Reentry Vehicles: Spheres vs. Blunt Bodies

The choice of reentry vehicle configuration reflected additional differences in approach. The central and most visible difference between the Vostok and Mercury spacecraft was their external configuration. Beneath the streamlined launch shroud, the orbital reentry portion of Vostok was spherical, while the basic shape of Mercury was a truncated cone. The spacecraft designers studied the alternative shapes for reentry vehicles and made their choices based upon standards established within their own programs.

The Soviets, under the leadership of Sergei Pavlovich Korolev, chief designer of spacecraft, reviewed the different possibilities and chose the sphere for their reentry configuration. According to Korolev, among non-lifting shapes the spherical reentry body alone possessed an inherent dynamic stability as it plunged back into the earth's atmosphere. He rejected the conical craft, because its tendency to pitch and yaw would have required an elaborate attitude control system, plus greater reliance upon man as pilot rather than man as passenger.*

[67] The orbital configuration of Vostok consisted of a spherical cabin with an attached equipment cluster.** 13 Prior to descent, the spacecraft was oriented for reentry by means of a solar sensor located in the equipment compartment. This maneuver aimed the retrorockets so that they fired along the line of flight, slowing the craft as it entered its descent trajectory. Upon termination of retrofire, the cabin separated from the instrument section, which subsequently burned up as it entered the atmosphere. Vostok was then a simple sphere, descending along a ballistic trajectory, protected from the intense reentry temperatures by an ablative coating that shielded the entire craft.*** 14

Vostok reentered like a bullet, following the path dictated by the retrorocket impulse; there was no attitude control. By placing the sphere's center of gravity behind and below the cosmonaut, the spacecraft designers assured Vostok pilots from Gagarin to Bykovsky and Tereshkova the proper orientation for ejection from the "lander" when it reached 7,000 meters. At that altitude, the bolts securing the pilot's hatch were severed explosively, and the hatch was blown away. Two seconds later the cosmonaut and his couch were ejected from the craft to begin a parachuted descent to 4,000 meters.**** At that height, the cosmonaut continued his return by means of his own parachute. Also at 4,000 meters, a parachute opened to slow the final descent of the spacecraft.15

In their study of reentry, the Americans evolved their own theories regarding optimum spacecraft configuration. In June 1952, H. Julian Allen of the NACA Ames Aeronautical Laboratory addressed the problem of structural heating during atmospheric reentry. His research led to the formulation of the "blunt-body principle," a radical departure from the streamlined aircraft of the early fifties. Allen's work indicated that a blunt shape would be most suitable for a body reentering the earth's atmosphere, since 90 percent of the friction heat would be dissipated through the bow shock wave. Tests five years later, in 1957, with a scale model Jupiter-C nosecone demonstrated [68] that the remaining heat could be dissipated through use of an ablative coating on a heatshield. Although his studies were directed toward resolving the nosecone reentry problem of the ballistic missile, they were later applicable to the Mercury spacecraft. During the ensuing years, heat-resistant materials of the ablative and heat sink types were perfected by government and industry.

Beginning in 1954 and continuing through 1958, Allen and two associates, Alfred J. Eggers, Jr., and Stanford E. Neice, examined the relative merits of three types of hypersonic spacecraft - ballistic, skip, and glide. They prepared in early 1954 a theoretical discussion of the alternative configurations that could be used for manned spacecraft, "A Comparative Analysis of the Performance of Long-Range Hypervelocity Vehicles." For manned satellite missions, any of the three craft could be boosted to orbital velocity by a rocket and then be separated from the launch vehicle for either free flight or earth orbit. The skip vehicle, which would reenter the atmosphere by an intricate series of dips and skips, would require the greatest boost capacity, and would encounter excessive aerodynamic heating during reentry. The glider-type craft, although heavy, would require a smaller boost capacity and would have a greater degree of pilot control during the reentry phase of the mission; the glider was a promising concept, but it would also be a long term project, since it would require extensive engineering and development. The third option was the ballistic shape, which was simply a blunt, non-lifting, high-drag projectile. Although without aerodynamic controls, its blunt configuration would provide superior thermal protection to the pilot, and its lighter weight would permit longer range missions. Moreover, the deceleration forces would be minimized if the vehicle reentered at the correct angle. The Ames researchers concluded that "the ballistic vehicle appears to be a practical man-carrying machine, provided extreme care is exercised in supporting the man during atmospheric entry."16

[69] As time passed, Eggers became convinced of the superiority of the manned satellite glider over the ballistic satellite, but he also knew that the rockets then on the American drawing boards could not put the glider into orbit. He had two concerns when he thought of using the ballistic vehicle - the deceleration loads and the absence of control once the craft entered the atmosphere. The latter problem dictated a large landing area, perhaps as much as several thousand square kilometers. By late 1957 Eggers was proposing a semi-ballistic vehicle in which the best elements of the glider and the ballistic shapes were combined. Further progress on manned spacecraft was influenced by the Air Force and by research in progress at the Langley Memorial Aeronautical Laboratory.17

On 29-31 January 1958, the Air Research and Development Command held a closed conference at Wright-Patterson Air Force Base, during which 11 aircraft and missile firms outlined for Air Force and NACA representatives their classified proposals for manned satellites. These variations on the three basic configurations discussed previously ranged in projected weight from 454 to 8,165 kilograms and involved mainly the use of multistage launch vehicles. Since there was such a difference in technology among the various proposals, the estimated development time ranged from one to five years. Looking back on this period, Robert R. Gilruth recalls:#

Because of its great simplicity, the non-lifting, ballistic-type of vehicle was the front runner of all proposed manned satellites, in my judgment. There were many variations of this and other concepts under study by both government and industry groups at that time. The choice involved considerations of weight, launch vehicle, reentry body design, and to be honest, gut feelings. Some people felt that man-in-space was only a stunt. The ballistic approach, in particular, was under fire since it was such a radical departure from the airplane. It was called by its opponents "the man in the can," and the pilot was termed only a "medical specimen." Others thought it was just too undignified a way to fly.18

While subject to considerable criticism, the concept of a simple ballistic manned satellite gained important support from a group of NACA engineers who started work on just such a spacecraft, borrowing on the experience and technology available in recent research on nosecones for intercontinental ballistic missiles. Max Faget was one of the key members of the NACA group interested in this effort. In January 1958, he had identified himself as a supporter of the ballistic reentry vehicle when he proposed to NACA Headquarters that a non-lifting spherical capsule be considered for orbital flight. [70] NACA expressed little interest in the idea, but Faget continued his studies of ballistic vehicles and spoke out for adoption of this concept when occasions arose. Less than a week after an Air Force man-in-space conference in March 1958,## Gilruth called Faget and a group of top Langley engineers together to discuss a NACA conference on high speed aerodynamics, scheduled to begin at the Ames laboratory on 18 March. The "Langley position" that emerged from the conference reflected the thinking of Faget and his colleagues on a ballistic spacecraft launched by a ballistic missile booster.19

The Ames conference was the last in a series of formal symposia; as such it attracted nearly 500 people from NACA, the military, and the aircraft and missile industry. The 46 papers presented during the three-day meeting summarized the most advanced aerodynamic thinking within the Advisory Committee's laboratories on hypersonic, orbital, and interplanetary flight. Faget presented the first paper, "Preliminary Studies of Manned Satellites - Wingless Configuration: Non-lifting," in which he and his co-authors pointed out the inherent advantages of the ballistic approach. First, ballistic missile research, development, and production experience was directly applicable to this type of spacecraft. Equally significant, the choice of a ballistic flight trajectory minimized the amount of automatic stabilization, guidance, and control equipment required on board the craft, thus saving critical weight and reducing the chance of equipment malfunction. Faget and his associates also demonstrated that their proposed craft could be returned from orbit by a modest-power retrorocket system. The Langley engineers went so far as to propose a specific ballistic configuration - a cone, 3.4 meters long and 2.1 meters in diameter, protected on the blunt end by a heatshield. He concluded that "as far as reentry and recovery is concerned, the state of the art is sufficiently advanced so that it is possible to proceed confidently with a manned satellite project based upon the ballistic reentry type of vehicle."20

The Mercury spacecraft grew out of this 1958 conceptual study prepared at Langley. After an additional two months of design studies, preliminary specifications for a manned satellite were drafted during June by Langley personnel under the supervision of Faget and Charles W. Mathews. Following a number of revisions and additions, these specifications were used for the Project Mercury spacecraft contract with McDonnell Aircraft Corporation. [71] All this work occurred during the months in which the National Aeronautics and Space Act was being drafted and enacted by Congress. Gilruth remembered working out of the old NACA building in Washington during the summer of 1958; it had been hot, humid, and busy.21

In designing the Mercury spacecraft, the key word was simplicity. The goal was a spacecraft that represented "the simplest and most reliable approach - one with a minimum of new developments and using a progressive buildup of tests." Employing these criteria, "It was implicit . . . that we use the drag-type reentry vehicle; an existing ICBM booster; a retrorocket to initiate descent from orbit; a parachute system for final approach and landing; and an escape system to permit the capsule to get away from a malfunctioning launch rocket."22 Although Vostok and Mercury emerged from the design process with different external configurations, their designers had met the same problems and had made some remarkably similar decisions. Undoubtedly, the key decision was to keep the first step into space a simple one. While the Mercury space vehicle would become more complex and sophisticated...

[73] ...during the developmental process, the emphasis on reliability and relative simplicity remained.

* The role of man in space flight has been one of the basic and continuing philosophical differences between the Soviet and American space programs. Americans have sought to make the astronaut a central figure in the operation of the spacecraft, especially in his ability to veto automatic systems. The Soviets have preferred to rely upon automated systems on the ground and in the air, with the cosmonaut playing a secondary and more limited role.

** K. P. Feoktistov, who had prime responsibility for design details of Vostok, described the two sections as "a recoverable capsule (accommodating the spaceman and his life-support equipment, flight controls, communication, on-board systems controls and landing controls) and an instrument compartment (housing various instruments and units of spaceship systems controlling orbital flights, communications, telemetering measurements, orbit parameters, power supply, etc.); that is, all that contributed to orbital flight alone."

*** Hartley A. Soulé recalls that in American circles the spherical "shape was specifically criticized because the weight of the material to completely shield the surface from reentry heat would [have precluded] launching with programmed ICBM boosters." The Soviets had the launch vehicle capability that kept this extra weight from being such a serious concern. Some American designers favored the spherical shape to reduce the problems associated with attitude control, but others feared that "the lack of orientation might result in harm to the occupant during the deceleration period."

**** According to one source, this delay was incorporated after the loss of a pilot who was testing the ejection seat system during a drop test of the Vostok.

# Robert R. Gilruth had been Assistant Director of the Langley Aeronautical Laboratory since 1952 and was named Manager of the Space Task Group, which was assigned responsibility for Project Mercury on 5 Nov. 1958,

## The Air Force held a working conference on 10-12 Mar. at the Air Force Ballistic Missile Division, Los Angeles, in support of its program "Man in Space Soonest" (MISS). At that time, the Air Force concept consisted of three stages-a high-drag, no-lift, blunt-shaped spacecraft to get man in space soonest, with landing to be by parachute; a more sophisticated approach by possibly employing a lifting vehicle or one with a modified drag; and a long-range program that might end in a space station or a trip to the moon.

13. P. T. Astashenkov, Akademik S. P. Korolev (Moscow, 1969) (available in translation as Academician S. P. Korolev, Biography, Foreign Technology Division edited translation HC-23-542-70, pp. 185-186); and Konstantin Petrovich Feoktistov, "Razvitie sovetskikh pilotruemuikh kosmicheskikh korablei," Aviatsiya i Kosmonavtika, no. 11 (1971): 36-37 (available in translation as "Development of Soviet Manned Spacecraft," National Lending Library for Science and Technology, Boston Spa, Yorkshire, England, and available from NASA as N73-15876). Feoktistov stated the following reasoning for adoption of the sphere: "The aerodynamic characteristics of the sphere, the drag coefficient and the position of the centre of masses were well known for the entire velocity range (from the first cosmic [i.e., orbital velocity] down to subcosmic velocity). In addition, the problem of maintaining stability of movement of a spherical vehicle in the atmosphere could be easily solved by just shifting the gravity centre of the vehicle off the centre of the sphere. This provides for the static stability and, as revealed by computations, for good dynamics of vehicle movements around the centre of masses even in the case of arbitrary orientation of the vehicle prior to re-entry and in descent when controls are no longer available."

14. Astashenkov, Academician S. P. Korolev, Biography, pp. 185-186; Hartley A. Soulé to James M. Grimwood, 29 Aug. 1965; Swenson, Grimwood, and Alexander, This New Ocean, pp. 71-72; and Ames Aeronautical Laboratory, "Preliminary Investigation of a New Airplane for Exploring the Problems of Efficient Hypersonic Flight," 18 Jan. 1957. In appendix B of the Ames report, there is a description of a proposed 1.5-meter spherical ballistic spacecraft, pp. 30-31.

15. U.S.S.R. Academy of Sciences, comp., Kosmicheskiy korabl Vostok (Moscow, 1969); available in translation as The Spaceship "Vostok," Foreign Technology Division edited translation HT-23-705-70, pp. 5-6; and Leonid Vladimirov, The Russian Space Bluff, David Floyd, trans. (London, 1971), pp. 89-91. Vladimirov indicates that a Peter Dolgov was killed when his space suit was ripped during a test of the ejection system. "Korolyovs [Korolevs] reaction to Dolgov's death was to take a number of urgent and clever measures. First he had the exit hatch made larger. Secondly, he increased to two seconds the interval between shooting off the hatch and the operation of the ejector mechanism."

16. H. Julian Allen, "Hypersonic Flight and the Reentry Problem," Journal of the Aeronautical Sciences 25 (Apr. 1958): 217-230; Alfred J. Eggers, Jr., "Performance of Long Range Hypervelocity Vehicles," Jet Propulsion 27 (Nov. 1957): 1147-1151; and Swenson, Grimwood, and Alexander, This New Ocean, pp. 55-82. The authors of This New Ocean describe the background of NACA and Air Force research into the problem of reentry vehicle design; also see William M. Bland, Jr., "Project Mercury," in The History of Rocket Technology Essays on Research, Development, and Utility, Eugene M. Emme, ed. (Detroit, 1964), pp. 214-215.

17. Swenson, Grimwood, and Alexander, This New Ocean, pp. 68-69.

18. Robert R. Gilruth, "Memoir: From Wallops Island to Mercury; 1945-1958," paper, Sixth International History of Astronautics Symposium, Vienna, Austria, 13 Oct. 1972, pp. 31-32.

19. Swenson, Grimwood, and Alexander, This New Ocean, p. 86; Grimwood, Project Mercury: A Chronology, NASA SP-4001 (Washington, 1963), p. 17; "How Mercury Capsule Design Evolved," Aviation Week, 21 Sept. 1959, pp. 52-53, 55, and 57; and David A. Anderton, "How Mercury Capsule Design Evolved," Aviation Week, 22 May 1961, pp. 50-71 passim.

20. Faget, Benjamin J. Garland, and James J. Buglia, "Preliminary Studies of Manned Satellites - Wingless Configuration: Nonlifting," in "NACA Conference on High-Speed Aerodynamics, Ames Aeronautical Laboratory, Moffett Field, Calif., Mar. 18, 19, and 20, 1958: A Compilation of Papers Presented," pp. 9-34, reissued as NASA Technical Note D-1254 (Langley, Va., 1962).

21. Grimwood, Project Mercury: A Chronology, pp. 19-24; Gilruth, "Memoir: From Wallops Island to Mercury," pp. 34-37.

22. Gilruth, "Memoir: From Wallops Island to Mercury," p. 37.