Lunar Orbiter
Lunar Orbiter is the name of five US lunar probes , which from 1966 to 1968 as the orbiter to the moon in a close orbit circled to measure it and to analyze the gravity field.
All five space probes, launched by NASA from August 10, 1966 at intervals of 88 to 90 days, were successful, only the third orbiter had minor failures. The photos and measurement data were the basis for an exact lunar atlas , which was created in 1968 and also recorded the back of the moon .
mission
The main task of the Lunar Orbiters was to accurately map the surface of the moon by photographic means. Landing sites for the manned moon landings of the Apollo space flights should then be selected on the basis of the images . First attempts were also made to selenodesy , the measurement of the moon (Greek: Selene ) and its gravity field . The inner structure of the earth's satellite and the so-called mascons under the lunar crust were also a research topic.
The lunar orbiter missions 1 to 5 were the continuation of the Ranger explorations of three lunar regions in 1964/65 (17,000 images from Ranger 7 to 9, including extreme close-ups before impact ) and succeeded without any failure. They took place around the same time as surveyor missions 1 to 7 and their soft landings . The first rocket tests to reach lunar orbits took place in 1960 with two Pioneer probes and in 1964 in the Ranger program.
The probes were launched with a two-stage Atlas-Agena -D rocket and swiveled into a strongly elliptical orbit around the moon, the periseles (points closest to the moon ) being around 200 kilometers above the surface. Compared to the lunar orbit speed of the web speeds differed by a few percent.
For Lunar Orbiters 1 to 3, orbits with a low orbital inclination were chosen, which led exclusively over areas near the equator . Lunar Orbiter 4 and 5, however, were brought to polar orbits that a mapping allowed the entire lunar surface.
Technical equipment
The probes had a height of 1.68 meters and a width of 5.65 meters, measured over the extended antennas . The launch mass varied between 386 and 391 kilograms, depending on the orbiter. The re-ignitable orbit correction engine worked with Aerozin 50 and nitrogen tetroxide and delivered a thrust of about 450 Newtons.
Two cameras with a wide angle and a telephoto lens were used. Photographs were taken in pairs side by side, with the image section of the telephoto lens always in the center of the wide-angle photograph. During the exposure, the film was moved to compensate for the speed of the spacecraft. The film used was 70 mm unperforated Kodak Special High Definition Aerial Film (SO-368), 79 meters of which was carried along. This film was developed and fixed automatically by contact with a so-called Kodak Bimat film. After completing the photographic recordings, the negative film could then be electronically scanned from end to beginning and radioed back to earth. For this purpose, a light beam with a diameter of 0.005 mm scanned the film in transverse strips (framelets) 2.68 mm wide with 17,000 lines. The film was then advanced by 2.54 mm and the next frame set was scanned. The scan of a complete pair of images took 43 minutes.
On earth, the received image signals were stored on data tapes and each frame was exposed by a cathode ray tube on 35 mm film, from which replicas of the original images were made by stitching together. This explains the stripes that run through every lunar orbiter photograph.
Course of the five missions
- Lunar Orbiter 1 launched on August 10, 1966, and entered lunar orbit after four days. From the 26th orbit of the moon on August 18, he began to record and transmitted a total of 229 images until the crash on October 29, 1966. (Takeoff weight: 386 kg, incline: 12.14 °)
- Lunar Orbiter 2 launched on November 6, 1966, entered lunar orbit four days later, and transmitted 817 images by impact on October 11, 1967. (Takeoff weight: 391 kg, orbit inclination: 11.97 °)
- Lunar Orbiter 3 launched on February 5, 1967, entered lunar orbit three days later and transmitted 626 images until the crash on October 10, 1967. Because of some malfunctions, Lunar Orbiter 3 is not considered to be quite as successful. (Takeoff weight: 386 kg, slope: 21.00 °)
- Lunar Orbiter 4 launched on May 4, 1967 and reached the moon four days later. Incontrast to the previous missions, the orbit was much higher and almost polar. The probe took 546 pictures up to the crash on October 31, 1967. As a result, the front of the moon was almost completely covered and about 3/4 of the back. (Takeoff weight: 390 kg, incline: 88.80 °)
- Lunar Orbiter 5 launched on August 1, 1967, and on August 4 also swiveled into a polar, but more elliptical, lunar orbit that was closer to the surface. As of August 6, 1967, 844 images were transmitted, including a. from the back of the moon not yet fully captured. Lunar Orbiter 5 crashed on the moon on January 31, 1968. (Take-off weight: 390 kg, incline: 85.00 °)
Results
The lunar orbiter probes mapped the moon with an accuracy of 60 meters. The resulting lunar atlas is still part of the standard of lunar research today. The potential Apollo landing sites were photographed particularly well, with resolutions up to 2 meters. In particular, the oblique views with tele optics were among the most noted photos of their time. The image of a rising earth above the surface of the moon, taken on August 23, 1966, went down in history. Lunar Orbiter was also the first US probe program that did not fail seriously.
In the side program, the acquisition of precise orbit data for the analysis of the lunar gravitational field was successful. From this data it was possible to detect mascons for the first time, strong mass concentrations in the subsurface of the moon.
Similarly, the fact of the moon's eccentric center of mass , the cause of its bound rotation , was derived from orbital disturbances of lunar satellites. NASA also tried a kind of triangulation around the back of the moon, with some success . The photos of the space probes from the surface of the moon were used to calculate their orbits over the back side - invisible from the earth - in the manner of a photographic reverse cut . Last but not least, experience was gained in space navigation near the moon.
digitalization
All 1,500 data tapes of the five Lunar Orbiter missions are currently being digitized as part of the Lunar Orbiter Image Recovery Project (LOIRP). The project leader is Dennis Wingo, who leads a small team of engineers. The high resolution and detail of the restored photos surpass all other pictures of the moon to this day (as of 2010). Thanks to this high quality of the restored photos, it will now be possible to make a comparison with other photos of the moon - such as those that the Lunar Reconnaissance Orbiter has taken since 2009 - and to document changes on the lunar surface (e.g. due to intermittent meteorite impacts) to be able to. The US space agency funds most of the LOIRP research. It also provides the accommodation in which the team has found its home: a former McDonald's restaurant on the grounds of the NASA Ames Research Center in Mountain View , which is why it is jokingly called McMoon's.
See also
literature
- Marcus Tuner: Looking for the landing site. Kosmos / Franckh, Stuttgart 1967, DNB 458449865 .
- LJ Kosofsky ua: The moon as viewed by lunar orbiter. Washington 1970, OCLC 85937 . ( online @ NASA ADS, accessed March 26, 2011)
Web links
- NASA: Lunar Orbiter (1966–1967) (English)
- Digital Lunar Orbiter Photographic Atlas of the Moon, 1971
- NASA: Destination Moon - A History of the Lunar Orbiter Program Online version of a NASA book with over 300 pages (English)
- Detailed description by Bernd Leitenberger
- LOIRP project for digitizing the raw data from the old magnetic tapes of the received raw data
Individual evidence
- ↑ Irene Meichsner: Century picture: The rising earth. In: Der Tagesspiegel . January 5, 2009, accessed November 8, 2011 .
- ↑ Angelika Franz: Analogue NASA pictures: The moon treasure hunters. In: Spiegel Online. March 23, 2010, accessed November 8, 2011 .
- ↑ USGS Astrogeology: Lunar Orbiter Digitization Project. Retrieved November 8, 2011 .
- ↑ Lunar Orbiter Image Recovery Project (LOIRP) Overview. NASA , accessed November 8, 2011 .
- ^ First Moon images no longer lost in Space. (Video) In: YouTube . Associated Press, accessed November 8, 2011 .