RogerBW's Blog

Ithacus and SUSTAIN 09 December 2015

Ithacus was a 1966 study by Douglas, producers of the DC- series transport aircraft and the Thor IRBM, for a sub-orbital troop transport.

The designer was Philip Bono, who reused elements of his ROOST (Recoverable One-stage Orbital Space Truck) and ROMBUS (Reusable Orbital Module-Booster & Utility Shuttle) studies from 1962 and 1964; these were the first serious engineering proposals for reusable vertical takeoff and vertical landing single-stage-to-orbit spacecraft.

This design family was based on an actively-cooled plug-nozzle engine, a variable-geometry design with a movable blockage in the rocket nozzle, which could change the shape of its exhaust to maintain efficiency over a wide range of air pressures. Liquid hydrogen fuel would be circulated through the plug to stop the latter from melting, and this would also serve as an active heat shielding system during re-entry. To lower the weight of things like skin and structure, ROMBUS was to be huge, over 200 feet high (some sources say 95 but I don't find this plausible), 78 feet across, with a fully-loaded weight of over 6,000 tons and a payload capacity of 450 tons to LEO. (ROOST was twice as heavy for the same capacity; ROMBUS got the weight down by using jettisonable external hydrogen tanks rather than being fully reusable.)

That was probably a reasonably workable idea, if very optimistic, but the cost of building and testing such a huge vehicle would have been far too high for NASA alone; so, perhaps inspired by USMC General Wallace M. Greene who was proposing rapid-response forces, Bono proposed an intercontinental troop carrier variant, the Ithacus, for responding to "brush wars" before they got out of hand. This was essentially the same engine and fuselage as ROMBUS, with the same 450 ton payload. It would carry a battalion of 1,200 soldiers ("Rocket Commandoes"), plus equipment, on a sub-orbital flight path, thus removing some of the need for American bases overseas and giving the ability to respond to a crisis anywhere in the world in less than an hour.

(The personal jet-pack appears to have been entirely a flight of fancy on the part of the artist at NASA.)

Another version, the Ithacus Jr, would have carried 260 soldiers or 33.5 tons. These would be launched from an aircraft carrier, fuelled by electrolysis driven by the carrier's nuclear power plants, and sent in pairs: one full of troops, the other with all their equipment. (One assumes this was to get US Navy buy-in for the project, but as the illustration shows the carrier couldn't be used for much else until after the hangar boxes had been removed.)

Recovery of the empty Ithacus would obviously present some difficulties: if it were fully fuelled for a return flight, it would need a proper launch facility in order for the massive thrust of its main engines not to generate shockwaves and kick up huge amounts of débris, damaging the vehicle as well as its surroundings. Reducing the fuel load, so that it could take off with lower thrust and fly only a few hundred miles at a time, was thought to be more practicable; then it would be hauled aboard a Saturn-style crawler and moved onto a cargo ship for return to the USA. But you'd still need to get liquid hydrogen and oxygen into the recently-pacified trouble spot.

The tactical implications don't seem to have been studied in as much detail. Consider: you are a Bad Guy by American standards. Your military forces are causing trouble somewhere. You're probably more or less aligned with the USSR. US reinforcements are on the way, coming in nearly vertically, with a great big infra-red (landing thrust would be a minimum of 10MN) and radar (from re-entry ionisation) trace; you can't miss them, and they're not terribly agile. By 1966 the S-75 Dvina (SA-2 Guideline) surface-to-air missile, with its 200kg warhead and 82,000 foot ceiling, has been in service for nearly ten years: the North Vietnamese have them (as the USAF is finding to its cost). Now I don't know just how damageable the plug-nozzle engine would be, but this is certainly a thin-skinned aircraft, and if you can knock it out at any sort of altitude all 1,200 troops are out of action before they can fire a single bullet. You also score a huge publicity coup: "They dropped soldiers on us from space, and we still beat them!" So the Ithacus can't drop "anywhere in the world" – it has to be somewhere out of any conceivable hostile SAM cover, and then the troops have to go overland to where the fighting is. (Even then, accidents are much less survivable than accidents to aerodynamic transport aircraft.)

A payload allowance of 826lb per soldier, including their own body weight, doesn't allow for anything in the way of heavy equipment: it's about 20% more than the allowance for paratroopers aboard a C-130. This is a very light infantry unit, with no tanks or even APCs (the contemporaneous M113 weighs around 2,100lb per soldier, even without the troops and their personal kit).

Also: what happens if they don't immediately win? It's like an amphibious or parachute assault: you aren't going back the way you got in, and you don't have much in the way of spare ammunition or food. Only you don't really want to leave your hugely expensive assault spacecraft lying around for the enemy to capture, so you'll probably have to destroy it if things go badly…

So in how many situations do you have a non-SAM-covered landing zone where 1,200 light troops can be reasonably sure of winning the fight? Ithacus Jr suffers further because it reduces that to 260 troops with even less equipment, and given the huge range of the thing, putting it aboard an aircraft carrier just seems pointless: why send it in from an ocean launch when you could send it in from the continental USA in only a few minutes more?

There's also the concern that, well, the USA launching a great big suborbital rocket towards a trouble spot just might be interpreted as an ICBM.

This may be part of why the idea never went anywhere, though given some of the things that did get built I suspect it was mostly the cost. Bono went on to design the smaller Pegasus VTOVL (intended for very-high-speed transport and disaster relief, bearing in mind this was also the age of Concorde and other SST development) and SASSTO vehicles; none of his designs was built, and he died three months before the first flight of the loosely related DC-X.

The complete failure of the project to get anywhere didn't stop it from being included in The Usborne Book of the Future (1979), a huge influence on the young RogerBW. These images are very clearly inspired by the NASA art for Ithacus and Pegasus VTOVL.

One consideration that rarely gets mentioned is that a suborbital transport like this is basically the same thing as a full space launch vehicle: the speed through the atmosphere and delta-V demands are high enough that you can't take significant short-cuts just because it's not intended to achieve orbit. This isn't a simple up-and-down trip like SpaceShipOne: you need nearly as much sideways speed as if you're going all the way. (I suspect that heavy lift to orbit was always Bono's real goal anyway.)

The idea of a suborbital troop transport was resurrected in 2002, with the USMC's SUSTAIN (Small Unit Space Transport and Insertion) concept (possibly to use the USAF's HOT EAGLE). This time, rather than worrying about foreign bases, the idea was to avoid having to ask countries for overflight rights; this seems largely to have been spurred by a failed mission in November 2001 to try to find Osama bin Laden, where the USA actually had to negotiate with Pakistan in order to move its troops through Pakistani airspace. Imagine!

This is all very much on paper, but the scheme was for a two-stage vehicle based loosely on SpaceShipOne (ahem, see above). This was to carry 13 Marines plus their equipment, and land on a runway rather than vertically. So you wouldn't have quite such a huge infra-red plume, but to all the other problems you've now added the need for a conflict where 13 Marines can make a difference (someone's been watching too many action films), and where the enemy can't park a truck across the runway. (Hey, why not have them parachute out?) The only nominal point of this is that national airspace claims currently end at 50 miles altitude, but does anyone in the US really expect a foreign country to say "oh, you flew over us at 51 miles up, we're just fine with that, rah rah Murica"? This got some talk in 2005-2006 but seems to have faded away since then.

But the concept art is really cool.

(I believe this is by Peter Bollinger, working for Popular Science.)

How could the idea be a useful one? Really you need something better than conventional rockets, just as you do for a cheap surface-to-orbit launcher. Use one of the nuclear engine designs, particularly one that can heat air for thrust while in atmosphere, and the payload starts to be a larger fraction of the overall vehicle mass. And as the fuel mass goes down, you might get a certain amount of ability to manoevure as well: something that can make a suborbital insertion to a few hundred miles out from the trouble spot, then hedge-hop at supersonic speeds, might have more of a chance. Keep it small, to put in a squad or two, and frankly to be more expendable than a 1,200-soldier craft. It's useful for embassy hostage rescues and similar small sudden missions. Throttle down, air-drop the troops or land vertically, and fly away again; you still have a limited range of conflicts in which it does much good, and it's probably not worth the money to develop unless you're also using it as a general-purpose space launcher, but at least it can have some effect.


  1. Posted by Michael Cule at 11:42am on 09 December 2015

    Gosh, but the art's pretty. I wonder why they depicted the rocket being transported standing up? Even then I'm sure they moved the big ones lying down except when actually going to the launch pad.

    Didn't you tell me that NASA killed this in order to give priority to a scheme of their own... which then went nowhere?

  2. Posted by Ashley R Pollard at 01:45pm on 09 December 2015

    I came across these in the late sixties early seventies when I got the Bono & Gatland manned spaceflight books (Frontiers of Space). Happy memories.

  3. Posted by RogerBW at 02:03pm on 09 December 2015

    The basic ROOST/ROMBUS concept has all the acceleration bracing fore-and-aft, so maybe it's just simpler if you keep it upright all the time.

    It was the DC-X that NASA took over (because it had had some successful and some failed flights) and then killed, because it wanted the X-33 (precursor of VentureStar) instead. That was to be SSTO with vertical launch and unpowered runway landing. But the X-33 was one of those "all the new technologies at once" ideas, and had so many problems it was in turn killed before it flew.

  4. Posted by John Dallman at 09:44pm on 10 December 2015

    I had Bono & Gatland too. That was a fun future.

    The problem with the nuclear-suborbital vehicle is that if your mission into Terrorist-land goes wrong and the vehicle gets captured, you've just given them a bunch of fissionable material. It's going to be highly enriched uranium, and making bombs from that is a load easier than making the stuff in the first place.

  5. Posted by RogerBW at 09:50pm on 10 December 2015

    True, though if the "nuclear Ithacus" can use air as reaction mass it can fly some distance away after dropping off the troops - that won't be as fast as it got there in the first place, but it doesn't have to be.

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