Why even the new version of Elon Musk's Big F* Rocket is suboptimal for Mars colonization
Elon Musk recently revealed the slimmer version of his Big F* Rocket, down to 106m high, 9m of diameter and 31 Raptor engines from 122m high, 12m of diameter and 42 Raptor engines.
Beyond that reduction in size, little of the architecture itself has changed, there still are 2 stages: the booster and the ship.
The booster is tasked with taking the ship to Earth orbit before being released and landing back to the ground to be reused. Once refilled with propellant while in orbit, the ship, which has its own engines (4 Raptor ones and 2 sea-levels smaller swiveling ones), hasto reach escape velocity and exit Earth gravity well to insert itself onto a transfer orbit to Mars, once there capture Mars orbit, and at last land onto the surface of the Red Planet, using first aerocapture (slowing down thanks to the resistance of the Mars atmosphere)and then retropropulsion for the finish. Once on Mars, before it can be reused, the ship needs to get refilled with fuel (methane) andcombustive (O2) that will have to be produced there through what is called "in situ resource utilization" (or ISRU in brief). Technically, frozen water H2O found in the permafrost will be broken down into O2 and H2 through electrolysis powered by electricity produced by solar panels, while CO2 from the atmosphere will be reacted with H2 to produce methane (CH4) through the Sabatier reaction.
Now to understand what's wrong, or say, not optimal, with that architecture, we need to detail the different steps and requirements of a trip to Mars undertaken with colonization in mind.
When it comes to the energy needs, we can basically identify 3 main phases:
The first 2 phases are actually the most energy-consuming. And for both 2016 and 2017 BFR versions, the architecture is the same:the booster is tasked with phase 1, but the ship on its own has to handle phases 2 and 3.
That's precisely where the design flaw lies. The ship Elon Musk says is best optimized to go to Mars also has to take care of phase 2. Meaning a part of the dry mass of the ship (i.e. excluding fuel, combustive, cargo, passengers) will be taken all the way to Mars while it's only needed to escape Earth orbit. What a waste!
With the 2017 BFR system, the ship is only used once every 4 years for an Earth-to-Mars trip. Indeed, say the ship leaves in 2024, it will get there 6 months later, and will have to wait for another 1 year and 6 months until the next window of opportunity in 2026 to go back to Earth. It would then reach Earth 6 months later, that is 2 years and 6 months after it left, and would hence have missed by 6 months the 2026 window of opportunity to go to Mars trip (which roughly opens for 5 weeks every 2 years). It would then have to waitfor another 1 year and 6 month until 2028 before it can be reused to go to Mars again, that is precisely 4 years after it left Earth theprevious time.
But why have only one booster (B) and such a ship (S)?
One of the suggestions made by Robert Zubrin, engineer and president of the Mars Society, is that there should be 2 boosters (let's call them B1 and B2) and one hab (HAB) with its own propulsion system. Such a HAB would be much smaller than Elon Musk's 2017 ship (S).
With such an architecture B1 + B2 + HAB:
What's radically new with this system is that instead of the 2017 BFR ship S that is only used once every 4 years, we get:
Now I guess it's more obvious why even the 2017 version of the BFR isn't optimal!
But we could go even further with the criticism.
As Elon Musk is clear about his colonization intent, it's safe to assume that:
These assumptions lead us to realize yet another wasted opportunity: why send the entire ship S all the way back to Earth? Or eventhe whole HAB in our latest suggestion above?
Efficiency-wise, with colonization in mind, Elon Musk should fragment further his architecture, and split the HAB in 2 parts:
So the HAB would become EMV + ERV. EMV + ERV would make the whole trip from Earth to Mars and then land on Mars. EMV would then stay on Mars and be used by colonists as a habitat for the Mars base. And only the ERV, equipped with its own propulsion system,and featuring a much smaller habitat big enough for maybe 10 people, should be designed to make the trip back to Earth for those unimpressed by the red emptiness.
So we go from B + S where S is used once every 4 years for the Earth-Mars trip…
...to B1 + B2 + EMV + ERV where B2 is used 10 times per 4-year period, and EMV is recycled as a hab by the colonists.
Come on Elon, you still have time to update your plans before rushing with production!
Why we shouldn't send humans to Mars anyway
Question isn't really "Can we technically send Humans to Mars?", sooner or later we'll be able to, most likely thanks to Elon Musk'shard work, but, "Is it desirable? Shall we go?"
And I believe that the answer is no we shall not!
And this for 2 main reasons:
Here is the rational :
There are 2 classical objections raised by Humans-to-Mars enthusiasts:
These appealing objections do not resist close scrutiny. To read detailed rebuttals, you can read these articles Have we contaminatedMars already? and Does Earth Share Microbes With Mars Via Meteorites - Or Are They Interestingly Different For Life?
Others would recognize these risks, but then argue that they are worth taking in the light of what stands to be gained from sendingHumans to Mars.
Five mains reasons are put forward:
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