The present invention relates to a method of operation of a space vehicle equipped at least with one device cooperating with a celestial body, wherein rotation of the space vehicle takes place around at least one axis of the space vehicle.
Such space vehicles, for example satellites, have long been known, for example Japanese Patent 1115096, which describes a method for imparting rotation (spin) to a satellite by means of spin wheels.
One problem in the operation of satellites in orbit is optimal energy collection by means of solar generators. For this purpose the satellites are usually equipped with at least one solar-generator surface which can be disposed either directly on the satellite body or can be in the form of deployable solar-generator panels. One difficulty in energy collection by means of such solar generators is in the optimal orientation of the solar-generator surface toward the sun.
This is addressed in U.S. Pat. No. 6,017,003 in which a natural rotation of the satellites of 360xc2x0 per orbit is produced, in order to keep the solar generators oriented toward the sun at all times and thereby to guarantee a maximum of energy collection. On the other hand, constant orientation toward the sun of the surfaces of the satellite, and the solar generators in particular, also leads to intense heating of the corresponding surfaces, especially the solar-generator surfaces. It has been found that excessive heating of the solar generators impairs their power output.
The problem of heating due to incident solar radiation is disclosed, for example, in U.S. Pat. No. 6,102,339, and a solution is proposed of using radiation-shielding devices which, however, increase the satellite mass unnecessarily and complicate the entire satellite structure.
German Patent 19544641 describes the problem of the thermal cycles caused in earth satellites due to alternating light and dark phases and the associated thermomechanical loads for solar generators. In this patent, such loads are intended to be compensated by appropriately improved electrical conductors.
B. J. Saint-Jean, in xe2x80x9cTheoretical considerations for a preliminary design of a solar cell generator on a satellitexe2x80x9d, NASA TN D-1904, 1963, also describes the thermal cycles that occur in rotating satellites.
Similar problems pertaining to optimal orientation of a space-vehicle device which cooperates with a celestial body can also be encountered. For example, in connection with communication devices of the space vehicle that communicate with corresponding transmitting and/or receiving devices on a celestial body such as the earth, or even in measuring and observing devices, which are used to survey or observe certain celestial bodies.
An object of the present invention is to obtain the optimal use of space-vehicle devices that cooperate with a celestial body. For possible application to solar generators, the objective is then to collect a high yield of energy from the solar radiation incident on the space vehicle while avoiding the disadvantages of the prior art.
This object is achieved according to the invention by a method for operation of a space vehicle, wherein the space vehicle is equipped at least with one device cooperating with a celestial body. In the method rotation of the space vehicle around at least one axis of the space vehicle is imposed, as has already been long known in the prior art for satellites. It is now provided, however, that the rotation takes place not uniformly but instead the rotation of the space vehicle is slowed when the device cooperating with the celestial body is oriented substantially toward the celestial body. In this way, there is obtained a rotation of the space vehicle with different rates of rotation depending on or whether an appropriate device of the space vehicle is substantially oriented toward the celestial body with which it is supposed to cooperate, or whether it is facing away therefrom. If a plurality of identically acting devices or different devices cooperating with different celestial bodies are disposed on the space vehicle, slowing of the rotation can be achieved whenever one such device is oriented substantially toward the corresponding celestial body. The word xe2x80x9csubstantiallyxe2x80x9d as used here means that slowing does not have to take place only when the device is exactly oriented toward the celestial body, but instead, as is already necessary for reasons of reduction to practice, it is provided that slowing of the rotation takes place in a certain angular range around this exact orientation, or in other words around the line connecting the space vehicle and the center of the celestial body, for example, in a range of xe2x88x9245xc2x0 to +45xc2x0, although the deviation can also correspond to smaller angular ranges, such as 30xc2x0 or 15xc2x0, or even a range smaller than 10xc2x0. This will also have to be adapted to the solid-angle region occupied by the celestial body as viewed from the space vehicle.
By this method, there is achieved a combination of the advantages of rotation of the space vehicle around a body axis and the advantages of longer orientation of the devices toward the corresponding celestial bodies with which they cooperate, achieved because of the slowed rotation in these intervals. Thus cooperation with the celestial body is optimized.
As already mentioned, the devices cooperating with a celestial body can be, for example, as solar-generator surfaces, communication devices, or measuring or observing devices. The space vehicle can be designed, for example, as a satellite traveling in an orbit, or else as a space probe or any other type of space vehicle.
For the special application of the inventive method with regard to at least one solar-generator surface of the space vehicle, it is provided that the rotation is slowed when the normal to at least one solar-generated surface is oriented substantially toward the sun. If, however, the normal to the solar-generator surface is always inclined by a particular angular value relative to the line connecting the space vehicle and the sun during rotation, or in other words if, in particular, the axis of rotation of the space vehicle is not perpendicular to the line connecting the space vehicle and the sun, slowing of the rotation takes place when the projection of the normal to the solar-generator surface onto the plane connecting the space vehicle and the sun is oriented substantially toward the sun. In this way, the cooperation with the celestial body, which takes place here through the energy output, can also be optimized for these cases. Compared with uniform rotation, there can be achieved slowed, intensive irradiation of the full solar-generator surface, thus avoiding excessive heating of the solar-generator surfaces by the rotation of the space vehicle, which produces respective cycles of irradiation and showed condition for the individual solar-generator surface.
This method can be applied for solar generators in particular if the solar-generator surface is formed by solar-generator panels that are not deployed or are only partly deployed. In such a case, it is particularly difficult to provide the necessary energy for the space vehicle, and so optimal utilization of the incident solar radiation is of great importance for energy collection
For all of the foregoing cases it can be provided that the rotation is slowed by means of spin wheels. In principle, jets or similar thrustors or other space-vehicle actuators with equivalent effect can also be used for this purpose, although precisely for the case of thrusters the anticipated fuel consumption would usually be relatively high.