SpaceX

The strongback now is fully retracted, Falcon 9 and Dragon are on internal power, and the launch director has given the final approval for launch.

During the next minute, the Falcon 9 flight computer will start its final round of prelaunch checks while the rocket’s propellant tanks come up to flight pressure.

The gantry-like strongback support structure is retracting away from the Falcon 9 rocket.

The Falcon 9’s Merlin engines are being chilled down prior to launch and the autosequence is under way, leading down to liftoff expected at 4:43 p.m. EDT.

Here’s a look ahead at the remaining countdown milestones and the sequence of events during the Falcon 9’s climb to orbit:

Hour:Minute:Second – Event
00:10 – Falcon 9 begins engine chill prior to launch
00:07 – Dragon to internal power
00:02 – Range Control Officer (USAF) verifies range is go for launch
00:01:30 – SpaceX Launch Director verifies go for launch
00:01 – Command flight computer to begin final prelaunch checks
00:01 – Pressurize propellant tanks
00:00:03 – Engine controller commands engine ignition sequence to start
00:00:00 – Falcon 9 liftoff
00:01:11 – Vehicle goes supersonic
00:02:30 – 1st stage main engine cutoff (MECO)
00:02:34 – 1st and 2nd stages separate
00:02:41 – 2nd stage engine starts
00:10 – 2nd stage engine cutoff (SECO)
00:10:30 – Dragon separates from 2nd stage
00:12 – Dragon’s solar arrays deploy
02:20 – Dragon’s Guidance, Navigation and Control bay door opens

The SpaceX Dragon capsule secured atop the Falcon 9 rocket measures 12 feet wide and 23.6 feet long. Tucked inside are 6,913 pounds of cargo, including more than 250 science and research investigations planned for use during the space station’s Expeditions 47 and 48. These investigations include a mix of commercial and academic payloads aimed at advancing NASA’s journey to Mars while making discoveries off the Earth that can benefit life on Earth.

For more information on the specific payloads flying on SpaceX CRS-8, check out this in-depth overview.

Also catching a ride to the station today is the Bigelow Expandable Activity Module, or BEAM, that will attach to the space station and demonstrate expandable in-space habitat technology. Once attached to the station, the BEAM will expand to roughly 13 feet long and 10.5 feet wide, providing a large-volume area in which astronauts will periodically retrieve sensor data and assess the module’s condition during its two-year test mission.

Liquid oxygen and RP-1 fuel are starting to flow into the Falcon 9 rocket’s first- and second-stage propellant tanks and the terminal countdown has started.

The Falcon 9 — named after the Millennium Falcon spacecraft from the Star Wars film series — stands 229 feet tall and measures 12 feet wide. Its nine first-stage Merlin engines generate a combined 1.53 million pounds of thrust at liftoff.

Coming up in the next few minutes, the launch conductor will take a launch readiness poll and give the final go-ahead to controllers to begin loading flight propellants into the Falcon 9. That activity, called tanking, is scheduled to start at about 4:08 p.m.

The two-stage rocket’s Merlin engines — nine of the first stage and one on the second stage — are powered by a combination of liquid oxygen and highly refined kerosene called RP-1.

Clear skies are apparent in these screen captures from NASA TV.

Sealed aboard the Dragon spacecraft are nearly 7,000 pounds of science research, crew supplies and hardware heading to the International Space Station in support of the Expedition 47 and 48 crew members.

SpaceX CRS-8 is the company’s eighth mission to deliver cargo to the orbiting laboratory under NASA’s Commercial Resupply Services contract.

To learn more about the important role Commercial Resupply has in NASA’s exploration goals, read on.