March 21, 2012
Elon Musk: Half Million Dollar Mars Round Trip?
Can Musk be serious?
Rocket entrepreneur Elon Musk believes he can get the cost of a round trip to Mars down to about half a million dollars.
I am skeptical.
Think of it from the perspective of energy costs. Not only does the energy have to be expended to move your body to Mars and back. But also all your food and energy, oxygen recycling, drugs, and assorted supplies have to be carried there with you. That all takes many more times energy.
Here's what I want to know: How to calculate the energy costs of a human trip to Mars? How much mass has to be moved per person? Just in supplies how much has to be sent to Mars for, say, a 180 lb person? 20 times their weight? 50 times? Then there is the fuel and the spacecraft. What's the total mass ratio of everything else per pound (or kg) of person.
Musk thinks he can get the cost of lifting weight into space below $1000 per lb. But suppose he gets it to $500 per lb. A half million dollars still only pays to lift 1000 lbs into Earth orbit. Most of that mass will be used to lift other mass to Mars (mostly fuel burned to move other fuel). He acknowledges the need for a 2 orders of magnitude cost reduction. I'm skeptical he's going to succeed at that in the next 10 years.
Space travel comes down the cost of moving mass around. We need orders of magnitude cheaper costs of getting stuff into orbit and then moving stuff out of Earth orbit and then into Mars orbit.
Robert Zubrin (Entering Space/ The Case for Mars) discusses this extensively in his two books. Very interesting.
He proposes sending 6 tonnes hydrogen and making the fuel for the return trip from the hydrogen and the CO2 in the Martian atmosphere. He proposes sending a small nuclear reactor to power the reaction. There is also a lot of water at the poles, or they could make it as a by-product of making the return trip fuel so the people wouldn't need to bring water. Which will also cut down a lot on the cost.
I don't see it mentioned in the article you linked to, but Musk stipulated the time frame for this prediction was "30 to 50 years." If we can get a moderately vigorous space industry started in the near future (which is what Musk is personally trying to do), then that should give plenty of time for the infrastructure to be in place to support this level of cost. Especially if nanotech/robotics/AI come together to spur the growth in technology and general wealth that many predict -- without destroying Humanity in the process, that is.
He specifically talks about having fuel and other basic resources available on Mars itself.
Your headline is incorrect.
He said a million dollars for half a round-trip.
That is possible, even advisable.
Also, the $1000/lb to orbit is a short-term, not a long-term, goal for Space X. Musk has already mentioned the possibility of $10/lb or less (essentially fuel costs only) if launch vehicles could offer similar re-usability as airliners. Space X rocket engines are designed for multiple use cycles, and their recent simulations suggest rocket-powered landings are possible for lower stages. The Paul Allen/Burt Rutan Stratolaunch venture with Space X should be seen in this light: by being able to fly to a arbitrary launch location, it makes it possible to easily recover the first stage at a convenient spot down range.
Going by the international space station's performance, at least 3 kilograms of supplies would be needed per person per day. But technically it doesn't need to be that much. A person would need roughly .4 kg dry weight of food a day and a roughy similar amount of oxygen. Rather than using liquid oxygen, water would probably be used instead as it is easier to handle and can be electrolysised into oxygen and hydrogen. The hydrogen could then be combined with CO2 to create water and methane. The methane would be dumped and the water drunk. Most water use could be recycled. The international space station isn't at the level of water recycling where they can do without water resupply, but they do pretty well. Activated charcoal or other filters would be required to stop the crew farting themselves to death. So with food, oxygen, filters, and maybe a little water, a person would need about a kilogram of supplies a day. This would be a bare minimum. A Hoffman minimum energy transfer orbit trip to mars and back takes about 970 days, so at least a tonne of supplies would be needed per person.
On a longer trip people end up needing devices for medical care and other purposes that do not figure into a shorter trip. One has to take lots of stuff along that one might not need because one can't predict which devices, drugs, etc will be needed.
Some drugs and medical equipment would be taken, but not every contingincy can be planned for. After a point it would become cheaper to simply let astronauts run the risk of dying and if necessary run multiple missions until one meets with success. Judging from Mir and other missions, if initially healthy people are sent, it seems likely that there is a good chance a mars mission could get away with a first aid kit, kidney stone medication, some antibiotics, pain killers, valium, and cyanide capsules. Depending on the value put on astronaut lives, it might be better to have a shorter, faster mission, rather than a longer, cheaper, 970 day mission. The long slow return journey after 14 months of one third earth gravity on mars is something even Russian cosmonauts haven't had experience with.
In general, putting something on an escape trajectory requires about 10 times the money to put it into orbit.
I believe I know where Elon got his number.
First and foremost, he assumes he can make his vehicles reusable, as his grasshopper project is the first step in that. He has noted that he expects that with very high volume, combined with re-usability for the Falcon series rockets, he can drop his costs by 2 orders of magnitude. That is $10/ lb. to LEO. That would mean about $100/lb. to escape velocity. Remember that Elon wants to settle Mars, not just take a tourist trip. So, he's assuming settlement,with its high numbers of settlers, and reusability.
$100/lb. divided into $500,000 gives us 5,000 pounds for each individual headed to the Mars settlements. That isn't too bad an estimate, when you consider the things that can be done to recycle air and water condensed from the cabin air. Urine and other water losses would have to be electrolyzed and recombined as pure water, because of the problem with ammonia removal by lesser means. The great majority of water loss is through the breath and perspiration into the atmosphere of the cabin, however.
The surface mass of a habitat goes up with the square of the radius. The volume goes up with the cube of the radius. The Ba 330, has a 6-man crew, IIRC, and a 20 tons mass, IIRC. With the Falcon Heavy with Raptor lifting 50 tons, and reusable that is an inflatable cruise habitat for 15 people with the same volume/ person as BA 330. The first trip to Mars costs more, but when you stop in LMO and load propellant for the trip home, later crews get to reuse the vehicle. Expended are 2 Dragon Capsules, in landing. That's 20 tons. So. The mass for the settler landers is 20 tons, which stays on Mars with them to provide transport. That's 1.333 tons of the 5,000 lbs., or 2,666 pounds. That leaves 2,333 lbs. for the settler, his unrecycled food, and all equipment he brings. Better bring a light additive manufacturing module, to make stuff for staying in the settlement. That's at least 200lbs., even with 10 years more development. So, you are left with just about 2,000 lbs. of food, for a 180 day (non-Hohman Transfer) journey. If it's reconstituted with onboard recycled water, that should be more than enough. Any excess to food needs can be mass devoted to more equipment for making Mars into home.
All on $500,000, given Elon's assumptions.