WASHINGTON, D.C. (NASA PR) —Many human spacecraft -— Mercury, Apollo, Russia’s Soyuz, and China’s Shenzhou — include tower abort systems that “pull” the crewed capsule away from a failing rocket. Although its design has proven to be reliable, it comes with inefficiencies. Rather than depending on this heritage design, NASA’s commercial crew partners are developing innovative alternative approaches that not only will allow crews to reliably escape from a launch vehicle accident, but also should prove less costly for missions to low-Earth orbit.
Previous and existing abort systems consist of independent rockets and thrusters that extend above a capsule. Used only during an emergency abort, these systems provide the thrust needed to rapidly remove a crewed capsule from the dangerous vicinity of a rocket accident and orient the capsule for a controlled descent and landing.
During a nominal ascent, once past the point where the tower is needed for a potential abort, the entire system is jettisoned and discarded since the spacecraft are not designed to carry excessive weight all the way to orbit and back to Earth. Thus, every launch requires a brand new abort tower complete with fuel, control systems, and support structure.
For some applications, this is the necessary solution because of the combination of acceleration required for the ascent profile and the spacecraft’s weight. For example, NASA’s Orion Multi-Purpose Crew Vehicle will include a tower abort system due to its higher mass for beyond Earth exploration missions. It offers the opportunity to shed mass that is not needed for the beyond Earth operations.
NASA’s CCiCAP partners, on the other hand, are able to optimize for the low Earth orbit mission. They are designing systems that share functionality with other systems on the spacecraft, and in some cases will be reusable.
Boeing’s CST-100 includes four dedicated launch abort engines (LEAs) on the aft end of the service module that work in conjunction with the nominal orbital maneuvering and attitude control thrusters.
These LEAs are based on heritage designs from the Atlas II program, and are fed by the same fuel system as the rest of the service module’s propulsion. When an abort is not performed, the unused propellant becomes available for use during other phases of the mission. By sharing functionality and fuel in this manner, the abort hardware is simplified and mass is minimized relative to the heritage tower approach.
“Our use of previously flight-proven hardware, and an optimally integrated design approach, ensures this critical CST-100 safety system will safely return the crew if required with minimal penalty to nominal mission capabilities,” said John Mulholland, Commercial Programs vice president and program manager for Boeing.
The abort system for the SpaceX crewed Dragon capsule will consist of eight “SuperDraco” engines attached to the side of the spacecraft. These engines use the same fuel and oxidizers as the Draco thrusters currently flying on the cargo Dragon, but produce greater thrust that is needed for abort escape from the Falcon 9 rocket in an emergency. If no abort occurs, the reusable engines will provide thrust to cushion Dragon’s landing. To date, the SuperDraco engines have undergone 58 hot-fire tests for a total run time of about 117 seconds.
According to SpaceX Project Manager Garrett Reisman, “The SuperDraco development and test effort is indicating that this newly designed engine will surpass our original requirements.”