Read the Details Before "Improving" Musk's Plan for Mars
Andrew Mayne News

Read the Details Before "Improving" Musk's Plan for Mars

In a Jalopnik post titled Here's How To Fix The Big Problems With Elon Musk's Mars Spaceship that’s making its way through the iO9, Gizmodo Gawkerverse, blogger Jason Torchinsky offers his suggestions on how to improve the design Elon Musk and his team at SpaceX came up with for the Interplanetary Transport System. First, let me say that it’s exciting that we live in a time when we can discuss the pros and cons of an actual mission to Mars. That said, Torchinsky’s suggestions, while showing a good grasp of space history, would either kill all 100 passengers and destroy the spaceship or take twice as long to get there and back AND cost several times more to do so. While his plan is presented as a way to reduce complexity and save costs, it does the exact opposite. The reason is based primarily on Torchinsky attributing the elegant, aerodynamic design of the spaceship as some Elon Musk quirk, when in fact, it’s critical to making the entire system so cost-effective. The Interplanetary Transport System In Musk’s plan (check it out here), a booster on Earth would push a spaceship into orbit (we’ll call it the spaceship), land, get loaded with a tanker, push that into orbit and land again. After the tanker fuels the spaceship, it would land and the operation would be repeated four more times, filling the spaceship’s fuel tank to capacity. The spaceship would then fire its engines, carrying 100 people and a half million pounds of cargo to Mars at about 50,000 miles an hour. Three to six months later (depending on the transfer window) the spaceship would reach Mars and slow itself down in the atmosphere using what’s called aerocapture. (This is where you use the friction of the air to reduce your speed as you loop around and either land or go into orbit.) To accomplish this, the bottom side of the spaceship is covered in heat resistant tiles. The alternative to aerocapture is to carry just as much fuel as you used to leave Earth orbit to slow you down when you reach Mars. This is simple physics, it takes an equal amount of energy to stop you. By using aerocapture, the spaceship gets there twice as fast. Not using it would mean having to save half its fuel for slowing down – which means taking twice as long to get there. This could be the difference between a six month journey and spending a year in space… After the spaceship lands and everyone hops off, it would use a special process to convert water from the surface and carbon dioxide from the atmosphere into methane and liquid oxygen to refuel. The rocket would then leave when it’s in the right transfer orbit and head back to Earth. It’s an elegant solution that gets 100 people and an enormous amount of cargo to the planet in a very fast time at a ridiculously low price that makes real colonization a possibility. The Torchinsky Variation Let me explain Torchinsky’s attempts at improving the plan and why well-intentioned, they’re misguided and seem unaware of how Musk’s plan actually works. First, Torchinsky wants to put five tankers into orbit before the spaceship is launched. He says that this will reduce the complexity of the launch. While that’s debatable, it also means you need five times as many tankers, adding at least half a billion dollars to the construction costs. And that doesn’t even include the time cost (will it take five times as long to build them?) or the other capital costs (five times the factory space and launch storage.) Several decades into the program, Musk wants to have thousands of spaceships and tankers. But getting there means starting this in the most cost-effective practical way. One tanker. One booster. One spaceship. Torchinsky’s second major modification comes from a mistaken assumption – leading to an either catastrophic or extremely expensive solution that causes an even greater problem than the one he thinks he’s fixing. In looking at the sleek lines of the spaceship, Torchinsky makes a comment about this being the product of a flaw in Elon Musk’s thinking, claiming that Musk is trying to make an elegant, all-in-one spaceship for the same reason he put Falcon-Wing doors on the Tesla Model X – because they look cool. Torchinsky believes that the better solution would be to make the spaceship half the size and have it push a habitat resembling a hybrid of the International Space Station and Russian Soyuz technology. Torchinsky points out that they’re both proven designs. (So is a Conestoga wagon, but I just wouldn’t want to take a cross country trip.) He’d have his smaller spaceship leave the habitat in orbit (requiring less fuel for the rocket to launch from Mars) land, unload, refuel (same process as Musk’s), take off again and then push the habitat back to Earth orbit on the return window. His primary goal is to reduce the amount of fuel it takes to leave the surface of Mars. Which is an unnecessary step and makes for a solution much, much worse than the one he’s trying to solve. 1. The first thing he overlooks is that Musk’s spaceship is designed for aerocapture (using the atmosphere to slow down.) The ISS definitely is not designed for. And I’ll add, while the Soyuz is dependable, it’s never returned to Earth from a Martian or even Lunar velocity. Aerocapture means that after you take off from Earth orbit, you only need enough fuel onboard to land on Mars after the atmosphere slows you down. This a small fraction of the amount of fuel it took to accelerate. The entire purpose of Musk’s “rich-guy/gal SUV” thinking as Torchinsky perceived it, is to make an aerodynamically shaped spaceship with smooth edges and a heat shield that can reduce the fuel needed by half (if the goal isn’t to burn up in the atmosphere.) This was a brilliant engineering decision and not a marketing one. Torchinsky’s big platform with inflatable modules and no heat shield can’t do aerocapture. The only way it would avoid burning up or flying past Mars if it was going as fast as Musk’s shipe would be to have the spaceship do an orbital entry burn – requiring approximately the same amount of fuel it took to leave Earth. This requires double the fuel and double the fuel tanks. The alternative is to go half as fast, taking twice as long to get there. Bad enough, but it gets worse. 2. Torchinsky’s half-sized rocket that lands and refuels on Mars has to carry the same amount of fuel as Musk’s full-sized one back up into orbit to then dock with the platform and push it back to Earth. Keep in mind the bulk of Musk’s spaceship or any other rocket is fuel tanks. Torchinsky’s spaceship would actually have to be much larger than half-sized to carry the amount of fuel needed to make this happen (unless he wanted to add extra fuel tanks to the platform and do multiple launches.) 3. After Torchinsky’s not really half-sized rocket is pushing the platform back to Earth there’s another major problem: If he wants to go as fast as Musk’s spaceship, there’s no fuel to slow down. Remember Musk’s aerocapture capable spaceship? It only needs enough fuel to land after it slows itself down from Mars velocity using aerocapture (or go into a parking orbit and get refueled by a tanker.) Unless Torchinsky put even more tanks on his platform and did even more refueling trips on Mars, his non-aerodynamically designed platform will burn up or sail past Earth, eventually spiraling into the sun. If he wisely decided to use half the fuel, then he’ll have enough to enter Earth orbit and not kill everyone. The only problem is this means it’ll take twice as long, effectively doubling the entire round trip. Summing it up Even omitting the cost of multiple tankers in Earth orbit part, Torchinsky’s solution of “stripping down” the spaceship and using it to push a detachable habitat has not only added the cost of a fourth vehicle (the habitat), but quadrupled the amount of fuel required and the fuel tanks needed. Trying to use the same amount of fuel and conserving half for deceleration means doubling the trip time, putting people in space for up to a year both ways. Space is hard. Besides the thousands of complicated details we’re still trying to figure out, there’s the basic physics where overlooking one small detail can make all the difference. Torchinsky saw Elon Musk’s beautiful spaceship and decided that it was designed that way as a folly, putting looks above engineering. When in fact, Musk is an extremely pragmatic engineer and a brilliant economist. He starts with first principles and works from there until he reaches a solution that nature will allow to function and economics will make a reality. Putting humans on Mars and the rest of the Solar System is going to be challenging – it’s also the most significant human development since our ancestors left Africa. Musk’s plan to start this process may have pitfalls and engineering flaws we haven’t discovered yet, but the criticisms made by Torchinsky are unfounded and would make things much less efficient (if not fatal.) I will say that Torchinsky is spot on in that we need to take a good look at existing solutions to see what works. The Russian space program did some amazing things(their rocket engines were first rate.) And NASA’s accomplishments are in part why this is even possible. But pointing this out to Musk is silly. He knows all that. Lest we forget, Musk’s ambition to build his own rockets started when he went to Russia to try to buy an ICBM so he could send a greenhouse to Mars. When they jerked him around and didn’t take him seriously, Musk decided he’d hire some amazing people and do it himself. Now he’s the single biggest threat to the entire Russian space industry. Underestimating him or his engineering prowess is a losing proposition.

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