On Wednesday’s post we discussed about “human rating” certified spacecraft. Discussing about NASA’s human rating certification, to achieve such a level, systems must implement additional processes, procedures, and requirements necessary to produce human-rated space systems that protect the safety of crew members and passengers on NASA space missions. Human-rating is an integral part of all program activities throughout the life cycle of the system which includes:
- Design and development
- Test and verification
- Program management and control
- Flight readiness certification
- Mission operations
- Sustaining engineering
- Maintenance, upgrades, and disposal.
The three broad requirements (General Requirements, Safety and Reliability Requirements, Human-in-the-Loop Requirements) have further sub-categories. The key points are as follows:
- The vehicle crew habitability and life support systems shall comply with NASA Standard 3000 and NASA Space Flight Health Requirements for crew habitability and life support systems design.
- Spacecraft operations in proximity to or docking with a crewed vehicle shall comply with joint vehicle and operational requirements so as to not pose a hazard to either vehicle. Provisions shall be made to enable abort, breakout, and separation by either vehicle without violating the design and operational requirements of either vehicle. Uncrewed vehicles must permit safety critical commanding from the crewed vehicle.
Safety and Reliability Requirements:
- The program shall be designed such that the cumulative probability of safe crew return over the life of the program exceeds 0.99. This shall be accomplished through the use of all available mechanisms including mission success, abort, safe haven, and crew escape.
- A crew escape system shall be provided on ETO vehicles for safe crew extraction and recovery from in-flight failures across the flight envelope from prelaunch to landing. The escape system shall have a probability of successful crew return of 0.99.
- The vehicle shall provide the flight crew on board the vehicle with proper insight, intervention capability, control over vehicle automation, authority to enable irreversible actions, and autonomy from the ground.
From all the above points, it is clear that, while it is relatively easier for sending space probes, rovers, orbiters, etc. to space; it becomes quite challenging and difficult for human space missions. As it involves repeated testing and development of new technologies. Accidents such as Apollo 1, Space Shuttles (Challenger and Columbia) have further focused on no room for error. The figure below shows the Dragon Crew Module under test and the final test which resulted in an anomaly on the test stand.