The lightweight spaceship (commonly abbreviated to LWSS) or (rarely) small fish^{[1]} 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.
Tagalong
In April 1992, David Bell found a tagalong for two lightweight spaceships (or two middleweight spaceships or two heavyweight spaceships). It can be extended indefinitely by attaching it to the back of itself. Interestingly, a hivenudger with symmetric rear (that is, both rear spaceships being of same "weight") can pull this tagalong.
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,^{[3]} leading to a way of constructing the LWSS using 5 gliders.
A different one-glider seed that fits inside a 12 × 12 square can be found in the octohash database;^{[4]} it is a constellation of a blinker and an eater 1, itself constructible with four gliders.^{[5]} There are 60 matches in the octo3obj database which are clean one-glider seeds for the LWSS.^{[6]}
x = 15, y = 18, rule = B3/S23
9bo$8bo$8b3o7$9b2o$9b2o3$13b2o$bo11b2o$obo$obo$bo!
#C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]]
#C [[ ZOOM 8 Y 8 THEME Book AUTOSTART GPS 20 T 0 PAUSE 1 T 159 PAUSE 1 LOOP 160 ]]
A three-object 1G seed for the LWSS (click above to open LifeViewer)
x = 11, y = 10, rule = B3/S23
7b2o$8bo$5b3o$3o2bo4$8b2o$8bobo$8bo!
#C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]]
#C [[ ZOOM 8 THEME Book AUTOSTART GPS 20 T 0 PAUSE 1 T 63 PAUSE 1 LOOP 64 ]]
A two-object 1G seed for the LWSS (click above to open LifeViewer)
Random soups investigated by Achim Flammenkamp emitted one LWSS for approximately every 615 gliders.^{[7]} The LWSS is also the eighteenth most common object on Adam P. Goucher's Catagolue.^{[8]}
↑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.