30th Anniversary of HartRAO’s participation in global space geodesy networks

Official opening by  Minister Naledi  Pandor

CNBC Africa outside broadcast at HartRAO

Delegates tour HartRAO facilities

 

The9th IVS General Meeting and the 30th Anniversary of Geodesy at HartRAO

By Dr Graham Appleby

Hartebeesthoek Radio Astronomy Observatory (HartRAO) recently hosted the 9th International VLBI Service for Geodesy and Astrometry (IVS) General Meeting.

All environmental research, including critical studies into global sea-level change, ice-mass balance, regional deformation and post-seismic effects, which is based upon knowledge of precise locations both on the surface of the Earth and in orbit around it, depends on the science of space geodesy.

Ultimately, the environmental research community charges the discipline of space geodesy with providing a robust and accessible Terrestrial Reference Frame with millimetre accuracy. Recognising the societal importance of this work as a basis for much other space science, the United Nations in 2015 passed the resolution "A Global Geodetic Reference Frame for Sustainable Development", co-sponsored by 52 member states, which urged member states to implement open sharing of geodetic data and invited them to commit to improving and maintaining national geodetic infrastructure as an essential means to enhance the global geodetic reference frame.

Both the realisation of a global frame and the precise determination of the orbits of Earth observation satellites within that frame require accurate observations from a network of ground-based observatories distributed worldwide. Crucially, the techniques of Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) are central to the realisation of the reference frame – the SLR technique through accurate range observations of the LAGEOS(or Laser Geodynamics Satellite) geodetic satellites defines the origin of the reference frame (the geo-centre), and the VLBI radio-astronomy technique through observations of distant quasars defines the space-orientation of the frame and, jointly with SLR, its scale, or size.

Observatories such as HartRAO that operate both these modern geodetic techniques on the same site are absolutely crucial to this international enterprise. This critical contribution from Hartebeesthoek is made all the more important by the unique geographical location of HartRAO in the relatively sparsely instrumented southern hemisphere and it being the sole facility on the whole African continent.

HartRAO should make all possible efforts to sustain and improve its observational contributions to this worldwide enterprise.

Dr Graham Appleby, Head, NERC Space Geodesy Facility, Herstmonceux, UK, has led the UK Space Geodesy Facility through a period of rapid development, such that it is currently a world leader in the SLR technique. He is particularly interested in the analysis of laser-range observations for reference frame studies and for identifying small systematic range errors in stations from the network. He hopes to convince funding agencies to include VLBI on site at Herstmonceux. He is the immediate past chair of the Governing Board of the International Laser Ranging Service.

 

The International VLBI Service and HartRAO – tying the world together

By Dr George Nicolson

South Africa occupies a unique position in the southern hemisphere, situated at the base of one of three widely separated continents, with thousands of kilometres of ocean surrounding them. The Hartebeesthoek Radio Astronomy Observatory (HartRAO), with its 26-m and 15-m radio telescopes, takes advantage of this and plays a pivotal role in global networks of radio telescopes using a technique known as Very Long Baseline Interferometry, or VLBI. Its contributions in this area are recognised internationally.

VLBI is used to create a radio telescope equivalent to the size of the Earth. It was originally developed to study the size and structure of very small objects known as quasars, which are among the most powerful and distant objects in the known universe. Quasars define a celestial reference frame, which is far more stable than the visible stars used by seafaring navigators. They provide the key for accurate measurement of the locations of widely spaced radio telescopes, achieving an unprecedented accuracy of about one cm.

HartRAO has been involved in VLBI since 1970. From 1961 to 1974 the facility was operated by NASA for tracking lunar and planetary spacecraft. The writer used the 26-m antenna during idle time between tracking operations to conduct research into radio astronomy and collaborated with a group using similar NASA antennas in Australia to pioneer intercontinental VLBI in the southern hemisphere.

In the modern world, precise knowledge of position has become increasingly important. On Earth, accurate position location has become commonplace with the ubiquitous application of GPS in cars and cellular telephones. At the scale of the solar system, space agencies have achieved the remarkable feat of landing spacecraft on distant planets in a target zone the size of a small city.

To achieve these accuracies requires a global network of stations located across the Earth's surface, with positions known to levels of one cm. This network defines the terrestrial reference frame and, because the continents drift, continual updating is essential. Changes in the rotation and orientation of the Earth, such as polar wandering, must also be monitored at an equivalent level. Without all of this, accurate positioning would not be possible.

In March, over one hundred international specialists will gather in Gauteng for the Annual General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS), to discuss the latest research results in their field and plan future developments. The IVS comprises 43 member organisations, 30 operational VLBI facilities and multiple other centres distributed in a variety of institutes around the world. It coordinates VLBI operations, analysis and distribution of data products, and future technology development.

This year HartRAO celebrates 30 years of precise VLBI measurements. These show that Africa is moving in a north-easterly direction at a rate of 25,5 mm per year as a consequence of continental drift. Other results contribute to the measurement of changes in global sea levels, possibly attributable to climate change, and are important for predicting future flooding of low-lying coastal areas. The position of the 26-m telescope also defines the South African reference datum for national land surveys, Hartebeesthoek94, enabling the integration of geo-spatial data in the world arena. Long-time series of measurements are essential to achieve and maintain the accuracies required for all these applications.

HartRAO is a National Research Facility, and falls under the Astronomy Sub-agency of the National Research Foundation. In addition to VLBI, it operates a number of sophisticated and complementary instruments that support other global programmes such as satellite laser ranging (SLR) for accurate orbit determination. A precision GPS receiver forms part of a global network that constantly measures the orbits of the GPS satellites, ensuring that the accuracy of the GPS system is maintained.

There are only four facilities in the world where these three sub-facilities are co-located at one site. Known as fiducial stations, they are critically important because they provide accurate inter-comparison of measurements made by three independent systems.

South Africa has a regional responsibility to participate in and support international programmes where our unique geographic location, existing facilities and expertise allow us to contribute and add value. As a fiducial station, HartRAO enhances the global networks, so it is important that that it enjoys continued support and is regularly upgraded to maintain compatibility with international networks.

A new dedicated 12-m VLBI antenna will be built at Hartebeesthoek later this year. HartRAO will then embark on a new phase where the measurement accuracy will be improved from 1 cm to 1 mm, continuing a 30-year tradition supporting international science.

Dr George Nicolson, was Director of HartRAO from 1975 to 2003. He obtained MSc and PhD degrees in radio astronomy based on research using the 26-m antenna during the period that it was operated by NASA. He was a member of the team that prepared South Africa's successful bid for the Square Kilometre Array (SKA), and is a consultant for the South African SKA Project.

 

Joining hands in radio astronomy

By Christopher S Jacobs

"Many hands make light work," my grandmother used to say. I learned from her that, by working together, we can combine our talents and resources so that – what at first seemed like an insurmountable task – becomes possible to do.

Now, many years later, I am no longer a child. I work as a deep-space navigation engineer in California. Nevertheless, the wisdom embodied in my grandmother's adage stayed with me over the years and is as important as ever.

We live in rapidly changing times. Our cultures and the natural world are moving in new directions, some of which may lead to harmful or even disastrous consequences. Climate change and sustainable lifestyles are constant topics of conversation. Will sea levels rise to such an extent that the lives of millions of people will be affected?

How should we, as a global community, respond? How can we work together?

Perhaps an example can suggest a way forward: this week, just outside Johannesburg, scientists from all over the globe are gathering to find ways to work together more effectively. I am part of this group of over 100 scientists from 22 countries, spanning five continents – and each of us is looking for ways to share our knowledge and build collaborations to solve challenging problems.

Our specialty is measuring signals coming from outer space as a way of determining positions on the ground with pinpoint accuracy. It is indeed this pinpoint accuracy that will enable us to monitor changes in sea level quickly, thus gaining precious time to make decisions and organise a response.

To give more detail, we track a variety of satellites, using both radio signals and lasers, as well tracking naturally caused radio signals from the cores of distant galaxies a billion light years away. We call these objects "quasars". They are exotic objects powered by super-massive black holes some a billion times more massive than our Sun. The energy from these black holes powers radio beacons that shine as brightly as an entire galaxy!

My own research focuses on measuring these quasar beacons. I have been working for over 30 years refining our technique, but it is never been just me working alone. I am part of a worldwide community that has been working together for decades. By sharing resources and expertise, we are now able to pinpoint stations on the ground to within a few millimeters, and this is a tracking system that spans the globe.

While a single station working by itself is a small start, by combining our stations together into a synchronised network, we achieve results that are 100 000 times more accurate! This is the power of teamwork.

As I address you here today, I am in a special place, namely, the Hartebeesthoek Radio Astronomy Observatory outside of Johannesburg in South Africa. I am looking out the window at a radio telescope that is 26 meters in diameter, which receives signals from the distant quasars at the edge of the universe. Next to the radio telescope are GPS satellite trackers and other kinds of telescopes, which focus lasers on satellites overhead to track their orbits.

This site at Hartebeesthoek is the only one of its kind on the African continent and one of only a handful of sites worldwide capable of bringing together all these devices into a synergistic system capable of watching the motions of the Earth at the millimeter level, which is required for tracking sea-level changes. Only by leveraging this synergy can we achieve the accuracy needed to solve the problems before us. Only by bringing together workers from numerous complementary fields will we have the expertise to get the job done. Many hands do indeed make light work!

I believe that it is time for the world to unite in an effort to solve the challenges before us. We have been given the potential to use reason to see with our mind's eye the nature of the problems that we face and to come up with solutions. Hartebeesthoek Radio Astronomy Observatory and its sister sites are providing us with the tools for working together and thereby achieve success.

My hope is that the lessons learned in my own field can be a source of encouragement to others in their own fields – in government, academia and industry.

My hope is that, by joining many hands together, what would otherwise be an overwhelming task will become light work.

Christopher S Jacobs has been an engineer/scientist for 32 years for the NASA Jet Propulsion Laboratory, California Institute of Technology. He specialises in the construction of global reference frames, both for terrestrial and celestial applications. All opinions expressed are his own and do not necessarily reflect the opinions or policies of NASA and/or the California Institute of Technology.