Apollo: 240,000 miles to the Moon and back

On July 16, 1969, the five F-1 engines on the mighty Saturn V ignited for their most critical test of all: generating one and one-half million pounds of thrust each, they launched three Apollo astronauts into the first leg of their journey toward the moon. After the first and second stages were exhausted and jettisoned, the third stage took over, adding just enough speed to achieve Earth orbit. During this “parking” orbit, the astronauts checked out all systems to determine that they were operating correctly. Then, when the “launch window” (best period of time to begin the translunar flight) was opened, the third stage fired again, increasing the speed to escape earth orbit and began the trajectory toward the Moon.

On the way to the Moon, the Command Module (CM) containing the three astronauts, together with the Service Module (SM) containing the electrical power supply equipment and the SM propulsion system, separated from the third stage of the Saturn V, turned 180 degrees in space, and docked nose-to-nose with the Lunar Module (LM), which was contained in the top of the third stage. The combined Command-Service Modules (CSM) and LM then separated from the third stage and continued toward the Moon.

Approaching the Moon at a speed of about 5200 mph, the astronauts fired the SM rocket engine to slow the spacecraft to about 3600 mph, allowing it to swing into orbit approximately 80 miles above the lunar surface. Transferring to the LM, two astronauts fired TRW’s LM Descent Engine to achieve a transfer orbit (an orbit which intersected the Moon), while the CSM remained in lunar orbit. At an altitude of about 50, 000 feet, the LM Descent Engine fired again, braking the velocity to zero at about 200 feet above the lunar surface. At this point, the astronauts used the Descent Engine together with the control jets on the LM, moving horizontally as necessary, then descended to the selected landing spot.

During their stay on the Moon, the astronauts transmitted direct telecasts and radio descriptions, took photographs, and collected rock samples to bring home in vacuum-sealed containers. In addition, they set up a group of lunar surface experiments, which continued to radio information to Earth for as long as a year. These experiments reported on such phenomena as temperature changes, radiation levels, moonquakes, and micrometeoroids (tiny particles of matter in space).

lever de terre

Earth-rise as seen from the Moon, Apollo 8, bearing astronauts Borman, Lovell and Anders, orbited the Moon on Christams Eve, 1968, and returned with this now-famous photo of the Earth as first seen by man from outer space.

To begin their return flight, the two astronauts fired the Ascent Engine to rejoin the still-orbiting CSM containing the third astronaut. The lower stage of the LM, having done its job, was used as a launch platform for the upper stage and was left behind on the Moon. Achieving the proper orbit at the proper time, the LM docked with the CSM. The two astronauts transferred to the CSM, and the LM was jettisoned and left in lunar orbit. The SM rocket engine ignited once more to build up lunar escape velocity, of about 5460 mph. Beyond 29,000 miles from the Moon, the Earth’s gravitational pool became dominant, increasing the return speed to about 25,000 mph – the same velocity at which the crew left Earth just eight days before.

After using the SM rocket engine for final course corrections the astronauts jettisoned the SM, and the CM plunged toward the Earth.

The re-entry corridor of correct flight path into Earth’s atmosphere represented one of many phases during the mission when the functioning of men and machines had to be extremely precise – when tolerances were very close, and performing within them could have been a matter of life and death.  Only 40 miles wide, this extremely critical path had to be kept at an angle of 5 ½ degrees to 7 ½ degrees to the Earth horizontal. It the angle was too steep (over 7 ½), re-entry would have been too rapid, and the “g-loads” from hidden deceleration would have exceeded the human limitations of the astronauts inside. If it were not steep enough (under 5 ½ degrees), the CM would skip off the outer surface of the atmosphere like a stone skipping across water and out into Earth orbit.  If that had happened, the astronauts would have been trapped in orbit, with no means of ever getting back.

But the correct path was maintained, the three astronauts re-entered Earth’s atmosphere at about 25,000 miles per hour, with the CM heatshield reaching temperatures at around 5, 000 degrees F, and air resistance rapidly cut the velocity to s safe point for parachute deployment and landing in the South Pacific.

The thrilling climax to the Apollo program, when the astronauts actually made their trip to the Moon, was followed closely by everyone. But like the peak of an iceberg protruding above the water, their launch and safe return were only the visible portion of a program so massive as so complex as to rank among the largest efforts ever undertaken by men. Few of those who witnessed the launch will be able to comprehend the magnitude of preparation, or the number of calculations, trials, failures, and recalculations which preceded the flight.

For example, long before the Saturn V blasted off from Cape Kennedy (Cape Canaveral), it had flown its mission many times under simulated conditions in a TRW computer.  Working from data collected during ground tests, the TRW developed computer models of the Apollo propulsion systems. These models, which were updated and refined as flight data were obtained, have been used to plan Apollo missions and to analyze their results.

The great heat to which the Apollo spacecraft was exposed during ascent and re-entry through Earth’s atmosphere made it necessary to scrutinize very carefully its structure as well as its materials and coatings of the spacecraft for thermal stability, and the internal structure for thermally-induced stress.

A successful lunar landing required the LM landing radar to provide extremely accurate readings of the craft’s altitude, attitude, and speed of approach. The experts provided a comprehensive evaluation of this subsystem through computer simulation.

Fuel, oxygen, hydrogen, electrical energy and water were consumed during the lunar flights. These consumables had to be carefully budgeted to allow margins of safety without unduly increasing spacecraft weight. Scientist prepared consumable budgets and integrated them into preliminary flight plans.

In addition to these systems analysis tasks, scientists and engineers computed launch trajectories and reference mission trajectories; performed ranch safety analysis; short analysis and post-flight trajectory analysis; and provided re-entry mission planning support.

These are only a few of the more than 130 analytical tasks the team performed for Apollo, covering almost every aspect of the various Apollo missions.

A network of tracking stations around the world was established by Project Mercury, augmented for Gemini, and redesigned and expended for Apollo. One group of network stations followed the Apollo spacecraft at launch and during Earth orbit, and again at the end of the flight after the Moon trip was finished. When the spacecraft left the Earth orbit and passed out of range of these stations, tracking them switched to a second group of stations, containing powerful transmitters and sensitive receivers which were dependable for communications at great distances.

To test this vast network and to help train the personnel who operated the stations comprising it, TRW produced two test and training satellites from its ERS series of spacecraft.  Primarily, an orbiting transponder (combination receiver/transmitter capable of increasing the energy level of the received signal and retransmitting it on a different frequency), these satellites were used by NASA to check the Manned Space Flight Network, much as an orchestra conductor sounds each instrument prior to a concert.

44-pound stowaway: Barely noticed as it piggy-backed a ride on the Thrust Augmented Delta rocket that sent TRW`s Pioneer 8 into orbit around the Sun, the TRW-built Test and Training satellite was injected into a low earth orbit. It was used to train communication personnel and check out the equipment of NASA`s Apollo tracking network. A similar spacecraft accompanied Pioneer 9.

The Test and Training satellites belong to the family of TRW Environmental Research Satellites, an entire series of small spacecraft designed specifically for economical “piggyback” launches with larger payloads. A low-coast, reliable, quickly-assembled unit, the ERS may range in weight from 1,5 to 45 pounds. Source de l’image: astronautix.com

In 18 of these world-wide ground locations, as well as in a number of shipboard stations, TRW provided communication units known as Signal Data Demodulator Systems. Whether the astronauts were on the launch pad waiting for blast-off or whether they were on the surface of the Moon, these units relayed astronaut biochemical data (temperature, pulse, etc.), as well as video and voice communications, and – if these had failed – even simple radio telegraph key signals.

A highly reliable guidance system in the LM guided the astronauts from the CM to the Moon’s surface and back. This extremely critical system helped the astronauts maintain the correct LM altitude and course for a safe landing in the target area. During the ascent stage, it helped them in the ticklish job of launching into the precise orbit for rendezvous and docking with the CM. These tasks, seemingly simple in themselves, required precise and rapid determination of vehicle position, attitude, velocity, and course, as well as solution of complex guidance and navigation formulas.

Because these were such crucial tasks, the LM was equipped with a backup guidance system which operated in parallel with the primary system. This backup system is known as the LM Abort Guidance System, and would have allowed the astronauts to safely take over direct control of the lunar mission in the event of a primary guidance malfunction.

The LM/AGS is a strapdown inertial guidance system which uses the technique of strapping the inertial instruments required for sensing attitude and velocity to the vehicle. Conventional inertial guidance techniques require the mounting of the gyros and accelerometers on a stable platform. Eliminating this platform reduces the number of moving or electromechanical parts, thereby decreasing the size, weight, and power consumption of the subsystem as compared with a conventional inertial platform.

saturn v

Saturn V – The Apollo Moon Rocket. Poised on its launch pad at Kennedy Space Center is a Saturn V rocket like the one which carried three astronauts to the Moon. The Saturn V stands over 363 feet high. It developed over 7, 5 million pounds of thrust at liftoff.