Nuclear propulsion (astronautics)

This article treats space Propulsion, for the systems of nuclear propulsion terrestrial or maritime, to see atomic Moteur.

The nuclear propulsion is the technique of use of the nuclear energy to obtain a space Propulsion more powerful or more effective.

Advantages

The energy density of the nuclear reactions (fission, fusion, annihilation matter-antimatter) is 10⁷ with 10⁹ higher than that of the chemical reactions. That makes it possible to consider enormous improvements of the specific Impulsion of the systems of propulsion. Indeed, l'

I_ {sp}

ideal can be expressed according to this density:

I_ {sp} = 144,22 \ sqrt E

where the impulse is in seconds and the density

E

in kJ /g.

However, there are innumerable technical difficulties in the effective coupling of nuclear energy with the propelling fluid ejected by the engine of the spaceship. For example, a chemical rocket propelled by an engine RL-10 functioning with the mixture LOX/LH2 recovers in kinetic energy more than 80% of the ideal energy of the chemical reaction between propellents. No concept of nuclear propulsion reaches this effectiveness.

Moreover, in the case of the thermal or electric (NTP) nuclear propulsion (NEP), the total energy density (energy brought back to the mass of all that is ejected) is very far from the ideal because this energy is used for heating or accelerating a great quantity of fluid. On the other hand, this defect does not apply to the concepts of propulsion ejecting only the products of the nuclear reaction concerned.

Classification

Variations

Electric nuclear propulsion

The field of the electric nuclear propulsion (NEP), in which a nuclear reactor is used only as energy source to feed from the ionic engines, raises technically only of the electric propulsion.

Nevertheless, certain concepts of vehicle use a bimodal propulsion : the operations in the strong fields of gravity (near planets) requiring a Rapport weight/thorough important are done using a thermal nuclear propulsion. Left the well of gravity, in the interplanetary transits, the nuclear reactor functions with a weaker mode, in cycle closed with radiator and turbine producing the power intended for the operation of an electric engine of better $I_ {sp}$ .

This type of hybridization can combine any kinds of nuclear and electric propulsions. The most common approach and to pair an engine in solid heart of type NERVA with an ionic propulsion. The profit brought strongly depends on the nature of the mission of the vehicle because it is based on a compromise between strong the poussée /weak impulse of mode NTP (report/ratio T/W > 0,1 and $I_ {sp}$ ≈ 900 S) and weak the poussée /strong impulse of mode NEP (T/W < 10^-3, $I_ {sp}$ of 2000 with 5000 S).

Increase LOX

|} A means of further increasing the push of a nuclear engine is to proceed to a kind of “Postcombustion” by oxygen injection in the conduit. The most known application is LANTR ( LOX Augmented Nuclear Thermal Rocket ) imagined by S. Borowski and using oxygen produced on the Moon (LUNOX). This additional push is done with the detriment of the specific impulse.

The obvious advantage of this capacity to vary the push and to be able to combine the weight ratio/thorough and the specific impulse in an optimal way according to the phases of the mission of the vehicle (in particular lunar takeoff, injection or ejection of the terrestrial orbit).

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