48 votes
Accepted

What eliminates the velocity when occupants return from ISS to earth, and how much?

Nearly all the velocity is cancelled by atmospheric deceleration of the descent module, before its parachutes are deployed. ISS orbital velocity is around 7700 m/s. An initial retro-burn of the ...
38 votes
Accepted

If you release a tool outside the ISS in space will it remain at the "same" place forever?

It will not. Once released, the object is in a very slightly different orbit from the space station. If you put the object further out or further in from Earth than the space station it will be ...
  • 4,901
36 votes

Why did the space shuttle's altitude go down after reaching 108,000m?

The drop in acceleration around 40s into the flight is the shuttle throttling down to reduce the aerodynamic load on the vehicle. It then accelerates when past this point. The drop in acceleration at ...
  • 4,405
32 votes
Accepted

Interstellar Travel Thought Experiment

Does this logic make sense? Has anyone thought of this before? Yes, it's been considered. In the literature it's known as the "incentive trap". There are a couple of academic papers on it, ...
31 votes

Are rockets faster than airplanes?

Rockets are much faster than airplanes for most of their flight. Here's a graph of a Space Shuttle launch: The red line is speed. It's in ft/s, 1000 ft/s is 1097 km/h. So At about 45 seconds, the ...
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26 votes

What eliminates the velocity when occupants return from ISS to earth, and how much?

The process is described here, which answers nearly all of your question. The reentry burn removes about 120 m/s of velocity from the capsule (that's your 1) and the final impact is 15 miles per hour ...
25 votes
Accepted

Why is Voyager/Pioneer so slow compared to Parker Solar Probe?

Physical First and foremost, the physical reason is that objects accelerate as they approach massive bodies and decelerate as they recede: Parker Solar Probe achieves its peak orbital speed (almost ...
  • 9,854
23 votes
Accepted

How hard do you have to throw something off the ISS to make it deorbit?

@user3715778's answer is correct. Throwing will not make enough of a difference in the orbit to reenter Earth's atmosphere de-orbit promptly. Let's run the math using the vis-viva equation: $$v^2 = GM ...
  • 148k
21 votes

Are rockets faster than airplanes?

A rocket isn't automatically fast - a small firework rocket may be no faster than a car. The important point is that rockets carry their own oxidiser and aren't limited by the need to interact with ...
18 votes

What is the fastest rover that has ever traveled on the surface of an extra-terrestrial body?

The manned Apollo Lunar Roving Vehicle from Apollo 17 holds the record of 17km/h achieved by Eugene Cernan. Apollo Lunar Roving Vehicle was also present on Apollo 15 and 16. For traditionally ...
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15 votes

Travel Speed in Space

Currently functional and proven technology is limited to basically no interstellar travel at all. To reach one of our stellar neighbors (like Proxima Centauri), one of the fastest space probes we have ...
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15 votes

Why should the velocity through the nozzle throat be sonic?

Uwe's comment on the question is spot on. The characteristics of the flow through the nozzle depend critically on the pressure ratio - the two pressures being the pressure at the entrance to and exit ...
14 votes

How to calculate the speed of rotation of a given point on the Earth's WGS84 ellipsoid, about its axis?

NOTE: This answer was provided for a different, very basic question which didn't specify the WGS84 ellipsoid; it's illustrative of the basic principle as applied to a spherical Earth. Still, not bad ...
13 votes
Accepted

What is the required burn to keep a satellite at a Lagrangian point?

What is the required burn to keep a satellite at a Lagrangian point? tl;dr: typical station keeping delta-v for a halo orbit around Sun-Earth L1 or L2 points are of the order of 2 to 4 meters/sec per ...
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12 votes

A spacecraft is travelling at X units per hour. But relative to what exactly? Does it depend on the orbit? How?

Your concerns are all perfectly valid - giving just a number doesn't tell a lot. So, in all proper publications, the reference system has to be mentioned. Typically, the reference is the body the ...
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11 votes

Did a spacecraft ever use an atmosphere to accelerate away from a planet?

Your premise is incorrect. In no case does "skipping off the atmosphere" leave you going faster than you arrived, engines on or not.
11 votes
Accepted

Did a spacecraft ever use an atmosphere to accelerate away from a planet?

Entering the atmosphere introduces drag, which could only reduce your energy. That is, reduce your speed relative to the planet. If you hit the atmosphere at 18,000 mph at too shallow an angle you ...
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11 votes
Accepted

Minimum velocity needed to cross Karman line

When you ask about the minimum velocity needed to cross the Karman line there are 2 things you could mean. The first thing is that you could mean the minimum velocity needed on the ground going ...
10 votes

How hard do you have to throw something off the ISS to make it deorbit?

There is a great video by Scott Manley, which specifically addresses your question: Could An Astronaut Throw Something From Orbit To Earth? The short answer is no, humans can not provide enough ...
10 votes
Accepted

How often do we get information from the Voyager spacecrafts?

We get information from the Voyagers just about every day for 8-16 hours per day. Getting the information requires that a dish antenna be pointed accurately in Voyager's direction, so that gives two ...
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10 votes

Are rockets faster than airplanes?

Rockets don't actually mostly go up, they try quite hard to go up as little as possible. While flying, gravity is always accelerating you downwards at 9.8 m/s^2. This means that any fuel spent ...
9 votes

What is the fastest rover that has ever traveled on the surface of an extra-terrestrial body?

The highest speed was recorded by an Apollo Lunar Roving Vehicle: The rovers were designed with a top speed of about 8 mph (13 km/h), although Eugene Cernan recorded a maximum speed of 11.2 mph (...
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9 votes
Accepted

At what point of travelling progressively faster around the Earth you are not going to fall back again?

This is a great question! tl;dr From a circular orbit, a little more or less velocity just makes your orbit slightly elliptical. If your orbit happened to be very close to the Earth's surface (LEO ...
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9 votes

What is the terminal velocity of SpaceX Starship?

I have been looking for the same thing. The only mention I found was on a blog post (https://www.neowin.net/forum/topic/1402753-spacex-starship-sn8-15km-test-flight/) which stated 66-68 m/s for SN8. ...
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9 votes

If you release a tool outside the ISS in space will it remain at the "same" place forever?

Great question to illustrate small but measurable effects of orbital mechanics! NO, even if both wrench and ISS are idealized point masses in the same circular orbit. The mass of the ISS imposes a non-...
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8 votes

How would you eject an object from an airlock for maximum velocity?

You can't open an airlock hatch to vacuum until the pressure inside is essentially zero. The hatch opens inward and is held closed by tons of force if there is any appreciable delta pressure. ...
8 votes

Why is Voyager/Pioneer so slow compared to Parker Solar Probe?

You have probably seen funnels like the above in shopping malls. Drop a coin in the funnel and it will move slowly at the edge and move faster as it nears the center. This is a good model of a ...
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8 votes

How hard do you have to throw something off the ISS to make it deorbit?

0 m/s At the altitude of the ISS, atmospheric drag—the effect of particles stealing your momentum—will decay most if not all orbits. The ISS has to make regular adjustments to it's orbital speed to ...
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8 votes
Accepted

What is the fastest we could travel in space, or have ever traveled in space?

If you want speed, look for mass. Things closest to the Sun will tend to be moving the fastest. For example the Messenger spacecraft reached almost 63 km/s when in an elliptical orbit who's ...
  • 148k
7 votes

Is it theoretically possible to create absolute velocity?

Which is the reference point? is not answerable because we are free to choose any point and velocity as a reference to calculate the position and velocity of an object. There isn't any universal ...
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