In preparation for this week’s progress report on Starship development, SpaceX’s fully-reusable spaceship, company CEO Elon Musk tweeted out “Starship Animation,” a video depicting a Starship flight to Mars. He then responded to his own tweet, “This will be real in our lifetime.” Indeed, SpaceX has plans to send the first humans to Mars sometime in the 2020s, establishing a city on Mars by 2050.

That would be wonderful, of course. But how realistic is it?

While strongly supporting an eventual manned mission to Mars, former International Space Station Commander Chris Hadfield doesn’t think it happens anytime soon. He explained to New Scientist magazine:

“It’s as if you and I were in Paris, paddling around in the Seine in little canoes saying, ‘We’ve got boats, we’ve got paddles, let’s go to Australia!’ Australia? We can barely cross the English Channel. We’re sort of in that boat in space exploration right now. A journey to Mars is conceivable, but it’s still a lot further away than most people think…I think ultimately we’ll be living on the moon for a generation before we get to Mars.”

Hadfield believes that, with current technology, the trip is simply too long—about 300 million miles, over 1,200 times further than the Apollo spacecraft traveled to get to the moon—for astronauts to get there safely. Apollo 17 (1972) currently holds the record for the longest manned mission away from Earth orbit: 12 days, 14 hours. A round trip to Mars requires 1,016 days (~34 months), making its duration over 83-times longer than that of Apollo 17. Food supplies and electrical power requirements for such a Mars voyage would be huge. 

Our guest on The Other Side of the Story this coming weekend, mathematician and space exploration expert Donald E. Pauly, agrees. He breaks down some of the challenges we must overcome first before a manned Mars mission is even remotely feasible.

Pauly gives credit where it is due. As seen in the illustration below, Musk has successfully reduced the cost of spaceflight by 5 to 1 by reusing the first stage of his Falcon 9 rockets. His latest design for a methane-powered Super Heavy booster with a Starship mounted on top can also reuse the second stage. The Starship/heavy booster combination is significantly heavier than the Saturn V rocket, which put 12 men on the moon and maybe the largest practical rocket design. This combination shows the promise of another 10 to 1 reduction in cost. 

Starship is designed to enter the atmosphere of either Earth or Mars by using steerable flaps and thermal tiles to keep the rocket’s skin from burning up. Its control flaps allow it to orient itself sideways for maximum drag during atmospheric entry. The atmosphere of Mars is thick enough to burn up unprotected spacecraft but too thin for everything else, including parachutes. Provisions for operation in an atmosphere and the required streamlining both add a good deal of weight and cost. These are unnecessary for freighters cruising long distances in a vacuum.

Pauly has spent some time mathematically and chemically trying to figure out just how we can get to Mars with humans staying on the red planet for a period of time. We can’t prove everything you are about to read is precisely correct, but we think it is a reasonably well-thought-out scenario. We conclude from this study, just as Col. Hadfield maintains…

Humans will get to Mars and survive, but not anytime soon. Please read on.

While Starship can be used to travel to Mars, current programs have little chance of success. For example, if Starship is refueled in Low Earth Orbit (LEO), it could perform a successful landing on Mars. But it would not have enough fuel to leave the planet and could barely escape to Low Mars Orbit. It also cannot carry much freight. Musk has proposed using solar power to manufacture rocket fuel on Mars. Solar cells are nearly worthless on Earth, and the Sun is 2.5 times dimmer on Mars. Therefore, it will take 500 tonnes of solar cells to manufacture enough rocket fuel to fill up a starship. It will also take nearly six months to do the job. About 50 tons of lithium batteries would also be needed to provide power at night. These batteries would be difficult to keep warm during cold Martian nights and winters. The average temperature at the equator on Mars is -63 ° C. A nuclear reactor making the same amount of power will weigh 20 times less, and so is a far more sensible option than solar. Indeed, nuclear power must be available to power spacecraft and for the propellant plants. 

Further, after an eight-month trip to Mars, a Starship will have to wait on the planet for another 540 days for a favorable alignment of the orbits of Earth and Mars to return home even with refueling. The crew will do exploration and construction work on Mars during that wait.

Phobos, a football-shaped moon of Mars, is only 27 x 22 x 18 km in size with no atmosphere. It is more hospitable to humans than the planet itself since it has such a low gravity. On Phobos, a single astronaut can easily lift equipment weighing hundreds of pounds on Earth. Phobos will be turned into a supply dump and plantation, a basecamp for operations before descending to Mars. It is possible that the organic material from the meteorites and the oxygen in the rocks on Phobos can be turned into rocket fuel. However, samples of that material must be first sent to Earth in order to design the chemical plant.

Mars is also a prime location for manufacturing rocket propellants. There is undoubtedly water ice on Mars, and its atmosphere is almost totally carbon dioxide (CO2). A chemical plant can be designed and tested on Earth that will require only electric power to make propellant from the materials on Mars. Pre-fabricated and later assembled on Mars, it must be close to a supply of water ice on the Martian surface. One Megawatt of power will make enough propellant to fill the rocket tanks in five months, with the propellant plant being installed on Mars on the first trip there by Starship. This must be followed by the installation of a differently designed propellant plant on Phobos if feasible. Its power needs would also be about 1 megawatt, all powered with nuclear reactors. 

A crew of four people will need 400 grams of food each per day throughout the almost 3-year mission. This is a total of 1.6 metric tonnes of food for the mission. The crew will generate waste of 5 metric tonnes of CO2 and 2 tonnes of water. The water is easy to recycle, but the CO2 is not. A small recycling plant must be on board to recycle the CO2 and recover the 3.6 tonnes of oxygen from the CO2. There will be perhaps an additional tonne of nitrogen-containing waste. Crop growing in artificially-lighted greenhouses on Phobos can recycle all this waste and turn it back into food. 

International Space Station flights have repeatedly shown that a few months in zero gravity makes astronauts too weak to walk when returning to Earth. Yet, it is essential that crew members arrive both on Mars and Earth and be fit to walk and work. Therefore, a centrifuge must be provided for the crew to exercise in the presence of artificial gravity. Spinning at one revolution every four seconds, an 8-meter-long centrifuge can fit inside the 9-meter diameter Starship, providing artificial gravity to a pair of astronauts at a time.

In part 2 of this article, we will explain the realistic plan proposed by Donald Pauly, our guest in this weekend’s radio show, The Other Side of the Story, to get to Mars.

References relevant to this topic:

– https://www.spacex.com/vehicles/starship
– https://www.teslarati.com/spacex-how-to-refuel-starships-in-space
– https://forum.nasaspaceflight.com/index.php?topic=48757.60
– https://en.wikipedia.org/wiki/Phobos_(moon)

Reuse cost
– https://www.thespacereview.com/article/2893/1

Masses
– https://space.skyrocket.de/doc_lau/super-heavy-starship.htm

Starship belly flop
– https://m.youtube.com/watch?v=BqJ5bKuApbs