# 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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311 views

### Could a drone escape Mars' atmosphere?

Is it possible that a multi-rotor polycopter of some kind could escape Mars' atmosphere from its own propulsion?
277 views

### Questions about the Dynamic Solid Tide

I found the following plot in the book Satellite Orbits; Models, Methods, Applications by Oliver Montenbruck and Eberhard Gill, Springer, 2000. The figure and description can also be found in google ...
214 views

### Which perturbs LEO satellites more, the Moon's gravity directly, or the changes in Earth's gravity field due to the Moon?

Reading this tutorial answer on models of Earth's gravity field I was realized that I'd never thought of it as time dependent. According to it, the biggest short term changes in the shape of Earth's ...
700 views

### Different perspective of tidal force on Earth's ocean

From the book "The Science of Interstellar" by Kip Thorne. On Chapter 4 of the book, there is a diagram on the explanation of moon's gravity influence on Earth's ocean. Where diagram A is labeled as ...
600 views

### Besides retarded gravitation, anything else to worry about when calculating MU69's orbit from scratch?

For fun I'd like to use Hubble Astrometric data for example the observations listed at the bottom here to numerically estimate the orbit of 2014 MU69 as well as its uncertainties. My plan is to use ...
236 views

### Smallest planet where human type life could evolve and survive?

Most exoplanets making the news are larger than Earth. I wonder about the smaller worlds, how small is too small? Reword to keep the question narrow enough to be answerable. When the Earth was ...
106 views

### Question about variation of Law of Gravitation

In the book, Fundamentals of Astrodynamics, the author provides a different form of the Law of Gravitation $$\ F_g = - \frac {GMm} {r^2} \frac {\mathbf r}{r}$$ So the book says that the \${\mathbf r} ...
283 views

### Forces acting upon you between Apoapsis and Periapsis

When moving in an elliptical orbit from the Apoapsis toward the Periapsis could you class yourself as being pulled (falling) towards the Periapsis and then your velocity after is then pushing you ...
314 views

### Orbit decay, why gravity doesn't increase 'vertical speed'

To use some reference let's take the ISS. The ISS has an orbital speed of 7600m/s. At the altitude of the ISS ~400km the force of the gravity it's about 8m/s2. It will take about 16 minutes to the ...
892 views

### Deriving specific impulse from exhaust velocities? [duplicate]

I can't remember where I heard it but I thought that dividing the exhaust velocity by the gravitational pull of a body, it is possible to find the specific impulse of the rocket engine. However, what ...
245 views

### At what point in the atmosphere does a returning space object adopt the rotational speed of planet earth and how?

Given that everything on earth is rotating at the same speed as Earth, it is simple for an item leaving the earth surface to return to the earth surface. However, once an object has left the earth's ...
292 views

### Is it possible, using known acceleration laws, to drastically lower force required to leave Earth's Gravitational pull?

Just a silly theory to illustrate my question. If we were to build a globe (or a detached runway, could be any structure really as long as it goes around earth and meets on both ends) around the earth,...
1k views

### What is the gravity inside a rotating cylinder?

There is the popular question “What is the gravity at the center of the Earth?”. And the answer is zero, because the forces cancel out. And then the gravity increases linearly as you move to the ...
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### extreme longevity of geostationary orbits

I was speculating that geostationary satellites could be around possibly for billions of years (i.e. much beyond the point where plate tectonics would have erased all traces of human civilization on ...
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### What is the formula to calculate how much fuel is needed for a rocket?

I'm theoretically trying to launch a rocket for a school project and therefore I chose Saturn V. I took its weight of 140.000kg (308 647 pounds) and I'm trying to calculate how much fuel it'd take to ...
431 views

### What's considered the boundary for “earth orbit?” [closed]

According to this CNET article, The last time a human broke free from Earth's orbit was the Apollo 17 mission in 1972. I thought that the moon orbited the Earth, and that visits to it were still ...
2k views

### Could an Earth volcano impart escape velocity on lightweight matter?

When a big volcano erupts like Krakatoa or Mt St Helens does it send steam, smoke, dust, rocks high enough and fast enough to escape Earth? Could any lightweight matter from a volcano actually get ...
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### Have we attempted to experimentally confirm gravitational time dilation?

Mark Adler wrote in an answer to a different question that We would expect that Voyager 1's local time is faster than Earth time by about one part in one hundred million. I don't think that ...
302 views

### Gravitational assists from bodies other than planets

Gravity assists are pretty important for interplanetary travel. NASA uses them mainly because they can save time, energy, propellant, and expenses. But so far, all of the gravity slingshots have used ...
992 views

### Does the detection of gravitational waves prove we can travel faster than the speed of light?

From what I have read gravitational waves cannot travel faster than the speed of light. And since gravitational waves are part of the fabric of space, wouldn't that disprove the idea behind an ...
139 views

### A Space Gravitational Bus Route - is there such a thing? [closed]

Don't know if this is already been thought of, if it has it would be cool to know the name? Fundamental problem in how the public sees space transport, the problem is we see it as firing a rocking ...
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### Can a smart phone function in space?

I recenty came a across a doubt... Can a smart phone be used in space? Obviously you aren't going to get any data signal, but will the functions like touch screen, GPS, accelerometer, vibrator, etc, ...
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### Why can't ion engines be used for launch? [duplicate]

Not to sound rhetorical but if a Ion engine was used it would start at 1 mile an hr and then the speed would continue exponentially. So theoretically wouldn't that make it possible to break free ...
5k views

### Can you take a bath on Mars?

A common picture of someone floating on the Dead Sea or Great Salt Lake, shows how high you float. l If you had that water in a bath tub, I don't think you would sink to the bottom, you would just ...
244 views

### What are the challenges of a large Bola style Habitat

A quick calculation for 1g spin gravity at a leisurely 1 round per 20min gives a radius of 360km. Assume, we find a strong enough material for lightweight cables, what are the challenges for ...
550 views

### Is space travel possible from a large planet? [duplicate]

I was playing with a rocket design simulator, and I noticed that if I set Earth's gravity to be much higher than it is today, it became impossible to design a rocket that could reach escape velocity. ...
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### Does NASA use Newtonian model of gravity for plotting the course of Juno or general relativity?

With the huge mass of Jupiter and its fast, approximately 10 hours daily rotation, there may be substantial twisting of space-time around it. A distortion of such magnitude that may call for ...
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### Shear forces between Shuttle, tank, and boosters - what pushes what?

This is the question that I should have asked here. The space shuttle and the two solid rocket boosters (SRBs) are mechanically attached to the giant tank. SRB's, shuttle, and tank all experience ...
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### How quickly could we detect a change in a mascon?

Let's say we had a probe in orbit around the moon mapping out mass concentrations (mascons), as we've done in the past. Unexpectedly one day, a massive object lands on the surface of the moon, an ...
423 views

### Am I supposed to modify the gravitational constant with scale and why do fps & time scale changes cause my orbit to break?

I am using Unity3D and writing C# Earth Mass: 5.972e+22 Earth Velocity: [0,0,0] Earth Radius: 63.71 ISS Mass: 4194.55 Starting ISS Velocity: [76.50, 0, 0] ISS Altitude: 4 Gravitational Constant: 6....
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### Synthesizing gravity

There are substances with such massive density that a relatively small volume, could contain an immense mass. Given a substance like neutronium, could you conceivably synthesize gravity for a space ...
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### Can you ride a bicycle on Deimos?

Deimos is the small moon of Mars. The surface gravity is 0.003m/s2 (compare to Earth @ 9.807 m/s2). In theory a person with a bicycle could launch from and land on Deimos with a bicycle and a ramp. ...
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### I am having trouble calculating my classic orbital elements and am at a loss on where to look

I am using Unity engine and C#, and am trying to work out a way to plot future 2D orbital trajectories. I currently have a two-body setup. The planet has a mass of 1000000, the satellite a mass of 1. ...
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### How much resolution did gravitational maps of Earth have before GRACE?

Today, our highest-resolution gravitational maps of the Earth are from the Gravity Recovery and Climate Experiment (GRACE) project, launched in 2002. Before GRACE, how fine was the resolution of ...
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### Earliest gravitational map of a planet/moon?

When was the first gravitational map of a planet or moon made by measurements from space? I'm guessing it was a map of Earth, since that's the closest planet to us,[citation needed] but for all I've ...
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### Least artificial gravity needed to maintain health on a one year space trip?

What is the least gravity needed for human health on a one year space trip?
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### Why would the dual keel space station design have been more stable?

According to the space station Freedom wikipedia page and this reddit thread, a dual keel structure would have been more stable than the final ISS design. Can someone explain why? And if a gravity ...
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### Where is Luna 1?

Luna 1 was the first attempt by the Soviet Union to crash land into the surface of the moon but narrowly missed after a programming error becoming the first man-made object to escape Earth's ...
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### Using a probe to take gravitational measurements of the interior of the sun

Could one use a space probe to orbit the sun close enough to take measurements of angular / spherical gravitational field variations similar to what Juno plans to do for Jupiter? Since the sun ...
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### Source for up-to-date values of Mars' standard gravitational parameter

Wikipedia currently gives the standard gravitational parameter of Mars as: $$GM_{Mars} = 4.2828(9) *10^{13} (m^3/s^2)$$ The (9) is the uncertainty of the last digit, so it works out to about ...
152 views

### Can we displace earth? [closed]

From the gravitation equation it is clear the earth gets pulled but we fall due to negligible mass. But, if each and every person on the earth takes a jet-pack and jumps to a height equivalent to 20 ...
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### If you swam towards Earth from Space would there be a point when you started falling?

Ok, this is a question from a student in my class that was inspired from us watching the ISS Live Earth Feed. He wanted to know if there was a point in space when you would start falling. He likened ...
5k views

### Did the Mars rovers actually confirm the gravity of Mars?

For years the theoretical calculated gravity of Mars has proliferated science texts and Internet documentation - but did the rover actually do a test to confirm the theoretical gravity is truly equal ...
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### How strong is the Sun's gravity at the distance of Jupiter's orbit?

I had read that the Sun's gravity at the distance of the Earth's orbit was 0.0006 times that of Earth's gravity. So, I was wondering what it would be further out, at the distance of Jupiter's orbit.
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### Why does a gravity capture require a loss of velocity?

I've read a gravity capture of an object requires the captured object to lose velocity by some means (impact, third body tidal force, etc). Is there not a possible encounter that happens at a low ...
1k views

### How does the gravity of Earth change as you climb a space elevator?

I'm doing research for a movie. If you were in a space elevator/tower at an altitude of 250 miles, how much gravity would you experience? (I've heard various estimates of .9Gz and .65Gz) How about if ...
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I am reading this paper from the NTRS, Passive stabilization of the Long Duration Exposure Facility (LDEF), about (not surprisingly) gravity-gradient stabilization of the LDEF satellite. It looks ...
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### What kinds of objects could we potentially observe through gravitational waves? [closed]

With the discovery of gravitational waves, I keep hearing that we now have a "totally new way to explore the universe." But as I understand it, gravitational waves are only detectable when they come ...