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), has to 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:
- 1. Putting the ship in Earth orbit
- 2. Escaping Earth orbit
- 3. Inserting onto a Mars transfer orbit, capturing Mars orbit and landing on Mars using retropropulsion
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:
- B1 would send (B1 + HAB) into Earth orbit, then would get released and land back on Earth straight away to be reused several times per window of opportunity (they open every 2 years as we've said)
- B2 would help the HAB escape Earth orbit, would be released just short of it, and would land back on Earth right after, also tobe reused
- the HAB would leave alone to Mars, would land on it, and could be sent back to Earth without any need for a booster there (Mars gravity is weaker, and its atmosphere much thinner)
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:
- a booster B2 that can be used up to 5 times per window of opportunity (considering that each window of opportunity lasts around 5 weeks and that a successful launch and escape from Earth orbit takes one week), that is 10 times every 4 years (as there's one opportunity every 2 years), against 1 every 4 years for ship S in charge of the same phase 2. That is, the part of thedry mass designed for phase 2 of the Earth-Mars journey will be used 10 times more often per 4-year period in one case (B2) than in the other (S). Ten times more, that's an order magnitude more, no small potato!
- a HAB that would be used once every 4 years at most, just like S, but which would be significantly smaller, and hence cheaper, than S, because it wouldn't have to handle phase 2, only phase 3.
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:
- there will be a great need for housing space on Mars where to host the colonists, right ?
- even if colonists should have the option to come back to Mother Earth (unlike with the not-so-serious Mars One initiative), many less people would want to claim their return ticket than go there in the first place, or else we don't really have colonizationhappening
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:
- an EMV for Earth-Mars Vehicle
- and an ERV for Earth Return Vehicle
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:
- 1. It would increase dramatically the risk of forward contamination of the Mars surface with our earthly microbes, that would ruin our unique chance to study a pristine Mars
- 2. All the reasons advanced to vindicate Humans to Mars are either wrong or can be addressed in a way that sparesMars
Here is the rational :
- If Humans go to Mars, they'll have no other choice but to bring with them their microbes, it's inevitable as for a start there are more microbes in our body than even body cells! And we're not even counting microbes in the air we'll breathe in the ship andMars base.
- These microbes are bound to find their way to the Mars surface at some point, whether it be after a crash (close to two thirds of the 40+ missions to Mars failed to this day), or because of air leaks from the hab's airlock or from the spacesuits which are designed to leak some air at the joints to facilitate movement.
- Some of our microbes will be able to resist for quite some time the harsh Martian environment, at least as spores. We call them extremophiles. Chroococcidiopsis for instance is a microbe that can withstand huge temperature swings as well as prolonged ionizing radiations.
- We cannot rule out to this day the existence of habitats where life can metabolize on the Mars surface. And I do mean surface : many ideas of such surface habitats have been suggested (salty seeps, melt water under clear polar ice, ice fumaroles, dune bioreactors among others).
- Mars is a connected environment as it has an atmosphere, even if very thin, and is swept by large dust storms spreading across the whole planet. No matter where Earth microbes would be released, they would reach potentiel habitats in a matter ofyears, decades at most. The iron oxide found in the dust would actually protect microbes from cosmic rays and UVs. Once in these habitats, if they exist, they could start again to metabolize and grow. It's been demonstrated that some cyanobacteria, when put in a chamber simulating Mars surface conditions (same air, temperature, pressure, UV, etc.) and partially in theshade, have been able to show measurable activity and carry out photosynthesis, absorbing humidity from the atmosphere (relative humidity reaches 100% at night on Mars). Lichens, which are multicellular lifeforms, did the trick as well !
- Our microbes could possibly then share genes with some potential Mars life (if they share a common ancestors), that would completely confuse our search. Their amino acids would get mixed up with current Mars life (if any), remains of past Mars life (if life ever arose there) or any prebiotic chemistry on its way to life. That would again confuse our very sensitive devices and ruinthe whole study.
- We cannot rule out a common ancestor for Earth life and possible present or past Mars life. Life could have originated on Earthand contaminated Mars through panspermia, or the other way around (as Mars had a liquid ocean before Earth did), or maybe life came from elsewhere and contaminated both planets. In such a scenario, any Mars life would probably be our Archaebacteria's cousin. The issue is we have only identified, let alone DNA-sequenced, a very limited share of the Earth microbial world. Some microbiologists say there are probably thousands of billions of microbe species on Earth, 99,999% ofwhich have not been identified! Only 10 million species have been documented out of at least one thousand billions, out ofwhich 100,000 have been DNA-sequenced, that's 0,00001% of the total ! And even less, that is, 10,000, have been grown in Petri dishes. So in case of a mix up with Earth and any potential Mars life, how are we supposed to tell one from another? Whyagain take such a huge risk to confuse the study?
- Last, we cannot rule out either that our microbes will threaten potential Mars life, or its remains, whether directly or indirectly, by accident. It doesn't need to have co-evolved with it to be harm it. See the Legionnaires' disease, caused by a microbe that evolved to feed on the Ameba, a unicellular organism, but which happens to be able to target our white blood cells by coincidence and hence infect humans. Or Earth life could simply end up eating Mars life's food and starve it indirectly forinstance. Any such harm would make the study of Mars (which had liquid oceans for a billion years!) much harder if not impossible, Mars would never be the same again. It would be an irreversible move, best to extensively debate it before it is too late.
There are 2 classical objections raised by Humans-to-Mars enthusiasts:
- 1. We already sent our microbes to Mars on the back of our rovers, so harm has already been done, it's too late, no need toworry about it any more
- 2. Mars gets a lot of meteorites from Earth, and it's possible that microbes could survive such a trip aboard a meteorite, so again any harm that could be done with Earth life has been done, so no need to fuss about that threat any more
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:
- It will speed up our search for Mars life as humans will be more efficient than robots only, it will more than compensate for the microbes we'll bring with us.
- That's highly dubious, as robots actually let us do more using less money. Small robots can go to remote corners clumsyhumans in spacesuits will never be able to. Robots will only get better and more autonomous thanks to AI. And we could also think of having people in the orbit of Mars tele-operating robots in real time on the surface, this NASA study says such a mission with six crew members in Mars orbit could achieve the same exploratory and scientific return as three conventional crewed missions to the Mars surface.
- It will be an engineering challenge that will capture the world's imagination and generate a new wave of scientists, engineers and inventions we'll all benefit from.
- Not convincing as there are so many other technical challenges we could, and have, set ourselves, like putting an end to climate change, to hunger. Or what about building a base on the Moon, or a space orbital colony?
- To start a new civilization shaped by pragmatism and ingenuity, and that will reinvigorate our current earthly one.
- One may argue that given the harsh realities of Mars, for a long time life there will be closer to the military style found in submarines than to what we could think of in a libertarian utopia. In any case, such a goal would well be achieved at much lesser costs here on Earth, and on our oceans to be more accurate, thanks to seasteaders!
- To ensure our species' survival. We are supposedly threatened by life extinction events, man-made or not, such as a huge asteroid impact, a thermonuclear war, super volcanoes, a gamma ray burst, super solar storms, a black hole, a collision with a rogue star or planet, a supernova, an AI catastrophe or a pandemic. Hence we need to become a multi-planetary species as soon as possible. This is of course Elon Musk's and Stephen Hawking's thesis
- On close inspection, either these rare events would also annihilate any Mars settlement at the same time as Earth life, or they wouldn't be life extinction events to start with. Meaning once event is over, there would be survivors, the Earth would remain the most habitable zone in the solar system for humans, and people the best positioned to repopulate it would be these survivors, and not far away Mars colonists. To read more detailed rebuttals, please check these articles : WhyResilient Humans Would Survive Giant Asteroid Impact - Even With Over 90% Of Species Extinct and Could Anything Make Humans Extinct In The Near Future?
- Beause it would be fun, the most exciting adventure to watch ever. Remember how the Moon landing got watched by 600 million people? That's the other reason to go for Elon Musk, after all "it's important to have a future that is inspiring andappealing. I just think there has to be reasons that you get up in the morning and you want to live" as he puts it.
- That would probably be the most stupid reason to jeopardize our unique chance to study a pristine Mars. And for therecord, moon landings were quickly forgotten, didn't even make the headlines for the last ones. So those who want to seehumans land on Mars so as to witness history are probably the ones that will get bored the fastest after some time. Would be a pity to make such an irreversible move just for that one-time adrenaline rush, wouldn't it?