Talk:Hohmann transfer orbit

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Transfer orbits in general

Not all transfer orbits are Hohmann transfers. In practice, you seldom get a perfect minimum energy transfer orbit. Instead, you must use an affordable transfer orbit - i.e., one with a relatively low fuel cost.

The reason the Hohmann transfer orbit mathematics are simple is that both the departure and the arrival occur at (opposite) apsides of the transfer ellipse. A more general sort of transfer involves only one of the end points of the intended trajectory - either departure or arrival, but not both - occuring at one of the transfer orbit's apsides. The transfer path itself is a segment along the transfer orbit that might, or might not, include the other apside.

I've prepared a text based treatment of this more general transfer orbit solution for the "physics forums" website. If someone wants to construct a version of my treatment for Wikipedia, giving me credit for the original work, I'd have no objection.

The URL is

http://www.physicsforums.com/showthread.php?t=29524

Incidentally, I have another essay posted on "Physics Forums" that relates to the determination of the elements of an asteroid's orbit using the Method of Gauss on telescope observations from Earth at three different times. The URL for that essay is

http://www.physicsforums.com/showthread.php?t=36657

Credit in that case would be to me and to the Russian astronomer A. D. Dubyago.

Jerry Abbott

Pronunciation??

How is "Hohmann" pronounced? unsigned comment by 69.132.53.190 01:36, 2 June 2007

hōmân -- emphasis on the first syllable. First syllable rhymes with "Joe". Second syllable rhymes with "John" (kind of). Karl Hahn (T) (C) 02:12, 2 June 2007 (UTC)

Error - delta V equations are actually total velocities not impulses

The velocities listed as delta V's are not the change in velocity required to complete the maneuver, but rather they are the total velocity at the point of maneuvering.

To get the change in velocity one must subtract the current velocity in the orbit.

I am changing the equations to reflect that these are total velocities at periapsis and apoapsis, and not delta V's.

I would like to add equations that reflects total delta V for both impulses, by subtracting the velocity of a circular orbit at that altitude, but since I'm at work I can't do that immediately, so anybody else feel free to add that if they want! Mattski (talk) 23:28, 17 January 2008 (UTC)

Your change does not seem correct, take e.g. r1=r2. The subtraction is already in the formulas.--Patrick (talk) 01:45, 18 January 2008 (UTC)

Sorry for the bad edit. I was using the formulas on the page and getting incorrect answers because I was using altitudes instead of radii. I redid the derivation and these formulas are indeed correct delta-v's. 65.160.147.253 (talk) 21:30, 18 January 2008 (UTC)

By impulses astrodynamics engineers mean instantaneous changes

Is there some way to make clear in the lead paragraph of the article that the two engine burns are assumed to take place in zero time, i.e. they each create an instantaneous change in delta-v? The lead sentence is already a bit lengthy.... (sdsds - talk) 03:37, 28 May 2008 (UTC)

Formula Questions

The G in the formula should be changed to a nice greek Gamma in my eyes

It shouldn't. The G you refer to is the Gravitational constant and is very standard practice Cole.christensen (talk) 09:00, 30 October 2008 (UTC)

Where it shows the vis viva equation, the equation has an M but the meanings for the parameters only mention a mu (greek letter). Which is?

mu is the Standard gravitational parameter, M is the mass of the larger object Cole.christensen (talk) 09:00, 30 October 2008 (UTC)

Deceleration wording confusion

This is confusing:

At the other end, the spacecraft will need a certain velocity to orbit Mars, which will actually be less than the velocity needed to continue orbiting the Sun in the transfer orbit, let alone attempting to orbit the Sun in an Mars-like orbit. Therefore, the spacecraft will have to decelerate and allow Mars' gravity to capture it.

A spacecraft that has Hohmann transferred from Earth's orbit to Mars's will have a linear velocity of about 21.4 km/s, where Mars is going around the Sun at about 24.1 km/s.

That's not a deceleration. What will happen in practice is that the craft will be slightly ahead of Mars in the orbit, and let Mars "catch up with it."

Perhaps what the article meant to say is that the craft will decelerate relative to Mars.

Direction of engine firing confusion

This statement seems backwards, or at least ambiguous:

"Hohmann transfer orbits also work to bring a spacecraft from a higher orbit into a lower one – in this case, the spacecraft's engine is fired in the opposite direction to its current path"

To go into a lower orbit, you would fire the engine in the same direction as the current path, that is to say, the rocket engine's exhaust would be emitted in that direction.

Perhaps less ambiguous would be something like "the spacecraft's engine is fired to create a thrust in the opposite direction to its current path".

Spope3 (talk) 23:49, 9 November 2008 (UTC)

Broken link

Reference 1 appears to be broken. --Coosbane (talk) 21:01, 7 February 2009 (UTC)

periapsis vs. apoapsis: it depends on whether transferring into a higher or lower orbit!

The article had a mistake in attributing the first delta-v to periapsis; that's clearly only so when transferring from a lower into a higher orbit. I've corrected the mistake, generalizing the article to transfers from a higher into lower orbit as well. The edit was reverted, on the grounds of "unencyclopedic tone." Could you please elaborate on that? I guess you (i) agree with the need for the edit but (ii) doesn't agree with the particular wording. If you don't care to reword rather than revert, correctness should take precedence over tone. 128.138.43.113 (talk) 02:41, 9 March 2009 (UTC)

Sorry, I think I jumped the gun a little too fast there. The revert stating "unencyclopedic tone" did not refer to the edit that I was concerned with, which remains in effect. So I take back my protest. 128.138.43.113 (talk) 04:08, 9 March 2009 (UTC)