Interstellar Spacetime Catapult

Interstellar Catapult 1
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 a halo of void bubbles, controlled by the guidance system housed within the catapult structure. The packages will be received after 164 years, with a maximal deviation of 10 meters.


Halo Drive based accelerators used to launch cargo to relativistic or near-relativistic velocity. The rarity of the S5 (or higher) minds needed to construct them and supply the necessary control interfaces means that 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 methods of cargo launch. It can also be used for transportation 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 receiver station are the only major investments and can (at least in theory) gain economy of scale.

Electromagnetic or mechanical catapult-like systems have been widely developed for in-system travel, such as the Federation Fast Forward System (F3S) of the Solar System or the Djed rotovator networks. While the technology is more efficient than reaction drives and more accessible than reactionless ones, it has a harder time competing against beamrider or mass-stream based systems, which can offer higher final velocities and payload throughputs. Electromagnetic interstellar catapults remained a theoretical possibility for a long time, but were eventually developed into an economically viable technology, mainly in systems without stargates.

During the expansion of the Mutual Progress Alliance in the 4000'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). In 4315, the Fifth Toposophic company/clade Emek demonstrated a working prototype of a halo-based space-time catapult, sending streams of multimillion ton masses over a distance of one light-year at the MPA engineering testing range at Antares.

Operating Principle

The basic space-time catapult is a swarm of void bubble units, very much like that used in a Halo Drive. However, unlike a Halo Drive, the swarm is not associated with, or controlled by, a single specific vessel, but is instead operated by a dedicated AI controller that is distributed across the entire swarm system. Under the control of its AI guidance mind, the catapult will link with one or more designated cargo pods or ships, accelerate them to some predetermined velocity, and then release them to continue on to destination while returning at high speed to the launch point to repeat the process with another payload. Void bubbles operating on their own can start, stop, and change direction instantly while traveling at nearly the speed of light, so a distance that took hours or days to cover while accelerating a payload can usually be retraced in a matter of minutes or hours, depending on the final velocity attained by the cargo before it is released. Depending on the durability of the cargo, and how urgently it is required, the catapult swarm may link with it gravitationally to compensate for acceleration forces, or limit itself to magnetic linkage alone, accelerating to cargo to interstellar velocities while subjecting it to multiple gravities of acceleration.

Once at destination, the cargo may be met by another Halo swarm to be decelerated to interplanetary velocity, or use onboard magbraking and reaction drives to perform the same task. Final orbital insertion is performed using the catapult swarm, onboard reaction systems, or some combination of the two, depending on the urgency of the payload and how busy the local catapult unit is with other cargo.

Methods of Operation

During travel, the cargo needs to be protected from collisions with interstellar dust and cosmic radiation. This is often done by first launching a somewhat broader "sacrificial" 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 extremely minimal spaceships (after being outfitted with thrusters, insulation, and life-support systems).

Many catapult cargoes are protected and shepherded by herder spacecraft, specialized bots or vecs with propulsion systems and rudimentary intelligence.

While passenger traffic is in principle possible, most sophonts prefer to travel in a less bare bones fashion than the majority of catapult systems are inclined to provide and will usually turn to the local beamrider network, self-powered starship, or engenerator link to cross the interstellar void.

Space-time catapults are widely used in the Hinterregions and Outer Volumes, as a cheap alternative to stargates. They work well in archipelagos and clusters of systems, with fixed relative positions and regular shipments. While the construction of a Halo swarm catapult requires godtech systems and high-end AI (both usually so far away that centuries can pass just in the order and delivery process) , the finished product has an operational lifetime of thousands of years and can be readily managed by the modosophont level AIs and maintenance crew.

Since they are generally used for low cost, large volume deliveries, space-time catapults don't often operate at extremely high c fractions. However, there are exceptions and in those sorts of cases, the maximum speeds can reach very high percentages of the speed of light. Space-time 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 light-years, 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. The results were sufficiently horrifying that such activities were banned by a combination of treaties and god-tech level blocks installed in the control software.

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Development Notes
Text by Todd Drashner
Original concept by Anders Sandberg
Initially published on 28 October 2000.

Completely revised October 2014