
Launch relay
NCSU-High-Powered-Rocketry-Club/Launch-Relay-KiCAD
KiCAD files for the rocket launch detection relay board
AOTEExtended
The ACPL-217(AT) is a transistor, Photovoltaic Output Optoisolator made by AOTE in a SSOP-4 package with 4 pins.
PCBKit's library has its footprint (Package_SO:SSOP-4_4.4x2.6mm_P1.27mm, from KiCad's library), ready for a KiCad board. 4,100 are in stock at JLCPCB (part C48686290). 1 open-source board in 1 repository on GitHub use it.
The library has no symbol for this part yet.

NCSU-High-Powered-Rocketry-Club/Launch-Relay-KiCAD
KiCAD files for the rocket launch detection relay board
Yes. the footprint Package_SO:SSOP-4_4.4x2.6mm_P1.27mm, both drawn on this page. PCBKit places them on a board for you when you design with it.
SSOP-4, with 4 pins. Its footprint is drawn on this page.
AOTE publishes it: the Datasheet link on this page opens it.
JLCPCB lists it as part C48686290, with 4,100 in stock; the sellers' links on this page open their listings.
Parts like it in the library: the AT3H4B-CUH-S by AOTE, the HT-3H4-BTP1 by HENGTUO ELECTRONICS, the LTV-214B by AOTE and the MP3H4B(T1)-GV by miracle. Check their datasheets: a part that fits the footprint may still differ in its ratings.
1 board in 1 repository on GitHub; the most starred are listed on this page, with their KiCad files.