From time immemorial, humans have been fascinated with space. The urge to know whether there is life in the other planets of our Solar system, and the Universe at large, has kept us probing into space deeper and deeper. The year 1903 signalled the flight of the first man-made, heavier than air vehicle. And by the 1950s, we had artificial satellites rotating the Earth. Soon we started to think of sending space probes to other heavenly bodies. The first try had to be our Moon, it being the closest to us. Initially there were unmanned flights and once they succeeded, it was time for man to set foot on the Moon. In 1969, we just did that. Manned explorations of the Moon confirmed the already arrived at conclusions - that it has got no atmosphere and so no life is possible.

As our interests on the Moon faded *, we shifted our sights to the neighboring planets. Venus was found to be extremely hot with a very high atmospheric pressure of 90 bar. The other neighbouring planet had roughly the same Earth day of around 24.6 hours. False observations of the astromer Percival Lowell concluding that there were canals+ all through the planet suggested that there may be intelligent life on it. And this evoked a wide interest. This planet where our focus has shifted now is the red giant Mars. Unfortunately, the planet has been found to contain carbondioxide as its chief atmospheric constituent and its atmosphere is very thin too. Our present interests have narrowed down to knowing whether there was life on Mars in the past.

The recent landing of the American Mars Rover Spirit has caused quite a flutter. Spirit is the second successful probe to land on Mars in the last 27 years since the Viking landers 1 & 2 landed successfully in July & August of 1976 respectively. By the time this article is published, the second Rover Oppurtunity too would have landed (scheduled landing date, January 26). Some 20 probes of different countries have failed inbetween. The last spaceship to land before Spirit was the British Beagle 2 which was supposed to have started sending photoes from Christmas day 2003. (Its silent till now. Its team will again try communicating with it from January 22.)

To journey to Mars is quite a thing. Mars is at a minimum distance of 55 million km from Earth. Thats roughly 140 times the distance to the Moon. A Mars Rover had to travel a minimum distance of 450 million kilometres in about 7 months for reaching Mars.

School physics had taught us of how a rocket is propelled. It simply follows Newton's third law. The rocket that carries the satellite or spacecraft is given a tremendous boost so that it escapes the gravitational force of the Earth. This phase relies mainly on liquid or solid chemical fuels. But what happens once the satellite is put into orbit? Think of a spacecraft like Viking or Voyager. Its not possible and unneeded anyway to have a rocket propulsion system to take a craft all the way to Mars and beyond. Once the gravitational field of the Earth is overcome, then the spaceship has to move in near vacuum. All that a spaceship is made to do is a free fall into the planet of choice. Occasionally, say once in a few months, it is powered by its thrusters for course correction. This is mostly achieved by chemical fuels (for example, compressed nitrogen is sent through a nozzle providing the required thrust). Solar power panels, fuel cells and batteries help in the functioning of the other systems apart from propulsion.

Another interesting way a spaceship gets assisted in its journey to distant worlds is by a phenomenon called gravity assist (also known as gravitational assist, fly by or slingshot effect). A planet's gravitational field can be used to help in varying the speed of a spaceship to a great extent. This can be thought of like throwing a ping-pong ball (the spaceship) at the blades of a rotating fan (the planet). While the fan blades lose some speed, the ball's thrown away at a much higher speed with a change in direction. Cassini, the spaceship to Saturn has done flybys of Earth, Venus & Jupiter. It reaches Saturn in July of this year. And Mariner 10 did a slowing down fly by of Venus (by coming in the opposite direction of the Venus' orbit) on its way to Mercury.

Looking at the future of space aviation, other ways of propelling a spaceship can be possible too. Nuclear (fusion) powered spaceships can easily be thought of. But the Outer Space Treaty of 1967 forbids nuclear reactions in outer space. Controlled nuclear reactions if allowed can make the spaceships still faster. Ion propulsion is yet another thing. Its key principle is that a voltage difference between two conductors can accelerate ions which then can be used to produce thrust. One more highly discussed option is that of an engine using antimatter. When matter and antimatter collide, a lot of energy is released. The first antimatter to be produced was positron (positive electron, the antimatter of electron) and scientists are now envisaging a anti-proton or anti-neutron engine. If such an engine can be made, it will be possible to travel at amazing speeds and the percentage of fuel as part of the payload can very much be decreased.

Taking all the above into perspective, its clear that we aren't in the real Space Age yet. We may see man landing in Mars in the next few decades. And this leads to the possibility of traveling beyond Mars to the Jovian system. Thats the least one can expect to happen in the near future. Journeying to other stars seems a very distant possibility. Till then, we will be sending unmanned probes into interstellar space and continue scanning the skies with our powerful radio telescopes, expecting some technically advanced civilization in another world to contact us.


* The statement is not completely true. Many nations who are in their space program infancy (including India) will try to send missions to the Moon first. Also, President Bush has recently spoken about creating a Lunar Space Station.

+ The Italian astromer Schiaparelli first observed canali across the planet Mars. canali in Italian means channels but got wrongly translated into English as canals, meaning engineering structures and hence intelligent life. This might have prompted Lowell to come to the wrong conclusions. Lowell's contribution to astronomy was discovery of Pluto. The first 2 letters of the planet are got from his name.