Honeysuckle Creek Tracking Station
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Introduction About this page.
The Antenna Basic technical details.
The RF System The ultimate radio receiver.
Operations How operations were conducted.
Missions Missions while I was at HSK.
Links to Other Sites Links to Honeysuckle Creek related sites.
Selected NASA pictures on one page Planets and spacecraft (547 Kb)

 

Introduction

Honeysuckle Creek Antenna and Snow

I worked at Honeysuckle Creek Tracking Station during the mid nineteen seventies. This NASA tracking station was located at Honeysuckle Creek near Canberra in Australia. My time was after the Apollo moon missions, when the station had joined the Deep Space Network (DSN). This page is to give a small insight into what such a station did, and how it worked. The station was closed down early in the 1980's, and the site has been returned to the National Park, but the antenna lives on, having been moved to the Tidbinbilla tracking station nearby. Only its number on the DSN network has changed!

 

The Antenna

The 26m Antenna

Focussing

The Antenna was a Cassegrain type. Just as for equivalent reflecting optical telescopes, the signal is intercepted by the parabolic main reflector surface of the dish, and directed onto the sub reflector near the point (vertex) of the four supporting legs (quadrapole). From there the signal is focussed into the cone shaped 'launcher', the waveguide entry point, and passes through the centre of the main dish. The 'dish' was 26m or 85 feet in diameter. The surface had individually adjusted plates that were adjusted using a laser for high shape accuracy. The operating wavelength is 'S band' around 2.2 Ghz, chosen in part for the atmosphere's transparency. This means the beam width was around 0.5 degrees and the gain about 52 dB (from memory).

Mount

The antenna used an 'X - Y' mount instead of the 'hour angle declination' or Azimuth-Elevation' mounts more commonly used. This mount does not have a 'zone of confusion' when pointing straight up. The choice probably reflects the US Navy origins of this kind of antenna. A ship's motion has to be removed by servo control to maintain an accurate tracking attitude. An 'Az El' mount can find itself having to move through almost 360 degrees for a small increment in position. This is sometimes called the 'keyhole' effect. In the picture the antenna moves on two axes at right angles to each other, each driven by the large gears.

Drive

The larger lower axis was powered by two 75 horsepower hydraulic motors. One opposed the other to control backlash. This amount of power gave a fast movement rate of 3 degrees per second. The antenna was controlled by one of several servo systems, but was normally driven by computer predicts for the very weak deep space network signals. The computer was provided with precalculated positions and times, guiding the antenna slowly across the sky. With most missions the spacecraft appeared to move much as the sun, although at different times.

The X-Y mount

 

The Radio Frequency System

 

The transmitter room is just behind the dish

The radio system was known as the 'Unified S Band' or USB system. This is because the telemetry, command, tracking, ranging and doppler extraction are all in one 'unified' system with superior performance.

Transmitter

The transmitter used a large Klystron, capable of producing up to 20 kW of radio energy. Coupled with the 50 dB or so of antenna gain this provided a very high energy beam. The system used digital phase modulation of a precision carrier signal. The klystron power supply was a 'Ward Leonard' type of motor generator set to generate a controlled 10-20kV at 3 amps. This power was provided by several one Megawatt Caterpillar diesel generator sets, generating the 110V @ 60 Hz that the station used. There was no 'Australian Power' on site.

Receiver

The receiver front end used a Maser. This is like a laser for radio - Microwave Amplification by Stimulated Emission of Radiation. The solid state Maser devices were made from ruby, cooled by liquid helium at about 4 degrees Kelvin. The pump source for the Maser was a small Klystron operating at about 10 GHz. The Maser device provided almost noiseless amplification of the minute incoming signals. The system temperature was around 32 degrees Kelvin, and the receiver signal threshold was about -172 dBm for a 1 Hz bandwidth. This is about 10-20 Watts! The receiver had an IF frequency of 50 MHz. It produced an output for the demodulator as well as sum and difference channels for the monopulse radar tracking system.

Antenna Diplexer

The transmit and receive signals were continuously present in the same antenna. They differed in level by up to 240 dB, which is a ratio of 1024. The separation of the transmit and receive directions (considering both transmitting and receiving were continuous from the same antenna) was achieved by two devices. A set of waveguide filters separated the two directions according to frequency, while a waveguide hybrid device called a 'magic T' separated the signals according to flow directions - it certainly seems like magic. The loss of the desired signals was only a fraction of a dB.

Demodulator

The demodulator used a Kostas Loop method to extract the phase modulation, and also the doppler shift. The doppler shift was predicted, and appropriate changes made to the synthesiser settings for the phase locked loops. The data (with the usual weak signals) just looked like noise. This was digitised by a 12 bit Analogue to Digital converter, and further processed by computers which magically extracted the data from the noise. Some sort of algorithm using pseudo random code was used but I never knew much about this.

Tracking

The station had several purposes - to send commands and receive telemtry from the spacecraft, and to 'track' its position. The position tracking was achieved using range and doppler derived from the radio signal. The transmitter frequency was very precise (1 x 10 -12 error). This frequency was shifted by a precise ratio at the spacecraft, so that the received frequency is still directly related to the transmit frequency at the tracking station. The difference was used to determine the doppler shift, which in turn was related to the angular velocity of the spacecraft. This doppler shift was corrected for earth rotation to become part of the position determination. The other part is the range, determined by how long the signal took to return. A pseudo random code mixed with the modulation helped determine the timing, considering the Round Trip Light Time (RTLT) can be many hours. Easy to see why computers were so useful!

Processing and Communications

There were many computers. At one stage I remember about 16 'Modcomp' minicomputers were networked together. These processed command and telemetry more or less in real time as signals were received and sent. Some data was recorded on analogue tapes, some on digital tapes, and some sent directly to the US for further processing and display. These computers had 16 bit processing, with 5 Mb removable disk drives, and occasionally suffered event showers on the star configured networking.

 

Operations

The station was normally manned by three shifts, 24 hours a day. We came from Canberra and surrounds by a car pool. The workers included power station operators, stores, cooks, gardeners, security, mechanical techs, radio techs, antenna techs, computer techs, comms techs, administration, engineers and quality assurance. I hope I didn't miss anyone there! A typical shift consisted of a shift leader, three or four USB/Antenna techs and the same again of computer/comms techs. The total staff was around 120 I think.

A Tracking Pass

Shift Techs performed a pre-track count-down, with physical inspection of antenna, loading of computers from paper tape into magnetic core memories, and verification tests such as measuring system temperature. The space craft came over the Eastern horizon, followed by the handover from Goldstone (California) to HSK , then about eight hours of tracking, followed by the handover to Madrid (Spain). All tracking was controlled from the US with a continuously operated voice line. Honesuckle Creek was known as Station 44.

Handovers

As the earth rotates it is necessary to pass the spacecraft being tracked from one station to the other every eight hours or so. A special procedure was used with the object of providing only smooth phase changes at the spacecraft as the transmitter at one station was turned off and the transmitter at the next station was turned on. The spacecraft and station receivers used phase locked loops, so a sudden jump in phase could cause them to 'drop lock' with attendant embarasssment. The technique was for the outgoing station to tune the transmitter frequency slowly out to meet the incoming station. The frequencies was chosen so the different effects of doppler at each station would cause the transmitted signals from the two stations to arrive at the spacecraft on the same frequency at the same instant of changeover. At the designated time the outgoing station would turn off the transmitter while the incoming station would turn on the transmitter, with a one second overlap allowed. Then the incoming station could slowly tune the transmitter to get the signal in the middle of the doppler range again. If the spacecraft receiver 'dropped lock' due to jerky tuning, it could take up to 16 hours to know that the attempt to reacquire it was successful, when the signal returned. One trap was to tune to a sideband of the main signal instead of the carrier. The tracking predicts were essential, and transmitted from the US using landline before every pass.

Launches

A launch started months beforehand with training countdowns. These qualified the equipment and the staff. The lauch did not always go off as expected. Cancellations and delays meant there could be errors in the tracking predicts. The data rate was high (about 1 megabit instead of the usual 'cruise mode' 8 bits a second). To compensate, the signals from the spacecraft were strong, so manual tuning could be carried out using the spectrum analyser display. The tracking could often be done with a smaller antenna (and so a wider beam). Launch phase could use the monopulse tracking system where the signal is tracked by the phasing of the beam. Another difference was that the spacecraft appeared on the western horizon, moved west to east at a high rate, slowed down as it came over our longitude, then started to move west as the spacecraft achieved orbital speed. I was present for some launches of Viking and Voyager spacecraft among others.

 

Missions

The Main HSK Building

The Apollo series was the reason for being of Honeysuckle Creek station. Following this series, it was used for the US Skylab Mission and the joint Apollo/Soyuz Mission with US and Soviet Union participation. Remember the CCCP written down the side of the Soviet Rockets? Then the station moved to the NASA Deep Space Network (DSN), with some changes to the equipment and operations. The DSN is managed for NASA by the Jet Propulsion Laboratory (JPL) based near Pasadena, which is managed in turn by Caltech. Another NASA body was the Ames Research Centre in Mountain View California. Ames was formed for research into aircraft in 1939 by NACA (NASA forerunner), and provides mission support such as computers, among its many facets. The Langley research centre is in Hampton Virginia. It was the first research centre for the National Advisory Committee for Aeronautics (NACA), from which NASA was formed. This link about NASA - Langley history - gives a short understanding of NASA's achievements. The missions I was involved in are:

See the NASA sites (in the links to other sites topic below) for far better explanations of missions.

This page has NASA images selected from the missions. (547 Kb download)

 

Links to Other Sites

There is an excellent book about Hneysuckle and the Apollo Missions by Hamish Lindsay. It is called 'Tracking Apollo to the Moon'. It published by Springer. ISBN 1-85233-212-3. This book gives a good insight into how and why the Astronauts did things.

NASA link about NASA - history

Nasa Link about HSK in the Appollo moon missions era.

Mike Dinn's comprehensive pages about the Dish (Australian movie) and Honeysuckle during Appollo 11. Mike was the supervisor during the Apollo 11 landing.

NASA info about Viking and Voyager missions.

Australian Broadcasting Commission - Footprints on the moon.

John Saxon's HSK Page (look for the mailing list if you are ex HSK)

Nasa site about Viking 1 and 2.

Nasa site about Pioneer 10 and 11.

Nasa Pioneer home page

Nasa site about the Voyagers.

Nasa site for a Spectacular Solar Flare (loads slowly but worth it!)

Nasa and JPL Voyager Project Home Page - Interesting to see the distance and velocity, with RTLT and other current spacecraft status.

Nasa space images from various sources but especially Voyager solar system images.

The Max-Planck-Institut für Aeronomie links for Helios 1 and 2 spacecraft.