GoSlash27

Vegetal, u would be "mu"; the parent body's mass times the universal gravitational constant. Excess velocity... If you figure out the DV required for a Hohmann transfer from your current planet's orbit about the sun to your destination's orbit about the sun and completely ignore the planets themselves, that would be the excess velocity. Best, -Slashy

Hey y'all! I just came up with a simple formula to determine the optimal radius to begin the transfer burn for minimal DV: r=2u/Vxs2 I ran this on a few examples in my spreadsheet to make sure it checks out. In the above example, the minimal DV altitude for Duna to Kerbin direct would be 563,291m. For Kerbin to Duna, it would be 7,775,080m. Best, -Slashy

Plusck, Sure thing. DV from 580km Duna orbit is 584.1 m/sec, and it's definitely the minimum for a direct departure from Duna orbit. And you're absolutely correct; there is a conflict between Oberth and the gravity well. Too far down increases your gains from Oberth, but those gains are outstripped by gravity losses. There is a "happy spot" for each Hohmann transfer. Kosmognome, I can assure you, Mr. Oberth is accounted for Best, -Slashy

GarrisonChisolm, You're welcome and de nada. I never got into math much when I was in school either, but I found out later on that I actually enjoyed it when there wasn't so much pressure. If you hang around KSP, you will eventually get very good at math. It's a gateway drug Best, -Slashy

So for the answer... A Hohmann transfer from 60km Duna orbit to Kerbin is 615.6 m/sec A Hohmann transfer from 10km Ike orbit to Kerbin is 446.6 m/sec. You would save 169 m/sec by transferring direct from Ike. Best, -Slashy

Before I give the answer, let me outline how the math works. It's much less frightening than you think. Step 1: Figure out the Hohmann transfer from one body to the other. This uses the uniform circular motion and vis-viva equations. They're just plug 'n' play. Subtract Duna's orbital velocity about the sun to get the excess velocity; Vxs. Step 2: Figure out your orbital velocity about Duna at your current altitude. Uniform circular motion. Step 3: Figure out escape velocity from Duna. This is always your orbital velocity times the square root of 2. Vorb*sqrt(2)= Vesc. Step 4: Figure out your transfer velocity. Vtx= sqrt(Vesc^2+Vxs^2) Step 5: Subtract your orbital velocity from the transfer velocity. DV= Vtx-Vorb. For a transfer from low Ike orbit, you would calculate a theoretical burn from Ike's orbital radius and treat it as Vxs, and repeat steps 3 through 5 for Ike's SoI. That's really all there is to it. It's tedious, but not difficult. Or at least it's tedious until you set up a spreadsheet to do it for you. Best, -Slashy

I don't think it's possible to end humanity with nukes. A nuclear war would be calamitous, but not an extinction event. My money is on either the S.M.O.D. https://twitter.com/smod2016?lang=en or a weaponized superbug.

Laie, This is an orbital mechanics question I can actually help you with The Hohmann transfer from a Kerbin- like orbit about the sun is a straight vis-viva problem. 918.3 m/sec. Doing the same transfer from low Kerbin orbit actually takes *more* DV; 1,078.3 m/sec. So why does it take more? Where is the benefit from our Oberth effect? Well... The Oberth effect gives you "free" kinetic energy thanks to your velocity, but a lot of that gets traded off because you have to climb out of a gravity well that wouldn't be there if you were merely in a kerbin- like orbit about the sun. In this case, getting out of the gravity well costs more than you would save from the Oberth effect, so the total DV cost is higher. If you were to leave the Kerbin system from a higher circular orbit, you could maximize your DV savings. For example, the DV cost to transfer from an 8 Mm altitude above Kerbin is only 649.4 m/sec. Any higher than that and the Oberth loss outstrips the gravity gain. Any lower, and the opposite happens. But wait... there's more! If we raise the orbit to a Munar- like orbit about Kerbin, our DV cost goes up a bit to 656.8 m/sec, but we can use the Oberth effect from a low Munar orbit to slash this even further. Orbiting the Mun at 10 km altitude will occur at 556.9 m/sec. Ejecting to Munar escape would be 556.9*sqrt(2)= 787.6 m/sec. The excess velocity to get us to Duna from there is the aforementioned 656.8 m/sec. So the total velocity required to make the transfer is figured out Pythagoras style; sqrt(656.8^2+787.6^2) = 1,025.5 m/sec. And we already have over half of that thanks to our orbital velocity (yay Oberth!), so the DV cost to get to Duna from low Munar orbit is only 468.6 m/sec. The general rule is that the Oberth effect benefits you for far targets and hurts you for close targets. You can get to any interplanetary destination cheaper from low Munar orbit than you can from low Kerbin orbit, but the savings are *much* higher for close targets like Duna and Eve. TL/DR; you can save a lot of DV by refueling in low Munar orbit and leaving from there. HTHs, -Slashy

Yeah, that definitely sorted it out. Given v,r, and u, the velocity at apoapsis is: Vap= (2vru-v^3r^2)/v^2r^2 simplified;;; 2u/vr-v= Vap Thanks again! -Slashy

Steel, That got it for me. ru/(2u-v^2r)= SMA. That gives me something to hang my hat on! Thanks! -Slashy

I'll try that. Thanks! -Slashy

Padishar, That's how I would normally do it, but unfortunately the vis-viva is insufficient for this problem. Neither the apoapsis nor the eccentricity of the orbit are given in this problem. Best, -Slashy

I'm trying to work out a formula for deriving the eccentricity of an orbit from mu, an object's velocity, and the object's altitude. I'm not having any luck so far... As an example: I have a craft in low Kerbin orbit. r= 670 km and mu= 3.532x10^12. Vorb= 2,295.8 m/sec. If I add 10% of Vorb so that V=2525.4 and r= 670 km, What is the resultant apoapsis and what is the velocity at apoapsis? This seems like it should be a very easy problem, but it's giving me fits. How do I go about solving this? Best, -Slashy

*IF* you don't care about mass efficiency or cost effectiveness. Which generally applies to sandbox play. If the criteria is merely "let's make a really 'uge rocket", then yeah, 3.75m engines are the way to go. But if you design for efficiency, it's a different story. When you scale back your payloads and design lifters to get them into space for cheap, the little 1.25m engines start to shine. Especially the Reliant. There aren't many engines that can put a payload into orbit cheaper than the LV-T30, and it's literally the lowest tech LF&O engine in the game. Best, -Slashy

YargJay9991, Yeah you did Did you notice the hex code you needed to enter to enable it? 41 70 72 69 6c 20 46 6f 6f 6c Try plugging that into an ascii conversion. Best, -Slashy

^ I'll second that. For career use, you want to use whatever engine will get your payload to orbit as cheap and light as possible. Not only are the 1.25m engines available early in the tech progression, but they are among the best engines in the entire game for career use. They are *horribly* underrated IMO. Their advantages won't be noticed by people who primarily play sandbox, but for career use they're absolutely awesome. Best, -Slashy

*snip* "Well, there's your problem." Yeah, the stock contract system and "world's first" awards won't work and play well with R.O. If you're going pure stock, then it's a totally different story. In that situation, the "world's first" records are plenty to keep the program rolling, so there's no grinding involved and the contracts are no longer a side- quest system. Now... I'm not the type of guy to advocate getting a mod in most cases, but in this case I kinda have to. I don't see how the stock contract system could ever work with both stock *and* R.O. Best, -Slashy

Yeah, I'm having the same problem. I'm used to using CTRL+ Print screen for screen caps, but the info disappears as soon as I hit CTRL. There's got to be a better way to set that up. Although none of my catches have been "whoppers" so far... Best, -Slashy

I wouldn't say that sandbox "precludes" such things, but it definitely makes them more cumbersome. I *could* keep a list of which parts I am allowed to use, how large/ heavy my launchers are allowed to be, and how much money I am allowed to spend... but why would I want to do that when career mode does it for me? I enjoy playing career mode because it is more challenging than sandbox. Once I have "beaten" career mode (unlocked everything and made it economically self- sustaining), I lose interest and start a new career. So in that sense, yes... I *do* feel like personal restrictions aren't enough and I prefer (not "need") a gated progression. Best, -Slashy

MarkyMark, That's a fine looking shuttle! I'm sure you'll get it all sorted out with the above advice. Adding on to Reactordrone's comment, you can actually mimic the split rudder on the real shuttle by using 2 rudders and reversing the deployment direction of one of them. A couple pics I hope you'll find helpful: Good luck! -Slashy

TotallyNotHuman, You can use the reverse rocket equation to figure that out. You're simply replacing unused propellant with payload. e^(DV/9.81Isp)= your wet-to-dry ratio; Rwd (Rwd-1)/Rwd= the percentage of your orbital mass that is fuel. So multiply that by the ship's mass in orbit and you have the tonnage that is propellant that could be payload instead. The simpler way to do it is to simply launch and record the units of fuel/ oxidizer you have left. 90 fuel+ 110 oxidizer is a tonne. It's not advisable to simply tack on payload without removing propellant, as that will reduce your thrust to weight ratio. That will increase the DV necessary to achieve orbit and leave you short. Good luck! -Slashy

dino1984, I maintain 45 seconds before apogee during the full- throttle portion of the insertion burn. I have trouble doing this with less than .7 t/w ratio. Best, -Slashy

dino1984, I use a t/w of 0.7 for my orbital insertion stage and 0.5 for transfer stages. Best, -Slashy

I think Aetharan's got it right. Programmers are called code monkeys. A group of monkeys is a squad. Squad is also the term for a small group of soldiers. So... Chimp, Army helmet, 'Squad". Best, -Slashy