GoSlash27

Clipperride, I agree with the others here. The easiest way to deorbit debris is to not leave it in orbit in the first place. Any stage that is boosting another stage to orbit is ditched just before circularization when the Pe is still in atmosphere. Any stage that is used to place other payloads in a highly- eccentric insertion will have enough DV left over to do a deorbit retroburn. Usually with a recovery package so it can be recovered intact. It's not difficult to keep LKO litter- free. Just a little additional planning. Best, -Slashy

Zoidos, KSP is actually an evil scheme to encourage you to not suck at math Best, -Slashy - - - Updated - - - nohelmet, Probably because they're way smarter than me And I have actually said this before (as have others), but I don't believe it's ever been put into an easy- to- find tutorial in such plain language. Best, -Slashy - - - Updated - - - OhioBob, This seems to explain the disparity nicely. I think I'll just keep the error in my spreadsheet and err on the side of caution (no kerbonaut ever complains about a little extra DV). And thanks about a gazillion for the http://www.braeunig.us/space/orbmech.htm reference. It's been absolutely indispensable! Best, -Slashy

True. I have used LV-Ns in conjunction with RAPIERs for my super- economical designs, but the $/tonne advantage isn't very much in the long run and the headaches tend to go up even though it's working with a single fuel. In a career game, it's worth it to upgrade from TJ/ vacuum rocket to RAPIER (at least for big tankers)... But once that is done the unit cost advantage of upgrading to LV-N vacuum propulsion isn't worth the hassle IMO. It just plain doesn't save enough money to pay for the exercise. Best, -Slashy

regex, We wouldn't necessarily aim to place our craft into that parking orbit. It's only when we're planning on fueling it from a source that's at that altitude or higher. Actually placing the craft there from low orbit costs more DV than launching from there saves. Plus there's a whole boatload of practical considerations like hitting transfer windows, possible interference from moons, etc. But to answer your question, r = 2μ/v∞2 would be the simplest algorithm. You would calculate V∞ by a Hohmann transfer about Kerbol from your source planet to the destination. That's solved in the usual way; know your source and destination planets' SMA and Kerbol's gravity well μ. That's in the wiki. from that, you have the SMA of the transfer orbit; (r1+r2)/2 You also need the source planet's orbit velocity, which is sqrt(μ/r1) So now all you need is your orbital velocity leaving the source planet on the transfer vtx= sqrt(μ(2/r1-1/SMAtx)) Subtract the source planet's orbital velocity from the transfer velocity and that leaves V∞. Best, -Slashy

I've finished the transfer calculator and worked out "optimal" transfers between Kerbin and the other planets. The altitudes lead to some interesting conclusions. Also, the optimal altitudes are identical in both directions. Kerbin->Moho K 680km 1,661 m/sec M 30 km 2,416 m/sec Kerbin ->Eve K 11 Mm 551 m/sec E 23 Mm 598 m/sec Kerbin ->Duna K 7.7Mm 649 m/sec D 570 km 584 m/sec Kerbin -> Dres K 980km 1,477 m/sec D 30 km 1,292 m/sec Kerbin -> Jool K 350 km 1,918 m/sec J 180 Mm 1,242 m/sec Kerbin -> Eeloo K 220 km 2,089 m/sec E 20 km 1,366 m/sec In the case of Jool, the most efficient altitude for the return is out near Pol's orbit, but of course you can't aerobrake out there. It would therefore seem most efficient to aerobrake at Laythe as well as safer. Best, -Slashy

Ohio Bob, I had noticed the same thing as I was manipulating the spreadsheet. I'm going to try to pad it out to predict DV budgets from any planet to any other. I don't have hyperedit, so I'd need somebody else to get empirical results to confirm it. Best, -Slashy

I think he's just an OCD germophobe. Best, -Slashy

Garrison Chisolm, You're going to be pretty much exactly following Duna's orbit about Kerbol. Your maneuver node patched conics should reflect this. To get back to Kerbin cheaply, you will want to do the entire burn close to Duna where your velocity is highest (yay Oberth!). Not a problem *unless* your periapsis is positioned all wrong for the transfer. You want to leave Duna retrograde to Duna's orbit around Kerbol, so your periapsis needs to be somewhere between Duna's dawn terminator and noon. If it's not there, you're in danger of running out of gas. Good luck! -Slashy

MKI, I'm just using jets and plain old vacuum rockets (Terrier or Poodle, depending) for low- tech spaceplanes. For high tech, it's RAPIERs all the way. I'm focusing on eliminating drag instead of adding power and it's showing good results for me. Best, -Slashy

Ohio Bob, Not a problem; it's science! As long as I have a probe in the neighborhood, is there any other intercept you'd like empirical data for? I'm sitting at 11 Mm with 1,179 m/sec DV. I've also got a probe sitting at 75km altitude. Best, -Slashy

OhioBob, I just finished up my test, and this concept is definitely sound. *Proof of concept dance* With the re-jiggered v∞values I provided, here's the results: Predicted DV to Eve intercept at 70km: 1,043 m/sec. Actual DV to Eve intercept at 75km: 1,035 m/sec Predicted DV to Eve intercept at 11Mm: 551 m/sec Actual DV to Eve intercept at 11Mm: 537 m/sec Still a hair high on the prediction, but pretty darn close. Why do I keep coming in under the estimated value?? Best, -Slashy

Ohio Bob, I took the liberty of reverse- engineering your process here in a spreadsheet and everything seems to line up... except that my intercepts are still coming in under- budget. I can't figure out why It wasn't all for naught though; I was able to recalculate the V∞ to reflect the actual excess velocity on a Hohmann transfer to each body*. This gave results that were still a little behind what I'm seeing in- game, but lines up precisely with all bodies in the subway map in the wiki. Body/ V∞/ÃŽâ€V at 70km transfer/Calculated optimal altitude/ÃŽâ€V at optimal altitude Moho/2,349/1,712/680km/1,661 Eve/779/1,043/11.0Mm/551 Duna/918/1,078/7.70Mm/649 Dres/2,088/1,564/1.06Mm/1,477 Jool/2,713/1,935/360km/1,918 Eeloo/2,955/2,094/220km/2,089 It looks like a transfer to Eve would show the discrepancy best. I'll try it tonight. Best, -Slashy *Method: Excess velocity is simply what would be the DV on the first burn of a Hohmann transfer from one body's orbit to another. I calculated that using both Kerbin's and the target's semi- major axes.

Well... it's cheaper, but not necessarily better. It's only better if your entire mission package can fit in a single launch. Otherwise modular assembly is the way to go. Best, -Slashy

OhioBob, I haven't thanked you for this work yet, so thanks! I think you've just come up with the most organized way to look at the problem. Best, -Slashy

Norcalplanner, It should always show a DV savings to retroburn to LKO first, no matter what. But the benefit of doing it would diminish with lower starting altitudes. Eventually to the point where it's not saving enough to be worth the trouble. I don't think there's a hard line where it's "worth it", especially when you factor in cosine losses. At some point, the savings are lost in the noise floor and you'd say "Meh. Let's just go". Best, -Slashy

I would think it has to be something like this. Otherwise... why would we *not* assemble in orbit? Lifting an entire ship in one go severely limits it's size and mass, while assembling in orbit removes the bottleneck. Best, -Slashy

Hmm... Nobody's mentioned all the biomes on KSC itself, including the rooftops. There's lots of freebie science there. Best, -Slashy

juanml, I don't know for a fact that the low altitude retroburn would be "best", but it's definitely what I would do. If you're already in an elliptical orbit to intercept Gilly, the circularization burn at that end is cheap. Coming into Eve at interplanetary velocity, OTOH... it's expensive if you don't do it efficiently. And FWIW aerocapture at Eve is still a thing. You've just got to be a little more careful. Best, -Slashy

xtoro, Because the small price in DV for the retroburn is more than made up for in velocity when you do the actual ejection burn. When you're orbiting at high altitude, your energy difference is potential rather than kinetic. Kinetic energy is what gets you places. Retroburning to lower Pe transforms your potential energy into kinetic energy, allowing you to save DV on the transfer. As an example, try it both ways from 6.8Mm. The two burn maneuver will cost you a lot less DV in the end. Trust me, we've been all around this subject with lots of empirical testing to hash it out. Best, -Slashy

Destroyer, First thing that springs to mind for me is this: You're sending 20 Kerbals in 1 go. A Mk3 spaceplane would be much better for this job. It's got way less mass and drag for the payload. It would also greatly simplify your design, thus further reducing drag. *edit* I knocked this together as a quick proof- of- concept. Still uses 2 RAPIERs and carries the same payload. It exceeds Mach 4.4 in air breathing mode with no fuss. You'd probably want your spaceplane to look a little prettier, though. Best, -Slashy

OhioBob, I always send my missions assembled and fueled in orbit. I'm certain that the most economical (from a DV standpoint) approach is to start at a higher altitude, drop the periapsis, then hit the transfer. But launching direct from higher up? It's never worked out in my practice. I've bookmarked this page. I'll have to ponder this... Best, -Slashy

OhioBob, I can see where you're coming from and this approach definitely has merit, but as a practical matter it doesn't quite pan out. I was able to achieve a Jool apoapsis with less DV in both cases and the "intercept" required less DV from the lower orbit. Something's off here, but I can't see what it is. I'll have to ponder it... Best, -Slashy

Mr. Chris, Orbit is totally do-able within the part restriction and pad limit you outlined. In fact, the LV-T30 can do it in a single stage. If you balance it properly, you should need 18 FL-T100 tanks and a single T-30 engine. *edit* Proof of concept. And since the T-30 can lift more than this, it's simply a matter of stacking in more tanks. You'll run out of part count before you exceed this engine's lifting capacity. Best, -Slashy

To circularize in a single burn without throttling, you pitch to add radial-in once you've established apoapsis. It's a tricky maneuver to execute manually, and it helps if your upper stage is weak. Best, -Slashy

MHoram, Thank you so much! This is exactly the thread I was looking for! Best, -Slashy