I've long been a believer in Orbital Colonies, huge habitats (initially) in Earth Orbit with tens of thousands of inhabitants, in very Earth-like settlements spinning for 1.0 gravity.
But Science Fiction (whether written or watched) has overwhelmingly assumed that we will find Earth-like worlds around many (perhaps most) Sol-like suns. Astronomers have not helped to clarify that vision, describing "habitable zones" that allow liquid water somewhere on the surface of a planet, somewhere allowing stable orbits, and somehow allowing Earth-like atmospheric pressures and potentially oxygen/nitrogen atmospheres. Personally I would prefer temperatures closer to freezing than to boiling. I also prefer gravity near Earth's 1.0G (not half, certainly not double). I also prefer a fairly wet planet, like the Earth (70% ocean), and not a water world or a dry desert pole-to-pole. Hey, beaches are nice, but water is a necessity! And seasons are nice, and a day length of anywhere near 24 hours would be great. Not tidally locked to its sun (infinite day length), and not spinning like a top, but actually we could live with that.
Note that first of the two planets in our Solar System closest to the Earth is Venus (97% gravity, a day that is 117 Earth-days long, with 92 times the air pressure at 867 °F, not exactly a pleasant spring day on Earth. Did I mention that the atmosphere is composed of 96.5% CO2?).
And the other planet is, of course, Mars, which has 38% of Earth gravity, only 1% of the Earth's air pressure, also almost entirely consisting of CO2. In Mars' favor, however, is its day length of 26 hours, and its surface temperature which ranges from −243 to 68 °F. Shirt sleeve weather on a good day! It's 1.4au from the Sun, which means that we'll need twice the area of solar panels to generate the same electrical power as on Earth. There is so little atmosphere that radiation and meteorite impacts are serious problems, and we can't venture "outdoors" without serious pressure and oxygen support, suggesting that we live underground instead of in the pretty surface cities depicted in so much literature.
The Mars of Edgar Rice Burroughs was always a fantasy.
But Mars has long fascinated space hopefuls: it's visible, it's reachable, and it has climate and weather (the icy poles switch from north to south and back by the seasons, and there are planet-wide dust storms that are visible in telescopes on Earth). One of those fascinated by Mars is Elon Musk, and he brings thousands of fellow Mars colony enthusiasts, not to mention a Starship big enough to move a serious mass of people and supplies from here to there and back, at a small fraction of the price charged by "Big Space".
A lot of people DO believe in moving humanity to additional planets, and Mars is the easiest planet to reach from Earth. So Mars is first! Elon Musk founded SpaceX largely with people who believe in Mars as a potential habitat for Humanity.
Here are a few thoughts about placing a colony on Mars. I'll be expounding of several of these in future posts.
The current version of the
SpaceX Starship / Superheavy consists of a 1st stage (booster) that
is 9 meters (30 feet) in diameter and stands 71 m (233 ft) tall. It is powered
by 33 Raptor 2 engines that burn CH4 and LOX. The 2nd stage
(Starship) is also 9m (30 ft) in diameter, 52 m (171 ft) tall, and powered by 6
Raptor 2 engines. Note that the Starship is designed to be refueled in orbit,
so it can be launched with a full 100 or 150 (or eventually 200) Mg (Megagrams,
or Metric Tons) of payload, and refueling in orbit (via a tanker version of
Starship) allows it to carry a full payload all the way to Mars. The payload
bay is the inside of the 9 m stainless steel tube, which tapers down to nothing
at the top. The full-width portion of the payload bay is about 11 m tall.
All-in-all, there is over 1100 cubic meters of payload space, which is
comparable to the entire ISS (International Space Station). And the next (Block
3) version of both Starship and Superheavy are a bit larger.
For my purposes, the key points are:
- Mars
transfer launches occur in ~month-long windows that occur every ~26
months. The average transit time is about 3.5 months (assuming aerobraking at Mars), less with more fuel
(or less payload), longer with more payload (or less fuel).
- You
must carry enough supplies to get to Mars, and live there until you can
grow your own food, etc., OR receive resupply. Since you might NOT successfully grow
your food, the smart thing is to take at least 30 months of supplies! Note
that “supplies” include everything not available on Mars, including
computers, LEDs, PDAs, lubricants, electrical components, solar panels,
batteries, TOILET PAPER (and every other kind of paper), plus all of the
nutrients needed to grow the next generation of crops (like nitrogen, phosphorus, potassium, calcium, magnesium, & sulfur, plus a smattering of micronutrients). Look
around you: How much of your environment consists of plant products (wood
and paper), or petroleum products (mostly plastics of many types)? Don’t
forget fabrics!
- SpaceX
is planning to send a few Starships to Mars (carrying supplies but no
colonists) during the next window (late 2026) proving that Starship can
make it that far and successfully land. Hopefully with all of the ships landing within walking distance of each other.
- Another
goal is to produce CH4 and LOX on Mars, to have return fuel ready for use.
- Starships
carrying colonists would depart during the following window, very early 2029,
in a fleet of multiple Starships, most of which would carry only equipment
and supplies.
- The
first colonists would likely live on the Starships for several months as
they build a place to live, and the farms to sustain them.
- I think the ideal solution is to fill each Starship with standardized modules,
and live in some of them while others are unloaded. Eventually, all would
be unloaded.
- Each
module would be a cube 2.75 meters (9 feet) on a side. They might be
configured as tanks (water?), supply rooms, plant grow rooms, or simply
rooms for living and working. Note they can be pre-configured, possibly
(for example), as greenhouses already recycling CO2 and H2O into food and
oxygen, things we’ll need both during the journey and on Mars. But note
that we only need 25% of the greenhouse space to recycle CO2 into O2 as we
would need to produce food to eat (it makes sense to have a fraction of the
greenhouse space during the transit and early Mars habitation).
- Recycling: per NASA, each day the average colonist consumes 0.835 kg of O2, 0.617 kg dry food,
and 3.909 kg of H2O, while producing 0.998 kg of CO2, 0.109 kg of dry
waste, and 4.254 kg of waste water. The water clearly needs to be
recycled, and the CO2/O2 as well. Dry waste contains vital nutrients that are
needed to grow more food! There are also many minor chemicals that must be
dealt with, such as ammonia, methane, and other gases produced by sweating
and breathing and farting. Note that, on average, we eat about 25% of the
plants that we grow. For example, we eat corn, but not the husks, cobs,
stems, leaves, or roots. We eat tomatoes, but all those leaves and stems
are poisonous to us. This means that the CO2 we exhale is only sufficient
to grow about 25% of the next crop! We need to turn ALL of that crop waste into CO2,
water, and minerals, perhaps by digging it up and burning it. Or we could
dig it up and feed it to fish, chickens, rabbits, and goats. Maybe some
fungi, or some worms. There are many forms of burning, only one is really
fast. Composting is really slow. Did I mention that the total dry food above does
NOT include crop, food prep, or plate waste? So we really need 10%-40%
more than the dry totals above (0.617 kg/colonist/day), plus even more if we save part of our crops for a rainy day...
- SpaceX
plans to have a crane on each Starship (heading to Mars) that will be used
to ferry colonists and supplies (I think whole modules) to the surface.
Plans include a huge cargo door, but I’ve never seen plans for Starship
that include air locks (which I’m sure will be a requirement).
- Unlike
the pretty SpaceX depictions of cities on Mars, the lack of atmosphere and
magnetosphere mean that meteorites and radiation are serious long-term
problems: we will need to live (and work, and conduct agriculture)
underground. So, imagine laying out the modules, stacking as appropriate,
then covering them with two or three meters of dirt!
My questions:
- What is
the optimal number of colonists per Starship? 8? 16? SpaceX says that a
Starship can carry 100+ passengers, but that is for Earth-to-Earth
missions like a commercial aircraft.
- What
fraction of the needed supplies (including O2, H2O, & food) should we
recycle during the journey to Mars, and during our early months ON Mars.
Note it will take a while to build infrastructure (such as solar panels to
gather energy), and then it will take about 4 months to grow a crop (which
we can repeat every 4 months). At least while growing the crop we’ll have
all the O2 we can handle (actually, more, about 3 times more!). Do we take
the water we need, or just (thoughts and prayers) hope we can quickly find
and access underground water? How long does that take?? At least CO2 is plentiful on Mars.
- Until we have a complete ecosystem on Mars, we'll need more CO2 & fertilizers & water than we'll produce (from consuming foods), and we'll produce more O2 and wastes than we can use. We'll need a LOT of water to grow crops, even with perfect recycling, because every kg of plant matter stores about 3kg of water, so by the time you've grown enough crops to feed a colonist for 4 months, you have stored over a metric ton of water in the plants (NASA estimates minimum biomass at 1.5 Mg/colonist).
- Initially, we'll likely grow our foods in hydroponic / aeroponic systems similar to the vertical farming units now growing fresh vegetables near you (aka "container farms"). These work great for veggies (lettuce, spinach, etc..) but less well for fruiting crops (tomatoes, peppers, squashes, beans) or underground crops (onions, potatoes, carrots, garlic). But they do work. They don't work all that well for cereals (wheat, rice, corn, cane) and our normal diets depend on them for the majority of our calories! Research is needed: I can't imagine life without breads, pasta, rice, and corn products even excluding HFCS! Of course, I can't imagine life without milk, cheese, bacon, beef, and more. NASA funded several studies on the minimum crops needed for full nutrition, most of which returned a list of 15-20 crops, and when I did my own list the minimum was more like 50 crops, and I could easily justify 100+ once you include variants like bell peppers, poblano peppers, jalapeno peppers, cayenne peppers, etc.. Just the spices alone are scary.
- We need a great deal of redundancy in our Mars farms! At least triply redundant (let's grow crops in at least three widely separated areas, not connected via water or direct air supplies so that pests or molds or viruses don't kill everything at once), plus we'll need different growing conditions in any case, as some crops like it hot, others like it cold, some like it dry, some like it wet, and of course some like it "just right". There are a lot of other variations such as length of day, or necessary changes in nutrients to induce blooming, stuff like that. Plus, we don't want all of the crops harvesting at once, we'd like to spread it out to simplify the labor and processing involved, and minimize storage. Note that "greens" can often be grown very quickly, even planting-to-harvest in as little as a month, using optimal conditions including 24-hour lighting. Yes, we'll be using LEDs to light our crops. (see https://ramblingsonthefutureofhumanity.blogspot.com/2009/11/lighting-our-space-habitats.html).
- What
should our infrastructure (modules, shelves, tanks, etc.) be made out of?
Starships are made from stainless steel, but that is heavy. I would
suggest using UHMWPE (Ultra-High Molecular Weight Poly-Ethylene) since it
is stronger than most steel, and is lighter than water. Steel has a
density of 7.8 Mg/M^3, while UHMWPE has a density of 0.97. The strength of
steel varies from 300 MPa (Mega Pascals) to 2000 MPa, while UHMWPE has a
strength of perhaps 3,000 MPa. It’s thus 10 times stronger and 8 times lighter,
meaning 1 kg of UHMWPE is as strong as 80 kg of common steel! Plus, it is used as
armor on Earth, as the strongest mooring lines for container ships, and is
an excellent radiation shield! The only downsides are that it softens at
boiling water temperatures, is flammable, and is really hard to glue, cut
(machine), or paint.
- What is
the fraction of people Starships or supplies only Starships? Elon only says that more Starships will be carrying equipment and supplies than colonists.
- The Sun
only produces about half the energy at Mars compared to at Earth. So you
need twice as many solar panels, and you can’t use wind or hydro or fossil
fuels for energy. Also, the sun doesn’t shine at night or during dust
storms! So we need batteries, a lot of them. Should we take modular
nuclear generators? After all, those rare planet-wide dust storms can last for months!
- We will need pollinators on Mars from the get-go. Honeybees require large colonies (25,000 to 100,000 bees), and about 1 sf of wildflower per bee (and you do get honey!). Bumblebees are happy in colonies of 50-100 individuals, so they can pollinate much smaller greenhouses. But they don’t make honey.
- How soon should we introduce fish / fowl / mammal meats? What about
shrimp? Are goats adequate for meat and milk and cheese?? It might be
easier to start vegetarian, but it takes about 30% more planting area for a vegetarian
diet (since we have to find a way - other than eating - to recycle all of the uneaten
portions of the crops).
- Should we allow pregnancies? After all, with only 38% of Earth's gravity, we don't know if human children can thrive, and we suspect children raised in such low gravity will never have the strength of muscles and bones to be able to visit the Earth.
- How
soon can we allow pregnancies? Note you have an “outpost”, not a “colony”,
if there are no children. Should we only allow colonist who are young,
fertile, and married?? Define “young”, and define “married”. We WILL need
a growing population to become a self-sufficient industrial civilization
before the Earth stops being able to ship supplies to Mars.
- Can we
live without gravity for the journey? Note it takes a lot of exercise (2+
hours per day) to mitigate the worst of the zero-gravity side effects.
NASA targets 2,800 kcal/person/day with the needed exercise, versus 2,000
for a normal person. We can get gravity by tethering two ships
nose-to-nose and spinning them end-over-end. Complicates course changes
and telecom, and raises the question of can we do entirely without zero-G
toilets and showers? Note, too, that gravity greatly improves the ability
to keep the air clean and messes controlled. The ISS demonstrates many of the problems with trying to live in a zero gravity environment (try Googling ISS clothing, bathing, personal hygiene including zero gravity toilets, etc., and don't forget the odors).
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