Satellite For The Past Present And Future

Present theories argue that, around 200 million years ago, a giant 'super-continent' known as 'Pangaea' (Greek for 'all lands') existed in the middle of a vast ocean which covered 70% or more of our planet's surface. Within the next 20 or 30 million years, this gigantic landmass gradually began to break apart into several 'smaller' continents and by 150 million years ago cracks had begun to emerge in the most northerly of these new landmasses. Molten rock, coming from deep within the mantle, poured up through the cracks and pushed the plates further apart.

Carrying the fragments of the super-continent with them, these plates gradually began to drift apart, leaving newly created sea-floor between them. Moving no faster than a few centimetres per year, the continent we now know as North and South America is today 4,800 km away from the one we call Eurasia. Rifting is still going on. For example, the East African Rift, where the continent is in the process of splitting apart, will ultimately form an island from what is presently its 'east coast'.

Modern maps offer tantalising hints of Pangaea's existence, suggesting that parts of West Africa might slot neatly, jigsaw-like, into the coastline of North America and Brazil. However, since coastlines are affected by sea-level and hence are subject to change over extended periods of time, the lines of the continental 'shelves' have become a more reliable marker of where the landmasses were pulled apart.

In order to track these slow tectonic movements, LAGEOS-2's entire aluminium skin was literally covered with the 426 retroreflectors, which gave it the appearance of a gigantic golf ball. Each one had a flat face and a prism-shaped 'back'; the bulk of them were made from suprasil - a fused silica glass - and four from germanium. Its aluminium-and-brass design evolved from a series of trade-offs: on the one hand, it had to be heavy enough to minimise the effects of non-gravitational forces, yet light enough to be placed into a high, stable orbit around the Earth.

Preparations to launch the satellite had been going on for some years, but moved into high gear on 29 September 1992 when LAGEOS-2 was installed into Columbia's payload bay at Pad 39B. Attached to Italian Research Interim Stage (IRIS) and LAGEOS Apogee Stage (LAS) boosters, it proved an unusual sight as it was transferred from its transport canister to the Shuttle. The whole ensemble was housed in a Pacman-type cradle like that used on STS-5 and STS-61C. Almost seven years after Challenger, there was a sense that STS-52 harked back to the Shuttle's early days of launching commercial satellites.

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