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Sometimes, the Red Planet is really far away from our own blue world. Image source: Boeing.

NASA is going to Mars. This much we know -- but the devil is in the details.

For example, "going to Mars" isn't quite as simple a proposition as, say, going to Minneapolis. Here on Earth, when you want to fly from point A to point B, drawing a straight line between the points will usually do the trick. Mars, in contrast, is a moving target -- sometimes close to Earth, and other times... on the opposite side of the Sun.

Planning your flight
If you want to travel to Mars most efficiently, therefore, you need to time your trip carefully. "Mars Close Approach" or "Mars Opposition" -- when Earth is positioned between Mars and the sun -- is the best time for a trip, permitting one-way travel times of as little as six months (depending on the speed of your spaceship). But Mars Opposition only occurs once every 26 months.

And even then, "close" is a relative term. This year, Earth will approach within 0.5 astronomical units of Mars -- 46.5 million miles. In 2018, we'll get down to just 0.38 AU -- but there's no chance of throwing together a manned Mars mission by then.

Our next close pass doesn't come around until 2033, when we'll get within 0.42 AU of Mars. Then, in 2035, we'll approach to 0.38 AU -- 35 million miles, or 24% closer than this year's approach. This implies both a faster transit to Mars and back, and less exposure of the astronauts to weightlessness (and radiation). It makes a 2033 departure, and 2035 return trip, the best plan for NASA to get to Mars.

Another complicating factor is the fact that we don't currently have a spacecraft capable of carrying astronauts to Mars. Luckily, though, the need to wait for a 2033 Mars Close Approach may give NASA just enough time to build the spaceship we need.

Choosing your connection
Looking forward to a "mid-2030s" Mars mission, Boeing (NYSE:BA) put together an excellent short film on the six elements that NASA believes will be necessary to construct such a spaceship. These are, in order:

Pieces 1 and 2: Space Launch System and Orion
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Image source: Boeing.

The Space Launch System is the sine qua non for any Mars mission. "If you're going to go to the Moon or farther, you need a really big rocket to do that," says Boeing Director of Space Exploration Systems Mike Raftery.

Boeing and rocket-engine partners at Orbital ATK (NYSE:OA) and Aerojet Rocketdyne (NYSE:AJRD) are building SLS. Atop it sits the Orion crew capsule, built by Lockheed Martin (NYSE:LMT). Orion will be reusable multiple times -- which is good news -- because Boeing says it will need to build about "five or six" SLS rockets.

This is because before the trip to Mars can really begin, NASA will need to send up...

Pieces 3 and 4: Habitat and Space Tug
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Image source: Boeing.

Earth's mission to Mars will not be a one-shot deal. You can't just launch SLS directly from Earth to Mars and land there. For purposes of the Mars mission, it's better to think of SLS and Orion as a "shuttle service," shifting all the elements necessary for the Mars mission from Earth's surface to a rendezvous point in Earth orbit -- there to be assembled for Mars departure.

The "spaceship" that will make that big trip from Earth to Mars will consist of a large Habitat for the crew to live in and an electrically powered, ion-driven "Space Tug" that will haul the Habitat to Mars.

And not just the Habitat. Two final pieces still need to be put in place before the Mars mission can depart.

Piece 5: Mars Lander
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Image source: Boeing.

Upon arrival at Mars, the space tug will release a Mars Lander, by way of which the astronauts will descend to the planet's surface. Using an inflatable heat shield to protect itself at the beginning of its descent through the atmosphere, then firing landing rockets at the end, the Mars Lander will make a soft landing on Mars.

Piece 6: Mars Launcher
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Image source: Boeing.

Some time later, these same astronauts will reascend to Mars orbit by way of a Mars Launcher. Once again, they'll rendezvous with the Space Tug, reinhabit the Habitat, and finally depart for Earth.

In the meantime, in between time
Quite some time may elapse between descent and ascent, however. And here's why the close proximity of Mars to Earth in both 2033 and 2035 makes this pair of years especially propitious for a manned mission to Mars. In theory at least, even accounting for a multi-month trip to Mars and a multi-month trip back, the astronauts will have several months on Mars to conduct experiments -- perhaps as long as a year.

And here's the key thing for investors to keep in mind: Such an opportunity as this one, with back-to-back extreme proximity between Earth and Mars, will not come again until 2050-2052. Thus, a trip to Mars in 2033, and a return trip in 2035, really is a can't-miss opportunity for NASA -- and that tells us that if at all possible, NASA will not miss it.

In all likelihood, the next 17 years will see a space race of such proportions that we've not seen since the Apollo missions of the 1960s, as billions -- and tens of billions, and perhaps hundreds of billions worldwide -- of dollars are poured into the effort to ensure we do not miss this opportunity.

The time for investors to start investing in this is now. And -- at least until SpaceX decides to IPO -- Boeing, Lockheed Martin, Orbital ATK, and Aerojet Rocketdyne are all great places to start looking for those investments.

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Every couple of years, Mars and Earth get really close together -- and that's the time to go to Mars! Image source: Boeing.

Rich Smith does not own shares of, nor is he short, any company named above. You can find him on Motley Fool CAPS, publicly pontificating under the handle TMFDitty, where he's currently ranked No. 278 out of more than 75,000 rated members.

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