INTERPLANETARY ROBOTS

Randii Wesson, Jet Propulsion Laboratory, NASA / California Institute of Technology, on 18 July 2002

JPL (the Jet Propulsion Laboratory), launched its first spacecraft, Explorer 1, on 31 January 1958 from Caltech campus.. It carried one instrument, a Geiger counter that was provided by James Van Allen and discovered the Van Allen radiation belt. Now it has a budget of $1.4 bn. p.a., 5,200 employees and a site covering 177 acres in the mountains.

Mr Wesson was project scientist for the Giotto mission to Halley's comet and is now involved in the future missions planned to explore the solar system and the Origins Programme, which tries to answer the two questions: where do we come from? - how did life begin on Earth; and are we alone in the Universe?

The exploration of the solar system began with surveys of the Earth that photographed and measured a wide variety of the changes in the atmosphere, the oceans and on the land surface. These provide explanations for and enable predictions of the future course of climatic, environmental and man-made occurrences, such as hurricanes, El Nino and forest fires.

This exploration has extended since the 1962 Mariner programme to the other planets and to comets and asteroids. One of the earlier programmes, the Voyager 1 & 2 spacecraft, launched in 1977, gave us the first pictures of Jupiter, Saturn and Uranus and are still sending information during their voyages into the depths of space at 1 million miles per day. Communication with them by the Deep Space Network of three large dishes at Aricebo, Madrid and Canberra requires the reception of a signal of one billionth of one billionth of a watt, since the Voyager transmits only 23 watts - and data is still being obtained.

The future programmes for the next 10 years include: two Mars landers in January 2004; the Cassini mission to Saturn and Titan in 2004 and 05; the Space Interferometry Mission in 2010, and the Terrestrial Planet Finder Mission in 2012. During this period existing spacecraft will continue to provide data: the Deep Space satellite with its very successful ion-drive engine has just completed its programme; Stardust will collect and return a sample of dust from a comet tail; Genesis will measure and sample the solar wind; Deep Impact will crash into the head of a comet and return a sample; the Space Infra-Red Telescope will be launched, and Earth surveys will continue.

Why spend all this money? - to improve our lives; to understand the planets; to learn more about our Universe. We may need to colonise another planet if we wreck this one, but we may be able to prevent ourselves wrecking this one. There may be more advanced civilisations `out there' who could help us.

Discussion

Three interesting points were made:

Although Voyager is travelling at 1M miles per day it will take hundreds of years to reach another star; if we want to visit a planet around another star we should plan a voyage of 25 years duration and that requires a speed up to trillions of miles a day, accelerating for the first half of the voyage, decelerating for the second half.

Control of distant spacecraft from the Earth will not be possible because of the time it takes for radio signals to reach them. The craft will have to have autonomous on-board control covering every imaginable eventuality.

When the Mars landers get there in 2004, the control team will have 90 days before the batteries of the landers expire (no nuclear power generators are allowed on Mars). But the day on Mars is approx 24¼ hours so the controllers on Earth will have to start their shifts half an hour later each day!

Donald Lovell