How to set mechjeb for launch to avoid excessive overheating in launch phase?

[Pawelk198604]

BTW this new update is really great I love to watch my kerbal smile when they're in orbit

[Harry Rhodan]

By not using to much engine power in the first place. Honestly if your first stage liquid engine can lift itself easily and still doesn't have enough juice to go alle the way to orbit just add more fuel and not solid  boosters. You can also save a lot of drag by not shaping your rocket like a mushroom. The 2.5m heat shield is more than enough for the 2.5m pod.

[Foxster]

What? Just...what?

[Pawelk198604]

19 minutes ago, Harry Rhodan said:

By not using to much engine power in the first place. Honestly if your first stage liquid engine can lift itself easily and still doesn't have enough juice to go alle the way to orbit just add more fuel and not solid  boosters. You can also save a lot of drag by not shaping your rocket like a mushroom. The 2.5m heat shield is more than enough for the 2.5m pod.

I would like to know how to program the mechjeb  to reduce acceleration during the ascent phase, I know that is possible to program it to reduce engine power in accordance too dynamic pressure. 

When I fly the rocket myself in career mode I usually feel it, and I rarely use  mechejb  for it because it requires a loot in tech development points  

[Atkara]

Haven't used MJ myself but, looking at the ascent guidance tab you had open for a while in that video, I'd try setting the acceleration limiter to 15m/s² (instead of it's current 40) if I was you.

Edited October 16, 2018 by Atkara

[Gargamel]

You can limit the acceleration, under the "limit acceleration" button, I leave mine at 20 m/s, but that's an old habit from a way old version, just never changed.

You can also limit Max Q. 

[Snark]

Moving to Add-on Discussions, since this is primarily about a mod.

Though it's worth noting that if you have a question about a particular mod, the best place to ask the question is usually in that mod's thread, since that's where the mod's expert users (and author!) tend to hang out, and therefore one of the most likely places to find answers. 

[Pawelk198604]

4 hours ago, Gargamel said:

You can limit the acceleration, under the "limit acceleration" button, I leave mine at 20 m/s, but that's an old habit from a way old version, just never changed.

You can also limit Max Q. 

But what value put for Max Q?

[shdwlrd]

Looks like a typical MJ launch to me. The only changes I would suggest is use the 2.5m decoupler and fairing base; get rid of the SBR's or at least put some nose cones on them. Also you can limit the thrust for the SBR's.

4 hours ago, Gargamel said:

You can limit the acceleration, under the "limit acceleration" button, I leave mine at 20 m/s, but that's an old habit from a way old version, just never changed.

You can also limit Max Q. 

You can to this, but using SBR's is going limit the effectiveness of the acceleration limiter since they can't be throttled.

[Gargamel]

19 hours ago, shdwlrd said:

You can to this, but using SBR's is going limit the effectiveness of the acceleration limiter since they can't be throttled.

With max Q, yes it gets a bit tricky.    But for max acceleration,  Set your thrust limiters on the SRBs down so that your TWR on the pad is at it's optimum amount, whatever that may be per your liking.   And then as you launch, the main engines will be slowly throttled back to maintain that acceleration setting.   Eventually, the main engines may shut off completely, but this only "adds" dV to that stage, as MJ sees it.  Hopefully by this point you'll be high enough that a little extra acceleration won't hurt, and it shouldn't last for too long.   You should pick SRB's that burn out around this point.   

I use this method on most of my launches.    Allows for the main engines to act as both the lifter, and orbital insertion engines.    With a little tweaking and practice, I will only have a few dV left after obtaining orbit; or more optimally, the main stage will drop off when my Pe is like 20km, so that they will de orbit and be recovered by the Stage Recovery mod, and there's only a bit of burn left to complete by the payload stage. 

19 hours ago, Pawelk198604 said:

But what value put for Max Q? 

The default is 20k, but I've had more success with 18k.    I don't use it that much on Kerbin, I get more use out of it on Eve.   it was either @Rocket In My Pocket or @ZooNamedGames or even @Geonovast who suggested the 18k previously, maybe they can expound on that....

[Geonovast]

Wasn't me.  I have no idea where max Q is.  I wouldn't mind knowing though!

[Rocket In My Pocket]

1 minute ago, Gargamel said:

The default is 20k, but I've had more success with 18k.    I don't use it that much on Kerbin, I get more use out of it on Eve.   it was either @Rocket In My Pocket or @ZooNamedGames or even @Geonovast who suggested the 18k previously, maybe they can expound on that....

I know just about zip when it comes to MechJeb. Can't imagine it was me, unless I heard it elsewhere and repeated it?

Just now, Geonovast said:

Wasn't me.  I have no idea where max Q is.  I wouldn't mind knowing though!

Same lol, what is max Q?

[Geonovast]

1 minute ago, Rocket In My Pocket said:

Same lol, what is max Q?

I know what it is, I just don't know where it is on Kerbin.

You need to watch more STS launch videos!

[Rocket In My Pocket]

2 minutes ago, Geonovast said:

I know what it is, I just don't know where it is on Kerbin.

You need to watch more STS launch videos!

Well...

Now I'm sure it wasn't me that said it lol.

[Foxster]

On 10/17/2018 at 4:29 AM, Pawelk198604 said:

But what value put for Max Q?

Whatever you need to stop a craft from burning up during ascent. On Kerbin its rarely needed unless you have too much engine and so your TWR is too high. 

On Eve with its soup-like atmosphere it can be essential and you may need to tweak down the max-Q to reduce aero-heating (and drag losses) until your craft can survive ascent. 

[ZooNamedGames]

18 hours ago, Rocket In My Pocket said:

Same lol, what is max Q?

Max Q is the point a rocket reaches the peak atmospheric resistance and the most force is exerted on it during launch. (Imagine stepping on a coke can, the foot being the atmosphere and the can being the rocket).

[Stoney3K]

Supposing you launch from Kerbin, acceleration limiter is your easiest friend here. If you put that at a modest 2g (which is 19m/s2) your engines will throttle back according to how much fuel they burnt during the ascent.

Your acceleration will be pretty much constant, and you have more control over your craft as opposed to launching at full blast with a high TWR which will restrict the craft to a trajectory of "straight up" because any steering is ineffective.

As an added advantage, launching with an almost constant acceleration means that your time to rendez-vous an existing spacecraft will always be roughly the same, regardless of payload or even craft mass, because the craft trajectory depends on acceleration only.

[Pawelk198604]

On 10/23/2018 at 2:19 PM, Stoney3K said:

Supposing you launch from Kerbin, acceleration limiter is your easiest friend here. If you put that at a modest 2g (which is 19m/s2) your engines will throttle back according to how much fuel they burnt during the ascent.

Your acceleration will be pretty much constant, and you have more control over your craft as opposed to launching at full blast with a high TWR which will restrict the craft to a trajectory of "straight up" because any steering is ineffective.

As an added advantage, launching with an almost constant acceleration means that your time to rendez-vous an existing spacecraft will always be roughly the same, regardless of payload or even craft mass, because the craft trajectory depends on acceleration only.

Thanks  

[Ruedii]

Don't put your engines too close together, and certainly don't clip engines together.

Second, you shouldn't need that much power to launch anyhow.   You need about 2.0-4.0 TWR for the first 20-40 seconds of launch followed by 0.5-1.5 TWR for the remainder.

Angle 5 degrees from horizon, lock to surface-forward and get your time to apoapsis to between 45s to 1m and hold it there until the apoapsis reaches the desired height (between 70.1km and 80km, really your choice).   After that, circularize at apoapsis and you are good.

p.s. Now I'm going to prepare to be called a heretic for suggesting you need less launch power.

Edited October 30, 2018 by Ruedii
closing joke.

[Pawelk198604]

New episodes of my Kerbal adventure