Lunar mission launch sequence

The Saturn V carried all Apollo lunar missions. All Saturn V missions launched from Launch Complex 39 at the John F. Kennedy Space Center. After

the rocket cleared the launch tower, mission control transferred to the Johnson Space Center in Houston, Texas.

An average mission used the rocket for a total of just 20 minutes. Although Apollo 6 and Apollo 13 experienced engine failures, the onboard com

puters were able to compensate by burning the remaining engines longer, and none of the Apollo launches resulted in a payload loss.

The first stage burned for 2.5 minutes, lifting the rocket to an altitude of 42 miles (68 km) and a speed of 6,164 miles per hour (9,920 km/h) and burning 2,000,000 kilograms (4,400,000 lb) of propellant.

At 8.9 seconds before launch, the first stage ignition sequence started. The center engine ignited first, followed by opposing outboard pairs at 300-millisecond intervals to reduce the structural loads on the rocket. When thrust had been confirmed by the onboard computers, the rocket was "soft-released" in two stages: first, the hold-down arms released the rocket, and second, as the rocket began to accelerate upwards, it was slowed by tapered metal pins pulled through dies for half a second. Once the rocket had lifted off, it could not safely settle back down onto the pad if the engines failed.

It took about 12 seconds for the rocket to clear the tower. During this time, it yawed 1.25 degrees away from the tower to ensure adequate clearance despite adverse winds. (This yaw, although small, can be seen in launch photos taken from the east or west.) At an altitude of 430 feet (130 m) the rocket rolled to the correct flight azimuth and then gradually pitched down until 38 seconds after second stage ignition. This pitch program was set according to the prevailing winds during the launch month. The four outboard engines also tilted toward the outside so that in the event of a premature outboard engine shutdown the r

emaining engines would thrust through the rocket's center of gravity. The Saturn V quickly accelerated, reaching 1,600 feet per second (490 m/s) at over 1 mile (1,600 m) in altitude. Much of the early portion of the flight was spent gaining altitude, with the required velocity coming later.

Apollo 11 S-IC separation

At about 80 seconds, the rocket experienced maximum dynamic p

ressure (Max Q). The dynamic pressure on a rocket varies with air density and the square of relative velocity. Although velocity continues to increase, air density decreases so quickly with altitude that dynamic pressure falls below Max Q.

Acceleration increased during S-IC flight for two reasons: decreasing propellant mass; and increasing thrust as F-1 engine efficiency improved in the thinner air at altitude. At 135 seconds, the inboard (center) engine shut down to limit acceleration to 4 g (40 m/s2). The other engines continued to burn until either oxidizer or fuel depletion as detected by sensors in the suction assemblies. First stage separation was a little less than one second after cutoff to allow for F-1 thrust tail-off. Eight small solid fuel separation motors backed the S-IC from the interstage at an altitude of about 67 kilometers (42 mi).

The first stage continued ballistically to an altitude of about 109 kilomet

ers (68 mi) and then fell in the Atlantic Ocean about 560 kilometers (350 mi) downrange.

S-II sequence

After S-IC separation, the S-II second stage burned for 6 minutes and propelled the craft to 109 miles (176 km) and 15,647 mph (25,182 km/h– 7.00 km/s), close to orbital velocity.

For the first two unmanned launches, eight solid-fuel ullage motors ignited for four seconds to give positive acceleration to the S-II stage, followed by start of the five J-2 engines. For the first seven manned Apollo missions only four ullage motors were used on the S-II, and they were eliminated completely f

or the final four launches. About 30 seconds after first stage separation, the interstage ring dropped from the second stage. This was done with an inertially fixed attitude so that the interstage, only 1 meter from the outboard J-2 engines, would fall cleanly without contacting them. Shortly after interstage separation the Launch Escape System was also jettisoned. SeeApollo abort modes for

more information about the various abort modes that could have been used during a launch.

About 38 seconds after the second stage ignition the Saturn V switched from a preprogrammed trajectory to a "closed loop" or Iterative Guidance Mode. The Instrument Unit now computed in real time the most fuel-efficient trajectory toward its target orbit. If the Instrument Unit failed, the crew could switch control of the Saturn to the Command Module

's computer, take manual control, or abort the flight.

About 90 seconds before the second stage cutoff, the center engine shut down to reduce longitudinal pogo oscillations. A pogo suppressor, first flown on Apollo 14, stopped this motion but the center engine was still shut down early to limit acceleration G forces. At around this time, the LOX flow rate decreased, changing the mix ratio of the two propellants, ensuring that there would be as little propellant as possible left in the tanks at the end of second stage flight. This was done at a predetermined delta-v.

Five level sensors in the bottom of each S-II propellant tank were armed during S-II flight, allowing any two to trigger S-II cutoff and staging when they were uncovered. One second after the second stage cut off it separated and several seconds later the third stage ignited. Solid fuel retro-rockets mounted on the interstage at the top of the S-II fired to back it away from the S-IVB. The S-II impacted about 4200 km (2,300 miles) from the lau

nch site.

S-IVB sequence

Unlike the two-plane separation of the S-IC and S-II, the S-II and S-IVB stages separated with a single step. Although it was constructed as part of the third stage, the interstage remained attache

d to the second stage.

During Apollo 11, a typical lunar mission, the third stage burned

for about 2.5 minutes until first cutoff at 11 minutes 40 seconds. At this point

it was 2640 km downrange and in a parking orbit at an altitude of 188 km and velocity of 7790 m/sec. The third stage remained attached to the spacecraft while it

orbited the Earth two and a half times while astronauts and mission controllers prepared for tra

nslunar injection (TLI).

This parking orbit is quite low by Earth orbit standards, and it would have been short-lived due to aerodynamic drag. This was not a problem on a lunar mission because of the short stay in the parking orbit. The S-IVB also continued to thrust at a low level with hydrogen vents to settle the propellants in their tanks, and this thrust easily exceeded aerodynamic drag.

For the final three Apollo flights, the temporary parking orbit was even lower (approximately 150 kilometers (93 mi)), to increase payload for these missions. For the two Earth orbit missions of the Saturn V, Apollo 9 and Skylab, the orbits were much higher and more typical of manned orbital missions.

On Apollo 11, TLI came at 2 hours and 44 minutes

after launch. The S-IVB burned for almost six minutes giving the spacecraft a velocity close to the Earth's escape velocity of 11.2 km/s (40,320 km/h; 25,053 mph). This gave an energy-efficient transfer to lunar orbit with the moon helping to capture the spacecraft with a minimum of CSM fuel consumption.

About 40 minutes after TLI the Apollo Command Service Module (CSM) separated from the third stage, turned 180 degrees and docked with the Lunar Module(LM) that rode below the CSM during launch. The CSM and LM separated from the spent third stage 50 minutes later.

If it were to remain on the same trajectory as the spacecraft, the S-IVB could have presented a collision hazard so its remaining propellants were vented and the auxiliary propulsion system fired to move it away. For lunar missions before Apollo 13, the S-IVB was directed toward the moon's trailing edge in its orbit so that the moon would slingshot it beyond earth escape velocity and into solar orbit. From Apollo 13 onwards, controllers directed the S-IVB to hit the Moon.[15]Seismometers left behind by previous missions detected the impacts, and the information helped map the inside of the Moon.

Apollo 9 was a special case; although it was an earth orbital mission, after spacecraft separation its S-IVB was fired out of earth orbit into a solar orbit.

On September 3, 2002, Bill Yeung discovered a suspected asteroid, which was given the discovery designation J002E3. It appeared to be in orbit around the Earth, and was soon discovered from spectral analysis to be covered in white titanium dioxide paint, the same paint used for the Saturn V. Calculation of orbital parameters identified the apparent asteroid as being the Apollo 12 S-IVB stage. Mission controllers had planned to send Apollo 12's S-IVB into solar orbit, but the burn after separating from the Apollo spacecraft lasted too long, and hence it did not pass close enough to the Moon, remaining in a barely-stable orbit around the Earth and Moon. In 1971, through a series of gravitational perturbations, it is believed to have entered in a solar orbit and then returned into weakly-captured Earth orbit 31 years later. It left Earth orbit again in June 2003. Another near-earth object, discovered in 2006 and designated 6Q0B44E, may also be part of an Apollo spacecraft.