SSTOs help

[MrAnonymous]

I need some advice on making a good SSTO. I could never seem to be able to build one. Any advice would help, thanks. Also advice for different types of SSTOs ie: crew shuttle and cargo shuttle.

[helaeon]

I'd go take a look at the SSTO thread in the spacecraft exchange. Definitely look at Cupcake's. I don't even bother with space planes anymore, it's all VTOL dropship SSTOs and jet-rocket hybrid SSTOs now unless doing a heavy lift.

Also SSTO doesn't have to be a jet thing at all. I have several lander designs that can put themselves into orbit around Kerbin.

You'll want about 4800 delta-v with a TWR of at least 1.4-1.6 to start if you're using pure rocket engines.

Jets are a bit different and that depends on how against airhogging you are (lots and lots of intakes to raise your operational ceiling and how long you get the TWR boost on the turbojets). If you're willing to use lots of cubic octagonal struts and lots of ram intakes you can get to orbit with some decent cargo very very easily. Like, only needing to fire your rocket for about 40 m/s to circularize.

Flight profile is very different from a rocket and you probably will be more actively piloting it. That may be why your SSTO's aren't working out is you don't have a good flight profile. So where they're going wrong will be helpful information.

The other thing people do is bring too much fuel. Bring only enough oxidizer that by the time you're ready to go to rockets your liquid fuel and oxidizer ratio has equalized. You can do that with the tweakables. No point in lifting all that extra oxidizer, and really you don't need that much fuel, so the less you bring the less you lift, the better your TWR is and the easier it is to make orbit.

[Hodo]

Definitely look at the SSTO thread as helaeon said. I don't agree on the don't bother with space planes bit. Do what you want.

I excel in space planes, and am more than willing to give any help I can. If not I can suggest Cupcake, or Curzan as others to look to for advice on a decent SSTO.

[m4rt14n]

Theres an awesome tutorial in the Tutorial sub forum on all jet related, vtol and ssto.

[Jouni]

There are two main classes of SSTOs: spaceplanes and jet-boosted rockets. Most people build spaceplanes, because they are ultimately more interesting and more efficient, if also harder to build. Jet-boosted rockets (or VTOLs, dropships, landers etc.) tend to be easier and more practical.

In either case, the most important thing to learn is how to get the most out of an airbreathing engine. If you climb too fast, you run out of air too soon, forcing you to switch to rockets at a low speed and a low altitude. On the other hand, flying too low will just waste time and fuel in fighting drag. Usually it's the best to get above 10 km as soon as possible, and then start turning so that you are flying almost level at 20 km. After that, keep accelerating while climbing at a slow but steady pace (e.g. 20-40 m/s), until you are about to run out of air. At that point, switch to rockets, close the intakes, and pitch up until you get your vertical speed to at least 100 m/s.

I've never had enough patience to build useful spaceplanes, so I'm mostly using jet-boosted rockets. This crew shuttle was originally designed as a Laythe lander, but it works well at Kerbin as well. The switch to rockets usually happens at 32-33 km while flying around 1900 m/s (surface speed).

The cargo version of the same ship has been designed for 5-tonne payloads, but it can lift larger payloads as well, if they have engines to finish the orbital insertion.

[m4rt14n]

How effective are these jet boosted rockets when using FAR? I think for starting you should learn how to build a regular jetplane first. The ssto, after that VTOL then dropship. IMHO.

Making VTOL is hard enough, flying it is even harder. Correct me if I'm wrong here, dropships are VTOL all the time.

Edited February 20, 2014 by m4rt14n

[Claw]

I need some advice on making a good SSTO. I could never seem to be able to build one. Any advice would help, thanks. Also advice for different types of SSTOs ie: crew shuttle and cargo shuttle.

To be honest, there are so many things to talk about that it's hard to give tips/hints without a specific question. Especially when "SSTO" means different things to different people.

If you're asking about spaceplanes and are unfamiliar with aerodynamics, check out Keptin's aero article.

http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures

I wrote an airborne tutorial that goes along with it. The demo craft is not a space plane, but can be easily converted and demonstrates basic aero.

http://forum.kerbalspaceprogram.com/threads/65638-Basic-Airplane-Space-Plane-Aero-Tutorial

If you're familiar with all that, check out the tutorial subforum. It's full of a variety of tutorials. If videos are your thing, here are some from Cruzan and others that are a little more advanced without being overwhelming.

http://forum.kerbalspaceprogram.com/threads/54903-KSP-Quick-Guides-Plane-SSTO-Tutorials!-*SSTO-Video-Just-Released*

http://forum.kerbalspaceprogram.com/threads/43693-Tutorial-Advanced-SSTO-Design

Edited February 20, 2014 by Claw
added link

[capi3101]

OP: I suppose the first think to ask is what exactly you're looking to build - a spaceplane, or a single-stage rocket. The term SSTO applies to both. I'm a specialist in SSTO booster rockets, at best an amateur with SSTO spaceplanes. But I'll pass along what I know about both.

Both types of SSTO start with the payload, of course - the bit you want to get into space - and more importantly, its mass. The payload part does absolutely nothing while the rest of the craft is tasked with getting it into space. So you figure that up first. For spaceplanes, the payload is everything you want to add except jets, jet fuel tanks and intakes. For rockets, it's everything except the fuel tanks.

Now, for SSTO rockets, the general guidelines are as follows:

1) Your payload fraction is 4%. These are super-inefficient rockets we're talking about here, the opposite end of the spectrum from asparagus. So, if you've got a 10 tonne payload, you can expect to launch it with a rocket that has a total mass of approximately 250 tonnes.

2) Your launch TWR is going to be 1.2. This helps you figure out how much thrust you're going to want at liftoff using the standard TWR equation (TWR = T/Mg, T=TWR*Mg). That 250 tonne rocket will require 2,943 kN of thrust to take off, so you're looking at two Mainsails (12 tonnes) or five Skippers (20 tonnes). Design-wise, the Skippers are easier. That ups your deadmass to 30 tonnes -10 for the payload and 20 for the engines.

3) Your Isp for the entire launch is going to be the atmospheric Isp. This isn't true but it generates a fuel reserve. For the Skipper, that's 300.

Now you just solve Tsiolkovsky backwards to figure out how much fuel you need to generate 4500 m/s of delta-V, using the assumption that the fuel tanks have a 9:1 full-to-dry mass ratio (i.e. M=9Md), and that part of both M and Md is the deadmass:

dV=ln(M/Md)*9.81*Isp

dV=ln(9Md+x/Md+x)*9.81*Isp

ln(9Md+x/Md+x) = dV/(9.81*Isp)

(9Md+x/Md+x) = e^(4500/(9.81 * 300)) = 4.613801

9Md + x = 4.613801Md + 4.613801x

4.386199Md = 3.6138019x = 3.613801*30 = 108.41403

Md = 24.71708, M=9Md = 222.45372 tonnes

Take that figure and divide by the number of stacks you want - one per engine, so 5. Each stack will need about 44.491 tonnes of fuel in it - take that figure and divide by 0.5625 (the mass of an FL-T100 fuel tank) and round up - you'll need 80 FL-T100 fuel tanks per stack. Then its just a matter of picking a combination of tanks that will give you that much fuel. In this case, you want an Orange tank (64 FL-T100 equivalents) and an X200-16 (16 FL-T100) equivalents) in each stack (64+16 = 80). All told you have 200 tonnes of fuel, 25 tonnes of fuel tanks, 20 tonnes of engines and ten tonnes of payload, for a total rocket of 255 tonnes (so the 250 estimate wasn't that bad). Empty, that sucker's mass is 55 tonnes, your Isp is 300 - so working Tsiolkovsky forward, it has 4,514 m/s of delta-V. You have five Skippers for 3,250 kN of thrust, so your launch TWR is 1.299, a good starting spot.

Flying a single-stage rocket is a matter of playing with your throttle - you won't need all that thrust once you're up in the atmosphere. Fly it like you would a normal rocket but watch your gee meter as you ascend, and keep it right at the top of the green zone; if it goes above that level, throttle back. By the time you're high in the atmosphere, you should be burning horizontal around one-third thrust.

My notes on SSTO spaceplanes are a little less comprehensive - the general guidelines I go with are:

1) One turbojet engine per 9-12 tonnes of payload (depending on the number of intakes you add). Include any rockets you intend to make the final push to orbit in your payload calculations.

2) One Mk1 or Mk2 fuselage per turbojet engine (preferably the Mk2, but in practice the Mk1 is easier to work with)

3) One pair of swept wings per 6 tonnes of craft. Delta Wings are the same but they don't have as good of a mass to lift ratio.

4) No fewer than three Ram intakes per engine. Each whole number increase in the ratio of Intakes to Engines adds another half-tonne to the amount your jets can handle.

(i.e. 3:1 gives you 9 tonnes per engine, 4:1 = 9.5t, 5:1 = 10t, 6:1 = 11 t, 7:1 = 11.5 t, 8:1 = 12t - note that this is a guideline, not a hard and fast rule).

You want your center of lift slightly behind the center of mass. Slightly above is also good for stability. Your control surfaces need to be as far away from their axis of motion as possible to ensure good control. Rudders need to be as far back as they you can manage and not lined up with the center of mass. Ailerons as far out on the wings as possible, elevators as close to the tail as possible. If you do elevons (combination aileron/elevator), put them somewhere in between. A pair of small control surfaces offers more lifting power than a large control surface for half the mass. Gear must be perpendicular if you want to make if off the end of the runway (actually, if you want to make it as far as the SPH taxiway before exploding); the rear gear need to be lined up with the center of mass if you want to take off without relying on the "ski-jump" design of KSC's runway. Expect to go into the drink the first dozen times you try to make a new design take off.

Good luck.

[palioxis1248]

Protip: For reasonably-sized spaceplanes, you generally shouldn't need more than 160 units of jet fuel. Of course if you're aspiring to be the Whackjob of spaceplanes, all bets are off.

[capi3101]

^^^

That depends on what you want to do with your plane. One-man orbiters? Yeah, you can get there with one engine and one Mk2 fuselage just fine. Cargo plane? You're gonna want more than that. I have examples of both if I can find the screenies...

[Hodo]

How effective are these jet boosted rockets when using FAR? I think for starting you should learn how to build a regular jetplane first. The ssto, after that VTOL then dropship. IMHO.

Making VTOL is hard enough, flying it is even harder. Correct me if I'm wrong here, dropships are VTOL all the time.

Learning to make a VTOL is hard, once you work out a system they become a fair bit easier to build. As for flying them, that is a matter of player skill.

[MaverickSawyer]

Tip I just figured out myself for spaceplanes: DON'T carry a full load of fuel and oxidizer. You won't need all of it, and carrying a full load will cause your ascent to take much longer and be much more tricky. My Valkyrie designs use about a half load of fuel and a touch over a third of a load of Ox.

If you fly it right, she'll get to orbit with plenty of fuel and ox for orbital ops, and a touch more fuel than ox, allowing you to use the jet engine again if you don't make it back to the KSC on a proper glidepath and have to go around.

[Hodo]

I pack a full load of fuel and ox into orbit, but some of my space planes go to the Mun and back in a single stage.

[Armchair Rocket Scientist]

Tip I just figured out myself for spaceplanes: DON'T carry a full load of fuel and oxidizer. You won't need all of it, and carrying a full load will cause your ascent to take much longer and be much more tricky. My Valkyrie designs use about a half load of fuel and a touch over a third of a load of Ox.

http://i.imgur.com/Vr4hfOG.png

If you fly it right, she'll get to orbit with plenty of fuel and ox for orbital ops, and a touch more fuel than ox, allowing you to use the jet engine again if you don't make it back to the KSC on a proper glidepath and have to go around.

Doesn't that mean you're carrying around dead weight in empty fuel tanks? Why not just build your plane with the amount of fuel and oxidizer needed to carry the payload you want to the orbit you want?

[Armchair Rocket Scientist]

How effective are these jet boosted rockets when using FAR? I think for starting you should learn how to build a regular jetplane first. The ssto, after that VTOL then dropship. IMHO.

Making VTOL is hard enough, flying it is even harder. Correct me if I'm wrong here, dropships are VTOL all the time.

An aerodynamically shaped jet-boosted rocket would probably still work, but like in stock it would be less efficient than a plane due to gravity losses.

Something like Cupcake's dropships would probably have a lot of drag at supersonic speeds, and potentially be uncontrollable.

[DovahMarat]

For SSTOs, take a look at CruzanAK's channel. He makes nice tutorials about Spaceplanes.

Link:

[LordFjord]

A few suggestions when you want to learn howto spaceplane SSTO:

- Start small. The bigger they are, the harder it is to design them properly.

- Start simple. A cockpit, jetfuel, rocket fuel, 2 wings, a Rapier engine, air intakes, some wheels and you are basically good to go into space

- Familiarize yourself with how to balance the plane: center of mass, center of lift (CoL a little bit behind CoM to get a stable flying plane)

- Test test test. See how high/how fast it can go before it switches the rapier to rocket mode. When it switches (or ideally a bit before that), pull up and and fly it just like a rocket from high atmosphere to space.

[MaverickSawyer]

Doesn't that mean you're carrying around dead weight in empty fuel tanks? Why not just build your plane with the amount of fuel and oxidizer needed to carry the payload you want to the orbit you want?

Because I later refuel in orbit and use the same ship to go to a Munar or Minmus station. I usually have to aerobrake on the way back down the gravity well, but that's no problem for a spaceplane.

Also, having the empty space allows me to trim the craft by shunting fuel from tank to tank as needed.

[barrenwaste]

My advice for sstos...stay away from the Rapiers. You can get into space using less fuel and carrying more weight with a jet/rocket combo than with rapiers. I would also suggest experimenting with small square struts. If you invert them and snap them on you can connect an engine to both sides of the strut, allowing two engines inline so that you do not have the problems of balance and thrust at high altitudes (30k+) that other sstos often run into. As to vtol versus stol, the stol platforms are generally easier for most people to fly and more intuitive. Ultimately, the vtol's are generally able to carry larger payloads per size, though. I prefer the stol style myself, but it eventually comes down to just your preferred flight style.

[LordFjord]

@barrenwaste: Rapiers are really fine to get started with SSTOs. I know that clipped engines can be more effective, but that's a bit more advanced topic. Same with stacking/clipping intakes. Sure, they make the craft more effective, use less fuel to orbit, but for starters things should be as simple as possible with as few things to worry about as possible.

[MaverickSawyer]

I used RAPIERs for my first unmanned designs, but have found that two B9 small SABRE intakes feeding a stock turbojet can haul a decent-sized craft nearly to orbit. Toss a pair of AIES MODOC-2s on for OMS, and you're set. (BTW, I'm using porkjet's new Spaceplane Plus parts, found over at his dev thread here.

[barrenwaste]

@LordFjord I'd have to disagree with rapiers being simpler. They lack power and have a higher rate of fuel consumption. This means the build is much more complex when min/maxing fuel, weight, and lift. It also means that flying the rapiers leaves less room for new pilots to err and recover. Also, I recommend building with the inverted strut, but it is quite simple to make an ssto that uses jets and rockets without that technique. I find it a handy one to leran, though, as the inverted small strut is invaluable with stacking intakes, engines, fuselages, and various other odds and sods. Because the rapier is so poor, because the technique is so handy, because the jet/rockets allow for more error, I recommend staying away from the rapiers.

[Jouni]

@LordFjord I'd have to disagree with rapiers being simpler. They lack power and have a higher rate of fuel consumption. This means the build is much more complex when min/maxing fuel, weight, and lift. It also means that flying the rapiers leaves less room for new pilots to err and recover. Also, I recommend building with the inverted strut, but it is quite simple to make an ssto that uses jets and rockets without that technique. I find it a handy one to leran, though, as the inverted small strut is invaluable with stacking intakes, engines, fuselages, and various other odds and sods. Because the rapier is so poor, because the technique is so handy, because the jet/rockets allow for more error, I recommend staying away from the rapiers.

Fuel min/maxing is completely irrelevant when learning to build SSTOs. It's much better to carry a lot of extra fuel, so that you can get to orbit even with a bad ascent profile, as well as recover from mistakes. Similarly, all the advanced techniques that rely on using more parts for efficiency gains (e.g. using turbojets and rockets, using more than one intake per engine, using cubic octagonal struts for anything) are just counterproductive. They force you to concentrate on small details, while obscuring the major points.

It's better to start simple. First learn to get something like this into orbit reliably.

When you can do that, start adding nonessential parts that make the SSTO more interesting or useful. Batteries and solar panels to keep SAS operational. Some combination of wings, control surfaces, landing gear, landing struts, and parachutes for returning back to Kerbin safely. Docking ports and RCS to make refueling possible.

When you can reliably build a SSTO to perform a real mission, it may be time to start thinking about efficiency.

[barrenwaste]

@ Jouni I agree, when you can reliably build a ssto that can handle a real mission, then start adding extras like science modules, vtol capability, payloads, and docking ports. I disagree that they should start with the ship you pictured. That is a rocket, and it doesn't incorporate the techniques needed for either vtol or stol sstos. Learning to build and fly that is counterproductive. I also disagree with you on what is essential and what is not. I find that any work, any mission, that you need a ssto for requires enough fuel, power, and lift. Those are essential and are needed for a reliable ssto, so discounting them while learning is also counterproductive. It would be better for them to fly one of the provided airplanes, look at it, and think on how to put a rocket on it.

[Jouni]

SSTO means single-stage-to-orbit. It can be a rocket, a spaceplane, something fired from a surface-based launch system, or something completely different. What matters is that everything you have on launchpad or runway should reach orbit. Everything else is nonessential.

The main difference between a spaceplane and a jet-boosted rocket in stock KSP is that spaceplanes can be a bit more efficient. That can be important when you are looking for the last few percentage points of payload fraction, but that's all. The jet engines in KSP are so powerful that everything flies pretty much the same way with them, no matter whether it has wings or not. Wings just make flying harder, unless the ship is properly balanced.

Building planes and building SSTOs are two separate things to learn. If you don't know either, trying to learn them by building spaceplanes can be a bad idea. It's usually faster and easier to learn SSTOs and airplanes separately, before combining them into a spaceplane.