zeppelinmage

I know the basics; my interplanetary flights have all been "direct" flights at transfer windows with mid-course corrections. Akin to my "Ballistic" picture above. I'm wondering if there's any reason to use a different method; the "Hohmann" picture above. In my example, I spent twice the DV to save three days' flight time via solar orbit. Again, I admit I am less than skilled in optimizing flights, and my numbers may not be 100% representative. I understand all maneuvers should be performed at ideal speed locations (periapsis/apoapsis); but if your orbit is largely circular, wouldn't that difference would be negligible? (all my orbits above are close to circular.) Interestingly, the "Ballistic" option makes all necessary maneuvers at once (acceleration and inclination change) for a direct injection into the target SOI, and costs far less. Doing straight prograde accelerations with a separate normal/anti-normal inclination change via solar orbit costs twice as much. Where does that extra DV come from? Is it simply due to changing frame of reference (SOI)? Wouldn't my vessel's velocity relative to the sun be the same, regardless of what SOI I'm in? Therefore, the required delta-v should be the same?

Just noticed your edit. I'm actually not using that calculator. Rather Kerbal Alarm Clock for transfer windows. I'm just comparing options, which would be better in terms of "flight time" vs "delta-v". Also, your first option would be more akin to a bi-elliptic transfer, would it not?

Okay, forget the terminology. I'm just trying to compare methods of reaching a target destination. I just wanted a label that made sense for each. Since you could technically apply "Hohmann" and "Ballistic" to both. At any rate, this is what I'm trying to find out. I just loaded up a "test" flight to Jool, with maneuver nodes. "Ballistic": Delta-V: 2086.1 m/s Flight time: 272 days Wait time: 100 days "Hohmann": Total Delta-V: 4050.7 Flight time: 369 days Wait time: 0 days (Three maneuvers: 1: exit Kerbin SOI, 2: inclination change, 3: Jool encounter.) * Both flights leave Kerbin in the same direction - prograde into Kerbin's orbital path. * I computed the "ballistic" path first, so technically the "100 days" occurred before launch of the "Hohmann" option. But that shouldn't affect the final comparison, IMO. Now I acknowledge my KSP skills are less than ideal, and these are likely pretty gross estimations. But for this particular flight, it costs nearly twice the delta-V to save three days. My question is... is this true in all cases? Also, the "Hohmann" option could concievably include gravitational slingshots. The cost to exit Kerbin SOI was 1244 m/s. Would it save anything to launch "right away", perform slingshots over those "extra" 100 days, and arrive in Jool spending only 1200 m/s?

The idea is the same. Ballistic is the "straight" path to your target planet. The other option would be to escape to solar orbit first, then perform a Hohmann transfer to your target's orbit.

This is more of a curiosity... What's a better option for interplanetary orbital transfers? Ballistic, or Hohmann? Is it better to wait for a window and send your ship on a ballistic course, or to say "meh" and launch anytime, performing a solar Hohmann transfer when it is ideal. Here's my thinking: Hohmann transfer: - don't have to wait for a window - "easier" to match inclination - total flight time longer - potentially less course corrections? Ballistic: - Need a transfer window - all inclination changes can be performed at the initial burn - "fire and forget" method. Mainly what I'm wondering is if there is any Delta-V savings at all with either method (Oberth, maybe?), and which would take more time. I suspect the Hohmann transfer would be more temporally expensive as you'd have to orbit the sun at least once to get an encounter... but then, you'd have to wait for a window anyway if you waited in LKO for a ballistic trajectory.

Arrived in the Joolian system tonight. Would have been a lot sooner, but this is in my Career save. I had a few other flights that had encounters/windows before this ship did. (That happens when it takes a year to transfer out to Jool...) Now I have to start planning my moon encounters/landings. That'll be over the next couple days.

Update! After the successful landing on Duna, and SCIENCE performed, Jeb re-boarded the lander to return home. I was debating on leaving him on the surface until a Kerbin window opened up, but since the CM was on a polar orbit, that could have been... problematic. Instead, I lifted off pretty much immediately. During descent, EVA and ascent, the CM had completed exactly one orbit of Duna, so lining up the rendezvous was quite routine. While docking, I began to reconsider the wisdom of using the CM as a return stage back to Kerbin. Both the CM and lander were, effectively, half empty. Why lug around that extra CM weight when I can transfer all that fuel to the lander and use that as my return stage by itself. So, once docked, I transferred the fuel, jettisoned the CM, then gave it a lithobraking trajectory. After that, I had 3000 m/s of Delta-V in my lander. With so much left, I decided to give Ike a visit. Unfortunately, I had to burn ~1100 m/s just to fix my inclination. By the time I got to LIO, I had 1500 in the tank. Just shy of being able to land, take off, and return home. Ah well, would have liked to plant a flag. Next time, Ike. So, instead, I left the lander in LIO while I awaited a window to Kerbin. While I was up there I took the time to EVA Jeb and repack the 'chutes for Kerbin landing. The return burn was pretty straight-forward, had a couple mid-course corrections to give an aerobrake trajectory. Locked in at 32km. Took two orbits to burn off enough speed to land. When I started to descend for landing, I noticed a worrying sight... Those mountains look rather close, don't they? To make sure I didn't lithobrake unintentionally, I burned a little retrograde to ensure my landing was in one of the valleys. It was a bit hairy coming in. Then my parachutes didn't deploy when I staged them. (Next time I'll make an action group.) But with some deft fingers and strategic use of land render lag, I got all four opened with about 80m left (The drogue was more cooperative, since I manually deployed that one earlier.) And we landed! Hooray! Jeb is happy to be home after a two-year mission. And, of course, he is raring to go on the next rocket. I collected 800 science. I could have gotten more if I hit more biomes, but I've already maxed out the tree, so it wasn't a priority. Lessons learned: * Add about 1000 m/s more Delta-V to visit Ike. My calculations above only included an encounter. Though I might have been able to land if I was a little more burn-conservative. * Action group for parachutes! Especially if one is planning to re-pack to use later. * The Poodle worked well enough for this mission. But next time I will probably stick with just 909s. I didn't see much appreciable difference in burn times between the two... and Poodles are heavy. * Plan to jettison more weight to save fuel. If I had planned on it, I could have collected the science from my instruments and jettisoned them, saving quite a bit of weight. Plus, if I had a small tank and 909 under the capsule I could have got rid of those other 4 tanks. Redesign for next time.

An update, since my window finally opened up. (Yes, more than a month later. lol.) Sorry about the dearth of pictures. I completely forgot about this thread until just now. >_> The burn to Duna was fairly standard, got a good intercept right from Kerbin. It was a few million km too high, so I had a couple correctoin burns. One halfway there, and another just inside Duna SOI. Between the two, I think I burned somewhere near 200-300 m/s of delta-V. Luckily, I have plenty. Got an aerocapture at 12km ASL altitude, and simply circularized at 53km on the other side. Another few hundred m/s. My orbit isn't perfect; 70 degree inclination. I'll have to drop inclination when I leave for Kerbin again. Anyway, once I got in orbit, I separated my landing module from the unmanned CM. A quick burn to drop periapsis below the surface, I waited for entry. I calculated a "suicide burn" to get a good idea of when I need to start bleeding off speed, even though I have 'chutes. I wanted to make sure I got a good landing. Landing ended up partially powered as I burned about 800 m/s or so to drop orbital speed before popping my drogue and main chutes. Getting close to landing I was still above 10 m/s, so I burned a little more to drop landing speed to around 5. Success! Jeb is my first Kerbal to stand on a body outside Kerbin SOI. Later, I'll lift off, re-dock with the CM, and head back home.

While waiting for my Jool Mothership to reach its destination, I had a Duna window open up. So, I sent my lander out that way. My first landing outside Kerbin SOI.

Yeah, I figured out what my problem was... the SAS modules (probe cores) on the radially-mounted landers were countering the action from the main module. I disabled them, and the ship moves now. Slowly, but it moves.

That was the intention; I only loaded mono on my landers. But because my single SAS module isn't strong enough, I was forced to use mono to move the ship around. I have 12 units left, and I'm not even out of Kerbin SOI yet.

Also... laaaaaaaag... I started an 18-minute burn... half an hour ago. And it still says I have 12 minutes left. Gah!

Thanks. Still burning 2 hours later, btw. lol. Had to F9 once, and then had to do two burns as I couldn't get far enough from periapsis to get a good burn time without impacting Kerbin. Lessons learned (so far): * Moar SAS * 85km is way too close for such long burns * Moar monoprop * 6x LV-N is the bare minimum. (I can't believe I even considered 3x!)

Set aside some time tonight to get working on this challenge. Finally beginning my 42-minute ejection burn from Kerbin.

Managed to orbit my very first SSTO spaceplane. Granted, it's basically just a few fuel tanks with wings and a cockpit on, but still, it's an accomplishment ticked off. EDIT: And landed!

Phew! Finally got the mothership together, landers and all. Next step, ejection burn to Jool. But that'll have to wait a day or two - I have some other projects that must take precedence.

So close, yet so far. There was logic here, I assure you. I was afraid that, because my lander is asparagus-staged, the legs might clip fuel lines when they deploy, so I was planning to dock it to the mothership with legs extended. It worked perfectly in the VAB, because of course it did. Of course, in practice, the legs caught on other hardware and refused to let the docking ports connect. Ah well, just means another slight adjustment.

Now that is what I was hoping to see. Helio-slingshot into Jool. Very nice, you get #1! (51 km/s, holy kerbal!)

That's a problem I saw when designing my landers as well. It's the old Tyranny of the Rocket Equation. As you get heavier, adding Delta-V becomes an exponential problem.

Well, the idea of the challenge is to "get as much science as possible," so the Bay and Goo would be required. (I also wanted to make it somewhat mass-alike in payload.) But, if you want to submit this, I can make a "mini probe" leaderboard for options such as this.

I have two I'm kind of attached to. Sonbin Kerman was my Mun Exploration expert. He bounced from biome to biome collecting massive science. Halfred did the same thing, but for Minmus. Since I was with them for so many missions, I've grown attached to them. Or, as a famous android might remark, "I have become accustomed to their presence." Right now, Halfred is commanding my Farscape One station, and Sonbin is awaiting my Jool-5 mothership to be ready for crew.

I've officially started. Got my drive section in orbit; the largest thing I've ever launched (250t). Took me two days just to get it up there. The next launches should be a lot saner. Smaller/lighter payloads, easier on my laptop to handle. Hopefully I'll get the rest up and docked over the next couple days, and I'll launch for Jool probably mid-week.

Thanks for the input guys! In the end, I made a hybrid asparagus/onion design (7 stages on 6x symmetry) based on Kasuha's and Mr. Rocket's designs. 930 parts, it lagged my little laptop to death. Only 1-2 FPS at launch. LoL. It got a lot better once I was able to shed spent stages. In the end, I was able to get it into 84x91km orbit, with about 75 m/s of delta-v left over.

Following some catastrophic user error undesirable vehicle performance, an abort sequence was fired on my newest large lift rocket. (Read: all stages were fired at once.) The effect was rather... aesthetically pleasing. Especially with the Mun in the background.

Nicely done. You're now the top of the (admittedly short) leaderboard.