Steve Jackson Games - Site Navigation
Home General Info Follow Us Search Illuminator Store Forums What's New Other Games Ogre GURPS Munchkin Our Games: Home

Go Back   Steve Jackson Games Forums > Roleplaying > GURPS

Reply
 
Thread Tools Display Modes
Old 08-05-2020, 09:53 AM   #1
acrosome
 
acrosome's Avatar
 
Join Date: Aug 2010
Location: The Land of Enchantment
Default [Spaceships] Can't find the right propulsion system

Hi, all. I'm trying to find an appropriate propulsion system for little work pods and inter-ship lighters, for in the space near stations, in work areas, etc. These are not long-range vehicles so they don't need massive delta-V. But they probably do need acceleration measured in something larger than milligees, if only for time management concerns, so Ion and VASMIR drives are out.

In this setting (TL10) there is a limited superscience switch that makes antimatter extremely cheap and things like the antimatter plasma torch possible. But for small craft like this such systems wouldn't be used since every Tom, Dick, and Harry welder or taxi pilot can't be trusted with a drive that spews radioactive death.

So for the life of me the only option I seem to be able to find is a chemical rocket. But this seems like overkill at 3G acceleration. What I really need is just some sort of OMS, y'know? Have I missed some other option?
acrosome is offline   Reply With Quote
Old 08-05-2020, 10:02 AM   #2
TGLS
 
Join Date: Jan 2014
Default Re: [Spaceships] Can't find the right propulsion system

Quote:
Originally Posted by acrosome View Post
So for the life of me the only option I seem to be able to find is a chemical rocket. But this seems like overkill at 3G acceleration. What I really need is just some sort of OMS, y'know?
Yeah, 3g is way too much for something like the OMS. It was, erm, what was it:

Quote:
The RS-25 engines were throttled at T+7 minutes 30 seconds to limit vehicle acceleration to 3 g.
Oh. Well never mind then.

--

More seriously, is Antimatter Thermal not acceptable for a lower power system?
TGLS is offline   Reply With Quote
Old 08-05-2020, 10:39 AM   #3
Fred Brackin
 
Join Date: Aug 2007
Default Re: [Spaceships] Can't find the right propulsion system

Quote:
Originally Posted by acrosome View Post

So for the life of me the only option I seem to be able to find is a chemical rocket. But this seems like overkill at 3G acceleration. What I really need is just some sort of OMS, y'know? Have I missed some other option?
If "oms" means Orbital Maneuvering System such as found on the Spece shuttle that _was_ a chemical rocket. In fact it was one using hydrazine and nitrogen tet (storable at room tempeature though hgihly toxic) for fuel. It would ahve had a lower isp than the SSMEs but not an order of magnitude lower.

The OMS were a small pair of engines compared to the SSMEs and you could use a smaller than the normal SM chemical rocket for your workpod. That would cut accelration down to 1 G.
__________________
Fred Brackin
Fred Brackin is online now   Reply With Quote
Old 08-05-2020, 11:03 AM   #4
Michael Thayne
 
Michael Thayne's Avatar
 
Join Date: May 2010
Default Re: [Spaceships] Can't find the right propulsion system

Quote:
Originally Posted by acrosome View Post
Hi, all. I'm trying to find an appropriate propulsion system for little work pods and inter-ship lighters, for in the space near stations, in work areas, etc. These are not long-range vehicles so they don't need massive delta-V. But they probably do need acceleration measured in something larger than milligees, if only for time management concerns, so Ion and VASMIR drives are out.

In this setting (TL10) there is a limited superscience switch that makes antimatter extremely cheap and things like the antimatter plasma torch possible. But for small craft like this such systems wouldn't be used since every Tom, Dick, and Harry welder or taxi pilot can't be trusted with a drive that spews radioactive death.

So for the life of me the only option I seem to be able to find is a chemical rocket. But this seems like overkill at 3G acceleration. What I really need is just some sort of OMS, y'know? Have I missed some other option?
For the purpose you're describing, I really like nuclear thermal rockets. Antimatter thermal rockets might be preferred if antimatter is cheap. Sure they have a non-zero radioactive death factor, but a much smaller one than a torchdrive, and in space where everyone needs shielding against micrometeors and cosmic background radiation anyway, it might not be that big a deal. Another option is HEDM rockets but the whole "fuel tends to explode" factor might scare some people off.
Michael Thayne is offline   Reply With Quote
Old 08-05-2020, 11:11 AM   #5
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: [Spaceships] Can't find the right propulsion system

The problem you have is mostly that 5% of mass in rocket engines is a lot of rocket. Just use partial modules.
__________________
My GURPS site and Blog.
Anthony is offline   Reply With Quote
Old 08-05-2020, 12:01 PM   #6
AlexanderHowl
 
Join Date: Feb 2016
Default Re: [Spaceships] Can't find the right propulsion system

Yes, smaller systems would be a good idea. For example, a -1 SM HEDM rocket would provide 0.67g of acceleration and two -1 SM fuel tanks with HEDM reaction mass would provide 0.33 mps of delta-v (it actually has better performance than antimatter catalyzed water, which would end up being 0.2g/0.4 mps of delta-v).
AlexanderHowl is online now   Reply With Quote
Old 08-05-2020, 12:26 PM   #7
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: [Spaceships] Can't find the right propulsion system

I would avoid HEDM if not needed, seeing as it tends to be explosive. Systems with low delta-V requirements are typically willing to trade performance for safety.
__________________
My GURPS site and Blog.
Anthony is offline   Reply With Quote
Old 08-05-2020, 12:44 PM   #8
johndallman
 
Join Date: Oct 2010
Location: Cambridge, UK
Default Re: [Spaceships] Can't find the right propulsion system

Quote:
Originally Posted by Fred Brackin View Post
The OMS were a small pair of engines compared to the SSMEs . . .
They were, in fact, the basic same engine as used in the the Apollo Service Module, which is definitely smaller than the Shuttle. A later version is being used in the Orion spacecraft's service module: good rocket engine designs can stay around a long time.
johndallman is offline   Reply With Quote
Old 08-05-2020, 01:08 PM   #9
Kale
 
Kale's Avatar
 
Join Date: Aug 2005
Location: Cowtown, Canada
Default Re: [Spaceships] Can't find the right propulsion system

You can use Smaller Systems to convert a single system into three systems of one size (SM) smaller: You can replace a 3G chemical rocket with a 1G rocket and two small fuel tanks, all one SM smaller than the ship. This gives 2/3rds the capacity of a full SM sized fuel tank. If you want to go really small, you can convert down by two SM levels and get 10 systems at SM-2 for a single full sized slot. Each rocket would provide 0.3G of thrust at that level.
__________________
FYI: Laser burns HURT!
Kale is offline   Reply With Quote
Old 08-05-2020, 01:22 PM   #10
AlexanderHowl
 
Join Date: Feb 2016
Default Re: [Spaceships] Can't find the right propulsion system

Quote:
Originally Posted by Anthony View Post
I would avoid HEDM if not needed, seeing as it tends to be explosive. Systems with low delta-V requirements are typically willing to trade performance for safety.
Antimatter also tends to explode, and it seems to be ubiquitous in the setting. If you do not want HEDM, you can do chemical rockets for 1g and 0.1 mps.
AlexanderHowl is online now   Reply With Quote
Reply

Tags
rockets, spaceships

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Fnords are Off
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 10:43 PM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2020, vBulletin Solutions, Inc.