Periyar NagarPublic Library hosted the monthly meet of its Science and Nature Club on Sunday, July 31, 2016. Dr. Duraiswamy Navaneetham Ph.D., explained the science and history behind ‘Rockets and Missiles’.

The upcoming talk on Sunday, September 4, 2016 will be at 6 pm at the library. The talk titled ‘Space Exploration’ will cover human missions into space & to the moon and planets.

The Periyar Nagar Public library is located at the intersection of Karthikeyan Salai and Kandasamy Salai at Periyar Nagar. All are welcome to the talk and registration is free. For more details contact 9962565743 or check https://sites.google.com/site/coovamlizards/explore

Rockets and Missiles – excerpts from the talk

What are rockets and missiles?

A rocket is a vertically ascending, usually chemical powered cylindrical or conical object that launches objects or people into the space. A rocket gets thrust from a rocket engine. Rocket engines work on the basis of the famous Newtonian Third Law of Motion - ‘Every action has its equal and opposite reaction’. While rocket engines burn fuel into hot air at the bottom, the expelled hot gas pushes the rocket forward in the opposite direction into the space.

When a rocket is fired and it climbs into the space perpendicular to the surface of the earth, it in fact fights gravity and atmospheric friction and escapes into space with its payload (kept safely at the top). The rocket’s speed needed to fight the gravitational pull of the earth in order to escape the gravity of the earth to enter into the space is about 7 km per second. This is equivalent to more than 40, 000 km/hour and is called Escape Velocity.

What are rockets and missiles used for?

Rockets carry payloads to their target destination. Civilian rockets propel their payload of humans, satellites or interplanetary spacecrafts into space. Whereas military rockets, called missiles, propel explosives. Missiles are used for offensive purposes, such as destroying a target, like an enemy base. The payload on a missile is called warhead, which can be conventional explosives (bombs) or nuclear material to be detonated at the impact site.

How rockets are constructed?

High performance rockets and missiles are usually multi-staged modular system. That means multiple thrust engines are added in modular stages and are tandem arranged and ignited sequentially. For example Indian PSLV rockets consist of 4 stages. The 1st stage module, also the largest and at the bottom of the rocket is fired first, while the other engines in its 2^nd, 3rd and 4^th stages are not fired. When the 1st stage is completely burnt and its entire fuel exhausted, the 1^st stage module along with its engines are programmed to be automatically removed from the rest of the rocket. This removal process is called ‘stage jettisoning’. At this point the 2nd stage is ignited and the process is repeated at each consecutive stage until the payload reaches the intended point in space. Jettisoning process makes the rest of launch vehicle relatively lighter, so it accelerates faster and works more efficiently. In some rockets, smaller ‘strap-on boosters’ are attached to the 1^st stage module and are ignited simultaneously with the 1^st stage to gain additional thrust.

What are the types of rockets?

Rockets are chosen depending on where the payloads are to be deployed in space. The rocket may be sending a satellite into orbit very close to the earth, say few hundred km or a bit away from that, say 35,000 km or it may even be launching a spacecraft to the moon, mars or Pluto. Accordingly the different kinds include:

(1) Low orbit, including polar orbit launch rockets usually used for launching satellites to revolve around the earth in the 200 – 400 km range. Remote sensing satellites, weather satellites and Internal Space Station are placed to revolve in and around this height over the earth. (2) Geostationary orbit launch rockets usually used for placing satellites to revolve around equator at some 35, 000 km from the earth. (3) Interplanetary transfer orbit rockets follow certain other specification as these rockets place space probes in specific orbits, in order to further sling-shot the probe into its specific trajectory to a planet.

What are the missile types?

Missiles are of various types based on their target range.

(1) Short range ballistic missiles - SRBM – usually less than 1000 km, (eg. Akash, Prithvi missiles).

(2) Medium range ballistic missiles – MRBM - usually between 1000 – 3500 km, (eg. Agni I & II missiles).

(3) Intermediate range ballistic missiles – IRBM – between 3500 - 5000 km, (eg. Agni III & IV missiles).

(4) Intercontinental ballistic missiles – ICBM – over 5000 km, (eg. Agni V & VI missiles).

These ballistic missiles could be land-to-land (Prithvi) or specialized anti-tank missile (Nag) or ship-launched (Dhanush), anti-aircraft surface to air (Akash or Trishul), or long distance (Agni).

Apart from these Ballistic missiles there is another class of missiles called Cruise missiles. BrahMos is a low altitude hypersonic cruise missile developed by India & Russia. Unlike ballistic missiles, Brahmos missiles travel at low 15 km height at the speed of 3 Mach. (1 Mach is the speed of sound equivalent to 1225 km/hour). BrahMos is short range and highly accurate in warhead delivery.

What are reusable launch vehicles?

Rockets are usually one-time-use objects. Certain launchers can be resued. American and Russian shuttles are designed to deliver the payload into the space with very powerful rockets. And they return back with human and cargo, and land on earth like aircrafts. Shuttles undergo multiple launch and land cycles. While America and Russia did away with these kinds of spacecrafts due to cumbersome launch, landing, maintenance and human safety issues, India is trying its hand on shuttle technology by recently launching a scaled model of its own reusable spacecraft that looks physically similar to the Americans’.

What kind of rocket fuels are used?

Based on the kind of fuel used, rocket engines are of two types. Fuels for rockets are either solid or liquid. Entire stage can be fueled by a single type of either solid or liquid fuel.

In PSLV (Polar Satellite Launch Vehicles), solid and liquid fuels alternate in each stage:

Stages 1 & 3 use hydroxyl-terminated polybutadiene – solid fuel

Stage 2 uses Dimethyl hydrazine and nitrogen tetroxide – liquid fuel

Stage 4 uses Monomethylhydrazine and mixed oxides of nitrogen – liquid fuel

In GSLV (Geostationary Satellite Launch Vehicles), solid, liquid and cryogenic liquid stages are used:

Stage 1 Strap-on boosters use hydroxyl-terminated polybutadiene – solid fuel

Stage 2 Dimethyl hydrazine and nitrogen tetroxide – liquid fuel

Stage 3 Liquid hydrogen and liquid oxygen – Cryogenic fuel

Cryogenics means fuels at extremely cold conditions, usually below minus 150 degree C.

Who were the stalwarts in modern Indian rocketry?

The pioneers of rocket science in India were Dr. Vikram Sarabhai, Prof. Satish Dhawan and Dr Brahm Prakash. The father of Indian nuclear energy, Dr. Homi Bhabha also played a role in the initial initiatives. The baton was later passed on into the able hands of Drs Kalam, RN Agarwal and the like.

What are the countries with rocket technology?

Very few countries of the world have mastered the technique of successfully launching rockets. Here is a list of countries and a sample of their successful rockets currently in use:

China - Long March 7

European Space Agency - Ariane 5

India - PSLV and GSLV

Japan - F 2 and Epsilon

Russia - Soyuz and Proton

Ukraine – Zenit

USA – Atlas 5, Delta 2, Falcon, Pegasus and Taurus

Where are India’s rocket launch facilities?

Rocket launch is a highly specialized and complicated endeavor. It needs a dedicated launch facility fairly isolated from human population. While civilian rockets are launched by Indian Space Research Organization (ISRO), the defence department’s missiles are launched by the Defense Research and Development Organization (DRDO).

ISRO has two launch pads in a facility in AP just north of Chennai, called Satish Dhawan Space Center at Sriharikota island. This location is also called Sriharikota High Altitude Range (SHAR). On the other hand, the military’s missile test facility is at Abdul Kalam Island (Wheeler Island), off the coast of Chandipur in Odisha. Real-world combat launches are done from mobile trucks or ships or aircrafts.

Vikram Sarabhai Space Center at Thumba near Thiruvanandapuram, has the Thumba Equatorial Rocket Launching Station (TERLS). This was originally used for launching early versions of developmental rockets called Satellite Launch Vehicles (SLV). Nowadays rockets launched from this site are restricted to atmospheric research rockets called “sounding rockets”.

Where are some other rocket launch facilities around the world?

American rockets are usually launched from National Aeronautics and Space Administration’s (NASA) launch facility at Kennedy Space Center & Cape Canaveral Air Force Station in the Florida state, and Vandenberg Air Force Base in California. There is also a privately funded launch facility called Mojave Air and Space Port in California! China uses Jiuquan Satellite Launch Center & Xichang Satellite Launch Center. Russia primarily uses Kazakhstan's Baikonur Cosmodrome as it was done during the Soviet era. European Space Agency (funded and managed by a several European countries) uses the Guiana Space Centre at Kourou in South America.

Conclusion

Rocket technology is a technically difficult science and a financially very expensive proposition. Successful rocketry involves building a rocket, building a satellite or spacecraft, launching it perfectly, ground control facility to track the rocket in flight and tracking the satellite once it gets into orbit. All this needs a highly specialized human resource, so only a handful of nations have mastered this technology. Space technology is used for constructive purposes like communication, espionage, weather monitoring & research and space exploration. Unfortunately it also is employed for destructive military causes like bombing.