Many questions about SSTO's, Shuttles and spaceplanes in general.

[Wanderfound]

- airbreathing SSTO spaceplanes are great as cargo haulers to carry stuff to LKO (Low Kerbin Orbit) and for use on Laythe. I would advise against using them for much else. I have some experience with interplanetary SSTO spaceplanes and I can tell you: they're not worth the trouble. They take a ton of design effort, are stupidly big and heavy, are generally less efficient than purely rocket-powered ships and can't really do anything other than the specific task they were designed to do. They may be somewhat cheaper because you don't discard any hardware, but the small cost saving is not worth it.

"Big and heavy" is not compulsory:

The last one is arguably a bit big, but it is carrying 26 Kerbals...

There is a bit of an efficiency cost in hauling your wings through space, but there's enough range available to a nuke ship that there's usually plenty of ÃŽâ€V to spare. And given the hefty cost of interplanetary ships, the benefit of 100% recovery is nothing to sneeze at. And with DRE in play, bringing a large non-winged ship through reentry is extremely challenging.

Besides, interplanetary spaceplanery pays for itself in style and cool.

[Captain Vlad]

Other spaceplane tips...

1. Make good friends with your action groups panel. When I first started tinkering with planes I realized how rocket-oriented staging was and how maddening trying to click on an engine to turn it on and off was. Have 'push to' buttons for turning your engines on, off, closing inlets, etc.

2. Flight profile is everything. Early on, you may build a nice bird that you can't get into space, then weeks later learn a different way to fly it and find it'll make orbit with plenty of fuel to spare. The basic SSTO ascent profile is thus: 45 degree climb until 10-15,0000 meters, level out as much as possible and keep climb reasonable until your engines simply cannnot suck any more air and your speed is near-orbital, then pitch up to 45 again to set at least a 70K apoapsis. Then circularize like any other craft.

Some designs you make might be able to use a much simpler profile, or some might not be capable of the basic profile (usually the last pitch-up) but can make orbit anyway...but that seems to be the 'basic' idea.

3. Problems you will most likely have: running out of air before you're high/fast enough, loss of control (especially spins) at high speed/altitude, loss of control on re-entry with nearly-empty tanks. There's multiple reasons for all these, but all are very solvable and people here are usually happy to help, so just ask specific questions and you'll likely get either specific answers or requests for screenies so they can analyze your ship in detail.

4. Download Kerbal Engineer. Having actual numbers instead of guesstimates for your thrust/weight ratio is a God-send. It doesn't alter anything about the parts your using, it just gives you more information about your plane. It's so unobtrusive even I use it, and I'm an old fuddy duddy about most mods (that seems to be changing...).

5. Listen to everything other posters have said about Center of Mass and Center of Lift.

[Van Disaster]

I will second "profile is everything". Just take it easy & let the plane climb at the speed it's happy with, don't try to force it to be either too fast - it will get very twitchy and it's a waste - or too steep, when it will eventually stop flying in the direction it's nose is pointing as it runs out of lift.

RE interplanetary spaceplanes - wings aren't actually that much mass & as everyone's mentioned, rather useful no matter what the atmosphere is made of. Lugging air-breathing engines around is a bit horrible though unless you're going directly to Laythe...

Edited January 12, 2015 by Van Disaster

[Tassyr]

GUYS! GUYS! THANKS TO YOUR HELP, I DID IT!

DEFIANCE 2 MADE IT INTO ORBIT!

AND later made it back down. Now all I gotta work on is getting enough fuel to dock with my station...

[Monger]

The thing is: SSTOs combine two very different fields of engineering which have conflicting interests. For example:

• Rocketry avoids air fraction by reducing the surface of the craft. Flight on the other hand aims for big surfaces to generate lift
  
• Rocketry carries its own oxizider, and therefore needs to optimize for oxidizer efficiency. Flight is based on using an external, basically unlimited oxizider, and therefore only needs to optimize for fuel efficiency
  
• Rocketry is based on creating thrust by carrying its own medium, flight is based on creating thrust within an existing medium
  
• Rocketry requires the center of mass to be in line with the center of thrust. Flight requires the center of mass to be in line with the center of lift
  

etc. pp.

I recommend that you learn a couple of techniques before going on to SSTOs, for example: creating big airplanes, creating airplanes for very high atmospheric flight, creating first stages that are able to reach space (not orbit) and land again at a specific spot in one piece.

I think, SpaceX is right to strive for full reusability first before striving for SSTOs. It is perfectly okay to have two or more stages, if all stages are fully recoverable. In KSP, this unfortunately means that you usually have to reach at least space before returning the first stage

[eddiew]

Heh, good stuff

I can't help thinking that you've got a lot of wing there - and thus a lot of drag. I think you could literally cut it down to a Delta and a 'B' on each side, and still be fine with four rapiers

[GoSlash27]

GUYS! GUYS! THANKS TO YOUR HELP, I DID IT!

DEFIANCE 2 MADE IT INTO ORBIT!

AND later made it back down. Now all I gotta work on is getting enough fuel to dock with my station...

There ya go! It's only difficult the first time

Just out of curiosity, what was the problem before?

Congrats,

-Slashy

[Tassyr]

The problem before was a lack of understanding of how to mix jet and rocket engines, altitudes, and flight paths. The latter mostly. I had no idea how to make the ship pitch into space properly.

[KerbMav]

There ya go! It's only difficult the first time

Speak for yourself!

Congrats Tassyr!

[Voculus]

Congrats, Tassyr! It just gets better from here on out, as you learn how to throw ever larger ships into orbit.

[Pecan]

The problem before was a lack of understanding of how to mix jet and rocket engines, altitudes, and flight paths. The latter mostly. I had no idea how to make the ship pitch into space properly.

Well done, like I said before with practice you get to the point where it just 'clicks' and you can put something together pretty quickly.

The number of air intakes you provide per jet/rapier has a big affect on how high and fast you can get before switching to rockets/closed-cycle. I usually put lots but the trick is to place them behind the CoM, otherwise their drag will make the vehicle want to flip.

[Cirocco]

GUYS! GUYS! THANKS TO YOUR HELP, I DID IT!

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

DEFIANCE 2 MADE IT INTO ORBIT!

AND later made it back down. Now all I gotta work on is getting enough fuel to dock with my station...

grats! that thing looks pretty slick too! two suggestions to improve it:

1) add a couple more intakes (the long slender radial ones look really nice)

2) if you use the following placement order, your engines will never experience an asymetric flame-out, and you'll be able to use them in the airbreathing mode up to over 30km height: first place all the air intakes you want a single engine to use, then place said engine. Then place all the intakes you want the next engine to use and then place said engine. Repeat until you've placed all engines and make sure you don't use the symmetry tool or alt-click to copy the parts.

[Starwhip]

Yep. You've taken your first step.

Now go take 500 more.

SSTO's are more of a concept than a set build. Once you make your first, it suddenly becomes much, much easier. My most recent WIP is this one.

It needs more jet thrust, though: the stock jets don't complement it.

So far, the best SSTO I've made is this one.

As you can see, it can get far. *Really* far...

Eventually, you'll figure out the best SSTO methods for you.

What I can give as advice is the following:

-Crewless vessels are lighter

-More jet engines are better, but require more intakes

-Don't be ashamed to air-hog.

-Give it more wings.

[Tassyr]

Hey so, uh. To all you people. Have you ever run into a problem where docking a spaceplane to a station throws the orbit off as if constant thrust were being applied, even with RCS and Engines -shut down?-

[LethalDose]

Hey so, uh. To all you people. Have you ever run into a problem where docking a spaceplane to a station throws the orbit off as if constant thrust were being applied, even with RCS and Engines -shut down?-

Yep, I've seen this especially happen with stations to which a claw had been docked to sometime in the past. The game's in beta /shrug. bugs are to be expected, which is why deactivating quicksaves is, IMO, moronic.

[Van Disaster]

Make sure you've got any piloting aid disabled before you make the docking connection... otherwise yeah, just a thing that happens.

[Captain Vlad]

DEFIANCE 2 MADE IT INTO ORBIT!

AND later made it back down. Now all I gotta work on is getting enough fuel to dock with my station...

Congratulations, man!

[Tassyr]

Make sure you've got any piloting aid disabled before you make the docking connection... otherwise yeah, just a thing that happens.

define piloting aid? Because I could dock segments to this damn thing fine before, but now the SHUTTLE it was built to handle won't dock And it's almost entirely stock. There's two whole non-stock parts.

[Janos1986]

Yesterday I found out that the rotate gizmo really comes in handy with heavy SSTOs.

I solved the issue of excessive nosediving by tilting jet engines upwards by a couple degrees, enough to dramatically increase the plane's climbing capabilities but not enough to spin out of SAS comfort zone midflight.

Here comes the crosspost:

Javascript is disabled. View full album

[Cirocco]

Yesterday I found out that the rotate gizmo really comes in handy with heavy SSTOs.

I solved the issue of excessive nosediving by tilting jet engines upwards by a couple degrees, enough to dramatically increase the plane's climbing capabilities but not enough to spin out of SAS comfort zone midflight.

Here comes the crosspost:

http://imgur.com/a/ZnV0v

hm, that IS an interesting idea. It would allow your CoM to be more to the front of the craft, which would solve a lot of problems for heavy SSTO's which need a lot of engines in the back, shifting the CoM very far backwards.

I wonder how it would affect your flight behaviour when you re-enter atmosphere with near-empty tanks and a CoM that is a lot more to the back though? If my reasoning is correct, a center of thrust above the CoM would make your plane flip upwards very easily, especially if the CoM moves closer to the center of thrust and the plane becomes lighter.

Hang on, as I'm writing this post I just figured something out: what if you angle all but 2 of your jet engines to help with climbing and keeping the nose up when the tanks are full, and only use the 2 non-angled ones upon re-entry and return to the runway? You wouldn't need a lot of thrust anyway when you've lost all that weight from the fuel...

This.... this could work....

Holy Kraken if this works the way I think it will... this could solve so many problems I have with in-flight shifting CoM...

I must test this when I get home from work!

Edited January 13, 2015 by Cirocco
reasoning was incorrect

[Wanderfound]

Don't just use the rotation tools; the offset tool is also very useful for balancing spaceplanes. Shifting lateral engine pods and wings up or down a smidgeon can neutralise the CoM/CoT misalignment issues that often trouble spaceplanes. It also lets you get away with offset engines like this:

Fire up RCS Build Aid, switch it to engine mode, make sure only the active engines are in the first stage and then wiggle things about until you get the torque figure as close as possible to zero. Works for offset engines as well as neutralising the nose-up torque frequently caused by the off-centre mass of the vertical stabiliser.

[Janos1986]

hm, that IS an interesting idea. It would allow your CoM to be more to the front of the craft, which would solve a lot of problems for heavy SSTO's which need a lot of engines in the back, shifting the CoM very far backwards.

I wonder how it would affect your flight behaviour when you re-enter atmosphere with near-empty tanks and a CoM that is a lot more to the back though? If my reasoning is correct, a center of thrust above the CoM would make your plane flip upwards very easily, especially if the CoM moves closer to the center of thrust and the plane becomes lighter.

Hang on, as I'm writing this post I just figured something out: what if you angle all but 2 of your jet engines to help with climbing and keeping the nose up when the tanks are full, and only use the 2 non-angled ones upon re-entry and return to the runway? You wouldn't need a lot of thrust anyway when you've lost all that weight from the fuel...

Well...

In my design I put 2 reaction wheels behind the ram intakes, so the SAS effect is even stronger when running out of fuel. But even when the aircraft is almost empty, the CoM harldy shifts back, staying in the middle of the cargo bay and in front of the CoL, and the engine tilting is so minimal that is barely noticeable, and a tiny tiny bit of tendency to nose up actually helps while gliding to a safe landing.

To be honest, even the rocket engines are tilted slightly upwards, makes it easier for the final orbital climb since the plane tends to level when turning on the rockets.

After the circularization and docking operation with my space station, which is up at about 100km, I am left with some 250 deltaV worth of rocket fuel in the side tanks.

What does Janos do when he's done with his fiddling in orbit then?

After the short re-entry burn, Janos takes the oxidizer and transfers it in the front tank as counterweight, and the rest of the liquid fuel in the back tank for the jet engines.

Basically reaction wheels + oxidizer counterweight + balanced fuel tanks = happy plane.

Even I'm 100% sure that every single one of this actions I take are not fundamental to land safe and sound, I have more than one countermeasure if anything goes sideways.

So here.

Edited January 13, 2015 by Janos1986

[Van Disaster]

define piloting aid? Because I could dock segments to this damn thing fine before, but now the SHUTTLE it was built to handle won't dock And it's almost entirely stock. There's two whole non-stock parts.

I have little experience with the SAS in 0.90, but if you were using Mechjeb's SmartASS ( the new SAS seems to have lifted half of it's functionality without change ) during docking then sometimes I found the combined craft after docking would still be using SmartASS with whatever settings it had previously - and if you now have a very off-centre set of RCS or reaction wheels, bad things can happen if it all attempts to change orientation.

Otherwise yes, have had stations attempt to deorbit after docking without any apparent orders to do anything.

[LethalDose]

Got a 0.90 question for people. I've seen a lot of SSTOs in this thread with two air-breathing engines. Is anyone have trouble with asymmetric flameouts? Unless I'm mistaken (and I may be. I've played less than 30 mins of 0.90.... stupid dissertation...), custom actions groups are locked behind the last level of the SPH.

Have they finally fixed the asymmetric delivery of air to multiple airbreathing engines or is there another way people are getting around the crappy fuel logic?

Or are we still using action groups to shut off the engines?

[Tassyr]

Got a 0.90 question for people. I've seen a lot of SSTOs in this thread with two air-breathing engines. Is anyone have trouble with asymmetric flameouts? Unless I'm mistaken (and I may be. I've played less than 30 mins of 0.90.... stupid dissertation...), custom actions groups are locked behind the last level of the SPH.

Have they finally fixed the asymmetric delivery of air to multiple airbreathing engines or is there another way people are getting around the crappy fuel logic?

Or are we still using action groups to shut off the engines?

Honestly I just manually cut it to rocket engines just before flameout time. I've run into asymmetric flameout about half the time otherwise.