asurob

Been away for a year and things have changed

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I decided to fire it up since the game was 1.0.5 and curious about what had changed. I updated it and was raring to get off the launch pad.

Except my rocket designs suddenly don't get into orbit :-(.  Okay that's no big deal I can use old reliable mechjeb which I had come to depend on like an old friend..

Except the latest version 2.5.5 doesn't seem to work with KSP.   Is there something I am just missing with mechjeb (rockets don't turn when getting to orbital heights)or am I borked?

Help me Obi-Jeb help me.

 

Thanks.

Edited by asurob

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The aerodynamics have changed quite a bit.  If you're rockets are flipping below 20-30km, try adding tail fins at the bottom.  A high TWR at launch will help get stabilization from the tail fins lower in the atmosphere.  The dV maps say you need 3200m/s to achieve orbit, but for my first tries I was using up about 4000 m/s.  

If your craft is tall and has tail fins at the back you will get a pretty stable gravity turn.  Launch without SAS on, and turn the rocket to about 95-90 degrees east right off the bat.  Aerodynamics low in the atmosphere will keep the rocket from falling over too quickly.  The rocket will turn horizontal naturally.  Once the rocket turns horizontal turn on SAS and keep it pointed parallel to the horizon.  You need to tweak your initial turn and thrust so that by the time you are horizontal your Ap is at least above 60 km, hopefully a little higher.  If it's at 60 you will probably still make it to orbit, but you'll spend a long time in the atmosphere (without time warp) before you can make a circulariztion burn.  

There's re-entry heat too.  The entry level capsule can survive re-entry without a heat shield if you drop your Pe to about 30-35 km from LKO.  Parachutes tear off a lot more easily, but you get a visual indicator for when they're safe to deploy.  The parachute icon in the staging menu will be red when its unsafe, yellow when its risky, and green when its safe.  Right clicking on the parachute will also tell you that info.  

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Thanks some good tips...I will play around with fins a bit.  I had heard they made heat an issue...something I need to pay attention to.  Most of my rockets get to about 20K and then start flipping...so what you say makes sense.  Back to tinkering :-).

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20 minutes ago, asurob said:

Thanks some good tips...I will play around with fins a bit.  I had heard they made heat an issue...something I need to pay attention to.  Most of my rockets get to about 20K and then start flipping...so what you say makes sense.  Back to tinkering :-).

Heat IS an issue (but not with most rocket launches).  Aerodynamics are an issue.  Re-entry is a big issue.  Plus just about all the parts have changed in the past year; you might recognise them but it's likely their stats have changed.  After a year, you're starting again, have to un-learn a lot of what you learnt about KSP design, construction and flight but at least you keep 'real-world' undertanding of orbital mechanics, etc.

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Your safest bet is to add fins to the back as you said.

Your payload should be inside a fairing to cut down on drag, and if its to wide compared to the rest of your rocket you will also create to much drag at the top of your rocket.

I personally haven't used ascent guidance for mechjeb since the update, I would assume it would work since its a critical feature.

 

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Mechjeb 2.5.4 and 2.5.5 are working great with 1.0.5 including ascent guidance (earlier versions did not).  Your problem must lie elsewhere

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Its my own opinion. You not even understand the KSP basic mechanism yet. The reading on your gameplay screen tell you everythings that you need to know (without meckjeb). Its just how far you can interpret them. Read the navball, read the altimeter.

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4 hours ago, Kerbol Macrosystems said:

The aerodynamics have changed quite a bit.  If you're rockets are flipping below 20-30km, try adding tail fins at the bottom.  A high TWR at launch will help get stabilization from the tail fins lower in the atmosphere.  The dV maps say you need 3200m/s to achieve orbit, but for my first tries I was using up about 4000 m/s.  

If your craft is tall and has tail fins at the back you will get a pretty stable gravity turn.  Launch without SAS on, and turn the rocket to about 95-90 degrees east right off the bat.  Aerodynamics low in the atmosphere will keep the rocket from falling over too quickly.  The rocket will turn horizontal naturally.  Once the rocket turns horizontal turn on SAS and keep it pointed parallel to the horizon.  You need to tweak your initial turn and thrust so that by the time you are horizontal your Ap is at least above 60 km, hopefully a little higher.  If it's at 60 you will probably still make it to orbit, but you'll spend a long time in the atmosphere (without time warp) before you can make a circulariztion burn.  

There's re-entry heat too.  The entry level capsule can survive re-entry without a heat shield if you drop your Pe to about 30-35 km from LKO.  Parachutes tear off a lot more easily, but you get a visual indicator for when they're safe to deploy.  The parachute icon in the staging menu will be red when its unsafe, yellow when its risky, and green when its safe.  Right clicking on the parachute will also tell you that info.  

Except that most of my larger, taller rockets flip below 20 km. This is WITH fairings. Ironically, shedding the fairing almost always seems to remedy the issue, and here I thought fairings were supposed to do the exact opposite of the results I get. And I do add fins at the back of the rocket, still that happens. In some cases I even use the larger fins and still no luck.

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9 minutes ago, Der Anfang said:

Except that most of my larger, taller rockets flip below 20 km. This is WITH fairings. Ironically, shedding the fairing almost always seems to remedy the issue, and here I thought fairings were supposed to do the exact opposite of the results I get. And I do add fins at the back of the rocket, still that happens. In some cases I even use the larger fins and still no luck.

This. Removing the fairings seems to always work out for the better.

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9 minutes ago, Dizzle said:

This. Removing the fairings seems to always work out for the better.

Yeah... no idea. Even with pencil thin payloads under pencil thin fairings, the issue seems to just pop up almost every time. Although most especially with larger, wider fairing payloads. I read that wider fairings tend to create more drag, but if that's the case, it doesn't explain why my thinner fairings sometimes have that issue as well... maybe it's o longer a matter of gravity turning at 10 km, but perhaps later?

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The fairings do seem to cause random lift. I switched to Procedural Fairings and it works fine. 

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5 hours ago, asurob said:

I decided to fire it up since the game was 1.0.5 and curious about what had changed. I updated it and was raring to get off the launch pad.

Except my rocket designs suddenly don't get into orbit :-(.  Okay that's no big deal I can use old reliable mechjeb which I had come to depend on like an old friend..

Except the latest version 2.5.5 doesn't seem to work with KSP.   Is there something I am just missing with mechjeb (rockets don't turn when getting to orbital heights)or am I borked?

Help me Obi-Jeb help me.

The current version of MJ works just fine in 1.0.5.

However.......

The stats of all the old engines you're familiar with have changed, sometimes considerably.  All of them (mass, thrust, ISP).  Many new engines have been added.  Aerodynamics are now a thing (long, skinny rockets with tail feathers), as is re-entry heating (so heat shields), so you can't use the same launch profiles as before.  You need a gradual curve all the way up instead of the old "vertical to 10km, 45^ to 30km, horizontal thereafter" thing.  But on the plus side, it now only takes about 3500m/s to reach LKO instead of 4500.  Just keep your TWR at or below 2-2.5 until you're up in the stratosphere.  And forget aerocaptures at Jool, Laythe, and Eve, or even returning from thence to Kerbin.  Duna's the only place that works reliably these days.  So bring enough fuel to capture on thrust alone, or learn to use Tylo to gravity-break you into Jool orbit.

Hmmm, let's see, what else?  Nuclear engines now produce gobs of unrealistic heat so require adding unrealistic radiators to your ship.  Air-hogging for SSTOs is so dead that you now hardlky need any intakes at all, and the jet engines;' thrust will just fall off the table at about 23km long before they run out of air.  This means that SSTOs will need nearly 2000m/s or rocket fuel just to reach LKO, let alone do anything useful once there.  So no more itty bitty SSTOs, they're all flying fuel tanks, especially if they carry more than just 1 pilot.

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21 hours ago, Der Anfang said:

Except that most of my larger, taller rockets flip below 20 km. This is WITH fairings. Ironically, shedding the fairing almost always seems to remedy the issue, and here I thought fairings were supposed to do the exact opposite of the results I get. And I do add fins at the back of the rocket, still that happens. In some cases I even use the larger fins and still no luck.

Where is your CoM in relation to your stable rockets?  If it's really low you might need to put small control surfaces up top. Control surfaces need to be as far as possible from the CoM to have their best effect.

 

If it's really high up you might not be "balancing" on the CoT. Early on in the flight your rocket needs up be able to up. Instead of standing up on the ground it's now standing up on a giant pillar of fire. Just like on the ground, if the CoM gets past its supports  (aforementioned fire) it falls over. There are a couple ways to treat this. 

You can reduce your pitch-over angle. This keeps the CoM over the CoT. Adjust thrust as you climb so that you don't waste all your fuel going vertical. 

Start your pitch over later. Your rocket won't have a preferred attitude once the atmospheric forces become negligible

Make your booster base wider. This works just like making a wide base for a building. A building of highly explosive rocket fuel. 

Use radial engines in the atmosphere.  Attaching your boosters higher might also do the trick. If you can get to CoT above the CoM then your rocket is basically hanging off of the engines instead of balancing over them. Getting the CoT closer to the CoM will still help. It will make the lateral travel of your thrust base smaller for every degree of pitch over. 

This could also be speed related. I'm not great with that, but the aero forces overlay (F11?) Might tell you something. If that's the case the plane/SSTO guys will have better advice. 

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