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Elon Musk Unveils Concept of How SpaceX Will Take Humans to Mars
The Wire Science
The Wire Science

Elon Musk Unveils Concept of How SpaceX Will Take Humans to Mars

28/09/2016
Mars. Credit: SpaceX

Vasudevan Mukunth is the science editor at The Wire.

Musk estimated that between 20 and 50 trips to Mars would be necessary to set up the first full-fledged colony. This would take 40-100 years.

Mars. Credit: SpaceX
Mars. Credit: SpaceX

Elon Musk wants to get humans to Mars and make us an interplanetary species. He’s been saying this (maybe not in as many words) for almost a decade now, but the details of how he’s going to achieve that have only just been getting clearer. On September 27, at the ongoing International Astronautical Congress (IAC) in Guadalajara, Mexico, Musk uncovered the ‘Mars vehicle’, the transportation concept that will ferry humans from Earth to Mars to set up the first colonies from the early 2020s.

The vehicle will be built and operated by SpaceX, the private spaceflight company that Musk is the CEO and founder of. How it operates has to do with the economics of getting to Mars. Specifically, the economics of getting people to Mars at the “median cost of a house in the United States”. This is about $100,000 (Rs 66.5 lakh). SpaceX’s plan is to first carry 100 humans, and over 200 with more advancements. Musk had some ideas about how this could be done.

1. Using fully reusable spacecraft and boosters – SpaceX has already started reusing the first stage of some of its Falcon 9 rockets. In typical launches, the first stage separates from the rest of the rocket once the latter has been hefted to a particular height and falls back toward Earth, burning up in the atmosphere or crashing into the sea. However, SpaceX’s Falcon 9 first stage has been shown to be able to land upright using retrograde thrusters at a designated spot. More on this here.

2. Producing propellants on Mars – To allow vehicles to be reused and to allow humans on Mars to return to Earth easily (instead of having to ship propellant in a separate mission there; imagine how much simpler this would’ve made the plot of The Martian)

3. Using the right propellants – Which propellant is used determines the dimensions of the vehicle that will be powered by it. Musk currently has his eyes set on ‘deep-cryo methalox’, which is liquid methane and liquid oxygen, in a SpaceX Raptor engine. The Indian cryogenic engine CE 7.5, recently used onboard the GSLV F05 mission, uses cryogenic hydrogen and liquid oxygen as propellants. Methalox has four advantages over the hydrogen-oxygen combo.

  • Hydrogen has very low density, so meaningful quantities of it will occupy very large containers. Methane is about eight-times denser.
  • Methane is cheaper than hydrogen to source and procure
  • Methane is easier to produce on Mars than hydrogen is because the Martian soil contains water and the Martian atmosphere, large amounts of carbon dioxide. The two compounds can be combined in a Sabatier reactor to produce methane.
  • Loading cryogenic hydrogen into a propellant tank and then transporting it is a nightmare. Hydrogen leaks very easily and reacts violently with oxygen. In August 2013, the GSLV D5 mission was called off 74 minutes before launch because a propellant had leaked during the pre-pressurisation phase, which precedes the loading phase.

Apart from these, Musk also said that it is essential to be able to refuel while the spacecraft is in orbit. First, a two-stage rocket will liftoff from Launchpad 39A, currently under construction at the Kennedy Space Centre in Cape Canaveral, Florida. It will place the second stage – the Mars vehicle carrying humans – in orbit around Earth. The first stage, a booster, will return to Earth in 20 minutes to land upright on the launchpad from which it took off. It will then be fit with a propellant tank and sent back up.

The propellant tank will transfer its contents to the Mars vehicle in orbit and then return to Earth. According to Musk, three to five trips of the tanks will be needed to fully fill the vehicle. And once that’s done, the juiced-up Mars vehicle will set off to the red planet, assisted by two solar panels generating 100 W of power. Musk estimated the journey would take between three and five months. He also hoped that this would eventually be brought down to one month.

An animated video accompanying Musk’s presentation showed how all of this would play out.

(Notice how the video ends showing Mars turning green-blue and cloudy like Earth?)

According to Musk, “Not refilling in orbit would require a 3-stage vehicle at 5-10x the size and cost”. He added that, “combined with reusability, refilling makes performance shortfalls an incremental rather than exponential cost increase.”

Other measures to improve the Mars vehicle’s performance include using a tank made of carbon fibre. Carbon fibre, typically reinforced with a polymer, is renowned for being extremely strong and light at the same time. As a result, Musk projected that the Mars vehicle would be able to lift 550,000 kg to the low-Earth orbit. The GSLV Mk-III, due its first test flight in December, will be able to carry 5,000 kg to the same orbit. However, what is truly jaw-dropping is the rocket’s physicality itself. It will be 122 metres tall, 12 metres wide and weigh 10,500 tonnes at liftoff.

The Mars vehicle will be 49.5 metres tall and have a dry mass of 150 tonnes. It will cost $200 million to make.

Musk estimated that between 20 and 50 trips to Mars would be necessary to set up the first full-fledged colony. This would take 40-100 years, which is not bad at all given what’s being accomplished: interplanetary colonisation. The supplies to set things up will be sent on separate ‘cargo’ missions onboard SpaceX’s Red Dragon capsules.

Then again, Musk’s plans are still only barely better than fanciful because, despite the clarity SpaceX seems to have apropos the engineering, he hasn’t specified how humans will live in the Mars vehicle, or on Mars, for months at once. Nor did he mention how they would be protected from the harsh solar radiation on the journey to Mars. What he did mention is that there would be zero-gravity games to play on the way.

Other things Elon Musk said at the IAC

 

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