# Types of spaceships

There are many different **types of spaceships** in Conway's Game of Life and related automata. The following are the terminology that are in common use. This page contains only very general terminology that applies to wide varieties of spaceships.

## Contents

## Universal classifications

Classifications that apply to both elementary and engineered spaceships.

### Flipper

A **flipper** is a spaceship (or oscillator) that forms its mirror image halfway through its period. All flipper spaceships are glide symmetric and conversely all glide symmetric spaceships are flippers. All of the functional standard spaceships are flippers.

### Glide symmetric spaceship

A spaceship is said to be **glide symmetric** if it undergoes reflection and translation simultaneously. It is not difficult to show that a spaceship is glide symmetric if and only if it is a flipper.

### Non-monotonic spaceship

A spaceship is said to be **non-monotonic** if its leading edge falls back in some generations. The first non-monotonic spaceship to be found was the diagonal 13-engine Cordership, by Dean Hickerson in April 1991. The first orthogonal example was found by Hartmut Holzwart in August 1992, which has period 4 and travels at speed c/4. In April 1994, Holzwart found examples of period 3 spaceships with this property, and this is clearly the smallest possible period. Another well-known non-monotonic spaceship is the weekender. 114P6H1V0's front part is non-monotonic, and so is the whole ship (unless its corresponding pushalong is introduced).

### Knightship

A **knightship** is a spaceship of type (2m,m)/n (that is, a spaceship that moves two cells horizontally for every one cell it moves vertically). Knightships must be asymmetric and their period must be at least 6, which makes searching for them using programs like lifesrc very difficult. An elementary would-be knightship, dubbed "almost knightship" was found by Eugene Langvagen on March 23, 2004, which would be a period-6 knightship if it weren't for two cells that are incorrect in its sixth generation.^{[1]}

By analogy with the corresponding fairy chess pieces, spaceships of types (3m,m)/n, (3m,2m)/n and (4m,m)/n would be called camelships, zebraships and giraffeships, respectively.

Alternatively, 'knightship' may refer to any spaceship that travels in an oblique direction (not diagonally or orthogonally). In June, 2010 Dave Greene constructed the first true knightship in Life, which is based on Gemini and travels at a velocity of (4096,8192)/c35567490.^{[2]}.

In July 2014, a knightship, based on a different principle and dubbed half-baked knightship, was built in a joint effort. Very slow self-constructing knightships with the minimum step size of (2,1) -- or spaceships with any other (x,y) step size -- can now be created using known Geminoid technology. The general method involves programming a universal constructor to build large constellations of objects. These "seed" constellations are designed to be triggered by a single glider collision, to produce a slow salvo capable of destroying and rebuilding the universal constructor at the correct offset. No examples have been completed as of December 2014.

In December 2014, Brett Berger constructed a (23,5)c/79 knightship, the first "fast" knightship in Conway's Game of Life.

### Other rules

Many automata extremely similar to Life have knightships and related technology. For example, Pedestrian Life has a naturally-occuring family of (5,2)c/190 ships, as well as a natural (101,3)c/1884 puffer; tdrylife has a slope 3 ship puffer that can be stabilized.

## Elementary classifications

Classifications that only apply to elementary spaceships.

### Standard spaceship

A **standard spaceship** is a glider, lightweight spaceship, middleweight spaceship, or heavyweight spaceship. That is, it is one of the original spaceships that have been known since 1970. Many failed standard spaceships like the overweight spaceship and the b-heptomino as well as the hassled object in the roteightor also display standard-like behavior and can be hassled. Nontrivial flotillae of interacting elementary spaceships do not count as standard spaceships. A **non-standard spaceship** is any other spaceship.

### Edge-repair spaceship

An **edge-repair spaceship** is a spaceship that has an edge that possesses no spark and yet is able to perturb things because of its ability to repair certain types of damage to itself. The most useful example is edge-repair spaceship 1, which can destroy Herschels as it travels. Another well-known example is edge-repair spaceship 2, which can destroy beehives.

### Flotilla

A **flotilla** is a spaceship composed of a number of smaller interacting spaceships. Often one or more of these is not a true spaceship and could not survive without the support of the others. Flotilla 1 is the most common example, and it contains an overweight spaceship escorted by two heavyweight spaceships.

### Frothing spaceship

A **frothing spaceship** is a spaceship whose back end appears to be unstable and breaking apart, but which nonetheless survives (compare with frothing puffer). The exhaust festers and clings to the back of the spaceship before breaking off.

### Smoking ship

A **smoking ship** is a spaceship that produces smoke. If the smoke extends past the edge of the rest of the spaceship, then it can be used to perturb other objects as the spaceship passes by. Running gliders into the smoke is often a good way to turn or duplicate them, or convert them into other objects. Sometimes the smoke from a smoking ship may itself be perturbed by accompanying spaceships in order to form a puffer. Simple examples of a smoking ship are Schick engine and Coe ship. Sometimes combinations of smoking tagalongs are puffers - such as a P48 blinker puffer produced by attaching two Coe engines to LWSS's pulling the Schick engine.

## Engineered classifications

Classifications that apply only to engineered and engineerable spaceships.

### Self-constructing spaceship

The first oblique spaceship to be discovered, Gemini, was found in May, 2010 with a velocity of (5120,1024)c/33699586. It uses twin universal constructor mechanisms sharing a single construction recipe in the form of long streams of gliders. Each universal constructor builds a copy of itself at a fixed offset, while simultaneously disassembling the previous copy of itself and reflecting the construction recipe 180 degrees to feed into the new copy of its twin.

A similar "Geminoid" construction mechanism has been shown to be workable in the Conway's Life replicator. Geminoids may use either a pair of (much smaller) universal constructors, or just a single constructor for both ends of the spaceship.
Several designs have been proposed for Geminoid spaceships^{[3]}, and some theoretical work has been done resulting in a completed Geminoid spaceship pattern in a model rule.^{[4]}. As of November 2015, the only Geminoid spaceship completed for any Lifelike rule is the diagonally traveling "Demonoid".

## See also

- List of spaceships
- List of glide symmetric spaceships
- List of non-monotonic spaceships
- List of smoking ships
- Spaceship terminology
- Tagalong

## References

- ↑ "PLife Home Page". Retrieved on May 22, 2009.
- ↑ post on the conwaylife.com forums
- ↑ "Geminoid Challenge forum discussion". Retrieved on July 23, 2014.
- ↑ "Geminoid Particles rule forum discussion". Retrieved on July 23, 2014.