The Interplanetary Transport System

Space has been on my brain a lot lately. One of the causes was the long-awaited presentation by Elon Musk at the International Astronautical Congress (IAC) last month. During the talk, he finally laid out the details of his “Interplanetary Transport System” (ITS). The architecture is designed to enable a massive number of flights to Mars for absurdly low costs, hopefully enabling the rapid and sustainable colonization of Mars. The motivation behind the plan is a good one: humanity needs to become a multi-planetary species. The sheer number of things that could take civilization down a few pegs or destroy it outright is frighteningly lengthy: engineered bio-weapons, nuclear bombs, asteroid strikes, and solar storms crippling our electrical infrastructure are some of the most obvious. Rampant AI, out-of-control self-replicating robots, and plain old nation-state collapse from war, disease, and famine are some other threats. In the face of all those horrifying things, what really keeps me up at night is the fact that if civilization collapses right now, we probably won’t get another shot. Ever. We’ve abused and exhausted the Earth’s resources so severely, we simply cannot reboot human civilization to its current state. This is the last and best chance we’ll ever get. If we don’t establish an independent, self-sufficient colony on Mars within 50 years, we’ll have solved the Fermi Paradox (so to speak).

But Musk’s Mars architecture, like most of his plans, is ambitious to the point of absurdity. It at once seems like both fanciful science fiction and impending reality. Because Musk works from first principles, his plans defy socio-political norms and cut straight to the heart of the matter and this lateral approach tends to rub the established thinkers of an industry the wrong way. But we’ve seen Musk prove people wrong again and again with SpaceX and Tesla. SpaceX has broken a lot of ground by being the first private company to achieve orbit (as well as return safely to Earth), to dock with the International Space Station, and to propulsively land a part of a rocket from an orbital launch. That last one is particularly important, since it was sheer engineering bravado that allowed them to stand in the face of ridicule from established aerospace figureheads. SpaceX is going to need that same sort of moxie in spades if they are going to succeed at building the ITS. Despite their track record, the ITS will be deceptively difficult to develop, and I wanted to explore the new and unsolved challenges that SpaceX will have to overcome if they want to follow through on Musk’s designs.

SpaceX ITS Diagram

The basics of the ITS architecture are simple enough: a large first stage launches a spaceship capable of carrying 100 people to orbit. More spaceships (outfitted as tankers) are launched to refill the craft with propellants before it departs for Mars during an open transfer window. After a 3 to 6 month flight to the Red Planet, the spaceship lands on Mars. It does so by at first bleeding off speed with a Space Shuttle-style belly-first descent, before flipping over and igniting its engines at supersonic speeds for a propulsive landing. After landing, the craft refill its tanks by processing water and carbon dioxide present in Mars’s environment and turning them into propellant for the trip back to Earth. Then the spaceship simply takes off from Mars, returns to Earth, and lands propulsively back at home.

Now, there are a lot of hidden challenges and unanswered questions present in this plan. The first stage is supposed to land back on the launch mount (instead of landing on a pad like the current Falcon 9 first stage), requiring centimeter-scale targeting precision. The spaceship needs to support 100 people during the flight over, and the psychology of a group that size in a confined space for 6 months is basically unstudied. Besides other concerns like storing highly cryogenic propellants for a months-long flight, radiation exposure during the flight, the difficulty of re-orienting 180 degrees during re-entry, and the feasibility of landing a multi-ton vehicle on soft Martian regolith using powerful rocket engines alone, there are the big questions of exactly how the colonists will live and what they will do when they get to Mars, where the colony infrastructure will come from, how easy it will be to mine water on Mars, and how the venture will become economically and technologically self-sufficient. Despite all of these roadblocks and question marks, the truly shocking thing about the proposal is the price tag. Musk wants the scalability of the ITS to eventually drive the per-person cost down to $200,000. While still high, this figure is a drop in the bucket compared to the per-capita cost of any other Mars architecture on the table. It’s well within the net-worth of the average American (although that figure is deceptive; the median American net-worth is only $45,000. As far as I can figure, somewhere between 30% and 40% of Americans would be able to afford the trip by liquidating most or all of their worldly assets). Can SpaceX actually achieve such a low operational cost?

Falcon 9 Production Floor

Remember that SpaceX was originally targeting a per-flight price of $27 million for the Falcon 9. Today, the price is more like $65 million. Granted, the cost to SpaceX might be more like $35 million per flight, and they haven’t even started re-using first stages. But it is not a guarantee that SpaceX can get the costs as low as they want. We have little data on the difficulty of re-using cores. Despite recovering several in various stages of post-flight damage, SpaceX has yet to re-fly one of them (hopefully that will change later this year or early next year).

That isn’t the whole story, though. The Falcon 9 was designed to have the lowest possible construction costs. The Merlin engines that power it use a well-studied engine design (gas generator), low chamber pressures, an easier propellant choice (RP-1 and LOX), and relatively simple fabrication techniques. The Falcon 9 uses aluminum tanks with a small diameter to enable easy transport. All of their design choices enabled SpaceX to undercut existing prices in the space launch industry.

But the ITS is going to be a whole other beast. They are using carbon fiber tanks to reduce weight, but have no experience in building large (12 meter diameter) carbon fiber tanks capable of holding extremely cryogenic liquids. The Raptor engine uses a hitherto unflown propellant combination (liquid methane and liquid oxygen). Its chamber pressure is going to be the highest of any engine ever built (30 MPa. The next highest is the RD-191 at 25 MPa). This means it will be very efficient, but also incredibly difficult to build and maintain. Since reliability and reusability are crucial for the ITS architecture, SpaceX is between a rock and a hard place with its proposed design. They need the efficiency to make the system feasible, but the high performance envelope means the system will suffer less abuse before needing repairs, reducing the reusability of the system and driving up costs. At the same time, reusability is crucial because the ITS will cost a lot to build, with its carbon fiber hull and exacting standards needed to survive re-entry at Mars and Earth many times over.

It’s almost like the ITS and Falcon 9 are on opposites. The Falcon 9 was designed to be cheap and easy to build, allowing it to be economical as an expendable launch vehicle, while still being able to function in a large performance envelope and take a beating before needing refurbishment. The ITS, on the other, needs all the performance gains it can get, uses exotic materials and construction techniques, and has to be used many times over to make it an economical vehicle.

All of these differences make me think that the timeline for the development of the ITS is, to put it mildly, optimistic. The Falcon 9 went from the drawing board to full-stack tests in 6 years, with a first flight a few years later. Although the SpaceX of 2004 is not the SpaceX of 2016, the ITS sure as hell isn’t the Falcon 9. A rocket using the some of the most traditional and well-worn engineering methods in the book took 6 years to design and build. A rocket of unprecedented scale, designed for an unprecedented mission profile, using cutting-edge construction techniques… is not going to take 6 years to design and build. Period. Given SpaceX’s endemic delays with the development of the Dragon 2 and the Falcon Heavy, which are a relatively normal sized spaceship and rocket, respectively, I suspect the development of a huge spaceship and rocket will take more like 10 years. Even when they do finally fly it, it will take years before the price of seat on a flight falls anywhere as low as $200,000.

Red Dragon over Mars

If SpaceX manages to launch their Red Dragon mission in time for the 2018 transfer window, then I will have a little more hope. The Red Dragon mission needs both a proven Falcon Heavy and a completely developed Dragon 2. It will also allow SpaceX to answer a variety of open questions about the mission profile of the ITS. How hard is it to land a multi-ton vehicle on Martian regolith using only a powered, propulsive descent? How difficult will it be to harvest water on Mars, and produce cryogenic propellants from in situ water and carbon dioxide? However, if SpaceX misses the launch window, I definitely won’t be holding my breath for humans on Mars by 2025.

5 Things NASA Should Have Never Cancelled

NASA has a long history of cancelling the most exciting and promising projects in its portfolio, instead opting for the safer and less expensive options (which invariably develop ballooning budgets and dismal success records). While I don’t mean to bash the totality of NASA in this post, I do want to lament a few of the best ‘could-have-beens’.

AAP Venus Flyby Schematic

Schematic for the S-IVB wet workshop.

The first is the Venus flyby of the Apollo Applications Program. This would be similar to the Skylab missions, except that instead of launching a pre-built laboratory, the third stage of the Saturn V would be converted into a ‘wet workshop’ living space after using all of its fuel. This would enable the spacecraft to be launched on a trajectory to pass by Venus and then free-return to Earth. I’ll be the first one to point out that manned flybys are not particularly useful scientifically; nonetheless, having the achievement of sending humans into interplanetary space under our belt would be really cool. Then again, being able to say that we’ve ‘already done it’ may have tempered our drive to do it again — much in the way that sending people to the Moon holds less appeal now. For better or for worse, the AAP got dropped along with the rest of the Apollo program in favor of the the Space Shuttle.
 
NERVA mockup

A scale mockup of the NERVA rocket.

In any case, I’ve always believed that the Apollo program took a fundamentally flawed approach to space travel. Instead of scaling up existing technologies, we need to develop more efficient methods that aren’t rooted in the old ‘stick a tin can on an ICBM’ method. This is why the cancellation of NERVA research was so disappointing. NERVA was a nuclear thermal rocket, meaning it used a nuclear reactor to heat up hydrogen propellant. The program was highly successful, and showed great promise in enabling manned missions to Mars without significantly larger rockets than we already had at the time. However, the NERVA program got dragged down with the demise of the Apollo program, and only recently have we seen the rise of a possible replacement technology (electric propulsion).

 

 
But why settle for the 154 ton payload promised by the NERVA-augmented Saturn V? That’s peanuts compared to the 10,000 TONS to LEO made possible through nuclear pulse propulsion. Yes, I’m talking about Project Orion. While, I’ve never been a fan of the concept, I have to admit that 10,000 TONS for (at most) $5 billion is really appealing. Even one such launch would basically make establishing a Mars colony trivial. However, Project Orion never got off the ground (so to speak), because nobody really liked the concept of propelling a spaceship with nuclear bombs. Go figure.

Project Orion Concept Art

One of the longer Orion designs


 
So after Apollo got cancelled and most beyond-Earth projects got trashed, we were left with boring stuff like Single-Stage-To-Orbit completely reusable spacecraft built with off-the-self components. Wait, WHAT?! Yeah, that’s right. In 1985 we had the ability to build a reusable SSTO with almost entirely low-cost commercially-available components.
Delta Clipper Experimental

Sure it looks weird, but it’s awesome!

However, nobody was interested in funding the project. Eventually it got picked up by the DoD’s SDIO (Strategic Defense Initiative Organization), and a team of engineers built a scaled-down version of the craft called the DC-X. It was created to test the concept of a propulsive vertical landing, fast turnaround, and other novel concepts. The project was wildly successful, and showed huge amounts of promise. Perhaps because of this success, it never got much funding, and eventually the SDIO was closed down and NASA reluctantly picked up the DC-X project. With minimal funding and personnel, the DC-X team continued to make fabulous advances and show promise. When the test spacecraft finally had a mishap and caught on fire, NASA refused to front the mere $50 million repair bill, mostly because the DC-X conflicted with their own SSTO project, the X-33.
 
VentureStar size comparison

The VentureStar is one of the fatter spaceplane designs.

Oh yeah, NASA had its own SSTO in development. The X-33 was a suborbital scale version of the proposed VentureStar. The VentureStar was an entirely reusable spaceplane, unlike the Space Shuttle. It launched vertically, landed horizontally, and only used hydrogen-LOX, unlike the Space Shuttle, which required toxic SRBs to get into orbit. The only roadblock to the X-33/VentureStar’s development was the fuel tanks, which were a tricky dual-conic shape. The materials science necessary to construct the fuel tanks was still in its infancy, and so the program got axed (although soon after cancellation, a group of engineers actually constructed a fuel tank which fulfilled all the necessary constraints).

Most of the programs mentioned here were, in one way or another, dropped in favor of the Space Shuttle, which slowly became an embarrassing farce and regrettably set back spaceflight by a good 20-30 years by causing the cancellation of these promising programs. The saddest thing is that we now have the technology to easily solve most of the technical hurdles faced by these programs, but with NASA’s limited budget and vision, we are stuck paddling around LEO with conventional, non-reusable chemical rockets. Even SpaceX’s innovation and drive pales in comparison to the 100% reusable SSTOs mentioned here.

Does Space Exploration have an ROI?

It’s easy to dismiss the current space program as a giant waste of money. Collectively, the world spends billions upon billions of dollars launching tiny pieces of metal into the sky. How could that possibly be better than, say, building a school in India or providing clean water to poor African countries, or even spending it domestically to improve our country? In the face of recent budget crises, this cry gains even more clout.

And indeed, a lot of space programs are very wasteful, especially NASA and the Roscosmos. However, this is generally due to the fact that politicians treat space as a football — another barrel of pork for their constituents. When politics and space exploration mix, you get bloated programs like the Space Shuttle and the new SLS. It’s much better when the politicians set broad goals (AKA land on the moon), fork over the money, and let the engineers work their magic. Otherwise you get a twisted maze of bureaucracy and general management which ends with wasted money and subpar designs.

But let us not forget that NASA has produced a number of very tangible technological advancements, which is summarized here better than I could. In addition, satellites are a cornerstone of the global communications network, not to mention the Global Positioning System, which is satellites. Although communications satellites are now built and launched by commercial ventures, NASA was the first and only customer for a while, and allowed companies to get some expertise in designing and building rockets. Furthermore, the space industry employs tens of thousands of people, all possible because of initial government funding.

However, those examples involve geostationary orbit at the most. What is the practical value of going out and scanning the other bodies in our solar system. Why should we launch space telescopes and space probes? If you don’t believe in the inherent value of knowledge, here is a very down-to-earth example (so to speak): the Solar and Heliospheric Observatory (SOHO) watches the sun 24/7 from L1. It gives us an advance warning for solar flares, allowing satellite operators enough time to turn their expensive pieces of equipment away from the sun, shielding the most delicate electronics from the impending wave of radiation. It is estimated that SOHO has paid for itself 10 times over in this fashion.

Finally, part of space exploration is the attempt to answer some of the big questions. Deep space telescopes answer some part of “Where did we come from?”, and probes to the surfaces of other planets and moon are often trying to answer “Are we alone?”. If you think this is far too sentimental an appeal, I urge you to imagine the ramifications if a future mission to Europa found microorganisms living in the oceans under the ice, or a mission to Mars found lithophiles buried under the Martian regolith. How would world philosophies change?

Regardless, we may be spending too much money and spending it in the wrong places. I submit to you the Indian space program, which designed and launched a mission to Mars for about 75 million dollars. I think the US should follow India’s example and lean towards frugality and very specific, directed goals. Accomplishing a single mission for a small amount of money is better, in my opinion, than developing several high-profile, high-cost programs simultaneously.

While my language and previous post may make it seem like I am opposed to any sort of space exploration, I am merely of the opinion that our society views space exploration in the wrong way. Space exploration should not be about sending humans to other bodies, at least not right now. It should be about trying to find out more about the rest of our solar system, so we can extrapolate and make predictions about the other systems and exoplanets we are discovering. And if all else fails, it can be a platform for many kinds of materials and electronics research.

Say “No” to Manned Spaceflight

I like the idea of people walking around on other planets as much as the next guy, but at the end of the day I can’t go away with a clear conscience without making this point. There is no reason for a manned space program, either now or in the immediate future. In fact, it would be quite irresponsible of us to go mucking around on other balls of dirt.

Much like the archaeologists of the past who used ancient scrolls to keep their fires going, any serious presence or in-situ resource utilization could be inadvertently destroying priceless research subjects. Imagine if we started harvesting ice from asteroids, and then discovered that very old ice tends can contain detailed records of proto-stellar conditions in the Solar System. Even things like rolling robots across Mars or slamming probes into the Moon are calculated risks. We’re pretty sure we won’t mess up anything important, but we aren’t sure. Paradoxically, we can’t be sure what we’re missing without taking some of these risks.

Nonetheless, sending advanced primates to do the job of fast, clean, accurate robots is as irresponsible as it is stupid. Animals are hosts to trillions of bacteria, and if even one strain gets onto the surface of Mars, say, and adapts to the not-so-inhospitable conditions, it’s all over. We rely on the hard vacuum of space to kill off any potential infection vectors on robotic spacecraft, but we can’t do the same for humans. If we’re going to be sending humans to any place remotely capable of developing life, we need to be almost 100% sure there is no life there to begin with, or that the presence of invasive species of bacteria won’t eliminate it.

Even if we make sure to within reasonable doubt that there is no longer or never was life on Mars, we might be screwing ourselves in the long run by sending humans to colonize. If a mutant strain of bacteria spreads to cover the planet like the stromatolites of ancient Earth, and starts eating up what little oxygen is left, then any terraforming efforts could be foiled before they begin. Imagine if our engineered bacteria produces oxygen as a byproduct, and a rogue strain works in the other way. We’d have created a widespread stable ecosystem that leaves us asphyxiating out in the cold.

The two arguments in favor of long-range manned spaceflight have never held much water for me, even if I wanted them to. First, the “putting our eggs in one basket”. Now, current manned spaceflight has nothing to do with the colonization of space. If we were serious about spreading a permanent, self-sustaining presence to another planet, we would have to completely reorganize the existing attitude and institutions surrounding manned spaceflight. Currently, the world’s collective manned spaceflights are a road to nowhere. The ISS is a good sandbox for learning about long-term missions, but we don’t really use it like that.

The second argument is economic. I’ve gone over this is previous posts, but the short of it is that it will be a long time before its profitable to go off-world for resources — unless, that is, there is an exterior source of funding. It’s conceivable that a mild industry might build up around mining space ice for fuel and 3D-printing components. However, at some point funding has to be provided by someone interested in scientific exploration or the intrinsic value of space exploration. A self-contained space economy with Earth as the main buyer is not viable. Perhaps there exists a chicken-egg dilemma: a permanent off-world colony needs industry to survive, and industry needs off-world colonies to thrive.

That’s the cold, hard reality of the matter. I don’t want to have this opinion, but avoiding the truth about manned space exploration isn’t doing anybody any good.

Interstellar Colonization Will Never Happen

There really isn’t an economical explanation for why a civilization would engage in long-range interstellar colonization.

To begin with, though, let’s look at interplanetary colonization. Why, for example, would someone fund the establishment of a permanent colony on Mars with the intent for it to become eventually self-sustaining? It’s not to relieve population pressure. Stuff is so ridiculously expensive to get into space that you’d be better off (from a monetary perspective) paying the people to live in the Sahara. It’s not for resources; asteroid mining is almost certainly a feasible economic opportunity, but the cost of lifting resources into orbit is again the obvious barring factor. It could be scientific, but scientific missions wouldn’t need to be self-sustaining or long-term. Perhaps a stint of 20 years on the surface. It could be done by a separatist group (plenty of people want to go start small settlements in the wilderness), but even if the money was raised (which is unlikely), the colony will lie on the fringes of human society. They would probably be unable to arrange a return trip, even if they wanted to, and nobody else (except more fringe groups) would want to continue colonization.

There is one argument that seems reasonable: outposts could serve as refueling stations for outbound craft (asteroid mining operations, etc). However, it would make more sense to pull these resources from asteroids and place an automated fuel refinery in high orbit around Mars (or other suitable candidate).

Many of the reasons listed above carry over to interstellar missions. The only difference is that groups would have much more trouble raising money for the mission, and that now lifting stuff into orbit isn’t the only tough part, but also accelerating your spaceship to a speed which makes for a bearable trip length.

Here are some scenarios where we do send a colonizing mission: we discover evidence of alien life, or the ruins of an alien civilization. It would only make sense to send a colonizing mission. Sending a scientific detachment with a planned return trip would be so expensive that it wouldn’t be worth it. I mean, it would be worth it, but nobody would be able to raise the funds.

Another scenario in which most of the above arguments go out the window: we build a space elevator. That removes the gateway for getting into orbit. We could expect many more people accessing and living in orbit (because they feel like it and the price is low enough). Once the population already flying around the solar system reaches a critical mass, colonizing Mars becomes a trivial step.

ADDENDUM

Actually, it came to me after I wrote this post that there may be one reasonable explanation for colonizing Mars: if we fail to find an economical way to increase biomass production either on Earth or in space, we will need large tracts of arable land. Terraforming Mars would provide this. However, the cost of lifting and storing that biomass may make it less preferable to aerocultures in orbit.

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