Jouni

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About Jouni

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  1. When I use serial staging, 50-60% of launch mass is propellant for the first stage. Because I prefer launching with a low initial TWR, maybe 1.2 to 1.3, and because the sea level Isp of the appropriate engines is slightly below 300 s, the first stage lasts for 120-150 seconds. This produces 2000-2700 m/s. The staging altitude depends greatly on the propellant mass fraction, the intended orbit, and the TWR of the second stage. If I use boosters, the core stage lasts for 3-4 minutes, which is often enough to reach orbit.
  2. OP had a pilot and six passengers in the craft, which sounds like a Mk1-2 pod in addition to the hitchhiker. Reentry becomes much more deadly, if you double the mass without increasing the cross section.
  3. I have been avoiding Laythe, because I don't want to design spaceplanes. A few days ago I started pretending that there is no oxygen on Laythe and that rocket landers are the only option. Since then, I have been testing variations of this basic design: I first tried using the inflatable heat shield as a heat shield, but it works better as a reentry parachute. There should be enough parachutes for a Laythe landing, though the fairing base can be used as crumple zone if necessary. Aerospikes are rather useless without thrust vectoring, so I'm using a few Twitch engines for guidance during the early ascent. The lander is capable of reaching LKO, so it should probably work on Laythe too.
  4. The "Tube" part of London Underground uses tunnels with inner diameter as low as 3.56 m. The largest trains running in them have capacity for 930 passengers.
  5. Reentry from the Mun with a hitchhiker, a Mk1-2, a 2.5 m heat shield, and some parachutes is barely survivable. Put your periapsis to ~35 km, set navball to surface mode, and tell SAS to hold retrograde. The heat bar on the hitchhiker will probably go red, but it usually won't explode. There are around three main issues: The heat tolerance of the hitchhiker storage container is low. Using a part with higher tolerance as a heat sink between it and the heat shield will make the reentry easier. The reentry vehicle is unstable, because the hitchhiker is a large part with low mass. Placing more mass between it and the heat shield will make holding retrograde easier. Airbrakes might also work, but I find the idea silly. There is a lot of mass behind the 2.5 m heat shield, and the atmosphere can't slow it down quickly enough. A larger heat shield would help, but it would also make the vehicle even more unstable. One simple solution is to add a heat shield without ablator between the hitchhiker and the actual heat shield. This increases payload mass from ~8.5 tonnes to ~9 tonnes, but otherwise it's very cheap.
  6. Maybe we have a difference in terminology here. For me, light rail basically means large fast trams. They run on streets on their own lanes in dense areas and use separate tracks in sparsely built areas.
  7. These are two separate issues. If there are more than four buses per hour on a single route, it starts being cheaper to build light rail instead. Many routes converge on main streets. If there are 20 routes, 80 buses/hour in a single direction is still manageable, while 100 buses/hour means trouble. That sounds more like heavy rail than light rail. In the projects I'm familiar with, light rail costs around €10-15 million/kilometre.
  8. This is another effect of low population density. Buses are scalable downward but not upward. Main routes in dense cities often require so high passenger capacities that you cannot fit enough buses on streets and bus stops. I am somewhat familiar with public transport in Europe. The rule of thumb is that light rail becomes more cost-effective than buses when you would need more than four buses per hour on the same route. The initial investment is higher with light rail, but it is offset by lower operating costs. Buses need more drivers because they carry less passengers than trams, and you also have to replace the vehicle several times more often.
  9. Population density is much more important for trains than speed. If you have enough passengers, rail traffic is more cost-effective than any other form of land transport. You need much less drivers and other staff than with cars and buses, and even the infrastructure investments are lower than for a highway with the same passenger capacity. The minimal sufficient population density is rather high, however. If your cities are sparse enough that most people can commute by car, there are too few passengers on any given route, and trains don't make sense.
  10. I circumnavigated Tylo, even though I didn't plan to do it. I also climbed several high mountains and visited the poles and the anomalies on the same trip. The key seems to be making the rover large enough that little bumps don't matter. Mission report: The mission was mostly stock, except for MechJeb and Docking Port Alignment Indicator. Two launches from Kerbin, four kerbals, 46 flags, and 16 days on the surface.
  11. Part 14: The Monolith I took a long detour through the night to see the random monolith. Also some thoughts on the rover. After completing my Tylo circumnavigation, I had a really bright idea. I had detected a new anomaly at 14N 6E, so I decided to go there. The rover was at the cave almost halfway around the world, and the entire trip would be through the night side of Tylo. So I started driving towards west. Except that I didn't. The motheship went below the horizon just when I was starting, and the rover could not move without a link to Kerbin. Jeb spent the hour climbing on top of the cave, but it was too dark, and the screenshots showed only Jeb and the flag. I started by driving west to get out of the black area around the cave, and then turned northwest to follow the great circle to the destination. On the average, I managed to drive around 150 km during the hour the mothership was visible, and then I had to wait for an hour for it to reappear. The great circle reached as far north as 67N before turning south. The northernmost part of the trip was close enough to the terminator line that I managed to get a direct link to Kerbin for a few hours. After that I had to alternate between driving and waiting again. Driving in the darkness is efficient, as there is nothing to see. I spent much less time exploring and much more time driving forward than during the circumnavigation. For most of the time, the route managed to avoid major mountains and craters. Some regions were bumpy, limiting the safe speed to 30-40 m/s, while other regions had smoother terrain, where I could safely drive 50-60 m/s. The last three hours saw some impressive mountains and valleys, though it was still too dark to take screenshots. I summited one 10 km mountain just because it was there. Jool rose above the horizon after the route turned south. As the great circle from the cave to 14N 6E passes near 0N 0E, navigation was easy after that. Jool basically showed the way. After reaching the target area, I spent half an hour searching for the anomaly. RoveMate, which supposedly has 100% detection rate, was completely useless. I managed to spot the monolith visually before the scanner detected anything. After parking next to the monolith, RoveMate finally detected something – but the reported location was almost 20 km off. My great Tylo expedition is almost over. I only have to launch back to orbit and return the crew to Kerbin. The original plan was to land near the cave and explore a bit, but things got out of hand. I drove almost 1.5 times around Tylo, visited both poles, and climbed several mountains rising above 10 km. The rover wasn't even designed for long-distance driving, but it served well enough. It had many flaws that would have been easy to fix: The center of mass is too high even after transfering fuel from the ascent stage to the descent stage. Kerbals often fall to ground when they try to climb back to the rover, because there are not enough fixed ladder pieces on the forward tank. The battery capacity is too low for mountaineering. The wheels are not placed completely symmetrically, and the rover has a slight tendency to turn right after hitting a bump. A command seat would have enabled driving during the night. Some lights would have been useful for screenshots. Part 15: The Journey Home The return trip was not too different from my other interplanetary trips. After completing the Tylo expedition, it was time to return home. I transferred fuel back to the ascent stage and launched. What was left on Tylo is still a fully functional rover, and it might even work better with a lower center of mass. The mothership returned from a 1000 km highly inclined orbit to rendezvous with the ascent stage, and then the crew returned to the ship after 16 days on Tylo. I believe I left 46 flags to mark the route traveled by the rover. (The lonely flag is from an earlier mission.) Then it was time to return home. Luckily there was a good launch window almost immediately. A spaceplane retrieved the crew, as usual. And then everyone was back home.
  12. Part 13: Back to the Cave I completed the circumnavigation. Some parts of Tylo are really dark during the night. I completed the Tylo circumnavigation. After picking up Jeb, who had tried some mountaineering near the north pole, I headed towards the cave. The terrain between 89N and 87N was the worst I have seen on Tylo: countless of bumps of all sizes. Things got easier below 87N, but I had to stop almost immediately. Because the rover is controlled by a probe core, I need constant communications with Kerbin. It hadn't been a problem so far, but now Jool decided to block the Sun. It took an hour before the communications were restored. The terrain was very easy for a while, and there was even a large flat area where I could safely drive at 110 m/s. When I was coming up from the south pole, the Sun was never too far below the horizon, and I had a direct link with Kerbin. Now it was around midnight, and I could only drive for an hour when the mothership was above the horizon, and then wait for another hour when it was below the horizon. I had to stop twice: at 65N and at 51N. After 51N, the terrain became worse. First I was surprised by a 2 km deep crater in what appeared to be level ground, and then I reached the black area surrounding the cave. I had to reduce speed, as there was no way to avoid bumps in the darkness. Finally I reached the cave at 40N and planted flag 36 next to flag 2 which was already there. That's not the end of the expedition. When I was scanning the terrain before landing, I located another anomaly in addition to the cave. I managed to lose the location on the way, but now the mothership has discovered it again. It's located at 14N 6E, or almost halfway around the world from the cave. I guess I'm heading there next.
  13. Part 11: Full of Stars The high ridge didn't lead to the north pole either. Jeb discovered something surprising. I was already at 76N, so it was only a short trip to Tylo's north pole. The terrain was a bit rough at times, but it didn't take long to reach the polar region. From distance, the north pole didn't look as bad as the south pole. About 1 km from the pole, the ridge became too narrow to drive, so I sent Jeb to scout ahead. The thing's hollow — it goes on forever — and — oh my God! — it's full of stars! Apparently somebody had misassembled the planet. This may be as close to the north pole as it's possible to go. I'm going to try the lowest valley tomorrow anyway. Part 12: Jeb Goes Mountaineering The lowest valley was even worse. I had almost reached Tylo's north pole, but a terrain glitch blocked the way. I decided to try approaching the pole from the lowest valley instead. The rover can easily descend 37-degree slopes – sideways. It took a while, but eventually I managed to find a way through the ridge maze to the mouth of the valley. The valley became too steep to drive, so I sent Jeb to climb. You can see the rover on the valley floor. After careful measurements, Jeb determined that the terrain glitch is located directly on the pole. Jeb decided to take the scenic route back. You can again see the rover in the picture. A couple of hours later near 89N.
  14. Part 8: Driving through the Night The nights are long and dark on Tylo. It was a long night. I started from the south pole of Tylo and drove north along the prime meridian. There was some regional variation, but the terrain was really boring. I couldn't see much in the darkness either. I saw the first signs of the morning at 24°S, and the Sun finally rose at 7°S. Part 9: Crater Country Two giant craters, the zero point of Tylo, and some interesting terrain. Last time my Tylo circumnavigation had reached a crater rim at 7S. Today I continued following the prime meridian north, crossing two major craters and stopping at 35N. The point where the prime meridian met the equator was rather boring. On the other hand the terrain between the two craters was quite interesting. I often had to drop out of physics warp to keep the rover from crashing. There was a convenient ramp going down into the second crater. It descended 3 km in around 20 km of smooth terrain. It was time to do some mountaineering after the crater, as I had noticed an interesting peak on the north wall. The mountain was bigger than I expected. The batteries ran out of power on the way up. 8 RTGs were not enough for going uphill, and the terrain was too steep for the brakes, so I had to some interesting maneuvers to avoid sliding all the way down. Ultimately I reached the summit, which was around 6 km above the crater floor. Part 10: More Mountains I crossed another major mountain range and continued north over boring terrain. Last time I stopped at 35N after crossing two major craters. Today my Tylo expedition continued north. At first, the terrain was quite interesting. The mountains started getting higher, though not as high as the Mountains of Utter Ridiculousness in the south. Some serious mountaineering was required. The mountain range ended at 49N. The edge of this relatively flat summit area was at 10.5 km, though scanners revealed that the highest point nearby would have been 11.2 km. The plains were almost 5 km below the summit area. After driving 3/4 around Tylo, I was familiar enough with the rover that I could just drive straight down without looking for an easier route. Then it was hundreds of kilometres of boring flat terrain. At around 73N, the ground around the prime meridian got rougher, as I saw the first signs of the ridges rising towards the north pole. I moved a bit east for easier driving, and then continued until 76N.
  15. Part 5: Mountains of Utter Ridiculousness I crossed what may well be the highest mountain range on Tylo. Today I crossed a mountain range on Tylo. Starting from 32S, I went around the ridiculous crater and encountered even higher mountains. The highest peak I climbed was 11788 m, but there were probably higher ones nearby. The valleys between the mountains were often 4-5 km deep. Fortunately I had learned to brake effectively when going downhill, so most of the time I could just cross the valleys. The last major peak of the range was at 56S. Its altitude was around 11650 m. From there, the ground descended steeply towards the lowlands. Sometimes too steeply. Today's leg ended at 64S. In the last 90 km, I descended from the 11.65 km mountain to 2.5 km lowlands. Tomorrow I should be able to reach the south pole. Part 6: South Pole I tried to reach the south pole by driving on the highest ridge. Today was a short day. After the Mountains of Utter Ridiculousness, the rest of the way to Tylo's south pole was easy driving. After cresting a ridge at 87° 22' S, I saw Jool for the first time on the trip. Soon afterwards I reached the maze of jagged ridges also known as the south pole of Tylo. Navigating the maze took a while. But finally I was able to plant a flag on the south pole. Or at least as close to the pole as possible. The actual pole was 235 m further south. And who knows how far down. Part 7: South Pole, Again I tried the lowest valley instead. Today I started from the ridge above Tylo's south pole and descended to the pole itself. Finding the way down wasn't easy. The starting point was the peak on the left side of the picture. As we all know, when you are standing on the south pole, you are hanging upside down. (Val actually seems to be standing on the vertical wall.)