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Found 6 results

  1. Hello! Firstly, I know questions like this one have already been made both in and out of the forums before, yet every thread I found and read do not fix my problem or give me an idea of what I'm doing wrong. Also, sorry if this ends up a bit too long and technical, I want to try and make it as clear and detailed as possible, especially when explaining the math I did, so it doesn't confuse or give the reader a headache. So... I finally decided to play KSP [more] seriously, disabling "revert flight" and trying to calculate the rocket performance and everything else before launch to minimize failures. I'm playing the Enhanced Version for the Xbox, which should be pretty much a 1.2 stock for PC. The rocket I have is comprised of two stages: the first one has 3 engines, a center Swivel one (with 2 FL-T800s on top), and two radially mounted Reliant engines in an asparagus setting (so they have one FL-T800 on top each, with both of these fuel tanks feeding into the center one directly above the Swivel - this way, once the radial tanks are expended, they will be jettisoned with the Reliant engines). The second stage is the orbital stage, having a single LV-909 Terrier with a FL-T400 on top (will talk about it later on). The goal of this rocket is to carry scientific equipment to a space station at a 200km circular orbit over Kerbin, where it's currently being assembled for a mission to Minmus. The problem I initially has is that the Delta-V calculation I done for the first stage gave me a result of ~1899m/s², which theoretically should not have been enough to allow me to leave Kerbin's atmosphere (as "Delta-V out" of Kerbin is 2500m/s²). Yet, I managed to dock with the intended station with about 60% of fuel remaining in the second stage (no cheats involved, I swear). I've done all the calculations based on what's available at wiki.kerbalspaceprogram, making use of the "Advanced Rocket Design" and "Cheat Sheet" topics. Will go over the math now: Starting up, I calculated the average Isp of the three engines at sea Level, which was pretty much: (F1+F2+F3/(F1/Isp1)+(F2/Isp2)+(F3/Isp3) being F=Thrust at sea level. This gave me an AvgIsp of 261 (which I called Isp1). Right after, I got the total mass of the craft (M0=28556t) and the first dry mass (aka: the mass with empty radial tanks before dropping them and the Reliants; which I called M1=20556). I also calculated the new mass right after dropping the radial tanks and with full center tanks and swivel engine (M2=16646); and dry mass for empty center tanks (M3=8646). Based on this, I calculated 2 delta-Vs for the first stage: Delta-V1, while both the Reliants and Swivel were firing; and Delta-V2, after the Reliants were dropped and only the Swivel was firing and taking fuel from it's own tanks now. So, Delta-V1 = Isp1(261)*g[9,81]*ln(M0/M1)[0,32] obtaining a value of ~819m/s². Did the same for Delta-V2, calculating the Isp2 for the Swivel only part of the flight, for which I got an Isp2 of ~167.9; then Delta-V2 of 1070m/s² I then made the sum between both Delta-Vs, obtaining that nasty odd value of ~1889m/s². As for the second stage, it gave me a Delta-V value of 276.6m/s², adding the whole sum to 2175m/s² (which shouldn't even be enough to take me out of Kerbin's atmosphere, let alone docking. The whole flight from Launch to a circular 200km orbit should require ~4844.88m/s², more than twice what I had! Some thought and considerations (and questions): 1. I know the Delta-V I calculated is lower than the real Delta-V, since, for all the first stage engines, I only accounted for the Sea Level Isp and ignored the Vacuum Isp - while in reality the higher I went, the more Isp I'd have, thus increasing my Delta-V - although I don't believe it would have such an impact on the Delta-V. 2. I tried being efficient during the atmospheric flight, avoiding overspeed and unnecessary drag, which caused me to lower the throttle quite a bit (especially while the 3 engines were firing) and in turn increase the engine-on time, resulting in more Isp since I was ever higher with the engines on. This goes back to point 1, since I only considered Isp for Sea Level even though half of my fight happened at high altitude / low pressure / higher Isp environments. Could this also justify the Delta-V discrepancy? 3. Is there a way I can calculate Isp at an specific altitude so I can be more accurate (instead of only taking into account the Vacuum Isp for the 2nd/orbital stage and ASL Isp for the first stage)? 4. I tried repeating the math but assuming I'd not fire the Swivel until the Reliants were dropped. In the end it gave me a noticeably higher Isp and Delta-V, although still not as high as theoretically necessary. This is kinda odd though, shouldn't firing all engines together but feeding only from the radial tanks be more effective? Thanks. Would love to hear what I've been doing wrong and hope I didn't give too much headache to people trying to read this. (And yes, I'm super jealous of you PC players with all the fancy Kerbal Engineer calculating stuff!) Cheers.
  2. I have an equation that shows the target speed you need to reach to have a successful hohmann transfer: V = 1878968 * sqrt(2/RInitial-2/(RLowest + RHighest)) It's always worked in the past, but I recently tried to use it to find the target velocity for a transfer around the sun. When I plug in the numbers, I get a ridiculous answer of 16 m/s, and I don't know why. The weird thing is, I tried looking this formula up on Google to see if I missed something, and I cannot find it anywhere. Has anyone else used this formula?
  3. Hi Everyone, I've been working on a spread sheet in Excel, for various calculations relating to KSP. This is firstly, to learn more about the Physics and Math involved in KSP [and Space flight in general], and secondly, because I was thinking of starting a Barebones Career, as in only adding parts and planets in terms of mods and not anything like KER or Mechjeb, and possible doing IVA only's. [not sure if I'm that confidant with my KSP skills yet though ]. So far I have: - Hohmann Transfer Bi-Elliptic Transfer Interplanetary Transfer Satellite Minimum Altitude Satellite Transfer/Phasing Orbit Rocket Equation (REq) deltaV - available REq - Total Mass for required deltaV REq - deltaV remaining [WIP] TWR To Add I have just started on the Rocket Equation [it's giving me a Headache already and I've not started to turn it around yet] [Ok now starting to turn it around, headache still coming] Questions to everyone: - Would anybody else want a copy? What else should I try to add? What format should I distribute in? If even wanted. [i'll add others as they come up] Anyone who is interested please post so I know it will be wanted. First draft - some sheets are WIP https://drive.google.com/file/d/0B8rJGx3hp3uJUTFPQWNhWE5Xb28/view?usp=drivesdk Updates: - Sheet added References and/or inspiration: - Link1 - Interplanetary How-To Guide by @Kosmo-not Link2 - and the PDF version of @Kosmo-not's Guide provided by @Nexus24680 Link3 - Special Thanks to @OhioBob and his Website Link4 - Inspired by @Nexus24680's Orbital Calculator Link5 - Orbits calculator spreadsheet By @Gaarst TBC - Satellite Minimum Orbit Calculator By TBC TBC - Satellite Orbit and 'Spacing' Calculator By TBC Link8 - Interplanetary Trajectories with Low TRW (and No Math) By @Brainlord Mesomorph [Testing Needed] Link9 - The "reverse rocket equation" explained By @GoSlash27 [some Tabs WIP] If anyone knows who or what thread(s) the Satellite stuff come from, 'cos for the life of me I can not find them again?
  4. 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?
  5. UPDATE: New thread created for 3D model that does everything this model does and more. Original post below: I've been exploring optimization solutions lately for my interplanetary communications network, and was having a hard time wrapping my head around some of the math and picturing the system in my head. So I did some research and learned some equations and relationships and found a nice free graphing software to bring it all together. I worked out the polar coordinate equation for each planet's elliptical orbit and plotted it. What came of the exercise was a scale model of the Kerbol System, viewed from the top down, with all planets' orbits represented accurately in terms of: major and minor axes foci (Kerbol in the correct position) eccentricity longitude of ascending node (how a planet's orbit is tilted relative to a reference direction) argument of periapsis (where the Pe is located; given relative to the longitude of the ascending node) (As far as I can tell, imgur album embedding is broken at the moment--please correct me if I'm wrong--so forgive the screen-captures.) ^Model overview ^Inner planets ^Tidied up a little (disabled grid-lines, too) ^Just Kerbin, Jool, and Eeloo nicely visualized The only thing this tool doesn't properly portray is orbital inclination, as that would be in a third dimension. I may look into that soon. We'll see. To use: Download and install GeoGebra on damn-near any platform, or use the web app Download the .gbb file I've l inked here from Dropbox Open, explore, modify... enjoy! At the moment, it's a fairly bare-bones item, with only the most essential information included, but it may just end up growing into something more substantial, whether for my own use, or at the request of the community. I don't know if any licensing is necessary here, but if it is, let's say.... MIT (referring only to the .gbb I've shared. GeoGebra has its own licensing policy). A few notes for clarity: Scale is in megameters (1Mm = 1,000km = 1,000,000m Visibility of elements can be turned on/off in the left pane. This can help with crowding when zoomed out past the inner planets. Π is used to denote the location of the ascending node (normally I would use ☊ but GeoGebra does not support it) Ω denotes the longitude of the ascending node (an angle) ω denotes the argument of periapsis (an angle) γ is used to denote the reference direction, along the x-axis (normally I would use ♈ but GeoGebra does not support it)
  6. Hi, I'm not new to Kerbal Space Program but I still don't know one thing. I don't know how much Delta-V I need to get to a planet or moon. If someone could tell me how to calculate the amount of Delta-V I need I would really really REALLY appreciate it. Thanks for looking at my post