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

Mars Expedition 1969: NASA’s Waterloo (Integrated Program Plan, Part I)

A cutaway view of the Mars craft proposed by MSFC in 1969.

A cutaway view of the Planetary Mission Module (centre) and Mars Expedition Module (right) on top of the Nuclear Shuttle (fully visible on the second ship in the background). Public domain image from the Marshall Space Flight Center, NASA. Click for a larger view.

What it was: NASA’s follow-up to the Apollo program. A manned mission to Mars would have been launched in November 1981, brought twelve men to Mars—six of them landing—and then returned to Earth in August of 1983 (with a flyby of Venus along the return route). There would be two more manned missions by the end of 1985, and a manned base by the middle of 1987.

Details: Neil Armstrong stepped onto the Moon on July 21, 1969 and the obvious next question was “Now what?”

NASA had been answering it intermittently for years prior to this but now they got down to business. In particular, while they supported the Apollo Applications Project they were not content to stick to those missions’ main goal: to find out new things to do with the hardware they had already developed. Quite reasonably they decided that they needed to carry onwards and upwards with their engineering. Not only was a manned mission to Mars the obvious next step from an exploratory standpoint, it had the advantage of requiring that they move beyond Apollo equipment.

To that end they turned once again to Wernher von Braun. This was the culmination of his life dream: he’d published a Mars program in 1948, made a splash with the variant of it published in Collier’s in 1954, come up with another smaller expedition in 1956, and then sponsored the so-called EMPIRE and UMPIRE studies in 1962-64. On August 4, 1969 he made a presentation of what would be his final Mars proposal to the Space Task Group (STG), chaired by Vice President Spiro Agnew.

The mission was to be the penultimate part of a two-decade effort, the Integrated Program Plan, which could really be thought of as “Apollo 2.0”: another vast effort with an end goal, designed to replace the one that had just finished. As such it was part of an integrated whole that developed orbital operations into a finely tuned science, first by practicing with the Apollo Applications Program space stations and lunar base. One of the tools was to be a new space-only booster based on NERVA—which is to say, the first ever nuclear thermal rocket. This piece of equipment, dubbed the Nuclear Shuttle, was intermediate in mass between the second and third stages of a Saturn V, and had a higher specific impulse than any rocket ever flown.

Individual Nuclear Shuttles would be fueled in orbit with liquid hydrogen and used to push men and cargo to the Moon, then the empties returned to Earth orbit when they could be refueled and used again—up to ten times in all. Regular Saturn V launches would occur all through the early to mid-70s, building a space station and generally preparing the necessary infrastructure to be a “gas station”.

Meanwhile the other necessary equipment would be tested as part of an Apollo Moon base (basically a revival of the ALSS Lunar Base, which had been cancelled when new Saturn V production went into hiatus). There would be tests of the Nuclear Shuttle by the end of 1977, and 25 men living on the Moon by 1982.

With all that shaken out, the Mars mission would begin on November 12, 1981 with two ships launched on a Mars-bound a trajectory from low-Earth orbit. Each would consist of three Nuclear Shuttles strapped in tandem and a Mars craft made up of a Planetary Mission Module (PMM) habitation section and a Mars Excursion Module (MEM) lander mated to the tip of the one in the centre. The two side Shuttles would get the centre one and its payload up to speed, then peel loose and re-enter Earth orbit for reuse, while the two diminished mission craft would carry on their way.

There were two because the mission had the unique profile of backing itself up. Strictly speaking only one would be necessary for the mission, but the second would fly in formation to be a lifeboat in the case something went horribly wrong on the first—and the first served the same purpose for the second.

This kind of redundancy was necessary because the mission’s twelve crew were going to be away a long time. They’d arrive at Mars on August 9, 1982, stay there for almost three months, and then return to Earth for August 14, 1983: 640 days in all. In theory you wanted to minimize the weight of what you sent, but no margin for error meant nothing could go wrong without endangering the whole mission. NASA had always operated on the principle that you needed something to work with in case of an emergency, a principle that would prove its worth a few months after von Braun’s presentation when one whole side blew off of Apollo 13’s CSM and the astronauts on board were able to ride the excess margins back to Earth. Away from Earth for far longer than any space mission flown to that point, the Mars expedition would get its margin by literally flying two missions at once.

While at Mars six astronauts would stay aboard the PMM and Nuclear Shuttle combinations, flying in an elliptical orbit (a clever innovation by von Braun which made docking harder but cut the mass needed for the mission in half). After a remote sampler determined that it was safe to descend, six more astronauts would go to the surface in two groups of three aboard the Mars Expedition Modules, a capsule derived from the cone-shaped Apollo Command Module. They would slow down in what had only recently been discovered to be Mars’ very thin atmosphere by combination of a parachute, a ballute (a balloon-shaped inflatable parachute that works well at low atmospheric densities), and finally retrorockets starting three kilometers up.

Cutaway view of a MEM

Cutaway view of a MEM lander. Public Domain image from NASA’s Humans to Mars: Fifty Years of Mission Planning, 1950-2000. Click for a larger view.

A MEM could support its crew on the ground for up to sixty days, then its upper stage could climb back into orbit for rendezvous with the PMMs and Nuclear Shuttles. The latter would then fire up one more time and start the long journey back to Earth on 28 October, 1982.

The mission was not quite done, however. Their trajectory would take them back inside Earth’s orbit on a flyby of Venus on February 12, 1983. While this was a second opportunity for scientific study, it was primarily a speed-shedding maneuver. Four probes would be dropped on the way by.

Having got the right trajectory and speed, the two Mars craft would pull into Earth orbit where they would dock with the space station (while not the Orbiting Quarantine Facility, which was proposed several years later, it would serve the same purpose). From there they would be picked up by the Space Shuttle for the last leg of the journey home. If for whatever reason the space station didn’t exist or wouldn’t be suitable for this, the mission could be designed instead with an Apollo-style command module would let the crew splashdown directly to Earth.

Note that four of the Nuclear Shuttles had returned to LEO near the start of the mission; now the last two had done the same and so had their associated Mars craft. Only the MEMs would have been used up. Accordingly the ships would be refurbished and sent out again in 1986. Meanwhile, a second pair of ships would have been launched early in 1983, and on return be re-launched in 1988. By mid-1989, the intention was to have a 48-man semi-permanent base on Mars.

Bearing in mind that the proposal was part of a larger manned space effort including the Space Shuttle and a Moon base, the total cost of NASA’s programs was estimated about US$7 billion per year through at 1976 and $8 to 10 billion for the few years after that. The Space Task Group accepted von Braun’s Mars proposal and the NASA Integrated Program Plan as a whole, and passed it on to President Nixon on September 15, 1969.

What happened to make it fail: There was an utter disconnect between what NASA thought they should get in funding and what everyone else in the government was willing to give them. Even the Space Task Group was uneasy about the von Braun plan and offered two decompressed (and cheaper) versions of it—one where the Mars landing didn’t take place until 1986 and another where the landing was the goal but there was no set date for it. They still underestimated the opposition they would face.

Mariner 7 flew by Mars the day after von Braun made his presentation to the Space Task Group, and appeared to back up what Mariners 4 and 6 had shown previously: that Mars was a dead world, cratered not overly different from the Moon. We now know that by bad luck these missions happened to photograph the most inhospitable parts of Mars rather than the (slightly) more Earth-like northern Hemisphere, but that realization was in the future. Initial jubilation over Apollo 11 faded within a few months in favour of hard questions about why men had to go to Mars in light of what had been learned.

There was also a strong sense among the public and politicians that the United States had to get its house in order down on Earth. Protests against the Vietnam War were at their height and the country was still reeling from the urban riots of 1968. The Republicans had been voted back into power in the presidency in response (though the Democrats still controlled Congress) and Nixon was to continue the squeeze on the NASA budget that his Democratic predecessor had begun. When his director of the Office of Management and Budget Robert Mayo—an observer on the STG—objected to NASA’s proposal for FY 1971 coming in 29% over the cap he had imposed on them (US$4.5 billion instead of $3.5 billion) he convinced Nixon to put his foot down and NASA’s entire manned space program entered a death spiral.

By the time the dust settled almost all of von Braun and NASA’s programs had been cut. On March 3, 1970 Nixon announced that he’d allow only a truncated Apollo program, one space station (Skylab) and a commitment to the Space Shuttle. NASA would try one more Mars proposal in 1971; Wernher von Braun left NASA in 1972 and died in 1977 even before his proposed mission would have launched.

What was necessary for it to succeed: Almost everything was pointing against a Mars mission being approved in 1969. Public opinion was dubious (a Gallup poll in July 1969 found 53% of Americans against it—as Apollo 11 was going on!), the political interest to explore space was fading away in the Democratic Party as John F. Kennedy receded into the past, and Nixon was struggling with paying for the Vietnam War just as the US economy was sliding into recession. After his presidency various inside sources reported that he had been looking for a way to wrap up Apollo without looking like “The Man Who Killed the Space Program”; ironically, the less-ambitious options included in the STG’s report gave him the loophole he needed to dive through.

One possibility that could have brought about the mission would be a virtual tie in the space race, with the Americans and Russians getting to the Moon in a dead heat or possibly even the Russians getting a man on the Moon first. Under those circumstances the US might have committed to “Space Race, Round 2” and go for Mars. But this is a hard one to get flying, for all that it’s about the closest we’ve ever been to seeing a manned Mars mission. Even if it had been approved how much it would have had to shrink and delay as it rode out the 1973 Oil Crisis and the jittery economic conditions that lasted into the early 1980s is an open question.

Some very nice renders of this mission can be found on the DeviantArt page of Drell-7, AKA Tom Peters.