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Everything posted by RCgothic

  1. Isn't there a maximum temperature that can be reached by solar light concentration? Thought a recent xkcd what-if covered it. 5000'C. With a max temp that means max exhaust velocity, which limits ISP. Of course that's probably better than chemical rockets, so maybe no problem. Solar thermal electric would probably have better ISP for a fuel limited design, even with the corresponding efficiency penalty.
  2. This is mostly because the orbital velocity out there is so slow. In this part of the solar system extra dv pays real dividends. New horizons made it in 1/10th that time. Of course you also have to have the dv budget for capture and return, but some fuel could be mined once you got there and the rest is just a sufficiently large rocket. For mind-bending quantities of large. These are just things that require budget, not impossibilities.
  3. Of course we could, money no object. All it takes is dv and time. It would be much harder than reaching Eeloo, but the main obstacles are budget and reason to go. Nothing PB666 mentioned makes doing it impossible.
  4. I think this is quite confusing, and a bit garbled, particularly bringing in Newton's laws which aren't really relevant to max q. At any instance there are three basic forces acting on a rocket: Thrust, Drag and Gravity. The Newton's first law merely states that an object in motion remains in motion unless acted on by an outside force. This is, these days, a statement of the obvious and not specifically relevant to max q. Newton's second law can be written to state that the rocket's acceleration is the residual force on the rocket divided by the rocket's mass. This is only slightly relevant to max q, allowing us to divine something about the magnitude of each force from the rocket's acceleration over its flight. The force due to thrust is a designed and understood value. The force due to gravity is easily derived. The force due to drag is tricky to calculate. But because you can watch the rocket to determine its acceleration, you can use the second law to work back and determine what the drag is. That's where the second law is useful. Newton's third law states that each force has an equal and opposite reaction. This merely means, e.g., that for all the force drag is exerting on the rocket, the rocket exerts an opposite force on the air. It does NOT mean that the forces acting on a body have to be balanced - per the second law there could be no acceleration if this were the case. In considering a rocket we only care about the force acting on the rocket and don't really care what forces act on the air, or the exhaust, or the Earth so the third law is not specifically relevant.
  5. The solid booster fire command isn't given until the SSMEs are verified on, and the hold-down bolts are detonated at the same instant. Once the shuttle's SRBs were ignited, the vehicle was committed to liftoff. But even so I hesitate to contemplating a full firing of the boosters on the pad whilst strapped to a full tank of hydrogen until the sound suppression system exhausts its 300,000 gallons in just 20s...
  6. The Space Shuttle was particularly problematic because the solid rocket boosters couldn't be shut off and would cook anything attempting to get away from the failing boosters. Between booster ignition and booster separation: Structural failure of any part, (booster, tank or shuttle) was not survivable. Significant booster thrust differential was not survivable. Failure of a booster to properly ignite was not survivable. One or two main engines out was survivable on condition everything held together until after booster separation. Three main engines out was not survivable. Basically IMO the only business solid rockets have anywhere near manned launches is in the launch-escape system and ullage motors. The sooner they replace the SLS solids with advanced kerolox boosters the better.
  7. I think it's worth mentioning that there were reasons for the different launch profiles under consideration. Direct Ascent was the least complex, although it required the largest rocket and the most fuel. Remember that in the initial stages of mission planning, nobody had ever attempted a docking in space. They didn't even know how to rendezvous! As most KSP'ers know, it's pretty counter-intuitive and even by Gemini 4 they hadn't worked out the orbital mechanics. Buzz Aldrin had to write a doctoral thesis on the subject. Direct Ascent is the profile for people who don't know how to rendezvous and dock rockets. Earth Orbit Rendezvous was the cheapest option on the table, because it used the smallest rockets. But as previously mentioned in this thread, the logistics are complicated. You either need to have all the rockets ready to launch near-simultaneously, requiring duplication of assembly facilities, launch pads, mission control rooms etc, or you need to plan for a long in-orbit dwell time which is also non-trivial due to loss of ISP for hypergolics or fuel boil-off for cryogenic stages. And do all those missions have to be sent up manned? At the time automation wasn't great, so probably. Manned systems are a load of payload you wouldn't otherwise have to send up. Also, nobody had ever assembled anything in orbit, which was another complication. And complications add risk, development time, and dilute the budget savings. Lunar Orbit Rendezvous is a nice compromise if you can master the docking. It requires a medium-sized rocket (in moon rocket terms, obviously the Saturn V turned out to be the largest ever built), and only one docking rendezvous and docking in lunar orbit. That's ultimately why it was chosen. Dual Orbit Rendezvous is a hybrid of Earth Orbit Rendezvous and Lunar Orbit Rendezvous with both use of in-orbit assembly and a separate lunar lander, and is the theoretically best approach should all the challenges be mastered.
  8. Today I fought a Kraken. I'm on a hard no saves no reverts no respawn career, and after an EVA over the ice caps I was afflicted by a bug. Spaceship 1, which has made many successful tourist flights, suddenly was not slowed by atmospheric entry. And the heat shield wasn't working properly. Fortunately, if I alt-f4 out it didn't kill my kerbals and gives me another go at it. But I had to do this about eight times and re-install install all my mods before the kraken relented. Grrr, Bug, basically.
  9. It's basically a case of sticking fins on the rocket until the CoL in the VAB is 2-3 rocket diameters behind the CoM (To make sure it stays there - CoM moves back in flight). If your rocket is too fat and short, you'll have aerodynamic issues. If your rocket is too long you'll get a spaghetti failure. A way to mitigate spaghetti failure is to make the centre stack shorter and strap on some boosters. Failing that, turning off SAS for a while helps. If your fins are placed right and you haven't pitched too far over too soon that should keep you stable until the atmosphere becomes mostly irrelevant above 40km.
  10. Objective 1, Reputation! Got my reputation up to -18 (from low of -284). Spaceship 1's passenger flights are now so routine that the game's stopped giving me tourist contracts. Oh well, it's equipped for eva rescues too. Objective 2, Science! Built a rover to snag up some KSC science. I've reached a stage where orbital science is limited to goo, materials, temperature, crew reports and EVA, and I'd snagged most of those. I could have got more by going to the Mün or Minmus, but my new rule is probes and test flights before manned. And with RT installed, a probe with no solar panels doesn't get that far. Well ok, I managed a flyby. But it went dark long before being able to transmit anything back. So yeah. KSC Rover. Collected enough to get my first 90-tier science unlocked and solar panels for my probes. One upside of my reputation calamity is that flying loads of contracts was really healthy for my budget, so I'll be able to upgrade the research centre for sample returns shortly. Objective 3: To The Mün! Following the successful Müna 1 flyby, four successive failures of the Müna 2 science return mission (3 Spaghetti booster failures, then, following booster redesign, 1 out of EC before Münar rendevous despite 8 batteries) led to a change in priorities. New ground-based research has led to the invention of solar panels, which for the first time makes permanent Kerbin satellites a possibility. A G1 3-probe relay network has been established for near-Kerbin communications, with intermittent Münar capability (the basic solar panels are still insufficient to recharge the on-board batteries following a pass through Kerbin's shadow with a dish powered.) This new capability (turned on when needed)should be enough for a Müna 3 probe to establish Münar orbit without the risk of KSC being on the wrong side of the planet at a crucial moment. Müna 3, unlike its predecessor, will new be capable of remaining powered until the close of its mission. Müna 3 will be followed with an unkerballed test of the Apollo hardware and its heatshield on a free-return trajectory.
  11. Hauled my reputation up to -45 from -285. That decline penalty really hit me hard...
  12. I wouldn't attempt to put a dish on a ground station. At least, not every ground station. Keeping one powered through a three hour night is definitely non-trivial in an early career game. Not convinced by the ground station approach, but if you do it's probably better to keep to communotrons for most relays and leave the dishes to dedicated stations. I tend to put dishes in high polar orbits where they're unlikely to be eclipsed by the mun and they only experience night at certain times of year. If there are three of them then even then only one will ever be eclipsed or in night at once and the others should be powered with decent line of sight. Batteries then become a nice optional extra. Long-range dishes actually sound like a good idea for a polar molniya orbit - more so than Kerbin relays. It's a good way to keep their availability high, their night requirements will be short as they move quickly past Kerbin's shadow, and the additional signal lag at interplanetary distances is small.
  13. Encountered a bug last night. Re-entered a mk1 pod, passenger cabin, heat shield and some parachutes with a PE of ~30km. I've done this almost a dozen times with the same craft, the only difference is I've started going EVA on orbit. It just wouldn't slow down. By 15km it was still going over 2km/s. Normally I'd be under 500m/s on that re-entry profile. It was bizarre.
  14. If we're still talking about remote tech, I can think of a couple of a few disadvantages to the molniya 'petal' compared to a more traditional relay network: Constructing it is probably four launches rather than just one. I've previously put up 21 relays in that many launches to LKO. If your AP is above ~1100km you'll need something bigger than the communotron 16 to ensure connectivity. Higher orbits leads to increased signal delay compared to a low-orbit relay network.
  15. It's not an advantage to keep fuel or engine to burn lower in the atmosphere. You just increase your mass to drag ratio, which means you're going faster when things start getting nasty. Definitely dump that fuel as soon as possible, even if it means burning radial to keep your pe up. I second a 45-50km pe and broadsided entry, turning prograde only when your reaction wheels can't hold it anymore. Good thing you packed reserve chutes. I do too!
  16. Today I realised that declining contracts was what was giving new negative rep, so I've spent an evening flying tourists and VIPs to orbit in a mk1 passenger cabin to make up ground. I play very risk averse right now, with no saves or reverts. Re-entry is one thing I can't build abort modes into however, and it hasn't stopped making me nervous. One re-entry in particular had me very nervous, after a too-shallow accent burnt off the re-entry fins and barely made orbit. Up to -200 rep from a low of -284...
  17. Molniya orbits have a specific use - quasi-stationary above a particular surface location at high latitudes. They're similar to geostationary orbits, where you want to minimise the amount that your surface-based dish has to move. Point at a particular patch of sky and there'll always be a satellite there. Let's discuss these two orbits a bit: Geosynchronous Orbits Geostationary orbits (or Geosynchronous Equatorial Orbits: GEO) acheive this by matching the orbital period to the earth's rotation in a circular orbit. Because a geostationary satellite is exactly over the equator it remains perfectly stationary from the earth's reference frame and your surface dish therefore doesn't need any off-axis or tracking capabilities. They also remain perfectly stationary with respect to each other, which simplifies sat to sat communications, making global relay networks simpler. However there are a couple of disadvantages. Because they have to orbit at a specific height very closely, and because there's a minimum spacing between satellites before you start to get radio interference, there are only so many satellites that can operate in GEO. Yes, countries and corporations actually have arguments about this, and there's an international body that mediates. Secondly, for countries in high latitudes to point your dish at a satellite in GEO means pointing it at or near the horizon, which is very bad for reception because you start picking up ground-based interference. Molniya Orbits You can't get a satellite to hover over a high latitude in a circular synchronous orbit. Inclined orbits must necessarily cross the equator, which means your satellite will disappear below the horizon frequently. Worse, it moves rapidly across the sky, meaning you have to track it with your dish. It also shares an orbital height with sats in GEO and thus takes up a slot. Molniya orbits attempt to solve a couple of these problems for high latitude applications. Because satellites in eliptical orbits move more slowly near apoapsis, if you place them in a highly eliptical orbit they spend most of their time in the higher part of their orbit. Orbits don't need to be circular to have a period of 24 hours, so you can place them in a highly eliptical inclined orbit and they will appear to 'dwell' over a particular surface location at the same time each day, which means your surface dish can again be pretty simple as long as you're prepared to wait. Or you can discard the 24h requirement and have several sats in still more eliptical orbits. You won't get the same satellite at the same time each day, but as they're further away each satellite will spend even more time in an even smaller area of sky, and by the time it's leaving your area of reception another will be entering it. There are also any number of these orbits, so bandwidth slots are far less restricted. There are a couple of drawbacks to molniya orbits (as might be expected). Because they go much further away, they require more signal power and bigger dishes to communicate with. Secondly, because the orbits are not circular it's much harder for satelites to stay in contact with each other as the angles between them change wildly over the course of an orbit. Note: For mission control, having a satellite with a high dwell time isn't a huge problem, because you can just invest in a dish that can track it and hire ground stations over the horizon for when you can't see a satellite directly. Dwell time becomes much more important in commercial applications. 100,000 trackable dishes, paid for by households? GEO and Molniya suddenly look much more attractive. KSP Anyway, in KSP even Remote Tech does not model dish orientations, with each dish having perfect 360deg tracking. Tell a dish it's trying to point at KSP, and as far as it's concerned it actually is, no matter that it's physically pointing at Jool at this instant and the angle to KSP is changing at 25deg/s. It is thus highly unlikely that any stock solution will concern itself with which way dishes are pointing. It's a level of difficulty too far for most casual players. So in KSP we don't have to deal with dish orientation/tracking, and we're not trying to reach 100,000 households with simple dishes. There's just no need outside of a specific contract to put a satellite in KEO or Molniya. They're not more useful than any other orbit. Me, Personally When playing with Remote Tech, I use a network of 3 sats at approximately 800km altitude. This gives them enough line of sight over the horizon to allow them some margin for error for phase angle and phase angle drift. In actuality, they go in an orbit with an orbital period of a round number of minutes and a 5/6th orbital period that is also a round number of minutes. They aren't in stationary orbits, but they don't have to be. All dishes in this game have perfect tracking. I use Excel to work out the target orbital height/period and KER to match those in game. I launch three sats on the same launcher to the target apoapsis and 5/6th orbital period. I detach one sat and use its on-board monoprop to circularise. I like my sats heavy, but with loads of RCS they circularise pretty easily. Two orbits later the launcher has fallen 1/3 of an orbit behind (because 5/6 period!) and I detach and circularise a second relay at apoapsis. Two orbits later I do the same thing again. Finally, I disable most of the onboard RCS, and use just one or two thrusters and fine-control mode to exactly match orbital periods using KER. These usually don't end up being perfectly circular! That's far too much of a pain. There may be 100m or so between apoapsis and periapsis. It's only the orbital period that matters and usually I get them down to 0.01s per orbit, which is enough to keep them in phase for ages. High mass/low thrust help do this accurately. Maintenance-free relay network! And even if they do fall out of phase, just deboost the offending sat into a fractional orbit for a few rotations before circularising and fine-tuning again. But I've never actually had to do that yet. Expanding the network is a variation on this theme.
  18. So apparently I missed the update to inflict reputation penalties for declining contracts due to sandboxing for 1.0.5. I'd been wondering why my reputation was going negative my new career game.
  19. Jettisoning engines is not Single Stage To Orbit, btw.
  20. I've between trying to do this recently. Building in safe abort modes is a cool challenge. But having an EVA glitch whilst on 4x warp kill Jeb was most unwelcome.
  21. And now I've killed Bill. That's the first time I've burnt up on ascent! Time to start over again I think.
  22. Oops, killed Val already. Forgot suborbital could be deadly.
  23. Landed on and returned from Duna for the first time!
  24. 1093m/s. Beacon assisted parking brake. Sepratrons have the best twr. This was built for a challenge thread, and was briefly the challenge leader before being overtaken. The trick is keeping it in a straight line, which is basically just luck. @tewpie managed >1200m/s before the end of the runway.