The caption at the base of this stamp reads Weltraumlabor which the internet translates for me as space laboratory or SpaceLab.
SpaceLab was a collaborative project between NASA and the European Space Research Organisation (now the European Space Agency) to create a lab module which would sit within the Space Shuttle. Construction started in 1974 and, whilst it sat out the first couple of Shuttle missions, it became a fixture of more than 20 missions between 1983 and 2000. SpaceLab included lab modules, external pallets for carrying stuff and an igloo module, which carried specialised equipment on non-manned flights. (I’m paraphrasing quickly here, forgive me if I’m getting things wrong!)
Check out the first link for the quick summary and the second for more detail…
https://en.wikipedia.org/wiki/Spacelab
https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/spacelab.html
Stamp of the Day 