likk9922 Posted July 18, 2011 Share Posted July 18, 2011 So, I've only had this program for a couple of days. It's pretty great, I have to say. But I'm having a big issue.My first missions (the 'Hermes' missions) were originally planned to reach a height of 500k and re-enter Kearth's atmosphere, and then I had planned to go on to various missions escaping Kearth's gravity, orbiting, etc. etc.Hermes I hit 100k, Hermes II managed 200k, and Hermes III reached 300k. Beyond a three or four stage rocket, however, things seem to stall out. Adding more rockets seems to make it extremely unstable even with a dozen SAS modules. It simply becomes too heavy or too delicate, and after more than a dozen tries I've still failed to reach the same heights as Hermes III was capable of.My basic plan is to use a liquid rocket with three fuel tanks (as more seems to take more fuel to achieve lift and acceleration than the benefit it provides) and basically get it as close to being out of the atmosphere with solid fuel thrusters.Is there a better strategy? Any tips for increasing stability? I just feel stumped... Link to comment Share on other sites More sharing options...
Finrandojin Posted July 18, 2011 Share Posted July 18, 2011 well without seeing your builds it's hard to say what needs fixing. So I will just post my 'surefire' rocket that get's me to orbit 95% of the time.parachute---command capsule---decoupler---SAS module---fuel tank---fuel tank---liquid rocket---decoupler---SAS module---tricoupler---fuel tank fuel tank fuel tankfuel tank fuel tank fuel tankfuel tank fuel tank fuel tankengine engine enginefirst stage had 6 boosters on radial decouplers for use at launch. Link to comment Share on other sites More sharing options...
likk9922 Posted July 18, 2011 Author Share Posted July 18, 2011 Well, it seems that any more than 7-9 rockets in the first stage causes serious stability problems with the rockets jostling around because they aren't attached to any more than radial decouplers or flipping and spinning the craft horribly (if not shearing off) because they're on the end of a line of stack decouplers.I guess I just don't understand how you build a big rocket, and it seems like little rockets don't have the oomph.... Link to comment Share on other sites More sharing options...
Finrandojin Posted July 18, 2011 Share Posted July 18, 2011 I guess I just don't understand how you build a big rocket, and it seems like little rockets don't have the oomph....simple and small desings outperform wobbly doomstacks 9 times out 10. Link to comment Share on other sites More sharing options...
Johno Posted July 18, 2011 Share Posted July 18, 2011 My current main launcher is the Delta IVc. It's based on Sordid's Delta IV, but it's considerably revised. It has been reconstructed using the symmetry tool, and I have added wings for stability in the midrange phase. Most importantly we have replaced the original 1 1/2 stage design with a 2 1/2 stage design; the spacecraft itself now has a service module and orbital maneuvering system. Achieves orbit with ease. Currently testing on escape. Escape looks good, but I'm unsure about how much maneuvering fuel I'll need to get the boys home.*Note: The SRBs on the radial booster stacks are non-functional; they are there simply to hold the liquid-fueled boosters in place (because this was originally a simulation of an existing real-world rocket). I'm sure that with the addition of some decouplers you could make them part of the boost phase as well. Link to comment Share on other sites More sharing options...
DaHitch Posted July 18, 2011 Share Posted July 18, 2011 I've been able to come up with a somewhat large-ish rocket that will deliver thrust up to 500K from the surface with a top speed of about 4000m/s. Due to the way the stages are set up its also perfect for getting into orbit.I've fiddled with several other types of designs since, but this seems to be the most stable/powerful combo I can come up with. Everything else I made so far always sacrificed one for the other.I present to you Freedom 7:The philosophy behind this craft is to have 1 stage at the top which will act as a retro-package to return to Kearth.The 3 fuel-tank stage beneath it is used to get the craft into orbit and trim said orbit.Everything below the first 2 stages has as only purpose to propel the upper 2 stages out of the atmosphere.Construction:Stage 00ParachutePod-------------Stage 01Decoupler-------------Stage 02SASFuel TankLFE*Top Booster Package*-------------Stage 03Decoupler-------------Stage 04SASFuel TankFuel TankFuel TankLFE-------------Stage 05Decoupler-------------Stage 06Tri-Coupler3x SAS3x Fuel Tank3x Fuel Tank3x Fuel Tank3x LFE-------------Stage 073x Decoupler*6x Radial Decoupler*-------------Stage 08*6x SRB*3x SRBThe *Top Booster Package* is mounted on top, but fired at life-off, so adjustments to staging are needed.I have however improved on this design by adding some more boosters to the life-off stage. The basic design & philosophy is the same, but the extra boosters provide a bit more oomph at lift-off and make sure that the bottom section of the craft is able to propel the final 2 stages all the way out of the atmosphere. The booster package accelerates the rocket to ~100m/s to an altitude of 6000m, after which the 3 remaining LFE's take over. They take the remaining rocket up to about 30-40.000m at ~450m/sThis design requires even more fiddling with the staging though, but nothing too difficult I'd reckon. I also added 3 SAS to the booster section in order to compensate for a tendency to roll & bank.Freedom 7_Revision2:One note about both designs: due to the high COG caused by the boosters mounted at the top it is crucial to apply SAS as soon as the simulation starts in order to prevent the rocket from tumbling over on the launchpad. This high COG will also induced some movement, so it's important to wait for the pod to point straight up before launching, otherwise the rocket will take off at an angle. This is similar to the twang the Space Shuttle performs irl.It should also be mentioned that both rockets -though stable- have a slight tendency to roll left & bank right (at 90°) with the SAS turned off until the tri-coupler is jettisoned. The roll can be easily overcome by small control-inputs, as can the bank. Or if you do not correct the bank angle it will actually help pick up horizontal speed to make getting into orbit even easier. Link to comment Share on other sites More sharing options...
Finrandojin Posted July 18, 2011 Share Posted July 18, 2011 everytime I see people mount SRB's on their top stage I die a little inside. Link to comment Share on other sites More sharing options...
DaHitch Posted July 18, 2011 Share Posted July 18, 2011 Maybe so, but they work.I've been trying to come up with several other designs (without boosters on top) and I'm simply unable match the performance of Freedom 7.Currently I'm trying to construct an SSTO, but things aren't going as smooth as I'd hoped. I'm able to just graze the upper portions of the atmosphere, but unable to pick up enough speed to stay there, even when using the retropackage to build up speed. Link to comment Share on other sites More sharing options...
Finrandojin Posted July 18, 2011 Share Posted July 18, 2011 Maybe so, but they work.I've been trying to come up with several other designs (without boosters on top)hmmm I'll share a tip with you to get some more oomph out of vanilla parts. I've attached a pic of the first stage on my most powerfull rocket.The trick is to take a triple stack and then attach radial decouplers evenly around it(maximum of 9 can be attached) now put a single SRB on every radial decoupler, now you can attach fuel tanks underneath the SRB's. Also this is an extremely stable desing, I often find myself noticing the deviation form horizontal only after 30 seconds after launch and engage SAS.I've also attache the .craft file for the rocket, feel free to modify it, but be warned that the staging is very complicated and tedious to reconfigure after changes. Link to comment Share on other sites More sharing options...
Millitron Posted July 18, 2011 Share Posted July 18, 2011 I have made a little modification to the liquid fuel tanks to allow them to be connected to radial decouplers, since I am 90% sure it is done occasionally in real life. This way you can cut the SRB thats on the radial decoupler. The mod can be found here http://kerbalspaceprogram.com/forum/index.php?action=dlattach;topic=303.0;attach=441 Link to comment Share on other sites More sharing options...
Finrandojin Posted July 18, 2011 Share Posted July 18, 2011 I have made a little modification to the liquid fuel tanks to allow them to be connected to radial decouplers, since I am 90% sure it is done occasionally in real life. This way you can cut the SRB thats on the radial decoupler. The mod can be found here http://kerbalspaceprogram.com/forum/index.php?action=dlattach;topic=303.0;attach=441yes I've actualy modded my coupler so fuel tanks can be mounted directly on them but I don't use these modified crafts in challenges where modded parts are verbotten. Link to comment Share on other sites More sharing options...
likk9922 Posted July 18, 2011 Author Share Posted July 18, 2011 As it turns out, I'm not a bad engineer. I'm just a terrible pilot. Always maximizing thrust will allow you to get much higher than trying to maximize fuel usage..... :Thanks to everyone, though! Link to comment Share on other sites More sharing options...
Tim_Barrett Posted July 21, 2011 Share Posted July 21, 2011 Sometimes rockets can bee too big. Unless they are cleverly made instead of attaching akajabillion boosters for launch, you wont get too far.Simplicity wins, for now, or atleast until planetary travels are introduced Link to comment Share on other sites More sharing options...
Recommended Posts