What must I change in my game-play to make SSTOs with payloads?

[Shaun]

I've been to Florida for two weeks, so I was so excited to hear about the release of V.1.0. Upon beginning the new version, I noticed the jet engines have been completely overhauled in the way they work and no longer work at altitudes in excess of 30km. I've managed to make a few SSTOs that can get into LKO, but anything bigger I struggle with; e.i fitting a cargo bay with a 2T payload. I get into suborbital, but never have enough dV to get into orbit and hence leave orbit afterwards.

I think I must be making mistakes in the ascent as I seem to be wasting so much fuel:

What is the proper way to ascend?

What are the best engines to use? (I figured RAPIERs as they're only 0.2T heavier than turbojets, but they have a hard time getting above 340m/s sometimes).

How much dV should I have after my jet engines cut out?

Would additional intakes keep my thrust up any longer?

Thanks.

[n0xiety]

This has been asked alot and actually i posted this same answer before.

This here is a quick ascent spaceplane that doesn't care about fuel much. I made it so when you start climbing with 20 degrees it adjusts its own climbing degree as it goes up so you don't have to touch anything and micromanage and it reaches 120km orbit in about 9 real life minutes. This one can carry 2 tons easy, 3 tons if you push it. Tho you can always remove the clampotron and crew cabin modules and get 3 more tons of capacity making it go up to 6 tons. Now pay attention how the cargo bay and point of mass is aligned perfectly so any cargo that you can take wouldn't effect the planes stability. Another thing is notice how the wings are swept upwards and that causes the lifting point to go over the mass point which is great for stability. Always have your mass point a bit forward and under the point of lift. Align your point of mass and point of thrust horizantally for the space part of your ascent. This is not needed that badly for the atmosphere part since your ailerons will be able to compansate but it still is good to have your thrust aligned always. I use external fuel tanks for this design. You do not have to ditch them if you wanna cut down on the cost but that would save 100 more liquid fuel for the atomic engine when you reach orbit and total cost is about 1k dollars empty so yeah... Another thing is always make sure your plane is stable at every stage of the flight. I have seen so many people complaining about their planes flipping out and getting into flat spin when they reenter atmosphere. This is caused by fuel getting consumed and point of mass shifting. Make sure your plane is always stable at every part of the flight as the fuel gets consumed.

Another thing is you need to lock unnecessary options from your ailerons. Like tail(rudder) is only for yaw and wing tip(ailerons) are only for roll while middle(elevators) are for pitch. You can always use pitch on your tail by adding 2 controll surfaces(elevators) to sides but spaceplanes with no tail works better. You can always use action keys to create flaps. Notice how i use flaps while reentring and landing. Well that is about it i guess hope this helps mate.

Keep in mind this is not actually an optimized craft i bet a more experienced player could make it to orbit with even more liquid fuel left for the nuke. I just like it fast and don't like to micromanage much thats all.

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[Shaun]

My aircraft is always stable and I know about the control surfaces. I am fine with designing aircraft, I'm just wondering how much more fuel and thrust I need to get said payloads up?

P.S. I'm talking about SSTOs, and because your aircraft has drop tanks, I think that counts as staging.

[n0xiety]

That is true but you can always keep the tanks as i said but that would cost 100 to 200 more liquid fuel usage since im allready out in space when i drop the tanks, nuke can take the empty mass easily. And as i said again this is not an optimised plane at all i just like fast stuff. I see some people creating great ssto planes and have guides how to ascend with them. Most veterans claim they climb the first part of atmosphere going 100m/s for fuel saving... Then it takes 25 minutes to reach orbit which i just don't like. The same reason why i don't like nuke or ion engines. If there was a viable physical fast forward sure it would work great but right now it's just a pain to use. I find SSTO rockets alot easier. Allready made one that can go to minmus without droping anything and has everything needed for mining. It can just keep on going to every planet after refueling itself. Only planet that it doesn't work is the obvious choice Eve. And we all know how Jool is.

[Red Iron Crown]

Here's a somewhat simple cargo SSTO plane I made:

Carries ~9 tons of cargo to a 75x75km orbit, with enough fuel left to deorbit and fly around in air for a while. I've found RAPIERs to be the best choice for SSTOs so far, they are the airbreathers that can work at the highest speed, 1 intake per engine is plenty.

Ascent goes something like this:

1. T, Z, Space, hold S until it pivots up and takes off, retract gear and climb at 45 degrees. Speed will slowly build but not exceed 300m/s.

2. Just below 10km begin gradually pitching down until reaching about 10 degrees at about 12km.

3. Build speed while slowly climbing, expect to see reentry effects. Should reach at least 1200m/s before running out of air, I've gotten it over 1400m/s.

4. When the thrust starts to die off, press 1 to toggle into rocket mode (usually a bit above 22km).

5. Point just above prograde while rockets are burning, raise Ap to 75km.

6. Cut engines, point prograde, and coast to Ap (it should be a few minutes away).

7. Burn at Ap to raise Pe to about 75km.

Steps 2, 3 and 4 are the critical ones. It *must* build enough speed while in efficient air-breathing mode to make the rocket burns shorter, and you want to keep the off-prograde component of the burns as small as possible. It is between 14km and 20km where the bulk of the acceleration will happen.

Sometimes it's hard to know whether a design isn't working because of piloting or design issues, so here's the craft file for this plane so you can practice the ascent. If you'd like to make it a bit easier you can remove some of the ore from the test payload (take it from the middle tank for balance reasons). Once you're confident you can fly an airbreathing SSTO to orbit, then you can start playing with designing your own with more confidence.

[Chris_2]

I've been to Florida for two weeks, so I was so excited to hear about the release of V.1.0. Upon beginning the new version, I noticed the jet engines have been completely overhauled in the way they work and no longer work at altitudes in excess of 30km. I've managed to make a few SSTOs that can get into LKO, but anything bigger I struggle with; e.i fitting a cargo bay with a 2T payload. I get into suborbital, but never have enough dV to get into orbit and hence leave orbit afterwards.

I think I must be making mistakes in the ascent as I seem to be wasting so much fuel:

What is the proper way to ascend?

What are the best engines to use? (I figured RAPIERs as they're only 0.2T heavier than turbojets, but they have a hard time getting above 340m/s sometimes).

How much dV should I have after my jet engines cut out?

Would additional intakes keep my thrust up any longer?

Thanks.

Try adjusting your flight profile? After getting above 35 km, you basically want to pitch down to the horizon, and throttle back so the apoapsis stays ~1 minute in front of you and not further ahead. Drag losses above 45km get very minimal, so a long low power burn is much more efficient. Maybe even equip your craft with a LV-909, as this engine has the best performance/weight ratio for the required delta-V, and probably sufficient thrust to perform this long low power burn (except when you're building a really heavy SSTO you might want multiple LV-909's).

Edited May 14, 2015 by Chris_2

[guitarxe]

Here's a somewhat simple cargo SSTO plane I made:

https://dl.dropboxusercontent.com/u/61004449/KSP/1.0/screenshot94.png

Carries ~9 tons of cargo to a 75x75km orbit, with enough fuel left to deorbit and fly around in air for a while. I've found RAPIERs to be the best choice for SSTOs so far, they are the airbreathers that can work at the highest speed, 1 intake per engine is plenty.

Ascent goes something like this:

1. T, Z, Space, hold S until it pivots up and takes off, retract gear and climb at 45 degrees. Speed will slowly build but not exceed 300m/s.

2. Just below 10km begin gradually pitching down until reaching about 10 degrees at about 12km.

3. Build speed while slowly climbing, expect to see reentry effects. Should reach at least 1200m/s before running out of air, I've gotten it over 1400m/s.

4. When the thrust starts to die off, press 1 to toggle into rocket mode (usually a bit above 22km).

5. Point just above prograde while rockets are burning, raise Ap to 75km.

6. Cut engines, point prograde, and coast to Ap (it should be a few minutes away).

7. Burn at Ap to raise Pe to about 75km.

Steps 2, 3 and 4 are the critical ones. It *must* build enough speed while in efficient air-breathing mode to make the rocket burns shorter, and you want to keep the off-prograde component of the burns as small as possible. It is between 14km and 20km where the bulk of the acceleration will happen.

Sometimes it's hard to know whether a design isn't working because of piloting or design issues, so here's the craft file for this plane so you can practice the ascent. If you'd like to make it a bit easier you can remove some of the ore from the test payload (take it from the middle tank for balance reasons). Once you're confident you can fly an airbreathing SSTO to orbit, then you can start playing with designing your own with more confidence.

H.. how is your plane so stable in flight? The centre of mass is way in the back, the centre of lift is even further back, and nowhere near the centre of mass. Yet it flies so very well... I don't understand. This completely shakes the very foundations on what I have been trying to base my plane designs on.

[AaronLS]

H.. how is your plane so stable in flight? The centre of mass is way in the back, the centre of lift is even further back, and nowhere near the centre of mass. Yet it flies so very well... I don't understand. This completely shakes the very foundations on what I have been trying to base my plane designs on.

Often my SSTO's are similar.

It seems to help keep the nose forward. When your center of lift is behind your mass it also means your drag is higher there and your plane will not flip around as easily when under very high thrust.

Sometimes it's a struggle to keep the nose up like this. If lift is too far back then it's too hard to keep the nose up.

It can also cause problems when gliding back in for a landing. My SSTO's usually have a terrible glide profile. I usually glide in nosed down at about 10 degrees then pull up at last moment which barely levels me out for a hard landing on my wheels.

So there's definitely a disadvantage of having the lift that far back. Often when I've tried moving it forward towards CoM then my plane never stabilizes while descending and just flails around all the way to it's death because I can't get the nose to stay forward or even prograde.

[Sean Mirrsen]

Center of lift and drag way towards the back helps keep stability as your fuel drains and your center of mass moves back. It's in the basics of spaceplane building.

[Red Iron Crown]

H.. how is your plane so stable in flight? The centre of mass is way in the back, the centre of lift is even further back, and nowhere near the centre of mass. Yet it flies so very well... I don't understand. This completely shakes the very foundations on what I have been trying to base my plane designs on.

The CoM is fairly far back on purpose. I tried to align it with the middle of the cargo bay, that way the plane would have similar flight characteristics if a lighter payload was substituted or after the payload is released. (Protip: Ore containers are dense when filled, if a plane can get to orbit with the bay full of ore it should be able to get there with any other payload that fits.)

As for stability, it's less important how far ahead/back the CoL and CoM are than how they are positioned relative to each other. CoL behind the CoM will make a plane that wants to point forward, even if they're both toward the back of the plane.

[Shaun]

Ok well I just made an SSTO capable of carrying 5 tonnes to LKO, but it weighs almost 40 tonnes when fuelled, so I'm getting only 12.5% of payload mass into orbit. Zero fuel weight without payload is around 20 tonnes. Wondering if this is any good...

[Red Iron Crown]

Ok well I just made an SSTO capable of carrying 5 tonnes to LKO, but it weighs almost 40 tonnes when fuelled, so I'm getting only 12.5% of payload mass into orbit. Zero fuel weight without payload is around 20 tonnes. Wondering if this is any good...

I struggled with getting any useful payload at all at first. Payload fractions in excess of 30% are possible, my best are about 25%. Nothing wrong with a 12.5% fraction, but there is room for improvement.

Show us a pic of what you have and we can offer better advice for improving it.

[Dogface]

Here's a somewhat simple cargo SSTO plane I made:

Carries ~9 tons of cargo to a 75x75km orbit, with enough fuel left to deorbit and fly around in air for a while. I've found RAPIERs to be the best choice for SSTOs so far, they are the airbreathers that can work at the highest speed, 1 intake per engine is plenty.

Ascent goes something like this:

1. T, Z, Space, hold S until it pivots up and takes off, retract gear and climb at 45 degrees. Speed will slowly build but not exceed 300m/s.

2. Just below 10km begin gradually pitching down until reaching about 10 degrees at about 12km.

3. Build speed while slowly climbing, expect to see reentry effects. Should reach at least 1200m/s before running out of air, I've gotten it over 1400m/s.

4. When the thrust starts to die off, press 1 to toggle into rocket mode (usually a bit above 22km).

5. Point just above prograde while rockets are burning, raise Ap to 75km.

6. Cut engines, point prograde, and coast to Ap (it should be a few minutes away).

7. Burn at Ap to raise Pe to about 75km.

Steps 2, 3 and 4 are the critical ones. It *must* build enough speed while in efficient air-breathing mode to make the rocket burns shorter, and you want to keep the off-prograde component of the burns as small as possible. It is between 14km and 20km where the bulk of the acceleration will happen.

Sometimes it's hard to know whether a design isn't working because of piloting or design issues, so here's the

for this plane so you can practice the ascent. If you'd like to make it a bit easier you can remove some of the ore from the test payload (take it from the middle tank for balance reasons). Once you're confident you can fly an airbreathing SSTO to orbit, then you can start playing with designing your own with more confidence.

Thanks a lot, that helped. I was having trouble getting past 20km. With your guide I got to 50km the first time. Now I just have to do some heat management and it looks like I may make orbit. Thank you.

Edited May 19, 2015 by Dogface

[spacenut1337]

I was trying to make space planes a part of my career mode, but I'm having a hard time making one that can get any kind of payload to orbit. All the examples I see have rapiers or nukes which I don't have yet. Eventually I got a payload-less plane to orbit and back again, which was a nice victory, and then decided to try a NASA Shuttle-style ship, which turned out to be even harder!

[ajburges]

I was trying to make space planes a part of my career mode, but I'm having a hard time making one that can get any kind of payload to orbit. All the examples I see have rapiers or nukes which I don't have yet. Eventually I got a payload-less plane to orbit and back again, which was a nice victory, and then decided to try a NASA Shuttle-style ship, which turned out to be even harder!

Nukes are actually asuboptimal choice for a space plane. Their horrid TWR makes them challenging to get to orbit with. Their efficiency only breaks even if you regularly fly past minmus. However they remain popular because they allow for oxidizer free designs.

Rapiers are hands down the best space plane engine. They have the best hypersonic performance and also double as a rocket. The only other practical aerobic engine for a space plane is the turbo jet. The turbo jet has better trans-sonic performance than the rapier. That means you need fewer of them for you aerobic profile (rapiers are drag limited, turbos are speed/altitude limited). In exchange you need dedicated anaerobic engines and more rocket dV to orbit. All said, you want about .7-.8 TWR and 2Km/s (conservatively) on rockets for a comfortable accent.

A NASA modeled shuttle is a real undertaking. A few hours of research will show you how a rocket without radial symmetry is a challenge. 3 stages with radically different thrust vectors, mass centers, and lift vectors. I'd instead advise a Kerbal shuttle: build a jet (basic fine) with an OMS, point vertical, add moar boosters (symmetrically of course).

Keep in mind, jets and wings are dead weight in space. Shuttles are about making the part that returns to surface worth more. Space plane SSTOs make that portion worth more still by using the air as a free oxidizer.

[rtxoff]

I struggled with getting any useful payload at all at first. Payload fractions in excess of 30% are possible, my best are about 25%. Nothing wrong with a 12.5% fraction, but there is room for improvement.

Show us a pic of what you have and we can offer better advice for improving it.

In your save file:

On the 2 outer Rapiers automtatic mode switching still activated, is this intended? Also on the action key 1 your intakes are not getting closed when switching.

I tried the plane but with my flying skills i lack 140m/s dV for a stable orbit. I really don't see the point why 1.0.2 makes it so hard to get into orbit with the Rapiers.

My opinion is still that Rapiers need some balancing to make them more playable.

[Red Iron Crown]

In your save file:

On the 2 outer Rapiers automtatic mode switching still activated, is this intended? Also on the action key 1 your intakes are not getting closed when switching.

I tried the plane but with my flying skills i lack 140m/s dV for a stable orbit. I really don't see the point why 1.0.2 makes it so hard to get into orbit with the Rapiers.

My opinion is still that Rapiers need some balancing to make them more playable.

Er, I must have moved an older version of the craft file over to my dropbox, they should all be on manual mode switching. I don't bother closing the intakes, by the time I switch modes drag is hardly a factor (not sure closing them even makes a difference to drag in the new aero).

Since writing that ascent profile on the previous page I've gotten a bit better with it, I've gotten to orbit with almost 300m/s remaining plus a bit of extra LF.