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The Valkyrie is a theoretical spacecraft designed by Charles Pellegrino and Jim Powell (a physicist at Brookhaven National Laboratory). The Valkyrie is theoretically able to accelerate to 92% the speed of light and decelerate afterward, carrying a small human crew to another star system. [1]
The Valkyrie's high performance is attributable to its innovative design. Instead of a solid spacecraft with a rocket at the back, Valkyrie is built more like a cable car train, with the crew quarters, fuel tanks, radiation shielding, and other vital components being pulled between front and aft engines on long tethers. This greatly reduces the mass of the ship, because it no longer requires heavy structural members and radiation shielding. This is a considerable advantage because in a rocket every extra kilogram of payload (dry mass) will require a corresponding extra amount of propellant or fuel.
The Valkyrie would have a crew module trailing 10 kilometers behind the engine. A small 20-cm-thick tungsten shield would hang 100 meters behind the engine, to help protect the trailing crew module from its harmful radiation. [2] The fuel tank might be placed between the crew module and the engine, to further protect it. At the trailing end of the ship would be a second engine, which the ship would use to decelerate. The forward engine and the tank holding its fuel supply might be jettisoned before deceleration, to reduce fuel consumption. [1] The tether system requires that the elements of the ship must be moved "up" or "down" the tethers depending on flight direction.
Initially, the Valkyrie's engine would work by using small quantities of antimatter to initiate an extremely energetic fusion reaction. A magnetic coil captures the exhaust products of this reaction, expelling them with an exhaust velocity of 12-20% the speed of light (35,000-60,000 km/s). As the spacecraft approaches 20% the speed of light, more antimatter is fed into the engines until it switches over to pure matter-antimatter annihilation. [2] It will use this mode to accelerate the remainder of the way to .92 c. Pellegrino estimates that the ship would require 100 tons of matter and antimatter to reach 0.1-0.2c, with an undetermined excess of matter to ensure the antimatter is efficiently utilized. To reach a speed of .92 c and decelerate afterward, Valkyrie would require a mass ratio of 22 (or 2200 tons of fuel for a 100-ton spacecraft). [1]
At such high speeds, incident debris would be a major hazard. While accelerating, Valkyrie uses a device that combines the functions of a particle shield and a liquid droplet radiator. Waste heat is dumped into liquid droplets that are cast out in front of the ship. As the ship accelerates the droplets (now cool) effectively fall back into the ship, so the system is self-recycling. During deceleration, the ship will be protected by ultra-thin umbrella shields, augmented by a dust shield, possibly made by grinding up pieces of the discarded first stage. [1]
The chief feasibility issue of Valkyrie [ citation needed ] (or for any antimatter-beam drive) lies in its requirement of tons of antimatter fuel. Antimatter cannot be produced at an efficiency of more than 50% (that is to say, to produce one gram of antimatter requires twice as much energy as you would get from annihilating that gram with a gram of matter). Since half a kilogram of antimatter would yield 9×1016 J if annihilated with an equal amount of matter, [3] this quickly adds up to enormous energy requirements for its production. To produce the 50 tons of antimatter Valkyrie would require 1.8×1022 J. This is the same amount of energy that the entire human race currently uses in about forty years.
This may be solved by creating a truly enormous power plant for the antimatter factory, probably in the form of a vast array of solar panels with a combined area of millions of square kilometers or many fusion reactors. Alternately the antimatter-fusion hybrid drive the Valkyrie uses to accelerate up to 0.2 c would require much less antimatter and, with an exhaust velocity of 30–60,000 km·s−1, still compares quite favorably with competing engines such as the inertial confinement pulse drive used by Project Daedalus or Project Orion. The Valkyrie's lightweight construction could also be applied to a wide variety of space vehicles.
By using tethers there is no rigidity between ship elements and engines. Without active acceleration or thrust to pull and straighten the tethers the slightest imbalance, excess force, or the moving of the ship elements into different flight configurations pose a danger for collisions between ship elements and engines. As long term space flight at interstellar velocities causes erosion due to collision with particles, gas, dust and micrometeorites the tethers are literally lifelines. [4] [5] Changing course or turning the ship requires re-positioning or aligning every ship element and presumably consumes more fuel in doing so.
As the liquid droplet radiators (LDR) are deployed on the other side of propulsion and the main body, the droplets and the collectors are exposed to the other half of the heat energy from the gamma radiation from the antimatter annihilation. If the total area of the collectors are larger than the radiation shield the LDR would serve to cool itself rather than the shield for the ship's main components. [6]
A superficially-similar interstellar spacecraft is featured in the movie Avatar . [7]
Interstellar travel is the hypothetical travel of spacecraft between star systems. Due to the vast distances between the Solar System and nearby stars, interstellar travel is not practicable with current propulsion technologies.
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, Venus and Mercury. 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.
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric entry.
A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. Existing and proposed mass drivers use coils of wire energized by electricity to make electromagnets, though a rotary mass driver has also been proposed. Sequential firing of a row of electromagnets accelerates the payload along a path. After leaving the path, the payload continues to move due to momentum.
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.
The Bussard ramjet is a theoretical method of spacecraft propulsion for interstellar travel. A fast moving spacecraft scoops up hydrogen from the interstellar medium using an enormous funnel-shaped magnetic field ; the hydrogen is compressed until thermonuclear fusion occurs, which provides thrust to counter the drag created by the funnel and energy to power the magnetic field. The Bussard ramjet can thus be seen as a ramjet variant of a fusion rocket.
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.
Spaceflight is an application of astronautics to fly objects, usually spacecraft, into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in orbit around Earth, but also includes space probes for flights beyond Earth orbit. Such spaceflights operate either by telerobotic or autonomous control. The first spaceflights began in the 1950s with the launches of the Soviet Sputnik satellites and American Explorer and Vanguard missions. Human spaceflight programs include the Soyuz, Shenzhou, the past Apollo Moon landing and the Space Shuttle programs. Other current spaceflight are conducted to the International Space Station and to China's Tiangong Space Station.
Project Orion was a study conducted in the 1950s and 1960s by the United States Air Force, DARPA, and NASA into the viability of a nuclear pulse spaceship that would be directly propelled by a series of atomic explosions behind the craft. Early versions of the vehicle were proposed to take off from the ground; later versions were presented for use only in space. The design effort took place at General Atomics in San Diego, and supporters included Wernher von Braun, who issued a white paper advocating the idea. Non-nuclear tests were conducted with models, but the project was eventually abandoned for several reasons, including the 1963 Partial Test Ban Treaty, which banned nuclear explosions in space, amid concerns over nuclear fallout.
Relativistic rocket means any spacecraft that travels close enough to light speed for relativistic effects to become significant. The meaning of "significant" is a matter of context, but often a threshold velocity of 30% to 50% of the speed of light is used. At 30% c, the difference between relativistic mass and rest mass is only about 5%, while at 50% it is 15%, ; so above such speeds special relativity is needed to accurately describe motion, while below this range Newtonian physics and the Tsiolkovsky rocket equation usually give sufficient accuracy.
Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible uncrewed interstellar probe. Intended mainly as a scientific probe, the design criteria specified that the spacecraft had to use existing or near-future technology and had to be able to reach its destination within a human lifetime. Alan Bond led a team of scientists and engineers who proposed using a fusion rocket to reach Barnard's Star 5.9 light years away. The trip was estimated to take 50 years, but the design was required to be flexible enough that it could be sent to any other target star.
An orbital spaceflight is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee around 80 kilometers (50 mi); this is the boundary of space as defined by NASA, the US Air Force and the FAA. To remain in orbit at this altitude requires an orbital speed of ~7.8 km/s. Orbital speed is slower for higher orbits, but attaining them requires greater delta-v. The Fédération Aéronautique Internationale has established the Kármán line at an altitude of 100 km (62 mi) as a working definition for the boundary between aeronautics and astronautics. This is used because at an altitude of about 100 km (62 mi), as Theodore von Kármán calculated, a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift from the atmosphere to support itself.
In spaceflight an orbit insertion is an orbital maneuver which adjusts a spacecraft’s trajectory, allowing entry into an orbit around a planet, moon, or other celestial body. An orbit insertion maneuver involves either deceleration from a speed in excess of the respective body's escape velocity, or acceleration to it from a lower speed.
ICAN-II was a proposed crewed interplanetary spacecraft that used the antimatter-catalyzed micro-fission (ACMF) engine as its main form of propulsion. The spacecraft was designed at Penn State University in the 1990s as a way to accomplish a crewed mission to Mars. The proposed ACMF engine would require only 140 nanograms of antiprotons in conjunction with traditional fissionable fuel sources to allow a one-way transit time to Mars of 30 days. This is a considerable improvement over many other forms of propulsion that can be used for interplanetary missions, due to the high thrust-to-weight ratio and specific impulse of nuclear fuels. Some downsides to the design include the radiation hazards inherent to nuclear pulse propulsion, as well as the limited availability of the antiprotons used to initialize the nuclear fission reaction. Even the small amount required by the ACMF engine is equal to the total antimatter production at the facilities CERN and Fermilab over many years, although these create antimatter only as a byproduct of physics experiments, not as a goal. ICAN-II is similar to the Project Orion design put forth by Stanislaw Ulam in the late 1950s. The Orion was intended to be used to send humans to Mars and Venus by 1968. The ICAN-II also, in a sense, utilizes nuclear "bombs" for thrust. However, instead of regular fission bombs like the Orion would utilize, ICAN-II uses what are, essentially, many tiny hydrogen bombs, set off by a stream of anti-protons. Ecological concerns would probably require that ICAN-II be assembled in space.
Field propulsion is the concept of spacecraft propulsion where 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. Proposed drives that use field propulsion are often called a reactionless or propellantless drive.
In astronautics, a black hole starship is the theoretical concept of a starship capable of interstellar travel using a black hole as an energy source for spacecraft propulsion. The concept was first discussed in science fiction, notably in the book Imperial Earth by Arthur C. Clarke, and in the work of Charles Sheffield, in which energy extracted from a Kerr–Newman black hole is described as powering the rocket engines in the story "Killing Vector" (1978).
Space travel under constant acceleration is a hypothetical method of space travel that involves the use of a propulsion system that generates a constant acceleration rather than the short, impulsive thrusts produced by traditional chemical rockets. For the first half of the journey the propulsion system would constantly accelerate the spacecraft toward its destination, and for the second half of the journey it would constantly decelerate the spaceship. Constant acceleration could be used to achieve relativistic speeds, making it a potential means of achieving human interstellar travel. This mode of travel has yet to be used in practice.
The liquid droplet radiator (LDR) or previously termed liquid droplet stream radiator is a proposed lightweight radiator for the dissipation of waste heat generated by power plants, propulsion or spacecraft systems in space.