ACTS: Europe and Russia Try Again

acts

A somewhat notional view of the ACTS as envisioned once its capsule shape was selected in 2008. By developing a command module with relatively steep walls, the ESA and Roscosmos hoped to solve the problem of cramped quarters aboard the Soyuz, and handle up to six crew. Adapted from an image by Jérémy Naegel, used under a Creative Commons ShareAlike 3.0 license. Click for a larger view.

What it was: A traditional capsule-based spacecraft to be developed jointly by the European Union and Russia, after those two failed to reach agreement on the Kliper lifting body (and further on Europe failing to the get the Hermes spaceplane off the ground).

Details: It’s been interesting the last twenty years or so to watch the gold standard for new crew return vehicles move away from small spaceplanes and lifting bodies back to capsules, as had been the preference through the 1960s. The watershed was sometime around 2006, when mockups of NASA’s Orion ceased to show a lifting body and changed to a capsule, and right about when the tandem of EU/Russia stopped looking at the Kliper and started talking about the Advanced Crew Transportation System (ACTS).

At the end of 2005, the Kliper foundered on the fact that Russia was to design and build it almost entirely. Despite that failure, the ESA was still fetching about for a crewed space project as they had also been rebuffed in approaches to the United States about sharing development of Orion’s capsule prior to Kliper. And so Russia came back into the picture within a few months.

As it happened, the EU had been working on the ATV, an unmanned supply spacecraft for the International Space Station, and it had already been noted that it bore a certain resemblance to a spacecraft service module. “Why not,” the thought ran, “have Russia develop a crew capsule to put on top of an adapted ATV?” Do so and you’d end up with something usable in Earth orbit for short missions, such as going to the ISS.

csts_eurosoyuz

The so-called “EuroSoyuz” first envisioned for the ACTS. This image is even more notional than the previous, based as it is on ideas being considered at the time and not any actual plans. The habitation module at the left, in particular, never progressed beyond an intent to make one eventually. Image by Jérémy Naegel, used under a Creative Commons Attribution 3.0 License.

Initially the craft was envisioned by RKK Energia as sort of “Soyuz, Mark 2”, which Energia called the Soyuz-2, with a Soyuz-shaped re-entry module, if not the one from an actual Soyuz. Rather it would be oversized, perhaps derived from work down on a mid-80s Soyuz replacement called the Zarya. This had stuttered along as late as 1995, when it was jointly proposed by Energia, Khrunichev and Rockwell as a lifeboat for the ISS. The ESA and Russia committed to a two-year study of the idea, with the ultimate intention of producing a spacecraft that could orbit the moon. This configuration was still in the lead as of August 2007.

The study’s mid-2008 deadline coincided with that year’s Farnborough Air Show, and the details that were announced then had moved on from the initial concept. Now the upper half of the ACTS was a conical capsule, built by the Russians and integrated by them onto the European service module. Many sources describe it as Apollo-like, but it was fairly different in being much more vertical, a mere twenty degrees from vertical on its side walls. This was a throwback to a proposed European capsule, Viking, which had popped up for a while immediately post Hermes before fading out after one subscale, suborbital test (the Atmospheric Reentry Demonstrator) in 1998.

Though the craft was not designed to the point of precise specs, we know that it would have probably have been under 18,000 kilograms, as one of the proposed ways of getting one to orbit was via Kourou Space Centre on top of a crew-rated Ariane-5, though figures bounced around from as low as 11 tonnes and as high as 20. The Russians also talked about launching the ACTS from Vostochny, probably for use on an Angara A5 (though that rocket is still under development even as late as December 2016); a Proton was also a possibility if the difficulties of launching cosmonauts on top of rocket fueled with nitrogen tetroxide and UDMH, and there was nebulous talk of a Zenit derivative (a rocket that had not been used.in Russia as the dissolution of the USSR left its manufacturer in Ukraine).

The capsule would have been five meters across the base and with its high vertical angle would have been roomy enough for six astro/cosmonauts (or four, if going to the Moon); one source reports 2.5 cubic meters of space, but this is no larger than a Soyuz and seems unlikely.

Ultimately the plan was to have a habitation module too, and the responsibility for this was assigned to Europe, but until the core ACTS spacecraft was much further along this was little more than a planned future commitment, with no details at hand. At the forward end, ACTS would at first have a Soyuz-style docking arrangement to take advantage of the matching ports on the ISS. Once it began its lunar missions, though, the plan was to have a common active/passive system with the Americans’ future craft so that joint missions would be easier.

On re-entry, the Russian-made capsule would have borrowed a trick from previously mentioned Zarya: a re-entry to land under a minimal parachute, with primary responsibility for landing being passed on to 12 solid rocket motors that would begin firing at about 300-800 meters up. Retractable landing legs were also mooted, as part of a general desire to make the capsule re-usable (with one Russian official hopefully suggesting ten flights in a lifetime). Rumor had it that this hair-raising retro-motor approach was made necessary by the Russians insisting on their historical requirement that their crews return to land in Russia, and with much of Central Asia now thoroughly Kazakh, the area they had to hit was much smaller than before—and parachutes normally cause one to drift quite a bit.

What happened to make it fail: Europe started showing signs of cold feet in the spring of 2008, just as the ACTS was making its splash at the Farnborough Air Show. The reasons are bureaucratically murky, but seem to have reflected the ascendance of a faction in the ESA that wanted to focus on “ATV Evolution”, a more ambitious approach where they’d upgrade the ATV so that it could return cargo, then upgrade the return module into a capsule, and then even turn it into the core module of a small space station. All this would be indigenous to Europe, with no Russian involvement.

ACTS might have survived this, but two competing financial tides worked against it. The Great Recession kicked off in late 2007, and for the next six years Europe had to deal with repeated sovereign debts crises that made money scarce. Not only was ATV Evolution shelved, even a shared spacecraft with the Russians was too expensive.

In the other direction we had a surging price for oil and gas (bar a severe but short drop near the start of the recession), reaching $140 per barrel in June 2008. Replete with petrodollars, Russia came to the conclusion that they didn’t need to put up with European waffling any more and could go ahead with their own, solo version of the ACTS. Political opinion at home favored this course anyway, and local laws on technology transfer made it difficult for Roscosmos and Energia RKK to come up with a legal framework for transferring technical information on Soyuz and other ACTS-related work out of Russia. This last issue is what is generally cited in official ESA documents as the main cause of ACTS’ failure.

Then in August 2008, Russia invaded Georgia in support of separatists there, followed by a gas pipeline dispute with Ukraine in January of 2009 that affected several EU countries. European confidence in Russia as a partner nosedived, and it became politically distasteful for the ESA to continue working with their Russian counterparts on such a high-profile project. Both sides quietly went on their way.

What was necessary for it to succeed: ACTS as such could have gone ahead in the face of most of the difficulties just listed. Certainly the financial crisis could have been ridden out for a few years, and the Russia oil boom didn’t last. What’s been the real killer has been the frosty relationship between Europe and Russia, kept chilled by further events like the latter’s clandestine invasion of eastern Ukraine. It’s difficult to see ACTS restarting any time after 2008, despite occasional French noises about re-establishing partnership with Russia.

Unlike most other projects discussed here, though, ACTS didn’t lead to no flying craft, or even to one. Rather it’s changed into two, and that’s not even counting the ATV Evolution which the ESA bravely claims is still on the table despite little sign of movement for about eight years. The Russian ACTS derivative was first called the PPTS, then it became the PTK. While that project has faced a long and slow road, it was formally dubbed Federation this year and, is still looking like it will fly in the 2020s.

On the European side, NASA announced in January 2013 that the previous design of the Orion service module was being replaced with an ATV-derived service module for at least the EM-1 unmanned test out past the Moon, currently scheduled for a year next September. Whether it will be used again after that mission is an open question, but so far it looks like it’s going to be used once. The initial idea that the ATV would work if someone else supplied a capsule for it was right, they’d just picked the wrong partner at first.

So the ACTS has survived after all, and did so by being cut in two. As mentioned, the Russian half has a name already, but seems fitting to name the as-yet-anonymous American/European half after King Solomon.

Sources

“Advanced Crew Transportation System”, Anatoly Zak. RussianSpaceWeb.com.

“Collapse of ESA-Roscosmos Crew Vehicle Partnership Holds Lessons”, Peter B. de Selding. SpaceNews.

“Potential European-Russian Cooperation on an Advanced Crew Transportation System”, Frank De Winne. Belgian Science Policy Office.

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LANTR LTV/LEV: A New Way to the Moon

lantr-lev-side-by-side-comparison

Two versions of the LANTR LTV/LEV. On the left is one suggested for a SSTO launcher that could carry 20 tons to orbit and had a 13.5 meter payload bay. The one on the right could fit in a 9.5 meter cargo bay, at the cost of using less efficient methane for lander fuel, a smaller crew capsule, and a fiddly tank-within-a-tank to hold some of the craft’s liquid oxygen oxidizer. Public domain image composited from two separate diagrams in NASA’s Human Lunar Mission Capabilities Using SSTO, ISRU and LOX-Augmented NTR Technologies A Preliminary Assessment. Click for a larger view.

What it was: A mid-90s proposal for a lunar mission using an innovative rocket engine for the trip to the Moon and some basic lunar industry to refuel its chemically-driven lander for the trip back. It was one of the first proposals for a Moon mission to try and move away from a brute-force Apollo-style mission that was impossible to fund.

Details: The core difficulty with a Moon mission, or a mission to much of anywhere really, is that you need such massive vehicles. The Saturn V, for example, was 2950 tonnes when fueled, and was 111 meters tall. It was accordingly expensive: approximately US$700 million in 2016 dollars. Reusability was the route taken in the decades since to try and bring this down, but the Space Shuttle ended its life costing US$450 million per launch and for a considerably smaller payload being taken to orbit too.

By the early 1990s, in-situ resource utilization (ISRU) was seen as the next coming thing for making missions cheaper. This is to say, don’t haul all the mass you need up into space, take advantage of whatever mass is already there wherever you’re going. The difficulty here is that that mass is useless rock and, to a much lesser extent, water ice. The most obvious thing to do would be to refine cryogenic rocket propellants from it, as both rock and ice can be sources of oxygen and hydrogen. By the mid-90s people had been thinking for several years about how to do that, and what what would be possible once it could be done.

The most famous fruit of this effort was planning for Mars missions, partly because the vehicles for a traditional flight there would be ridiculously large even by Saturn V standards and partly because Mars’ carbon dioxide atmosphere is almost trivially easy to turn into methane (a decent rocket propellant) if you bring along some hydrogen from Earth. Less well-known is a lunar mission using ISRU which was developed at NASA’s Lewis Research Center.

In the early 1990s Lewis had been involved in the development of a nuclear rocket of an unusual type, what they called a LOX Augmented Nuclear Thermal Rocket (LANTR). A regular nuclear thermal rocket like NERVA runs on pure hydrogen, not burning anything at all and simply relying on nuclear power to heat the propellant and produce a high specific impulse. Unfortunately liquid hydrogen is very low density, and so the tank to hold it has to be large—and it doesn’t matter how light something is if you literally can’t fit it into the cargo bay of the Space Shuttle, or however else it is you’re planning on getting it into orbit.

The LANTR solved this problem by using liquid oxygen along with the hydrogen. After being heated by the reactor, the hydrogen was mixed with oxygen, which would then burn. This had the paradoxical effects of reducing the engine’s specific impulse, but also radically reducing the amount of hydrogen needed and making the necessary hydrogen tank much smaller. Liquid oxygen is seventy times denser than LH2, so its tank would be small too. The usual mix of oxygen to hydrogen is near 1:2 (as the chemical formula “H2O” would suggest), but even when mixed 5, 6 or 7:1 with the hydrogen the reduced specific impulse of the LANTR was still considerably better than you got with a conventional LOX/LH2 rocket while also being smaller than a pure-hydrogen nuclear rocket..

artist

“Artist’s Illustration of a Self-Contained, Modular LUNOX Production Unit”, plus an astronaut apparently taking a selfie. Public domain image from A Revolutionary Lunar Space Transportation System Architecture Using Extraterrestrial LOX-Augmented NTR Propulsion. Click here for a larger view.

The leap to lunar ISRU came with the realization that oxygen was a major component of the Moon’s soil. For example, the orange soil famously (and excitedly) discovered by Jack Schmitt during Apollo 17 contained hydrated iron oxide, and was rich in oxygen and water. At Lewis, the combination of LANTR and ISRU for a Moon mission crystallized in a flurry of papers spearheaded an engineer there, Stanley Borowski, in combination with a variety of colleagues. Rather than go with an already compact Moon mission using entirely Earth-sourced oxygen, why not use the Moon’s native oxygen for oxidizer on the way back? The result would be smaller and cheaper still.

The result was a proposal to build a Moon landing ship that was embedded in some basic Lunar industry that would be set up prior to the crewed landing. The first step would be to send an automated lander with a teleoperated mining equipment to a site where ilmenite or some other oxygen-rich rock had been pinpointed from orbit. Also included would be a 35-kilowatt nuclear reactor, which would provide the heat to break down the lunar rock with the hydrogen that would be brought along too, producing water. The water in turn would be broken down to oxygen and hydrogen, the former being stored and the latter recycled to start the process again on the next batch of rock.

Once 10.5 tons of liquid oxygen had been built up (a process which would take a year), the LANTR LTV/LEV (Lunar Transfer Vehicle/Lunar Excursion Vehicle) crewed mission would begin. Here a little bit of variation appears. When first suggested in 1994 the craft was assumed to be using a Shuttle-C, a derivative of the Shuttle for cargo only, to get to orbit—the LANTR wasn’t powerful enough to lift the whole works by itself (and no-one was very keen on firing a nuclear engine at ground level in any case). The Shuttle-C was already a cancelled project, however, and by 1995 NASA had been pinning its hopes on the VentureStar or some similar SSTO. At the time the LANTR LTV/LEV was being bruited about, the size of the SSTO’s payload bay hadn’t been nailed down and while NASA had specified 20 tons to LEO it was unclear how long the cargo it carried could be, Accordingly Lewis Research Center came up with two LANTR LTV/LEV configurations, each of which would be lifted in three pieces and mated in orbit.

If the SSTO gave them 13.5 meters to work with, the result was a 58.8-ton, 26.2 meter-long craft. Compare that with roughly 140 tons and 35 meters for the Apollo LM/CSM/S-IVB that launched the Apollo astronauts to the Moon. This version of the LANTR LTV/LEV would have be entirely fueled by LOX and LH2, excepting (presumably, as none of the sources say) hydrazine for the RCS thrusters as usual. On top was a curiously inverted command module; the author could find no discussion of how that was handled when time came for re-entry, so one presumes rotatable seats for the crew.

The longest part of this variation was the joint LH2/LOX tank for the transfer vehicle, while the widest was the bulbous hydrogen tanks on the lander. Both had to go to get into the smaller 9.5-meter SSTO payload bay suggested. The lander was switched to a more-compact but less efficient fuel, liquid methane, while one of the two oxygen tanks for the LANTR was moved to inside the LH2 tank, and outfitted with a double wall that would keep the supremely cold hydrogen from solidifying the oxygen within. The resulting craft was slightly lighter at 58.5 tons and definitely shorter at 24.2 meters, but in return they had to come up with some way of shaving 700 kilograms off of the crew capsule. Both variations of the capsule were approximately the same size as the Apollo CM, though the first’s was slightly larger than the second.

profile

The LANTR LTV/LEV mission profile. Note the direct descent and direct return. Public domain image via NASA from Human Lunar Mission Capabilities Using SSTO, ISRU and LOX-Augmented NTR Technologies A Preliminary Assessment. Click here for a larger view.

There was no LM, though, because the LEV was a direct-descent, direct-return vehicle. This did mean that if the stay on the lunar surface was to be of any length, a third mission, automated like the LOX plant, would have to be sent beforehand to give the astronauts a habitat. The LEV itself was inadequate otherwise.

What happened to make it fail: Though the mission was considerably cheaper than an Apollo-style trip to Moon—Johnson Space Center was looking at the time to spend less than US$1 billion on a Lunar return mission—not even that amount of money turned out to be available in NASA’s budget, particularly after the decisions were taken to continue with the Space Shuttle and build the International Space Station around the same time as the proposed first flight of a LANTR LTV/LEV’s, around 2001.

It also didn’t help that the craft came to an unwieldy size. It was intended to be launched on the VentureStar, and that never came to fruition. A comparable mission restricted to launch vehicles that actually existed needed one Shuttle mission and one launch of a Titan IV (which could lift longer payloads than the Shuttle could), a peculiar and expensive combination.

Something like it still could have begun as late as the about ten years ago, but then a discovery about the Moon put the final nail in its coffin. From 1994 through 2009 it became increasingly clear that the Moon had ice in some of its South Polar craters, with the case being settled by the Chandrayaan-1 probe. This changed the game for ISRU, since ice is a lot more useful raw material than lunar soil. Essentially all serious planning for a Moon mission since then has reflected this, and lunar rock has fallen by the wayside.

What was necessary for it to succeed: Much like the First Lunar Outpost, the LANTR LTV/LEV’s best bet would have been at the time the Clinton Administration was trying to decide how to help occupy the former Soviet Union’s rocket scientists so that they wouldn’t end up designing missiles for who knows what country. The decision to go for an joint space station rather than a joint lunar mission or base was a relatively easy one, given the USSR’s experience with stations, but it’s not too difficult to see the US deciding to go for the public relations spectacle of the Moon over the more staid ISS.

Otherwise the LANTR LTV/LEV is a sound concept if the promised Isp advantage holds, to the point that (by the standards of this blog) something much like it still would be worth building and flying. The primary difficulty with it in 2016 might be, oddly enough, that it’s too small. Sixty tons falls into the “between two stools” range that we discussed in the entry on the R-56, too big for something like an Ariane 5 or Delta IV Heavy, but too small for the upcoming SLS. Given that you’re going to have to use an SLS and that rocket will quickly outstrip 60 tons by a lot, why not design a spacecraft that uses up the extra payload capacity? Fans of SpaceX’s Falcon Heavy effort might want to take some notes, though.

Sources

A Revolutionary Lunar Space Transportation System Architecture Using Extraterrestrial LOX-Augmented NTR Propulsion. Stanley K. Borowski, Robert R. Corban, Donald W. Culver, Melvin J. Bulman, and Mel C. Mcilwain. 1994

Human Lunar Mission Capabilities Using SSTO, ISRU and LOX-Augmented NTR  Technologies A Preliminary Assessment. Stanley K. Borowski, 1995

High Leverage Space Transportation System Technologies for Human Exploration Missions
to the Moon and Beyond. Stanley K. Borowski and Leonard A. Dudzinski. 1996

The Early Lunar Shelter: Stay Just a Little Bit Longer

Garrett AiResearch Lunar Shelter

The Garrett Early Lunar Shelter, showing its roots in the LM Truck and, in turn, the LM that actually landed on the Moon. The tanks draped around it are hydrogen and oxygen for the fuel cells, shelter pressurization, and recharging the astronauts’ suits after EVA. Public Domain image via NASA from Early Lunar Shelter Design and Comparison Study, Volume IV. Click for a larger view.

What it was: A two-astronaut shelter/living quarters for use with the Apollo program once it had progressed to needing 30-day stays on the surface, studied in 1966-67 by Garrett AiResearch at NASA’s request. Variants for three astronauts and for a mobile version that could be hitched to a lunar rover were also examined.

Details: Certain big names show up repeatedly in conjunction with the American space program: North American Rockwell, Grumman, Boeing, Lockheed, and so on. Around the fringes, though are less familiar names such as Bendix and TRW. Another one of the latter was Garrett AiResearch, a mid-sized aerospace pioneer best known (at least as far as the space program goes) for designing and building the atmosphere controls for Mercury, Gemini, and Apollo.

In 1966, NASA commissioned Garrett to move beyond what they’d done to that point, and work on a  full-fledged, if tiny, Moon base. Dubbed the “Early Lunar Shelter” (ELS), the intention was to build it following the J-Class missions—what turned out to be Apollo 15 through 17. Having progressed from short surface stays like Apollo 11 to longer ones that had a lunar rover to work with, like Apollo 17, the next step was to be month-long stays and that required more than a single LM.

From the beginning, the Moon landings had been quite restricted in mass, as much of an LM was taken up with astronauts, the consumables they needed, and the fuel and engines needed to get them back to the CSM for the flight home to Earth. If you could forgo all of that with an automated lander, you could haul a lot more equipment to the Moon—to wit, 4.67 tonnes of it.

The fruit of this thinking was the LM/T, or Lunar Module Truck, which was for all intents and purposes a rocket-powered mule that would head to the Moon some time before its associated astronauts would start their journey in their own LM (called the LM Taxi in this context). Landing close to the LM/T, the astronauts could walk over, unload everything, and enjoy a huge quantity of equipment as compared to Aldrin and Armstrong.

There were any number of configurations for the LM/T, constrained only by the volume an LM occupied on top of a Saturn V and the limit to the mass it could safely land, but the Early Lunar Shelter was the answer to one particular question: “Suppose we devote the Truck’s volume entirely to living quarters for two astronauts and the scientific equipment they’d use. What would that be like?”

What Garrett came up with was a stubby cylinder, 8.1 feet in diameter and 16 feet long (2.5 meters by 4.9 meters) which rested on its side above the LM/T’s descent stage, looking not unlike contemporary bathyscaphes. It would be launched atop a Saturn V along with a crewed CSM, which would dock to a hatch on its upper side, then ferry it to the Moon after the usual Saturn IV-B trans-lunar injection. After reaching their destination, the CSM would disengage and return its crew to Earth, while the ELS would land automatically.

The shelter could sit on the Moon for as much as six months before its astronaut-dwellers arrived (thanks to another Saturn V/CSM combination), with a minimum seven days prior to their launch for checkout of the shelter. A SNAP-27 radiothermal generator would power the ELS until activation. Once aboard, the minimum time the astronauts would use it was assumed to be 14 days, with 50 days being the upper end of possibility. The first day days of the mission would be devoted to the astronauts activating the shelter for their use, unloading it, switching the shelter to running off fuel cells (which would also supply water) and transferring the RTG to their LM Taxi so their ride home could be deactivated but kept “alive” until it was needed at the end of the mission.

Interior layout of the Early Lunar Shelter

The interior layout of the ELS, same source as previous. One presumes the outer hatch was closed when the toilet was in use. Click for a larger view.

The interior of the shelter was to be divided into two main areas. One was a lunar EVA airlock taking up one end, the CSM hatch on top being used solely for docking with a CSM. It would have been big enough for two astronauts at the same time as well as storage of two hard space suits. The bulk of the shelter was 628 cubic feet (17.8 m3) of living space. Though about half of this would be taken up with supplies, bunks, and spacesuit storage, its shirt-sleeve environment compared well with a regular LM’s 4.5 cubic meters of habitable volume. Alternatively, as the Moon does supply gravity, the ELS can be sized another way: it would have had 68 square feet of floor space (6.3 square meters).

The arrangement of bunks/radiation refuge quarters in the ELS.

The spartan arrangement of bunks/radiation refuge quarters in the ELS. No Apollo astronaut was taller than 71 inches. Same source as previous. Click for a larger view.

The shelter was double-walled aluminum and fiberglass (the latter in the inside), with 58 mils (0.058 inches, or 0.15 cm) between them for meteoroid protection—the usual tactic, as invented by Fred Whipple. The other major danger entertained was radiation, and the aluminum walls couldn’t be made thick enough to sustain 500 rads (a hypothetical solar flare) without weight close to a half ton more than was otherwise necessary. Accordingly the study suggested putting the necessarily numerous  PLSS recharging canisters (for the life-support backpack worn while on the surface) stored in water filled sleeves around the bunk area located at the opposite end from the airlock. Altogether, they, the walls, and the bunk material made an acceptable, if awfully cramped, radiation refuge for everyone on-board.

One final, intriguing safety touch was the dual-purpose boom attached near the airlock. While primarily intended for unloading instruments or a rover, it would also have been used to get an incapacitated astronaut up next to the entrance to the shelter.

Arranged around and behind the shelter were four tanks: one compressed gaseous oxygen, one liquid oxygen, and two liquid hydrogen. These weren’t intended for use with the Truck’s landing engine—it had its own tankage—but rather for use by the astronauts and the fuel cells (and so, accordingly, their water). Garrett pinpointed the storage of LOX and LH2 for up to six months before the astronauts arrived as the main technical challenge facing the ELS.

Another issue was what atmosphere they would breathe: pure oxygen at 5.0 psia, or nitrogen/oxygen mix comparable to Earth. The former was desirable for mass reasons, and to keep the ELS as close in technology to the rest of the Apollo program as possible, but Garrett were concerned that there were no medical studies of a pure oxygen atmosphere for a long period of time; the 30-day maximum they note was apparently just an educated guess. They ended up punting the problem down the road as essentially an issue of how much they could keep the ELS from leaking; if that could be minimized, the problem was moot. Safety concerns weren’t mentioned at all, and in fact the final filing of Garrett’s study was on February 8th, 1967, not even two weeks after the Apollo 1 fire. After that the CSM would switch to a oxy-nitrogen atmosphere for launch, though the LM would stay with the low-pressure pure oxygen.

Mobile ELS variant, hitched to a notional rover.

The Mobile ELS variant, hitched to a notional rover. Same source as previous. Click for a larger view.

As well as being a shelter, the ELS would have been a miniature scientific outpost. It would be equipped with a drill capable of getting 100 feet down into the Moon’s crust, carry explosive charges for seismic readings, and had three remote instrument stations that would be deployed far from the landing site thanks to the extended EVA capability the shelter would provide. All told, the shelter would come with 3470 pounds (1.57 tonnes) of science gear, while the shelter itself was a remarkably light 985 pounds (447 kg). Add in the expendables and altogether it could be successfully landed on the Moon by the LM/T with a mere pound and a half to spare. Let it not be said that they didn’t squeeze all the juice out of this one.

If the project had gone ahead, Garrett anticipated that the ELS would be operational in 1972. The study is silent on cost, apparently because the construction work was to be handed off to Grumman, and so it was their problem.

What happened to make it fail: It got caught up in the rapid ramping down of the Apollo program that started in 1968, not least the fact that Saturn V production was shut down and the rockets they had were all they were going to get.

By scrimping and saving (and cutting a couple of Moon landings) NASA managed to save Skylab, and eventually the detente-driven Apollo-Soyuz Test Project, but that was it. As any mission involving the Early Lunar Shelter was going to require two Saturn V launches it was an obvious target for a cut, taking up as it would two slots that could be used by two different, separate Moon missions. It was one of the first things to go, and did not make it out of 1968.

What was necessary for it to succeed: It’s interesting to compare the Early Lunar Shelter to the other Moon bases we’ve examined so far, Barmingrad and Project Horizon. Both were hugely ambitious and nowhere near happening in reality, while for this project the key word was early. A lot of people tend to conflate Moon bases with lunar colonies, or at least the next rank down of permanently inhabiting the Moon even if the personnel are swapped out periodically. What NASA put its finger on was that we’re not likely to make that big a leap all in one go. The first lunar bases are probably going to be temporary, just like the first space stations were before we worked our way up to Mir and the ISS.

On that basis it’s easy to get the ELS to fly, as it was a big part of the logical next step in lunar exploration (ignoring the elephant in the room that was automated exploration, mind you). With probably no more than some minor redesigning there could have been one on the Moon just a few years after when Garrett AiResearch pictured it: 1972.

As ugly as the post-1969 picture was for NASA’s funding, it’s not too much of stretch to see the three or four more necessary missions past Apollo 17 making it through the budget grinder and “Apollo ELS” flying sometime around late 1974 or early 1975. It’s a lot likelier than much of what NASA proposed post-Apollo 11, at least, if only because one mission like that would be as much or more of a punctuation mark at the end of the program as any other mission bar Apollo 11 itself.

Sources

Early Lunar Shelter Design and Comparison Study, Volume I and Volume IV, W.L. Burriss, N.E. Wood, and M.L. Hamilton. Garrett AiResearch. Los Angeles, California. 1967.

The R-56: “Yangel Works for Us”

Thre possible arrangements of the R-56 rocket

Three possible arrangements of the R-56 rocket. The one on the right is the “4-4-1” module arrangement initially favoured, while the one at centre is close to the monoblock version finally settled on (it is missing the flared skirt necessary to house all of its engines). Original source unknown.

What it was: A four-stage rocket proposed by OKB-586 in the early 60s. It was aimed at the Moon, despite having a payload of 40 to 50 tonnes, making it much lighter than any of the Saturn V, N1, or Energia. It still would have lifted more than any rocket being flown in 2016.

Details: In February 1962 Nikita Khrushchev organized a meeting of the USSR’s Defense Council with the main missile designers in the Soviet Union at his dacha in Pitsunda (a resort town in the Georgian SSR) for the purpose of rationalizing their missile and space programs. The main players were Sergei Korolev with OKB-1 and Vladimir Chelomei with OKB-52, but a third invitee was Mikhail Yangel, the head of OKB-586.

While Korolev had surged to the head of the Soviet space program post-1957 and initially stood first in ICBM development, all based on variations of the R-7 rocket, by 1962 he had lost leadership in the latter to Yangel. The previous November his R-16 had become operational, and its use of storable propellants made it more militarily desirable than the liquid oxygen-using R-9 that was OKB-1’s response. Though the R-9 could be fuelled and fired in roughly the same amount of time, the feeling among almost everyone but Korolev was that storable fuels were the way forward when it came to developing a nuclear strike capability that could be used with little notice.

Meanwhile a fourth man and his bureau was working behind the scenes. Valentin Glushko had been trying to make large engines that used LOX for oxidizer. The tremendous vibration in his prototypes led to combustion instabilities that caused, as they say, “rapid disassembly”. Convinced that the problem could not be cracked, he had come around to storable propellants, and this had become a problem between him and Korolev. OKB-1 was pushing ahead with the N1 and, while storables were considered for that project, the writing was on the wall: Korolev wanted LOX and kerosene, or LOX and liquid hydrogen. A few years previous Glushko could have pushed back effectively, but Khrushchev had been downsizing the USSR’s military aviation efforts, and underemployed bomber-designing bureaus had been growing new departments devoted to rockets—the N1 would end up flying, for sadly abbreviated distances, using engines developed by Nikolai Kuznetsov’s OKB-276.

Glushko hedged his bets by teaming up with Chelomei on the UR-700 and the UR-500, which were aimed at the 70+ and 20-tonne payload targets set by Khrushchev. The former was to be a super-heavy interplanetary space launcher and the latter was a combination heavy LEO space launcher and ICBM. The smaller of the two figures was apparently selected due to the test of the RDS-220 hydrogen bomb (better known by the name given to it in the West, the “Tsar Bomba”) a few months earlier. This 100-megaton demonstrator had come in at just under 27 tonnes, and it was thought that refined versions with about half the yield would come in several tonnes less than that.

These two rockets were OKB-52’s proposal to the Defense Council meeting. OKB-1 countered with the already-underway N1 and, for the smaller launcher, the N2, which was essentially the N1 with its tetchy first stage removed. Seemingly out of worry that OKB-1 would still prevail, Glushko had arranged for another card in his hand—Yangel.

A relative newcomer to the space side of missile work, Yangel had earned a reputation as someone who listened to the military with the R-12 and R-16 missiles, in contrast with Chelomei and Korolev, who were viewed to varying extents as prima donnas, or at least less than entirely focused on military applications of their rockets. Yangel parleyed this approval into an unmanned satellite launch that was to go ahead the next month: Kosmos-1, the very first mission of the soon-to-be-ubiquitous Kosmos program that represented the large majority of Soviet launches from 1961 until the fall of the USSR. Yangel was interested in extending his nascent space work into manned programs, at least to the extent of designing the rockets for them, and he and Glushko had initially worked on creating a rocket, the RK-100, using the same storable propellant engines that OKB-52 was designing for Chelomei. If Glushko failed to unseat Korolev through Chelomei, then teaming with Yangel would give him another bite at the apple.

The RK-100 was a clustered rocket and Yangel was reportedly displeased with the particular design that his OKB-586 came up with. In any case the first comprehensive space policy statement by the Soviet government, made in 1960, ruled out any possibility of it going forward. At this point the focus shifted to another Yangel-Glushko collaboration. Once again a clustered approach was used. Working on the base of a booster “module” resembling the smaller rockets with which OKB-586 had had success, this new rocket consisted of four modules on the first stage, four on the second, and then a core booster being the third and final stage. This proposal was dubbed the R-56, and Yangel brought it and another design, the R-36, to the conference.

What he didn’t do was go head-to-head with Korolev and Chelomei. As initially conceived the R-56 would slot into the space between the 20 and 70 tonne launchers, lifting 30-40 tonnes or so, while the R-36 was much smaller than any of the other rockets mentioned, aiming for a sweet spot in automated satellite launches around 1-2 tonnes to LEO.

The meeting did not go well for Yangel’s crewed space ambitions as by April a turgidly named decree called “On the most important projects of intercontinental ballistic and global missiles and carriers of space objects” was issued. It instructed the bureaus involved to go for the N1 as a space vehicle, the UR500 (which would eventually become the Proton) as both a space vehicle and ICBM, and the R-36 solely as a missile—though it too would become a satellite launcher one day, the Tsyklon. However, in the few weeks of space between the original meeting and the decision, Glushko began lobbying the Strategic Rocket Forces and Dmitri Ustinov about not only the “4-4-1” module version but one with a “7-6-1” configuration that he said would lift 70 tonnes—obviously the direct challenge to the N1 and UR-700 that Yangel did not make himself. His efforts paid off. While not authorizing the R-56, OKB-586 were given permission to at least study the “4-4-1” configuration.

A year later, in 1963, the order for the R-56 was revised to specify that it should lift 40 tonnes to LEO. While Yangel’s bureau studied modular rockets that could handle this new requirement, for all intents and purposes they went back to the drawing board and settled on a completely different approach: a four-stage “monoblock” arrangement, to use the Russian term. This is the familiar, boosterless approach where each stage is singular and is merely put on top of another singular stage—the Saturn V being the most famous example of this. The first two stages of this R-56 did the heavy work of getting a payload into orbit, while the third was used to get it to geosynchronous orbit, if that was the intended destination. The optional fourth stage would be for the extra push needed on lunar and planetary missions.

The first stage would be outfitted with sixteen RD-253 engines, the same one to be used on the UR-500 (which had six) and which was ready to fly in July, 1965. This cluster of engines was actually wider than the intended 6.5-meter diameter of the first stage, so it was installed with a short skirt which enclosed 8.2 meters at the base. The second stage had one of the same engine, equipped with a modified bell tuned for operations in vacuum, as well as a small steering engine that produced 15% of that stage’s total thrust. The third stage tapered from 6.5 meters down to 4 meters in diameter, which was the gauge of the rocket up to the top of its 67.8 meter tall stack. Loaded up with Glushko and Yangel’s preferred N2O4 and UDMH, it would weigh in at 1421 tonnes. Compare this with the Saturn V’s 110.6 meters and 2970 tonnes, or the Energia’s 2270 tonnes (not counting Buran) and 58.765 meters. While not in their class, this new R-56 was heading in their direction. If it had been built to spec, it would have been able to lift a little over 46 tonnes to a 200-kilometer orbit when launched from Baikonur, or 12.6 tonnes to the Moon.

What happened to make it fail: All the meetings and decrees regarding the Soviet space program failed to straighten out the USSR’s lunar program. At the end of 1963, multiple boosters and spacecraft were still in play, and the Soviet leadership had still not even formally authorized an attempt by their country at the Moon landing. In an effort to finally settle things, in March 1964 Yangel proposed to the Military-Industrial Commission that Soviet space efforts be split three ways: OKB-1 would work on the lunar spacecraft, Chelomei’s group would get the automated probes to the Moon and the planets, and he would build the rockets.

The Commission turned him down, reasoning that too much work had been put into the N1 already for it to be replaced now. There was reportedly also some discomfort with the fact that the R-56 would need two launches (at minimum) for a Moon mission, which implied a docking in orbit at a time when the first Soviet docking was more than three years in the future.

Yangel then petitioned in succession both Dmitri Ustinov and Leonid Brezhnev (seven months from becoming leader of the USSR, but then in charge of the space program and a native of Dnepropetrovsk where OKB-586 was based). Neither would back him, and the R-56 was formally cancelled by another decree, “On speeding up work on the N1 complex”, that was made on June 19, 1964.

After the Moon program was finally approved in August of 1964, Yangel’s bureau was assigned to work on the terminal descent/ascent engine for the LK-1, the program’s lunar lander. It thus had the distinction of being one of the few pieces of the Soviet Moon landing craft to make it into space, as it was tested successfully in orbit three times in 1970-71.

What was necessary for it to succeed: The main problem with the R-56 program seems to have been Yangel’s willingness to let go, as opposed to the on-rushing bulls that were Korolev and Chelomei. If he’d been willing to push harder or been a little luckier during the 1962 meeting he might have won the day—Sergei Khrushchev specifically says that he thinks his father would have picked the R-56 at that time if Yangel had presented first rather than last.

On the other hand, even down to 2016 no-one has ever built a rocket with a payload capacity in the 40-50 tonne range (SpaceX’s under-development Falcon Heavy is closest, at 54.4 tonnes). Smaller is fine for almost all launches, and crewed missions absolutely require more if going to the Moon or beyond (barring the construction of a larger craft using multiple launches, which has also never been done). There’s good reason to believe that even if it had flown, the R-56 might have ended up not being good for much of anything.

Sources

“Heavy Launch Vehicles of the Yangel Design Bureau, Part 1”, Bart Hendrickx. Journal of the British Interplanetary Society, vol. 63, Supplement 2. 2010

“Heavy Launch Vehicles of the Yangel Design Bureau, Part 2”, Bart Hendrickx. Journal of the British Interplanetary Society, vol. 64 Supplement 1. 2011.

Nikita Khrushchev and the Creation of a Superpower, Sergei Khrushchev. Penn State University Press. 2001.

“Barmingrad”: The KBOM Lunar Base

KBOM Lunar Base, "Barmingrad"

A simple schematic of the KBOM lunar base, showing nine of the base module arranged in the proposed figure-8 pattern. Click for a larger view. Based on a blueprint diagram printed in Russia in Space.

What it was: An extensive late-60s/early 70s study of a Soviet lunar base to follow up on the N1-L3 lunar landing.

Details: American lunar base designs, and most Soviet/Russian ones, have generally been quite conservative. They usually consist of upgrades to lunar landers that allow astronauts to stay on the Moon for weeks or months, often with the aid of logistics landers that are more of the same. Detailed study of the construction of something more like a permanent settlement or an Antarctic base is actually quite rare. On the US side we have premature examples like Project Horizon, but in the USSR we had what was probably the most developed of the entire Space Race: Barmingrad.

OKB-1 was swamped with work by the mid-60s, a side effect of Sergei Korolev and Vasili Mishin’s instincts to hold on to as many crewed and automated programs in the aftermath of Vladimir Chelomei‘s grab for control in Khrushchev’s latter days. When in November 1967 the Soviet government launched the Galaktika program to study the exploration of the Moon, Mars, and Venus, they had already informally farmed off study of a lunar base to KBOM, headed by Vladimir Barmin. By March of 1968 this had crystallized into the Columb sub-study and KBOM really set to work developing what was informally dubbed “Barmingrad”.

The choice of KBOM was a bit surprising in that they were the bureau assigned to designing rocket launch facilities for the USSR—the moon base was their first non-terrestrial assignment. Even so, Barmin, his chief A. Chemodurov, and the people assigned to the work took the project with enthusiasm, probably extending far beyond what they were expected to design. Ultimately their work stopped only because the N1-based Moon program was cancelled in 1974.

What they came up with was an ambitious plan based around a multi-use module, which they studied in a variety of configurations before settling on one as the best. The module was 3.5 × 8.5 meters consisting of a rigid section and an expandable section. The expandable section would allow the module to be shipped as roughly a cube and then, once on the Moon, would double the module’s length. At each end as well as on one side of the rigid section was an adapter that  would join two modules together and serve as an access point between them, or allow the attachment of a specialized section, such as the airlock that was to serve as the base’s “front door” for EVA.

Nine of the basic modules would be shipped to the Moon and arranged as two rows of three, with the remaining three serving as “crossbeams”, altogether forming a figure eight. Excepting the aforementioned airlock, this section of the base would be surrounded by berms of regolith and covered with a layer of the same to a depth of 40 centimeters (16 inches), all in the name of radiation protection.

The base was to house 12 cosmonauts, with connections to X-ray and optical telescopes for scientific study, a power source (either a nuclear fission reactor or solar panels), three radiators to dump the base’s waste heat, a unit for cracking oxygen from lunar regolith, and a deep drilling rig. The cosmonauts could get around by walking or, if they needed construction equipment or wanted to travel longer distances, using one of several rovers based around a Lunokhod-like six-wheel chassis. The base would be resupplied by landing craft carrying a logistics module which could be docked to the base, unloaded, and then discarded. By 1974, the base module had reached the mockup stage and KBOM were exploring the ergonomics of their work.

That said, “Barmingrad” took on a life of its own, and KBOM carried on expanding their base design well in to the far future, ultimately using it as the core of a full-fledged Lunar colony with a population of 200, the radical increase of necessary living volume being accommodated by inflatable domes.

What happened to make it fail: When Mishin was replaced as head of TsKBEM (previously OKB-1) in May 1974, Valentin Glushko swept away all of the N1-L3 program in favor of his own ideas. This included a moonbase of his own, LEK, and so Barmingrad was cancelled as part of the coup.

What was necessary for it to succeed: Glushko in turn had his moonbase cancelled along with much of his proposed program about 18 months later, as the Soviet space effort pivoted towards Energia/Buran and space stations. If he’d not cleared the board when taking over from Mishin, that was an 18-month window in which to produce some success with the N1 that might have convinced the Soviet leadership to carry on—and there’s some reason to believe that the success would have come in that timeframe, even if a change in heart is more dubious. At the end of that line was the KBOM moonbase.

Sources

Zak, Anatoly. “Going to the Moon…to stay”, Russia in Space: The Past Explained, the Future Explored. Apogee Prime, 2013.

OLS: The Orbiting Lunar Station (Integrated Program Plan, Part III)

OLS Schematic

The (surprisingly crude) schematic of the OLS from North American Rockwell’s Orbiting Lunar Station (OLS) Phase A Feasability and Definition Study, Vol. V. Public Domain image via NASA.

What it was: An April 1971 study by North American Rockwell, commissioned by NASA, on putting an eight-astronaut space station in polar orbit around the Moon.

Details: There was a short period of time prior to NASA settling on the Integrated Program Plan when some within that organization advocated a more conservative “space stations everywhere” program instead. A combination of NASA administrator Thomas Paine’s insistence on being bold and Spiro Agnew’s enthusiasm for Mars got the focus shifted to the Red Planet, but the space agency did its due diligence and took a look at the suggested stations in the context of the IPP.

From the standpoint of the 21st century, the most unusual of of these was a space station around the Moon, plainly dubbed the Orbiting Lunar Station, or OLS for short. North American Rockwell got the contract to flesh out the idea and dropped the result on NASA desks in April of 1971, just as Apollo 13 was gripping the world.

NASA’s basic intention was that the orbiting station would have several purposes. Scientific study of the Moon from orbit was one, and so was a supporting role for a surface base—communications with the Far Side, for example, or serving as an emergency shelter, or as a command station for remote rovers (thus alleviating the roughly 2.5 second round-trip delay between the Earth and the Moon). There was also a requirement to use the station for astronomy, including an intriguing suggestion to perform high-resolution X-ray astronomy using the edge of the Moon as an occulting edge, and the idea that the station would serve as an excellent test bed for the systems that would be used in the orbiting command centers that would probably feature during interplanetary missions.

What North American Rockwell presented was a station that would have been launched on a Saturn INT-21 (essentially a Saturn V without its upper stage, similar to what was used to launch Skylab) or in the cargo bay of the then-conceptual Shuttle that NASA was working on. After being checked out in LEO by a crew which would return to Earth, the unmanned OLS would be sent into lunar orbit using a Nuclear Shuttle, and then the first eight-astronaut expedition to the station would be sent using another. The vagaries of the Moon’s orbit around the Earth suggested a mission every 109 days to the station, with North American Rockwell arbitrarily deciding to swap half the crew out each time. After ten years, the OLS would be decommissioned.

As to where the astronauts were going, exactly, North American Rockwell came up with two possibilities. One was a purpose-built station, to which they specifically assigned the name OLS, while the alternative was a refit of a modular station originally built for Earth-orbital activities, which they dubbed the MSS. The end result was functionally the same, however, so for the purpose of simplicity we’ll focus on the OLS.

DeckPlans

The four habitable decks of the OLS. Composite image from the same source as previous. Click for a larger view. Public Domain image via NASA.

The station would have been built around a cylindrical core module 60.83 feet long and 27 feet in diameter (18.5 × 8.2 meters). It would have four receptive docking ports around its side, and one “neuter” port on each end, all intended for docking visiting ships or expansion with further modules later. Within were six decks, four of which were pressurized for human habitation. Access between these decks was provided by a series of circular openings on the station’s long axis; the exception was between decks 2 and 3, which were connected by a hatch that could be sealed off in the case of emergency.

One of the end ports would be used to attach a 33.42′- (10.2 meter-) long power module, which would unfurl four solar arrays totaling 10,000 square feet (929 square meters) hooked to regenerative fuel cells for storage, while one of the four receptive ports would house experiments that needed “a clear field of view” (the astronomy experiments, one presumes) and a bay for storing and repairing satellites the station would drop into other lunar orbits. Altogether it would have a dry mass of 107,745 pounds (48.75 tons); compared to other stations it would have been intermediate in size to the larger Skylab and the smaller Salyut-7.

The core module would also have a radiation shelter on the second deck, containing a secondary control room, backup galley, and toilet, protected by the stations 16,000 pounds of water (roughly 7250 liters) stored in a jacket around the shelter. The water was also used by the thermal radiators to deal with what NAR termed “the significantly more severe” environment in lunar orbit.

The OLS’s ten-year lifespan was specifically targeted to the 1980s, giving some idea of how long North American Rockwell though it would take to get it up and running.

What happened to make it fail: Like the rest of the IPP with which it was associated (with the partial exception of the Space Shuttle) the OLS ran into the avalanche that was the early 1970s. As well as major budget cuts and indifference on the part of the government and the American public toward space ventures, it had the additional problem of no high-level advocate. NASA administrator Tom Paine in particular was critical of the “stations everywhere” approach and preferred Wernher von Braun‘s more audacious Mars mission. There it would be only a minor part, if it existed at all.

What was necessary for it to succeed: You’ve got to start somewhere, begin with an administrator or a “rock star” like von Braun backing it to the full. Then all you have to do is prevent the economic troubles of the 1970s, end the Vietnam War, and somehow get one of the President or the general public on side. Piece of cake.

If you relax the requirement for success to include a lunar station not directly descending from NAR’s study, the situation gets a little easier. The American and Russian space agencies have discussed the possibility of a lunar station as a follow-up to the ISS, and it’s to North American Rockwell’s credit that both have described a setup not too dissimilar from the OLS. Though NASA still seems more interested in an asteroid redirect mission or a Mars mission at the moment, there’s a halfway decent chance that, about sixty years after the fact, the OLS’s descendant will take flight.

Sources

Orbiting Lunar Station (OLS) Phase A Feasibility and Definition Study, Vol. V; Space Division North American Rockwell; Downey, California; April 1971.

The Space Shuttle Decision; T.A. Heppenheimer; NASA History Office; Washington, DC; 1999.

 

 

 

The Reusable Nuclear Shuttle: To the Moon, Again and Again (Integrated Program Plan, Part II)

Sample Nuclear Shuttle configurations

A 1971 slide prepared by Marshall Space Flight Center showing an unloaded Nuclear Shuttle (top) and two configurations with a various components docked to its forward end (middle and bottom). Public domain image by NASA via Wikimedia Commons. Click for a larger view.

What it was: The solution NASA envisioned to the difficulty of getting large payloads to anywhere much beyond Earth with mere chemical rockets. Something like a dozen of them would serve as the brute force “trucks” of the American space program beyond Low Earth Orbit.

Details: We’ve already discussed some aspects of the Integrated Program Plan, NASA’s ambitious 1969 proposal to follow up the Apollo Moon landings with a new goal and new technology. The new goal was a manned Mars Mission, but the new technology had two particular pieces that would do the grunt work of building a space station and a Moon base as intermediate steps to the red planet: a reusable orbiting space plane (not yet dubbed the “Space Shuttle”) and the Reusable Nuclear Shuttle (RNS), many of which would have been built. It would have been the space plane’s role to get astronauts and cargo into low Earth orbit, while the RNS would have been used for the “high frontier”, so to speak. If something was going to go higher a few hundred kilometers, it would be offloaded from the spaceplane to an RNS, and then sent on its way—potentially to the Moon, or even beyond.

The RNS was suited for this task and similarly restricted from landing on Earth for one reason: their engines were given oomph by a nuclear reactor, but approaching one too closely at the wrong angle would expose a person to a fatal dose of radiation.

Start with the Nuclear Shuttle’s advantages. A variety of factors affect the power of a rocket, but the dominant number is the specific impulse (ISP) of the propellants it uses (to be precise, it’s a proportional measure of how much propellant the rocket has to use to add or subtract a given amount of velocity, though confusingly its unit is the second). With variations due to several other factors, rocket engines that use UDMH and N2O4 produce a specific impulse in the neighbourhood of 280 seconds, while LOX/LH2 is much more efficient at around 450 seconds (the low density of liquid hydrogen hamstrings it, though, so it’s often only used in upper stages where the rocket is already well underway and moving fast).

Unfortunately, all chemical fuels with a better ISP than that are either fantastically explosive, corrosive, toxic, or some hellacious combination of all three of those characteristics. Even at that, the best known ISP ever obtained (with a tripropellant of lithium, hydrogen, and fluorine) is 542 seconds.

Ultimately this because chemical propellants depend on chemical bonds, and there’s only so much energy you can contain in those. Quite early on rocket engineers realized that a good way to higher ISP was to use a different source of energy. In the absence of real exotics like nuclear fusion and matter/antimatter reactions, nuclear fission was the way to go. Hydrogen heated by a nuclear reactor can have an arbitrarily high ISP; it’s just a matter of how much heat one can get away with before the physical components of the engine are melted away.

When John F. Kennedy made his famous 1961 speech that started the race to the Moon he made a largely-forgotten reference to the Rover nuclear rocket, a contemporary project that was working on a preliminary nuclear-fission powered rocket. This in turn led to successively more advanced nuclear engines with the colourful names KIWI, Phoebus, and Peewee-1. By the end of 1969, NASA had a design for a functional nuclear rocket engine, the NERVA-2.

NERVA-2 would have had a specific impulse of 825 seconds in vacuum, and be able to burn for 20 minutes and produce 399.5 kilonewtons of thrust. Compare this to the J-2, NASA’s comparable workhorse engine (used on the second stage of the Saturn V, among others): it produced 486.2 kN of thrust, but was far less efficient at just 421 seconds of ISP. Accordingly, even though the NERVA-2 was far larger and heavier than the J-2 (having an entire nuclear reactor on board does that), the savings on propellant mass and the mass of the tanks needed to store it would make any spacecraft using one smaller than the same spacecraft based around a J-2.

Getting to the Moon is considerably more difficult than getting to orbit—you need to add another 3 to 4 kilometers per second to your orbital speed—and so the radically reduced fuel consumption of a NERVA-2 engine was very useful. Enter the Reusable Nuclear Shuttle. This was a conceptually simple ship: a single large fuel tank containing LH2 would have a NERVA-2 attached to one end, while the other had a docking adapter that could connect up to a variety of payload containers. Attach your payload, light the engine, and the RNS would push the payload into high orbit, to the Moon, or even beyond. Ideally you’d also put it on a trajectory which would let it return to Earth orbit, as the NERVA-2 was designed for ten round trips before it would be unsafe to light up again.

The disadvantage of the RNS lay in the radiation environment it produced. The rocket’s exhaust was only marginally radioactive and so arguably acceptable to allow on a launchpad, but in the event of a containment breach on the ground or, worse, in the air the engine would have sprayed uranium all over the environment. Even in the heady days of the late 1960s this was considered too risky, so the plan was to launch an RNS on top of a Saturn rocket using conventional fuels—if the Saturn blew up, the reactors were sufficiently ruggedized that they could survive the accident intact and fall into the ocean safely (by 1960s standards anyway).

What was more problematic was the NERVA-2 in orbit. Once the reactor was up and running it needed a great deal of shielding to protect approaching astronauts. As shielding was heavy, the RNS wasn’t going to have much of it. Instead the approach chosen was the have a “shadow shield”, where the propellant tank and any propellant aboard would provide most of the shielding. This meant that humans getting close to an RNS had to approach it from the front at a fairly shallow angle, using the bulk of the RNS to cover them from the reactor. If they approached from the sides or, God forbid, the aft where the engine was located they were assured of radiation sickness or death. Even on top of the RNS, a crew member would get about the recommended annual maximum radiation dose each time the engine fired.

Nevertheless, the advantages of the RNS outweighed the disadvantages in NASA’s collective mind, and the Integrated Program Plan called for it to be the workhorse of the space program beyond Earth orbit. Each would be used up to ten times (with refueling gingerly taking place after each use), after which it would be discarded in a high orbit due to its extreme residual radioactivity. With it, crews and payloads could be sent to the Moon and returned, and ultimately the American manned Mars mission craft envisioned for the early eighties would be perched on top of three of them.

What happened to make it fail: As with much of the IPP, the nuclear shuttle never got built because of a combination of disinterest from the Nixon administration and the falling budgets that that caused. Of all its parts, only the re-usable Space Shuttle and its rocket stack made it off the ground.

The RNS has its own particular story embedded in this larger tale, though. For many years the nuclear rocket engine program had been championed by New Mexico Senator Clinton P. Anderson, as much of the work on NERVA had been done at Los Alamos. Just as NERVA-2 was ready to become operational he became seriously ill and unable to press his case as much as he had in the past. The White House convinced Congress to pull the plug on the nuclear rocket on the grounds that it would be the basis of a manned mission to Mars, a goal about which Congress was quite negative at the time. The plan was that the freed-up funds could be used for the more-practical Boeing 2707, a Mach 2.7 supersonic commercial passenger plane similar to the Concorde or the Soviet Tu-144. Ironically, Anderson had enough clout remaining in the Senate to apparently engineer a 51-46 vote against moving ahead with that project; the House of Representatives soon followed. While the exact maneuvering involved has never been documented, the vote was widely considered retaliation for the cancellation of NERVA.

Regardless, with its funding quickly dwindling despite Congressional efforts to keep it going, NERVA was cancelled on January 5, 1973, and the Reusable Nuclear Shuttle was dead.

What was necessary for it to succeed: Like much of the Integrated Program Plan, the RNS was doomed by the political currents in Washington, within NASA, and in the general public. When it came down to picking something to move forward on NASA picked the Space Shuttle and the hope that one day they would be able to move on to a space station from there. The RNS ranked third (with the Moon base and Mars landing fourth and fifth) on their priority list, and they even tried very hard to claim that without the Space Shuttle they would not be able to get any nuclear shuttles into space. This was not actually true as the initial plan to use NERVA involved an upgraded Saturn rocket, but it was a measure of NASA’s determination to do anything to get the Space Shuttle built.

Ultimately that’s the main route to getting the RNS into the sky. NASA engaged in a great deal of internal debate from 1968 to 1970 over whether to continue with ballistic capsules or move on to a reusable, winged orbiter. Related to this was the debate over whether or not to focus on Earth orbit as a testing ground or push hard into the rest of the solar system. If both debates had gone the other way, a nuclear engine would have been very attractive to planetary mission planners and the money would have been there to continue with NERVA and the RNS–despite Congress’ objections to Mars missions, the presidential Office of Management and Budget had considerable discretion to ignore how it was told to allocate the money it received until a post-Nixon backlash in 1975.

Instead the arguments settled around a winged orbiter and sticking close into Earth unless the mission was unmanned, and we got the space program that we did from 1975 to the first decade of the 21st century. Nuclear rockets were revived for a short while during the days of the Strategic Defense Initiative’s Project Timberwind, but again it never came to anything.

Even if the RNS got built, there’s the possibility that it would have been much restricted in use or even cancelled outright no matter what successes it scored. The Three Mile Island accident in 1979 soured the American public on nuclear power in general, and after the Challenger explosion in 1986 NASA became very leery about dangerous payloads–for example, deciding against the planned Centaur-B booster that was to be orbited aboard STS-61-G later in the same year for the purposes of getting the Galileo probe to Jupiter. While both were specific incidents, they were each the culmination of long-term cultural trends that likely would have choked off the use of the RNS no later than the mid-1980s, and possibly earlier if one of them was involved in an accident.