OhioBob

I stated playing KSP last July. Since then there's not much I haven't tried yet within the Kerbin system, having successfully completed most of the common Mun/Minmus missions, i.e. unmanned landings, manned landings, bases, rovers, etc. I've also launched and manned an orbiting space station, though it was pretty small. I haven't yet undertaken any really large in-space construction projects. I've gotten pretty good at rendezvous and docking, though I still need more practice at performing pinpoint landings. I've fulfilled most of the contracts that are available around the Kerbin system. I've successfully landed an unmanned lander on every planet except Moho and Jool. My trip to Moho was supposed to be a landing but I messed up and didn't have enough propellant to land after I got there, so I only managed to orbit. Of course it's not possible to land on Jool, but I did orbit and I sent an unmanned probe on a descent through Jool's atmosphere. I've also landed unmanned landers on Gilly, Ike and Bop. The only planet that I've landed on and returned from is Duna, having done it first unmanned and then manned. Duna is also the only planet to which I've sent Kerbals outside of the Kerbin system. I also pulled off a successful rescue mission when my first manned mission to Duna inexplicably exploded (apparently the deep space kraken got me). I've also captured an asteroid and placed it in an orbit around Kerbin. I've fulfilled several of the planet/moon exploration contracts. So far everything I've done has been using expendable rockets. I don't use any of the mods that allow recovery of rocket parts*. I also haven't done anything with jet engines or SSTO. So far I've shown no interest in planes or spaceplanes, other than briefly playing around with a few of the stock planes in sandbox. * I've actually used only a couple modes (most specifically KER). I also use stock aerodynamics (I downloaded NEAR but decided against installing it). My plan is to wait until version 1.0 is available before I consider if and what additional mods I want to try.

As other have said, it's really not important to know the value of argument of periapsis and/or longitude of ascending node to complete a contract. Just eyeballing it and matching the orbit as closely as possible is usually good enough. The contracts are actually quite forgiving. I have sometimes been giving credit for achieving an orbit while I was still fully intending to make another burn to obtain a better match. If you want to know more about argument of periapsis and the other orbital elements, the following provides a good explanation: http://www.braeunig.us/space/orbmech.htm#elements

For Vall, the border between "in space high" and "in space low" is 90 km. Vall has no atmosphere, so "in space low" extends all the way down to just above the surface.

How do you know your hours? Is there a counter somewhere?

This looks like the post you are referring to... http://forum.kerbalspaceprogram.com/threads/104239-Leveling-Up-Kerbals-The-Training-Program?p=1630130&viewfull=1#post1630130 This would explain FleetAdmiralJ's problem, while it looks like he has 8 points he really only has 7.75. The chart in the Wiki really should show the actually fractional points awarded.

It sure does. I just looked at the Wiki and I agree with the OP that it very clearly says 6 points for landing. It implies that, for Mun and Minmus, there is no difference between "land" and "plant flag".

I think the Kerbal must plant a flag on Minmus to get the 6 points. If the OP only landed then he probably didn't get the full 6 points that he thought he was getting. The Wiki may need to be edited if it says 6 points for "landing on Minmus" rather than "planting a flag on Minmus". (ETA) This might need some testing to verify. We can send two new Kerbals with no current experience to Minmus, have one plant a flag and the other not. When they get back we can see if the one leveled up and the other didn't. I'll test this when I get chance, unless somebody wants to beat me to it.

Yep, that's the one. It looks like I didn't quite remember it right - the Kerbals must orbit Mun, not just pass through its SOI. - - - Updated - - - Yes, apparently. It's my understand that each individual crewmember must plant a flag to get the points.

There's a really good thread about this somewhere but I can't find it. As of now a Kerbal only needs to gain 3 levels to acquire full abilities. I think the minimum requirements to earn the necessary XP went something like this: (1) go to orbit, (3) plant a flag on Minmus, (3) enter Mun's sphere-of-influence orbit Mun, and (4) exit Kerbin's sphere of influence.

As of right now, "Stock and Rockets" because that's all I've done. I'll probably eventually try out FAR/NEAR, but I've been holding out to see what Squad comes up with in their new aero model. I've also been holding out on playing around much with planes/spaceplanes until the new aero model is released. I'll probably always have a preference for rockets, however.

The fuel percentages are based on the parts that we have to work with in game. For example, most of the fuel tanks have an 8/1 ratio of propellant to dry mass, meaning they are 89% propellant. That's an absolute upper limit. By the time we add engines and decouplers, this lowers to about 80%. I think 80% is probably the practical upper limit for a single stage, after which it's better to add another stage rather than stacking on more fuel tanks. Of course, as you say, there are some applications where the ÃŽâ€V requirement is low enough that it's not necessary to have a very high mass ratio. To be honest, I'm not really following what it is you are trying to do. I just gave you some numbers based on my experience for you to do with as you please.

My first Duna landing (maybe two) was just a land and transmit mission, which one came off without a hitch. The next one was an unmanned land and return mission. This was before I figured out how to make a precision approach to the planet. I came in way too far north an ended up in a high inclination orbit. Rather than wait for my intended landing site to rotate into my orbital plane, I picked another site, but unfortunately it was at much higher elevation than I believed. I was still almost horizontal when the chute fully deployed. That left me with almost no time to react and get slowed down. Needless to say, it was not one of my better moments. Fortunately I had done a quick save, but the save was at a point in which I was already committed to the landing. On the replay I was able to slow down enough to land, but barely. I didn't have a big fuel margin to work with so I had to be miserly in how much propulsion I used. It was definitely sweaty palms time. In the end I was able to complete the mission and gain some good experience. For my next manned mission I had a much better plan in place. - - - Updated - - - I have a spreadsheet that let's me calculate the terminal descent velocity of a lander with different numbers of parachutes. Using that spreadsheet I produced the following table. These numbers are, of course, for Duna. Across the top is the altitude in meters above Duna 'sea level' (0 to 3000 m). Down the left side is the metric tons per parachute, including the parachute mass (1 to 10 t/chute). This is based on a Mk16 or Mk2-R parachute. A Mk16-XL can support twice the mass. The numbers that populate the chart is the terminal velocity in meters per second when the parachute is fully deployed. [TABLE=width: 500] [TR] [TD][/TD] [TD=align: center] 0 [/TD] [TD=align: center] 500 [/TD] [TD=align: center]1000[/TD] [TD=align: center]1500[/TD] [TD=align: center]2000[/TD] [TD=align: center]2500[/TD] [TD=align: center]3000[/TD] [/TR] [TR] [TD]1[/TD] [TD=align: center]6.3[/TD] [TD=align: center]6.9[/TD] [TD=align: center]7.4[/TD] [TD=align: center]8.1[/TD] [TD=align: center]8.8[/TD] [TD=align: center]9.5[/TD] [TD=align: center]10.3[/TD] [/TR] [TR] [TD]2[/TD] [TD=align: center]8.9[/TD] [TD=align: center]9.7[/TD] [TD=align: center]10.5[/TD] [TD=align: center]11.4[/TD] [TD=align: center]12.4[/TD] [TD=align: center]13.4[/TD] [TD=align: center]14.6[/TD] [/TR] [TR] [TD]3[/TD] [TD=align: center]10.9[/TD] [TD=align: center]11.9[/TD] [TD=align: center]12.9[/TD] [TD=align: center]14.0[/TD] [TD=align: center]15.2[/TD] [TD=align: center]16.4[/TD] [TD=align: center]17.8[/TD] [/TR] [TR] [TD]4[/TD] [TD=align: center]12.6[/TD] [TD=align: center]13.7[/TD] [TD=align: center]14.8[/TD] [TD=align: center]16.1[/TD] [TD=align: center]17.5[/TD] [TD=align: center]19.0[/TD] [TD=align: center]20.6[/TD] [/TR] [TR] [TD]5[/TD] [TD=align: center]14.1[/TD] [TD=align: center]15.3[/TD] [TD=align: center]16.6[/TD] [TD=align: center]18.0[/TD] [TD=align: center]19.5[/TD] [TD=align: center]21.2[/TD] [TD=align: center]23.0[/TD] [/TR] [TR] [TD]6[/TD] [TD=align: center]15.4[/TD] [TD=align: center]16.7[/TD] [TD=align: center]18.1[/TD] [TD=align: center]19.7[/TD] [TD=align: center]21.3[/TD] [TD=align: center]23.2[/TD] [TD=align: center]25.1[/TD] [/TR] [TR] [TD]7[/TD] [TD=align: center]16.6[/TD] [TD=align: center]18.0[/TD] [TD=align: center]19.6[/TD] [TD=align: center]21.2[/TD] [TD=align: center]23.0[/TD] [TD=align: center]25.0[/TD] [TD=align: center]27.1[/TD] [/TR] [TR] [TD]8[/TD] [TD=align: center]17.7[/TD] [TD=align: center]19.2[/TD] [TD=align: center]20.9[/TD] [TD=align: center]22.7[/TD] [TD=align: center]24.6[/TD] [TD=align: center]26.7[/TD] [TD=align: center]29.0[/TD] [/TR] [TR] [TD]9[/TD] [TD=align: center]18.8[/TD] [TD=align: center]20.4[/TD] [TD=align: center]22.1[/TD] [TD=align: center]24.0[/TD] [TD=align: center]26.0[/TD] [TD=align: center]28.3[/TD] [TD=align: center]30.7[/TD] [/TR] [TR] [TD]10[/TD] [TD=align: center]19.8[/TD] [TD=align: center]21.5[/TD] [TD=align: center]23.3[/TD] [TD=align: center]25.3[/TD] [TD=align: center]27.4[/TD] [TD=align: center]29.8[/TD] [TD=align: center]32.3[/TD] [/TR] [/TABLE]

Most of my rocket designs are about 80% propellant and about 20% dry mass when the payload is excluded. With the payload its more like 67% propellant and 33% dry mass. The 80/20 breakdown is typical of my larger launchers. On smaller launch vehicles it tends to be more like 75/25.

I'd like to add one more thing to what MicroMars wrote... At some point as you draw close to the target, say a few hundred meters out, you should change focus from your active ship to the target ship. After making the switch, you'll need to select the approaching ship as the target's target. Adjust your attitude so that the docking port is facing the approaching ship. Assuming the docking port is on the nose of the target, turn the ship until the nose is pointed at the center of the "towards target" marker on the Navball. Now switch back to the active ship and continue the docking. If the target has no ability to turn, that means you'll have move the active ship into a position that lines it up with the target's docking port. This greatly increases the difficulty. It always a good idea to include some form of attitude control on target if for no other reason than to assist in the docking.

I've only landed on Duna a handful of times, so I'm by no means a well-seasoned pro. However, from what I've experienced, the one thing that I'd warn about is this: If you plan to land at a fairly high altitude and/or with few parachutes, chances are you won't have killed all your horizontal velocity by the time you have to go to propulsion. It's likely you may need to cancel out some horizontal speed with your engines during you final descent or else you could touchdown with some lateral motion and topple over. This certainly doesn't mean an exceedingly difficult landing, but it is something to be prepared for. You don't want to mess up your landing because you were caught off guard by something you weren't expecting (like I was once). For my first manned Duna landing I decided to play it safe. I included enough parachutes and landed at a low enough elevation that I was almost assured to be descending vertically with negligible horizontal velocity. I calculated beforehand what my descent speed would be (about 15 m/s) and what my final burn had to be to assure a nice soft landing. Basically all I had to do was hit a button when I reached to right altitude (60 m) and I landed Soyuz-style without difficulty. I certainly don't disagree with anything KerikBalm wrote, but his method sounds a bit more challenging. If you're up for the challenge then by all means go for it.

I typically use aerobraking at Eve and Jool, but for my above referenced mission to Duna I decided against it. The spacecraft wasn't all that big and it didn't require all that much fuel using an LV-N engine. I could still launch the whole mission on one rocket. Had my spacecraft been bigger I probably would have elected to do an aerocapture. I saw that thread the other day. Pretty cool! Nice looking rocket and spacecraft.

I've done only one manned (or is it kerballed?) landing and return from Duna. I agree that a Kerbodyne tank sounds like overkill for a LV-N rocket. I was able to complete my mission with nothing more than a X200+16 + X200-8. You can see my spacecraft in the image below. The little vehicle on top is an Ike lander that I separated and flew to Ike after entering Duna orbit. The Mk1-2 command pod served a multi-function role as space habitant, Duna lander, and Kerbin reentry vehicle. My mission launched all on one launch vehicle and required only one docking - in Duna orbit between the command/service module and the unmanned propulsion stage. Perhaps the screenshot can give you some ideas for constructing your own mission. Fortunately I still have my notes from when I flew that mission. Below is my pre-flight ÃŽâ€V budget: Launch ≈ 4550 m/s Trans-Duna injection ≈ 1060 m/s Mid-course corrections(s) ≤ 30 m/s Duna orbit insertion (75 km) ≈ 640 m/s Site selection/plane change ≤ 300 m/s Descent orbit insertion ≈ 40 m/s Landing, final braking ≈ 40 m/s Ascent to Duna orbit (50 km) ≈ 1400 m/s Plane change (if needed) ≤ 100 m/s Rendezvous & docking ≈ 85 m/s Trans-Kerbin injection ≈ 560 m/s Mid-course corrections(s) ≤ 50 m/s Some of these numbers - i.e. trans-Duna injection, Duna orbit insertion, and trans-Kerbin injection - will vary depending on your specific launch window. The others are estimates and contingencies. As you can see, landing takes very little ÃŽâ€V as most of the braking is done with parachutes. I used four parachutes for Duna landing, which are the one you see mounted to the decoupler. (The parachutes mounted to the command pod were for landing back at Kerbin.) I didn't fire my engine until I was 60 meters above the ground. Of course I selected a landing site that sat at a low elevation to take maximum advantage of the atmosphere. Landing at a higher elevation will require more propulsion because parachutes will be less effective in the thinner air. I don't think I used any of the 300 m/s contingency for "site selection/plane change". This was just in case I miscalculated and got myself into an orbit from which I couldn't reach a good landing site. - - - Updated - - - Definitely watch some of the tutorials on YouTube. Understanding and mastering use of the Navball is critical. I figured out rendezvous pretty quickly, but docking was a pain until I really learned how the Navball fit into the whole equation. Now 90% of the rendezvous and docking it done entirely with the Navball. You also have to learn to maneuver with RCS. Once you've closed to within a few hundred meters of your target, it's all RCS. (ETA) Something else I forgot to mention about the ÃŽâ€V budget. It gets a little tricky because the different maneuvers are performed in different configurations. Some maneuvers are performed by the lander and some by the propulsion stage. And some of those performed by the propulsion stage are performed before landing (with a fully fueled lander attached), and some are performed after landing (with a nearly empty lander attached, or perhaps no lander). When I use KER to find the ÃŽâ€V of the propulsion stage, it gives me the number based on it always being attached to a fully fueled lander. The actual ÃŽâ€V that I'll get out of the propulsion stage in the order that the maneuvers will actually be performed is higher than what KER tells me. I found it best to perform all the ÃŽâ€V calculations by hand to make sure it was getting done correctly. Also be careful to check the fuel in your tanks before you separate and land. In my case when I burned the engines on the propulsion stage, the first fuel tank that it drew from was the topmost tank that's part of the lander. Before separating I had to transfer fuel back into that tank. Had I not checked it, I would have landed on Duna with an empty fuel tank. You might want to also top off your RCS tanks.

That’s really the most logical method. If you’re custom designing for a specific payload, there’s probably no other good way to do it. That’s what I use to do, and I still do it in early career mode. I also always custom design the upper stages to meet each mission’s specific requirements. However, I found that many of my lower stages ended up looking the same, so I decided to just formalize it with a group a standard designs that I could save as subassemblies. I've found that it saves me a lot of time. Most of my subassemblies were built in the reverse of what I normally do, i.e. from the bottom up. I’d pick an engine to serve as my first stage and then build a launch vehicle around it. After I had a design I’d confirm its maximum lift capacity by launching dummy payloads. I’d then save it as an X-tonne LV. In order to build a bigger fleet of launch vehicles to meet a broadening range of payload sizes, I started adding SRBs to give me a large range of liftoff thrusts. Even with the standard subassemblies I can still customize a little bit to my specific payload by off loading propellant and/or limiting thrust.

The best I've been able to do in stock using two stages is 17.5%. I like to keep things simple, so 2 stages or 2 stages + SRBs is about all I've experimented with. It doesn't surprise me that more complex staging designs can get to 20% or more.

I’m glad you got it to fly. I generally judge how well I did on the ascent by how much ÃŽâ€V it takes to circularize the orbit. My objective is to be below 100 m/s, with 50 m/s being about the best I’ve been able to achieve. If I’m much more than that then I know I didn’t hit my cutoff conditions quite right and I need more practice. I’m by no means perfect as I still botch it every now and then. When I first started playing KSP I used a spreadsheet similar to yours, mainly to compute the mass of my stages and to compute the ÃŽâ€V. Now that I’ve added KER I don’t do that anymore. I now just scratch out my designs on a piece of paper like I did in the example that I gave. Early in a career game things change so fast with the acquisition of new technologies that I tend not to be very formal in my launch vehicle designs. I just throw something together on a case by case basis that gives me the ÃŽâ€V I need. I have enough experience at this point that I know how not to overdesign things too much. After I’ve unlocked all the rocket parts I switch to using a fleet of stock designs that I have saved as subassemblies. I’ve got nearly 20 designs ranging from 1-tonne launchers all the way up to an 80-tonne launcher. After I’ve designed a payload I just snap on the smallest launcher that has a lift capacity equal to or greater than my payload mass (though in some cases cost may be the deciding factor). The majority of the designs are 2-stage liquid, though about a third of them are augmented with 2 to 4 strap-on SRBs. I just recently added two new designs that use 6 strap-on SRBs as the first stage with an air-lit liquid core as the second stage. I get a payload fraction of only about 0.13 with these, but they’re cheap because of the extensive use of solids. I mostly like to avoid complex staging designs even though they have the potential to be more efficient than my preferred 2-stage approach. Complex staging, such as asparagus, I find to be more expensive than it's worth. The best payload fraction I’ve able to achieve with any of my launchers has been 0.175, which is my 80-tonne launcher. I haven’t actually needed it yet in any of my games, though I’ve confirmed its capability by launching a dummy payload. This is what it looks like (shown without payload): The first stage uses a cluster of five Mainsails and the second stage uses a single Kerbodyne KP-2L. It may look like I'm using asparagus staging, but that's not the case. The four outboard engines are rigidly attached without decouplers. The propellant feeds from the center tank to the outer tanks. When the center tank goes dry, the center engine cuts off to lower the TWR. The four outboard engines continue to run until they drain their individual tanks (in about 38 seconds), then the entire first stage drops away as a unit. I just noticed the above in your OP. I initially didn’t read it close enough and thought the 4500 m/s was the vacuum ÃŽâ€V, which is how most people around here calculate it. The general consensus is that it requires a vacuum Isp of 4550 m/s to attain orbit, which my own experience agrees with. One thing I learned from my simulations is that the actual ÃŽâ€V needed to attain orbit, calculated using actual ISP, is about 4400 m/s. I’ve found that if you average SL Isp and vac Isp for the first stage, and use vac Isp for the second stage, you’ll come very close to calculating the actual ÃŽâ€V. I think this works better than the method you’ve described.

With a well designed 2-stage liquid fuelled rocket I typically get about 16%. You're not too far off from that so you're doing pretty good. Regarding tips, you should check out the following thread, in which, by coincidence, we're having a very similar conversation. http://forum.kerbalspaceprogram.com/threads/107763-Designing-Launch-Vehicles (edited to add) With an all-solid first stage my payload drops to about 13%. With a combination of a liquid first stage and SRB strap-ons I can still get close to 16%. In all cases these percentages require flying a very precise and efficient ascent profile with little margin for error. A poorly flown ascent will reduce these percentages. This is also assuming a low orbit of about 75 km. I also find that my designs using large and extra large parts generally get better payload fractions. When I build rockets from small parts I usually don't do any better than about 13%. Also note that these percentages are when pushing the launch vehicle to its maximum performance. Sometimes it is necessary to overdesign simply because we're forced to round up to the next biggest available part. It's not always possible to construct the most ultra-efficient rocket for a particular payload size. I should also note that my comments are based on the stock game without any of the aerodynamic mods. All things considered, your 13-15% sounds about right.

I'm not seeing your image but it's probably not necessary that I see it. Part of my design simulations was also trying to optimize the ascent profile, so its a good thing that you asked. With a 19.9 t payload you don't have much margin for error, but you should be able to get into a 75 km orbit. I typically start the pitch over just after passing 5000 m altitude. I execute a slow gradual turn, always trying to keep the level indicator on the Navball within a few degrees of the prograde indicator. Avoid sudden sharp turns. As the prograde indicator approaches the horizon, I level off my vehicle horizontally. If all has gone well, I should be able to accelerate up to about 2300 m/s at a cutoff altitude of about 50 km. I cut the engine just as the apoapsis passes 75 km. Ideally the prograde indicator should be about +3 degrees at engine shutdown. The orbit circularization burn should be less than 100 m/s. The thing that takes practice is getting the prograde indicator to drop at the right rate to get an efficient turn. If the rate is too fast or too slow you have to correct by producing a fairly large separation between the level indicator and prograde marker, and that wastes ÃŽâ€V. If you make a really good turn, the level indicator never needs to go outside the yellow circle on the prograde indicator. BTW, I just edited my design example. I wrote Mainsail for the second stage when I meant to write Skipper. If you're using a Mainsail then that could be your problem. I can also see your image now. It certainly looks like the design I described, and it looks like you're using the Skipper engine. I see no reason why you shouldn't be able to get 20 t into orbit with that.

I've flown the same basic rocket design (just in various sizes) long enough that I'm reasonable good at hitting the 4550 m/s number. Of course I still often fly with some safety margin because there aren't enough parts in the game to always be able to custom design a rocket that exactly matches my requirements, thus I usually end up rounding up little bit. For example, I might use a 20-t capable LV to launch a 18-t payload. When I first started playing KSP, I also aimed for a liftoff TWR of around 2. That was before I understood how bad the drag model was. After I learned how aerodynamics worked in the game, I ran a bunch of computer simulations to try to come up with an optimized design, which is what led to my rules of thumb. When I put those rules to use in the game I was happy with the results and have since stuck to it. It's nice to discover that my results agree with what most of the KSP community has independently derived.

Let me first stipulate that I use the stock game, i.e. no FAR/NEAR. The rules of thumb that I use that have given me good results are: 1) Two stages to get to LKO (additional stages on top of that for whatever my mission is) 2) Vacuum ÃŽâ€V of 4550 m/s (actual ÃŽâ€V about 4400 m/s) 3) Stage 1 TWR at liftoff ≈ 1.65 4) Stage 2 TWR at ignition ≈ 1.30 5) Ratio of Stage 2 thrust to Stage 1 thrust ≈ 0.35 Using these guidelines I typically get a payload fraction of about 0.16. I also frequently use strap-on SRBs to get my liftoff TWR right. (edited to add) Now that I’ve given you my rules of thumb, I might as well show how I put them to use to design a launch vehicle. This might serve as a tutorial for new or inexperienced users who may be struggling to design a good rocket. If you always use these guidelines you’ll produce launch vehicles that perform to a fairly consistent standard. I’ve done this enough times that I’m confident in the 0.16 payload fraction. So let’s say I want to design a rocket to launch a 20-tonne payload. My total rocket mass will be approximately, 20 / 0.16 = 125 t Since I want a Stage 1 TWR of 1.65, my first stage thrust should be, 125 * 9.81 * 1.65 = 2023 kN Therefore I choose to use a LFB KR 1x2 (2000 kN). My ideal Stage 2 thrust is, 2000 * 0.35 = 700 kN I choose the engine the gets me closest to this thrust, which is the Rockomax Skipper (650 kN). Since I want a Stage 2 TWR of 1.30, the mass of the second stage and payload should be, 650 / 9.81 / 1.30 = 51 t Therefore the ideal Stage 1 mass is, 125 – 51 = 74 t Since my first stage already consists of a LFB KR 1x2 (42 t), and I require a decoupler (0.4 t), I can add the following in the form of additional tanks and fuel, 74 – 42 – 0.4 = 31.6 t This is done by adding one X200-32 (18 t), one X200-16 (9 t) and one X200-8 (4.5 t). I now must figure out what fuel tanks to add to the second stage. I have 51 t to work with, from which I subtract the engine (3 t), decoupler (0.4 t) and payload (20 t), 51 – 3 – 0.4 – 20 = 27.6 t So I add one X200-32 (18 t) and one X200-16 (9 t) fuel tank. My launch vehicle is now complete. Computing the ∆V I find that it will produce 4,546 m/s, just what I need to get to low Kerbin orbit. Things don’t always work out as nicely as they did in this example, so compromises sometimes have to be made. However, if you follow these design guidelines as closely as possible, you should get good results. Also note that the upcoming aero changes will likely mean I'll have to revise my rules of thumb.

The first thing that I notice is that your total fall time is incorrect. Since gravitational acceleration varies with height, velocity vs. time isn't a linear function. You can't simply call your average velocity 1/2 of your final velocity. The second thing I'd recommend is to not base the start of your burn on time, but rather on altitude. Since you haven't quite reached the ground yet when you have to start the burn, your velocity at engine start will be a little less than your calculated velocity of 122.874 m/s. Let's call it 120 m/s (we can check this latter). Your velocity at touchdown is given by v = (a + g) t + vo where vo is your 120 m/s initial velocity, a is your applied acceleration, and g is the acceleration of gravity. It's not clear from your post whether your 12.61 m/s2 acceleration is that resulting from thrust only or whether it has been reduced to account for gravity. I'm going to assume the former. Near the surface of Minmas, g = 0.49 m/s2. Let say you want your touchdown velocity to be 1 m/s. We therefore have, 1 = (-12.61 + 0.49) t + 120 t = 9.8185 s The distance travelled during the burn is give by d = (a + g) t2 / 2 + vo t Plugging in your numbers we get d = (-12.61 + 0.49) * 9.81852 / 2 + 120 * 9.8185 d = 594 meters Therefore you should start your burn 594 meters above the ground (allowing a little bit for the time it takes to throttle up). We can now go back to the VisViva equation to check the velocity at an altitude of 594 m. I get 120.5 m/s, which is close enough to the assumed velocity of 120 m/s. Also note that the acceleration of your spacecraft will increase slightly as you burn propellant, though with less than a 10 second burn this is unlikely to be much. If your decent velocity starts to go to zero before reaching the ground, just back off on the throttle a little bit to increase your fall rate.