Elon Musk founded SpaceX with the goal to deliver humans to Mars. In order to achieve that goal, SpaceX will need to lower the cost of rocket launches and increase rocket reliability. SpaceX has taken big steps to accomplish this by attempting to reuse its Falcon 9 first stage rockets and deciding to use a single liquid fueled rocket engine design. If SpaceX achieves its goal, it would fundamentally reshape the rocket industry.
“If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred. A fully reusable vehicle has never been done before. That really is the fundamental breakthrough needed to revolutionize access to space.” –Elon Musk
SpaceX points out that the vast majority of the cost for a launch is the physical rocket, the fuel is only 0.4% of the total launch cost. At least one of SpaceX’s commercial customers is looking for a 30% savings by the reuse of the rocket. The rockets are based on a simplistic design as possible for rocket science with added fuel to allow the rockets to return on land. Our immediate question is how reliable will reusing the same rockets launched into low Earth Orbit (with up to 23,000 pounds of payload), reentering the atmosphere and landing safely back on the ground?
To add to the complexity, SpaceX has an aggressive development plan where rockets designs are continually upgraded. This development cycle does not allow for a mature design, which would usually be required to undergo extensive testing and operational use to ensure rocket reliability. Without a mature design, the SpaceX reliability team has limited data for each rocket design iteration. As design changes are made, more variables are introduced into the product reliability. SpaceX hardware designs follow a schedule more typical of software designs, however, rocket testing is much more expensive than software testing. As SpaceX President Gwynne Shotwell stated, “We’ve proven we can change the vehicle design to make it better without impacting mission reliability.” From a reliability engineering standpoint, that is quite a statement. Clearly the SpaceX reliability team believes it collects enough test and performance data and has completed necessary failure analysis to make various design changes and not adversely impact rocket reliability and mission assurance. In the past, the rocket launch industry has been more conservative and created a stable design to produce repeatedly on an assembly line that will achieve known mission and rocket reliability targets.
The aggressive development benefits are the exponential technology learning by the various design changes, designers can quickly make changes based on flight experience, and produces higher performance for engines and fuels tanks. The positive should be weighed against the severity of the issues: the lack of a mature design, limited sample data, difficulty in determining root causes and lack of significant flight hours on a design.
The other factor that enhances SpaceX rocket reliability is the fact that it uses a single liquid fuel engine design for all its rocket engines. The NASA shuttle and the United Launch Alliance (ULA) Delta IV rocket both use a combination of liquid fuel and solid fuel rocket engines. By only having one engine design the rocket and reliability engineers can focus all their efforts on making Falcon 9 rocket engine as reliable as possible. That means SpaceX engineers only need to have one rocket engine FMECA, one testing program, one supply chain, approximately half the components, etc.
SpaceX is pushing the limits of rocket technology to drive disruptive changes in the rocket launch industry. Reliability and safety cannot be sacrificed in the pursuit of cost effective launch vehicles. Engineers will need to fully utilize all of the reliability tools, maintenance, and monitoring available to continue to produce safe and successful rocket launches.