The idea of nuclear propulsion is to use Nuclear reactions like nuclear fusion or nuclear fission to produce enormous amounts of energy, which then can be converted into thermal or electrical energy. This energy can then be used to generate thrust, in order to provide propulsion and power sources.
NUCLEAR
REACTIONS: NUCLEAR FUSION AND FISSION: In Nuclear fusion, one or more nuclei
are combined to produce enormous energy, the same process by which our Sun
fuses Hydrogen atoms into Helium by a chain-reaction with other nuclei,
emitting Positrons and Neutrinos. This creates a difference in mass between the
Hydrogen and the Helium atoms which then gets converted into energy as by
Einstein's theory of special relativity which says that "The energy
produced by an object is equivalent to its mass times the speed-of-light
squared," i.e., E = mc^2. The mass of the Helium atom is less than the
combined mass of the Hydrogen atoms. The lost mass is converted into energy.
This happens because of extreme pressure and heat in Sun's core. At first two
protons fuse, creating an unstable atom but due to weak-nuclear force's Beta+
decay, one of the protons gets converted into a Neutron and the reaction
releases a Positron and an Electron-Neutrino. Then this atom (i.e., Deuterium)
fuses with another Proton to form a Helium-3 nucleus and releases a Gamma ray.
At last, two Helium-3 nuclei fuse to form a Helium-4 nuclei, which is a stable
atom and it also releases 2 Protons back into the Star's core. Whereas, in
nuclear fission, a heavy atomic nucleus like Uranium-235 is split into two or
more smaller nuclei, releasing a large amount of energy. This reaction is
initiated by a neutron, which causes the heavy nucleus to become unstable and
break-down. The process also releases extra neutrons which can lead to extended
reactions.
[Nuclear fission reaction]
[Nuclear fusion reaction]
ROCKET PROPULSION: Rocket propulsion is
a process in which the energy released by combustion of fuels is used to create
thrust by releasing them from a nozzle and propelling the rocket by Newton's
third law of motion. Newton's third law of motion says that every action has an
equal and opposite reaction. In a rocket, when the combusted gases come out,
they are pushed outward by the rocket and the reaction is that the gases push
the rocket in the opposite direction with the same amount of force as the rocket
did. This makes both the rocket and gases to accelerate towards their own
directions. This is done by Newton's second law of motion, which is, F = ma. It
says that acceleration is directly
proportional to force and inversely proportional to mass; Let us assume that
there is a rocket and it's mass is 1,00,000 kg and its lowest velocity is 1,800
m/s (in upward direction) and it takes 20 minutes to get into its highest
velocity, which is 70,560 m/s (in the upward direction). Now to calculate the
acceleration, we need to divide the later velocity – initial velocity by the
later time - initial time, which is (v2 - v1) / (t2 - t1) = (70,560 m/s - 1,800
m/s) / (1200 sec - 0 sec) = 68,760 m/s / 1,200 sec = 57.3 m/s^2. Now to
calculate the force, we need to use the equation, F = ma. Where m is the mass
and a is the acceleration. Now, F = ma = 57.3 * 1,00,000 = 57,30,000 N. Now let
us think that the rocket expels the thrust with a force of 57,30,000 N (the
same force at which the rocket is pushed), that means it is the same amount of
force with which the gases push the rocket. These forces are equal and opposite
due to Newton's third law of motion. (All these calculations are done
regardless of external forces and pushes like aerodynamic drag, Gravity, etc.).
[Liquid
Propellant Rocket propulsion system]
---NUCLEAR PROPULSION---
Nuclear
propulsion is a type of rocket propulsion in which the thrust isn't made by the
combustion of fuels but by converting nuclear energy into electrical or thermal
energy and use that energy to create thrust and use Newton's second and third
laws of motion to propel the rocket. Many private and government companies are
researching on such an engine. The main advantage of nuclear propulsion is its
efficiency. It can produce energies which are million times more than the
energy use to achieve the reaction. Especially the fusion reaction, but the
fusion reaction is extremely difficult to achieve because it requires extreme
pressures and temperatures and, in a rocket-propulsion system, there is already
a vast requirement for power! Whereas, nuclear fission reactions are much more
stable, controllable and efficient. They can even create a self-sustaining
reaction which can generate much more energy than the initial input. However,
nuclear fission propulsion does have its own disadvantages like:
*It
can't be used to launch a rocket from Earth due to its poor thrust-to-weight
ratio and radioactive output which can lead to environmental catastrophes.
*The
technology required in such a propulsion system is extremely complex and
difficult, especially about the shielding part and heat control.
*In
case of an accident, the consequences may include radioactive output in the
space which can create problems in later missions.
There
are three types of nuclear propulsion technologies on rockets:
1)
Nuclear-Thermal-Propulsion (NTP): In this type of Nuclear propulsion
technology, the reactor heats up a gas, like Hydrogen and then expels it
through the nozzle to produce thrust. It is double as efficient than the best
Chemical rockets. This allows for more acceleration, however, it can generate
the thrust for a short period of time than the NEP and requires significant
amount of fuel.
2)Nuclear-Electric-Propulsion
(NEP): In this type of Nuclear propulsion technology, the energy generated by a
Nuclear reactor is then converted into Electricity (by an energy conversion
system) which is then used to power electrical thrusters which then accelerate
ionized gases like Xenon to generate thrust. The thrust generated by a NEP
system is significantly less than the thrust generated by NTP but it can
generate thrust for a long period of time and requires less fuel than NTP.
3)Bimodal-Nuclear-Propulsion (BNP): In this type of Nuclear propulsion technology, a single reactor handles both NTP and NEP, based on the situation and state of the path and rocket design.
[Nuclear-Thermal-Propulsion]
[Nuclear-Electric-Propulsion]
USES
OF NUCLEAR REACTIONS IN INTERPLANETARY TRAVEL, OTHER THAN PROPULSION: Nuclear
reaction can be used in various other technologies like power generation on
Moon and Mars to sustain human life there and set up camps on Moon for missions
like Artemis missions.
---CONCLUSION---
Nuclear reaction technology is advancing beyond the realm of theory to become a practical and integral part of humanity's future in space. While still in a developing phase, this incredible power source holds the potential not only for rocket propulsion but also for sustaining human life and infrastructure on other celestial bodies. The current focus on highly controllable fission processes provides a reliable stepping stone. Recent reports from space agencies like NASA say that in 2025 only, General Atomics and NASA, announced the success of a test of nuclear fuel designed to withstand the extreme temperature and pressure required for a nuclear thermal propulsion reactor. Also, NASA is planning to settle the first Nuclear Reactor on Moon around 2030. With the discovery of Helium-3 on Moon (from deposits of Solar winds), the days of fusion reactors are also not too far.
The continued pursuit of nuclear propulsion, whether through NTP, NEP, or integrated BNP systems, will be crucial for the establishment of an interplanetary travel network. This technology requires innovation in safety, shielding, and system design. By overcoming through these hurdles, we will unlock the next era of deep-space exploration, powered by the forces that ignite the stars.
By: Bijoydeep Ghose, Batch 28