GURPS spaceships - Atmospheric braking

adimar · 01-29-2010, 06:05 AM

Hi all.
I stumbled into an interesting entry in wikipedia.
http://en.wikipedia.org/wiki/Aerobraking
If I understand this correctly it looks like this would save half the transit fuel of space launched vehicles, since no reaction mass is "wasted" on decelerating...
I wanted to ask how you would stat Atmospheric braking systems?
What would it's limitations be?
i.e. can you decelerate from any speed? In any atmosphere density? etc...
what would be the minimum dDr of a spacecraft using this method?

10x 4 your help.
Adi

Phantasm · 01-29-2010, 06:36 AM

Over in the Spaceships 7 thread someone mentioned gasbags. I'd look at adding one or more of those systems to your design.

Note to self: get some cash flow so I can buy Spaceships 3 through 7.

Ulzgoroth · 01-29-2010, 11:29 AM

I don't think there are any constraints listed on the ability of spaceships to use aerobraking.

There also, unless I'm forgetting something, aren't any rules for skimming the edge of the atmosphere, so if you want to do anything other than ditch all your interplanetary velocity you're on your own devices.

Snoman314 · 01-29-2010, 12:14 PM

There are plenty of scenarios in that the ships in spaceships make possible where aerobraking isn't an option. Basically, you already have to be going slowly enough that you can skim the atmosphere and lose enough velocity to get below escape velocity, without having to dive in so deep that you'll burn up. Its viable when a ship is doing say, a minimum energy hohman transfer orbit, because the approach velocity to the destination planet isn't too high.
As for specific rules, I'm not sure, but I'd suggest that there should be a fairly small maximum delta-v given by each aerobraking pass. And of course if the first pass isn't enough to allow the planet to capture you in orbit, you'll have to use engines anyway.

OneSeventeen · 01-29-2010, 01:17 PM

Yeah, so you also have to be worried, depending on the size of your ship and the velocity with respect to the planet, about what your (re)entry will do to the atmosphere and those that have a use for it. How much friction would be created by, say, Superman flying around the equator at ocean level in one second? Would that have an appreciable effect on the temperature of the air he's moving through? What if we replace Superman with something large enough to carry, you know, several people? Like a space ship.

I don't want to rain on anyone's parade, I'm just sayin'. There's more math to be done (if you care about this nit-picky level of realism).

Ben

01-29-2010, 06:05 AM	#1
adimar Join Date: Jan 2010	GURPS spaceships - Atmospheric braking Hi all. I stumbled into an interesting entry in wikipedia. http://en.wikipedia.org/wiki/Aerobraking If I understand this correctly it looks like this would save half the transit fuel of space launched vehicles, since no reaction mass is "wasted" on decelerating... I wanted to ask how you would stat Atmospheric braking systems? What would it's limitations be? i.e. can you decelerate from any speed? In any atmosphere density? etc... what would be the minimum dDr of a spacecraft using this method? 10x 4 your help. Adi

01-29-2010, 06:36 AM	#2
Phantasm Join Date: Jun 2006 Location: On the road again...	Re: GURPS spaceships - Atmospheric braking Over in the Spaceships 7 thread someone mentioned gasbags. I'd look at adding one or more of those systems to your design. Note to self: get some cash flow so I can buy Spaceships 3 through 7. __________________ "Life ... is an Oreo cookie." - J'onn J'onzz, 1991 "But mom, I don't wanna go back in the dungeon!" The GURPS Marvel Universe Reboot Project A-G, H-R, and S-Z, and its not-a-wiki-really web adaptation. Ranoc, a Muskets-and-Magery Renaissance Fantasy Setting

01-29-2010, 11:29 AM	#3
Ulzgoroth Join Date: Jul 2008	Re: GURPS spaceships - Atmospheric braking I don't think there are any constraints listed on the ability of spaceships to use aerobraking. There also, unless I'm forgetting something, aren't any rules for skimming the edge of the atmosphere, so if you want to do anything other than ditch all your interplanetary velocity you're on your own devices. __________________ I don't know any 3e, so there is no chance that I am talking about 3e rules by accident.

01-29-2010, 12:14 PM	#4
Snoman314 Join Date: Sep 2009	Re: GURPS spaceships - Atmospheric braking There are plenty of scenarios in that the ships in spaceships make possible where aerobraking isn't an option. Basically, you already have to be going slowly enough that you can skim the atmosphere and lose enough velocity to get below escape velocity, without having to dive in so deep that you'll burn up. Its viable when a ship is doing say, a minimum energy hohman transfer orbit, because the approach velocity to the destination planet isn't too high. As for specific rules, I'm not sure, but I'd suggest that there should be a fairly small maximum delta-v given by each aerobraking pass. And of course if the first pass isn't enough to allow the planet to capture you in orbit, you'll have to use engines anyway.

01-29-2010, 01:17 PM	#5
OneSeventeen Join Date: Oct 2007 Location: Austin, TX	Re: GURPS spaceships - Atmospheric braking Yeah, so you also have to be worried, depending on the size of your ship and the velocity with respect to the planet, about what your (re)entry will do to the atmosphere and those that have a use for it. How much friction would be created by, say, Superman flying around the equator at ocean level in one second? Would that have an appreciable effect on the temperature of the air he's moving through? What if we replace Superman with something large enough to carry, you know, several people? Like a space ship. I don't want to rain on anyone's parade, I'm just sayin'. There's more math to be done (if you care about this nit-picky level of realism). Ben __________________ My roleplaying blog: Maximizing Rockmost Quirk: Describes real people in GURPS character creation terms. [-1] Azure, two bars ermine.