Difference between revisions of "Tutorial:Basic SSTO Design"

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This tutorial explains how to build a [[single-stage-to-orbit]] (SSTO) spaceplane that is able to launch into space and return without jettisoning any parts.
  
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Hello, I am Suzaku a dedicated SSTO enthusiast. In the ideal world all spacecraft are launched via mass driver or any kind of launch system that does not rely on costly fuel and materials in order to reach orbit, however until that is implemented into KSP craft will have to rely on internally contained power for the launching of spacecraft into orbit and beyond.
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== Powerplant ==
 +
Any craft that hopes to get anywhere needs engines. For SSTO craft there are two popular options: jet engine/liquid fuel engine combinations and the CR-7 R.A.P.I.E.R.
  
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So lets get started!
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===Jet Engines===
  
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== Bare Essentials ==
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Jet engines are high-efficiency, high-thrust, low-cost engines but require an atmosphere to operate. In the case of SSTO craft, we will need jet engines that can perform as high as possible to justify their inability to perform in a vacuum. Currently the [[J-X4 "Whiplash" Turbo Ramjet Engine]] is by far the most sensible choice. While the [[J-33 "Wheesley" Turbofan Engine]] is lower cost and consumes less fuel and money, the Whiplash is capable of decent performance at high altitudes where the Wheesley cannot keep up.
  
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SSTO are by leaps and bounds far harder to construct than a vertical launch space vehicle in KSP. Not only do you need to concern yourself with Center of Gravity, Center of Thrust, and structural integrity, now you also need to focus on Center of lift, aerodynamic drag, Angle of attack, and Horizontal structural integrity.
+
Jet Engines are powered by liquid fuel and intake air. Liquid fuel can be supplied from regular rocket tanks, but jet fuselages are a far more sensible choice due to their lower cost and mass per unit of liquid fuel. Intake air is provided by air intakes. Depending on how many you place, your jet engines' effective service ceiling can be anywhere from 15km to 30km. The [[Shock Cone Intake]] is currently the air intake with the highest amount of potential air intake.
  
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Lets get started.
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===Liquid Fuel===
 +
Liquid fuel engines, which burn both liquid fuel and oxidizer, are what will carry your craft into orbit once the air becomes too thin for jet engines to operate. The [[T-1 Toroidal Aerospike "Dart" Liquid Fuel Engine]] is one of the better choices due to its low profile and high specific impulse (it performs better than other engines). For more economy-minded builders, the [[LV-T45 "Swivel" Liquid Fuel Engine]] is not a bad choice. However, its huge size can make it tricky to take off from the runway without destroying the engine.
  
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Just to note, this tutorial does not cover the vertical take off vertical landing SSTOs, only the Horizontal Space Plane type SSTO.
+
===R.A.P.I.E.R Engines===
 +
The [[CR-7 R.A.P.I.E.R. Engine]], introduced in KSP version 0.23, is your go-to "two in one" solution for all your SSTO needs. It can function as both an air breathing engine in "Air Breathing" mode and a much more powerful rocket engine in "Closed Cycle" mode. Putting out 465.462 kN of thrust in Kerbin's atmosphere at mach 3.7 and 180 kN in vacuum, the CR-7 R.A.P.I.E.R engine is truly a beast of an SSTO engine.  Although the engine can automatically switch modes, for best performance one should watch the thrust output (by right clicking the engine in flight) and forcibly switch all rapiers to closed cycle once your orbital speed plateaus.  Setting up an action group is the best way to do this and to close the intakes at the same time.
  
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== Why build an SSTO ==
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==Stability==
  
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SSTOs are hailed as the future of Spacecraft, not only are they far more cost effective than multi-stage rockets, they are also safer and capable of landing and taking off at traditional runways.
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'''One of the most important factors to how well an SSTO will perform is its aerial stability.''' A stable craft is going to be more desirable than an unstable craft. There are several forces in Kerbal Space Program which have an effect on the flight characteristics of SSTO craft.
  
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== Is it impossible to build an SSTO ==
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===Center of mass===
 +
One is [[Center of mass]]. This is the point from which there is an equal amount of mass in each direction and acts as a fulcrum for any rotational forces. The center of mass of any craft will shift as a result of burning fuel, but this is especially critical for SSTOs as spin-outs and otherwise catastrophic stability failures will hinder its ability to reach space.
  
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Nonsense, many people say it is in version 0.16, but I think they don't understand the nuances of building an SSTO and then blame it on the game. SSTOs are capable of reaching orbit, the Mun, Minimus! and beyond! (I even broke orbit of the Kerbin Sun with a SSTO)
+
===Center of lift===
 +
The second is [[Center of lift]]. This is arguably the most important characteristic an SSTO designer should consider when building. To prevent craft spin-outs and otherwise catastrophic stability failures, it is important that the center of lift always be to the rear of the center of mass.
  
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== Symmetry ==
+
===Center of thrust===
 +
A sometimes overlooked factor is [[Center of thrust]]. This is where force will be acting upon your craft to push it forward. Though this is a non-issue for most SSTOs, it is wise to check that your center of thrust is roughly in line with your center of mass and lift.
  
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Spaceplane SSTOs by nature are not symetrical, the tail, landing gear, etc. all will change the aerodynamic drag profile of an SSTO. Many people enjoy building a SSTO that looks similar to a typical aircraft, however many fail to consider that aircraft are designed to thrust and operate inside of an atmosphere fighting against gravity and therefore the center of gravity for such craft does not need to be in line with the center of thrust. If the center of gravity is not in line with the center of thrust, the vehicle will either spin constantly when attempting to thrust outside of the atmosphere or will have a tendency to pitch up and or down.
+
The bottom line: Ensure your center of mass is always ahead of your center of lift and your center of thrust is in line with your center of mass.
  
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== Liquid Fuel or Solid Fuel? ==
+
==Additional Systems==
  
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There is basically only once choice for a type of fuel for a SSTO. Liquid. A SSTO is exactly as it is described, a single stage to orbit craft which must not jettison any part of it in order to reduce operating cost and increase passenger safety. Anything once drained is dead weight on an SSTO and therefore power to weight must be put into consideration. Solid fuel boosters can be used for take-off, however it must be noted that they are quite heavy and does affect your center of gravity quite a bit.
+
These are common features of SSTO craft. The command pod is, as always, a must, and the others, though technically optional, are recommended in most cases.
  
−
== Center of Gravity ==
+
=== Command Pod ===
 +
The possibilities are limitless. You can create either manned or unmanned SSTOs. Just remember than manned ones have crew and unmanned have electricity. The [[Mk1 Cockpit]] is an example of a manned command pod, while the [[Probodobodyne HECS]] is an unmanned command pod. A probe will require a fairing or cargo bay to maintain aerodynamics.
  
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There is nothing else more important in SSTO design than center of gravity. As your vehicle consumes fuel it cannot jettison stages into a smaller and smaller stage that has its center of gravity maintained at a close to center position. The center of gravity for a SSTO will rapidly move forwards and backwards as fuel tanks are expended and this applies without changing the aerodynamic profile of the craft and therefore the fuel tanks must be positioned in such a way that they will not rapidly shift from the front to the rear after a tank is drained.
+
=== Takeoff Gear ===
 +
It is possible to launch a craft using the [[TT18-A Launch Stability Enhancer]] and land using parachutes. For conventional SSTOs, however, the [[LY-10 Small Landing Gear]] is what you'll use to take off. Remember to retract these wheels right after takeoff to reduce drag, as well as to extend right before landing.
  
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== Center of Thrust ==
+
A parachute can be useful for SSTOs as it removes the need to perform a landing. Simply deploy to return to the ground safely.
  
−
The same that applies to all other spacecraft, however once again ceneter of thrust should be in line with the center of gravity for any spaceship, even SSTOs.
+
=== SAS ===
  
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== Center of Lift==
+
Since the standard cockpits are supplied with their own [[SAS]], it is mostly unnecessary to add additional SAS (such as reaction wheels) to your SSTO. However, large craft may require external SAS to help maneuver with the extra mass, and you can always disable external SAS at your whim.
  
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This is the Killer issue for most players when it comes to making a SSTO. Most players have the tendency to design the coolest looking ship they can possibly design and then try to fly it. Some even try to copy real-life craft and attempt to fly it and then blame the game when the craft fails miserably. Once again, remember you are building a SSTO out of rocket parts which weigh 4 times more than aircraft components. There is no guarantee that the parts used in KSP are of the same mass of the parts used on the craft you are trying to imitate and therefore don't expect too much out of copy craft.
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SAS is a stability augmentation system and helps your craft fly straight. In order to accomplish this, it provides [[w:Torque|torque]] (the rotational analogue of [[w:Force|force]]). This helps your craft change directions. Control surfaces can provide torque while moving in atmospheres, while reaction wheels can provide torque while stationary or in vacuum.
  
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Traditionally the center of lift should be slightly in front of your center of gravity for lower speed craft or slightly behind it for higher speed craft. If the center of lift is in front of the center of gravity it will promote the tendency to pitch up and enhance maneuverability, a positive attribute for low speed low altitude craft.
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=== RCS ===
  
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For high speed craft if the center of lift is on the center of gravity (a very bad thing will explain why in a second) or in front, it will cause aerodynamic instability. Typcially a SSTO should have its center of lift slightly behind the center of gravity as it provides aerodynamic stability during high speeds as well as the restance to turning on its axis. Center of lift can be changed by aerodynamic resistance as well.
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A [[Reaction Control System]] is required for maneuvering in a vacuum, a must-have if you plan to actually perform tasks in orbit. Simple orbiting/deorbiting does not require RCS, though an RCS coupled with SAS can make flying heavier/less stable craft much easier.
  
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== Angle of Attack During Takeoff ==
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RCS is activated the with the "R" button with stock controls, first and foremost. RCS is fueled exclusively by [[monopropellant]] tanks. When your monopropellant stores are depleted, your RCS will fail to function.
  
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Angle of attack is nothing more than the angle of the lifting surfaces in comparison to the ground. The greater the angle the greater the lift that will be generated as the vehicle is moving forwards off the runway. The energy required to lift the vehicle off of the runway if the wings are perpendicular to the runway or at a negative angle is exponentially greater than if the wings themselves were generating some lift as the vehicle moves forwards as the craft will be relying on nothing but the lift generated by the far smaller control surfaces.
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=== Aerodynamics ===
 +
Specifically Wings and Control Surfaces. These are what allow the SSTO to function as an atmospheric craft. The [[Delta Wing]] is a solid choice, with a large surface area handy for attaching additional objects to, as well as being rather symmetrical and easy to work with.
  
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On a side note, if the angle of attack is too steep and the craft does not have enough thrust to take off it will generate instability for the craft where one wheel might lose contact will the runway and cause a tendency to yaw to one side. Also, if the craft too great of an angle of attack for the engines to compensate then the vehicle will stall and fall back down.
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However, the Delta Wing is fixed and cannot provide any kind of maneuvering (it only makes your plane fly). In order to turn in-atmosphere, you are going to need control surfaces. The numerous elevons, rotating winglets, and canards are all considered control surfaces. Control surfaces have the distinction of being to pivot or otherwise react to controls, providing lift in certain directions. This is contrasted with regular winglets, which are fixed and cannot move.
  
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The angle of attack can be adjusted on any craft by moving the rear landing gear so that it sits higher up into the fuselage than the forwards landing gear.
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=== Power ===
 +
Depending on your conditions, you may need to provide additional [[electric charge]] for your SSTO. This can be stored in [[battery|batteries]] and/or supplied by [[Solar panel|solar panels]], [[PB-NUK Radioisotope Thermoelectric Generator|RTGs]], or [[fuel cell|fuel cells]]. Electricity is used to turn the ship via its [[Reaction wheel|reaction wheels]], to transmit [[science]] back to [[Kerbin]] with [[Antenna|antennas]], to conduct research in [[Mobile Processing Lab MPL-LG-2|Mobile Processing Labs]], to operate [[Ion engine|ion engines]], and to operate [['Drill-O-Matic' Mining Excavator|mining excavators]] and [[Convert-O-Tron 250|resource converters]]. Without sufficient electric charge, crafts may be unable to rotate due to loss of power, and unmanned spacecraft may become completely inoperable. In general, at least 1-2 solar panels are recommended for nearly everything going into space.
  
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== SAS ==
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Extra batteries may be desirable if you do not have enough power production to meet the needs of your antenna(s) when transmitting data back to Kerbin. For example, if you're going to take an ion-powered spaceplane to Eeloo and want to use a [[Communotron 88-88]] antenna to send back an orbital gravity scan, the antenna will require 100 electricity per second for 3 seconds. You could store that much energy in three [[Z-100 Rechargeable Battery Pack]]s (0.03 mass), or you could try to produce it as you use it with 125 RTGs (10 mass), or, due to the distance from Kerbol, you'd require 244 [[Gigantor XL Solar Array]]s (73.2 mass). The batteries are the obvious winner in this case.
  
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SAS is almost required for any spaceplane, a computer that can stabilize your craft faster than you can react is invaluable for a vehicle with a constantly shifting center of gravity.
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=== Putting the pieces together ===
 +
Now that the basics of SSTO design have been covered, it is time for you to assemble your first SSTO.
  
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== RCS and Vectoring Engines ==
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Remember to consider everything above to create a working SSTO.
  
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RCS is useful in space only, however due to pod torque mechanics it is not entirely necessary for smaller SSTOs unless the need to dock arises
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===Troubleshooting===
  
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== Advantages of a SSTO ==
+
Answers likely questions people may run into when designing SSTOs. However, if you even try to build an SSTO you will need a basic understanding of Kerbal Space Program physics, so check there as well if this can't answer your question(s).
  
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* 1/100th the operating cost of a traditional multi-stage spacecraft
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;It doesn't take off.
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* The ability to land at any runway and take off after a simple refuel
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:Make sure your landing gear is placed such that your craft can achieve a positive angle of attack while it's on the runway. Typically you'll have either a nose wheel and two wheels slightly behind centre of mass that act as a fulcrum (your elevators push down on the tail and lift the nose, rotating around the rear wheels), or a tail wheel that's placed higher than two other wheels (which are ahead of the centre of mass) so that the craft has a positive angle of attack even when stationary on the runway and will naturally lift off at the right speed without pitching upwards.
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* No required re-assembly or hoisting vertical required after each mission
 
  
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== Disadvantages of a SSTO ==
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;It spins out on the runway.
 +
:Make sure your landing gear is placed symmetrically and your center of mass and lift are both in the center of the craft. A common issue with wing mounted landing gear is they will be 5 degrees toe in or 10 degrees toe out.  Use the SHIFT key to make smaller rotations to get them aligned straight.  You will also need horizontal aerodynamic stability, which is classically accomplished with a vertical tail fin. As with launch stability of rockets, you may find your pilot has too much control authority in the yaw dimension and is overcompensating - try using a different part as a tail fin.
  
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* Must keep all original components from launch
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;I keep blowing up my engines when trying to lift off
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* Poor thrust to weight ratio when compared to typical multi-stage rocket designs
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:Be slightly gentler on the stick, change the layout of your engine modules to be slightly forwards, or make your landing gear taller so your tail won't hit the ground when you pitch up.
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* Cannot be built too heavy due to horizontal structural weaknesses
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* Extremely complicated design process
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;It flips out whenever I move/start flying.
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* Must be designed to operate as an aicraft as well as a spacecraft
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:This is likely a result of a poor center of mass/lift. If this occurs just after liftoff, check these in the [[Spaceplane Hangar]]; you will be most likely find your answer there. If this occurs late-flight, it is a result of either something breaking off or fuel moving around and changing the center of mass (probably the latter). This is a relatively easy to fix problem. Before entering the atmosphere again, move your fuel forwards to hopefully place the center of mass ahead of the center of lift.
 +
 
 +
;I can't reach orbit
 +
:This is the result of not having enough Delta-V, or just poor flying. For most SSTOs, a safe procedure is to: Take off and climb at only 5 degrees. This should allow the RAPIERs to accelerate past 400m/s (the speed at which their thrust begins to increase) easily. Slowly pitch up to avoid overheating. Keep at around 15 degrees to allow the plane to accelerate past 1000m/s. At around 20-25km, your engines will flame out and so you should switch to your vacuum engines. Cut the engine when your Ap passes 70km. Wait until you get near to your Ap and circularise.
 +
 
 +
;I hit the runway when landing and died.
 +
:Coming in for hot landings (usually above 80 m/s) will cause your aircraft to either bounce off the runway or blow up. Slow your descent by throttling back when around a kilometer from the runway, then nose up slightly and deploy landing gear and flaps (right click your ailerons and elevators and deploy them - this will generate extra lift and drag). When you contact with the tarmac, apply brakes. If you die again you were either too fast or your center of mass was off. If you can't slow down enough, try adding air brakes and deploying them before landing.
 +
 
 +
;How can I make landing easier?
 +
:Just burn retrograde when in orbit until your trajectory is intersecting with the planet. Have a parachute or two on standby and deploy them when you think you're close enough to the ground (they will activate for you but will induce significant G-force on your craft). You will probably not land where you wanted.
 +
 
 +
;Is there any way to make it better than it already is?
 +
:Chances are if you have already reached this point it is unnecessary to create a new craft for the purpose of this previous craft. Your SSTO is no longer a prototype and is finally a complete, but better yet working design! You can always modify the design to suit a particular need.
 +
 
 +
== See also ==
 +
* [[Tutorial: Basic Plane Design]]
 +
* [[Tutorial: Spaceplane basics]]
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* [[Tutorial:Spaceplane to Laythe]]
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 +
[[Category:Tutorials|Basic SSTO Design]]

Latest revision as of 08:01, 14 January 2024

This tutorial explains how to build a single-stage-to-orbit (SSTO) spaceplane that is able to launch into space and return without jettisoning any parts.

Powerplant

Any craft that hopes to get anywhere needs engines. For SSTO craft there are two popular options: jet engine/liquid fuel engine combinations and the CR-7 R.A.P.I.E.R.

Jet Engines

Jet engines are high-efficiency, high-thrust, low-cost engines but require an atmosphere to operate. In the case of SSTO craft, we will need jet engines that can perform as high as possible to justify their inability to perform in a vacuum. Currently the J-X4 "Whiplash" Turbo Ramjet Engine is by far the most sensible choice. While the J-33 "Wheesley" Turbofan Engine is lower cost and consumes less fuel and money, the Whiplash is capable of decent performance at high altitudes where the Wheesley cannot keep up.

Jet Engines are powered by liquid fuel and intake air. Liquid fuel can be supplied from regular rocket tanks, but jet fuselages are a far more sensible choice due to their lower cost and mass per unit of liquid fuel. Intake air is provided by air intakes. Depending on how many you place, your jet engines' effective service ceiling can be anywhere from 15km to 30km. The Shock Cone Intake is currently the air intake with the highest amount of potential air intake.

Liquid Fuel

Liquid fuel engines, which burn both liquid fuel and oxidizer, are what will carry your craft into orbit once the air becomes too thin for jet engines to operate. The T-1 Toroidal Aerospike "Dart" Liquid Fuel Engine is one of the better choices due to its low profile and high specific impulse (it performs better than other engines). For more economy-minded builders, the LV-T45 "Swivel" Liquid Fuel Engine is not a bad choice. However, its huge size can make it tricky to take off from the runway without destroying the engine.

R.A.P.I.E.R Engines

The CR-7 R.A.P.I.E.R. Engine, introduced in KSP version 0.23, is your go-to "two in one" solution for all your SSTO needs. It can function as both an air breathing engine in "Air Breathing" mode and a much more powerful rocket engine in "Closed Cycle" mode. Putting out 465.462 kN of thrust in Kerbin's atmosphere at mach 3.7 and 180 kN in vacuum, the CR-7 R.A.P.I.E.R engine is truly a beast of an SSTO engine. Although the engine can automatically switch modes, for best performance one should watch the thrust output (by right clicking the engine in flight) and forcibly switch all rapiers to closed cycle once your orbital speed plateaus. Setting up an action group is the best way to do this and to close the intakes at the same time.

Stability

One of the most important factors to how well an SSTO will perform is its aerial stability. A stable craft is going to be more desirable than an unstable craft. There are several forces in Kerbal Space Program which have an effect on the flight characteristics of SSTO craft.

Center of mass

One is Center of mass. This is the point from which there is an equal amount of mass in each direction and acts as a fulcrum for any rotational forces. The center of mass of any craft will shift as a result of burning fuel, but this is especially critical for SSTOs as spin-outs and otherwise catastrophic stability failures will hinder its ability to reach space.

Center of lift

The second is Center of lift. This is arguably the most important characteristic an SSTO designer should consider when building. To prevent craft spin-outs and otherwise catastrophic stability failures, it is important that the center of lift always be to the rear of the center of mass.

Center of thrust

A sometimes overlooked factor is Center of thrust. This is where force will be acting upon your craft to push it forward. Though this is a non-issue for most SSTOs, it is wise to check that your center of thrust is roughly in line with your center of mass and lift.

The bottom line: Ensure your center of mass is always ahead of your center of lift and your center of thrust is in line with your center of mass.

Additional Systems

These are common features of SSTO craft. The command pod is, as always, a must, and the others, though technically optional, are recommended in most cases.

Command Pod

The possibilities are limitless. You can create either manned or unmanned SSTOs. Just remember than manned ones have crew and unmanned have electricity. The Mk1 Cockpit is an example of a manned command pod, while the Probodobodyne HECS is an unmanned command pod. A probe will require a fairing or cargo bay to maintain aerodynamics.

Takeoff Gear

It is possible to launch a craft using the TT18-A Launch Stability Enhancer and land using parachutes. For conventional SSTOs, however, the LY-10 Small Landing Gear is what you'll use to take off. Remember to retract these wheels right after takeoff to reduce drag, as well as to extend right before landing.

A parachute can be useful for SSTOs as it removes the need to perform a landing. Simply deploy to return to the ground safely.

SAS

Since the standard cockpits are supplied with their own SAS, it is mostly unnecessary to add additional SAS (such as reaction wheels) to your SSTO. However, large craft may require external SAS to help maneuver with the extra mass, and you can always disable external SAS at your whim.

SAS is a stability augmentation system and helps your craft fly straight. In order to accomplish this, it provides torque (the rotational analogue of force). This helps your craft change directions. Control surfaces can provide torque while moving in atmospheres, while reaction wheels can provide torque while stationary or in vacuum.

RCS

A Reaction Control System is required for maneuvering in a vacuum, a must-have if you plan to actually perform tasks in orbit. Simple orbiting/deorbiting does not require RCS, though an RCS coupled with SAS can make flying heavier/less stable craft much easier.

RCS is activated the with the "R" button with stock controls, first and foremost. RCS is fueled exclusively by monopropellant tanks. When your monopropellant stores are depleted, your RCS will fail to function.

Aerodynamics

Specifically Wings and Control Surfaces. These are what allow the SSTO to function as an atmospheric craft. The Delta Wing is a solid choice, with a large surface area handy for attaching additional objects to, as well as being rather symmetrical and easy to work with.

However, the Delta Wing is fixed and cannot provide any kind of maneuvering (it only makes your plane fly). In order to turn in-atmosphere, you are going to need control surfaces. The numerous elevons, rotating winglets, and canards are all considered control surfaces. Control surfaces have the distinction of being to pivot or otherwise react to controls, providing lift in certain directions. This is contrasted with regular winglets, which are fixed and cannot move.

Power

Depending on your conditions, you may need to provide additional electric charge for your SSTO. This can be stored in batteries and/or supplied by solar panels, RTGs, or fuel cells. Electricity is used to turn the ship via its reaction wheels, to transmit science back to Kerbin with antennas, to conduct research in Mobile Processing Labs, to operate ion engines, and to operate mining excavators and resource converters. Without sufficient electric charge, crafts may be unable to rotate due to loss of power, and unmanned spacecraft may become completely inoperable. In general, at least 1-2 solar panels are recommended for nearly everything going into space.

Extra batteries may be desirable if you do not have enough power production to meet the needs of your antenna(s) when transmitting data back to Kerbin. For example, if you're going to take an ion-powered spaceplane to Eeloo and want to use a Communotron 88-88 antenna to send back an orbital gravity scan, the antenna will require 100 electricity per second for 3 seconds. You could store that much energy in three Z-100 Rechargeable Battery Packs (0.03 mass), or you could try to produce it as you use it with 125 RTGs (10 mass), or, due to the distance from Kerbol, you'd require 244 Gigantor XL Solar Arrays (73.2 mass). The batteries are the obvious winner in this case.

Putting the pieces together

Now that the basics of SSTO design have been covered, it is time for you to assemble your first SSTO.

Remember to consider everything above to create a working SSTO.

Troubleshooting

Answers likely questions people may run into when designing SSTOs. However, if you even try to build an SSTO you will need a basic understanding of Kerbal Space Program physics, so check there as well if this can't answer your question(s).

It doesn't take off.
Make sure your landing gear is placed such that your craft can achieve a positive angle of attack while it's on the runway. Typically you'll have either a nose wheel and two wheels slightly behind centre of mass that act as a fulcrum (your elevators push down on the tail and lift the nose, rotating around the rear wheels), or a tail wheel that's placed higher than two other wheels (which are ahead of the centre of mass) so that the craft has a positive angle of attack even when stationary on the runway and will naturally lift off at the right speed without pitching upwards.
It spins out on the runway.
Make sure your landing gear is placed symmetrically and your center of mass and lift are both in the center of the craft. A common issue with wing mounted landing gear is they will be 5 degrees toe in or 10 degrees toe out. Use the SHIFT key to make smaller rotations to get them aligned straight. You will also need horizontal aerodynamic stability, which is classically accomplished with a vertical tail fin. As with launch stability of rockets, you may find your pilot has too much control authority in the yaw dimension and is overcompensating - try using a different part as a tail fin.
I keep blowing up my engines when trying to lift off
Be slightly gentler on the stick, change the layout of your engine modules to be slightly forwards, or make your landing gear taller so your tail won't hit the ground when you pitch up.
It flips out whenever I move/start flying.
This is likely a result of a poor center of mass/lift. If this occurs just after liftoff, check these in the Spaceplane Hangar; you will be most likely find your answer there. If this occurs late-flight, it is a result of either something breaking off or fuel moving around and changing the center of mass (probably the latter). This is a relatively easy to fix problem. Before entering the atmosphere again, move your fuel forwards to hopefully place the center of mass ahead of the center of lift.
I can't reach orbit
This is the result of not having enough Delta-V, or just poor flying. For most SSTOs, a safe procedure is to: Take off and climb at only 5 degrees. This should allow the RAPIERs to accelerate past 400m/s (the speed at which their thrust begins to increase) easily. Slowly pitch up to avoid overheating. Keep at around 15 degrees to allow the plane to accelerate past 1000m/s. At around 20-25km, your engines will flame out and so you should switch to your vacuum engines. Cut the engine when your Ap passes 70km. Wait until you get near to your Ap and circularise.
I hit the runway when landing and died.
Coming in for hot landings (usually above 80 m/s) will cause your aircraft to either bounce off the runway or blow up. Slow your descent by throttling back when around a kilometer from the runway, then nose up slightly and deploy landing gear and flaps (right click your ailerons and elevators and deploy them - this will generate extra lift and drag). When you contact with the tarmac, apply brakes. If you die again you were either too fast or your center of mass was off. If you can't slow down enough, try adding air brakes and deploying them before landing.
How can I make landing easier?
Just burn retrograde when in orbit until your trajectory is intersecting with the planet. Have a parachute or two on standby and deploy them when you think you're close enough to the ground (they will activate for you but will induce significant G-force on your craft). You will probably not land where you wanted.
Is there any way to make it better than it already is?
Chances are if you have already reached this point it is unnecessary to create a new craft for the purpose of this previous craft. Your SSTO is no longer a prototype and is finally a complete, but better yet working design! You can always modify the design to suit a particular need.

See also

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