Jump to content

Atmospheric Efficiency/optimal ascent speeds in 1.0?


ShunterAlhena
 Share

Recommended Posts

Pre-1.0 I used the "Atmospheric Efficiency" readout on Kerbal Engineer to guide my ascent. I kept it as close to 100% as possible, figuring that this held me at optimal ascent speed (just fast enough to minimize fuel wasted on gravity, just slow enough to minimize fuel wasted on aerodynamic drag).

However if I do this in 1.0, I go so fast that I get REENTRY heating during ascent (which obviously means that fuel is wasted on drag).

What are the optimal ascent speeds now?

Link to comment
Share on other sites

That metric is no longer useful. Now you should go as fast as you can while not blowing up or flipping out of control. Or both.

I've found that 1.6 TWR (which was my benchmark in pre-1.0 stock atmo) is too much for me. 1.4 seems a lot better. I have a rocket that can get into orbit with less than 3300m/s of vaccuum dV and I think it's TWR starts at 1.4 exactly.

There is a far larger emphasis on finesse, now, and far less on punching hard and/or following the same formula for every single rocket.

Link to comment
Share on other sites

That metric is no longer useful.

Really? It's been working fine for me so far. Much more and I start to burn.

(btw, your asteroid glider is probably my favorite ksp creation. :D Top. Notch.)

Link to comment
Share on other sites

Just like with the old aerodynamic model, you can gauge whether or not you're hitting terminal velocity by the reentry effects appearing, so what I do is just use those as a gauge, gradually adjusting thrust while watching the flames to keep them as dim as possible (then, when they disappear, ramping up thrust ever so slightly until either maxed or the flames reappear).

It isn't the most scientific approach, but I've found that it still *generally* works for my various SSTOs (though the sooner you punch through the lower atmosphere and hit a good cruising altitude - just on the cusp of losing intake air - the better; this is different from the old model, where terminal velocity seemed to be higher for whatever reason, thus allowing one to spend more time at lower altitudes building speed). For rockets, you're pretty much in the clear and able to hit the gravity turn with reasonable (maybe not *quite* optimal, but I haven't measured yet) efficiency once you get past 11km; start full-thrust until you start seeing white, then back off until you're at that 10-11km mark (at which point ramp up the thrust again).

Most calculators probably haven't been adapted to the new physics model yet, so they're going to be off. Until then, "use the Force, Luke" and you'll be fine.

Link to comment
Share on other sites

IRL the terminal velocity speeds away from you too fast to follow, like the new aero, and as such isn't something you need to follow, unlike in legacy aero where the terminal velocity was soup-ish low. As others mentioned, rather pay attention to making a proper gravity turn to avoid wasting fuel on gravitational drag, and avoid going too fast and overheat.

Also, you can still travel at the most efficient velocity, i.e. terminal velocity, AND find yourself burning up. It's plasma.

Link to comment
Share on other sites

Really? It's been working fine for me so far. Much more and I start to burn.

(btw, your asteroid glider is probably my favorite ksp creation. :D Top. Notch.)

Sorry, by "that metric" I was addressing the OP's reliance on atmospheric efficiency. :) 1.8G is probably about what I'm at a bit after launch, considering I start at a 1.4 TWR and it goes up from there.

Link to comment
Share on other sites

is there any quick way of knowing rough TWR using the G meter?

i'm used to being a cheat and having mechjeb tell me my TWR(as well as limit speed to terminal velocity)

i started thinking that 1g would be twr of 1, but then science let me know that 1 g is standing still

Link to comment
Share on other sites

is there any quick way of knowing rough TWR using the G meter?

i'm used to being a cheat and having mechjeb tell me my TWR(as well as limit speed to terminal velocity)

i started thinking that 1g would be twr of 1, but then science let me know that 1 g is standing still

Right at launch, any TWR less than 1 and you feel just that 1 G from gravity. After that, you're accelerating + feeling gravity so you get G equal to TWR.

It gets more complicated once you're not going straight up (and once you're farhter from the surface and feeling less gravity) but that's the gist of it.

Link to comment
Share on other sites

I actually quite like the way we need to completely re-learn how we design and fly rockets. My next save will feel even more like a real space program as I need to test launch vehicles, gather data etc... how much dv to get to the moon? No idea! :)

Link to comment
Share on other sites

I'm loving having to relearn everything too. Just got to space for the first time. Again. And it was just as delightful as the first first time I got to space.

Right now I'm trying to use my vertical velocity to control my gravity turn. The rocket wants to tip faster if I'm going slower. So I launch at full throttle, start turning five or so degrees at 100m/s, and then let the rocket fall over and try to ride the throttle so that it's around 45 degrees at 10km altitude. And then from there throttle up a bunch, and try to stick to around 60 or so degrees at 20km. Those numbers will probably be tuned as I get the hang of the new atmosphere.

Link to comment
Share on other sites

I'm loving having to relearn everything too. Just got to space for the first time. Again. And it was just as delightful as the first first time I got to space.

Right now I'm trying to use my vertical velocity to control my gravity turn. The rocket wants to tip faster if I'm going slower. So I launch at full throttle, start turning five or so degrees at 100m/s, and then let the rocket fall over and try to ride the throttle so that it's around 45 degrees at 10km altitude. And then from there throttle up a bunch, and try to stick to around 60 or so degrees at 20km. Those numbers will probably be tuned as I get the hang of the new atmosphere.

This is very much what i found as well (including the glee of making orbit for the first time again ;) ). Slight alteration on my part: I aim for just over 30° at 10k and 45-50 at 20k. Once I hit 25k I pitch over more agressively.

Link to comment
Share on other sites

It seems that you want to do about what you did for FAR, maybe slightly more aggressively. My old "30 at 30" seems to work but not be *quite* as efficient as maybe "30 at 25" would be.

FYI "30 at 30" means you want to be aimed at the 30 degree marker (so over halfway to the horizon) when you Apoapsis (not your altitude) is 30km. I'm still testing, but it may be better to be aimed at the 30 degree mark when your apoapsis is at 25km.

Link to comment
Share on other sites

  • 2 weeks later...

Do any math nerds want to revisit this? I'll be honest I've been known to do some TWR and dV calcs but this gets above my pay grade. I've been feeling my way through the gravity turn but what about ascent speed? Any good Altitude/velocity benchmarks?

Link to comment
Share on other sites

Pardon the off topic... Mr. Horseman, have you tried flying your asterplane in 1.0.2 to see how that thing falls like a brick from hell fly? It could be fun! :D

No, but I tried it in FAR and learned enough to know not to bother. :D

Link to comment
Share on other sites

  • 3 weeks later...
I use KER. I've never been able to figure out what "atmospheric efficiency", was.

(All my atmosphere were quite efficient at being an atmosphere!)

Unless it has changed it was just a simple ratio of your velocity to terminal velocity expressed as a percentage.

Edited by lincourtl
Link to comment
Share on other sites

  • 2 years later...
On 28.04.2015 at 10:54 AM, ShunterAlhena said:

Pre-1.0 I used the "Atmospheric Efficiency" readout on Kerbal Engineer to guide my ascent. I kept it as close to 100% as possible, figuring that this held me at optimal ascent speed (just fast enough to minimize fuel wasted on gravity, just slow enough to minimize fuel wasted on aerodynamic drag).

However if I do this in 1.0, I go so fast that I get REENTRY heating during ascent (which obviously means that fuel is wasted on drag).

What are the optimal ascent speeds now?

Shunter, i may assume, Kerbin emulates Earth atmosphere by placing high temperature layer high enough. This is area, where highly energetic ionospheric electrons occur. Moving through the area at high speed leads to heat buildup due to fast absorption of electrons' kinetic energy. Stay at that height long enough, and you get warm anyway. Supersonic flight well below leads to significant relative heat buildup due to adiabatic compression of rushing air.

Link to comment
Share on other sites

Thread is too old,  the issue has changed with all revisions of atmo drag and thermal effects in KSP since then. Should a similar question arise with a current version of KSP, users should open a new thread instead. Locked.

Link to comment
Share on other sites

Guest
This topic is now closed to further replies.
 Share

×
×
  • Create New...