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Landing the Eagle

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Obviousman:
These were passed to me by some friends: first a chart that combines Armstrong's heart rate [in crimson], the altitude & descent rate of the L.M. [in blue], program points/alarms [in yellow], abort count [in red] and G.E.T. [in grey].

Under that, by the same author, is a 4K YouTube clip (39 mins in length).

Enjoy!



http://landingtheeagle.com/articles/visualizing-the-approach/

https://youtube.com/watch?v=WUhlewTx_KQ

bknight:
A little stressed for the last couple of minutes.  :)

Obviousman:

--- Quote from: bknight on July 10, 2019, 10:33:16 AM ---A little stressed for the last couple of minutes.  :)

--- End quote ---

Wimp. Tell him to harden up.

(VTIC)

ka9q:
I hadn't heard all of these loops before so I was particularly interested to hear the telecom network guys report signal acquisitions and signal strengths. When referring to a receiver, "lockup" means that it has detected, acquired and is tracking the spacecraft carrier signal with a "phase lock loop", a circuit for matching a noisy received sine wave (like a radio carrier) with a locally generated sinewave of matching frequency and phase. This is needed to further demodulate the signal, with Doppler tracking data as a side product.

You'll also hear references to "locking up on a sidelobe", which means something different. As a high gain antenna like that on the LM is pointed away from the correct direction, the signal gets weaker, reaches a minimum, and rises to another peak with a lower amplitude than when pointed in the right direction. These smaller response peaks are called sidelobes, and they can confuse the automatic tracking mechanism into tracking one instead of the desired mainlobe. The Telcom ground controller erroneously thought this was happening with the LM antenna, which was tracking the continuous uplink from earth. Later somebody figured out the real reason for the comm problems: the last-minute addition of the RCS plume detectors to the LM. They hadn't been taken into account in LM orientation planning, so the LM antenna was trying to look through one at the earth. Later during powered flight, they try an unscheduled yaw maneuver that helped greatly. LM pitch was also changing, with the earth rising higher in the sky.

Sidelobe lock is much less likely to happen today. An onboard computer can use orientation information from an IMU plus navigation data about its own position and that of the earth to generate "open loop" antenna pointing estimates to get the antenna well within its main lobe. Then the closed loop tracking servo can take over without being fooled.  The LM computer wasn't powerful enough to do this, so it was up to Aldrin to manually slew (steer) the antenna where he thought it should be, then go back to automatic closed-loop tracking.

Signal strengths are given in dBm, decibels relative to 1 milliwatt. These are always negative numbers, so if somebody says "120" they really mean -120 dBm, i.e, 1e-12 times 1 milliwatt, or 1 millionth of a millionth of a milliwatt. Larger (more negative) values indicate a weaker signal. More than one size antenna was being used, and the 210' (now 70 meter) antennas naturally got stronger signals.

Obviousman:
It was interesting, wasn't it?

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