Air-deployed, Lift-assisted Booster Vehicle (ALBV)
A rocket-powered, air-deployed, lift-assisted booster vehicle (ALBV) could efficiently carry small payloads to orbital, supraorbital or suborbital altitudes and velocities. The ALBV is secured beneath a conventional carrier aircraft and dropped therefrom at launch altitude and velocity, which contributes significant total energy to the ALBV's ascent trajectory. The ALBV has wings, which generate aerodynamic lift to assist in vehicle ascent, and tail fins, which perform attitude control while the vehicle is in the sensible atmosphere.
After drop launch, an innovative "vertical-S" maneuver is performed using aerodynamic control, causing the ALBV to ascend on a near-theoretical optimal trajectory. In the preferred embodiment, the wings and tail fins are jettisoned as the vehicle exits the sensible atmosphere and aerodynamic lift ceases. This represents a dramatic improvement over prior approaches to orbital payload launch, as it approximately doubles the useful payload that can be carried by the booster compared to identical ground-launched vehicles.
An expendable rocket vehicle advantageously designed for air launch from the underside of a carrier aircraft could deliver small or large payloads to orbital, supraorbital or suborbital velocities and altitudes. The rocket vehicle includes a wing and controllable fins which provide aerodynamic lift and attitude control, respectively, while the vehicle is traveling in the sensible atmosphere. A plurality of stages are utilized, and the wing is expendable and is attached to a first stage of the vehicle for jettison with that stage.
In operation, the rocket booster vehicle is mounted to the underside of the wing or fuselage of a carrier aircraft, e.g., a Lockheed L1011, Boeing B-52, or a special purpose aircraft, and is carried to altitude for drop launch. The vehicle is thereafter released from the carrier aircraft in a horizontal or near-horizontal attitude, and the first stage is ignited. Thereafter, the vehicle performs an innovative "vertical-S" maneuver, comprised of an initial aerodynamically controlled pitch-up to an ascent flight path angle preferably of less than about 45°, followed by a subsequent aerodynamically controlled pitch-down of the vehicle after a maximum value of .rho.V.sup.2 is reached. In the final portion of the vertical-S maneuver, first stage burnout occurs, the first stage and connected aerodynamic wing and fin surfaces are jettisoned and the second and any subsequent stages accelerate the vehicle to orbital, supraorbital or suborbital altitudes and velocities in a conventional way.
By launching the booster vehicle from a carrier aircraft while in flight, the carrier aircraft's velocity and altitude (kinetic and potential energy) add directly to the ascent energy of the booster vehicle.
Because of the advantageous use of aerodynamic lift, the present invention may be designed to a size and configuration permitting horizontal deployment from a carrier aircraft at high altitudes (e.g., 40,000 feet) and velocities (e.g., 0.80 Mach number). As will be appreciated from the foregoing, aerodynamic lift is utilized to assist the rocket booster in the non-vertical ascent of the vehicle through the sensible atmosphere. In addition, while in the sensible atmosphere, trajectory control is performed by attitude control of the aerodynamic surfaces of the vehicle. Consequently, the aerodynamic lift assists in overcoming gravity losses, which have heretofore been counteracted primarily by the thrust of the rocket boosters in conventional booster vehicles. Moreover, thrust direction losses are reduced since the total velocity vector turning angle is much smaller than that of a ground-launched vehicle, most of the turning is effected at low speeds and a significant amount of turning is achieved with aerodynamic lift.
Moreover, the launch of the orbital vehicle at high altitude, when followed by the above-described vertical-S maneuver, enables the vehicle to fly an ascent trajectory which differs from both the ideal no-atmosphere horizontal launch trajectory and the near-vertical trajectory typically used for ground launches in the Earth's atmosphere, and which avoids the attendant disadvantages normally associated with launches within the atmosphere. In particular, the low atmospheric density .rho. at the launch altitude and relatively low velocity at the deployment point minimize aerodynamic and aerothermodynamic loads on the structure, enabling use of a substantially non-vertical flight path. In the preferred method, an initial pitch-up of 45° or less provides a suitable atmospheric density gradient to avoid destructive peak aerodynamic and heating loads. Moreover, after peak aerodynamic load is reached, the vehicle is pitched down to approach the ideal horizontal, in-vacuum trajectory discussed above.
Additionally, because a substantially non-vertical flight path is feasible, gravity losses are further reduced as the gravity force component in the thrust direction is decreased and the gravity force component perpendicular to that direction is counterbalanced by the wings' aerodynamic lift.
Furthermore, jettisoning of the wing and fins after they cease providing useful lift and aerodynamic attitude control further increases vehicle efficiency and increases payload capacity compared to, say, the US Space Shuttle or the Jackson, et al. vehicle described above, which must carry their non-expendable wings all the way to orbit.
Also, air launch of the vehicle permits any desired orbital inclination to be achieved efficiently because the launch can occur at any desired latitude and angle of inclination, thereby obviating the need for any inclination change maneuver during booster ascent or after orbit is reached.
Still further loss reductions are achieved in the design of the rocket motors. Because the motors are fired only at atmospheric pressures at 40,000 feet and upwards, larger nozzle exit areas with higher expansion ratios may be employed, improving propulsive efficiency and greatly reducing atmospheric thrust reduction losses.
Significant advantages over prior art vehicles and launch methods are achieved by the vehicle and method, which render it feasible for wide-scale orbital, supraorbital or suborbital payload transport.
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