Weather Permitting - GPS Declassified: From Smart Bombs to Smartphones - page 26

leton made an epic voyage to South Georgia to summon help in the most sea-
worthy lifeboat, the James Caird . His 850-mile route was through an area called
the Furious Fifties, the zone between fifty and sixty degrees south latitude,
where little land area interrupts the water circulating around the South Pole.
Missing South Georgia meant certain death since no other inhabited islands
were within reach. But taking accurate sightings of the sun is difficult on the
rolling deck of a small craft in wind-tossed seas. When they approached South
Georgia, his navigator, Frank Worlsey, told Shackleton that he “could not be
sure of our position within ten miles.” 2 Given their exhaustion, the lifeboat's
poor condition, and the danger of missing the island completely or being swept
away, they headed for the nearest point of land on the uninhabited west coast
of South Georgia. Landing successfully, they faced two difficult alternatives.
The first was to sail around the island. Shackleton rejected that due to the poor
condition of the James Caird. The second was climbing through the uncharted
mountains and wastelands of South Georgia to the whaling station of Strom-
ness. That had never been done, but Shackleton and the strongest two of his
companions accomplished this feat, which even modern climbers with the
best gear available find difficult.
Navigational Challenges
Prior to the balloon's development in the latter part of the eighteenth century,
navigational challenges were mainly two-dimensional and could be separated
into land versus sea travel. These two modes present similar but not identical
navigational challenges. The navigator wants to safely travel from the current
position, point A, to the destination, point B. Often, there are hazards to be
avoided or interim points to be reached for resupply. Maps or sea charts pro-
vide useful information, but two-dimensional maps distort the three-
dimensional earth. And the earth is not a perfect sphere, which adds to the
mapmaking and navigational challenge. An eighteenth-century French expe-
dition to South America showed that Sir Isaac Newton was correct in his hypoth-
esis that the earth is fatter at the equator than it is at the poles. 3 Gravitational
variations exist in both the earth and the moon. One of the challenges in Apollo
11's landing was a lack of understanding of the moon's gravitational variations.
This was intensively studied between Apollo 11 and 12, allowing Apollo 12 to
make a pinpoint landing near the unmanned exploratory craft Surveyor 3.
Land travel has an advantage over sea travel in that there are more physical
landmarks to help ascertain your position. Many landmarks are man-made,