Below this introduction is part for the historic website of the GPS Signal Science Division of the Collaborative Research Centre for Satellite Systems, the CRCSS. This Centre was directed by Dr Elizabeth Essex-Cohen of La Trobe University, with much GPS and ionospheric research being undertaken at La Trobe University, but other GPS related, especially more applied application research being undertaken at other Australian centres.
Readers are advised to start at the homepage of the GPS Signal Science Division of the CRCSS. The homepage includes a brief accounts of plans for CRCSS research conducted at other Australian centres. However the value of this site was greatly enhanced by providing an account of the history of satellites, and of Australia's involvement in this history.
Elizabeth Essex-Cohen + model of FedSat

Elizabeth Essex-Cohen with 1:1 FedSat model
The revamp of this historic webpage is dedicated to Dr Elizabeth Essex-Cohen (1940-2004) who in 1974 was the only Australian involved in the design of the US Air Force satellite navigation system NAVSAT, initially conceived of as a purely military system, later renamed GPS, and made generally available when Selective Availability was turned off in May 2000. After her initial contribution in the GPS design stage, she returned to the US Air Force Geophysical Research Station in 1978 as a NASA Senior Post-doctoral Fellow, engaged then in basic ionospheric studies. Returning to Australia in 1979 , she actively continued her research on the ionosphere, and was active in lobbying for the second Australian satellite, FedSat. She was in charge of GPS science program for FedSat.
Sadly she suddenly became seriously ill, and was hospitalised in the Xmas following the actual launch of FedSat. She had a partial remission in January 2004, enabling her to participate in an International Beacon Satellite Workshop held in Hobart, January 2004. But she then relapsed, and passed away in March 2004. After her death, a huge manual was found amongst her books, which was the Operators Manual for a Satellite of the 1960's; on her death she was probably the only Australian with over 35 years involvement with satellite technology.
To fully appreciate Elizabeth's pioneering work one needs an overview of GPS, while on this page an account is given of the GPS satellite constellation system, and brief explanation how and why the ionosphere interfere's with the use of GPS

A selection of Elizabeth's scientific papers is available here, whilst the account of her lifelong involvement in GPS is detailed here This page dates from early 1997.
Orbit with the La Trobe Eagle
La Trobe University is a major facility in the plans for the Australian Cooperative Research Centre for Satellite Systems (CRCSS).
To establish the CRCSS, the Federal government has already pledged $20 million over seven years.
Plans call for the CRCSS to launch its first satellite, FedSat 1 in time for the centenary of Federation in 2001.
La Trobe is the only Victorian university that is in the CRCSS.
Once the CRCSS is formally established at the end of 1997, there will be new opportunities in Space Science and Technology for both undergraduate and research students. Subject to the final exchange of contracts formally establishing the CRC for Satellite Systems, top-up scholarships will be available for post-graduate students. Contact the listed researchers for details.
CRC for Satellite Systems
Listed Researchers in ATMOZ-GPS
Probing the atmosphere and ionosphere using GPS Signals
Elizabeth Essex-Cohen
Dr Elizabeth Essex
Space Physics Department
Faculty of Science, Technology and Engineering
La Trobe University
Melbourne, Australia 3083
Dr Essex is the research manager for GPS Signal Science within the CRC for Satellite Systems. She is directing a program that uses GPS signals, received a ground stations in Australia and Antarctica, to probe the geosphere. Experiments on-board FedSat 1 will study the occultation of GPS SV signals, probing all levels of the atmosphere.
  • Space based and Ground based Computerised Ionospheric Tomography
  • Mapping the Ionosphere in the Australian and Antarctic Region
See the text summary of her research projects.
dr Harvey A Cohen
Dr Harvey A. Cohen
Computer Science and Computer Engineering
La Trobe University
Dr Cohen is a listed researcher in the CRC concerned with scientific platform and computing. These experiments lead to the production of terabytes of data that need to be accessed by researchers. FedSat 1 and other satellites to be launched by the CRCSS have to form an integrated system as far as communication, control, and data collection is concerned. Within this system are FedSat 1, the 24 SV GPS satellites, a Singapore LEO satellite to launched shortly, and ground stations. Sophisticated system simulators have be developed to evaluate experimental designs and constraints for on-board experiments. The great amount of atmosphere and image data collected by our LEO satellite during each orbit has to be massaged and compressed on-board so that it can be sent to a ground station during the brief time that the satellite is overhead. See the text summary of his CRCSS related research projects. Dr Cohen is webmaster for these CRCSS web pages, as well as : the Image Engineering Index
Sounding the Atmosphere
using GPS Signals

The objective of the GPS/Occultation experiment is to use signals from GPS satellites almost occulted by the Earth. Such signals have a path an important component of which is through the lower atmosphere. GPS signals indicate to remarkable precision the instant of trasnmission, and we know with precision the location of the SV, and of the receiving satellite Using near-occultation data we will be able to take temperature, pressure, and other measurements at hundreds of points on the Earth every day, extending from near the surface up through the ionosphere. See Overview of GPS/MET University Corporation for Atmospheric Research.

FedSat is shown in low earth orbit about the earth, atmosphere and ionosphere indicated. In a larger orbit of 12 hours period are shown the 4 GPS SV's (Space Vehicles) that traverse the same orbit. The total GPS sysytem involves 24 SVs in 6 orbits inclined at 55 degrees to the equator. Just one of the 4 SVs is in (near) occultation, and the GPS signals received by FedSat have passed through the atmosphere and ionosphere.
Space Weather
Ionospheric Tomography
FedSat 1 will have a GPS antenna that can detect signals from (almost) vertically above. We know precisely when and where GPS signal packets started out from and where and when FedSat received them. By comparing GPS signals of different frequencies, we can infer, after a mammoth "tomographical reconstruction" just what is going on -- in real-time -- through the atmosphere.
Topex/Poseidon Experiments
The Topex/Poseidon satellite, a joint NASA/CNES Project uses radar to measure sea heights accurately, of special interest in global warming studies. The NASA altimeter on board Topex/Poseidon measures the difference in the delays of two radar pulses of different frequencies, (technically the Ku and C band pulses) Dr Essex and her research students use this difference in the time of the two pulses in the mapping of the ionosphere, especially over the expanses of the southern hemisphere oceans.

Black Hole Over Tasmania
Punching a hole in the Ionosphere
The fact that major rocket burns can punch a short-lived hole in the ionosphere was discovered by Michael Mendillo, of Boston University. Two holes in the ionosphere were deliberated punched in 1985 by firing the thrust rockets of the Space Shuttle Challenger over Tasmania and also over Boston. CRCSS key researcher Elizabeth Essex collaborated with Michael Mendillo in monitoring this historic experiment. Such a short-lived hole provides access on Earth to astronomical information normally hidden by the ionosphere.

Post-graduate Projects in Satellite & Space
Science at La Trobe University
CRC Satellite Systems Home Page