Shuttle Capability Research Articles

The new AP101S general-purpose computer (GPC) for the space shuttle

This paper describes the development of the new AP101S General-Purpose Computer (GPC) for the Space Shuttle Orbiter. The GPC is the primary data processing computer on-board the Shuttle. It controls and monitors spacecraft functions. In recent years, the requirements for expanding the Shuttle's capabilities have surpassed the capabilities of the current GPC, the AP101B. This upgrade necessity and expected longevity of the Space Shuttle program has given birth to the AP101S GPC. The AP101S evolved from a line of pipeline processors flexible enough to support the Space Shuttle requirements. It offers many features vital to the expected needs of the space program. This paper describes the design philosophy, methodology, primary features, and functionality of the AP101S. The testing and development, which led to the integration of the processor are also detailed. Finally, the application of using it on-board the Space Shuttle Orbiter is portrayed. Indeed, the AP101S is an integral part of an aggressive and expanding Space Shuttle program, and is one which will serve well into the future.

Controllability of Remotely Piloted Spacecraft with Delayed Feedback

In order to fully exploit the Shuttle orbiter's payload delivery and retrieval capabilities and to provide on-orbit servicing of other spacecraft systems, a remotely piloted free-flyer will be an essential element of the developing space transportation system. Not only will a free-flying system be able to deliver payloads to a significantly higher orbit than can the Shuttle, it will be able to retrieve satellites from their operational orbit and return them to the orbiter or the earth for servicing. Ultimately, the free-flyer can be used in the construction of large space systems that exceed a single Shuttle launch capability. Following completion of its mission, the free-flyer can return to the earth, or it can remain in orbit for storage between Shuttle missions to eliminate relaunch expenses. The free-flyer may be controlled from either the aft flight deck or a ground based station. Remote control from a ground based station has distinct advantages because it will eliminate all requirements imposed on the Shuttle for aft flight deck and cargo bay flight support equipment and interfaces.

Shuttle lidar resonance fluorescence investigations 2: Analysis of thermospheric Mg^+ measurements

Shuttle lidar measurements of magnesium-ion (Mg+) number density in the ionosphere (80-500 km) have been numerically simulated. A set of recently defined system parameters are used to assess the system performance. These simulations take into account the saturation effect of atomic absorption due to the high intensity of the laser, which is seen to be important in making near-field or daytime measurements. When the saturation is important, a calibration procedure must be used to correct the systematic error introduced by this effect. Both the nadir- and zenith-viewing configurations have been considered because the altitude of the Shuttle was assumed to be 300 km. The background level in these two configurations is discussed, and we show that the background level for zenith-viewing with the assumed lidar system parameters is negligible. The calibration of the lidar system parameters by means of Rayleigh backscattering from atmospheric molecules in the stratosphere is examined. This method is shown to require extra care because of the wavelength used (2796 A), which lies within a strong absorption band of ozone causing large transmission errors. The Shuttle lidar capability for Mg(+) measurement is compared with the requirements for conducting scientific investigations in the thermosphere.

Potential cost reductions for three STS/Spacelab mission modes

Based on the results of studies carried out by ESA several possibilities are discussed to achieve mission cost reductions for large Spacelab instrument facilities as compared to their flight on several 7-day duration Spacelab missions. As an example three scientific telescope facilities are selected (LIRTS, EXSPOS, GRIST) which are defined to a Phase A level. Three new mission modes are considered: • —Shuttle attached Spacelab mission mode with extended flight duration (up to 30 days) for which the application of planned capability extensions and new elements of the STS/Spacelab (e.g. Short Spacelab Pallets, Power Extension Package) are investigated. • —Shuttle deployed mission mode, for which the telescope, accommodated on a Spacelab pallet, is docked to the Power Module, a new element of the Space Transportation System under study by NASA. • —Free-flying mission mode, for which Shuttle launched dedicated missions of the facilities are considered, assuming varying degrees of autonomy with respect to supporting services of the Shuttle. Reduction of costs have been considered on the levels of single mission cost and total programme cost. Fundamentally the charges for the instrument can be reduced by constraining the mass/volume factors with respect to the Shuttle capability. However, the instrument as part of a payload is only viable if an acceptable resource sharing including observation time can be achieved. Any single instrument will require several mission opportunities or one mission which achieves a similar or longer total observation programme. Based on an identification of instrument modifications of the Phase A baseline designs to favour cost reductions and on a derivation of technical requirements, constraints and finally budgetary cost comparisons an attempt is made to assess the advantages and disadvantages of the different mission modes. The favoured option for GRIST is a 2–3 weeks sortie mission followed after refurbishment by a longer Power Module docked mission. For LIRTS and EXSPOS the free-flying pallet modes are very attractive in terms of the longer durations achieved and in terms of cost per unit operating time.

The shuttle development and its growth potential

During the next two decades, we will establish the foundation for the 21st century's accomplishments in space. The Space Shuttle vehicle will become the cornerstone for that foundation by providing economical opportunities for space exploration and utilization. Reusability of the Shuttle vehicle is the key to its economy. The major developmental challenges encountered in the Shuttle program are typified by the complexities involved in designing the reusable propulsion and thermal protection subsystems. We successfully met such challenges and are nearing the launch of the first Shuttle orbital flight. Our immediate goal is to enter the Space Shuttle operational phase because only then will we fully understand the unique capabilities of the Shuttle. Concurrent with our effort to begin Shuttle operations are our initial efforts to expand Shuttle capabilities, extending them significantly beyond those of the current baseline system. Shuttle payload capacity and mission-duration capabilities are to increase considerably during the next decade. Just as present Shuttle performance specifications and development timetables were guided by the space program plans and forecasts of the 1960s, so will the development of long-range space programs be determined by our near-future achievements. We anticipate that the Space Shuttle will play a critical role in those achievements.