TL7 Spaceship Design

[AlexanderHowl]

Orion drives could function with pure fusion reactions for the bombs, though that would be a TL9 civilization (or TL^). Using pure fusion devices would negate any radioactive fallout and would potentially allow for a cheaper bomblet (probably $125,000 per ton). At TL9, it could also have safeties that would prevent criminal theft and/or terrorist attacks.

[Verjigorm]

Originally Posted by scc

No society/civilization would ever sign off on Orion Drives for civilian use, especially in atmosphere. First there's the whole problem of mass produce nuclear ordinance for civilian use, sooner or later a terrorist WILL get their hands on one, but more importantly there's no way you can avoid releasing radioactive material.

I'm trying to work within the constraints of TL7(5+2). There's just no other plausible lift system at TL7 that can deliver what you want: cheap, ready access to space. We don't even have that now, and we're arguably on the cusp of TL9. At TL7, you're essentially constrained to delivering about 5% of your total mass as payload to orbit, or using extremely insane ideas like the Orion drive.

Once you get into Orbit, access to the other moons isn't so bad: according to Atomic Rockets' Ring Raiders page, the highest dV needed to transfer between Saturnian moons would be 9,300 m/sec of dV for a one way trip, that's around 5.8 mps of delta-V, with most of the dV costs falling between 2 km/sec and 6 km/sec. 16 tanks of Chemical Rocket fuel(can be RP-1, which may be readily available in the moon system of Saturn or a similar gas giant) is only 4.8 mps(7.7 km/sec), while an NTR can give you around 9.6 mps for 16 tanks. As a way of comparison: Getting from Low Earth ORbit to Low Lunar Orbit takes approximately 4.85 km/sec.

Some of your assumptions are going to have to change, or you're going to have to introduce handwavium superscience. I dislike superscience(though the Fusion Torch is just on the edge of "plausible", there's several proposed methods to get such performance), so I'd be more willing to play with the tech assumptions.

Perhaps they have TL9 fission technology? That'd certainly allow some decent payload into orbit: 3 NTW Ram-Rockets produce 1.5g, enough to take off without wings, and 9 tanks gives you 5.67 mps dV, leaving you with 8 systems(40% mass) for payload(including, of course, the control room, structural(armor), crew quarters, etc), which isn't that bad at all. And once in orbit, you can get away with a single engine(OR, even a smaller enginer), allowing either more fuel tanks for additional dV or payload.

And the advantage of an NTR is that it runs off extremely plentiful materials: you need water, ammonia or methane, all of which are really plentiful in a gas giant's moon system. Hydrogen gives the best economy, but requires more processing and has it's inherent problems with storage, Methane is sub optimal because the carbon contained in it will tend to "soot up" the engine, and scrubbing down the engine to get rid of it becomes a lot more difficult when the engine is RADIOACTIVE DEATH!

[Fred Brackin]

Originally Posted by Verjigorm

I'm trying to work within the constraints of TL7(5+2). There's just no other plausible lift system at TL7 that can deliver what you want: cheap, ready access to space. We don't even have that now, and we're arguably on the cusp of TL8. H!

I know this is just a minor mistake but to keep everything straight we're currently (2020) very late in TL8. Indeed, if we were on an Accelerated TL progression we passed into TL9 at the first of this year.

Or we could be on a Retarded progression and 30 years away. Probably, since TL9 stuff is coming in piecemeal (like always) we've got some TL9 stuff already and might be 30 years out on others. Personal body armor is a place where we're probably TL9 and computers we're close on.

[Fred Brackin]

Originally Posted by AlexanderHowl

Orion drives could function with pure fusion reactions for the bombs, though that would be a TL9 civilization (or TL^). Using pure fusion devices would negate any radioactive fallout

I have come to beleive less and less in pure fusion bombs but for Orion Drive they actually aren't what you want unless perhaps you can go for one of the aneutronic reactgions.

The easiest fusion reactions (De+T, DE+DE) give 80% of their energy in the form of neutrons. To transfer that energy to your pusher plate you have to have collisions with the nuclei of the plate. This will leave your pusher plate progressively more and more radioactive and if you don't retain all the mass of your plate you've got your radioactive fallout there anyway.

Dision would actually be better (for the ship at least) as fission reactions give you 94% of their energy as heavy charged particles. you could consider a hybrid MAG-ORION scheme then.

To my knowledge, the amount of serious engineering work that has been done on ORION is absolutely zero. It might be a TL7 _concept_ but hardware would almost certainly have to come later in the TL progression. If we started serious engineering now it'd be TL9 before you saw anything concete.

[Verjigorm]

Originally Posted by Fred Brackin

I know this is just a minor mistake but to keep everything straight we're currently (2020) very late in TL8. Indeed, if we were on an Accelerated TL progression we passed into TL9 at the first of this year.

Or we could be on a Retarded progression and 30 years away. Probably, since TL9 stuff is coming in piecemeal (like always) we've got some TL9 stuff already and might be 30 years out on others. Personal body armor is a place where we're probably TL9 and computers we're close on.

Yeah, I need to go back and edit that to say "cusp of TL9". Depending on how some current developments(looking at you Starship) shake out, we may see affordable access to space in the next decade or two, or we may not.

[Ulzgoroth]

Originally Posted by Fred Brackin

I have come to beleive less and less in pure fusion bombs but for Orion Drive they actually aren't what you want unless perhaps you can go for one of the aneutronic reactgions.

The easiest fusion reactions (De+T, DE+DE) give 80% of their energy in the form of neutrons. To transfer that energy to your pusher plate you have to have collisions with the nuclei of the plate. This will leave your pusher plate progressively more and more radioactive and if you don't retain all the mass of your plate you've got your radioactive fallout there anyway.

Dision would actually be better (for the ship at least) as fission reactions give you 94% of their energy as heavy charged particles. you could consider a hybrid MAG-ORION scheme then

From what I've seen you don't normally try to drive Orion with the direct fission particle output. Orion propulsion charges contain a bunch of strategically-placed material that absorbs a bunch of the nuclear output and gets flung at the pusher plate.

[AlexanderHowl]

In the case of a neutronic fusion reaction, you would probably use a sheet of boron surrounded by a mass of ice, as the combination is an adequate neutron absorber. I do agree that aneutronic reactions are better though.

[Johnny1A.2]

Originally Posted by Fred Brackin

To my knowledge, the amount of serious engineering work that has been done on ORION is absolutely zero. It might be a TL7 _concept_ but hardware would almost certainly have to come later in the TL progression. If we started serious engineering now it'd be TL9 before you saw anything concete.

True. OTOH, some serious theoretical work was done, if work had proceeded back in the 1960s, by now we'd either have viable Orion-drive spacecraft or we'd probably know why it just isn't practical. There's no way to say since that practical work was not done.

But it's certainly plausible that it could have worked, and it's the only really viable known way to get large-scale, long range space flight at TL7.

[Verjigorm]

I'm not going to beat the weeds too much for the Orion: If you don't want to use it, you definitely don't have to. And there's significant reasons not to use it: in addition to the fallout, nuclear proliferation risks, there's also the fact that it can't be used to land, so you'd either need to expend the whole affair(an expensive idea) or devote a substantial portion of it's payload to a secondary method of re-entering(which cuts deeper into the mass ratio). And, we don't need it. I do continue to think that you may want to increase the techlevel a skosh, as TL8 and TL9 offer some useful and interesting space propulsion.

But let's talk about what we CAN do with TL7 rocketry, because it's not all bad. 4.73mps will put us into orbit, which is a substantial discounter compared to earth, and that same amount of deltaV will allow us to travel to around 90% of the locations in the moon system, once in orbit. Which is an immense benefit: for the same technical difficulties as we had going to the moon with Apollo, the Kobillons have access to two habitable worlds, and 4 that are not habitable? That's not bad at all.

Once in Orbit, a ship with 9 tanks of fuel can reliably hope from orbit of one moon to atleast one other moon via hohmann, and we're talking about transfer times that are fairly short, ranging from as few as eight hours up to maybe a month. As they say "half way to anywhere".

If you used staged rockets for lift vehicles, you can push your payload fraction to around 12% of your total mass, instead of 5%.

An SM+9 rocket is approximately something the size of a Saturn 5. If you choose to do a full-sized upper stage, you'll have to shed some tanks. Fortunately, you can use a halfsized or smaller engine, and still take off from Kobillon(though realistically you'll probably lose more dV to the atmosphere and gravity due to sluggish acceleration), which would allow us to get up to 3.24 mps from our first stage, requiring us to get the final 1.5 or so mps from our 1000 ton SM upper stage into Orbit, and requiring 9 to 10 systems(technically 8.6 fuel tanks and .3 Engine), leaving a substantial amount of systems available for crew/passengers/cargo.

If you can do orbital refueling, either by launching from Kobillon's surface, or you've established a mining/refining operation on another moon, you can easily shuttle around 450-500 tons to another moon, which could be as many as 500 people to around a third of the possible destinations(where you can use passenger seating due to the transfer time being less than 24 hours), though 200 or so non crew passengers sounds more reasonable for the majority of the trips(that's assuming bunks instead of cabins, so cramped and crappy is the rule).

If you can develop a reliable means of reusing your vehicles, that would be a pretty big deal, too. If you throw a SLS on your 16 tank lift rocket, you can still deliver an upper stage, without the upper stage having to use it's own dV to reach orbit, and you get to reuse your lift vehicle, which really helps drop the launch costs. I still think that full-fledged colonization and regular travel between the moons is a feature of a TL5+3 society rather than a TL5+2 society, however the plentiful locations to visit may certainly fuel more investment into space exploration and further development of the technologies needed.