PROTOTYPE SOLAR POWER SATELLITE OPTIONS B. R. Sperber - Boeing Aerospace Company K. E. Drexler - Massachusetts Institute of Technology An optimal path cost minimization problem is presented every time a new system is implemented. A system like the solar power satellite (SPS) is a special challenge because the anticipated development costs are large and, due to optics, the microwave power transmission link can not economically be scaled down to powers of less than a gigawatt. This paper addresses the choice of options for the prototype SPS, which is currently the least well defined of the three major items in the SPS development program. (The other two major items are the construction base and the heavy lift launch vehicle.) The reason for undertaking any development program is to reduce the risk of failure of subsequent projects. Risk is quantifiable and is basically the program cost multiplied by the reduction in probability of program success due to the risky action. According to Kierolff (Ref. 1) there are four classes of risk. (See Table l) While in an ideal society prototyping would only reduce technical risks, in the real world it may reduce the effects of the other three types of risk by allowing them to be quantified earlier. In the case of the prototype SPS, the mathematical criterion for when one should prototype is D Cf = Cp, where D is the difference in program probability of success with and without the prototype option being considered, Cf is the cost of program failure and Cp is the prototype cost. With careful and judicious evaluation of the parameters in this relation (or one very much like it--the one here is very simplified) an objective choice of program plan can be made. (Ref. 2) Current thinking on requirements for SPS prototypes result in lists like Tables II and III. The generally accepted most difficult technical aspect that the prototype will have to demonstrate is the safe and efficient transmission of commercial amounts (greater than 10 Mw) of power from synchronous orbit to the Earth's surface through all types of atmospheric conditions. The important similarity parameters of the microwave power link are frequency, beam efficiency, desired sidelobe levels and a real atmosphere and ionosphere in the beam path with full scale power density (approximately equal to received power/area) propagating through. Transmitted power/area is not critical for reasonable simulation of full scale beam conditions, although it is an important parameter that should be achieved in in-space subarray tests. For efficient power transmission at S band, the product of the transmitting and receiving areas must be approximately 1 ol 4 m1*. To realistically test atmospheric and ionospheric effects the received power/area should be that of the full scale satellite (currently 230 w/sq. meter). As a result, the power and aperture area of the transmitting antenna are set once the size of the receiving array is decided. That decision follows from a simple cost minimization exercise. The most common SPS design, termed "conventional" for purpose of this paper, consists of separate solar and microwave transmitting arrays connected by DC busses and rotary joints. The designer of a prototype of a conventional SPS has a critical choice to make. He may transmit a beam which reaches full scale SPS peak power density on the ground using an oversized, quite nonstandard low power density transmitting array, or he may retain standard subarrays in a smaller than full scale aperture for less than full power density on the ground. Because the former choice results in a design physically larger and quite unlike
RkJQdWJsaXNoZXIy MTU5NjU0Mg==