Using Traveller ships and deck plans for ships with reaction drives
- Thread starter Thot
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Wouldn't that depend on how much energy the contragravity generator was drawing to do its job? I mean, strictly speaking the same claim could be made of an escalator: start at the bottom with a mass M, drop mass M when it reaches the top for the energy - but the escalator uses more energy getting it there than can be recovered by dropping the mass.
Sure, but if it doesn't, you don't gain anything and could as well use a different method, like wings and a jet engine.
Say you have contragrav that counteracts 1 G and want it to obey conservation of energy. That means you'd need 0,5*9,81m²=48 Watts per kilogram of your ship to keep it at the same altitude. Or 50 KW per ton, 50 MW for a 1000-ton (100-200dton) ship (like a Scout/Courier or some freighters).
Compare this to the engines of the Eurofighter Typhoon: 60 kilonewtons of thrust for a 16 ton-ship, which is enough for about 3m/s² acceleration, that is equivalent to about 3,75 Watts per Kilogram.
The basic issue is: We, as SF fans, have utterly unrealistic expectations.We want a spaceship that basically looks like an airplane, and has airplane dimensions. But that's not going to happen, not in a world that is anywhere near the real one. Sure, we can make up magic that allows for flying such things, but what's the point?
Why don't we just shrug and accept that a SSTO ship is 300 meters tall for a small free trader, consisting of 95% or more fuel? Isn't it just simpler and more honest to ourselves to accept this simple fact?
I can handwave on-board fuel production methods and extremely efficient starport services, which make the enormous amounts of fuel required dirt cheap, into being a lot easier than altered laws of physics. Also, I can simply accept that later chemical rockets are a lot safer and a lot more reliable than today's, while also being a lot cheaper.
Sure, in such a universe, a Tigress class dreadnought will have far less impressive stats. But as everybody is bound by the same rules, it will still rule local space, even if that local space is smaller than in the OTU.
Why don't we just shrug and accept that a SSTO ship is 300 meters tall for a small free trader, consisting of 95% or more fuel? Isn't it just simpler and more honest to ourselves to accept this simple fact?
I can handwave on-board fuel production methods and extremely efficient starport services, which make the enormous amounts of fuel required dirt cheap, into being a lot easier than altered laws of physics. Also, I can simply accept that later chemical rockets are a lot safer and a lot more reliable than today's, while also being a lot cheaper.
Sure, in such a universe, a Tigress class dreadnought will have far less impressive stats. But as everybody is bound by the same rules, it will still rule local space, even if that local space is smaller than in the OTU.
mike wightman
SOC-14 10K
Have you taken a look at the SSTO spaceplanes on the drawing board today?
https://en.wikipedia.org/wiki/Skylon_(spacecraft)
made possible my this engine:
https://en.wikipedia.org/wiki/SABRE_(rocket_engine)
Add a TL or two and a fusion power plant...
https://en.wikipedia.org/wiki/Skylon_(spacecraft)
made possible my this engine:
https://en.wikipedia.org/wiki/SABRE_(rocket_engine)
Add a TL or two and a fusion power plant...
It's also TL8. Until jump drives appear at TL9, it is sufficient. It is not unreasonable to postulate a significant improvement at TL9, enough to allow landing and takeoff from uninhabited size A worlds (and I think this specific requirement allows a useful drive for gaming).
mike wightman
SOC-14 10K
That's where the fusion powered plasma rocket kicks in...
One thing to consider is that a jump/ftl capable craft under such a paradigm is unlikely to also be able to take off and land from worlds and carry a meaningful cargo/lots of weapons and armour.
Interface craft and beanstalks, electromagnetic 'first stage' (fire your interface craft along a railgun), all may be the order of the day if you don't want to introduce magitech.
Starships that can take off and land would be specialist scout/exploration rather than traders or warships due to the space and mass taken up by the interface engines.
Would make for an interesting setting...
Basic physics stands in the way there (which is why Traveller assumes magic tech that violates physical laws).
E=1/2m*v²
That will always be true. If you increase exhaust velocity, you increase energy requirement to the square.
We know the theoretical maximum output of a fusion reactor (also basic physics, essentially). You could thus work with a fusion rocket with an exhaust velocity of something like 50km/s, so for 10% of your ship' mass as reaction mass, you get 5 km/s delta V. As the basic value for my initial considerations, I found that 120km/s would be the minimum required for using the Traveller deck plans. You could possibly do that with electric propulsion, but the energy you need for that is beyond the capability of fusing hydrogen atoms (!), even assuming extremely advanced reactors and engines that somehow don't kill the crew. (Antimatter reactors have a lot of other drawbacks, not just that they are batshit crazy dangerous in normal operation mode).
It is not by chance that human present-day technology uses chemical rockets. They are, all things considered, very likely the best deal that is available in this universe. Today, next century, and in ten thousand years.
I have come to the conclusion that my campaign will have to work with that. Chemical rockets all they way. Even ion drives and such are basically too energy expensive and to low-power, even for interplanetary travel - it is just that we have this odd fixation with a low overall spacecraft mass, instead of just finding ways to make liquid hydrogen and liquid oxygen a lot cheaper and chemical rockets a lot more reliable.
That means no existing Traveller deck plans. It means an orbiter "mothership" and a landing craft or some way to get down and up again - possibly a comparatively "small" vertical takeoff and vertical landing rocket that launches mostly empty to save weight for the landing (with a separate drop capsule to get down everything else), and with the ability to make its own fuel from available materials with a highly automated, efficient process.
For an interstellar society that has (as the only real magic) some FTL drive, but is hard-hard SF in everything else, there will be rentable vertical landing and takeoff carrier rockets at every starport (much like naval tugs today), and every port will have an orbital component (otherwise it isn't a starport).
But that basically means the premise stated in the subject of this thread is not achievable. Traveller deck plans are, if you allow the slight exggeration, from the genre of fantasy, not SF, because they aren't science, but magic.
mike wightman
SOC-14 10K
I still don't see why you would use chemical rockets for interface craft once you have a mature Skylon/SABRE engine...
Ion drives/plasma rockets for spacecraft...
Ion drives/plasma rockets for spacecraft...
Sure, but I am into making my own game worlds anyway.
Transhuman Space is beautiful, but it still makes extremely optimistic assumptions about hot fusion power (a concept that may actually never work for making net energy available), and doesn't really answer the question why we should do all that space travel. 2300 AD is interesting (I always liked good military SF), but somewhat outdated, not only because all the WW3 backhistory.
I have an idea... let me start a different thread for it.
The current version from Mongoose reworks the history in the period covered by Twilight 2000 and a bit beuond, but keeps the same general "modern" setting in 2300.
So they just postponed the Third World War? Interesting. Maybe I should grab a PDF or two.
Anyway, After further consideration, there are actually a few cases where Traveller deck plans might work: Basically, for all unstreamlined ships that then serve as mere "jump ferries". The XBoat tender, for instance, or the Kugashin class Lab Ship.
Even the Tigress class dreadnought (looking at GT Starships here, which has a cross-section of the vessel) would, due to its 40% tank, actually work as an interstellar vessel to defend or attack jump points. Its delta V would be merely
Also, while looking at my old copy of the German translation of "Merchants and Gunboats", the Gazelle class close escort jumped into my view... with its drop tanks!
In fact, a lot larger drop tanks might actually do the trick for all the ships. If such tanks are extremely cheap to produce (possibly even with an automated on-board factory or robot swarm?) and still sturdy, it would work... even for the smaller boats for planetside travel, where we'd just assume that the drop tanks come with their own heat shield. They would have to be massive, of course... but it should work!
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160 km is high enough to use ion drives... and the ISP is high enough that it's far less an issue.
(Tho' it trades that for increased time to EV...)
So we now also have to build a third rocket into our ship, plus a big fat reactor to power the ion drive. And in order to have a meaningful acceleration, it needs to be a really, really, really big reactor...
The phrases "meaningful acceleration" and "ion drive" are not compatible.
Yes, and that is also because of (among other things) E=1/2m*v².
Winchell's calculations on Project Rho / Torchships calculate a plasma torch drive with 0.3-g acceleration requires 450 GW of power and puts out 0.108 kilotons/second. And that's just an 8.3-hour burn to 90 km/s, coast, flip, and burn for another 8.3 hours to stop. It's not constant acceleration.
He also calculates that you can reduce the power requirements by 90% (close to a Saturn V stage-one thruster) and only add a few days of travel to a weeks-long journey.
450 GW is a lot of power, and a requires a lot of fuel.
In Winchell's calculations, he's imagining a 1000 metric ton (1,000,000 kg mass) ship carrying half that much in fuel (500,000 kg). These tons are the same weight as Traveller's tons of hydrogen (whose volume make up our displacement-tons). So that 1000-ton ship is actual mass, not displacement.
Didn't someone share a tonsOfDisplacement-to-tonsOfMass ratio elsewhere?
He also calculates that you can reduce the power requirements by 90% (close to a Saturn V stage-one thruster) and only add a few days of travel to a weeks-long journey.
450 GW is a lot of power, and a requires a lot of fuel.
In Winchell's calculations, he's imagining a 1000 metric ton (1,000,000 kg mass) ship carrying half that much in fuel (500,000 kg). These tons are the same weight as Traveller's tons of hydrogen (whose volume make up our displacement-tons). So that 1000-ton ship is actual mass, not displacement.
Didn't someone share a tonsOfDisplacement-to-tonsOfMass ratio elsewhere?
Some of the fastest probes we've sent got a HUGE raft of delta-V from ion drives.
It's VERY significant - just not rapid.
