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 ...
Anthony X's user avatar
  • 17.5k
76 votes
Accepted

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

Gravity is everywhere. There is never any actual true "zero gravity" in the universe. But if you're in freefall - meaning following gravity's pull rather than resisting it, or being blocked ...
Stilez's user avatar
  • 1,886
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 ...
Starfish Prime's user avatar
70 votes

Have we attempted to experimentally confirm gravitational time dilation?

You don't need a space probe. Or an aircraft. Or even a car. NIST has measured the predicted general relativity time dilation due to a change in altitude on Earth of one foot!
Mark Adler's user avatar
  • 58.2k
69 votes

If human space travel is limited by the G force vulnerability, is there a way to counter G forces?

The problem isn't so much that humans cannot sustain high G forces for any extended length of time: The problem is that rockets cannot. If a rocket could sustain 1 g acceleration for a bit over a day, ...
David Hammen's user avatar
  • 74.8k
69 votes

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

The biggest give away is the size of this chamber: its too big for any of the known NASA's KC-135 or ZG's 727-200. That leaves us one other candidate: their Russian counterpart IL-76 MDK The interior, ...
user3528438's user avatar
  • 1,641
64 votes
Accepted

Why did Voyager 1 lose speed after the sudden gain in speed from gravity assist?

It's the gravitational attraction of the Sun. Voyager was moving away from the Sun and was pulled back by its gravity. Since Voyager was not moving directly away from the Sun, it's trajectory also ...
Steve Linton's user avatar
  • 19.6k
61 votes

How much stronger does gravity have to be for space travel to be impossible?

There's no "bright line" at which space travel would become impossible; a slightly stronger gravitational pull would require bigger and more expensive rockets. Linear increases in gravity require ...
Russell Borogove's user avatar
57 votes
Accepted

Did the Mars rovers actually confirm the gravity of Mars?

The "gravity of Mars" is not a number but rather a complex field. The most recent is remarkably detailed, made up to spherical harmonics degree and order 120, described by 29,512 coefficients: These ...
Mark Adler's user avatar
  • 58.2k
57 votes
Accepted

Does it require less energy to reach the Sun from Pluto's orbit than from Earth's orbit?

Yes. 1st scenario: A spacecraft orbiting the Sun at Earth distance vs. Pluto distance, shedding its orbital velocity The orbital velocity decreases with distance, according to the following formula, ...
SE - stop firing the good guys's user avatar
55 votes
Accepted

If a spaceship ran out of fuel somewhere in space between Earth and Mars, does it slowly drift off to the Sun?

What you're missing is some combination of the following: objects launched from Earth orbit are still in orbit around the Sun, objects in orbit don't need fuel to stay in orbit. All the planets ...
userLTK's user avatar
  • 1,784
53 votes

Could colonizing Moon dangerously affect its gravity?

No. The moon isn't that big but it isn't exactly small either. The moon's mass is 73,500,000,000,000,000,000,000kg, that's 73 sextillion, 500 quintillion kilograms. If we moved the whole of mount ...
GdD's user avatar
  • 20.3k
53 votes

Does Virgin Galactic experience real weightlessness?

This is a point worth emphasizing: When you dive off a high dive, or go on a free fall ride at an amusement park, or fly on Virgin Galactic, you are experiencing weightlessness in exactly the same way ...
Mark Foskey's user avatar
52 votes

Have we attempted to experimentally confirm gravitational time dilation?

In addition to specific probes like the one mentioned by called2voyage, the effect is significant enough that it affects everyday operations. For example, the GPS constellation needs regular clock ...
Bear's user avatar
  • 1,565
50 votes
Accepted

How does a space probe maintain its trajectory while passing through the extreme gravitational field of the gas giants of our solar system?

The trajectory was not only "unhindered" - it was enhanced! Knowing mass of the planet you can calculate very precisely how the trajectory of a probe flying by will be affected. You modify the ...
SF.'s user avatar
  • 55k
47 votes

If human space travel is limited by the G force vulnerability, is there a way to counter G forces?

Ignoring the major point that human tolerance of G forces is not the limiting factor on space travel, plenty of thought has been made on how to counteract G forces, not least by 60s sci-fi writers. ...
Ingolifs's user avatar
  • 6,458
45 votes

Escaping moons conflict with what I understand of gravity

A very good question! The reason is essentially to do with tides. And a slightly over-simplified summary is: If the moon orbits more slowly than the rotation of the parent body (as our Moon does, 12 ...
Martin Kochanski's user avatar
41 votes

Unix Epoch in International Space Station

POSIX time doesn't include leap seconds, and is not implemented the same way in every UNIX, so it routinely gets inconsistent for several seconds every couple of years. It is not a high-precision ...
Ryan C's user avatar
  • 7,942
40 votes

Have we attempted to experimentally confirm gravitational time dilation?

Yes, time dilation was experimentally confirmed by Gravity Probe A, launched by NASA on June 18, 1976. The clock rates of two masers (one on the probe and one on Earth) were compared, and it was ...
called2voyage's user avatar
  • 23.7k
39 votes

Is there a self-rounding celestial body from which an Olympian could jump into space?

No. Saturn's moon Mimas is the smallest body in the solar system known to be rounded through self-gravitation, and it still has a surface escape velocity of 159 m/s, far above the speed achievable by ...
notovny's user avatar
  • 5,439
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 ...
Mark's user avatar
  • 15.3k
38 votes
Accepted

Can you take a bath on Mars?

Short answer, No different from Earth in floating. Buoyancy in water or any fluid is based on the weight of water displaced. Floating is based on the weight of the item displacing water. This is ...
Josh King's user avatar
  • 2,429
38 votes

When staying indoors, can missing gravity be replaced with blowing air?

in a building or closed vehicle on another planet, maybe air pressure could be used to imitate gravity There is no need to imitate gravity on another planet, because planets have gravity. Of course, ...
Jörg W Mittag's user avatar
35 votes
Accepted

How can a rocket approaching the Karman Line then return to earth faster than 53 m/s terminal velocity?

53 m/s is the approximate terminal velocity of a human skydiver. The terminal velocity of a 7-ton metal dart is quite a bit higher. Larger objects tend to be affected less by atmospheric drag than ...
Russell Borogove's user avatar
35 votes

Why did Voyager 1 lose speed after the sudden gain in speed from gravity assist?

Additionally, the probe has just passed a large planetary body with its own gravity well. The probe has to climb up out of that planet's gravity well which costs momentum. There is a net gain in ...
Criggie's user avatar
  • 681
33 votes
Accepted

Could colonizing Moon dangerously affect its gravity?

No, there would be no measurable effect. But we can consider two things: force and mass. Let's imagine we planned very poorly, and always landed our ferry craft in the same Earth-moon orientation (so ...
OrangeWombat's user avatar
33 votes
Accepted

Does Virgin Galactic experience real weightlessness?

Yes, for a few minutes. It is similar to what is done in a zero gravity airplane flight, but a longer period of time. Also, orbital weightlessness is basically the same thing, the spacecraft and you ...
PearsonArtPhoto's user avatar
  • 121k
32 votes

Unix Epoch in International Space Station

No. Computer clocks are inaccurate. They rely on constant corrections to maintain the correct time. Since their inaccuracy is much bigger than the time speed difference between earth and the ISS, it ...
Antzi's user avatar
  • 12.6k
32 votes
Accepted

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

If the only acceleration is due to the large mass's gravity, and the mass is not exceptionally large, or exceptionally close (i.e. close approach to a black hole or a neutron star), the astronaut will ...
Russell Borogove's user avatar

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