The Dragon cargo-spaceship is carrying about 2,630 kg (5,8000 lb) of pressurized mass and will return about 1,770 kg (3,900 lb) of various materials.
One of the really cool (to me) items being sent up is called The Atmosphere-Space Interactions Monitor (ASIM). This monitor surveys severe thunderstorms in Earth’s atmosphere and upper-atmospheric lightning, or transient luminous events, from its perch on the exterior of the European Space Agency (ESA) Columbus module. These include sprites, flashes caused by electrical break-down in the mesosphere; the blue jet, a discharge from cloud tops upward into the stratosphere; and ELVES, concentric rings of emissions caused by an electromagnetic pulse in the ionosphere.
The launch is scheduled for 20:30 UTC / 04:30 ET. Coverage begins around 20:15 UTC / 04:15 ET. I say “about” because the start time is dependent on Space X. The link will be up so you might have to check back.
What if the launch does not happen for whatever reason, there is a back up date /time in 24 hours later.