SSTO Start Guide

[Gogeek]

This is a start guide to help build and fly SSTOs (Single Stage to Orbit) space planes.

I was looking for some SSTO help and did not find much except for http://www.reddit.com/r/KerbalSpaceProgram/comments/1diign/the_pinolallos_ssto_guide

That was a good start but I wanted a little more information.

SSTO’s have two sets of engines: Turbo Jet and Rocket. The concept of the SSTO is to use the Turbo Jet engine to get close to orbital velocity and then use the rockets to push your craft into orbit.

The Turbo Jets are very efficient compared to rocket engines so you want to use them as long as possible in the assent.

So I after +30 tries (probably closer to 50) I managed to gleam a few design ideas and some better practices.

So to start we need to go the Space Plane Hanger. SSTO design is a series of trade-offs: takeoff, normal flying, hyper-sonic flight, orbital insertion, reentry, and successful landing.

Though harder to design and fly, SSTO are more efficient (fuel-wise), have no debris, and completely reusable.

Design (Duct tape and Bailing wire):

Let’s start with a simple plane. This is a simple crew transfer plane to deliver kerbals to an orbiting space station in Low Kerbal Orbit (LKO).

As you can see that I highlighted the three (3) key center markers for the plane: Center of Mass (COM), Center of Lift (COL), and Center of Thrust (COT).

The relationship between the three (3) markers is crucial to how the plane will behave in flight. Over many failed tries, I found that all of them need close or in a horizontal line,

with the center of mass and lift very close.

Placement is key; if the COL is back of the COM the craft will be nose heavy, and if the COM is behind the COL then will be tail heavy.

The difference of height between COL and the COM will show how much or little of lift your plane has. It’s best to have the COL above the COM.

The COT needs to be in line with the COM. If there is offset between the two, plane will veer under power.

(This could be a way to take off easier with the thrust slightly below the COM). I generally keep COT center-lined.

Your craft needs rigid wings. The more wobble in your wings the harder to accelerate down the runway without the plane veering off.

Use struts to stiffen your craft’s wings. I found that it makes a big difference when taking off.

You want to make sure your plane has enough thrust with the jet engines. Pinolallos suggests 1 Turbo Jet for every 10 tons.

I use a ratio of 1 Turbo Jet to 8 tons myself. Still you need a lot of thrust to takeoff and go hypersonic.

I use forward canards for pitch control and two (2) or more winglets for yaw control.

For the most effect, place control surfaces away from the COM/COL.

To make sure your plane has fuel lines to any engine away from the fuselage so you can control how fuel is routed to them.

This can prove useful in later phases of the flight (i.e. reentry).

You can modify the ram intakes to increase air flow. http://imgur.com/KgBes5H

Landing gear should be placed in a triangle pattern will the point at the front. There is generally less mass there so you don’t need as much support.

With heaver planes you might want to double up the back gear. When taking off the plane will pivot up on the back gear so make sure there is clearance for your engines.

Tip#1: To enhance your takeoff, have the back landing gear shorter than your front gear. That way your wings have a small positive angle of attack making takeoff easier.

Take Off (run run Run, Jump!!):

Take off is one of the easier phases of flight because it is so simple: Activate your ASAS, (if hot keyed) activate the engines, and throttle up.

You might need to tap your yaw keys (‘A’ or ‘W’) to keep you straight as your craft accelerates down the runway.

When you feel you are fast enough then tap to pitch key (‘W’) up to gain some altitude.

Tip #2: If you are having difficulty taking off for lack of lift. Toggle your rockets with a command key (say #5)

and use the toggle to give your plane a burst of rocket thrust for a few of seconds (3-10 sec) to get airborne.

Flight/Hyper-Sonic/Orbital (flapping, flapping faster, Heave Ho!!):

Your craft is in the air, now to get into space. After the plane clears the runway and is few hundred meters up, put your craft into a step climb around 45º. Keep that angle of attack (AOA) until you reach 20,000m. With most of the air below your plane, is now time to be fast. Your plane should be already traveling over 400m/s already now and need get close to orbital speeds. So pitch down so you AOA are around 10º and your craft is slowly ascending. Allow your plane to accelerate to near orbital speeds (~1700 m/s).

Height (m) 	Speed		AOA/Assent Vector*	Assent		Air Intake	Pressure**
1000 (1K)	115 m/s		40º / 30º 		+100m/s		12.5		0.817
7.5K		200 m/s		45º / 30º		+100m/s		10.1		0.220
10K		260 m/s		45º / 30º		+100m/s		8.0		0.138
15K		370 m/s		45º / 30º		+100m/s		3.7		0.050
20K		580 m/s		30º / 10º		+50m/s		1.4		0.018
23K		760 m/s		30º / 5º		+50m/s		0.7		0.010
27K		1150 m/s	10º / 5º		+30m/s		0.5		0.004
28K		1500 m/s	0º / ~0º		+10m/s		0.7***		0.003
30K		1700 m/s	0º / ~0º		+10m/s		0.4		0.002

I couldn’t go higher with jets as my plane was fish-tailing and losing control. I needed to engage the rockets to push into orbit.

Height (m) 	Speed		AOA/Assent Vector 	Assent		Air Intake	Pressure
50K		2300 m/s	35º / 15º		+100m/s		0.0		0.0004
Orbital 	2200 m/s 	0º / ~0º		N/A		0.0		0.0

* The accent vector is the actual angle of accent of your craft. Your craft might be pointed higher, but the resulting thrust, gravity, and air flow lowers the AOA.

** The pressure is set at 1.0 at sea level for Kerbin (Pk = e^(-Height/5000)) with Height in meters.

*** As your plane accelerates though the air you can gain air pressure to the engines and that’s why even at 1/300 the pressure at sea level your jets will work.

You use much less rocket fuel and oxidizer to get into orbit. In orbit the plane will act like any other rocket in Kerbin orbit, so remember to add those RCS thrusters.

Your craft, given enough rocket fuel, can ‘fly’ to other planets.

Tip#3 your oxidizer supply is very limited and looking at the “Resources†or engine fuel gauge you can give you a false sense of plenty. Don’t be fooled, double check your oxidizer levels.

Reentry (hot, Hot, HOT!!):

This is the most perilous part of the flight. It is where it is the easiest to lose control and tumble.

I have lost many a plane to reentry. No fun at all.

One of the first things you should do is move all available fuel to the front of the plane.

Being nose heavy will help in keeping your craft more stable on reentry. It is best to do the transfer in orbit.

If you don’t, your plane will be more unstable and can fall tail side to Kerbin.

The craft need to be within 10º to 20º from pro-grade, this way you won’t flip and tumble. So keep you craft nose as close to forward as you can.

The plane will use its flight surfaces and be able to control the decent.

Tip#4: If you start tumbling, don’t panic! You can recover you plane. When you plane is in the lower part of the atmosphere (say ~15,000m)

you can punch your thrust to maximum (include rockets if you have them). Thrusting will help regain control of your craft, because the flight surfaces will start to work.

Point towards pro-grade to establish control even if you are flying straight down. Then after you control level out and cut power for normal flight.

Landing (Soft landing in one piece):

This part is anticlimactic compared to reentry (except for runway landings). As your speed will be around 100m/s. Still you need to be even slower to land off runway.

The best way to land is to force a stall and lightly drop the plane to the ground. At speeds less than 100 m/s your Kerbals will have a fair chance of survival even is the craft breaks up.

For a runway landing, heading is the key. On the runway you don’t need to stall and drop, just glide in and touch your rear landing gear.

My next generation SSTO shown above is perfectly aligned to the runway, but...

The approach vector is off slightly off as shown by the Nav Ball. That means I’m drifting to the right.

It didn’t end well, yet Bill Kerbin walked away.

Tip#5: A longer SSTO will be more resistant to flipping in flight and reentry. Also a heavier craft will be easier to control (less twitchy).

So there whole flight from takeoff to landing.

I hope this helps save many hours of trial and error as you figure things out.

So have fun FLYING your Kerbals into orbit!!

[Javster]

Are you sure you press W for pitch up? I use a joystick now but I think W might be pitch down!

Another thing: I read that in a real plane, in a perfect landing, you hear a stall warning just before touching the ground. I think this corresponds with your guide.

[WafflesToo]

I can't wait for the Devs to fix that bug.