One of the biggest obstacles to space exploration is the lack of a propulsion system which will allow us to reach a destination in a meaningful period of time and return.
The New Horizons one way mission took ten years to get to Pluto. Planned missions to the moons of Jupiter and Saturn will take five to ten years to reach their objectives. A round trip to Mars could take three years depending on the length of time spent on the surface.
Testifying before the House Space Subcommittee on Thursday March 17 2016 NASA Administrator Charles Bolden had this answer when asked about the need for “game changing” propulsion:
“We are on a journey to Mars and most people believe that in the end nuclear thermal propulsion will probably be the most effective form of propulsion to get there.”
Unfortunately Mr. Bolden’s statement “most people believe” has not yet translated into a commitment by the Agency to develop nuclear thermal propulsion system within a specific period of time.
As a result, the Agency is stuck planning all of its missions, manned or robotic, using chemical propulsion to lift off from Earth and then gravity assisted boosts from planets to reach the exploration site.
Mission objectives, the number and size of instruments, scientific goals, and staffing requirements for the 2020’s and beyond are all constrained by the limits imposed by 1960’s propulsion capabilities.
NASA’s interest in nuclear propulsion dates back to the NERVA and Project Orion programs of the 1960’s. NASA’s current focus is on fusion.
Fusion occurs when two light atoms combine to make a heavier atom. Not all of the mass of the original atom is retained, and the unincorporated mass is released as energy.
Fusion differs from fission in which an atom is split apart releasing its mass as energy, and in the process creating and releasing radioactive material as well.
Both processes are explained by Einstein’s famous equation e= mc2.
NASA is apparently pursuing two possible nuclear thermal propulsion lines of research.
The first is at the Marshal Space Center in Huntsville Alabama where is exploring the viability of nuclear propulsion system technologies. Included in their research is work with a simulator which allows testing of technologies to be done with non-nuclear fuel.
The second approach is through the award of a NASA Innovative Advanced Concept (NIAC) grant to MSNW LLC headed by Dr. John Slough of the University of Washington
Dr. Slough and his MSNW team are working to develop a Fusion Driven rocket (FDR) which would employ a process whereby the energy created by fusion is released directly into the engine’s propellant. Current processes use fusion to create electricity which in turn is used to create the force necessary to convert the propellant to energy.
Quoting Dr. Slough from NASA’s website about the FDR:
“It employs a solid lithium propellant that requires no significant tankage mass. The propellant is rapidly heated and accelerated to high exhaust velocity (> 30 km/s), while having no significant physical interaction with the spacecraft thereby avoiding damage to the rocket and limiting both the thermal heat load and radiator mass. In addition, it is believed that the FDR can be realized with little extrapolation from currently existing technology . . . “
While NASA is taking steps to develop nuclear thermal propulsion and other propulsion technologies, the fact remain that none has been identified as the definitive replacement for the current system.