how to build a large working SSTO for 1.0.2 - 1.0.4 ?

[Nich]

I am going to have to disagree I managed 57t payload with a 128t starting weight by going level past 350ish pull up to 15 degrees until 10 km. go down to 8 degrees (this should get you 1350m/s before engines flame out) burn LF/OX at a 5-8 degree angle of attack until AP reaches 75km.

I only used 4 rapes and 2 whiplashes. giving 21.33t per engine. Lift is based off V^2 just like drag so wasting energy to pop out of the ATM doesn't really help you as your SSTO creates more lift then drag but turning 15-20 degrees at large AOAs will eat up a lot of your speed and you are now burning against gravity again.

The hardest part was not snapping the MK3 cargobays in half when going from 15 to 8 degrees at 1000m/s+

[ajburges]

I am going to have to disagree I managed 57t payload with a 128t starting weight by going level past 350ish pull up to 15 degrees until 10 km. go down to 8 degrees (this should get you 1350m/s before engines flame out) burn LF/OX at a 5-8 degree angle of attack until AP reaches 75km.

I only used 4 rapes and 2 whiplashes. giving 21.33t per engine. Lift is based off V^2 just like drag so wasting energy to pop out of the ATM doesn't really help you as your SSTO creates more lift then drag but turning 15-20 degrees at large AOAs will eat up a lot of your speed and you are now burning against gravity again.

The hardest part was not snapping the MK3 cargobays in half when going from 15 to 8 degrees at 1000m/s+

Thats why you need to be careful with your final pitch-up manuver. You don't want to build vertical speed as much as you want to adjust course a smidgen to leave atmo faster. You still have significant drag in the 22-32 km range, but turbo jets will never give the thrust needed to build or maintain velocity and rockets are thirsty. If you can shorten your time here without major steering losses, you'll see fewer drag losses (in theory). The pitch-up also increases lift via a greater AoA. Just make sure you don't lose velocity in your manuver.

RAPIERs fly faster and higher. You thus have less room to pitch-up, but the idea remains the same.

The root cause of asymmetric flameout, the resource distribution rules, was never fixed. The new jet mechanics simply sidestep the rule. Jet trust, and thus resource consumption, fall off at high altitudes and higher Mach numbers. The happy consequence is that most reasonable designs for 1.0+ don't have problems with asymmetric flameout because the engines don't generate much thrust at the time of death regardless. If you have control issues at flameout, it's a sign you don't have enough intakes out that your flight profile is wrong.

Edited June 29, 2015 by ajburges

[scavenger]

You still have significant drag in the 22-32 km range, but turbo jets will never give the thrust needed to build or maintain velocity and rockets are thirsty.

1- correct, at 22k the turbojets cannot maintain either speed or climb. I HAVE to trigger the rocket no matter what. What you see in the youtube videos like people going to 32-36 with jets only is NOT possible anymore.

2- The flameout happens between 25.8k and 26.9k depending on your speed, so at some point I do not see how you can not use them both for some time.

RAPIERs fly faster and higher. You thus have less room to pitch-up, but the idea remains the same.

3- certainly but the point when I started the post was not to use them yet, just turbo jets.

The root cause of asymmetric flameout, the resource distribution rules, was never fixed.

4- I never experienced asymmetric flameout as when it happens, I already rely on rocket, cf point 2

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I am going to have to disagree I managed 57t payload with a 128t starting weight by going level past 350ish pull up to 15 degrees until 10 km. go down to 8 degrees (this should get you 1350m/s before engines flame out) burn LF/OX at a 5-8 degree angle of attack until AP reaches 75km.

I only used 4 rapes and 2 whiplashes. giving 21.33t per engine. Lift is based off V^2 just like drag so wasting energy to pop out of the ATM doesn't really help you as your SSTO creates more lift then drag but turning 15-20 degrees at large AOAs will eat up a lot of your speed and you are now burning against gravity again.

The hardest part was not snapping the MK3 cargobays in half when going from 15 to 8 degrees at 1000m/s+

I tried your idea and went at 1118m/s at 12,600m and the SSTO totally exploded. No dismantle, just a big explosion. So it doesn't work for large SSTO since the heat induced is just too big. thank you anyway. Now I am gonna try the ajburges idea.

[ajburges]

I never got in the habit of going that fast at angels 12. Even in 1.02, the heat generation was a tad too much.

Even if my craft could go supersonic earlier, my standard turbojet flight plan does not allow me to push past 275 m/s until Ap hits 10 km. I gravity turn into prograde to punch through the Mach barrier ASAP and attempt to set AoA such that I hit .9-1 km/s at angels 16. I choose .9-1 km/s at 16 km because that is one of the optimal performance points of turbojets they only loose power further along. While those wonderfully efficient engines still have power and I still have air (16-20 km) I try to shift prograde up as much as possible using wing lift. I limit myself to an AoA 15 degrees off prograde and engage rockets as soon as I start loosing speed. Until closing intakes helps drag, I ignore flameout to focus on flight profile. At 32 km I start transitioning to a ballistic profile to complete my gravity turn. Transition to be complete by 36 km. At this point I reconfigure stage groups and tune my throttle settings using the map view as reference.

[scavenger]

I'm having to tweak my current cargo hauler; recent version seems to have harmed it a little.

For a turbo rocket mix, I try to reach 1 km/s by 16 km. Past that in any direction sees rapid performance loss. Once I get that speed, I use my wings and jets to pitch up, keeping as much speed as possible. Lift surfaces are the most efficient way to change heading at those speeds. I hit the rockets when I start losing any speed. Once I pass 28 km, I bring heading inside of the prograde circle. At 36 km, I set SAS to follow prograde and tune throttle for optimal gravity turn.

In design, I want rocket dV of 1.8 km/s with full TWR of at least unity. Jets as needed to break the sound barrier.

I tried this idea too, and it works pretty much as usual. I cat get into orbit with just fuel enough to get back to Kerbin and that's all.

- The climb angle to 16k is 20deg and you get 1044m/s

- then I switch to 60deg until AP is 75k then I orbit as usual

- problem is pitching this way, you get only 1500m/s after 70k, so to orbit you have to burn much more dV, like 900m/s.

Either way, what you gain on one hand you loose on another.

[Nich]

The reason you exploded was your SSTO has too much engine back off the throttle, remove some thrust or add to your payload. Also I may have forgot to mention SLOWLY pitch down. I start at 10 km but do not hit 8 degrees until 16 km. My design simply didn't have the power to break the sound barrier at 10 km. I also didnt want to climb to 10 drop to 9 to break the sound barrier then accelerate and try to pitch up without breaking my SSTO.

What do people use to record their flights? I would love to find another 6%

[ajburges]

I tried this idea too, and it works pretty much as usual. I cat get into orbit with just fuel enough to get back to Kerbin and that's all.

- The climb angle to 16k is 20deg and you get 1044m/s

- then I switch to 60deg until AP is 75k then I orbit as usual

- problem is pitching this way, you get only 1500m/s after 70k, so to orbit you have to burn much more dV, like 900m/s.

Either way, what you gain on one hand you loose on another.

60°, that's crazy! You have 50% cosine loss of trust. I find a 30° pitch is a good compromise, but I frequently just fly 15° above prograde until the atmosphere diminishes.

Orbital velocity is a about 2.4 km/s at 20 km. You only need enough pitch to see you to that speed before you hit Ap. Getting the correct pitch earlier just has the added bonus of leaving the last of the significant atmosphere quicker. With that advice, pitch will be related to TWR.

Extremely low TWR craft (nuclear planes mostly) may want an entirely different approach. The required pitch for a gravity turn is too great. Instead, they can be better off flying at the edge of the atmosphere (32-35 km) using lift to keep them aloft at suborbital speed. The reduced drag that high grants more efficiency while accumulating orbital velocity. You establish atmospheric orbit and just do a Hoffman transfer out of the atmosphere. This is also likely the most thermally demanding flight profile in KSP today. I last tried it in 1.02 and the guages were displayed the whole flight. Nothing blew up though.

[Nich]

Well it is good we agree at least there ajburges. I just tried it again with my launch vehical and I was unable to get past 45. Not even close to circularizing. Tried it again at 30 degrees (about 15-20 degree AOA) with the same results but it felt like I was just about to bring PE out of Kerbin. My best results are 15' until 10 km tip down to 8' very slowly (should hit 8' around 16 km at 1200ish) switch the rapes at 23ish and 1390ish then just set up 5-8 degrees above propgrade. Burn until AP reaches 73km (this will bleed down to 70 km (PE will already be at 18ish km by the time you need to circularize)

Edited June 30, 2015 by Nich

[scavenger]

OK I will try 30° instead of 60° lol

BTW I didn't explode because I was pitching, it just exploded because of the heat generated.

To picht, as you can see I use SmartAss with SURF mode, where I change angles slowly by 2° increments

nice thought though: for the first time I went flameout before triggering the rocket, thanks to the great speed of 1044m/s at 16k.

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60°, that's crazy! You have 50% cosine loss of trust. I find a 30° pitch is a good compromise, but I frequently just fly 15° above prograde until the atmosphere diminishes.

So I tried. Problem is, if you keep at 30° with 1044m/s and increasing speed, with a TWR of 1.1 you do NOT gain altitute. Worse, by 1,200m/s and more, at 29,000m altitute, with 30° you start falling again because you passed the AP, and the plane becomes uncontrollable and start spinning.

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With 45° slope during the rocket time, i have better results as I can orbit with AP/PE = 80k/70k and I keep like 625dV, which is barely enough to RDV with a station and go back to Kerbin.

Since the plane is empty, my deduction is that for this king of SSTO with 3 cargo bays, it is impossible to make a cargo ship with turbo jets engines only. One have to unlock the RAPIER no matter what.

but thank you for the first advice, ajburges, as it is the easiest way to get into orbit I tried so far, if not the best efficient.

Edited June 30, 2015 by scavenger

[ajburges]

OK I will try 30° instead of 60° lol

BTW I didn't explode because I was pitching, it just exploded because of the heat generated.

To picht, as you can see I use SmartAss with SURF mode, where I change angles slowly by 2° increments

nice thought though: for the first time I went flameout before triggering the rocket, thanks to the great speed of 1044m/s at 16k.

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So I tried. Problem is, if you keep at 30° with 1044m/s and increasing speed, with a TWR of 1.1 you do NOT gain altitute. Worse, by 1,200m/s and more, at 29,000m altitute, with 30° you start falling again because you passed the AP, and the plane becomes uncontrollable and start spinning.

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With 45° slope during the rocket time, i have better results as I can orbit with AP/PE = 80k/70k and I keep like 625dV, which is barely enough to RDV with a station and go back to Kerbin.

Since the plane is empty, my deduction is that for this king of SSTO with 3 cargo bays, it is impossible to make a cargo ship with turbo jets engines only. One have to unlock the RAPIER no matter what.

but thank you for the first advice, ajburges, as it is the easiest way to get into orbit I tried so far, if not the best efficient.

Can you share your ship or at least images? My craft aim for unity TWR with takeoff weight. The loss of some fuel (and gain in TWR) should not be enough to make or break accent.

My turbojet Mk3 space plane is able to carry payloads in its triple cargo bay (the middle size ones). It struggles with dense loads though. I expect it to need to borrow fuel from orange tank class payloads to make dV budget. The craft is still seeing tweaks, but I can list its stats.

It just launched my Minmus research station. The thing had a full mass close to an orange tank and the plane needed to steal a quarter of the stations fuel after a bad accent (the sound barrier was being problematic). The poor thing landed with a full Mk3 segment of surplus oxidizer!

[scavenger]

sure!

There are plenty along posts but you have to open them all and I know it's annoying, I don't do it either...

Here is the latest version I was talking about: B52 drill SSTO v9.7 BOT

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Cargo empty, it goes to orbit with like 625dV left at 75k.

I currently am trying another version with cargo full of orange tank and all, but it's another version with 4 more jet engines since the wings are not sufficient to lift when cargo is full.

the first pic show you the CoM/CoT/CoL and just above is what you can fit in the cargo

[selfish_meme]

Just built a 4 Whiplash, 4 Swivel and 1 nuke SSTO with the large mk3 cargo bay 77t. Got it to 71x93k orbit with 800 units of fuel left (after seriously messing up the ascent while changing a nappy, had to come back down from 20k), which with the nuke could get you pretty far or with the swivels some serious payload into orbit. It's even easier than with Rapiers as the ascent is just fly up till 10000m then go as fast as you can while climbing slowly at 1 or 2', engage the rockets, slowly tip up to 20' then follow the prograde marker until apoapsis. I didn't get a screenshot, but will provide one later if anyone needs it.

[scavenger]

I finaly made it with the 26th version of my cargo, which include a fairing for the rocket to lessen drag:

you can see on the second pic that i get an full orange tank into orbit and have plenty of fuel to rdv with any station and get back to Kerbin

I had to pump the 2 rockomax grey tanks out of the cargo bay, though.

ascent curve is:

20' till 25k, then 15' till your jets shut down. You should be at 1200m/s by 30k

then you trigger the rocket once you lose speed OR AP is not climbing. You keep 20' no more because you need to have speed is your TWR is less than 1.5

Once you are at 1800m/s or more, you go to 40' until AP is 75k or more, whatever is your goal. then circularize.

Your speed at the AP should be around 2000m/s already

My conclusion: SSTO is nice, and a great challenge too, but honestly, just to spare 80,000$ to put an organge tank in orbit, what a loss of time...

and the risk of the rentry and all, to me it's not worth it. But I made it and that was the goal

[ajburges]

A fairing on the rocket nosel...

GENIUS!

Please tell me fairings have full recovery. Or at least cost less than a nose come and decoupler.

Edit: OTOH my current standard flight profile lights rocket engines for 6 seconds at angels 10 to break the sound barrier. Afterburners are too weak man. Still, if I can get the fairing for cheap enough...

Paradoxically, I do so much work with space plane SSTOs, I can fly them more reliably than I can rockets.

Edited July 7, 2015 by ajburges

[Sharpy]

So I tried. Problem is, if you keep at 30° with 1044m/s and increasing speed, with a TWR of 1.1 you do NOT gain altitute. Worse, by 1,200m/s and more, at 29,000m altitute, with 30° you start falling again because you passed the AP, and the plane becomes uncontrollable and start spinning.

With TWR 1.1 you are gaining speed. Do not worry about altitude, keep the flight level or barely climbing. As long as you gain speed, even slowly, you're fine. Once you reach the orbital speed, altitude will come all by itself with your climb to the apoapsis.

There are two schools of launching SSTO. The first is to jump above the atmosphere and quickly burn to reach orbital speed before you sink back in. The other is to soldier on through the atmosphere gaining speed against all the drag, allowing the altitude to rise as lift increases with speed and gravity pull vanes as you're approaching orbital speeds, and while it takes a long time and uses lots of fuel, it works too.

[Sharpy]

Both schools have their advantages and disadvantages.

The atmospheric climb wastes a lot of fuel on fighting drag, and takes much longer to reach the orbit - the nuke struggling against the drag gains speed really slowly and as result it's often a good ten minutes since whiplash sputters out until you're in the orbit. And once up there you have only your weak (but efficient) nukes for propulsion.

The ballistic jump requires an intermediate engine of high thrust, and the Oxidizer infrastructure to support it. The extra engine and its fuel cuts into your payload mass and atmospheric stage TWR, and your ascent must be steep enough for it to have enough time (until apoapsis) to gain the speed, resulting in ugly orbits as you can't afford waiting for apoapsis - you perform a continuous burn that ends often long after that point. But an "unforseen" advantage is that you have a powerful engine on board, so if you need to perform fast, strong burns, e.g. matching speeds or stopping in a fast fly-by, you have the TWR to do it. Also, having three types of engines all of which must be symmetric with its own kind creates considerable design challenges.

I have yet to try some lightweight "ballistic jump" SSTOs. The ones I built so far were simply huge, e.g. a Rhino engine, four orange tanks, sixteen whiplashes, two nukes, a large LF fuselage. OTOH I need to see how well my atmospheric ascent SSTOs scale up - the ones I built so far were quite tiny - utilizing just one nuke and one Whiplash - but the results were promising even if the climb time could make one fall asleep.

Of course that's all without RAPIERs. They really change the SSTO game, playing both as jets and as the "intermediate engines".

Edited July 8, 2015 by Sharpy

[ajburges]

With TWR 1.1 you are gaining speed. Do not worry about altitude, keep the flight level or barely climbing. As long as you gain speed, even slowly, you're fine. Once you reach the orbital speed, altitude will come all by itself with your climb to the apoapsis.

There are two schools of launching SSTO. The first is to jump above the atmosphere and quickly burn to reach orbital speed before you sink back in. The other is to soldier on through the atmosphere gaining speed against all the drag, allowing the altitude to rise as lift increases with speed and gravity pull vanes as you're approaching orbital speeds, and while it takes a long time and uses lots of fuel, it works too.

I go for a hybrid approach. Enough TWR to ballistically ascend to 50 km ASAP followed by a slow measued burn once Ap hits 50 km. Above 50 km you lose at most 60 dV to drag in a low eccentricity half orbit. The Oberth effect gains of a good gravity turn at this point outweigh the drag losses. (Or at least I assume so). The lower ascent orbit can also help with your rendezvous in launch to intercept missions because of the shorter period. Since I have the power for a ballistic ascent to 50 km, I can choose to screw efficiency if I launched too soon.

Since the changes from 1.03, I find trying to build speed below 50 km with a low TWR engine a losing affair. Too low (sub .7 range) and you can't even reach 50 km effectively.

One advantage SSTO rockets have is they just zip through that part of ascent. Sometimes too fast even!

Edited July 8, 2015 by ajburges