The photon torpedo, an imaginary weapon of science fiction, is a space torpedo armed with a matter/antimatter bomb. The concept is frequently mentioned within the fictional Star Trek, where these weapons are often part of a starship's and space station's armaments.
Photon torpedoes are most useful for combat while ships are engaged in warp speed travel, as phasers, which are confined to the speed of light, are not generally usable. The Starfleet Technical Manual does list a number of ways a phaser can be used at greater-than-light speeds, though, as several television episodes have violated the prior "rule."
Starfleet, the military/exploratory arm of Federation, uses a number of different versions of the photon torpedo with various guided, un-guided, and high-speed versions. The Mark IV and Mark V torpedoes are micro torpedoes that are used aboard small ships like Danube class runabouts and shuttles.
The photon torpedo was first introduced during the second season of Star Trek: The Original Series. During the run of DS9, photon torpedoes began to be replaced by more powerful quantum torpedoes, which have also been used in the more recent Star Trek films. The Romulans have never used photon torpedoes, instead relying on plasma torpedoes.
Star Trek: Voyager had an ongoing story of a limited supply of photon torpedoes as they were impossible to replicate. Of the 40 torpedoes Voyager was stated as carrying, 93 were used in the course of the series, implying that this problem was somehow overcome off-screen. This is further supported by the fact that the self-replicating mines used in the Star Trek: DS9 episode Call To Arms are essentially photon torpedoes without the propulsion system.
During their mission, the starship Enterprise, NX-01, encountered two species that used photon torpedoes, the Klingons and Vissians. When the Enterprise was reassigned to the Delphic Expanse, Starfleet technicians installed these new torpedoes, which were called photonic torpedoes.
Photon Torpedo Specifications
Photon torpedoes are launched from specific launchers usually installed on ships or stations. For example, the Intrepid class starship has four launchers, two forward and two rear of the spoon-shaped saucer. These launchers can typically fire multiple torpedoes simultaneously or single torpedoes in rapid succession. A photon torpedo is usually self-guided, though in some situations it can be directly controlled by the ship that launched it.
A typical photon torpedo is an elongated elliptical tube that measures 2.1 m in length, 0.76 m in width, 0.45 m in height, and 247.5 kg in dry mass. These launchers are also used to launch similarly shaped science probes and can perform burials in space.
Note: The typical tube-shaped torpedo casing was first alluded to in Star Trek: The Motion Picture and actually seen in Star Trek II: The Wrath of Khan. It was never seen in Star Trek: The Original Series, nor was there any implication of an actual casing that was used during TOS.
Photon torpedo casings are known to be extremely tough, capable of surviving intact high-speed entry into the atmosphere of an M-class planet. A photon torpedo can also survive the subsequent high-speed impact into the surface and burial deep in the liquid core of said planet, such as in the episode Pen Pals. Torpedo casings are also often used for various probe designs - e.g. the Class IX Long-Range Multimission Warp Probe.
A standard Next Generation photon torpedo holds 1.5 kilograms of small pellets of anti-deuterium and 1.5 kilograms of similar deuterium suspended in a magnetic field. Yield is reduced by including fewer pellets. The torpedoes do not have their own warp drive, but they do have a warp sustainer engine that can keep them going at faster than light speeds, if launched by a ship at those velocities.
The emissions created by a photon torpedo detonation can be modified on demand, though the modifications can often take several hours.
Photon Torpedo Physics
Through basic calculations we can derive that the maximum energy produced by a detonation of a TNG photon torpedo. The basic power of the annihilation of 1.5 kg of deuterium by 1.5 kg of anti-deuterium is approximately 64.53 megatons (E=mc²). Unfortunately, currently Starfleet does not appear to have the ability to focus the blast photon torpedoes at a single target (ref. TNG episode "The Nth Degree"). Therefore, in an optimum situation we can expect the shields of the target vessel to receive about 30% of the energy, with the rest of it dispersing uselessly.
To delve deeper into the subject, consider the fact that the resulting energy is emitted in various ways (such as gamma rays and exotic particles). At the same time we know that photon torpedo casings are extremely tough and dense - as mentioned above one survived intact a fall from orbit into an atmosphere of a planet. This density allows us estimate that the photon torpedo casing can absorb a significant amount of the energy emitted by the deuterium-antideuterium annihilation.
For an approximation, lets assume that only 90% of the energy is absorbed by the casing. Just as during a nuclear detonation process, the result of this absorption will create a plasma fireball traveling at an enormous velocity composed out of the superheated torpedo casing. If we assume the same time scale as for a standard nuclear weapon, the plasma ball will expand at 30 km/s, impacting the target of the photon torpedo. If we continue the analogy with nuclear weapons, the fireball at the same time emits various types of radiation, the types of which are dependent on actual torpedo casing composition.
To sum up, these calculations tell us that a photon torpedo detonation will deliver approximately 17 megatons of energy to the target vessel in the form of a physical impact and various types of radiation.
- "Photon torpedo" at Memory Alpha
- "Photon torpedo" at STARTREK.COM
- "Advanced Space Propulsion Study - Antiproton and Beamed Power Propulsion"
- "Nuclear Weapons Frequently Asked Questions"