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
Apollo 15 was the first of the new 'J' type missions, which was to bring a greater mobility and endurance to lunar exploration. It had originally been planned as a 'H' type mission with two EVA's using the 'rickshaw' handcart; but with budget cuts forcing the cancellation of one Apollo mission and the postponement of two more, it was decided to uprate Apollo 15 and reclassify it. 'J' missions were to provide the means to extend the lunar surface stay time to three days in order to exploit sites with multiple, but closely grouped features. They would encompass three separate EVA's and provide mobility in the form of motorized transport to extend their range beyond walking distance.
The 'Extended' lunar module incorporated larger fuel tanks, to increase the descent hover time, and increased supplies of water, oxygen, and batteries to extend the surface stay time. Also included was almost double the array of scientific experiments taken on previous missions. As a result, Apollo 15 lunar module's all up weight increased to 36,500 pounds, compared to Apollo 11, which weighed 33,200 pounds. To carry the increased weight, the LM's descent engine's power was increased by modifications including the enlargement of the efflux nozzle.
Further improvements to the 'J' class mission equipment included a redesigned space suit with greater flexibility at the waist, and the PLSS capacity extended to increase the individual EVA surface stay time to over seven hours, plus an additional two hour safety margin. For the first time, the orbiting service module would also carry an array of remote sensors in its spare bay, now labelled the Scientific Instrument Module (SIM) bay. The SIM bay would also house a small satellite to be launched into lunar orbit prior to return to earth.
Lunar Rover Vehicle
The greater part of the weight increase was due to the inclusion of a new innovation, the Lunar Rover Vehicle (LRV). Housed during flight on the descent stage, the LRV was a collapsible, electrically driven four wheeled car, popularly known as the 'Rover' or 'Moon Buggy'. Designed and built jointly by NASA's Marshall Space flight Centre and Boeing, it was intended to give the astronauts greater mobility and range to increase the mission's exploration capability.
Stowed against the side of the LM's descent stage in a collapsed configuration, the Rover was designed to unfurl as it was deployed onto the surface. The chassis frame was hinged in two places so that the front and rear axles with the wheels were folded across the centre part of the chassis. All four wheels also folded inwards, across the chassis. As the Rover was removed from its bay by pulling a series of lanyards, the hinged chassis unfolded under the influence of a series of spring loaded actuators and the wheels deployed sideways. The moveable parts were then locked into position by latch pins that were pushed home by the crew when the Rover was settled on the ground.
The Rover carried both crew members side by side in canvas frame seats. The commander seated on the left and the LM pilot on the right reflected their respective positions in the LM. Steering the vehicle was accomplished by a T shift handle which controlled the four wheel drive through individual electric motors located at each wheel. Pushing the T shift handle forward produced forward or reverse drive, depending on which had been selected from a separate switch; while pushing it left or right provided directional control to the front and rear wheels. The steering and drive to the wheels could be configured to either front or rear, or all four wheels together. Pulling the T shift back provided braking and a parking lock. The Rover's wheels were constructed of a woven wire mesh that incorporated a tread pattern on the contact surface, while the crew were protected from dust thrown up from the wheels by orange plastic guards.
Power was provided by a 120 ampere hour battery with a second, similar battery in reserve sufficient to propel its 460 pound weight over its theoretical range of 30 miles, at speeds up to seven miles per hour. On the rear of the vehicle a framework provided storage for samples and sampling tools. Mounted over the right front wheel was a colour television camera that was to be controlled remotely from mission control through a 'S' band directional aerial mounted over the opposite front wheel. Direct television communication with mission control depended on the aerial being manually aligned to within 2 degrees of the earth's orb at each stop; while voice and telemetry went through a low gain aerial mounted in the centre of the Rover. The alignment of the low gain aerial was not so critical, it being necessary to align it to within only 30 degrees of the earth. A further mounting for a 16mm sequence movie camera was provided on a swivel pillar beside the crew seats to provide a steady photographic platform.
The Rover also provided a computerized navigation system to give the crew a return bearing to the LM when out of sight. After initial zeroing in on the locality of the LM, revolution counters on the wheels provided the distance travelled, and when combined with heading information from the computer it gave a range and bearing back to the LM which was accurate to within a hundred yards. The Rovers range was limited by a 'walk back constraint' imposed by the mission rules which limited the distance it could travel outbound, to that which the astronauts could walk back in the event of the Rover's failure.
The multiple feature site chosen for its suitability as the first 'J' mission and the fourth lunar landing was to the Hadley-Apennine mountain region, 26 degrees north of the lunar equator. The Apennines are an arcuate mountain chain which was thrown up by the impact that created the Imbrium basin, forming the basin's south-eastern rim. Formed from single monolithic blocks, the massifs of the Apennine mountains are among the highest points on the lunar surface, towering over the designated landing spot by some 14,000 feet.
Flanked by Mount Hadley, the highest massif in the range, and the 12,000 foot Mount Hadley Delta adjacent to the landing zone required a steep (26 degree) angle of descent once the Apennine Front had been cleared. The Front's steep face adjacent to the basin formed the Apennine Front; and the landing site was to be in an enclosed valley on a patch of mare with the less than poetic name, Palus Putredinis (Swamp of Decay), located on the outer fringe of the Mare Imbrium (Sea of Rains), where it abutted the Front. At the foot of the mountains adjacent to the landing area, at the base of Mount Hadley Delta, another feature, Hadley Rille - a mile wide, sinuous canyon cutting 1,000 feet into the mare - crossed the valley floor and ran out into the Imbrium basin.
Landing at Hadley-Apennine
The crew of Apollo 15, Commander David R Scott, LM pilot James B Irwin, and CM pilot Alfred M Worden were all US Air Force personnel, consequently 'Falcon', their lunar module was named after the US Air Force academy's falcon mascot. The command module was named after the explorer Lt James Cook's ship 'Endeavour', which had sailed from England to Tahiti in 1769 to observe the transit of the planet Venus across the sun.
Launched on the 26 July, 1971, into a low (94 mile) altitude Earth parking orbit, Apollo 15 was allowed to just skim the upper fringes of the atmosphere as a fuel conservation measure. The heat generated from atmospheric friction during the one orbit in which the spacecraft systems were checked out, was considered to be an acceptable trade off for the weight of fuel saved. Apollo 15 carried out the TLI burn and withdrawal of the LM in routine fashion and arrived in lunar orbit 4 days later.
Scott and Irwin in 'Falcon' separated from the CM and began their descent to Hadley-Apennine. Tracking the crafts descent, Houston advised Scott that he was about a mile south of the planned flight path; and, as 'Falcon' pitched over in the final phase of the powered descent, Irwin was able to glance out of the cabin window and observe the peak of Mount Hadley above him as 'pings' brought the craft down towards the plain beside the Rille. Initially Scott was unable to recognise the landing point due to indistinct features in the undulating terrain, but eventually identified a group of craters called 'South Cluster'; and, with the rille in front of him, he blipped the Landing Point Designator hand controller to the north to find a relatively flat spot within a few hundred yards of the planned landing point.
Nearing the surface, the engine's efflux began to kick up much larger quantities of dust than had been experienced on previous landings, which effectively obscured the surface. Scott brought 'Falcon' down to a heavy landing with the rear two landing pads in a shallow crater that he hadn't been able to see, causing the craft to list back and to its left 11 degrees. The impact on touchdown brought the exclamation 'Bam...!' from Irwin as they thumped into the lunar landscape at over six feet per second.
Scott: 'Okay Houston... the Falcon is on the Plain at Hadley'
Post landing examination of the craft showed distortion in the engine's nozzle, which had occurred at touchdown as the nozzle came too close to the raised edge of the crater they had settled over.
After the post landing checks had been carried out, the crews first task was to carry out a 'Stand-Up EVA'. Depressurising the LM, Scott removed the upper (docking) hatch of the LM to view the surrounding terrain, taking panoramic photographs of the local features. He spent thirty five minutes with head and shoulders outside the craft photographing and describing the terrain and answering questions from the mission control 'back room' geologists. Eventually the SEVA was closed out and Scott and Irwin settled down to an eight hour rest period; and, for the first time, the crew of an Apollo mission were able to sleep without the encumbrance of space suits. While asleep, mission control monitored a worrying loss of oxygen pressure from the LM's cabin. They woke the crew early to find the source of the leak, which was eventually traced to a urine dump valve that had been left uncapped after use. Once rectified the crew prepared for their first moon walk.
First EVA: Hadley Rille, and St George Crater
Scott, on stepping off the LM's ladder:
As I stand out here in the wonder of the unknown at Hadley, I sort of realise there's a fundamental truth to our nature, Man must explore... and this is exploration at its greatest.
The first EVA began with the removal of the LRV from its stowage on the LM. Possibly due to the heavy landing, Scott found that the deployment arm for the Rover had become detached from its pivot in the descent stage; but he was able to refit the arm without difficulty. However, the backward list of the craft also made deployment of the Rover difficult; and it required both astronauts pushing against the LRV to get it far enough away from its storage bay to enable it to deploy and unfold.
With the Rover set up, Scott tried out its systems and gave it a short trial run. He soon found that the front wheel steering would not function. After unsuccessfully trying a reset of the power supply to the front wheels, he and mission control decided they would have to continue the traverse with rear wheel steering only. The television camera operation was checked out by Ed Fendall, controlling it remotely from earth as he would also do for the subsequent two missions (this eventually earned him the nickname 'Captain Video'). After initiating the navigation system, the next difficulty was experienced by Irwin, who could not get his seat belt latch to engage. The strap, without an adjuster, had been fitted to size on earth where his weight and that of his suit and PLSS had compressed him into his seat, and the belt was adjusted accordingly. What had not been taken sufficiently into account was that his one sixth weight on the moon did not compress the seat far enough to allow the catch to engage. Eventually he was able to pull the belt tight enough to engage the catch but it would prove troublesome at each stop.
The route for their first traverse in the Rover was to take them south-west to a sharp bend in the rille at the base of Mount Hadley Delta , then around the base of the mountain to where St George Crater had impacted into its lower flank adjacent to the rille excavating the lower bedrock. Finally, the traverse would take them east to sample a small crater named Flow, which had excavated a slump of material deposited on the mountain's escarpment thought to be from the mountain's upper levels.
The outbound ride provided by the Rover across the undulating plain was exciting. Even at five miles per hour, in one sixth gravity the car would buck and roll with more than one wheel leaving the surface at a time. Scott's attention was kept focused on the driving while Irwin had to hang on, unable to read his navigation maps. Their route brought them to the edge of the rille; and, after a stop to sample the edge of the thousand foot deep canyon, they continued along the edge to a ninety degree bend in the rille at the base of Mount Hadley Delta.
They took further samples at Elbow Crater on the edge of the rille, and carried on around the bend to St George. It soon became apparent that the crater was not going to provide the samples that had been expected. St George Crater was very old, almost as old as the Hadley Delta itself, and the expected ejecta from the crater had been gardened into the regolith or lost into the rille itself.
It was decided by mission control to cancel the third sampling stop at Flow Crater, as the traverse was running behind time and Scott's suit was using more cooling water than expected. On the return journey, as Scott drove down the lower slope of the mountain back towards Elbow, he manoeuvred the Rover through a number of tight turns; and, at one point, a front wheel dug into the sloping surface and spun the Rover through 180 degrees, adding a heart stopping moment to the journey. As they followed the navigation system bearing back to the LM they were able to observe a thin line that ran horizontally along the base of the foothills surrounding Mount Hadley 15 miles to the North East. The lava flow, which had welled up to create the plain, had reached a high point and later contracted to leave a tide mark on the surrounding hills over seventy feet above its current level.
On return to the LM Scott and Irwin chose a site about a hundred yards away from the LM and set about deploying the ALSEP. Radiating from the central power generator were a combination of similar experiments to those left on previous by Apollo missions 12 and 14:
- A Passive Seismic Experiment (PSE)
- A Lunar Surface Magnetometer (LSM)
- A Cold-Cathode Gauge Experiment (CCGE)
- A Solar Wind Composition Experiment (SWCE)
- A Solar Wind Spectrometer (SWS)
- A Suprathermal Ion Detector Experiment (SIDE)
- A Lunar ranging Retro Reflector (LRRR)
In addition, the experiment package included a Heat Flow Experiment (HFE) to measure the amount of heat generated from within the moon and radiated to space. This would indicate whether the moons core was still active; but the experiment would require drilling two holes to place sensors at least 10 feet under the lunar surface.
As Irwin removed the ALSEP and set up the experiments, Scott was required to drill the two holes to place the heat flow experiment sensors and a third as a core sample. After drilling three feet of the first hole the electric drill slowed as it bit into heavy resistance and locked up. Despite applying all his weight he was unable to penetrate further than five feet and had difficulty withdrawing the drill shaft more than a few inches from the hole. Mission control decided that the hole would have to do and instructed Scott to insert the first sensor. The same occurred with the second hole; and, as time was running out, he was obliged to close down the EVA for the day, leaving the drill jammed in the hole.
Second EVA: The Front, Spur, and Dune Craters
Overnight another problem had occurred inside the LM that had to be rectified before commencing the EVA. A connection on a filter to the drinking water spigot had leaked a large quantity of water onto the cabin floor. Irwin and Scott had to seal off the spigot's valve and dry out the cabin interior before carrying on with the EVA.
The traverse planned for the second day was to drive out to Mount Hadley Delta, where its lower slopes met the plain and travel two miles east along The Front, making three sampling stops. The object was to find an impact crater that had excavated the talus and exposed the underlying rock of the mountain, which it was thought would consist of Anorthosite, the original lunar crust material. Inexplicably, before setting off on the second traverse, the Rover's front wheel steering was discovered to be in working order, and Scott found the Rover to be more controllable than it had been on the rear wheels alone.
On the outbound journey, they passed to the west of the South Cluster group, where they were to have made their first sampling stop, but which had now been cancelled due to time constraints. Instead, they would drive by it to see if it would be worth sampling on their return if time permitted. The time saved was to be used, on their return to the LM, on the heat flow experiment drill holes, which still had to be completed and were considered by the back room geological team to be of greater importance.
Picking their way around the cluster, they found the going was made difficult by a large boulder field pitted with craters. Driving by the cancelled stop at Dune Crater, the largest of South Cluster, they were able to see that there were a number of large blocks on its inner face unearthed from its 300 feet depths. Instead, they pressed on up the lower slopes of the talus and onto the incline at the Front, but were unable to find a suitable crater which had excavated bedrock. The slope was heavy with thick dust that made progress on foot slow and the footing unsure. At one point, Scott tripped and fell to all fours on the 20 degree slope. None of the samples taken on the talus showed any sign of the original crustal material.
Moving on to a second stop further up the incline, Irwin spotted a large boulder, which appeared to have a green tint. On dismounting the Rover it began to slide sideways down the slope and Scott had to hold it with one wheel out of contact with the ground until Irwin came to his assistance. As Irwin held the Rover, Scott sampled the rock, which proved to be a breccia with a crust formed from glassy spherules. On later analysis it was thought that the crust had originated from a fire fountain venting from a fissure formed after the Imbrium Impact. From their high vantage point, Scott was also able to photograph the plain below them with the LM now almost 4 miles away.
They progressed further along the Front to Spur Crater. As they approached its northern flank, Scott noticed a rock with a white capping standing out of the regolith. As he sampled the rock, the white corner broke off, exposing a glinting white interior. 'I think we've found what we came for.' he said. The rock was almost entirely plagioclase, the major part of anorthosite; and, at 4.1 to 4.5 billion years old, it pre-dated the Imbrium event to the origin of the lunar crust. It was the second oldest rock returned on any Apollo mission and was subsequently to be dubbed the Genesis Rock. Further samples taken at the edge of Spur provided black and white impact melt breccias dated at 3.85 billion years also having their origins in the original lunar crust.
They began the return journey down the slope with time in hand to return to Dune Crater in the South Cluster, a pit 300 feet deep with a cluster of boulders on the rim and shelving on the inner walls showing what appeared to be layering of deposited material. Dune had penetrated through the regolith and a sample taken from one of the larger boulders on the rim indicated that the mare plain had been built up from a succession of layers of lava flows. After sampling the boulders on the rim, they returned across the plain to the LM.
After off-loading their samples, the heat flow and deep core sample still remained to be completed. Scott returned to the drill and tried to free it by running it without applying pressure and letting it find its own drill rate. Eventually it penetrated to 5 feet, but Scott was again unable to withdraw the drill shaft from the hole, as the flutes were clogging up and gripping the shaft, preventing its removal. After backing off and recycling the drill several times, Scott managed to withdraw the shaft but could not get the sensor in further than three feet. Withdrawing the drill had separated the shaft sections, and the upper shaft had drilled in beside the lower half. On mission control's OK, the sensor was emplaced and Scott carried on with the core sample. This again proved troublesome. After penetrating more than 8 feet the core tube seized in the hole, and Scott again had to leave the drill in place overnight.
Third EVA: Core Sample and Rille
The third EVA was planned to drive to the edge of the rille and progress northwards, sampling the edge where thinning of the regolith had exposed bedrock. From the edge it was planned to cross the plain to the North Complex, a cluster of craters which were thought to have volcanic origins. Scott was keen to visit the North Cluster, because it promised to yield evidence of its volcanic origins, but was dismayed to be told by mission control that they wanted him to retrieve the core sample that morning before setting off on the traverse. This would put the visit to North Cluster in doubt due to the walk back time constraint.
It required both Scott and Irwin pulling on the drill to withdraw the top sections of the core one at a time, using the drill for purchase. Meanwhile, mission control had found that the clutch of the drive mechanism to the television camera had overheated while standing in the direct sunlight during the rest period, and they could not operate it remotely. Scott and Irwins' exertions went unobserved, until Irwin noticed the camera pointing at the ground and repositioned it manually. The last four sections of the core tube were locked together and would not unscrew by hand. Scott first attempted to separate the treadle plate at the base of the core tube, using a vice which was mounted on the geology palette on the Rover; but he soon found that, due to a design oversight, it had been assembled the wrong way around and would not grip the tube. By now, Scott's irritation with the equipment failures was beginning to show in his exchanges with Capcom Joe Allan at mission control, and he was advised to leave the core sample on the ground and proceed with the next part of the EVA.
Also brought forward in the timeline was a test of the Rover, which was to be photographed with the 16mm movie camera to evaluate its design and performance. Scott put the Rover through turns, stops, and speed runs, producing a rooster's tail plume of dust in his wake, while Irwin tried to record the event. On checking the film cartridge Irwin found it still registering full; but the film was not advancing, and the test had not been recorded. On the original schedule, Scott and Irwin would now have been at the rille. With 45 minutes wasted on the core retrieval and the Rover test, the visit to North Complex was looking less likely than ever.
With the final traverse of the mission under way at last, Scott drove flat out for the rille looking for the first stop at Scarp Crater on the rille's edge. After sampling Scarp, they moved onto the rocky edge of the rille where the regolith had thinned, leaving large outcrops of rock. As he moved along the rille edge, Scott again tripped and fell in the full view of the TV camera, which was now working again. Recovering, he walked out to the downward sloping edge to sample the exposed bedrock and photograph the opposite rille wall. The wall of the rille displayed layering of outcrops of rock, which showed that the mare had been laid down by multiple flows of lava rather than one single inundation.
As the astronauts disappeared out of sight of the camera, mission control was becoming more concerned that their astronauts were '...on the edge of a precipice'; and, after repeated requests by Allen, there was general relief when they returned to the Rover's field of view. Irwin and Scott took further core samples at the edge of Scarp Crater, before moving on north along the rille's edge. They had time for one last stop at Rim Crater to take photographs and a couple of grab samples; but the time taken with the heat flow and core sample at base had taken its toll, and the run to North Complex was cancelled.
On their return, Scott was able to separate one of the four sections of the core sample, leaving the three part sample just short enough to stow separately in the LM. After stowing the samples and equipment, Scott franked a number of first day cover stamped envelopes. Then, with his back to the LM, he faced the television camera and produced from his suit pocket a pair of falcon's feathers. He said:
In my left hand I have a feather, in my right , a hammer. And I guess one of the reasons we got here today was because of a gentleman named Galileo, a long time ago, who made a rather significant discovery about falling objects in gravity fields. And we thought, 'where would be a better place to confirm his findings than on the moon?' And so we thought we'd try it here for you. The feather happens to be, appropriately, a falcon feather for our Falcon. And I'll drop the two of them here and hopefully they'll hit the ground at the same time.
On a simultaneous release the feather and the hammer dropped to the ground together.
'Mr Galileo was correct...' said Scott, as the back room scientists applauded.
Scott's final task was to drive the Rover out a distance from the LM to a point where the TV camera could watch the lift off. He left a small Bible on the Rover's dash panel; and, beside the Rover, he laid a figure of a fallen astronaut and a small plaque recording the names of all the astronauts and cosmonauts that had lost their lives in the furtherance of space exploration. The Rover carried its own message, 'Man's first wheels on the moon. Delivered by Falcon, July 30, 1971.'
Lift-off from the moon was televised to audiences on earth from the camera mounted on the Rover and accompanied by an Air Force march. As the ascent engine ignited, a cloud of debris from the descent stages covering flew in all directions. As it settled, it left a strangely desolate, lifeless scene, surveyed only by the camera. Rendezvous with 'Endeavour' took place one and a half hours later, and 'Falcon' was sent back to impact on the moon's surface and enable calibration of the seismograph.
In keeping with the scientific exploration theme, 'Endeavour' was the first craft to carry survey equipment in the service module's Scientific Instrument Module (SIM) bay. Using lenses developed for military use, the equipment included a forward looking mapping camera and a wide view panoramic camera with film cassettes, each containing several thousand frames. Remote sensing equipment included a laser altimeter, which mapped the terrain to an accuracy of three feet; while X-ray, Gamma ray, and Alpha particle spectrometers gathered further data.
Worden, as command module pilot, operated the equipment from orbit, while Scott and Irwin walked the surface below. Worden's moment came later when he deployed a sub satellite into lunar orbit and carried out a 35 minute space walk to retrieve the film canisters from the SIM bay during the return voyage to earth.
After re-entry, one of Apollo 15's three parachutes failed to deploy fully; but the craft splashed down safely in the Pacific Ocean on 30 July, 1971, to be recovered by the USS Okinawa. As no evidence of contamination had been found on any previous crew, it was not thought necessary to keep them in isolation after this nor any future missions.