What are the baiscs of rocket design?

[John Doe]

What are the basic principles of rocket design, as to be able to accomplish orbit, etc. and, more importantly to avoid an Apollo 1 situation (i.e. blowing up on the pad), or a challenger situation (i.e. blowing up less than a minute after liftoff)? I also find that when I add an extra fuel tank / engine toward the top of the stack, immediately below the command module, that I have these sorts of problems, despite adding winglets to the extra fuel tank. (note that I'm running an early demo version of the program). 

[Hodari]

You don't really need to worry about Apollo 1 or Challenger type situations in this game since parts don't randomly fail(aside from bugs of course).  The three main things that will cause a part to actually fail are impact, overheating, or too much stress being placed on it.

Impact:  Obviously, make sure you don't hit the ground too hard.  For landing anyplace with an atmosphere, make sure you use enough parachutes and come in at a shallow enough angle to give the atmosphere time to slow you down so you can deploy them.  For other landings, use your engines to slow yourself down.  Landing legs are good once you get them or until then, you can use something like girder segments if you really need to.  The other main impact risk will be when staging.  Make sure you allow enough clearance between booster stages and the rest of the rocket, using the larger decouplers if needed.  Keep your rocket in stable flight while staging and not turning(even using autopilot to follow prograde marker).  Allow a couple seconds to make sure you've fully cleared the old stage before starting the engines for the next one if you can.

Overheating:  Mostly this is an issue during reentry, so again, make sure you come in at the right angle.   If you have plenty of fuel left over, you can also lower your apoapsis a bit first.  If you're really coming in fast(interplanetary missions espcially), you may also want to use aerobraking over several different passes through the atmosphere before doing your final reentry.  Other sources of overheating will be ISRU units and nuclear engines(use radiator panels for these) and some of the larger rocket engines(lower thrust levels or don't use them for too long at one time.

Stress:  Keep the shape of your rocket as aerodynamic as possible.  Use struts where needed(especially on the larger SRB's) to hold things in the right positions and stop them from bending too much.

Other than that, the main design principles are:

Keep your mass as low as possible.  Each kg of mass you add means more fuel that you need to bring.  And then more fuel to lift THAT extra fuel.  And so on.  And then possibly more powerful engines to lift all of that as well.

Use staging to keep that mass down by getting rid of mass(especially empty fuel tanks) as soon as it's no longer needed.

Keep your design symmetrical.

Start designing your rocket with the END of your mission and work backwards from there.  Figure out what you need to bring back to Kerbin first(crew capsule, heat shield, parachutes, any science experiment data etc) and design that stage first.  Then figure out the most efficient way to get that back from wherever your mission was going and build that stage.  Then figure out what you need in order to get THAT stage to where it needs to be and so on untol you get all the way back to your initial launch.  At each stage, make sure you will have everything you need(don't forget things like batteries and solar panels), but keep the mass down as much as possible.

Use the right engine for each stage as well.  In general, look for the highest specific impulse while still getting the thrust to weight ratio you need.  During launch, you probably want a TWR of around 1.5.  While in orbit or flying between planets, it doesn't matter as much, but if it's too low, your burns will take forever(had some with ion engines that were 20+ minutes) which isn't much fun and makes it much harder to time them properly.

Keep your center of mass forward.  This is mostly an issue when using the larger fuel tanks and trying to stack more than one on top of each other.  They'll use up fuel from the top one first and work down from there which is the opposite of what you want.  This means the rocket will start out fine and then about 10km up, the CoM has shifted far enough back that it will start to flip and become uncontrollable.  If this becomes a problem, either use radial attachment instead or split each tank into its own stage.

Using a mod like Kerbal Engineer Redux which shows the delta-v and TWR for each stage of your rocket as you are building it will be very helpful in allowing you to plan out your missions.  It's possible to calculate these values manually, but doing so every time you change anything will be a real pain, so using a mod will make the game much more fun.

And finally, save often and if something does go wrong, try to figure out what happened, go back, and fix it.

[John Doe]

1 hour ago, Hodari said:

You don't really need to worry about Apollo 1 or Challenger type situations in this game since parts don't randomly fail(aside from bugs of course).  The three main things that will cause a part to actually fail are impact, overheating, or too much stress being placed on it.

Impact:  Obviously, make sure you don't hit the ground too hard.  For landing anyplace with an atmosphere, make sure you use enough parachutes and come in at a shallow enough angle to give the atmosphere time to slow you down so you can deploy them.  For other landings, use your engines to slow yourself down.  Landing legs are good once you get them or until then, you can use something like girder segments if you really need to.  The other main impact risk will be when staging.  Make sure you allow enough clearance between booster stages and the rest of the rocket, using the larger decouplers if needed.  Keep your rocket in stable flight while staging and not turning(even using autopilot to follow prograde marker).  Allow a couple seconds to make sure you've fully cleared the old stage before starting the engines for the next one if you can.

Overheating:  Mostly this is an issue during reentry, so again, make sure you come in at the right angle.   If you have plenty of fuel left over, you can also lower your apoapsis a bit first.  If you're really coming in fast(interplanetary missions espcially), you may also want to use aerobraking over several different passes through the atmosphere before doing your final reentry.  Other sources of overheating will be ISRU units and nuclear engines(use radiator panels for these) and some of the larger rocket engines(lower thrust levels or don't use them for too long at one time.

Stress:  Keep the shape of your rocket as aerodynamic as possible.  Use struts where needed(especially on the larger SRB's) to hold things in the right positions and stop them from bending too much.

Other than that, the main design principles are:

Keep your mass as low as possible.  Each kg of mass you add means more fuel that you need to bring.  And then more fuel to lift THAT extra fuel.  And so on.  And then possibly more powerful engines to lift all of that as well.

Use staging to keep that mass down by getting rid of mass(especially empty fuel tanks) as soon as it's no longer needed.

Keep your design symmetrical.

Start designing your rocket with the END of your mission and work backwards from there.  Figure out what you need to bring back to Kerbin first(crew capsule, heat shield, parachutes, any science experiment data etc) and design that stage first.  Then figure out the most efficient way to get that back from wherever your mission was going and build that stage.  Then figure out what you need in order to get THAT stage to where it needs to be and so on untol you get all the way back to your initial launch.  At each stage, make sure you will have everything you need(don't forget things like batteries and solar panels), but keep the mass down as much as possible.

Use the right engine for each stage as well.  In general, look for the highest specific impulse while still getting the thrust to weight ratio you need.  During launch, you probably want a TWR of around 1.5.  While in orbit or flying between planets, it doesn't matter as much, but if it's too low, your burns will take forever(had some with ion engines that were 20+ minutes) which isn't much fun and makes it much harder to time them properly.

Keep your center of mass forward.  This is mostly an issue when using the larger fuel tanks and trying to stack more than one on top of each other.  They'll use up fuel from the top one first and work down from there which is the opposite of what you want.  This means the rocket will start out fine and then about 10km up, the CoM has shifted far enough back that it will start to flip and become uncontrollable.  If this becomes a problem, either use radial attachment instead or split each tank into its own stage.

Using a mod like Kerbal Engineer Redux which shows the delta-v and TWR for each stage of your rocket as you are building it will be very helpful in allowing you to plan out your missions.  It's possible to calculate these values manually, but doing so every time you change anything will be a real pain, so using a mod will make the game much more fun.

And finally, save often and if something does go wrong, try to figure out what happened, go back, and fix it.

The problem I seem to be having is that when I attempt to modify the stock model (The Kerbal 5) in a very simple way, by adding an extra fuel tank / engine assembly / winglets as its own stage in the rocket, (which I am adding just below the command module in the stack) Once I get it out to the pad, I get an apollo-1 situation in the sense of going BOOM right there on the pad, the second I light the first stage, OR i get the challenger effect- (i.e. going BOOM at less than a minute after liiftoff ) usually as a consequence of hitting the ground because the whole stack wants to to pitch / yaw so much that the direction of velocity ends up being horizontal and then DOWN. I wouldn't think that adding one extra stage  (adding about 20m or less  to the original 85m high stack) would change the center of mass, etc.

[Hodari]

In that case, hit f3 and see exactly WHAT part of it is blowing up first and why.  Probably either something wrong with your staging is causing an engine to fire into another part and overheat it, or there's a structural failure somewhere in which case you need to either redesign that section or add more struts to make it stable.

[Wemb]

1 hour ago, John Doe said:

The problem I seem to be having is that when I attempt to modify the stock model (The Kerbal 5) in a very simple way, by adding an extra fuel tank / engine assembly / winglets as its own stage in the rocket, (which I am adding just below the command module in the stack) Once I get it out to the pad, I get an apollo-1 situation in the sense of going BOOM right there on the pad, the second I light the first stage, OR i get the challenger effect- (i.e. going BOOM at less than a minute after liiftoff ) usually as a consequence of hitting the ground because the whole stack wants to to pitch / yaw so much that the direction of velocity ends up being horizontal and then DOWN. I wouldn't think that adding one extra stage  (adding about 20m or less  to the original 85m high stack) would change the center of mass, etc.

Well, firstly, design your rocket so it looks like other things that fly like that - i.e. arrows and darts. You put the heavy stuff at the pointy end, and put the fins/winglets at the back.

As for the rocket going 'boom' on the pad, this shouldn't ever happen unless you've done something very odd indeed with parts that aren't properly secured, or unless you're firing an engine that's somewhere in the middle of your rocket, rather than just the bottom stage - check your staging.

The pitching and yawing can be caused by several things - as I said, putting fins on the top of the rocket instead of the bottom won't help. Also, flying with no fins or insufficient fins will do this.  Also, flying too fast too soon can do this - don't accelerate too quickly low in the atmosphere - this will cause an instability to get worse, not better. Finally, keep your rocket pointed toward the prograde marker as much as possible when you fly through air - the more 'off-target' your point the rocket, the more likely it will be to go out of control. Try keeping, as much as possible, the rocket pointing in the same direction as it's travelling.  Sure you need to steer it, but small gentle corrections, not big turns.

Good luck!

Wemb

Edited April 25, 2016 by Wemb

[N_Danger]

To add to the advice given. 

When launching a rocket.

You should search the forums for Gravity Turn. This basically means after lift off when going around 50-100 m/s gently nudge the rocket over about 5 degrees. It should then, if designed well enough, fly it self to about 30 km up. Easier said than done I'll admit, you have to experiment over and over to find the sweet spot.

 Make sure you have fine control on. You get this by pressing the caps lock key by default. This will reduce the magnitude of the control inputs. Carefully use SAS if things get unstable but don't leave it on all the time at the beginning of the flight, it will mess up a good gravity turn.

Good Luck! Remember if you aren't blowing things up occasionally you aren't trying hard enough.

[cicatrix]

Make your rocket aerodynamic (yes, pointy and slim).

Make your rocket symmetric (at least in the beginning). There are buttons in the editor - show center of mass, show center of thrust - they must be aligned on the direction of travel.

Your construction should be strong - use struts to avoid vibrations and wobbliness. 

At liftoff the rocket flies slowly and aerodynamic fins do not help much - use a reaction wheel near CoM or several (turn SAS on).

If your rocket is overpowered (big thrust) you might experience heavy aerodynamic drag in the lower atmosphere. 

(Here's a great moment for installing KER) - Ideally, your TWR should be around 1.2-1.5. For upper stages it can even be less than 1.

Be careful when separating radial stages - they can collide with the rocket. Use sepratrons.

 

In flight - do not try to steer your rocket agressively. Actually you should do it several degrees at a time. Watch your prograde vector - if your nose points too far away from it your rocket can overturn, flip and disassemble in flight due to heavy aerodynamic drag.

KSP even as a simulator respects physics and though it forgives some mistakes the real life wouldn't it tries to model the physics pretty accurately, so consider the same forces that affect real rockets. 

 

[John Doe]

I'm thinking it might be a center of mass issue. My basic design is using a tri-coupler to construct a relatively Heavy and massive portion as a first stage, much like the first stage of the sat 5 rocket,  (three large tanks each with their own engine firing at once AND three SRBs , one attached to each tank, which is the only real odd thing about the stack, mind you removing the SRBs does not seem to make too much of a difference in flight. ) which makes up a little more than the total height of the the rocket. I've kept everything else  as slim as possible, looking loser to the top most stages of an saturn II-B (in its late form)  with my center of mass just a bit below the tri-coupler.  The center of thrust is a bit lower but vertically in line with the center of mass.  It seems that I am unable shift my center of mass upwards to account for the total length of the parts. The logs are showing that the SRBs are firing and then the main engines firing, just before i decouple the stability enhancers. most the time once I get up off the pad and have SAS on, the rocket once to pitch pointing the engines directly At me to where I'm travelling horizontally on the z axis as opposed to travelling vertically on the x axis. The resulting stack looks something like a Saturn II-B mounted to the massive bottom stage of the Saturn V. Its behaving as though its top-heavy, but yet my center of mass is quite low on the stack as a whole.

[N_Danger]

 Are you using struts at the bottom of the tri-coupled tanks by the engines to tie them together? When I have used Tri-Couplers in the past if I didn't do that things would flex all over the place at the bottom making the rocket uncontrollable. If you are doing that then try fins of some kind on the bottom by the engines.

Think of the rocket as a lever rotating around the current CoM. You will have aerodynamic forces trying to push one way at one end and you need some combination of fins, engine gimbal and sas pushing the other way at the other end to keep it in line.

[John Doe]

No, I'm not using anything but the tri-coupler with a decoupler sitting on top of it to seperate the whole tri-coupled section as a single stage, with the ability to decouple the SRBs once they burn out to decrease drag.  The only major structures below the tri-coupler are  the three (relatively large) fuel tank / engine assemblies with two sets of symmetrical winglets , symmetrically placed radial decouplers attached to these tanks  upon which the SRB's are placed symmetrically  as low as feasible on the stack, and the pyrotechnic stabilizers ( which are attached to the stack just above the 3  SRB's) to hold the rocket to the pad until both the SRBs AND the first-stage liquid engines are both fired up at full throttle. My aim is to make the 10,000 m mark with 2 minutes into the mission. A cross section of this looks much like a triangle with the apex of the triangle facing away from the tower. I've included screenshots of the stack without the launch stability enhancers attached.

 

Edited April 25, 2016 by John Doe

[Greenfire32]

Basics of rocketry eh? Pointy end up.

[ghpstage]

What do you mean its behaving as though its top heavy? That would generally be a good thing!

Having your drag centre above your CoM will cause it to want to fly back to front and it will try to turn itself upside down as a result The only thing that would stop it from doing so in such a situation is a whole heap of control authority.

You don't necessarily have to move your CoM upwards, theres a limit to how much you can do that due to parts and staging. What you can do instead is push the centre of drag downwards (we don't have a UI feature to seee this but CoL is a similar concept), add fins to the bottom, take unnecessary ones off the upper sections.

Edited April 25, 2016 by ghpstage

[John Doe]

By top heavy, I mean that it wants to pitch so much that I'm going straight along the z axis, which happens just after I go into the second burn at around 40,000 m, pointed at 45 degrees to the right. SAS will bring me back vertical and  then the next thing I know I get a nasty pitch. (and thats assuming I clear the tower in one piece due to much the same problem )  Here are the flight results.

[reapersms]

Most of this is some random guessing.

It looks like your fins on the upper stage are asymmetric, this will certainly make it pull toward the fins on the way up. They should probably be attached with 3x or 4x radial symmetry, and preferably as low on the stage as possible. You can probably ignore them for the topmost stage, you should be so far up that the fins will do almost nothing for you by then, and the pod should have enough torque to handle orientation.

You should probably stick a strut or two between the three columns of tanks below, to keep them from bending into each other. I could see them getting a little noodly at full thrust near the end, which is good for glorious fireworks, not so good for going to space.

What engines are you using? It looks like you've got 30's or 45's on the bottom stage, a 909 in the middle, and another 30 or 45 on the upper. My gut instinct would be to swap the 909 with the middle stage. A 909 with that much above it is not going to be particularly efficient for getting to orbit unless you're going almost completely sideways by the time you turn it on.

When are these stages dropping? 909's aren't going to be very worthwhile below ~10 km or so.

[John Doe]

The engines are 30s on the bottom stage.  The middle stage's engine is a 909 , with another 30 on the top stage. I'm thinking of switching to all 30's the whole way through. The thing is that I'm reaching around 40,000m around 2:30 or so. The bottom stage seems to be working well enough right up until its time for the first decoupling, by which point the velocity is around 500 to 600 m/sec. The velocity continues to climb as i fire up the 909 in the second stage, but for some reason will not stay on prograde, initially being off by left yaw. However, at least based on the indication of the nav ball, it will start to roll as i correct my prograde vector, and thus will accelerate me to a 201,000 m suborbital Ap with less than 30 seconds to drop the middle stage (which still has most of its fuel left by this point) aim on the prograde vector, and fire up the remaining 30 to attempt to accomplish orbital insertion. Problem is that by the time I manage to actually do all this I've passed the initial suborbital Ap and am about halfway back down and by this time have no chance of raising the Pe above the required 60,000 m or so required for orbital insertion. I'm also considering maybe switching the top most 30 with the 909 to try to solve this.  I've also found that letting the SRB's carry for about the first 400 to  800m  before firing up the three 30's in the bottom stage at full throttle tends to prevents the problem with the explosions that I was seeing. The problem seemed to be that the exhaust from the 30s in the bottom stage were blowing up the SRB's on the pad. I figured this out by pointing the camera view straight down on top of the nose cone prior to launch, watching the SRBs go BOOM in disbelief the second I fired up the 30s just seconds after the starting up the SRBs for liftoff.

[John Doe]

Well, going all 30's seems to work well, but for the fact that raising the Ap is still not happening fast enough, and my velocity at Ap is still much too fast, sending me into descent much too quickly before the Ap manages to raise enough to establish a high enough Pe. The stack, btw is 89m high.

Edited April 26, 2016 by John Doe

[N_Danger]

 Above 20 km the fins have very little effect. On your upper stages stick to SAS and/or engine gimbal for control for stages above that altitude. 

Edited April 26, 2016 by N_Danger

[reapersms]

That log isn't showing anything about the SRBs, the exhaust heat damage it's talking about is the 909 in the middle heating the stack decoupler above the tri-coupler.

Unless the radial decouplers holding the SRBs on are attached to the engine instead of the fuel tank, I don't think that could be cooking them. The SRBs themselves might be mounted high enough to cook the decouplers with their own exhaust though...

The caveat about the fins still applies. They don't look remotely lined up properly for anything. The yaw pull is probably the asymmetric drag (from only having them on one side of the rocket), and the attempts of manual control or SAS to correct for that is rolling it (also due to them only being on one side of the rocket, and not particularly well angled)

It sounds like you ascent path is probably not close to optimal either. If you're heading straight up, and then attempting to go prograde around apoapsis to boost into a circular orbit, that will be *exceedingly* wasteful, especially if you are trying t odump the second stage when your Ap hits your target, to circularize on the upper stage.

 

New suggestions:

Maybe adjust the vertical placement of the SRBs slightly to make sure they aren't cooking the decouplers, or getting cooked by the 30's -- I can't recall ever running into this sort of issue, but I haven't used SRBs much in a while.

Redo the fins on the middle and upper stages. Try one set on the middle stage, with 4-way symmetry on, and make sure they're lined up with the arrows on the decoupler. You probably don't need them for the upper stage. -- Fins on a rocket are good for two things, overall stability, which wants them as far back as possible, and general pitch/yaw control. The best way to get the control is 4 fins at 90 degree angles. Any other configuration is going to start trying to twist them in odd directions, resulting in strange pulls. You certainly want them symmetric around the center of the rocket, or it will throw the center of lift and center of mass off of the center of thrust, which will flip the rocket eventually. What happens the CoM moves further and further towards the fins as you burn off fuel, and at some point the force from the engine overpowers the torque from the fins or ASAS.

Switch the 909 and the middle 30. If control is still an issue, turn the 30 into a 45 (for engine gimballing, to give better control above 40km) -- the 909 is not a high thrust engine, but has very good efficiency in vac. The 30 & 45 have a lot of thrust, but aren't as good in a vacuum, and the 30 can't angle the thrust for extra attitude control.

Assuming you have good enough TWR, which I think you should, apply a *slight* bit of pitch eastwards (try 5-10 degrees at most) when you hit 70 m/s or so, and follow the surface prograde vector to 25 km or so. After 25km, switch the navball to orbital mode and point at that prograde. -- atmospheric drag ceases to be particularly significant after 10 km, the main issue is heating. Ideally you want to be angled such that the part of your thrust towards the ground just barely outdoes gravity (to keep the rocket going up), with the bulk of it pointing sideways (to spend as much of your lower stage fuel building orbital velocity as possible)

Around then, switch to map view, pull up the navball, and do your steering from there. If you want to be really efficient with it, try to fiddle with the throttle to keep your time to apoapsis around 40-50s, though keep it above 20% or so throttle. When it hits your target altitude, cut throttle, and blip it occasionally to deal with air drag. When done properly, this will result in a circularization burn of less than 100 m/s or so of delta-v. -- If you just go straight up, your orbit has an apoapsis of 200km, periapsis of -600 km. If you do a lot of sideways burning, you have an apoapsis of 80-100 km, and a periapsis of 20-40km. The first case you'll need to put 1500-2000 dV into it to round it out to something orbital, the latter will need 30-80.

You will probably have far more fuel left than you know what to do with, and the ride up will be a bit warm.

One last thing -- that ASAS probably quits working completely about 3 second after you shut off your engines. The reaction wheels in the asas and the pod both need electric charge to run, and I see no batteries or solar panels to provide it. The engines should generate enough to keep them running, but only when the engine itself is running.

[John Doe]

OK, I've found that with this slightly bigger rocket, I have to wait roughly until 25,000 m before executing the 45 degree yaw. This gives me a nice comfortable 3 minutes to Ap., though a very odd orbital path, with Ap at 3,063,772 m, and a Pe of only 104,458 m. The grey debris orbit was higher than any of the orbits I've managed to muster from the stock Kerbal 5, from which I developed from.

[John Doe]

And yes, I did address removing one of the pairs of winglets from the middle stage, moving a pair down to the bottom of the stage. The orbital view from near Ap is amazing, yet a bit uncomfortable considering its an orbital flight.

[John Doe]

49 minutes ago, reapersms said:

That log isn't showing anything about the SRBs, the exhaust heat damage it's talking about is the 909 in the middle heating the stack decoupler above the tri-coupler.

Unless the radial decouplers holding the SRBs on are attached to the engine instead of the fuel tank, I don't think that could be cooking them. The SRBs themselves might be mounted high enough to cook the decouplers with their own exhaust though...

The caveat about the fins still applies. They don't look remotely lined up properly for anything. The yaw pull is probably the asymmetric drag (from only having them on one side of the rocket), and the attempts of manual control or SAS to correct for that is rolling it (also due to them only being on one side of the rocket, and not particularly well angled)

It sounds like you ascent path is probably not close to optimal either. If you're heading straight up, and then attempting to go prograde around apoapsis to boost into a circular orbit, that will be *exceedingly* wasteful, especially if you are trying t odump the second stage when your Ap hits your target, to circularize on the upper stage.

 

New suggestions:

Maybe adjust the vertical placement of the SRBs slightly to make sure they aren't cooking the decouplers, or getting cooked by the 30's -- I can't recall ever running into this sort of issue, but I haven't used SRBs much in a while.

Redo the fins on the middle and upper stages. Try one set on the middle stage, with 4-way symmetry on, and make sure they're lined up with the arrows on the decoupler. You probably don't need them for the upper stage. -- Fins on a rocket are good for two things, overall stability, which wants them as far back as possible, and general pitch/yaw control. The best way to get the control is 4 fins at 90 degree angles. Any other configuration is going to start trying to twist them in odd directions, resulting in strange pulls. You certainly want them symmetric around the center of the rocket, or it will throw the center of lift and center of mass off of the center of thrust, which will flip the rocket eventually. What happens the CoM moves further and further towards the fins as you burn off fuel, and at some point the force from the engine overpowers the torque from the fins or ASAS.

Switch the 909 and the middle 30. If control is still an issue, turn the 30 into a 45 (for engine gimballing, to give better control above 40km) -- the 909 is not a high thrust engine, but has very good efficiency in vac. The 30 & 45 have a lot of thrust, but aren't as good in a vacuum, and the 30 can't angle the thrust for extra attitude control.

Assuming you have good enough TWR, which I think you should, apply a *slight* bit of pitch eastwards (try 5-10 degrees at most) when you hit 70 m/s or so, and follow the surface prograde vector to 25 km or so. After 25km, switch the navball to orbital mode and point at that prograde. -- atmospheric drag ceases to be particularly significant after 10 km, the main issue is heating. Ideally you want to be angled such that the part of your thrust towards the ground just barely outdoes gravity (to keep the rocket going up), with the bulk of it pointing sideways (to spend as much of your lower stage fuel building orbital velocity as possible)

Around then, switch to map view, pull up the navball, and do your steering from there. If you want to be really efficient with it, try to fiddle with the throttle to keep your time to apoapsis around 40-50s, though keep it above 20% or so throttle. When it hits your target altitude, cut throttle, and blip it occasionally to deal with air drag. When done properly, this will result in a circularization burn of less than 100 m/s or so of delta-v. -- If you just go straight up, your orbit has an apoapsis of 200km, periapsis of -600 km. If you do a lot of sideways burning, you have an apoapsis of 80-100 km, and a periapsis of 20-40km. The first case you'll need to put 1500-2000 dV into it to round it out to something orbital, the latter will need 30-80.

You will probably have far more fuel left than you know what to do with, and the ride up will be a bit warm.

One last thing -- that ASAS probably quits working completely about 3 second after you shut off your engines. The reaction wheels in the asas and the pod both need electric charge to run, and I see no batteries or solar panels to provide it. The engines should generate enough to keep them running, but only when the engine itself is running.

I should have to consider this. And HOW then would that 909 be heating ANYTHING up, when it wasn't burning, in the first place? (and mind you those run reports were from after I had addressed the SRB problem, which was caused by firing up the the bottom stage's 30s while I was still held down to the pad by the three Launch Stability enhancers, which I got rid of entirely, as I couldn't figure out how to get them to release After firing the SRBs but BEFORE firing the 30s.

[reapersms]

Did you not have it set to trigger in the same stage as the decoupler? What I see there is a decouple event, a few seconds of delay, then the heating messages. That looks a lot like the lower stage burning out, hitting stage to decouple, waiting a bit, and then throttling up or staging the middle stage engine. The middle stage would coast ahead a little bit, due to having less drag than the lower stage, but gravity would pull it back some, probably leaving it right at the edge of the heat effects for a second or so, which shows up in the log.

IIRC there isn't any meaningful throttle response lag for the stock engines, so you should usually just stage the launch clamps in the same group as the engines or SRBs for the first stage anyways. There are some mod engines that have a spool up delay where it is important to delay it a bit, but with stock you're just burning off SRB fuel (probably a good chunk of it for the fleas, they don't burn for very long) or cooking the launchpad.

It looks like you still have the fins set up like the tail end of a fighter jet. Is it still pulling in odd directions on the way up?

[John Doe]

3 hours ago, reapersms said:

Did you not have it set to trigger in the same stage as the decoupler? What I see there is a decouple event, a few seconds of delay, then the heating messages. That looks a lot like the lower stage burning out, hitting stage to decouple, waiting a bit, and then throttling up or staging the middle stage engine. The middle stage would coast ahead a little bit, due to having less drag than the lower stage, but gravity would pull it back some, probably leaving it right at the edge of the heat effects for a second or so, which shows up in the log.

IIRC there isn't any meaningful throttle response lag for the stock engines, so you should usually just stage the launch clamps in the same group as the engines or SRBs for the first stage anyways. There are some mod engines that have a spool up delay where it is important to delay it a bit, but with stock you're just burning off SRB fuel (probably a good chunk of it for the fleas, they don't burn for very long) or cooking the launchpad.

It looks like you still have the fins set up like the tail end of a fighter jet. Is it still pulling in odd directions on the way up?

The only thing its really doing that's all that odd or eccentric is wobbling in the sense that would give you the impression its gonna break in two between the tri-coupler and the decoupler attaching the first stage to the rest of the stack. (though this isn't too bad- was just a little disconcerting the first couple test runs, not knowing what to expect, and it actually appears to be pogo oscillations, to boot! ) but other than that it now seems to be pretty much behaving itself. I've found that I'm having to wait until around 35,000 m or so (about the time the first stage decouples from the stack in flight) to execute any turns, because if I turn before this, my acceleration is too great to have enough time to correct vector to burn prograde to raise the Ap/Pe. If I turn at the 10,000 m  mark, I'll end up raising Pe to around 50,000 to 60,000 max, and because the velocity is so great, I usually end up having to throttle up the engines and decouple them from the stack to avoid ending up planting it nose-cone first in Kerbin- impact crater and all.  But I find that it works fine to delay the turn by about 1.75 to 2 times the the standard turn altitude. Reason being is because by the time I'm getting ready to burn prograde to raise the AP, invariably my velocity will already be close to orbiting velocity, at somewhere in the neighbourhood of 1,000 m/sec.  what appeared to be causing the nasty handling was that extra set of wings that I pulled off the middle stage. Now that I've got this craft in basic workable condition. I also have tested with/without SRBs- and the SRB's are giving me enough thrust that they're probably what's getting my velocity as high as what it is, as the velocity drops by about 700 m/sec without the SRBs.

[John Doe]

I would say thanks to everyone for taking the time to help me out. The other space simulator I play doesn't really involve building a custom stack so much as flying NASA's  STS stack. This has been a radically different thing all together. The STS stack practically flies itself on its own, with autopilot doing most of the work of navigating to the propper vectors and controlling velocity. Most of the work then becomes taking the steps to decouple the stack at the right times, though the most challenging aspect of that has been landing the thing. I've yet to NOT belly flop the orbiter on the ground due to the velocity- around 1,000 m/sec on average at around 5,000 ft that you have to bring to practically zero within 5 seconds.

[cicatrix]

I may be late for the discussion, but have you used struts to tie the three stocks together at the bottom / middle? I think they wobble and this is what causing you trouble. If they're only attached to the tri-couple adapter it's no wonder that you're having difficulty with steering it.