To study and encourage popular interest in all branches of Science.

Newsletter Christmas 2005

Dear Member,

On behalf of the Council, I send you Christmas Greetings.

HSS Lecture Meetings in the Crypt Room at St John’s Church, 8.15 pm.
December 15th Professor Bill McGuire (University College London): Surviving Armageddon, Solutions for a Threatened Planet.
January 19th Ray Batchelor (Buckinghamshire Chilterns College): Why Anything can mean Anything.
February 23rd Dr Philip Jones (MatraBaeDynamics): Satellite Navigation.
March 23rd Professor Helen Haste (University of Bath): The Moral Messages of Science.
April 27th Professor Basil Hiley (Birkbeck College): Einstein and Quantum Theory.

Gravitational Tractor for Towing Asteroids.

As you can see above, our December lecture concerns various threats to our planet. One such is a collision with an asteroid or a comet. Such an event some 65 million years ago is thought to have killed off the then dominant species on the planet, dinosaurs. I suspect that they had little foreknowledge of what was coming, but our scientific knowledge and astronomical technique allows us to know several years before impact and offers the possibility that we could destroy or deflect the asteroid. An interesting article in Nature [1] by Edward T Lu and Stanley G Love of NASA under the above title proposes a method of deflection.

There have been several proposals, and films, about docking a space craft to an asteroid and using a rocket engine to push it into a different orbit. The authors point out several problems: the surface is likely to be rough and unconsolidated, asteroids rotate and propulsion would have to be intermittent or time taken to stop the spin. Their suggested alternative is for the spacecraft to hover above the surface using the force of gravity as a tow rather than a physical connection. The rocket thrusters would be canted miss the asteroid. The scheme is insensitive to the nature of the surface and the internal state of the body and its rotation. The engines would need to be controlled, since the hover point is unstable.

The authors calculate that a spacecraft of 20 tonne mass could tow a 200m diameter asteroid provided it can maintain a thrust of 1 newton. The change in velocity is small but they calculate that it would be able to deflect adequately given a lead time of 20 years. They say that the 20 tonne nuclear-electric vehicles proposed in NASA’s Prometheus programme would use 4 tonnes of fuel to achieve the 15 km/s rendezvous and 400 kg for the deflection.

Deflecting a larger asteroid would require a heavier spacecraft and more hover time or lead time. However in the special case of a close approach followed by a later return, the deflection needed to prevent impact can be many orders of magnitude less if applied before the first approach [2].

For example asteroid 99942 Apophis, a 320 m asteroid will swing by the Earth in 2029 at a distance of about 30,000 km; it has a small probability of returning to strike the Earth in 2035, but a very small deflection made a few years before 2029 could ensure that it does not. The authors say that a 1 tonne gravitational tractor with a conventional chemical rocket providing only 0.1 newtons of thrust for 1 month would suffice.

And now for the bad news ----


Another threat facing us rather earlier is that of a human flu pandemic originating from bird flu. There has been much publicity already in the media about the virulence of the H5N1 virus among birds but so far only about 60 people have died and it is thought that they caught it directly from birds. Unfortunately the influenza virus is capable of enormous variation in the surface proteins which enable it to attack human cells and our immune system is hard put to keep up. But is it that important as flu is only a mild and brief illness? This may be true of the current strains of human flu, to which we have developed some immunity. Moreover we are able to manufacture vaccines to encourage immunity amongst the more vulnerable people. But there is a lesson to be learnt from previous pandemics.

The “Spanish” flu of 1918 was truly deadly. It killed some 50 million humans, more than the number killed in the 1914/18 war. Scientists have now completed the last three segments of its genome [3]. They have done so in order to understand its origin and its unusual virulence. All eight segments of its genome differ in significant ways from other human flu sequences, suggesting that it did not come from a strain that had previously infected people. Taubenberger says, “It is the most bird-like of all mammalian flu viruses”.

In Science [4] in the same week a laboratory in Atlanta has used the sequence to replicate the virus and test it on mice. After four days it had generated 39,000 more virus particles in the animal’s lungs than a contemporary ‘Texas’ strain; all mice died within 6 days of infection, none from the Texas strain. The team has tried replacing some of its genes but has been unable so far to determine what combination is critical to virulence. Eventually our improved understanding should be of use in vaccine and drug design.

Other scientists have, however raised concerns about “the danger of reconstructing a virus that represents perhaps the most effective bioweapons agent now known.” [5] The scientists are still arguing whether the ‘biosafety level-3’ is sufficient as there have been three escapes of the SARS virus from such labs. Maybe the consequences would not be as serious as there is some human immunity to the 1918 virus because subsequent strains are in part derived from it [6].

The whole genome sequence has now been put on the GenBank database – a condition of the paper’s publication. There are currently no government controls on what sequences can be used, though some synthesis companies screen their orders for pathogenic sequences. Taubenberger admits that there can be no absolute guarantee of safety, “But what we are trying to understand is what happened in nature and how to prevent another pandemic. In this case, nature is the bioterrorist”.

Back to today’s avian flu. It has already mutated from chickens in 1997 to water birds and in October 2004 23 tigers died in a cat to cat infection. We must assume that it will mutate to a human virus. If so, much will depend on its human infectivity and mortality. Too great and rapid a mortality would kill off an epidemic before it could spread, so the real fear is of a high infectivity and moderate mortality that with modern air travel would become a global pandemic. Antiviral drugs like Tamiflu may help to palliate, but a vaccine will be critical.

We must bring our modern scientific knowledge and techniques to prevent a pandemic, but pestilence is one of the four horsemen of the apocalypse.

Peter R Wallis.


[1] Nature, 10th November 2005, p 177. Back
[2] Carusi et al., Icarus 159, p 417, 2002. Back
[3] J K Taubenberger et al, “Characterisation of the 1918 influenza virus polymerase genes”, Nature 6 Oct 2005, p 889 Back
[4] T M Tumpey et al, 310, p 77. Back
[5] Richard Ebright, Rutgers University of Piscatawy. Back
[6] Tumpey. Back


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