A "nuclear lightbulb" is the nickname for a specific type of nuclear-powered rocket engine or energy source. In a nuclear lightbulb, the coolant/propellant is separated from the nuclear fuel by a quartz wall. Although the reactor reaches temperatures of approximately 25,000°C (45,030°), most of the radiation is in the hard ultraviolet range, which quartz is practically transparent to. Therefore the quartz wall does not melt or boil away, by the propellant, probably hydrogen, does. Alternatively, a nuclear lightbulb could be used to generate electricity through photovoltaics (solar cells).
Because nuclear energy permits many more joules per gram of fuel than chemical energy sources, a nuclear lightbulb would be a superior form of rocket propulsion to the type used today. But due to the uneasiness about sending nuclear materials into space, this technology has never been used in space. Several experimental designs have been built and run successfully.
A great advantage of a nuclear lightbulb-powered rocket would be its complete reusability. Only the nuclear fuel would need to be replaced. Because of the power density of uranium pellets, which would be the fuel, the ship could have a payload making up 30% of its total weight! In traditional chemical-powered spaceflight, this is unheard of, where the payload makes up 10% or less of total mass. One plausible design that could be built with present-day technology for similar cost to Space Shuttle booster rockets would have a payload of approximately two million pounds.
Not only would a nuclear lightbulb be more efficient for igniting hydrogen fuel, it would also be capable of providing power for numerous uses on board the ship, by using photovoltaics. This would permit orders of magnitude more power than spacecraft designs based on solar or chemical power plants. Enough power for people to even live in space comfortably, as long as enough uranium is brought along.
