Coming Home: Reentry and Recovery From Space

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This study represents a means of highlighting the myriad of technological developments that made possible the safe reentry and return from space and the landing on Earth. This story extends back at least to the work of Walter Hohmann and Eugen Sänger in Germany in the 1920s and involved numerous aerospace engineers at the National Advisory Committee for Aeronautics (NACA)/NASA Langley and the Lewis (now the John H. Glenn Research Center at Lewis Field) and Ames Research Centers. For example, researchers such as H. Julian Allen and Alfred J. Eggers, Jr., at Ames pioneered blunt-body reentry techniques and ablative thermal protection systems in the 1950s, while Francis M. Rogallo at Langley developed creative parasail concepts that informed the development of the recovery systems of numerous reentry vehicles.
The chapters that follow relate in a chronological manner the way in which NASA has approached the challenge of reentering the atmosphere after a space mission and the technologies associated with safely dealing with the friction of this encounter and the methods used for landing safely on Earth.

The first chapter explores the conceptual efforts to understand the nature of flight to and from space and the major developments in the technologies of reentry and landing that took place before the beginning of the space age in 1957.

Chapter 2 also investigates the methods of landing once a spacecraft reaches subsonic speeds. Once the orbital energy is converted and the heat of reentry dissipated, the spacecraft must still be landed gently in the ocean or on land. Virtually all of the early concepts for human space flight involve spaceplanes that flew on wings to a runway landing; Sänger's antipodal bomber of the 1940s did so as did von Braun's popular concepts. However, these proved impractical for launch vehicles available during the 1950s, and capsule concepts that returned to Earth via parachute proliferated largely because they represented the "art of the possible" at the time.

Chapter 3 tells the story of reentry from space and landing on Earth from the beginning of the space age through the end of the Apollo program. During that period, NASA and other agencies concerned with the subject developed capsules with blunt-body ablative heat shields and recovery systems that relied on parachutes. The Department of Defense (DOD) tested this reentry concept publicly with Project SCORE (Signal Communication by Orbiting Relay Equipment) in 1958 and employed it throughout the CORONA satellite reconnaissance program of the 1960s, snatching in midair return capsules containing unprocessed surveillance footage dangling beneath parachutes. With the Mercury program, astronauts rode a blunt-body capsule with an ablative heat shield to a water landing, where the Navy rescued them. Project Gemini eventually used a similar approach, but NASA engineers experimented with a Rogallo wing and a proposed landing at the Flight Research Center (now Dryden Flight Research Center) on skids similar to those employed on the X-15. When the Rogallo wing failed to make the rapid progress required, NASA returned to the parachute concept used in Mercury and essentially used the same approach in Apollo, although with greatly improved ablative heat shields.

At the same time, the DOD pursued a spaceplane concept with the X-20 Dyna-Soar orbital vehicle that would have replaced the ablative heat shield with

a reusable metallic heat shield and a lifting reentry that allowed the pilot to fly the vehicle to a runway landing. This is also the general approach pursued by the

DOD with its Aerothermodynamic Elastic Structural Systems Environmental Tests (ASSET) and Martin X-23A Precision Reentry Including Maneuvering

reEntry (PRIME) vehicles. NASA and DOD also experimented with lifting body concepts. Engineers were able to make both of those approaches to reentry and landing work, making tradeoffs on various other capabilities in the process. The eventual direction of these programs was influenced more by technological choices than by obvious decisions.

Even as Apollo was reaching fruition in the late 1960s, NASA made the decision to abandon blunt-body capsules with ablative heat shields and recovery systems that relied on parachutes for its human space flight program. Instead, as shown in chapters 4 and 5, it chose to build the Space Shuttle, a winged reusable vehicle that still had a blunt-body configuration but used a new ceramic tile and reinforced carbon-carbon for its thermal protection system. Parachutes were also jettisoned in favor of a delta-wing aerodynamic concept that allowed runway landings. Despite many challenges and the loss of one vehicle and its crew due to a failure with the thermal protection system, this approach has worked relatively effectively since first flown in 1981. Although NASA engineers debated the necessity of including jet engines on the Shuttle, it employed the unpowered landing concept demonstrated by the X-15 and lifting body programs at the Flight Research Center during the 1960s. These chapters lay out that effort and what it has meant for returning from space and landing on Earth.

The concluding chapter explores efforts to develop new reentry and landing concepts in the 1990s and beyond. During this period, a series of ideas

emerged on reentry and landing concepts, including the return of a metallic heat shield for the National Aero-Space Plane and the X-33, the Roton rotary

rocket, the DC-X powered landing concept, and the Crew Exploration Vehicle (CEV) of the Constellation program between 2005 and 2009. In every case,

these projects proved too technologically difficult and the funding was too sparse for success. Even the CEV, a program that returns to a capsule concept

with a blunt-body ablative heat shield and parachutes (or perhaps a Rogallo wing) to return to Earth (or, perhaps, the ocean), proved a challenge for engineers. The recovery of scientific sample return missions to Earth, both with the loss of Genesis and the successful return of Stardust, suggests that these issues are not exclusive to the human space flight community. As this work is completed, NASA has embarked on the Commercial Crew Development (CCDev) program in which four firms are competing for funding to complete work on their vehicles:

• Blue Origin, Kent, WA-a biconic capsule that could be launched on an Atlas rocket.

• Sierra Nevada Corporation, Louisville, CO-Dream Chaser lifting body, which could be deployed from the Virgin Galactic

• White Knight Two carrier aircraft for flight tests.

• Space Exploration Technologies (SpaceX), Hawthorne, CA-

• Dragon capsule spacecraft; also a partial lifting body concept to be launched on the Falcon 9 heavy lifter.

• The Boeing Company, Houston, TX-a 7-person spacecraft, including both personnel and cargo configurations designed to be launched by several different rockets, and to be reusable up to 10 times.

These new ideas and a broad set of actions stimulated through the CCDev program suggest that reentry and recovery from space remains an unsettled issue in space flight. This book's concluding chapter suggests that our understanding of the longstanding complexities associated with returning to Earth safely has benefited from changes in technology and deeper knowledge of the process; however, these issues are still hotly debated and disagreement remains about how best to accomplish these challenging tasks. Engineers have had success with several different approaches to resolving the challenges of reentry and landing.

Discovering the optimal, most elegant solutions requires diligence and creativity. This history seeks to tell this complex story in a compelling, sophisticated, and technically sound manner for an audience that understands little about the evolution of flight technology. Bits and pieces of this history exist in other publications, but often overlooked is the critical role these concepts played in making a safe return to Earth possible. Moreover, the challenges, mysteries, and outcomes that these programs' members wrestled with offer object lessons in how earlier generations of engineers sought optimal solutions and made tradeoffs.

With the CCDev program-a multiphase program intended to stimulate the development of privately operated crew vehicles to low-Earth orbit currently underway-NASA is returning to a capsule concept for space flight. This may prove a significant development, and this history could help enlighten the NASA team about past efforts and the lessons learned from those efforts.


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