Flamsteed Astronomy Society

Fred Watson — September 21, 2008

“Navigation & the Inter-planetary Superhighway”

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Space travel’s equivalent of the jet-stream is “ gravity assist”.  A space probe can use a fly-by of a planet to speed up (or slow down) by interacting with the planet’s gravitational field.  A good example is the Cassini-Huygens mission to Saturn.  Cassini used fly-bys of Earth, Venus, and Jupiter to help it get to Saturn using much less fuel.  Fred took us through a review of the spectacular Cassini mission which has produced a flood of information about Saturn and its moons including some of the most breath-taking images seen yet.  (See the reports from our two Flamsteed visits by Prof Carl Murray).

Fred Watson  (pic: Mike Dryland)

Gravity assist — Cassini mission profile with fly-bys of Earth, Venus, & Saturn

And what of the ‘Inter-planetary Superhighway’?  Fred introduced us to Joseph Louis Lagrange, the Italian mathematician whose 1772 analysis of orbital dynamics (the 3-body problem) identified the ‘ Lagrangian Points’ — relative positions around the orbits of two bodies that are stable sites for a satellite to sit without falling towards either.  The Lagrangian Points for the Earth & Sun are used for artificial satellites (eg WMAP at L2), and points for Jupiter and the Sun accumulate asteroids — the so-called ‘ Trojans’.   Extending Lagrange’s ideas to the whole solar system, NASA has calculated a network of routes between the planets to exploit the Lagrangian Points and produce an ‘ Inter-planetary Superhighway’ or transport network.  These routes would require the least fuel to travel between the planets, but would be very slow indeed — not the choice for manned flight, but maybe ideal for robotic spacecraft.

The ‘Inter-planetary Superhighway’ — lowest cost routes exploiting the Solar System’s Lagrangian Points

Lagrangian Points

Fred wrapped up the evening with a book-signing before he and his tour group were packed-off back to their West London hotel.  Next morning they were due back at the ROG for a run-around tour, then off to Cambridge, Bath, Stonehenge, the Hague ...   “If this is Monday 10am it must be Greenwich!”

Someone has to do it.