02-23-2017, 12:07 PM | #1 |
Join Date: Aug 2004
Location: Hamilton, Ont. CANADA
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[Space, Spaceships] Total ΔV for Interplanetary Travel
When calculating the total ΔV for an interplanetary trip, do we have to add the ΔV for breaking planetary orbit (both from the origin and braking to the destination) to that of the interplanetary transfer orbit?
Dalton “who is working on a One-Tangent Burn Orbit spreadsheet” Spence
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02-23-2017, 12:22 PM | #2 |
Join Date: Feb 2011
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
You want the sum of the ΔV required to break orbit from the origin, the ΔV used in the transfer itself, and then, yes, the ΔV expended to attain orbit at the destination.
In theory. In practice, good piloting can reduce the ΔV needed on arrival, and if the destination has an appropriate atmosphere and you have a ship that can handle hypersonic atmospheric burns, you can use areobreaking to achieve orbit at the destination for a fraction of the ΔV cost. All of this assumes a Hoffman transfer, which is generally both simple and low-ΔV-cost. The downsides are that it requires specific windows to work well, and it's fairly slow. If one has very large reserves of ΔV, it's possible to fly from the origin to the destination directly, and I think there's notes on that in GURPS Space. Or Spaceships. Can't remember. Best of luck! |
02-23-2017, 12:24 PM | #3 |
Join Date: Jul 2008
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
On consideration, I think that's probably necessary.
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02-23-2017, 12:34 PM | #4 |
Join Date: Jun 2006
Location: On the road again...
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
How much difference is there if launching from Earth's surface as opposed to being launched from a facility already in orbit?
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02-23-2017, 01:28 PM | #5 |
Join Date: Jul 2008
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
Per Spaceships p37, going surface to escape costs planetary escape velocity, while going from low orbit to escape costs 30% of escape velocity.
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident. |
02-23-2017, 01:39 PM | #6 | |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
Quote:
The limit case for infinite thrust is ΔV = sqrt( escape velocity ^ 2 + transfer velocity ^ 2 ) - orbital velocity, to either enter or leave orbit. For example, from low earth orbit (escape velocity = 11.2 km/sec, velocity = 7.92 km/s) to a Mars transfer orbit (2.9 km/s) requires sqrt( 11.2^2 + 2.9^2) - 7.92 = 3.65 km/s, which is barely more than the 3.28 km/s required to break orbit. Launch direct from ground saves the fuel required to circularize your orbit. Last edited by Anthony; 02-23-2017 at 02:36 PM. |
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02-23-2017, 03:11 PM | #7 | |||||
Join Date: Aug 2004
Location: Hamilton, Ont. CANADA
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
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Dalton “still working on his Mars Semi-Cycler” Spence
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02-23-2017, 03:26 PM | #8 |
Join Date: Jan 2005
Location: Gothenburg, Sweden
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
So it won't work with Linux? :o)
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02-23-2017, 04:39 PM | #9 |
Join Date: Feb 2011
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
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02-23-2017, 05:58 PM | #10 | |
Join Date: Aug 2007
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Re: [Space, Spaceships] Total ΔV for Interplanetary Travel
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It's usually a glossed over effect and I know of no easy databases but the planets of our solar system mostly do have different orbital planes..
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space, spaceships |
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