credit NASA / Lockheed Martin / caption: Flight Orion 1’s software will differ to Orion 2 or 3
Below and in the extended section of this blog posting are answers from the Orion project office regarding decisions taken for the Orion crew exploration vehicle’s software and how its development is to be phased to ensure verified flight software is available for the Orion 1 mission. Read flightglobal.com’s related Orion software story here
1 Can you confirm that Orion’s software code is now estimated to be around 1.1 million lines?
1.1 million source lines of code (SLOC) falls roughly in the middle of the range of software sizing estimates the project has conducted in recent months. Software sizing estimation is an art that employs differing methods and requires assumptions about complexity, functionality and content that is highly dependent on the details of the application for which the software is written.
Since Orion is in preliminary design and the systems, subassemblies and component designs are now being revealed, the details upon which more precise software sizing estimates will be based are still being validated. We believe the Orion software sizing estimates reflect the current requirements and needs for Orion, and are well within the historical software quantity needed for a spacecraft of this complexity.
2 Can you confirm that a planned zero based vehicle software scrub to an Orion 2/IOC flight minimum will not be completed by PDR?
The Orion System PDR this year will include all required entry criteria for software and the review will assess software maturity against the exit criteria established by the agency. PDR is an early milestone in the design process after which most of the flight system detail designs will occur.
Software is no different. However, after each subsystem design review (described below) to be held prior to PDR, the associated application software content will be validated and software sizing estimates will be updated with the more mature functional and performance based knowledge of each subsystem. As in every area of Orion system design, this process will seek to identify simplifications (or possible deferrals) that will reduce software functionality demand and therefore should reduce the estimated quantity of flight software required.
Through this, we may also realize near-term cost and schedule benefits in our plans to achieve IOC within our commitments. The zero based vehicle software scrub approach is a management tool to determine the hypothetical minimum software capabilities required to fly this spacecraft for the first few ISS missions. Automation and other software capabilities will be added for IOC and beyond to optimize vehicle safety, mission, and operational capabilities.
The software scrub is not required to complete by PDR, and is not part of Orion’s PDR success criteria. The flight software functional scrub is in fact dependent on PDR maturity of Subsystem and spacecraft design to properly evaluate potential software reductions or deferrals beyond Initial Operational Capability (IOC). The final integrated results of this optimization will be available for an Orion software life cycle review planned for early next year.
3 Can you confirm that GN&C is the first focus for the software work being carried out prior to PDR?
No. Software architecture, requirements validation and initial software development work has been ongoing since the start of the Orion project. Leading into PDR, software will be reviewed at the vehicle level as it relates to interfaces, data structures, communication protocol, etc. It will also be assessed at the level of applications as software relates to and interacts with the system hardware. Most every system has some application software. Every system is conducting a subsystem design review in preparation for the Orion system level PDR.
Among the Orion systems, GN&C is first to conduct their subsystem design review at which GN&C software will be discussed. Based on this early review, GN&C may be selected as a pathfinder activity to evaluate the process and approach for the flight software functional scrub (described above).
4 Can you confirm that the only automation planned for Orion 2 flight software will be where time to criticality functions do not allow for human response?
No. Orion 2 will implement considerable automation beyond that which is required for time critical crew safety. For example, Orion 1 will be flown without crew and will be a full LEO mission demonstration including launch, on-orbit operations, rendezvous with ISS (to some defined stand off distance), entry, landing and recovery operations.
Orion 2 capabilities will be based on the requirements and increased certification required for a human rated mission. There are many automation functions that will be exercised on the unmanned Orion 1 prior to Orion 2 IOC that do not depend on crew interaction in realtime. As part of the flight software functional scrub activities (described above) we may identify candidate software functions for deferral beyond IOC, including some capabilities which the crew could reasonably be expected to safely execute early in the operational phase until implemented later.
