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Analogy

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  1. Awesome, guys, thanks. I have to go run an errand right now but I have downloaded your modified .crafts and will be checking them out when I get home.
  2. Uh... No. Your center of mass moves backwards as you burn fuel. You drain from the top tanks first, so the top end of the rocket gets lighter. This keeps moving the center of mass back until the last tanks drain, then it moves forward again. Top-heavy rockets are more controllable by thrust-vectored engines for the same reason that it's easier to balance a broom on your finger from the handle end than the bristle end. You have a longer lever on which to act. Look at the staging. Those engines are hauling 5 3200L tanks, which are necessary to provide enough delta-v to visit every SOI in the system. One or two nervas will do about... 1 m/s^2 of acceleration with that. Would you want to try and calculate a 2000 m/s burn with that using only KSP's (lack of) orbital planning tools, or would you rather take a mass penalty and put enough thrust on your vehicle to make those burns a little easier? All of the transfer calculators assume a burn which is short enough that it can be considered instantaneous for the purposes of the calculations. You need at least .3 or .4 TWR to do that. One nerva pushing 5 large tanks is a TWR of about .06. I would love to see anyone demonstrate a successful interplanetary transfer burn using one or two nervas pushing 16000L of fuel without resorting to extensive trial and error. Did you not pay *any* attention to my post? I mention that this is a *grand tour* mission in the *very first sentence*. Nothing is landing on anything. There aren't even any landing legs on the craft, anywhere. I assure you they are. The thrust to weight ratio of the vehicle never drops below about 1.5, perfectly reasonable for a super heavy lifter. Yes, a bit on the low side, but not wastefully so. When I don't run into tumbling or random explosions, the vehicle hits orbit with fuel to spare before separating the interplanetary stage. Is it seriously too much effort to throw the .craft into your saves directory and watch mechjeb try to fly it?
  3. Thrust to weight ratio is about 1.5 at the beginning of each stage, maybe 2.5 max at the end. That's well within decent tolerances.
  4. My standing theory about the cause of vehicles losing control is that as fuel is used, the center of mass moves downward because you have full tanks on bottom and empty tanks on top. Moving the center of mass toward the center of thrust means that thrust vectoring has less ability to exert control authority over the craft. Usually, figuring out how to move mass upward or thrust downward at that point in the launch helps me out. The other theory is that as boosters drop off, so are all the bracing connections between them, so the vehicle is a bit more wobbly.
  5. Quick possible theory on the random exploding booster: Because it's near the end of the stage, the thrust to weight ratio at that moment is fairly high, could it be G-forces making the connection fail?
  6. I'm trying to design a craft that can accomplish a grand tour - visit the SOI of every object in the Kerbol system. So, nuke engines, lots of fuel, and a booster to put all that fuel into orbit. So, the problems: * Near the end of the third stage, it has a tendency to start uncontrollably spinning out of control. Usually between 6 and 8 tanks empty. * However, the last few iterations, it's started randomly exploding around the time of second stage separation. No collisions, and no real changes to the part that's exploding. It's the same one every time, and around the same time in the flight, but I can't identify what's causing it. I've gotten this craft into orbit. Now with no fundamental design changes, it's failing to do so. Help me KSP forum, you're my only hope. http://imgur.com/a/lZnet http://analogy.cupofnoodles.com/ksp/Grand%20Tourist.craft
  7. I'm already doing that in my design, can you look at it?
  8. I'm having a similar problem with this attached craft. Works fine up till near the end of the third stage, then it starts tumbling all over the place. Everything's braced pretty well. Putting winglets on causes things to collide with each other on stage separations.
  9. Delta-V is the total amount of velocity change a vehicle is capable of. It's a function of total thrust, amount of fuel, specific impulse, and total mass of the vehicle. The same engine burning the same amount of fuel but having to push a more massive vehicle will get less delta-V. Pretty much every maneuver you make in KSP requires a certain amount of delta-V to perform, so the amount of delta-V your vehicle is capable of represents, basically, where you will be able to go with it.
  10. Apart from figuring out how to work with rockets that use fuel lines, you also need to make it ignore sepratrons.
  11. Pretty much everything I do is a variant of the first craft I posted in this thread. A bunch of boosters around a central core feeding fuel into each other so that just one pair of boosters is draining fuel at any time. I'll vary the number of boosters, amount of fuel, and types of engines depending on what my payload requirements are. The second craft I posted is an example of this process in action. Because I was only allowed to burn a certain amount of fuel, the craft ended up a lot lighter, so I used fewer booster pairs so that the amount of thrust was matched to the weight of the vehicle, and also to reduce the amount of vehicle weight tied up in engines. I switched the inner engine to a trio of lighter engines with higher isp to get myself better fuel efficiency once the vehicle was light enough and high enough that it didn't need a lot of thrust anymore. Heh, exactly.
  12. I would bet that SRBs are allowed... I tend to avoid them in my designs since they make very little difference in the overall payload capacity of my rockets unless I use a lot of them, to the point where my vehicles stop being simple and elegant. Part limit is not my limitation to getting mass into orbit. I got 5 large tanks (16,000L) into orbit with around 200 parts, still way under the 350 part limit. The limitation is fuel. IMO it would be fairly difficult to get very much more than 2 large tanks (6,400L) on 45kL of fuel burned unless you resorted to an extremely kerbalish rocket... I tend toward simplicity with my vehicles which resulted in me using the large but fairly inefficient rockomax engines on my launcher... If you were willing to put up with the complexity it's possible that a large cluster of the smaller engines might do you better. More mass for the same thrust, but higher isp, I haven't done the legwork to figure out if the trade is worth it.
  13. All right, this time I burned about 44,500L of fuel to put 6,800L into orbit. Again, completely unoptimized mechjeb trajectory, and the craft becomes a bit unstable just before the second stage separation so that probably wasted a bit of fuel... I probably need to work on where the craft's center of gravity goes relative to its center of thrust as fuel gets used up but too lazy to do it now. Anyway... Yeah. EDIT: Added a new .craft which adds a NERVA to the top stage and modifies the struts. The NERVA's so tall that is raises the center of gravity by pushing the top stage's tanks further away, so there is no longer the instability as the second stage runs out of fuel, and as a bonus, you can now explore the Kerbin system with your 6400 L of fuel. I dunno what that is in delta-V, but at 800 isp it's like, a lot. You'll have to add a parachute and another decoupler if you wanna come home though. That might bust the fuel requirements for launch over 45kL, unless messing with the launch trajectory gets you some extra efficiency.
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