# What is Delta-v: Definition and 14 Discussions

Delta-v (more known as "change in velocity"), symbolized as ∆v and pronounced delta-vee, as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such as launching from or landing on a planet or moon, or an in-space orbital maneuver. It is a scalar that has the units of speed. As used in this context, it is not the same as the physical change in velocity of the vehicle.
As a simple example, take a conventional rocket-propelled spacecraft which achieves thrust by burning fuel. The spacecraft's delta-v is the change in velocity that spacecraft can achieve by burning its entire fuel load.
Delta-v is produced by reaction engines, such as rocket engines, and is proportional to the thrust per unit mass and the burn time. It is used to determine the mass of propellant required for the given maneuver through the Tsiolkovsky rocket equation.
For multiple maneuvers, delta-v sums linearly.
For interplanetary missions, delta-v is often plotted on a porkchop plot, which displays the required mission delta-v as a function of launch date.

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1. ### B Delta-v from Lagrange points to lunar surface?

What is the delta-v requirements from each of the Earth-Moon lagrange points to landing on the lunar surface? What would be the best software I could use to visualise and calculate that kind of thing? Thanks.
2. ### B How to calculate time with delta-v and velocity?

Is this correct? Why the time is minutes instead of seconds? Thanks!
3. ### B Orbit circularisation/insertion spreadsheet

I am trying to create a spreadsheet that will calculate: The minimum delta-v required to circularise the orbit of a projectile that has been fired horizontally from the Earths surface at a given velocity. Completely ignoring atmospheric drag. See the attached spreadsheet. The steps are...
4. ### Maximum delta-v of a rocket engine

So I was browsing wikipedia when I encountered: What does this exactly mean? How does one calculate for this? << Adding link to the table >> https://en.wikipedia.org/wiki/Spacecraft_propulsion#Table_of_methods
5. ### B Delta-v for orbit if already at ideal velocity and altitude?

Lets assume you could fire a 100kg projectile using a coilgun at 1 degree above the horizon and have it arrive safely at 400km altitude traveling at 7.8km/s (or slightly more if that helps). How much delta-v would it need to correct its trajectory into a stable orbit? If it matters let's...
6. ### Delta-v to overcome atmospheric and gravity drag at 13km?

Wikipedia says that: Atmospheric and gravity drag associated with [space] launch typically adds 1.3 to 1.8 km/s to the launch vehicle delta-v required to reach normal LEO orbital velocity of around 7.8 km/s (28,080 km/h). Does anyone know, or know how to calculate/estimate/simulate the delta-v...
7. ### Relationship between characteristic energy and delta-v

Firstly, apologies if this is in the wrong thread. I'm currently writing a presentation on the physics of getting a spacecraft from Earth to Mars in the near future. In my research I've come up against Porkchop plots which seem to plot contours of equal characteristic energy so you can find...
8. ### Find delta-v; Hohmann transfer orbit

Homework Statement A space vehicle is in circular orbit about the earth. The mass of the vehicle is 3300 kg. The radius of the orbit is 2RE. It is desired to transfer the vehicle to a circular orbit of radius 4RE. An efficient way to accomplish the transfer is to use a semielliptical orbit...
9. ### Question on delta-v and escape velocity?

I apologise if this isn't the right place to post this. If I was to calculate the escape velocity of a body, e.g. the Earth which is approx. 11.2km/s, could this then be used as the delta-v in the ideal rocket equation to calculate the mass ratio needed? This would be for both a trip to...
10. ### Delta-v for Hohmann transfer from hyperbolic trajectory to circular orbit

I get different result than stated in the book. What am I doing wrong? Homework Statement A spacecraft returning from a lunar mission approaches Earth on a hyperbolic trajectory. At its closest approach A it is at an altitude of 5000 km, traveling at 10 km/s. At A retrorockets are ﬁred to...
11. ### Delta-V Correction needed after launch?

Hi guys, I want to know - roughly - how much delta-V a satellite must expend to get from its launch insertion orbit to its final orbit. Let us assume that we're putting a LEO craft up. The launcher is has the performance to reach this orbit, and is launched at the right time and...
12. ### Space Shuttle delta-V: How much is available at the ISS altitude?

I recently read that the STS orbiters have up to 300 m/s of delta-V available considering the weight of the orbiter and the quantity of propellant in the OMS. I also recall that leaving orbit requires some 100-150 m/s of delta-V depending on altitude. If deorbiting takes 100-150 m/s, then is...
13. ### A proposal to reduce the delta-V to orbit.

To reach orbit you have to have your vehicle have a horizontal, i.e., tangential, orbital velocity, of about 7,800 m/s and have sufficient altitude, say at least 100 km, the altitude considered to be "space". To get to this altitude you have to have a separate velocity in the vertical direction...
14. ### Hohmann transfer orbits (delta-v)

I am writing an essay on Space travel for my A level coursework. I am writing about Hohmann transfer orbits. At the moment I am using the wikipedia page: http://en.wikipedia.org/wiki/Hohmann_transfer_orbit It explains how you can derive this: From this: I can't do the in...