1. Field of the Invention
This invention relates to the ejection of a spacecraft from a launching vehicle and more particularly to an improvement in the gyroscopic ejection of a spacecraft.
2. Description of the Prior Art
Spacecraft such as satellites have been deployed with linear and angular velocity from a launching vehicle such as the NASA Space Transportation System, i.e., Space Shuttle, successfully. An example of such a spacecraft is disclosed in U.S. Pat. No. 4,326,684, which is particularly adapted for mounting within a cradle positioned within a bay of the Space Shuttle. The specific construction of the cradle can be seen, for example, in U.S. Pat. Nos. 4,324,374 and in 4,303,214.
U.S. Pat. No. 4,290,570 describes the mechanism by which a spacecraft is removably attached to the open ended cradle. U.S. Pat. No. 4,300,737 describes locking mechanisms in the cradle that can be remotely controlled for locking and relocking the spacecraft. The manner in which the spacecraft is deployed with linear and angular velocity is disclosed in the above reference and in U.S. Pat. No. 4,359,201. Finally, U.S. Pat. No. 4,213,586 is of general interest.
The spacecraft is attached to the cradle and is restrained during the initial takeoff and transportation of the launching vehicle into space. When the launching vehicle has reached its parking orbit, the attitude of the spacecraft will be set by the attitude of the shuttle and this attitude is maintained during ejection from the shuttle by simultaneously imparting both linear and angular momentum to the spacecraft. This spin provides a gyroscopic stabilization.
In the launching mode, the payload bay doors are opened on the Space Shuttle, and release mechanisms between the cradle and the spacecraft, such as pyrotechnically activated release mechanisms, are fired. A preloaded ejection spring can cause a spacecraft to rise and rotate until the outboard pivots on one side of the spacecraft contact pivot seat members or pads mounted on the cradle. This pre-ejection movement continues until an anchor rod or tether reaches its stop. After settling for a few minutes to eliminate nutations, an ejection mechanism, such as a spring, is activated so that a pivot or pair of pivots on the other side of the spacecraft define an axis of rotation about which the spacecraft will accumulate its angular rate. The rotation of the spacecraft provides sufficient gyroscopic stability to maintain attitude until the spacecraft reaches a predetermined distance from the orbiting launching vehicle. A perigee kick motor can be fired to launch the satellite to an operating orbit.
An advantage of this type of ejection or launching of a spacecraft from the launch vehicle is that it is relatively simple and that it does not require any active control of the spacecraft prior to the firing of the perigee propulsion stage. The cradle remains with the launching vehicle and, when mounted on a reusable launching vehicle such as the Shuttle, may be reused for subsequent launches of spacecraft.
The payload bay of the Space Shuttle is approximately 15 feet in diameter and 60 feet long and it is capable of carrying 65,000 pounds. The dimensions of the payload bay of the space shuttle and the high cost per pound of orbiting a spacecraft has imposed certain limitations on the dimensions of the spacecraft to be launched from the Space Shuttle and on the construction of the cradle to support these spacecraft. In this regard, some designs of spacecraft require a certain cantilevered support from the cradle while the actual construction of the cradle must be within strict weight limitations. These design limitations, plus the hostile environment of space, provide inherent problems in establishing a stable support structure to permit relative movement of the spacecraft during launching.
Accordingly, there is still a demand in the prior art and it is expected there will be a continued demand to provide further improvements in deployment systems and support structure for spacecraft to be deployed from a launching vehicle. The unique limitation of forces exerted during the initial takeoff of the launching vehicle from earth, the extreme limitations on weight, the drastic temperature changes, plus the constraints of providing relatively simple fail safe mechanisms will continue to challenge the abilities of designers in this field.