The first space rocket was a modified ballistic missile. Launched by the former Soviet Union, Sputnik 1 (flying on board a modified R-7 ballistic missile) was the first man-made entity that flew into earth's orbit. Since then, mankind has never looked back attaining one milestone after another.

One objective that has been long cherished by scientific community across the world is the exploration of deep space. So far, man has been able to penetrate only till the edges of our solar system, when un-manned robotic probes such as Voyager 1 and 2, Galileo, Cassini, and others have successfully reached and explored planets like Saturn, Uranus, Neptune, and Pluto. What lies beyond is still a mystery to most of us.

Well, it's not really a mystery. A probe named Pioneer Xi and both Voyager 1 and 2 have gone out of our solar system but have not yet sent any worthwhile scientific information. Further, visible light and other different types of radiations emanating from distant sources have been evaluated in order to understand what constitutes outer-space, or the entire Universe. However, these observation posts have been more localized (either rooted on earth or hanging in the earth's orbit). What is still missing is man's own journey to these planets and beyond them.

Well, that has to wait, and probably wait for a long time. There are many technical hurdles that have to be overcome before we even step outside the dangerous Van Ellen belt surrounding the Earth. Let us have a look at them and ascertain for ourselves how deep space exploration can be done.

* Deep space exploration requires extensive life support systems inside a single space-going vessel. Men and women would not be able to survive if there is not supply of air, food and water.

* Considering this need, there has to be an immense amount of cargo payload to be incorporated into the ship, which would be apart from the scientific modules, engines, power supply systems and similar other stuff. The sum total (in terms of weight) of all this would be phenomenal (at least a couple of million tones). Lifting off this weight at the escape velocity of 11.0 kmps would require burning at least 5 times the fuel by weight. This is not possible at all. We would need to find another alternative.

* The best way out would be to make this inter-galactic ship in the orbit of the earth, just like the way the International Space Station is being made right now. Once it is assembled in outer-space, it can be fired to reach escape velocity without spending too much on-board fuel.

* We also need to develop better propulsion systems, engines whose fuel supply is easy to replenish. The current solid rocket propellants are too dangerous and bulky. Liquid Oxygen and Hydrogen-fuelled engines are perfect but they need to be made more safe and powerful to propel man's intergalactic or inter-solar endeavors.

* A way would have to found out to limit the factor of ageing that would eventually come into play while traversing the enormous distances in deep space. Even if, theoretically speaking, we are able to attain the speed of light we would still require at least 4 and-a-half years to reach the nearest star. In such a case, a way would have to be found out to preserve the human body from the damages caused by ageing.

If the space engineers are biologists are able to find out a way around these problems, then probably we can look forward to a space exploration in within hundred years from now. If the manned-Mars expeditions of NASA become a reality within the next two decades, then perhaps the same technology can be used to explore celestial systems that lie beyond our own solar system.