I don't know much science but was curious about it.

So, what I've seen in movies is that there are lot of objects in the space and many other space items (made of rocks, moving stars etc.). So when the vehicle is traveling to Mars, why doesn't it collide with those objects? How does it remains safe?

Secondly, how does it know Mars is this way? Does it calculate and correct its path itself from time to time so its trajectory is accurate or do NASA computers and scientists have control of it like a remote control car, or do they just define a trajectory in the beginning, define a target (Mars) and it keeps traveling on it (if yes, how can it be so accurate)?

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    $\begingroup$ For navigation: space.stackexchange.com/questions/33840/spacecraft-navigation. But about the trajectory, it is calculated mostly using computers which help decide on a trajectory that takes a feasible time and fuel. These calculations are based on orbital mechanics (mainly governed by gravity) $\endgroup$ Commented Apr 18, 2020 at 19:12
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    $\begingroup$ This question is really too broad, you should address separately each flight phase (from ground to Earth orbit, from Earth orbit to Mars orbit, Mars orbit insertion, de-orbit and landing on Mars). Moreover, you should forget most of what Hollywood movies could have teach you (movies are done to be visual, rocket science to be efficient), except maybe few movies such as apollo13 $\endgroup$
    – Manu H
    Commented Apr 20, 2020 at 17:39
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    $\begingroup$ Could you please edit to focus on one question? I will surely vote to reopen if you could do that, and I'm sure others will do too. $\endgroup$ Commented Apr 22, 2020 at 14:06

1 Answer 1


Movies are misleading.

Space is enormous, and almost entirely empty. Even our ”asteroid belt” is mostly empty space; we have flown several missions straight through the belt to the planets beyond without hitting anything.

Low Earth orbit has collected quite a bit of space junk over the years, but even so, interplanetary probes spend only a very short time in that area, so the risks are very small.

As for your second question, the initial trajectories for missions to other planets as they leave Earth orbit are quite accurate, but we do have “remote control” and invariably make small midcourse corrections to the spacecraft. See this question and answer for more information.

  • $\begingroup$ * the initial trajectories for missions to other planets are quite accurate* this is also defined by computers before launch? Or after launch? I don't think at start, because initially every rocket flies at 90 degree upwards, not in direction of planet. $\endgroup$
    – Vikas
    Commented Apr 18, 2020 at 20:47
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    $\begingroup$ Correct, I meant the initial trajectory after departure from Earth orbit. $\endgroup$ Commented Apr 18, 2020 at 21:12
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    $\begingroup$ The articles might go into complicated description, but the concept is pretty simple. If you want some "hands on" experience, I'd recommend you give Kerbal Space Program a try. It's a rocket building/flying game, and according to a guy who worked at NASA, it's better than them at teaching orbital mechanics: xkcd.com/1356 $\endgroup$
    – csiz
    Commented Apr 19, 2020 at 2:56
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    $\begingroup$ @csiz said guy is also a comedian, so take that recommendation with a pinch of salt (and it’s not like he worked in a department related to orbital mechanics / was taught orbital mechanics by NASA). $\endgroup$
    – Tim
    Commented Apr 19, 2020 at 9:10
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    $\begingroup$ @George I think the most significant errors are due to how rocket engines burn and gimbal. There are delays between a command being issued by the computer and a fuel valve closing and the rocket engine shutting off. Of course the effect is probably modelled, but it's not perfectly accurate. There are also mechanical errors in pointing the engine in the right direction. And small errors at the start of a trajectory make a big difference after millions of km in space. The closer you are to the target, the less the errors matter, so mid way corrections are easier, but they use more fuel. $\endgroup$
    – csiz
    Commented Apr 19, 2020 at 18:41

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