Science in Science-Fiction: Interplanetary Spacecraft Part 1

Posted on Saturday, June 1st, 2013 at 02:30

Space ships are a staple of science fiction. Whether it’s a Corellian YT-1300 light freighter, a Jupiter class mining vessel or a galaxy class cruiser sooner or later in a lot of Sci-Fi movies and books the characters go out into the cold, unforgiving depths of space. Spacecraft aren’t even really science-fiction anymore, like submarines, death-rays, and cyborgs, space ships have stepped off the page and been engineered (okay, maybe not death-rays); they are science-fact, not fiction.

An enormous space freighter cruises through the stars.

Space freight may be a future reality.

We (humanity as a whole that is, individual nations can consider their own accomplishments here) have built disposable one shot capsules, orbiting space-stations, lunar landers, all manner of robotic explorers and even a few reusable shuttles to low-earth orbit. We might soon be asteroid mining and establishing small science outposts — its no longer apposite politically to talk in terms of ‘colonies’ with their Imperial connotations — but I won’t hold my breath. We need better space ships if we are ever going to realise our potential as a species. I don’t necessarily mean that we need to have anti-gravity drives and the ability to pop over to Mars for an afternoon (that may come, but not for a few centuries yet) I mean some Science-Fiction solutions to space-faring that are actually within our grasp, if we can just find the funding…

Do we have to go?

Sure we could stay here on Earth, consuming resources until there aren’t enough to do anything else. It is a possibility, and imagine what that’s going to be like, when we don’t have enough resources to feed everyone or even get food to market— pretty dystopian really— or instead imagine a future where huge numbers of people leave Earth, heading into interplanetary space, easing some of that pressure as they begin to exploit other resources. If you want to stay on Earth with all the problems that life here is going to face — that’s fine — but it might help you to send some people off to try and workout how to survive on the moon or Mars or inside an asteroid, because some of the tricks they perfect may make life a little better on Earth too.

A brief history of whoosh…

As far as I can find the first story to discuss the potential of a chemical rocket flying up into space was written in 1656 (Cyrano de Bergerac’s ‘The Comical History of the States and Empires of the Moon), and in 1705 Daniel Defoe postulated the possibilities of liquid-fuelled rocket engines in ‘The Consolidator’, but realistic depictions of space-flight and rocketry had to wait until the 1920s. Around that time German Physicists and rocketeers, like the pioneering Herman Oberth following in the giant footsteps of Konstantin Tsiolkovsky (and the Woolwich armoury if this wiki page on Tsiolkovsky Rocket equations is to be believed), had worked out the basic math of riding a continuous roaring explosion and were able to launch a few simple rockets into the heavens, their early work sparked the imagination of German and French Science Fiction writers and before too long these European writers caught the attention of Hugo Gernsback and he had these tales translated for his ‘Amazing Stories’. All of which lead to Philip Francis Nowlan writing Armageddon 2419 A.D. which was later serialized as Buck Rogers throughout the thirties and then revived in the 80s Buck Roger’s original comic strip was imitated by a number of other papers, but none saw as much success as Flash Gordon. The Flash Gordon serial was so popular that it was actually turned into a film serial before Buck Rogers got optioned, and while the early serials are a little hokey (and not at all cokey) they pale like Peter Duncan with his hand in a tree trunk compared to the high camp awesomeness of this version. Throughout the twenties and thirties was a golden age for science-fiction with mankind’s imagination reaching into deep space with huge rockets (that often seemed to feature gliding wings), but when we actually started making space rockets we discovered that in order to get up there you had to leave most of the rocket behind. Our first forays into space mostly consisted of placing a tin-can onto a huge rocket and even having the rocket built in stages so that each part only had to lift its own fuel and not the empty rocket beneath it as well. This trick took us to the moon, but chemical explosions are a dangerous and (more importantly) an inefficient way of lifting or pushing something. If we want to go further out we are going to need a better solution. So we can break the problem down a bit. The problem is essentially one of three parts.

  1. Launch
  2. Gadding about
  3. Landing

There ain’t no such thing as a free launch

Getting out of a gravity well is a huge ask. Gravity is a weak force, but when you put billions of kilos of mass in one place it tends to add up, and Rockets are not an efficient way of fighting it, even the most efficient commercial rocket launches have a cost in excess of $4,000/kg and although the numbers have been coming down due to efficiency in the engines, it is a fact that fuel costs are rising.

But there are alternatives to rocket launches…

Really, there are. We don’t have to just strap ourselves to a rocket to get into space, it just happens to be the easiest to build at the moment, and of course one of the problems with proven technology is that it is very, very difficult to get someone to invest in a new way of doing something. That said there are some, just-beyond-the-horizon ideas that look very promising, even if we have been waiting for some of them since before the moon landing sets were built in Nevada…

Rail guns

A mass driver station envisaged for the moon. Image from lunatect.com

Rail guns, Mass drivers or Electromotive Linear Accelerators are another way of launching, they rely on electromagnetically accelerating the launch vehicle along the ground, up a mountain or through a vacuum filled tunnel, up to an orbital velocity and then letting go. Because this technology uses electrical motors (essentially) it is much more efficient than rockets. Although it is worth bearing in mind, that depending on how we build one, huge efficiency losses may occur trying to plough through all the atmosphere between down here and up there. Even so some estimates are that we could get launches as cheap as $300/kg quite quickly with this method. We could probably build a to low earth orbit railgun within a decade with suitable investment, which would be great for satellite launches, but not so good for human beings probably, as the G-forces would almost certainly be too high for humans for an even halfway reasonable development cost. Rail guns in one form or another turn up all over science-fiction, but using them specifically for launching spacecraft from earth is quite a late development in science-fiction although Heinlein did lob a capsule with passengers from the moon to earth in ‘The Moon is a Harsh Mistress’ all the way back in 1966.

Buoyant Launch Platforms

They have a lot of names, all quite silly (Rockoon! Honestly…), but what they all amount to is using balloons to get the spacecraft up to a really high launch height. Ideally the balloons would be rigid carbon structures that contain vacuum as these could give the most possible lift. Imagine a whole launchpad and control center becoming so light that it can float high in the atmosphere carrying a small rocket that can zip off from the balloon. Too much? Well imagine instead a high altitude hydrogen filled weather balloon launching an amateur rocket instead, we’ll see a Kickstarter attempt before too long… Weirdly though I haven’t found any examples in Science-Fiction… Anyone got one?

Towers, Beanstalks, Elevators and Celestial Castles

Building a tower to heaven is a pretty old dream for mankind, and one that modern engineering considers an impossibility. There is simply no way we can calculate that a free-standing structure could reach up beyond the atmosphere. There simply are no materials that we know off which could withstand the compression that the materials own weight would exert, but as with bridges we might be able to use tension rather than compression to cross that gap. If we can build a satellite that will orbit the Earth and dangle down a strong enough cable, that might let us get up to Earth orbit with some efficiency. In fact estimates are that a dangling cable with a huge solar array providing power could raise loads almost for free once the costs of development are paid for. Although more conservative estimates say $220/kg would not be an unreasonable cost. There are problems with space-elevator technology though, the first being that with modern materials it just isn’t possible. We need better ways of producing nano-fibre and monomolecular materials that are at least 35,000 kilometres long, it could take a while, or we might crack it in a decade, you can never tell with innovation. We might not be able to distinguish between a true tower and a dangling space-elevator, so they both are often grouped together as “Tsiolkovsky Beanstalks” although the man himself referred to them as celestial castles. He saw them as a flying spaceport dangling a cable to the ground for people and goods to climb up and down in elevators. Space elevators are often seen as the most likely way we will become space-faring in science-fiction. Many authors favour the approach, from Arthur C Clarke and Robert A Heinlein through Larry Niven and Stephen Barnes to hip indie authors, in fact you can see a non-definitive list here. Of course the space-elevator is not necessarily the most likely system. Reaching all the way to the ground is unlikely to ever be solved, more likely we will use a Skyhook, which is the same thing only it doesn’t actually touch the ground, instead payloads rendezvous with the lower end in low earth orbit, hook on and then climb up the cable to a higher orbit. And there are even more bizarre variants on the system including ring-belts which orbit rather like the rings of Saturn but dangle down skyhooks or space-elevators. Such a construction is at least centuries away, if not millennia.

Launch Loops

Launch Loops are like sky railways

Launch Loops could be the way forward (from http://launchloop.com)

“Invented” (imagined may be a more accurate term until one is built) by Keith Lofstrom the Launch Loop is a ring of cable about 2000km long held aloft by having an inner cable accelerated to high speed at either end which throws the middle up towards orbit. The momentum of the inner cable is capable of supporting the outer sheath and any craft or satellites that are being launched. Any launching craft use magnetic induction in the inner core to ride the line up to a low earth orbit when they activate a rocket motor to climb free into a stable circular or even escape orbit. The Launch Loop would be quite expensive to run (you’d want to keep it operating rather than turning it on and off a lot), but while operating it can lift incredible amounts of payload. Lofstrom calculated that a $30 billion dollar Launch Loop could offer 3G (that’s about as much acceleration as a playground swing exerts) launches at an incredible $3/Kg, that’s less than a £/lb! If we plan on exploiting the resources of the solar system any company working on the project would do well to consider building a launch loop to construct and fuel their space fleet.

Rotovators

Imagine a huge cable, twice as long as a normal space elevator that is rotating. The rotation and orbit are all carefully controlled to sync up with the rotation of the planet underneath so that at the ground point the cable actually comes to a momentary standstill just touching the ground — or rather the hook on the capsule. As the planet rotates away and the cable swings back up it carries away the capsule, imparting an interplanetary escape velocity on the vehicle. The only problem is that the rotovator can’t really operate through an atmosphere and any momentum lost to the capsule must be made up again in the tether or eventually it will drop out of the sky, and the Rotovator will act like its other namesake as the tether whips repeatedly into the surface of the planet or moon below. A variant of the rotovator tether is used by the heroine of the Charles Stross novel “Saturn’s Children” to travel between two of the inner planets.

Laser Launch

A laser launch system is rather simple. You take a vaguely rocket-shaped conical craft with a highly polished concave mirror in the place where normally a rocket engine would go. You then take a high powered laser and focus it on the mirrored chamber. The air (or a fuel at higher altitudes) in the chamber is heated to incredible temperatures and explodes from the chamber propelling the rocket upward. Carefully pulsing the laser light can control the thrust and allow a spin stabilized rocket (you can use a jet into the chamber to impart the spin and provide reaction mass) to climb all the way to orbit. At the moment the only tests that have been performed have had limited success, reaching heights of a few hundred feet using 10 kilowatt (or close order) lasers. Getting higher will require much larger lasers and far more investment. The system does have a number of advantages, chiefly being that fuel costs are minimized, and should something go wrong then the only loss will be a single craft and perhaps a laser. Hopefully laser launch systems could be mounted on high mountains near the equator and boost small payloads for a cost that could get as low as $30/kg (although more likely taking into account the costs building a powerful enough laser $180/kg is more likely). Laser launch systems seem like a good bet for commercial satellite launches, they would be cheap enough that corporations should be able to develop and sell launch packages direct to companies and universities allowing our space sciences to develop more rapidly through direct experimentation. Laser launching is not common in science-fiction (for some reason… I guess we’re more used to lasers in pistol or carbine form), can anyone come up with a good example?

Hybridization

Most likely the future of space launches are going to be a hybrid vehicle. A space plane, that uses jet engines (of one sort or another) that transfer over to rocket motors at high altitude to nudge up into a Low Earth Orbit. There is even a chance that such a craft is already being operated by USAF although we probably won’t know for sure for another decade or so if the history of Military Aviation teaches us anything. I expect we will see a balloon hybrid launch before too long, as it is an easily developed technology that could minimize launch costs for emergent technological nations near the tropics. We’ve already seen hybrid launches get into space and win prizes, but so far they haven’t achieved orbital injection (they haven’t stayed up), give it thirty years or so and I imagine we’ll have a truly reusable hybrid launch platform capable of getting up and away from earth. Such a vehicle may actually be necessary to clear away obsolete craft and space debris that is cluttering up the space lanes already, so I can’t see it being too long before some nation decides to commission one. Laser hybridization could be used with large lasers mounted on large low altitude planes launching upwards. Launch Loops are already a hybrid concept, as a rocket is required to kick off to true orbit. Almost all the concepts could be combined with rotovator, skyhook or space elevator technology to allow craft that only just reach space to be snatched up into higher orbits or flung out into space. Such an operation would require incredible timing, but may actually be within the reach of our current technology, with kevlar cables standing in for the carbon nano-tubes that we really require for a while (which limit the lengths of the cables greatly and the speeds that the tethers can operate at). If we get the right sorts of investments it would be easy to speculate on an open market of space launches, ride a plane up to a Balloon Platform, transfer to a light rocket which then connects in low orbit to a skyhook, ride the sky hook up to high orbit before swapping over to a rotating tether to throw us off to the moon or even Mars for only a couple of grand a ticket. So that’s it we’ve got up into space… but how do we get around once we get up there? I’ll explore that in the next post in the series…

 
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