need help SSTO's

[joethebeast22]

my rocket game is off the chart, too comfy with rockets, and i have been going through dozens of SSTO's, and for them to either lose air at the end of the climb and spin out of control, or spending all the fuel getting to orbit OR once in orbit, only running on fumes and not being able to do anything but retro fire to get home :/ need help and tips here, thanks guys, i have been trying oh so very hard for months, with little to no success :/

[juanml82]

To prevent asymetric thrust, caused more air going to one engine that the rest, you should build placing one engine (no symmetry) first, then all the intakes for that engine, then the next engine, then its intakes, rinse and repeat.

I think three shock intakes (the SP+ ones) per rapier/turbojet provide enough air to endure at 25-30 km (as long as asymmetric thrust is avoided) without the need to clip dozens of intakes.

[Claw]

Hi joethebeast22,

Pictures of what you've created so far would help, since we can give you specific advice on what you're designing. juanml82 provided some good advice about asymmetric thrust issues and intakes. I do the same thing, although I typically place my intakes, engine, intakes, engine in that order, but I think it'll work either way. I also agree that you only need three ram or three shock intakes per TurboJet at the most. More helps, but you aren't really going to see much of an increase unless you double them.

Also, you can try looking around in the spacecraft exchange forum for ideas. There are several good examples in there.

Good luck,

~Claw

[Pecan]

my rocket game is off the chart, too comfy with rockets...

Jets can be a problem, but if you're so happy with rockets why not simply SSTO with them?

Much simpler builds over a wider range of payloads and easier to fly as well.

[el_coyoto]

Building SSTO is indeed a more difficult challenge than rockets (at least in my case), but I also find it very rewarding.

There are some very good resources on this forum, among which :

• Basic Aircraft Design Explained Simply With Pictures : this amazing and beautifully illustrated thread deals with aircraft and flight in general, but the explanations are really clear and might help you with general aircraft design (I've had several "ah ah" moments reading it although I've been playing for a while...).
  
• This thread troubleshoots several common SSTO problems, including ascent profiles (6th item).
  

Of course, there are many more equally good threads that you can find on the Drawing Board.

Don't hesitate to post pictures or videos of your craft, people here will be very happy to help you improve your planes and help become a better plane designer : you don't have to stay all alone in your SPH without getting help and input from the amazing community that populates this forum!

Fly safe!

[Clockwork_werewolf]

Building SSTO's is a tough thing to do.

Pictures would help but there are a few suggestions that I can give.

Burnout is a big problem and usually the hardest to deal with. Some people add up to about 15 intakes per engine but this looks silly or can lead to needing to clip many parts inside of each other thus enticing the Kracken.

I always stick at least on nuke on an SSTO so that I can do orbit alterations or deorbit burns for half the fuel BUT this is only worth it on larger SSTO's as on smaller ones the mass of the nuke (2.5) is more than the fuel mass you save. You need to have at least 2.5 tons of fuel left before this helps. You can however use the nuke in the assent burn (after running out of air) as past about 2k the nuke is a better rocket than anything else that uses oxidiser.

I like the Rapiers as they tend to have a much lower burnout ratio than turbo jets. As long as you don't give them access to all your fuel they can also give you the thrust to get out of most of the atmo. With the new (ish 0.24) nacelles I build rapier nacelles with one nacelle, one FLT-200 tank, one rapier and one ram intake. This doesn't give them quite enough air or liquid fuel but you can make some intake nacelles and pump some fuel from them and just generally customise from there.

I also like to add a few reaction wheels to keep the craft steady and also to point it's nose upward for the escape burn. Quite often at high speed the momentum forward is so strong that getting the craft to turn more than 20 degrees upwards a problem and you use a lot of rocket fuel burning forwards in the atmosphere rather than upwards out of it. The more you turn upwards the less air goes to the intakes so starting the turn ends your air breathing mode and you want to get out of the atmo as fast as possible before it saps your forward momentum or you use rocket fuel to fight it.

but if you're so happy with rockets why not simply SSTO with them?

Perhaps for the same reason I started building them. After a while I realised I hadn't built any and it was a skill I wanted. Rockets can build fast and heavy SSTO's but they aren't much of a challenge once you have them learned. The other point is that without mods, landing an SSTO rocket on the runway or landing pad of KSC in carrier mode is very VERY hard. My deorbit burns usually only put me within 2-20k of KSC and I then fly my SSTO or shuttle back to the landing pad. This kind of distance is very inefficient with a rocket SSTO.

[Red Iron Crown]

my rocket game is off the chart, too comfy with rockets, and i have been going through dozens of SSTO's, and for them to either lose air at the end of the climb and spin out of control, or spending all the fuel getting to orbit OR once in orbit, only running on fumes and not being able to do anything but retro fire to get home :/ need help and tips here, thanks guys, i have been trying oh so very hard for months, with little to no success :/

I'm a long-time rocket guy/newish spaceplane guy, so I am sympathetic. Air-breathing spaceplanes are a good bit different from pure rockets both in construction and ascent path.

My observations:

- The advice about intake/engine ratio and order of placement given above is good. However, it will not prevent asymmetric thrust but instead delay it until later in the climb.

- Intakes are draggy. If possible, place them behind the CoM to increase stability.

- About one turbojet per 10 tons or so of total vessel mass is a good rule of thumb for beginners. More mass per engine can be made to work but is more challenging.

- More SAS makes asymmetric thrust easier to control.

- Action groups are nearly essential. One to toggle the air-breathing engines, one to toggle the rockets, and one to toggle the intakes. If using Rapiers, disable automatic mode switching and use an action group to toggle modes (the automatic mode is very conservative and switches to rocket mode too early for my taste).

- The ascent profile is different from a rocket. I've had good success with: Climb at around 45 degrees until about 15km, then level off. At 20km your climb rate should be less than 100m/s, by 30km it should be less than 20m/s or so. This is where the plane builds its speed to near-orbital velocities. Alt-right click the engines and watch their thrusts carefully, when one drops below the other(s) throttle back a bit until it returns to even. Repeat until there is not enough air to keep running the engine at all (usually at ~55km altitude/~2300m/s orbital speed), then shut them down. Close intakes and coast to AP (should be well out of atmo) and perform the small circularization burn with rockets (usually 100m/s or less).

- Designs with only one air-breathing engine are much easier to manage because there is no thrust asymmetry. Start with a small design, just enough to carry a crew without payload to orbit until you get the hang of the ascent.

All this advice applies to the stock aerodynamic model, if you use FAR/NEAR things are a bit different. I'm not experienced enough with those mods to comment on them.

[Geschosskopf]

my rocket game is off the chart, too comfy with rockets, and i have been going through dozens of SSTO's, and for them to either lose air at the end of the climb and spin out of control, or spending all the fuel getting to orbit OR once in orbit, only running on fumes and not being able to do anything but retro fire to get home :/ need help and tips here, thanks guys, i have been trying oh so very hard for months, with little to no success :/

The way the various factors play out in the game, a spaceplane is pretty much just an alternative to the rocket lower stages of a conventional lifter. IOW, you have a payload you want to get to LKO. You can either put it in a spaceplane or stack it atop an orange tank and Mainsail. But just as you don't expect to take the Mainsail with you to another planet, same goes for the spaceplane. So bottom line, the typical spaceplane can't do much more than get itself and its payload to LKO. After that, the payload needs some other way to get to its ultimate destination.

Now, of course it IS possible to get spaceplanes to other planets, but it's usually not worth the hassle unless the spaceplane itself is the mission payload, like to fly around on Laythe. There are a bunch of ways to do this, none of which are particularly good, such as:

• Refueling the spaceplane in LKO. This is limited by the efficiency of the spaceplane's rockets and its rocket fuel capacity. RAPIERs suck at efficiency, 909s are better, but you're still not going to have a lot of transfer delta-v this way and you'll definintely need to refuel again at your destination.
  
• Using LVNs as the spaceplane rockets, but their weight and low thrust limits the size of the spaceplane and any payload it can carry.
  
• Using ion engines on the spaceplane for transfer burns. This has the least impact on the size of the spaceplane and its payload but results in horribly long transfer burns.
  
• Docking a transfer tug to the spaceplane. Works good but complicates the spaceplane design, depending on its docking port arrangement.
  

Note that most of these options require you to set up a supporting infrastructure ahead of time, using conventional rockets. And in any case, the only stock cargo bay is the new SP+ Mk2 thing in 0.25, which only holds 1.25m parts and a 1-man lander can won't even fit inside without poking through the top and bottom. So unless you go with B9 or whatever, you can't use a spaceplane to carry any significant payload anyway.

So, the bottom line on spaceplanes is that they should be viewed primarily as a complicated, time-consuming way to get relatively small payloads (probe satellites or multiple Kerbals) to LKO. This is all they can reasonably be expected to do, and even this requires way more design effort and playing time both ascending and landing than you'd spend lifting the same load on a rocket. It's possible to make spaceplanes that can do more than this, but the hassle involved increases exponentially with the spaceplane's utility. There's really no trick to building SSTO spaceplanes; once you've done it once, you'll have no trouble in the future. The main reason most folks don't use spaceplanes is because of their limited payload capacity, the time they consume, or both.

[capi3101]

my rocket game is off the chart, too comfy with rockets, and i have been going through dozens of SSTO's, and for them to either lose air at the end of the climb and spin out of control, or spending all the fuel getting to orbit OR once in orbit, only running on fumes and not being able to do anything but retro fire to get home :/ need help and tips here, thanks guys, i have been trying oh so very hard for months, with little to no success :/

Been there myself - I can/have rocketed to Jool and back but still have issues with spaceplanes. I'd start with Keptin's illustrated guide which el_coyoto was kind enough to provide to you already. I'd then suggest taking a look at DocMoriarty's KSP Space Plane Construction and Operation guide - it focuses on transport planes and VTOL craft primarily, and it was designed for 0.24.2 (so the new 0.25 spaceplane parts are not in it just yet), but it still gives you some hard numbers to shoot for for more basic designs. Start small with spaceplanes - learn how to design them, how to fly them properly, and how to land them. I'd also suggest starting in the sandbox...

DocMoriarty's engine configuration is much like the one Clockwork_werewolf described. Only variation - he adds a tri-coupler to the front of the engine nacelle, and sticks three Ram intakes on the front. He also sometimes puts all of the fuel in one or two main rocket fuel tanks and runs fuel ducts to the nacelles; as he points out, the lower part count reduces lag. The nacelle still allows for radial placement of the assembly, which is nice.

With 0.25, I'ma wondering about that Shock Cone Intake - if you need two (use a bi-coupler) or if you could get away with just one per engine (.4 increasing to .8 intake air over a 0.012 intake area, as opposed to a steady 0.2 intake air over a 0.01 intake area for Ram Intakes - with the disadvantage of the Shock Intake being a nearly three-fold increase in mass, which, if you need three Ram Intakes to do the job of one Shock Intake, is no disadvantage at all).

Edited October 10, 2014 by capi3101

[Alshain]

If your using stock aerodynamics, Spaceplanes are downright unintuitive. Things that should fly, won't and things that shouldn't do. The biggest thing I can suggest for those who want to build planes is NEAR or FAR, because only with one of those will the plane fly as you would expect it to fly.

For engines, your going to have a few of options, you can use an dual mode like Rapiers, but you can also build with separate rockets. The key is avoiding asymmetrical thrust when one flames out. The problem is you must have your thrust centered with the CoM so you end up with either 2 jets 1 rocket, or two rockets, 1 jet (at least till you get to bigger, more complicated designed). 2 jets give you more power if the plane is bigger, but you have to manually shut off the engines to avoid flameout. 1 jet is less powerfull but you can allow the jet flame out on it's own without consequence. Rapiers, 48-7S, and Toroidal Aerospikes are your best rocket options. You can of course use any engine but these will offer the best fuel efficiency without overloading the plane (like an LV-N would) and you don't need a lot of power because your jet engines do all the atmospheric work.

LV-1R and 24-77 make good counter rotation engines. While in space, some planes have a tendency to want to rotate hard because the wing, tail, or jet position raises or lowers the CoM. It's a symtom of only being symmetrical in one direction, unlike a round rocket. You can aim the LV-1R and 24-77 to counteract any rotation you might have from the main engine. I have one plane in my imgur album in particular that has high mounted engines (named Hawk). The fuel for those engines causes severe rotation, while in the atmosphere the ailerons can more than compensate, but that doesn't work in space, so I added 24-77s aiming slightly down to fix that.

Feel free to browse my Imgur album in my signaure, I'm going to be re-doing it soon and adding a bunch more designs I don't have in there yet and even making the craft files available. But you can see several of these design options. Just be warned all of my planes are designed for Ferram Aerodynamics.

For practicality, capi3101 is right. Rockets are easier. However, designing planes is it's own reward for those who enjoy it. If all you want is a station builder or to go to other planets, stick to rockets. That said, I've built 2.5m stations using nothing but planes, but I only did it to prove I could. That's kind of what planes are, at least to me. I just enjoy challenging myself to see what I can design next.

Edited October 10, 2014 by Alshain

[joethebeast22]

Jets can be a problem, but if you're so happy with rockets why not simply SSTO with them?

Much simpler builds over a wider range of payloads and easier to fly as well.

idk, just like the bigger challenge posed by jet to rocket ssto's i guess

[Pecan]

...just like...

That's all the reason you need :-)

Just making sure everyone was aware that SSTO rockets are available, practical and easy.

There's always someone who thinks "Single Stage To Orbit" means "spaceplane" or "a vehicle that goes to Mun". I'm particularly interested in this at the moment because Wanderfound and I are planning a "World of SSTO" tutorial/debate and I will be concentrating on rocket SSTOs because I don't enjoy all that tedious mucking around in atmosphere.

Which is odd, because the last 7 vehicles I've built have all been spaceplanes.

[Stratzenblitz75]

If you want to build SSTOs in stock KSP, you must first clear your mind of how you think space planes are supposed to work, you won't be needing that here.

Ok, done? good, now we can harness the true power of stock TurboJets without being bogged down by "realism".

To design an efficient and powerful Stock SSTO, first determine how much payload/mass you want to put into orbit.

Then, go to the VAB, create a rocket like you normally would, but instead of adding rocket engines, add turbojets and intakes (two RAM intakes per turbo engine is usually enough) according to this trick, until your TWR is greater than 1.5.

Add one 909 or NERVA engine and struts.

Add reaction wheels for control.

Add parachutes if you intend to recover the SSTO.

You're done! No wings required!

Flying it also easy, just get it to 30 Km, level off and gain speed until you reach orbital velocities. Then use your single engine to complete the 50-100m/s circularization burn.

Using these easy steps, you can have an SSTO that can lift almost twice its mass in payload to LKO while only burning a few thousand funds or less in fuel. Also, pay no attention to the naysayers, stock SSTOs can easily lift over 100 tons to orbit.

....

If you want to get more serious about SSTOs and space planes, I highly recommend FAR. It makes building SSTOs more difficult, but more rewarding and realistic.

[Pecan]

...Also, pay no attention to the naysayers, stock SSTOs can easily lift over 100 tons to orbit...

I love everything about your designs except the part-counts (but will still be voting for you in the http://forum.kerbalspaceprogram.com/threads/93779-SSTO-Spaceplane-Airplane-Design-Contest-II-Akademy-Awards).

This SSTOs a 100t payload with 52 parts.

[capi3101]

I love everything about your designs except the part-counts (but will still be voting for you in the http://forum.kerbalspaceprogram.com/threads/93779-SSTO-Spaceplane-Airplane-Design-Contest-II-Akademy-Awards).

This SSTOs a 100t payload with 52 parts.

http://i.imgur.com/iCBdSA0l.png

Hey Pecan, is that screenie in 0.25? My local instance of NREP is telling me it's incompatible; that's why I ask.

Love me a good SSTO rocket - they're easier to design overall and not all that terribly difficult to fly; big trick with them is that you can't keep your throttles to the stops the whole way up (not if you want to make it up, that is).

Don't get me wrong; SSTO Spaceplanes are pretty awesome, more so if you can get them to work the first time...

[Pecan]

Hey Pecan, is that screenie in 0.25? My local instance of NREP is telling me it's incompatible; that's why I ask....

Sorry, no - I haven't tried adding NRAP to 0.25 yet, I'm going through the vehicles in my tutorial to make sure they work in stock.

The SSTO rockets I have at the moment launch with a TWR around 1.2 and maintain full-throttle all the way. The trick is that since they'd be tearing themselves apart with TWR >5 by the time they get to 75km I build some stacks to burn-out early, which is why the port & starboard stacks in that picture are shorter than the others. The biggest annoyance I find it having to tweak the remaining engines to 20% throttle in order to make a de-orbit burn with any accuracy and remember to put them back to 100% before landing! Doh!.

The thing I really haven't spent much time on yet is vertical launch/landing jet SSTOs. As Stratzenblitz75 says, they're THE way to do it for easy cost-efficiency.

[tsotha]

As others have noted, at least in the beginning start with a single engine. If you have two they won't cut out at the same time, so you'll need to manually switch over to rockets before they run out of air.

Start simple. Make a spaceplane with one turbojet, two 48-7S rockets, and three ram intakes. If you baby it you can get a 150/35 orbit before you have to switch to rockets. Personally, I think this is an easier plane to design and fly than one using Rapiers.

And yes. Planes are much harder than rockets. CoM is important, and it moves as you burn fuel. When I started it wasn't uncommon for my prototype to achieve orbit without a hitch and then tumble uncontrollably during reentry.

[capi3101]

When I started it wasn't uncommon for my prototype to achieve orbit without a hitch and then tumble uncontrollably during reentry.

Oh yeah, that's happened to me too...

Prototype careens off to one side of the runway and explodes. Check.

Prototype flies straight into the ocean. Check.

Prototype flips up, does a loop, does another loop, tries another loop and then flies into the ground. Check.

Prototype runs out of gas just short of achieving orbital velocity. Check.

Prototype goes into a flat spin and Goose ejects into the canopy. Everybody's done that...

.......I haven't had one burn down, fall over and then sink into the swamp. Yet.