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“Why can’t we land on Mars” is a common question sent to us here at Universe Today. The answer is multi-layered, but the most pressing issue is the velocity of the spacecraft and the amount of cargo space needed to carry enough fuel to safely slow the craft and then return it to Earth.
All spacecraft that return to Earth use the atmosphere to slow themselves down so that they can land. The Space Shuttles shed thousands of km/h of velocity using atmospheric braking. The challenge of landing on Mars arises because the Martian atmosphere is only 1% of Earth’s, so using it to slow down is not feasible. NASA and other space agencies have used disproportionately large parachutes to compensate, but that is not enough and the spacecraft will then fire their retro-rockets to slow down even more. If the spacecraft is heavy enough or the instruments are especially sensitive, the spacecraft can use an airbag system to bounce across the surface of the planet. Despite all of these precautions, to date, 60% of the missions attempting to land on the surface have crashed.
Another challenge to landing a manned mission on Mars is the time that has to be spent in travel. Current technology does not allow us to simply shoot a rocket directly at the planet any time we please. The fuel needed to combat the Sun’s gravity just enough to reach Mars, but not overshoot it, is beyond the capacity of current spacecraft. To overcome that storage shortage, spaceflights have to utilize Hohmann transfer orbits and be launched in a window of opportunity that will allow them to arrive when Mars and Earth are at their closest approach to each other. The transfer orbits require a long explanation, so, for the sake of space, they allow a spacecraft to use two engine impulses to arrive in orbit instead of a maintained burn. (Click here for the long explanation). Using these orbits causes the trip to last 214 days one way. Just imagine being in the small cabin of a spacecraft(about the size of a small car) for 458 days in a row with two or three other people.
As if landing a spacecraft on Mars was not complicated enough, it gets harder to do the heavier a vehicle is. The technology we have today is not up to the task of safely landing anything that weighs more than a metric ton, say a space shuttle or even a capsule the size of those used to land on the Moon. NASA engineers are working on all of these issues as we speak, so the solution should present itself in the next few years.
We’ve also recorded an episode of Astronomy Cast all about Mars. Listen here, Episode 52: Mars.