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Apollo Pathfinders

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Project Apollo: The Beginnings | Mission Planning | Landing Site Selection | Earthbound Support Systems
Astronaut Selection and Training | The Saturn V | The Saturn 1B | The Apollo Spacecraft
Guidance and Navigation | Command and Service Modules | The Lunar Module
Assembling and Launching | Pathfinders | The Early Missions | Apollo 11, The First Landing
The Intermediate Missions | Apollo 15 Exploration | Apollo 16 Exploration | Apollo 17 Exploration
Skylab and Apollo-Soyuz | Conclusion

In the early 1960s, the only information available to NASA scientists of the conditions likely to be encountered on the lunar surface were from Earth-based telescopic observation and remote radar sensing. The best available photographs could only resolve lunar surface features down to about 60 feet. Speculation within the scientific community on surface conditions ranged widely and warnings by some scientists that the lunar surface would be found to be many feet deep in soft dust into which a lander would sink without trace, or that the terrain would prove to be too rough for a landing were all unknown factors that could not be dismissed. Hard evidence was in short supply and NASA needed more accurate data which could influence the spacecraft design and landing site choice.


Part of the solution came in the form of an unmanned deep space probe under development at the Jet Propulsion Laboratory in Pasadena, California. Named Ranger, the spacecraft was originally intended to be a versatile probe that could carry various scientific experiments and to be used for a number of deep space scientific expeditions. Ranger was seconded to the Apollo program to obtain the necessary lunar data. A series of embarrassing failures had already blighted its development almost to the point of cancellation as the first six Rangers failed to complete their missions. On 31 July, 1964, Ranger 7 finally succeeded and returned close up photographs of the lunar surface with its bank of six forward facing television cameras as it plunged in a terminal dive to destruction in the Mare Nubium (Sea of Clouds). It returned 4,316 pictures with its closest images to the surface, taken at an altitude of less than a mile, showed final resolution features down to three feet.

Two more Rangers followed in 1965. Ranger 8 plunged into Mare Tranquillatitus (Sea of Tranquillity) at a shallow angle and Ranger 9 into Alphonsus crater returning almost 13,000 pictures between them. The resolution of the returned images was a four hundred-fold improvement on earth based observations, but because of the probes near vertical final trajectory the gain in resolution was offset by the reducing area coverage. The images indicated that the surface was relatively firm but further evidence of its ability to support the weight of a manned spacecraft was required.


Also under development with JPL another probe, designated Surveyor, designed as a soft lander was called into use with the Apollo program. On 2 June, 1966, Surveyor 1 touched down in the 'Oceanus Procellerum' (Ocean of Storms) within the confines of the Flamsteed ring, bounced and touched down again. Its only instrument was a television camera that transmitted nearly 11,000 pictures of its surroundings before expiring in July 1967. Surveyor 2 destined for the Sinus Medii lost contact and crashed into the lunar surface but Surveyor 3 touched down, bounced and slid slightly down the gently inclined inner face of the crater wall in which it had landed. In addition to its television camera, Surveyor 3 carried a soil mechanics surface sampler. This experiment was a scoop on the end of a extendible arm that could be remotely controlled from the mission control centre to dig trenches and move rocks within its four feet reach while being viewed through the television camera. Surveyor 3 dug four trenches measuring the resistance of the surface soil to the scoop's pressure and transmitted 6,000 pictures before expiring after only one lunar night.

Another attempt to land in the Sinus Medii failed when contact with Surveyor 4 was lost two and a half minutes before touch down and was presumed to have crashed. Surveyor 5 landed successfully in a crater in the Mare Tranquillitatis (Sea of Tranquillity) on 10 September 1967, 40 miles from the Ranger 8 site. In place of the scoop Surveyor 5 carried an Alpha particle back-scattering experiment to analyse the chemical content of the soil. After taking readings the craft was commanded to fire its thrusters causing it to make a hop of a few feet to a second location where it repeated the experiment. Surveyor 5 returned another 19,000 pictures of the inside of its crater despite being unable to see over its rim.

Surveyor 6 finally broke the run of bad luck with the Sinus Medii when it landed on the 10 November 1967 with its alpha-scatterer and television camera. After gathering information it performed a hop of nine feet to a second location and returned 30,000 pictures. With sufficient data covering the likely equatorial landing sites for Apollo the last Surveyor in the series was released from the Apollo project and given over to the scientific establishment to use as they wished. The choice came down to Tycho crater, which was not a likely Apollo site due to its rough terrain, where Surveyor 7 was sent complete with scoop, alpha-scatterer and television camera on 6 January, 1968. It landed safely but the deployment arm of the Alpha scatterer jammed and had to be moved into place by judicious use of the scoop mechanism. Surveyor 7 returned data and another 21,000 pictures.

Ranger and Surveyor finally established that the Mare plains were formed from lava flows and although cratered were flat enough to provide clear landing areas. The surface material was found to be composed of dust and loose particles but was sufficiently compacted to bear the weight of a manned lander. The next question to be answered still remained, where should the first landing should take place.

Lunar Orbiter

Where Ranger and Surveyor were projects in their own right begun before NASA's commitment to a lunar landing and subsequently seconded to support the Apollo program, Lunar Orbiter was born directly out of the Apollo program as a pathfinder for potential Apollo landing sites. Developed by the Langley Research Centre and running concurrently with the Surveyor program it used film-based cameras with wide angle and high-resolution lenses to survey the lunar surface in close detail. Its primary purpose was to photograph proposed landing sites for certification in the equatorial region of the moons nearside from an elliptical orbit with its perilune over the target area.

Lunar Orbiter 1 arrived in a lunar orbit inclined at 11 degrees to the equator on 14 August, 1966, and began returning pictures four days later. A fault in the close-up camera's motion compensatory mechanism caused the pictures to smear and all but a few of the close-up photographs were of poor resolution but it did manage a few good frames of the farside face. The remainder of the wide scan images were good and during one pass the craft was turned to shoot the earth rising above a lunar landscape for the first time. Lunar Orbiter 1 was then de-orbited to crash into the moons farside and clear the way for the following attempts.

Lunar Orbiter 2 began operations on the 18 November, 1966. This time the camera worked faultlessly and began to capture images of 13 primary Apollo Landing Sites in the northern sector of the ALZ. Another photograph taken at an oblique angle captured a stunning image of the terraced crater Copernicus which was subsequently released to the press and was hailed as the 'Picture of the Century' through world-wide media publication.

Lunar Orbiter 3 was placed in a lower and more inclined orbit on 8 February, 1967 to cover the sites of both previous probes in greater detail and re-shoot the poor images from Lunar Orbiter 1. A fault developed with the data transfer mechanism resulting in a loss of 30 per cent of the pictures but sufficient information was obtained to satiate the needs of the mission planners.

20 groups of prime landing sights stretching along the ALZ were covered by the first three orbiters. With the photographic evidence available from the three probes the site selection board was eventually able to narrow the choice down to five individual sites for the first landing attempt. Two, Apollo Landing Site 1 (ALS1) and ALS2, were located in the eastern Mare Tranquillitatis with a back up ALS3, in Sinus Medii practically plumb centre on the moons visible face. tarm189 ALS5 in the Oceanus Procellarum at the north western end of the ALZ was the final back-up if the launch window slipped more than two earth days. ALS4, also in Procellarum, was available as a backup for launches taking place during winter months.

The successes of the first three orbiters released the remaining three planned orbiters for other duties. One was ultimately cancelled, but Lunar Orbiters 4 and 5 were duly despatched on 4 May, 1967, and 1 August, 1967, respectively and placed into highly inclined orbits at 85 degree to the equator. The orbital height was also higher placing them in a position to map almost the entire surface of the moon including the largely unseen far side. From these photographs later Apollo missions would be planned outside the restrictions of the ALZ.

The Gemini Missions

Very little was known about the effects that living and working in space would have on human physiology, or indeed if it was even possible to exist in that environment for the time needed to complete a round trip to the moon. Various fears concerned doctors centred around the weightless conditions. It was feared that eyeballs would deform or bulge so far that it would render the owner unable to focus his eyes, or that the heart's automatic nervous system would fail after prolonged weightlessness or that the inner ear which relies on gravity to enable the sensing of 'up' or 'down'; would cause constant nausea. On long term flights bones were expected to demineralise and muscles to atrophy. All these and more required answers before committing astronauts to prolonged flights away from the relative safety of low earth orbit. The only way to obtain the answers was to place the men in space and see the results.

It was also necessary to try out the theories and investigate the practicalities of rendezvous and docking between separate spacecraft and their ability to change orbits which would be necessary to use the LOR mode. An interim program was designed to investigate all these questions using an 'Advanced Mercury' spacecraft that would be capable of flights in earth orbit of up to two weeks duration and with its own propulsion engine the ability to shift orbits. The program was announced in December 1961 as Mercury Mk II, but was later given the name 'Gemini' reflecting its two man crew capability.

The first two 'Gemini' flights were unmanned tests of the two seat spacecraft using 'Titan' boosters to obtain orbital flight. Gemini III, the first manned Gemini mission with Virgil 'Gus' Grissom and John Young aboard, lifted off on 23 March, 1965, and orbited the earth three times to demonstrate the ability to shift their craft into a different, higher orbit during the flight. This crucial manoeuvre would be necessary to complete a rendezvous and link up of the LM and CSM in a lunar orbit. Grissom, the second American in space, had named his Gemini spacecraft 'Molly Brown' after the stage play The Unsinkable Molly Brown a current Broadway hit stage show of the time. He had been criticised after the loss of his 'Mercury' capsule that sank when the hatch was blown on splashdown. Although the name remained on the Gemini craft, NASA did not appreciate the irony and banned all further names in the Gemini program, referring to them only by their flight numbers, with Roman numerals.

Missions in the Gemini series continued with each new flight staying up longer and carrying out more ambitious tasks. Gemini IV lifted off on 3 June, 1965, for a four-day flight which was to include a rendezvous with the second stage of their own Titan booster after separation. Also as a last minute addition to the flight plan, a spacewalk, due to the Soviet spacewalk by Aleksei Leonov from Voskhod 2 almost three months earlier. This came much to the surprise of his wife, who had not been informed of the EVA, when to her consternation she realised as she listened to the transmissions between spacecraft and mission control that he was 'going outside'. Ed White became the first American spacewalker, spending some 20 minutes outside his spacecraft at the end of an umbilical cord during which he experimented with a hand held, gas powered manoeuvring unit. Evidentially he enjoyed the walk so much that he had to be ordered back into the spacecraft by his commander Jim McDivitt.

The Gemini program progressed but not without its problems. On 21 August, 1965, Gordon Cooper and Pete Conrad began an eight day mission to test the use of fuel cells to provide the Gemini spacecraft with power instead of batteries which had hitherto been used. Also on test was the first use of rendezvous radar necessary to locate and bring together two spacecraft. Both were to be extensively used in the Apollo spacecraft. Just after obtaining orbit, Gemini V launched a pod equipped with a flashing strobe light and containing a radar transponder that was to act as a target to home onto. Faults developed with the oxygen tank pressure that supplied the fuel cells which resulted in a curtailment of the radar experiment before it was completed, but sufficient oxygen pressure was eventually recovered to continue the flight for its full span.

Walter Schirra and Thomas Stafford in Gemini VI were to rendezvous and practice the docking manoeuvre with an unmanned 'Agena' target rocket, but were stood down when the 'Agena' was destroyed during its take off. Instead, NASA delayed Gemini VI's launch until Gemini VII was ready and on 4th December 1965, Gemini VII took off with Frank Borman and James Lovell aboard for a planned 14 day duration flight. Borman and Lovell were to explore the effects of long term weightlessness on the human frame. Eight days later Schirra and Stafford in the now re-numbered Gemini VIA, tried again only to have the launch aborted when an electrical plug vibrated loose and the engine shut down on the launchpad.

On their third attempt Schirra and Stafford finally followed Gemini VII into orbit on the 15th December 1965. Their mission to rendezvous in orbit with Gemini VII was carried out successfully six hours later as they closed to within three feet and flew in formation with Gemini VII. Stafford manoeuvred his craft around Borman and flashed a card with the written message 'Fly Navy' before separating and returning home. Borman and Lovell stayed in orbit before returning to earth after 14 days and 206 earth orbits. During their flight two of the three on-board fuel cells, and two manoeuvring thrusters failed, but they set a new endurance record and establishing that humans could live under weightless conditions for the duration of a lunar mission.

The next docking attempt was to be by Gemini VIII piloted by Neil Armstrong and David Scott. They successfully completed the first docking between spacecraft, with their target Agena, but one of the Gemini's manoeuvring thruster stuck on, firing continuously and sending the linked craft spinning around its horizontal axis. Thinking that the fault lay in the Agena, Armstrong separated from the target before the rapidly building rotational forces tore them apart. The fault however was in one of the Gemini's thrusters and without the mass of the Agena, the speed of rotation of the Gemini increased to almost a full revolution a second before he could isolate the faulty thruster. His efforts to regain control of the craft had used most of his manoeuvring fuel supply and he was forced to control the spin by firing the back-up re-entry thrusters. This forced abandonment of the mission and an early return to earth after only ten and a half hours. The Agena's engine was fired to place it into a 250 miles high holding orbit.

On the 28 February the prime crew for Gemini IX, Elliot See and Charles Bassett, were killed when the wing of their aircraft clipped the roof of a building at the McDonnell plant in St Louis while attempting a landing in poor visibility and cartwheeled into an adjacent parking lot. Ironically the building housed their partly completed spacecraft which was undamaged although eighteen other people were injured. The back-up crew of Tom Stafford and Eugene Cernan took over as the prime crew.

On the 18 May, 1966, another target Agena for Gemini IX blew up as it ignited on separating from its Atlas first stage booster. After the problems experienced during the previous flights NASA and the Gemini manufacturers McDonnell, had devised a back-up target-docking module known as the Augmented Target Docking Adapter (ADTA). It was an Agena without fuel or engines that could be made ready at short notice and launched by a single stage Atlas. The first ADTA was quickly readied and successfully launched into orbit on 1 June.

Stafford and Cernan followed on 3 June in the Gemini spacecraft to carry out another attempt at rendezvous and docking. After three orbits they approached their target to find that the clamshell nosecone that protected the docking mechanism had not fully detached and was still covering the target ring. The nosecone with its lipped beak like end was gaping open and skewed at an angle giving the target the appearance of an 'angry alligator'. With the nosecone still in place, docking was impossible and Stafford and Cernan could only photograph their target and carryout a number of rendezvous exercises and station keeping with the target.

Cernan carried out the second American spacewalk to test the mobility of their spacesuits and was also scheduled to test a new Astronaut Manoeuvring Unit (AMU). The AMU was a strap on manoeuvring pack with its own propulsion and control system to allow the spacewalking astronaut to manoeuvre himself between targets. Housed in the rear service area of the Gemini craft Cernan was scheduled to spacewalk to the service bay, extract and don the unit to test it. Without handholds on the exterior of the Gemini he found that he was unable to gain sufficient leverage to extract and completely don the unit. After several attempts he became exhausted with his efforts and overheated inside his suit causing his helmet to mist up. Tired and unable to see beyond his helmet's faceplate he was eventually forced to give up the task and return to the spacecraft. His efforts lasted two hours and ten minutes, long enough to become the first astronaut to spacewalk around the world. After a rest period Gemini IX re-entered on 6 June.

Gemini X crewed by John Young and Mike Collins were the first crew to successfully dock with another space vehicle and complete its mission. Launched on 18 July, 1966, Young and Collins docked Gemini X with its target Agena after four orbits and using the Agena's engine powered themselves backwards, into an elliptical orbit of 180 miles by 475 miles and in doing so become the world altitude record holders. The high orbit took them into the lower reaches of the Van Allen radiation belts that surround the earth where they measured the amount of radiation. After a rest period, two burns of the Agena's engine took them into a 185 by 240 mile orbit which was timed to meet up with the Gemini VIII Agena target left circling the earth the previous March.

Collins was scheduled to carry out two spacewalks. The first, a stand-up EVA, to be carried out on the night side of earth, involved opening his hatch and standing up in the hatchway to carry out a number of experiments including taking navigational star sightings and ultra violet photography. With the photography almost completed, as the spacecraft entered the daylight side both crewmen's eyes began to water until neither can see fully. The experiments had to be curtailed to get Collins inside the craft and their helmets off. The fault was attributed to the simultaneous use of two suit fans that circulated oxygen through the crew's spacesuits. It was thought that dislodged particles from the lithium hydroxide filters, used to scrub carbon dioxide from the suit breathing circuit, had been passed to the suit helmets which caused the eye irritation.

After jettisoning the Agena Young and Collins fired the Gemini's thrusters to close with the Gemini VIII Agena some 95 miles ahead. Young closed in and kept station just below the target while Collins exited the spacecraft for his second EVA to retrieve a micro-meteorite experiment on the Agena's surface. Using a 50 foot umbilical his first attempt to reach the Agena ended in failure as he bounced off the target. Using a hand held manoeuvring unit on his second try he jetted across to the Agena and was able to grab a handful of wiring inside the craft's adapter cone as he passed. He experienced similar difficulties to those that Cernan had encountered, and was unable to get handholds to stop himself twisting away from the Agena as he worked to remove the micro-meteorite package.

By bracing himself against the Agena and hanging onto the wiring he finally got sufficient purchase to retrieve the package. His efforts caused him to become entangled with his umbilical supply hose and sent the Agena into a tumble. Young, who was trying to keep Collins in sight and manoeuvre the Gemini without blasting Collins with the Gemini's manoeuvring thrusters finally advised him to 'Get out of that mess babe'!. Collins pulled himself back to the Gemini hand over hand using the umbilical to end the EVA. On re-entering the spacecraft found that the Hassleblad camera he had been using to record the events, which had been clamped to a bracket on his chest had become detached and lost. They re-entered earth's atmosphere on 21 July.

Gemini XI went into orbit on 12 September, 1966, crewed by Pete Conrad and Dick Gordon. Their first objective was to rendezvous with their target Agena in their first orbit. This required the crew to carry out their own orbital calculations and update their computer manually to carry out the final burn to meet up with their target. Launched as the Agena passed overhead they went into orbit 15 miles lower than the Agena and caught it as they passed over Australia. As they made their first pass over Hawaii they docked and informed control that they had succeeded.

On the third day of the flight they used the Agena's engine to boost their height to over 850 miles taking the altitude record from Young and Collins. On returning to their original height they began the first EVA to carry out more ultra violet photography of star fields. While waiting to come around to the earth's night side they also became the first astronauts to fall asleep while standing up in the spacecraft's open hatchway.

Their next objective was to experiment with artificial gravity. Separating from the Agena after hitching the two craft together with a 30-foot tether they induced a rotation of the Gemini around the Agena to create centrifugal force to mimic gravity within the spacecraft. After several abortive attempts to get the two craft rotating they found that the two craft tended to drift together while the tether acted like a giant skipping rope. After a period the two craft settled down and began an effective rotation and the pair waltzed their way around the world. Gemini returned to earth on 15 September 1966 after 47 orbits.

Gemini XII was the final Gemini mission and was intended to resolve the remaining unanswered questions from the preceding flights. The main question remaining was how to carry out effective work in weightless conditions. Jim Lovell and Buzz Aldrin launched in Gemini XII on 11 November, 1966, and docked with their target Agena only to find that a faulty fuel pump in the Agena prevented them from proceeding with their planned high altitude flight. Using the experience gained by Cernan and Collins, Aldrin had practised his EVA in a water immersion tank with full-scale mock-ups of the Gemini equipment to simulate weightless conditions. Using handholds, rails and 'golden boots' that wedged into footholds, Aldrin was able to demonstrate that working in weightless conditions was practical, provided sufficient support and restraints were provided.

Gemini XII re-entered on 15 November, 1966, to bringing the program to its conclusion. It had proved the capability of humans to live and work in space for long duration's and that orbital manoeuvring, changes of orbital plane, rendezvous and docking between spacecraft was practical. The Gemini program as a whole, also provided a hard core of experienced astronauts ready to take on the challenge that was Apollo.

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