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Found 6 results

2. ## Determine Altitude in Kerbin Atmosphere of Stage

Hey everyone, I recently have been sucked into this game, and I'm loving the math. My question is this simple, determine the altitude a rocket will achieve on full fuel burn of a single stage. I've done a lot of research and have come up with the following example problem to test my algorithm/process of calculation. Let me know what you guys think of below and what I'm missing or potentially a force I haven't considered into the calculation such as lift, as you'll see my answer is off by nearly 3,300m. (For the sake of simplicity the rocket travels straight up in a vertical dimension only.) Known Values of my Rocket: Full Mass [MFull] (Entire Rocket) : 7.5t (7,500kg) Empty Mass [MEmpty] (First Stage Depleted) : 4.5t (4,500kg) Fuel Mass [MFuel] (Both LQ and OX) : 3.0t (3,000kg) Isp [Isp] (Reliant Engine) : 265 sec Thrust [FT] (Thrust Force Atm.) : 205.2kN (205,200N) LQ Rate [BLQ] (Burn Rate of LQ) : 7.105 u/sec OX Rate [BOX] (Burn Rate of OX) : 8.684 u/sec LQ Volume [VLQ] (LQ Fuel 45% Mix) : 270 u OX Volume [VOX] (OX Fuel 55% Mix) : 330 u Known Values of Kerbin: Accel. Kerbin [g] (Accel. of Gravity) : 9.81 m/sec^2 First I will calculate the time required to burn through the fuel mixture. This time will be needed in the final calculation. Tburn =VLQ /BLQ =VOX / BOX << >> 270u / (7.105u/sec) = 38.0 sec Next I convert burn rate units from volume/sec to units of kg/sec. (I assume 1u = 5kg of both LQ and OX) BLQ_M = BLQ * (5kg/u) << >> (7.105u/sec) * (5kg/u) = 35.525 kg/sec BOX_M = BOX * (5kg/u) << >> (8.684u/sec) * (5kg/u) = 43.42 kg/sec BTOTAL= BLQ + BOX << >> 35.525kg/sec + 43.42kg/sec = 78.945 kg/sec (M *Dot = Mass Flow Rate) Determine effective exhaust velocity of rocket motor related to Specific Impulse and Gravity. (NASA Formula) Ve= Isp * g << >> 265sec * 9.81m/sec^2 = 2,599.65 m/s Determine acceleration of rocket (Found this formula on a physics forum, not sure if valid) a = Ve ( BTOTAL / MFULL ) - g << >> 2,599.65 m/s * (78.945kg/sec / 7,500kg) - 9.81m/s^2 = 17.554 m/s^2 Apply classical kinematic physics equation for displacement with acceleration. (Vertical Axis only...) deltaX = 0.5 * a * (Tburn^2) << >> 0.5 * 17.554m/s^2 * (38sec ^ 2) = 12,673.988m So in the end this calculation results in an effective altitude of 12,673.98 meters. If anything, I expect drag (if simulated) among other forces to take away from this value. Instead the opposite occurred, my actual test flight while holding steady to the center of the NavBall resulted in roughly 16,000 meters altitude at 38 seconds into flight (after stage finished burning). Any ideas?
3. ## Does KSP Module Mach/Altitude ?

At sea level, Mach 3 is around 1021m/s but by the time you get to 60,000ft or 18,288m it's down to around 885m/s. Does KSP model this change when it comes to the performance of jet engines that vary thrust depending on your velocity?
4. ## How to calculate altitude from pressure on Kerbin

Hi all, I've been busily procrastinating on a Spaceplane performance guide. I've got to a section where i'm discussing the effect of altitude on jet engine performance, ie. what's the best altitude for penetrating sound barrier, what's best for hitting max airbreathing speed. Looking at the config file of the rapier, I can see that at 0.35 atmospheres of pressure, we have a thrust multiplier of 0.5. At 0.08 , thrust multiplier falls to 0.3 (looks like a sweet spot to me) , then at 0.018 we still have 0.09 (still somewhat decent, we thrust has only fallen half as much as pressure - drag - has , right?). Above that things go south very quickly. The thing is, is there a way to convert these pressure numbers, expressed in "atmospheres", into actual altitudes I can use when flying an aircraft? The KSP wiki has a table of pressure (in atmospheres) vs altitude (in km), but there are only 11 data points and inconveniently the numbers in the config file fall in between. It's not a linear relationship of altitude vs pressure so interpolating it won't be very accurate. My best guesses are at these numbers correspond to 6km (thrust multiplier 0.5) , 14km (thrust multiplier 0.3) and 23km (thrust multiplier 0.09), but is there any tool to calculate the numbers properly?
5. ## Exploding at 2600m constantly

Seems any time I make a rocket, the game decides to more than rapidly explode my rocket at around 2500-2600m. Basically, I'll get close, the game will get jittery. Then the rocket goes and splits apart at insane velocities. I've seen it sometime explode so badly that parts burned up in the atmosphere. I've tested this with a few different rocket designs and looked at the post mission report and basically it shows catastrophic failure of dozens of components within less than a second. This kinda leads me to believe it's some kind of game engine _ clownery and not my design. The fact it also happens at 2600m almost all the time is telling. I did a debug with unbreakable parts and it STILL does it. I did a debug with no gravity and was able to gently hover past the 2600m mark at around 100m/s? It happens in both the 64bit version and the not-64 version. ship design doesn't seem to be a factor, but speed and/or gravity might? Note also in previous versions! This rocket worked! Now I can't get one past 2600? I don't know what's goin on.
6. ## Altiude set Deployable Fairing

A rather intersting thought crossed my mind tis morning when I was playing Kerbal and in fact this idea could work (after all we ahve Parachutes that Depoy or open when the vehicle htis a certain alttitude above the surface.. But this idea takes the idea and reuns it in reverse.. Everyone who builds a craft that has aerodynamic fairing either has to stage the fairing properly so that it opens when a certain event hpappens of you deply it maually (This is one thing that I du..) But what if the fairing wer eto autodeply when the vehicle reaches a certain altitude.. . IN a way it's like the parachutes hwe have in game abut run in reverse.. (forexample the part could be set with a deply area that would range from say 35,000 mets all the way up to 70,000 meters.. And you could set this deploment altitude before you launch. (Much like you can set the parachuts an or the ablation for a heat shiled.. So then the real question is, could this work? an if so what type of coding would it take to make it work/ Thoughts? Space_Coyote