SpaceX Now Counting Down to Sunday Evening Launch

T-15 minutes

Although there has been little official word regarding the exact cause of last Thursday’s launch scrub, SpaceX and SES are now targeting this evening at 6:46 pm ET for launch of the SES-9 mission. While the launch window runs to 8:20 pm, the expectations are that if the Falcon 9 Full Thrust does not lift off at the end of the original countdown, the effort will be delayed until Monday. The principle reason is that SpaceX is using super chilled liquid oxygen (LOX) in order to maximize its propellant load through the increased density of molecules which are literally packed closer together. Any delay in the countdown will allow the LOX to begin warming and losing density, limiting the rocket’s performance with each passing second.

Two factors are at play here. First, the SES-9 satellite, weighing in at 5,251 kg fully loaded, significantly exceeds the Falcon 9’s published performance to GTO of 4,850 kg. That in itself is necessarily a critical due to the fact that the official numbers include both a healthy margin, as well as a leftover propellant amount for first stage return. However, in order to meet a timeline significantly altered by the interruption following last year’s CRS-7 failure, SpaceX agreed to change the original launch profile, and use a different trajectory than was first planned, one which includes allowing the second stage to run until dry rather than use a time specific shutdown. Now, with the margin narrowed, every fraction counts, which is what prompted SpaceX to delay loading the propellant until the last possible second. It may have been one second too many, particularly if the ground handling equipment did not perform precisely as specified.

Today’s weather conditions are nearly ideal, both at the Cape Canaveral launch site, as well in the Atlantic Ocean landing zone northeast of the Bahamas. According to the latest NOAA weather buoy data, wind speeds are 13.6 knots with gusts to 17.5, and seas are running a very manageable 5 feet.

SpaceX technical webcast:

SpaceX hosted webcast:

The original launch story is here: New Day, New Play; SpaceX Counting Down to Falcon 9 Launch, Possible Landing.

Mission Timeline:

COUNTDOWN Hour/Min Events

• 00:34 Launch Conductor takes launch readiness poll

• 00:30 RP-1 (rocket grade kerosene) and liquid oxygen (LOX) loading underway

• 00:10 Falcon 9 begins engine chill prior to launch

• 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

LAUNCH AND SATELLITE DEPLOYMENT

Hour/Min Events

00:01 Max Q (moment of peak mechanical stress on the rocket)

00:02:36 1st stage engine shutdown/main engine cutoff (MECO)

00:02:40 1st and 2nd stages separate

00:02:47 2nd stage engine starts

00:03:42 Fairing deployment

00:09:01 2nd stage engine cutoff (SECO-1)

00:27:07 2nd stage engine restarts

00:27:55 2nd stage engine cutoff (SECO-2)

00:31:24 SES-9 satellite deployed