Ultra-heavy spaceplanes

[Guest]

Back to KSP after a hiatus.

I set myself a challenge to build the heaviest (stock) spaceplane I can manage. I'm currently up to lifting well over 70 tons to LKO in a beast with three large Mk3 cargo bays. It'll loft two of the orange fuel tanks easily with the third cargo bay carrying some extra fuel, or just about an entire space station using all three bays. 

It re-enters cleanly and flies well, but landings are kinda hairy because it's not altogether familiar with the concept of gliding; deadstick and dry it's more like falling really -- I drop down at a scary steep angle, flare up at just above the ground and then sort of plop there and a lot of the time some pieces fall off. My next objective is to refine the design to address that problem.

My self-imposed goal is a 100 ton payload. I've gotten close -- I had one design that could loft that much, but it was a one-way trip only as the dry CoM went too far back and it re-entered in reverse.

Anyone else building these things? Any tips, designs, or pointers to share?

[Mikki]

Well, i leave this here, 179 tons to 106km orbit. All stock.



Thats a goal. And it does reenter and land nicely:

Edited December 24, 2017 by Mikki

[Guest]

Oh-ho, interesting, not to mention impressive. It looks like you're carrying the cargo pod externally. Very clever idea and gives a lot of versatility to designing the payloads too (although I suppose you have to shroud them if they're not aerodynamic to start with). I also notice you're using a mix of Whiplashes and Rapiers for propulsion. I take it the mix is more efficient than pure Rapiers?

How do you make that big wing hold together? I'm having to use struts to stitch up mine so it doesn't collapse on the runway, and I don't see any on yours. Is there a construction technique I'm missing out on?

[DualDesertEagle]

And I'm already happy about having reached LKO with just enough fuel to re-enter the upper atmosphere with no payload whatsoever...

[Whackjob]

This is something I haven't - and probably should at some point - do.  It could be interesting, seeing how large a space plane I could make, and more interesting still, whether or not I can actually achieve orbit.  Or even space.

EDIT:  Closest I ever got was this, and it wasn't finished:

Edited December 24, 2017 by Whackjob

[Guest]

Made an improved version. It has slightly larger cargo volume than the first version (because the "utility" stuff is now tucked away in a Mk2 cargo pod in the centre hull, rather than taking up a part of the central bay) with about equal lifting capacity, perhaps even a little more. I replaced the central hull with a row of Mk2 tanks (I'm still tweaking the mix, this one's a bit heavy on fuel and a bit low on oxidiser). I also switched to Whiplashes for two of the engine clusters, and yes indeed it is more efficient and I also have a feeling they work better at low altitudes, plus when I switch the Rapiers to closed-cycle the additional acceleration squeezes just a bit more from them. This one is rather easier to land; the Mk2 hull provides a good bit more lift. Still a bit of a handful but not a complete nailbiter.

This one lifts 70 tons easily, which means I could certainly push it a bit more. With careful tweaking it just might hit my 100 ton target, but pretty soon I will get thrust-limited which means a redesign, as there's just no way to fit more engines on it. I would probably have to go with engine pods on the wings like in Mikki's design, otherwise the CoM would go too far aft when dry.

@Whackjob that one looks it has masses of lift but is really un-aerodynamic. How do you figure on building enough velocity to get into orbit?

[KerikBalm]

I'll leave this here:

I don't know its payload to LKO in stock, as I use it in a 3x Rescale system where LKO requires a velocity of over 4,000 m/s and thus the drag losses are massive

 

Its all stock even if the planet and payloads aren't neccassarily.

Payload capacity is over 110 tons, payload fraction I think I got as high as 13% for the 3x rescaled system. I'm sure it would be over 35% in a stock system, probably more like 40%, and it can take off with a mass of 900 tons... so I'm going to guess its payload capacity in the stock system would be over 300 tons 

[KerikBalm]

30 minutes ago, Brikoleur said:

@Whackjob that one looks it has masses of lift but is really un-aerodynamic. How do you figure on building enough velocity to get into orbit?

That is definitely a pre-1.0 design before the aerodynamics overhaul. One can tell its an old version by those old landing gear.

1 hour ago, Brikoleur said:

I also notice you're using a mix of Whiplashes and Rapiers for propulsion. I take it the mix is more efficient than pure Rapiers?

How do you make that big wing hold together? I'm having to use struts to stitch up mine so it doesn't collapse on the runway, and I don't see any on yours. Is there a construction technique I'm missing out on?

I used to think that the Whiplash and rapier combo was more efficient, but I moved to pure rapier designs. Maybe it works better in stock than in a 3x system. One wants to maximum airbreathing altitude and speed, and to minimize frontal area. Rapiers deliver higher speed and altitude, and also can go closed cycle without adding a separate stack for rocket engines like the KR-2L or vectors or aerospikes (although you can part clip multiple engines in one stack to have lots of thrust for a small frontal area without their thrust being blocked by the engine "behind" them according to their stack order.

As for the construction, did you enable advanced tweakables so that you can do part autostrutting?

And in my last post, if it wasn't clear, a part behind the payload undocks and redocks before reentry. This helps keep the CG aligned as well.

My current design isn't quite like that one, its now unmanned, and the wings have changed a bit... but I haven't uploaded pics to imgur.

I did upload 2 videos of it though:

 

 

[Guest]

Those are some very cool designs. It looks like if you want to loft truly massive loads you need to break away from things that look like traditional planes and go with lots of modular engine clusters that you can stack at will, as well as an external cargo pod rather than cargo bays. Clever idea to make one of the thrust modules un- and re-dockable.

I did some tweaking and pushed the payload limit of that design to 90 tons. It juuust miiight go up to 100 with even more careful tweaking but I'm starting to doubt it. I'm getting thrust-limited and have to spend way too long in the soupy lower atmosphere. Tried with pure RAPIERs and that doesn't work at all: they don't have enough grunt at low speed/altitude to get me into the ramjet phase.

[sh1pman]

My tiny, minimalistic 144t to LKO-capable SSTO.

https://imgur.com/a/3ZFnf

As for the tips, if you can accelerate to 1000m/s below 5km, then your design is good.

[Guest]

With only 16 Rapiers? Nice. Ugly though 

[sh1pman]

2 hours ago, Brikoleur said:

With only 16 Rapiers? Nice. Ugly though 

Yep, 16 Rapiers. I wanted to make something unusual 

[fourfa]

Not my design but I watched some of the build streams:

https://kerbalx.com/KSpaceAcademy/KSA-Kilotonderbird-1000t-v2

1000 tons to orbit

[Vanamonde]

This exchange of spacecraft has been moved to Spacecraft Exchange. 

[Guest]

Behold, the flight of the Tigermoth. Payload 218,216 kg to LKO. Completely stock.

Re-entry:

(and a beauty shot, climbing to apoapsis for the circularisation burn)

This one is a lamb. Plenty of grunt to get into orbit, easy to fly, easy to land. Only difficulty is with the centre of thrust/centre of mass which means orbital burns have to be done gently; I also switch off six of the topmost engines when switching to closed-cycle, and switch on RCS with a couple of verniers at the tail holding the attitude. This payload is pretty close to the limits of this design; with a bit of tweaking it might be possible to pile on a few tons more but not dramatically more. The fuel load for this test flight wasn't perfectly optimised; after reaching orbit I had 3383 fuel and only 173 oxidant left. But even after I balanced it I don't think it would make much difference to the payload.

EDIT: Since 218 tons is obvious overkill (the limiting factor will be volume, not weight, most of the time), I scaled down the design by pruning the engine clusters from 9 to 7 RAPIERs per cluster. That'll still loft a 200 ton payload while being more efficient with more moderate 150 plus/minus payloads, as well as easier to fly, land, and manoeuvre in orbit.

The Tigermoth-200:

Edited December 26, 2017 by Guest

[qzgy]

Spaceplane?

No idea how much it weighs. But its big, and was able to get a station into Duna Orbit.

I want to make a bigger one soon-ish.... I have so many projects I need to work on....

[Guest]

Single stage to Duna? That is impressive. How does it handle on re-entry and landing?

[SchweinAero]

On 26.12.2017 at 9:04 AM, Brikoleur said:

Single stage to Duna? That is impressive. How does it handle on re-entry and landing?

From the pics it looks more like a plane-shaped vessel to Duna orbit with a ton of extra boosters, some of which are solids.