Gyaan shared by readers (Vivek Kapila)

Space Debris and related terms

Ever since the space race began, misfiring rocketry and misconceived missions have strewn Low Earth Orbit with about three lakh pieces of junk, aggregating to thousands of tonnes of metal and ceramic.

• They range in size from burnt-out rocket engines to tiny nuts and bolts. But since they are whizzing about at the speed of rifle bullets, size doesn’t matter. A half-inch screw could puncture the hull of a spacecraft, or even the space faring dreams of humanity.
• Space junk has been recognised as a hazard.
• the Australian National University had gathered $60 million in state grants and private investment for a Cooperative Research Centre (CRC), an observatory which will target space junk. And then it will build lasers to zap them like the Death Star. 
• the CRC has the relatively modest ambition of dislodging junk from orbit and into atmospheric re-entry. If they time re-entry over the night side of the planet, they can guarantee free stratospheric fireworks displays to light up the lives of generations to come.

Space debris, also known as orbital debris, space junk, and space waste, is the collection of defunct objects in orbit around Earth. This includes everything from spent rocket stages, old satellites, fragments from disintegration, erosion, and collisions. Since orbits overlap with new spacecraft, debris may collide with operational spacecraft.

• Impacts of these particles cause erosive damage
• Damage can be reduced with "Whipple shield", which, for example, protects some parts of the International Space Station. However, not all parts of a spacecraft may be protected in this manner, e.g. solar panels and optical devices (such as telescopes, or star trackers), and these components are subject to constant wear by debris and micrometeoroids. 

Whipple Shield

  

The Whipple Shield is the first spacecraft shield ever implemented. It was introduced by Fred Whipple back in the 1940s, and is still in use today. Simply, it consists of placing a sacrificial bumper, usually aluminum, in front of the spacecraft, thus allowing it to absorb the initial impact. The Whipple bumper shocks the projectile and creates a debris cloud containing smaller, less lethal, bumper and projectile fragments. The full force of the debris cloud is diluted over a larger area on the spacecraft rearwall.

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Kessler syndrome: The Kessler syndrome (also called the Kessler effect, collisional cascading or ablation cascade), proposed by the NASA scientist Donald J. Kessler in 1978, is a scenario in which the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade—each collision generating space debris which increases the likelihood of further collisions.
One implication is that the distribution of debris in orbit could render space exploration, and even the use of satellites, unfeasible for many generations.
A runaway Kessler syndrome would render the useful polar-orbiting bands difficult to use, and greatly increase the cost of space launches and missions. Measurement, growth mitigation and active removal of space debris are activities within the space industry today

Road to urban future

• Paris example: Smog wrapped the city and air pollution increased beyond safe limits. Pollutants, particularly particulate matter measuring less than 10 micrometre in diameter reached unsafe levels of 180 micrograms per cubic metre, against the WHO’s permissible limit of 50 micrograms per cubic metre (24-hour mean).

• Though bad weather contributed to this high concentration, the principal cause, as is often the case, was increased fuel emission.
• The city authorities had to take drastic steps to reduce pollution since prolonged inhaling of particulate matter would cause respiratory diseases, lung cancer and cardiovascular ailments.
• They imposed restrictions on the use of cars, permitting vehicles with odd and even number plates to ply only on alternate dates and encouraging shared use of cars. People were allowed to use buses, Metro rail and other public transport, besides shared bicycles, free of charge during weekends.
• The reasoning was that restrictions and incentives would encourage commuters to shift to public transport, thus reducing pollution.
• Initial reports indicated that these measures worked, and congestion had come down by 60 per cent. Free use of public transport cost the city about $5.5 million a day, but considering the public-health interest it was a necessary investment.

• Lesson for Indian cities:

• The Central Pollution Control Board has listed more than 70 cities that have violated ambient air quality standards. Places such as Delhi and Ludhiana have unacceptable levels of PM{-1}{-0} — 198 and 259 micrograms per cubic metre respectively.
• Mitigation efforts thus far have been limited to improving the fuel efficiency of vehicles. Enhancing emission norms is necessary, but equally critical is the need to increase the use of public transport.
• The Environment Pollution (Prevention and Control) Authority for the Delhi region, in a recent report, stated that all gains made by converting buses and three-wheelers to Compressed Natural Gas have been lost to a rapid increase in the number of private vehicles. The level of particulate matter has increased substantially over the years.
• Though various urban policies have stated that public transport is a priority, on the ground, investments have not matched intentions. The modal share of public transport has steadily declined in the large cities. It is only in recent years that State governments are trying to increase transport options by building metro rail networks.
• Integrating city functions with transport plans and encouraging non-motorised transport such as cycling are also critical. The future of Indian cities is inextricably tied to the improvement of public transport.

WW-I Indian heroes to be honoured by U.K.

Indian soldiers who took part in World War I will be honoured by the United Kingdom through a series of events commemorating the 100th anniversary of the war this year
-One million Indian soldiers fought the war and over 70,000 Indian servicemen died.
-The Indian Army during World War I contributed a number of divisions and independent brigades to the European, Mediterranean and the Middle East theatres of war in World War I. One million Indian troops would serve overseas, of whom 62,000 died and another 67,000 were wounded. In total 74,187 Indian soldiers died during the war.
-In World War I the Indian Army fought against the German Empire in German East Africa and on the Western Front.

British India (today known as India, Pakistan, Bangladesh) was controlled by Britain and thus India officially declared war on Nazi Germany in September 1939. The British Raj, as a possession of Great Britain, formed part of the Allied Nations and sent over two million volunteer soldiers to fight under British command against the Axis powers. 

- several Indian Princely States provided large donations to support the Allied campaign during the War
-India also provided the base for American operations in support of China in the China Burma India Theater.
-The Muslim League supported the British war effort while the largest and most influential political party existing in India at the time, the Indian National Congress, demanded independence before it would help Britain. London refused, and when Congress announced a "Quit India" campaign in August 1942, its leaders were imprisoned by the British for the duration.
- Meanwhile, Japan set up an army of Indian POWs known as the Indian National Army with the help of Indian revolutionaries who were seeking independence from the British.
- The financial, industrial and military assistance of India formed a crucial component of the British campaign against Nazi Germany and Imperial Japan. India's strategic location at the tip of the Indian Ocean, its massive production of armaments, and its huge armed forces played a decisive role in halting the progress of Imperial Japan in the South-East Asian theatre
- The Indian Army during World War II was one of the largest Allied forces contingents which took part in the North and East African Campaign, Western Desert Campaign and the Italian Campaign. At the height of the World War, more than 2.5 million Indian troops were fighting Axis forces around the globe
-After the end of the World War, India emerged as the world's fourth largest industrial power and its increased political, economic and military influence paved the way for its independence from the United Kingdom in 1947