What is the ‘window’ in which a human visiter to mars must get off the planet before it gets too far away from earth? As I understand it it take 2 years for Mars to come back around and be near enough for things to be sent there. So if the astronaught missed his window he’d have to wait 2 years on Mars.
Basically, you have two choices: either a six-week stay (more or less) or a year-and-a-half stay (more or less). Those are the two windows, depending upon whether you choose the opposition or conjuction landing (don’t recall off-hand which one goes with which).
http://athena.cornell.edu/mars_facts/sb_launch_window.html
So you’re looking at “a range of days” here.
I think the OP was referring to how long a stay you have to have on Mars, presuming a launch when Earth and Mars are in the right positions for a minimum-energy Hohmann trajectory, and then how long a wait you have before you can make the minimum-energy return trip.
The length of the Earth year and the Mars year respectively are 365.24 days and 686.95 days. That puts the synodic period at 779.90 days. Assuming they both have circular orbits (which I realize is not so good an assumption for Mars), the orbit which hits Earth at perihelion and Mars at aphelion has a period of 517.71 days, so a one-way trip would take half this, or 258.86 days.
I get that the trip from Earth will have to arrive at Mars 162.80 days after syzygy, where 162.80 = (258.86 / 365.24 - 1/2) × 779.90. And the return trip will have to leave Mars 162.80 days before syzygy. This makes the smallest stay 454.31 days.
So the answer to the OP is, more or less, spend as much or as little time as you like. Just be sure to bring the appropriate amount of fuel with you for your return.
And speaking of Hohmann transfers, how does any other transfer orbit work? Earl Tucker mentioned opposition transfers. What’s up?
Considered this thread dead…
Question-what is it about Mars? Ever since I was a kid science fiction movies, books, and many speculative conversations have been about visiting, or visitors from, Mars. I guess there’s something about its name or appearance that makes it fascinating. But think about this-what about planets and stars outside our solar system? Or maybe even outside our galaxy or one day, maybe, if the reality of existence is what I think it could be, in a whole other universe? Let’s go far (just making sure of course we can get back safely before we embark). I’m thinking that everyone will see on the universal and dimensional scales just like they inevitably do (some taking longer than others) in personal life that they’re not the only game in town, in addition to maybe finding valuable minerals, colonizable satellites/planets/etc. So let’s reach out and go! Who’s going with me?
This gives a brief overview of opposition vs. conjunction transfers:
A couple of things: first, the rampant speculation about life or intelligence on Mars ever since the spurious sighting of “canals” there. Secondly, the fact that Venus turned out to be an inhospitable hell that no one is planning to visit soon. Thirdly, the outer planets and their moons are much too far away to even consider manned visits with currently available technology. Fourth, Mercury is hot, barrent, and not very easy to reach. That pretty much limits manned exploration to the Moon and Mars.
Unfortunately, that link doesn’t explain the orbital mechanics very well. Does it involve Venus or Earth gravity assists? Or a high-energy trajectory that uses more fuel but cuts the mission time and so reduces the supplies needed?
Interstellar flight is many orders of magnitude more difficult than interplanetary fligt. Besides, we don’t even know if there are earth-like planets around nearby stars. There are plans to find and observe such planets, the major one being NASA’s proposed Terrestrial Planet Finder project.