The lightweight spaceship (commonly abbreviated to LWSS) or (rarely) small fish is the smallest orthogonal spaceship, and the second most common spaceship after the glider. It moves at speed c/2 and has period 4 (and is therefore often referred to as 2c/4). It was found by John Conway in 1970.
A three-object one-glider seed for the lightweight spaceship, consisting of two blocks and a beehive, is used in the pattern Patterns/Life/Breeders/switch-engine-breeder-MR.rle included in Golly's pattern collection. The seed constellation itself can be constructed with four gliders, leading to a way of constructing the LWSS using 5 gliders.
↑There are two collisions, each with two escaping LWSSes. One collision (headerless RLE 8b2o$9bo$b2o6bobo$obo2b2o3b2o$2o2b2o$6bo!) has final population 158. The other collision (b2o$obo$2o6b2o$9bo$9bobo$10b2o2$12bo$11b2o$11bobo!) has final population alternating between 367 and 373.
↑There are 28 results where two lightweight spaceships escape.
↑There is one collision (headerless RLE obo$b2o$bo75$75bo$76b2o$75b2o$80bo$79b2o$79bobo!) with two escaping lightweight spaceships. The final population is 377.