Exotic Propulsion for Small Craft

[marginaleye]

Does anyone have any thoughts on rules for fuelling an AZH (advanced zero-to-hypersonic) engine with liquid hydrogen, instead of hydrocarbon distillates?

I've been toying with the idea of trying to run a campaign without contra-gravity or reactionless thrusters. Given such restrictions, getting up into orbit becomes a lot more difficult, particularly if one assumes that the exhaust from HEPlaR drives so destructive that using them within the atmospheres of inhabited planets is usually prohibited. The best answer seems to be some sort of "fly-into-orbit" hypersonic shuttle with an air-breathing "advanced zero-to-hypersonic" (AZH) engine (which includes has a built-in rocket booster, for the final kick up into orbit).

As written in T4 FF&S, however, the AZH engine burns hydrocarbon distillates in "air-breathing" mode, and only switches over to a liquid hydrogen/oxygen mixture in rocket mode. I've done some reading on the subject of hypersonic aircraft, and discovered that (at one point, at least), the NASA's "X-30 National Aerospace Plane" (NASP) was supposed to be fueled entirely with liquid (well, actually "slush") hydrogen.

Can anyone suggest rules for how to adapt the rules for AZH engines in T4 FF&S to hydrogen consumption while still in "air-breathing" mode? The Traveller universe seems to run on fusion, so fueling ground-to-orbit shuttles with ubiquitous liquid hydrogen (instead of relatively exotic hydrocarbon distillates) would certainly be more convenient, from a purely economic/logistical point of view. Furthermore, exploration and military vessels would prefer to carry hydrogen-fueled shuttles, since they could keep them refueled "in the field," using "skimmed" hydrogen, purified onboard.

 

[shield]

The TNE fusion fire and steel states that the various hydrocarbon burning engines can be modified to burn hydrogen with no loss of power or efficiency. The biggest problem is that the rocket will use a certain tonnage of fuel and the low density of hydrogen means that fuel tonnage takes up a lot more volume than the equivalent tonnage of petrol.

Cheers
Richard

 

[marginaleye]

The TNE fusion fire and steel states that the various hydrocarbon burning engines can be modified to burn hydrogen with no loss of power or efficiency. The biggest problem is that the rocket will use a certain tonnage of fuel and the low density of hydrogen means that fuel tonnage takes up a lot more volume than the equivalent tonnage of petrol.

Very interesting.
So there are no differences in any of the engine's other characteristics either (its volume, mass and price per unit volume, and so forth)? Thanks, by the way, for the quick reply.

Needless to say, dropping contra-gravity and reactionless thrusters will probably throw a huge monkey-wrench into the canonical starship economics rules. The cost of hauling things across interstellar distances would probably be about the same, since the jump-capable freighters would use relatively fuel-thrifty HEPlaR drives for in-system maneuvers (while I have to admit there is a certain charm in the idea of a universe in which everyone is puttering along with ion-drives and gas-core nuclear thermal reactors, I think that might be going a bit too far), the cost of the "last (couple of hundred) miles," from orbit to the planet's surface, would be huge -- a substantial percentage of the cost of the whole trip. Asteroid belts would become much more attractive places to colonize, and many things (ores, most foods, etc.) just wouldn't be worth hauling at all. There would be military consequences too, of course (shipping enough troops to occupy another planet effectively would be nearly impossible).

 

[Rupert Boleyn]

Originally posted by marginaleye:

There would be military consequences too, of course (shipping enough troops to occupy another planet effectively would be nearly impossible).

Only if you had to drag them out of the gravity well of another planet first. Getting down is fairly cheap - it's getting into orbit that hurts.

 

[marginaleye]

Only if you had to drag them out of the gravity well of another planet first. Getting down is fairly cheap - it's getting into orbit that hurts.

The implication would be that troops would have to be garrisoned up in space, and only shifted "dirtside" when absolutely necessary. Some empires might pay enlistment bonuses to belters (not quite as big as the price of hauling a ground-hugger up into orbit), but I doubt that would really solve the problem...

But keeping eating, breathing troops in space would be expensive and difficult, too. It would, for instance, be very hard to keep their skills sharp without regular dirtside training, and in a universe without contra-grav lifters and reactionless thrusters, artificial gravity probably wouldn't exist either, so maintaining good physical condition would be hard (unless there's a bio-technological way to prevent weightlessness-induced degeneration). The best solution might be to "train 'em up, freeze 'em down (in low berths, of course), and thaw as necessary." Only a tiny fraction of an empire's troops would be "warm" at any given time. Rather creepy, really...

 

[P.v.de Oliveira Verissimo]

I imagine that on developed worlds this would be less of an problem: i'm thinking of space elevators, mass drivers and laser rockets.

I'm not sure of the cost of electricity in Traveller, but the last two options might even be viable in the basic setting.

For less devoleped worlds, i imagine lots of shuttles....

See this link Shesso Type-18 DeadLift Shuttle for a relative low-tech rocket to get cargo in orbit, and here {/url] and [url=http://www.islandone.org/LEOBiblio/]here for more propulsion ideas.

I wouldn't like to be in the neighberhood if someone is using a fusion pulse engine though...

 

[P.v.de Oliveira Verissimo]

Oops!

I screwed up.

Enfin, see the IslandOne website.

BTW, Space stations/colonies would play a bigger role in this setting; i imagine spacers who have never set a foot on terra firma.

"Yeah, i've been to the Sol system. Earth? What did i had to see there?"