An illustration of the Delta 4 rocket to launch the Eutelsat W5 satellite. Photo: Boeing

The first Boeing Delta 4 rocket will race from its Florida launch pad into an orbit stretching 19,000 nautical miles above Earth Saturday to deploy its European-built communications satellite cargo at the culmination of a 37-minute flight.

The day's 71-minute launch window extends from 5:38 to 6:49 p.m. EST.

But the weather forecast is very pessimistic. The latest update, issued Thursday morning, calls for an 80 percent chance conditions will scrub the launch. See the full weather report and rules here.

If the Delta 4 doesn't fly Saturday, the next attempt isn't expected to come until Tuesday evening. The mission's customer, Paris-based satellite operator Eutelsat, requested delaying the backup launch attempts until after the height of the Leonids meteor shower, which peaks early Tuesday morning.

We present a preview of the events to occur during the Delta 4's maiden voyage with this chart:

T-00:05.5	Engine start
	The Rocketdyne RS-68 main engine begins to ignite as the liquid hydrogen fuel valve is opened, creating a large fireball at the base of the rocket. The engine powers up to the 101 percent level of thrust for a computer-controlled checkout before liftoff.
T-00:00.0	Liftoff
	The rocket's two strap-on solid rocket motors are lit, the four hold-down bolts are released and the maiden flight of Delta 4 is underway from Cape Canaveral's pad 37B. The pad's three swing arms retract at T-0 seconds.
T+01:02.3	Max-Q
	The vehicle experiences the region of maximum dynamic pressure. Both solid motors and the RS-68 liquid hydrogen/liquid oxygen engine continue to fire as the vehicle heads downrange, arcing over the Atlantic.
T+01:40.0	Jettison solid motors
	Having used up all their solid-propellant and experienced burnout six seconds ago, the two Alliant-built strap-on boosters are jettisoned from the Delta's first stage. The spent casings fall into the ocean.
T+03:53.5	Begin engine throttling
	With engine shutdown coming up and the axial acceleration reached, the RS-68 powerplant starts throttling down from 101 percent. It will achieve a 58 percent throttle at T+3 minutes, 58.5 seconds.
T+04:04.8	Main engine cutoff
	The first large all-American rocket engine developed in a quarter-century completes its first launch as the RS-68 shuts down.
T+04:15.8	Stage separation
	The Common Booster Core first stage -- making its first flight -- and the attached interstage are separated in one piece from the Delta 4's upper stage. The upper stage engine's extendible nozzle drops into position as the first stage separates.
T+04:29.3	Second stage ignition
	The upper stage begins its job to place the Eutelsat W5 spacecraft into space with the first of two firings. The stage and its Pratt & Whitney RL-10B-2 liquid hydrogen/liquid oxygen engine is basically identical to the Delta 3 upper stage flown previously.
T+04:39.0	Jettison payload fairing
	The four-meter diameter composite payload fairing that protected the W5 cargo atop the Delta 4 during the atmospheric ascent is no longer needed, allowing it to be jettisoned in two halves.
T+13:06.4	Upper stage shutdown
	The RL-10 upper stage engine shuts down to complete its first firing of the launch. The rocket and attached satellite reach a parking orbit of 100.0 by 321.2 nautical miles with an inclination of 27.3 degrees.
T+23:26.4	Restart upper stage
	After a 10-minute coast period, the upper stage is reignited to finish the task of boosting W5 into the intended orbit. The stage's pitch program begins six seconds after restart and lasts until moments before engine cutoff.
T+28:25.7	Upper stage shutdown
	The powered phase of the Delta 4's mission to loft W5 concludes. The targeted geosynchronous transfer orbit is 290.3 by 19,420.1 nautical miles with an inclination of 13.5 degrees.
T+28:55.7	Maneuver to deploy attitude
	The upper stage uses its thrusters to maneuver into the proper orientation for release of W5. This attitude maneuver will last until T+30 minutes, 20.7 seconds.
T+37:11.2	Begin spin-up
	The next step in preparing for deployment of the payload is spinning up the stage like a top to 1.5 rpm.
T+37:35.7	Spacecraft separate
	The W5 telecommunications satellite is released into space from the Delta 4 rocket. Operated by Eutelsat of Paris, W5 will use its onboard engine later to reach geostationary orbit where it will match Earth's rotation and appear fixed above the equator at 70.5 degrees East longitude. The craft's 24 Ku-band transponders will serve western Europe, Asia and northern Australia.

Image and data source: Boeing.