Having some SSTO difficulty

[AmbApe]

I am trying(and currently failing) to design a SSTO plane to fit my needs. Im trying to make a plane that includes the mk2 cockpit, an mk2 crew cabin and preferably an inline docking port. I'm trying to keep the total craft weight at under 25T and have about 1k dV after reaching orbit. Ive tried rapiers, turbojets, aerospikes in any number of groupings and no luck. I have in the past made several SSTO's but i just cant seem to break out of 75k orbit with just enough to return. Any suggestions or designs would be a great help.

edit: using stock aero, as for parts only major part mods im running are KW rocketry, KAS, and procedural tanks

Edited April 24, 2015 by AmbApe

[TheXRuler]

Well the 25t mass limit could be a problem, my SSTO Spaceplanes are usually somewhere around 300t with 60 tons to orbit. As long as you are fine with using NERVAs (don't know why but some people seem to hate them) there is one thing I could think of. Try sticking two R.A.P.I.E.R. engines on your craft, with a single LV-N in the centre. Then put the R.A.P.I.E.R. engines in an action group so you can toggle them on and off as needed. Usual ascent profile, except that you might want to stay in the lower part of the upper atmosphere a little longer than usual to gain some more speed low down, then use the atmosphere to kick you AP as high as possible, switch to the LV-N and point a little above your prograde vector. Then toggle your R.A.P.I.E.R. engines on and off if needed to keep your AP far enough ahead. Alternatively you might try using large solar cells and multiple PB-ION electric thrusters as these have insane ISP. However I don't think they will be enough to circularize, maybe if you combine multiple PB-IONs with a single LV-N you could use the LV-N when you need a little more uumph and the PB-IONs to get the additional orbital dV. Beware the long burn times with the PB-ION though. For the Xenon Tanks it might be best to hide them in a cargo bay so as to have them shielded from reentry and drag.

Edit: Also, welcome to the forums, hope you enjoy it.

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If you are looking for some inspiration you might want to check out [thread=90747]Wanderfound's Kerbodyne SSTO Division[/thread], he is like a dark magician for stock SSTO's or just head over to the Spacecraft Exchange. If you need some ideas on how to build a certain thing in stock I strongly reccomend the [thread=43086]Open source thread for construction techniques[/thread].

[FlipNascar]

It may be a combination of design and piloting. It took me a fair while before I was able to actually get them to work, and mainly that was through disassembling other craft and reading all the tutorials on the subject. If your 25T limit is exact, you can get away with either a combo Turbo-Rapier (attach a Rapier, then attach the Turbojet to the Rapier and use the offset tool to clip it in a bit). Or for an easier ascent, throw on two turbojets, and attach a couple of the little Rockomax 48-7S. To make it easier, you'll probably want 3-4 intakes per engine.

Here's one I use as a simple crew shuttle - albeit not fit for your purposes as it's got too many crew cabs (two), and uses an inline Mk2 cockpit and a shielded docking port, but you could probably replace a crew cabin with fuel and that may well give you the 1k dV you need. I call her the Kestrel I. About 14t at launch, makes orbit easily. Just fly her sensibly, it's a spaceplane not a fighter jet. Check the craft file for the action groups - https://www.dropbox.com/s/elau3ng56n2gony/Kestrel%20I.craft?dl=0. And read this tutorial too (you may notice similarities between GoSlash27's design there, and the one I have... It's no coincidence: http://forum.kerbalspaceprogram.com/threads/102182-So-you-want-to-build-a-space-plane-%28-25-stock%29?highlight=SSTO

[capi3101]

Somebody's going to be smarmy and point out that "SSTO" can include rockets, so I'll do that and get it out of the way.

Now to buisness - I'm assuming you're in stock aero; that's going to make a huge bearing on what kind of craft you'll need to build. The three things you specify - a Mk2 Cockpit, a Mk2 Crew Cabin and an Inline Docking Port, come out to 4.66 tonnes by themselves. Now, since you're in stock, you can pull stock shenanigans; those three things can compose your fuselage in and of themselves (if you were going with, say...FAR, you'd have to worry about making that aerodynamic - which actually isn't that difficult all told but still a bite in the backside).

So basic design process: your paywad is 4.66 tonnes. Assume 25% paywad fraction, therefore your final plane will weigh in the neighborhood of 18.64 tonnes - it's doable. Each RAPIER engine can lift 13 tonnes in stock, so you need 2 RAPIERs to do the job.

Given that you've got two RAPIERs, design your plane assuming they'll be lifting their maximum - so plan for 26 tonnes. 40 Units of LF times 26 tonnes - you need 1040 units of Liquid Fuel. 25 units of Oxidizer times 26 tonnes - you need 650 units of Oxidizer. There are several different single tanks that have that kind of capacity, but use whatever combination you want; any of the Mk3 fuselages or adapters would work, as would a X200-32, while none of the Mk2 fuselages would give you what you need with just a single part but you could do it with two or three. 26 Tonnes of plane, so 26 total lift coefficient; you'll need 13 pairs of Delta Wings/Wing Connector A/Wing Connector B. And you'll want six RAM Intakes, plus do all the normal crap required to build a spaceplane that won't want to fly backwards. That'd get you to orbit, give you some room to fool around a bit, then land. And that's pretty much it.

I suppose you could go with Turbojet/24-77 combos. You'd still need two Turbojets with 3-4 24-77s a pop; but then you could plan for thirty tonnes (Turbojets being able to lift about 15 tonnes in stock). You'd probably wind up just as light, but with more power to you (those 24-77s would give you as much thrust as an LV-N, but they'd be almost ten times less massive).

If you're in NEAR or FAR, I can't go into details since a lot of that will depend on the final shape of your plane. I'm also still an amateur there. I think you could get it done with under 25 tonnes, but I'm not 100% sure...

Now, what you might consider doing is adding a pair of FL-T800s/LV-Ns, which, like XRuler suggested, you'd use simply as the interplanetary engines (the RAPIERs would be solely for the takeoff and landing portion of the flight). That would add 13.5 tonnes to your payload - so you adjust the numbers; your 4.66 tonne payload becomes an 18.16 tonne payload requiring a 72.64 tonne plane. I don't know if your 25 tonnes is a hard limit or not, but I won't go into details given that design constraint.

Anyways - if 25 tonnes is a hard limit, you're probably going to have to give up something. At best with stock aero, your total payload is going to have to be 6.25-6.5 tonnes or thereabouts. With 4.66 in the Mk2 Cockpit, Mk 2 Cabin and Inline Docking Port, you've got 1.84 tonnes for a fuel tank and engine. An LV-N by itself comes in at 2.25 tonnes, so those are out. Next best Isp in space is the LV-909, Aerospike or Poodle, and of those the 909 is the lightest, at 0.5 tonnes - leaving 1.34 tonnes for fuel. So maybe an FL-T200 plus part of an FL-T100. I don't think that's going to get you 1000 m/s of delta-V, but you might give it a shot to see anyways.

Edited April 23, 2015 by capi3101

[TheXRuler]

Just wanted to comment on capi's post, if you only add one LV-N you only add 2.25t, so you'd add 8 tons in total, if I got capi's calctlations right. it would however give you a massive increase in dV, since it is more than twice as efficient in vacuum. I don't have much experience with stock planes (I have always used FAR), but I would think that turning off the RAPIERs as soon as you reach ~50km will give you a lot more dV for the same amount of fuel, thereby reducing total weight. Also, if you are using stock, replace the RAPIERs with two turbojet engines, as these have more thrust, and about 10 times the efficiency. Then stick on a bunch of intakes and reach ~2000m/s on jets alone, circularize with the LV-N and you should have a lot of dV left for orbital shenanigans.

Ahhh stock aero-model you so silly ^^ Don't rely on that though as turbojet behaviour will probably change drastically with the 1.0 update. Eg. in FAR they wil lsimply explode if used far above mach 4

Edited April 23, 2015 by TheXRuler

[FlipNascar]

I'm seeing this as a challenge.... Time to go to the SPH and get this done as lightly as possible.

So given that we've got a few more days of Souposphere as we know it... It can be done.

Single Turbo-Nuke (Nuke clipped into Turbojet (stolen from the open source aesthetics thread), aesthetically pleasing and also helps balance out the thrust, so perhaps a bit cheaty...), and clipped two teeny elevons into the front somewhere because on the second flight I ran out of control authority around 20,000m. First flight had balance issues so rearranged the modules so to speak.

I present to you the Featherlite-2, has no handling, and you have to keep on top of it. But you can always use the Nuke for a bit of a boost (I did). 6 Kerbals to LKO (148km) and 2,401dV remaining. 15.9T at launch according to the SPH info tab.

You can Download here

Pics:

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Job done.

Edited April 23, 2015 by FlipNascar
Gon done built it.

[Maukse]

2 turbojet, 1 nuke and 2 48s are what you need. I'll show you my design later

[TheXRuler]

Wow FlipNascar, that is really impressive I have to try remoddelling my S2-Wide Monstrosity with nukes to turn it into an interplanetary ship. I see great potential there... :3

Link to the corresponding post

Also, I would rep you again but sadly I can't rep a post twice.

[Tex_NL]

What you're looking for is something like this:

[FlipNascar]

Wow FlipNascar, that is really impressive I have to try remoddelling my S2-Wide Monstrosity with nukes to turn it into an interplanetary ship. I see great potential there... :3

Link to the corresponding post

Also, I would rep you again but sadly I can't rep a post twice.

I can do that, only because I floundered for long enough. And then read somebody else's tutorial...

Also if anyone does download and use the Featherlite-2; it's got no RCS...

@Tex_NL: What does that thing weigh? To me it looks like you don't really have enough wing area on that.

[Maukse]

I'm afraid I can't do that for 25 tons, so I did it for 18.6 tons, mk2 cockpit, mk2 crew and a docking port.

Around 1700 m.s in the tanks after reaching a 75 x 75 Kerbin Orbit (and I forgot to empty the cockpit RCS, damn !)

2 Turbojet (a bit overkill), 1 LV-N and 2 48s. all parts are stock

....ty piloting - mechjeb helps avoiding turbojet flame-out.

I am confident such a plane could be used even without 48-s (only LVN) with a better pilot.

I usually go for 300 m/s speed at 10km, then I go for a lower climb rate and let the speed improve till' 1000m/s circa 20km altitude.

The turbojet can reach 1400-1450m/s, and then we have to cut some power due to lack of intake air => time to start the LV-N, with already 800 ISP, it helps.

Keep the turbojet running - they still give thrust. Once the jet thrust fall circa 30kN, I shut them down, close the intakes, and start the 48-s for a bit, with an non-optimized mechjeb ascent program.

60 jet fuel left once in orbit, enough to safely land at KSC with a good reentry.

Keep in mind that the whole design might be totally BS with KSP 1.0 (reentry, and change in aerodynamic model).

This shuttle is my design for crew transfer to my munar orbital station.

I still have to improve it, like, doing all the transfer / return with no mechjeb helps, and then try to do it with no 48-s engines.

But no time for that yet)

*EDIT : 85-90 m/s take-off speed, not very efficient, but getting the gears closer to the center of mass is likely to create troubles with the LVN engine. I have to optimize that too (maybe a higher ground clearance ?), and then I might have a Laythe-transfer able SSTO that can land & take off from these islands !

Edited April 23, 2015 by Maukse

[Starhawk]

I have a craft that could easily be modified to fit your requirements.

The Bat Trans 6 transports 6 Kerbals (of any profession) to LKO. Currently, it only has about 720 m/s remaining once achieving an 80 x 80 km orbit. It only masses 8.64 tonnes on the runway so there's plenty of room to modify the design with larger fuel tanks to get the desired delta-v. It has only a single turbojet and two 48-7S engines for orbital maneuvers.

I found the inline docking port quite inefficient, so I simply placed a regular clamp-o-tron on the belly. I always have to dock it visually. For whatever reason the navball doesn't accurately represent the location of the port (maybe because I moved it with the offset gizmo).

Other than that, it works beautifully.

Craft file here.

Happy landings!

[Tex_NL]

...

@Tex_NL: What does that thing weigh? To me it looks like you don't really have enough wing area on that.

From the top of my head it weighs something in the order of 23 tonnes. I have no idea how it flies with stock atmosphere but with the more realistic NEAR it flies like a dream.

[capi3101]

From the top of my head it weighs something in the order of 23 tonnes. I have no idea how it flies with stock atmosphere but with the more realistic NEAR it flies like a dream.

In stock there aren't enough lift generating parts...

That is an advantage of NEAR and FAR - your planes will work with fewer parts overall and will look like planes; stock aero lets you be more creative in the design IMHO. But I'll stop there; no need to digress into a discussion of the virtues of each aerodynamic model, especially not with the current stock aero going away in a few days.

[Hodo]

In stock there aren't enough lift generating parts...

That is an advantage of NEAR and FAR - your planes will work with fewer parts overall and will look like planes; stock aero lets you be more creative in the design IMHO. But I'll stop there; no need to digress into a discussion of the virtues of each aerodynamic model, especially not with the current stock aero going away in a few days.

You are right that is a topic of another very heated discussion. Which for the life of me I dont understand why people dont like FAR or NEAR, but hey each their own. But yet these same people are cheering at the new aerodynamic model which maybe much like NEAR. Go figure.

[SmashingKirby148]

I just never bother with planes cause they never work with me. I'm better at rockets.

(and since I can't build planes, I call the SPH (Space Plane Hanger) the RG (Rover Garage) XD )

[capi3101]

You are right that is a topic of another very heated discussion. Which for the life of me I dont understand why people dont like FAR or NEAR, but hey each their own. But yet these same people are cheering at the new aerodynamic model which maybe much like NEAR. Go figure.

In my experience it's the steep learning curve (steeper than stock for damn sure) coupled with a lack of real quality tutorials. I've been trying to figure FAR out my own self for the past two months, and I would say I was pretty good at planes in stock before I made the switch. Take this as a modest example:

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This will fly just fine in stock, but it'll give NEAR and FAR a screaming hemmorage...

Anyways, enough thread hijacking - what were we talking about again?

I just never bother with planes cause they never work with me. I'm better at rockets.

(and since I can't build planes, I call the SPH (Space Plane Hanger) the RG (Rover Garage) XD )

If the present stock aero wasn't going away in a few days, I'd recommend DocMoriarty's KSP Spaceplane Construction and Operation Guide as a good place to get ideas. It's largely where I got the numbers I rattled off earlier in this thread

Man, that's probably going to be the last time I get to recommend that guide to somebody...

[TheXRuler]

Good lord that is one hideous plane Oo stock aero up till now was completely crazy ^^

[Hodo]

In my experience it's the steep learning curve (steeper than stock for damn sure) coupled with a lack of real quality tutorials. I've been trying to figure FAR out my own self for the past two months, and I would say I was pretty good at planes in stock before I made the switch. Take this as a modest example:

http://imgur.com/a/F6K86

This will fly just fine in stock, but it'll give NEAR and FAR a screaming hemmorage...

Sorry but that thing is HIDEOUS, and wouldn't even consider flying in the real world, which is what FAR does.

FAR isn't that complex as long as you keep in mind that there are certain laws that can not be broken, but can be bent.

And of course the number one rule for aircraft, "If it looks right it will fly right!"

[AmbApe]

Thanks to all the suggestions, I think I have it. I pretty much followed Tex_NL's example with an additional turbojet in the center position. Total mass is at 23,945k, I followed an 80° ascent to 10k, level out to 20° til 30k then just followed the velocity vector until i got my desired ap height. was left with about 940 dV which is more than enough to meet up with my station at 300k orbit with plenty of emergency fuel. I really appreciate all the quick response from everyone. Thanks again

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EDIT: Went back and tidied up the fuel lines and added struts, also added another small fuel tank clipped into the center body, forgot a pair of up facing rcs ports but it still docked smooth as can be with 400+ dV to spare.

New mass is at 24,588kg with a TWR of 1.25

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Edited April 24, 2015 by AmbApe

[capi3101]

Good lord that is one hideous plane

Sorry but that thing is HIDEOUS...

I'm in total agreement with you guys - it's an ugly-ass...I'll say "contraption" instead of "plane". That said, it did its job and it did it well - Mun and back, with a tonne of science, with all parts retrieved and total mission cost only about √1500, the cost of the fuel expended. Still haven't built a replacement for it in FAR; not sure how I'd do it, since the lander won't fit in a cargo bay (not even a Mk3 Cargo Bay - it's that wide across).

Looks like you've got yourself a pretty good plane there, OP.

[Hodo]

I'm in total agreement with you guys - it's an ugly-ass...I'll say "contraption" instead of "plane". That said, it did its job and it did it well - Mun and back, with a tonne of science, with all parts retrieved and total mission cost only about √1500, the cost of the fuel expended. Still haven't built a replacement for it in FAR; not sure how I'd do it, since the lander won't fit in a cargo bay (not even a Mk3 Cargo Bay - it's that wide across).

Looks like you've got yourself a pretty good plane there, OP.

Who needs a lander?

Those were some fun designs. I am working on replacing the first one.