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Efficient ascent plans for SSTOs


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Hello fellow KSP players. I am relatively new to making SSTOs but I noticed that some of the planes have a hard time going into orbit even with enough fuel. I’m curious if it’s my ascent profile or my angle of attack and I was wondering if there is a preferred profile for certain types of space planes. Thanks in advance. 

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I'm not the expert on SSTOs, but here's a few tips:

  • You want to get as fast as you can in air-breathing mode.  With RAPIERS I like to see 1,500 m/s or better in air-breathing mode.  1,600 m/s is better.
  • At those speeds heat will be an issue, so chose parts wisely.  If parts are blowing up due to heat, you may need to locate those parts somewhere else, or replace them with parts with better heat tolerance.
  • Get supersonic as quickly as you can.  Below 5,000 m 400 m/s is supersonic.
  • Here's a flight profile that usually works for me.  I generally use RAPIERS for SSTOs:
    • After takeoff, I fly a very shallow climb until reaching 400+ m/s, the prograde icon is about 5 degrees above the horizon.  Some players actually just level off a few hundred meters above sea-level.  
    • After reaching 400+ m/s (supersonic) I start to gradually aim for a climb of about 10 degrees above the horizon.  That means the prograde icon is 10 degrees above the horizon.  
    • I use air-breathing mode until the engines stop accelerating the ship, around 25,000 m or so.  Then I switch to closed-cycle.  
    • Ideally you want to reach 1,500 m/s or better before switching to closed cycle.  1,600+ is even better.

If you aren't able to reach at least 1,500 m/s, you probably have a drag issue that needs to be addressed.  I see so many drag issues that it's not really possible to address them all.  One big mistake I commonly see is players using too many fuselage sections.  A single long fuselage is much better than two or three or more tubes.  Every lateral nacelle you tack on adds a lot of drag.  You don't want that.

You may need to adjust your climb profile based on your craft design.  But in general you want to get supersonic as quickly as possible, then continue in a shallow climb so that you hit 1,500+ m/s at about the same time your engines lose thrust in air-breathing mode.

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56 minutes ago, 18Watt said:

I'm not the expert on SSTOs, but here's a few tips:

  • You want to get as fast as you can in air-breathing mode.  With RAPIERS I like to see 1,500 m/s or better in air-breathing mode.  1,600 m/s is better.
  • At those speeds heat will be an issue, so chose parts wisely.  If parts are blowing up due to heat, you may need to locate those parts somewhere else, or replace them with parts with better heat tolerance.
  • Get supersonic as quickly as you can.  Below 5,000 m 400 m/s is supersonic.
  • Here's a flight profile that usually works for me.  I generally use RAPIERS for SSTOs:
    • After takeoff, I fly a very shallow climb until reaching 400+ m/s, the prograde icon is about 5 degrees above the horizon.  Some players actually just level off a few hundred meters above sea-level.  
    • After reaching 400+ m/s (supersonic) I start to gradually aim for a climb of about 10 degrees above the horizon.  That means the prograde icon is 10 degrees above the horizon.  
    • I use air-breathing mode until the engines stop accelerating the ship, around 25,000 m or so.  Then I switch to closed-cycle.  
    • Ideally you want to reach 1,500 m/s or better before switching to closed cycle.  1,600+ is even better.

If you aren't able to reach at least 1,500 m/s, you probably have a drag issue that needs to be addressed.  I see so many drag issues that it's not really possible to address them all.  One big mistake I commonly see is players using too many fuselage sections.  A single long fuselage is much better than two or three or more tubes.  Every lateral nacelle you tack on adds a lot of drag.  You don't want that.

You may need to adjust your climb profile based on your craft design.  But in general you want to get supersonic as quickly as possible, then continue in a shallow climb so that you hit 1,500+ m/s at about the same time your engines lose thrust in air-breathing mode.

Wow thanks you so much! I don’t have access to my laptop at the moment but I’ll be sure to test these out. 

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The ascent profile depends on the craft.  A light one like a MK1 based SSTO can climb and accelerate quite well while a heavy MK3 based one can struggle to get up to speed and has to stay low until it does build up enough speed to make the climb out of the atmosphere.   You should start off with the MK1 as it is easier to fly.

You probably do not have rapiers yet and that is not a real problem.  Whiplash and rocket combinations do just fine but tend to have short ranges.  Rapiers and NERVs are the best overall, but I got a Whiplash and rocket MK1 to the Mun and back.  Barely. 

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1 hour ago, miklkit said:

The ascent profile depends on the craft.  A light one like a MK1 based SSTO can climb and accelerate quite well while a heavy MK3 based one can struggle to get up to speed and has to stay low until it does build up enough speed to make the climb out of the atmosphere.   You should start off with the MK1 as it is easier to fly.

You probably do not have rapiers yet and that is not a real problem.  Whiplash and rocket combinations do just fine but tend to have short ranges.  Rapiers and NERVs are the best overall, but I got a Whiplash and rocket MK1 to the Mun and back.  Barely. 

I play on sandbox so I have all the tech already unlocked.

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6 hours ago, 18Watt said:

I just use RAPIERS.  The weight savings from not putting NERVs on my ship more than makes up for the loss of DV in space.

I say it depend on use.  for an light plane who only go to LKO its no point with NERV but for something longer range or heavier they makes sense. 

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Just an additional tip: You are going to need to reach a minimum speed of (GM/R)^(1/2) = 2,296 m/s for a 70-km circular orbit. Though lower speeds are required at higher altitudes, the overall delta-V cost will always increase the higher you go, so engineer for 2,296 m/s minimum in orbit. A minimum delta-V for getting to 70 km is (2GM(1/r - 1/R))^(1/2) = 1,109 m/s (not accounting for losses due to drag). If you fly to the east, you have some "free" delta-v due to Kerbin's rotation equal to 2*pi*r/T = 174.9 m/s. Flying to the west means you need that much more. (Any other direction, use trig or just add 175 m/s ...KIS 'n all.)

Taken together, you'll need a minimum delta-V (without accounting for drag) of 2,296 m/s + 1,109 m/s +/- 174.9 m/s = 3,230 m/s to 3,580 m/s.

As you know, the less extra delta-V you carry in fuel, the less you'll use to get up there.

EDIT: This also works for rockets. It's trickier to apply to spaceplanes due to the insane efficiency of air-breathing engines, but good to keep in mind so your fuel isn't making you use ...more fuel. :P

Edited by xionix4
BTW
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14 hours ago, 18Watt said:

I just use RAPIERS.  The weight savings from not putting NERVs on my ship more than makes up for the loss of DV in space.

If all you want to do is get into LKO, then that is true.  If you want to actually get anywhere, then NERVs are needed.   I have been trying to get some range out of a Dart powered spaceplane and it just ain't happening.

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I routinely take SSTOs to the surface of Minmus and back.  With an on-board ISRU, almost the entire solar system is reachable.  I have not managed to reach Moho with Rapiers, for that I’ve used SSTOs which are Ion powered in space.

However, I find SSTOs most practical for shuttling crews to LKO or possibly out to Mun or Minmus.  Beyond that I find standard rockets much more practical for hurling things beyond Kerbin’s SOI.

Personally, I don’t really have the patience to wait for Ion engine burns, or even Nuke burns.

Now that you mention it, I haven’t taken a plane to Laythe in a long time.  Might be time to do that again!

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