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Build a Submarine That Can Get To Orbit

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I already spent a few hours trying a few things,  the problem is i've never made a submarine before and its hard.

I've made a couple of seaplanes that can go to Minmus, it's not that hard once you can hydrofoil.

The problem with subs is that practically everything floats.     After crash landing my seaplane,  i was surprised to discover that NERVs float.

Guess that explains why life rafts all say "penalty for improper use ,  £300",  they are made of Uranium and improper use violates non proliferation treaties.

Liquid fuel and oxidizer tanks float too.    Xenon sinks,  but i'm not too sure about building a Xenon/Jet SSTO,  unless i incorporate a load of wings and batteries, which float really well.


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You need quite a bit of ore tank to sink which leaves a small margin of Liquid fuel, oxidizer and engines to make orbit. So I think a Rapier spaceplane is the best option to minimize fuel use.

That then is a submarine with at least small wings on it.

The question is, do you allow this or is that then considered a spaceplane that can sink and not a submarine? Technically a submarine that uses rockets to get to orbit is still a rocket in ksp so I assume a spaceplane will do?

Finally, submarines usually don't stage. So should this be a SSTO submarine?

I hope I was clear about the challenge being unclear to me. If it is exactly as the title says then anything that sinks that can make orbit but doesn't stage will do. I'm just verifying.

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I figured this was worth trying, so I made this thing.


I figured this was about the simplest thing that could possibly work. And, surprisingly enough, it does!

Powered by six slightly clipped RAPIER engines and weighted down by two large ore tanks, this vessel has slightly positive buoyancy but also more than enough thrust to overcome it. It can make its way from the runway to the sea, dive several hundred meters under the surface (or more, if you disable part pressure limits), resurface and even take off directly from underwater to orbit!

(To pull off this particular maneuver, I strongly recommend switching the engines temporarily to closed-cycle mode just before surfacing, as the airbreathing mode has TWR < 1 at low speeds. This craft has excess oxidizer as ballast anyway, so feel free to use it up. The custom action group 1 toggles the engine mode. Also don't forget to jettison the ore in the ballast tanks before takeoff.)

Here's a few select screenshots from the test dive / flight; I have a few more in the full album on imgur







Here's the craft file, if you want to give it a try yourself. 

Note that I didn't include any particular provisions for a safe return or landing. You might be able to land the craft like a plane if you're really good, but with no real wings to speak of it has the glideslope of a brick. In principle, a SpaceX style tail landing might also be doable. Or, if worst comes to worst, just bail the crew out in midair and let them parachute down to the surface. Hey, it worked for Gagarin! :D 

Edited by vyznev
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This is a really good challenge. I have an almost-but-not-quite, using a modified version of a submersible plane. My biggest problem right now is I run out of oxidizer before I can get my orbit circularized.   Adding more tanks is a mixed bag at best, and the added weight also means the plane is a lot more troublesome when trying to water land.  I reckon there is room for improvement in my flight profile, and I hope I can squeeze out enough to just squeak my way into a stable orbit. But for what it is worth, it will get to space.  I'll post a video if I manage to get a stable orbit.


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I 've now had limited success with this thing.  It generates enough downforce with its wings to force itself below the surface,  i was 50m down at one point.   It does well on the going to orbit part too,  would probably send Val to Minmus.      Where the design fails is that it can't land in the sea, at least not when fuelled up - things always break off, and it is no longer spaceworthy.  I had to land on the beach and drive into the water. 

Also, as a boat it is horrible.     Pitch stability goes negative if you pitch down too much, overwhelms the controls and sends it into bunt.   Then it floats to the surface on its back and can't be righted.

The design decision to mount the wings low is probably to blame.    With the fuel mass all being down there,  the engines are above CoM and there is a huge pitch down torque, if you gun the throttle before it's got some water speed, it does its swap ends trick.    Also,  it is more stable floating inverted, with the heavy engines under the light wings.

Perhaps if i add sharp dihedral i can get the inboard wing to be the first thing to touch the water, without screwing my CoM so much.

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1 hour ago, AeroGav said:

Perhaps if i add sharp dihedral i can get the inboard wing to be the first thing to touch the water, without screwing my CoM so much.

Stock aero does weird things with dihedral. You might be trading one set of stability problems for another.

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  • 1 month later...
50 minutes ago, EvermoreAlpaca said:

A little bit hacky, but the easiest way to ballast a craft is to clip a bunch of radial ore tanks into a utility bay and close the door.  Just open the door to ascend to the surface =)z

But then it is no longer a viable submarine.  I think the goal should be a sub that can get to orbit, return and still be a submarine.

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  • 2 weeks later...

OK,  I've had some measure of success with this design.


(recently updated with rudder tabs and a slightly recessed nose cone, and some action groups - hopefully dropbox updates the link automatically)

First off, going to space, it does easy


It can also go under water .     It's a bit squirrelly when flying under water,  pitch down too much and yaw stability goes to hell.    Shortly after this it started tumbling , so i set prograde hold and began climbing vertically to the surface at 35 m/s.   Shot out of the water like a submarine launched nuke missile.. which i suppose it is.    Plenty of fuel left for the flight to orbit - the first screenshot in this post is from later in the same flight.


Actually landing it on the water without busting off the shock cone intake at the front is the hardest part.   At first I was stalling into the water at the lowest possible speed,  tail touching down first then the nose comes slamming down.  I managed an intact landing by coming in more level,  about 10 degrees pitch, just under 50 m/s , with a tiny bit of power on.   Still this is by far the most marginal aspect of the craft and the hardest part to get right.


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