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From the launchpad to the Mun in 13 seconds

Ninety-Three

By Ninety-Three
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Ninety-Three

Ninety-Three

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Over in the challenges thread, I discovered that if you make a really light ship, and attach 700 decouplers, they propel it pretty high.

screenshot54.png

screenshot53.png

It works because decouplers exert a fixed amount of force, which, when multiplied by 700 decouplers and applied to just one capsule and a bunch of virtually weightless struts, makes you go very, very fast.

There are some problems with the approach: Firstly, 700 decouplers takes around half an hour to load, and you need every one of those decouplers to get your speed. That's because you have to use the heavy manned capsule: you're going to lose 95% of your speed to low-altitude drag, so the low-drag capsule is a necessity over the much lighter probe core. You also can't attach anything to it: it turns out that once you get into the neighborhood of thousand-G impulses, things start to tear off. While attempting to solve these problems, I ended up creating the vessel I dubbed Plaid.

zR38VUa.png

lqv8AGX.png

Plaid is a mere 300 parts, loading in seconds. It's basically a line of struts with decouplers stuck on the bottom, and a detatchable probe core. The RCS block is instantly annihilated by the acceleration, but it looks pretty at launch.

Now, I'm sure you're eager to get to the whole 'Mun in 13 seconds' thing I mentioned in the title. This is what happens when you "launch" Plaid.

xkDU4e1.png

HG0Tfmo.png

The game's readouts have a bit of trouble catching up to the absurd speeds generated, but take a look at the numbers in that second screenshot. Plaid is leaving Kerbin at nearly a million meters per second. This is possible because Plaid is built with a strut as its core piece: the probe core is left behind on the ground, meaning all of the decoupler force transfers into those virtually weightless struts, accelerating them to completely insane speeds.

But Plaid isn't just shooting off into space.

Dm1kgvN.png

syUExQe.png

Plaid has a destination.

2vyYYoc.png

It's going there very, very fast.

yP0aF87.jpg

kaUyFcZ.png

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So there you have it. A 300 part craft can accelerate to over one million meters per second, and reach the Mun before someone five kilometers from the launchpad hears it leave.

I've created two albums, one showing Plaid's journey, and one showing the construction. The basic principle can be scaled up as far as your computer can handle. Exceeding the speed of light is left as an exercise for the reader.

UPDATE: Youtube user Stun_gravy has used decouplers and ladder physics to

. To Duna. In just 35 minutes. AWESOME! Edited by Ninety-Three
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Specula

Specula

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I impacted at speeds a little higher than KSP was meant for, causing me to end up buried 6 km down in the Munar soil.

LOL.

Any chance of getting the craft file to play with?

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Tw1

Tw1

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That's awesome! I wonder if you played about a bit, you could launch just enough weight with it to impact the Mun with reasonable speed, and carry enough fuel to land a tiny probe.

Until then, this is the most kerbal launch vehicle ever.

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Ninety-Three

Ninety-Three

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wonder why you're using those blue stack decouplers. Aren't they heavier for the same power as compared to the regular ones?

They are, but that's irrelevant. When they decouple, they separate themselves from the ship, which stops their mass from counting. Those decouplers have the highest force available, and with weight out of the question, the only thing that matters is how CPU intensive the part is. Generally the best way to go about that is a low part count, so we use the blue ones.

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Ninety-Three

Ninety-Three

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I wonder if you played about a bit, you could launch just enough weight with it to impact the Mun with reasonable speed, and carry enough fuel to land a tiny probe.

I'm afraid not. As I mentioned in my first post, the decoupler launch is not friendly to ships. A thousand Gs of acceleration is enough to tear off every piece but the core, the reason Plaid stays together is that struts don't have physics calculations run on them. Any "real" part will tear off if you get going more than a few hundred meters per second.

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SirJodelstein

SirJodelstein

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Incredibly awesome. Does it work without the RCS block? And how do you switch from the probe core on the ground to the launched part? If it moves so fast, i would assume that it leaves the "switchable" range way to fast to get a chance to switch controls.

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Trobby888

Trobby888

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Wow....Really awesome.

I tried to launch plaid just now. The problem though is that KSP seems to be having trouble keeping up with the insane velocity. All that's happening on my screen is that the camera acts like a ship moving in a straight line away from Kerbin, accelerating at roughly 100m/s^2, and the struts aren't seen.

How did you manage to get the struts and the 800000 ms-1 showing up on your screenshots?

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jwenting

jwenting

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They are, but that's irrelevant. When they decouple, they separate themselves from the ship, which stops their mass from counting. Those decouplers have the highest force available, and with weight out of the question, the only thing that matters is how CPU intensive the part is. Generally the best way to go about that is a low part count, so we use the blue ones.

true, but if you release them in sequence, rather than all at once, you're carrying the weight of them up (albeit quickly decreasing).

And if they have the same power as the others, you'd get higher TWR from them.

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Tw1

Tw1

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I'm afraid not. As I mentioned in my first post, the decoupler launch is not friendly to ships. A thousand Gs of acceleration is enough to tear off every piece but the core, the reason Plaid stays together is that struts don't have physics calculations run on them. Any "real" part will tear off if you get going more than a few hundred meters per second.

Not even with unbreakable joints on? But then, I'm sure I've broken things that have had unbreakable switched on.

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Ninety-Three

Ninety-Three

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And how do you switch from the probe core on the ground to the launched part? If it moves so fast, i would assume that it leaves the "switchable" range way to fast to get a chance to switch controls.
I tried to launch plaid just now. The problem though is that KSP seems to be having trouble keeping up with the insane velocity. All that's happening on my screen is that the camera acts like a ship moving in a straight line away from Kerbin, accelerating at roughly 100m/s^2, and the struts aren't seen.

How did you manage to get the struts and the 800000 ms-1 showing up on your screenshots?

Press space, and then immediately (during the three second, 1 frame lag spike) press escape. After the decoupler lag abates, you should end up looking at Plaid 1 frame above Kerbin with the game paused. Unpause and follow it out. For a few moments, KSP may refuse to show accurate numbers, but it'll get there quickly. Also, you may have to try the launch a second time, every now and then in testing Plaid would experience some problem and not exhibit the behaviour I documented here.

How far does it go if Mun isn't in the way?
Mein Gott...that's terrifyingly awesome. Makes me wonder, though-interplanetary transfer possible?

With one million meters per second of dV, Plaid's capable of interstellar transfer if you aim it well.

Really, think about what traveling at nearly one million meters/second means. Plaid can achieve escape velocity from the surface of the sun.

true, but if you release them in sequence, rather than all at once, you're carrying the weight of them up (albeit quickly decreasing).

And if they have the same power as the others, you'd get higher TWR from them.

Here's an example of why that's not effective, using some math-friendly made-up numbers. We have a ship that weighs 0.1 tons equipped with 11 1-ton decouplers that each exert 10 kN of force.

My way, we'd decouple them all at once, applying 110 kN to the ship, and earning 1100 m/s of dV. The way you're suggesting would split them into stages of 10 and 1: the first stage would exert 100 kN on 1.1 tons, for just ~91 m/s dV, and the second stage would exert 10 kN on 0.1 tons, for 100 m/s, totaling 191 m/s.

Like you said, if you release in sequence, you're carrying the weight of all of them up, and that's hugely inefficient because your ship is virtually weightless otherwise. It's best to decouple all of them on the ground, which takes us back to weight not mattering.

Not even with unbreakable joints on? But then, I'm sure I've broken things that have had unbreakable switched on.

I haven't tried that, I'll have to give it a go. If unbreakable joints are still breakable though, I'm doubtful they can withstand Plaid's sixty million Gs.

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Ninety-Three

Ninety-Three

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Ready... aim...

"Fire" just doesn't seem sufficient. Does anyone say "Ready, aim, plasma"?

How did you make it not tip over? (Like must decoupler powered crafts do)

What is there to tip? Here's a diagram of Plaid without the silly decoupler stacking:

Plaid.png

What could be more stable than that?

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numerobis

numerobis

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Is the RCS block there just to give the craft a mass, to avoid dividing by zero on launch?

Struts aren't "nearly" weightless, they are not physically significant. That means no mass, no drag, no getting burned by exhaust gases, etc.

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