4.0 LUNAR ORBITAL EXPERIMENTS

Four lunar orbital experiments were conducted on Apollo 14: the S-band transponder experiment, the downlink bistatic radar experiment, gegenschein/Moulton point photography from lunar orbit, and the Apollo window micrometeoroid experiment (a space exposure experiment not requiring crew participation). Detailed objectives associated with photography while in lunar orbit and during transearth flight axe discussed in addition to the aforementioned experiments. The evaluations of the lunar orbital experiments given here axe based on preliminaxy data. Final results will be published in a separate science report (appendix E) when the data have been completely analyzed.



4.1 S-BAND TRANSPONDER

The S-band transponder experiment was designed to detect variations in the lunar gravitational field caused by mass concentrations and deficiencies, and establish gravitational profiles of the spacecraft ground tracks. This will be accomplished by analysis of data obtained from S-band Doppler tracking of the command and service module and lunar module using the normal spacecraft S-band systems.

There were some difficulties during the prime data collection period (revolutions 3 through 14). Two-way telemetry lock was lost many times during revolutions 6 and 9 because of the high-gain antenna problem, making the data for those revolutions essentially useless. At other times maneuvers, orientations, and other operations interfered with the data. However, sufficient data were received to permit successful completion of the experiment objectives. Preliminary indications are that the mass concentrations in Nectaris will be better described and the distribution of gravitational forces associated with the Fra Mauro formation will be better known. The data will also permit other features to be evaluated.



4.2 BISTATIC RADAR

The objectives of the bistatic radar experiment were to obtain data on lunar surface roughness and the depth of the regolith to a limit of 30 to 60 feet. The experiment was also designed to determine the lunar surface Brewster angle, which is a functi-on of the bulk dielectric constant of the lunar material. No spacecraft equipment other than the normal spacecraft systems was required for the experiment. The experiment data consists of records of VHF and S-band transmissions from the command and service module during the frontside pass on revolution 25, with ground-based detection of both the direct carrier signals and the signals reflected from the lunar surface. Both the VHF and S-band equipment performed as required during revolution 25. The returned signals of both frequencies were of predicted strength. Strong radar echoes were received throughout the pass and frequency, phase, polarization and amplitude were recorded. Sufficient data were collected to determine, in part, the Brewster angle.



4.3 GEGERSCHEIN/MOULTON POINT PHOTOGRAPHY FROM LUNAR ORBIT

The experiment required three sets of photographs to be taken to help differentiate between two theoretical explanations of the gegenschein (fig. 4-1). Each set consisted of two 20second exposures and one 5-second exposure taken in rapid succession. One set was obtained of the earth orbit stability point in the earth-sun system (Moulton point) to test the theory that the gegenschein is light reflected from a concentration of particles captured about the Moulton point. Two additional sets were taken to test another theory that the glow is light reflected from interplanetary dust that is seen in the anti-solar direction. In this theory, the brightening in the anti-solar direction is thought to be due to higher reflectivity of particles exactly opposite the sun. For an observer on earth, the anti-solar direction coincides with the direction of the Moulton point and the observer is unable to distinguish between the theories. From the moon the observer is displaced from the anti-solar direction by approximately 15 degrees, and therefore, can distinguish between the two possible sources.

The 16-mm data acquisition cam ra was used with an 18-mm focal length lens. The camera was bracket-mounted in the righthand rendezvous window with a right angle mirror assembly attached ahead of the lens and a remote control electrical cable attached to the camera so that the Command Module Pilot could actuate the camera from the lower equipment bay. The flight film had special, low-light-level calibration exposures added to it prior to and after the flight which will permit photometric measurements of the phenomena by means of photographic densitometer and isodensitrace readings during data reduction. The investigators also obtained ground photography of the phenomena using identical equipment and film prior to the time of Apollo 14 data collection.

The experiment was accomplished during the 15th revolution of the moon. The aiming and filming were excellent and the experiment has demonstrated that long exposures are practicable.

Figure 4-1.-Camera aiming directions for gegenschein/Moulton point photography.



4.4 APOLLO WINDOW METEOROID EXPERIMENT

The objective of this experiment is to determine the meteoroid cratering flux for particles responsible for the degradation of glass surfaces exposed to the space environment. The Apollo command module windows are used as meteoroid detectors. Prior to flight, the windows are scanned at 20x to determine the general background of chips, scratches and other defects. During postlfight investigations, the windows will again be scanned at 20x to map all visible defects. The points of interest will then be magnified up to 765x for further examination. The Apollo 12 and 13 side windows and hatch windows were examined following those flights and the results were compared with preflight scans. No meteoroid impacts larger than 50 microns in diameter were detected on the Apollo 12 windows although there was an increase in the number of chips and other low-speed surface effects. The Apollo 13 left-hand-side -window had a suspected meteoroid impact 500 microns in diameter.



4.5 DIM-LIGHT PHOTOGRAPHY

Low-brightness astronomical light sources were photographed using the 16-mm data acquisition camera with the 18-mm lens. The sources included the zodiacal light, the galactic light, the lunar libration region (L 4 ) and the dark side of the earth.

All star fields have been readily identified and camera pointing appears to have been within one degree of the desired aiming points with less than one-third of a degree of image motion for fixed positions. This is well within the limits requested prior to flight, and it confirms that longer exposures, which had been originally desired, will be possible for studies such as these on future Apollo missions. The zodiacal light is apparent to the unaided eye on at least half of the appropriate frames. The galactic light survey and lunar libration frames are faint and will require careful work. Earthdarkside frames of lightning patterns, earth-darkside photography during transearth coast, and S-IVB photographs were overexposed and are unusable.



4.6 CONMAND AND SERVICE MODULE ORBITAL SCIENCE PHOTOGRAPHY

This photography consisted of general coverage to provide a basis for site selection for further photography, interpretation of lunar surface features and their evolution, and identification of specific areas and features for study. The Apollo lunar missions have in the past obtained photographs of these areas as targets-of-opportunity or in support of specific objectives.

The Apollo 13 S-IVB impact area was given highest priority in orbital science photography. The target was successfully acquired on revolution 34 using the Hasselblad camera with the 500-mm lens, and the crew optical alignment sight to compensate for the spacecraft's motion. Second priority was given to the lunar module landing target which was obtained with the lunar topographic camera on revolution 14. However, the camera malfunctioned and subsequent photography with this camera was deleted (section 14.3-1).

A total of eight photographic targets was planned for handheld photography using color film; three were to be taken with the 500-mm lens (a total of 35 lunar degrees), and five with the 250-mm lens (a total of 130 lunar degrees). The 500-mm taxgets were successfully acquired. Three of the five 250-mm targets were deleted in real-time for operational reasons (60 lunar degrees), and two were successfully acquired (70 lunar degrees). A total of 65 percent of off-track photography has been successfully acquired.

The earthshine target was successfully acquired using both the Hasselblad data camera with the 80-mm lens and the 16-mm data acquisition camera with the 18-mm lens.



4.7 PHOTOGRAPHS OF A CANDIDATE EXPLORATION SITE

High-resolution photographs of potential landing sites are required for touchdown hazard evaluation and propellant budget definition. They also provide data for crew training and onboard navigational data. The photographs on this mission were to be taken with the lunar topographic camera on revolution 4 (low orbit), and 27 and 28 (high orbits). During revolution 4, malfunction of the lunar topographic camera was noted by the Command Module Pilot. On revolutions 27, 28, and 30, the 70-mm Hasselbald camera with the 500-mm lens (lunar topographic camera backup system) was used to obtain the required photography. About 40 frames were obtained of the Descartes region on each revolution using the crew optical alignment sight to compensate for image motion. The three targets were successfully acquired.

To support the photography, a stereo strip was taken with the Hasselblad data camera with the 80-mm lens from terminator-to-terminator including the crew optical alignment sight maneuver for camera calibration.



4.8 VISIBILITY AT HIGH SUN ANGLES

This photography was accomplished to obtain observational data in the lunar environment for evaluating the ability of the crew to identify features under viewing and lighting conditions similar to those that would be encountered during descent for a T plus 24 hour launch. The results will have a bearing on decisions to land at higher sun angles, which, in turn, could ease launch and flight constraints. Photography of the lunar surface in support of this detailed objective was obtained using the Hasselblad data camera and the 80-mm lens. This was done for three targets, two on the moon's far side and one on its near side.



4.9 TPANSEARTH LUNAR PHOTOGRAPHY

Photographs were taken of the visible disc of the moon after transearth injection to provide changes in perspective geometry, primarily in latitude. The photographs will be used to relate the positions of lunar features at higher latitudes to features whose positions are known through landmark tracking and existing orbital stereo strips. The photography was successful using the Hasselblad data camera with the 80-Mm lens and black-and-white film. Additional coverage with the 70-mm Hasselblad camera and the 250-mm lens using color film was also obtained.

Chapter 5 - In-Flight Demonstrations Table of Contents Apollo 14 Journal Index