The KSP Caveman Challenge 1.11.x - 1.12.x

[JAFO]

3 hours ago, WarSprite said:

So, armed with Basic Science I set out to grab Science Jr in all four situations.

A most creative approach.. don't think I've seen anyone lob up 4 Science Jr's at a time before, not at this stage of a run, anyway.

 

3 hours ago, WarSprite said:

Thanks JAFO   But I'm not stuck yet... as I commented, I just had to spend a bit for Basic Science and all the goodies in that node. I still can't reach other situations yet, but I can do more science in the four situations that I can reach.

I should be clear... I'm OK with Kerbin atmosphere / space, it's just farming the Kerbin biomes that I'm trying to avoid.

I probably spoke a little too soon.  The real wall will be once you've harvested all the high/low Mun science. At that point, all the easy "low hanging fruit" is gone, and I suspect you'll find it hard getting enough science to unlock items essential to progress further. But.. best wishes. I'd love for you to prove me wrong.

[WarSprite]

Time for a quick update, Jeb going orbital

I've had the ability for a while, but I wanted to mop up all the sub-orbital science experiments before moving on.

 

Flight #11 - Orbit Kerbin!

The orbiter is simple enough, just a LV-T45 Swivel with eight FL-T100 tanks, and a pair of RT-10 Hammer solids for the initial kick. Flying it was OK. The ascent profile is rather sub-optimal; between the high TWR at lift off, and only having basic stability assist, I can't get it leant over far enough. However the rocket has plenty of delta-v margin to handle that and still circularise in a stable LKO.

https://drive.google.com/file/d/13BMQ_oauKQlR77DN_dEojBjrBGabrDrT/view?usp=sharing

https://drive.google.com/file/d/1JuVXx_OKI_q-CQngfTzmhQQz8-AbNNoA/view?usp=sharing

After checking out a nice orbital sunrise over Kerbin, it's time for Jeb to head home.

https://drive.google.com/file/d/1u04Jqmi9ljaew5ykkLaEDvMLunMtz3Hv/view?usp=sharing

https://drive.google.com/file/d/1KyrxfVMjJOmnUur0wVs-alvwZKyqfWGD/view?usp=sharing

And the best bit about the whole flight? Jeb reaches level 1, and is allowed to push the Prograde / Retrograde hold buttons now :-)

https://drive.google.com/file/d/1TyIbKSJU74d0oyQIVUwcaFfWcsAExfrW/view?usp=sharing

 

After this flight I have 104 science in the bank. It's time to move on to other celestial objects; I'm planning on doing Minmus before Mun, because despite the game's story, we all know that Minmus is easier. There's no way I'm going there with current tech, so I research General Rocketry and Advanced Rocketry, getting me the Terrier. That leaves me with enough tech for Minmus, and 39 science left in the bank.

Next time : Minmus!

 

 

 

[paul_c]

Don't forget if you aren't going down the path of remote probes, you need to get the Kerbal BACK from Minmus as well as there! You start out with 2 pilots so you can afford to lose just 1, the rehire cost will wipe you out otherwise. With no quicksaves etc....you need to be 100% sure you can get them back, somehow or other.

[WarSprite]

31 minutes ago, paul_c said:

Don't forget if you aren't going down the path of remote probes, you need to get the Kerbal BACK from Minmus as well as there! You start out with 2 pilots so you can afford to lose just 1, the rehire cost will wipe you out otherwise. With no quicksaves etc....you need to be 100% sure you can get them back, somehow or other.

Hey Paul, yep, I remember 

I already had a look at Caveman Normal, where I developed quite a few rockets, and a quick go at Caveman Hard that I didn't document. Having looked at those is what makes me think trying a documented run with my aspirational goals is worth a punt.

I take on board your point about being *sure* about the flight. So for this next one, I have a higher performing rocket, but it's a bit harder to fly on the ascent, and I don't need the performance for a fly-by, so I'm using the easier to fly rocket for that very reason.

3 hours ago, JAFO said:

I probably spoke a little too soon.  The real wall will be once you've harvested all the high/low Mun science. At that point, all the easy "low hanging fruit" is gone, and I suspect you'll find it hard getting enough science to unlock items essential to progress further. But.. best wishes. I'd love for you to prove me wrong.

I'm really not sure how it's going to work out JAFO. Right now I'm actually more confident about the science than I am about funding. I made notes on what science I can grab with which nodes previously, but I never made notes on funding, and I'm a touch nervous on that front. At the moment the World Record Keeping Society is more than paying my way, so I'm hopeful that the trend continues. As always, time will tell.

I'm going to leave this post, and do another for the actual flight notes.

[WarSprite]

So the flights are going to slow a little in tempo now, as they become longer and more involved. I'm also surprised at the time it takes to upload screenshots and produce the write-up for the thread.

 

Flight #12 - Flyby Minimus

When I've had a previous look at a Normal difficulty run, I did quite a bit of development on a Mun flyby rocket. It turned out to have more than enough performance to manage a few other missions after the Mun flyby, so it's going to see some heavy use now.

I'm just going with one of each experiment. It's only a Topaz run, not a NCD run, so I don't need suck every last drop of science, and I'll be happy with the single experiment grabbing the bulk of the science for the Mystery Goo and Science Jr. The rest of the rocket started as my Kerbin orbiter. The solid boosters got replaced with LV-T30 Reliant engines which are a bit more mass efficient. I added a Terrier upper stage after the Swivel, and then the experiments on top of that. The whole thing is topped with the command module and an experiment box; I'm not bringing the experiments back, just the data.

 

Ascent is a bit of a mish-mash. It's a high TWR design, so I fly a fairly sharp kick into the gravity turn, and it flies low and fast. This launch was at 1,600 m/s and 23km altitude when it staged on to the Terrier to finish the ascent and circularisation. A 71km LKO left me with 1,670 m/s in the tank, which is a good launch for me on this rocket.

https://drive.google.com/file/d/1y3ljeP5HAYI57QQ4a__FXg52GM43TJ--/view?usp=sharing

 

I don't inclination match Minmus while in LKO; when I tried that during development, it used about 250m/s delta-v which is far too expensive. So the next thing is the transfer burn. True caveman navigation - break out the sundial, point the top at Minmus and zoom in to Kerbin; wait until your ship as at four o'clock and mash the big button. In this case since I'm aiming for a fly-by I only pushed apoapsis out to 45Mm, actually 45.36Mm - at that distance a little thrust goes a long way, so my precision isn't great.

https://drive.google.com/file/d/1_C7iVZoEIvNF-mYgmlFimGJRPwjLnASc/view?usp=sharing

https://drive.google.com/file/d/1fq-AfP9XUpeR2gonVxzEt5nQU_hGgiA6/view?usp=sharing

 

Anywhere around half way out on the transfer journey I came out of time-warp, and burned so raise my apoapsis up to the Minmus orbital plane. It's not a full plane match, but it means I'm close enough to the right point for the encounter when I reach apoapsis. This only used 24m/s this flight, which is much nicer than the cost to do a full plane match while orbiting Kerbin.

https://drive.google.com/file/d/1w_HWlYPhuZU8aWBcXfi8x1MBkV4uNq5Y/view?usp=sharing

 

The actual Minmus encounter happened just before apoapsis. Not perfect, but hey, I blame the caveman navigation! Minmus isn't quite so bad that you need to hold a protractor to the screen for a fly-by, I find "about 4 o'clock" by eyeball seems pretty reliable. Perfectionists may disagree    Switched out of map view to grab that sweet sweet science, and I remembered to suck it all into the science lunchbox; I forgot on one flight in development, and that was... irritating.

https://drive.google.com/file/d/1ToNOCFecaoYAAQF5EetT1hg2rtfv896k/view?usp=sharing

https://drive.google.com/file/d/1n9vSl7Pgx0PoGXoaxTQcICV0b7Ai5hAz/view?usp=sharing

 

Then it was just coast out of the Minmus sphere of influence. It has such a low gravity that I dropped back to Kerbin nearly unchanged, with a 157km periapsis. Very little adjustment needed to drop this to 41km, which is my preferred re-entry. I find 41km a sweet spot that keeps the command pod temperature enough below the limit that I'm comfortable Jeb will keep grinning like a loon, and not explode in a ball of fiery death. I had 714m/s delta-v left in the tank when I jettisoned the engine at the edge of the atmosphere, so plenty of performance in this design 

https://drive.google.com/file/d/1hutaiqs_vs2QoaK32ETVVacgWBQxAXNX/view?usp=sharing

https://drive.google.com/file/d/1UAyVYb_0ZjPpnVBetXW9-AI65z5f_Nz9/view?usp=sharing

 

So, that was the Minmus fly-by. An extra 106 science from that flight including the recovery and WRKS bonuses. I am now back above my "bail out" margin of having 45 science spare to build a jet-rover to farm the KSC if I don't manage to stick to my personal goals on this run. It's comforting to have that safe fall-back position! I'm hopeful I can do it, but I'm very aware that JAFO and paul_c have much more experience than I do, and are both a bit skeptical.

Next time : A low orbit of Minmus.

 

[JAFO]

Impressive work so far.. carry on!

 

8 hours ago, WarSprite said:

I am now back above my "bail out" margin of having 45 science spare to build a jet-rover to farm the KSC if I don't manage to stick to my personal goals on this run. It's comforting to have that safe fall-back position!

Don't forget that if a jet-rover isn't in the science budget, there's always the good 'ol Caveman Science Roller to fall back on.  You should already have all the parts you need for that. A bit more painful to get around, for sure.. but it gets the job done!

[WarSprite]

10 hours ago, JAFO said:

Don't forget that if a jet-rover isn't in the science budget, there's always the good 'ol Caveman Science Roller to fall back on.  You should already have all the parts you need for that. A bit more painful to get around, for sure.. but it gets the job done!

That's a good point, and I've previously used them when starting out to grab a couple of KSC biomes for that little boost at the start. I think I should have that nice safe margin to grab the Aviation node whenever I need to now. I'm past the parts that I thought might be close on science points. So on that note, on to the Minmus orbit...

 

Flight #13 - Orbit Minmus

Let me start by saying that I'm not superstitious; having said that, if it could go wrong with flight 13, it did.

I'm using the same design as the previous flight - as commented it's got a fair performance margin, so is good for a few missions yet. Launch and ascent looked pretty nominal, but I was a little disappointed at only having 1,619 m/s left in the tank after reaching LKO. No matter, still plenty of margin on the flight. I did the sundial navigation, and pushed apoapsis out to 46.1 Mm (aiming for 46.3) since I want a close encounter for low orbit. Midway on the transfer, pause, and burn in a roughly anti-normal direction to drop my apoapsis down onto the Minmus orbital plane. This took 42m/s which is a little high, I guess I caught Minmus near the peak of it's inclined orbit. Here's an image showing mid-transfer inclination match after completion - you've seen the rest of the ascent and navigation ideas on the previous flight.

https://drive.google.com/file/d/1Nf60GNaSP21G2CJgJ1x6Y6-F2-P9jrd0/view?usp=sharing

 

The Minmus encounter happened a bit after apoapsis, which is always a bad sign. There may be something to that "protractor against the screen" navigation after all. Sure enough the encounter itself turned out to be horrible, with a 1.19 Mm periapsis. I guess I left the transfer a little late, and could have done with being a few degrees earlier to start the the burn.

https://drive.google.com/file/d/1_z5hnpe8w-sO--PZgIjeshgP_h7T-dxC/view?usp=sharing

 

I had a good look at previous flight notes from rocket development, and reassured myself that there was still plenty of fuel for orbit and return, so went ahead with the orbit, rather than aborting and returning to Kerbin with an unplanned flyby. It was important to be confident, since dropping into low orbit is definitely the point of no return. After circularising a 29 km low orbit, I was left with 372 m/s in the tank.

https://drive.google.com/file/d/1aeJPT0GKNhGyx8UX_f0NrWcHYSaOyWf5/view?usp=sharing

 

I switched out of the navigation screen to grab the science (and store it in the lunchbox!) and found one of my mistakes. You can see it pretty clearly in the next image.

https://drive.google.com/file/d/14x9F4eUdoiNp9RtV07_c4Hf3Ko171jDd/view?usp=sharing

Spoiler

Yep, I forgot to take Jeb's toys away. It's always a little surprising the impact that those 49kg on your upper stage can have to total performance. I've never made that mistake before during sandbox development, but it's now added to my pre-flight checklist. An even better solution would be to poka-yoke it by finding a useful way to bring the design to a hair under the 18 ton mark so that it can't launch with the unnecessary mass of the parachute and jetpack.

 

Getting home from Minmus (or Mun) is just more sundial navigation. Set Kerbin to the 12 o'clock position, zoom in, wait for your ship to be at the appropriate place to leave the SoI in a retrograde direction. I find between 12 and 1 o'clock is good for getting out of Minmus, and from a 29km orbit I've had good luck with a 280 m/s orbital speed.

https://drive.google.com/file/d/14gmQN9anb1LAtzH2akjFjtax0o1jBIsQ/view?usp=sharing

 

So I coasted out of the Minmus SoI quite happy with myself, that is until I saw the 8.8 Mm periapsis I had over Kerbin. After a pause for coffee and contemplation, I figured that there wasn't anything clever I could do, I just had to hope there was enough propellant to adjust this for re-entry. It took 114 m/s to bring my periapsis down to 41.5 km for re-entry, more than I think I've ever used getting back to Kerbin. I still don't understand what was different about this flight that the periapsis was so high; I'll have to think on that. Surface speed at re-entry looked acceptable, so I staged away the engine and let the command pod ride it out. I had 117 m/s in the tank at the edge of the atmosphere, which is OK, but considerably less than I had expected for this flight.

https://drive.google.com/file/d/1_KMGv38qbB2sC2ptnozx92mXlPWG9K5w/view?usp=sharing

 

The final surprise of flight 13 was on landing. I had earned a little more science than I had expected! A quick look explained why, when circularising Minmus orbit, I overshot, and dipped my periapsis below the surface before correcting. Hence the recovery (and WRKS) awarded a few additional points for a suborbital flight, rather than the planned orbital points. In total the flight added 162 science, giving me 307 science in the bank.

Overall that was a bit of a mess. The lift off mass is easily fixed by adding the pilot's inventory to my checklist. I should consider checking where Minmus is in its orbit, and if it is at the high or low points, maybe orbit Kerbin a few times before performing the transfer burn. I need to find a way to be a bit more precise on the sundial navigation if possible; the protractor would work, but I don't have notes on the "perfect angle" to burn at. And I could really do with understanding why my periapsis was so terrible on return to Kerbin. The only thing that kept the flight going was having a number of flight notes from development that reassured me that although I was "off nominal", I still had the performance margin on the rocket to complete the planned flight. There were no clever manoeuvres that saved it, just a healthy safety margin in the rocket performance.

Next time, landing on Minmus.

 

Edited May 24, 2021 by WarSprite
Fixing typos :(

[JAFO]

4 hours ago, WarSprite said:

Midway on the transfer, pause, and burn in a roughly anti-normal direction to drop my apoapsis down onto the Minmus orbital plane. This took 42m/s which is a little high, I guess I caught Minmus near the peak of it's inclined orbit.

This is one of the reasons I prefer my own technique for encountering Minmus.. I always arrive at Minmus just as it's crossing Kerbin's orbital plane, and therefore there are no corrections to be made at all. Might not save a lot of dV, but every little bit helps!

 

4 hours ago, WarSprite said:

After circularising a 29 km low orbit, I was left with 372 m/s in the tank.

Ummm.. why go to the expense of circularising? So long as your Pe drops below 30km to get your "low space" science, you're good to go. Dropping your Ap down below 30km as well, is just an unnecessary waste of fuel.* There's nothing magical about a circular orbit, other than the visceral satisfaction it provides. Elliptical orbits are often just as good, and can, in fact, be more useful.

* Though with an elliptical orbit, you should try to make your escape burn at close to Pe, so as to maximise the benefit you get from the Oberth Effect.

Edited May 24, 2021 by JAFO

[WarSprite]

Dammit, I'd just started the write-up on the next flight when a notification of reply came in! Forums... I can't bear to leave a reply un-read.

1 minute ago, JAFO said:

This is one of the reasons I prefer my own technique for encountering Minmus.. I always arrive at Minmus just as it's crossing Kerbin's orbital plane, and therefore there are no corrections to be made at all. Might not save a lot of dV, but every little bit helps!

Yep, I absolutely agree, that avoiding wasting delta-v is a really good plan. I think I had previously been lucky and not had such an extreme adjustment to make. On my next flight (complete, write-up pending) I did a Kerbin orbit to get Minmus close to its midpoint. It was better, but still not perfect - I definitely have scope for improvement.

3 minutes ago, JAFO said:

Ummm.. why go to the expense of circularising? So long as your Pe drops below 30km to get your science, you're good to go. Dropping your Ap down below 30km as well, is just an unnecessary waste of fuel.* There's nothing magical about a circular orbit, other than the visceral satisfaction it provides.

I'm not sure on that one. I absolutely agree that there are savings to be made. Likewise on my landing, why orbit at all? Just come in to the encounter, drop periapsis to ground level or below and land. However, for better or for worse, I'm finding that I do better on the Caveman Challenge with known quantities. If I circularise at 30km I *know* how I should exit. If I'm landing and I circularise at 9km I *know* what delta-v I should use in the landing. Having that predictability is really helping me in both planning manoeuvres, and in ensuring that I have enough delta-v and don't need to abort the flight. *shrug*  just me and my quirks I suspect 

Anyway, back to the write-up of the next flight...

[WarSprite]

Latest update on my Topaz challenge attempt.

Flight #14 - Minmus Landing

This is a bit more demanding, so I'm switching to a later iteration of that original "flyby" rocket. I've swapped the Swivel in the second stage for a Reliant, which lets me add another fuel tank. The down side is no gimbal around max-Q so I need to get the gravity turn set up and "good" very early on in the flight. The up side is 224 m/s more delta-v which I really need for a Minmus landing.

Launch was nominal. With the slight increase in mass on the upper stage, it flies slightly slower, under 1,600 m/s at staging to the Terrier, but not enough to make any difference to the launch profile. With the scary bit out of the way I was in a 71 km LKO with 1,852 m/s in the tank. That tweak to the design really helps. Minmus transfer and plane correction burns went well, so I was set for an encounter with 912 m/s left in the tank. Thankfully my timing was a bit better on the sundial, and it was a much nicer encounter than the previous flight, having a -16km periapsis.

https://drive.google.com/file/d/1MFRMt0O16C9sNPe7f2QIwGl3zjpusJXJ/view?usp=sharing

https://drive.google.com/file/d/1DGeYvI2PJlmcQ41tQHUF_kuUYDSbeudQ/view?usp=sharing

 

A small burn in roughly radial-out lifted the periapsis to 9.0 km, and I circularised at periapsis (sorry JAFO!)  leaving 748 m/s in the tank. One benefit of circularising was that I got to choose a nice comfy landing zone (the Greater Flats) with much less chance of a nasty mountain stepping out and ambushing me, or falling over on a sloped landing site. From a 9km orbit I tend to do the landing burn at 300~320 meters, and that left me a touch high, but some gentle burns got it set down on the flats to do the science. Overall the landing cost 206 m/s of delta-v which isn't my best, but is acceptable.

https://drive.google.com/file/d/1rJd6BXDlpZjuvR7M1TkqOkZQlcgc6WDc/view?usp=sharing

https://drive.google.com/file/d/1PQpP60qh1Eu5odfd1t9L_kwQ_t6UAkdS/view?usp=sharing

https://drive.google.com/file/d/1a2Covce1hw_BM57BCgkN_Mud3xTAAl8r/view?usp=sharing

 

Take off is fine, I just need to be careful to not overshoot my target apoapsis, and I circularised at 9 km low orbit; again, that's for having a predictable exit burn. Fire the engine around 1 o'clock up to 330 m/s orbital velocity, and cruise away from Minmus. I still don't understand the problem on flight #13 but thankfully this return dropped me into the Kerbin SoI with a far nicer periapsis of 314km. A small burn to drop this down to 41.5 km and a long cruise later, I was back at the edge of Kerbin's atmosphere. Surface speed looked sensible so I staged away the engine and the last 166 m/s of propellant, and floated down to land.

https://drive.google.com/file/d/1uIGrdngvbZOiUjqfXeomu266ghUcYbHd/view?usp=sharing

https://drive.google.com/file/d/10oAik3CG9MXgqRjqKXH0ECjO0VjQI3ZJ/view?usp=sharing

 

So there we are, first Minmus land and return complete. That netted me 204 science, giving me a total of 512 science in the bank. Also nice is that the funds from the WKRS are more than covering flight costs; I'm up to 210k funds, so much less worried about running out than I was a few flights ago.

I could complete the challenge farming Minmus, but firstly that flight was a bit scary, and secondly I'd like to move on to other celestial objects, hence the next planned flight will be a Mun flyby. It's following the story (flyby, orbit, landing) but putting Minmus before Mun, since it is an easier nut to crack.

Next time, Mun flyby.

[WarSprite]

Captains log, stardate  *bzz*  *crackle*

Flight #15 - Mun Flyby

After a Minmus landing, the first couple of flights to the Mun (flyby and orbit) are going to be easy. I'm back to the safe variant of the rocket with the Swivel, to reduce the chance or problems on launch. I still find the ascent to orbit the worst part of the whole flight.

Launch and ascent were nominal, leaving me with 1,677 m/s in the tank at my 71 km LKO. To avoid a big gravity turn sending me off into the stars, I push apoapsis to 9.5 Mm for a fly by. Timing on the transfer burn was another good one, with an encounter *just* before Kerbin apoapsis, giving me a nice wide fly by without too much gravitational acceleration from the Mun.

https://drive.google.com/file/d/1Xu0kzy5thiXnMbG5d7IFF0bJtujAw4N2/view?usp=sharing

https://drive.google.com/file/d/1LltZJAJBzDAoMpbRFGfEIMnFcryQ1Cmr/view?usp=sharing

 

The science run was fine, and return to Kerbin had a 13km periapsis, taking a massive 4 m/s of propellant to raise to 41.0 km for re-entry. Here's my obligatory two shots of grabbing the science, and of the start of re-entry. A lower surface speed and more remaining propellant than the Minmus flights 

https://drive.google.com/file/d/153_SXxhNEwOT2bTyT_aD0UAG7oGiu5e3/view?usp=sharing

https://drive.google.com/file/d/1O0zavZCfQ7R0uy2iqNMMfcTlaXuFvXly/view?usp=sharing

 

That quick little run added 83 science, giving me a spare 595 science in the bank.

Next flight will be a Mun orbit.

Edited May 24, 2021 by WarSprite
Fixing typos AGAIN

[WarSprite]

And the last easy one...

Flight #16 - Mun Orbit

I used the same rocket as previously of course. Launch was OK, but I could tell the profile was a little high - I didn't drag the kick into the gravity turn quite far enough. Still, the 1,656 m/s in the tank was more than good enough to continue. I used the full 11.4 Mm apoapsis for a solid encounter. I was a bit surprised at how much before apoapsis it happened, but that's sundial navigation for you. It was a nice one with a -3km periapsis. A touch of radial out to get that out of the ground, and I was soon in a 55 km orbit.

https://drive.google.com/file/d/1O0iaCAFlEmmg_3lvQQno9SAwc-Jqf86c/view?usp=sharing

https://drive.google.com/file/d/1lwFpYFDJxSiV1rqTyUj6bsMC57uIRRfq/view?usp=sharing

 

A quick trip through the science instruments, and it was time to head home. A 1:30 clock burn to 780 m/s orbital speed took me away from the Mun, and dropped me back into Kerbin's SoI with a -211 km periapsis. A touch low from previous notes, but easy enough to raise up to 41 km for re-entry. The surface speed looked good, so another safe landing for Jeb.

https://drive.google.com/file/d/1AMYv0-aG7UtIa-XkVbWzi7o9PtE3leJC/view?usp=sharing

https://drive.google.com/file/d/1uMdB89K6rgTHzp_XOK-UV8fCGOwOO-sY/view?usp=sharing

 

That orbital flight netted 119 additional science, bringing the balance to 715 spare in the bank. Together with the 153 science that I've already spent, I'm most of the way there 

 

However, I now feel that I'm a little stuck. I could just farm Minmus, but I'd rather avoid that, and stick to new flights. In particular I'd love to do a Mun landing, since that would finish the Kerbin storyline. The problem is that I've never developed a Caveman rocket for Mun land and return; the gravity well makes that non-trivial for cavemen    The 715 science in the bank can unlock seven Tier 5 nodes, so I have a fair choice of toys to play with, but a definite lack of experience on how to squeeze *that* much extra performance out of the ship. I've some ideas with a final stage using a Spark, and of course an OKTO would be lighter than the Command Pod, but my gut reaction is that part count starts to look daunting. It may be a while until my next flight report while I spend a *lot* of time finger-painting ideas on the cave wall. 

[JAFO]

On 5/25/2021 at 8:39 AM, WarSprite said:

and of course an OKTO would be lighter than the Command Pod

Should you happen to have your heart set on a crewed landing, don't forget that a Mk-1 Lander Can is also lighter than the command pod. That's why I use it on my Caveman Minmus Landers.

[WarSprite]

13 hours ago, JAFO said:

Should you happen to have your heart set on a crewed landing, don't forget that a Mk-1 Lander Can is also lighter than the command pod. That's why I use it on my Caveman Minmus Landers.

It's a good call on the Lander Can JAFO, definitely. I haven't used it on my "standard" rocket, since I didn't have the nodes when I needed that rocket... and it's just kept going ever since.

I'd actually love to do a crewed landing on the Mun. Having said that, I'm "nearly there" with a probe core, and given how tight that is, I suspect the rocket equation is just way to punishing on the extra mass on the final stage. Well, at least for my design skills!

So, back to the drawing board, a few refinements, a couple of practice runs in Sandbox, and I'm hopeful I shall have something that works!

[paul_c]

On 5/24/2021 at 4:25 PM, JAFO said:

This is one of the reasons I prefer my own technique for encountering Minmus.. I always arrive at Minmus just as it's crossing Kerbin's orbital plane, and therefore there are no corrections to be made at all. Might not save a lot of dV, but every little bit helps!

 

I do the same (for the Challenge). There are 2 times of the day when Kerbin and Minmus align. Every dV saved due to an efficiency is good, imagine being 4m/s short at some later point in the flight....

On 5/24/2021 at 11:39 PM, WarSprite said:

 I've never developed a Caveman rocket for Mun land and return; the gravity well makes that non-trivial for cavemen    

There's 2 routes (or choose both):

- Orbital docking, ie send 2 things up, join together a "normal" spaceship and a "mainly fuel tank" ship
- Get into remote probe stuff. You'll need a comms network (which can be as simple as 2x satellites, if you do it on the cheap - but I did 3) ideally; and if you use the OCTO, you also want some kind of reaction wheel too otherwise you'll have no control.

If you're into the manned flights thing, and joining 2 or more, then 1 manned and 1 remote makes sense otherwise you need 2x command modules and there isn't much performance advantage once that 2nd CM is there etc, its just bigger.

ETA I've done Mun land-return within the 1 craft, 30 parts limit. Its VERY tight for performance but possible. Its so marginal, that I only did it once or twice then reverted to docking stuff, mainly because I could then visit many biomes but only need 1 'return to Kerbin' and all the heatshield & parachute gubbins.

[WarSprite]

8 hours ago, paul_c said:

- Get into remote probe stuff. You'll need a comms network (which can be as simple as 2x satellites, if you do it on the cheap - but I did 3) ideally; and if you use the OCTO, you also want some kind of reaction wheel too otherwise you'll have no control.

Hey Paul, thanks for the input!

I've been heading down the route of probe launcher development, rather than crewed docking.  In Sandbox I haven't seen any problems with comms needing a network. Do you have any feedback on what difficulty level you start to need to launch relays?

8 hours ago, paul_c said:

ETA I've done Mun land-return within the 1 craft, 30 parts limit. Its VERY tight for performance but possible. Its so marginal, that I only did it once or twice then reverted to docking stuff, mainly because I could then visit many biomes but only need 1 'return to Kerbin' and all the heatshield & parachute gubbins.

I'm going to be happy with a single biome land / return for this, so the probe development is looking hopeful. But yep, definitely finding out the part limit hurts for probe development. Spent a couple of hours last night wanting "just one more part" before I had an epiphany. Mind, those moments when you crack an irritating problem are rather nice 

[paul_c]

You'll need a relay constellation to avoid blackout on "the dark side of the Mun". in Caveman challenge, there is only the HG-55 available. 

If you position 3x satellites equally in a circular orbit which is altitude at least the radius of the body, you'll have 100% comms except maybe wisps of the edges (eg if the satellites are equatorial, then you might have a momentary dropout exactly at a pole). Pragmatically, put them much higher than the radius and you can afford a bit of leeway in their exact phase and orbit.

I think I stuck 3x HG55 onto the relays (they are quite heavy and draggy though) and it was marginal when orbiting at 2000km but otherwise, no worries on comms.

[WarSprite]

Well probe design for the Caveman Challenge was a new experience    I'm so used to the Command Pod (just point it at a sensible periapsis) that the odd little challenge in probes was a surprise. So I thought I'd share my "lessons learned", firstly in case anyone can suggest better ways of doing things, and secondly in case anyone new to the challenge is reviewing the thread and wants some random inspiration.

 

Science Box Recovery :

Having discovered the hard way that the low temperature limits on probe cores make recovery "interesting", my first thought was avoid recovering the core at all, and just return the science. This is remarkably easy to get working; if anyone isn't familiar, just point your ship to a reasonable periapsis, activate a parachute on the science lunchbox, and stage it off your probe. The game will class it as debris, but as long as you use the Tracking Station and switch to your science box, you can "ride it down" through the atmosphere; it won't be deleted, and you're credited with the science when it touches down. It works a treat, and those things are fantastically resilient. The only issue is that they are "debris" not a "vessel" so you don't get science credit for "Recovery of a vessel from X" or WKRS records (or any contracts). If the experiment science is all you want, then in my opinion this is definitely the way to go with probes. I wanted those recovery points too, so filed this as "useful" and moved on.

 

Parachutes :

A Mk12-R radial drogue is more than enough for a bare science box, and is just enough to recover a science box and Stayputnik, but for anything larger the impact velocity is a bit high, so I use a Mk16 or a MK2-R radial parachute. I'm used to manually staging my parachutes when I'm happy with the altitude and surface speed, so it took a little while for me to be comfortable with staging in space and letting the automatic parameters pop the laundry out. If you're only recovering the science box you have to do this, as the lunchbox can't activate the chute; if you're recovering a probe core it's a good idea to do this anyway, just in case you run out of electric charge and the probe dies before you manually activate the chute  (don't ask me how I know that). I've taken to setting the pressure to 0.32 as this deploys at just under 7 km (on Kerbin) inside the "troposphere". If the vessel is still travelling too quickly for the parachute at that altitude, you've set your periapsis too low, and it's going to be a "shovel and trash bag" recovery regardless.

 

Electrical Power :

Probes and reaction wheels need electrical power. You don't actually need solar cells at all; with careful use of "hibernation mode" on the probe core outside of your manoeuvre windows, a small battery is adequate for exploring the Kerbin system. Given the part count limits on the Caveman Challenge, eliminating two to four solar panels is a real help. Be aware that it's hard to find somewhere to put the Z-100 Battery Pack that doesn't stick into the plasma stream on re-entry, and if it does, it will burn off. If that happens, the core's built in electrical charge doesn't last long. One solution is the Z-200 Battery Bank that is stack mounted so not in the air stream, and benefits from a higher temperature tolerance. Another solution is designing the probe for aerodynamic stability so that you don't need the probe core to be functional during re-entry and hence don't need electrical charge.

 

Probe Design for Re-Entry :

The probe cores all have low temperature thresholds. I can't bring them in on their own, and need to use a heat shield. It turns out that, contrary to some forum advice, a 0.625 meter heat  shield can shield the probe cores, but only just. The probe cores are only just shielded, so are very sensitive to not pointing exactly retrograde; when they're not exactly retrograde, the edges of the probe core stick out past the heat shield and into the plasma stream. When you're arriving with a surface speed of 3,000 m/s or more, putting any part of the probe core into the hot plasma, even just an edge , will mean that it will overheat and explode in a matter of moments . If I'm manually driving a probe down, I find the OKTO's built in reaction wheel a bit weak for pinpoint aiming, so like to have an external reaction wheel for better control authority. This helps my bad driving keep the probe very close to exactly retrograde, and hence the probe core behind the heatshield.

However, an even better solution is to make the probe aerodynamically stable. If the probe is stable, you just get it roughly retrograde at the top of the atmosphere, turn off SAS altogether, and it just tucks in and sits behind the heatshield all the way down with no risk of overheating. Slashy wrote a lovely post pointing out sectional density and drag considerations when choosing the stack order in your probe. I actually still had issues despite following his suggestions, and suspect his probe design was relying on the drag of the OX-STAT solar panels to stabilise the probe. I don't have solar panels to apply drag to the back of the probe. My eventual solution was to turn the science lunchbox sideways and radial mount it on the top of the stack; the drag from this acts wonderfully as "tail feathers" at the back of the probe, and the side of the box is the perfect size for a Mk2-R radial chute.

 

 

Heat Shield :

As discussed, I find a small science return probe can be perfectly shielded by the 0.625 meter heat shield. I started with the engine still on the front, but found that the extra mass and lower drag from the engine shape meant that even on a gentle re-entry, the probe did not shed enough speed to safely pop the laundry. Hence now I set up the periapsis and stage the engine and tanks away. With the heat shield, probe core, science box and parachute, I have found the recovery to be very insensitive to periapsis. Anything under 41 km will come in in one pass, and (so far) anything over 20 km survives the re-entry. I need to test lowering the periapsis further to find the lower limit that the probe survives. My experience on heat shield ablator has been counter-intuitive for me. The steeper your re-entry the less ablator you seem to use. Even though part temperatures are lower on a high periapsis gentle re-entry, you are spending more time at high relative velocity to the atmosphere, and hence at high apparent kinetic energy / temperature, so you use more ablator. For my probe anything under 40 km recovery periapsis is using less than 10 units of ablator, so you can skim the heat shield down for lower mass, and better upper stage delta-v.

 

Launcher :

Having a working probe and space vehicle, you need to get it off Kerbin. I found I really needed the Airstream Protective Shell. Most of my designs are high TWR launchers, and the fragile probe parts really don't like the temperature on ascent. Even when I redesigned the launcher for lower TWR and a gentle ascent, all those probe parts are quite draggy, and launcher stability was a real problem without a fairing. Part count has been a bigger problem than weight limit, so I ended up using just one fairing adapter, fairing anything fragile or draggy in one large shield, and damn the extra mass.

 

So that's been my experience so far. I'm sure this is all old-hat for the regulars, but hopefully there is something useful somewhere for anybody new to the challenge. I really can't stress enough the benefits of an aerodynamically stable probe re-entry. You don't have to drive it, it's really resistant to overheating, you don't need electrical power, you don't need (or want) an engine - stable re-entry simplifies everything. Feedback and suggestions for improvement are always welcome!

 

[WarSprite]

Well, after a bit of a learning experience, and many design iterations and tweaks, I now have not one, but two probe designs. I've spent a couple of days running practice flights on the first design, and today was happy enough to load the craft to my Caveman game and finally progress a little further.

This first probe has a couple of advantages; it uses fewer tier 5 science nodes, so can be used earlier in the challenge, and it has huge reserves of delta-v. The penalty for this is that it only carries the thermometer and barometer; I'll need to fly my second design for a full science package. Unusually for me, this first design is a low TWR launcher; no big deal, and I'm not sure why most of my designs end up as high TWR launchers, I just need to take the ascent a little more gently with this.

I had a good think about Paul's comments on communication relays. It seems that range attenuation isn't a problem for the Mun (at least on Hard difficulty), it's just the blackout when you're behind the Mun. I flew a good few practice flights in Sandbox arranging manoeuvres so that I never needed to do anything behind the Mun. This does not give you full flexibility for every trajectory and landing site, but for a simple "put down anywhere on the Mun" it seems to work just fine, and saves designing and launching communication relays.

One thing I needed to keep reminding myself is that it's "just a probe". If I splash the flight I'm just wasting 11K funds, it's not like I'm losing Jeb. That's not to say "be complacent", but when I keep reminding myself of that it takes some of the pressure of the flight.

Before the flight I had to unlock more nodes for the first time in a while. This design needed me to add Electrics and Flight Control for the probe, General Construction and Advanced Construction for the fairing, and Propulsion Systems for the Spark engine. Spending on these nodes left me with 355 science in the bank before the flight.

 

Flight #17 - Mun Landing

I'll start with an image taken in the VAB of the design in case anyone is interested; 7,618 m/s of vacuum delta-v on the total stack. Launch was nominal leaving me in a nice 71 km LKO with 4,133 m/s in the tank for the Mun mission.

https://drive.google.com/file/d/1lEn-b1zdRjtQgYY8M-U4G3UpVaKg2Ron/view?usp=sharing

https://drive.google.com/file/d/10Ny2loDW7JuDntFwGQ6Lf0lFjc1vrZIc/view?usp=sharing

 

The Mun transfer burn went well, and gave me a nice encounter just after Kerbin apoapsis, with a 85 km Mun periapsis. A touch of radial in at the edge of the system brought the periapsis down, and then I circularised at periapsis. The orbit was near equatorial, and just missed the Northwest Crater; a minor correction allowed me to pick that for a landing site.

https://drive.google.com/file/d/1edFdsul4WYT9E22Rfp4F6MdSJk2McrQ4/view?usp=sharing

 

While practicing this flight I found that Minmus has left me with bad habits. When reaction wheels can pick the ship up you're less careful about the landing. The Mun is not so forgiving; use landing legs, set down somewhere level, and keep the ship pointy-end up while you land   One thing that I've been doing with this design is turning off the fuel feed on the FL-T200 on the lander. This causes it to drain the FL-T100 first, which in turn lowers the centre of mass when it comes to a Mun landing. It's just a minor benefit, but anything that helps keep the ship upright is a good thing for me. Murphy's law means that the little tank empties during the descent / landing stage, but it turns out to not be a huge deal to then enable the propellant flow back on the large tank. I took the descent carefully, and burned more fuel than an optimum landing using 885 m/s to land, but the design has a large margin, so that didn't worry me.  Once down, I did the science (yep, all TWO experiments), sucked the data into the lunchbox, and got ready for lift off.

https://drive.google.com/file/d/1rcGv_S6NBHmrUWmfPU1yzsp_vg4H3Mws/view?usp=sharing

https://drive.google.com/file/d/15vUJp1l0ylRHg2BQLS58r8hrV3Ky-FPx/view?usp=sharing

 

Back in orbit I hit an escape burn at about 02:30 on the clock to 810 m/s orbital speed. This gave a lovely trajectory out from the Mun, dropping me back into Kerbin's influence with a periapsis of 400km. During testing I've been staging the engines away at the Mun end of the encounter, and have noticed that due to the light weight of the probe, the impulse from the decoupler makes a significant change in velocity and hence periapsis. In this design it drops the periapsis about 20 km, so I burned for a 45 km periapsis, then staged the engine away. There was 996 m/s propellant left in the tank at this point - the design really is overkill. That left the probe core recovery package with a 25 km periapsis, which is just fine. I timewarped close to Kerbin, came out of hibernation, pointed the package retrograde, and turned off SAS altogether. As remarked in my development notes, the stable design just tucks in behind the heatshield and naturally follows retrograde direction all the way down with no thermal problems at all.

https://drive.google.com/file/d/1wg-NggGALjGG5zyLTNJk4wPuvLjbJUss/view?usp=sharing

https://drive.google.com/file/d/1RCdbwT0GRQ3fqVbiZZeMKJJjfHvOi4L7/view?usp=sharing

 

The science haul on this flight was unsurprisingly small given that it only carried two experiments. Recovery awarded 48 for the experiments, 18 for the recovery, and 3 from the WRKS. Those 69 points brought me to 424 science in the bank. That's more than enough for the extra nodes that I want for the more advanced probe, so it's all good. The main thing for me was proving a probe land / return within Caveman limitations.

My next flight will be another Mun landing, with the next probe for a full science package. It may be another couple of days before I make that one - I still need to practice flying the advanced design, and it has considerably less delta-v available, so will be a touch more challenging.

 

[WarSprite]

So while flying practice flights, I had a bit of a "D'oh" moment on the next design. I had been using a X200-16 tank, Rockomax adapter and Skipper engine to keep the parts count down. I realised that I can get the same tank capacity in the same two parts using FL-T800 tanks unlocked in the same node as the X200-16. I don't know why I overlooked that previously, but hey-ho. The tweak to using FL-T800 tanks and a Reliant left me with a little more mass allowance for more delta-v. Some of the extra delta-v is taken up by the longer ascent of the low TWR design; the Skipper excels in a quick fast ascent on an 18 ton rocket, but if you fly a sensible profile the Reliant is a net win over my previous thoughts.

The other benefits of the revised low TWR design are that you can use the tiny reaction wheel (the Skipper needed the small reaction wheel for more control authority) so I no longer needed the Advanced Flight Control node and of course, without the Skipper,  I don't need the Heavy Rocketry node. So I had to unlock Fuel Systems node for the large tanks, and the Miniaturisation node for the TS-06 Stack Separator, leaving me 244 science in the bank.

The new low TWR design flies much like the previous probe, so after a couple of launches I was ready for a flight in my Caveman game.

 

Flight #18 - Mun Landing and Science

This one has 7,586 m/s delta-v in the stack. That's not quite as useful as it sounds, since 1,380 m/s is in the ascent stage; you have to land and complete the science before using that, but it's still a healthy margin. The gentle take off went well and left 4,026 m/s in the tanks for the mission after reaching LKO.

https://drive.google.com/file/d/1dUpr2Y0I1PMb5mZwFpTv91Td_ECpOwQr/view?usp=sharing

https://drive.google.com/file/d/1IDYdExdzYstkIaJIwAiHmXPg0hOisoAs/view?usp=sharing

 

The normal sundial navigation for Munar transfer, and I had a nice retrograde encounter with -126 km periapsis. Having managed to score the Northwest Crater on the previous flight, any landing spot was a good one - I didn't need to worry about avoiding the "common" Lowlands biome. The landing used 730 m/s worth of propellant, leaving 745 m/s delta-v in the landing stage in addition to the ascent stage. Given that the Mun landing was the phase of the flight that could prove tight, this was an excessive safety margin, but I'd rather that way than running out of propellant.

https://drive.google.com/file/d/1LifNuCw4D01u40ZZj5hQPbKju1i21eTF/view?usp=sharing

https://drive.google.com/file/d/1sSgP9YyMPedlUVIz4ReL0CL33CPxHYiu/view?usp=sharing

 

On practice flights I've been staging on the surface and just using the ascent stage, to ensure it had the legs for return to Kerbin. It does, but since there was fuel left in the lander, no need to waste it in the real run, so I took off using the lander, and staged in orbit before my escape burn. The weaker TS-06 separator only drops periapsis by about 10 km, so back in Kerbin's sphere of influence I set a 40 km periapsis before staging the engine away. This dropped me to a 31 km periapsis as hoped. A cruise home, point retrograde, turn off stability assist, and re-entry went as expected.

https://drive.google.com/file/d/1eI-MXWs8VskL1OAiDGQMmhw9rK3iCbsQ/view?usp=sharing

https://drive.google.com/file/d/1X9VgP7NpqVw3vwGvrsHtzNrIVxDFcDLN/view?usp=sharing

 

When I got rid of the last engine I still had 1,088 m/s in the tank which is a really large safety margin on the flight. I suspect you could forget the TS-06 Stack Separator, and build this with the TD-12 Decoupler to save unlocking the Miniaturisation node.

The full science package on this probe netted 132 points from experiments, however since I've previously landed on the Mun, only 3 points for recovery and none from the WKRS. That brought my total to 379 science in the bank.

So that's Minmus and the Mun "completed"  in that they have both seen fly-by, orbit and landing. The total science haul is getting close, but it's not there yet. So for the next flight I'm sending Jeb off for a Kerbol orbit, to stick with the idea of visiting new places rather than farming biomes on objects that I've already been to.

 

[JAFO]

Things are going well! 

 

On 5/31/2021 at 4:23 AM, WarSprite said:

One thing that I've been doing with this design is turning off the fuel feed on the FL-T200 on the lander. This causes it to drain the FL-T100 first, which in turn lowers the centre of mass when it comes to a Mun landing.

Just so you know, you can set tank-use priorities in the VAB (right-click on the tanks) so that they are drained in the desired order, that way, often there's no need to turn off fuel feeds. (There are times it's still a useful thing to do, though.)

[WarSprite]

On 6/2/2021 at 4:14 AM, JAFO said:

Things are going well! 

Thanks for the encouragement JAFO !

 

On 6/2/2021 at 4:14 AM, JAFO said:

Just so you know, you can set tank-use priorities in the VAB (right-click on the tanks) so that they are drained in the desired order, that way, often there's no need to turn off fuel feeds. (There are times it's still a useful thing to do, though.)

Sounded awesome! So I looked and couldn't see any such option in my game. So I googled. Dammit, "Advanced Tweakables" option in settings.

That's fantastic. Not just for the lander, but for many of my regular Caveman rockets, draining the bottom tanks to move CoM up and improve stability before reaching Max-Q is a fantastic thing!

How did I not know about this?!?    Thanks for the pointer JAFO 

[WarSprite]

After the Mun landings with probes, it's time for a nice easy crewed flight to pick up some more science.  After my learning with probes, I've made some small changes to the manned ship, switching to a single Reliant booster for lift off and a hence a low TWR design. This leaves a little more mass / parts budget for fuel tanks, so a little better delta-v. I don't need it for this flight, but I can't resist tinkering with designs. Jeb likes having a bit more propellant to play around with though 

 

Flight #19 - Kerbol Orbit

I sent Jeb off on a quick trip out of Kerbin's sphere of influence. Dropping outside the SoI made sense as an easy situation to reach to get some more science. It wasn't my best launch on this design, but 2,060 m/s in then tanks after I reached LKO was still far more than needed, so good enough.  In test flights I've tried leaving Kerbin by pushing escape velocity to the listed 3,431 m/s but this uses more propellant than basing it on just getting out of range of the 84.16 Mm Kerbin sphere of influence. So at about 8 o'clock on the sundial I boosted apoapsis to a target of 84.5 Mm. I was a little late on the burn, and overshot on the thrust a little, but no big deal on either count. The trajectory still put me in the prograde direction ahead of Kerbin in its orbital path, which is what I wanted.

https://drive.google.com/file/d/15h8FJE6h5torbTlmrZ9gZfCnyDO40FgO/view?usp=sharing

 

A long coast along the orbit, and Jeb found himself outside Kerbin's sphere of influence, so it was time to do the science thing. That just left a retrograde burn to slow orbit around Kerbol down to 9,280 m/s and then I just let Kerbin catch up to Jeb. Given the large apoapsis of the flight I bottled out of my normal 41 km periapsis for Kerbin re-entry and thrust for 41.5 km and a shallower re-entry. In practice this didn't make much difference to my surface speed at Kerbin, but did mean that I skipped out of the atmosphere for a (thankfully) quick orbit before finally coming down. Lesson learned, trust your numbers from your test flights.

https://drive.google.com/file/d/1g8n9aUlEnnkSjoXlVFC11_SiDIa6JOse/view?usp=sharing

https://drive.google.com/file/d/1wuez9tK9IL8jguQ8gibWomtsfbYISdOQ/view?usp=sharing

 

Whilst it's not as big a deal for me as when Jeb did his orbit of Kerbin and reached pilot level 1, having done Minmus landing, Mun orbit, and now Kerbol orbit, he has levelled up and can now push all the SAS buttons     Of course, having target hold marker available would be nice for docking manoeuvres, if I went down the orbital docking route.

https://drive.google.com/file/d/125hGXALSUZAwy4LIRpNSLCvay7TMW9GV/view?usp=sharing

 

This flight netted 72 science from experiments, 19 from recovery and 6 from the WKRS bringing me to 476 science in the bank. I've had Kerbol planned from the outset, but only known for the last flight or so what was now confirmed. It is not quite enough! That's a tantalising 19 science short of completing the challenge.

I'm now not quite sure what to aim for. I can of course farm somewhere I've already been for the remaining science, or even break my personal targets and just do a few Kerbin biome spots. Easiest would be two flights to pick up the points for recovery from Minmus orbit, and recovery from Mun sub-orbital flights. However, given that I've kept trying to visit new places on this run, those are slightly less appealing when I look at the delta-v map and see how close Duna is. I think some test flights in Sandbox may be called for...

 

Edited June 5, 2021 by WarSprite
Fixing typos.

[WarSprite]

In my last post I shared that I was 19 science short of completing the challenge. Having looked at the delta-v maps on the net, Duna looked like a tempting target to get that last bit of science. I'm relatively new to the game, and have never left the Kerbin system and gone interplanetary before, so visiting somewhere new was also an appealing target. It also turned out to be a bit of a learning experience 

My thoughts were that according to the delta-v map, my manned rocket has the range for Duna, and that Duna has a nice low inclination (unlike Eve) simplifying the journey. At interplanetary distances an unmanned probe seems unlikely to work (range attenuation of the control signal), confirming my thoughts of sending Jeb in my current iteration of crewed rocket on a fly-by to pick up my last science points in space high over Duna.

I have a memory that I've previously read that launch window calculators are considered "allowable" in the challenge since you're not changing anything in game, just using the information from your Caveman game to get some decisions, but still making the flight in your primitive game. So I started practicing in a Sandbox game using the excellent Launch Window Planner. I quickly got to the point I could reliably get an encounter with Duna and perform the fly-by.

That's around about when I found out that space is big, and planets (even in the compressed KSP system) are small. Getting Jeb back from Duna turned out to be a lot harder than getting him to Duna in the first place.

My problem is self administered by using a single 18 ton caveman launch, which limits how much performance is "in the tank". It has plenty of delta-v to reach Duna and do a fly-by, but not enough to enter orbit around Duna and then later burn for a return to Kerbin. If it did, then those same launch window planners would make getting Jeb home a lot easier. Even worse, having boosted to an elliptical orbit to reach Duna there isn't quite the delta-v left to drop apoapsis back down to Kerbin's orbit and "just let Kerbin catch me" at some point.

I tried a lot of sundial navigation, and even got Jeb home a couple of times, but nothing that I could make work reliably. Time to do some reading on orbital mechanics. After a couple of false starts I now have a little spreadsheet that takes a couple of numbers from my orbit and Kerbin's orbit, and gives me a suggestion on how to get the two to intersect at the same space and time to recover Jeb. After a few test flights this seems to work quite reliably in my Sandbox development game.

So yay! Ready to send Jeb on a fly-by past Duna to pick up the last of the science 

@JAFO - can you confirm that external launch window calculators and spreadsheets are considered "allowed" in the Caveman Challenge?  Not mods to the game, but external tools where you transcribe information you read from the game in to the tool, and then use the information the tool provides to make your in-game flight decisions and manoeuvres. Specifically I have been using the Alex Moon Launch Window Planner :

https://alexmoon.github.io/ksp/

 

[JAFO]

22 hours ago, WarSprite said:

@JAFO - can you confirm that external launch window calculators and spreadsheets are considered "allowed" in the Caveman Challenge?

Confirmed.

Edit: The rules in the OP have been updated to reflect this.

Edited June 8, 2021 by JAFO