Radial in-flow particle bed nuclear rocket engine and method

A method comprising:

• during a first time period at a nuclear rocket engine:
• by a pump, pumping a propellant:
• from a propellant reservoir at a supply temperature;
• through a cold side of the pump;
• to a set of moderator coolant channels, extending axially within a moderator, to cool the moderator;
• to a hot side of the pump to operate the cold side of the pump;
• into a fuel bore of the moderator occupied by a fuel element in an axial direction parallel to the longitudinal axis of the fuel element;
• through a cold shell perforation of the fuel element in a radial direction;
• through a fuel bed of the fuel element comprising a set of nuclear fuel particles defining a set of interstitial volumes the propellant flows through to heat the propellant to a first outlet temperature;
• through a hot shell perforation of the fuel element in the radial direction;
• and
• out of the fuel element in the axial direction;
• and
• out of a thrust nozzle to produce a first thrust;
• and
• locating a reflector, arranged about a set of fuel elements and the moderator, at a first closed position to reflect neutrons toward the set of fuel elements to maintain a fission rate of the set of fuel elements above a threshold fission rate;
• during a second time period:
• locating the reflector at a second open position to release neutrons from the nuclear rocket engine and to reduce the fission rate of the set of fuel elements to below the threshold fission rate;
• by the pump, pumping the propellant:
• from the propellant reservoir at the supply temperature;
• through the cold side of the pump;
• to the set of moderator coolant channels to cool the moderator;
• to the hot side of pump to operate the cold side of the pump;
• through a cold shell perforation of the fuel element in the radial direction;
• through the fuel bed of the fuel element to heat the propellant to a second outlet temperature less than the first outlet temperature;
• through the hot shell perforation of the fuel element in the radial direction;
• out of the fuel element;
• and
• out of the thrust nozzle to produce a second thrust less than the first thrust.

A method comprising:

• during a first time period at a nuclear rocket engine:
• locating a reflector, arranged about a set of fuel elements, at a first angle to:
• reflect a first proportion of neutrons toward the set of fuel elements to maintain a first fission rate of the set of fuel elements above a threshold fission rate;
• and
• reflect a second proportion, less than the first proportion, of neutrons out of the nuclear rocket engine;
• by a pump, pumping a propellant:
• to a set of moderator coolant channels, extending axially within a moderator, to cool the moderator;
• through the set of fuel elements to heat the propellant to a first outlet temperature proportional to the first fission rate, the set of fuel elements extending axially within the moderator and isolated from the set of moderator coolant channels;
• and
• out of a thrust nozzle to produce a first thrust;
• and
• during a second time period:
• locating the reflector at a second angle to:
• reflect a third proportion of neutrons toward the set of fuel elements to reduce a second fission rate of the set of fuel elements to below the threshold fission rate;
• and
• reflect a fourth proportion, greater than the third proportion, of neutrons out of the nuclear rocket engine;
• by the pump, pumping the propellant:
• to the set of moderator coolant channels to cool the moderator;
• through the set of fuel elements to cool the set of fuel elements and to heat the propellant to a second outlet temperature less than the first outlet temperature and proportional to the second fission rate;
• and
• out of the thrust nozzle to produce a second thrust less than the first thrust.