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 :

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Technical Report No. 11, Two Australian baselines for the PAGEOS world triangulation, by Klaus Leppert, 1972.

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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.

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Recollections by Andrew Porteous.

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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.

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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.

 

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.

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.