We reside in an period of renewed house exploration, the place a number of companies are planning to ship astronauts to the Moon within the coming years. This can be adopted within the subsequent decade with crewed missions to Mars by NASA and China, who could also be joined by different nations earlier than lengthy.
These and different missions that can take astronauts past Low Earth Orbit (LEO) and the Earth-Moon system require new applied sciences, starting from life help and radiation shielding to energy and propulsion.
And on the subject of the latter, Nuclear Thermal and Nuclear Electrical Propulsion (NTP/NEP) is a high contender!
NASA and the Soviet house program spent a long time researching nuclear propulsion in the course of the Area Race.
A number of years in the past, NASA reignited its nuclear program for the aim of creating bimodal nuclear propulsion – a two-part system consisting of an NTP and NEP component – that would allow transits to Mars in 100 days.
As a part of the NASA Revolutionary Superior Ideas (NIAC) program for 2023, NASA chosen a nuclear idea for Section I improvement. This new class of bimodal nuclear propulsion system makes use of a “wave rotor topping cycle” and will scale back transit occasions to Mars to only 45 days.
The proposal, titled “Bimodal NTP/NEP with a Wave Rotor Topping Cycle,” was put ahead by Prof. Ryan Gosse, the Hypersonics Program Space Lead on the College of Florida and a member of the Florida Utilized Analysis in Engineering (FLARE) staff.
Gosse’s proposal is one among 14 chosen by the NAIC this yr for Section I improvement, which features a US$12,500 grant to help in maturing the expertise and strategies concerned. Different proposals included revolutionary sensors, devices, manufacturing strategies, energy methods, and extra.
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Nuclear propulsion primarily comes down to 2 ideas, each of which depend on applied sciences which have been totally examined and validated.
For Nuclear-Thermal Propulsion (NTP), the cycle consists of a nuclear reactor heating liquid hydrogen (LH2) propellant, turning it into ionized hydrogen fuel (plasma) that’s then channeled by way of nozzles to generate thrust.
A number of makes an attempt have been made to construct a check this propulsion system, together with Mission Rover, a collaborative effort between the US Air Power and the Atomic Vitality Fee (AEC) that launched in 1955.
In 1959, NASA took over from the USAF, and this system entered a brand new section devoted to spaceflight purposes. This ultimately led to the Nuclear Engine for Rocket Car Software (NERVA), a solid-core nuclear reactor that was efficiently examined.
With the closing of the Apollo Period in 1973, this system’s funding was drastically decreased, resulting in its cancellation earlier than any flight assessments may very well be carried out. In the meantime, the Soviets developed their very own NTP idea (RD-0410) between 1965 and 1980 and carried out a single floor check earlier than this system’s cancellation.
Nuclear-Electrical Propulsion (NEP), then again, depends on a nuclear reactor to supply electrical energy to a Corridor-Impact thruster (ion engine), which generates an electromagnetic discipline that ionizes and accelerates an inert fuel (like xenon) to create thrust. Makes an attempt to develop this expertise embody NASA’s Nuclear Programs Initiative (NSI) Mission Prometheus (2003 to 2005).
Each methods have appreciable benefits over typical chemical propulsion, together with the next particular impulse (Isp) ranking, gasoline effectivity, and nearly limitless power density.
Whereas NEP ideas are distinguished for offering greater than 10,000 seconds of Isp, that means they’ll preserve thrust for shut to a few hours, the thrust degree is kind of low in comparison with typical rockets and NTP.
The necessity for an electrical energy supply, says Gosse, additionally raises the problem of warmth rejection in house – the place thermal power conversion is 30-40 p.c underneath preferrred circumstances.
And whereas NTP NERVA designs are the popular methodology for crewed missions to Mars and past, this methodology additionally has points offering enough preliminary and last mass fractions for prime delta-v missions.
For this reason proposals that embody each propulsion strategies (bimodal) are favored, as they might mix the benefits of each. Gosse’s proposal requires a bimodal design primarily based on a stable core NERVA reactor that would supply a particular impulse (Isp) of 900 seconds, twice the present efficiency of chemical rockets.
Gosse proposed cycle additionally features a stress wave supercharger – or Wave Rotor (WR) – a expertise utilized in inside combustion engines that harnesses the stress waves produced by reactions to compress consumption air.
When paired with an NTP engine, the WR would use stress created by the reactor’s heating of the LH2 gasoline to compress the response mass additional. As Gosse guarantees, this may ship thrust ranges similar to that of a NERVA-class NTP idea however with an Isp of 1400-2000 seconds. When paired with a NEP cycle, stated Gosse, thrust ranges are enhanced even additional:
“Coupled with an NEP cycle, the obligation cycle Isp can additional be elevated (1,800-4,000 seconds) with minimal addition of dry mass. This bimodal design allows the quick transit for manned missions (45 days to Mars) and revolutionizes the deep house exploration of our Photo voltaic System.”
Primarily based on typical propulsion expertise, a crewed mission to Mars might last as long as three years. These missions would launch each 26 months when Earth and Mars are at their closest (aka. a Mars opposition) and would spend a minimal of six to 9 months in transit.
A transit of 45 days (six and a half weeks) would scale back the general mission time to months as a substitute of years. This is able to considerably scale back the most important dangers related to missions to Mars, together with radiation publicity, the time spent in microgravity, and associated well being considerations.
Along with propulsion, there are proposals for brand spanking new reactor designs that would supply a gradual energy provide for long-duration floor missions the place photo voltaic and wind energy usually are not all the time out there.
Examples embody NASA’s Kilopower Reactor Utilizing Sterling Expertise (KRUSTY) and the hybrid fission/fusion reactor chosen for Section I improvement by NASA’s NAIC 2023 choice.
These and different nuclear purposes might sometime allow crewed missions to Mars and different places in deep house, maybe ahead of we expect!
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