Pion Drive Anti-Matter Rocket
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Pion Drive Anti-Matter Rocket |
| Pion Drive Amat Rocket - Data Panel
Summary: The Pion Anti-Matter drive harnesses the energy released in atomic or subatomic matter-antimatter annihilations. Compared to fusion or ion drive the Matter-Antimatter engine is incredibly powerful, with the highest energy density of any atomic material, and producing an Isp of up to several million seconds. Despite its huge isp its thrust-to-weight ratio is still comparable with that of chemical propulsion, allowing lift-off from a planetary surface. However, the exhaust plume is highly radioactive and cannot be used near inhabited areas. Anti-matter is also costly in many systems. For this reason, most standard amat ships will rarely exceed 0.01 c. Basic Propulsion: Reaction Specific Impulse [sec]: 105 to 106 Fuel: amat Reaction Mass: see above Minimum Technology Required: microtech/nanotech Matter Manipulation: microscale/nanoscale (precision materials) Controller required: advanced non-sentient or sentient computers First Introduced: Interplanetary Age Used by: Many polities, clades, individuals and groups away from the Nexus, in low resource solar systems and among members of the Deeper Covenant, out on the periphery, and among some anti-ai luddite groups Used in: high speed interplanetary, some deep space groups Construction Costs: Autofac: high (bulky, precision materials); Hylonano: rather expensive Running cost: very expensive (amat) Advantages: very good performance, not as high exhaust signature as picotech-amat or GUT-drive, does not require dedicated hyperturing Disadvantages: requires very large quantities of amat (expensive and highly explosive), exhaust is highly radioactive, requires dedicated ai, unstealthy when engine is firing, interstellar capacity and general performance greatly inferior to picotech-amat and GUT drive Normal Acceleration: 0.1 to 3 g Normal Top/Cruising Speed up to 0.01c (3000 km/sec); with much more amat use can attain >0.1c but this is very rare |
A matter-antimatter powered rocket works by keeping the charged antimatter in an electronic bottle and in a slow controlled fashion releasing them to hit ordinary mater. The resulting reaction releases highly energetic pions which are propelled out the magnetic coil nozzle. The pion mass and kinetic energy provide thrust, and isp is anything up to 100,000 to 1,000,000 seconds.
In a high-Isp antimatter rocket, protons and antiprotons are annihilated in a magnetic bottle. Use of higher atomic number nuclei is less practical, as neutrons liberated upon annihilation cannot be guided in a magnetic nozzle.
Engines such as this are more expensive than fusion, amat pulse, and amat thermal. One problem is controlling the waste energy from the matter-antimatter reaction. Waste heat requires massive cooling radiator fins to avoid melting the engine core. Much of the energy is in gamma radiation that is normally dispersed, and hence requires a great deal of shielding to protect the instruments, payload, and of course any biont passengers. Even after years of firing the engines they still remain highly radioactive.
In part because of their inefficiency, pion drive amat ships are extremely wasteful as regards fuel. Even a small sized interstellar vehicle with a cruising speed of 0.1c would require about 750,000 kilograms of amat for a single mission (acceleration-deceleration). This is not only expensive but extremely dangerous, in the event of a power failure, the result would be a catastrophic blast. For this reason most polities forbid amat ships from docking close to populated habitats, setting aside special docking stations, which in turn implies extra inconvenience for loading and unloading of cargo.
Like other high ISP drives, the pion drive amat rocket is very unstealthy. However it is still not as bad as the ultra-efficient amat or the GUT drive rocket, which is one reason this type of propulsion is preferred by some clades, despite the much lower isp.
The reason for the stealth factor still being superior to more efficient propulsion systems is as follows. The annihilation products are primarily pions, with some kaons. The negative and positive pions escape out the magnetic nozzle before they decay. The neutral pions decay almost immediately to photons, but these photons are isotropic in the spacecraft reference frame. The pions decay to muons, which travel about 1 km before decaying to electrons. Electrons and positrons annihilating in the reaction chamber also produce isotropic radiation.
The density of positrons and electrons in the exhaust is limited by the need for their kinetic pressure to be less than the magnetic pressure of the confining magnetic field. Only about 10-8 of positrons annihilate in 1 km of exhaust (assuming a residual random kinetic energy of about 1 MeV), with similar figures for muons and charged pions. Positrons that don't annihilate escape to interstellar space, where their trajectories are bent by interstellar magnetic fields. A 100 MeV positron in typical interstellar magnetic fields has an orbital radius on the order of millions of kilometers. It will generally complete many orbits, losing energy to synchrotron radiation and collisions, before finally annihilating. By the time it does annihilate it will likely have its direction of motion randomized, at least perpendicular to the local magnetic field lines. This means that it is difficult to track a normal amat rocket by its exhaust
