|All alone in the gray: the Apollo 17 Lunar Module Challenger photographed by its crew from a distance of about two miles. Image credit: NASA.
Apollo 9 tested the CSM, LM, and the Apollo space suit in low-Earth orbit (3-13 March 1969). Apollo 10 (18-26 May 1969) tested the CSM and LM in lunar orbit and rehearsed the Apollo lunar descent procedure down to an altitude of 50,000 feet.
Apollo 11 (16-24 July 1969), the first lunar landing attempt, was also a test flight, though it is seldom seen that way today. In an effort to make that first landing as easy as possible, engineers directed the Apollo 11 LM Eagle to the northern Sea of Tranquility, one of the flattest stretches of lunar equatorial terrain scientists could find. It was, however, also a U.S. victory in the Cold War with the Soviet Union and the first time humans had explored an alien world first-hand. Scientists and engineers fought a running battle over the degree to which scientific exploration should play a role in Apollo 11, and President Richard Nixon telephoned moonwalkers Neil Armstrong and Edwin "Buzz" Aldrin to read a celebratory speech as they stood next to the U.S. flag.
Eagle landed downrange of its planned landing site. Its overworked computer might have flown it into boulder-filled West Crater had it not been for the quick thinking of former X-15 rocket plane test-pilot Armstrong. Apollo 12 (14-24 November 1969) thus became a test of the Apollo system's ability to make a pinpoint landing. The ability to reach a predetermined spot on the moon was important to scientists planning Apollo geologic traverses. It also helped to ensure safety. The Apollo 12 LM Intrepid landed on the Ocean of Storms, another flat plain, just 600 feet from its target, the derelict Surveyor 3 lander, which had preceded it to the site on 20 April 1967.
Any Apollo mission might have failed catastrophically far from Earth, a point driven home by the explosion on board the CSM Odyssey during Apollo 13 (11-17 April 1970). Hollywood scriptwriters notwithstanding, failure was an option during Apollo missions. Apollo pushed the limits of 1960s technology to do extraordinary things.
The Apollo Program had, in fact, claimed lives before the first Apollo spacecraft left Earth: the AS-204 (Apollo 1) fire killed Gus Grissom, Ed White, and Roger Chaffee during a launch pad training exercise on 27 January 1967, barely a month before their planned launch. Because the Apollo 1 fire occurred on the ground, engineers could take apart the AS-204 CSM piece by piece to try to trace the fire's cause. Even so, they never conclusively identified its ignition source.
A December 1964 report by R. Moore of the Project RAND think-tank anticipated that accidents taking place on the moon would be even more difficult to analyze. Moore proposed that NASA continue the Ranger lunar probe series to enable photography of lunar crash sites. The last four Rangers each carried a battery of six television cameras intended to return images to Earth as the spacecraft plummeted toward destructive impact.
If, for example, Eagle had crashed in West Crater, then NASA would have dispatched a Ranger to image the site. Ranger seemed well suited to aiding accident investigators: Ranger 7, which struck the Ocean of Storms on 31 July 1964, had imaged features as small as 18 inches wide in its final seconds before impact.
|Ranger 7, 8, and 9 were designed for close-up photography of the lunar surface. Image credit: NASA.
They began by acknowledging that telemetry could provide valuable accident data: they added, however, that "certain types of failure can be imagined which would not permit enough data to be transmitted to support a diagnosis." In those cases, they wrote, observation from lunar orbit might be the only way to collect data that could guide engineers in their efforts to redesign the Apollo system to avoid similar accidents.
Byrne and Piotrowski then looked at the image resolution necessary to make useful observations of an accident site on the moon. To locate and identify an intact LM, which measured a little more than 20 feet tall, images showing details as small as 10 feet across would be needed. Eight-foot resolution would be needed to determine the status of the LM's 12-foot-tall ascent stage; for example, if it had lifted off from the descent stage and then crashed on the surface. Four-foot resolution would suffice to determine whether the LM had tipped over.
The ability to resolve features as small as a yard across would enable engineers to assess landing site roughness and slope. Two-foot resolution would, they estimated, be adequate to discern astronaut bodies on the surface. One-foot resolution would reveal whether the LM landing gear had failed, "hazardous sinkage" had occurred, the LM ascent stage crew cabin lay open to vacuum, or an explosion in the LM had scattered "litter" around the landing site.
Byrne and Piotrowski then took stock of the cameras and telescopes expected to be on board the CSM during a normal lunar mission and their performance if the CSM were orbiting 80 nautical miles (n mi), 40 n mi, or 10 n mi above the accident site. They suggested that CSM propellants budgeted for rescue of astronauts on board an LM ascent stage that attained only a low orbit could be used to lower the CSM's altitude for accident site observations.
The CSM's scanning telescope would, despite its name, not magnify objects, so would be of "no value" as a diagnostic tool, Byrne and Piotrowski judged. The sextant, on the other hand, could magnify objects 28 times. The Bellcomm engineers found that the sextant would offer 8.6-foot resolution at an orbital altitude of 80 n mi, 4.3-foot resolution at 40 n mi, and 1.1-foot resolution at 10 n mi. (Apollo CMPs did in fact use the sextant to spot LMs — or at least the shadows they cast — on the lunar surface.)
The sextant was, however, designed to superimpose a pair of star images, could not be used to photograph objects, and, with a field of view only 1.8° wide, would require a highly skilled operator to spot an LM at all. This would be the case especially at lower altitudes, when the CSM would be moving fastest relative to the surface. Byrne and Piotrowski estimated that an astronaut searching the surface with the sextant at an altitude of 10 n mi would at most have 10 seconds in which to find and observe an accident site.
|Apollo 12 Command Module Pilot Richard Gordon trains with cameras and lenses in a Command Module simulator before his November 1969 flight to the moon. Image credit: NASA.
Other constraints would, however, conspire to reduce camera performance. In particular, there was the problem of image motion compensation. Experience gained through Earth photography during the Gemini V mission (21-29 August 1965) showed that astronaut movements were jerky, not smooth, when tracking and photographing targets. Jerky tracking would cause image "smear," reducing resolution.
Byrne and Piotrowski recommended that the CMP mount the Hasselblad 500EL securely in a new-design clamp or bracket at either the CSM hatch window or one of the side windows after he located the LM site. He would then fire the CSM's Reaction Control System thrusters to roll the spacecraft and keep the surface target in his camera's field of view as the CSM passed over it. This form of image motion compensation was unlikely to be perfect; for one thing, roll rate would be affected by factors beyond the CMP's control, such as the distribution and movement of liquid propellants in the CSM's tanks.
As with the sextant, time-over-target would pose a constraint. The Bellcomm engineers assumed that the CMP would need at least 30 seconds to locate the LM on the moon, 15 seconds to prepare the camera and roll the CSM, and 15 seconds for photography.
For a CSM at an altitude of 80 n mi, an LM on the lunar surface would remain in view for two minutes and 24 seconds. This was ample for photography, but at that altitude resolution would be inadequate — no better than 10 feet. At 40 n mi of altitude, the CMP could keep the LM in view for 90 seconds. At 30 n mi, he would have about 60 seconds — the minimum necessary — to find and photograph his target. Byrne and Pietrowski thus selected 40 n mi as the optimum altitude for accident site photography.
The Bellcomm engineers looked at adding a special cartridge of high-contrast film and a 500-mm f/8 lens for the Hasselblad 500EL, and at replacing the Hasselblad 500EL with the Zeiss Contarex Special 35-mm camera and 200-mm f/4 and 300-mm f/4 lenses. These had already reached space on board Gemini V. They noted that both cameras would yield a resolution of about one yard at an altitude of 40 n mi with a secure mounting bracket and adequate image motion compensation. In the end, they favored the Hasselblad 500EL with 500-mm f/8 lens and high-contrast film because it would be about eight pounds lighter than the Zeiss camera.
Byrne and Piotrowski noted that the camera system and techniques they proposed would have uses other than accident site investigation. They might, for example, be used to photograph the landing site after a successful LM landing. This would, among other things, enable scientists to precisely locate the post-deployment position of the Advanced Lunar Scientific Experiment Package, a suite of instruments the moonwalkers would deploy some distance away from the LM. Images of the landing site might also assist geologists in understanding the context of the samples the moonwalking astronauts would return to Earth.
"A Suggestion for Extension of the NASA Ranger Project in Support of Manned Space Flight," Memorandum RM-4353-NASA, R. C. Moore, The RAND Corporation, December 1964.
"Diagnostic Observation of Lunar Surface Accidents – Case 340," C. Byrne & W. Piotrowski, Bellcomm, Inc., 7 November 1967.
What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)
What if an Apollo Lunar Module Ran Low on Fuel and Aborted Its Moon Landing? (1966)
"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)