International Space Station Marks 20 Years Since First Launch, in Photos
Tuesday marks the 20th anniversary of the start of the assembly of the International Space Station (ISS).
The first module, called Zarya, was launched on Nov. 20, 1998 on a Russian Proton rocket and became the building block for the station.
It has since been expanded with over two dozen additional modules to expand the capabilities of the floating research laboratory.
In this gallery, we look back at the work of the ISS.