Spacecraft

A spacecraft is a vehicle that travels through space using an external and passive method of propulsion, while a spaceship flies through space by means of active propulsion via an internal engine and propellant fuel. A spacecraft is a Type I technology used for sub-light impulse speeds before the invention of faster-than-light methods of travel. Initially spacecraft are for interplanetary travel but later can be used for close interstellar travel.

Spaceships can launch and land by themselves whereas spacecraft need launch-assist and land-assist mechanisms.

Launch-assist mechanisms

Skyhook	Non-rotating orbital tethers which are elongated satellites that have a low altitude docking platform; a zero-G core; a high altitude counterweight platform; the cables that bind the platforms together; and elevator cars that travel between the platforms
Orbital ring	As occupancy on a skyhook increases, it may become necessary to extend the structure of the skyhook in both directions along its orbital path, resulting in a complete ring encircling the entire planet or moon. With a tubular space runway, the spacecraft enters the runway and is accelerated inside it, similar to a vactrain.
Bolo	A Bolo is a rotating tether that rotates more than once per orbit. Its purpose is to either speed up or slow down a spacecraft that docks with it. The word is derived from bola which is a throwing weapon made of ball weights on the ends of interconnected cords, that spin around a centrifugal axis similar to the mechanics of a bolo.
Rotovator	Derived from rotor and elevator, rotovators are rotating tethers with a rotational direction such that the lower endpoint of the tether is moving slower than the orbital velocity of the tether and the upper endpoint is moving faster. This is a satellite that rotates like a wheel. As with the bolo, the energy given to the payload must be made up with rocket engines or mass drivers. This can also provide cheap surface transport.
Space elevator or beanstalk	An extremely strong cable (usually made of buckminsterfullerene) lowered from a geosynchronous satellite and anchored to the ground, often with a counterweight at the outer end to provide some extra tension and stability.
Launch loop	Launch loops use a stream of linked magnetic units to raise payloads above the atmosphere for launch, typically about 80km up. At the top the loop runs horizontally for thousands of kilometers. Can also help with evacuating a planet.
Space fountain	A space fountain consists of a looped stream of massive particles constrained in magnetic fields, supporting a tall structure. It is used for access to space, but tether technology or reaction drives or mass drivers must be used to place payloads in orbit. Space fountains are used to support megastructures.
Electromagnetic catapult or mass driver	Railguns use electromagnetic forces to accelerate projectiles to very high velocity using a pair of rails and a sliding armature. Can be fired from orbiting platforms. An advancement to this are gauss rifles or coilguns that use finely-controlled electromagnetic forces to accelerate a projectile. Accelerating magnets are arranged as four long 'rails' that can produce a complex, finely-controlled field within the barrel with no electrical contact between the rails and the projectile, unlike a railgun. See also: Mass driver
Space gun	A space gun, sometimes called a Verne gun because of its appearance in From the Earth to the Moon by Jules Verne, is a method of launching an object into Low Earth orbit, from where attached rockets could be fired or the objects could be "collected" by maneuverable orbiting satellites. This method was also used by Martians in The War of the Worlds to propel their spacecraft from Mars to Earth, not considered practical or even possible.
Beam-powered propulsion	Rockets and jets powered from the ground via a beam, for example gigawatt lasers

Land-assist mechanisms

Aerobraking	Allows a spacecraft to reduce the high point of an elliptical orbit by repeated brushes with the atmosphere at the low point of the orbit. Magnetic sails can also be deployed as interstellar brakes.
Aerocapture	Converts an incoming hyperbolic orbit to an elliptical orbit in one pass
Parachutes	Can land a probe on a planet or moon with an atmosphere, after a heat shield entry.
Airbags	Can soften the final landing.

First spacecraft used rocket or chemical engines that created a thrust reaction by expelling mass. Then electromagnetic, ion, plasma and pulse detonation engines came along until more advanced propulsion technology was invented. With field propulsion, no propellant is necessary but instead momentum of the spacecraft is changed by an interaction of the spacecraft with external force fields, such as gravitational and magnetic fields from stars and planets.

In the 1950s, the Orion Project proposed a nuclear rocket propelled by a succession of nuclear blast waves from a stream of atomic bombs. A spacecraft would drop a series of atomic bombs out its back, creating a series of powerful blasts of X-rays. This shock wave would then push the starship forward. It was estimated that an advanced version of Orion would weigh 8 million tons, with a diameter of 400 meters, and be powered by 1,000 hydrogen bombs. Eventually the Nuclear Test Ban Treaty of 1963, which prohibited aboveground testing of nuclear weapons. killed the idea of nuclear rockets.

The $100m Breakthrough Starshot is the first serious attempt to design and engineer an interstellar space probe that could reach the nearest star system within a generation. This involves a ground-based light beamer pushing ultra-light nanocrafts (miniature space probes attached to lightsails) to speeds of around 0.2c. Such a system would allow a flyby mission to reach Alpha Centauri in just over 20 years from launch. A number of hard engineering challenges remain to be solved before these missions can become a reality.

The lighthugger uses quantum mechanics.

Spacecraft Propulsion methods:

Magnetic sail	A Magnetic Drive Sail, magsail or winglee, acquires thrust or momentum via a light boost (like the solar wind) and then a ramscoop feeding a conversion drive to accelerate to 0.5c or more, then decelerate to 0.1c or less using magnetic braking. A magnetic sail could also thrust directly against planetary and solar magnetospheres.
Solar sail	Solar sails (or light sails or photon sails) use radiation pressure exerted by sunlight on large mirrors attached to a sail-like structure. Sunlight is eight times more intense in space than on the earth. High-energy laser beams could be used as an alternative light source to exert much greater force than would be possible using sunlight: this beamed energy propulsion is a beam sail or boost beam and the battery of lasers could be installed on the moon. One problem with a solar sail is that it is difficult to stop and reverse, since light moves outward from the sun. One possibility is to reverse the direction of the sail and use the destination star’s light pressure to slow down the spacecraft. Another possibility is to sail around the distant star, using the star’s gravity to create a slingshot effect for the return voyage. And yet another possibility is to land on a moon, build laser batteries, and then sail back on the star’s light and the laser beams from that moon.
Laser sail	Laser sails on unmanned craft use thin very large sails made of ultra-light reflective material. These are propelled by terawatt lasers
Maser sail	Maser sails use microwave laser beams, or masers, for propulsion, and consist of a thin mesh capable of interacting with the longer wavelength of these beams.
StarChip nanocraft	StarChip is a centimeter-sized, gram-scale, early interstellar spacecraft designed for journeys to nearby stars. It's a robotic nanocraft fitted with light sails, traveling at speeds of up to 20% of the speed of light, taking between 20 and 30 years to reach a star system. Each space probe nanocraft carries: Sub-gram scale digital cameras Sub-gram scale processors Sub-gram scale photon thrusters with 1W diode lasers A 150 mg atomic battery, powered by plutonium-238 or americium-241 Light sail no larger than 4 by 4 meters Laser communicator with data rates 2.6-15 baud per watt of transmitted power The StarChip can also use the slingshot effect, a gravity-assist maneuver that involves sending a spacecraft around a planet, like a rock from a slingshot, thereby using the planet’s gravity to increase the spacecraft’s speed. It's also possible to send the microchip spaceship around Jupiter’s magnetic field, which is 20,000 times greater than the earth’s field, accelerating the nanostarship with the same magnetic force that is used to hurl subatomic particles to trillions of electron volts in our atom smashers.
Bussard ramjet	This is a ramjet fusion rocket engine capable of interstellar travel, using electromagnetic fields as a ramscoop to collect and compress hydrogen from the interstellar medium to achieve thermonuclear fusion. The scoop would have to be over 150 km in order to collect enough hydrogen, so it would have to be assembled in space. The magnetic field then directs the energy as rocket exhaust opposite to the intended direction of travel, thereby accelerating the vessel. Bussard calculated that if a 1,000-ton ramjet engine can maintain the acceleration of 32 feet per second squared (or the gravity felt on the earth), then it will approach 0.77c in just one year. Since the ramjet engine can run forever due to the inexhaustible supply of hydrogen in deep space, it could theoretically leave our galaxy and reach the Andromeda galaxy, 2,000,000 light-years from earth, in just 23 years (notwithstanding the time dilation issue of millions of years passing on earth but the astronauts aging only 23 years).
Electric sail	An electric solar wind sail uses the dynamic pressure of the solar wind as a source of thrust. It creates a "virtual" sail by using small wires to form an electric field that deflects solar wind protons and extracts their momentum. This "e-sail" gets its momentum from solar wind ions, whilst a solar sail is propelled by photons.
Antimatter Ship	These release anti-hydrogen so that it interacts with uranium238 on an ablated light sail to produce neutrons and emissions that leave the sail at enormous speeds. The push is essentially a nuclear-stimulated ablation. An antimatter rocket engine would work by dropping a steady stream of antimatter particles down the rocket chamber, where it combines with ordinary matter with a massive 100% efficient release of energy. The explosive gas is then shot out one end of the chamber, creating thrust. Antimatter may occur naturally around the outer planets, in the asteroid belt, or the Van Allen radiation belts around Earth.
Reactionless and antigravity drives	These are anti-gravity and perpetual motion propulsion systems requiring the gravitational polarization of matter. Positive mass is attracted towards the Earth, and negative mass is repelled. A negative mass at rest beside a positive mass would begin to accelerate. The negative mass (which repels all matter) would push on the positive mass, but the positive mass (which attracts all matter) would pull on the negative mass. If the two objects weigh the same, they will chase each other and will neither separate nor collide. Energy and momentum is conserved, and the net energy cost would be zero. For high spacecraft accelerations, compact masses with densities like neutron stars or black holes are used. A Special Relativistic Antigravity Machine involves gravitational and electric fields. In electromagnetism, charge is surrounded by a spherically symmetric electric field. In gravitation, mass is surrounded by a spherically symmetric gravity field. Much as a magnetic field is due to the motion of an electric charge or current flow, a moving mass or mass current will give rise to a new kind of gravity field called a protational field. Accelerating a mass flow through the machine would result in a constantly increasing protational field inside, which will create a gravity field to cancel the field of the Earth. A General Relativistic Antigravity Machine makes use of mass in a flat spacetime which causes a curvature, and that a rotating mass causes spacetime to rotate too. A rotating torus of dense mass will create a force in the direction of the motion, equivalent to a gravity field which cancels the gravity field of the Earth. An Inertia Redistribution Antigravity Machine uses the tensor quantity of inertia. It redistributes inertial mass so that some of it is pointing in new directions. If the machine makes the starship’s mass heavier in the horizontal plane and proportionately lighter in the vertical plane, a relatively tiny amount of force applied vertically would cause relatively large accelerations in that direction, with inertia being conserved. An inertialess spacecraft must have its engine act upon every atom of the vessel so that it can start and stop almost instantaneously. With no forward inertia, people would not be thrown from their seats, and sharp angle turns and hairpin bends would have no effects on occupants.
Electromagnetic drives	The electromagnetic drive or EmDrive is a perpetual motion reactionless propulsion system that generates thrust without fuel by converting electrical energy via microwaves. Forces are created by reflecting microwaves between opposite walls of a cavity, achieving thrust. The cavity is cone-shaped, providing unequal force between the walls. No microwaves or anything else leaves the device, and so it is considered reactionless. A prototype consisted of a cone-shaped hollow engine set inside a highly shielded vacuum chamber where microwaves are fired. Detectable thrust may not have been coming from the engine itself, originating from another source such as the interaction between engine cables and the Earth’s magnetic field.
Direct Fusion Drive	Direct Fusion Drive (DFD) is a low radioactivity, nuclear fusion rocket engine designed to produce both thrust and electric power for interplanetary spacecraft. There is no intermediary electricity-generating step. Adding propellant to the plasma flow results in it functioning like an ion thruster. It can produce between 5–10 Newtons thrust per each MW of generated fusion power, propelling a spacecraft with a mass of about 1,000 kg to Pluto in 4 years, Mars in 4 months and Titan in 2.6 years.
Gravity Catapult	Freeman Dyson proposed a Contact Binary Catapult. A spacecraft approaches a binary white dwarf system where they are orbiting each other at close range. By swinging in very near to one star on the proper trajectory, the spacecraft benefits from gravitational slingshot or Newtonian "gravity whip" effect, reaching a velocity of 0.7c. A Black Hole Catapult requires a stellar mass rotating black hole, then travel around it in the direction of spin very near to the equator, with the black hole's rotational energy converted to linear kinetic energy of the spacecraft. Velocity would be extreme, as would the tidal forces, so advanced dampening technology would be needed. A Neutron Star Catapult is also possible, with similar effects. This consists of a rotating torus of dense matter (such as neutronium) turning inside out like a smoke ring. A spacecraft fired through the center of the massive hoop could be kicked up to very high velocities depending upon the rotational energy of the torus.