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Will I Ever See Space Again? (Rocket Launch Issues)


Bandus
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Pre-KSP 1.0 I had no problem at all, at the very least, getting ships into orbit. It was the easiest part of the flight for me. Now, however, something has gone awry and I'm not quite sure what it is. Basically, when I try to launch a rocket (a design I've used successfully in the past), whenever I start to angle it to begin to gain horizontal velocity it continues the maneuver, uncontrollably, until it flips and points completely upside down. I checked COM, because I have a sneaking suspicion it is related to this, however it is just about in the center of the rocket which I thought was, more or less, the proper place for it.

I am really at a bit of a loss as to why the rocket is flipping over. Any thoughts/help would be appreciated.

2015-10-06%2012_54_12-Kerbal%20Space%20Program.png?dl=0

Edited by Bandus
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In the new aero model, you're almost required to have fins at the bottom of the rocket for stability. Your previous designs probably don't have them.

Also, make sure you cover anything aerodynamically "dirty" at the top of the rocket with fairings, and keep weight as far towards the nose as possible.

You can't go straight up to 8k and tilt way over anymore, either. Start your gravity turn at about 50-70m/s by tilting over 2-3 degrees, and then follow the prograde marker. Pointing your rocket outside of the prograde circle too low in the atmosphere (below about 35km) will often result in RUB-ing. (rapid unplanned backwardness)

Slowing down a bit lower in the atmosphere can help, too.

Edited by SpeedDaemon
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Perhaps you need to angle it less? When I launch I usually pitch it over just a few degrees once its reach 100 m/s or so, then I let it follow the prograde marker at least until its above the bulk of the atmosphere. Also you may want to reduce the amount of gimbal on your engines so your pitch input doesn't result in a too rapid rotation of the vehicle.

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(a design I've used successfully in the past)

Here is your mistake, i think.

Lots of things changed since 0.9, don't try tu reuse older designs. Try to make a new, simple design.

Oh, and as SpeedDaemon said, use fins at the bottom of the rocket.

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I have seen space again! Thank you for the rapid answers.

I had fins on it, but I moved them down the rocket further. I think the primary problem was how I was attempting to ascend and roll. I was still trying to do a rapid gravity turn at around 10k...also 100% thrust...

Less thrust, a more conservative turn, as suggested, resolved my problem. Thank you again!

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Fins + earlier, but slower pitching.

If your rocket is stable enough (ideally), you should be able to launch, get a bit of speed (50-100m/s as others have said) pitch over 5 degrees, wait a second or three to stabilize then turn off SAS and let gravity and drag turn you over. Use the throttle to keep under 300m/s below 5km and then to control your AP.

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I have seen space again! Thank you for the rapid answers.

I had fins on it, but I moved them down the rocket further. I think the primary problem was how I was attempting to ascend and roll. I was still trying to do a rapid gravity turn at around 10k...also 100% thrust...

Less thrust, a more conservative turn, as suggested, resolved my problem. Thank you again!

Congrats! Don't forget to mark the thread as answered.

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Like others have said, the aerodynamics have come a long way from the early days. Fins actually matter now. Nose cones help reduce atmospheric drag, etc. Make sure you are using engines with Thrust Vectoring while in the atmosphere because that increases responsiveness and reduces the tendency for it to tip. Also, pay attention to center of mass and how fuel is expended while ascending because many designs can become especially top heavy as they ascend. (Again, depends on how you built the vehicle.)

It's especially true that going WOL (wide open throttle) while ascending not only generates excessive heat (if your TWR is high enough) but it makes it a lot harder for Reaction Wheels, Thrust Vectoring, SAS to keep the launch vehicle on it's current heading. So bringing down your throttle a little may also provide a more stable ascent and gravity turn.

Finally, with all the aerodynamic changes, a lot of us stopped the usual "gravity turn at 10k" method. It's just fine to start your gravity turn at 1k and slowly get to 45 degrees by 10k and then maintain that until you reach your target apoapsis.

Oh, and never forget to check for wobbling or anything weird like that. Struts and more struts. Just had to throw that out there because a spacecraft noodle like to flop over and do all sorts of crazy things.

I hope some of this helps!

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Like others have said, the aerodynamics have come a long way from the early days. Fins actually matter now. Nose cones help reduce atmospheric drag, etc. Make sure you are using engines with Thrust Vectoring while in the atmosphere because that increases responsiveness and reduces the tendency for it to tip. Also, pay attention to center of mass and how fuel is expended while ascending because many designs can become especially top heavy as they ascend. (Again, depends on how you built the vehicle.)

It's especially true that going WOL (wide open throttle) while ascending not only generates excessive heat (if your TWR is high enough) but it makes it a lot harder for Reaction Wheels, Thrust Vectoring, SAS to keep the launch vehicle on it's current heading. So bringing down your throttle a little may also provide a more stable ascent and gravity turn.

Finally, with all the aerodynamic changes, a lot of us stopped the usual "gravity turn at 10k" method. It's just fine to start your gravity turn at 1k and slowly get to 45 degrees by 10k and then maintain that until you reach your target apoapsis.

Oh, and never forget to check for wobbling or anything weird like that. Struts and more struts. Just had to throw that out there because a spacecraft noodle like to flop over and do all sorts of crazy things.

I hope some of this helps!

Absolutely good advice. Once I stopped putting the throttle to full, right from launch, things immediately became easier. Also, as KerBlammo said earlier, reducing the gimbal on all the engines to 50% helped too. I was able to launch with 100% gimbal, but it was far more touchy that way.

Community of KSP is still awesome and I greatly appreciate that as a returning player!

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Absolutely good advice. Once I stopped putting the throttle to full, right from launch, things immediately became easier. Also, as KerBlammo said earlier, reducing the gimbal on all the engines to 50% helped too. I was able to launch with 100% gimbal, but it was far more touchy that way.

Community of KSP is still awesome and I greatly appreciate that as a returning player!

You don't and won't need to touch gimbal limits (I never have on my successful rockets). Simply lock the upper few tanks so fuel is taken from the bottom stack and thus keeping the rocket top heavy (which is good).

OR simply use "fine" control mode by pressing CAPSLOCK. This should turn the "+" needles green and vice versa if you hit CAPSLOCK again (beware: there is a bug that sometimes if you ALT-tab or do some menu stuff, the fine control mode will work in the opposite way no biggy though, just alt tab and turn CAPSLOCK the other way and it'll go back to normal). This way you limit how quick your rocket responds. This works with any control method (RCS, reactionwheels, fins, space plane control surfaces, etc.)

I'm no expert and each flight profile I have is wildly different, but I typically go for slow deliberate pitchover after I reach a couple of KM up. Though I have noticed that from rocket to rocket, some just never want to 'hold' where you move the nose while in the atmosphere and you'll spend some time fighting it to keep it pointed the way you want. In that case, I just let it reach a higher altitude and try to pitchover again. Once your CoM is in control (locking the upper tanks until you drain the lower ones, or your rocket stages in a way to do this) and you're in the thinner atmosphere, you shouldn't flip much at all. Space planes are another story though. :)

Once I figured out the 'issue' I almost never need fins. Especially now that I mostly launch 2.5m cargo/capsules using the 3.5m engines, quad nozzle (Mammoth?) or the single nozzle one (Rhino?).

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Not sure about other people, but I used to always have SAS on pre 1.0, but now I never have it on during ascent. It tends to overcompensate and throw my heading around, while leaving it off lets the atmosphere keep me pointed mostly prograde.

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Not sure about other people, but I used to always have SAS on pre 1.0, but now I never have it on during ascent. It tends to overcompensate and throw my heading around, while leaving it off lets the atmosphere keep me pointed mostly prograde.

There is some truth to this. I find that having SAS on can often cause wobble or instability in a certain longer/complex rocket, making it impossible to hold your heading, while in others it is needed to keep the rocket pointed steady. I suppose it all depends on the design.

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Sadly, I still seem to be having trouble. Earlier in the thread, the explanations I received helped. Then I attempted to build a similar rocket and nothing seems to be working again. Clearly there is something I am missing so I've decided to post both .crafts and I am hopeful people can tell me if it is a design issue, etc. I greatly appreciate the info!

https://www.dropbox.com/s/rc3tvd518m9uw8q/MAGDY%20TeleSat%20Mk1.craft?dl=0 -- This rocket I am able to launch and get into orbit using the info provided previously in the thread.

https://www.dropbox.com/s/f43z3o87ttpd7jq/MAGDY%20EnviroSat%20Mk2.craft?dl=0 -- This rocket, while different, is pretty similar to the first. However, almost immediately on launch it starts leaning to the South and even if I correct this, at around 8000-9000 meters (typically moments after the first stage) it becomes uncontrollable.

Edit:

follow the prograde marker
I let it follow the prograde marker

Also, I think I may be confused on this comment even though I thought I understood it. The prograde marker doesn't seem to move unless I angle the ship outside of it. If I follow it, it seems to never get me to a point where I am gaining significant horizontal velocity.

Edited by Bandus
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Sadly, I still seem to be having trouble. Earlier in the thread, the explanations I received helped. Then I attempted to build a similar rocket and nothing seems to be working again. Clearly there is something I am missing so I've decided to post both .crafts and I am hopeful people can tell me if it is a design issue, etc. I greatly appreciate the info!

https://www.dropbox.com/s/rc3tvd518m9uw8q/MAGDY%20TeleSat%20Mk1.craft?dl=0 -- This rocket I am able to launch and get into orbit using the info provided previously in the thread.

https://www.dropbox.com/s/f43z3o87ttpd7jq/MAGDY%20EnviroSat%20Mk2.craft?dl=0 -- This rocket, while different, is pretty similar to the first. However, almost immediately on launch it starts leaning to the South and even if I correct this, at around 8000-9000 meters (typically moments after the first stage) it becomes uncontrollable.

Edit:

Also, I think I may be confused on this comment even though I thought I understood it. The prograde marker doesn't seem to move unless I angle the ship outside of it. If I follow it, it seems to never get me to a point where I am gaining significant horizontal velocity.

Bandus,

I just downloaded your problem child and fired it up.

1) First issue is it's way over- powered. It's hitting 3G off the pad and that will make it tough to control in a hurry.

2) The upper section is crazy- wobbly over the boosters. It flies like Lamar's javelin in Revenge of the Nerds.

You'll have to tone down some of the control responses to iron that out or find the weak point and shore it up.

Nevertheless, I was able to orbit it with fuel left in the central booster stage. I think it's a lot more rocket than is actually needed for this job.

EnviroSat_zpsqptxta8j.jpg

Best,

-Slashy

Edited by GoSlash27
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@GoSlash27 - I sincerely appreciate the advice. Might I ask for suggestions on improvements? Granted, I appreciate it is more than enough power, but I would like to understand how you were able to make it work. Thanks!

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Bandus,

If I were to design a lifter for that payload it would look like this:

Mk3-1_zps9oklfyql.jpg

Mk3_zpssfi9xihk.jpg

http://wikisend.com/download/962642/MAGDY EnviroSat Mk3.craft

Improvements...

I designed the Mk3 lifter mathematically before I built it. Upper stage was the lightest solution for a minimum acceleration of .7G, 2.2t payload, and 1,800 m/sec DV.

Lower stage was the cheapest solution for 5.6t payload, 1.4G minimum acceleration, and 1800 m/sec at 50% average atmospheric density.

It's amazing what you can do when you flip the rocket equation backwards :cool:

AFA how I was able to work with your lifter...

I left the throttle at 50% and handled it very carefully with the SAS turned off. As Harry Rhodan said, it has way too many reaction wheels, active gimbaling, and active fins.

I launched it vertically at 50% throttle until it hit 90 m/sec, then mainly steered it through the prograde gravity turn by modulating the throttle.

Best,

-Slashy

Edited by GoSlash27
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