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TT213

How to find the best SSTO ascent path ?

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Hello :)

Yesterday I managed (with some efforts) to put a SSTO on Minmus. That was the first time I landed somewhere else than Kerbin with spaceplanes, so you can understand how happy I was. :D

And because of that, I tried to do it again today. Sadly for me, I tried as much as I could during 5 HOURS.. with absolutely no luck.  I always ended splashing down into the sea, unable to leave Kerbin atmosphere. :(

I know it's possible 'cause I did it yesterday, but I simply can't anymore. :rolleyes:

 

Can someone please help me ? :blush:

I play with "stock" parts, and I haven't unlocked the rapier engine yet.

 

 

Main Specs of the SSTO :

-  TWR : 1,08

- Total Dv : 7,383

-  Dv with only space engines turned on : 1,021

- Mass : ~ 27 tons

 

2 Pictures  :

Spoiler

1517262472-screenshot125.png

1517344099-screenshot137.png

 

THANKS IN ADVANCE for your help ! :D

 

Edited by TT213
Grammatical errors everywhere (French)

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There's a few changes that could be made to help with that craft but it does look like it should make orbit OK. 

I don't know the "best" way to make orbit with an SSTO (and it does depend on the craft) but what usually works for me is a gentle climb (~10°) until about mach1.5. Then climb a little steeper (~15°) until the jets flame out and then burn just above prograde until a decent Ap is made. Head to Ap and circulise.

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10 minutes ago, Foxster said:

There's a few changes that could be made to help with that craft but it does look like it should make orbit OK. 

I don't know the "best" way to make orbit with an SSTO (and it does depend on the craft) but what usually works for me is a gentle climb (~10°) until about mach1.5. Then climb a little steeper (~15°) until the jets flame out and then burn just above prograde until a decent Ap is made. Head to Ap and circulise.

It does the orbit, since it's with that SSTO I've landed on Minmus yesterday. I'll try with what you said, hope it will works !

Edited by TT213

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tt213,

If memory serves, the Whiplash works best if you dwell in the 18- 22km altitude range to max out the airbreathing velocity. Getting supersonic should be a breeze with such a high t/w, so shoot for 18 km and then slowly climb as you build speed from there. The nukes will give you a low t/w, so plan on dwelling at 43 km to build orbital velocity, then let it loft out.

Best,
-Slashy

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I have two working SSTO's, a smaller one, which can do a seriously steep ascent with no problem:

bIbYINR.jpg

And my big Diamondback;

pJq2dFW.jpg

I actually have a video of the Diamondback going into orbit (to prove it could make it without cheating.)

 

In each case, I had to launch them a few times, and experiment with different angles of ascent, until I found the sweet-spots. I also discovered the first one has a lot more range to play around with as far as ascents and all that, whereas the Diamondback has to be fairly precise each time, or it won't make it.

I would recommend backing everything up, then playing around and experimenting, until you find what you did that first time to get her to Minmus.... Then write it down! :wink:

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2 hours ago, Foxster said:

There's a few changes that could be made to help with that craft but it does look like it should make orbit OK. 

I don't know the "best" way to make orbit with an SSTO (and it does depend on the craft) but what usually works for me is a gentle climb (~10°) until about mach1.5. Then climb a little steeper (~15°) until the jets flame out and then burn just above prograde until a decent Ap is made. Head to Ap and circulise.

Managed to make it by doing a little like you said, however with a little change !

The 2 Wisplash weren't powerful enough to reach Mach 1.5 at 15km altitude, I had to use the 4 engines at the same time to get an 70km apoapsis. A lot of fuel has been lost because of this, but I'm now in ~100km orbit, with 1500ms (Dv) left. I can now go on Minmus again ( finally :D), but probably not travel back to Kerbin. I guess it's all about optimization now ! :P

 

1 hour ago, GoSlash27 said:

tt213,

If memory serves, the Whiplash works best if you dwell in the 18- 22km altitude range to max out the airbreathing velocity. Getting supersonic should be a breeze with such a high t/w, so shoot for 18 km and then slowly climb as you build speed from there. The nukes will give you a low t/w, so plan on dwelling at 43 km to build orbital velocity, then let it loft out.

Best,
-Slashy

Quickly after being in stable orbit, I tried your method (partially combined with Foxster's one, about the 10° climb). Max speed of ~1250km/h at 20km altitude, did a slow climb trying to get at 40km altitude and lost ALL my vertical speed. By burning fuel for a long time, it has lost a lot of mass, and I finally got an ~70km orbit, but with only 800ms left :/

I don't know why it does that, I tried it both times and sadly it didnt worked as expected. :(

Thanks anyway  ! :) 

 

1 hour ago, Just Jim said:

I have two working SSTO's, a smaller one, which can do a seriously steep ascent with no problem:

 

Spoiler

bIbYINR.jpg

 

And my big Diamondback;

 

Spoiler

pJq2dFW.jpg

 

I actually have a video of the Diamondback going into orbit (to prove it could make it without cheating.)

Spoiler

 

 

 

 

In each case, I had to launch them a few times, and experiment with different angles of ascent, until I found the sweet-spots. I also discovered the first one has a lot more range to play around with as far as ascents and all that, whereas the Diamondback has to be fairly precise each time, or it won't make it.

I would recommend backing everything up, then playing around and experimenting, until you find what you did that first time to get her to Minmus.... Then write it down! :wink:

GEEZ ! I made my flight path a little like you : 20°degrees until 6500m (what you did), then I aimed at 30° and at 10km altitude, I turned on LV-N engines : With an ~100km orbit, over 2000Ms (Dv) left ! WAY, WAY better than what I ever expected to get. Almost the half of the fuel unused too, and there wasn't any optimzation at all ! :D

 

Thanks a lot all three of you, I can sleep in peace now ! :sticktongue:

Edited by TT213

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We may have a better chance to figure out what is wrong with some details of your flight profile. Things like what is your pitch/AoA/vocitity/altitude at some points of you trajectory

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22 minutes ago, Spricigo said:

We may have a better chance to figure out what is wrong with some details of your flight profile. Things like what is your pitch/AoA/vocitity/altitude at some points of you trajectory

I hadn't any exact SSTO ascent path before making this topic. Sometimes I was going up to 15km, reaching 1200m/s and going up again. Sometimes else I was going to 20°, keeping that angle then hoping for leaving Kerbin Atmosphere.

And as I said, it always failed. But now it works really great, much better than expected :D

 

I just need now to "optimize" my SSTO, and the ascenth path too. :sticktongue:

 

Edited by TT213

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  1. after takeoff, climb at such a pitch that you still accelerate noticably, if not quickly.
  2. (probably not a problem for your vessel) if you have trouble braking the sound barrier (300-350m/s), pitch down to make it easier.
  3. now find a good middle ground between acceleration and climb rate. From looks, your craft should be good for at least 1200m/s. If you find yourself going much slower than that by the time the jets run out of oomph, you've been climbing too steep.
  4. Kick in the Nervas when jet power drops off noticeably. Don't wait for the jets to flame out.

So far so good. Now for the tricky bit: those double Nervas don't produce all that much thrust, and the Whiplashes flame out comparatively early. There's basically two ways to get from atmospheric flight into space:

  • pull up, up, up while the jets still have some power, trading some airspeed for climb rate. The idea is to toss you high up and buy time for the Nervas to bring you up to orbital speed before you fall down again. That approach is tricky because going either too steep or too shallow will result in failure.
  • keep using your wings: see to it that you *don't* climb very fast around the time your jets lose power. The idea is that you don't hop out of the denser atmosphere on momentum, but stay in a regime where airspeed under your wings will keep you afloat at all times. That's a lot easier to do, piloting-wise, but you will experience more heat. If you burn up, add more wings.
Edited by Laie

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1 hour ago, TT213 said:

GEEZ ! I made my flight path a little like you : 20°degrees until 6500m (what you did), then I aimed at 30° and at 10km altitude, I turned on LV-N engines : With an ~100km orbit, over 2000Ms (Dv) left ! WAY, WAY better than what I ever expected to get. Almost the half of the fuel unused too, and there wasn't any optimzation at all ! :D

Awesome!!!  I am so glad I could be of help!!!  :)

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I'd favour the zoom climb. NERVAs already have awful thrust, you don't want to kneecap that further by hampering them with drag. Turn on the nukes as the Whiplashes start to fail to reduce the proportion of thrust you lose to drag losses, point your nose 30 degrees or so to the horizon, and get yourself up above 40km ASAP, then level out again for the orbit insertion.

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Gravity turn is the best way to go. Just pitch over a little bit after liftoff (how much depends on the TWR you have) and then don't touch the controls except for throttle.

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9 minutes ago, Kosmo-not said:

Gravity turn is the best way to go. Just pitch over a little bit after liftoff (how much depends on the TWR you have) and then don't touch the controls except for throttle.

 

While I appreciate the joke and point -- that not all SSTOs are spaceplanes -- the OP very kindly included pictures of the actual craft they're trying to find the ascent path for. A gravity turn would not be optimal :P

Edited by foamyesque

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1 hour ago, Kosmo-not said:

Gravity turn is the best way to go. Just pitch over a little bit after liftoff (how much depends on the TWR you have) and then don't touch the controls except for throttle.

Have to disagree. Better is when you don't even need to worry about the pitch. Just fire and forget.

And, IMHO, specially rewarding if the craft is a plane.

 

In any case, OP's craft don't seems to be designed for that.

 

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I was going to say, "When are you staging your nukes? If you're not staging them until late, try a little earlier so they are burning in parallel with the ramjets."

But clearly I was beaten to the point. :) 

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