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20th of March 2019
50th Anniversary of Apollo 9
This month marks the 50th anniversary of the Apollo 9 mission, which spent 10 days in low Earth orbit testing the Command and Service Module and the Lunar Module. In his essay on the Apollo 9 mission Hamish Lindsay recounts that, when Apollo 9 was in Australia's longitude range, the plan was for Honeysuckle Creek to track the Command and Service Module (CSM) and Tidbinbilla the Lunar Module (LM). However, Tidbinbilla’s antenna (built for deep space tracking) was much slower than Honeysuckle’s. While the CSM and LM were separated, Honeysuckle Creek’s antenna couldn’t see both spacecraft at the same time and the Tidbinbilla antenna wasn't capable of following either of them at their high speeds in low Earth orbit.

The Tid team worked out that they could use a very much wider beamwidth acquisition antenna on the dish and drive the antenna under computer control from horizon to horizon at its maximum possible rate, catching the LM in the leading edge of the antenna beam as it rose, and progressively flying through the antenna beamwidth and out the other side as it set. The LM would be in the main antenna beam long enough for the required commands to be transmitted to it. NASA, after a series of deomstrations, accepted this as the operational procedure and communications with the LM, pictured above, worked well throughout the mission. (Image credit: ApolloArchive.com scan by Ed Hengeveld, and www.honeysucklecreek.net)

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