Mainly lack of funding. Research is required in multiple areas, but mainly propulsion systems, radiation shielding and life support systems. These areas can help to bring the cost of such a missions down. Basically with current technology a mission to mars would be feasible but tremendously expensive.

Reason? NASA is stupid... plain and simple... how many mars landers crashed so far? Realistically, I think we're going to see more private work done in space exploration in the future... just look at the 'X-10 challenge' (might have the wrong spelling or phase). The developers got a few million I think... and it led to commercialized trips to space.

NASA is not stupid, NASA does not make decisions which missions it has to perform, this is purely a political decision. The x-prize also did not lead to any commercial trips to space but rather commercial sub-orbital flight, basically a glorified roller coaster ride. The private sector might be able to overtake some tasks of NASA in the upcoming years but a mission to mars will not be possible using only private contract in the foreseeable future...

Thanks Mr.Egbert Jan Veen,i understood why for certain things we are not getting open answers.Reality is hard to believe and to convince.to common mass. Even it is highly impossible,people tends and wants to believe falsehood.like extra terrestical beings,which are near impossible out of reach.

Well the possibility of extraterrestrial life, I would say is quite big given the size and number of stars in the universe, the possibility of intelligent life decreases in chance but is still highly feasible. Given the physical restrictions of our universe however getting into contact with a civilization which is 1. advanced enough to contact us 2. close enough to send a signal of measurable strength and 3. did not annihilate itself in the process of evolution is extremely unlikely to say the least. Within the currently know physical boundaries there is no foreseeable way for us or any other form of intelligent life to come into contact with each other.

@Egbert - opinions vary. So your saying the politicians are to blame for the multiple failed missions concerning mars? And concerning the 'x-prize' it was a considerable accomplishment concerning the private sector and space, not to mention, the results happend much faster in comparison to NASA's capabilites over the last 40~50 years in my mind.

@EGBERT ,The radiation endurance , already they are staying in spacelab for six months.They seems to be having provisons for slx months or more.or it is just appearance,it is the intermediate shuttle flights.Does it means that, cosmic radiations are at higher levels ,when we move away from sun.

@Ravi, the ISS and other space stations are still well within the Earth's Magnetic Field and therefore are protected from solar radiation. The radiation doses would depend on the time of exposure and the intensity, these would both be much higher then for example the case would be with a lunar mission. It is possible to add a passive radiation shielding but this requires many tons of additional mass for a potential spacecraft. A solution here would be active shielding but research in these kind of shielding methods is still in its infancy. In general radiation is stronger when closer to the sun, but the radiation within an earth orbit does not differ that much from a martian orbit. Additionally Mars lacks an magnetic field to shield potential astronauts (or cosmonauts and taikonauts :-)) against radiation.

@Timothy, Politicians are the main cause yes for not achieving a mission to mars yes, NASA simply cannot perform a thee times as complicated and thus three times as expensive mission on only a third of the budget (when measuring in today's dollars). Additionally every time there is a governmental change within the US, missions from previous administrations get scraped and new plans are made up. This leads to an periodical destruction of knowledge gained from these projects. Think of it like an oil tanker which is on a 60 year journey and changes captains every 8 years or so, which completely changes the destination and path. Concerning the private sector and space, I agree with you that this is a really impressive feat which they have performed much better then NASA ever did. One of the reasons they managed to do this however was a commercial incentive, namely the potential market of space tourism. A first manned mission to mars would be a mainly political undertaking, as the scientific benefits are negligible considering the cost and the capabilities of rovers, because of this, it could never be undertaken by by private companies as they would operate on a profit seeking basis and in a high risk, political mission like this, no profit can be made.

Thanks Mr.Egbert Jan Veen .

In most cases solar wind affects our satellites,and our spacelab,this happens very often.

Earth's magnetic field ,whereas at greater distances, such as in outer space, it diminishes with the cube of the distance. Where the prime meridian intersects with the equator, the field strength is about 31 microteslas.

Well, this is usually not a problem, as most space qualified equipment is radiation hardened, the problem is if you have instead of the usual solar wind, a solar storm or a coronal mass ejection. A storm large enough could disrupt satellites in highly elliptical or geostationary orbits, due to their high energy particles (so not the usual gamma radiation) in extreme cases these storms could also effect the electronics of LEO satellites and the ISS, luckily these storms can be seen before hand and appropriate counter measures can be made.

Thanks,Mr.Egbert Jan Veen

@EGBERT,Earth and Mars are at different orbits around sun.We can start while the Mars is in neighbourhood,but while coming back,we have to wait, or the vehicle has to orbit sun, to get near Mars.Heard that lot of planet leviation is must,when we visit outer extreme planets like Uranus,Please.

Well human exploration of gas giants is quite pointless anyway as there is no foreseeable scientific benefit at all of sending humans to perform work there (there is no surface to land on). For the case of mars, as this is already complicated enough to get there, there is always a small mission window of getting there and getting back. Favorable orbits using manageable delta-V's (change in relative speed) requirements dont come around often (perhaps only once a decade), this depend on the alignment of the planets and the corresponded possibility of using gravity assisted slingshot maneuvers of planets and moons. This process is called trajectory calculation and, because of the variety of factors involved can lead to several mission trajectories with each having its own mission times, delta-v requirements, thrust requirement etc. Im not sure what you mean with planet levitation, but for mars with its low atmospheric density and lower gravity, the lift off requirements would be lower then here on earth.

@Christ, what kind of truth are you talking about?

@EGBERT,Earth and Mars are at different orbits around sun.We can start while the Mars is in neighbourhood,but while coming back,we have to wait, that is the vehicle has to orbit sun, to get near earth (not Mars), earth and mars are in continues orbit around the sun,but the periods are different,some times they are close by,the same side of sun,sometimes taking other position opposite side of the sun,to take the shortest distance to save fuel and hence payload(poor voluntarily disturbing atmosphere,to know what i am writing by echo response, from all spheres including radio tracking me,without knowing what i am doing,that is why lot of errors by me sir,this is our india,crab attitude)manned vehicle can wait,or orbiting sun,no energy spent and wait till Mars get. near,or take the longest path as such.Heard that lot of planet around leviation(sling shot) by vehicle is must to save fuel (less payload vital),when manless vehicle visit outer extreme planets like Uranus,Please.sorry for troubling again and again and taking your valuable time

I know this, but you are thinking too much in distances like they would be on earth, to go from earth to mars, you have to achieve a certain change of delta-v to change from an earth orbit to a mars orbit (orbit intersection). Using various slingshot maneuvers and a propulsion system with a high thrust/specific impulse ratio, this can be achieved. These slingshot maneuvres have to be done because space-time is curved, think of it like trying to cross a mountain range with a bike, the most optimal and efficient way of getting there is rarely to go straight on, but rather to use the curves of the mountain and the speed you can build up with going downhill to cover the power needed to go uphill.

Check out the following link for some more information: http://www-spof.gsfc.nasa.gov/stargaze/Smars1.htm

Thank you very much sir.My doubt is this,while we are in an orbit around a planet or sun,virtually no fuel is spent. But we move from Earth to Mars in a straight line,decelleration by sun's gravity,to overcome more fuel is spent,hence slingshot manouvers,here no intermediate planets for slingshots.

High thrust/specific impulse,hydrogen less weight, volume more,heard solarwind ever acclerated sailing in space inside our solar system,ofcourse unmanned ,pertaining to years of time to pickup speed,probably more efficent fuels,less payload,cryogenic,why not trying atomic fission generated thrust,particular about this atomic energy in space travel,feasibility sirs.

I heard plasma produced ions getting acclerated and making thrust,feasibility,sirs.

@Egbert Jan Veen ,gone through the prescribed NASA link,understood satisfactorily.Understood is orbiting is less fuel(nil), that is why long elliptical (moon is o.k),but elliptical as far as Mars.