Project Orion ground launch

[The Duchess of Zeon]

Sea Dragon from the 1960s is basically what you're proposing; Todd Shipyards (up here in Washington State) concluded they could build the things, being not beyond the capabilities of any yard capable of building submarine hulls from the 1960s, and that it would have a cost per kilogramme to low earth orbit one-fourth that of Saturn V.

[Sky Captain]

How feasible would be something like scramjet engine powered by nuclear heat? I`m thinking about reusable nuclear spaceplane that for most of the ascent uses atmospheric air as a reaction mass and onboard propellant only for final orbital insertion. Such a craft if feasible potentially could have very high payload fraction because it would need to carry very little onboard propellant. If it uses wings for lift then it even do not need to have thrust to weight greater than 1 allowing to use safer less powerful engines.

[kinnison]

I find it interesting to read some of the really old (early 60s) design studies for Orion. It is noted that the fallout problem gets rapidly easier, certainly per unit mass launched, with increasing vehicle size. Why? Simply because the larger designs really have to use pulse units with an ever-increasing fusion component to the yield, and fusion explosions produce less fallout as a proportion of yield than do fission ones.

This would mean that the takeoff has to use a nuke (how many SRBs can one get to light at once anyway?) but it does mean that one can launch something REALLY BIG. The largest vehicle in the studies was one of eight million tons (about three million tons payload) launched using megaton-range explosions. For reference, this thing has about four times the mass of the Great Pyramid. It would, because some of it has to be hollow, have to be about a kilometre high. Right out of the space operas, huh? Multiple-million ton spaceships a kilometre long, with lots of really big mechanical parts (bomb-launching guns, skyscraper-sized shock absorbers...)

I wish someone would write an alternate-history story with this sort of stuff as the setting. It needs a new name, though - steampunk is taken. I would do it myself but have neither the skill nor the time.

One possible feature that might make things interesting is that using such technologies for space travel would convince any hypothetical aliens witnessing it that the human race is irretrievably insane...

[Starglider]

How feasible would be something like scramjet engine powered by nuclear heat?

Feasible, but probably not worth the hassle. Scramjets have low thrust-to-weight, and it would have to be some kind of combined cycle ram/scram/rocket, which means complex variable engine duct geometry. There was a successful nuclear powered ramjet design in the late 50s/early 60s, but that operated within a narrow speed range. A better idea is probably a hybrid of the LACE/SABRE engines from Skylon and the nuclear lightbulb design; augmenting the liquid hydrogen reaction mass with liquified or near-liquified air should improve the ISP considerably. Even still, it's something you'd put in your advanced model, the extra complexity wouldn't be worth it in your first nuclear SSTO.

One possible feature that might make things interesting is that using such technologies for space travel would convince any hypothetical aliens witnessing it that the human race is irretrievably insane...

On the contrary, not building them when they're clearly the best solution might convince aliens that the human race is irretrievably insane...

[Modax]

A better idea is probably a hybrid of the LACE/SABRE engines from Skylon and the nuclear lightbulb design; augmenting the liquid hydrogen reaction mass with liquified or near-liquified air should improve the ISP considerably.

Thanks, that article on nuclear lightbulb rockets is really exciting! To think that we have the technology to build a spacestation around Saturn in the next couple decades is staggering...there really ought to be some sort of pro-nuclear NGO or lobby group to get started on changing public opinion on this stuff.

[Sky Captain]

How feasible would be something like scramjet engine powered by nuclear heat?

Feasible, but probably not worth the hassle. Scramjets have low thrust-to-weight, and it would have to be some kind of combined cycle ram/scram/rocket, which means complex variable engine duct geometry. There was a successful nuclear powered ramjet design in the late 50s/early 60s, but that operated within a narrow speed range. A better idea is probably a hybrid of the LACE/SABRE engines from Skylon and the nuclear lightbulb design; augmenting the liquid hydrogen reaction mass with liquified or near-liquified air should improve the ISP considerably. Even still, it's something you'd put in your advanced model, the extra complexity wouldn't be worth it in your first nuclear SSTO.

Yeah seems with the ISP the nuclear lightbulb engine could provide small gain in payload by using atmospheric air as extra reaction mass probably is not worth the additional engine complexity for the first generation nuclear powered SSTO craft. For example Skylon spaceplane if equipped with such an engines could probably lift 60 - 80 tons of cargo to orbit.

Although public opinion needs to be changed considerably for such a craft to become acceptable. When it`s hard time for people to accept new nuclear power plants imagine the reaction from various environmentalist groups if any space agency proposed to build and routinely fly in Earth atmosphere a nuclear powered rocketplane. Even if it is as safe as commercial airliners anti nuclear crowd would scream it`s gonna kill everyone in the event of crash exaggerating the associated risks by many orders of magnitude. It would be quickly dubbed the Flying Chernobyl. Of all countries probably China has the biggest chance to build something like that in a near future. In a western world such a project simply would`t get the funding.

[18-Till-I-Die]

The largest vehicle in the studies was one of eight million tons (about three million tons payload) launched using megaton-range explosions. For reference, this thing has about four times the mass of the Great Pyramid. It would, because some of it has to be hollow, have to be about a kilometre high. Right out of the space operas, huh? Multiple-million ton spaceships a kilometre long, with lots of really big mechanical parts (bomb-launching guns, skyscraper-sized shock absorbers...)

I wish someone would write an alternate-history story with this sort of stuff as the setting. It needs a new name, though - steampunk is taken. I would do it myself but have neither the skill nor the time.

Interesting you mention that, but i actually used those immense, skyscraper like Orions in a story, called "boomers", and using antimatter bombs instead of nukes for vastly smaller size per bomb with the same output. Though at the time the story was taking place, circa about 3057 AD, they were almost totally obsolete as differential sails and disjunction drives(void sails and Hawking Engines, respectively) had taken their place as STL drives.

Still it meant that most of the ship was "payload", i.e. crew areas and such, cause the mass required for several multimegaton antimatter weapons was considerably smaller than fusion bombs. Also they can get up to like 80% of lightspeed in a sprint.I didn't come up with that idea, either.

I remember asking about it around here, a long time ago, how big a nuke it'd take to get the thing up to that speed before i found the whole antimatter bomb idea. The thread is probably still floating around somewhere here.

[Starglider]

Still it meant that most of the ship was "payload", i.e. crew areas and such, cause the mass required for several multimegaton antimatter weapons was considerably smaller than fusion bombs.

Slight problem there in that if you have an accident you will have a gigaton explosion at the launch site (due to containment failure of all stored antimatter), whereas fusion devices are generally inert unless deliberately initiated.

[18-Till-I-Die]

There are no "launch sites" these ships are space-only, for that very reason. They use shuttles, hanging on arms on the outside of the ship with corridors for entering or exiting them, to get from planetside to space.

Good news is, you can use that trick where the ship uses acceleration to similate gravity. This further decreases cost, making Boomers popular with independent traders, so even though they were hilariously outdated compared to those big void sail-equipped "gigatankers", there were still a couple hundred billion flying around out in the...what to call it, the backwaters. The outer systems, frontier, Unknown Regions, what have you.

[CaptainChewbacca]

I find it interesting to read some of the really old (early 60s) design studies for Orion. It is noted that the fallout problem gets rapidly easier, certainly per unit mass launched, with increasing vehicle size. Why? Simply because the larger designs really have to use pulse units with an ever-increasing fusion component to the yield, and fusion explosions produce less fallout as a proportion of yield than do fission ones.

This would mean that the takeoff has to use a nuke (how many SRBs can one get to light at once anyway?) but it does mean that one can launch something REALLY BIG. The largest vehicle in the studies was one of eight million tons (about three million tons payload) launched using megaton-range explosions. For reference, this thing has about four times the mass of the Great Pyramid. It would, because some of it has to be hollow, have to be about a kilometre high. Right out of the space operas, huh? Multiple-million ton spaceships a kilometre long, with lots of really big mechanical parts (bomb-launching guns, skyscraper-sized shock absorbers...)

I wish someone would write an alternate-history story with this sort of stuff as the setting. It needs a new name, though - steampunk is taken. I would do it myself but have neither the skill nor the time.

One possible feature that might make things interesting is that using such technologies for space travel would convince any hypothetical aliens witnessing it that the human race is irretrievably insane...

I'm working on an alternate history where a consortium of alien business enterprises starts conducting a proxy war through human allies on earth in the 1980's. They'd have to deal with their own UN, the galactic media, and 'human rights' (it was supposed to be an analogy for the invasion of Iraq and Afghanistan). The reason why they are allowed to invade earth is because we aren't a spacefaring power. But, during the course of the story the US-Soviet alliance (yes, alliance) manages to capture enough alien hardware that they cobble together a super-orion ship and launch it. It gets into orbit, sucker-punches an alien command-carrier, and that's enough to get us qualified as a 'galactic partner' in trade and commerce, and force the war to an end.