Encyclopedia Astronautica
1975.07.23 - Apollo (ASTP) in-flight experiments

Some minor experiment hardware problems developed during the final days of the mission, but for the most part the crew members worked through their flight plan - which included 23 independent experiments - with few difficulties. After a relatively quiet day of work on the 22nd, the major part of the 23rd was devoted to preparing for and conducting the doppler tracking experiment (MA-089). The day was also marked by a press conference from space and jettison of the docking module.

Paired with the geodynamics experiment (MA-128), these investigations were designed to verify which of two techniques would be best suited for studying plate tectonics (movements of the earth's substrata) from earth orbit. Where the geodynamics experiment utilised Apollo and ATS 6 in an attempt to measure these movements (the so-called low-high approach), the doppler tracking experiment involved the use of two satellites in low earth orbit (the low-low approach) to measure the existence of "mass anomalies" greater than 200 kilometres in size. When the jettisoned docking module and the CSM were separated by 300 kilometres, they would theoretically have their orbits affected by the greater gravitational forces exerted by these mass anomalies. As their orbits were perturbed, the radio signals transmitted from one to another would correspondingly be affected.

Prior to releasing the docking module on its separate journey, the crew had participated in a second press conference from space. Deke Slayton's statement that he had done nothing in space that his 91-year old aunt could not have done sent reporters scrambling to find out her name (Mrs. Sadie Link) so they could meet their deadlines. After donning their space suits, the crew vented the command module tunnel and at 2:41 jettisoned the docking module. Filled with all their trash and used equipment that need not be returned, the DM tumbled into space at exactly the proper rate. Stafford and his team then executed their separation manoeuvre so that they could take the necessary doppler measurements. The docking module would continue on its way until it re-entered the earth's atmosphere and burned up in August 1975.

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