by Phil Baldock
Introduction
Have you ever seen a map from an epic fantasy novel? Actually, a real ancient map rarely disappoints in this field. They’re full of warnings of rough seas, rocks and monsters. They offer circuitous paths to distant and beautiful lands.
The real world is completely different, of course. It’s more accurate to picture it just as a series of economic zones, a network of millions of office and factory workers concocted to make it possible for you to have cancer inducing fast food delivered to your door minutes after an advert convinces you to want some. Wiser now, we can see the dragons and promised beautiful lands for what they really are: slightly differing languages and GDPs per capita, a handful of large animals not yet extinct outside of plexiglass prisons and oceans filled with varying densities of degrading plastic food containers.
So the story goes.
The modern world invites you to believe that the Universe is mechanistic and wonderless, that the deep beauty our ancestors saw in everything is fictional and childish. I’ve come to believe that modernity is not as limitless as it imagines itself to be, in time or space. Some of us might well escape it in future through various means, the one I discuss here being grandest of all: by travel amongst the stars. Pushed to define that new frontier the layperson of today grasps for the most boring model possible to describe it, having learned from experience in the mainstream education system the idea that the truth should be disappointing and unremarkable by definition: space is just a 3D empty volume in which things can move with rockets, you see. This misses the mark entirely. Interplanetary space is completely untamed in all the ways least like our world. It has its own unique rules and logic. Just like the deep forests of Earth, even today, one needs only move out from civilisation just a little and the spirit behind the maps our ancestors built becomes clear once more. Where do we start?
Well, for one thing…
1) Gravity is Everywhere
Much like the wind, the force due to gravity permeats everything in space. If you’re moving (and you’re always moving w.r.t. The Sun) and you don’t feel an acceleration this is because you’re moving in a natural and unforced path. You’re feeling a force downwards now because you can’t follow your natural path towards The Earth’s core: the floor is in the way. Thank goodness. As a natural consequence of this you can always tell when you’re doing work against gravity and when not, simply by the force you feel. Typically a journey through space consists of one brief acceleration, 5 minutes of intense rocket burn for example, followed by many months or even years of the ship feeling almost no external forces at all before another 5 minutes of intense acceleration when you get where you’re going. You can, in fact, float on the “currents” of the field produced by the combination of the various gravitationally significant objects at play across the Solar System in all manner of natural curves, often ellipses, taking you hundreds of millions of km in arching silence exactly until a force acts on you from some other source. Whether this force arises as the result of rocket work, solar sail pressure (however slight!), the plasma output from a proximate nuclear explosion, it doesn’t matter in the slightest: if you’re in freefall it’s because you’re following gravity’s baseline plan for you, if you’re not in freefall you’re escaping it in some way. This is a point zero because it’s critical for following everything else: space is not lacking gravity at all, it’s always there in the background.
2) Distance is Nothing: Delta V is Everything
The first big idea to get about realistic space travel is that something being close by does not automatically make it an easy place to reach. As an example, Mercury orbit is one of the most expensive places to reach from Earth. You have to get to Earth escape velocity, add another 3.6 km/s of rocket work to get you on an intercept course and then slow down for another 1.6 km/s just to barely get into orbit. It’s another 4 km/s to reach the surface. By contrast, getting to Saturn straight from Earth in one step (what’s called a Hohmann Transfer) is only about 4.2 km/s rocket work passed Earth escape velocity. Using HydroLOx and starting from Earth escape velocity one gets to Saturn for about 80% of the propellant needed just to barely get into an orbit around Mercury. If you want to circularise and then actually land on Mercury you discover that reaching Saturn naively from Earth escape takes easily 3 times less HydroLOx.
What’s my point?
Mercury is, at closest approach, about 50 million km away from Earth.
Saturn never gets closer than 1.35 billion km.
Why should Mercury be so much more difficult to reach than a planet more than a billion km distant from us? Quite unlike the Earth, space has no intrinsic drag associated with it. This means it is typical to be able to cruise with elegant ease for decades without drag from microscopic dust or sunlight robbing more than a few m/s from your spacecraft. As elsewhere in this list, when you go, whether your destination has an atmosphere or strong gravity well, the eccentricity and inclination of its orbit, what your destination has available to you for resupply when you get there, these are the questions that drive transport costs at scale. The issue that comes with distance is, often, travel times. Going by Hohmann transfer in both cases, getting to Mercury takes perhaps 3.5 months while getting to Saturn takes more like 6.5 years.
3) Violent Storms Without Wind
Aerobreaking aside, there are rarely incidences in space travel where one finds one’s craft effected in any meaningful way by aerodynamic forces. The pressure from sunlight reflecting off your hull amounts to very little: if the Empire State Building were to be a spaceship exposed to light on one side at Earth’s distance from the Sun under ideal conditions it would barely feel a light pressure equivalent to the weight of a strawberry across its whole form. The Solar wind is even less dramatic. Unless you go out of your way to capture the pressure of such things they can frequently be ignored. Similarly, the threat of a shower of micrometeorites is remote and easily avoided: sensors work much better without an atmosphere to distort and obfuscate their readings. A map of the Solar System that tracks such things would not be particularly interesting, at least outside of unique and special cases like Saturn’s rings. Don’t let this deceive you though: the map is real and critical, the weather reports as crucial to a journey’s planning as they are for crossing the Atlantic in the age of sail. Just because it’s not populated by wind and rough waves doesn’t make it trivial. The real danger in space is radiation. It comes from multiple sources, varying year by year in cosmic cycles whose rhythm you must carefully follow or risk disaster. The Sun, Earth, Jupiter, deep space, all contribute their sources or else reflect and distort radiation from a neighbouring one. Like the sea, circumstances can change in a matter of hours. Depending on their design (anything we’re likely to make this century) all living things aboard a ship whose survival is sufficiently desired will need to be moved at haste into shelter behind thick armour in anticipation of a Solar Proton Event or Coronal Mass Ejection. Jupiter’s radiation belts are particularly nasty, a permanent and angry maelstrom that the bravest or most desperate would chance should they desire the tremendous delta v possible using its immense gravity well creatively. Cosmic rays are the scurvy of deep space missions, a slow but eventually dangerous phenomenon requiring deliberate plans for a crew to survive a long journey in good condition.
4) Barnacles and Rust
Sea water is about 0.35% salt by mass, combining with its rich variety of living things and crack growth driven by swings in temperatures and turbulent wave stresses to make it immensely corrosive over time to historic ship designs. Clusters of molluscs attached to the hull must be periodically cleared in dry docks to prevent them degrading its material and causing unnecessary drag. Space travel of course has neither of these things, in fact it barely has any oscillatory forces at all comparable to waves. After the ten minutes of rocket work needed to initiate a typical mission a spacecraft might travel for over a year with no physical stresses at all besides interior cabin pressure (which doesn’t vary) until another 10 minutes of aerobreaking or rocket work to slow down at the destination. In some senses though maintenance problems can end up worse in space. How?
For one thing, vacuum is quite a special environment. Basically every material tends to want to boil away to some degree, characterised by what’s called its vapour pressure. Essentially, a material’s vapour pressure is a measure of its tendency to want to boil away: if the surrounding pressure from atmosphere is lower than this it will tend to spontaneously start boiling. The hotter something gets the higher the vapour pressure and so, in the famous case of water, it gets to 100 oC at sea level pressure on Earth and starts boiling away. In space, of course, Earth’s 101 KPa of pressure isn’t anywhere in sight: the pressure is very close to zero. As a result, even tiny vapour pressures from solid metals, for example, are sufficient to cause them to gently boil away (the word is sublimate when it’s straight from solid to gas) even at room temperature, heated perhaps by habitable volume behind them, sometimes condensing on nearby colder structures and coating them with thin layers that fundamentally change their properties. Uncoated magnesium alloys have been particularly bad for this in past use, sometimes breaking spacecraft by coating cameras and other equipment with thin but highly reflective layers that make them useless. All materials, however, and particularly metals and plastics, will tend to do this to some degree. The real problems are inside the ship. The combination of humans, complex networks of high technology and zero gravity for long periods of time has lead to serious difficulties in the past. The Space Station Mir, towards the end of its life, famously started to show abnormally high levels of dangerous bacteria and other micro-organisms in its interior atmosphere. Lifting up an access panel, a team of Cosmonauts sent to repair the station found a sphere of milky white watery pus around the size of a basketball hovering at a point spared from the local air currents. Evolving rapidly in their new environment and with a plethora of starting genetic codes among millions of different organisms sent adrift from every bead of sweat, nature’s brilliance became manifest. Using differing metals as a battery, some organisms deliberately corroded circuits and other exposed materials to power their biology. In the dark and absent fresh dead skin or other waste to eat some microbes were even able to metabolise radiation passing through the station as a faint energy source. Then of course there’s the black mold everyone’s heard about on a window of the ISS, growing on the outside of the station. This is serious stuff, potentially threatening long term human missions. Submarines have otherwise very similar conditions to space stations but they don’t get anywhere near this bad. This probably means that artificial gravity is a vital first step and massive improvement, forcing the floating fluid droplets that form the perfect homes for such organisms out of the air and on to surfaces where they can be drained away or mopped up. It’s likely not enough though. Plenty of innovations will be needed and likely plenty of drydock operations in the meantime, more frequent and more invasive than I’d prefer.
5) Gateways And Bridges
Our map, along with dangers, speaks of lighthouses and safe passages. Our version of the Trade Winds in space would be deep gravity wells. Some, in particular The Sun and Jupiter, have hazards that would frustrate a close approach (radiation for Jupiter, radiation and extreme heat for The Sun). Others, like Earth as our starting point, are easy to use and essential for efficient travel. This manifests most strongly in the Oberth effect: if you reach escape velocity by rocket work and exceed it you’ll get to leave with more velocity than if you paid for it out in free space. The effect is strongest when the delta v you need is small compared to your gravity well’s escape velocity. As an example, accelerate 550 m/s beyond Earth escape and you’ll get to interplanetary space with 3,500 m/s instead. It’s easiest to picture the gravity of a planet pulling you back as you leave. The faster you’re going the less time it has to slow you down as you fly off. Tricks like this and the famous gravity assist can, under the right circumstances, give you tremendous propellant savings.
6) Riches Are Found On Planets
I’ve heard a lot of talk about getting platinum from metallic asteroids and so on. In reality, almost all asteroids are relatively undifferentiated and lacking in ores: the platinum and germanium and gold are indeed all there but they’re spread out thinly. Having to process a billion tonnes of asteroid to get a few hundred tonnes of rare elements makes the whole proposal a little less attractive economically. There are, however, plenty of places in the Solar System where you can find an isolated cave filled with an almost pure mineral made of insanely rare things. Galena is mostly lead sulphide, PbS, but sometimes a half percent of silver in there too. Monazite, my favourite example, can be found with the rare Earth element cerium (for catalysts), lanthanum (specialist electronics), as well as uranium and thorium (nuclear energy) all in the same ore. Such things happen only in the presence of large amounts of water or living things for billions of years or in the aftermath of transient cataclysmic energies like volcanic activity and asteroid impacts. Earth, then, is one of the better places to come for these. Venus would be good too if only we could reach the surface. Mars is the best extraterrestrial bet.
The more common materials, however, can be found distributed much more widely, in particular water and other volatiles can be found as layers of ice tens if not hundreds of kilometres thick on every moon or large body you care to name passed the Ice Belt (Saturn and beyond, basically). In our part of the Solar System it’s metallic iron-nickle-cobalt and relatively undifferentiated basaltic type rock compositions that you’re likely to find floating around as an asteroid body.
There’s naturally a lot more to this and surely more still to be discovered or invented: famously, oil would not even warrant inclusion as a resource on a map until the means to utilise it had been invented and developed. A map of the Solar System that included lifeforms would be truly astonishing to see. In less than a century’s time we might well be able to start drawing such a map – filled with life we bring ourselves or, more profoundly, life already there waiting to be discovered.
In Conclusion
The maps we must leave for generations yet to come must to do more than just accurately describe the physical and material world, which is clearly not all that there is. The human experience extends greatly beyond contour lines and the market value of this or that regional mining export – fail to take this into account and, like most such official documents and compilations of our sad and dry age nobody will read it! The experience of a narrow stretch of ocean, eerily quiet and permitting gut-wrenching undulations in its misty distance, suddenly breached by an exotic ocean mammal that lead the people who braved maelstroms and starvation peering overboard to draw it in as a sea monster is presently incomprehensible to us moderns. Can you expect such an experience on the basis of something you saw on Google Maps? Some YouTube reaction video you left a comment on once?
The people qualified to fill a map of our Solar System in properly have yet to fully develop. Some are almost certainly yet to be born at all. They’ll need to actually go to the places they mark in for their impressions to be authentic, their poetic ideas to actually mean something. This quick list, however, contains within it many necessary grains of truth that any such map must contain.
Whether we live to see it or not, the future must be filled with such artefacts, holy and unique for the reason the original ancient maps are: each point needed someone to really be there to record it.
2024-05 (submitted 10/14/2024, updated 15/06/2024)
