PLAD

These are very interesting and entertaining reports. At your space agency's public presentation of the Mars landings, a reporter looking suspiciously like my space agency's lead designer wearing sunglasses and a fake nose asks "how fast were the Mars landers going when they popped the drogue chutes and the main chutes?".

Thank You! Impressive UNSA mission reports, by the way! Your E-V-M-E mission was dramatic, and I learned something from seeing how you were able to correct for the suboptimal starting boost from earth orbit.

I executed an opposition-class mission to Duna, where I flew by Eve on the way home from Duna, some time ago, here it is. Back in those days we only used Earth time (24-hour days and 365 days in a year) so you will have to translate my departure, flyby, and arrival dates into Kerbin time if you use that. You don't have to look through the album for dates, I give a summary in the post. Note that at the end of the post show a path for flying by Eve while on the way to Duna. I've written a tool that searches for flybys like the Eve flyby you will need either on the way to Duna or when coming back from it, so you can search for other opportunities. Here's an example of a Flyby Finder search that shows a Kerbin-Eve-Duna-Kerbin path. Arrowstar's TOT can also plan missions like this. http://imgur.com/Xl67ivX I like these because they allow an abort of the mission if some problem prevents the Duna landing, you can just fly by Duna and shoot home for no extra dV. And if you land, there is of course a window immediately available for getting home if you only spend a day or two on Duna. (though it requires higher-than-usual dV) I personally prefer going Kerbin-Eve-Duna, because the departure burn to get from Kerbin to Eve is not much larger than a typical Kerbin-Duna burn (maybe ~200m/s more), but the Duna-Kerbin burn is smaller than a Duna-Eve burn (for flying Duna-Eve-Kerbin) when heading home. You have a higher arrival speed at Duna though, but if you can aerobrake that eliminates that disadvantage.

Thanks for the note, I find his addon extremely useful for getting the most efficient launches easily and was looking forward to this.

I certainly use your addon every time I execute an FF or Alexmun generated transfer. It is terrific. I never want to bother you or anyone to update stuff because you are doing it for free, and it is a lot of work to figure out what needs to be changed after every update and then write and test it (and I am glad for those who take them time to test it well), but I will say thank you for keeping this up. That is an odd new crash scenario. I'd agree that while it makes sense to have the initial path go through the center of the planet, it isn't necessary to be that exact because you can never execute the actual burn in LKO that accurately. Anything within a couple thousand km or so of center is plenty good enough.

I downloaded it from Dropbox and scanned it with my virus checker and didn't see anything, then compared the download to the original I uploaded and didn't see any changes, then recompiled it from the original source code and still don't see any differences between that and what I pulled off of Dropbox. (When you say 'it' I assume you mean the .exe.) So I'm down to a few possibilities: -There is a virus and it hides from my checks. -I'm using an old language and a virus checker might misinterpret unusual code as a virus. I don't use Avira so I can't check this. Does anybody else see this? I wrote FF to not write anything to disk at any time so it should be easy to spot any misbehavior.

Am I allowed to use a mission for both the easy and medium-level entries? I continued my 914m/s easy-level entry from the point where that ended and I made it back from Jool orbit to Kerbin. The delta-V count depends on how you define 'hitting' Kerbin- do exploding fiery chunks raining down on Kerbin count as hitting it? (or a 'thermally suboptimal descent' as I call it) Or can an 'orbit with a periapsis of <70km' be a hyperbola instead of an ellipse? If so, I made it from Jool orbit to Kerbin atmospheric interface for 49 m/s, added to the original 914m/s to get there gives 963m/s for the round trip. If the ship has to survive and get into a closed orbit around Kerbin, I did a modified ending of the mission where instead of piling it in at 4600m/s I flew J-K-K-E-K to arrive at a much more manageable 3400m/s. Then I let aerobraking do almost all of the work and got into a closed orbit around Kerbal with the periapsis lower than 70km for 96m/s of main engine dV, plus 3.4 units of monopropellant which adds another 2m/s, for a total of 98m/s plus the 914 to get there equals 1012m/s to get from LKO to Jool orbit and back to Kerbin orbit.

I wrote a little spreadsheet just for deciding when to launch from the major launch sites in RSS to fly to Earth's Moon. It is down near the bottom of the first post in my FF for RSS thread, it's called "MoonfinderB". This gives the details: I haven't verified the rotation speed for the Earth in the latest version of RSS (the one for KSP 1.1.x) though the config says it is the same as the previous version so I think it is good. The Earth's rotation period changed a few times over the various versions of RSS so I put a method to check each new version on page 2 of the spreadsheet. Note the one place it doesn't always work for is Kourou since that is at a lower latitude than the Moon's inclination, but from Kourou you should just launch when it passes directly under the Moon's orbital plane. Of course then you have the trick of figuring out what launch azimuth to use...

E-V-M windows are somewhat rare, however the following changes to the screen you show will find the next one: Hit "add" three times so the search window start dates are moved forward 300 days, so Earth will be 3106, Venus 3150, and Mars 3200. Then more importantly the search periods for Venus and Mars need to be increased, Venus from 100 days to 400 days and Mars from 200 days to 400 days. Your "V at SOI" is a bit low, try 5000m/s instead of 4400. Then you should find solutions. The previous window I found is to press 'subtract' 4 times so Earth starts at 2406, with the window periods at 400 and 400 days and Vinf at 5000m/s as above. It is often hard to get the first 'hit', try raising the V at SOI way up and enlarge the search periods way out ( I start at 1000 days) until you find something and can narrow the parameters.

Hello, and welcome to the forums! I do not know if you have just started using KSP with RSS installed, my first comment would be that it is good to use stock KSP for a while before moving to RSS as it is much harder than stock. If you have been using RSS for a while then I recommend starting with the two tutorials in the first post of this thread, one that is just for RSS and the one for basic Flyby Finder. -PLAD

I felt bad about using an old mission for this challenge, so I did a new one using KSP 1.1.1. I used a technique I've wanted to try for a while, and it worked! Here's the entry, LKO to Jool orbit for 914m/s. I have trouble seeing the paths KSP draws on the screen, so I've enhanced some of the pictures to make them clear so that others can try this method. It's basically two tricks sewn together, it starts with a Mun multi-flyby path and jumps to a KEKKJ path. The hard part was the jump, but enough jabbering... These are .jpgs, I'm curious if there will be a noticeable difference in load time. There is still room for improvement, if I started with the 5-Mun-flyby method I used in my KX-to-Duna-and-back flight it could theoretically be done for about 15m/s less, and I made about 10m/s of mistakes, so in theory a perfect pilot could do this for about 890m/s. It won't be me though, once of this was enough. It is way too much work to save the 100m/s or so over a normal KEKKJ flight for anything but a challenge. So this is my easy entry, I might try getting back to Kerbin (since the ship is in a useful orbit of Jool), but hard and ultra-hard are too much for me because I have a lot of trouble with spaceplanes.

I've done a few low-dv missions to Jool in the past, here are my two best, would either of them qualify? I did this one way back in KSP 0.23.5. LKO to Jool atmosphere with 1010m/s. I then aerobraked in Jool's atmosphere to capture into orbit, that would require a major heatshield with the latest KSP versions. After the aerocapture 1 more m/s put me in a stable Jool orbit, so 1011m/s from LKO to JO. If the aerobrake nullifies the above entry, I did this one using a Tylo flyby to capture into a closed orbit about Jool. This one took 1018m/s from LKO to Jool orbit. I really like this one since the craft was an SSTO with only 8 stock parts plus Mechjeb. Although that was in version 0.90, so it wouldn't make Kerbin orbit with the modern Rapier. (Note it took 1024m/s from LKO to Laythe surface, though I see that's irrelevant to this challenge.) I would suggest that entries have to give details on the route flown from Kerbin to Jool, showing major maneuver sizes and times so others can try the path. Jool and return for the fewest m/s adds an interesting wrinkle to this...

I made another try at an S1L1 cycler, this time using a big carrier and launching crew from Kerbin and landing them at Duna to see how those procedures would go. I also flew above Duna instead of beside it. Conclusions: -It takes about 2400m/s to get from LKO to a rendezvous with the cycler as it flies by Kerbin. -It takes about 200m/s to get from the cycler to Duna's atmosphere if a 20-hour transfer time is allowed. -With my skill at its current level the cycler uses a couple hundred m/s per one complete cycle. -Flying more above Duna than to its side allows a reduced flyby effect on the cycler path, and only needs a few m/s of z-axis corrections later. It is rather difficult (for me anyway) to plan the next cycle because I would need to see the 2nd-from-now Duna flyby before the next Duna flyby occurs, and the game can't reasonably be used to plot that many flybys ahead. As a result I need a lot of course corrections. Therefore I need a tool that plans this like Flyby Finder does. I shall be messing around with that for a while. The other option for people trying this would be to accept some very distant Duna flybys, where you never get closer than a million km or two to Duna. It is easy to keep coming back to Kerbin every cycle, the hard part is the Duna encounter. You'll note that the ships that get from Kerbin or Duna's surface to the cycler have to have more than enough dV to get straight to Duna (or back to Kerbin) on their own, so the only reason to do all this is to have the gravity and habitable volume of the cycler during the interplanetary transfers. And the cycler is only in use for about 10% of the time. It seems a lot of trouble for what you get.

GoSlash27, Yup. There is no energy to be gained by going K-K-somewhere, as long as no maneuver or flyby changes the path while you're out of Kerbin's SOI. You can change the direction you leave Kerbin at, but why not just launch in that direction in the first place and save a year of time? Well, wait... there are some neat tricks that just a tiny VILM can do though, for instance your needed departure path from Earth might have a very high inclination to Earth's equator, such that you would have to launch into a 90-degree-inclined orbit. This costs a lot since you lose the 400+ m/s of your launch site by not launching due East. So instead launch due East and then depart Earth into a Solar orbit that comes back to Earth a year later, but 90 degrees before you encounter Earth do a tiny normal thrust that gives you a 90-degree inclined flyby of Earth. Now you leave Earth in a highly inclined plane for just a couple of m/s more than a due-East launch would require! This competes with a bi-elliptic-style plane change, but is an example of why one might do a K-K flyby. Someone brought up the timing issue for the K-E-K-K-J flight, it is true that the mission is timed so that you cross Jool's orbit when it is there, and if you skipped the 2nd flyby you wouldn't encounter Jool even if you had the right direction after the first flyby. However the mission start is timed to take the 2 flybys into account, I use K-E-K-J flights sometimes if I'm in a hurry, but they are less efficient because the single flyby of Kerbin doesn't leave in an optimum direction so you have to start with more energy.

This thread is bringing up enough issues for about 5 threads, but here is my take on the initial question. @eddiew , if you leave Kerbin with a certain v-infinity (this is the speed your craft has relative to Kerbin just before it leaves Kerbin's SOI) and fly around the sun for a while and come back without making any maneuvers or flying by any other bodies, you will arrive back at Kerbin's SOI with exactly the same v-infinity as you had leaving (except of course you are coming in instead of going out). You can then flyby Kerbin and head back out of it's SOI moving in a different direction relative to the Sun then you had before, but you will once again leave Kerbin's SOI with the same v-inf as you had arriving. The big deal is that your craft's velocity is added to Kerbins velocity, and if, for instance, you leave Kerbin going 'backwards' relative to Kerbin's orbit around the Sun you will drop in towards the Sun, but if you leave Kerbin going 'forwards' your speed is added to Kerbins and you will go further away from the Sun. If you leave Kerbin at the right angle your orbit around the Sun might have the same period as Kerbin but be much more eccentric or inclined than Kerbin's, in which case you will encounter Kerbin exactly a K-year later. But always you will arrive back at Kerbin with the same v-inf you had (relative to Kerbin!) when you left it. An example of this is my Kerbin-Eve-Kerbin-Kerbin-Jool path, if you look at the craft's Kerbin departure angle relative to the direction of Kerbin's orbit around the sun you will see that although the v-inf is the same for both Kerbin passes the departure direction is different, and this is why the first pass only goes out to about Dres' orbit but after the second pass you get all the way to Jool. I took screen shots that point it out in the album. Indeed, the reason that two Kerbin passes are needed is that the ship is going too fast for Kerbin to turn it all the way to the right direction in just one pass. The excitement comes when something changes your path while you are outside Kerbin's SOI. In the example above that thing is the flyby of Eve. As a result of that, with no other changes, you come back to Kerbin with nearly 2km/s more of v-inf relative to Kerbin. Another thing you can do is make a small thrust while as far away from Kerbin as possible, this will cause you to come back with a much larger change in your v-inf than the thrust was. This is called a V-Infinity Leveraging Maneuver (VILM) and is the trick that the Juno probe to Jupiter is using. @Mad_Maelstrom came up with a way to plan this maneuver in the Kerbol system, check out his post here. This is also part of the trick that the Messenger probe used, after every flyby of Mercury it would do a VILM while opposite the Sun from its Mercury encounter, in this case it would greatly reduce the next flyby speed of Mercury (think of it as the Juno-maneuver being done backwards). I think what you are looking for is the VILM. To touch some other issues in the thread, Flyby Finder can also handle the Outer Planets Mod planets if that is the mod system you are using ( I haven't tried Kerbol Plus Remade so I don't know what that changes). There is a complication to the v-inifinity rule if you are flying around the moons of Jool, and to a lesser extent Mun, in that the 2-body method that KSP uses causes some inaccuracies if you leave a moon's SOI at the planetward or anti-planetward edge. For instance, you might have noticed that if you are in an orbit that just barely leaves Laythe's SOI, say by only 1 m/s, you will fly outward past Tylo if you leave Laythe's orbit at the anti-Joolward side. This is because while you are climbing away from Laythe the game is not taking extra energy away due to you also climbing away from Jool, because you are only in the SOI of Laythe. You can use this by approaching a moon on the inside and flying by so you leave on the outside and get some free energy, I use this in my Mun multi-flyby path that gets to Mun from LKO for only 845m/s instead of the normal 856 from a 75x75 orbit. But that is another story. (To me it is an entirely acceptable approximation and it compensates for not being able to do 3-body tricks like flying through L2 or L3 to leave a planet for free.) And then there's the trick that Vector found where you use a flyby of Mun during a flyby of Kerbin to change your Vinf, you can get to Duna or Eve for 873m/s from LKO with that one.

You are partly right, one of the simplifying assumptions all the cycler searchers make is that only Earth will affect the path of the ship, Mars will do nothing. There are two problems I see with that though, the smaller one is that in the real world Mars will always have some influence, and even in KSP you have to stay pretty far away from Duna to keep out of it's SOI, and by keeping far away from the destination planet you require a very long ride in your shuttle (depending on how much dV you're willing to have the shuttle use to get from the cycler to Duna). The bigger problem is that Duna's orbit isn't circular so the actual synodic period between it and Kerbin varies from cycle to cycle- in my 2nd test run above the cycler's closest possible pass to Duna to keep it on the right schedule was nearly 2 million km, because Duna was near its perihelion and moving faster than average. (And it's even worse in the RSS.) To me that leads to shuttle rides so long you might as well skip the cycler altogether. In practice the cycler will have to vary from the ideal path and the cheapest way to do that is use Mars to move it. In this paper the people who discovered the S1L1 cycler give an actual mission plan for an S1L1 that takes into account the real motion of Earth and Mars, take a look at table 6, one of the Mars passes is at less than 8000km altitude. Unfortunately this means that actually flying one of these things will require detailed advance planning. A Kerbin-Jool cycler is an interesting idea, as that is a long trip requiring a large start boost and a big cycler could save a lot of fuel. I took a look for paths using Flyby FInder and couldn't find any acceptable ones. My first suggestion would be to capture the cycler at Jool for free using Tylo, then kick it back to Kerbin for free when your mission is done. If you could do a flyby of Kerbin that goes back to Jool in 1212 days (so 2 solar orbits later, a reasonable near-Hohmann orbit between Kerbin and Jool can have a period of 606 days) without slowing at Kerbin you would have a cycler that goes K-J-K-J-etc. for almost nothing. 606 days is 5.7 Kerbin orbits though so you would only encounter Kerbin once in those 1212 days. Argh...that's no good. I dunno. I'll watch that thread to see if you find something. -edit-note all times are in given in Earth days.

Seeing this old thread come back to life is nice, trying to win this challenge drove me to write my Lambert spreadsheet which then evolved into Flyby Finder. However Metaphor owned this one, check his post on April 8th 2014, he does indeed do a Messenger-style flight, flying by Eve twice and then Moho 8 times to reduce his Moho orbital insertion burn to an extremely small value. I tried to improve upon it but only managed 3 Moho flybys before my insufficient skill sent me off course. It takes a lot of practice to do this stuff well.

That is an interesting question. My guess is that a z-axis only perturbation from Duna will not change the period of the Solar orbit, which is the desired result. I'm going to try it. The trick is that the ship has to stay in the plane of Kerbin's orbit between those two Kerbin flybys so a small thrust might have to be done later to get back in that plane... although it might not if the Duna flyby is just right... This stuff is tricky. Yesterday I tried to run the S1L1 path when starting with 50m/s more (so 1305 instead of 1255) just to see what happens. It turned out I could still find a path that repeats every 454.8 days, the biggest change was the timing of the 1st Kerbin flyby- instead of 301.25 days it was 299.25 days, but the second leg could be made 2 days longer (so 155.5 days instead of 153.5) by flying by Kerbin a little closer. In other words if one of the two 'legs' of the trip is made longer by adding energy, the other one can be made shorter to compensate just by adjusting the Kerbin flybys. It makes me wonder why the discoverers chose the timing for the 1st flyby that they did- my guess is that they chose it so that the two Earth flybys happen at exactly the same altitude, or maybe it's the minimum energy that works. More experiments! I could figure it out much faster with the right tools. This is the sort of thing that drove me to write Flyby Finder, but this would be much more complicated and might be beyond me. Here is a paper giving a robust Lambert multi-orbit algorithm, look at equation (5) on page 5, that's the formula that has to be iterated using the values for F'(Xi) and F''(Xi) from the appendix. Holy crap! The even bigger problem is that there can be more than 1 solution for getting from here to there in a set time when multiple orbits are allowed, so how does a program pick the best one, or how do you display all the possibilities in the output? This is what stumped me in trying to add 360-degree double flybys to Flyby Finder. On the bright side, I will never, ever tire of playing KSP. There are too many interesting things to be tried.

A cycler is a craft that repeatedly passes between two or more planets. The concept is that a large spacecraft with lots of amenities could be used as a residence for long interplanetary trips, smaller shuttlecraft would do the high-delta-V transporting of the crew between the destination planets and the cycler as it flys by. I've seen it discussed a lot in KSP, but here are some articles on the concept. Quick introduction: Mind-numbingly complicated but thorough: I'm not sure of the practicality of cyclers over fast high-energy missions, but the search for cycler paths fascinates me a great deal. Earth-Mars cyclers are the most studied. Almost all papers I've seen make 3 simplifying assumptions about the motions of the planets to ease the search, as follows: 1) The orbits of Earth and Mars are circular and coplanar. 2) Mars' orbital period is 1.875 times Earth's. 3) Mars makes no change to the cycler's path, only Earth does. As we shall see, these assumptions cause problems when it comes to actually flying these paths. Some of the cyclers are described are ballistic, that is, after the cycler is placed in its path no further dV needs to be expended other than small course corrections. Others require substantial manuevers to keep them on track, for instance the Aldrin cycler requires a 230m/s or so correction every synodic period. Kerbalnot posted his execution of the Aldrin cycler in KSP here, check it out. A key element to cycler trajectories is that the positions of the planets and the ship repeat after a set time, this time has to be a multiple of the Synodic period of the two planets. In the case of the ideal Earth-Mars this is 2.143 years, for the real planets it is 779.95 days or 2.135 years, for Kerbin and Duna it is 227.38 Earth days or 909.5 Kerbin days. This means that if your ship leaves Kerbin on a given day, and then comes back to it 454.76 Earth days later with the same energy and moving in the right direction it can repeat the Kerbin-Duna-Kerbin path indefinitely. Note the requirement about the energy! It is easy to find a path that goes K-D-K, and even one that does it in 455 days, but it will come back with much more energy that it left with because of that flyby of Duna! If you don't use a Duna flyby or a deep-space maneuver then it is tricky to get back to Kerbin when it is that extra .135 orbits further in its path, so the big challenge in cycler searches is moving the apsis of your Solar orbit forward. In the last few years a very good cycler orbit has been discovered for the Earth-Mars run, it is called an "S1L1-Ballistic cycler". Here's the paper by the original discoverers. Here's a video of the path: Check out the low Earth and Mars intercept speeds, most other cyclers fly by much faster, especially ones that repeat after only two synodic periods. This cycler works even better with Kerbin-Duna because Kerbin's orbit really is circular, so running it in stock KSP is a great way to study it. Also Duna's SOI has a limit, so you can fly fairly close to Duna without it affecting your path unlike in the real world. So I first figured out the S1L1 path without the flyby of Duna, I wanted to see if Kerbin system could emulate the flyby angles and rotation of the apsis necessary without the complication of flying by Duna. Here it is. Note I'm using Earth time, I'll translate to Kerbin time below. I'm using a great little mod called Slingshotter, it is helpful for planning this sort of thing. Success! My ship returned to Kerbin 456.4 days after leaving it with only 9m/s less V-infinity. It only used 11m/s for course corrections after the initial 1255m/s to get started. Note that one cycler would only do the Kerbin-Duna run once every 2 synodic periods, and only in one direction. You would need another one timed to encounter Duna on the way in for the return trip, and another in-out pair to cover the other synodic periods. These limitations are common to all cyclers, I've seen paths that would require 14 cycler ships in order to be able to get a ride inwards and outwards every synodic period! So in Earth days if you initially leave Kerbin at 0 you must fly by it again on day 301.24 and day 454.76. In Kerbin time this is day 1205 (2Y 353D) and day 1819 (4Y 115D). Now I ran the path again, but this time with a flyby of Duna. Ouch! The flyby of Duna added a lot of energy. I think this can be compensated for by flying by alternating sides of Duna, or one could stay outside it's SOI at all times. That leads to spending several days in the shuttle vehicle and a couple hundred m/s of dV to get from the far-away cycler to the planet and back though. The bigger problem is that Duna's orbit is not circular and so it will not be in the same place relative to Kerbin every 454.8 days! This means you must change the cycler orbit constantly back and forth to pass close to Duna each time. This could be done using flybys of Duna, but I don't have a tool to calculate how to set this up yet. I need something that handles multi-orbit, symmetric double flybys. In Kerbin time this cycler started Y1 d67.68, flew by Duna Y1 d104.3, 1st Kerbin flyby Y2 d2.8, 2nd Kerbin flyby Y2 d158.4. In Kerbin time this is start Y1 d267.72, Duna Y1 d414.2, 1st K Y4 d190.2, 2nd K Y5 d386.6. Has anyone else tried this?

I actually don't determine the LAN of the start orbit in the calculations, though it is a reasonable assumption as it could be figured out from what is calculated. However Okder came up with a superb addon for Mechjeb that tells you when to launch, shows the best parking orbit, and sets up the transfer node to the first flyby planet (in KSP as you are running it), all you need from FF is the start day and flyby day at the first planet. I put a review and runthrough of it in it's thread. It beats being given just the LAN, I recommend it.

Flybys! I know of two tools for finding flybys in KSP, my Flyby Finder and Arrowstar's TOT. It is possible to leave Kerbin at a random time and find flyby opportunities by chance because the Kerbol system is small with high-gravity planets, but using the tools above makes it much easier to achieve a specific objective. Here is what I have found after doing many, many flybys to and from all the stock planets. In general only Eve, Kerbin, and Jool should be used for flybys as the other bodies are too small to be worth the trouble. Here's how I get to them all... To get to Moho from Kerbal you should fly by Eve. This is both the hardest one to execute and the one that gives the most benefit, little Moho is moving so fast that even a small mistake in timing the Kerbin departure or Eve flyby will make you miss Moho. However once your ship is in an orbit that crosses Moho's orbit it is usually easy to plan a Moho encounter several orbits out with only a small adjustment to your path. Even better is to go Kerbin-Eve-Eve-Moho but that requires a double flyby which neither FF nor TOT can plan for you. I use my Lambert spreadsheet to find double flybys, it can be found in the FF post. It requires trial-and-error to find a flyby, if you study this old challenge you will find us working out things like when the best times to flyby Eve are and how to set up the Eve double encounter. To get back from Moho to Kerbin you should also use Eve, Moho-Eve-Kerbin is rather easy if you can wait a year or two at Moho for the next window. No flyby needed to get to Eve, though you can save about 60m/s by using a Mun flyby, see the link in the Jool flyby below. No flyby needed to get to Duna, but you can go K-Eve-Duna if you want to get to Duna cheaply outside the normal Hohmann windows from Kerbin. See here for an example of this. Dres is the hardest. I have found that using a flyby of Duna to get to Dres is not useful, because Duna is too small to change your path much if you fly by it with enough energy to get to Dres, so the windows are very rare (~30 Kerbin years apart) and the gains are less than 50m/s. I even tried a K-D-D-D-Dres (triple flyby!) and find I spent more on mid-course corrections than I saved in using Duna. However, it is can be advantageous to use Jool to get to Dres! Although it takes about 200m/s more to get to Jool than Dres you can knock more than 500m/s off your Dres arrival speed for a net savings. If you use Eve to get to Jool you can save even more. To get to Jool cheaply you should go to Eve first. Using typical values (rather than best possible with perfect alignments) it costs about 2000m/s to get from low Kerbin orbit directly to Jool. It's about 1900m/s to go K-Duna-Jool. It's about 1300-1500m/s to go K-Eve-K-Jool. It's about 1100m/s to go K-E-K-K-J. Here is a thread that gives mission examples of KEKKJ. I found that superb window using Lambert and trial-and-error. Another intriguing option for getting to Jool is a Juno-style Kerbin flyby with a deep space manuever. Check out this post for how to get to Jool for about 1550m/s. To get to Eeloo you should fly by Jool. Because they orbit so slowly there are extended periods with no fast and cheap window for this, but if you can get to Jool it can throw you to Eeloo wherever it is if you are patient. Note that you can use Eve to get to Jool and from there to Eeloo, check out this trip I made using KEKKJ-Eeloo, and then Eeloo-J-K to get back. Nowadays with the modern aero model requiring lower Kerbin re-entry speeds it is useful to flyby Eve on the way back from the outer system to reduce your Kerbin arrival speed. Remember the concept of synodic periods, in the Flyby Finder primer I give a table showing the periods between which the relative positions of the planets repeat, if you find one good window it will often repeat after a set period. NASA uses more tricks than FF or TOT can calculate, for instance deep space maneuvers and multiple orbits between encounters, I do not anticipate writing anything that handles those anytime soon. Does Rich Purnell play KSP? And a final note on flybys- they are not too forgiving of errors in timing. The more flybys you do the more precise the early ones have to be or you will require bigger and bigger course corrections to stay on track, or you might miss the last planet altogether. Try to leave the start planet within an hour of the time that TOT or FF gives you, and remember when doing mid-course corrections that it is more important to have your flyby periapsis at the right time than at the right altitude or speed.

I've just released version 0.83. It adds a "subtract" button to the 'Change all search dates by' field to go along with the "add" (was "increment") button. I also added a new field to the detail box which gives the start boost for a given path if you were to start in an equatorial orbit instead of an inclined orbit. There was a discussion about this in another thread some time ago, now you can compare the two ways to see if it's worth the extra trouble of getting into an inclined orbit. This release also fixes a bug in the day converter box, it used to give a value for the UT days that was one too low. The outputs in the table, graph, and detail box were correct so this wouldn't have affected any flight calculations.

There was a challenge to get from Kerbal to a Moho landing with as little dV as possible a while back. It is here. In the end a messenger-style path was used as it was best. The real probe flew by Venus twice then Mercury twice and entered Mercury orbit on its third pass, Metaphor did 8 flybys of Moho to cut his arrival speed down incredibly low. If you look closely at the albums you can figure out at what times they launched and did their flybys. Note that back then there was only Earth time (24 hour days/365 day years). It took a lot more dV to get into Kerbin orbit back then too, so take that into account in your dV estimates for a modern mission. Some other people have done Messenger-style trips since then, but no one has ever beaten Metaphor's trip. That strategy of flying by Mercury and then doing a deep-space maneuver to correct for your next Mercury flyby is hard. (For me anyway!) But it can cut the total dV required by 30% over a standard Hohmann trip.

That's a good idea, and not hard to make. Hmmm... there are a couple of other small tweaks I've been thinking about, I'll push out a small upgrade in week or so.

Thanks! The Soviet LK lander had some pretty bold mission parameters, not the least of which was putting a lone astronaut on the Moon. Its c.g. had to be within 30mm of the thrust axis or it wouldn't be stable...and the astronaut had to spacewalk to and from it to the Earth Return Stage. And they actually made three Earth-orbit test flights of it. At least the lander docked to the ERS before the spacewalk, with the small open lander designs you would have to jump across open space to get back to the ERS. Both sides came up with some even more extreme designs in the early '60s, before the Outer Space Treaty was signed and they no longer had to worry that the first nation to put a man on the Moon would claim the Moon as theirs. I recall there was an early plan by the US to land a lone astronaut on the Moon before they had a way to get him back! They would finished development and construction of a return vehicle while he was waiting on the Moon for about a year, kept alive with resupply missions. Darn, I just looked for a reference to that plan and didn't find one, does anyone remember its name? Edit: found a nice secondary source here. I don't think I can find the December 1962 Aerospace Engineering article online though. Of course, that is a mission most of us (me included) have done early in our Kerbal careers, without exactly meaning to.