Delta 4’s military launch bumped by commercial SpaceX flight, but good weather expected

The Delta 4 will launch from Complex 37. Credit: ULA

CAPE CANAVERAL — With the SpaceX scrub earlier this week and the time needed to convert the Eastern Range over to the Delta 4, liftoff of that rocket carrying an internationally-purchased military communications satellite for the Air Force has been bumped to Saturday evening.

Liftoff of the United Launch Alliance Delta 4 carrying the Wideband Global SATCOM 9 spacecraft is scheduled to occur at 7:44 p.m. EDT (2344 GMT). The launch window will remain open for 75 minutes to 8:59 p.m. (0059 GMT).

After SpaceX scrubbed its launch early Tuesday, the company invoked its backup Range date of early Thursday.

Despite the 43-hour turnaround between SpaceX’s next attempt and the Delta 4’s scheduled launch, the Range ruled late Tuesday it could not support the military satellite flight on Friday evening. That automatically moved the Delta 4 to Saturday.

The Eastern Range provides the required safety and tracking services for all launches from the Space Coast.

The chances of allowable weather for the Delta 4 on Saturday stand at 90 percent, with only a slight concern for cumulus clouds during the launch opportunity.

“The next cold front will be dropping southward into northern Florida late on Saturday, but will remain relatively weak and not track through Central Florida until Sunday morning. Weather should be favorable for MST rollback during the day and for the evening launch,” forecasters at the 45th Weather Squadron say.

“The primary concern for launch is cumulus clouds forming in advance of the front, however they should be of minimum vertical development and very isolated.”

The launch time conditions are expected to include only a few low-level clouds and some scattered high clouds, good visibility, ground winds from the southwest at 10 gusting to 15 knots, a relative humidity of 64 percent and a temperature of 66 degrees F.

Sunday’s backup launch window, if needed, should have 80 percent favorable weather.

“For Sunday, the relatively dry cold front tracks through Central Florida in the morning and drops into Southern Florida by afternoon. Skies will be fair, however winds will be 17 knots gusting to 25 knots throughout the day. During the morning, winds will be from the northwest then veering to north by evening. The primary concern for a 24-hour delay is lift-off winds, however the wind direction will be from a favorable (~010 degrees) azimuth during Sunday’s launch window,” forecasters say.

An on-time liftoff at the opening of the window would occur 12 minutes after sunset but well within twilight conditions.

The closest free public viewing location is along Route 401 in Port Canaveral, some 8.6 miles from the launch pad, according to

The WGS 9 spacecraft is an international contribution to the U.S. military’s highest-capacity, worldwide communications satellite constellation. Canada, Denmark, the Netherlands, Luxembourg and New Zealand funded construction of this satellite in exchange to bandwidth from the entire global network.

The Boeing-built WGS network provides high-volume communications anytime, anywhere to soldiers, ships, aircraft and drones.

Here’s a look at some stats about the mission. This will be:

  • The 377th Delta rocket launch since 1960
  • The 35th Delta 4 rocket mission since 2002
  • The 7th Medium+ (5,4) configuration to fly
  • The 53rd main engine from RS-68 family used
  • The 11th RS-68A main engine flown
  • The 56th-57th-58th-59th GEM-60 solid rocket motors flown
  • The 479th production RL10 engine to be launched
  • The 38th RL10B-2 engine launched
  • The 29th Delta 4 rocket launch from Cape Canaveral
  • The 37th launch from Pad B at Complex 37
  • The 20th use of Delta 4 by the Air Force
  • The 105th Evolved Expendable Launch Vehicle flight
  • The 118th United Launch Alliance mission since 2006
  • The 85th ULA launch from Cape Canaveral
  • The 47th ULA launch for the Air Force
  • The 28th Delta 4 under the ULA banner
  • The 3rd ULA launch this year
  • The 1st launch of the Delta family in 2017
  • The 9th Wideband Global SATCOM satellite
  • The 3rd Block 2-Follow On WGS satellite
  • The 7th WGS on Delta 4

See earlier WGS 9 coverage.

Our Delta archive.