Built a complicated SSTO/Transcontinental aircraft, with all the abilities including all experiment apparatuses, ladders, docking, cargo, etc. Adding more, and more parts and capabilities, up-sized the landing gear... build, build, build..... → Launch... ground clearance problems, revert, fix. → Launch, landing gear out of alignment? what? Fix them, move gear a little down, a little out. → Launch. Success! I get it to Kerbin north pole, Pilot jumps out to celebrate and plant a flag! Woohoo! Ok, let's get back in and go home.
..... Ladder doesn't reach the ground because I made the landing gear too tall.
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Needed to make a low budget science gathering journey to Mun, it was incredibly difficult (for me, at the time) finally get it all designed, under budget, and with JUST enough dV to get there and back. Launch, fly, fly, fly, mechanic of the orbitals, sketchy landing... nothing broken... alright! Science time!
..... forgot the experiment equipment.
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(years later...) Planning Mun mission to collect all possible science from each of the Mun's biomes, wonderfully designed, allowed for beautiful execution of the mission. I collected tons of science from each of the biomes, it took a while, and careful course plotting (biome hopping) to use as little dV as possible. Leave the Mun, return home, checking the list of science collected, notice an absence of gravity scans. That's odd. Those experiments don't have to be reset after they are run... What the heck happened?!?
Go to the VAB, load up the craft ..... not a single Gravioli Detector was installed on the craft. Have to go back to each Mun Biome.
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More Science experiment woes:
Early in career mode, need science points, load up a craft with the science equipment I have unlocked... ok let's do this! Get to destination... No Materials observation?!?!
..... I had installed a Mobile Processing Lab, and not a Science Jr. because the parts look exactly the same.
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Needed a satellite around Kerbol, designed one, launched it, burn to make Kerbol orbital insertion burn... Success! Time warp out of Kerbin SOI, into Kerbol SOI to circularize orbit... warp, warp, warp..... go back to normal view from map view... Can't control anything? No connection?!?!?
..... chose the wrong antennae, I was out of range.