If all goes according to plan, Falcon 9 will launch into space, jettison its Deep Space Climate Observatory (DSCOVR) satellite, and return to Earth to land on a 300-by-100-foot barge off the coast of Florida. DSCOVR will orbit Earth for 110 days to monitor the planet's solar winds, which are capable of disrupting power grids, aviation, and GPS.

During last month's launch, the Falcon 9 landed too heavily on the barge. Many factors could contribute to today's success or failure, but this is still only a test. If tonight's landing fails, SpaceX will just launch again later. If the launch is aborted, SpaceX has scheduled another launch for Monday at 6:07PM ET. You can watch the launch above, on NASA TV.

Update 6:31PM ET: The launch has been scrubbed because of issues with a first stage transmitter and range radar. See our story on the canceled launch.