Prime Edition

OMAIR AHMAD
FULL SPECTRUM

Omair Ahmad is a Delhi-based writer. His last book was Kingdom at the Centre of the World: Journeys into Bhutan (Aleph, 2013).

The trash that circles the world

Crashed space debris.

The Earth has a greedy love and holds us close with its gravity. It takes a great deal of power to escape the planet's grasp. The escape velocity — or the speed necessary to escape the pull of gravity — from Earth is 11.2 km per second, or 40,320 km an hour, more than 32 times the speed of sound. It is not easy to achieve these speeds. In fact no spacecraft really tries. At such high speeds the thick atmosphere close to the ground would heat a spacecraft to such high temperatures that it would be destroyed. Instead most spacecraft are launched into sub-orbital flight between 200 to 2,000 km up, and then accelerated out of the atmosphere.

It takes a lot of power to accelerate spacecraft to such speeds and to such heights, and this is done through a series of stages, between two to five, in which progressive parts of the space vehicle are discarded as the fuel within them is used up. For example India's latest spacecraft, whose first stage was tested in December 2014, was the Geosynchronous Satellite Launch Vehicle Mark III (GSLV Mk III). It lifts off with two S200 booster rockets. These booster rockets burn solid fuel: a mix of ammonium perchlorate, aluminium and hydroxyl-terminated polybutadiene. The rockets take merely two minutes to burn up more than 400 tons of fuel between them. Then the two Vikas engines kick in, burning a mix of unsymmetrical dimethylhydrazine propellant and dinitrogen tetroxide. The last stage is a CE20 engine which burns liquid hydrogen and liquid oxygen.

Most of the discarded stages of this fall back to the Earth — mainly into the ocean, from which many of them are recovered, and some are reused — but some of these are only discarded when the spacecraft have left the pull of earth's gravity. These join the half a million or so pieces of debris already floating around. These are largely natural debris, little pieces of rock and particles from destroyed meteors little more than a centimetre across. Nevertheless, the tug of gravity pulls them around the Earth at speeds of about 28,000 km an hour. At such speeds even such tiny particles can do great damage. There are about 20,000 or so pieces of debris, especially those of manmade origin that are about ten centimetres in diameter. These pose serious risks, and a number of agencies have dedicated programmes focussed on monitoring these alone, and calculating how to avoid them in case they damage satellites or spacecraft. Since 1993 the lead coordinating agency between countries has been the Inter-Agency Space Debris Coordination Committee which conducts annual meetings to compare the latest research on "measurements, modelling, protection and mitigation".

As more and more satellites are launched into orbit for a wide variety of work from telecommunications, to navigation, to weather monitoring, humans continue to add to this debris around the earth. There is no real way to clean it up either. We cannot merely blow it up. In fact when the Chinese government tested its anti-satellite weapon, destroying an old satellite in space in 2007, it added more than 3,000 pieces of debris to the ones already floating around. One option was the use of reusable spacecraft, of which the Space Shuttle was the most famous. Unfortunately the Space Shuttle programme was one of the most expensive space programmes, costing an estimated $1 billion per launch. Single use, multi stage rockets have remained much cheaper, and remain the primary means of propulsion for spacecraft.

Nevertheless the costs of debris have never really been calculated as part of the space flights. If every launch puts up more metal spinning around at colossal speeds, possibly doing damage to any and all other satellites already in existence, then maybe we have not really been calculating the costs right. Pollution, whether biological or chemical, or in the form of greenhouse gases, has been one of the great problems in calculating costs of projects. It does not factor in, because it has a long-term, multi-generation effect. And in essence the debris we are adding around us with every space flight is a form of pollution whose costs we have never really counted.

Hope rests in the new generation of reusable spacecraft. Many of them are those involved in the Space X private commercial space flight programme. Some have names like Grasshopper, Dragon V2 or Falcon 9, but their ultimate aim is similar: to make space flight commercially viable. At some point the costs that they have to start calculating are the costs of debris, and in this they are already ahead, since most of the Space X crafts are reusable. The European Space Agency, though, is probably the leader in this, with its planned Programme for a Reusable In-Orbit Demonstrator for Europe (PRIDE) system. This February it tested its wingless plane, the Intermediate eXperimental Vehicle (IXV), which flew almost the whole way around the planet, reaching a height of 412 kilometres. Let us hope for the continued success of such programmes, so that we do not become a planet ringed with trash.

 
Newer | Older

Creative-for-SG


iTv Network : newsX India News Media Academy aaj Samaaj  
  Powered by : Star Infranet