a half video is about the essential part of InSight's EDL event cropped out from ...
not_Prince's user avatar
  • 1,507
22 votes
1 answer
7k views

Why aren't the ISS's nor Space Shuttle's radiators black?

As we know, from a surprising corollary to Kirchhoff's law of thermal radiation, just as darker* objects absorb more light (and therefore energy), darker objects also radiate more light (at lower ...
geometrian's user avatar
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21 votes
4 answers
4k views

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

I have read articles and seen videos explaining why an SSTO (Single Stage To Orbit) rocket* is not possible. But I was wondering... What would be required to achieve this? Answers can be literally ...
Outsider's user avatar
  • 578
20 votes
4 answers
8k views

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

I've received comments that explain to me that the analogy between rocket attitude control during a hovering maneuver and the act of balancing pencil on the end of a finger is a helpful and good one; ...
uhoh's user avatar
  • 149k
20 votes
3 answers
4k views

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

Imagine the following thought experiment: An astronaut is inside an extremely large room within a space station. Suppose that she, for whatever reason, is initially at a zero velocity with respect ...
Paul's user avatar
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19 votes
4 answers
6k views

Why can't we launch from space?

So this may be a stupid question but I was wondering why we couldn't launch from space. I know that most of the fuel that we spend is for escaping Earth gravity. Yet, if we have already done this with ...
bobthebuilder's user avatar
18 votes
7 answers
4k views

What is measured with g-forces?

When sitting at rest, a typical "g-meter" shows a value of one, however the meter is not accelerating. In orbit, it shows zero, but is under constant acceleration. The actual force of ...
Innovine's user avatar
  • 4,625
18 votes
1 answer
6k views

Person falling from space

A person at rest 500 km above the Earth falls straight downwards. She has a snug magical force field around her that is totally rigid and completely protects her from outside heat. The force field ...
CapIsland's user avatar
  • 199
18 votes
2 answers
2k views

Is the Flyby Anomaly still a thing?

The Flyby Anomaly is a name given to an unexplained, unexpected difference between the best theoretical calculation of a change in several different spacecraft's velocities due to flyby (Gravity ...
mike's user avatar
  • 1,646
17 votes
4 answers
4k views

How does centripetal force produce artificial gravity

I think I lack a fundamental knowledge of physics to answer this myself. In many sci-fi stories, there is a rotating spaceship that gives the feeling of being pulled "downwards" against the sides of a ...
Premier Bromanov's user avatar
16 votes
1 answer
5k views

Why do some meteors explode in air?

I was reading about the Tunguska and Chelyabinsk meteors and I wonder what would cause a meteor to explode in the air, instead of hitting the surface?
Zgr3doo's user avatar
  • 273
16 votes
1 answer
2k views

Does the "Tennis Racket Theorem" apply to the ISS? Does it rotate around its intermediate (unstable) axis?

Wikipedia's Tennis racket theorem begins: The tennis racket theorem or intermediate axis theorem is a result in classical mechanics describing the movement of a rigid body with three distinct ...
uhoh's user avatar
  • 149k
15 votes
3 answers
3k views

Spacesuit with no thermal insulation. Would person inside freeze or overheat?

Let us say I have a theoretical super thin spacesuit which has zero thermal insulation. As if person would be naked in space, but all other variables - pressure, oxygen, food and other life support ...
ShoulO's user avatar
  • 355
15 votes
1 answer
685 views

How much energy is lost by damping yaw from a SpinLaunch?

SpinLaunch hopes to launch a 200 kg satellite from a ground-based centrifuge, at 5000 mph, and more troublingly, at 450 rpm aka 7 tumbles per second. (The 3000 rpm figure mentioned in its tech sheets ...
Camille Goudeseune's user avatar
14 votes
2 answers
4k views

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

I was think about different ways spacecraft could feasibly move around and I came across Reaction Wheels as a way they can rotate. So I was curious if a complex system of them could be used to propel ...
SentiCarter's user avatar
14 votes
1 answer
3k views

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?

Question: 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? Are there fundamental engineering ...
uhoh's user avatar
  • 149k
14 votes
4 answers
1k views

How do spacecraft measure onboard gravity?

How do spacecraft measure onboard (micro)gravity at any given point in time (especially when subject to the gravitational fields of multiple bodies)? I'm guessing that rudimentary accelerometers won't ...
coleopterist's user avatar
  • 6,063
14 votes
2 answers
3k views

Till what altitude above earth sounds can be heard?

In the new video of SpaceX SAOCOM 1B launch and landing RCS thrusters and other sounds can be heard during boostback burn. Falcon 9 boostback happens at nearly 100 Km altitude. Does the air density at ...
Ashvin's user avatar
  • 2,888
14 votes
4 answers
2k views

How does Spinlaunch manage the counterweight right after launch?

Spinlaunch has successfully launched a suborbital test vehicle from a 1/3 scale demonstrator, see for instance aviationweek.com or space.com. While spinning up the arm, perfect balance is achieved ...
jrouquie's user avatar
  • 291
14 votes
1 answer
2k views

Now that Perseverance is "hot" (RTG in place) and before it gets to deep space, how will it stay cool?

As soon as they are assembled MMRTGs continuously produce about 2,000 watts of heat energy. That dips only slightly when they are connected to a load and producing electrical power (about 125 watts ...
uhoh's user avatar
  • 149k
14 votes
2 answers
2k views

Why does the Earth lose rotational velocity in the vacuum of space?

I think it is a well-known fact here that the Earth is slowly losing rotational velocity over time (some 1.4 milliseconds of the day are gained per hundred years). Eventually, this means that the ...
Premier Bromanov's user avatar
13 votes
7 answers
10k views

Could a space colony 1g from the sun work?

Let me break down my thoughts and I have no science background so let me know if this could even be possible. Have the colony on an object like a big asteroid or a similar man made construct. Have ...
Matthew Kay's user avatar
13 votes
6 answers
3k views

Why does this formula say rocket efficiency depends on velocity?

Wikipedia gives the following equation for the efficiency $\eta_p$ of an engine here: $$\eta_p= \frac {2\, (\frac {v} {v_e})} {1 + ( \frac {v} {v_e} )^2 }$$ where $v$ is the rocket speed and $v_e$ ...
Nightrider's user avatar
  • 2,035
13 votes
1 answer
2k views

Why is the sunny side of JWST's sunshield purple and covered with silicon?

After about 08:52 in Destin's Smarter Every Day's Why Are there Holes in the James Webb Sunshield? (Explained by My Dad) - Smarter Every Day 270 (linked below) ...
uhoh's user avatar
  • 149k
13 votes
1 answer
2k views

Largest radius sphere with Earth's surface gravity on which you could jump at escape velocity? Bigger than B612?

In the book Le Petit Prince by "French aristocrat, writer, poet, and pioneering aviator Antoine de Saint-Exupéry" the main character lives on an extremely tiny asteroid with the name B612. It is this "...
uhoh's user avatar
  • 149k
12 votes
1 answer
2k views

If Earth had a second moon, where would it be positioned? [closed]

Could Earth theoretically have another moon, beside the existing one, that would have a stable orbit? If it is possible, could Newtonian physics describe where it would be (i.e its position relative ...
Hale's user avatar
  • 231
12 votes
4 answers
8k views

Accelerometer in space

If my understanding of the General Theory of Relativity is correct, according to the Equivalence Principle, forces due to gravity and acceleration are indistinguishable. If that's the case, then an ...
Super-intelligent Shade's user avatar
12 votes
8 answers
5k views

Is it possible to get a spacecraft into earth orbit using Linear Eddy Current Braking on an orbital runway?

The "Space Runway" [I have slightly edited this to clarify some issues that have been raised] Luke Parrish mentioned an unusual and novel space launch method to me. The idea is to get a spacecraft ...
Roko Mijic's user avatar
12 votes
4 answers
3k views

How can a yo-yo de-spin maneuver reverse the rotation?

I just read about yo-yo de-spin as a measure to reduce the spin of objects. The basic idea is simple and makes sense, but then I read this: As an example of yo-yo de-spin, on the Dawn Mission […] ...
Ingo Bürk's user avatar
11 votes
3 answers
6k views

Could a human jump off Mimas without return?

A similar question has already been asked on dwarf planet Ceres: Could a Human reach escape velocity by jumping from the surface of Ceres (a dwarf planet)? Ceres has 2.9% of Earth's gravity. Saturn's ...
user27822's user avatar
  • 414
11 votes
4 answers
3k views

What causes a rocket to be destroyed during launch other than leaking fuel?

There were some famous accidents where rockets launched and just went up into flames. Many had something to do with leaking fuel in some sort. I want to focus on aerodynamic stress however, like when ...
JustAGuy's user avatar
  • 121
11 votes
2 answers
2k views

Earthing system in space?

On Earth, we have a good reason to deploy electric devices with an "Earthing system": this helps to avoid dangerous leak currents on surfaces. Now how is this solved on a spacecraft?
J. Doe's user avatar
  • 2,890
11 votes
3 answers
2k views

Physics and math behind flight through solar system [closed]

I wrote a program that simulates a solar system. I was able to calculate the locations for every planet on its elliptical route for any given time. In a second project, I managed to simulate newtonian ...
joe's user avatar
  • 373
11 votes
1 answer
674 views

Can (human) gas propel someone in a contained space station?

I am NOT trying to be lewd, but I had a student ask this. Yes, she may have been tongue-in-cheek, but I promised to answer her. And yes, I am trying to keep this as practical as possible. If and ...
Mikey's user avatar
  • 2,941
11 votes
1 answer
1k views

Can you have a rainbow on any bodies in the solar system besides Earth?

We know from Flying on dense atmosphere planets & moons that many bodies in our solar system have sufficient atmosphere for at least the concept of flying to be considered. What about the ...
James Jenkins's user avatar
11 votes
1 answer
987 views

Star-shaped artifacts in SAR images of the "Suez Canal traffic jam seen from space"

Wikipedia's 2021 Suez Canal obstruction links to the Sentinel-1 synthetic aperture radar (SAR) image of the Traffic jam in the Gulf of Suez caused by the obstruction as seen by the Sentinel-1 ...
uhoh's user avatar
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