The M-2b lifting-body configuration was a blunted conical lifting-body shape consisting of a 13° half-apex cone angle and a flat upper surface. This configuration had conventional landing capabilities, a low weight relative to glider systems, and required less booster modification than the systems with a large planform. The afterbody surfaces were boat-tailed to minimize the base drag for subsonic flight and to achieve trim with a nose-up angle of attack. The vehicle was sized to keep the weight as low as possible and retain the center of gravity in an appropriate location. Technical assistance in the development of this vehicle was received from the Missiles and Space Vehicle Division of the General Electric Company.
Ames wind-tunnel data showed a hypersonic L/D of 1.3 and a subsonic L/D of 3-5 for the M-2b configuration. This high subsonic L/D allows the M-2b lifting body to make a conventional landing with a minimum touchdown speed of 346 kph.
Normal landing was accomplished by touchdown on aft skids using a mechanical energy-absorbing system. The forward gear consisted of an air-charged oleo and dual wheels which were stored in a pressurized and cooled compartment during flight. Direct pilot vision was provided as an aid in landing and for observation during the other phases of flight. The forebody section separated for pilot escape during the various phases of the flight. The escape capsule was recovered by parachute and utilized crushable structure on the bottom of the capsule for energy absorption. The payload compartment was located in the pressurized aft section of the vehicle. Expendables were located in the extreme rear in individual pressurized containers. This arrangement allows the pilot to separate himself from the payload, auxiliary power unit (APU), expendables, and control surfaces in the event of an emergency condition.
Maneuver capability of the M-2b device during reentry provided a lateral-range variation of 1660 km from the orbital path and a longitudinal-range variation of 3,670 km, when maneuver was initiated at 7,000 m/s. The normal reentry exploration corridor for the M-2b configuration was between the trajectories for CL, max, alpha=0° and (L/D)max, alpha=45°. The corridor was approximately 6,700 m in the hypersonic region and 18,000 m in the lower subsonic region.
The standard Titan booster for suborbital program was modified to increase tank stiffening and add 23 square meters of fin area, with a total weight change of 953 kg. This booster can boost the M2b to a burnout velocity of 6,000 m/s and a range of 4,525 km. A 1,800 kN-thrust Titan-Centaur booster provided orbital velocity with a potential growth in allowable weight of 14 percent.
Various structural concepts were investigated for the M-2b vehicle. A re-radiative heat-protection system was considered most suitable because of the high heating rates which were experienced for long periods of time. Nose equilibrium temperatures were 2150° C. The bottom surface varied from 1,500° C immediately aft of the nose cone to 1,000° C on the lower surface behind the escape capsule. The leading edges of the fins and control surfaces reach temperatures above 1,250° C.
A concept was investigated in which the re-radiative heat-protection shield also carried the primary air loads. Coated niobium alloy was proposed as the primary structural material, because of the low oxidation rate of niobium as compared with coated molybdenum alloys. This hot load-carrying structural concept provided a lighter weight vehicle. However, the materials, processes, and fabrication techniques involved with refractory alloys would have required considerable development before sufficient confidence could be established to permit its use on a manned vehicle.
So the insulated and cooled structural concept which was chosen for the M-2b vehicle consisted of a hot, nonstructural outer shell, made of refractory materials, insulation, and passive water walls, which protected the inner aluminum load-carrying structure. Greater confidence existed in the structural integrity of this concept since aluminum was used for primary load-carrying structure.
A Chance Vought developed "Zirod" design was used to withstand the 2,150° C temperature experienced on the nose of the vehicle. In the areas on the vehicle where the temperature was between 1,000° C and 1,900° C, combinations of zirconium oxide foam, molybdenum, fibrous alumina insulation, and a water wall were used. For areas with temperatures below 1,000° C, Rene 41 sheet was used for the external surface, backed up by a Rene 4l corrugated sheet, MIN-E-2000 insulation, and a water wall. The thickness of the structure was sized for a maximum temperature limit of 50° C on the internal aluminum structure.
The internal load-carrying structure consisted of an aluminum shell, supported by conventional aluminum frames, bulkheads, longerons, and shear beams. Pressurized compartments, formed by the load-carrying skin, bulkheads, and shear beams, were used for the pilot and the equipment. Access to these areas was provided by access doors or panels. Structural continuity for body axial and bending loads was provided by the four longerons which also distributed the boost loads. Explosive attachments were provided for separation of the escape capsule from the vehicle. Shear continuity between the escape capsule and the vehicle was provided at the separation bulkhead by the use of fore-and-aft shear pins. Aluminum frames, attached to the load-carrying structural shell, distributed the shear loads throughout the vehicle. These frames were also designed to minimize structural deformation under the outer insulation shell.
The M-2b mass breakdown for/a one-orbit mission was:
Gross mass: 4,259 kg (9,389 lb).