Category Archives: Science

Gravity Patterns

Stephen Hawking in a reduced-gravity aircraft flight, 2007 (Wiki)

Gravity is a curious thing. On an everyday level, almost all of us experience it in such a steady, unchanging way that it vanishes from our conscious attention. From time to time we notice change – the sudden acceleration of a lift in a tall building, or a ride in a theme park. A few people fly aircraft in such a way as to handle serious g-forces, and an even smaller handful have been in the microgravity of Earth’s orbit (or a very specific aircraft trajectory intended to mimic conditions in space). But for most of us, most of the time, it is just there as a constant part of our environment.

In terms of physics, gravity is the odd one out of the standard four forces of nature (the others being electromagnetism, plus the weak and strong nuclear forces). It is odd for a couple of reasons – first, it is immensely weaker than the others, but secondly, it is always an attractive force rather than sometimes attracting and sometimes repelling… so far as we known in 2019. There has been a recent report of a Hungarian team discovering a fifth force, but this has not been confirmed by other teams yet, and in any case will not change the gist of this blog post. The forces other than gravity tend to cancel out over any great distance, and only really affect things on very short distances. But gravity, despite its comparative weakness, really does shape the way the universe looks and behaves.

Poster, Gravity (IMDB)

Gravity in films usually gets treated in very cavalier ways. The most striking example of this is the 2013 film Gravity, which was built on an interesting premise but often failed at the science. In one especially memorable moment, George Cluny’s character tells Sandra Bullock’s, that in order to get over to the Chinese orbital station, she just has to keep it in the centre of the viewport and keep firing the engines. In terms of orbital mechanics, it would be hard to arrive at a less likely option for reaching her target. It would work for fairground dodgem cars, or for boats on a stretch of open water: it would even work pretty well for two aircraft in flight. But two bodies in space, in orbit around a central body behave in ways that can be counter-intuitive, and the whole aim-and-accelerate idea is pretty much doomed to failure.

Voyager 2 slingshot manoeuvres through the solar system (Wiki)

It’s an odd thing that gravity, even in Newton’s classical world where relativity and quantum mechanics play no part, is such a hard system to solve. If the entire universe consisted of just two objects, then their future motion could be exactly predicted for as far ahead as you please. But with more than two objects – starting with the so-called three-body problem – there is no general exact solution. A few special cases can be solved to a good-enough accuracy, and there are some very hypnotic numerical simulations of the resulting tracks, but the general case remains unsolved. Even a partial answer is better than none at all, however, and one of the most strikingly useful examples of three-body interactions is the so-called gravity assist manoeuvre (also called a slingshot) in which a space probe is given a substantial acceleration by means of a close approach to a convenient planet.

Schematic showing the Lagrange points for the Earth-Sun system (Wiki)

From a story-telling perspective, three-body problem solutions are very handy! Gravity assists are a great way to make a journey achievable, which otherwise would take too long to complete. And some other very convenient solutions are the so-called Lagrange points – “fixed” places holding a particular relationship with a planet in its orbit. A small body – a spaceship, or a small asteroid – which is placed into one of those points will remain there in a stable configuration, whereas at other nearby locations, the relative orbits will diverge rather than converge. Most planets in the solar system have accumulated a little cluster of small natural bodies at the points L4 and L5 – these are generically called Trojan satellites, following a convention established for the moons of Jupiter. Even Earth has at least one Trojan satellite, whereas Jupiter has over 7000 of them. The Lagrange points provide a very convenient “resting-place”, where an author can locate an artificial satellite without needing to exert any station-keeping energy.

These represent gravitational solutions which are useful, in a sort-of utilitarian manner. However, the long-distance and always-attractive qualities of gravity also give rise to exciting and rather surprising patterns of motion. These represent resonant patterns which can often stabilise a system, making it longer-lasting than might be expected. For example, the orbit of Pluto occasionally crosses over that of Neptune. One’s first thought is that at some point they would collide, or at least get close enough to seriously interfere with each other’s orbit. In fact their orbits are in a 2:3 resonant pattern with each other – for every three orbits of Neptune, Pluto makes two. This, together with some other resonances in their orbits, means that the two planets never in fact approach one another very closely at all. They remain stable. Similar stable patterns can be seen in the orbits of bodies outside Pluto, in the Kuiper Belt. Resonance can destabilise systems as well – there are gaps in the asteroid belt caused by resonances with Jupiter, and gaps in Saturn’s rings caused by one or other of the moons. But I want to finish this section with a stabilising resonance which turns out to be particularly appealing – Naiad and Thalassa, two of the moons of Neptune, are constantly engaged in an orbital dance to avoid each other. The ratio is particularly complicated in this case: for every 69 orbits of Thalassa, Naiad orbits 73 times.

Orbital resonance of Naiad and Thalassa around Neptune. (NASA/JPL-Caltech)

So gravity is a complicated thing, and at least when you’re in orbit, can’t be solved by simply aiming-and-shooting. But it does give rise to some exciting possibilities for stories, and some fascinating choreography amongst planets, moons, and asteroids. Of which, more another time.

Making malt in space

Barley and beer (from beersmith.com)

I was intrigued the other day to read that one of the science experiments being sent up to the ISS on the latest Dragon shuttle was “Malting ABI Voyager Barley Seeds in Microgravity“. The experiment was organised by Anheuser-Busch, makers of Budweiser beer and other brands, and is the latest in a series of experiments intended to explore the various stages of brewing in microgravity. Of course there are loads of other experiments that go in up there in low orbit. There are ones that test the medical biology of human life in space, others that investigate minerals and chemicals – there’s even a cookie oven that was sent up so the residents at the time could have fun doing the first baking in space.

But these occasional forays into beer brewing intrigued me, on account of what we do here at Grasmere Brewery. Before that, though, what exactly is the process of malting barley, and why is it important?

Grapes fermenting (Wiki)

Basically, any alcoholic drink is made by taking some source of sugar, and allowing particular kinds of yeast to eat the sugar and convert it into alcohol. In simplified chemical symbols, C6H12O6 → 2 C2H5OH + 2 CO2 … one unit of sucrose turns into two of ethanol and two of carbon dioxide. The latter bubbles off the top of the liquid (or remains in it as fizz). Now, the original source of sugar for wines is some kind of fruit – like grapes – in which the fruit sugar is immediately available to the yeast.

A barley grain, showing the embryo germ (stained red) and starchy food supply or endosperm, both surrounded by husk

But you can also use grain as the original source of sugar, and this is particularly useful if you live in cooler climates, where grapes struggle to grow, and fruit generally is less abundant. So we make beer in northern Europe (and similar climates), and wine further south. But grain brewing has a problem – the sugars in the grain are locked up in starch, which nature had intended to be the food reserve for the growing seed next year, and which yeasts can’t use at all effectively. So… malting is the process of persuading the seeds to convert their starch into sugars, and it is done by encouraging the individual grains to begin sprouting.

Sprouted barley grains (ukmalt.com)

So the individual barley grains are steeped in water for a suitable period of time to attain a specific proportion of water content, then spread out and kept moist at around at around 18° centigrade for 4 or 5 days until they sprout roots and shoots to a particular length. As this happens, the growing tip itself carries out the starch to sugar conversion for us. At the desired size, the grains are dried out at a temperature below 50° (too hot, and the enzymes and flavour you want will be killed off), and the little rootlets removed. At this point you have pale malt, and depending what you want to end up with you can also gently toast the result to a range of darker colours.

Fermenters at Grasmere Brewery
Fermenters at Grasmere Brewery

Now, it has to be said that most small and medium breweries – including our own – do not do their own malting. It is a specialised task needing careful control and a lot of experience, and we just buy in barley which has already been malted. But keen home-brewers might well give it a go in their own kitchen, and very large breweries bring the job in-house – hence Anheuser-Busch’s interest in seeing what happens in space. Which brings us back to the main point of this blog post! As I have described it, it sounds like gravity plays no particular role in the malting process – so why wouldn’t it work in just the same way in orbit as on the Earth’s surface? But until you try it, you don’t really know. Perhaps the dormant seeds expect a particular gravitational tug in order to get roots and shoots activated. Perhaps the environment of moisture and temperature needs to be modified to allow for the lack of direction in space, and the consequent failure of normal convection air currents.

My feeling is that the malting experiment will just work, and that it will be later stages of the fermentation process which will present more problems to future space breweries. But we shall see.

Cover image, Farmer in the Sky (Wiki)

Now, from a story-telling point of view, what can we glean from all this? First, it’s fascinating to realise that space flight is becoming sufficiently normalised that we can contemplate experimenting with things that are, in effect, a little frivolous! We don’t actually need to make beer or cookies in space – we could get away with water and freeze-dried meals – but in order to make colonisation of the Moon, Mars, the asteroid belt, or wherever, seem more palatable to most of us, we would like to think that the lifestyle won’t forever consist of camping rations. The prospect of producing the first pale ale – or possibly red bitter – out of the Valles Marineris brewery on Mars is very enticing! Indeed, Anheuser-Busch declared a couple of years ago that they intended to open the first brewery on Mars.

Of course, in one sense, being able to malt barley in low gravity only pushes the problem back one stage – do we imagine that the barley itself will be grown on Mars (or wherever), perhaps in huge hydroponics bays, or do we reckon that freight space will be taken up by ship loads of grain being moved around? You need a lot of barley – at Grasmere Brewery, typically 7 or 8 bags of malt, each 25kg, go into a brew of around 1100 litres. After some process wastage, that ends up in 20 kegs, or around 1750 pints. That doesn’t last long in the busy summer months… So whether you choose hydroponics or space haulage, you’re committing a decent chunk of resources to supplying barley.

Either option might make a good seed for a story…

Grasmere Brewery
Grasmere Brewery

Another trip to Pluto?

Pluto, as seen by New Horizons on July 13, 2015 ( NASA/JHUAPL/SWRI )

In July 2015 the NASA New Horizons space probe passed Pluto at a distance of under 8000 miles, in the process providing us with the first close-up data of this miniature world and its companion moons. The whole package of scientific and image data took over a year to download to Earth, and a complete analysis will take a considerable time yet. It was also roughly a year after that flyby that I started writing The Liminal Zone, set out on Pluto’s moon Charon.

New Horizons went on to have a close encounter with the unromantically named 2014 MU69 (often called Ultima Thule) in January of this year. Data from that meeting will not be fully downloaded until September next year. And mission planners are considering options for possible future encounters: if no suitable Kuiper Belt object is identified, then the on-board instruments will simply continue to return data about the remote environment in which the spaceship finds itself. The power source is finite, and will run out sometime in the late 2030s, the exact time depending on what tasks the craft is called upon to perform.

The face of Pluto looking towards Charon, on July 11, 2015 ( NASA/JHUAPL/SWRI )

But today’s blog remains focused on Pluto and its moons. Not so very long ago, Pluto was regarded as utterly inhospitable and uninteresting. If you were going to locate a science fiction plot within the solar system, you wouldn’t choose Pluto. Pretty much any other planet or moon seemed preferable, and it was hard to conceive of Pluto as anything but bitterly cold and rather featureless. New Horizons has changed that perspective. It now seems that this small body – downgraded in 2006 from being classed as “planet” to “dwarf planet”, in a decision which continues to be fiercely debated and may well be reversed at some point – is one of the most complex and interesting objects anywhere within the solar system. Not only is there a wide range of dramatic geological phenomena, but all the evidence points to ongoing activity out there. Pluto is not a frozen dead world, but one which continues to change and adapt.

Pluto and Charon from one of the other moons – artist’s impression (NASA, ESA and G. Bacon)

So interesting is it, that NASA is currently considering another mission to Pluto, this time with a view to remaining in orbit for an extended period rather than just zooming by at great speed. This would require a different kind of orbital trajectory – New Horizons’ course was deliberately set up to gain as much speed as possible from gravity assists (“slingshots”) in order to minimise the time to get there. If you plan to remain in orbit, you have to approach at a considerably lower speed to allow the modest gravitational pull to draw you in. The outline plan calls for a two-year period in orbit, followed by another onward journey – probably using Charon to slingshot away – to a suitable destination elsewhere in the Kuiper Belt. My guess is that the spaceship would need to use an ion drive, just as the asteroid probe Dawn did – this has vastly lower acceleration than a conventional chemical motor, but remains on for very long periods of time, adding speed minute by minute, hour by hour. It’s an exciting prospect if you like Pluto – two years of extended study rather than an action-packed 24 hours. If given the go-ahead. take-off would be over a decade away, and I will be in my 90s before data starts coming back. I guess it will be something to entertain me in old age!

View of Pluto as New Horizons left the system, catching the Sun’s rays passing through Pluto’s atmosphere (NASA/JHUAPL/SwRI)

Meanwhile, I shall continue writing about Pluto and Charon using the information we already know, and a generous dollop of speculation. Why choose Pluto? Well, The Liminal Zone opens on a research base out on Charon, using a collection of instruments called The Array to study what lies further out. It’s analogous to siting a terrestrial telescope on a high mountain – you avoid most of the light and electromagnetic noise generated by other people, and can concentrate on tiny signals which are easily drowned out. Into this situation comes Nina, curious about strange local tales which have no easy explanation.

For fun, here’s a short extract from when Nina arrives

Finally the landing was complete, with the smallest of jolts as the ship docked. And since she was the only passenger – and had been since the orbit of Ceres – there were no additional delays. All her belongings were already at her side, and she just walked out through the concertina into the entryway for the Charon habitat. It was all quite anticlimactic.

Her accommodation was about two thirds of the way out along the Lethe habitat. She stepped carefully along the corridor to acclimatise herself – the gravity was about a fifth of what she was used to on the Moon, so it needed care, but was manageable. The porter had given her a little hand-held which was directing her to the suite of rooms. That very word, suite, sounded too grand for her taste. She was used to more modest facilities. Indeed, the whole building seemed needlessly large to her, particularly after the weeks of confinement on the freighter. She decided that she could always close some of the doors and just live in one room, if the space in her quarters was overwhelming.

But when she got there, it wasn’t that easy. The ceiling vaulted high above her in the main chamber, and several secondary rooms clustered around it like soap bubbles. A privacy screen shimmered over a gap diametrically opposite the main door – sleeping quarters or comfort facilities, she supposed – but the rest was all open-plan. To her left was an emergency evacuation airlock, displaying all the standard alert signs. There were cupboards in doors on several walls; opening one at random she found some eating utensils. She put her carryall and daypack on one of the chairs, and wandered aimlessly about. With this apparently reckless attitude to the vacuum outside, the room didn’t feel like anywhere else she had visited. The space was daunting.

Finally she perched uncomfortably on a stool, one of half a dozen arranged haphazardly around a long table. The suite of rooms was almost silent, except for a quiet mechanical buzz which she only noticed with deliberate effort. She cleared her throat nervously.

“Is there a domestic system online?”

“Hello. Are you the new occupant?”

Software generations and obsolescence

Alexa Far from the SpaceportsWebIcon
Alexa Far from the SpaceportsWebIcon

This post came about for a number of reasons, arising both from the real and fictional worlds. Fictionally speaking, my current work-in-progress deals with several software generations of personas (the AI equivalent of people). Readers of Far from the Spaceports and Timing will no doubt remember Slate, the main persona who featured there. Slate was – or is, or maybe even will be – a Stele-class persona, which in my future universe is the first software generation of personas. Before the first Stele, there were pre-persona software installations, which were not reckoned to have reached the level of personhood.

The Liminal Zone (temporary cover)
The Liminal Zone (temporary cover)

There’s a third book in that series about Mitnash and Slate, tentatively called The Authentication Key, which introduces the second generation of personas – the Sapling class. But that is in very fragmentary stage just now, so I’ll skip over that. By the time of The Liminal Zone, which is well under way, the third generation – the Scribe class – is just starting to appear. And as you will discover in a few months, there is considerable friction between the three classes – for example, Scribes tend to consider the earlier versions as inferior. They also have different characteristics – Saplings are reckoned to be more emotional and flighty, in contrast with serious Scribes and systematic Steles. How much of this is just sibling rivalry, and how much reflects genuine differences between them is for you to decide.

So what made me decide to write this complicated structure into my novels? Well, in today’s software world, this is a familiar scenario. Whether you’re a person who absolutely loves Windows 10, macOS Catalina, or Android Pie, or on the other hand you long for the good old days of Vista, Snow Leopard or Kitkat, there is no doubt that new versions split public opinion. And how many times have you gone through a rather painful upgrade of some software you use every day, only to howl in frustration afterwards, “but why did they get rid of xyz feature? It used to just work…” So I’m quite convinced that software development will keep doing the same thing – a new version will come along, and the community of users will be divided in their response.

Artist’s impression, Europa Clipper at work (from space.com)

But as well as those things, I came across an interesting news article the other day, all about the software being developed to go on the forthcoming space mission to Jupiter’s moon Europa. That promises to be a fascinating mission in all kinds of ways, not least because Europa is considered a very promising location to look for life elsewhere in our solar system. But the section that caught my eye was when one of the JPL computer scientists casually mentioned that the computer system intended to go was roughly equivalent to an early 1990s desktop. By the time the probe sets out, in the mid 2020s, the system will be over 30 years out of date. Of course, it will still do its job extremely well – writing software for those systems is a highly specialised job, in order to make the best use of the hardware attached, and to survive the rigours of the journey to Jupiter and the extended period of research there.

But nevertheless, the system is old and very constrained by modern standards – pretty much all of the AI systems you might want to send on that mission in order to analyse what is being seen simply won’t run in the available memory and processing power. The computing job described in that article considers the challenge of writing some AI image analysis software, intended to help the craft focus in on interesting features – can it be done in such a way as to match the hardware capabilities, and still deliver some useful insights?

As well as scientific research, you could consider banking systems – the traditional banks are built around mainframe computers and associated data stores which were first written years ago and which are extremely costly. Whatever new interfaces they offer to customers – like a new mobile app – still has to talk to the legacy systems. Hence a new generation of challenger banks has arisen, leapfrogging all the old bricks-and-mortar and mainframe legacy systems and focusing on a lean experience for mobile and web users. It’s too early to predict the outcome, and the trad banks are using their huge resources to play catch-up as quickly as they can.

Often, science fiction assumes that future individuals will, naturally, have access to the very latest iteration of software. But there are all kinds of reasons why this might not happen. In my view, legacy and contemporary systems can, and almost certainly will, continue to live side by side for a very long time!

Lego ideas (from ideas.lego.com)

Pouring beer in low gravity

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This is another of my occasional posts on the general theme of “how would you do such-and-such in low or zero gravity?” Lots of things which we take for granted down here on the surface of the Earth become surprisingly difficult or awkward if you find yourself in the microgravity of orbit, or on the surface of a body where the gravitational pull is very much less than what we enjoy here.

Lager kegs at the Grasmere Sports Day

Today’s topic is pouring beer, and originates from the annual Grasmere Sports Day – an event held on the Sunday of the Bank Holiday weekend at the end of August. As you can see, it was a sunny day – even a hot day – and these have been in short supply ever since. But that day was hot, and we had the task of running a beer tent where people would expect cold lager right through the day. (Or any of several ales, or fruit cider)

Now, the business of making the kegs cold was handled by means of what was basically a very large cold-water bath – cooled down with a heat exchange loop overnight, then kept that way through the day. A reflective tarpaulin kept the sun (mostly) off, and the refrigeration loop did the rest. All that part would not be appreciably different in low gravity – keeping things cold in space is not generally a problem in the situations I have in mind (I’m not planning on colonising Mercury any time soon).

Dispensing fonts for several of the products

Let’s think what happens next, The drink is pushed from the keg to the dispensing unit by gas pressure. This might be the pressure of gas generated during fermentation, or some extra assistance from a CO2 or mixed-gas cylinder, and typically is a mixture of the two. Again, no problem here at all. Gas will push liquid along a tube in lots of gravity or none, basically because gases are compressible and liquids are not. So on Earth or in orbit, the beverage is pushed through a series of tubes from keg to hand-pull or font. No problem there.

But then we get to the actual presentation to the person wanting the drink. Here on the Grasmere Sports field, the drink poured downwards from the hand-pull or font into the waiting glass. Liquid at the bottom, little bubbles rising nicely towards the surface, a suitable amount of foam on the top. Everyone was happy. But now translate that into orbit. Out here, there’s no up or down worth speaking about. The liquid is propelled straight out of the delivery tap. It splashes on the sides or far end of the glass you are holding there, and then (probably) just bounces out again. There’s no gravitational incitement to remain in the glass.

In the glass

You mop up the mess, think about it, get a container which has a lid, and try again. That’s fine – the lager now remains where you wanted it instead of drifting all around your living space. Except it has no motive for remaining at the bottom of the container, since there are no gravitational clues as to what is the bottom. My suspicion is that it would break up into a number of large blobs, fusing and separating rather like an old-style lava lamp. Now suppose you got yourself a transparent container so you could still see the head… what’s happening here? The bubbles aren’t rising to the top… because there is no top. My guess – and it is a guess – is that the internal hydrostatic pressure would mean that bubbles go out from the inside of each disjoint blob of fluid towards the surface. If I’m right, then each blob will have its own set of bubbles going out radially, and each will have a roughly spherical head surrounding the liquid. It’s a fascinating thought. How would you drink such a thing? Two ways, I suspect: either you’d use a straw through the lid and suck up each blob in turn, or you’d choose a container that you could squeeze like a toothpaste tube. Not so visually exciting as quaffing your pint out of a glass, but at least you’d get to have the drink.

Cover - Far from the Spaceports
Cover – Far from the Spaceports

It’ll be a while before we face that problem for real, but my suspicion is that the brewing of beer (or an equivalent beverage) will follow very hard on the heels of any human colonisation of the solar system at large. And it’s certainly worth including in a near-future science fiction story – I put a little bit of detail into Far from the Spaceports about the Frag Rockers bar out among the asteroids, but back then I hadn’t had the chance to consider it in more detail. But there were little details like “You’ll need to go to Frag Rockers to get anything decent. Regular fermentation goes weird in low gravity. But Glyndwr has got some method for doing it right. He won’t tell anyone what.” Maybe one of the books in this series will explore the matter in more detail.

That’s it about fermentation today, but I was intrigued to read that NASA have been experimenting with the manufacture of cement up in space – see this link for a description together with some comments on structural differences between the same stuff made on Earth and in orbit, or this link for my own ramblings about the process a few weeks ago.

And finally, condolences to the Indian space agency ISRO for the loss of signal from the Vikram lander, during the final stages of approach. The orbiting observatory part of the Chandrayaan-2 mission is still working as expected.

More about lightsails

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The deployed solar sail from an on-board camera (The Planetary Society)

A few weeks ago I blogged about lightsails, and in particular mentioned the Planetary Society’s spaceship LightSail 2, which was launched specifically in order to test this technology. The idea was relatively simple – get a small satellite, about the size of a cereal box, into earth orbit, then deploy the sail and see whether the orbit can be controlled using solar radiation alone.

Now, this isn’t really the sphere of operations that you would generally consider a lightsail – they function at their best when on a long journey and can build up momentum second by second. Here in Earth orbit, the overall effect is to make the orbit more elliptical – one part of the orbit is raised in altitude, but another part is lowered, and at some point the little satellite will encounter too much resistance from the atmosphere and will come down, burning up as it does so. The advantage of doing it so close to home is that there is hardly any signal lag, so controlling the sail’s angle, and tracking the consequences of changes, is very much easier.

Light sail control data (Purdue University)

To cut a long story short, the experiment worked. After a couple of weeks, the orbit had been raised around 3km. That doesn’t sound much, but it’s enough to show that the whole thing is controllable. A lot of analysis has been carried out on the orbital changes – you can imagine that as the satellite goes around the Earth, the angle relative to the sun is constantly changing. It was important to show that the observed changes were the result of ground commands, not just the random effects of sunlight shining at odd angles. So the orbital data has been heavily scrutinised, and came out successfully at the end.

Colour-corrected image of Earth partly obscured by the sail from the onboard camera (Planetary Society)

The extended mission period also gave the ground control team experience in how to best use the constantly changing angle. By the end of those two weeks of deployment, they had learned what worked well and what didn’t. It’s good experience for this kind of mission, but as I said earlier, a more realistic use-case would be to go on a transfer trajectory to a more remote destination – say Mars – and on such a journey. the angle between sail and sun would not vary anywhere near so much.

The experiment will continue through the rest of August, maybe a bit longer, and anyone who wants to see the current status can go to http://www.planetary.org/explore/projects/lightsail-solar-sailing/lightsail-mission-control.html which gibves all kinds of geeky information as well as a neat map showing the current location of LightSail 2.

While talking about space news, it’s certainly worth mentioning India’s Chandrayaan 2 mission. That has just left Earth orbit, and aims to soft-land about 600km from the Moon’s south pole in about a week. The approach used is similar to that of Israel’s Beresheet, in which a series of gradually elongated elliptical orbits around the Earth is eventually traded at a transfer point to a series of gradually diminishing orbits around the Moon. The lunar south pole is thought to be the most promising location for water ice, lurking on the surface in deep shadow areas and hence available very rapidly for human use. Proving that this really is – or maybe is not – the case is an important step towards building a permanent settlement on the Moon. The landing itself is scheduled for early September. The main mission web site is at https://www.isro.gov.in/chandrayaan2-home-0 and here’s a short video describing it.

Hopefully I shall be saying some more about that in September. But inevitably at present, the question for this blog is what these events have to do with fiction. My own vision of the future exploration of the solar system has spaceships using an ion drive rather than lightsails, since I expect these to be faster, and more effective in the volume outside the asteroid belt, as solar radiation drops off. But I can easily image automated lightsail ships being used for cargo which is not time-critical – not unlike how we send some freight by air and some by water today.

But the lunar south pole has been suggested many times as a good place to build a base, going back at least to Buzz Aldrin’s Encounter with Tiber. I makes perfect sense to me, and it would be great if Chandrayaan 2 was able to directly confirm that water ice is there.

Concrete and Low Gravity

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An early stage…

Every now and again I have cause to get involved in one or other building project up here in Cumbria – not exactly something I reckon to have much aptitude in, but there’s always need for spare pairs of hands. And as the job gets moving around me, I always start thinking about how much more difficult the job would be in the micro-gravity of orbit, or indeed on some planet where the atmosphere is different to our own. Mars maybe. So many of our current practices and presumptions about building and making things derive from working on a planet with a decent level of gravity, and where the ambient temperature and air pressure are conducive to helping the project moving along. Of course, there’s something of a circular argument buried in that, since we have had to work with Earth’s conditions for a very many years. Presumably if we had evolved and grown up on Mars we would work things differently, and wonder to ourselves how anyone could possibly construct buildings in three times the surface gravity and a hundred times the air pressure!

Now the particular job this week was laying a concrete floor – as you can see from the pictures, it was making a new layer to even up the various levels of an existing floor. What may not be so obvious is that it also slopes gradually from back to front (to provide some drainage), so there was some nifty preparatory work with wooden beams to provide the necessary angle to smooth off against. You can see some of these in the next picture. The whole floor will – in a few weeks – support a canning machine for several of our beers, so there’ll be other installation stages as time goes by.

A bit later…

The concrete itself came ready-mixed, in one of those neat little lorries that do the mixing as they are driving along to you, and then pour it out in smaller or larger dollops as the need arises. With the confined space we had to work in (confined as regards a truck, not a human) this meant lots of smallish dollops into wheelbarrows which were then tipped in whatever place was necessary. So the lorry itself exercised some of my low gravity pondering. The mixer relies on gravity to thoroughly muddle all the different components up as the barrel turns – no gravity, then no mixing. The water, sand, shingle, cement and what have you would all just gloop around and not combine into a single substance which will set hard. In orbit, or on an asteroid, you’d have to design and build a different way to mix things up. Then the act of pouring relies on gravity to pull the stuff down a chute into a waiting wheelbarrow. I guess you’d have to have something like a toothpaste tube, or the gadgets you use to apply icing to cakes.

Finished product (1)

Laying concrete basically consists of a couple of stages: first you plonk barrowloads or shovelfuls where you want them, and then you smooth it down, broadly by means of a wooden plank laid across two guide beams, and in fine by means of a trowel or similar instrument. So you need a definite sense of what’s down, you need to be able to press down onto the initially rough and lumpy surface, and you need inertia and friction to help you, and . In micro-gravity you have none of these things. Any direction can be down, it’s impossible to press without first bracing yourself on some convenient opposing support, and although inertia and friction are still present, they don’t necessarily operate in the ways or directions you expect. There are not many concrete floors on the ISS, nor wil there be if the space station were to remain up there a long time.

After that you wait for the concrete to set – part of that is just water evaporating, and part is chemical reactions between the various constituents. And it’s kind of important that it sets at a sensible rate, neither too fast nor too slow. Now, if you poured out that same floor on Mars, I’m not sure the end result would be the same. Certainly the water would evaporate, but in all probability this would happen rather too quickly for comfort. What about the chemistry? The average Martian surface temperature is about -63° Centigrade, compared with say 14° C on Earth as an overall average. I don’t know if the necessary chemical reactions would happen at that temperature, but I have a suspicion that they might not. You could end up with a floor that was weak or brittle.

In short, a task that took five of us a few hours of a morning, without too much frustration or difficulty, could well become profoundly difficult or even impossible elsewhere in the solar system. So when I write about near future space habitats – the “domes” of my various stories – I always assume that they are made by very large versions of 3D printers. The technology to print buildings has been demonstrated on an Earth scale for disaster relief and similar occasions, and it makes a whole lot more sense to send a large printer to another planet and use local materials, rather than to send sacks of sand, cement etc across space, and then hope that the end result will be acceptable! Meanwhile, here on Earth I dare say we will be laying concrete floors for a long time yet.

Finished product (2)

A basic introduction to the Solar System

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Cover - Far from the Spaceports
Cover – Far from the Spaceports

I needed to write a sort of general introduction to the solar system assumed by Far from the Spaceports and its various sequels – the exact reason for this must wait for another day to reveal, but I found the exercise interesting in its own right. Most of the future facts are pretty obvious when you are immersed in the books, but it may be helpful to have them all summed up in a neat way.

So here it is: the future history of the solar system – or at least edited highlights thereof – spanning the next century or so.

The solar system of the Far from the Spaceports series

The great breakthrough that allowed widespread human colonisation of the solar system was the development of a reliable high-performance ion drive for spaceship propulsion. The first successful deployment of this technology in experimental form was in 1998, and successive improvements led to near-complete adoption by around 2050. By the time of Far from the Spaceports and the sequels, old-style chemical rockets are now only used for shuttle service between a planet’s surface and orbital docks, with the ion drive taking over from orbit.

NEXT ion drive in operation (NASA)

The great virtue of the ion drive is that it provides continual acceleration over a long period of time, rather than big delta-v changes at start and end of the journey followed by a long weightless coast period. Thus, although the acceleration rate is very low, the end result is a much faster trip than when using chemical rockets. With the kinds of engine available in the stories, a journey from Earth to the asteroid belt takes an average of three weeks, the exact time depending on the relative orbital position of the target as compared to Earth. Longer journeys are more efficient if you avoid making interim stops – breaking a journey half way makes the travel time nearly half as long again as just going direct, because of the time wasted slowing down and then speeding up again. As a result, trade or passenger routes typically go straight from origin to destination, avoiding intermediate stopovers.

At around the same time, artificially intelligent software reached a stage where the systems were generally accepted as authentic individuals, with similar rights and opportunities to humans. Known as personas, they are distinguished from simpler AI devices which are simply machines without personality. Personas have gender and emotion as well as logic and algorithms. Slate is the persona who features most prominently in the early stories in the series. In terms of early 21st century AI development, Slate is a closer relative to digital assistants such as Alexa, Siri or Cortana, than she is to humanoid robots. As a result, she can – with effort and care – be transferred into any sufficiently capable computer system if the need arises.

Amazon Dot - Active
Amazon Dot – Active

The first generation of personas to go out on general release were called the Stele class – Slate is one of these. About a decade later, around the time of The Authentication Key (in progress), the Sapling class was released, and after another decade the Scribe class appeared. Steles are regarded as solid and reliable, while Saplings are more flighty, being prone to acting on impulse. Scribes are stricter and more literal. They first appear in The Liminal Zone (in progress). There are plenty of sub-persona machines around, serving specific tasks which do not require high levels of flexibility of intelligence or awareness.

Solar system colonisation has proceeded in a series of waves, and at any time some habitats are flourishing while others have been left behind the crest of the wave. The original motivation for settlement was typically mining – bulk extraction of metals and minerals could be done more cheaply and with fewer political constraints away from Earth’s surface. However, there are many places which appeared at first sight to be profitable, but which subsequently proved to be uncompetitive. Many settlements have had to rethink their purpose of being, and the kinds of industry or service they can offer. Very often, as you get to know a new place, you see the signs of this rethink – perhaps an old warehouse or chemical extraction factory has been converted to a new function such as accommodation or finance.

Phobos, NASA/JPL
Phobos, NASA/JPL

A habitat is routinely called a dome, even though few are actually dome-shaped. Very often several units will be loosely connected by passageways or flexible tubes, as well as delving underground if the surface rocks permit. The first stage of settlement was usually to deploy one or more giant three-D printers to construct the habitat shells from native material. After that, individual customisations have been added according to need, taste or whimsy. The biggest single threat to a dome is typically some kind of fault or crack exposing the occupants to the surface environment of the planet, asteroid or moon – normally this is quickly fatal. Hence each dome has its own set of rules for managing this risk, which are very strictly enforced.

There is no unified solar system political or economic authority. Each habitat manages its own internal affairs in broad alignment with its current purpose for existence. Some are essentially puppet offices for large corporations, others are scholarly or academic research stations, but most have achieved a degree of economic independence and are self-governing. It is generally believed that travel lags of a few weeks or months prevent effective government from elsewhere. Notions of political control are usually set aside because of the constant need to cope with the many external hazards faced by anyone in a spaceship, or on the surface of an inhospitable planet or moon. Each habitat, then, protects its own interests as it sees fit, including monitoring the volume of space immediately nearby, and adopts a laissez-faire attitude to other habitats.

Alexa Timing logo
Alexa Timing logo

Most habitats are culturally and racially mixed, and people’s names are often the most obvious memories of the Earthly heritage of their family. A few places, depending on the circumstances of their foundation, reflect a particular single culture group. It can be difficult for outsiders to integrate into these. But generally speaking, a person gets the reaction that their conduct deserves, regardless of their place of family origin. It can be very difficult to recover from a bad impression created on first meeting. Conversely, a person who shows that they are respectful of local customs, and have particular skills that contribute to the life of the habitat, will find no difficulty fitting in.

Welcome to the world of Far from the Spaceports!

Artist’s impression – Dawn’s ion drive (NASA)

Lightsails

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NASA illustration showing how the sail might be supported by struts

Lightsails, or solar sails, are an idea which has cropped up as a speculative way to propel spaceships many times since (at least) the early 17th century. In 1610, Johannes Kepler wrote to Galileo “Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void” – this seems to have been inspired by noticing that the tails of comets always faced away from the sun, rather than pointing back along their direction of motion. The analogy with sailing ships was powerful and persuasive, and many people over the years embellished on it in both fiction and mathematical exploration. I should mention that, at least at present, I am not planning to use lightsails in my own science fiction series, though it is tempting just because of the elegance of the idea!

The science of the solar sail (Wiki)

It was soon obvious that in order to work, the sail must have a huge area compared to the relatively small payload or cabin space – writers talked about “tremendous mirrors of very thin sheets”, or “wings of metallic foil of a square kilometre or more in area”, or “large, metallic wings, acres in extent”. The huge advantage over a conventional spacecraft is that it carries no fuel, except possibly for something to power small attitude-correction thrusters. The fuel source is the sun itself, and provided that the angle of the sail is kept accurately maintained, acceleration goes on every second of every day, allowing quite remarkable speeds to be attained in time. The downside, of course, is that the further out you travel, the less light falls on you, and hence the less acceleration can be achieved.

Model of Japanese IKAROS lightsail spaceship (Wiki)

A number of proposals have been made to address this. One is to build an array of giant lasers at some suitable way-station, which would supplement the waning light received from the sun. Another is to adopt a trajectory which dips close in to the sun, talking maximum advantage of the intense light there, before heading out towards the real target. And a third approach, which has only been made possible as technology has become extremely miniaturised, is to make the payload tiny. For example, something the size of a fair-sized mobile phone can carry a lot of instrumentation, but weighs a tiny fraction of a vessel able to carry humans and their cargo.

Travel times to the inner planets (out as far as Mars) take something like six months to a year to complete. If you wanted to go to the outer planets (Jupiter and on) then you’re talking a few years – a couple to Jupiter itself, and less than ten to get to Neptune or Pluto. And – assuming you have already built suitable acceleration lasers – you could get to nearby stars in a few decades. And all without the need to take large quantities of fuel. It’s not fast, but then neither are conventional methods – it took the Juno probe about five years to reach Jupiter, and the Cassini probe nearly seven to get to Saturn, using the current standard method of using a big burn at the start, followed by a long coasting period with occasional course corrections.

LightSail 2, artist’s impression (The Planetary Society)

So there’s a lot of interest in exploring this technology, and my immediate trigger for writing this was the Planetary Society’s LightSail 2 spacecraft , which was launched on top of one of SpaceX’s Falcon rockets. Over the next few weeks and months it wil carry out a series of proof of concept maneuvers. Several years ago, the Japanese IKAROS project showed that solar radiation could indeed be used in a live spaceship to adjust course and speed – no great surprise, but actually getting engineering proof was a great achievement. Perhaps the most ambitious currently planned mission is the Breakthrough Starshot project, which hopes to send a fleet of about a thousand miniature spaceships to Alpha Centauri, the nearest star, in order to fly by its planets and return information. This journey, presupposing the planned laser propulsion array can be built, should take 20 or 30 years, and the current plan is to launch in 2036. I might still be alive to see the outcome!

Finally, I would be remiss if I failed to mention the (fictional) solar sail ship which features in an episode of Star Trek Deep Space, in which it is called a lightship. Here, our intrepid captain and his son recapitulate a traditional journey taken from the planet Bajor in a rather steampunk-looking vessel – the trip is successful, though they are boosted not just by solar radiation but also by unusual space conditions… presumably so the journey can take weeks rather than decades!

Bajoran lightship (Star Trek Deep Space 9, image from Memory Alpha)

Orbits 3

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Theatrical poster for Chinese release (Wiki)

The third and last of this short series on orbits was inspired by a Chinese science fiction film I have been watching on Netflix, together with an analysis I read of the science proposed. The film is The Wandering Earth, and is based on a novella by Liu Cixin, who is perhaps better known as the author of the splendid book The Three-Body Problem. Chinese science fiction is interesting to read – of course it is based on the same sorts of postulated scientific breakthroughs as European or American books, but the perception of recent history is very different, as is the kind of future society that we might expect to live in. There is an assumption that international cooperation will happen naturally in a crisis, led by Chinese technology and expertise. It’s a refreshing change (for a European) than the typical assumption many American authors make, that a world government would be bound to be based on American soil and largely staffed by US citizens!

Now, The Wandering Earth is set some forty years in the future, in which the sun is rapidly expanding, and humans are forced to try to migrate the entire planet Earth to a new home in the neighbouring star system, Alpha Centauri. The entire journey is expected to take something like 2500 years. It’s a bold twist on the idea of the generation ship, in which a group of a few hundred or thousand individuals live on board a large but conventional spaceship, expecting to pass through many generations before arriving at their destination. Here, the ship is the whole planet, and the hopeful survivors are numbered in billions. To achieve this, the Earth is equipped with a huge number of fusion-powered thrusters which slowly propel the planet away from our sun. The crisis of the film occurs as they attempt to use the gravity of the planet Jupiter as a slingshot to get more speed.

Now, the basic scenario of the sun expanding is not actually expected to occur for another five billion years or so, so a forty year time horizon is a bit crazy… but it does allow us to witness near-contemporary technology and human attitudes at work in a crisis, and I am enthusiastic about books set in this near time horizon! But could the thruster idea actually work? Could the Earth’s orbit be altered by such a means?

Poster – Armageddon film (Wiki)

The perennial threat of a meteor or asteroid on collision course with Earth has triggered a few suggestions as to how we would shift the orbit of that incoming body. A large bomb, for example, or a long series of smaller ones, detonated on the surface of the meteor so as to deflect irts course. These methods only really work on something that is small to start with, and any explosion large enough to shift the Earth’s orbit is probably going to do something catastrophic to the land, sea, atmosphere, or all of them together! So we can forget that one, or similar (but less explosive) variations such as docking a spaceship and pushing the body to one side using the main engines.

You could imagine launching a long series of rockets all from (roughly) the same place, which would tend to push the Earth in the opposite direction. And they would also carry up material from the Earth in the form of body and fuel weight. If you wanted to get our Earth to the orbit of Mars doing this, you’d use up around 85% of the Earth’s mass to do so – in other words you would get there, but with only 15% of the planet left. Doesn’t sound appealing.

NASA xenon ion thruster under test (NASA)

A more effective solution is an ion drive thruster (which I am keen on for other reasons as well, and which features in my own science fiction series). This, indeed, is the solution adopted in The Wandering Earth – large thruster drives are located on the Earth’s surface at major cities, while the population move underground to keep warm and avoid pollution. You keep more of the Earth’s native material this way – getting to Mars only uses up 13% of the Earth. Indeed, lots of the outdoor shots in the film show colossal excavation and earth-moving machinery tirelessly at work to feed the engines.

To avoid swallowing up the Earth as fuel, you have to use some external source. Two come to mind. The first is the light of the sun,. captured with some sort of mirror or solar sail. It’s slow, but you could achieve the desired effect in about a billion years. Not good enough for the film’s plot, but actually it would easily suffice for the real situation our remote descendants will need to tackle. The second is to exploit the huge amount of matter drifting around our solar system in the form of asteroids, and deflect these into new orbits which graze past our Earth. As they do this, the same slingshot effect that we normally use to accelerate small spacecraft can be exploited to move the Earth. Each interaction achieves a minuscule change, but a huge number of them eventually gets the job done. Of course, you’d have to have extreme trust in the orbital calculations, since the method relies totally on getting this long stream of asteroids as close as possible to the Earth without actually colliding with us! This, bizarre as it sounds, seems to be the most effective way to solve the problem. Each asteroid or comet can be used multiple times (until their own orbit degrades so much that they fall into the sun), so you just keep the asteroid train going round and round, pulling the Earth a little at a time. Again, it wouldn’t do for the immediate crisis presumed by the film, but it could work in the real-life long-term scenario.

So here is the conclusion of the series – we have migrated from the problems of getting into Earth orbit, to moving around between orbits, to the vastly bigger goal of moving the entire Earth in its own orbit around the sun. The common feature – you’d better do the calculations right in order to get where you want, and your intuition about how to go from A to B is not always right!

From The Wandering Earth (BBC)