Trying to build reaction drive ship

[The Vrusk]

So, quick question using High Guard with Companion rules ...

How much fuel tankage would be required for a TL13 reaction drive (advanced: fuel efficient -20%) on a 600 ton ship to burn at 1G for 96 hours (to reach 1% lightspeed). My math skills suck and my calculations don't seem to work.

 

[Geir]

Plugging into my spreadsheet with only moderate caffeine intake, I get 1152 tons at -20% high efficiency. Which is bad for 600 ton ships...
At -60% really high efficiency I get 576 tons, which is barely plausible.
Reaction drive as written is not really suited for that level of velocity.
One of the next JTAS (probably #12) will include a fusion drive developed by the Hhkar which should be more efficient.

 

[The Vrusk]

Yeah, I had the same figures. OK. So, Star Frontiers ships powered by 1G reaction drives that need to reach 1% lightspeed to jump FTL are quite silly. in-game, the fuel tankage for an "ion drive" is fairly immense - allowing for 30,000 units of fuel each providing a turn of 1G. They also use "atomic" drives which I assume are fission-fragment which may be more ... plausible/explainable. I'm starting to think their "ion drives" are actually gas-core nuclear light-bulbs. But those still would require reaction mass.

I'm wondering if there is a way to hyper-compact reaction mass, such as making metastable metallic hydrogen?

I'm looking at 2300 AD and some third-party near-future supplements for answers. Also looked at Transhuman Space, but the math throws me.

 

[Condottiere]

I think I can safely say I've gone through all possible variations of spacecraft locomotion.

There are very few use cases for reactionary rockets in Mongoose Second, and none for long ranged transportation.

Unless you an harvest hydrogen atoms in sufficient numbers with a ramscoop.

 

[Baldo]

Also looked at Transhuman Space, but the math throws me.

https://www.amazon.com/GURPS-Spaceships-David-L-Pulver/dp/1556348169/ref=sr_1_1?crid=2IEE7LGLPNUMV
http://www.warehouse23.com/products/gurps-transhuman-space-changing-times
http://www.warehouse23.com/products/gurps-spaceships-8-transhuman-spacecraft

Just in case, have you looked at the revised books? Steve Jackson Games simplified Transhuman Space and its spaceships in the linked books above, maybe you can give it a try (they have lots of explanations and options for reaction drives: discover what happens if your drives burn ammonia or methane, for example).

 

[Reynard]

Reaction drive shows how much hard science sucks in science fiction.

 

[The Vrusk]

Yeah, screw it. Just build ships for my Star Frontiers game with good old Traveller maneuver drives. I'll still keep the zero-G and difficult planetary landings as those are part of the flavor. And laser blasters and inertia screens, of course.

 

[Reynard]

Somewhere in one of my Traveller folders I searched for the dimensions of the space shuttle to estimate volume at about 71 dtons without the wing and guestimating the wings adding another 15 dtons. I recreated the shuttle using High Guard first with only reaction drive then upgraded to equivalent maneuver. Later enlarged the ship to 100 tons so it could be refitted with jump 1. To say the least, the ship was not going too far. Big advantage was the shuttle, using Traveller physics, can take off without the booster assembly!

 

[Lurking Grue]

Reaction drive shows how much hard science sucks in science fiction.

Yeah, in order to have high-flying space opera, you're pretty much screwed if you try to go hard science, the reaction rocket way. It's not totally impossible, but you're likely going to have to have some hand-waves with spacecraft propulsion, veering away from true hard science, into a more "hardish science", i.e. something that's not utter technobabble but not hard science either. Be that as it may, reaction rockets describe a very different universe and pose quite a few dilemmas to solve when compared to one with reactionless thrusters.

I've been tinkering with this IMTU, using a version of TNE's HEPlaR drive as a base (which is a plasma rocket of sorts), but dropping its base efficiency some (as it is *very* efficient in TNE). I've added in a magnetic or gravitic (depending on how hand-wavy I want to go) accelerator to the exhaust bell, which further increases exhaust velocity to get more delta-V out of the drive. Nonetheless, the drive isn't getting you anywhere fast when compared to thrusters and you're quite limited in your thrust endurance. But that's okay with me as it is the mood I'm after, where ships do 1-2 hour burns and coast the rest of the way (before jumping). I've had to lessen the required jump fuel amount to get part of that fuel capacity for remass. Fortunately hydrogen is suitable for both the Jump Drive and the HEPlaR. This modified HEPlaR pretty much precludes planetary landings for most ships, because they wouldn't reach escape velocity and/or would incinerate the landing site. That's quite different from OTU and wouldn't suit most Traveller players at all, but it's the mood I'm after - starships usually carry landers/dropships for planetary landings and dock at orbital stations themselves. One of the big inspirations for this kind of universe has been C.J. Cherryh's Chanur Saga books (plus a bit of the Expanse thrown in). But enough of that, suffice to say, reaction rockets will inevitably change the Traveller universe into a very different beast than the OTU Mongoose one.

 

[Geir]

If you increase the exhaust velocity (specific impulse or ISP for those tinkering with 'real rockets') for a plasma or fusion drive, like Heinlein's old torch ships, you can get really good performance. Problem is when you look at the amount of energy (powerplant) you need to accomplish that and give the rocket any more than a minuscule thrust (like a very small fraction of a G) and then think about the second law of thermodynamics, then even if you're 99.99 percent efficient, you're going to melt the hull without massive (okay, not necessarily 'massive' but giant surface area) radiators to get rid of the waste heat (and then think about how you channel that heat to the radiators without melting the connectors). That's the problem with real 'hard science' reaction drives.

Stupid second law.

M-drive gets us around that with mumble, mumble, handwavium, mumble, gravometric disturbances in spinning quantum superconducting condensates - oh look over there, I just pulled a rabbit out of someone else's hat!

I once tried to make some fake science version of an gravity propulsion field just to model it, and it turns out that if any such thing did exist and was more energy efficient than a reaction drive, you could likely also use it to make a perpetual motion gravity pump and get energy for 'free'. But it's a game. So I accepted the premise in that light and moved on.

 

[The Vrusk]

Fun discussion. So what about fission-fragment drives? Those seem to match Star Frontiers' "atomic drives" and it loks like fuel consumption/reaction mass is quite small. Of course, they conveniently forget that the alien race determined to exterminate them could simply land a fission fragment small hull ship on a city to produce untold horrors. Atomic drives tend to have a nasty side effect.

Ya know, between 2nd Edition's Companion and High Guard, and 1E's various books, I can create darn near any crazy setting I want. LOVE the Companion book, as it scratches my itch to bring Traveller back to a great set of generic sci-fi rules not iron-clad bound to the Third Imperium setting. Of course, its easy to use all teh adventures - just change the names. I've run Ordeal By Eashaar (my God, they need to remake that for 2nd Edition) and made the Zhos into Star Wars Imperials and other "baddies."

 

[Reynard]

Found my space shuttle design. Seems I was attempting to fit maneuver and jump 1 in the shuttle frame. Had to make the frame larger to meet the minimum size. Anywho...

I found the size as mentioned in my last post. Total of 87 dtons. Hull is streamlined with aerofins, non-grav and light. Made it TL 7 with Reaction engine 3, Chemical power plant to run the lights and AC with enough fuel for 12 weeks. Standard bridge, computer 5 and Reaction(maneuver)/1 plus library. Sensors are TL 7 Basic(prototype) at DM -6. 22 dtons of cargo space (as per real shuttle), 5 Double staterooms for up to 10 crew as well as 8 acceleration seats for crew other than the commander and pilot. Add the heavy grappling arm.

Last is the reaction fuel. There was 7.75 dtons left. Calculation says it will last 10 combat rounds or 1 hour, 11 minutes and about 16 seconds. Travel from surface to orbit take 19 minutes. To reach Liberty Station, it takes 2 hours... oops. Maybe they will still need the booster assembly to get to orbit and use the on-board fuel for orbital maneuvering and landing.

They were SO relieved when they reached TL 9 with the advent of maneuver drive and, later jump 1.

 

[Lurking Grue]

Atomic drives tend to have a nasty side effect.

Well, nearly every relatively powerful reaction drive has nasty side effects. It's the Kzinti Lesson (by Larry Niven) at work: "a reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive."

 

[Baldo]

Atomic drives tend to have a nasty side effect.

Well, nearly every relatively powerful reaction drive has nasty side effects.

https://www.sjgames.com/pyramid/sample.html?id=6603

DRIVE HAZARDS
Antimatter plasma rockets and torches, fusion rockets and torches, super fusion torches, and all fusion pulse drives produce plenty of heat and hard radiation behind the spacecraft! Although the drives can be operated safely, environmentally conscious authorities are very likely restrict their operation near populated orbits or habitable worlds. This could either result in a total ban from use in inhabited areas, or it might just limit them to operations in out-of-the-way deserts, oceans, or high orbit. [...]

Antimatter pion and antimatter pion torch engines, and (probably) total conversion and super conversion torches will produce directional and highly lethal energy beams. Their danger zone may extend for hundreds or even thousands of miles behind the vessel! Such engines are likely to banned from operation anywhere near a settled planet's space. Spaceports may be placed on distant asteroids, or ships may require the equivalent of tug boats to boost them out far enough that they can safely use drives. [...]

Nuclear saltwater rockets and external pulsed plasma engines produce continuous or pulsed nuclear explosions outside the ship. If you take off from the ground with one of these drives, you'll be leaving behind a big radioactive crater . . . [...]

Ramscoops generate magnetic fields at lethal intensities in front of the vessel, likely covering hundreds or thousands of miles. [...]

Space drives not listed above aren't free of hazard, but if properly operated aren't likely to raise the hackles of local spaceport authorities. However, there may be specific regulations ("make sure a mass driver uses very fine dust!") but these are likely to apply to any spaceship operations. Superscience reactionless drives and stardrive engines may be perfectly safe or have nasty side effects, at the GM's discretion. [...]

 

[feld]

Just so I'm perfectly clear: this whole thread is only re: the Traveller setting and/or High Guard right? The new 2300AD Aerospace Engineer's Handbook's added much-needed reaction drives to the 2300AD setting and seems to use a little less unobtanium plumbing in it's reaction drives.

I'm still going thru the numbers though.

 

[feld]

If the OP wants I think this calculator here will give you what you apparently need:
http://gregsspacecalculations.blogspot.com/p/blog-page.html

It's a relativistic rocket calculator with in puts for spacecraft (s/c) mass, acceleration, etc. and provides answers to various useful questions in tailorable units.

I would put in the numbers myself for you and just give the answer to your question but I don't know the High Guard ship design system at all so I don't know the volume-ton to mass-ton conversion in use there.

Caveat: I've not checked this person's work but the equations for this aren't that tough to derive or find so it's likely that they got it right and got the bugs worked out by now.

v/r
feld

 

[Arkathan]

Just so I'm perfectly clear: this whole thread is only re: the Traveller setting and/or High Guard right?

Yes.

 

[Bryn the 2300AD guy]

Just so I'm perfectly clear: this whole thread is only re: the Traveller setting and/or High Guard right? The new 2300AD Aerospace Engineer's Handbook's added much-needed reaction drives to the 2300AD setting and seems to use a little less unobtanium plumbing in it's reaction drives.

I'm still going thru the numbers though.

The reaction drives are less plausible than the stutterwarp. Exhaust velocities > 1,000,000 mps which is literally impossible unless using antimatter as the power source. One burn in the Kennedy equates to the release of 9.8x10^15 joules, or just over 2 megatons of TNT. To put it another way, the Kennedy's fusion reactor takes almost 3 years to supply that much electrical energy.

Whenever an AEH ship lights up a thruster or OMS, it should be vapourised by the quantity of heat released.

Who needs nukes, when you have reaction drive "stone burners?"