Tracking Apollo-17 from Florida

Sven Grahn

Apollo 17 - the last lunar landing mission

  • The crew consisted of Eugene A. Cernan (Commander), Ronald B. Evans (Command Module Pilot) and Harrison H. Schmitt (Lunar Module Pilot).
  • The mission was launched on 7 December, 1972, 0533:00 UT from the Kennedy Space Center.
  • The CSM, LM and SIVB booster stage were inserted 11 min 53 sec after launch into an Earth parking orbit of 169 by 171 km.
  • After two revolutions, at 0845:37 UT, Apollo 17 was inserted into translunar coast.
  • Landing occured at 19:54:57 UT on 12 December, 1972 at lunar latitude 20 degrees 10 min North and longitude 30 degrees 46 min East.
  • My satellite tracking friend, Richard S. Flagg, then a radio astronomer at the University of Florida in Gainesville, talked me into going to Florida to watch the launch and track the spacecraft by radio. I will never forget it. Here is a brief account of that experience.

A visit to the Cape a week before launch

On November 29, 1972, the day of my visit the moon rocket Apollo 17 was on its launcher a few hundred meters from the beach of the Atlantic. It had been there since August and in the launch control center at the VAB preparations were going on for picking up the final countdown the following morning. I visited a telemetry station where data from the different stages of the booster was received and recorded. The station was a large room with ceiling-high rack sections for each rocket stage. These racks contained TM-receivers and discriminators. It was somewhat surprising that rather low frequencies were used for this telemetry. Instead of microwave equipment, which one could have expected, all telemetry frequencies were in the P-band, i.e. between 200 and 300 MHz.

The receivers were crystal-controlled and had wide-band FM discriminators, The noise figure was often high (10 dB), but this was compensated by low noise antenna pre-amps. From the TM-station data was passed on to meters and indicators in the control center (firing room). In this room a lot of engineers were placed at consoles to read off instruments and watch the condition of the space vehicle. In the future, i.e. when the space shuttle becomes operational, the idea was to reduce this work force by a factor 10 by the use of a computer system that fully monitors and supervises the checkout, launch and flight of a space vehicle.

In the nearby VAB work was on going on around the clock the with the next big space project, Skylab. On top of the large Saturn-5 booster the work and living section of the space station was mounted. The airlock and the astronomical observatory were still missing. At my visit a so called "refrigeration test" was going on, i.e. the system that keeps the sunny side of the station cool and the shadowy side warm was being tested. Despite the fact that the launch date was more than five months distant, intensive activity was going on around the cylinder-shaped can that was part of the space station when it was orbited in May 1973. Skylab used frequencies in the P-band just as the Saturn 5 booster did. Because Skylab orbited between 50oS and 50oN its signals were audible in Sweden


Titusville area changed on launch day

The countryside around the rocket base was very much changed on launch day. The lift-off was scheduled for ten o'clock at night, but already at noon campers and tourists gathered on the mainland coast north and south of Titusville, the nearest town of the space center.

I arrived there at about 11 a.m. with my friends from the Physics and Astronomy Department of the University of Florida (Gainesville) Dick Flagg and Wes Greenman. We set up a tracking station near a fruit-stand on the beach (see pictures below) just south of Titusville which was equipped to receive Apollo 17 on 258.5 MHz (TM from last stage of booster), 259.7 MHz and 296.8 MHz (up- and downlink AM voice signals from the spacecraft). This tracking station was situated about 20 km due west of the launch pad and consisted of a variety of homemade and surplus units (See block diagram below the lift-off picture). Using this equipment we planned to pick up signals during the launch phase and during two subsequent transits over Florida before the spacecraft would be propelled out of its parking orbit and into a moon-bound trajectory. 


The small tracking station in Titusville.
Dick Flagg (left) and Wes Greenman.

Dick Flagg and radios in the back of
the car


I open a soda pop can - it's a hot day!

During the course of the evening, the countdown proceeded smoothly and the spectators in the Space Center viewing area spent the time eating sandwiches and making music in various ways. Others watched the big rocket with large telescopes in which you could almost see the rivets in the tank walls of the huge "bird". As the countdown approached zero everybody's attention was focused on brightly illuminated ivory rocket which stood out starkly against the background of a tropical thunderstorm far away over the Atlantic.

At T~30 seconds (2152 local time) the countdown was halted by the terminal countdown sequencer that controls the final 3 minutes of the countdown. The error was quickly localized to the sequencer itself, and after having simulated the error and its fix in a laboratory in Huntsville, Alabama the problem was solved by applying "jumper wires"!!


Apollo-17 takes off from the Kennedy Space Center at 0533 UT on 7 Dec 1972.
Photo: Richard S Flagg.

The lift-off finally took place 2 hours and 40 minutes late at 0033 local time (0533 UT) December 7, 1972. The flame of the missile changed the Florida night into day and 15 seconds after lift-off the excited voices of the astronauts were heard on the loudspeakers in the viewing area. (The lift-off picture was taken by Dick Flagg.) Gradually the rocket faded into a little green speck of light that disappeared behind the thunderstorm 6 minutes after launch. Our little Titusville station picked up strong voice signals up to 8 minutes after launch on 259.7 MHz. Thanks to the clear weather the ignition of the second stage was clearly visible from the ground some three minutes (actually 165 seconds) after lift-off.

VHF monitoring of Apollo communications

We were lucky and got through the traffic jam and out of the rocket base very quickly and got back to Titusville in time for the first transit of the spacecraft over Florida. At 0208 local time (0708 UT on Dec. 7) we picked up the very characteristic PCM "buzz" on the TM frequency 258.5 MHz from the last stage of the Saturn 5 booster, which was still attached to the spacecraft. The rocket stage would be used 1 hours later to boost the astronauts towards the Moon. Shortly after hearing the telemetry signals we also picked up voice signals on 296.8 MHz. The astronauts were chit-chatting with the ground and we tracked the spacecraft across the sky with the helix-antenna. When Apollo 17 was due south of us we could clearly hear an astronaut say in our loudspeaker: "I just saw a shooting star over Miami". As Apollo 17 approached the horizon in the southeast the crew could be heard calling: Houston, 17, how do you read?"

On the next transit the spacecraft passed very close to the local horizon and telemetry and voice signals were picked up weakly between 0343 and 0346 local time (0843-0846 UT). A few minutes later (0354 local time, 0854 UT) Apollo 17 was fired out of earth orbit and changed from VHF transmissions to microwaves (2287.5MHz). 

 

Microwave signals from the Moon with a 9 meter parabolic dish

After a few days' rest we started preparations for microwave monitoring of Apollo communications. My radio astronomy friends had mounted a 9 meter dish on its mount on 28 November 1972 - while I looked on. The antenna was placed at the old radio observatory of the University of Florida near a little lake, Bivens Arm, outside Gainesville. The servo-mount was a piece of space history in its own right. It was used at Cape Canaveral in the beginning of the sixties to steer a command antenna for the first communications satellite Telstar!


28 November 1972: 9-meter dish is being installed on pedestal at Bivens Arm. Balance weights are on the ground.

The attempts to tune Apollo 17 was the first test of the 9 meter dish after its installation at Bivens Arm. The aluminum dish is Air Force surplus equipment. In the focus of the dish a feed antenna is placed to "illuminate" the surface of the parabola. The feed was a 30 cm by 10 cm cylinder and was only sensitive to left hand circular polarized radio waves. Its SWR (standing-wave ratio) was 1.2 over a 200 MHz range around 2300 MHz (S-band).

The signal from the feed was supplied to a tunnel diode pre-amp for S-band. This unit, the most critical item of the whole receiving system, had a 3 dB noise figure and enough gain to overcome the cable loss of the inch-thick coax cable that brought the signal from the dish to the listening post in a shed 25 meters away. In this shed the rest of the equipment was located.


The 9-meter dish at Bivens Arm

The receiver used for tuning the Apollo frequency 2287.5 MHz was a Motorola unit - surplus from the Apollo program itself. Only the local oscillator and the first mixer was used. The IF of the first mixer at 50 MHz was fed to a Vanguard Electronics Labs converter which brought this frequency down to 30 MHz. The final demodulation was done with a Collins R-390 shortwave receiver tuned to 30 MHz.

Voice signals from Apollo were frequency modulated on 1.25 MHz subcarrier, and by sidetuning the Collins receiver 1.25 MHz the voice signals were made available for demodulation. This could be done in two ways. The simplest method was of course slope detection with a 16 kHz bandwidth in the 455 kHz IF of the R-390. The other variant involved taking the 455 kHz IF out of the R-390 and feeding it into a narrow-band FM detector.

The dish could be steered with a 1o accuracy and the beamwidth at 2300 MHz is about 2o. But the Moon subtends only an angle of 0.5o in the sky. Pointing the antenna was therefore somewhat of a problem. Of course one could calculate where the Moon is supposed to be, but fortunately the weather was fine so the Moon was fully visible even during daytime. One person (usually me) placed himself behind the dish and directed the operator in the shed with hand signals until the antenna was pointing at the Moon. After the signal was acquired the position of the dish had to be corrected towards maximum signal strength every 4 minutes. The block diagram of the S-band receiving equipment is shown below.

On December 10, 1972 we picked up our first signals on S-band. The main carrier was 45 dB over noise and the voice subcarrier was 25 dB over noise. Apollo 17 passed. over the lunar disc between 1722 and 1819.10 local time (2222-2319 UT), and during these 57 minutes we measured a total Doppler frequency shift of 43 kHz (see figure below). The frequency numbers on the ordinate is the dial reading on the R-390 receiver minus 29000 kHz.

The spacecraft had entered orbit at 1447.23 local time (1947.23 UT), Initially the orbit was 97.4-314.8 km. The orbital period was then 128.2 minutes and the spacecraft would be seen from the earth for about 80 minutes. We clearly did not pick up the signal as the spacecraft appeared from behind the Moon. The doppler curve below is indeed not perfectly symmetrical which most probably is the result of the eccentricity of the orbit. The average speed in the orbit was 1.58 km/s. If the orbit had been perfectly circular at the 128.2 minute period the doppler shift for a simple transmitter would have been = 2287.5 x 1000 x 1.58/300000= 12 kHz. For a coherent transponder the doppler shift would be almost double this number (doppler shift on both uplink and downlink), i.e. 46 kHz. We observed about 43 kHz which is consistent with the fact that we did not catch the complete pass in front of the lunar disc.

f

On December 11, 1972  the lunar module landed on the Moon and at 1518 local time we picked up main carrier and telemetry from the surface of the moon some 80 minutes after touchdown. Unfortunately the astronauts soon changed to low power which prevented us from getting voice signals because of the too low signal-to-noise ratio. The lunar module transmitted on 2282.5 MHz, but we decided to shift back to the frequency of the command module in lunar orbit, i.e. 2287.5 MHz. The lone astronaut Evans was not very talkative except when he just appeared in front of the Moon or just before he disappeared behind it. At such times he changed to high power and on December 11 we could pick up our first voice signals from the Moon. At 1722.00 local time (2222 UT) Ron Evans said: "'Standby three zero" and at l722.30, i.e. 30 seconds later, we abruptly lost the signal as the spacecraft swung around the edge of the Moon.

The following day, December12, 1972  we concentrated on the command module and received strong voice signals on several occasions Listen to Ron Evans say: "The barber pole it is grey", referring to a barber pole-shaped control panel indicator). We also had an opportunity to test different FM detectors. To our great surprise slope detection worked amazingly well. When using this mode the receiver is slightly detuned so that the FM signal is placed on one of the slopes of the a selectivity curve of the receiver. In this way FM is converted to AM which is heard in the loudspeaker. When using slope detection the R-390 was operated with 16 kHz bandwidth to avoid resetting the main tuning too often because of Doppler shift.  The table below shows the entire log-book for our receptions of Apollo-17 (1). The elevation and azimuth of the Moon measured by the antenna and noted in the log is compared to the computed direction here.

Log-book for Apollo-17

Date Location Time (UT) Frequency (MHz) Event Remarks
7 December 1972 Titusville 0533 296.8 AOS Lift-off. AM voice
 

"

0541

"

LOS  
  Titusville 0708 258.5 and 259.7 AOS Telemetry from SIVB stage plus AM voice. "Saw a shooting star over Miami"
 

"

0714.30

"

LOS  
  Titusville0843258.5 and 259.7 AOS Weak telemetry and AM voice
 

"

0845.30 " LOS 
10 December 1972 Gainesville 1852 2287.5AOS Carrier. Elevation =33 deg. Azimuth=137 deg
 

"

1853 " LOS Equipment problems
  Gainesville 22212287.5 AOS Elevation=44 deg. Azimuth=202 deg
 

"

2238 "  Elevation=41 deg. Azimuth= 209 deg
 

"

2241 "   Voice subcarrier, trace of voice
 

"

2316 "  Elevation=37.5 deg. Azimuth=218 deg
 

"

2319.10 " LOS  
11 December 1972 Gainesville 1800 2287.5 AOSElevation=22 deg. Azimuth=117 deg, Carrier fx on R-390=29.957 MHz
 

"

1810 "   Voice signals
 

"

1822.30 " LOS 
  Gainesville 2018 2282.5 AOS Lunar Module. fx on R-390=31.529 MHz. LM landed at 1954:57 UT!
 

"

2105 " LOS Sudden switch to low power.
 

"

2124 " AOS Reacquired. Azimuth=169.5 deg. fx on R-390 carrier=31.556, TM 30.532, Voice 30.305 MHz
 

"

2130" LOS Off watch on this frequency. Receiver crystal changed to receive 2287.5 MHz again.
  Gainesville 2152 2287.5AOS CSM carrier.
 

"

2208 " LOS Briefly off watch because of equipment issues.
 

"

2212 " AOSEquipment back in operation.
 

"

2220 "   Voice subcarrier activated.
 

"

2222 "   First voice from the Moon: "Standby three zero"
 

"

2222.30" LOS CSM passes behind Moon's limb.
12 December 1972 Gainesville 1934 2287.5 AOS Voice
 

"

1941 "   Switch to low power
 

"

1945 " LOS Elevation=36.5 deg. Azimuth=123 deg
  Gainesville 2123 2287.5 AOS Brief loss-of-signal 2126-2128.
 

"

2159 "   Voice! Start recording.
 

"

2212 "   Perfect voice: "The barber pole - it is gray".:
 

"

2217 " LOS  

On December 14, 1972 I left Gainesville for Sweden. At Kennedy Airport I watched the astronauts leave the moon on a little pay-TV which you could find on many seats in the air terminal (see video clip below). So - the Apollo program was all over.

Four years later, in 1976, I had the opportunity to talk to astronaut Ron Evans when he visited my employer, the Swedish Space Corporation. He explained what the expression "the barber pole it is gray" actually meant. In the picture below from this occassion Ron Evans is of course the person on the left in the spectacular jacket and I am the fellow with the full beard (it was in fashion then).

It seems so far away, yet so close in time. Thank you Dick for convincing me to come to Florida to see the launch and track the spacecraft!

 

References

  1. Grahn, Sven, Tracking log kept during the tracking of Apollo-17 reproduced here. The first page is the log for 12 December, 1972. Time is given in p.m. EST. The second and third pages are for 10 December, 1972 (time is Eastern Standard Time in 24-hour clock format), page 4 is for 11 December, 1972 (time in p.m. EST) and page 5 is a summary sheet for 10 December 1972 (time in UT) while page 6 is the summary for 11 December 1972 (time in UT).The times for the various doppler readings are slightly different than those on pages 2 and 3. This is because the times on page 6 have been corrected by comparing my watch (which was used as the chronograph!) to standard time using a dial-in service. Page 7 is the summary log for 7 December, 1972 (time in EST a.m.).

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