We live in an era of re-exploration of space, with multiple agencies planning to send astronauts there the moon in the coming years. This is to be followed by manned missions in the next decade Mars by NASA and China, which other nations may soon join.
These and other missions that will take astronauts beyond Low Earth Orbit (LEO) and the Earth-Moon system will require new technologies ranging from life support and radiation protection to power and propulsion.
And when it comes to the latter Nuclear thermal and nuclear electric propulsion (NTP/NEP) is a top candidate!
NASA and the Soviet space program spent decades researching nuclear propulsion during the space race.
A few years ago NASA resumed its nuclear program for the purpose of developing a bimodal nuclear propulsion system – a two-part system consisting of an NTP and an NEP element – that could enable transits Mars in 100 days.
As part of the Innovative advanced concepts from NASA (NIAC) program for 2023, NASA selected a nuclear concept for Phase I development. This new class of bimodal nuclear propulsion system uses a “Wave rotor topping cycle” and could shorten the transit time to Mars to just 45 days.
The proposal entitled “Bimodal NTP/NEP with a wave rotor topping cycle,” was presented by Prof. Ryan Gosse, Area Director of the Hypersonics program at the University of Florida and a member of the Florida Applied Research in Engineering (FLARE) team.
Gosse’s proposal is one of 14 selected by NAIC this year for Phase I development, which includes a $12,500 grant to help mature the technology and methods involved. Other proposals included innovative sensors, instrumentation, manufacturing techniques, power systems and more.
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Nuclear propulsion is essentially based on two concepts, both based on thoroughly tested and validated technologies.
In Nuclear-Thermal Propulsion (NTP), the cycle consists of a nuclear reactor that heats liquid hydrogen (LH2) as a propellant and converts it into ionized hydrogen gas (plasma), which is then passed through nozzles to create thrust.
Several attempts have been made to test-build this propulsion system, including Project Rovera collaboration between the US Air Force and the Atomic Energy Commission (AEC) established in 1955.
In 1959, NASA acquired the USAF and the program entered a new phase dedicated to space applications. This eventually led to the Nuclear engine for rocket vehicle application (NERVA), a successfully tested nuclear reactor.
With the conclusion of the Apollo era in 1973, funding for the program was drastically reduced, leading to its cancellation before flight tests could be conducted. Meanwhile, the Soviets developed their own NTP concept (RD-0410) between 1965 and 1980 and conducted a single ground test prior to the program’s cancellation.
Nuclear-Electric Propulsion (NEP), on the other hand, relies on a nuclear reactor to power a Hall effect engine (ion engine) that creates an electromagnetic field that ionizes and accelerates an inert gas (like xenon) to produce thrust. Attempts to develop this technology include those by NASA Nuclear System Initiative (NSI) Project Prometheus (2003 to 2005).
Both systems have significant advantages over conventional chemical propulsion, including a higher specific impulse (Isp) power rating, fuel efficiency and virtually unlimited energy density.
While NEP concepts excel at delivering more than 10,000 seconds of Isp, meaning they can sustain thrust for nearly three hours, the level of thrust is fairly low compared to conventional rockets and NTP.
The need for an electrical power source, Gosse says, also raises the issue of heat dissipation in space — where thermal energy conversion is 30 to 40 percent under ideal circumstances.
And while NTP NERVA designs are the preferred method for manned missions to Mars and beyond, this method also struggles to provide adequate initial and final mass fractions for high delta-V missions.
For this reason, proposals are favored that include both types of drive (bimodal), as they would combine the advantages of both. Gosse’s proposal calls for a bimodal design based on a full-core NERVA reactor that would deliver a specific impulse (Isp) of 900 seconds, twice the performance of current chemical rockets.
Gosse’s proposed cycle also includes a pressure wave supercharger – or Wave Rotor (WR) – a technology used in internal combustion engines that uses the pressure waves generated by reactions to compress the intake air.
In conjunction with an NTP engine, the WR would use the pressure created by the heating of the LH2 fuel in the reactor to further compress the reaction mass. As Gosse promises, this will deliver thrust values comparable to a NERVA-class NTP concept, but with an Isp of 1400-2000 seconds. In combination with a NEP cycle said Gosse, the thrust values will be improved even further:
“Coupled with a NEP cycle, the duty cycle Isp can be further increased (1,800-4,000 seconds) with minimal addition of dry matter. This bimodal design enables fast transit for manned missions (45 days to Mars) and revolutionizes the exploration of space in our solar system.”
Based on conventional propulsion technology, a manned mission to Mars could take up to three years. These missions would launch every 26 months, when Earth and Mars are closest (aka Mars opposition), and would travel at least six to nine months.
A transit of 45 days (six and a half weeks) would reduce the total mission time to months instead of years. This would greatly reduce the main risks associated with missions to Mars, including radiation exposure, time in microgravity, and associated health concerns.
In addition to propulsion, there are proposals for new reactor designs that would provide constant power for long-duration surface missions where solar and wind power are not always available.
Examples are those of NASA Kilopower reactor with Sterling technology (KRUSTY) and the hybrid fission/fusion reactor selected for Phase I development by NASA’s NAIC 2023 selection.
These and other nuclear applications could one day enable manned missions to Mars and other places in space, maybe sooner than we think!
This article was originally published by universe today. read the original item.
