# FloppyRocket

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1. ## Kerpollo - A Complete Science Mode Run In 9 Acts

Thanks for the advice. What is the advantage of getting into a Mun orbit first? I found a transfer time that allows both getting a Moho encounter and doing the inclination burn at the same time. It did save a lot of delta-v. I do not totally understand what you're saying to do about the capture burn. Mostly what I learned from the Minmus mission was that it's really frustrating trying to use the maneuver nodes to set up a planetary transfer. The stock UI is awful for that - too much high-precision mouse clicking and fiddling. My knuckles have too many miles on them for that to be fun. And you can't move a maneuver node around easily when you're in low-Kerbin orbit, because it's the wrong SOI. I've learned all that again with the Moho mission. Eventually I managed to find an encounter that got me there. Unfortunately I'll have to revert and try again after adding a bit more delta-v to my stack, because I am about 400 m/s short of getting back.
2. ## Mun landing rocket design

@MPDerksen Here are some numbers comparing the (Terrier + X200 tank) vs. (Spark + 6x Oscar-B tanks) in your example: Assumptions: all tanks are full The mass of the "payload" (crew pod + science parts + batteries + legs) is 1.6 tons delta-v = 9.81 * Isp(vac) * ln(wet mass/dry mass) assumes I've done the math right with pencil/paper and a calculator - I'm away from KSP so math and factual errors are possible. I'm using the KSP wiki for the data, and it may or may not be up-to-date. Terrier w/ X200 tank Spark w/ Oscar-B tanks Engine mass (t) 0.5 0.1 Engine Isp(vac) 345 320 Tank mass (t) wet: 9.0 dry: 1.0 per tank : six tanks wet: 0.23 : 1.38 dry: 0.03 : 0.18 Total mass (t) wet: 1.6 + 0.5 + 9.0 = 11.1 dry: 1.6 + 0.5 + 1.0 = 3.1 wet: 1.6 + 0.1 + 1.38 = 3.08 dry: 1.6 + 0.1 + 0.18 = 1.88 delta-v 9.8 * 345 * ln(11.1/3.1) = 4,312 m/s 9.8 * 320 * ln(3.08/1.88) = 1,548 m/s Conclusion: The Spark w/6x Oscar-B tanks gives less delta-v than the Terrier w/ X200 tank, but it has the required delta-v and is substantially lighter (about 1/4 of the mass). Lighter total mass makes it easier to launch the lander from Kerbin and put it in Mun orbit. ================= Regarding how to install six Oscar-B tanks onto the lander: That is another question entirely, and a very good one. I can't answer it without getting on KSP and trying a few things. The Terrier is also 5x the mass of the Spark. Mass is always an important factor. There are always tradeoffs. Sometimes there is more than one choice that is good enough.
3. ## Mun landing rocket design

@MPDerksen In modeling the delta-v performance, the important engine factors are their mass and ISP. (Here I'm neglecting things like efficient launch trajectories within an atmosphere) Thrust is only really a major issue for a booster that lifts mass off of a planet. To get off the surface, the total TWR has be be > 1.0 for that body's gravity. Once you're in orbit, one downside to low trust is the increased burn time. Long burn time makes maneuvers a little more tricky to conduct accurately, because the maneuver node system assumes the delta-v is applied instantaneously. Comparing the Terrier and Spark: Terrier Spark Mass (tons) 0.5 0.1 Isp (vacuum - seconds) 345 320 Thrust (KN) 60 20 So the Spark is much lighter, but has only slightly lower ISP. It has much lower thrust, but for the mass of your lander module and the job of getting off the the Mun's surface (with its low gravity), it is sufficient. The mass of the engine plays a big role in the amount of delta-v that is created, because the engine counts in the dry mass. For higher delta-v, you want a high wet mass and low dry mass. The total dry mass is the payload, the mass of the engine, and the empty mass of the fuel tanks. Example numbers to follow...
4. ## Mun landing rocket design

@MPDerksen In the VAB, in the lower right corner of the screen, there is a little toolbar. One of the buttons is labeled "DV". Click on it, that opens the DV options menu. There you've got three buttons that are preset for different air pressure values - sea level (the default), an altitude you can set, and "vacuum". It always defaults to "sea level", so whenever you enter the VAB, you have to re-set it to "vacuum". I'll take a look at your questions about the relative delta-v values shortly.
5. ## Mun landing rocket design

I totally agree with starting from the lander and working backwards. A Poodle is excessively large engine-age for this task. Since you have to boost the lander into Mun orbit from Kerbin, you want the mass to be as small as possible. Assuming the "payload" part of the lander is the 2-Kerbal pod (dry), plus science parts, plus the docking port, batteries, solar panels, and landing legs amount to a total of 1.6 tons. Using a rocket design tool (like "KSP Optimal Rocket Calculator"), plug in 1400 m/s for min delta v, lower the min TWR to 0.3, and select "Kerbin" for the local gravity (even though you're landing on the Mun, the Isp of the engines is measured on Kerbin), disable the "add decoupler" option, and it coughs-up this design: Tanks: six Oscar-B Engine: one Spark Total mass: 3.05 tons, dv = 1569 m/s, TWR = 0.67 (that's plenty for launching from the Mun) That total mass then becomes the "payload" mass for designing the rocket that gets the lander up to orbit. Its delta-v requirement is 3400+860+310=4600 m/s (approx), plus whatever margin you need for pilotage skills. I usually add 10% for that. So maybe design the booster for 5,000 m/s total. Note that when you build the rocket in the VAB and attach the lander to it, the built-in DV tool is going to add the lander's delta-v to the total values displayed. That can be misleading. Also, set the VAB's DV tool to display "vacuum" values - the 3400 m/s standard for orbit is in vacuum values. At least, it works for me. Others have much more experience than me. You repeat the whole process for the "orbiter" that you need to get up there in order to bring the Kerbals back. Start from the pod that splashes down, that's your final "payload" mass. For launch you add up all the delta-v values to get into low Mun orbit. On the return trip, you need the same delta-v used to get there, except do not include the launch 3400 m/s, because you aerobrake for landing.
6. ## Kerpollo - A Complete Science Mode Run In 9 Acts

TWR doesn't matter when you're simply unable to use maneuver nodes to find a Moho encounter.
7. ## Kerpollo - A Complete Science Mode Run In 9 Acts

Mohollo mission update: Cannot figure out how to get a Moho encounter from low Kerbin orbit. Dratted frustrating.
8. ## Need rudimentary help about fuel flow

Well, that makes good sense - just use the dv values instead of the bar graphs. I totally overlooked that as an alternate. Yes, the two-way flow through decouplers had me pretty confused.
9. ## Need rudimentary help about fuel flow

Thanks for all your replies. After testing a couple of things, it looks like my concern about not using the symmetry controls was incorrect. Since it sets the priority values based on the staging setup, you can pretty much just leave it to sort out the details. With the fuel priority system, the fuel gauges in the staging menu (left side of the view screen) seem kinda useless. Even when only one pair of tanks are going empty, all of the gauges are draining identically. So to know when to stage-off an empty set of tanks, I have to keep RMB-clicking on the next tanks that I expect to go empty, so i can stage them off when they hit zero. You can't tell when to stage by loss of an engine, because the engines keep firing. In contrast, when using fuel ducts the left-side gauges clearly show when a tank is about to run empty, without having to click on any of the tanks. I'm off to try and make it work on a larger rocket (two layers of 6-stalk asparagus around a center core).

11. ## Kerpollo - A Complete Science Mode Run In 9 Acts

Status update: I'm currently stuck in the VAB because I can't get the fuel flow working correctly on this 3-section asparagus staged rocket. I posted a "need help" thread in the "Tutorials and Gameplay" forum area.
12. ## Need rudimentary help about fuel flow

Hi, I wasn't able to find some basic information about fuel flow on the Forums. Previously I've always used fuel ducts for asparagus-staged rockets, which I pretty much understand. But I'm looking at using decouplers and fuel priority, because I find the UI for attaching the fuel ducts pretty clunky and prone to deleting my whole rocket stack when I try to attach anything to the middle of a large asparagus stack. The image has a simple test ship for fuel flow. Advanced Tweakables is on. The decoupler has crossfeed enabled. Fuel Delivery Overlay is checked. Let's call the tank under the capsule the "main" tank, the tank to the left is the "aux" tank. I did not set the "p#" fuel priority numbers, they were automatically assigned. The green arrows (and the animation) point from the main tank to the aux tank, and also from each tank down to its engine. This seems to indicate that fuel is going to flow from the main tank to the aux tank. - and that therefore the main tank will empty first. But when I launch it, the opposite happens - the aux tank empties. That's consistent with what the "p#" values say - the highest priority number us used first, and 0 is higher than -10. So, here's the questions: 1) I'm confused where those "p#" values came from - I did not assign them. 2) The direction of the green arrows seems misleading. Or am I just interpreting it wrong? Or is the flow diagram buggy? 3) In the main tank info box, the "Flow Priority" row has these symbols: button labeled '-' value 10 value (0) button labeled '+' button labeled '0' What do these things do? I pretty much understand the + and - buttons, but I don't know what the (0) value means, and the '0' button doesn't seem to set anything to zero. This UI is non-obvious. 4) Why does the yellow node in the aux tank have some embedded red hoops? 5) For a larger asparagus-staged rocket, If you have multiple tanks with the same "p#" value, will they all drain at the same rate? 6) Does it matter in what order you build and attach each tank, or can you set the priorities later? 7) If you have multiple tanks stacked on top of each other, do you have to set the "p#" for each tank separately? Do they all need to have unique "p#' values? For a big rocket with lots of stacked tanks, setting them individually would be very tedious and error-prone. 8) Trial-and-error seems to indicate that you can only use the symmetry tools for placing the decouplers and enabling fuel flow - but you can't use symmetry tools for placing any of the tanks or setting the fuel priority values. Is this the way it's supposed to work? 9) Should I just go back to using fuel ducts? Thanks for any replies
13. ## Component Diameter?

I always though that this critical information should be more prominently visible.
14. ## Kerpollo - A Complete Science Mode Run In 9 Acts

@GRS, Planning the Mohollo mission now.
15. ## Kerpollo - A Complete Science Mode Run In 9 Acts

Thanks. At the time I thought I remembered that EVA between ships was allowed, but upon further review I can't find that in the challenge rules. I have a quick-save from the docking maneuver, if you like I can go back and see if I can jam the ships together by using a higher approach velocity. Given the tanks are on top of the lander, I was being a little careful about the approach speed - and it took a few minutes before I figured out what was happening. Once I got them magnetically soft-docked, I wasn't able to force a hard-dock just using the lander engine power. I also used ASDW fiddling to try and wiggle the ships together. I did not try using the orbiter main engine, because I didn't want to touch the delta-v budget. A couple of observations about that stuck magnetic docking. I used a launch re-vert to test undocking in LKO, but I didn't think to test docking. I noticed that when undocking, the lander shot-off at a brisk pace, rather than just the usual gentle nudge. I thought that was odd but ignored it. Ultimately I think that was some mild kraken-like behavior due to the tank interference. Re: the nosecones. Turns out that I hauled most of the asparagus stages all the way to LKO, so probably a couple more cones would have been useful. So far, on these outer planet missions, I've been consistently over-estimating how much delta-v is needed to get back. And I'm getting a sore mouse-knuckle from messing with the maneuver node adjustments trying to get planetary encounters. I only have three science instruments unlocked - temperature, barometer, and mystery-goo. And on the Eelollo mission I only remembered to install two of them. Haven't decided on what mission to tackle next. I need to look at the dv requirements and what booster parts I have unlocked, and get more practice at building big rockets.
16. ## Kerpollo - A Complete Science Mode Run In 9 Acts

I'm aware of the Gemini VII situation, that's why I said "take inspiration from", rather than "use Neil's strategy". Neil was trying to save his butt and his mission. Val was just trying to get rid of some magnetically sticky equipment.
17. ## Slowing down at DRES

To close the loop on the "best time to capture cheaply at Dres is when it is furthest from the sun" strategy, where is Dres in its orbit at Year 7 Day 249?
18. ## Kerpollo - A Complete Science Mode Run In 9 Acts

Eelollo Mission completed. Tech tree at the start of the mission: Ship Eelollo-A on the launch pad. Observe the amusing and random use of nose cones. Also, those with X-ray vision can observe that I forgot to put a temperature sensor on the lander. A lost science opportunity. Yes, it appears that I only fly at night. I have no idea why. Jeb on the Eeloo surface, Observe those artistically placed fuel tanks. They play a role in the following image. In Eeloo orbit after ascent. Notice the 0.4 m gap between the lander and orbiter? That's due to an interference problem caused by the tanks which was not evident during construction or un-docking. The tanks prevented full docking, but the magnetic docking force was strong enough to hold the ships in close proximity. Jeb collected his science data and EVA's to the orbiter, and it was Val's idea to take inspiration from Neal Armstrong on Gemini VIII, and separate the two craft by spinning the ships until the lander separated. Science return after landing and recovery. Kerbin re-entry went smoother than on Drespollo - only one revert was needed. The 2,600 m/s of dv remaining was burned off retrograde two minutes before re-entry, and a deep dive into the atmosphere racked up some big G-forces, but only used about 200 ablator. By an unplanned circumstance, landing was 80km from the Drespollo landing site in the grasslands. Next up - bigger rockets, for the more complicated missions.
19. ## Kerpollo - A Complete Science Mode Run In 9 Acts

Progress report: Status: Jeb, Val, and some random scientist are currently in orbit around Eeloo. The booster stage ran out of fuel exactly when a good-enough low Eeloo orbit was achieved. Observations: - Looks chilly down there. - A solar panel or two would have been nice for keeping the batteries charged.
20. ## Kerpollo - A Complete Science Mode Run In 9 Acts

Working on Eelollo. Asteroids - maybe a "target of opportunity" within the nine allowed missions.
21. ## Kerpollo - A Complete Science Mode Run In 9 Acts

I've never been far enough up the tech tree to have struts before.
22. ## How to convert an alex moon launch window into a maneuver node?

When i clicked on the "i" info button, the text box showed the prograde and normal parts of the burn. I tried that method, but it seems like when I set the burn dv at the date and time from the planner, it doesn't cause an intercept. I have to slide the node around as much as 30 days one way or the other, and and adjust the burn. That seems wrong, since all of the trajectory physics are on rails and the practice should match the predictions. So I'm likely doing something wrong. Is that 'retrograde" with respect to Dres' orbital direction, or with respect to my orbit around Dres? My retrograde direction changes pretty quickly when I'm in orbit, and the window planner can't know what my orbital phase is, it only asks for my orbital altitude. So probably it must be retrograde with respect to Dres' orbital motion, minus a couple a degrees one way or the other (whatever "88 degrees to retrograde" means). I've seen the reference figures for the angles, and I don't understand what "degrees to" means.
23. ## Kerpollo - A Complete Science Mode Run In 9 Acts

Drespollo completed. The ship: 1st stage - five Twin-Boar plus four Kickback. And a few struts for stability. Landed on Dres: Docked in Dres orbit after ascent. Recovered on Kerbin: And here's the Tech Tree that was in effect during the mission: Mission highlights: Getting to Dres was relatively straightforward, given unlimited reverts. Operations at Dres were nominal. Jeb eventually managed to find a return trajectory window departing from Dres, though the maneuver node twiddling knobs on that capsule now need replacing. Just barely remembered to undock the lander in Dres orbit - good thing to because it increased the dv available by about 300. The initial Kerbin Pe was around 3 Mm, then used two mid-course corrections to get it down to 40 km (again, using some reverts to fine tune the return trajectory to get a capture orbit). Screaming into the atmosphere 4300 m/s, there was 400 m/s of delta-v left, so burned that when she ship reached 80 km, then jettisoned the service stage. After the first aerobraking pass, the Ap was down to 200 km or so. Landed on the 2nd aerobraking pass, with 270 ablator left out of 800 initial. Total science collected: 1167.
24. ## How to convert an alex moon launch window into a maneuver node?

Sorry for posting this but I haven't been able to find an answer to exactly this question. Plenty of discussion about the Launch Window Planner mod, but I'm not using mods. Situation: I'm orbiting Dres and need to get back to Kerbin. I've got 1,700 m/s of delta-v to work with. Yes, I realize I might have to abandon the mission and go build a bigger rocket. But I'd like to evaluate how far off my rocket design is. Part 1: Without using any mods , how do I convert this transfer from the alex moon Launch Window Planner web page into a Maneuver Node? I've tried going to the correct UT time mark for the departure time, entering the two components of the Ejection burn (the 'i' info button says it's prograde 1263 m/s and normal 143 m/s), and from that I get basically into a large solar orbit that goes nowhere near Kerbin. So I'm doing something wrong - no idea what. Update: Upon further review, I realize the alex moon site doesn't know anything about my orbit around Dres, so just using the UT departure time isn't sufficient. So likely that's where all those angle values come into play, but there no way to enter those angles into a maneuver node. So perhaps a mod is required, if I want to avoid just endlessly tweaking on the maneuver node and dragging it around hoping to find a Kerbin encounter. Update to the update: (see strikeout above) Part 2: If I was to use a mod, which one that has been updated to work with KSP version 1.6.1?
25. ## [1.12.x] Transfer Window Planner v1.8.0.0 (April 11)

It's on page 23 of this very thread.
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