PLAD

Say, has anyone sent a RO mission to Mars that aerobraked into orbit? I figure you'll hit it's upper atmosphere (starts at 130km altitude) at between 6000 and 7500 m/s depending on your transfer path, and I'm wondering what vacuum periapsis will at least get you into a highly elliptical orbit without a braking burn. And how much ablative material it will use. I bet the corridor is really tight, what with that thin atmosphere. I've got Hyperedit so I can figure it out the hard way, but I thought I'd ask.

More coincidental. When I first touched the atmosphere I had the lift pushing down because I used a vacuum perigee of 65km, the highest I've yet tried. I made sure the 1st perigee would get down to about 58 km before rotating the lift to be upward. I stay upward until around 65km then try to stay between 70 and 60km as long as possible. I took that picture while in the middle of an up-down switch. I keep trying to lower the maximum gees during re-entry, my best is about 4.8 gees so far. Though I think the real astronauts took a less complicated path. I love the descent mode, it's yet another nice touch of realism.

Multiple flybys of the same planet can change your Kerbol periapsis even if you do no maneuvers or encounters of other planets. What they cannot change is your speed at a given altitude above the flyby planet. I use the speed at the moment you enter (or leave) the SOI of a planet as the reference speed, I call it the VSOI. In the Moho Challenge that Metaphor won with style you will find that his VSOI at the two Eve flybys was the same, he just changed the direction he was going relative to Kerbol. I was in that challenge, as I recall the first pass was to match the plane of Moho but not reach its periapsis, the 2nd flyby lowered the Kerbol periapsis to Moho's orbit. The reason that two passes were needed is that Eve does not have the gravitational chops to change your path all at once- you'd have to flyby well below it's surface to do the plane change and periapsis change in one flyby. Mind you I've tried that, unintentionally. Another example of this is my LKO to Jool for 1051m/s mission. I have to flyby Kerbin twice, notice I specifically show the direction and Kerbin-relative speeds I'm leaving Kerbin at after each pass, the first time is at a large angle from Kerbin's path around the sun and the 2nd pass departs much closer to parallel to Kerbin's orbit, thus the ship and planet velocities add up to a higher prograde speed around Kerbin and thus an apoapsis high enough to get to Jool. And as noted, Metaphor's repeated Moho passes lower his Kerbol periapsis because he does a deep-space maneuver after each one. Flying by 2 planets has the same effect (the 2nd planet flyby is like a deep-space maneuver), by going Kerbin-Eve-Kerbin-Eve you can build speed up to Kerbol escape velocity if you do it right. I know it's tooting my own horn but here is another extreme example of flybys, in my Jool-5 mission the carrier gets from LKO to a flyby of all 5 Jool moons and back to Kerbin on only 1415m/s by using 22 flybys. And there is a 2nd flyby calculator for KSP-Flyby Finder. It's not nearly as feature-rich as TOT but it's quick. PS- "NASAHireMe"-you have my new favorite forum name.

I consider Tsiolkovsky the most beautiful crater on the Moon. It's the mix of light and dark combined with that magnificent central peak that does it for me. I've been getting competent at missions to the Moon with the Realism Overhaul set of mods, and I finally was able to land a mission in it. Here it is. I vastly prefer Lunar Direct missions to Lunar Orbit Rendezvous missions because you can land anywhere without having to worry about getting back to the plane of the orbiter. And with the real Moon you also don't have to worry about the orbiter's orbit being unstable over time, if you want to spend more than a few days on the surface. So as my Kerbals continue to explore and develop the Moon I will go exclusively with direct missions. And they're only about 10-20% heavier at launch for the same cargo on the Moon as a LOR mission. I'm using all of the required RO mods, as well as most of the recommended ones except for Engine Ignitors and Remote Tech. And about 3/4 of the suggested mods as well.

I keep one install of KSP that is all stock except for Mechjeb and Hyperedit and I don't mess with that one. But I have a Realism Overhaul install where I removed all tanks and fairings (stock or mod), and every stock unmanned pod and utility part I don't use. (Thank you procedural tanks and fairings!) It still isn't enough to make room for all the mod parts I want, I'm going to try the idea above to remove the big IVA files. I love the fact that I can do this sort of thing if I want to.

Hello Nathan Kell! You have some superb mods here, I've been using Realism Overhaul for about a month now and am having a blast. I wrote an external program that searches for flybys in Kerbol System and now I am making a version that works for Real Solar System. I have a question: Earth's semimajor axis seems a bit small. In RealSolarSystem.cfg it's 149,494,366.257 km. I know the actual value varies a bit over time but the JPL value is 149,597,870.7km. This means the Earth's sidereal year in RSS is about 8 hours short. I can think of reasons you might tweak the values but I want to make sure it's deliberate. The other planets all closely match their actual values. Thanks for making these realism mods, they make an already exceptional game even better.

Funny you should ask about Real Solar System. I have been using the Realism Overhaul mod set for about a month now, it's been so fun I haven't touched Stock in that time. I always felt a bit guilty when aerobraking at Jool with a ship that had legs and struts sticking out all over the place, or sending a Kerbal on a 10-year mission to Eeloo with no food or air. For those who might take this as criticism of stock, it's not- I like the way one can start with most real-space difficulties turned off. It let me have a lot of fun learning the astrodynamics without having to worry about other aspects of space flight. Now I'm ready for more. Plus it's fun to think one could actually build the craft I've been building. I've got to post my Moon direct mission somewhere. In any case, I've mastered RO Moon missions and am turning my gaze to the planets, so that means I need... EDIT: I've moved all pictures of FF for Real Solar System to the release thread for it, link is below. I don't have to worry about whether to use the 24/365 or 6/426 time systems with this! It's not ready for prime time though. There have been some extra tricks in teasing out the planet start positions and the precise value of big G in RSS. I need to test the accuracy of the program out to 10 years or so to see if I have it right. I've only tested flights to Venus in the first 2 years so far, so I don't want to release it yet. But I'm working on it. Hah- you're immelman- I used one of your superb grand tour missions as a test of Flyby Finder's accuracy out to 20 years in stock. Have you done any big missions with Real Solar System? UPDATE: I have now released FF for RSS, it is here.

Here's how you can calculate when Kerbin will pass through the plane of any other planet's orbit, using Moho as an example. I always use Earth time, 365/24. In the official KSP wiki you can find the orbital parameters for all the KSP bodies. For Moho we find that its Longitude of Ascending Node (LAN) is 70 degrees. (We don't know what direction 0 degrees is yet but we'll get to that.) Moho's orbit crosses the plane of Kerbin's orbit twice, once going up and once going down. These two must be exactly 180 degrees apart, so we now deduce that Moho's descending node is at 250 degrees. This means if you leave Kerbin when it is at 70 degrees or 250 degrees you will be exactly in the plane of Moho's orbit. We determine these times by noting that the wiki says Kerbin's Mean Anomoly at 0s UT is 3.14 radians. This equals about 179.9 degrees, so now we know where Kerbin starts. Since Kerbin's orbit is circular it moves the same speed at all times, which is 360 degrees every 9,203,545 seconds, or 106.52251 Earth days. This is 3.3795673 degrees per day. Therefore Kerbin first crosses Moho's descending node at (250-179.9)/3.3795673 = 20.7423 days after game start and crosses Moho's ascending node at (360+70-179.9)/3.3795673= 74.003556 days after game start. Since the game starts at day 1 (and not day 0!) that means you can first launch from Kerbin into the plane of Moho's orbit on day 21.7423 and day 75.0036, and every 106.5225 days after those two dates. The reverse question is trickier, when is Moho in the plane of Kerbin's orbit? We know it will be when Moho is at 70 or 250 degrees, but because Moho's orbit is not circular it does not move the same distance every day. You have to use a Kepler algorithm to get the exact times. Moho first crosses Kerbin's orbital plane on days 13.128 and 25.09, and every 25.6453 days after those. An even more interesting challenge is determining when, for instance, Eve crosses the plane of Moho's orbit. Now you have to cross-multiply the normal vectors of the two orbit planes (which you find by cross-multiplying the radius and velocity vectors at a chosen time) to get the angle of the nodes, then use a Kepler algorithm to find when the planets are first at those points. I leave that rather hairy problem as an exercise for the reader. Note that none of these tell if Moho will actually be there when you arrive at its orbit. The best way to determine when to leave Kerbin for Moho is using a pork-chop plotter like Alex Mun's.

Try running an opposition-class mission using a flyby of Eve to minimize the time waiting on Duna. Here's an example I ran some time ago. I use the 365-day year/24-hour day system so you'll have to translate the numbers to the 426/6 system you are using. For about 1000m/s more than a Hohmann mission (assuming you aerobrake at Duna) you can get to Duna and back in just a few days over 1 Kerbin year with the right flyby if you spend only 1 day on Duna. I'll give an example in 365/24 format and then 426/6 format so you can catch if I make a mistake in translation: Leave Kerbin year 1 day 58 at 1288m/s from a 75x75km orbit, arrive at Duna Y1 day 94. Land, take off. Leave Duna Y1 day 95 at 1270m/s from a 75km orbit, flyby Eve on Y1 D146, arrive at Kerbin Y1 D166. I think in 426/6 that's Kerbin Y1 D232 - Duna Y1 D376. Duna Y1 D380, flyby Eve Y2 D158, arrive Kerbin Y2 D238. I never did try flying by Eve on the way to Duna. That might save d-V.

I think KSP is great the way it is, thanks to the availability of mods. I used Orbiter when it came out long ago, but the difficulty of doing basic tasks like building a rocket or landing made it harder to enjoy the excellent physics simulation. Stock KSP is a great way to be introduced to astrodynamics, I've had a lot fun the last few months playing with flybys to find the lowest-dv paths to the various planets, I can concentrate on that and ignore things like fuel boil-off or ignition counts. But I also made a Realism Overhaul install for when I want to wrestle with a lot of more realistic details. The key is I can tweak the features as I wish, so for me it will be a long time before I tire of this game. And getting around to the original subject of this thread, try Realism Overhaul with the recommended mods. No more returning from Mun in a command can with no heat shield, or launching a pancake!

Here is my all-rocket entry. 17.47 tons on the launchpad, but I used some of Mechjeb's autopilot functions so I'll lose a lot of score for that. It was fun to try and strip every unneeded kg from the command can. Using wings saved 0.06 tons over using a parachute (not counting the extra fuel it would have needed), and increased the total dV for the whole thing by 81m/s. And there is no reason to slow the command can into a low Munar orbit. It is all stock except for Mechjeb, do I still get the 'all stock' bonus? if so then 1747 points on weight minus 150= 1597 points minus the appearance points?

Yeeeehah! How long I've anticipated seeing those words... Thank you Ziv for keeping up this challenge, the time and effort committed looks quite large. And I've learned many, many useful things from studying all these entries. As an aside I checked on Mechjeb's accuracy on reporting jet dV by setting a jet hovering just above the launch pad for several minutes (using MJ's translation function in 'Vert' mode with V set to 0), then dividing the dV expended by (seconds spent hovering times 9.81). Ideally I'd get 1.0, but I get 1.25. As a control I tried it with a normal rocket and got 1.0. BUT, with the jet the thing bobs up and down like a clown on a trampoline (it's fun to watch) so the constant throttling up and down might be having an effect. So I shall consider indicated jet dV to be unusable for accurate mission dV, and all I can say is my mission did LKO to the Jool 5 landings to Kerbal surface for about 22000m/s.

It took me about a month to run the mission though I'd been testing designs and ideas for a long time before that, off and on. And the full-up runs to Mun to test the assembly. Maybe 60 hours spread over a couple of months. Insane, I know. But it's how I relax. I felt there was no way to beat Mesklin's low-mass entry, not that I was willing to try anyway. The low-dv path was tricky enough- trying to do it with a low-thrust ion drive, always worrying about the sunlight would have made it too tough for me. So I decided to go for the lowest dv possible since that's my favorite thing. I wish now I hadn't used the jet on Laythe since it distorts the numbers, but one of my design criteria was to keep it below 200 tons without using nukes. I'll be happy 2nd from the bottom of the low-mass subchallenge, if it mentions I did the mission with 22,124m/s. Although if I'd used a rocket and parachute on Laythe I could have done it with 18,000m/s. Unless I can prove that Mechjeb records jet delta-V incorrectly. I think some tests are in order...

I've wanted to do the Jool 5 challenge for a long time now, when I first found a 1051m/s to Jool path I was planning to use it for this. And now, finally, I managed to do it. I tried to do it with as little dV expended as possible through the wonder of flybys, here's a summary of the flight: -Poor Jeb had just a lander can for the whole 2 year, 301 day flight. I assume Kerbals can go into hibernation or something. -I did it in version 0.24.2. 0.25 came out after I completed flight testing and I wasn't going to redo it all. -197 ton launch weight, all stock except for Mechjeb. No nukes or ions and only one jet, used for the Laythe landing/takeoff. No buried parts except for a couple of the little cubic struts that I used as mounting points for motors (and for a while, parachutes- then when I ruled out 'chutes I couldn't get the struts out!) -22 flybys: 1 of Mun, 1 of Eve, 2 of Kerbin, 4 of Laythe, 4 of Vall, 6 of Tylo, 2 of Bop and 2 of Pol. -It is a carrier/fuel depo and a universal lander. The carrier never went into orbit around any moon, or more than 4 orbits around Jool without a moon flyby. It would drop the lander at each moon during a slow and low pass, then pick it up at a later pass. -Launcher/Carrier dV expended: 1070m/s from LKO to 0-degree inclination orbit around Jool just before dropping off the lander for the 1st time. 245 m/s from there to picking up the lander the last time. 100m/s from there to Kerbin atmosphere. 1415m/s total. -Landing dV expended. Remember the lander had to decelerate from flyby speed to landing, then takeoff and get back to escape speed to meet the carrier. Pol: 489m/s down, 504 up: 993 total. Bop: 633m/s down, 694 up: 1327 total. Tylo: 3493m/s down, 3412 up: 6855 total. Vall: 1186m/s down, 1278 up: 2464 total. Laythe is a special case because of the jet. Mechjeb said the jet expended 8256m/s but that seems really high for what it did, and for only using 41 units of fuel. 591m/s of rocket dV was used. And 223m/s for the parachute-less landing on Kerbin. Below are links to 7 Imgur albums detailing the trip . I may have gotten carried away with the pictures, sorry about that. Note that the "delta-V stats" that Mechjeb reports are confused by docking ports, and since the crossfeed goes on and off a lot the numbers go all over the place. The custom window "DV Expended" seems quite accurate as long as I recorded the carrier dV before it redocked and got zeroed out. http://imgur.com/a/13tuj http://imgur.com/a/yUjGt http://imgur.com/a/vxPWJ http://imgur.com/a/P65S0 http://imgur.com/a/D6WaS http://imgur.com/a/DOrHC http://imgur.com/a/kXCeC

I was proud of that trip to the Mun but I later saw a YouTube video of someone making it to the Mun's surface And Back to a soft landing on Kerbin in 59 minutes and 57 seconds. So mine would be a placeholder at best. But it is here: http://imgur.com/a/r10j1 Will this thread accept a section on 'Lowest dV expended from LKO to...". I've been slowly collecting a number of those but it's somewhat specialized because of the number of rules in the entries.

Yup, I had a lowest dv challenge for getting from LKO to Eeloo's surface some time ago. I did that for 1934m/s, just the part from LKO to low Eeloo orbit was 1324m/s. But I didn't note the fuel used anywhere and the ship wasn't manned so I can't use that. We had a great discussion over the best path to follow. I then entered in an SSTO to Eeloo and back challenge, and that ship was manned, and because it was SSTO and I recorded the weight at various points I see I got from LKO (74x74km) to a stable ~5x75 orbit around Eeloo for 1.56 tons of fuel+oxidizer (and 1192m/s). It used a command pod MK1 instead of the lander can MK1 though, since that is heavier is it allowed? I'd like to use that to enter in this if I can, though I can see a few ways that it can be beat by optimizing for fuel use instead of dV. It wouldn't be too easy though.

I just realized that the Mun's SOI is 'falling' towards Kerbin while the ship is in it, and as a result during the 34 minutes the ship is in it the Mun's speed changes 51m/s towards Kerbin (relative to the entry point) so no tricky calculation needs to be done when switching back. Doh! I am getting a bit off the topic of the original post here, I'd like to finish by saying that in my opinion KSP does a superb job of simulating flybys, plenty accurate enough for anyone not flying real spaceships.

We can be sure that only Mun's effects are considered while the ship is in Mun's SOI, as is done in by a patched-conic approach. Back in post #63 my first test ship entered Mun's SOI going 1179.4m/s relative to Mun. 34 minutes later, at the same distance from Mun and just before leaving it's SOI it is once again going 1179.4m/s relative to Mun. If anything else was affecting it's motion during that time it would not have been going that speed. In particular it was 2000km further from Kerbin at the end of the Mun pass so if Kerbin had been pulling it towards Kerbin then it would have been going about 70m/s slower just before leaving Mun's SOI. I think the question really is, what calculation does the game use when switching SOIs? If the game just switched the reference body but kept the velocity the same then the outward motion relative to Kerbin would have been about the same as it was going in- in this case 989m/s outward (modified a bit by the Mun pulling it outward and to the left relative to Kerbin during its flyby). Instead it has been reduced roughly properly. I'd love to see the algorithm they use for SOI switches, though we could figure it out the hard way.

Doh, Cantab you're right, I'm just checking that KSP does the patched conic approximation correctly. If I check it's performance against what would really happen I will find it off. Here's my favorite example of that, from my low-dV-to-Mun mission. I've just entered Mun's SOI and done no braking yet: I usually like my hyperbolas a little less.. closed... If Mun's influence had been working on the ship from infinity (or at least from Kerbin) I would have had to use about 245m/s to brake into that planned circular orbit instead of 209. So I'm not complaining. But yah, KSP's paths will differ from real-universe theoretical performance by dozens of meters per second and by flying right you can use this to your advantage.

Here's the experiment I did. I think KSP is doing everything just the way it should, given that it uses patched conics. (And I think it's great that it uses patched conics, because it makes it run much faster with not much loss of accuracy!)

I did some experiments and I think KSP does alright. I set up flights that went straight out from Kerbin at about 1000m/s at Mun's altitude and measured the outward speed at about 9200km, 11200km and 13500km 3 times- passing in front of Mun, behind Mun, and with Mun nowhere near. I had to use different altitudes to make the flyby periapsis and Mun-SOI-durations roughly the same. Summary- if you pass behind Mun (but through it's SOI) it does indeed reduce your outward speed loss, by 24m/s in my test (1900km perimun, 34 minutes in Mun's SOI). But if you pass in front of Mun it increases your outward speed loss by roughly the same. This happens even though Mun only changed the velocity vector by about 2 degrees. It all fits the math. But now I still don't know why my Mun flybys are so error-prone.

That is an interesting insight. Almost every time I do a Munar flyby on my way to Eve I have to do a 10-20m/s correction afterwards, no matter how precisely I try to do it. It reduces the 100m/s or so savings it looks like I'm going to get to only 80-90m/s when corrections are included. If KSP's path-predictor doesn't take this into account it would match the magnitude of the error quite nicely. Some experiments and number crunching are in order here... And thanks. At least 90% of what I know about KSP I got from reading other people's posts.

I use flybys all the time, maybe a little too much. As people have pointed out, it's quick to add more dV to a craft, but it takes a lot of precious real-world time to execute an overly complicated mission. But oh the things that flybys can do... I've made it from Low Kerbin Orbit (LKO, for me 75kmx75 or less) to Jool orbit for 1011m/s. I've made it from LKO to Eeloo's surface and back for 2897 m/s. I've made it from LKO to Mun's surface on 1644m/s and back to Kerbin for 813m/s. (That took 26 game days and about 20 real-world hours!) Metaphor made it from Kerbin's surface to Moho's surface for 7217m/s. And for the ultimate in using difficult flybys to save a little dV check out where Vector made it from LKO to Eve's surface for 873m/s! I haven't had the guts to try and use his trick to get to Jool for around 900m/s but I bet it could be done. I use Arrowstar's TOT and my own Flyby Finder and Lambert spreadsheet to plan the paths. Note that I know of no tool that can plan flybys of moons, just the planets. Some of the links go into great detail on how to use flybys. Good luck!

I tried to get the old Kerbal-X to the Mun and back again with the 6854m/s of dV it has, and failed, but I got from Kerbal's surface to Mun's surface and back again for the lowest delta-V I've seen. Here's the post I think this method is a little better than the bi-elliptic method because of the trick of only starting with 845m/s to get to the inner edge of Mun's SOI, then using multiple Mun flybys to get flung way out, then doing a small second burn to arrive at Mun with a very small relative velocity. But check it out, I tried to show everything so others could try it. I would be fascinated to see it be beaten. Summary of dV used: Kerbal surface to a 70x70 orbit(I used normal rockets): 4352m/s TMI: 845m/s Mid-course corrections and deep space burn: 2+13=15m/s Braking into a 6.3x8.8 Munar orbit: 208m/s Munar orbit to surface (5908 meters altitude): 575m/s So far it's 1644m/s from LKO to Munar surface, 5996m/s surface-to-surface. Munar surface to a 9.3x9.3 Munar orbit:584m/s Munar escape: 205m/s Course adjustments and deep space burn: 3+21=24m/s Total from Mun surface to Kerbin surface:813m/s MISSION TOTAL:6809 m/s. Of course, it took 26 days, including waiting for the emergency refueling mission to be sent from Kerbin.