The M-1 lifting-body reentry vehicle was a blunted cone shape that was 2.4 m long with a 3.7 m base diameter and a 30° half-apex angle. This vehicle enjoyed weight and cost advantages, a capability for growth to lunar re-entry velocity missions with minimum modifications, and a wide range of reentry trajectories. The upper surface was flattened to obtain a hypersonic lift-drag ratio of 0.5. Control was provided by reaction control jets and four low-aspect-ratio electrically actuated control flaps hinged near the cone base perimeter. Rear vision was provided the pilot through the use of a single mirror system. The conditioned equipment and payload compartment extended from the pilot's compartment to the interior structural shell. The 2.1-cubic-meter payload bay was located to the right of the pilot's compartment.
The M-l configuration included a parachute recovery system since the subsonic L/D of approximately 0.8 was too low for a conventional landing. Drogue parachutes were deployed at an altitude of 24,000 m and the main parachutes, at 4,200 m. In order to insure landing within the required 25-square-km area, terminal guidance was required during approach to the landing site to correct for wind conditions prior to deploying the drogue parachute. Both radio and inertial guidance systems were used for terminal guidance during re-entry and landing to provide continuous, accurate terminal guidance. Vehicle control during reentry and approach to the landing site could be either automatic or manual.
Maneuver capability of the M-l device during reentry can provided a lateral-range deviation from the orbital path of 260 km if maneuver was initiated at 7,000 m/s.
The normal reentry exploration corridor for the M-l configuration was considered to lie within the trajectory for CL,max; alpha = 0°, and a ballistic trajectory (CL = 0), which imposed limiting decelerations on the pilot (reentry angle of -2.5°). The corridor was approximately 18,000 m in the hypersonic region and 9,000 m in the lower supersonic region.
The booster suborbital missions was a standard Titan1 booster, modified to provide stability and to carry the loads imposed by the presence of the reentry vehicle. An l8-percent increase in tank wall stiffening and an additional 12 square m of fin area increased the booster weight by 503 kg. This modified Titan booster was capable of attaining a burnout velocity of 6,600 m/s with the M-1 reentry vehicle. A 400,000-pound-thrust Titan-Centaur booster could provide orbital velocity with a potential growth in allowable weight of 52 percent.
The basic structural concept for the M-1 vehicle utilized a cool, semimonocoque aluminum pressurized structure which was protected from high external flight temperatures by a polyethylene ablation cover. The ablation-cooled structural approach was used because it was more efficient for the short reentry times and high heating rates which were typical of a low L/D reentry trajectory. The ablation material was polyethylene which ablated at 300° C and had good insulation properties. The ablation thickness was based on a structural skin design temperature of 50° C.
The M-1 structure consisted of a pressurized load-carrying aluminum external shell which was reinforced with frames, bulkheads, and longerons. The frames were spaced at 20 cm and were used with the skin to withstand internal pressure loads. In addition, they provided longeron column stabilization and served as panel shear stiffeners to the skin. Bulkheads were used to separate the various pressurized compartments. Four longerons resisted fuselage bending loads and distributed booster, parachute, escape rocket, and landing loads to the external shell. The pilot's environmental compartment was an aluminum-frame structure, attached to the four longerons. Access to the pilot's compartment was provided by an inward opening hatch. Access to the equipment and payload compartments was provided by panels in the vehicle's top surface and in the aft bulkhead.
The weight breakdown for the M-1 for a one-orbit mission were as follows:
Gross mass: 3,299 kg (7,273 lb).
Payload: 454 kg (1,000 lb).
Height: 2.40 m (7.80 ft).
Span: 3.70 m (12.10 ft).