Directions to Mars
Anyone remember MapQuest?
This newsletter is dedicated to Ira Jacobson—whose confidence that one day I’ll step foot on Mars may actually inspire me to do it. I’ll never forget him saying, “you always look happy”, and I think that’s because of the beautiful family that he’s responsible for—for which I’m thankful every day. So if one day I end up making the trip like Ira always seemed to think I would, this is how I would get there.
Side note—he did not want to go to Mars. He was very clear about that.
—Matt
Mars is a hot topic here at It’s Not Rocket Science, and for good reason. It’s close by, relatively large, and the next logical step on the way to settling the solar system. It’s about half the size of Earth and has a characteristic red surface. While it’s a bit tacky, Mars wears it well. To be fair, she doesn’t have much choice. With a surface potent in Iron, oxidation is bound to occur. Like an old car sitting in the rain, Mars gets its brownish, reddish color from Iron reacting to the atmosphere, creating what is essentially rust. Size and color don’t matter, however, when it comes to orbits, and Mars has a particularly simple one. Generally speaking, it looks similar and is on the same “orbital plane” as Earth’s. This just means that, if you imagine a sheet of paper that contains the Sun and the Earth’s orbit, expanding two-dimensionally into space, Mars’ orbit would be on that same piece of paper.
There are technically infinite ways to get to Mars, but there’s only one best way. Generally, our two main goals in getting there are to minimize time and cost. Cost in this case just means fuel. At its closest, Mars is about 40 million miles away. At its farthest, it’s 250 million miles. So it stands to reason that we should just go straight there when it’s close. The problem here is Mars’ movement—it wouldn’t be there anymore once you got there.
To make up for this, you could leave earlier, and intercept Mars where it will be when you get there. This straight-shot approach would only take two months but you’d spend the whole time fighting against the gravity of the Sun. To do this you’d need a whole lot of fuel. In fact, it’s more fuel than you can physically carry. Instead, we’ll need to use a different approach, one where we can more efficiently plan our orbit and even use the gravity of the Sun to our advantage.
Instead of one long burn of fuel, wouldn’t it be nice if we could fire our engines only twice? Yes, that would be nice. Thank you for asking. Enter the Hohmann Transfer. The general idea behind this trajectory is to enter into an elliptical orbit around the Sun, where the nearest point of your orbit (periapsis) is the Earth and the farthest point (apoapsis) is your destination.
This way, you only have to fire your engines to get out of Earth’s orbit and again to slow down into Mars’ orbit. For the rest of the journey, you rely solely on small course corrections and the Sun’s gravity. Furthermore, for some more complicated orbital mechanics reasons, it’s most efficient to speed up at the nearest point in your orbit, because that is where you’ll be going the fastest. It’s also most efficient to slow down at the farthest point in your orbit, where you’ll be going the slowest. This isn’t all sunshine and roses, however, because you have to time your Mars approach just right. Small changes in speed or trajectory can result in you missing your target by millions of miles. Luckily, as we’ve discussed before, there’s no friction in space—nothing to slow the planets down. Because of this, they’re very predictable. And as long as we’re within a few thousand miles we’ll be just fine.
Notice that you actually leave Earth when Mars is close by, but you don’t get there until it’s on the complete opposite side of its orbit. Due to fuel considerations alone, this is the path NASA tends to pick. When you hear about a “Mars launch window”, this is what they mean. They’re waiting for Earth and Mars to be at the right spots in the sky so that when we send off our spacecraft in our highly efficient orbit, Mars will be there on the other side. This window only happens every 26 months. Given this extended time, NASA tries to have something ready to send for every launch window. All in all, using this approach will yield an 8-month travel time, giving astronauts plenty of time to get to know each other.
Spending 8 months in space is difficult. Even in relatively roomy space stations the record amount of time spent in space is just over a year. So, we’ll need to put some more work into spaceships before they’ll give humans enough room for a trip like this. They also need to carry all of the supplies for Mars once they get there. SpaceX, naturally, is working on this already. They’re currently working on Starship, an interplanetary spaceship capable of carrying 220,000 pounds to Mars. Oh, and it can land itself, obviously.
Mars is exciting. I have no doubt that one day humans will make it there. When and how? That we’ll have to see. Maybe one day you, or me, might make our way out to the red planet. But for now, I’ll stick with my classic excuse: I’m too claustrophobic.
Thank you for reading this week’s edition of It’s Not Rocket Science. I hope you enjoyed reading this as much as I did writing it. This is for you, Ira.
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Cover Image: The Hill
Brilliant Matthew.....