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Well, in order for it to remain stable, fuel has to flow upwards, so the CoM moves forward. Otherwise I would have to make it too stable to fall ass-first afterwards, during reentry. But when I set the fuel lines accordingly, I got like a gazillion symmetry bugs that made the tanks drain unevenly. It's the part of the design that actually took me more reverts until I finally got it right.

Rune. And a symmetry fuel drain bug mean pretty much a full rebuild because they are almost untraceable.

Ouch.. I have been bitten by that too man. Theres something very satisfying about setting up fuel flow and have it behave.

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Ouch.. I have been bitten by that too man. Theres something very satisfying about setting up fuel flow and have it behave.

Yup, but then again, I've been fighting bugs since I've been playing this game, so I won't let that stop me! :)

That one I built mostly because it looked cool. This one actually has a purpose: I set out to build a SSTO that could train six recruits at a time to lvl 3 by flinging them to Minmus to plant a flag, then pop out to solar orbit before coming back for an aerobrake, with a Munar flyby on the way back. Well, it does that... and quite a bit more. 3.5km/s on LKO is enough, right? ;) (KER's reading is confused because it thinks the nuke won't use the liquid fuel on the highlighted tanks)

Plus, the extremely low wing loading means it climbs like an elevator, and plows through Mach 1 without going needing to go level, even with a lousy 0.57 TWR on airbreathers. Don't ask me how I got the price to be an even 88k√. Oh, and the oxidizer reserve gives out just when your apoapsis reaches space, with an astounding precision.

HAI5Rcs.png

0zLdtSj.png

Rune. Now want to hear the fun part? I've flown it exactly once, the flight you see in the pic, and I don't know why I trusted it with crew without testing it out. Talk about eyeballing things...

Edited by Rune
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Does anyone have an SSTO that can ferry passengers to the Mun and back? The best I can do so far is 8 passengers, in a 100 x 100 orbit, with about 900 delta-V. Which I think is about minimal needed just to do a Mun fly-by, not get into orbit. I was really hoping for something that could do a dozen or so Kerbals to low Mun orbit, and then return. Which means having about 1200 or even 1500 delta-V capable from 100x100 orbit. Is this impossible in stock KSP? Am I asking for too much?
I made a 115 t stock Drone Spaceplane SSTO with a 9-man Lander in the Cargo Bay.

The Spaceplane has enough dV to go into orbit around the Mun, launch the Lander and return to Kerbin.

The Lander needs a pilot, but has plenty dV to land on the Mun and then return to Kerbin under it's own power and land using parachutes.

The Lander can also be launched from the Spaceplane right after the initial burn to the Mun. The Spaceplane can then do a small retroburn and return to Kerbin. The Lander has enough dV circularize at the Mun, land and return to Kerbin.

The Lander has a small amount of RCS to maneuver out of the Cargo Bay. No docking ports on either Lander or Spaceplane.

Album + Craft file

(Album includes Ascent Profile instructions and Action Groups are in the craft description)

FqPWayq.png

UaobCLH.png

Edited by Val
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And here I am...still can't get an SSTO in orbit that can actually do anything.

You know what I did when I couldn't make an SSTO? I downloaded one that actually could make it to orbit and followed the flight instructions. That helps a lot. Then I built my own that couldn't do much but fly. No payload. Then I built bigger and bigger. Gotta start small first to learn the basics.

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Well, in order for it to remain stable, fuel has to flow upwards, so the CoM moves forward. Otherwise I would have to make it too stable to fall ass-first afterwards, during reentry. But when I set the fuel lines accordingly, I got like a gazillion symmetry bugs that made the tanks drain unevenly. It's the part of the design that actually took me more reverts until I finally got it right.

Rune. And a symmetry fuel drain bug mean pretty much a full rebuild because they are almost untraceable.

I usually just manually pump some fuel forward before de-orbiting. Some of my planes need it, some don't. It helps to try to put at least some of your rocket fuel as far forward as possible. In front of bays, even.

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I usually just manually pump some fuel forward before de-orbiting. Some of my planes need it, some don't. It helps to try to put at least some of your rocket fuel as far forward as possible. In front of bays, even.

That works if your rocket is so stable, even with the fuel in the back it'll get to orbit without doing 360's. But that chem-powered SSTO has to go up point first, get down ass-first, and do it with an awesome fuel fraction, so no needless wing weight allowed. Making a fuel routing system that drains the tanks in such reverse order means the fuel flow actually works with me instead of against me, gradually making it more stable as the launch progresses through Max-Q, while it'll return to neutral, then reverse, as the last fuel drains out on the high atmosphere, to end the trajectory with the CoM on the other side of the "CoL" (actually, center of drag).

All in all, a handy trick, I encourage everyone to experiment with it. Don't think only about the CoL indicator on the VAB, actually try to imagine how our tanks become huge, light aerodynamic surfaces as they empty, and design with that in mind. And of course planes are a tad different, you want them to always remain stable in the same direction.

As to the comment about cargo bays, I'd phrase it differently: it's useful to put the cargo bay smack in the CoM, since then the flying characteristics won't change from empty to full.

Rune. Hope the tips help someone!

Edited by Rune
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... and do it with an awesome fuel fraction, so no needless wing weight allowed ...
In my experience, fuel lines, in stock aerodynamics, create more drag than they're worth. If you're worried about needless wing mass, then you shouldn't be using fuel lines either. They eat a lot of fuel during ascent on account of their drag.
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In my experience, fuel lines, in stock aerodynamics, create more drag than they're worth. If you're worried about needless wing mass, then you shouldn't be using fuel lines either. They eat a lot of fuel during ascent on account of their drag.

That is a good point, but let's recapitulate a bit. We are talking about this:

lN1MtL9.png

Mcerhob.png

znZXf0n.png

As you can see, if I was worried about drag I wouldn't have left the 3.75m node open on the back, or the tanks that the spikes are mounted on uncapped. It is a rocketship, and as such it climbs vertically, losing mass fast enough that drag losses are quite secondary to gravity losses during the lower atmosphere portion. It actually goes transonic just as you reach the second atmospheric bar, just when you start to tip over and your TWR starts to climb above two. On the other hand, having to invest more mass in making it stable both on the way up and down, I probably wouldn't have made orbit with such a "light" ship (only four spikes there, and 2.5mT payload, inside a cargo bay). Even lighter in parts, too, 55 even with the complicated fuel routing system. And of course, on the way back, the extra drag makes it brake higher, sooner, meaning the thermal environment is a bit more benign. Can't pitch up to level and cool off here...

Of course your standard winged SSTO is a completely different thing, but then again, that is why atmospheric engines draw fuel the way they do, I guess. And it works even better on your average tall launcher: a single fuel line going form the upper tank to the engine, and you don't need winglets on the bottom.

Rune. Excuse the dark,WiP pics.

Edited by Rune
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Guest Space Cowboy

Got to be a bit breezy in the outboard cabin modules. Seriously nice craft though.

I made my first ever pure passenger SSTO Spaceplane.

Weighs 282 t at take-off and has room for 160 Kerbals. Not that I have ever had that many Kerbals or Tourists in any career game ever.

http://i.imgur.com/Chzl4zA.png


http://i.imgur.com/GVkiAXc.png

Craft file

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...
Agreed. It certainly depends on the craft and ascent profile. Btw, it is a very elegant craft, both in form and function.
Got to be a bit breezy in the outboard cabin modules. Seriously nice craft though.
Thanks! And yeah, will have to RP that the intake air is somehow routed around the cabin and not through it. :blush:
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That is a good point, but let's recapitulate a bit. We are talking about this:

http://i.imgur.com/lN1MtL9.png

http://i.imgur.com/Mcerhob.png

http://i.imgur.com/znZXf0n.png

As you can see, if I was worried about drag I wouldn't have left the 3.75m node open on the back, or the tanks that the spikes are mounted on uncapped. It is a rocketship, and as such it climbs vertically, losing mass fast enough that drag losses are quite secondary to gravity losses during the lower atmosphere portion. It actually goes transonic just as you reach the second atmospheric bar, just when you start to tip over and your TWR starts to climb above two. On the other hand, having to invest more mass in making it stable both on the way up and down, I probably wouldn't have made orbit with such a "light" ship (only four spikes there, and 2.5mT payload, inside a cargo bay). Even lighter in parts, too, 55 even with the complicated fuel routing system. And of course, on the way back, the extra drag makes it brake higher, sooner, meaning the thermal environment is a bit more benign. Can't pitch up to level and cool off here...

Of course your standard winged SSTO is a completely different thing, but then again, that is why atmospheric engines draw fuel the way they do, I guess. And it works even better on your average tall launcher: a single fuel line going form the upper tank to the engine, and you don't need winglets on the bottom.

Rune. Excuse the dark,WiP pics.

neat rig, what's it's dv in low orbit?

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Agreed. It certainly depends on the craft and ascent profile. Btw, it is a very elegant craft, both in form and function.

Thanks! I'm glad you like it. :)

neat rig, what's it's dv in low orbit?

A grand total of about 150m/s, with the 2.5mT payload, at a roughly 75km circular orbit. So yeah, maybe not the longest-ranged craft. In fact, barely orbital if you have to rendezvous later. But that is by design, I like the challenge. And if you refuel afterwards, you have almost 4km/s back in the tanks.

Rune. It's also a reason I might not release it, a bit too tight for the average kerbal.

Edited by Rune
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