closette

202.8 kg remaining for the standard lander, 3.9x3.9km orbit, despite numerous attempts to get 203 kg. I\'m level with Kosmo-not! (Not for long I\'m sure). Landed with 109.1kg remaining, and what is that in the landed screenshot? The MunArch! @PakledHostage: I think I know what you mean, but for newcomers a rephrasing might help clarify (as well as a diagram). I think you mean 'in the plane of the hyperbola, turn towards the Mun'. My hunch is that in fact it would be better to turn more - 90 degrees to your velocity, not towards the Mun, since that would reduce periapsis by reducing both energy and angular momentum, and burning radially does not change the latter. I have a scribbled list of orbital equations that I need to work through though when I can get some quiet time...

I can\'t answer for your video settings which might preclude shadows (but also check that you are landing on the sunny side of the Mun with the sun not directly overhead). Landing can be frustrating but stick with it! Depending on your lander\'s weight, 4 m/s might break a lander leg (I use 4 legs, not the minimum 3), so practice hovering and descending at 1-2 m/s. Not much more difficult than nulling out your horizontal velocity. Having said that, I still mess up landings some of the time. I left a lot of stranded Kerbals on the Mun before I could get my RCS lander down safely. I watched how others did it on the many Mun landing videos on Youtube as well. Choosing one of the dark, flat plains is a good start. If you post a .craft file, description of your craft, and some screenshots of it close to landing, you may get more useful and detailed help.

With 111.9kg I was able to return to Kerbin\'s upper atmosphere, and aerobrake 4-5 times around before going in, but I did not land safely - I think it was an 80 m/s impact after running out of fuel at ~200m altitude. But it seemed do-able with some skill, luck and patience. You belong on that leaderboard. I just wish there were more new names doing this challenge. Despite the closely packed leaderboard, I have a hunch that we haven\'t found the optimum entry path yet...

Well I suppose there might be a smallest orbit where you make it once around Kerbin before the orbit decays, by having a large apoapsis outside the atmosphere to start with. Sort of a minimal aerobraking challenge. Unfortunately I'm seeing a lot of newer challenges that could do with following some informal guidelines that many of us have been using for a while, namely: - Define 'success' in terms of measurable criteria[/li] - Define the evidence ('proof') required unambiguously [/li] - Maintain an updated 'leader board' in the first post [/li] = Probably most important of all, at least try the challenge yourself first and post your own results and evidence. That usually shakes out any problems, including whether or not the challenge makes sense, or is even possible. [/li] I wish I could add these guidelines (not rules!) to the sticky post at the head of the Challenges forum but replies to it are disabled.

Soft landing, standard lander: 111.9kg remaining. (Still not as good fuel-wise as my 'hard landing' with 116.1 kg, Reply 18). I couldn\'t beat PakledHostage or Kosmo-not on the 3x3km orbit part although I tried a new strategy - making my initial burn not completely retrograde, but trying to 'turn inwards' to reduce the patched-conic-projected Pe to under 5km as efficiently and as quickly as possible. Perhaps I did not do it right as I ended up in an inclined orbit around the Mun. I ended up with 202.3kg remaining in a 3x6km orbit so gave up on that part of the challenge. BUT from there with a better gravity turn profile than I\'ve used before, I was able to soft land with 111.9kg left in the tank. I\'m beginning to like the multi-part challenge with more-than-1 leaderboard. If I miss one part I can still continue with the other. (Tarmenius, I know it means more work for you to keep track of it all). Also Tarmenius, you are not being fair to yourself. Your 4th test in Reply 19 shows you made orbit with 202.6kg remaining - that should be up there on the leaderboard! (You also have PakledHostage on there twice).

Great job. The question is - can 3 Kerbals fit in there? (Right now, probably yes, but after re-scaling...?)

...or some combination thereof! From your systematic investigations so far, I am confident you\'ll pin down the best strategy. Nice job on nudging into the lead. Calculating the theoretical best-case impulsive delta-V is a bit harder for this challenge as it crosses an SOI boundary but I\'ll have a go. Your step-by-step delta-V breakdowns are very helpful.

202.7 kerbalgrams (found the mouse!) and a nice shot of the Arch. Someone should try landing there from this challenge. I\'m pretty much doing the same thing each attempt, spending most of my time in low orbit waiting to reach one of the apses for a circularization burn. I\'m going to try some other strategies to see if there is another way to save more fuel and blow everyone else away. Landed intact for once at 108.3 kg remaining. Should be possible to do much better though...

Low-fuel lander: 99.78 kerbalgram (kg) remaining (from the quicksave file, I forgot to bring the borrowed 2-button mouse to school), I wasted a lot of fuel trying to get the 3.4x3.5km orbit within range. Landed with 14.48 kg remaining but toppled over and disconnected pod - typical for me these days! Why so few contenders in this challenge? It\'s very relevant to everyday game play, and just trying without winning is fun and makes one a better navigator overall. Perhaps changing the title to 'Optimal Munar orbit insertion challenge [stock]' might help?

202.57 kerbalgrams remaining on board for a 3.37 x 3.43 km orbit, which was a pain to establish and took a long time to circularize at maximum x2 time-warp. But patience paid off. Same strategy as others - retrograde before entering the Mun\'s SOI, with ~ 10km periapsis, then after entering SOI a short impulse towards Kerbin to reduce periapsis to about 6km, then lots of 'apse-chasing' at low time warp to finalize the orbit. After all that time I missed a nice shot of the Mun arch as I flew over it, and I messed up an attempted return to Kerbin, almost making it but killing the crew with a 23 m/s impact. Totally feasible for others to succeed from Mun orbit though. By the way I noticed that for this almost perfect circular orbit, rotating the spacecraft or even toggling ASAS on/off can change the peri- and apo-apsis by ~ 10 meters. P.S. @PakledHostage - very nice results and must have taken you a while to do so many trials. Your explanation is reasonable too.

By accident I have swung around the Mun and been headed straight towards Minmus. But Minmus\' gravity is so small that I doubt it can turn you around back to Kerbin. All my Mun-Minmus swing-bys would have ended up escaping Kerbin without some kind of intervention. One way to see if it\'s possible though would be to try the reverse - from the outer Kerbin system, swing by Minmus towards the Mun and see if that would deflect you back home.

144.9 kg after an exciting flight through the gorge and landing on the high ground at the end. Wish I could have video captured it. I had set periapsis just below ground level so the 'gravity turn' was very flat. I broke a lander leg but remained balanced on two at a precarious angle.

OK to change it by me, but I WAS in the lead for a moment with my hard landing (but intact fuel tank)...such brief but sweet glory which I shall never experience again (Sobs quietly). 3x3km seems a bit 'tight' for a final orbit and 5x5km would be better for time-warping, but I\'ll go with the flow, as long as there is some tolerance such as +/- 0.5 km on each, althout 2.5km is probably too low. This is already turning (pun intended) into a fascinating challenge, with applicability to many missions. By the way I came across this online calculator for going from orbital state to orbital parameters and back: http://orbitsimulator.com/formulas/OrbitalElements.html. Use M=9.76e20 kg for the Mun\'s mass, 1kg for the spacecraft mass, and set the 'Z' components all to zero for in-plane maneuvers.

Urm, not sure how I did this or whether it should qualify: 116.1385 kg remaining, but fuel tank detached on landing! I basically tried to reduce periapsis from outside the Mun\'s SOI first, adjusted after entering (since the patched conic seems to overpredict periapsis for this case), coasted to periapsis of about 6km altitude, tried to establish a circular orbit, but ended up doing a flat-ish gravity turn to the sunny side of the Mun. I lost control just before landing, but the quicksave file lists 116.1385 kg for the tank belonging to 'Munar Landing Challenge Debris'. Apparently right-click doesn\'t work for separated tanks. I\'ll try again later tonight - real life is pulling me away from this challenge! I don\'t mind being disqualified from the Leaderboard, but at least this shows that you can end up with more than 110 kg remaining if you are careful - more careful than me!

Thank you for trying this. Since IIRC 1 kg of fuel causes a delta-V of about 6.5 m/s for this fully fueled craft, in terms of delta-V and fuel to achieve a 3km circular orbit, I think the 'turn method, i.e. burning off-axis ~towards Kerbin wins despite the higher periapsis velocity. I just chose 'towards Kerbin' as an easy way of pointing almost at 90-degrees to velocity in the orbital plane, by the way. The results of this challenge will be very applicable to new users trying their first mission, so much like the approximate 'TMI burn at Munrise' I thought this could be a good rule-of-thumb. We\'ll see how good compared to the optimal results on the leaderboard. The actual optimum impulse direction to lower periapsis is probably some hard-to-calculate angle depending on how far out you are. (This also comes up when trying to return to Kerbin with a low perikerb after leaving the Mun\'s SOI). @PakledHostage, I know what you mean, but applying an impulse at exactly 90 degrees to velocity must increase orbital energy somewhat, since the resulting velocity is the hypotenuse of a right triangle, therefore higher than the original, but if the off-axis delta-V is small in comparison, it won\'t make much difference. Thanks for the reference for your and Kosmo-not\'s very relevant earlier discussion.

Regarding lowering the hyperbola\'s periapsis, I was following the advice given me at the end of the descent challenge (which I could verify by calculation if I wasn\'t feeling lazy) to burn at right angles to velocity to 'turn into' the Mun instead of just retrograde to reduce orbital energy. At large distances there does not seem to be a lot of difference to the initial delta-v required. The 'turn' method does add to the orbital energy, and therefore periapsis velocity, which seems less desirable, so if someone has done the calculations please share them. Otherwise I\'ll break out the pen and paper myself, and or try both experimentally starting with the persistent.sfs file for this challenge.

You set a tough standard to beat, Tarmenius. After a few crashes on the night side where I couldn\'t see the ground (thanks a lot!) and also one fly past the Arch, here is my easily beaten attempt: 90.7kg. The KSP 'sunrise' is rendered so well it hurt my eyes a bit to look at it. Well that\'s my excuse for the hard landing. Screenshots attached. And yes I borrowed a USB mouse just so I could right-click and get fuel state! I am including a map view screenshot as well so others can see what I am doing. My simple approach is: - coast into the Mun\'s SOI - burn towards Kerbin/KSC which is roughly at right angles to velocity, to reduce periapsis to about 10 km - coast a short while, then retroburn to reduce periapsis to around 5km. I do this also to make the periapsis closer to the daytime side of the Mun, not very successfully - gravity turn from periapsis and try not to hit the ~1400m ground too hard. Next time I think I\'ll circularize at periapsis instead, then orbit around to the daytime side to pick my spot, but for attempts so far I\'ve also been trying to land in the shortest possible time, which means in the dark.

Nicely set up, and it must have taken a fair amount of work. I almost missed it though - could you provide a link to this challenge from the munar descent one (perhaps put a link both in your first post and in the replies at the end)? Did you make the 'low fuel lander' by starting with the original craft and dumping fuel while making the craft oscillate back and forth or spin around so there would be no net effect, or did you have to start over? (Just curious - I\'ll be sticking with the full fuel version!). We should see some creative solutions to this one...

Thanks for the detailed responses and explanations - makes a lot of sense and this is something that should be in a Mun mission tutorial. I had been doing all my insertion burns tangential to velocity, but was beginning to realise that for the hyperbolic-to-orbit case that was less than optimal. I like your 'turning through the gate' analogy PakledHostage. I have attached one of the few papers I found on the subject of efficient capture - a bit tough to read but the diagrams at the end are interesting. They find that a 3-burn maneuver may be optimal in some cases, where there is a plane change. As for the next phase of the lunar landing challenge, my suggestion would be to - start just outside the Munar SOI on a free-return type path - shorter duration challenge, fewer variables, but you can still choose a different SOI entry point if you want to. - use the same craft we just used for this one, for comparison. Also, even though a low-impulse spacecraft would definitely change the optimal path, we\'d probably all end up using it at 100% or zero thrust anyway. At least with this 'typical' TWR spacecraft (for a lander) there is the possibility of doing some intermediate-thrust burns. - allow free choice of landing site. This gives a greater variety of screenshots for one thing, and we\'ve seen some ingenious uses of terrain in this challenge already! ...but I\'m confident that it will be a good test of planning and piloting skills regardless.

Tarmenius that\'s an excellent idea - perhaps it should be in a separate Challenge thread though (with a link back to this one). Just outside the Mun\'s SOI or just inside - I\'m not sure which is better. If just outside you do give us the additional option of changing the insertion point, true, but at least let\'s make sure that the velocity will still take a coasting spacecraft well inside the SOI (with some large periapsis on the hyperbola all the same), not just grazing the outer edge. In fact if you can manage it, an initial velocity vector typical of a 'free return' trajectory from Kerbin would be a good candidate for a Mun-mission-like challenge. (So if one does nothing, one leaves the Mun\'s SOI on a path towards Kerbin\'s SOI). Breaking out of free return and into a landing profile with high efficiency could provide some useful results for everyone. It would be nice if the challenge were still do-able by those with the 0.13.3 version of the game (it will encourage them to pay up and upgrade at a later date!). They don\'t have patched conics visible, but many of us did just fine without them. These challenges are hard to set up well, but you did an amazing job with this one. P.S. Thanks for your input into my question - still not sure what the best strategy is though. And some great flying through the gorge - the Force is strong with you.

Well on the subject of entering the Mun\'s SOI, here\'s a question I\'ve pondered and can\'t seem to answer without going through the math, but I feel I should be able to figure out conceptually, so please help... Let\'s say I arrive in the Mun\'s SOI on a hyperbola which has a periapsis of 200 km altitude (so 400 km from Mun\'s center) , and I want to end up in a 10km circular orbit (radius 210 km) for surveying a landing spot. No plane changes needed and time is no object. Should I either: - retro burn while far out to reduce the hyperbola\'s periapsis to 10km altitude, coast to this periapsis, then circularize, OR - coast to the 200 km periapsis of the hyperbola, retroburn into a transfer ellipse with a 10km periapsis, coast around the orbit to that ellipse\'s periapsis, then circularize (like a Hohmann transfer). Which is more fuel efficient (and why?). Or is there an even more efficient method (e.g. with 3 burns)?

Thrust to Weight Ratio (TWR) is fairly easy to calculate as long as you are careful adding up the numbers given to you in the VAB for the parts\' masses. (Note for fuel tanks, use the 'Full' mass, and NOT the 'units of fuel'). Some people refer to the VAB part masses in 'tonnes' and thrusts given in 'kiloNewtons' although it\'s not clear if that is the case. At least the units are consistent where 1 thrust unit will accelerate 1 mass unit at 1 m/s2. The numbers you give for your craft seem a bit high to me for its size - each tank has a mass of 2.5 and an LTV-30 engine a mass of 2 tonnes and a thrust of 200 kN. But I could be wrong. Note that you should use TOTAL mass at launch - not just for the liftoff stage - and obviously only the first stage 'active' engines for thrust. So assuming the numbers you give, the only thing you are missing is to convert the mass (tonnes) into weight (in kN), by multiplying by local gravity g = 9.8 m/s2. So your craft\'s weight is then (100 tonnes x g) = 980 kN, and the launch TWR is just the ratio 2250 kN / 980 kN = 2.3. That is pretty good for an efficient launch, and of course the TWR will increase as you lose fuel mass (and as Kerbin\'s gravity weakens with distance from its center, but not by much while you are still below a few hundred km altitude). Hope this helps.

Agreed, even when full of fuel this spacecraft has a starting thrust/weight ratio in Munar gravity of about 7.5, which is not 'infinity' but is greater than 1, i.e. during the burn the thrust force overwhelms the gravitational force. Also, perhaps more relevant, the burn times at apomun and perimun are short compared to the transfer time between them, so they appear _almost_ impulsive. Not using time warp would make this very apparent! It was completely reasonable to question the assumption, all the same. It is not quite so true for the gravity turn final descent, which may be one reason why some of the challenge leaders are beating the theoretical ideal maximum fuel remaining. PakledHostage your numbers for landing from a realistic SOI entry and fly-by look about right. Personally on Mun missions I try to set up a ~10 km periapsis for the fly-by, then time-warp to it, take a look at the Mun\'s surface and if I like what I see, either start a landing gravity turn, OR establish a 10km circular orbit which is a good altitude to look ahead for interesting landing spots. This is all in the same equatorial plane - doing a plane change would be 'cheaper' if done further out when the craft is falling at a much lower speed.

@Bioman222, Could you please add to your post some screenshots of your craft in action and perhaps a few words about the design so that people can see if it\'s something they want to download and try?

As with other challenges this one has inspired me to do a lot of reading and learning about orbital mechanics, even though I\'m not so great at the challenge itself. Regarding a bi-elliptic transfer, which I think means adding velocity to the 100km circular orbit, coasting to the resulting higher apoapsis, then subtracting velocity to lower your periapsis (or even to land directly), I don\'t think that can beat the 2-impulse + gravity turn method that most people are using. There would also be the question of what apoapsis to use for the intermediate ellipse? First I played with the KSP Orbit Mechanic Java tool available here http://kerbalspaceprogram.com/forum/index.php?topic=4707.0 selecting 'Mun', 'High to Low' and 'Bielliptic transfer' and trying out some intermediate orbits, but the total delta-v including killing the final tangential velocity before touchdown is always bigger than the ~ 670 m/s of the 2-impulse method. Also, compared to the method we\'ve been using, the bi-elliptic transfer: - increases your speed over the ground at periapsis, compared to the smaller intermediate orbit. - burns less fuel on the first impulse, which unfortunately means that you end up with a more massive spacecraft close to the ground. So the higher mass and higher velocity will take more fuel to slow down for a vertical landing. Still, I had to give it a try, boosting up to ~ 300 km first and then retro-firing to get a 1km periapsis. I was surprised that the fuel budget wasn\'t as bad as I thought. I was also surprised by the landing! It was on the night time side of the Mun so I could not see what was below, and as soon as I had killed my horizontal speed and pitched up vertical, I was on the ground! Screenshots attached. I have also attached paper on orbit transfers that deals with transfers between coplanar elliptical orbits. What has that got to do with landing on the Mun? Well we start out in an elliptical orbit (circular is a special case), and are trying to transfer to an elliptical 'orbit' with an apoapsis just above the ground and an eccentricity close to 1.00. The paper pretty much confirms that the 2-impulse method we have been using is close to optimal.