Carnarvon Location Project
Satellites and the various NASA tracking networks provided the opportunity to refine the geodesy of the Earth and in turn improve the accuracy of navigation at lunar ranges. The design of a special satellite – GEOS-B - meet these objectives led to the temporary location of a Tracking Camera and a Mobile Laser at the SPAN site to refine the location of the Apollo USB antenna.
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- <A href="#targetl">GEOS-B</A>
- <A href="#target2">Tracking Camera</A>
- <A href="#target3">Mobile Laser</A>
- <A href="#target4">Project results</A>
<A name="targetl"></A>Geos-B
Geos-B was launched on 11 January ’68 into a high retrograde orbit; maximizing shared-visibility periods for several stations at a time for geodetic measurements. These aimed to fix the precise location of participating observation stations to within 10m. Its prime purpose at Carnarvon was to refine the location of the USB antenna to provide more accurate tracking data for Apollo’s journey to the Moon.
But it also provided Carnarvon with many local opportunities to compare the tracking results of its several tracking systems through the simultaneous access to a wide variety of GEOS-B facilities: an optical beacon controlled by an accurate onboard clock, C-band radar and R&RR transponders, a passive radar reflector, and Laser corner reflectors. Carnarvon access was facilitated by STADAN network GEOS-B command control through the local R&RR station. <A href="#index">Back to the index</A>
<A name="target2"></A>Tracking Camera
A Satellite Tracking Camera arrived at the SPAN site early in 1968. On command from R&RR, the satellite could transmit a series of 5 or 7 precisely-timed flashes which the camera photographed against the star-filled background of the night sky. <A href="#index">Back to the index</A>
<A name="target3"></A>Mobile Laser
A Laser Tracking System, affectionately known as ‘Ruby Baby’, arrived at SPAN early in 1969 to contribute to the location project. Aided by pointing data provided by Q6, the Laser was tested in February ‘69 by reflecting pulses of light from a small array of corner reflectors carried on Geos-B. To trigger the laser required the discharge of a van full of large fully-charged capacitors; Jim Gregg remembers this producing a “thump like an artillery gun” accompanied by the popping of exploding capacitors which then had to be replaced for the next shot.
Navigating accurately to the Moon also required a better scientific understand the Earth-Moon relationship. A Laser such as ‘Ruby Baby’ could measure the distance to the Moon to an accuracy of 3 cm, so on each Apollo lunar landing a laser ranging retro-reflector (LRRR - a square array of 100 corner cubes) pointing back at Earth, was set up by the astronauts near their Lunar Module to reflect light back to the point of origin where ever that was.
The Laser’s very-narrow intense pulse-of-light spread to a diameter of about 6.5 Km at the Moon’s surface. A beam this wide still posed a technical challenge to point the laser accurately enough to hit a specific LRRR. Back on Earth a 40cm reflector telescope mounted alongside the laser received the ‘echo’; a minuscule reflection even during the best of Earth’s atmospheric conditions - only about one photon every few seconds. Extremely sensitive filtering and amplification equipment was needed to detect such a small reflection.
Over many years the Apollo reflectors revealed some surprising information. Perturbations of the Earth and Moon show that the Moon may have a liquid core and that the length of the Earth day has “distinct small-scale variations of about one thousandth of a second over the course of a year caused by the atmosphere, tides, and Earth’s molten core.” @@ <A href="#index">Back to the index</A>
<A name="target4"></A>Project results
Simultaneous three-way Geos-B ranging experiments using the laser, the optical camera and R&RR produced a more exact R&RR location of -24°54׳11.4״, 113° 42׳ 58.9״. @@ The FPQ-6 also participated in a world-wide refinement of the C-band radar network using Geos-B. The results from these two projects improved the accuracy of the USB antenna location. <A href="#index">Back to the index</A>
