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  Date: 11/18
  Program: 5:00 - 6:00 pm
   Zoom Meeting 

TGCC Chapter Program November 2021

Using Assume-Guarantee Contracts in Autonomous Spacecraft

Authors: James B. Dabney1, Pavan Rajagopal2, Julia M. Badger3


Organizations: 1University of Houston – Clear Lake, 2CACI, Houston, Texas, 3NASA Johnson Space Center

The rapidly increasing complexity and required autonomy of intermittently crewed spacecraft increases the importance of correct and reliable software-intensive systems. It has been shown that while 70% of software faults are introduced in the requirements and preliminary design phase of the system lifecycle, only 3.5% are found in that phase. Typically, approximately 60% of faults are identified in the verification activities late in the lifecycle, raising the cost-to-fix by a factor of at least 50. A complicating factor for data-driven emerging systems is that mission requirements will change as the mission progresses, and therefore, it is not possible to know or test every mission scenario that will be encountered. The Gateway Vehicle System Manager team is using assume-guarantee contracts as one means to address these verification challenges. Assume-guarantee contracts are used in the specification phase to ensure that the specified system satisfies key properties. Assume-guarantee contracts can also be used during mission operations to monitor system behavior and detect errant behavior. This presentation describes the approach the Gateway Vehicle System Manager team is using to exploit assume-guarantee contracts in development and operations. The presentation will discuss:

1. Identification of appropriate assume guarantee contract.
2. Specification of contracts to support early-lifecycle verification and clarify requirements intent
3. Available tools to evaluate implementation of assume-guarantee contracts and verify correctness
4. Identification and specification of assume-guarantee contracts for mission operations (runtime)
5. Available tools that are sufficiently mature to be candidates for runtime verification of contracts



James B. Dabney is Program Chair and Professor of Systems Engineering at University of Houston - Clear Lake, Houston, Texas where he directs the Systems Engineering Laboratory. His research interests include systems engineering process modeling, mechatronics, dynamics and control, robotics, aircraft trajectory optimization, and space systems verification and validation. He received the B.S. Degree in Mechanical Engineering from Virginia Tech in 1974, the M.S. Degree in Process Monitoring and Control from University of Houston -Clear Lake in 1993, and the Ph.D. Degree in Mechanical Engineering from Rice University in 1998. He is a Member of ASME and INCOSE.