Three integrated software products are being developed for use in the further development of autopilot systems for reusable launch vehicles (RLVs). The need for these products arises because of the unique nature of RLVs:
- RLVs employ differential throttlingas the primary means of longitudinal control during ascent. This approach to flight control necessitates autopilot systems because the way in which engine thrust signals control the rockets is counterintuitive to astronauts.
- Conventional controllers are not adequate for the multiple-input/multiple-output autopilot systems that are needed for RLVs (e.g., the VentureStar) that are equipped with linear aerospike engines and small conventional aerodynamic controls. The small conventional aerodynamic controls and the propulsion inefficiency that results from differential throttling necessitate the development of robust reconfigurable autopilot systems, as do the all-consuming goal of minimizing RLV weight and the need for interchangeable, swappable, and cooperative actuators that can alleviate attitude-control concerns in the event of single or multiple actuator failures.
One of the three developmental software products is intended for use in designing and simulating autonomous, robust, reconfigurable flight-control systems of both civil and military RLVs. This is a user-friendly software package that will greatly aid NASA, other government agencies, and industrial organizations working on linear aerospike space transportation systems and RLVs. It enables the designer to develop systems based on several control approaches, including hierarchical robust reconfigurable control and robust identification-based adaptive reconfigurable control. Genetic algorithms serve as the optimization tools in this package.
The second software product is one that provides an advanced software environment of testing and evaluation of the designs and software of autopilot systems. This product will determine the efficacy of these systems by evaluating the ease with which the systems can be reconfigured in the event of the multiple failure scenarios described below.
The third and final product is a real-time software prototype of an advanced robust reconfigurable autopilot system for an RLV. It is an on-line, real-time control software environment that provides control researchers and engineers with a convenient tool for the investigation and application of advanced control methods and real-time control in an RLV system.
The advantages of these three integrated software products and of autopilot systems designed by use of them are the following:
- These products will minimize the engineering design labor as well as the weight, cost, labor, and maintenance associated with the physical RLV.
- Autopilot designers will be able to design, simulate, evaluate, implement (in real time), and test their control system designs within the complete three-product package.
- A robust, reconfigurable autopilot eliminates the need for a human pilot, thus eliminating the possibility of loss of life as the result of a catastrophic failure or human error.
- The use of software products like these reduces the probability of losing an RLV and/or its payload in the event of a mission-threatening failure. A robust, reconfigurable autopilot system would minimize the need to abort the mission in the event of a single or multiple actuator failure by reconfiguring the RLV control system as necessary to approach nominal vehicle attitude control.
- In designing a robust, reconfigurable attitude-control system, the control actuators can be allowed to remain small, minimizing the vehicle weight and avoiding actuator-related overheating during reentry and descent.
- To minimize weight, a typical RLV design calls for fuel for both the main engines and the reaction control system to be depleted before descent. Thus, the need for reconfigurability of aerodynamic control surfaces becomes even more compelling during descent and landing in the event of a single or multiple aerodynamic actuator failure.