Australia’s Contribution to the PAGEOS Project

The PAGEOS (Passive Geodetic Earth Orbiting Satellite) spacecraft was a 30.48 metre inflatable sphere, that carried no instrumentation. It was the second NASA satellite in the National Geodetic Satellites Program. PAGEOS 1 was made up of 84 gores and 2 pole caps of 0.0127 millimetre aluminised Mylar film. The gores were 48 metres long with a maximum width of 1.24 metres and the pole caps were 1.02 metres in diameter. The primary purpose of the satellite was to provide a tracking target for geodetic purposes by providing a reflecting light source whose brightness was relatively independent of observer-satellite-sun phase angle. A short explanatory video may be viewed via this link.

Figure 1 : The PAGEOS geodetic network with its 45 ground stations (Number and Name) and the established baselines in red.

Figure 2 : (Top) Wild BC-4 Ballistic Camera static and on-site; (Centre) instrument system used in the PAGEOS satellite triangulation program consisting of the electronic synchronization unit in the large console and the BC-4 camera; (Bottom) typical site configuration with the BC-4 camera astrodome and demountable which housed the electronic synchronization unit (courtesy NOAA's Geodesy Collection).

PAGEOS was the earth orbiting target in a global cooperation Weltnetz der Satellitentriangulation (Worldwide Satellite Triangulation Network) planned by Hellmut Schmid (Schmid, 1974). The final network of 45 ground stations, listed in Annexure A, encompassed the globe with each ground station comprising instrumentation as shown in Figure 2 above and described at Annexure B. Note that some documentation says there were 46 stations. This number stems from the fact that after observing commenced the camera on Wake Island was moved some 50 metres in September 1967 due to flooding. This new site was given another number to avoid confusion. Schmid’s 1974 results list only 45 stations.

At suitable times, applicable ground stations simultaneously photographed the satellite against the star background. Photographing PAGEOS in at least two different parts of the sky, as seen from each pair of ground stations, established a direction from one station to the other. If three or more ground stations were involved at the same time, a network of directions could be established to determine, except for scale, the relative locations of the ground stations (Corpacius, 1964). From this stellar triangulation, the relative locations of ground stations 3000 to 5000 kilometres apart were obtained. To provide and maintain scale throughout the network, highly precise baseline distances were required within the network.

In this global triangulation, baselines on four continents were established; North America from Beltsville in Maryland east to Moses Lake in Washington State and south to Wrightwood, California; in Europe from Tromso in Norway south to Hohenpeissenberg in Germany and onto Catania in Italy; in Africa from Dakar east to Fort-Lamy, Chad; and in Australia from Perth, Western Australia east to Culgoora in NSW and north to Thursday Island off Cape York. Figure 1 above shows the 45 ground stations (Number and Name) and the associated network with the established baselines in red.

Figure 3 : (Left) Wild BC-4 site (red star) at Culgoora in then CSIRO Radiophysics Laboratory Radioheliograph compound (courtesy Goss (2013)) and right the installation at Culgoora showing centre the BC-4 camera astrodome and to its right the demountable which housed the electronic synchronization unit (courtesy NOAA's Geodesy Collection).

From 1967 to 1970 the majority of National Mapping’s geodetic resources went into refining existing surveys to generate these two baselines as shown in Figure 4 below. The Perth-Culgoora baseline comprised 162 surveyed segments with a final computed length of 3,692 kilometres and the Culgoora-Thursday Island baseline comprised 102 survey segments with a final computed length of 2,910 kilometres.

National Mapping’s activities are variously described in :

-	Technical Report No. 11, Two Australian baselines for the PAGEOS world triangulation, by Klaus Leppert, 1972.
-	Chapter 17, The Division of National Mapping’s Part in the Geodetic Survey of Australia, in The Australian Surveyor, June, September and December 1979: Vol.29, No.6, pp.375-427; Vol.29, No.7, pp.465-536; Vol.29, No.8, pp.581-638, by Reg Ford, 1979.
-	Recollections by Andrew Porteous.
-	Use of the MRA4 Tellurometer on the Swedish-Norwegian section of the Tromso-Catania PAGEOS baseline describing part of the European contribution to the PAGEOS project.
-	Earth Parameters From Global Satellite Triangulation And Trilateration, Mueller, II (1973), Proceedings Symposium on Earth's Gravitational Field and Secular Variations in Position, UNSW, describing the results obtained from 159 station global satellite triangulation and trilateration (including Baker-Nunn, BC-4, PC-1000 camera observations, SECOR, C-Band radar and EDM distance measurements) which indicate differences in the semidiameter and orientation of the Earth compared to results obtained from dynamicsatellite solutions.

Figure 4 : The survey route of the Australian baselines (after Leppert, 1973).

Finished in 1974, the PAGEOS network connected stations previously on seven different geodetic ellipsoids (International, Clarke 1866 and 1880, South American, Bessel, Everest, and Australian National) with an accuracy of better than 20 metres. A best fitting global ellipsoid was defined from these data with an equatorial radius of 6,378,130 metres. In 1984 when the GPS ellipsoid was determined at 6,378,137 metres the 1974 work was shown to produce a value to better than 1 part per million.

Barlier and Lefebvre, in their 2001 paper A New Look at Planet Earth : Satellite Geodesy and Geosciences, are less enthusiastic about the PAGEOS results. Although stating that the geocentric positions of the 45 stations published were considered at this time as making one of the first homogeneous global Earth reference systems, they also say the project was in fact a dead-end. Firstly, the 10-15 metre accuracy was not good enough, but the major disadvantage was that this new reference system was not accessible to the common user!

A report in September 2016 revealed that although PAGEOS suffered partial disintegration in July 1975 and a further break-up in 1976, what was thought to be the principal part of the satellite re-entered the earth’s atmosphere on 2 September, 2016 after lasting over 50 years in orbit.

Compiled by Paul Wise, December 2016

References

Barlier, Francois and Lefebvre, Michel (2001), A New Look at Planet Earth : Satellite Geodesy and Geosciences, The Century of Space Science, Kluwer Academic Publishers, accessed at : http://www.ipgp.fr/~tarantola/Files/Professional/Teaching/Seminar/Texts/Barlier-Lefebvre.pdf

Corpacius, AJ (1964), The Stellar Triangulation with Photographic Observations, Space Science Reviews, Vol.4, No.2, pp.236-261, accessed at : http://adsabs.harvard.edu/full/1965SSRv....4..236C

Goss, WM (2013), Making Waves, Springer-Verlag.

Leppert, Klaus (1973), Geodesy in Australia, 1956-72, Technical papers presented at 16th Australian Survey Congress, Canberra, 1973, pp.A1-A6.

National Aeronautics and Space Administration (1971), NASA Directory of Observation Station Locations, Vol.2 (Edn.2), NASA-TM-X-68819, NASA Goddard Space Flight Center accessed at : https://ntrs.nasa.gov/search.jsp?R=19720012596

Schmid, Hellmut H (1974), Worldwide Geometric Satellite Triangulation, Journal of Geophysical Research, Vol.79, No.35, pp.5349-5376.

Schmid, Hellmut H (1974), Three-Dimensional Triangulation with Satellites, NOAA Professional Paper 7, National Oceanic and Atmospheric Administration (NOAA).

Annexure A

The network’s 45 ground stations listed by Number with Name, approximate geographical coordinates, original Datum and Ellipsoid

Station Number & Name		Latitude	Longitude	Datum & Ellipsoid
1	Thule, Greenland, Denmark	76.5 N	068.5 W	Qornoq	International
2	Beltsville, Maryland, USA	39.0 N	076.8 W	North American 1927	Clarke 1866
3	Moses Lake, Washington, USA	47.2 N	119.3 W	North American 1927	Clarke 1866
4	Shemya, Alaska, USA	52.7 N	174.1 E	North American 1927	Clarke 1866
6	Tromso, Norway	69.7 N	018.9 E	European	International
7	Lajes AFB, Terceira, Azores	38.8 N	027.1 W	SW Base	International
8	Paramaribo, Surinam	05.5 N	055.2 W	Provisional South American 1956	International
9	Quito, Ecuador	00.1 S	078.4 W	South American 1969	South American
11	Maui, Hawaii, USA	20.7 N	156.3 W	Old Hawaiian	Clarke 1866
12	Wake Island, USA	19.3 N	166.6 E	Astro 1952	International
13	Kanoya, Kyushu, Japan	31.4 N	130.9 E	Tokyo	Bessel
15	Mashad, Iran	36.2 N	059.4 E	European 1950	International
16	Catania, Sicily, Italy	37.4 N	015.0 E	European	International
19	Villa Dolores, Argentina	31.9 S	065.1 W	South American 1969	South American
20	Easter Island, Chile	27.2 S	109.4 W	Astro 1967	International
22	Pago Pago, Samoa, USA	14.3 S	170.7 W	Samoa 1962	Clarke 1866
23	Thursday Island, Australia	10.6 S	142.2 E	Australian National	Australian National
31	Invercargill, New Zealand	46.4 S	168.3 E	Geodetic 1949	International
32	Perth, Australia	31.9 S	116.0 E	Australian National	Australian National
38	Revilla Gigedo Island, Mexico	18.7 N	111.1 W	Isla Socorro Astro	Clarke 1866
39	Pitcairn Island, UK	25.1 S	130.1 W	Pitcairn Astro 1967	International
40	Cocos Island, Australia	12.2 S	096.8 E	Anna Astro 1965	Australian National
42	Addis Ababa, Ethiopia	09.0 N	038.7 E	Adindan	Clarke 1880
43	Cerro Sombrero, Chile	52.8 S	069.2 W	Provisional South Chile 1963	International
44	Heard Island, Australia	53.1 S	073.7 E	Astro 1969	International
45	Mauritius, Mascarene	20.4 S	057.7 E	Le Ponce Astro	Clarke 1880
47	Zamboanga, Philippines	06.9 N	122.1 E	Luzon	Clarke 1886
50	Palmer Station, Antarctica, USA	64.7 S	064.4 W	Palmer Astro 1969	Clarke 1880
51	Mawson Station, Antarctica, Australia	67.6 S	063.0 E	Astro 1969
52	Wilkes Station, Antarctica, Australia	66.2 S	110.6 E	Astro 1969
53	McMurdo Station, Antarctica, USA	77.8 S	166.7 E	Camp Area Astro 1961-1962 USGS	International
55	Ascension Island, UK	08.0 S	014.3 W	Ascension Isl.  1958	International
59	Christmas Island, USA	02.0 N	157.4 W	Christmas Isl. 1967 Astro	International
60	Culgoora, NSW, Australia	30.3 S	149.6 E	Australian National	Australian National
61	South Georgia Island, UK	54.3 S	036.5 W	Astro	International
63	Dakar, Senegal	14.7 N	017.5 W	Adindan	Clarke 1880
64	Fort-Lamy, Chad	12.2 N	015.0 E	Adindan	Clarke 1880
65	Hohenpeissenberg, Germany	47.8 N	011.0 E	European	International
67	Natal, Brazil	05.9 S	035.4 W	South American 1969	South American
68	Johannesburg, South Africa	25.9 S	027.7 E	Buffeisfont	Clarke 1880
69	Tristan da Cunha Island, UK	37.0 S	012.3 W	Astro 1968	International
72	Chieng Mai, Thailand	18.8 N	099.0 E	Indian	Everest
73	Diego Garcia, Chagos, Mauritius	07.3 S	072.5 E	1969 Astro	International
75	Mahe, Seychelles, UK	04.7 S	055.5 E	Mahe 1971	Clarke 1880
111	Wrightwood, California, USA	34.4 N	117.7 W	North American 1927	Clarke 1866

Annexure B

The Wild BC-4 Ballistic Camera

The Wild BC-4 Ballistic Camera combined a modified Wild RC-5 aerial camera with a modified T-4 astronomical theodolite mount. An Astrotar lens of 305 millimetre focal length was originally used, but by the end of the world observation program in November 1970 all cameras except one had been equipped with a 450 millimetre Cosmotar (Astrotar-type) lens for an optimum combination of resolution and field of view.

The camera was stationary during exposure, so that star images were recorded as interrupted arcs across the photographic plate. Three rotating disk shutters were synchronized through a high precision gearing system. An external capping shutter was used to chop star trails for calibration before and after the satellite was tracked. Precise epoch time was established at each field station by transporting portable crystal clocks, or by relay through satellites, and was maintained through the use of a local oscillator and VLF transmissions. Timing accuracy for satellite images was ± 100-150 microseconds.

The 18 centimetre square image corresponded to a 22° square field of view (33° on the 305 mm model). The maximum aperture was f/3.4. Exposures were made on 215 x 190 x 6 millimetre glass plates. Stars of 8th and 9th magnitudes could easily be identified on the plates, but those of magnitude 6 and 7 were preferred because of the greater accuracy of their catalogue information.

The system weighed 650 pounds and was transportable. For observing the system was mounted on a fixed pillar in a small astrodome.