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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154 views

Have gravitation multipoles of Jupiter and Saturn beyond J2 been measured or at least estimated? At least the zonal harmonics?

This excellent answer has me wondering if there are any measurements or estimates of gravitational multipole moments of Jupiter or Saturn beyond J2. Here is what I found for J2 (in unitless form) in ...
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1answer
124 views

Time to fall into the Sun from Mars orbit

If a body starts to fall freely from Mars orbit towards the Sun, then how can we calculate the time to touch the Sun' surface? I have tried the third equation of motion that says R=(1/2 dg)*dt^2. ...
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2answers
238 views

Gravity mapping of grail mission

This I asked has answers about how gravity is mapped of earth using orbit data of the satellites as measured by ranging. Using ranging one can fit the model parameters to fit the orbit as it passes ...
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1answer
251 views

How quickly is the force of gravity exerted? Is a finite “speed of gravity” used in orbit calculations?

So I was reading a post of "What would happen if the sun disappeared". An excerpt: After eight minutes, the Earth would not only lose the sun's light and heat, but also its gravitational influence. ...
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1answer
458 views

Does Jupiter's high rotation speed affect its gravitational strength at the surface?

Jupiter's outer, equatorial atmosphere rotates at 12,517.12 meters/second, once every 9.5 hours, at a radius of 71,492 km. Geostationary orbital speeds for earth are around 3,000 meters/second, at a ...
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1answer
590 views

With what forces are Saturn's Rings cohesively held together? [closed]

With what sort of gravitation are Saturn's Rings held together? It is very spectacular and intriguing compared to the way Earth's gravitation acts. I do not have a basic or conceptual idea of what/...
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1answer
94 views

Could a Gravity Tractor be used for mining asteroids?

Recently, I came across the concept of the Gravity Tractor for the first time. And I was intrigued. https://en.wikipedia.org/wiki/Gravity_tractor A Gravity Tractor, as I understand it, is a concept ...
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2answers
290 views

why dose reentry speed need to be so fast [duplicate]

I have been wondering this since I was a kid. watching films of capsules and shuttles heating up and all that tile trouble and work that went into all. I would always wonder why they dont slow down ...
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1answer
286 views

Ceres gravity from spherical harmonics from Dawn, how to get the coefficients, definitions and potential?

update: I think I've found what I'm looking for. The file JGDWN_CER18C_SHA.TAB has what looks like spherical harmonics up to order 18, except I don't know the ...
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1answer
152 views

How heavy can a fuel tank get before making it heavier is a liability under any circumstances?

This Question may bend the boundaries of this community a little, since it's mostly about hypothetical rockets that would never be built. Considering a filled fuel tank has to withstand a lot of ...
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1answer
600 views

How do you calculate gravity loss (simplified)?

Assume a rocket with constant mass and thrust. To simplify things, we can ignore aerodynamic drag, and we'll also not perform a gravity turn, hence our flight plan is as follows: -Burn radially from ...
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1answer
238 views

Ballistic missile typical trajectory - along which path is it supposed to travel between Russia, China and US?

Today I was puzzled when my son was holding a school globe asking me to show with my finger a trajectory of a (nuclear) ballistic missile flying from US to China and Russia and vice versa (from Russia ...
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1answer
96 views

Tesseral Part of the Geopotential

I am working on the design of a constellation for academic purposes. I try to describe a phenomenon that appears in the simulations by means of analytic expression and I can't really find a good ...
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1answer
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} ...
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2answers
63 views

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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1answer
317 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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1answer
126 views

Is it possible to have a planet made entirely out of water? [closed]

Let's say we had a mechanism of adding unlimited amounts of water at a certain point in space. How much water could we add until the water molecules would turn into something else due to gravity? What ...
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2answers
474 views

At a height of 100 km, what speed do you need to be going to escape Earth's gravity?

I understand that the escape velocity of Earth is 11 km/s. However, Earth's gravitational sphere of influence is not infinite, so it is possible to go slower than that and still escape the sphere of ...
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1answer
353 views

Lambert problem solver needed for custom gravity in Python

I need to solve the Lambert problem, however, I have a custom gravity model. My ODE of motion is: ...
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2answers
278 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 ...
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0answers
58 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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0answers
41 views

How much higher could g be before we couldn't launch rockets? [duplicate]

Obviously having a higher gravitational acceleration makes it harder to get rockets into orbit / escape. How much stronger could earths gravity be before we would no longer be able to do the sort of ...
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4answers
914 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 ...
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2answers
411 views

What are the calculations for gas transport to the Moon with a pipeline?

This paper, acquired from this question about tethers on the Moon, describes LADDER, a mission to deploy a Lunar Space Elevator (LSE). The space tether, made of Zylon fiber, would be 264,000 km long,...
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2answers
247 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 ...
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1answer
306 views

What objects travel at the speed of light? [closed]

What elements travel at the speed of light. I was under the impression it was light and gravity but apparently electromagnetic waves (radio waves) travel that fast as well. And is element the right ...
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3answers
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,...
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2answers
134 views

Gravity Model measurement technique

Geopotential model are used whenever propgation has to be done of the orbit. Geopotential model models the potential of earth via spherical harmonics. These models are generally published by NASA as ...
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2answers
287 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 ...
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1answer
430 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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2answers
727 views

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 ...
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1answer
106 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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1answer
97 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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1answer
358 views

The Earth's Moon versus Phobos and gravity

Our Moon weighs 7.35 x 1022 kg and Mars' moon Phobos, weighs 10.6 × 1015 kg. How much would need to be added to Phobos to give it the same gravitational "impact" on Mars, as the Moon ...
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1answer
199 views

What is the highest gravity planet we could launch a single person from?

According to some reports a human can survive at up to ~5 gravities while other reports suggest launching from > ~2 gravities might not be possible with rocket engines. Many super Earths have surface ...
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1answer
246 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 ...
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1answer
180 views

How to calculate slowing effect of a planets gravity on a projectile that is launched upwards

The acceleration a ballistic projectile would experience at a certain height above a planet (neglecting any atmosphere) is given by $$a = -\frac{GM}{(R + h)^2}$$ where $G$ is the gravitational ...
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1answer
240 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 ...
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1answer
79 views

Would a space rocket launching from Ceres in a path to Jupiter be faster relatively to the sun than one launching from Earth?

Suppose you have a space rocket which when launching from Earth its speed relatively to Earth it's 11 km/s. For what I've read in another topic in Space SE, the orbital velocity of the planet where a ...
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1answer
247 views

How do you calculate the ∆v required to increase apoapsis to a certain height?

To calculate the ∆v needed to increase our apoapsis from a low orbit of 100km to 400km, we find the velocity at 100km using the semi major axis (which is 250km, in this case), and then find the ...
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1answer
704 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 ...
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1answer
194 views

Time dilation between Earth and a similar planet revolving around a supermassive Black hole [closed]

I was thrilled watching 'Interstellar'. It was only much later that I came to realize certain anomalies in the movie (like the scene in which McConaughey approaches the Gorgantua — his body ...
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0answers
91 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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0answers
207 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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0answers
78 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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0answers
38 views

why dark matter causes gravity as its property is different than ordinary matter? [closed]

For temperature, pressure, vacuum, electomegnetisum etc. there is only one physical phenomena responsible(it can not be created by other means). Is it true? If so, why dark matter causes gravity as ...
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0answers
100 views

Space model transfer to moon displacement [closed]

I'm having a problem with the insertion from a LEO orbit into a moon orbit/ moon flyby in my gravity simulator. I use the calculations listed below. I think it is due to the fact that the moon pulls ...
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0answers
46 views

How massive can a planet become before it is impossible to escape from using chemical rocket propulsion? [duplicate]

Assuming a vaguely Earth like world but with higher gravity, at what point is it no longer possible to launch a human being from the surface into orbit? Or anything into orbit?
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0answers
57 views

Seismic effects resulting from tidal action on Ganymede and Europa

What kind of seismic activity is going to be generated by the tidal forces exerted on these two moon's ice sheets by Jupiter? Would it be a great enough differential in the ice sheets to preclude ...
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0answers
154 views

Satellite altitude variances in orbit

I understand that all satellites must have burn corrections to keep their orbits where they are needed. However my question is specifically about what those changes are in magnitude from the desired ...