We reside in an period of renewed area exploration, the place a number of companies are planning to ship astronauts to the Moon within the coming years. This shall 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 may take astronauts past Low Earth Orbit (LEO) and the Earth-Moon system require new applied sciences, starting from life assist and radiation shielding to energy and propulsion.
And relating to the latter, Nuclear Thermal and Nuclear Electrical Propulsion (NTP/NEP) is a prime contender!
NASA and the Soviet area program spent a long time researching nuclear propulsion throughout the House 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 aspect – that might 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 Part I growth. This new class of bimodal nuclear propulsion system makes use of a “wave rotor topping cycle” and will scale back transit instances to Mars to simply 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 certainly one of 14 chosen by the NAIC this yr for Part I growth, which features a US$12,500 grant to help in maturing the expertise and strategies concerned. Different proposals included modern sensors, devices, manufacturing strategies, energy techniques, and extra.
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Nuclear propulsion primarily comes down to 2 ideas, each of which depend on applied sciences which were 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 gasoline (plasma) that’s then channeled by nozzles to generate thrust.
A number of makes an attempt have been made to construct a take a look at this propulsion system, together with Undertaking Rover, a collaborative effort between the US Air Drive and the Atomic Power 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 functions. This finally led to the Nuclear Engine for Rocket Automobile Utility (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 diminished, resulting in its cancellation earlier than any flight exams could possibly 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 take a look at 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 area that ionizes and accelerates an inert gasoline (like xenon) to create thrust. Makes an attempt to develop this expertise embrace NASA’s Nuclear Programs Initiative (NSI) Undertaking Prometheus (2003 to 2005).
Each techniques have appreciable benefits over standard chemical propulsion, together with the next particular impulse (Isp) ranking, gasoline effectivity, and nearly limitless vitality density.
Whereas NEP ideas are distinguished for offering greater than 10,000 seconds of Isp, which means they’ll keep thrust for shut to a few hours, the thrust stage is kind of low in comparison with standard rockets and NTP.
The necessity for an electrical energy supply, says Gosse, additionally raises the problem of warmth rejection in area – the place thermal vitality conversion is 30-40 p.c below supreme circumstances.
And whereas NTP NERVA designs are the popular technique for crewed missions to Mars and past, this technique additionally has points offering sufficient preliminary and closing mass fractions for top delta-v missions.
This is the reason proposals that embrace each propulsion strategies (bimodal) are favored, as they might mix some great benefits of each. Gosse’s proposal requires a bimodal design based mostly on a stable core NERVA reactor that would offer a selected impulse (Isp) of 900 seconds, twice the present efficiency of chemical rockets.
Gosse proposed cycle additionally features a strain wave supercharger – or Wave Rotor (WR) – a expertise utilized in inner combustion engines that harnesses the strain waves produced by reactions to compress consumption air.
When paired with an NTP engine, the WR would use strain created by the reactor’s heating of the LH2 gasoline to compress the response mass additional. As Gosse guarantees, it will 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, mentioned Gosse, thrust ranges are enhanced even additional:
“Coupled with an NEP cycle, the responsibility cycle Isp can additional be elevated (1,800-4,000 seconds) with minimal addition of dry mass. This bimodal design permits the quick transit for manned missions (45 days to Mars) and revolutionizes the deep area exploration of our Photo voltaic System.”
Primarily based on standard 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 an alternative of years. This might considerably scale back the key 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 new reactor designs that would offer a gentle energy provide for long-duration floor missions the place photo voltaic and wind energy should not all the time accessible.
Examples embrace NASA’s Kilopower Reactor Utilizing Sterling Expertise (KRUSTY) and the hybrid fission/fusion reactor chosen for Part I growth by NASA’s NAIC 2023 choice.
These and different nuclear functions might sometime allow crewed missions to Mars and different areas in deep area, maybe ahead of we predict!
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