If we lost the signal we would use the prediction sheet
to re-point the antenna and try to reacquire the spacecraft. Another technician,
or field engineer as we were called, would lock the receiver on the satellite signal, turn the tape recorder on at the proper
time as well as check each track to see if we were recording the required signals. After
the pass, the tapes recorded were labeled, packaged, and sent by way of the diplomat pouch to Goddard. If needed, we would give the controllers at Goddard a “quick look” at the data. The strip chart of the telemetry data would be spread out on a long table.
Using a template to locate the starting point, we could read, by interpreting the pulses on the chart, the status or
payload information the controllers wanted, i.e. what camera was on, battery power, what experiments were on, and so forth. The “quick look” information would be sent directly to them by way of
a Teletype message. This could even be done during the pass with a direct communication
link to them. They could then instruct us, by Teletype, to transmit a tone or
combination of tones to the spacecraft to change its status before we lost the signal.
(Long distance phone calls for that purpose were prohibitive.)
Sending a signal of instruction to satellites was very primitive. We
would start by transmitting an RF (radio frequency) signal; we called a carrier wave, to the spacecraft. The transmitter had buttons on its face. Controllers would
instruct us to, “Push tones 4,7,2 followed 20 seconds later by tones 2, and 6.”
When pushed, the buttons would cause the carrier wave’s frequency to be modulated in seven different frequencies, which we called tones.
A tone, or combination of tones would cause the spacecraft to respond in the way the controller wanted, i.e. turn on
or off an experiment or camera. The “quick look” would tell the controller
if the spacecraft responded correctly before we lost the signal over the horizon.
By the mid sixties Minitrack stations had given way to STADAN
stations, i.e. Satellite Tracking And Data Acquisition Network stations. (Later, the MSFN [Manned Space Flight Network] and STADAN were merged to become the Spaceflight Tracking and Data Network [STDN]). I had been transferred to the Goldstone
tracking station in the Mojave
Desert. We were constantly updating our equipment and could now lock
onto the satellite and let our new AGC (Automatic Gain Control) receiver send signals to drive motors that would move the
antenna to follow the spacecraft automatically. Unified S-band (USB) tracking
was revolutionary for its time, enabling transmission of spacecraft command, telemetry, range and range rate (tracking), voice
and television using a single, combined data link. Range and range rate
was a process where we would lock onto a satellite’s signal, transmit to it and measure the time it took our signal
to return, as well as the change in frequency (Doppler) due to the satellite’s movement through space. During this time I received an outstanding achievement award with the comment, “For recognized achievement through the Bendix
Field Engineering Corporation suggestion system in conjunction with his suggestion concerning fabrication of a device to remove
magnetic tape from the reel.”
Technology That Produced Today’s Practical
Satellites
Between December 1966 and May 1974 a series of satellites named the Applications Technology
Satellite (ATS) (http://msl.jpl.nasa.gov/Programs/ats.html) were
launched to conduct approximately 30 technological experiments and approximately 10 scientific experiments. The ATS series of spacecraft were created to explore & flight-test new technologies and techniques for communications, meteorological
and navigation satellites. Some of the areas investigated during the program,
included yoyo de-spin stabilization, gravity gradient stabilization, complex synchronous orbit maneuvers, and a number of
communications experiments. The yoyo de-spin was a procedure where two weights
attached to wires were released on opposing sides of a spinning spacecraft and slowly extended. Like a skater extending his arms to slow his spinning body, the weights did the same for the S/C. The weights and wires were then released and allowed to fly off into space. The gravity gradient experiment was similar. Long “arms”
were extend from the non-spinning S/C and acted like a long pole that a wire walker would used to balance himself on a high-wire;
balancing the S/C over the gravity of the earth. I remember seeing video from
the S/C showing the long arms flopping as they were extended. The ATS flights
also investigated the geo-stationary orbit environment and prototyped many of the technologies
used on the Tracking and Data Relay Satellite System and other commercial communications satellites. The TDRSS became a series of geo-stationary satellites that replaced ground stations in foreign countries
by relaying a low orbiting spacecraft’s signal’s to the ground. This
new coverage allowed manned spaceflights to increase its 15 minutes
per 90 minutes orbital communications to up to 80 minutes. Although the ATS satellites were mainly intended as test beds, they also collected and transmitted
meteorological data and functioned at times as communication satellites. I had some unique experiences while working with these spacecraft.
ATS-1 (http://msl.jpl.nasa.gov/QuickLooks/ats1QL.html)
ATS-1
was launched on 12/7/1966, examined spin stabilization techniques, investigated the geo-stationary environment, and performed
several communications experiments. Its VHF experiment tested the ability to act as a link between ground stations and aircraft,
demonstrated collection of meteorological data from remote terminals, and evaluated the feasibility of using VHF signals for
navigation. It also transmitted educational programs and provided health, research, and community services to the US and several Pacific island countries, including the Cook, Mariana, Marshall
and Caroline Islands, West and American Samoa, Melanesia,
New Zealand, and Australia.
The mission also provided the first full-Earth cloud cover images. (I have a
picture of the earth, which was made up of several pictures. When you tilt it
you can see clouds moving across the earth.) I transmitted signals from our station
that configured the spacecraft to be used as a communications link between remote parts of Alaska and a city that had doctors. The doctors
would tell the medics in the remote location how to treat any ailments they were confronted with. I remember listening in when a doctor told the medic how to treat a human bite.
ATS-2 (http://msl.jpl.nasa.gov/QuickLooks/ats2QL.html)
This
spacecraft was placed into an undesirable orbit due to a launch vehicle failure on 4/6/1967.
As a result, the spacecraft's gravity gradient booms could not be deployed, and some experiments were not functional.
The spacecraft was able to perform some of its experimental goals.
ATS-3 (http://msl.jpl.nasa.gov/QuickLooks/ats3QL.html)
ATS-3
provided regular communications service to sites in the Pacific basin and Antarctica, as well as emergency communications
links during the 1987 Mexican earthquake and the Mt. St. Helens disaster, and supported the Apollo Moon landings. The satellite was launched
11/5/1967 and also provided the first color images from space as well as regular cloud cover images for meteorological studies.
ATS-4 (http://msl.jpl.nasa.gov/QuickLooks/ats4QL.html)
This
satellite was launched 8/10/1968 and stranded in a much lower than planned orbit due to a launch vehicle failure, making the
spacecraft nearly useless.
ATS-5 (http://msl.jpl.nasa.gov/QuickLooks/ats5QL.html)
ATS-5
was launched 8/12/1969 included a demonstration using L-band signals to precisely locate ships, tests of an electric ion engine,
evaluation of the attenuation effects on RF signals by rain, and C-band communications tests. However, following the firing
of the satellite's apogee kick motor, ATS-5 went into an unplanned flat spin. The
vehicle recovered and began spinning about the correct axis, but in the direction opposite that planned. Let me tell you how that happened.
The apogee
kick motor was recessed within the tubular shape of the spacecraft. After it
rocketed the spacecraft into its geo-stationary orbit it needed to be released from the satellite. NASA scientists knew ATS-5 would be wobbling, or nutate, as we would say, causing the rocket motor to hit
and damage the sides of the spacecraft as it slid out of the tubular frame. Therefore,
we would have to stop the nutation before releasing the kick motor. Prier to
the ATS-5 launch, we used another ATS spacecraft (I don’t remember which one) to practice this procedure. We would fire a small gas rocket on its side and make the ATS nutate.
The nutation would also make the signal from the S/C wobble. This produced
a waving signal we printed on a strip chart. Watching the chart we would hold
our finger on the button and fire the gas jet at the precise point in the wave pattern that would result in stopping the nutation. I, and other field engineers at the station, practiced this procedure several times
and found we could stop the nutating ATS with no problem. However, on the day
of the launch, the controllers back at Goddard changed the procedure. They were
watching the waving signal from the nutating ATS-5, and told the field engineer at the station that was working the launch
(I was off that day.) to hit the button on their “mark” rather then on his own initiative as we had practiced. That bad decision on their part resulted in a slight delay in firing that caused ATS-5
to nutate more rather than less, causing the S/C to go into a flat spin. It came
out of the flat spin but in the wrong direction. As a result, the spacecraft's
gravity gradient booms could not be deployed, and some experiments such as the yoyo de-spin system were not functional. However, the spacecraft was able to perform some of its experimental goals.
I May Have Saved ATS-5 From Further Damage
The position
I was working at the time was as “Synchronous Controller.” It was
called that because we had to synchronize our commands to the spacecraft, with its spin.
This was especially critical if we needed to move the S/C from one orbit to another.
The maneuvering rockets needed to be fired at the right position of the spin in order to move it in the direction we
wanted it to go. Everything we did to the S/C was at the commands of a Spacecraft
Controller back at Goddard. He would say, “Enter command 721.” I would enter the command “721” and the S/C would respond with a signal
letting me know it was ready to execute 721. I would relay that information to
the Controller. The Controller would tell me to execute the command. I would push the button that would execute the command that was previously sent to the S/C and confirm
to the Controller that 721 was executed. Downlink signals sent from the S/C would
let us know what actually happened. Command numbers that were critical (non reversible)
to the S/C required an extra step. When they were sent to the S/C the S/C would
flag it and not execute even if I sent the execute signal until I sent an extra command ordering it to “override.” When I received such a “flag” I was responsible to tell the Controller
that this command was critical. The Controller would acknowledge the critical
command, confirm that that is what he wanted to do, and ask me to transmit the override signal; after which he would ask me
to “execute.”
It was
the Controller’s responsibility to know what 721 would do to the S/C. My
responsibility was to confirm that the command number I sent was the number he asked to transmit. However, we were not expected to blindly transmit command numbers to a S/C without knowing what they would
accomplish. Therefore, I studied the S/C handbook that explained what each command
number would do. I was in a series of commands to ATS-5 which the Controller
and I knew were critical and would need the additional override signal. The Controller
expected to hear my announcement of “critical command” which he would automatically ask an “override.” “Transmit 473 (I don’t remember if that was the actual number) he said.” When I reported back that 473 was critical he said, “Override and execute.” I thought to myself, “Wait a moment, that is the release command for the de-spin
yoyo.” Knowing that ATS-5 was spinning in the wrong direction I understood
that if the de-spin yoyo was released, the spacecraft would not slow down but cause the weights, at the end of the yoyo wire,
to slam against the spacecraft causing irrevocable damage. With a heavy emphasis
on the word “sure” I replied to the Controller’s override and execute instruction with, “Are you sure
you want to do that? That command will release the yoyo’s.” After a long pause the Controller came back with, “Disregard that execute command.” We continued the series of critical commands without further comment about the Controller’s
error.
ATS-6 (http://msl.jpl.nasa.gov/QuickLooks/ats6QL.html)
ATS-6 launched 5/30/1974 became the world's first educational satellite. During its 5-year life,
ATS-6 transmitted educational programming to India, the US and other countries. The vehicle also conducted air traffic
control tests, was used to practice satellite-assisted search and rescue techniques, carried an experimental radiometer subsequently
carried as a standard instrument aboard weather satellites, and pioneered direct broadcast TV.
(You can thank ATS-6 for your satellite TV reception.) The satellite also
played a major role in the Apollo/Soyuz docking in 1975 when it relayed signals to the Houston Control center. It was boosted
above GEO [stationary orbit] when thruster failures threatened to prevent further control of the spacecraft.
