The First Steps to the Antarctic High Plateau Michael Burton, John Storey, Michael Ashley University of New South Wales It has been known for several years that the Antarctic Plateau provides superb conditions for a wide range of astronomical observations, but the harsh environment has restricted our attempts to utilise it for scientific research. Our ever increasing technological prowess, however, has now reached the stage where a venture like the building of an astronomical observatory on the Antarctic high plateau is possible. Considerable activity is currently focussed at the US Amundsen-Scott South Pole base, where an observatory is now operating. The first steps are being made towards building a new high station at the 3,500m Dome C, one of the highpoints in the Australian Antarctic Territory. Before any new astronomical programme can be embarked upon, it is first necessary to gather environmental data to assess the suitability of the site, and compare it to other venues where the programme is conducted. In Antarctica, just gathering that data in the first place presents a challenge! There are, however, number of excellent reasons for wanting to pursue astronomy there, and this is driving the push to establish a site testing programme. First, the atmospheric water vapour content above the high plateau in summer averages just 0.2 to 0.5mm of precipitable water vapour (PWV), falling below below 0.1mm PWV in winter. This is much lower than anywhere else on the Earth, and dramatically improves the atmospheric transmission in the far-infrared and sub-millimetre windows over any other ground-based observing location. For instance, from the summit of Mauna Kea in Hawaii, the premier observing site currently in use, the PWV only rarely is as low as 1mm. Even then, the transmission at 350 microns, a wavelength near the peak of the energy distribution from heavily obscured proto-stars, is only 30%, and its high variability prohibits accurate calibration. However, on the Antarctic high plateau this window will be open for observation virtually all the time, and many other windows at shorter wavelengths in the far-infrared will be opened up for observation from the ground for the first time. Numerous spectral lines from fine-structure transitions of common interstellar atoms and ions can only be observed in this waveband. Secondly, the Antarctic high plateau will quite likely provide substantially better seeing at optical wavelengths than even the best mountain top sites currently operating. This is due to the combination of the high altitude (over 4,000m), extreme cold (creating an equivalent pressure altitude of over 5,000m) and small diurnal temperature changes. The micro-thermal fluctuations in the air temperature, which degrade the spatial resolution from the diffraction limit, are minimised by these site conditions. In addition, there is the possibility of significantly enhanced UV transmission due to the high altitude and reduced aerosol concentration in the atmosphere. Mitigating against these positive attributes, however, is a strong temperature inversion that can occur over the lowest few metres of the ground, requiring that a telescope be placed on a raised platform. Thirdly, the thermal background radiation from the atmosphere and telescope is considerably reduced, leading to dramatically increased sensitivities. For instance, in the near-infrared `K' band at 2.2 microns, the thermal background is reduced by a factor of 220 from Mauna Kea at 0C, to the South Pole -60C, both typical winter-time temperatures. In the spectral range from 2.27 to 2.45 microns the airglow emission from OH radicals and aurorae is minimal, and hence the total background level is vastly reduced compared to anywhere else on the Earth. It will open a new window for us to peer out into the Universe. Through it the drop in background radiation in the near-IR means that we can use a telescope of 2 to 3 metre aperture and outperform even the largest telescopes being built (with diameters of 10 to 16 metres) anywhere else on the Earth. Even larger reductions in the background can be expected at the highest part of the plateau, where the temperature drops to -90C! Importantly, this waveband is also the minimum in the zodiacal background radiation from Solar System dust, with scattered sunlight dominating at shorter wavelengths and re-radiated sunlight at longer wavelengths. The Antarctic high plateau may therefore provide a site with as dark a background as can be found anywhere within the inner Solar System. It is a window through which we can make the deepest cosmological studies back into the early Universe. Site Testing the Antarctic Plateau Currently our group at UNSW are participating in site experiments at the South Pole with colleagues from CARA and the Universite de Nice, aimed at verifying some of these statements made above. One experiment is to measure micro-thermal fluctuations in the air temperature, thus finding where the seeing degradation occurs. Its purpose is to determine how high above the ice a telescope needs to be placed to obtain superb seeing. The second experiment is measuring the strength of the background sky flux in the near-IR, in order to quantify exactly how big the gains will be for the new 'cosmological' window over telescopes elsewhere in the world. It is of course essential to have a detailed understanding of the nature of the observing conditions in Antarctica before we can seriously attempt to raise the funds needed to build a major observatory. The scope of the project and the challenge it presents demands that the advantages of Antarctica over other sites be quantitatively understood, so that resources can be concentrated in the best manner. This requires us to test sites elsewhere than the South Pole, and in particular on the high Plateau, to determine whether the gains will be significant enough to justify moving to another site where no established infrastructure exists. We thus need more information, and here enters JACARA and the Automated Astrophysical Observatory (AAO). The Joint Australian Centre for Astrophysical Research in Antarctica (JACARA) JACARA is the organisation we have set up in Australia to instigate an Antarctic astronomy programme. It developed following the recommendations of the Australian Working Group for Antarctic Astronomy (AWGAA), a study group who looked at the potential of Antarctica for astronomy. JACARA is centred on twin nodes at the School of Physics in the University of New South Wales (UNSW) and at Mount Stromlo and Siding Spring Observatories (MSSSO) of the Australian National University (ANU), with representation from the wider astronomical community. JACARA's purpose is to make Antarctic astronomy a reality for Australia. Our first project is the Automated Astrophysical Observatory. Lockheed's Remote Observatory In 1987, the National Science Foundation in the US funded the Lockheed company to develop a self-powered, self-heated field station. The prototype phase, which included deployment and field testing cost around $US 4 million. The robust, if unprepossessing metal container which emerged, was first adapted for the gathering of geophysical data from the remote Antarctic interior. The station was called an Automated Geophysical Observatory (AGO). Fortunately for us, the AGO is equally suited to powering astronomical instruments, requiring only a renaming - to ensure the accuracy of our acronyms! We have dubbed it an Automated Astrophysical Observatory (AAO, not to be confused with the Anglo Australian Observatory!). The AAO is a very well insulated portable laboratory, with a floor plan of 4.8 x 2.4m. Short term accommodation is provided for up to four people, who accompany the AAO to its destination, set up the experiments over a period of about one week, then leave the AAO to operate autonomously for the next twelve months. Power Supply A major challenge which Lockheed had to face was how to provide heat and electrical power for the full twelve months that the AAO would sit on the ice in sub-zero temperatures. There is little wind on the plateau, so wind generators are next to useless, it is dark for six months of the year, making solar power tricky, and environmental and cost considerations rule out radioisotope generators. Fuel cells typically have an operating life of only a few months, batteries are too heavy, and a diesel generator is unlikely to be sufficiently reliable. The solution chosen was a propane-fueled catalytic oxidiser, which produces 2.5 kW of heat, plus 50 Watts of continuous electrical power via a thermo-electric generator. With no moving parts, the thermoelectric generator is exceptionally reliable, and relatively inexpensive. Our experiments, therefore, have to perform within this 50 W power budget. Data Storage and Telemetry Data taken by the AAO is recorded on optical disk, and retrieved at the end of the 12 month deployment. However the health and status of the experiment can be monitored in close to real time via transmissions to polar orbiting Argos satellites. AAO Deployment The AAO is designed to fit exactly into the cargo hold of a ski-equipped LC-130, "Hercules" transport plane. In the initial "put-in" flight, the AAO is placed on the snow. It slides in and out of the back of the Hercules cargo hold, though not always smoothly. On one deployment, the Observatory was ejected with such force that it executed a complete barrel roll, coming to rest on its base! As a measure of its robustness though, it was reassuring to find that nothing was damaged! In the standard deployment cycle, approximately one week after the "put-in" the Hercules returns with a year's supply of fuel and retrieves the science team. The AAO then remains on the ice for the next twelve months, gathering data in an autonomous mode very similar to that of a deep-space spacecraft. Environmental Considerations Australia's claim to a substantial part of the Antarctic continent is increasingly being interpreted to mean that we have a special responsibility to ensure that all developments taking place on Australian Antarctic Territory are carried out with minimal environmental impact. It is difficult for us to fulfill this role, or to have any understanding of what is happening over the vast expanse of the Antarctic interior, unless we are actively participating in inland projects. The deployment of the AAO to the Antarctic high plateau represents a particularly good example of how vital research data can be gathered over a year-long period with an absolute minimum of disturbance to the environment. For example, apart from a brief period of about one week during set-up, there is no human presence. The AAO operates by itself, gathering and recording data for a full twelve months. This greatly reduces the electrical power requirements and site infrastructure. Life support systems and the problems of waste management are completely avoided. The AAO is flown in by Hercules LC-130 transport plane. The Hercules stays there only as long as required for unloading, and returns to pick up the set-up crew when required. The AAO can be flown out again at the end of the operation, leaving nothing but footprints and landing-skid marks in the snow. The power source for the AAO is liquid propane, which is oxidised cleanly and at relatively low temperatures over a platinum catalyst. The exhaust consists almost entirely of water vapour and carbon dioxide. The astronomical instruments themselves are entirely "passive". They simply measure the incoming light, and make no disturbance whatsoever to the environment. Specific Experiments We have identified the measurements required in order to complete a site testing programme, and thus the suite of experiments that are needed. These are: measurements of the near-IR (1-5 microns) sky brightness, determining the atmospheric transmission in the UV and visible (300-1100nm) and quantifying the effect of auroral emission throughout the region of our preferred site. As well, we need to determine the transmission, emissivity, and stability of the mid-infrared (7-30 microns) sky above the Antarctic high plateau, and directly determine the atmospheric ``seeing'' using a Differential Image Motion Monitor (DIMM). Finally we will have to measure the scale height of the boundary-layer turbulence using mast-mounted microthermal sensors. The Australia Telescope may provide a mm water vapour radiometer, while the DIMM will be provided by the Australian National University who already have a proven track in the design and construction of these instruments for site testing in less frigid climes. Our group at UNSW intend to concentrate on the UV and IR experiments, and the microthermal measurements. Setting up the AAO Although the US has already established a base at the South Pole, data gathered so far indicates that to really derive the maximum benefit from Antarctic conditions, the AAO should be set up at one of the high points of the Antarctic Plateau. Two potential prime sites have been identified, the 4,300m Dome A (or more prosaically, Dome Argus), and the 3,500m Dome C (which is sometimes known as Dome Circe, Concorde, or Charlie, depending on which reference source you chose!). Both sites are in the Australian Antarctic Territory, and are some 1000 kilometres away from the Pole. Moving there will not be an easy job! Dome A, being the highest point, is probably optimal for a wide range of observations, but suffers from auroral emission, and may be sited above the safety margin for aircraft take-off and landing. Dome C, on the other hand, is already the site where a new station is being constructed by the French and Italians, and lies near the centre of the auroral oval. Building our experiments to run in such locations will be a challenge! They have to be designed to run unattended for a full year, and to survive temperatures as low as -90C. So far, we have done very well with the installation of the IRPS and microthermal experiments at the Pole, which have been gathering data for over a year, but these instruments have required human presence to make them work. An international working group is now studying the problem, and advising on the instrument complement which can be operated in such a manner. Other Benefits Although the major aim of the project is that of site-testing, the resulting data will produce interesting science in its own right. It will be able to provide information on many aspects of the Earth's atmosphere, improving our ability for global climate modelling. It will also allow us to test a variety of technologies in an environment almost as demanding as that of space - at vastly reduced costs and risks. Most importantly, if our surmises about the improved information gathering potential are correct, we will be able to gain one of the best possible vantage points of the Universe at a fraction of the cost currently required to build very large or orbiting telescopes. Public Outreach The final aspect of this project is the development of a public outreach programme. Antarctic astronomy has tremendous potential as an exciting new endeavour for our country. It can attract some of the best engineers and scientists from around the world to Australia to participate and rise to the challenge. And it has the capacity to bring science to the public by capturing our sense of discovery of adventure, through bringing together two fields which each challenge the imagination, Antarctica and astronomy. We are developing an outreach programme at UNSW to foster these goals. Our programme is designed to communicate the results of our research, and bring back the thrill of discovery to a wider arena. Members of the Antarctic Working group have given talks about our work to a number of amateur astronomical societies around the country and we writing articles for popular consumption (like this one!). We have set up the JACARA world wide web page on xmosaic (the URL is http://www.phys.unsw.edu.au/~mgb/jacara.html ) where information on Antarctic astronomy is publicly available. For the future we hope to stage an exhibition at Sydney Observatory and the planned Antarctic visitor centre in Hobart. We are even planning a documentary length video on Antarctic astronomy and life at the South Pole!