With all the bruhaha going on about finding the ‘lost’ NASA moonlanding tapes, a conversation came up on a tech list I’m on regarding some of the misinformation floating around. Scott Dorsey, a man who has been involved in audio tech for many many years, sets the record straight:
He writes:
This article is wrong on a whole bunch of fronts.
The basic issue: there’s a 320 line, 5 fps camera on the lander. It has
a baseband output. There’s a wideband S-band link on a steerable antenna
on the lander as well. The astronauts point that antenna toward earth, then
then flip a switch that disables a lot of telemetry carriers and places
the video carrier onto the S-band link in its place.
Some folks in Australia (actually several stations at the same time) pick
the signal up with big high gain dishes. They have an Ampex FR-900 helical
scan recorder that uses 2″ tape, which they use to directly record the feed
off the S-band link (and they record the telemetry data, and the video data,
whenever they have a lock on the spacecraft). These tapes are lost.
They ALSO have a video demodulator, and they send the demodulated low rate
video over an an AT&T coaxial cable to the friendly people at Goddard.
The Goddard folks have a scan rate converter which consists of a Tektronix
storage CRT that is fed by the slow scan video, and a vidicon camera
pointed at the CRT. There is no 16mm camera involved.
There were also two more Tektronix CRTs located in a couple other locations,
fed directly off the slow-scan video. There are some 35mm photos that were
shot off these CRTs, which show very clean and sharp images. If someone
actually HAD shot 16mm kines off the SSTV monitors, we’d be in much better
shape than we were.
The folks at Goddard also had an FR-900, and they may or may not have also
recorded the landing. We do have a bunch of test recordings made at Goddard.
Now, a couple of folks at Ames Research Center, in conjunction with the
Ampex User’s Group, have actually resurrected a couple of scrapped FR-900
machines. This is something of a miracle in itself, seeing as how these
machines are mechanical nightmares. Currently the machines are giving okay
images although with a little bit of wandering that is possibly due to some
slop in the (grade 11) bearings on the head drum. These machines are
currently being used to transcribe the original Lunar Orbiter data tapes
as part of NASA’s program for mapping the moon in preparation for future
moon landings.
So… IF the tapes found in Australia are the right ones, they’ll be finding
out pretty quickly.
If anyone is really curious about how the actual Apollo video stuff works,
go to http://ntrs.nasa.gov/ and do a search on apollo landing video. There are a
bunch of documents on the Unified S-Band System, and a very good paper on
the evolution of the Apollo video cameras and formats from Apollo 8 through 17.
–scott
