Monday, 29 December 2014

Build the Enterprise, Or Not?

To Be or Not to Be

   Anyone with an interest in SF spaceships has probably come across the website of a man going by the moniker of BTE Dan; the website is Build The Enterprise, in which he sets out a proposal of how the American government might, if it so desired, build a real life version of Star Trek's famed Enterprise - minus the warp drive - the feasibility of which is hotly contested.  My personal opinion is that it is not feasible: technical considerations only, politics and economics are beyond my pay grade.  This blogpost will look at several elements of the BTE design, pointing out any possible flaws, and ways to remedy them, providing a case study in the design of a hard SF spaceship.


Along with budget the biggest factor affecting the design of a spacecraft is the mission it will fill.  Military and civilian technologies follow different approaches to the same problems, and within the civil field there are a multitude of roles with different technical requirements.  As we already have a design - the Enterprise -  it remains to find a mission by matching it to the Enterprise's characteristics as set out on the BTE website. 
  • large personell capacity - 1000 people for a few years
  • fast travel - 90 days to Mars
  • spin ring - simulated gravity in living quarters so that long term missions are not medically hazardous.
  • safety - tripple redundancy in major systems 
these give the Enterprise a clear role as a transport for humans throughout the solar system.  The spin ring and enclosed cargo areas make it unsuitable for a dedicated cargo ship, but as research and support facility it is right on target.  It is unlikely to be used as an exploratory vessel; the reason being it is simply too capable, that kind of overkill is reserved for unlimited budgets.  A small proof of concept ship might well take the first humans into Mars orbit, however.

General Configuration

   On the we site is is stated that one of the goals of the design is to retain the recognisable exterior of the Original Enterprise.  Connected with this are the two biggest problems of the design, the size and the shape.  A thousand person capacity is vast - the ISS has only - representing significant overkill for any possible mission.  Realistically a hundred crew would be the max, and for any spacecraft built in the near future 10-20 is far more likely.  This also reduces the tech requirements, helping to make it more plausible.  Shape; it has often been remarked that the Enterprise has pretty much the worst design ever from an engineering standpoint.  Those thin trusses connecting the Main to Auxiliary Hulls are a nightmare.  To give adequate margin of safety thy would be ugly expensive and grossly overweight for the job they do.  However, while the design can be scaled down, it cannot be changed it the goals of BTE Dan are to be met, making this the single most likely factor to making it unfeasible.

Yes, I know, this is a HALL thruster,
Engines & Power

   One thing that BTE Dan does get very right is the choice of power and propulsion systems, i.e. a nuclear-electric drive.  For fast interplanetary travel this is pretty much the only choice with current technology.  There is confusion over the naming of the drive with the selected VASIMR being called a 'ion drive', which it is not, but the choice is sound.  VASIMR is a plasma drive using magnetic containment and radio frequency coils to energise the plasma; from a design standpoint it is similar to a fusion drive with energy provided by external power instead of internal fusion.  Among the advantages are proven design, hydrogen remass, long life and reliability, good electrical efficiency, high Isp, and the ability to trade Isp for thrust.  Although BTE Dan decided on three drive units, it has been proposed that the VASIMR drives be installed in pairs, helping to cancel out their magnetic fields external to the drive itself.
   For the BTE design liquid hydrogen-oxygen engines are proposed for manoeuvres that require high thrust.  This seems like a good idea apart from the difficulty of storing LH2 for long periods of time, but given the amount of electric power available large electro-thermal rockets might be better.  Although giving slightly less thrust these have a higher Isp if using LH2 remass, and are very simple mechanically, where liquid-fueld engines are notoriously complexed.  
   Although ideally provided by a fusion device the power is most likely to be fission-thermal.  Even if a project like the ITER tokamak succeeds, it would need years before being perfected to the point where it is space-worthy.  With the greater experience in fission reactors these are a better be in the forceable future despite concerned about radiation.  Advanced concepts could be used, however, like MHD generators, sub-critical fission, vapour of liquid cores, etc.  One thing that the BTE design seems to gloss over is that of wast heat.  The Enterprise BTE Dan proposes needs 2.5 GW of electric power.  Assuming a fission to electricity efficiency of 40%(modern water cooled power reactors are around 30%) that is still 6.25 Gigawatts of was heat to dissipate.  BTE solution is to use the aluminium outer hull as a radiator, but it seems unlikely that this is an adequate solution.  Nor does the shape of the 'classic Enterprise' allow for external radiators without changing vastly the visual appearance.  Obviously a smaller version of the Enterprise with lower power needs becomes more realistic. 
Alternative, the Kelvin
   Given the flaws of waste heat, overall structural design, and the ridiculously large size proposed the BTE Enterprise seems to be a dead end for a spacecraft that could someday be built. But are any of the Star Trek ships viable?  I propose the Kelvin, seen in the beginning of the 2009 Star Trek movie under the command of Kirk's father.  Over the next few weeks I will be designing a spacecraft with the aesthetic of the Kelvin, capable of supporting a crew of 10-15, and able to make a rapid transit to Mars, or a destination in the Asteroid Belt.  I will include calculations, diagrams, specs, and possibly a 3D Blender model, so it will not be finished soon, but keep a lookout for a Build the Kelvin post.

Sunday, 21 December 2014

Unintended Consequences; Implications of the Torch-Drive

   Given that a force-field technology opens up the possibility of torch level spacecraft of almost any size, what does this mean for an author or screenwriter; what does it do the the 'Verse in which the device is used?  How force-field technology applied to spacecraft drives effects the created universe will be explored through the impact on spaceship design, commerce, government, and the military of a SF setting.  To simplify the discussion the shield will have the characteristics outlined in the last post; ability to reflect emr, withstand kinetic particles down to atomic radiation, and withstand mechanical pressures from confined plasma.  More specifically, this is about torch ships in a SF setting, allowed through the handwavium of forcefields.

 Spaceship Design

   The forcefield drive, as a torch level propulsion system, has an effect on the design of the spaceships used in the same 'Verse.  As a pure fusion drive it needs only a small amount of fuel/remass compared to a fission thermal craft, although still more remass is needed than in a electric drive craft.  NASA's Discovery II is a pure fusion design, but a forcefield drive is likely to have performance closer to a design utilising Zubrin's Nuclear Salt Water Rocket, or even higher.  Exhaust velocity for a physical nozzle is governed by temperature and pressure, two things that can be increased almost indefinitely if forcefields are assumed, making even relativistic Ve possible.
   It may be noted that in a hard SF setting a torch ship can have acceleration as low as 0.1g, meaning that structural design is probably similar to any other spaceship.  In classical space opera, however, torch ships are capable of constant - or at least extended - 1g burns, changing the structural requirements considerably.  At this acceleration a trip to saturn from Earth takes seventeen days, as opposed to the years needed by a conventional drive.  This means of course that requirements for food and air are greatly reduced; where a sub-torch ship would need hydroponics and closed cycle environmental systems, the torch ship can make do with canned food and air.  It also greatly reduces the physical and mental impact of the trip, meaning that passenger or casual trips are plausible.
   The acceleration also provides artificial gravity, removing the need for a spin-hab that would be necessary on a slower vessels to stave off the physiological impacts of prolonged weightlessness.  If considerable time is to be spent in orbit with crew onboard a spin-hab might be included, but it would have to be of the folding type, as shown.
Due to the high speed the torch ship reaches it would need much heavier whipple shielding than a slower craft, probably taking the form of a large disk protecting the bow, and in several layers; although that assumes that forcefield generators are to expensive to use except for engines.  It could become common, especially among military crews, to adorn the shield with the ship's emblem, or that of its owning country of company.  Also due to acceleration the structure will be more compact and solid than the structure of many sub-torch drive spacecraft.  Another factor is that as the forcefield used in the engine provides radiation shielding, there is no need for the extended central truss that is used in many designs to reduced irradiation of the crew.  Depending on the efficiency and operation of the forcefield the ship's radiators may also be smaller than a more realistic ship design, greatly changing the overall look of the ship.  The ship will doubtless have plenty of auxiliary electrical power, and so in a warship weapons will likely lean toward lasers and various electromagnetic projectile devices, which may affect the design somewhat.
   It is also important to note that the power of such drives enables truly massive payloads to be lofted into orbit, so there is no needed for space elevators, or other non-rocket space launch systems.  It does not mean that interplanetary or interstellar ships will be capable of landing on a planet; there parameters for space flight and surface to orbit are such that one vessel capable of both is in most cases impractical in the extreme.


   The vastly shorter trip times afforded by torch drive spacecraft has a significant impact on the commerce of a SF universe.  As can be seen from various tables on this page of Atomic Rockets the times are reduced as much as years for trips into the outer solar system, even with only 0.1g acceleration at the lower end of torch ship performance.  The most obvious implication is that with travel so mush easier far more people will be travelling.  As a result there will be regular dedicated passenger services, instead of the occasional spare berth on a mining or freight ship.  Secondly, any colonies in the outer system will be much larger and more diverse; the reduced trip time and difficulty allowing for more people to be thrown at a job, or even to immigrate.  Instead of a few sparsely manned mining bases there may spring up 'boom towns' filled with the kinds of characters far more likely to make for an interesting story than the staid types employed by the mining enterprise.  This large number of people will generate a secondary economy of luxury or possibly illicit items/services, offering large profits to the daring entrepreneur.  Another result of these torch ships is that although they can be made bigger than is possible with real technology, they will only have small crews, even a sole person.  On trips of months it would be psychologically dangerous to have one man aboard, and as I postulated in my first blogpost, it is unlikely that ships will be unmanned; with trips of a few weeks that is no problem at all.
   The nature of the cargo being transported also changes with the introduction of torch level drives.  If you are willing to travel a little slower a 0.1g torch ship can carry a lot more cargo at lower acceleration, for practically the same cost.  When mass budget is limited the cargo must be high return - rare earth metals, machinery and electronics, medicine, fissionables, etc. - with the ability to move more mass other commodities become more important - iron, copper, aluminium, etc.  I would think that the faster ships with larger mass budgets would also tend to favour a few large ships in the merchant fleet, rather than many smaller vessels; but it is a question beyond my pay grade.


   In the early stages of the colonisation of the solar system Earth will undoubtedly remain the political centre of attention.  On Earth will reside those who own the mining interests, those who buy the few valuables that space has to offer, and from Earth come ships bearing supplies without which any effort at industry or colonisation is doomed.  This is likely to be the same in any system with an inhabited planet; what the case would be in a newly colonised system is quite different, and the topic of another planned blogpost.  This, of course, enables all sorts of interesting shenanigans when a habitat or colony grows independent enough to want independence; a device that has been used to advance the plot of many SF works, among them Robert A. Heinlein's The Moon is a Harsh Mistress.  However, the inclusion of torch drives makes this situation unlikely in the extreme.  It seems to be the case that our solar system will function as a hydraulic empire, in which the water is replaced by technology that can only be manufactured on Earth.  As trip times are short, it is relatively easy to keep a few spares on hand and order more when needed, so any impetus to develop technological independence is removed from the colonists.  Purely social reasons for a colony to separate from Earth government may arise, but these are unlikely to lead to a armed conflict if the colony depends on Earth for technology.  There is also the fact that it will only take the Earth military, with its much vaster manpower, a short time to respond to any military action.


   In a setting or 'Verse of almost any kind there are bound to be small armed military vessels.  These will have the duties of providing patrols to anywhere not immediately visible from their home base, carrying diplomats and politicians, intelligence gathering, providing COIN and anti-terrorist mission support, boarding and inspections in orbital space.  They may be armed, but lightly; a few missiles, a chain gun, possibly a HV kinetic cannon or laser.  In the universe of forcefield enabled torch drives, however, large fleet ships, or any kind of direct warfare vessels are unlikely due to a ferocious device known as the torch missile.
   The torch missile is a simple device; a large independently targeted missile equipped with a miniaturised torch drive unit.  Most torch drives that have been theorised in the real world are incapable of too much miniaturisation, or are prohibitively expensive to be used as disposable weapons.  A forcefield drive, however, is only limited by the size and cost of the field generator; a variable which the author is free to adjust to suit the 'Verse.  Unless the forcefield used in the setting are so strong as to make any spaceship using them invulnerable to any amount of kinetic energy torch missiles will be able to destroy any ship.  All you have to do is launch enough of them at a high enough speed and some will get through the targets point defence.  Only one hit will be needed; no-one walks away from a impact with a ten tonne missile travelling at several hundred kilometres per second relative velocity.  And they have the same range as a ship unitising the same drive system, meaning that an attack can be launched from the surface of a planet or a orbital station as easily as from a battlestar - not to mention accelerations in the hundreds of g.
   The result of this is that conventional spacecraft are useless in a all-out war between proper and equal space militaries.  Battles will be between defensive systems and swarms or missiles - or between two opposing swarms.  If major warcraft exist, they may well fill in the role of mobile AAA batteries, tasked with the protection of a vital asset.  The military in space is thus unlikely to be as large as Army, Navy, or Air Force, composed mainly of orbital assets, and most of its personnel geeky technicians rather than glamorous pilots.

Further Reading
   A mine of information regarding torch ships is available on the Atomic Rockets website, along with various interesting tables that help explain their performance benefits; and Rocketpunk Manifesto has an excellent article on torch missiles, (somewhere).

Wednesday, 17 December 2014

Force-Fields; Not Just Defence

   Force-fields - or shields, screens, deflectors, etc. - have been a recurrent trope in SF since the creation of the genre; scarcely has there been a mainstream novel or movie that does not feature them to some extent.  Like many other SF magitech devices force-fields often shape the story and 'Verse in which it is set; without planetary defence shields the Rebel Alliance on Hoth would have had little chance against the might of the empire.  Star Wars is not alone, the universe of Dune, Star Trek, and countless others use the technology in a unique way.  Usually the factors and applications considered revolve around the primary usage of forcefields in SF, defensive measures for military vessels.  In this article I will look at a few, most of which have admittedly little impact overall on the 'Verse in which they are used, but which help to anchor the story and the readers attention firmly in the future world.

   For the sake of simplicity the forcefields in this blogpost are assumed to have the following characteristics; can be projected in a variety of geometrical shapes, have mechanical strength, repel kinetic and radiant energy.  It is also assumed that either the forcefield is invisible when in matter-repelling mode, or it can be tuned to block or admit certain frequencies of light.
  • Airlocks:  this has been seen in both Star Trek and Star Wars, and might be one of the least stupid of the non-defensive ways that forcefields have been used.  The entrance to the hangar bay has physical doors, a forcefield that allows slow moving shuttles to push through is activated when required.  As air molecules move quite fast, they cannot penetrate the field, and so pressurisation is maintained.  However, everyone had better remain in p-suits; a blown fuse could otherwise result in the inconvenience of explosive decompression.  Note that a real world device called a Plasma Window can achieve much the same result. 
  • Landing Gear:  this example comes from the SF comedy Galaxina, and is employed by the spaceship Infinity to overcome the problems with landing on uneven ground.  Like the forcefield airlock this is well and goo, until the power fails and several hundred or thousand tonnes of spaceship crashes to the ground.  While it would be somewhat foolhardy to equip a normal spaceship with these, they could serve for special landings where the ground is unhardened, say for military or rescue missions, with the forcefield acting like a futuristic giant snowshoe.
  • Structural Reinforcement: the ships of Star Trek's Federation are much maligned among engineers and those of scientific bent for their structurally stupid design.  The narrow struts connecting the hulls and warp nacelles are under incredible stress in any manoeuvre, and to come with this the ship uses Structural Integrity Fields.  Again, good until the power goes out, which is probably when you don't want the ship snapping into three pieces. 
  • Emergency Containment:  although - yes, power again - physical barriers are probably preferable for containing anything from prisoners to poisonous gasses, forcefields might prove indispensable in an emergency.  If they can power up in instants they could seal off an area far sooner than ponderous blast or containment doors, felling to seal off of dangerous situation in moments. 
  • Life Support:  the vacuum of space makes simple jobs a nightmare, pushing the costs or orbital construction sky high.  If a starship under construction in orbit could be enclosed with a forcefield just strong enough to contain an atmosphere, matters would be much simpler.  Even though for safety p-suits would still be worn, the 'air' could equally easily be there to enable plasma cutting as breathing.  A forcefield on a pant could be used as an emergency shelter from natural attacks such as volcanos, tsunamis, and hurricanes.
  • Power & Drive Reactors: the lower limit to the size and weight of a nuclear fission power supply is the critical mass needed for a sustained reaction.  However, if the forcefield is a perfect neutron reflector it is easy to see how it could cause even a few grams of uranium or plutonium to fission.  The resulting plasma could be confined by the forcefield and piped through a magnetohydrodynamic generator, the whole package limited in size only by the forcefield generators.  Fusion could be treated in the same way, opening up the way to abundant clean energy.  The most obtuse of the implications that result from this is the development of torch drive spacecraft, which I will discuss in a future post.
  • Energy Storage: antimatter is often proposed as the ultimate starship fuel; a misleading statement.  Like the use of hydrogen as car fuel, antimatter acts only as an energy storage device, a battery.  Starships need astronomical amounts of energy, so antimatter is used as giving the ultimate power-to-weight.  Create a hollow container from a forcefield, fill it with a vapour that absorbs a frequency of light allowed to pass through the field.  Energy is added to the 'battery' with lasers, and thanks to the phenomenon of electron shells the light released by the vapour is unable to pass the field, most of it at a different than original frequency.  A device such as this could have no limit to the energy contained, making 'nuclear hand-grenades' look like damp firecrackers.
  • Directed Energy Weapons: as anyone familiar with the Kzinti Lesson knows, the exhaust plume of a starship or torch drive spaceship is as deadly a weapon as can be found.  The Fission Fragment Rocket, possible to build in the real world, has an exhaust velocity of a few % of c, making it a deadly beam weapon at close range.  By piping the plasma from a fusion reaction out through a forcefield nozzle a devastating weapon could be created; it disadvantage a fairly short range due to the dispersion of the beam.
  • Airships: if a forcefield has no mass in and of itself, it makes the perfect airship hull.  Possibilities include vacuum airships, high temperature thermal, airships that change shape to attain supersonic speed, etc.  Nor would an airship built in this way suffer from the fragility of conventional designs, making it much more practical than any physical airship. 
  • Re-entry Shielding: for a large or fast spaceship a re-entry shield is much to heavy, despite the advantage in fuel reduction that the Leonov demonstrated.  A forcefield, especially if already fitted for military defence, is a perfect substitute, and if power fails, your probably screwed anyway.  By allowing aerobraking the available delta Vee for a mission could be doubled, or the fuel load halved; a significant improvement.  Also, as it could be much larger than the actual ship, and of a more aerodynamic shape, g-load could be altered to be less taxing.
  • Cassions & Civil Engineering: a cassion is a temporary dry-dock of sorts, built to enable the construction of underwater structures.  A forcefield by its virtue of easy deployment - on/off switch - is ideal for rapid or emergency construction.  
  • Tools: this is seldom seen, the only example I have personally come across being in Asimov's extensive 'Verse, where forcefield tools are far more capable than mechanical counterparts.  The advantages of such theoretical tools are many, and are discussed on Atomic Rockets.

Update (14 JAN 2015)
   As can be seen in the comments for this post, reader Yoel pointed out a two applications I had completely overlooked, so I'm adding them in.
  • Ramscoop:  the greatest challenge of constructing a Bussard Ramjet, one of the most advanced and powerful starship designs, is the construction of a magnetic field capable of collecting the interstellar hydrogen needed by the design.  A forcefield could be just the solution, especially if it is massless and frictionless.
  • Solar Sail: the solar sail is an interesting design that cannot ever come to its full potential due to material constraints.  In essence the solar sail uses the momentum of reflected sunlight or solar wind, having theoretically infinite delta Vee.  However, the mass of the sail, combined with the inability of find a material that will withstand solar heat at the closer, and thus more effective, distances means it is not likely ever to be widely used.  A forcefield, however, might be massless and perfectly reflective, making it the ideal method of producing a solar sail, and thus providing a reliable method of interstellar transport.  In fact, this is such an effective interstellar design that I have decided to do a post on Interstellar Transport, featuring such a design and explaining its implications. 

Monday, 1 December 2014

The Man in the Can: an argument for manned spacecraft.

   OK, this is my first post (ever), so a short explanation of the blog, its goals (at present), and content (planned).  It is not going to be a literary foray, although I may post some of my own work from time to time, it is concerned merely with the nuts and bolts of SF; the hows and whys of the setting and technology.  The Science before the Fiction, so to speak, and the way one shapes the other. 
   Most of the time I'll be looking at a particular technology or trope of SF - force fields, FTL travel, interstellar empires - and analysing the way that it would effect the setting.  I'll look at the science behind some of common technologies seen in 'hard' SF, and I'll make hypothetical examples, along with calculations and equations.  Sometimes I might do a 'case study', starting with a set of initial assumptions, and exploring the universe that they imply.  
   Although I'm creating this blog with the intent that it will help other writers and fans of SF, my motives are less than altruistic.  I harbour the hope that people with more knowledge than myself will stubble across it, comment, and enlighten.  So if you have ideas and opinions, please comment; constructive criticism is always welcome.  

   But on with the fun stuff and the subject of this post: the Man in the Can.

   It has been stated that SF fans, and people in general, connect better with human characters than they do with silicon chips(Bernside's Zeroth Law).  Thus, while a book or movie may have robotic or AI supporting characters, the protagonist is generally human.  In fact, for most of us SF addicts, the whole point of science fiction is to write, read, or watch people in various situations, especially on or around spaceships. Unfortunately for us, this is also the place people are least likely to be found in a Hard SF setting.  A military ship will have crew to make the higher order strategic and tactical decisions, but even they become redundant in the heat of combat, or in navigating between planets or stars.  Not that if the sole purpose of the ship is to fight, rather than gunboat diplomacy, even one human becomes pointless, as they limit acceleration, cannot themselves cope with the complex trajectories of space combat, and limit performance through the added mass of life support and extra armour.  For cargo vessels the conclusion is inevitable especially at a low tech level with the sorts of performance that most projected NASA designs have.  Not only does the crew take up mass budget that could be used for profitable cargo, but they force the trip time down to reduce radiation exposure and irreversible damage from zero-gee.  Of course, you can add a spin hab, shielding, but this adds cost and cuts away payload.  So while there might be a supervisor at the water mining station on Demios, the cargo ships will be basic drones, flowing a minimum energy, maximum time Hohmann transfer orbits.  They don't even need to be AI, very basic software will do the trick.  Also, much smaller spacecraft are possible, allowing external propulsion methods like mass drivers, magbeams, and solar sails to be more effective.

   However, all is not lost.  If there is no technical reason for the ships to be manned, a non-technical one can easily be fabricated.  Say a terrorist cell manages to hijack the controls of a few ten tonne capsules of rare earth metals from the asteroids, and uses the minimal guidance thrusters they posses to cause a collision with a space station, or some other space based asset.  Chaos ensues.  Without enough time to react such an attack would be devastation, and no government would want the possibility of it happening again.  Looking for someone to blame they settle on the transport company, and pin responsibility on them.  As a security measure - any computer can be hacked, so adding more powerful software does not do the job - they decide to build manned ships.  At the beginning of the flight the captain signs a document that gives him full responsibility for the ship, protecting the parent company from legal retaliation if another 'incident' occurs.  

   Naturally the company does not want to cut its profits by to much, so they skimp.  Tiny quarters, minimal life support, one crewman, and long travel times to reduce the energy budget.  The crew themselves are likely to be minimally trained, as even if something goes wrong there is little they can do; there is nowhere to pull over and top up the radiator in space.  Many of them would be the anti-social misfits how like the solitude, or people who need the money, assuming high wages.  Coast cutting measures also leads to story potential when a water tanker halfway between Earth and Mars begins to malfunction, and the lone crewman is caught up in a desperate struggle to stay alive.  In any case, it is a far more interesting setting than one in which robotic freighters are the norm.  It also suggests further antics down the track; a solar system in which ten tonnes modules are shot all over the system by magbeam is not one in which a interplanetary war is likely; one with a multitude of large, high capacity ships is.  Take out the cargo, add a rack of missiles, and the United Saturn Federation has its first warcraft to fight against the Terran oppressors.
   So there we have it, a reason to keep the man in the can.

   Feel free to comment and add anything that I've missed.