Thursday, 5 March 2015

Slow Interstellar Travel: The Enzmann Starship

The Slowship

   Generally speaking there are two approaches to manned interstellar flight.  One uses high technology to build a small(realativly) starship that can achieve a high fraction of the speed of light, making the journey in a few decades or less.  This has the disadvantage of relatively small payloads, making colonisation difficult without a fleet of ships.  The second alternative is to use a ship that travels at only a few percent of the speed of light or less, making the voyage in possibly hundreds of years.  These are the slowships.  Most commonly they are seen as worldships, each one capable of supporting thousands of people for hundreds of years.  This approach has the advantage that the ship is elf is a colony, making the initial settlement no different than the voyage that came before.  However, the ships are truly huge, and may be beyond the ability even of a united star system to construct.  One of these ships, and perhaps the most interesting for a author of hard SF, is the Enzmann Starship.


   The Enzmann starship is simple in concept.  A cluster of thermonuclear pulse engines, a habitat section holding ~200 people, a massive ball of frozen deuterium, and a cruising velocity of up to 0.3 c.  Conceived in 1964 by Dr. Robert Enzmann there have been several variants in which the size, number of drive units, and method of storing the fuel were explored.  Detailed information on the Enzmann is hard to find, however, so I am unable to venture into a discussion of the differences between the variants.

   The most iconic feature of the starship is the several millions tonnes of deuterium propellant stored as a gigantic sphere on the nose of the craft.  Originally this was to have been unconfined, the deuterium 'ice' supporting its own weight.  However, this was shown to be unfeasible and later designs used a seamless metal shell.  This was created by inflating a thin plastic balloon, on which metal plasma is deposited to form a flawless sphere.  I have no idea if this is really feasible, but it could be perfect for manufacturing habitats, starship hulls, planetary domes on airless worlds, and giant reflectors for photon starships.  It might also prove to be a viable technique for working with refractory metals, extremely difficult in the normal way of things.

   Annoyingly, the exact engines use are never discussed in any of the literature I managed to find.  That they are nuclear pulse units is always stated, but this is never clarified.  The deuterium fuel suggests that a arrangement similar to the Daedalus starship is intended, but with multiple smaller units, although a reason for this is not given, perhaps for redundancy.  Note that deuterium requires an external ignition system, unlike an Orion drive, which cannot be used in a cluster of engines - I think, again this was something I was unable to find a definitive answer on.  They could also be internal pulses, like the drive used in the Helios designs exempt that this has a Isp far to low for a serious interstellar starship other than, perhaps, a multigenerational starship.  The more modern development of the magnetic inertial confinement drive might fit the bill perfectly, although requiring a change of propellant.  Thinking about the number of engines used it occurred to me that as the starship is likely to be turned into a habitat when it arrives at the destination system, the drives could be stripped off and fitted to smaller vessels composed of other pieces of its structure, allowing the more rapid expansion of the colony.

   In some sources a cruising velocity of 0.3 c is stated.  This may well be attainable with a Daedalus style drive with high Isp, but seems unlikely for a thermonuclear pulse like Orion.  An interstellar Orion starship is often given a cruising velocity of 3% c, although it could be made slightly higher if the fuel fraction is increased considerably.  Magnetic/inertial confinement fusion, steady state or otherwise, could well provide the necessary performance.  The daedalus starship does not have a capacity large enough for a multi-generation voyage, which would be required with a 0.03 c cruise, but could carry sufficient range of ages to make a 0.3 c voyage possible.

   The final plausibility of the Enzmann starship is debatable, and depends on many assumptions about technology and construction that are answerable only through practical groundwork.  Such a large vessel would also require a very robust economy to produce.  However it basic configuration - multiple engines, large spin habitats, and a single huge fuel tank - have several advantages.  In a follow up post I will look at the what these advantages are, and the way they could be applied to a SF 'Verse to create a setting for interstellar colonisation.


  1. I am curious why SF decide to build their generations ship so huge, supporting thousands of colonists. The genetic bottleneck is the usual reason given.
    The concern is that with small group of colonists interbreeding will result with genetically damaged & retarded colonists. But that true to 'normal' humans.
    Every human have 23 pairs of chromosomes, females have 23 structurally identical pairs and mails have 22 structurally identical pairs.
    If a human have defect gene in one of his/her chromosome the parallel gene in other chromosome in the pair is backing up. Problems begin when someone inherent from his/her two parents defect gene in both chromosomes, rare in general, common in interbreeding.
    So, how to avoid genetic bottleneck without piling thousands of colonists?
    First- a human selective breeding program either it is on a global scale like seen in the movie "Gattaca" or on a small scale for the colonizing could produce 'flawless' human with no defect genes.
    Second – gene therapy on earth or/and in journey or/and colony could eliminate those genetic diseases.
    Third – if what ship and colony need is larger gene pool why carry massive 80kg human and not millions of fertilize ovum with the same mass? Such ovum will be implant in artificial womb and/or womb of crewwoman.
    All in all, combining one or more of the methods could result in a colonizing ship with a few dozens of people on board.
    Even with fastship that travels close to speed of light and have travel time of a few years, the crew will have the genetic bottleneck problem when starting to colonize the planet. So one or more of the three methods will be needed anyway.
    Those 3 technologies could create 'verses different from most SF 'verses.
    In modern time there is a common taboo regarding interbreeding, the source of this taboo is from the results of such ' marry & f**k your sister' are damaged children.
    But what if future genetic engineering could prevent those results? What's the reason to stick with such dogmas if genetic diseases are a thing of the past? Today people regards those things in disgusting and as an insult to someone (' U know why U so dumb? Cause your mummy & daddy have the same mummy & daddy'). What if those perfect Augment man & women will reject our ways of thinking?
    Even if there no colonizing spaceship in the 'verse - what will be the impact of those genetic engineering on those norms? Usually SF writers go on total Armageddon: wars between the improved and normal & dictator building an army of clones.
    I find it more refreshing to read SF raising some good questions rather than an old trope read several times before.


    1. Very good points as always, Yoel. I think the real limit on a starships voyage time is probably no more than a few generations, due to the lack of continuity between those who started the voyage and those who finish it. My favourite model is one in which there are two generations aboard, or a the most three, with a relatively small number of colonists. The ship starts out with the second generation as young children, or still unborn. By the time they reach the destination they have grown up and been trained by the previous generation, most of whom have died on old age. This could also prove very good for ensuring that a colony is tabula rasa, allowing it to develop more organically.
      Genetic Engineering... I will have to do a blogpost on it at some time. To me engineering an army of clones or super soldiers has always seemed a little far fetched; the real impact is on the civilian world. While currently there is some ground for people to argue against its use on humans, especially in creating 'designer babies' due to our relative lack of knowledge and skill, this will not always be the case. It is a debate that will rage for a long time, I feel. The movie 'In Time' showed similar effects in a society where people do not age; it was impossible to tell how to people are related by sight only. Very few SF authors explore such issues in any depth, and it is often incredible when done well.

  2. Doc E's website:

    Please credit any images you use. - webmaster M. Snyder

    1. If I might ask which image you are referring to?

  3. Just asking if you use any images or material from The Enzmann Starship site, that you credit the site and Doc E. It is amazing this site, Doc E is still alive and has released his entire archive to WKS (our company) to publish. If you want info on the Enzmann Starship or the man who designed it, this is the place. Starships Now! is his passion, still, after decades of suppression by the powers that be.