[dumb] Question about visiting Mars.

[Lobsang]

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.

[Earl_Snake-Hips_Tucker]

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).

[Duck_Duck_Goose]

http://athena.cornell.edu/mars_facts/sb_launch_window.html

The length of a launch window is often determined by the type of launch vehicle that is selected for a mission. There are many different sizes and capabilities of rockets. The payload indicates the type of equipment needed. When a launch vehicle is selected for a mission to Mars, it comes with a set of parameters for optimum performance. It has been designed to launch a certain amount of mass at a certain velocity.

Think of a shortstop throwing out a runner. The shortstop can most easily make a good throw if moving toward the “target” base. It is much harder, and requires a stronger arm, to throw the ball to the proper spot if the shortstop is falling backwards or leaning in the wrong direction. The same applies to a launch between Earth and Mars. The farther the launch is from the optimal time for lift-off, the more energy needed to get to the proper target.

If a rocket can barely do its assigned job under the best launch conditions, the launch window becomes very narrow. The more energy a rocket delivers for a particular payload, the wider the range of conditions it can handle. Then the launch window widens. But too much rocket wastes fuel and money. There has to be a balance between the mass of the payload and the energy capabilities of the launch vehicle.

For a mission to Mars, lift off is usually scheduled prior to an ideal launch day, but within acceptable conditions for the launch vehicle. This allows for weather-related delays or delays in getting the vehicle ready. A range of days after the ideal launch date make up the rest of the launch window. After this period of time, the trajectory between Mars and Earth becomes more difficult, the thrust of the launch vehicle becomes inadequate, and the window of opportunity for a mission to Mars closes for another two years.

So you’re looking at “a range of days” here.

[Lumpy]

@Duck Duck Goose

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.

[Achernar]

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.

[MonkeyMensch]

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…

[dopetalker]

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?

[Earl_Snake-Hips_Tucker]

@MonkeyMensch

And speaking of Hohmann transfers, how does any other transfer orbit work? Earl Tucker mentioned opposition transfers. What’s up?

This gives a brief overview of opposition vs. conjunction transfers:

http://www.aa.washington.edu/courses/aa101/aa101_27.pdf

[Lumpy]

@dopetalker

Question-what is it about Mars?

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?

[scr4]

@dopetalker

But think about this-what about planets and stars outside our solar system?

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.