I'm having a bad time.

[KerBlam]

This title is extremely dramatic. I'm having mixed (read: zero) success getting an early career(complete 4th tier)craft into LKO with enough dV to rescue some kerbals. I'm pretty good at rendezvous being able to get within 1km of anything in a couple of burns. My problem is I'm not getting enough speed in atmosphere so my circularisation burn is too long and it's using most of my dV. I'll post a screen of my craft when I get back to my pc.

I've watched Manley explain the gravity turn, and I'm following that notion, though my craft seems to want to head for the horizon at about 15k and while I can stand the craft up, it won't turn up. I.e massive side slip but it remains stable. 

Any ideas? Again I will post screenies when I can.

[KerBlam]

 

I realise the TWR at launch is high, but it's only when that 1st SRB is firing, which isn't for long. Also I used to have 2 KerbCans at the top, my plan was to rescue both Kerbals in one trip, but it was unstable and kept wanting to go backwards.

[Bandus]

@KerBlam While I am no means an expert, this is the type of ship I would build to rescue 2 kerbals from LKO: https://www.dropbox.com/s/pwgywcafbntc37h/Kerbal%20Rescuer.craft?dl=0

I am pretty sure all of the tech on it is from within the first 4 tiers, however, you may need to make minor adjustments to things like the wings used at the bottom and the radial parachutes used at the top.

Might I also recommend you read the following threads that may help you greatly?

http://forum.kerbalspaceprogram.com/index.php?/topic/128838-how-to-build-a-rocket-ship-for-a-mission/

and

http://forum.kerbalspaceprogram.com/index.php?/topic/122488-rules-of-thumb-for-building-cheap-and-cheerful-rockets/
 

Also, you might want to request this thread be moved to Gameplay Questions and Tutorials. Best of luck!

Edited January 8, 2016 by Bandus

[swjr-swis]

TWR of the last stage is a bit low if that's the one that burns at 15km, total dV appears enough to make it with room to spare, unless the MJ read out is wrong.

The ascent profile may be your issue: you should definitely not be horizontal at 15km yet, if anything it should be more like 45 degrees at that point considering the less than 1 TWR of that last stage. You don't mention if you're using MechJeb's ascent guidance.

Assuming manual control, you can give yourself a more repeatable experience so you can find an optimal profile: pre-lean your rocket about 5 degrees east by using the rotate gizmo on the core part. Engage SAS on the default stabilize, stage and lift-off, and switch to follow prograde only once you have built up a bit more speed, maybe around 100m/s. Let gravity guide the rest of the turn hands-off. If you're still flattening too low, build up more speed before engaging follow prograde.

Alternatively: test whether MechJeb's ascent guidance can bring it up to orbit. If MJ ends up way short as well, that low TWR last stage may be the limiting factor. If however MJ can do it, at least you know there is a working solution and you just need to run a few more manual 'simulations' to perfect it.

[Aethon]

I don't speak Mechjeb, but if I'm reading it right, 2976 atmospheric dv is a little low for a rescue.  Just making orbit is about 3250 m/sec.  I'm also not familiar with those fuel tanks and I can't tell what engine is under your main stack.  I would advise adding more fuel.  

As far as the gravity turn goes, try and keep your time to apoapsis between 45 - 55 seconds, either with throttle control or turning ahead of your prograde marker.  It's kind of tough to diagnose without actually seeing your launch.  

Hope this helps and good luck

[FullMetalMachinist]

Also, I notice that you have what looks like struts going from stage-to-stage. Ever since the great joint strengthening of 0.25* that sort of thing isn't really necessary, except for extremely large and wobbly rockets. All those struts are adding a ton of drag, while not contributing a whole lot to your stability. 

* I think, might have been 0.23

[swjr-swis]

4 minutes ago, Aethon said:

I don't speak Mechjeb, but if I'm reading it right, 2976 atmospheric dv is a little low for a rescue.  Just making orbit is about 3250 m/sec.

The dV numbers usually spoken of for getting to LKO are the vacuum numbers, and 4000+ should be plenty with room for inefficiency or corrections.

[KerBlam]

At this stage of career I don't have access to mechjeb ascent assistance so it is all manual, and honestly I would prefer not to use it unless absolutely necessary, and then I feel like the game is taken away from me. I miss the fun playability of 0.90.

I'm going to have to start from scratch with this vessel I can tell, as adding more fuel is not really an option without lowering TWR even further. It's too slow already so I can't see that adding fuel will fix that issue. About my only option that will probably be worthwhile is picking a better launch window so I don't need to spend as much dV catching up to the target. I don't have access to any more powerful engines... Why the hell are they making this so difficult? Is KSP just for the realists and math nerds now? 

The final stage engine is a terrier, before that it's swivel and before that is Reliant with hammer SRBs just to kick it off the pad.

I'll try extend the gravity turn to 45 degrees at 15k but I feel it may be difficult.

 

 

Edited January 8, 2016 by KerBlam

[Bandus]

2 minutes ago, KerBlam said:

At this stage of career I don't have access to mechjeb ascent assistance so it is all manual, and honestly I would prefer not to use it unless absolutely necessary, and then I feel like the game is taken away from me. I miss the fun playability of 0.90.

I'm going to have to start from scratch with this vessel I can tell, as adding more fuel is not really an option without lowering TWR even further. It's too slow already so I can't see that adding fuel will fix that issue. About my only option that will probably be worthwhile is picking a better launch window so I don't need to spend as much dV catching up to the target. I don't have access to any more powerful engines... Why the hell are they making this so difficult? Is KSP just for the realists and math nerds now? 

 

 

I legitimately wondered the same thing and while there is nothing wrong with using MechJeb, I can also tell you from my personal experience that it isn't a requirement. 

That said, I strongly recommend at least adding in http://forum.kerbalspaceprogram.com/index.php?/topic/17833-104-kerbal-engineer-redux-v10180/. It works fine even though it indicates version 1.0.4 and it honestly helped me understand rocket building in KSP more than any other mod I've used.

Also, regarding the ship I posted above, was that outside your tech requirements?

[KerBlam]

4 minutes ago, Bandus said:

Also, regarding the ship I posted above, was that outside your tech requirement

Not sure I'm afk at the moment but I will surely have a look. Thanks 

24 minutes ago, FullMetalMachinist said:

Also, I notice that you have what looks like struts going from stage-to-stage. Ever since the great joint strengthening of 0.25* that sort of thing isn't really necessary, except for extremely large and wobbly rockets. All those struts are adding a ton of drag, while not contributing a whole lot to your stability. 

* I think, might have been 0.23

The rocket was very wobbly before I added the struts. 

[swjr-swis]

15 minutes ago, KerBlam said:

At this stage of career I don't have access to mechjeb ascent assistance so it is all manual, and honestly I would prefer not to use it unless absolutely necessary, and then I feel like the game is taken away from me. I miss the fun playability of 0.90.

Understood and respected. Notice that I didn't bring up MJ's ascent guidance as 'the solution'. I just offered you to do a quick test, a pre-launch simulation if you will. The instructions before that are for a manual ascent.

[KerBlam]

2 minutes ago, swjr-swis said:

Understood and respected. Notice that I didn't bring up MJ's ascent guidance as 'the solution'. I just offered you to do a quick test, a pre-launch simulation if you will. The instructions before that are for a manual ascent.

Thanks. I'm not giving up so I'll keep you posted. 

[maceemiller]

As for your launch window, I normally go I into map mode and wait until the craft I am going to rendezvous with is nearly over the launchpad and then take off. With practice, by the time youve circularised your orbit you can be very close to rendezvouing immediately.  Hope it helps.

[FullMetalMachinist]

15 minutes ago, KerBlam said:

The rocket was very wobbly before I added the struts. 

In that case, might I suggest the Kerbal Joint Reinforcement mod? Honestly, since they changed the areo model in 1.0 the drag from struts can be murderous. I really think they are doing you more harm than good. 

[Bandus]

6 minutes ago, FullMetalMachinist said:

In that case, might I suggest the Kerbal Joint Reinforcement mod? Honestly, since they changed the areo model in 1.0 the drag from struts can be murderous. I really think they are doing you more harm than good. 

I also think KJR is invaluable!

[KerBlam]

I used to use KJR but it led to problems with docking ports not being able to undock. Has that been resolved?

[FullMetalMachinist]

4 minutes ago, KerBlam said:

I used to use KJR but it led to problems with docking ports not being able to undock. Has that been resolved?

Yes, that bug is listed as fixed in the cangelog in the OP for KJR for KSP v1.0.5

[Ehco Corrallo]

16 minutes ago, Bandus said:

I also think KJR is invaluable!

I'll second (third) this statement. KJR is especially helpful with tall rockets (like yours). 

57 minutes ago, KerBlam said:

Is KSP just for the realists and math nerds now? 

Not with Kerbal Engineer Redux. Someone else already has recommended it here, but it's worth mentioning again. KER basically does the math so you don't have to. It's incredibly helpful if you need to put more thought into your rocket. It also helps when people ask, "Well how much Delta Vee do it have?"

[Norcalplanner]

I'd echo those suggesting KJR.  It really ought to be stock.

I see a few issues with the design:

1) All the struts create a bunch of drag, which is slowing down your ascent and probably exacerbating any latent stability issues.

2) The TWR jumps down to 1.30 after the Hammers burn out, which is too low for that point in the ascent.  A gravity turn in KSP needs to have TWR increasing for at least 50 or 60 seconds before ratcheting down to something lower.  The next two stages also have a very low TWR.  I've found that the first 2,500 to 2,700 m/s need to be at a TWR significantly above 1.

3) I also don't quite understand how your last stage with a Terrier has so little power.  If you put a Terrier and an FLT-400 beneath a Mk1 capsule, you should have several thousand m/s of delta V and a TWR well above 1.  What are you carrying up top that's so massive?

Ideas and potential solutions:

First, cut out any extra weight from the top of the rocket.  Empty monoprop in the capsule, empty most of the ablator from any heat shield, see if you can lose a parachute, etc.  An upper stage powered by a Terrier should have at least 2,000 m/s of delta V.

Next, install KJR and remove all the struts. Also, relocate the fins so that they are on the cardinal directions of the rocket - it will make the gravity turn, as well as any other steering in atmosphere, much easier.

Lastly, if you've unlocked the Terrier, you've likely also unlocked the Thumper.  Consider ditching the radial stacks you have (Hammers and Reliants) and adding two or four Thumpers on radial decouplers instead.  Have them fire at the same time as the Swivel in the middle.  Put enough fuel on the Swivel for it to burn for at least two minutes.  Thrust limit the Thumpers in the VAB for an initial TWR of 1.3 to 1.4 or so, making sure that the TWR after they detach is at least 1.2.

Also, relocate the fins so that they are on the cardinal directions of the rocket - it will make the gravity turn, as well as any other steering in atmosphere, much easier.

Good luck!

[KerBlam]

31 minutes ago, Norcalplanner said:

I'd echo those suggesting KJR.  It really ought to be stock.

I see a few issues with the design:

1) All the struts create a bunch of drag, which is slowing down your ascent and probably exacerbating any latent stability issues.

2) The TWR jumps down to 1.30 after the Hammers burn out, which is too low for that point in the ascent.  A gravity turn in KSP needs to have TWR increasing for at least 50 or 60 seconds before ratcheting down to something lower.  The next two stages also have a very low TWR.  I've found that the first 2,500 to 2,700 m/s need to be at a TWR significantly above 1.

3) I also don't quite understand how your last stage with a Terrier has so little power.  If you put a Terrier and an FLT-400 beneath a Mk1 capsule, you should have several thousand m/s of delta V and a TWR well above 1.  What are you carrying up top that's so massive?

Ideas and potential solutions:

First, cut out any extra weight from the top of the rocket.  Empty monoprop in the capsule, empty most of the ablator from any heat shield, see if you can lose a parachute, etc.  An upper stage powered by a Terrier should have at least 2,000 m/s of delta V.

Next, install KJR and remove all the struts. Also, relocate the fins so that they are on the cardinal directions of the rocket - it will make the gravity turn, as well as any other steering in atmosphere, much easier.

Lastly, if you've unlocked the Terrier, you've likely also unlocked the Thumper.  Consider ditching the radial stacks you have (Hammers and Reliants) and adding two or four Thumpers on radial decouplers instead.  Have them fire at the same time as the Swivel in the middle.  Put enough fuel on the Swivel for it to burn for at least two minutes.  Thrust limit the Thumpers in the VAB for an initial TWR of 1.3 to 1.4 or so, making sure that the TWR after they detach is at least 1.2.

Also, relocate the fins so that they are on the cardinal directions of the rocket - it will make the gravity turn, as well as any other steering in atmosphere, much easier.

Good luck!

Great answer I will try all of this and post results.

[Streetwind]

While you are at it:

The radial decouplers on the liquid side boosters should be linking the bottom tank of said boosters to the main stack. And you should build tanks on top of that - as opposed to connecting the top tank and adding further tanks below. The reason is that the rocket engine is the object generating a force on the radial joint, and the further the rocket engine is from the decoupler, the more of a lever arm it has. You probably saw the radial boosters flailing around while under thrust with no struts to stabilize them - this is precisely because the radial decoupler is way too far from the engine. If it was on the bottom tank, you'd see no booster flailing even without struts, which greatly saves on drag.

Hope this helps!

[KerBlam]

11 minutes ago, Streetwind said:

While you are at it:

The radial decouplers on the liquid side boosters should be linking the bottom tank of said boosters to the main stack. And you should build tanks on top of that - as opposed to connecting the top tank and adding further tanks below. The reason is that the rocket engine is the object generating a force on the radial joint, and the further the rocket engine is from the decoupler, the more of a lever arm it has. You probably saw the radial boosters flailing around while under thrust with no struts to stabilize them - this is precisely because the radial decoupler is way too far from the engine. If it was on the bottom tank, you'd see no booster flailing even without struts, which greatly saves on drag.

Hope this helps!

Again. Good advice I will try implement.

Next Q. Can someone please link me to KJR that's compatible with 1.0.5 because I can't find it on curseforge.

Edited January 8, 2016 by KerBlam

[r4pt0r]

your numbers confuse me. I just keep tweaking the design until it works.

[Streetwind]

11 minutes ago, KerBlam said:

Next Q. Can someone please link me to KJR that's compatible with 1.0.5 because I can't find it on curseforge.

A good start is to look for the mod's forum thread here on the KSP forums. Since all KSP mods are required to declare some sort of license, you'll find almost no mods that don't have a forum thread, if only for that reason. And google finds them reliably.

The reason you can't find it on Curse is because it doesn't appear to be on Curse. Some modders were dissatisfied with Squad choosing Curse as the official mod repository and simply don't use it. A community-built alternative called KerbalStuff manifested, and you'll find a lot of mods there. KJR also uses KerbalStuff as its primary mirror.

There's also CKAN, a community-maintained mod manager that can download and install mods for you and automatically checks for incompatibilities. It isn't perfect, and doesn't recognize all mods under all versions, but for a lot of people it's the preferred method of modding KSP.

Edited January 8, 2016 by Streetwind

[Norcalplanner]

Yep.  Direct link to KerbalStuff KJR is here: https://beta.kerbalstuff.com/mod/53/Kerbal%20Joint%20Reinforcement