Spacetime Catapult
Interstellar Catapult
Image from Anders Sandberg
Interstellar catapult at Duktig of the Chronos Cluster, delivering a train of diamondoid unfolders to Ikaros for the terraforming of Ikaros III. The cargo is accelerated using local spacetime manipulation, producing an intense gravitational gradient that accelerates it with minimal force. The packages will be received after 164 years at Duktig, with a maximal deviation of 10 meters.

The first of the reactionless drives; the Spacetime Catapult

Large, even megascale structure which uses magmatter accelerators to launch cargo to relativistic or near-relativistic velocity. The cost of construction and maintenance is extremely high, meaning only fairly developed and rich systems that are not part of the nexus can afford them.

Launching objects using electromagnetic catapults is nearly as old as space travel. On airless worlds it is one of the most efficient ways of cargo launch. It can also be used for transports in interplanetary or interstellar space. Sending objects by catapult has the advantage of not requiring any expensive drives or ships to house the cargo; the catapult and reciver station are the only major investments and can (at least in theory) gain economy of scale.

While electromagnetic or mechanical catapult-like systems have been developed for in-system travel, such as the Federation Fast Forward System (F3S) of the Solar System or the Djed rotovator networks, the practice remains of limited use because the accelerations or jerks involved tend to damage bioids and cargo. Also, the competiveness and efficiency of in-system drives have often driven down profit margins so much that catapults become uneconomical. Interstellar catapults remained a theoretical possibility for a long time, but was eventually developed into an economical viable system, mainly in systems without stargates.

While drive technology at first concentrated on devising fields that could propel starships efficiently, there were serious interest in other applications. Sirius Dynamics and New Mars Applied Quantum developed several "launching fields" that could accelerate objects to high velocities. At first suggested both for megascale planetary launchers, weapons and even thrusters, they proved too energy consuming, heavy and dependent on high vacuum to work well with any of the applications.

During the expansion of the Mutual Progress Alliance in the 3000's, many systems lacked stargate links but needed to exchange material objects (especially for the enormous terraforming programs of the Kusilaire administration of the Ophiuichi Pyramid). Much work on applying field technology to interstellar catapults was done, and the Second Toposophic company/clade Emek could in 3315 demonstrated a working prototype, sending streams of multimillion ton masses over a distance of one lightyear at the MPA engineering testing range at Antares. Over the centuries, the system was deployed and refined into the current streamlined designs.

Operating Principle

The basic catapult is a linear accelerator containing magmatter tori and a meshwork of controlling ultratech systems. Protective foil, energy sources and direction adjustment systems surround the accelerator proper. A typical length is 20 kilometers, with a diameter of 100 meters. The object to be launched is introduced at one end, and a peristaltic drive field is applied creating a massive acceleration. When the object leaves the accelerator it may reach velocities of 0.1-0.5c. Usually a stream or train of cargo containers are launched together, and a launch report is beamed to the destination using laser link.

To make the principle work, the torus is constructed of a hyperdense magmatter superfluid, that also has to be compressible and have a high degree of internal cohesion, all while internal losses are minimized or recirculated. Such material is very challenging to make at S:2, and the rigors of the design process are speculated to be one of the triggers that leads to the development of both wormholes and void bubbles at higher S: levels. Such materials are generally called "supercritical hypermatter" and have many uses in transapient technology. Many upper S: devices use the topological properties of such materials in ways that modosophonts simply do not have the perspective to perceive, much less understand. These design points are so challenging that the design cannot be made portable, but the advantages of reactionless acceleration are so large that a way was worked out to use them anyway. Spacetime Catapults use several toruses in sequence, since each one has a fairly small gain. They are used to reactionlessly accelerate durable bulk cargo for interstellar delivery.

Methods of operation

During travel, the cargo needs to be protected from collisions with interstellar dust and cosmic radiation (if necessary). This is often done by first launching a somewhat broader "sacrifical" cargo in front of the cargo train, or by using standardised armored relativistic protection containers (often called relpros; the truncated octahedron or cubical relpros are extremely common in some systems, being used for a variety of purposes such as housing, radiation proofing or even outfitted with thrusters and used as extremely minimal spaceships).

Many magmatter catapult cargoes are protected and shepherded by herder spacecraft, containers with propulsion systems and rudimentary intelligence.

In the receiving system the train of cargo is slowed by a recipient deaccelerator. This requires extreme precision - an error of 10-14 degrees during launch will lead to a 100 meter deviation at one lightyear. Fortunately detailled information on the launch and far-system astrometry, as well as the mandated relpro position beacons, enables the recipient to plan the catch months or years in advance. Usually recipient systems either use a very long and wide "funnel" deaccelerator to stop the cargo. In some more primitive systems the cargo containers slow themselves using magnetic or solar sails. Lost cargo is of course highly dangerous, so reception zones are always high above the local ecliptic and recieving systems are only manned by automation or often upbacked aioids.

The major problem with field catapult launches is tidal forces. A very long object would have a front end move at a higher velocity than the back end during the acceleration phase, experiencing a potentially devastating tension. This is the reason most cargo containers are small (usually less than five meters) and sent in streams. It should be noted that a well tuned catapult does not produce any accelerations on the contents of the cargo. The cargo remains in free fall in the local gravitic gradient, only experiencing tidal forces and possibly higher order momenta. While passenger traffic is in principle possible, it usually requires very large accelerators to produce a sufficiently non-tidal field to allow a container containing bioids and their life support to be launched.

The field catapults are today in wide use in the outer volumes, as a cheap alternative to massive starship traffic or stargates. They work well in archipelagos and clusters of systems, with fixed relative positions and regular shipments. While the construction of a field catapult requires transapientech systems and high-end AI, the operation is much simpler and can be handled by the embedded AIs and maintenance crew.

Since they are designed for low cost large volume deliveries, they often don't operate at extremely high c fractions to reduce relativistic losses. A noticeable exception to this is where the receiving system uses a recuperating braking system, so the relativistic energy can be captured for local use. In those sorts of cases, the maximum speeds can reach very high fractions of c. Spacetime Catapults are widely used at 0.2 to 0.7c, more rarely at 0.7 to 0.84c, and occasionally at 0.85 to 0.95c. Their range is 20 to 2000 lightyears, with shepherd clades needed for any journeys over 100 light years or so.

During the Version War and afterwards some catapults were converted into relativistic launch weapons. They are not cost effective for small payloads, hard to shift aim with and very vulnerable due to their size and energy consumption, but very suitable for planetary bombardments of antimatter or relativistic projectiles. The combination of a field catapult and a small aiming stargate has been used as a very expensive but more flexible system strike weapon by the Solar Dominion and the MPA.
Related Articles
  • Catapult, Interstellar - Text by M. Alan Kazlev
    Large, sometimes megascale electromagnetic mass driver which uses a magnetic charge to accelerate cargo to high velocity. Much cheaper than a magmatter catapult and widely used by interplanetary polities that are not connected to the wormhole nexus. Sometimes used to accelerate shuttles to assist in rendezvous with an interstellar cycler. For fast catapults, the use of ordinary electromagnetism rather than magmatter acceleration means that only sturdy cargo that can survive the crushing g-forces can be conveyed by all but the largest (and hence lowest acceleration) catapults.
  • Flinger - Text by Todd Drashner
    Space-time catapult pair used for rapid transport of cargo and passengers between the primary wormhole pairs of a Relay system.
  • Herders
  • Magmatter
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Development Notes
Text by Anders Sandberg
M. Alan Kazlev, Mauk Mcamuk and Chris Shaeffer
Initially published on 28 October 2000.