Questions tagged [gravity]

Questions regarding the attractive force present between two masses. If about research in artificial gravity (i.e. manmade substitutes for gravity), please use the artificial-gravity tag.

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To what percentage of the speed of light you need to accelerate to get artificial gravity at 1g?

Let's say you have a very powerful hypothetical fusion or matter/antimatter drive on a spaceship and you want to travel to a star nearby. Can you get 1g artificial gravity by accelerating? Or close to ...
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4 answers
214 views

How can I find the x, y position of apogee and perigee, if I only have the value of distance vector (position) and velocity vector?

I am currently working on a 2D space simulator where I have two bodies; one is still and other is an orbiting object, which I can also control like a rocket. I'm using the Newton's gravity: $F = \...
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4 votes
2 answers
186 views

What is the largest possible rocky body? [closed]

Suppose you start with a rocky sphere about 12,742 kilometers in diameter and continuously add more rocky material such that you don't smash this sphere to bits. What is the upper limit for this? ...
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5 votes
2 answers
465 views

How does gravity change beyond L2?

Why does gravity appear to increase again on the far side of L2 from earth as indicated on the gravitational contour diagram? One would expect gravity to continue to decrease as the distance from sun ...
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3 votes
1 answer
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When calculating the six Keplerian Orbital Parameters, why do we need both Eccentricity AND the Semi-Major Axis? Doesn't one tell you the other?

Perhaps I am misunderstanding elementary math, but.... How is it possible to know the eccentricity of an ellipse (e) but not the semimajor axis (a)?
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6 votes
1 answer
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Why does the eccentricity vector always point towards the periapsis of an orbit?

I hope you know that eccentricity can be derived from the position and velocity vectors of a spacecraft (only applies to a two body problem) through this formula : $$\textbf{e} = \frac{\dot{\textbf{r}}...
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Since we humans are't able to process any dimensions like 4D and 5D, the distance between stars and galexies appers to be too far away [duplicate]

For exmaple a living oraganism of 2D world is unable to perseive a 3D world. Similary, do humans have such limitations to perseive the further dimensions that 3D, that could results in wrong ...
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7 votes
3 answers
543 views

Differences between numerical propagators

I am a trainee who is working on a numeric orbital propagator developed in the company. I can't show you the code but I can tell you that the propagator was developed to work in Simulink. My job was ...
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3 votes
2 answers
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Can "prolateness" be characterized by a $J_2$ coefficient like "oblateness"?

When an imperfect sphere can be obtained by rotating an ellipse around an axis, it is called a spheroid. There are two types of spheroids, oblate ones and prolate ones. Most solar bodies can be ...
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6 votes
3 answers
329 views

Could you survive very high G's if your whole body was accelerated uniformly?

Could you survive high g's if your whole body was accelerated uniformly (not just by the seat of a rocket pushing on your back)? Your body is really only affected by gravity if you are touching ...
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3 votes
0 answers
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Can Interferometery be Used to Shorten the Solar Gravitational Lens Focal

The solar gravitational lens's focal is around 550 AU which is very far. Can we send a few telescopes that will stop midway (let's assume 150 AU) to collect the light and work as interferometry?
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8 votes
1 answer
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Is 1/6 G enough for humans to stay healthy?

Micro-G is known to be detrimental to health in the long-term. However, the Moon is at $\frac{1}{6}$ G (while Mars is at ~$\frac{3}{8}$ G). Is $\frac{1}{6}$ G enough for humans to remain healthy in ...
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25 votes
3 answers
5k 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 ...
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1 vote
2 answers
143 views

Energy to "nudge" a planet to a smaller orbit

Suppose we wanted to move a mass-$m$ planet to a much smaller new orbit around our mass-$M$ Sun. We'll assume the initial and final orbits are circles of radii $r_i,\,r_f$ with $r_f\ll r_i$, so GPE is ...
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2 answers
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Would an increase of a planet's mass affect its trajectory?

If humans happened to colonize Mars some time in the future and increase its mass such that its gravity increases from 3.721 m/s2 to 9.8 m/s2, would it not fall into the Sun?
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8 votes
2 answers
840 views

Is the weightlessness in a swimming pool the same as in outer space? [duplicate]

Astronauts practice the weightlessness of space in a swimming pool. Is this weightlessness the same as in space? Lets ignore the friction with water imagine them to be suspended in liquid helium...). ...
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17 votes
7 answers
8k views

Is the zero gravity experienced in ISS the "artificial" kind?

I always wondered about the following: An astronaut floating inside a spaceship that is far from Earth or any other other planet will experience true zero gravity because there is negligible ...
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12 votes
3 answers
6k views

Does Virgin Galactic experience real weightlessness?

Does Virgin Galatic go into space high enough to experience real weightlessness? A CNBC article states it's more microgravity centrifugal: The spacecraft essentially does a slow back flip at the edge ...
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2 votes
0 answers
64 views

What does "1g ref" mean in the ISS Crew Notebook?

Earlier I happened across What's the small white gadget with two black buttons in this video of the International Space Station? via the HNQ list. I was intrigued by the snippet from the "...
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3 votes
2 answers
211 views

What is a gravity gradient?

The statement: 'For most of that day, Mir remained in a "gravity gradient," (sic) which basically means that the most massive part of Mir naturally pointed toward Earth.' is in https://...
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1 vote
0 answers
93 views

Gravitational potential [closed]

I understand how we calculate gravitational potential and how we set it to be zero at infinity, and I understand its value at he Earth's surface is $-64\,\mathrm{MJ/kg}$ by using $r$ as Earth's radius....
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2 votes
2 answers
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Science Contest Topic (space exploration)

I'm thinking of entering the Breakthrough Junior Challenge. It is a global science video contest in which participants have to explain a hard science/math topic in a 3 min video. Right now I'm ...
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0 votes
2 answers
134 views

Archimedes Principle on other planet [closed]

How does the Archimedes Principle work on other planets where the gravity is different.? Does the wood block will float exactly same in water tub on different planets as on Earth.?
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8 votes
1 answer
478 views

What does the Moon's gravity feel like? If you don't move, could you still tell you're on the Moon?

I am interested in descriptions and discussion from the Apollo astronauts. Almost all animals and many plants are sensitive to the earth's gravitational field. This is important for large mammals and ...
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1 vote
0 answers
219 views

What keeps galaxies together? [closed]

The super massive black hole at the centre of Milky Way has a mass of about 4 million times that of our sun. Is this enough to keep the entire galaxy together, is it this black hole which keeps the ...
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15 votes
2 answers
3k views

Would an astronaut experience a force during a gravity assist maneuver?

When an astronaut is inside of a ship accelerating (from engine burns), or decelerating (due to reentry) they experience a tug in a relative direction. Suppose an astronaut is in a space ship that is ...
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9 votes
2 answers
2k views

Can a satellite orbit the ISS?

Is stable orbit of a small satellite around the ISS theoretically possible with minimal station keeping?
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0 votes
0 answers
33 views

If I know the masses, positions, and velocities of two objects, how do I calculate their trajectories under gravity?

I was thinking about the effect of a near-miss with an asteroid upon the orbit of the earth around the Sun. My goal is to figure out a formula I could use for a visualization I'd like to build to get ...
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0 votes
1 answer
89 views

My vector math seems to be off in this 2D simulation of a solar system

I intend to simulate gravitational acceleration on a 2D plane (simplified, no gravitational constant). My code is interpreted without any error in the console, but instead of having the two circles ...
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5 votes
2 answers
178 views

Gravitational force of asteroid Bennu

How can the gravitational force of Bennu (being so weak) hold the spacecraft in orbit?
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0 votes
2 answers
125 views

Two spaceships fly straight, parallel to each other, tied to each other by a rope, and pass a black hole between them. What happens to the rope? [closed]

To elaborate more on what I mean: Two spaceships are flying parallel to each other, both going completely straight relative to the observer. Their distances between each other do not change, as the ...
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23 votes
7 answers
5k views

Unix Epoch in International Space Station

The International Space Station is in a different gravitational field than us on the Earth's surface. Almost all computers / protocols depend on the Unix epoch being consistent everywhere. The Unix ...
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1 vote
1 answer
125 views

Does gravity affect sweating?

I read this hot question. It's asked what is done with the sweat produced by astronauts in the ISS. This led me to question: does gravity affect the production of sweat? Is more, the same, or less ...
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2 votes
1 answer
502 views

How does a rocket go from gravity turn to orbit?

A rocket launch normally begins with a roll to align with the orbital plane and a pitch to allow gravity to gradually torque the rocket down as it climbs. The combined roll and pitchover maneuver last ...
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7 votes
5 answers
361 views

Can Oberth bike? Is biking up and down a series of hills a good real-world analogy for understanding either the Oberth effect and/or gravity drag?

When faced with a series of ups and downs while riding a bicycle, I try to pedal like mad near the bottoms to gain as much speed as possible. I do this due to some vague, ill-formed notion that either ...
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3 votes
2 answers
210 views

Simple explanation for the 2nd "cosmic speed"

Many sources can explain about the first, second and third cosmic velocities, but the explanations contain difficult formulas and are not easy to understand. I can check with a powerful magnet and an ...
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4 votes
1 answer
310 views

Is Earth's "pear shape" mostly J₃?

@OrganicMarble's answer to 1959 Peanuts cartoon about the Fischer ellipsoid (Earth is “pear-shaped”)? finally let me see the cartoon that Mathematician, Engineer and Geoscientist Irene Fischer wrote ...
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6 votes
2 answers
434 views

How does gravity vary in a gas giant's interior?

The Earth's gravitational pull in its interior looks like this: The pull remains about the same and increases even a bit till the outer core from where on it starts getting weaker till 0g in the core'...
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14 votes
2 answers
7k views

What is the context of this seemingly "zero-gravity" photo on Earth?

A man appears to be in zero gravity in a room which doesn't look like it could possibly be inside of an aircraft. If so, that's one gigantic aircraft, entirely unlike all the other photos of the "...
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2 votes
4 answers
276 views

History of investigation of lunar and Martian surface gravity

I wonder when it was discovered that the Moon has about a sixth of the Earth's surface gravity and that Mars has 0.38 g. I think that until Newton, everyone assumed there was the same gravity on every ...
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5 votes
1 answer
227 views

Why are all possibly habitable exoplanets higher mass than Earth?

I have been writing a scifi book in which I wanted to include real stars and planets as locations. It was simple enough to find a chart on Wikipedia that lists possibly habitable exoplanets, but I ...
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20 votes
2 answers
3k views

Escaping moons conflict with what I understand of gravity

I have known that the Earth's Moon, let's call it Luna (tip of the hat to The Expanse), has been slowly but surely increasing it's distance from the Earth by a small measure each year. This week I ...
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10 votes
5 answers
4k views

How does a planet's gravity push away smaller bodies that would otherwise intersect its orbit?

I was reading an article about dwarf planets online where I stumbled upon the following definition of a planet: The International Astronomical Union defines a planet as being in orbit around the ...
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3 votes
2 answers
134 views

If you fell into a crater on the moon in your spacesuit and no jetpack, is there a way to use low gravity to get out of the hole?

If you fell down a crater or hole on the moon, is there a way to exploit microgravity/low gravity to get to the top? Lets say your survived a fall into Aristarchus crater on the moon with a slow slide ...
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1 vote
0 answers
88 views

How much gravity could someone handle who lived his/her entire life in microgravity? [closed]

Let's say someone who was conceived and born in microgravity and spent his/her entire life on a space station in weightlessness until age 20 decides to land on a celestial body. How much surface ...
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9 votes
3 answers
3k views

How close would the Tesla Roadster with Starman have to get to Earth in order to become attracted and fall on Earth?

In 2091 the Tesla Roadster is said to maybe get closer to Earth than the Moon is. At Starman's current speed, would its location in 2091 be sufficient for the Earth to re-attract the Starman to let it ...
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1 vote
1 answer
153 views

What counts as "0 mGal" in these gravity maps?

In the following gravity map of Mars the changes in gravity are shown according to mass distribution: Map removed However, since no moon or planet other than the Earth with 9.80665 m/s² has a ...
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1 vote
0 answers
116 views

How much does it cost to land on a lunar mascon?

This answer to Delta-v for landing on the moon estimates that to go from a circular orbit at 110km to a landing on a spherical Moon would require an absolute minimum of 1736 m/s and the Apollo landers ...
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12 votes
4 answers
5k views

Did any spacecraft ever use the Sun's gravity for acceleration?

Space probes often use planets to accelerate onto a trajectory towards their goal(s) without having to consume too much fuel. But the fastest acceleration would be made through the Sun's gravity if ...
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19 votes
3 answers
6k views

Does lower gravity on Mars make it unsafe and unhealthy for humans?

I've been thinking about proposals to live on Mars. One idea is to create an artificial magnetic field to protect from solar radiation. Another idea is to warm the planet using solar mirrors. In the ...
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