Inventing Landings

A couple of weeks ago I published a post outlining the principle reasons why splashdowns were a not an appropriate long-term method for astronauts returning to earth. Pointing to the ease of splashdowns as the primary reason behind their use throughout the space race is, however, presenting half the story. NASA began pursuing land landings in 1959, well before the Space Shuttle was on the drawing board. The original goal was to use a land landing system from the start. (Pictured is a model Mercury spacecraft undergoing impact tests at Langley Air Force Base. 1958.)

When NASA’s inaugural Mercury program was in its infancy and the base decisions about the program were being made, one of the central unknowns in spaceflight was how to bring a spacecraft back to earth. Like designing astronauts, spacecraft, as well as launch vehicles, determining how to land a spacecraft was a new problem with precious little pre-existing knowledge on which to build.

The development of descent and landing procedures for any spacecraft is determined in part by the spacecraft itself; its size and shape plays a vital role in how it reenters the atmosphere and the ways it can possibly land. In the case of Mercury, the spacecraft was limited by the size and shape of the available launch vehicles; the Redstone that launched the first two suborbital flights and the Atlas that launched the remaining four orbital missions both had a fixed circumference and limited lift capacity.

Providing it met the weight and circumference limitations of the launch vehicles, the Mercury spacecraft could theoretically take any shape. It could be spherical like a satellite or cylindrical like a rocket. Its shape was unimportant during the flight. Without atmosphere, there is no drag produced by a spacecraft in orbit. What mattered was how the design behaved during the reentry phase. NASA considered design proposals from a number of external contractors, all of which were divided into two broad categories: lifting bodies and blunt bodies.

Lifting bodies designs are similar to gliders, their manner of falling through the atmosphere lies somewhere between an airplane and a stone. A spacecraft designed as a lifting body has no wings, but its aerodynamic shape gives it sufficient lift, which allows it to fly. As the spacecraft reenters the atmosphere, it encounters increasingly dense air. Once the air is thick enough to support the spacecraft, it begins to glide, allowing the astronaut to pilot the spacecraft to a controlled landing. Its shape in turn determines the amount of control. Certain designs produce more lift, allowing the pilot increased control. (Pictured are three sample designs of lifting bodies.)

NASA received a number of lifting body proposals for the Mercury spacecraft. Some focussed on simply controlling the speed of the spacecraft’s fall from orbit. The research and development group at the Langley Air Force Base (which was a satellite research centre of NASA’s) proposed a triangular planform, a sort of flat bottom spacecraft with a horizontal wing. Republic Aviation Corporation presented a similar flat triangular design.

Other proposals focussed on incorporating an increased amount of control. Bell Aircraft, the company responsible for Chuck Yeager’s sound barrier breaking X-1, presented a spacecraft that would be more manoeuvrable than a controlled descent, a design much closer to a glider. North American Aviation, who at the time was under contract with NASA for the X-15 program, proposed enhancing its existing model. The spacecraft would glide towards reentry, but the pilot would eject prior to landing. He would touch down safely by parachute while the spacecraft would be ditched into the Gulf of Mexico.

In opposition with the increased control and manoeuvrability of the lifting body proposals, the blunt body designs focussed more on making reentry survivable than in controlling the fall. Rather than using the force of the air against the falling spacecraft to generate lift, blunt bodies operate on the principle that increased drag transfers to less direct heat against the spacecraft. Blunt spacecraft have no aerodynamic qualities, and as such air builds up under the falling spacecraft faster. The result is a cushion of air, which slows the spacecraft and also protects it from the heat of friction with the atmosphere. The shape of the capsule can control the movement of the air, pushing around the spacecraft and protecting the astronaut. (Pictured are four exampled of blunt bodies reentering the atmosphere.)

The most well known champion for the blunt body design is engineer Maxime Faget (pictured). Faget proposed a blunt body spacecraft with a rounded bottom. Solid fuel rockets on this blunt end would fire, slowing the capsule in orbit to initiate its reentry. As the spacecraft entered the atmosphere, the retro rockets would jettison, revealing an ablative heat shield. The heat shield would absorb the heat from friction with the atmosphere and burn away, literally shielding the astronaut inside from flames. This shape provided the maximum amount of drag, harness the most slowing capacity from the natural fall.

Determining the shape and style of the spacecraft (either lifting or blunt bodied) determined the basis of the reentry method, but that was only half the battle. The spacecraft needed to land and the astronaut had to return safely.

Prior to 1958, satellites had been launched and had fallen back to earth, but nothing that had been sent into space had had to be retrieved. In 1959, the first such program was launched – the CIA based Corona satellite program.

Corona was a spy satellite designed to take pictures of enemy nation’s military bases from space. Without the technology to remotely transfer the image data to the CIA, the film canisters had to be retrieved from orbit and developed. In the interest of keeping the images and information out of the hands of enemy nations, the CIA opted for a physical recovery of the canisters.

The canisters were jettisoned from the satellite, reentering the atmosphere and falling towards the ocean. As the canisters fell, parachutes deployed to slow their descent. An aircraft carried out the actual recovery: a hook suspended underneath the aircraft body would snag the parachute as the pilot flew over the descending canister. If the hook failed to snag the canister, it would fall into the ocean where it was designed to sink. This was an additional measure taken to limit the possibility of other nations retrieving the film. (Pictured is an image of the retrieval system used during the Corona program. The parachute towards the bottom left is that of the film canister.)

So in 1959, the only descent method NASA knew worked was a parachute-controlled descent. But an actual landing from orbit had never been attempted let alone man-rated (made safe for a human pilot).  With almost nothing to build on, the engineers working on the Mercury program had to select and develop a method.

NASA considered building on the one piece of knowledge it had and pursue methods of slowing the spacecraft with a parachute and landing it at sea. Unlike Corona, however, the spacecraft would be designed to float until the astronauts could be recovered. Alternatively, the organization briefly considered developing a capsule-style spacecraft with small wings that could glide to a landing from orbit, a sort of modified lifting body. A third proposal married the two, using a parachute to first slow and then provide limited manoeuvrability during the final descent of the spacecraft.

Proposals for landing methods also came from outside NASA. The US Air Force submitted a longer-term multi-staged proposal for NASA’s consideration. Building off an initial parachute controlled descent, the second stage would apply the parachute to a more sophisticated aerodynamic body and eventually develop a spacecraft that could land on its own. The US Navy proposed a similar gliding parachute system. An inflatable wing would allow the astronaut to manoeuvre the spacecraft to a controlled landing on the water.

Another proposal came from the Langley Air Force Base. In 1958, the research group at Langley had given a lab space to amateur kite flyer and engineer Francis M. Rogallo. Rogallo had been working for nearly a decade on the idea that a sail could turn a spacecraft – even a blunt body design – into a glider during its descent. After joining Langley, Rogallo developed his most promising design: a two-lobed, single-curvature, suspension-load design.  The design combined the slowing benefits of a parachute with the manoeuvrability of a glider; the two-lobe sail mimicked the rigid yet flexible wings of an aircraft. (Pictured is Rogallo and his two-lobed single curvature suspension design.)

In the end, the simplest and most time-effective solutions won – Faget’s blunt capsule was chosen for the Mercury spacecraft, and the parachute and retrorocket system was chosen for its simplicity and alignment with the Mercury’s objectives. The three primary goals for the program were to investigate man’s ability to function in space, to orbit a spacecraft around the earth, and to bring both man and machine home safely. Nothing stipulated that the astronaut had to pilot the spacecraft to a controlled landing. With the mode decided upon, the focus turned to the landing site of the spacecraft: on the land or in the water. Both landing sites had benefits and drawbacks.

Bringing the Mercury spacecraft down on land was not without hazards. One problem was the likely damage sustained by the capsule. The Langley research group demonstrated through airdrop tests of small-scale capsules that the Mercury spacecraft would not fare well landing on an unyielding surface such as a dry lakebed or desert plain. Based on these small-scale tests, the force of impact was expected to be extremely severe.  New and more sophisticated shock absorbers, far better than any that had yet been developed, would be needed to spare the life of the astronaut inside.

Another problem was the surrounding environment. The heat shield of the Mercury spacecraft was designed to absorb the heat of reentry, forcing the hot air to move around the spacecraft rather than move into it. A consequence of this was that the heat shield would still be hot upon landing. If the hot capsule landed in a dry area, the environment surrounding the spacecraft could go up in flames in an instant.  Prairie and forest fires would become a very real possibility.

Splashdowns, conversely, held none of these hazards. The natural cushion of the ocean was sufficient to offset the force of the final landing; a parachute would be enough protection for the astronaut. The water would also cool the spacecraft. Not to mention there is a lot more open water available for splashdowns than dry lakebeds or flat, unpopulated land in the United States.

There were, of course, different hazards associated with splashdowns, but these were easier to overcome. The spacecraft could be made seaworthy. The spacesuits would ensure the astronauts would float. The Navy could assist the astronaut if he required aid in exiting his spacecraft. Tracking networks around the world followed the spacecraft throughout the mission, so NASA would know where to send recovery ships in the event the spacecraft splashed down off target. Primary, secondary, and contingency recovery zones were set up through the Atlantic and Pacific so no ship was ever too far from an astronaut in need.

All of these were methods that needed to be perfected prior to the first Mercury launch, but they were the simpler problems than developing the technologies needed to protect the astronaut from a hard land landing.

With the Gemini program, the question of landing methods was reopened and land landings were again a much sought after goal. In the early 1960s, different methods were proposed and tested, yielding concrete results clearly demonstrating the pros and cons of competing systems. The Rogallo paraglider wing was re-evaluated and ultimately selected as the method most worthy of pursuit in the quest for land landings.

To tack the Rogallo wing on to the end of Mercury would do it an injustice; its story is best told on its own. (Pictured is the Rogallo wing mated to a scale Gemini spacecraft.)

Suggested Reading/Selected Sources

1. Brauer, Karl O. “Landing Systems for Space Vehicles”. Spaceflight, February 1976, pp. 47-53.

2. Condon, Gerald and Tigges, Michael with Cruz, Manuel I. “Entry, Descent, Landing, and Ascent” in Human Spaceflight: Mission Analysis and Design, edited by W. Larsen and L. Pranke: Space Technology Series, McGraw Hill. 1999.

3. Kirker, J. W., Lee, J. B., and Hinson, J. K. “Earth-Landing Systems for Manned Spacecraft”. Turin: NASA. 1963.

4. Seamans Jr. , Robert C. “Parasail/Landing Retrorocket System”. Washington, December 3, 1964.

5. “The Mercury Project – Goals”. http://www-pao.ksc.nasa.gov/kscpao/history/mercury/mercury-goals.htm [Accessed August 8, 2010].

6. Carpenter, M.S, Cooper, L.G., Glenn, J.H., Grissom, V.I., Schirra, W.M., Shepard, A.B., Slayton, D.K. We seven: By the astronauts themselves: Simon and Schuster. 1962.

7. Grimwood, James. Project Mercury: A Chronology. Washington: NASA. 1963.

8. Ruffner, Kevin C. Ed. Corona: America’s First Satellite Program. Central Intelligence Agency: Washington. 1995

9. Thompson, Milton O. At the edge of space: the X-15 flight program: Smithsonian Inst Pr. 1992.

10. Swenson, LS. This New Ocean: a History of Project Mercury. Washington: NASA. 1998.

Comments

  1. says

    Well, they always said the Shuttle flew “like a brick”, but I’ve seen how the lifting bodies & X-15 flew, and Shuttle glided like a Piper Cub compared to those, IMHO.

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