MkIII SSTO spaceplanes. Feasible? Profitable?

[Cirocco]

So I've tried my hand at spaceplanes again yesterday for the first time since 1.0.2, and being the person that I am I immediately jumped to the MkIII parts in an attempt to build a super-heavy, possibly long-range SSTO.

And I kinda hit a wall: the sound barrier. My designs yesterday were completely unable to break mach 1 on airbreathing mode. I have some ideas now on how to streamline the designs, but I do wonder: Has anyone been able to go SSTO spaceplane or even super/hypersonic with MkIII parts? Almost all the SSTO spaceplane designs I've seen so far use MkII parts. And that makes sense: they're streamlined, flat and pointy and create a ton less drag. But I do wonder: can we still efficiently push stuff into orbit with MkIII parts and is it worth it?

For the most part, staged rockets seem vastly superior, but I'm not giving up on my spaceplanes!

I do so like it when my spaceships have wings

[Chris_2]

http://forum.kerbalspaceprogram.com/threads/119655-Yet-another-mk3-SSTO-UPDATE?p=1925036&viewfull=1#post1925036

Even VTOL SSTO:

http://forum.kerbalspaceprogram.com/threads/121328-Mk3-VTOL-SSTO-with-rotating-engines

I think you should forget the 'super heavy' part of your idea. A medium sized Mk3 seems to work pretty well, but anything larger than what I built has substantially more drag so also needs more (jet) thrust. There is no way to add these engines in an aesthetically nice way except if you want to double-clip engines or stuff like that...

4 Rapiers and 2 turbojets seems to be the sweet spot for me, and that limits the craft weight to about 70 tons.

Edited May 15, 2015 by Chris_2

[Old Foxboy]

Hi,

yes, it's hard. I kinda stacked 12 or 14 (can't remember) Reapers together. I used as few parts as possible to reduce drag and part count (my cpu...). I used the big wings as fuel reserves to reduce fuselage fuel tank count. In the end, i had a craft with a big cargo bay that could deliver a brown fuel tank equipped with RCS and docking port to be used as a refuelling station. I made it barely to orbit and back to KSC, but i am yet to touch down safely. Almost made it yesterday, but the balancing of the COG is very tricky once the very heavy payload is missing.

Here's the basic build:

I use the Big-S Delta wings instead of horizontal stabilizers at the back with a big elevon as control surface, the big Boeing-Style main wings right in front of them, and an assembly of basic wing parts to balance centre of lift. One of these basic wings was tilted a little bit to provide extra front lift (like a fixed pitch elevon). So you need 8-10 main wing sections, 4-5 on each side. Your milage may vary. The most important thing is to balance the lift in such a way so you don't have to pull a lot back to pitch up. Pulling up means your back elevons provide negative lift, your AOA will rise and so will your drag. you want to face all parts as straight as possible in the airflow.

Now for the flight profile, and that's as important as everything else: The main trick is to break the sound barrier and to get the Rapiers to run at their optimum efficiency.

After liftoff, which should occur after 2/3 of the runway or before, pull up to 40° pitch. You should accelerate to about 280+ m/s while climbing to 10.000 metres.

At 10.000 metres, enable PROGRADE SAS. That's very important, because by doing so, you minimize drag. Your craft now should fly ballistic and pitch down. At 0°, or maybe -5°, enable attitude hold SAS so you don't lose too much altitude. If your Reapers are not able to push you beyond the sound barrier now and accelerate further, go back to the drawing board.

Once the sound barrier lies behind you, gently (!) pull back to pitch up to around 15-20° and raising, maybe a little more (depends). Climb to 20.000, controlling throttle so you don't risk a flameout. Try to achieve at least 20-25° pitch at 25.000 metres, when the Rapiers start to fade out. Make sure your have plenty of speed right now, at least 1200 m/s. If you have less than 1000, your climb was too steep. If you melt before your reach 25.000, your climb was too shallow.

Your fuel should balanced in a way that you have slightly more liquid fuel that oxidizer left when you switch Rapier modes. Switch modes at 25.000, pitch 20°+ and 1200 m/s+, when the Rapiers fall below 50kN thrust or when your craft starts to decelerate. Try not to pull too much AOA between 25.000 and 35.000 to minimize drag, but don't let your nose fall below 10° pitch. Your goal is to raise apoapsis to 80.000, cruise through the atmosphere and circularize as usual.

Good luck!

[Ion Man]

MK III parts are no different to MK II. You also just need to apply the old rule of thumb that one Rapier/ Ramjet can lift around 10 tons, depending on your design even more.

You can get up to a 30% payload fraction with an SSTO spaceplane and also haul big landers or mining rigs into LKO.

I wouldn't build an MK III plane to go far beyond LKO, because you could easily build a smaller vessel with an LV-N or Ions to go further and carry it inside the cargo bay.

Try not to use the big airplane wings that can only stand 1200° heat, they will always be at the edge of collaps going in or out of the atmosphere.

The Rapiers have a weak spot right around 320 to 360 m/s, where you seem to be stuck and reached a point where you cannot go higher and faster at the same time.

You need to level or dive at 12 to 15 km height and get over 400 m/s, pull up to 10 to 15° and let the rapiers "load up" to 350- 400 kN of thrust. The plane can take around 1350 m/s without falling apart at 15 km if you get out of the dead zone in a timely manner.

Then, as soon as they fall beyond 20 kN at aroud 25k, switch mode, close all intakes and off you go.

Here's my most recent 1.0.2 design:

Red tank/ 35+ ton lifting capability to LKO, if you don't make any mistakes or waste fuel when ascending.

Orbit 75x75

Craft File:

Hit "1", once your thust is below 30 kN

http://pastebin.com/ckkDTzqx

Edited May 15, 2015 by Ion Man

[Old Foxboy]

Yeah that's about my idea, but i used the big wings and a MK III cockpit Did you clip the wings? And is the craft stable during reentry and landing without the heavy payload?

Also good you mentioned closing the ram air intake. Important to save some drag between mode switching and 35.000 metres.

[KerikBalm]

I need to see how it flies in 1.02, as it was a 1.0 design, that barely avoided overheating (and often did not)

quite the capacity:

[Ion Man]

Oo that is some monster plane. Nice! I failed horribly trying to build a "center loader" like this design.

And is the craft stable during reentry and landing without the heavy payload?

You need to transfer the remainig fuel into the front tanks, then it's stable, depending on payload and length, you should check it before you launch and remember how much fuel you need to place where, or if you need a set of small wings somewhere.

The wings are "clipped" within what you can adjust inside the SPH without using the relocate feature. They're not stacked. I also used some struts inside the wings, but all with regular stock zooming etc. 100% stock, no fancy stuff.

The plane tends to roll a little, so you're better off being gentle to any inputs

Edited May 15, 2015 by Ion Man

[Cirocco]

Sweet, thanks for all the replies guys. It seems the problem is simply not enough engine power. I was unaware of the 1 rapier per 10 tons rule, and was trying to push 110 tons of aircraft into space on 6 rapiers yesterday. I got some ideas to aesthetically mount a couple more, will hopefully be able show results tomorrow

It's also good to know that RAPIER's have a weak spot around 320-360m/s, I had noticed something like that but I wasn't sure if it was due to the engines or my ascent profile.

One idea I have been throwing around to compensate for this: SRB's that ignite at 300m/s to push past the sound barrier, then dump them. It does mean my design won't be fully SSTO anymore, but SRB's come cheap. I think I can stomach that loss

Also, chris, that idea of bringing the nuclear tug along in the cargo bay and mounting it in space is bloody genius.

[Borsek]

I like to make something similar to the interstellar/star wars mini hyperspace tug, bring my plane into orbit, and dock it onto a platform with LV-Ns, or for bigger planes, dock the LV-Ns onto the plane, then set course for laythe, of course. Bringing stuff into orbit is quite easy, but I tend to have less dV left now in 1.0 than with the kirby planes in 0.9.

[KerikBalm]

Oo that is some monster plane. Nice! I failed horribly trying to build a "center loader" like this design.

Well, I have "medium" sized lifters of the "center loader" design (I've been calling them twin boom designs, but whatever).

This one is much more modest, and I'm using it in my career game- its medium tech level, only needs lvl 2 facilities, and tech that you can get from lvl 2 R&D.

I rely very heavily on the center loader design... I did in the old aero, and in the new aero, I just need to put a shell around the payload. I have some designs that use the mk2 and mk3 cargo bays.. but I'm pretty sure I get 100% recovery as long as I keep the fairing base. At any rate, its still SSTO, as I don't jetison the fairing until in orbit (although if the mass reduction works correctly, I should jettison it a bit sooner, but I'm a bit worried about the fairing parts flying off when there is still significant aero forces + acceleration from firing engines, that may propel the discarded pieces back into my craft)

^ not much use of mk3 parts on that one though. That one I have fully tested in 1.02

It is also using something reminscent of this nuclear tug docking that you liked.

See, that medium lifter at the top of my post? It had trouble making orbit - too little thrust. So I wanted to add another engine, without adding much drag.

Solution: stick it on the back of the payload:

* Note: I often have extreme difficulties placing interstage fairings in the SPH, as you can see in that screen shot... the fairing would not close. In the end, for that one, I simply removed the engine, closed the fairing, and then put the engine back on, so it sort of clipped through the fairing... I hope I still get the drag reduction. My next version (which carried more liquid fuel, and had a FL-T100 instead of FL-T400 tank on the center LV-T45), I was able to close the fairing... its pretty frustrating.

In both these designs in this post, you'll notice center engines attached to the rear of the payload. They are not part of the payload. Instead, the payload is released, and then the center engine redocks up front where the payload previously attached.

In the large design, its a cluster of LV-Ns that shifts forward.

In the smaller design, its a LV-T45

This also helps solve a common design problem: Engines at the back lead to tail heavy designs when the fuel tanks are empty.

Shifting some engines forward definitely helps.

I don't like that nuclear tug solution, because it seems a bit inefficient to me: It takes up cargo space (meaning more dry mass needed to extend the cargo bay), and its dead weight for most of the flight.

My LV-Ns are lit as soon as the jet thrust cant maintain my speed and climb rate.

Why wait until one is suborbital, with very little dV left, to use the nukes?

The earlier they are used, the more you benefit from them. As soon as my LV-T45s fire, or the rapiers go to closed cycle, I want my Nukes firing.

[Wanderfound]

A small but very useful MkIII for FAR:

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Craft file at https://www.dropbox.com/s/287cxnw8vh57qep/Kerbodyne%20Astrotug.craft?dl=0

[T-Bouw]

I'm seeing some cool designs here!

Inspiration has struck me!

[goes off building one]

[KerikBalm]

Wanderfound.... I'm curious... what would you actually use that small mk3 thing for?

The cargo bay is very small, you can fit some small probes in it, maybe a rover, but not much...

I only use those small mk3 cargobays as either utility sections where I put probe cores, reaction wheels, RCStankes, soalr panels, etc (as you can see back on pg 1), or to extend the mk3 cargo bay.

And as a tug? why would you use that to pull stuff around? rapiers are not very good vaccum engines... if you're going to have a space tug pulling a cargo train, wouldn't you want nukes?

Why would you use a SSTO for this purpose... as a tug, its fuel capacity is small, and its basically just there to provide the engines, which are not very good engines.

Claiming: "Most importantly: the towbar. You can haul as many jumbo drop tanks and cargo modules as you like; virtually infinite range and payload."

Seems like a lot of hyperbole to me. Using that logic, anything you can strap a docking port to can have "virtually infinite range and payload"

Heck... with the claw, you don't even need a docking port on a vessel to claim "You can haul as many jumbo drop tanks and cargo modules as you like; virtually infinite range and payload."

Its small, it probably handles a lot better than mine... but I can't see it as being practical for anything other than a crew shuttle or small satellite launcher, both of which are already well served by mk2 based designs.

[Wanderfound]

The cargo bay can fit a Munlander (or scanning gear and several probes). As for the towbar, here's an old design with a similar concept:

It already has a couple thousand ÃŽâ€V unrefuelled in orbit, double that if you fill its integral tanks. And fuel efficiency doesn't matter when you can hook half a dozen Rockomax 64s on the back (which you can get to orbit cheaply by lifting empty and filling with a spaceplane tanker). Plus a laboratory, mining rig and maybe another cargo bay. But you need a rear mounted Snr docking port if you're going to do it without terminal wobbles. The spaceplane tug is also able to detach the train and visit Laythe or Duna (add some more Vernors and RCS retrothrusters if you're doing that, though).

Sure, the wings are dead weight in vacuum and the RAPIERs aren't as efficient as nukes. But the wings are wet wings (so not entirely dead weight) and the waste mass is a tiny fraction of the mass of the whole train. And with the sort of loads that this is intended to haul, nuke burns are painfully slow.

Edited May 15, 2015 by Wanderfound

[KerikBalm]

Meh...

It can't lift the train components, so its just a SSTO tug with inefficient engines.

I think your earlier design which has LV-Ns is better for that purpose.

Long burn times? slap on more LV-Ns.

Sure they are heavy, but compared to the train mass, its fine.

A lot of LV-Ns aren't good on a spaceplane? then make a dedicated space tug that gets refueled by spaceplanes...

I just don't see the point of a SSTO tug, when the rest of the stuff isn't SSTO'd, and the tug has poor vacuum dV.

[Wanderfound]

Well, there's also the point that if you can build one of these, you can also build a cargo SSTO capable of lifting the train segments.

If you were really attached to the idea of nukes, you could probably strap another pair of engines outside the lateral tanks; tuck them into the gap between the RAPIERs and put angled long nosecones on the front to blend them in to the structure. Put 'em on intercoolers to help control the heat. It wouldn't be quite as sporty on the way to orbit, though.

Edited May 15, 2015 by Wanderfound

[Mister Dilsby]

A small but very useful MkIII for FAR:

I like it a lot, will do something similar once I unlock the Sr. docking port!

(um, but don't you have a new 'launchpad' as of V1.0? )

[Laie]

Someone named LandFish2 came around with a truly beautiful vessel.

Ever heard of Eugen Sänger?

Reddit thread with craft file: http://www.reddit.com/r/KerbalSpaceProgram/comments/35iir7/

[Levelord]

When you R.A.P.I.E.R. clip/spam you can get pretty much anything into orbit regardless of design. I suppose I can say that I'm impressed with the aesthetic style, but it's got the engineering prowess of a hog.

[Old Foxboy]

Squad, add more Engines: We definitely need bigger jets, turboramjets and reapers that fit a Mk III design and have enough power. It's not that nice having to stack rows of reapers if you want to haul a huge craft into orbit.

[landfish2]

it's got the engineering prowess of a hog.

damn ): ima go tell the skylon people that real quick

[Wanderfound]

Here y'go:

Kerbodyne Astrotug N.

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Craft file at https://www.dropbox.com/s/mafmdsidy74djvu/Kerbodyne%20Astrotug%20N.craft?dl=0

[Levelord]

damn ): ima go tell the skylon people that real quick

I'm pretty sure the Skylon is using a grand total of 2 SABRE engines and not 20 odd engines clipped into each other.

[Wanderfound]

I'm pretty sure the Skylon is using a grand total of 2 SABRE engines and not 20 odd engines clipped into each other.

It's the twenty-odd ramscoops that are slowing it down. Lose some drag and you could ditch half the engines. Looks nice, though.

[katateochi]

I made a version of this 20 Kerbal crew transport SSTO a few days ago, but I didn't like how it looked. Since then I've improved on it (both appearance and performance)

Javascript is disabled. View full album

Uses 8 TurboJets and a Skipper engine. I really didn't like how the skipper looked on the back in the original version, so I recessed it slightly and built a fairing around it and I'm quite pleased at how that looks now.

As far as profitable goes, I'm using this to take large groups of tourists into orbit (where they then catch connecting flights). It's part of my reusable tourism program which is being very profitable.