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SSTO, Why u no fly?


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I have tried SO MUCH, and Gotten SO CLOSE, but just have never been able to put an SSTO into Orbit. Either There's too much weight, or not enough fuel, or not enough intakes, or not enough thrust, or the COM moves too much in flight . There's GOT to be a surefire way to do this. Everyone makes it look SO easy, even people that aren't Scott Manley. Does ANYONE have ANY suggestions for SSTO builds?

Edited by GamerMitch
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They can get up to about 30-34 km in the air before having to switch to rocket mode. push them to 72 km then circularize... once refuled in orbit you are set

- - - Updated - - -

I can take out the apollo mod parts and all you will need is b9 and spitfire

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Mitch,

SSTOs really aren't that hard once you've got the hang of them, even in stock KSP. The trick is learning how KSP aerodynamics work and building accordingly.

Rather than banging your head against the wall in frustration, why not just walk yourself through a development program?

Step 1: Build a basic jet-powered aircraft that is dynamically stable, so that it can take off, fly to the island, land, and return safely to KSC.

Step 2: Build a turbojet powered aircraft that can reach 29KM altitude and 2,000 M/sec and return safely to KSC

Step 3: Based on the results of step 2, build an SSTO that uses a liquid rocket engine to bridge the gap from 29KM and 2K to orbit.

Step 4: Build an SSTO using only RAPIER engines.

Best,

-Slashy

Edited by GoSlash27
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They can get up to about 30-34 km in the air before having to switch to rocket mode. push them to 72 km then circularize... once refuled in orbit you are set

- - - Updated - - -

I can take out the apollo mod parts and all you will need is b9 and spitfire

You mean Firespitter.

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Slashy,

I've been able to get to step 2, It's just the gap-bridging part that kills me. I try to add rocket engines and fuel, but they add too much weight. I try using the RAPIER, but It's thrust is too low and it NUKES fuel in its rocket mode. How can I get a good balance?

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okay.. how about this:

Before i perfected my arcadia and zeus designs with b9 aerospace, i was only using stock parts... i decided: mass = wasted fuel.. build something small with one turbojet engine and two of the lv909 engines.. give it no less than 12 intakes.. clip them or use the radial intakes.. it doesnt matter but one turbojet and 12 intakes... kick that to full power and ride it up to 32 km, switch with your action groups to the lv909, ride it up to 72 km and circularize.

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What does your flight profile look like? I find that how you fly it is almost as important as how it is built. Some of the first ssto planes I built but was not able to get into space, I can now get into space pretty easily knowing how to fly it right.

That too.. thats very important... knowing your crafts limits is also part of it.. such as how high can it fly exactly before it stalls... because right when it stalls is when you need to switch to rockets.

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Slashy,

I've been able to get to step 2, It's just the gap-bridging part that kills me. I try to add rocket engines and fuel, but they add too much weight. I try using the RAPIER, but It's thrust is too low and it NUKES fuel in its rocket mode. How can I get a good balance?

Well,

Getting the balance means building it balanced from the ground up rather than tacking on additional parts. If you've made it past step one, then you understand how to make an airplane statically balanced and dynamically stable. If you've made it past step 2, then you know how to juggle lift and drag and make an aircraft that's stable at high speed (which is somewhat different from step 1).

Step 3 just incorporates additional parts and an action group, but the same principles apply.

Build it statically neutral with the CoM coincident with your fuel so the CoM doesn't shift. Build it with some dihedral and yaw stability so it tends to correct it's own deviations, and a little nose- heavy. Build it with the higher drag stuff in back and the lower drag stuff in front so it won't want to flip at high speeds. Use high wing loading for less drag at altitude, but not so high that you can't get there.

For step 3, just pretend that the LF rocket engine and additional fuel/ oxidizer is payload. Use the air-breathing mode to get it to the jump- off point and let 'er rip.

If you'd like some rough rules of thumb I use, I'll pass them on.

Best,

-Slashy

Edited by GoSlash27
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Mitch,

Maybe we should plug in an additional step in the process;

2a) Build a turbojet powered plane that can carry a payload of 3 tonnes to 29KM at 2KM/sec.

Best,

-Slashy

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From your original question, it sounds like you're having problems keeping the CoM in one spot. The answer to this is to make sure that you carry the same amount of fuel in front of the CoM as behind it. You can either do that using a single tank or several. A straightforward way to do this is to make your first part a tank, then add parts in turn to the front and back, keeping the CoM indicator near the middle of the fuel tank.

You should be able to get a SSTO spaceplane to work with a single inline Turbojet and a pair of nacelle RAPIERs - I used that exact thrust package in my Peregrine SSTO (see the K-prize challenge) which I use to carry satellites up to LKO or even GSO.

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It's not so much the craft as it is your flight path, as mentioned before.

Take this little ship.

wyOhmh2.png

One of my first successful SSTO's, and if I remember correctly it only had 1 turbojet.

Now look here.

YLEWWed.png

One of my latest ones. It can actually carry a cargo, something I was quite proud of. (The little thing floating by the nose)

So here are my questions.

1 - How fast are you going when you light the rockets?

2 - How high are you when you light the rockets?

3 - When do you pitch to 30, 20, or 10 degrees?

4 - And when do you cut the rockets?

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Wat you really need to do is the following:

1. Fly up to about 22 km

2. Start flying almost horizontally at about 28 km. you HAVE to be going almost flat there, as anything above that has a lot less air and doesn't leave you much room for changes. Keep in mind that going up is a lot better than going down.

3. Get up to an orbit speed of about 2200 m/s, less may too but not lower than 2000 m/s. Faster is better.

4. You shouldn't be much higher than 30 km now, and lower than 31 km. Thrust as much in the vertical direction as possible.

5. At the apoapsis, thrust prograde until your periapsis no longer goes into the atmosphere.

6. Do whatever it is you wanted to do!

Some design tips:

1. Deside how much you want to be able to thrust in space and set your amount of oxidiser accordingly.

2. Never forget that your plane will also be flying at emptier tanks. You always should empty every tank completely to see the center of mass and lift for both full and empty tanks. Flying an unbalanced airplane later on will prove to be rather problematic. I had to find out the hard way after my plane crashed (Jeb surived though).

3. More intake is better.

4. Always go for more lift as apposed to more thrust. All your engines won't help if you haven't got enough lift.

5. Smaller better. You should aim for as little mass as possible.

6. Always go for the better intakes! They help a lot. If you need some mass balancing, go for intakes!

I personally use planes for part testing missions. For flight, suborbital and low orbit missions that test light parts, that is. Anyway, it is a nice source of income early in in the game, and the costs are extremely low. So go SSTO! Also, I use planes with high stupidity kerbals to do the "get some science from space around Kerbin" missions. If you want the credits back, you just land the plane.

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I have another hint for spaceplane (and high-speed aircraft) design.

Intakes are... tricky. The drag value they show in the VAB/SPH isn't really accurate. Intakes only use the drag value you see in the VAB/SPH when they're closed. In flight, open intakes act like they have higher drag values as they go faster.

This means that if you find that your plane is still flipping out even tho you have already made sure that the center of mass always stays ahead of the center of lift, look at where you put the intakes. If they're all towards the nose of the craft, then the high drag they have at high speeds will try to make the craft fly tail-end first.

This can be a really unexpected surprise, because the craft can take off just fine, fly great in the lower atmosphere, but then it gets really hard to control at high speeds for what seems to be no real reason.

Bottom line: No matter how many intakes you're using, they should be as far back on the airframe as possible.

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If RAPIER thrust is "too low", it strongly suggests that your ship is too heavy or that your piloting is at fault.

By the time you light the rockets (or switch the RAPIERs to closed cycle), you should be doing at least 1,500m/s horizontally and flying at least 30,000m up. At that speed and altitude, 175kN is plenty.

Have a poke at post #2 in the Kerbodyne thread linked below, or listen to the latest episode of the Kerbal Podcast (http://kerbalpodcast.libsyn.com/) for a piloting guide.

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SSTO = Single Stage To Orbit

Orbit = periapsis >69km around Kerbin, other altitudes if you're launching from other bodies

Single Stage = without throwing things away on the way up

Stayputnik, FL-T200, 48-7S

Like any vertical-launch vehicle you need a launch-TWR >1. It will take at least 4,500m/s deltaV to achieve orbit. These are the only principles you need, although ascent-path through an atmosphere is important.

Specific questions?

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It's not so much the craft as it is your flight path, as mentioned before.

Take this little ship.

http://i.imgur.com/wyOhmh2.png

One of my first successful SSTO's, and if I remember correctly it only had 1 turbojet.

Now look here.

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

One of my latest ones. It can actually carry a cargo, something I was quite proud of. (The little thing floating by the nose)

So here are my questions.

1 - How fast are you going when you light the rockets?

2 - How high are you when you light the rockets?

3 - When do you pitch to 30, 20, or 10 degrees?

4 - And when do you cut the rockets?

1-With my latest ship, I'm going around 700-1100m/s

2-I'm around 15000-30000m up

3-I go up to 45 right away.

4-I cut the rockets as soon as my AP is 71000m.

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1-With my latest ship, I'm going around 700-1100m/s.

There's your trouble; that's way too slow.

A good stock aero ship can beat 2,000m/s on jets alone; a FAR/NEAR ship about 1,700m/s. Don't touch the oxidiser until you've extracted as much speed from the jets as possible. Fly shallow, climb slow, shut off surplus engines and throttle down to extend your flight ceiling.

Build yourself a basic turbojet plane (similar to what's pictured below), and spend some time seeing just how high and fast it's possible to go. You'll find it educational.

screenshot47_zps939303bd.jpg

screenshot54_zps0d61ff94.jpg

Edited by Wanderfound
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If it feels wasteful to rise so slowly, keep in mind that turbojets get an Isp of about 10,000s or more until you start going really fast.

At 69km and 2km/s, your Isp is equivalent to a rocket at 9600s Isp, better than twice as good as ions and more than 10x better than nukes. To get as low an Isp as an LV-N, you need to be going over 2500 m/s orbit speed.

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I was having similar issues to yours not long ago. You can look at this thread for the full story:

http://forum.kerbalspaceprogram.com/threads/99982-SSTO-FAR-Deadly-Reentry-Help

There is a few things I learned that might be useful to you:

1. Piloting is somewhat more important than design.

2. Have faith in your aircraft. If built correctly, it can usually take a lot more punishment that you probably think. Trust it.

3. Keeping above in mind, don't be in a rush to climb up into upper atmosphere. Turn on precision controls, adjust your trim, sit back, and just enjoy the scenery. With my aircraft in the link above, the ascent into upper atmosphere happens in a "staircase" pattern: I climb, lose speed, aircraft nose pitches down, I gain speed, lose altitude, aircraft nose pitches up, I lose speed, gain altitude, so on and so forth. Before, I used to panic every time the nose pitched down. All I had to do was let go of the controls. My point is, don't try to over-control the aircraft. Let it fly. I almost exclusively fly with trim controls now.

4. Again, don't be in a rush to climb the atmosphere. Take it slow. You want to pick up as much speed as you can with the jet engines. Remember: Getting into orbit isn't about how high you are. It's about how fast you're going.

5. If you're not using RAPIERS, make sure, and make doubly sure that your engines are lined up. What I mean by this is, in the Editor, turn on the Center of Thrust marker. Reduce the Thrust Limiter on one set of the engines to 0. The CoT should NOT move. Repeat the same with the other set. If CoT moves, you may induce unwanted torque to the aircraft when you pitch, which can be catastrophic. Adjust these until the CoT does not move.

6. In order to minimize the effects of sudden change in thrust, throttle down as much as you can (don't flame-out the jets if you have more than one. This may create a change in yaw if one flames out before the other, and you won't go to space that day). Then switch to rockets. Then slowly throttle back up.

I hope these help! I know how frustrating it can be to get that thing into orbit, but keep trying!

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