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IMAGES Geostationary Satellite over East Africa Observed from Kitt Peak, Arizona WIllIAM LIVINGSTON s a solar observer on Kitt Peak in Arizona one has evenings free, and I have amused myself Awith photography of twilight phenomena. One such exposure near the McMath–Pierce Telescope in the early evening sky revealed, in addition to the expected star streaks, a curious line of three fixed “stars” (Fig. 1). These proved to be geostationary satellites, or geo-stats. That we were aimed at the equator of the sky may be judged by the red streak due to the equatorial Orion nebula and the three bright stars of Orion’s Belt. Since the latitude of Kitt Peak is 31°N, the sky equator is that distance south from directly overhead. Geo-stats are relay communication and environ- mental satellites with nearly circular orbits, in the equatorial plane of the Earth, and with an orbital period of one sidereal day—the time it takes the Earth to fully rotate measured relative to the fixed stars rather than the sun. If these three conditions are met, an artificial satellite will be stationary in space about 35,786 km (approximately 22,276 mi) above the Earth, FIG. 1. Our discovery of how to record geo-stat images on the equator of the sky: the three faint fixed “stars” and subject only to minor gravitational effects of the to the left of the red nebula streak are geo-stats. The moon, the sun, and an imperfectly circular Earth. lower left structure is part of the McMath–Pierce At night, stars will trail through a fixed camera time Telescope. exposure of this scene (Figs. 2a,b). Identification of satellites was done using the European Space Agency’s Satellite structures cannot be resolved because such (Flohrer and Fray 2016) “List of satellites in geosyn- details subtend less than 0.01 arc s (Hindsley et al. 2011). chronous orbit.” This list includes geostationary At the end of 2015, according to ESA publications dated objects, presumably because many satellite orbits are 3 June 2016, there were more than 400 objects within close but imperfectly circular. the geostationary band worldwide whose longitude and latitude were fixed and under intermittent control. Such control is maintained by periodic small gas discharges AFFILIATIONS: LIVINGSTON—National Solar Observatory, Boul- from the satellite—this is called “station keeping.” der, Colorado According to an international agreement, before the CORRESPONDING AUTHOR: William Livingston, gas supply is exhausted the satellite is supposed to be [email protected] boosted into a 300–400 km higher supersynchronous, DOI:10.1175/BAMS-D-18-0296.1 or “graveyard,” orbit. This operation requires the equiva- ©2019 American Meteorological Society lent of about 3 months of station keeping, depending on For information regarding reuse of this content and general the satellite. It will then no longer be geostationary, and copyright information, consult the AMS Copyright Policy. lunar and solar gravitation will cause it to move farther away from Earth over subsequent years (air drag is AMERICAN METEOROLOGICAL SOCIETY OCTOBER 2019 | 1877 Unauthenticated | Downloaded 10/09/21 10:52 PM UTC FIG. 3. Detail from a full-scale picture. The purple FIG. 2. (a) (top) 24 Mar 2014 (longitude range is −265° streak is again from the Orion nebula and the upper to −230°E) and (bottom) again on 13 Mar 2016 (same two bright lines are the belt of Orion. Direct TV 5 was longitude range). The latter contains on the left a trail launched from Baikonur in May 2002; it provided mainly image of the geosynchronous Solar Dynamics Obser- Spanish-language TV service. Echostar 10/11 were part vatory. (b) Detail of (a) showing the geosynchronous of the Dish network. Echostar 11 needs “station keep- Solar Dynamics Observatory, which is in a polar orbit ing” service since it moved slightly during the exposure. (13 Mar 2016). Anik F2 provided Internet service in the United States and Canada. negligible). Station keeping is expensive in terms of total satellite lifetime, and it is not always done. If you watch TV or use the Internet, geo-stats may be the relayed source of your signals. These satellites have expected lifetimes of 12–15 years. Their bright- ness in the sky is from reflected sunlight and has a stellar magnitude of 10–14 (recall the naked eye limit is around magnitude 6). Exceptions (called “glints”) oc- cur when chance solar reflections arise—for example, off solar cell arrays. In a glint, a geo-stat may be visible to the naked eye for around one minute. At present, a single 8-h fixed Hasselblad camera exposure on Fujichrome 100 film, with its 80-mm lens set at f/6.3 and its 40° field centered east–west on the cloudless sky equator, reveals about 38 geo-stat objects. Figures 2a and 2b are dual pictures taken 2 years apart on 29 March 2014 (top half) and 3 March 2016 (bottom FIG. 4. Records for 2008 and 2007 are practically identi- half). The fixed dots across the frames are geo-stats cal and show 12–13 satellites. Compare with the early transmitting to both North and South America. The record of 1989 with only 4 satellites, none of which camera position is near the McMath–Pierce Telescope agree with later epochs. 1878 | OCTOBER 2019 Unauthenticated | Downloaded 10/09/21 10:52 PM UTC FIG. 5. (a) Composite view of the east-to-west horizon on Kitt Peak: 47 geo-stats on 9 Feb 1999. (b) Larger and increased contrast of the eastern horizon as compared to (a). Intelsat 709 was actually over the East Africa country of Somalia. Imagine seeing an object over Somalia from Arizona! on 2,120-m-high Kitt Peak. Both exposures were from no “spy satellites,” since they are against the law approximately 1930 to 0330 MST. In this picture, most over the United States—but not so over the non- satellites are unchanged in position over the 2-year U.S. sky. I am told “secret” objects are not allowed span and only slightly changed in intensity. over the United States, but this term has not been An enlargement is seen in Fig. 3. Occasionally, explained to me. two satellite images will overlap because of a lack An example from our data of how the number of camera resolution. In this case, AnikF1R, a later of geo-stats has changed over the years is shown observation of the same area, overlaps AnikG1 (by in Fig. 4. 0.01° latitude) and the latter is not listed. Expanding our 40° field of view to the full span of At about $500 million each, including launch the sky over Kitt Peak is a horizon-to-horizon com- costs, the display in Figs. 2a and 2b thus represents posite assembled by Anna Malanushenka (Figs. 5a,b). $20 billion (U.S. dollars). Most geo-stats that we re- A detail of the east limb for 9 February 1999 is also cord can be identified and are largely commercial. shown in Fig. 5b. The satellites Intelsat 706 and In- Only one geo-stat here is labeled with a question telsat 709 were in fact over the Middle East (recall mark. The lack of an ID could be because it was its elevation is approximately 35,786 km above the launched after the ESA credits closed. There are Earth’s equator). AMERICAN METEOROLOGICAL SOCIETY OCTOBER 2019 | 1879 Unauthenticated | Downloaded 10/09/21 10:52 PM UTC Eventually this activity evolved into the TV and In- ternet, among other uses. Another example of Clarke’s imagination is seen in the movie 2001: A Space Odys- sey, which he coauthored. It is now somewhat ironic that the pictures in the present article were a product of such old-fashioned techniques: long time exposures on film; pointing of the camera in the sky over Kitt Peak by visually sighting due south toward the summit of Babo- quivari, our reference point, on the O’odham reservation in Arizona (Fig. 7), and the equator—over which sit stationary “stars”: geo-stats. FIG. 6. Geo-stats observed from Teide, Canary Islands, with identifications and west longitude. We have taken a few recordings on our travels us- ACKNOWLEDGMENTS. We acknowledge help from ing the same photographic method. One (Fig. 6) at Roger Lynds, National Optical Astronomy Observatory, Teide, in the Canaries, has good identifications, and and Anna Malanushenko and Jack Harvey, both then at the ownership is indicated. These observations proved the National Solar Observatory. helpful for identifications elsewhere near the horizon. Arthur C. Clarke (1945) proposed the practical use of the geostationary orbit for communication. FOR FURTHER READING Clarke, A. C. 1945: Extra-terrestrial relays: Can rocket stations give world-wide radio coverage? Wireless World, 51, 305–308. Flohrer, T., and S. Fray, 2016: Classification of geosynchronous objects. ESA, 178 pp. Hindsley, R. B., and Coauthors, 2011: Navy prototype optical interferometer observations of geosynchronous satellites. Appl. Opt., 50, 2692, https://doi .org/10.1364/AO.50.002692. FIG. 7. The author’s simple geo-stat recording setup on Kitt Peak. 1880 | OCTOBER 2019 Unauthenticated | Downloaded 10/09/21 10:52 PM UTC.

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