Lirtosiast

Ah, I missed that too. My spreadsheet gives zero overall payload fraction at 60% total MF to Kerbin orbit, so theoretically we only need a little more than that. It goes up by 5% for every 100 m/s slower than 500 m/s we land at, but if someone can get a SSTO with your engine balance to orbit with 60% total MF we're on our way to a Tylo SSTO. Maybe batteries would help? Bradley Whistance has a large percentage of batteries on his Laythe-Eeloo and two-trips-to-Eeloo SSTO as well as a general long range SSTO. Tylo isn't the best use of batteries, because the high gravity means the additional ion engines we need are heavier during the landing. Nevertheless we could use battery power 3 times when we're desperate for thrust: during Kerbin circularization, at the end of the Tylo landing, and at the start of the Tylo ascent. It would also make burns easier. Haven't done the math, but maybe the better mass ratio of the ion tanks makes battery power useful in situations like these now.

They have the same mass ratio as the 3.75m parts (so the same payload fraction to orbit etc. would be needed); also they're LFO tanks, so nukes are out. This doesn't completely rule it out, but anything with the large tanks would have less payload fraction than a NERV design.

@sdj64 You're correct. There was a serious error in my spreadsheet; I really shouldn't be doing this late at night! Now I'm getting similar numbers. 3.1% payload fraction with nukes and slightly lower with the Wolfhound. https://docs.google.com/spreadsheets/d/1RsHtqTvP85LdYsMRbufcYwQwO2TEs9F3RjNnSK5sqwk/edit#gid=491237559 However I think a 70% payload fraction is far too high given that @AeroGav could barely manage 50%-- and that was with an optimal SSTO engine balance, which is different from an optimal Tylo landing engine balance. Assuming 52% to suborbit and zero structural/wing mass we still have a -2.4% payload fraction (-15 tons on a 100 ton dry mass craft), or slightly worse with your engine balance.

It's not possible unless you count bouncing a fairing off Tylo's orbit at orbital velocity as "landing". I did the calculations for a 100 ton craft with one ion engine plus NERVs and RAPIERs, zero structural, wing, or battery mass, and horizontal landing and takeoff at 500 m/s. If it gets to Kerbin orbit with 80% payload fraction, the best possible mission plan with the best possible engine combination (12 NERVs and 10 RAPIERs; going any lower than 1 RAPIER/31t takeoff mass probably wouldn't yield a viable payload fraction) gives you minus 6 tons payload. Even a touch-and-go at 500 m/s yields a slightly negative payload. My math or one of my assumptions is wrong (if so, please tell me!). The KR-2L/RAPIER/ion system is impossible by an even greater margin, and any other stock engine is inferior to one of those two. I think this is closed. Again, correct me if I'm wrong. https://docs.google.com/spreadsheets/d/1OD7mtRem-ApGzy1eh4IsyvqDL_iB3cBtPh8KgyU_u60/edit#gid=491237559 EDIT: Accidentally doubled the engine mass the first time. Recalculated and payload fractions are positive with these assumptions: NERV/ion/RAPIER 100 ton dry mass craft, 72% payload fraction to suborbit gives a payload of about 13 tons or 3.1%.

Ever since the days of @tavert and @Kosmo-not we've known how to execute an efficient low-TWR landing: throttle to 100% and keep the ship at constant altitude by pitching down. But what if you're designing, say, a reusable mission to Tylo that uses both NERV and RAPIER engines? When landing on Tylo, how far do you pitch up, when do you switch on the RAPIERs, and at what thrust? @FleshJeb and I wrote a spreadsheet calculator for this purpose. It assumes a constant-altitude ascent/landing (pretty close to the optimum), and works for ascent or landing, and any types of engines. Simply enter parameters in the green boxes and your mass fraction, total dV expended, and ascent/landing profile appear in the blue boxes. Accuracy is within about 1-2% due to the CAL assumption and Euler's method. Calculator is here. ----- To implement: * Add table of engines and celestial bodies * Use a less inaccurate algorithm than Euler's method * non-CALs (hopefully the math is not difficult)

Rapiers wouldn't be worth the fuel if the arm is significantly heavier than this craft. Besides, the thrust would be near zero anyway when stationary at 26000 m. Reaction wheels don't have increased leverage when you put them on the outside of the arms. I think the best approach is secondary propellers on the arms, fairly close to the hub but still far enough away to get leverage (if the arm tip velocity is 1 km/s, and propellers are only effective below 250 m/s or so, we need them 1/4 of the way down the arm). Part count would be a challenge though. EDIT: They should probably be contra-rotating to avoid gyroscopic effects.

IIRC enough science can be acquired from Mun and Minmus to unlock the tech tree, so there's no need to go interplanetary. So the question is then whether it's advantageous to do a brachistochrone to Minmus or just an ordinary mission with a slightly higher dV expenditure. Considering that much biome hopping is necessary (meaning a heavier craft), and a full brachistochrone is probably only practical after the launchpad is upgraded a couple of times, the expense of going faster would be substantial. EDIT: Upon reconsideration this challenge sounds somewhat tedious, given the Abyssal Lurker video. I won't attempt it.

Do you mean km? 100 m above datum results in crashing into hills. And what's the winning criterion? Best replica? It's fairly easy to make a craft that just to Mun orbit and back.

I finished working out the math. First thing to note is that 5 engines is optimal, as I had guessed. 4 engines is theoretically better if the craft is extremely light, but 5 is probably realistically better since with higher TWR it's easier to land, easier to do gravity assists, and easier to circularize in Kerbin orbit. Assuming there are 0.6 tons of payload and 0 tons of landing gear dropped on Tylo ascent, our Kerbin ascent budget is at MOST 20.2 tons of liquid fuel to get the craft into Kerbin orbit. This means a 59.6% full tank. For every ton of landing gear, we lose about 2.3 tons of ascent fuel (4.6% more fuel) For every extra ton of payload, we lose 2.9 tons of ascent fuel (5.8%) For every 100 m/s below 500 we land and take off at, we lose 2-2.5 tons (5%). These numbers are fairly close but may change with piloting error. So if we include the 0.7 ton Mk3 engine mount as payload; and also include 3 medium landing gear (0.75 tons), we will need a 67.1% full tank in orbit. Keep in mind this is with perfect piloting* and assuming we can land and take off at 500 m/s. If we can only land and take off at 400 m/s, we need 72.0% fuel in orbit. My spreadsheet (here) is fairly user-friendly now if anyone wants to plug in other values. Should I start a separate "highest % fuel left in orbit" challenge so we can get an idea of the maximum possible fuel left in Kerbin orbit? EDIT: Got the Euler's method approximation working for Tylo ascent. Next is the Tylo landing one. Turns out Tylo ascent takes slightly less fuel than I had calculated before. EDIT: Works for Tylo landing now too. Calculations updated accordingly. * EDIT again: However, I'm assuming a constant altitude takeoff, which is not quite optimal when engines are dropped. Here's what I mean: Attached is a graph of the pitch for a constant altitude ascent as a function of horizontal velocity. The sharp spikes are artifacts, but notice how the pitch abruptly rises when we drop the first pair of engines at 1050 m/s, and the second pair at 1650? Smoothing the pitch out to something like the red line would prevent cosine losses. In piloting terms, this means using the extra power of 5 engines to loft yourself up a bit so that when your TWR drops, you don't smash into the ground. I'm not sure how much mass this would save though, and it's really difficult to calculate because now rather than optimizing for one variable, we're optimizing for a whole function: pitch as a function of velocity. Empirical testing with an actual Tylo lander is probably best. https://imgur.com/a/qtMhQ

@EpicSpaceTroll139 3 nuclear rockets? My spreadsheet gives a Tylo landing TWR of 0.96 with three engines, payload of 0.6 ton, and droppable landing gear of 1 ton. Of course you're landing at up to 500 m/s, which reduces effective gravity, so your effective TWR is 1.03ish... still, by the time you land you're pitching up at csc^-1(1.03)=80 degrees just to maintain altitude. If it's possible to land with acceptable dV from that it would be quite a challenge. Testing is definitely a good idea. It would be a shame to have to cheat in unbreakable parts, because if horizontal landings don't work this mission is probably futile. 5 m/s^2 in Kerbin orbit isn't too low, but it's low in comparison to PLAD who used a spacecraft with approximately 30 m/s^2. EDIT: Assuming 0.6t payload and 1t gear my calculator gives 2498 m/s with 3 engines compared to 1981 m/s with 5 engines for theoretical best Tylo ascent, and the additional mass makes it impossible to land. If the payload can be made as light as 0.6 tons, 4 engines might be the sweet spot.

Oh, interesting. Yeah, I decided the Mk3 tank would be the only possible approach pretty early on. What's your structural/payload mass? I've just been using 1.5 tons. As for the gravity assists to Jool, I think we can just use the 1011 m/s number and find a route when we need to . PLAD said under 997 m/s is impossible anyway. Did you take into account the low TWR on Tylo landing/ascent? It makes a pretty big difference; I don't think Tylo ascent will be achieved for under 2500 m/s or so with such a low TWR, and adding more than 5-6 engines reduces your delta-V budget too much.

While I was investigating Single Tank Tylo I thought to do a full spreadsheet analysis of this mission taking into account that xenon tanks now have much better mass fraction. The Rhino and LV-N are the two best engines. Of these the Rhino is easy to prove impossible: Payload fraction is minus 4 percent given the following assumptions. Vessel is returned to Kerbin in one piece. No separating the craft or deliberately exploding your xenon tanks. Wings, landing gear, etc. have zero mass. Payload fraction to Kerbin orbit is a little under 75%. I've never seen anything this high. Engines are infinitely divisible, but you can't have less than 1 engine. The vehicle has at least 0.01 TWR (even at 0.01 it is impossible to perform gravity assists with perfect efficiency). The best route (1011 m/s) to Jool is used. Your relative velocity to Tylo is small due to a Laythe assist. The best route back is used, only 100 m/s from Tylo escape to landing back on Kerbin. A 500 m/s touch-and-go Tylo landing is performed, never stopping on the surface. Descent dV is 2000, ascent and circularization dV is 2100. This is not possible without a near-infinite TWR. Tylo TWR > 1.15. Even though most of it is performed with the RAPIERs, Tylo landing and ascent has the same Isp as the Rhino. I'm pretty sure the LV-N is also impossible but it requires more than these loose bounds to prove. Will update when I find out what those are (or prove myself wrong). Probably will need to fire up Mathematica for a constant altitude landing simulation. To plug in different numbers, change values in the "Stats" or "Parameters" section of my spreadsheet, then perform the following steps: For a possibility analysis, set "Guess dry mass" to FALSE and "Possibility test" to TRUE. The box will light up red for negative payload fraction (impossible) and green for positive. To estimate the mass of a craft, enter something in "Payload", set "Guess dry mass" to TRUE and "Possibility test" to FALSE, and adjust the dry mass guess until it is equal to the actual dry mass.

Back in 2016, Hazard-ish used a nuclear engine with edited thrust and Isp values to land on Tylo and return, with the only source of fuel being a single large fuel tank. Here is a tentative stock, optimized version of this mission, using a mix of Hazard-ish's numbers, my own dV estimates, and Kerbin-Jool numbers shown to be possible in the past. The craft is like Hazard-ish's but with a large Mk3 fuselage, 5 stock nuclear engines, and an unknown optimized Kerbin ascent stage. Payload/structural mass is assumed to be 1.5 tons. There appear to be fewer possible approaches for this mission compared to SSTO Tylo (which given the other thread seems impossible) My mission profile with dV estimates is as follows: Maneuver dV (m/s) Put the vehicle into orbit. Must use less than 13.5 tons of liquid fuel. May be doable with electric propellers. Remaining mass: 60.15 tons. - Use Mun-Mun-Eve-Kerbin-Kerbin gravity assists to get a Jool encounter in 1011 m/s a la PLAD. Difficult because the max acceleration of the craft is only 5 m/s^2. 1011 Use a Laythe assist to capture in low Tylo orbit for 1020 m/s. (Capturing at low Tylo orbit from anywhere always costs 810 m/s) 1020 Do a 400 m/s horizontal landing on Tylo. High dV because your starting TWR is only 0.83 (landing TWR 1.15). Hazard-ish managed 150 m/s, already an impressive feat. 2500 Take off from Tylo horizontally at 500 m/s, dropping all but a single engine along the way. There is a slightly difficult calculation to determine exactly when the engines should be dropped; the optimum is to drop the last pair when the craft reaches 1700 m/s. 2533 Use a Laythe assist to get back home. For the last 100 m/s, use the EVA pack to push a 0.625m heatshield with a chair strapped to it. Use the Kerbal's parachute to land. 810+100 Total ~8050 I can't tell if this mission is possible or not. Margins are basically zero, so all of these difficult feats are necessary. It basically comes down to whether the Kerbin ascent, horizontal landing, and pushing the reentry vessel at the end are possible, but I'm not a good enough player to test any of those (only landed on Tylo once, and inefficiently at that, nor am I an expert on SSTOs or propellers). So my two questions are: 1) Will this mission plan work, if one can pilot the bloody thing? If not, why not? 2) Can anything be optimized further? I thought of a 300-400 m/s touch-and-go at Tylo, which probably makes the mission doable but isn't quite the same as a full landing. Here's the analysis in spreadsheet form: https://docs.google.com/spreadsheets/d/17JtG4sQc_FvpHZovDfvPAZIKkyoFxo45DA5bv964Zjw/edit#gid=0 (I'm new here so please move if this is the wrong subforum.)