United Launch Alliance (ULA) uses a unique version of its Atlas V countdown for human spaceflight missions, in the name of safety, to complete hazardous fueling operations and then place the rocket in a quiescent state before the astronauts board. 

Launch of the Crew Flight Test (CFT) is planned for May 6 at 10:34 p.m. EDT (0234 UTC) from Space Launch Complex-41 (SLC-41) at Cape Canaveral Space Force Station in Florida. A live countdown blog and launch webcast in collaboration with Boeing and NASA will be available on the ULA website. 

The Atlas V launch countdown begins 11 hours and 20 minutes before liftoff and features a four-hour planned, built-in hold at the T-minus four-minute mark for crew ingress into Starliner. 

Overseeing the start of the countdown is the "Preps Team" of console operators inside the Advanced Spaceflight Operations Center. Launch Conductor Dillon Rice will orchestrate the countdown procedures from the Launch Control Center while ULA Launch Director James Whelan is at the helm in the Mission Director's Center.  

This initial phase of the count will be spent powering up the rocket, running system checkouts, completing standard pre-launch testing and performing final preparations on the rocket and pad systems for propellant-loading operations. 

The Preps Team will lead the countdown through its first five hours, then a shift change occurs to hand each station to the "Tanking & Launch Team" of console operators. These counterparts take responsibilities for the next six hours through liftoff, led by ULA Chief Launch Conductor Doug Lebo and ULA Launch Director Tom Heter.  

The shift handover happens during the planned, hour-long countdown hold at T-minus two hours. Just before the hold concludes, readiness polls are conducted to authorize the start of cryogenic tanking. With the pad cleared of all personnel, the hazardous operation of liquid oxygen and liquid hydrogen filling the Atlas V rocket's stages for launch is performed. 

Once fueling is completed and the rocket's tanks placed into stable replenishment, the countdown enters the extended hold at T-minus four minutes. The Blue Team is dispatched to the pad's 200-foot-tall (61-m) Crew Access Tower (CAT) to ready the White Room and Starliner crew module for arrival of the astronauts, assist the crew into their seats and then close the hatch for flight.  

The team is comprised of eight specialists from ULA and Boeing. Dane Drefke, ULA's mechanical operations lead engineer serves as the Blue Team Leader (BTL). He is in charge of the Blue Team's activities and has an obligation to ensure everyone's safety. 

ULA's three representatives on the Blue Team begin activities by walking across the 48-foot-long (14.6-m) retractable catwalk extending from the CAT to the White Room. Their duties include verifying the White Room is safe for personnel to enter, establishing access to the capsule, deploying the environmental seal between the pad and spacecraft and setting up access platforms. 

The ULA members then switch places with five Boeing technicians, waiting in the wings on the CAT, led by Boeing's Pad Team Leader Nate Keyek-Franssen for assisting the crew into the spacecraft.  

The astronauts, commander Butch Wilmore and pilot Suni Williams, receive a final weather briefing and don their spacesuits before leaving NASA's Crew Quarters in the Neil Armstrong Operations & Checkout Building at the Kennedy Space Center. Departure to board Boeing's Crew Transport Vehicle (CTV) occurs about three hours and 20 minutes before launch. 

The trip to SLC-41 will take about 25 minutes, with the CTV arriving at the base of the CAT approximately two hours and 55 minutes before launch. The astronauts will take the elevator to Level 12 while the CTV convoy departs the pad and heads to the safe fallback area. 

Once crew ingress is completed, another weather briefing will be held 90 minutes before launch, to inform mission managers that conditions are suitable for the Blue Team to close the Starliner hatch and proceed with the countdown. Pending a go, Boeing technicians will close the hatch and perform cabin leak checks to verify the integrity of the seal. 

Boeing personnel then depart the White Room so that the ULA technicians can retract access platforms and deflate the environmental seal around the spacecraft to prepare the Crew Access Arm for rotation to the launch position later in the countdown. The entire Blue Team departs the pad about 35 minutes before liftoff. 

The access arm will be hydraulically swung away from the spacecraft 11 minutes prior to launch. The process will take about two minutes to reach the stowed position against the CAT. If the need arises, the arm can be redeployed in less than 15 seconds by dropping counterweights. 

Seven minutes before launch, Lebo performs the readiness polling of the launch team members, Ascent Flight Director Mike Lammers in Houston and the Starliner crew before Heter gives final permission to launch. The countdown clocks resume four minutes before liftoff to put the rocket on internal power, pressurize its tanks, arm systems and start the main engine. 

The daily available launch window is instantaneous, meaning there is only an instant in time each day for launch to occur. This split second happens when the orbital plane of the International Space Station passes over the launch pad, thereby enabling Atlas V to put Starliner on the proper trajectory to intercept the station for rendezvous and docking. 

The main engine and twin solid rocket boosters generate 1.6 million pounds (7.1 mega-Newtons) of thrust to begin the voyage of Wilmore and Williams. The commander will call out "roll program" as Atlas V clears the tower to place the astronauts heads-up for their ride to space. 

The main engine will ease back for a period of deep throttling, going into its throttle bucket during the region of maximum aerodynamic stresses on the rocket in the dense lower atmosphere and to lessen the G-loads on the crew. 

The solid rocket boosters burn for a minute-and-a-half, followed by the main engine revving back to full throttle, to triple the rocket's velocity through the remaining first stage of flight. 

Just over two minutes after liftoff, Atlas V will have burned nearly 500,000 pounds (227,000 kg) of fuel and weigh only half of what it did at launch. 

Following the first stage engine shutdown, the Atlas V common core booster will jettison from the Centaur four minutes and 35 seconds after liftoff. The Centaur ignites both engines 10 seconds later at an altitude of approximately 60 nautical miles (111 km). 

The Centaur burn will last just over seven minutes to deliver Starliner at the desired injection point for separation at T+plus 14 minutes, 55 seconds into a 98 by 39-nautical mile (181x72-km) suborbital trajectory, inclined 51.6 degrees relative to the equator. 

Atlas V will launch northeasterly from Cape Canaveral, paralleling the Eastern Seaboard and crossing the North Atlantic to accelerate Starliner to 17,475 mph (28,123 kmph). 

For Starliner missions, Atlas V takes a special trajectory to space that requires the Centaur upper stage to use two engines instead of one. The double-engine configuration allows the rocket to fly a flatter trajectory and ensure the spacecraft can execute an abort at any time to bring the astronauts back to Earth safely if a problem occurs. 

Dual Engine Centaur also enables the customized flight profile for Starliner that features just a single burn and a limited acceleration rate to manage the G-force experienced by the astronauts aboard.  

After Centaur releases Starliner, the spacecraft employs the same operational procedure as the space shuttle, which also launched on suborbital trajectories, by performing an orbital-maneuvering engine firing to reach a stable orbit about 15 minutes after separation. 

Learn more about the Atlas V CFT launch
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