Explosive Pulse Drives

Propulsion by means of explosive pulses entirely outside the vessel. Includes Orion Drive, Daedalus drive

Daedalus class
Image from Steve Bowers
A Daedalus external fission pulse interstellar vessel. Miniature pellets of deuterium are detonated in the hemisphere behind the ship, providing rapid pulses of thrust

Explosive Pulse Drive

Summary:The Explosive Pulse Drive uses large numbers of relatively small explosions which are serially detonated behind the spacecraft to produce a more or less smooth thrust. There are two types, the basic lo tech 'dumb' or inert model which uses a physical pusher plate and does not require sentient ai, and the high performance hi tech 'smart' model which requires advanced ai to coordinate the bomblets and the magnetic 'pusher plate'
See alsoFission Drive, Fusion Drive
Basic PropulsionReaction
Specific Impulselo tech: 10,000 to 35,000 sec
hi tech: 10e5 to 10e6 sec
Fuel:Fission bomblets, Deuterium or He3 pellets, rarely Antimatter bomblets
Reaction Mass:propellant material may be incorporated as shells around each bomblet
Minimum Technology Required:lo tech: Microtech, Nanocomposites
hi tech: Nanocomposites, Precision Nanotech, Sentient AI
Matter Manipulation:microscale/nanoscale (precision materials)
Controller required:lo tech: advanced non-sentient computers
hi tech: sentient ai
First Introduced:lo tech: Early Interplanetary Age
hi tech: Late Interplanetary Age
Used by:lo tech: mostly historical hobbyists, possibly a few isolated ludd or anti-ai groups
hi tech: 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:medium to high speed interplanetary and near-interstellar transport; generally impractical for true interstellar transport, although still used by some deep oort haloist groups
Construction Costs:lo tech: Autofac: medium (bulky, precision materials); Hylonano: reasonably cheap assuming presence of component materials
hi tech: Autofac: high (bulky, precision materials, requires exporting of some parts); Hylonano: somewhat expensive, requires presence of component materials. Requires trained and dedicated ai (generally turingrade or superturingrade)
Running cost:depends on availability of fuel
Advantages:reliable (lo tech), good performance (hi tech), reasonably easy fuel storage, can be made with materials in most solar systems, does not require amat (although amat may be used in some pulsed or external drives)
Disadvantages:insufficient isp for decent interstellar transport, unstealthy, produces radioactive exhaust, use for launches illegal in most polities
Normal Acceleration:lo tech: 0.01 to 0.1 g
hi tech: 0.05 to 1 g or more
Cruising Speedlo tech: 50 - 100 km/sec
hi tech: 50 km/sec to 0.1 c (depending on design and fuel availability)
Cybyota Ship under acceleration
Image from Steve Bowers
The alien xenosophont race known as the Cybyota continue to use fusion-pulse vessels for interplanetary and interstellar journeys; small fusion devices are detonated behind the shield at the rear of the vessel, and propel the ship during the acceleration phase
Explosive Pulse Fission/Fusion Drives
The Explosive Pulse Drive is powered by a series of continuous fission or fusion explosions behind the ship, and propelled by deflecting the explosive forces with reflectors. Typically, early designs used simple fission devices to generate plasma pulses. More advanced designs use fission/fusion staged explosive pulse units, antimatter catalyzed fusion explosive pulse units, antimatter-boosted explosive pulse units, and rarely, antimatter explosive pulse units.

The performance of the designs are mainly constrained by the material strengths available. Depending on ship design and pellet size, up to 200 explosions may occur every minute. Such a drive is somewhat like riding on a continuous stream of mini-nukes, equivalent to a 10kt bomb every second; the power output is in the regions of tens of terawatts. The exhaust velocity is as much as 6000 km s-1, and the drive plume is highly dangerous out to a distance of tens of thousands of kilometres.

Such systems are only reasonable for operations well away from planets or habitats; indeed the drive is of considerable use as a weapon. A ship using a pulse drive is also extremely unstealthy, and will be easily visible on the far side of the system.

Explosive Pulse Fission/Fusion Drive came into its own with the mass-production of ultra-light ultrastrong materials like Buckyfibre and other forms of Diamondoid, during the middle and late Interplanetary age. These much more advanced ships had pulse repetition rates of several hundreds per second, and replaced the heavy ceramic-carbon-metal composite pusher-plate for a powerful magnetic field, which channelled the charged particles into an exhaust. The tweak societies and some megacorps of the later interplanetary age often favoured this type of drive, and it still remains in use with a large number of clades and groups today away from the main nexus

Today Explosive Pulse Drive is a cheap and robust, relatively low tech system that does not require advanced AI piloting, and hence is widely used by a number of bioist, anthropist, and human supremacist clades and factions throughout the galaxy. While grossly inefficient and expensive as a star drive (even good sub-relativistic velocities are virtually impossible, due to the huge amount of reaction mass that would be required), they serve very well as a standard interplanetary vessel, especially in systems rich in He3.

Such designs, along with the internal fission drives, are the workhorses of the S:0 world. External Plasma Pulse drives avoid the difficult shielding problems of the Internal drives by moving the "drive chamber" completely outside the ship. Such designs are extremely wasteful of fertile, fissile, and fusion fuels, meaning internal drives have some competitive advantages, but since they do not need to contain the full power of the drive reaction, they can have a very high performance envelope for their S:level.

Early ships using fission pulse units and simple steel acceleration disks typically had Isps around 5000, a thrust to weight ratio of 5 to 1, and a total delta-v of 60 km/sec. A middle-ground ship using antimatter-initiated pure fusion pulse units and a primitive diamondoid acceleration disk typically has an Isp around 20,000, a thrust to weight ratio of 20 to 1, and a total delta-v of 180 km/sec+. An advanced antimatter-boosted (1 percent) fusion pulse unit design with an electromagnetically shielded nanotech-based programmable matter acceleration disk typically has an Isp around 100,000, a thrust to weight ratio of 100 to 1, and a total delta-v of 800 km/sec or higher.

External constant fission/fusion drives
Extremely wasteful and dirty even compared to the external pulse plasma drives, external fission/fusion drives are hybrids between internal fission drives and EPPs. They essentially move the fission drive outside the ship, but do not use pulse units, instead generating a constant fission or fission/fusion reaction. The thrust is transferred to the ship via an electromagnetically shielded programmable matter acceleration disk. Due to the constant burn, a very good shielding system is needed, at least as good as the best used for the internal drives, but since the reaction is not contained, much higher power levels can be tolerated, with similar high performance.

Indeed, such designs have higher power levels than either EPPs or internal fission drives, as the cost of enormous fuel consumption. The one outstanding feature of such a design is the tremendous thrust and acceleration levels possible, making such drives popular with S:0 military organisations. The most primitive of these use pure fission reactions and electromagnetic/diamondoid acceleration disks. More advanced versions use electromagnetic/nanotech acceleration disks and fission/fusion reactions. The most primitive of these designs has an Isp of around 30,000 seconds, a thrust to weight ratio of 200 to 1, and a total delta-v of 200 km/sec. The most advanced, using fission-fired D-D fusion reactions, has an Isp of around 1,000,000 seconds, a thrust to weight ratio of 300 to 1, and a total delta-v of 5000 km/sec.
 
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Development Notes
Text by M. Alan Kazlev, Mauk Mcamuk and Chris Shaeffer

Initially published on 06 December 2008.