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Spacecraft design

  1. Nov 22, 2014 #1
    I'm going to write a (semi) hard SF. I wonder whether i left out something from spacecraft design, or got something wrong?


    Armed cargo ship (used for piracy/commerce raid also)

    At the back of the ship, a large block contains the fusion reactor, the main ion thruster, the manuevering ion thrusters, and also the command computers. It is the realm of the engineers, due to sensitive electronics, cables, magnetic boots are not allowed here.
    After that, a long cylinder contains the heavy hydrogen fuel. It has got large radiator wings, and also a row of chemical thrusters meant for rapid dodge.
    The cargo block is a big cube, it has got a small living container with life support. They hide the fighters in it also.
    At the front of the ship, a hollow pyramid, meant to protect frontal sensors from high speed collision with micrometeors, when it is closed. Its opened when the frontal sensors are really needed, like landing on an asteroid mine, or combat.
    Since the ship is armed, the lasers are also hid in this pyramid.


    Battleship

    Looks like a giant icicle (with large radiator wings), almost a km long. In the middle of it, a dreaded spine weapon, a huge coilgun that launches missiles with 100 km/s. A missile shatters into a dozen smaller warhead in order to get through point range defence.
    The ship has got another spine weapon also, a free electron laser in order to defend itself. Together with smaller coilguns firing tiny unguided slugs, the ship is almost unkillable with a frontal attack.
    However it has two weakness : simultaneous attacks from different directions, and low acceleration.


    Fighter

    Since an asteroid mine offers cover from missiles (and the goal of wars is to capture them), and nuclear hardware isnt cheap (reusablity is good), instead of regular missiles, smaller than battleship warcraft and motherships like to use spacecraft originally developed for orbital combat. Since they are unmanned most times, they can be still expended like missiles.
    It has an egg like shape, with pointy nose to help landing on the surface of a planet, if that is needed. It has got high thrust low specific impulse nuclear thermo engines, thrusters facing in every direction.
    It is armed with a coilgun firing tiny unguided slugs with 100 km/s in order to deal with other fighters and attack point range defence from a distance. It also has got laser jammers and small shield like interceptor missiles.
     
  2. jcsd
  3. Nov 22, 2014 #2

    mfb

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    Spacecrafts do not have a "back". They have one or more directions of acceleration. If your fusion reactors are at one side, I assume your exhaust is always at that side as well. If you want to approach any object in space, for example, this side would look like the "front" as seen from this object.
    What does it do against small, cold, massive objects approaching it at high speed? And why would you want to attack it from the front anyway? An object that size is highly visibie over huge distances.
     
  4. Nov 22, 2014 #3
    What do you suggest instead of "back"? Well, in case of acceleration it is the bottom of the ship to the crew. Should i call it that, since it is also similar to present day spacecraft launched by a big rocket on the bottom?

    "What does it do against small, cold, massive objects approaching it at high speed?"

    It can have active sensors as well (maybe the laser in small energy continous stream can count as one), and spread out the beam in order to burn a number of shrapnels. Of course it is not unkillable, but pretty resistant.

    Detection and interception are different things, one has to build up proper interception courses, in order to attack with high speed from multiple directions.
     
  5. Nov 22, 2014 #4

    mfb

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    Bottom, engine side, whatever.

    Small, cold, black massive objects are hard to track, especially if you coat them like modern stealth airplanes to avoid radar detection.
     
  6. Nov 22, 2014 #5
    Thanks, i think bottom side will be good, proper terminology isnt marginal.

    But swallowing the microwaves heates up the object, also small cold stuff are unguided, with the sizes of space, even a battleship isnt easy to hit.
    Anyway, spacecraft has to be well prepared for encounters with small meteors, maybe statistically there isnt much chance even in the asteroid belt, but still.
     
  7. Nov 22, 2014 #6
    Sorry, stealth in space is impossible without' magic' technology.
     
  8. Nov 22, 2014 #7

    phinds

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    This makes no sense to me. Can you substantiate your statement in any way? Why would stealth technology care whether it's in an atmosphere or not?
     
  9. Nov 23, 2014 #8
    Depends on how you define stealth. You cant become invisible in air neither. A plane can reduce its radar cross section.
    In space the main problem is that you cant hide the flames of the thrusters, and it can be detected from very far.
    Then they will know where to search for you, and find you with active radars and lidars, even if one can reduce IR cross section with liquid helium, heat sinks, radiate heat toward the opposite direction, or outside the elliptic plane.
    At this point i assume that even small cold shrapnels can be detected from a distance, that one can still dodge or burn them. But i also employ the constraint (for epic reasons), that defence can be still overloaded with a kinetic swarm, and attack rockets have a superior range compared to lasers..
     
  10. Nov 23, 2014 #9
    I started typing all the reasons why I could remember, but it would save me about an hour of typing just to post this article I found instead.

    http://www.projectrho.com/public_html/rocket/spacewardetect.php
     
  11. Nov 23, 2014 #10
    Since we couldnt detect a kilotons meteor before it hit Earth, i have doubts whether that article isnt underestimate difficulties, however the basic assumptions are right, a dense recon network is much cheaper than spaceships.
     
  12. Nov 23, 2014 #11
    We have satellites with telescopes designed to look at giga-lightyear distant galaxies, we weren't trying to guard the Earth against incoming objects.

    An active-LIDAR system using a short, intense broadband burst of say, visible light to IR should be very hard for anything to completely absorb. Then the object will be visible even if it is at 3K.
     
  13. Nov 23, 2014 #12

    phinds

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    Which simply states, as the opinion of one poster, that stealth technology does not work in space. This is a useless reference. How about you spend just a minute or two posted even one valid reason why stealth technology would not work in space?

    I do understand that if you are firing chemical rockets out the back of your fighter, unless they are in a tight beam and you are masking them by heading straight for the target, they will be detectable but the exact same thing is true in the atmosphere. This is not a distinction of space-based detection.
     
  14. Nov 23, 2014 #13

    mfb

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    For spacecrafts. We were not discussing spacecrafts at that point.
     
  15. Nov 23, 2014 #14
    But in space, from a range that is much beyond interception range unless they are using relativistic projectiles...
     
  16. Nov 23, 2014 #15

    phinds

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    I have no idea what the intent of that statement is.
     
  17. Nov 23, 2014 #16

    russ_watters

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    So, to put a finer point on things:
    1. The "stealth" used by the stealth fighter and bomber is invisibility to radar (primarily). Since it is determined soley by materials type and shape, it will work exactly the same in space as on earth/in the atmosphere. A steath fighter in space would be just as invisible to radar as on earth.

    2. The arguments against are focused on other potential detection methods besides radar. And while it is true that they may still theoretically work, radar is primarily used for a reason: it is the best.

    The biggest problem for any detection method in space is the distances involved. If it were as simple as just pointing a SPY-1 radar out into space, we'd already have detected every asteroid in the solar system. A similar problem applies to IR: one way to defeat a heat seeking missile is to put yourself between the missile and the sun. In space, with much weaker heat sigatures, picking a spaceship out of the background of stars would be difficult.
     
  18. Nov 23, 2014 #17
    Yes, however the main point is that thrusters emit lots of heat, background clutter is much lesser than air, so a network of telescopes and recon probes can track the ship based on that trail. To achieve a big travel speed, the thrusters needs to be fired for a long time. While drifting slowly can reduce the spot distance, but also result in very long travel time, and during that, one recon craft might still spot the ship.
     
  19. Nov 23, 2014 #18
    My main point was, regarding stealth in space is that besides radar there are so many ways to detect a vessel easily that you mineaswell not bother making it undetectable to radar and put your resources into more propellant and/or payload.

    Its not the authors opinion in the article, besides him being an engineer, he merely points out known fact and common sense along with the hard data.

    Assuming their is a space war, and you take the time make your ships undetectable to radar, any military organization worth anything would guard against this and employ a wide variety of detection systems, passive and active.

    So essentially, without 'magic' tech, such as the 'cloaking device', total and plausible stealth is virtually unachievable in space. Trust me, I hated it to. I fought it. Then I came to accept it. Once you do, you can move on and look for other ways to make your space craft design hobby, novel, screenplay, fanfic or role playing more interesting.

    Your best stealth attack would be via infiltration, sabotage, and long range attack with relativistic weapons. Space pirates, or more accurately privateers, might be able to succeed to a degree in orbit above a planet or station with high traffic, where they can escape into sovereign space.
     
  20. Nov 23, 2014 #19

    mfb

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    Payload? We were discussing the detection of (unguided) bullets.
     
  21. Nov 23, 2014 #20
    Those could be considered a payload.

    You could still detect these however. Granted, it would be more difficult, and it would depend on how they were launched as to the ease of detection. Assuming you want them to reach the target within any reasonable period of time, you need to accelerate them. There are a few ways to do this.

    1. You accelerate the inert projectiles via conventional means, a gun turret for example. This means chemical or electromagnetic propulsion. These would create heat from the firing/power plant, EMR in the form in IR. This heat could be detected, but of course assuming your ship is maneuvering so could the propellant exhaust. In addition, residual heat would be present on the projectiles. Seeing as space has no temperature, these would show up like little beacons. Whether or not the target your firing at could do anything about it is another matter.
    2. Ok, you say i'll fire them more slowly but cold.... but how? I'll keep them exposed to space to keep them chilled and not use a gun. Well then you have other problems, if you open up your 'bay' to space well moving, aiming is more difficult. If your stationary, your a nice target. In addition, your payload is going to bloom like crazy over distance and slower moving projectiles can be easier to avoid.
    3. The final point however, what are your targets defenses? Does it have a space age Trophy type active defense system? CIWS? Mag/plas shields? Heavy armor? Is it even military? If not, there would be easier ways to destroy the target then via stealth. Detection does not necessarily mean defense.
     
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