Friday, August 13, 2010
The need for Planetary Defense
graphic by Fredrik Fahlstad
Our sophisticated and advanced civilization is vulnerable to natural threats that would have had little or no impact in the past. A volcano goes off in Iceland and international travel is in chaos. Had that volcano gone of a century ago it would have only been a concern to the people of Iceland. The Space environment presents us with new threats that can damage or even destroy civilization.
One is the threat of solar storms. Our Sun is a seething ball of gas that can send huge eruptions of plasma towards Earth. The resulting solar wind shock wave can completely disturbs Earth's magnetic field. Such storms effect our communications and electricity generation. In 1989 a solar storm caused black outs throughout Quebec. But that was nothing compared to the solar storm of 1859. That was so severe that telegraph operators received electric shocks and fires were ignited. If the Earth was hit by a similar storm today without warning it could cause a world wide catastrophe. Power station transformers would be destroyed, communications systems would be useless. It would be an major threat to our civilisation.
Impact events are another threat. The threat of the Earth impacting with an asteroid, comet or meteorite is real and has happened in the past. There are craters like Barringer and Henbury to prove it. Although the larger impacts are more rare the smaller ones are more common. The Tunguska event in 1908 had a explosive force between 5-30 megaton. That impact occurred over Sibera. It couldn't do much damage to civilization in 1908, but a 5 megaton blast over Russia today could have serious international consequences.
As well as natural threats there is the man made danger of space debris. Our spent rockets, dead satellites, etc are polluting Earths orbit putting multi million satellites and the essential services they provide at risk. Although efforts are being made to mitigate the problem space junk is still accumulating and colliding satellites only increase the amount of debris. In fact there’s a possibility a chain reaction of collision, the “Kessler Syndrome” could ground all manned flight.
Good sense tells us we need Planetary Defense. Thats usually defined as “ that activity concerned with protecting the Earth and its inhabitants from destruction due to impact by a large piece of space debris such as an asteroid or a comet” I have a broader definition “protecting Earth from man made and natural threats from Space”.
Whats needed is to put the Solar System under perpetual, high level surveillance so that the earliest warning can be given. We can start with Earth orbit. Tracking debris smaller then 10 cm is difficult and most debris is unobserved. Earth and Space based systems need to be put into place to provide adequate situational awareness. There has been much discussion as to how to clean up space but action needs to be taken to develop proper strategies and to implement them.
To detect interplanetary dangers large observatories can be placed in two of the best places for astronomy , the Sun-Earth L1 and L2 Lagrange points. L1 permanently faces the Sun and would be an excellent spot for a solar observatory. L2 is in the opposite direction and would be the spot to place an observatory looking at the rest of the solar system. There are already astronomical satellites at these positions but if high level permanent surveillance is required we need better. I'm proposing Hubble class telescopes or better. The great thing about Hubble was that astronauts could service the telescope allowing it to be repaired and upgraded. Thats why its been in use for over 20 years.
Of course you need to get there. The Sun-Earth L1 L2 points are 1.5 million kilometers from Earth so a human beyond Earth orbit capability should be a high priority. That capability, interplanetary cruise, will also be need to protect us from asteroids. Its not much use simply to know an asteroid is going to hit you need to be able to divert it . Despite much study no one is sure how to do so but one thing is known, changing the orbit of an asteroid enough to miss the Earth requires far less energy when the asteroid is a long way away then when its close. So action needs to be taken when the asteroid is several million kilometers away. Now, if a solar sail has to be attached or an nuclear device positioned on a rotating asteroid you going to need someone there to make on the spot decisions not rely on robots who will suffer a radio time lag.
In my view planetary defense is one of the best reasons for having a human space program and frankly more urgently needed then Moon bases or Mars missions. An interplanetary cruise system does not require landers, planetary bases etc so would be much cheaper but could still be expanded to interplanetary missions if there was the need and funds.
