Interstellar travel refers to the currently theoretical idea of interstellar probes or crewed spacecraft moving between stars or planetary systems in a galaxy. Interstellar travel would be much more difficult than interplanetary spaceflight. Whereas the distances between the planets in the Solar System are less than 30 astronomical units (AU), the distances between stars are typically hundreds of thousands of AU, and usually expressed in light-years. Because of the vastness of those distances, non-generational interstellar travel based on known physics would need to occur at a high percentage of the speed of light; even so, travel times would be long, at least decades and perhaps millennia or longer.
Interplanetary spaceflight or interplanetary travel is the crewed or uncrewed travel between stars and planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System. Uncrewed space probes have flown to all the observed planets in the Solar System as well as to dwarf planets Pluto and Ceres, and several asteroids. Orbiters and landers return more information than fly-by missions. Crewed flights have landed on the Moon and have been planned, from time to time, for Mars and Venus. While many scientists appreciate the knowledge value that uncrewed flights provide, the value of crewed missions is more controversial. Science fiction writers propose a number of benefits, including the mining of asteroids, access to solar power, and room for colonization in the event of an Earth catastrophe.
A nuclear thermal rocket (NTR) is a type of thermal rocket where the heat from a nuclear reaction, often nuclear fission, replaces the chemical energy of the propellants in a chemical rocket. In an NTR, a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor and then expands through a rocket nozzle to create thrust. The external nuclear heat source theoretically allows a higher effective exhaust velocity and is expected to double or triple payload capacity compared to chemical propellants that store energy internally.
A nuclear salt-water rocket (NSWR) is a theoretical type of nuclear thermal rocket which was designed by Robert Zubrin. In place of traditional chemical propellant, such as that in a chemical rocket, the rocket would be fueled by salts of plutonium or 20 percent enriched uranium. The solution would be contained in a bundle of pipes coated in boron carbide. Through a combination of the coating and space between the pipes, the contents would not reach critical mass until the solution is pumped into a reaction chamber, thus reaching a critical mass, and being expelled through a nozzle to generate thrust.
In a traditional nuclear photonic rocket, an onboard nuclear reactor would generate such high temperatures that the blackbody radiation from the reactor would provide significant thrust. The disadvantage is that it takes much power to generate a small amount of thrust this way, so acceleration is very low. The photon radiators would most likely be constructed using graphite or tungsten. Photonic rockets are technologically feasible, but rather impractical with current technology based on an onboard nuclear power source.
A fusion rocket is a theoretical design for a rocket driven by fusion propulsion that could provide efficient and sustained acceleration in space without the need to carry a large fuel supply. The design requires fusion power technology beyond current capabilities, and much larger and more complex rockets.
An antimatter rocket is a proposed class of rockets that use antimatter as their power source. There are several designs that attempt to accomplish this goal. The advantage to this class of rocket is that a large fraction of the rest mass of a matter/antimatter mixture may be converted to energy, allowing antimatter rockets to have a far higher energy density and specific impulse than any other proposed class of rocket.
Nuclear pulse propulsion or external pulsed plasma propulsion is a hypothetical method of spacecraft propulsion that uses nuclear explosions for thrust. It originated as Project Orion with support from DARPA, after a suggestion by Stanislaw Ulam in 1947. Newer designs using inertial confinement fusion have been the baseline for most later designs, including Project Daedalus and Project Longshot.
Antimatter-catalyzed nuclear pulse propulsion is a variation of nuclear pulse propulsion based upon the injection of antimatter into a mass of nuclear fuel to initiate a nuclear chain reaction for propulsion when the fuel does not normally have a critical mass.
Project Orion was a study conducted between the 1950s and 1960s by the United States Air Force, DARPA, and NASA for the purpose of identifying the efficacy of a starship directly propelled by a series of explosions of atomic bombs behind the craft via nuclear pulse propulsion. Early versions of this vehicle were proposed to take off from the ground; later versions were presented for use only in space. Six non-nuclear tests were conducted using models. The project was eventually abandoned for multiple reasons, such as the Partial Test Ban Treaty, which banned nuclear explosions in space, as well as concerns over nuclear fallout.
Nuclear propulsion includes a wide variety of propulsion methods that use some form of nuclear reaction as their primary power source. The idea of using nuclear material for propulsion dates back to the beginning of the 20th century. In 1903 it was hypothesized that radioactive material, radium, might be a suitable fuel for engines to propel cars, planes, and boats. H. G. Wells picked up this idea in his 1914 fiction work The World Set Free.
An antimatter weapon is a theoretically possible device using antimatter as a power source, a propellant, or an explosive for a weapon. Antimatter weapons are currently too costly and unreliable to be viable in warfare, as producing antimatter is enormously expensive, the quantities of antimatter generated are very small, and current technology has great difficulty containing antimatter, which annihilates upon touching ordinary matter.
An interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar space, which is typically defined as the region beyond the heliopause. It also refers to probes capable of reaching other star systems.
TMK was the designation of a Soviet space exploration project to send a crewed flight to Mars and Venus without landing.
A pure fusion weapon is a hypothetical hydrogen bomb design that does not need a fission "primary" explosive to ignite the fusion of deuterium and tritium, two heavy isotopes of hydrogen used in fission-fusion thermonuclear weapons. Such a weapon would require no fissile material and would therefore be much easier to develop in secret than existing weapons. Separating weapons-grade uranium (U-235) or breeding plutonium (Pu-239) requires a substantial and difficult-to-conceal industrial investment, and blocking the sale and transfer of the needed machinery has been the primary mechanism to control nuclear proliferation to date. Due to its not requiring a fission primary explosive to initiate a fusion reaction, the pure fusion weapon would also have greatly increased potential yield over current thermonuclear weapons.
AIMStar was a proposed antimatter-catalyzed nuclear pulse propulsion craft that uses clouds of antiprotons to initiate fission and fusion within fuel pellets. A magnetic nozzle derives motive force from the resulting explosions. The design was studied during the 1990s by Penn State University. The craft was designed to reach a distance on the order of 10,000 AU from the Sun, with a travel time of 50 years, and a coasting velocity of approximately 960 km/s after the boost phase. The probe would be able to study the interstellar medium as well as reach Alpha Centauri. The project would require more antimatter than we are capable of producing. In addition, some technical hurdles need to be surpassed before it would be feasible.
For the assassination attempt on Hitler, see Operation Valkyrie
Nuclear power in space is the use of nuclear power in outer space, typically either small fission systems or radioactive decay for electricity or heat. Another use is for scientific observation, as in a Mössbauer spectrometer. The most common type is a radioisotope thermoelectric generator, which has been used on many space probes and on crewed lunar missions. Small fission reactors for Earth observation satellites, such as the TOPAZ nuclear reactor, have also been flown. A radioisotope heater unit is powered by radioactive decay and can keep components from becoming too cold to function, potentially over a span of decades.
Direct Fusion Drive (DFD) is a conceptual low radioactivity, nuclear-fusion rocket engine designed to produce both thrust and electric power for interplanetary spacecraft. The concept is based on the Princeton field-reversed configuration reactor invented in 2002 by Samuel A. Cohen, and is being modeled and experimentally tested at Princeton Plasma Physics Laboratory, a US Department of Energy facility, and modeled and evaluated by Princeton Satellite Systems. As of 2018, the concept has moved on to Phase II to further advance the design.
