Description for the above graphic :
#C A very long period oscillator: 1800 generations. In more humorous
#C moments, known as the glider racetrack. Sometimes you're a glider,
#C sometimes a spaceship, and sometimes just a hole
#C -- David Goodenough
#C
#C This uses several reactions:
#C
#C The glider starts travelling SW, and enters a three-glider->LWSS
#C synthesis found by David Buckingham. There are two parallel streams
#C of gliders moving in opposite directions, a NW P30 and and a SE
#C P60. When idling, these fall into eaters, but when *THE* glider
#C arrives, a single instance of the synthesis takes place, sending a
#C LWSS west. The gun firing SE has to be P60 to let the LWSS escape.
#C
#C Next, the LWSS hits a glider going NE from another P60 gun, and is
#C converted back into a glider going SE. I'm not sure who this
#C reaction is due to.
#C
#C Next, the kickback reaction with a NE stream from a P30 gun is used
#C to turn the glider around so it's going NW, and send it back
#C through the stream from the P60. As far as the LWSS + glider to
#C glider synthesis goes, a P30 gun would be OK. However, since you
#C can't get a glider back through a P30 stream without a crash, I
#C need a P60 stream to let the glider back through.
#C
#C Now it goes to a shuttle that turns it NE, and then it hits a
#C stream of SE gliders from a P30 gun. When it hits the stream, it
#C destroys exactly one glider in the stream, creating a hole. When
#C idling, the stream hits another shuttle that turns it NW, and then
#C runs into what would be a P30 gun, except that the inbound stream
#C keeps it permanently turned off. This is part of the switchable P30
#C LWSS gun found by David I. Bell, AKA an in-line NOT gate for glider
#C guns. When the hole arrives, it allows a single glider to escape
#C NE, which is promptly turned SE by another shuttle.
#C
#C The glider then runs into the westbound output of a P120 LWSS gun,
#C in a reaction found by Dean Hickerson. It undergoes the same
#C glider+LWSS->glider reaction, creating a glider going NE. This is
#C then reversed to SW by the "ping" reaction with a PD, and at that
#C point it's on its starting path. It continues SW, and once again
#C enters the three glider LWSS synthesis, and thus the cycle repeats.
#C
#C David Goodenough, January 1995
I am sure glad I did not have to write all that.....
* a PD is a PentaDecathlon