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I misread an answer to My carrier pigeons have been replaced by spoons: how can I send messages?, thinking it was referring to a network of parabolic reflector dishes made of spoons orbiting the planet. This lead me to envisage a colossal trebuchet on a mountaintop launching a rocket-powered structure of spoons into orbit, though I have doubts about the realism of this plan.

Assuming that the Royal Mathemagicians have discovered Newton's Laws of Motion, and ignoring for now how they'd actually use an orbiting parabolic reflector dish, is this realistic?

  • How would they launch it far enough?
  • How would they adjust it into a stable orbit?
  • Would the spoon structure survive the forces involved?
  • Is this affordable for a medieval king?
  • Assuming a surface gravity of 1G, how small would the planet have to be for medieval technology to be capable of this feat?
    (A smaller planet would mean a lower atmosphere and atmospheric pressure, so there's a limit as to how small you can make the planet.)
  • What's the minimum required handwaving to make this possible?
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    $\begingroup$ These spoon questions make me think Tommy Wiseau has taken over worldbuilding stackexchange XD $\endgroup$
    – Matthew Dave
    Commented Aug 10, 2018 at 12:20
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    $\begingroup$ The SE model is *one-specific-question/one-best-answer." this question is too broad because it is asking more than one question. We're generally pretty lenient about that, but this is too much. $\endgroup$
    – JBH
    Commented Aug 10, 2018 at 15:46
  • $\begingroup$ @JBH The first two are mandatory, the third one could go (but then it wouldn't be about spoons any more), the fourth one is important and the fifth and sixth are to make it easier. What should I cut out of the question? $\endgroup$
    – wizzwizz4
    Commented Aug 10, 2018 at 16:06
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    $\begingroup$ :-) That's one way of looking at it. You need a chance to think through your question to better define its framework. That's actually the purpose of our question sandbox. Have you taken a question through the sandbox yet? You should, if only once. You'll learn a lot about framing questions. $\endgroup$
    – JBH
    Commented Aug 10, 2018 at 16:33
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    $\begingroup$ One last comment. People like Jules Vern could imagine things like launching capsules with cannons because the science didn't yet exist to prove it couldn't be done. That's what makes quality handwaving important today. Remember the purpose of handwaving is distraction, to draw attention away from the factual errors your story must ignore to proceed. People pay a ton of money for quality handwaving because they want to be entertained. What many people (even on this site) forget is that quality fiction is about the handwaving, not the science. Otherwise all you have is a textbook. $\endgroup$
    – JBH
    Commented Aug 10, 2018 at 16:42

2 Answers 2

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It's not possible, whatever the planet, to launch something into orbit with a single throw: any "orbit" created from giving something an initial trajectory (eg launching it from a cannon) will (in a vacuum) come back and intersect the initial start point (unless it hits something on the way, eg another part of the planet). If there is an atmosphere (thus providing drag on the way up) then the "orbit" is modified further, to crash into the planet sooner.

See https://en.wikipedia.org/wiki/Space_gun#Technical_issues

The only way to prevent it crashing back into the planet is to give it so much speed in the initial launch that it has escape velocity: In this case it will fly off into space, never to return, and you don't have an orbit either.

Rocket-borne satellites achieve a stable orbit by having the rocket constantly change it's velocity: as it gets higher up, it turns and blasts more "sideways" to achieve the orbit parameters. So, in order to get something into space you would need to have at least one additional "course change" somewhere on the way up.

I'd say that the minimum required handwaving would be targetted on this additional "burn" to get it to change velocity once it's in space. Perhaps some primitive form of actual rocket could be used: a rocket, after all, is just a slow explosion in a box with a hole at one end.

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  • $\begingroup$ The trebuchet would just be there to give it some initial velocity so the rocket didn't have to do all the work. This is more a question about how you'd do it with medieval technology; unfortunately, "primitive form of actual rocket" is too vague for point 2. $\endgroup$
    – wizzwizz4
    Commented Aug 10, 2018 at 11:33
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    $\begingroup$ I suggest a two-stage trebuchet. the first trebuchet hurls the second into a sub-orbital trajectory, the second one hurls the payload into a circular orbit once it reaches the apogee. Some work may be needed to ensure correct aiming and timing on the second trebuchet, Use of magic to accelerate the trebuchet-projectiles in multiples of their own mechanical force would get the needed velocities. $\endgroup$
    – Ruadhan
    Commented Aug 10, 2018 at 11:35
  • $\begingroup$ @Ruadhan2300 Wouldn't the second trebuchet need to be spring-loaded, considering that the first trebuchet would launch the second into freefall + drag? If spring-loaded, the whole trebuchet mechanism can be replaced by a spring-based cannon for better reliability. $\endgroup$
    – wizzwizz4
    Commented Aug 10, 2018 at 11:37
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    $\begingroup$ Good point, what you'd want is to get a third trebuchet on the back of the second, firing in the opposite direction to counter-force it. Alternately a spring-cannon would be easier to aim, but it's not a trebuchet (the superior siege weapon) so we don't care about that solution :) $\endgroup$
    – Ruadhan
    Commented Aug 10, 2018 at 11:38
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    $\begingroup$ @Ruadhan2300 Hey! All I care about is getting it to space and keeping it there, but still close enough that we can use it. $\endgroup$
    – wizzwizz4
    Commented Aug 10, 2018 at 16:19
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You need to hand-wave Adamantium

Low Earth Orbit velocity is 7 800 m/s, or Mach 23.

Now you said "trubuchet". Ok... let us assume we have a really big trebuchet... let us make it, say, 300 meters high. Let us assume the swing-sling is travelling in a circular arch with 300 meters diameter, for half a revolution before it is let go.

$300m \times \pi \approx 1000m$

So in 1000 meters travel you have to achieve a velocity of 7800 m/s.

Ok, so... during constant acceleration a, the distance travelled s is resulting velocity vmax times the time t over 2. And the resulting is the acceleration times the time.

$s = 1000m$

$v_{max} = 7800 m/s$

$s = \frac{v_{max} \times t}{2} \Rightarrow t = \frac{2s}{v_{max}}$

$v_{max} = at \Rightarrow t = \frac{v_{max}}{a} \Rightarrow$

$\frac{2s}{v_{max}} = \frac{v_{max}}{a} \Rightarrow a = \frac{v_{max}^2}{2s} = 30420 m/s^2 \approx 3000g$

There is no material we know that will survive an acceleration of 3000 g and not be crushed by its own weight. For an example of what happens when something made of metal experiences an acceleration of 3000g, this video is very illuminating (and mesmerising). In short: at those forces, it does not really matter what the thing is made of, because everything splats like it is made of putty.

So first you need to hand-wave Adamantium, otherwise your trebuchet, the spoon reflector and everything supporting them will fly apart on launch as if you tried to make a trebuchet out of soft clay.

But(!)...

If you have Adamantium... then you can build a space elevator, with no need for a trebuchet to reach space.

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    $\begingroup$ What you really need is a spell of Rigidbody Physics. treat the object as a non-deformable point-mass. Then G-forces cease to be a problem. can't use it for the space elevator though. $\endgroup$
    – Ruadhan
    Commented Aug 14, 2018 at 11:58
  • $\begingroup$ @Ruadhan2300 Hah, good one. :) $\endgroup$
    – MichaelK
    Commented Aug 14, 2018 at 12:03

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