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Questions tagged [velocity]

Questions about the distance objects or gases cover in a fixed amount of time while traveling in space, being launched or descending. Also for questions about speed-comparisons.

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10 votes
4 answers
3k views

What is the velocity of the ISS relative to the Earth's surface?

This was asked once before, but I believe there was no clear answer given and accepted. The ISS has an orbital period of 92.9 minutes, or 5574 seconds. If it were in a completely equatorial orbit, ...
1 vote
2 answers
262 views

What can possibly accelerate space elevator to these types of extreme velocities?

Is it possible for a space elevator not to just reach speeds of a few hundred km/h, but much faster. Since in the future, people might want to go up to GEO to maybe work there and come back home on ...
9 votes
3 answers
5k views

Maximum velocity achieved by solar sail

What is the maximum (theoretical) velocity that can be achieved by solar-sail technology? Can we get close to the speed of light with that?
0 votes
5 answers
469 views

Is the launch of a rocket slow because the change in velocity (delta_v) should be as small as possible because of energetic reasons?

Does it make sense to keep the launch of a rocket slow because the change in velocity (a.k.a. delta_v) should be as small as possible because of energetic reasons?
3 votes
1 answer
494 views

Calculate velocity vector of elliptical orbit given the position vector at that point, the instantaneous speed, the true anomaly, and the inclination?

Sorry if this is obvious, but I am an amateur at orbital mechanics and trigonometry was never my strong suit. I would like to calculate the velocity vector at a point in an orbit given: position ...
10 votes
2 answers
2k views

What's the motion of two connected satellites orbiting the Earth after their separation?

Let's consider the following problem (it's a job interview question): two satellites are orbiting the Earth in a circular orbit; they are rigidly linked by a tether which is always pointing in the ...
15 votes
2 answers
9k views

If we can make an Alcubierre drive, how fast can it move a ship?

Assuming we ever manage to solve the energy generation problem (and whatever other problems may face it) and build a functioning Alcubierre drive, how "fast" would we be able to travel? That is, from ...
0 votes
1 answer
76 views

Higher nozzle exit velocity generally means higher thrust right?

Higher nozzle exit velocity generally means higher thrust right? If that is the case, then a higher heat capacity could potentially lead to a higher exit velocity, thus higher thrust?
4 votes
1 answer
668 views

orbital speed to maintain relative position to the Earth

I note that the orbital speeds of the planets slow down with increasing distance from the Sun. Say we have a space station orbiting the Sun at a distance of about 400 million kilometres (within the ...
5 votes
3 answers
555 views

How fast could we go back to Uranus and Neptune?

Since SpaceX is making everything so much cheaper to launch into space. If we launch a pair of orbiters to Uranus and Neptune, how fast could they get there? They could be really light and small, so ...
-4 votes
1 answer
114 views

Will the initial velocity of an object in space get multiplied if a constant acceleration is applied? [closed]

Imagine an object travelling in space in the speed of 60 Kmph which took acceleration x if accelerated with the same x, will the object travel faster than 60 Kmph or travel in the same speed cuz of ...
0 votes
1 answer
145 views

Could time illusion be used to send a spacecraft faster than the speed of light?

In this article (https://www.nasa.gov/feature/goddard/2022/hubble-spots-ultra-speedy-jet-blasting-from-star-crash) it says: The Hubble measurement showed the jet was moving at an apparent velocity ...
4 votes
1 answer
363 views

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

My dad and I thought about a problem we had when discussing Earth's gravitational field. This wasn't the original question but I still would like to know the answer. So essentially my question is: Is ...
4 votes
1 answer
2k views

Minimum velocity needed to cross Karman line

When we travel in a car upwards on a slope (against gravity), we can keep driving the car at a constant speed without accelerating (without changing its speed). Theoretically, the only thing we need ...
2 votes
3 answers
1k views

Point Ahead Angle and Doppler Shift Frequency Changes Calculation with the tangential/radial velocity component for Inter-Satellite Link

While calculating the Point Ahead Angle we work with Tangential Velocity vector component and to calculate the Doppler shift i.e changes in frequencies, we work with Radial Velocity Vector component. ...
3 votes
0 answers
267 views

Exact speed/distance of JWST (& others in L1/L2 halo) from Earth; is it measured any differently than for more distant deep-space missions?

How is the exact speed and distance from Earth of the JWST or any spacecraft in a Sun-Earth L1/L2 halo orbit determined? While deep space missions require ranging at hundreds of millions of kilometers ...
4 votes
4 answers
2k views

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

What is the fastest vehicle currently in space? With our current technology, at what point does physics start to restrict our speed in space?
13 votes
3 answers
542 views

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

If I am walking, the ground is stationary, and I move $X \frac{\text{units}}{\text{hour}}$ relative to the ground. If I am in low-Earth orbit, then I am still moving $X \frac{\text{units}}{\text{hour}}...
1 vote
0 answers
140 views

How to correctly change velocity in space?

The solver of the Lambert's problem gives me a hyperbolic velocity to move to some position on orbit. But the spacecraft is moving on orbit and changing the velocity takes some time. So, when I ...
1 vote
1 answer
150 views

What is the equation to find how much fuel you need to reach a velocity? [closed]

Theoretically, I need to launch a rocket, and I need to find how much fuel I need to reach a velocity however I do not know the equation.
7 votes
3 answers
3k views

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

When a satellite reaches a Lagrangian point, it has a non-zero velocity $v_1$ because of the transfer orbit in which it had already been. What burn, say, $\Delta v$, one needs if the satellite is ...
-2 votes
2 answers
311 views

How come satellites and space stations that travel through space at Earth's speed do not disintegrate?

What I mean, if Earth travels through space at 1,700 km/hour, when a spaceship or other object leaves its atmosphere, should it not stay behind? And if it is gravity that keeps it near Earth, should ...
1 vote
2 answers
232 views

How to correct my real orbit and turn it into predicted ideal orbit?

I want to launch my ship to the purple ellipse orbit. But because of non-ideal world I have non-ideal ship orientation and non-ideal thrust impulse. So, my initial speed is a bit bigger and it's ...
24 votes
3 answers
9k views

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

If an astronaut doing a repair outside the International Space Station (ISS) gently lets go of a tool into space, will it keep "flying" (orbiting) at the same spot relative to the ISS where ...
14 votes
4 answers
4k views

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

I recently took a look at this little data sheet by NASA: Math and Science @ Work; Space Shuttle Ascent Time Altitude Velocity Acceleration Comment (s) (m) (m/s) (m/s^2) 20 1244 139 18.62 40 5377 ...
0 votes
1 answer
79 views

Standing still to move forward [closed]

If our galaxy is tracking through space at ~1.3mm, couldn’t we arrive at point B if we came to a stop at point A. i.e. decelerate to -1 g
19 votes
1 answer
3k views

Interstellar Travel Thought Experiment

I have been going over a bit of a thought experiment in my head lately. And wondering if someone more informed on the matter can share their thoughts Let's start with the premise that rocket/ ...
2 votes
1 answer
1k views

How to calculate the velocity vector in the case of a hyperbolic orbit?

The problem I'm trying to get a formula to calculate the state vectors $\vec{r}$ and $\vec{v} = \dot{\vec{r}}$ on an orbit, given a true anomaly $\nu$. I'm following the process described here : https:...
2 votes
1 answer
819 views

How do we get to Mars in a week (7 days)?

Looking at the times that are quoted to go to Mars (months) makes me wonder what speed do we need to get there in a week? Chemical rockets can get to ~4.5 Km/s, thermal nuclear rockets is about twice ...
6 votes
3 answers
14k views

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

Launches often happen near the equator in order to take advantage of Earth's rotation speed. This is why more launches are towards the East than towards the West. How can one calculate the speed of ...
4 votes
0 answers
230 views

Fastest Manmade Object

I remember reading somewhere that during the cold war, a nuclear weapon was placed underground with a manhole cover on-top and then detonated. I'm pretty sure the manhole cover then went orbital ...
28 votes
3 answers
7k views

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

During Expedition 41 Reid Wiseman and Alexander Gerst replaced a failed pump on the outside of the ISS. I am guessing they took the broken pump back inside the ISS and returned it to earth in one of ...
0 votes
1 answer
825 views

Terminal velocity on reentry?

I've seen many references to "terminal velocity" on reentry, e.g., prior to a Falcon 9 landing burn. And I'm confused by this. Because terminal velocity comes from drag which depends closely ...
7 votes
0 answers
110 views

Ingenuity Three Axis Velocity Derivation from Camera, Gyro and Altimeter

It seems that Ingenuity has a 4000 pixel camera, a gyro, inclinometer and an altimeter. Using these information, they are able to derive three axis velocity information. Thereby compensating for the ...
0 votes
1 answer
286 views

Constant Acceleration in Space. How much time for a given distance?

I have been researching a lot and can't make any sense of it all, so I am trying my luck here. I want to program a simple formula that gives me the travel time in space. I have a constant thrust of ...
7 votes
1 answer
1k views

What is the terminal velocity of SpaceX Starship?

What is the terminal velocity of starship on earth and mars during descent? Has SpaceX revealed or hinted the values of projected surface area and drag coefficient of the vehicle?
1 vote
0 answers
25 views

How do you balance speed and exposure time when trying to reduce heating? [duplicate]

I'm trying to understand how you choose your acceleration/deceleration and trajectory during launch and reentry to minimize aerodynamic heating.* Ignoring efficiency in terms of delta-v (best leave ...
12 votes
2 answers
6k views

Why should the velocity through the nozzle throat be sonic?

I have read (even on this site), that exhaust gas velocity is (normally?) sonic (exactly Mach 1) through the choke point of a De Laval, or convergent-divergent, nozzle: At the "throat", where the ...
2 votes
2 answers
211 views

How to calculate velocity components of a point on Mars surface w.r.t. Mars center?

I found altitude, speed and acceleration data of old mission Phoenix during EDL phase, but they are referred to Mars c.o.g. rather than to ground or to landing site: Position and velocity (...
2 votes
2 answers
222 views

Is aerodynamic control in an exosphere possible, in case velocity is high enough?

Exospheres are different than the lower parts of atmospheres (if there are any): the molecules don't collide anymore and it doesn't behave like a gas. However, it still causes some tiny little drag on ...
0 votes
1 answer
690 views

How much anti-matter is needed for an anti-matter propelled rocket to reach $P$ % ($P\lt{100}$) of the speed of light (c)?

I think this is a tough one. Imagine a rocket is produced which is propelled by a matter-anti-matter device. Its sole purpose is to reach high velocity. Which means the mass can be kept low, say $m$ ...
4 votes
1 answer
1k views

How do I calculate re-entry velocity when decaying from a circular orbit?

I am trying to find the velocity of an object during re-entry so that I can calculate the peak heat flux but I'm a bit stuck. I know how to find the velocity of the original, circular orbit (300km) ...
2 votes
1 answer
162 views

Knowing when to stop burning

Navigating in orbit usually relies on firing engines for some amount of time to achieve a specific velocity. This answer, for example, mentions "closed-loop guidance" for the ISS boosting. ...
1 vote
0 answers
445 views

What's the minimum speed for a spaceplane to reach outer space? [closed]

From a realistic point of view there must be a minimum speed in order to reach space in a suborbital spacecraft, let's say in a spaceplane. Like there's a first cosmic velocity (for orbit) and a 2nd ...
1 vote
1 answer
480 views

What would happen if you jumped out of a moving spacecraft?

I've watched a film where one of the characters claimed to have rapidly disembarked a moving spacecraft during a 5g burn (?!) and immediately wondered how he survived. For example, you're on a ...
2 votes
0 answers
86 views

Small Rocket Questions [closed]

I'm interested in space technologies and have basic understanding of rocket flights. When looking at large commercial rocket launches, i noticed that the lift of process from ground takes very long (...
0 votes
2 answers
203 views

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

If a spacecraft enters flat enough into the Earth's (or another planet's) atmosphere it will "bounce off" the Earth at a higher speed. That method can be used if a spacecraft has not enough fuel to ...
1 vote
1 answer
189 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 ...
0 votes
0 answers
35 views

How can the download speed increase from space probes? [duplicate]

It always seems to be a genuine question that is How can we download data from far away probes in instant. When New Horizons reached Ultima Thule, it took us quite a few months to have a great picture ...
5 votes
0 answers
2k views

Solar system galactic velocity vector relative to ecliptic plane

The Solar system moves through the Milky Way galaxy with velocity of 230 km/s. The ecliptic plane is located ~60 degrees with relation to the galaxy plane, according to this source. The page also ...