LESS: The Lunar Escape System

LESS-CM docking

The final moments of the open-to-space LESS rescuing two astronauts stranded on the lunar surface by a faulty lunar module. Getting to this point would have been difficult, but the alternative was death by suffocation within a few hours. Image from the NASA document Lunar Escape Systems, Volume I: Summary Report. Click for a larger view.

What it was: A proposed emergency booster from North American Rockwell that could be used by Apollo astronauts in the case that they were stranded on the Moon. It was built around the assumption that the stricken crew would be safe on the ground but with an LM that couldn’t take them back to the Command/Service Module in lunar orbit. Using fuel siphoned from the ascent stage of the lunar lander they would sit in open space, using their space suits for life support, and manually guide themselves into orbit for a rendezvous with the CSM.

Details: Under the influence of the USAF, NASA studied various ways of escaping a stranded ship in orbit. The Apollo program took a different tack, partly because of the difficulty of coming up with an escape system that would work to return the astronauts from such a distance and partly because weight on the lander was at such a premium. Serious work didn’t begin until NASA started planning for the long-duration missions that would lead up to an Apollo-technology lunar base.

The Apollo landings were divided into two phases. Apollos 11 through 14 were of relatively short duration, while Apollo 15, 16, and 17 were “J-Class” missions using the Extended LM to allow longer stays. The Extended LM also had a higher cargo capacity (which is why the final three Moon missions had a Lunar Rover to drive around in). Once the J-Class missions were done, later missions were to use two LMs, one of which (the “LM Truck”) launched unmanned from Earth solely to carry more equipment. With that in mind NASA looked into equipment that could be carried to make landing on the Moon safer.

Neil Armstrong said later in life that he’d had nightmares for two years prior to launch that he’d get back into the LM to begin the trip home and the engines would fail to start; apparently he wasn’t the only one, because one of NASA’s suggestions for the extra equipment tried to deal with the issue. In June 1970 North American Rockwell sent a first-stage feasibility report to NASA for the Lunar Escape System (LESS), based on a flying rover they’d already been working on (the Lunar Flying Vehicle, or LFV). By September of the same year they’d fleshed it out further, including some initial lab and engineering work.

The LESS was very bare-bones, but bear in mind that until something like it was added to the lunar lander the astronauts were facing certain death by suffocation if the LM failed on them. In that dire situation, the stranded men would take two hours to unload the LESS from the side of the LM (where it had been stored in a configuration looking for all the world like an IKEA flat pack) and then siphon fuel from the lander’s ascent stage tanks; the theory here was that if the LM was dysfunctional due to a landing hard enough to crack those, the astronauts weren’t going to be in any shape to rescue themselves anyway.

LESS Schematic

A schematic diagram of the LESS from Lunar Escape Systems, Volume II: Final Technical Report. Click for a larger view.

Having fuelled the LESS, the astronauts would not get in it, but rather sit on it, exposed to open space. The pilot would give them an initial kick skywards to 3000 meters (a trip that would take about sixty seconds), then heel the LESS over to thirty degrees so that they’d continue rising while also starting to make headway horizontally. At about 6 minutes they’d be high enough and have enough vertical velocity that they’d then turn over the rest of the way and head for the CSM completely horizontally. The LESS was to be equipped with three gyros to help determine the attitude of the ship.

Once they were in what they hoped was a 110 kilometer orbit, the LESS crew would make observations of the sun angle and (if launching during the day) the angle to the lunar horizon and their apparent speed over passing landmarks below. Using these they could calculate their actual orbit–by hand, as the LESS had no on-board computing ability and the astronauts spacesuits didn’t have enough air for ground control back on Earth to give them the figures they needed. While too high was obviously a problem, as the orbit was very likely to be elliptical rather than the ideal circular, too low at perilune was the main issue. After testing with simulators, Northern Rockwell blandly states that LESS rescues would obtain “marginally acceptable orbital accuracies in terms of avoiding lunar impact.”

The CSM pilot would likewise be trying to figure out where the LESS was going to be. The launch of the rescue craft would be timed so that as it reached its height (and assuming it was on target) it would pass within 20 kilometers before they started to diverge. Using a sextant to observe a flashing beacon on the LESS and using a VHF rangefinder, the CSM pilot would use his onboard computer to calculate an intercept with the LESS. Unfortunately the LESS not very visible to the CSM pilot if the LESS was too far from where it should be: only to a maximum 90 kilometers by eye. The North American Rockwell report says “Visibility and acquisition of the target with the CSM optics was found to be a problem” and suggests no solutions. Ultimately it came down to hoping that the LESS astronauts hadn’t missed their correct orbit by too much.

The CSM’s orbit would take it around the Moon, during which he’d execute a burn that would put him at the same place at the same time as the LESS before the end of its first orbit. If absolutely necessary he could bring his craft as low as 80 kilometers above the surface. The stranded astronauts would have at best a couple of hours of air left, so a second chance on the next orbit was out of the question.

It was very likely that the two would miss each other by some distance, anywhere up to one kilometer and with somewhat differing speeds, so as they got close it was necessary for the CSM to start a new maneuver to lessen the gap. Meanwhile the LESS crew would be changing the orientation of their craft so it pointed towards the nose of the CSM. The Command/Service Module actually flown to the Moon had a VHF transponder and flashing light beacon of its own for use with LM docking, and these would be turned on for a LESS flight, giving the astronauts on it a target to aim for.

Assuming all went well the LESS would dock with the Command Module using a special docking attachment on the latter’s nose. Once there was a firm connection, the astronauts could climb onto the CM and enter its hatch, opened from within by the CSM pilot.

At that point the CM’s cabin would be repressurized and the presumably relieved crew could begin the process of returning to Earth used by a regular Apollo mission.

What happened to make it fail: The late dates at which the feasibility studies came back to NASA are a clue. While the space agency was still planning for expanding the United States’ presence on the Moon, Apollo was shrinking quickly. The same month as the second report came out, budget cuts forced NASA down to just three extended LM missions, and there was no sign of funding for the longer missions they wanted after that. In fact it never came, and there was no need for the LESS to rescue astronauts because no-one was going to the Moon anyway.

What was necessary for it to succeed: It was part and parcel of the Apollo program’s continuation according to its initial plan. If Apollo had kept going, or been revived fairly quickly after going into abeyance for a while in the early 1970s, something like it would have been desirable until stranded astronauts had a long-term Moon base to return to in case of emergency. As long as the CSM was the only place to go to, LESS would have been a plausible addition to the astronauts’ equipment.

The difficulty here is that the Apollo program relied on the Saturn V, and the Saturn V stopped production in August 1968. The ability to start it back up again disappeared very quickly, and it’s estimated that NASA would have needed an extra billion dollars to keep it going after 1970. Without Saturn the entire Apollo program falls apart as nothing else is powerful enough to launch the heavy Apollo Lunar CSM/LM combination. Ultimately the success of the LESS comes down to avoiding the US’ budget crunch in the late 1960s, like so much else did in the American space program of the time.


MTFF/Columbus: Europe’s Space Station

Columbus docked to Hermes

The initial module of Columbus, the MTFF, docked with the proposed mini-shuttle Hermes. At this point the space station would be unpressurized and unmanned except when astronauts were retrieving its experiments, but the APM (which eventually evolved into the ISS module Columbus) would be attached later to add a small living space. Image source unknown, believed to be the ESA; if you know the source of this picture, please contact the author. Click for a larger view.

What it was: A European effort to turn their contribution to the American space station Freedom into an independent space station of their own, hoisted into orbit by ESA rockets and serviced by an ESA shuttle.

Details: The European Space Agency signed on to Ronald Reagan’s suggested internationalization of the Freedom station right from the moment he made the offer in 1984. They had been developing the pressurized Spacelab module for use in the Space Shuttle’s cargo bay since the early 1970s, and now pushed for the new space station to build on components derived from their work. As part of this they started the Columbus project, which among other goals would have them make one such component—the Attached Pressurized Module (APM)—on their own for inclusion in the completed Freedom.

Another part of the project was to be semi-autonomous right from the initial planning, though. The Man-Tended Free Flying Platform (MTFF) was to have been a two-segment unmanned Spacelab module which would detach from Freedom and move to a nearby orbit. This would allow for sensitive, teleoperated microgravity experiments away from the noisy, manned Freedom and, a round of experiments completed, it would return for maintenance at the main station.

During the mid- to late-1980s, though, Freedom had a rough ride in the US Congress and the ESA started developing contingency plans for what to do with Columbus if the American station was cancelled. Couple this with massive increases in prices to use the Space Shuttle—then the Challenger disaster temporarily making its cargo bay unavailable at any price—and from 1989-92 these plans culminated in an entirely autonomous station that the Europeans would try if remaining part of the now downsized and re-named Alpha (AKA “Space Station Fred”) became too unpalatable.

The initial station would have been the unmanned MTFF, but now the experiments would have been retrieved by the ESA’s Hermes shuttle, which along with the Ariane-5 rocket had been approved as an unrelated project in 1987. In 1991 the three were melded into one big project.


Two suggested expansions of Columbus beyond its initial two modules. Image source unknown, believed to be the ESA. Click for a larger view.

The MTFF, Hermes, and the French launcher were to be joined by a fourth piece of the puzzle: the APM, now divorced from Alpha. Once the unmanned MTFF-based station was proven, the APM would be completed and launched on an Ariane-5 (or possibly in an US Shuttle’s cargo bay, if renting it turned out to be cheaper and more convenient). It would then dock with the MTFF to produce an entirely European manned facility, Columbus. The long-term, if somewhat nebulous, plan was then to add more and more modules as time went by.

Statistics on the Columbus are surprisingly hard to come by. Based on the actual ISS module that was derived from it, though, we can presume that its two working modules would totaled about 14 meters in length, with the power module and station-keeping ion engine at the MTFF end adding about another 5 meters.  Its total mass would have been in the range of 25 to 30 tonnes, which would have made it a bit bigger than the Soviet Salyut stations, but less than 25% the size of Mir and about 6% the size the ISS. Accordingly it probably would have had the same sort of missions as the Salyuts, involving two or three astronauts for a few days up to several months.

The budget for the station was calculated at US$5.3 billion, including operations for five years.

What happened to make it fail: Two trends pulled the APM back to where it started: attached to the ISS.

First, the United States got its act together. The Space Station passed through another session budget shrinkage and soul-searching under Bill Clinton in 1993, but finally stabilized into what is recognizably the ISS that got built. As uncertainty over the American contribution faded away, and the Russians signed on to ISS rather than build Mir-2, it became clear that it would be safe to co-operate rather than go it alone—though the ESA did keep contingency plans for Columbus in place as late as 2001.

The ESA itself was also running into budget difficulties. The collapse of the Soviet Union did open up another possibility, as there was talk for a while of perhaps attaching the APM to Mir-2, but a related event back down on Earth proved to be more important. The costs of German reunification made Germany scale back its contributions to the ESA by nearly a fifth, which brought a budget crunch to the agency as a whole. With Hermes already over-budget, it was cancelled entirely, as was the MTFF, and the APM’s costs were scaled down by committing to the American station project after all—the name Columbus was co-opted for it alone rather than the entire project, and it became the Columbus science laboratory module that was attached to the ISS in February 2008. Only the Ariane-5 launcher managed to emerge from the crisis unscathed. As it turned out, the late 80s and early 90s were something of a Golden Age for European manned space exploration. Not only has the over all ESA budget been declining slowly since then, the percentage of it devoted to manned space travel has dropped precipitously. The ESA’s focus has shifted to more commercial uses of space such as telecommunications satellites and the Galileo satnav system.

What was necessary for it to succeed: The main necessity is the stillbirth of the ISS, which isn’t too hard to engineer. The Challenger disaster had called it into question, repeated budget cuts hit it in 1989 and 1990, and in June 1993 a bill to cancel its immediate ancestor Alpha had failed by only one vote in the House of Representatives.

Given that event, the budgets floated for MTFF even after the Germans had run into reunification money problems had it flying by 1999 so long as the ESA doesn’t make the real world turn into budgeting more for commercial applications that it did. This gives us the first component of the station.

If MTFF did get off the ground, the next component of the program was still very likely to have changed. Hermes was not going to fly on a reasonable budget in a reasonable timeframe, which kicks out one leg of the station’s autonomy. However if the MTFF had gone ahead it’s likely that the ESA could service it with an (relatively) quick upgrade to the simpler Automated Transfer Vehicle they had begun developing in the mid-1990s. It flies in the real world on unmanned missions to the ISS, and its manufacturer EADS Astrium has been floating a proposal to turn it into a manned capsule since 2008. British Aerospace had actually suggested manning and supplying the station using a capsule of their own design in the mid-80s, only to have it squelched in favour of the French mini-shuttle.

The combination of an MTFF serviced by a manned ATV would likely have worked, leading to the attachment of the APM and a completed, manned ESA station Columbus sometime in the middle to late 2000s.

Douglas Model 671/684: The X-15’s Shadow

Model 684

A schematic diagram of the Douglas Model 684. It was submitted to NACA in 1954 as part of the X-15 design competition. Though evaluation suggested it would be the superior suborbital spacecraft, it lost to North American Aviation’s bid. Image from “USAF Project 1226, Douglas Model 684 High Altitude Research Airplane”. Click for a larger view.

What it was: Douglas Aircraft’s 1954-55 attempt at a suborbital spaceplane, with support from the US Navy and eventually NACA, intended for testing high Mach numbers in the atmosphere. Launched from a bomber, it would use a ballistic flight to get as high as 344 kilometers and then use the drop back down into the atmosphere to build up speed.

Details: NASA’s predecessor, the National Advisory Committee for Aerospace (NACA), was devoted to basic aerospace research programs whose results could be used by industry to make better aircraft. By the 1950s hypersonic travel was in the cards and they resolved to develop a research aircraft that could reach Mach 7, solely for the purpose of studying the aerodynamic and heating problems of moving through the atmosphere at that speed. Interestingly, they were not interested in studying spaceplanes or re-entry, as they considered manned space travel something for the 21st century, but the speeds involved were creeping up on those issues regardless of their intentions. With that in mind engineers at their Langley Research Center roughed out a basic design that is recognizably the X-15.

A lot of NACA’s work was done in conjunction with the US Air Force and Navy, partly because they were the groups most interested in cutting-edge aviation and partly because the Department of Defense had a budget roughly 150 times larger than NACA did. Accordingly, basic design in hand, NACA met with the other two organizations on June 11, 1954 to discuss where to go next.

The Air Force had been working with Bell Aircraft—builders of the X-1 and X-2—but the Navy had been working with Douglas Aircraft on two successive planes, the D-558-1 and the D-558-2. At the meeting they revealed that they were in the early stages of getting Douglas to work on what the manufacturer called the Model 671 (informally known as the D-558-3 in years since, though that name was never actually assigned to it).

Unlike the NACA idea, the Model 671 was designed for height as well as velocity. Although the work done on it was still preliminary, Douglas had already come to the conclusion that they could make it reach 1,130,000 feet—or, in more modern terms, 344 kilometers. The International Space Station is actually allowed to drop as low as this before being boosted again, so this is well into space; Douglas did admit that the pilot would probably not survive the G forces of that flight and so recommended nothing higher than 770,000 feet (237 kilometers). The plane’s downrange capability was 850 kilometers for both high and low flights, which is suborbital, but for both in height and distance this is considerably farther than Alan Shepard went in Freedom 7.

Given that NACA and the Air Force were now looking at similar programs, the Navy cancelled the Model 671 and joined up to launch a design competition. On December 30, 1954 twelve contractors were invited; only four came up with proposals, probably because of the risk involved and the minimal profits that would stem from the two airplanes that NACA wanted built. Three of the replies were from Bell Aircraft, North American Aviation, and Republic Aviation.

Douglas replied with the Model 684. Their proposed craft would hit a maximum of 7300 kilometers per hour, and reach heights of 114 kilometers—in other words, they had to tone down the Model 671 just to meet the NACA requirements. Even at that, this is still the edge of outer space: the Model 684 would have been the first suborbital spaceplane.

As it was headed for space, the pilot compartment was completely pressurized, and could carry two if the research instrumentation was removed. Anyone onboard would wear a pressure suit (the X-15 program would actually develop the space suit used by Mercury astronauts), and in case of a dire emergency the entire forward fuselage would cut loose, push away from the main body of the craft on a small jet, and drift down to Earth under a parachute.

The Model 684 would have been lifted to about 30,000 feet by a B-50 Superfortress bomber where it would be dropped. At that point it would have ignited its liquid oxygen and ammonia engine and taken off on a trajectory for either speed or height. After reaching its apogee it would glide back to Earth, eventually landing at a long conventional airstrip at about 300 kilometers per hour.

Like the other proposals this was a “hot structure” craft, which is worth explaining. The Space Shuttle’s fuselage, for example, is built mostly of aluminum. As a result it’s completely incapable of standing up to the heat of re-entry and must be kept cool. In the particular case of the Space Shuttle this was done by covering it with ceramic heat tiles, but other cold structure options include ablative coverings (which the Model 671 would have used) or cooling using some sort of liquid inside the skin that would be allowed to boil off.

A hot structure, on the other hand, approaches the problem head on: build the fuselage out of a material that holds up to high temperatures. NACA had suggested to the design competitors that they might want to look at Inconel X, a nickel-chromium alloy that doesn’t begin to soften until very high temperatures. Three of the bidders took the hint.

The Model 684 would have used HK31, an alloy of magnesium, thorium, and zirconium which is no longer in use since the three percent that is thorium makes the alloy radioactive. At the time its relatively low radioactivity was not considered much of a problem, though, and it had the advantage of being much lighter than Inconel X. This meant that the Model 684’s skin could be much thicker, which would reduce costs and would dramatically increase the heat capacity of the plane and keep it from pushing 1000 Celsius on re-entry. The leading wing edges would be made of copper, which would conduct heat away quickly into the rest of the plane.

The total estimated cost for research and development, then the production of three planes, came to US$36.4 million, with the first flight anticipated by March of 1958.

What happened to make it fail: This one actually came quite close to existing, as it was a strong second in the NACA competition to the North American Aviation ESO-7487; in the formal evaluation it actually outscored its rival 152 to 150. Essentially the decision came down to unhappiness with the choice of the HK31 alloy for its fuselage over Inconel X. As a research craft, they wanted the X-15 to be subjected to the heat of hypersonic travel. Inconel X would go up over 800 Celsius when at the heights and speeds NACA wanted; HK31’s higher heat capacity would have kept the Model 684 to about 300 Celsius during the relatively short flights the X-15 would undertake. It was a better solution if one were just making this aircraft, but not if the whole point was to study high temperatures in flight for future aircraft.

Basically it came down to what NACA was looking to build. They didn’t want a spaceplane, they wanted a regular, if extreme, aircraft. The NAA ESO-7487 may not have been able go as high as the Model 671, but that was OK. In looking to make something that would be relatively easy to develop into something the Navy would want to buy later for service, Douglas was too ambitious for their own good. The ESO-7487 would become the X-15.

What was necessary for it to succeed: North American Aviation actually asked to withdraw from the X-15 competition in October 1955, after it had informally been awarded the contract but before it was official. A slew of new design work had come their way and they no longer thought they could make the 30 month deadline for first flight that the contract would impose.

NACA, the Air Force, and the Navy mulled over two options. Either they could award the contract to the Model 684 if it was switched to an Inconel X skin, or they could give NAA an eight-month extension. They decided on the latter course, but if they hadn’t the Model 684 would have flown.

Manned Venus Flyby: Apollo’s Hail Mary Pass (Apollo Applications Program, Part I)

MVF Cutaway

A cutaway view of the Manned Venus Flyby spacecraft. Based on Apollo hardware, this remarkable proposal would have sent three astronauts on a year-long mission to Venus and back. Public domain image from the 1967 NASA document Manned Venus Flyby, via Wikimedia Commons. Click for a larger version.

What it was: A proposed post-Moon landing manned mission using Apollo hardware. It would have launched during a good alignment of Earth and Venus in November 1973 and taken three astronauts on a flyby of the planet Venus, returning to the Earth 13 months after launch.

A later variation of the mission ambitiously suggested using a better conjunction in 1977 to visit Venus and Mars on an outbound leg and Venus again on the Earth-return leg, however most of the work done considered the shorter Venus flyby.

Details: By the mid-1960s NASA was well aware that if they successfully completed the Apollo moon landings they would probably face a severe decline in budget for the manned space program. In the hopes of proving their ongoing worth they developed a few different post-Apollo proposals using evolutionary versions of the Apollo hardware, including plans for a manned lunar base, space stations, and planetary exploration. The latter two of these goals were at first grouped under the name Apollo X, and then became the Apollo Applications Program (AAP).

By far the most ambitious of the AAP missions was a manned flyby of the planet Venus. After two preliminary missions in Earth orbit to test the technology, a Saturn V launch would lift an Apollo Command Module into orbit. As in a typical mission, the first two stages of the rocket would be jettisoned. However the uppermost stage, the Saturn IVB, would be kept and drained of any remaining propellant. Using gear stored where the Lunar Landing Module would have been placed in a Moon mission, the astronauts would then rig it as a habitation module.

The resulting 33-meter-long spacecraft would leave Earth orbit on October 31, 1973 and travel towards Venus for 123 days. There would be a flyby on March 3, 1974. The craft would have been aimed to pass Venus as close as 6200 kilometers above the surface (one planet radius) very quickly—orbital mechanics would have it moving relative to Venus at a clip of 16,500 kilometers per hour—crossing the lit side of the planet. A sidescan radar would map the portion of the planet they could see as they flew by, and the astronauts would perform spectroscopic and photographic studies.

A series of probes was to be dropped by the spacecraft, and they were specifically enumerated in the proposal for the Triple Flyby variant of this mission that was mentioned earlier. Near closest approach the MVF would launch an orbiter and fourteen planetary probes; the probes would communicate with the orbiter, which would then beam the results back to Earth. Altogether the probes were:

  • Six atmospheric probes, which would enter the atmosphere at six locations: the planet’s solar and anti-solar points, its terminator and equator, and the middle of the light and dark sides. They would drop in ballistically and try to determine how Venus’ atmosphere increased in density the closer one got to the surface.
  • Four meteorological balloon probes. They would float in the atmosphere and try to learn how the Venusian atmosphere circulated as well as study smaller-scale winds.
  • Two “crash-landing” probes that would try to photograph the surface on the way down, much like Rangers 7, 8, and 9 did with the Moon.
  • Two soft-landers that would take surface photographs, examine the soil, and measure Venusian weather.

As well as acting as a communications hub, the orbiter would use X-band radar to map the planet.

MVF Mission Trajectory

The MVF’s trajectory. Detail from Manned Venus Flyby. Click for a larger view.

After that burst of activity the MVF craft would then return home, taking 273 days more to loop out to 1.24 AU from the Sun on a hyperbolic trajectory and eventually swing back to Earth. The astronauts’ landing on Earth would happen on December 1, 1974—total mission time would be 396 days. The Triple Flyby variant would have taken more than 800 days starting in 1977.

When not at Venus, the MVF astronauts would have studied the Sun and solar wind as well as making observations of Mercury, which would be only 0.3 AU away two weeks after the Venus flyby. To keep them occupied otherwise their habitation capsule would have been outfitted with a small movie screen (to show 2 kilograms of movies allowed), and a “viscous damper exercycle/g-conditioner”. The crew would also be allowed 1.5 kilograms of recorded music, 1 kilogram of games, and 9 kilograms of reading material. Hopefully they would choose wisely.

What happened to make it fail: The MVF was part of the Apollo Applications Program, and the AAP was killed dead on August 16, 1968 when the House of Representatives voted to cut its funding from US$455 million to US$122 million. President Johnson accepted this as part of a larger budget deal that kept NASA’s near-term goals safe, though even at that the agency’s entire budget dropped by 18% between 1968 and 1969. The only AAP mission to survive was Skylab.

What was necessary for it to succeed: It’s tough to get this one to work as it’s difficult to see any advantage to sending people on this mission. Mariner 5 had already flown by Venus in 1967 and NASA was able to send a robotic orbiter as part of the Pioneer 12 mission in 1978, just a few years after MVF would have flown.

Even the many probes that the MVF would leave behind at Venus had no obvious connection to the manned part of the mission; it would have been easier to send an unmanned bus of similar size and drop the probes that way. There would be no need then for heavy food, water, or air, or the space for people to move around. And unlike the manned mission there would be no need to bring the bus back, greatly reducing the mission’s difficulty. About all the manned mission had going for it was an opportunity to see what kind of effect a year in microgravity would have on humans, and that could just as easily be determined using a space station in low Earth orbit.

On that basis we also need to be aware that Congress asked hard questions about the purpose of NASA’s manned Mars mission plans in the late 1960s and were hostile to all of them. If Mars wasn’t going to get any money, it’s hard to see what could influence them to fund a mission to Venus.

Finally it needs to be pointed out that no matter even if the MVF launched, nature itself probably had this mission’s number. We didn’t have a very good understanding of the Sun at that time, having only observed one solar cycle from above the atmosphere when the flyby was proposed in 1967. While the launch window was deliberately chosen to be near a solar minimum, and the flyby craft was to have a radiation lifeboat in the equipment module, the mission would have run into an unforeseen natural event on the way back to Earth.

On July 5-6, 1974 the Earth was hit by a big coronal mass ejection (CME), a storm of electrons and protons thrown off of the Sun. People down on Earth were protected by the planet’s magnetic field, as usual, but the astronauts coming back from Venus wouldn’t have been so lucky. Their line to the Sun was several degrees off from the Earth’s (at the time they would have actually looped out past Earth as their trajectory slowly took them back home), but CMEs can cover quite a bit of space. Had the mission actually flown, the astronauts on-board may well have died of radiation sickness after being hit with more (and more energetic) solar protons than their spacecraft was built to handle.

The saving grace here is that coronal mass ejections were discovered in 1971, so the initial plan probably would have been called off rather than risk casualties, or at least be reconfigured to give the astronauts the protection the 1967 plan failed to give them.

An interesting simulation (using the program Orbiter) of how the MVF mission would have run can be seen on YouTube.

Paracone/MOOSE/SAVER/AIRMAT: Escape Pods from Orbit

Paracone and MOOSE schematic drawings

Schematic diagrams of the Paracone (left) and MOOSE (centre and right) emergency orbital re-entry systems. Public domain image derived from two diagrams printed in the NASA publication Analysis and Design of Space Vehicle Flight Control Systems. Click for a larger view.

What it was: A last-line-of-defense system for getting astronauts out of orbit by ballistic re-entry when all else had failed. With it the endangered spacefarer could put a heat shield around himself and then skydive from orbit. Backwards.

Details: Getting a spacecraft’s crew out of orbit during a dire emergency has been a problem considered since the earliest days of the Space Age. A capsule returning from orbit hits the air at no less than 7 kilometers per second and needs a heat shield capable of handling something like 2,000 to 3,000 Celsius, which is beyond what even most solid metals can handle. What hope does a fragile person have? Since the mid-1970s the answer has almost always been “none whatsoever” and the solution to most problems in orbit has usually been to scramble another craft into orbit for rescue purposes, a situation that has thankfully never occurred as of this writing. But not everyone has always been so pessimistic (or realistic).

Self-recovery from orbit stems from efforts made at altitudes only moderately lower. By the mid-1950s the Air Force had become concerned with the greatly increasing height at which its planes were flying. The air where they went was so thin and so cold there was no way an unprotected human could survive a bailout, and so researchers and engineers went to work to find out what would be necessary to save a pilot who had to parachute from that height.

First came Operation High Dive, which hoisted dummies into the stratosphere and then dropped them to see what would happen. As well as the anticipated problems, the researchers made the discovery that a human form would spin as it picked up speed, often reaching 200 revolutions per minute—fast enough to kill if it kept up for the duration of the descent. Aerodynamic stability was needed.

Dummies would only take you so far, though: what about blood pressure or the fluid in one’s ears or eyes in a near-vacuum? What about air? What about freezing? Project Excelsior launched in 1959 and saw a person—Capt. Joseph Kittinger, to be precise—make three jumps from a balloon-lifted capsule. He wore a variation on the MC-3 partial pressure suit worn by high-altitude pilots at the time, bulked up with heating equipment and insulation to the point that it verged on a spacesuit. When falling from as high as 31.3 kilometers (where he was above 99% of the atmosphere) he naturally assumed a seated position with his back to the ground, and that discovery led to the proposed approach for orbital rescue in the next few years.

By the early 1960s the Air Force were sending pilots to the very edge of space: on July 17, 1962 Robert White got to 95.9 kilometers in an X-15. Once the X-20 “Dynasoar” was flying, Air Force personnel would be in orbit. Pilots get an ejection seat, that had been standard in Air Force planes since not long after WWII ended. The Dynasoar needed one and that was that.

Douglas Aircraft led off with the Paracone in 1963. Their suggestion was to build a shroud of nickel-chromium-cobalt alloy (René-41, which was also used to make the outer shell of the Mercury capsule) into the pilot’s seat. On ejection the astronaut would use an attached retro-rocket to slow his orbital velocity, then inflate the shroud into a rounded cone some 7.6 meters in diameter with himself in the centre of the concave side. The Paracone would drop into the atmosphere, keeping re-entry heat relatively low through its large surface area and low terminal velocity—only 42 kilometers per hour. The last of the Paracone’s speed would then be bled off the hard way: on crashing into land, it had a crushable nosecone that would have worked much like the crumple zones on modern automobiles. The astronaut could then get up and walk away, thus meeting the formal definition of a good landing, though the initial plan was that he might be as much as 800km away from where he aimed.

At about the same time, General Electric proposed the MOOSE—“Man Out Of Space, Easiest” though this was later backronymed to the more sedate “Manned Orbital Operations Safety Equipment”. This is the most famous of the options for getting out of orbit. It was a simpler and smaller system than Paracone: on ejection the pilot would pull a ripcord on his chest to trigger a canister of polyurethane foam inside a fabric container. When filled this would leave him partially embedded in an ablative heat shield 1.9 meters in diameter. After MOOSE’s solid retrorocket was fired, the pilot would re-enter with his back to the atmosphere. When he approached the ground he would pull a second ripcord on his chest that deployed a parachute—the shock of the parachute catching air would pop him loose of his foam casing and then the MOOSE would be left to its fate as the rescued astronaut drifted down. There appears to be no literature discussing what would happen if the pilot pulled the two ripcords in the wrong order.

As it happened the X-20 was cancelled in late 1963 (to be replaced by the Manned Orbiting Laboratory), but the idea of getting people out of space once more sophisticated stations were built remained. This led to two more proposals from contractors associated with the Air Force and NASA.

SAVER was Rockwell International’s contribution in 1966. The pilot’s ejection seat was virtually all of that rescue pod, and it had a solid heat shield on the back of it. The seat was supported by an inflatable balloon some ten meters in diameter, which slowed the craft to survivable speeds. AIRMAT, on the other hand, was suggested by Goodyear in 1968. Perhaps fittingly for that manufacturer it resembled a small blimp, with two astronauts riding inside it. Both systems once again had the stricken astronauts falling backwards to Earth as a fabric heat shield protected them. Neither design made it off the drawing board.

What happened to make it fail: A few tests were performed on the Paracone and MOOSE concepts. In the former case it was mostly wind tunnel tests to confirm the cone’s terminal velocity and impact tests on the nosecone. MOOSE’s ablative shield was heat tested, and one experiment was run to see if it would orient itself correctly in the air: a dummy wearing a MOOSE shield was tossed off a six meter bridge near Valley Forge, Pennsylvania (some sources say it was in Massachusetts somewhere), landing on its back in the water as hoped and then floating downstream.

But with the exception of a short period during the initial development of the Space Shuttle in the early 1970s, NASA has always taken the position that sending a rescue craft is the better way to go. With either of MOOSE or the Paracone, the agency would have had to develop new training for the astronauts and the contractors would have had to develop new materials and new technologies. At least with a rescue craft they were dealing with a spacecraft that they were going to be developing and testing anyway for the main missions.

So during the Apollo program the idea was to always have another Saturn V and Apollo craft ready to launch if the Apollo craft that was on a mission became stranded in Earth orbit. In the actual event this was not done, as it came to be recognized that the rescue mission was as likely to put another astronaut in jeopardy (the Command Module would have to be unsafely flown by only one person, so there’d be room for the three being rescued), and the de facto situation was that the astronauts in a Mercury, Gemini, or Apollo capsule were on their own once they reached orbit. Skylab did return to the idea with a modified CM that allowed for five on-board.

After the loss of the Space Shuttle Columbia, NASA’s approach for Space Shuttles was to have another Shuttle ready to go within 40 days so that it could be launched on a rescue mission if the first one could not return to Earth for whatever reason. The crew of the disabled Shuttle would simply wait out the interval on rationed air (carbon dioxide scrubbers being the limiting factor). After May 2009, the International Space Station was sufficiently large and capable that the plan became for anyone stranded in orbit to go to the ISS where they can be indefinitely supplied—since that’s the only place American and Russian astronauts are going these days, this is OK. The ISS itself always has a Soyuz-TM capsule attached to it for emergency re-entries in case the station becomes uninhabitable.

What was necessary for it to succeed: Despite the fact that returning from space essentially naked looks at first glance to be insane, there doesn’t appear to be any particular reason why it couldn’t work except for an interest in doing so despite the danger.

With the rise of commercial space flights, the author expects to see sometime in his lifetime a rich adventure-seeker in the mold of Richard Branson give it a shot purely for the sake of doing it.

Sänger-Bredt Silbervogel: The Nazi Space Plane

Sänger-Bredt Silbervogel spaceplane

Image of the Silbervogel taken from the 1952 translated edition of Eugen Sänger and Irene Bredt’s 1944 A Rocket Drive for Long Range Bombers. An inset of the entire craft at launch is at upper left. Public domain image.

What it was: A boost-glide intercontinental spaceplane. It would reach space, if not orbit due to lack of speed, but manage to get all the way around Earth once by repeatedly skipping off the upper atmosphere to gain more altitude. During World War II it was positioned as an extreme long-distance bomber (capable of, for example, carrying a 3600-kilogram bomb to New York City from a launch site in Germany), but it also would have made an interesting surveillance vehicle—utterly immune to being shot down and the next best thing to a spy satellite.

Details: Ever since space travel became even marginally possible doing so has been torn between two approaches. One is to stick a one-shot capsule of some sort on top of a rocket and then let it return ballistically after the mission is over; the other is to build a spaceplane which either gets to space under its own power or is launched on a rocket, and then is capable of gliding back to Earth. Theoretically planes are cheaper because of their reusability while capsules are easier to build. In practice, though, no-one’s ever been able to develop a spaceplane that could undercut a capsule because the added complexity of the plane adds back on to the saved costs. As a result, with the exception of the Americans’ long excursion into the Space Shuttle program, all spacecraft that were successful for more than one or two flights have been capsules.

Both approaches date back to the first time and place that had any chance at all of putting something into space, which is to say Germany in the 1940s. Wernher von Braun’s ballistic rocket approach has been the one followed by the USSR and China, while the United States used it into the 1970s and is returning to it now with the upcoming Orion MPCV.

Less well-known is Eugen Sänger and Irene Bredt’s Silbervogel (“Silverbird”) which was the first serious attempt at building a spaceplane, work on which contributed to the success of several other later spaceplanes that flew, and which itself was refactored and raised as a possibility as late as the 1980s.

Sänger began work on the concept in his original engineering thesis for the Vienna Polytechnic Institute. When it was rejected as too radical in 1931, he submitted a second, more acceptable thesis on a different subject, but arranged for the original to be published by a different route in 1933. At the same time he perfected a regeneratively-cooled rocket engine (which is to say that it used the expansion of the rocket fuel’s gases to carry away heat and keep the engine from overheating). His research couldn’t secure funding in his native Austria, but an article in the journal Flug (“Flight”) in 1935 attracted the attention of the Luftwaffe in Germany. He was invited to set up a research facility there, which he did in 1936 and then the real work on Silbervogel began.

By 1942 he had advanced the rocket engine which would power the craft, worked on the rocket sled and track which would be used for its initial boost launch, and worked out the aerodynamics of a plane that would be both subsonic and supersonic as well as flying in the near-vacuum of space.

The Silbervogel would have been a two-part ship. The spacecraft itself was to have been a 10-ton, streamlined plane with two stubby wings and two tailfins, both raked upwards at about ten degrees. Four fuel tanks took up most of the fuselage and contained liquid oxygen and kerosene which would burn in a single rocket engine over the course of 168 seconds. On the ground the plane would be mated with a rocket sled which would give it an initial boost from behind along a rail track for a mere ten seconds but with nearly five times the thrust as the spaceplane’s engine.

Once the Silbervogel completed both burns it would be moving at a minimum of Mach 13 (15,926 km/h) and as much as Mach 20 depending on its mission and payload, and reach a maximum altitude of anywhere from 31 to 121.5 kilometers, the latter value being well into space. Just to put this in perspective, the air speed record in 1944 was 1130 kilometers per hour (Mach 0.92), while the altitude record in an aircraft was 17.3 kilometers. Sänger and Bredt did not think small.

The Silbervogel would then begin a roller-coaster-like ride up and down into the Earth’s atmosphere, using its wings and angle of attack to skip off the denser air at about 20 kilometers up and regain altitude for another distance-eating hop. An example diagram in the 1944 paper discussed below shows no less than eight such skips before settling into a steady flight at 20 kilometers and a return to base after a complete trip around the world.

What happened to make it fail: It was too advanced for the time, and even Sänger (who underestimated the technical difficulties of the heat Silbervogel would have to endure when skipping into the atmosphere) thought that it would not fly for many years. As World War II heated up, the Nazi government officially put the program on hold in 1942 to save money and resources for weapon systems that could be used before the end of the ongoing fighting. Oddly enough, despite the stop Sänger was still assigned to it and continued work on it until 1944, as the Nazis looked at several possibilities for being able to bomb the United States from the Azores if fascist Spain and Portugal could be brought into the Axis.

In that year he and Bredt published their final version of their research, which was published as Über einen Racketantrieb für Fernbomber (translated after the war as A Rocket Drive for Long Range Bombers, a copy of which can be downloaded as a PDF). This remarkable document outlines how the Silbervogel would have looked and worked, as well as how it might have been used in a variety of ways—for example avoiding the difficulty of having to go the whole way around the Earth by setting up a second Silbervogel landing and launching base in the Japanese Marianas Islands or, better, in the occupied territory in California which the Japanese would helpfully conquer for the Nazis. A cheerful diagram showing the complete destruction of Manhattan from roughly Union Square north to the corner of 27th Street and Broadway and south to Houston Street is included, as this would be possible with a mere 84 sorties with 3600-kilogram bombs. Note that the Space Shuttle Discovery holds the record for the most flights above 100 kilometers by any one spaceplane, 39, racked up over the course of 27 years.

What was necessary for it to succeed: Under any reasonable circumstances, it wasn’t going to work as initially designed.  The design was simply too far advanced for the time, and Germany couldn’t come up with the physical resources or money to build one.

That said, if there had been no war, and if the Germans had had access to high melting-point molybdenum for its belly (or developed heat-resistant ceramic tiles as would be used on the US’s Space Shuttle), and if there had been the political will to spend those marks and metals—and that’s an awful lot of “ifs”—something like the Silbervogel could have flown around 1960. It likely would have been heavily redesigned by then.