Zhetaan

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About Zhetaan

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  1. Indeed, there were. The World's Firsts Society offered the altitude and other milestones as contracts prior to version 1.0.5. The system changed to a passive rewards scheme for completing these milestones when contextual contracts and a few other features were added (such as the Leadership Initiative strategy for increasing the new passive milestone rewards). If I recall the rationale correctly, then the problem was that because the original World's First contracts were only offered until the milestone was reached, and also because Mission Control at level one can only handle two contracts at once, it was entirely too easy to miss milestone rewards. Putting aside the problem of permanently missed content, it rewarded a play style where you built a rocket that was only exactly capable enough to complete the contract, and no more--which is silly, especially since contextual contracts specifically depend on having satellites in orbit that can do more. Anyway, @arb8743: Welcome to the forum, as others have said. You get the world's first rewards simply for reaching the milestones, so feel free to build a good, capable rocket. I do not recall the altitudes that count for the milestones, but when you reach one, the messages tab at the upper right corner of the screen in flight mode (the one with the radio beacon icon) will blink with colours. It will tell you what you've earned.
  2. Indeed, that is the case. I am not quite certain why I interpreted this statement: ... as meaning that you were having problems with your nuclear engines, but I did. That being said: It was not my intention to be rude. It may not account for much, but I did not perceive my remarks as being such when I wrote them. Nevertheless, you do have my apologies for any slight. Even unintentional hostility does nothing to further my purpose in posting, which is to provide help and information to those who ask for it (though I freely admit that my apparent inability to closely read your posts is quite frustrating to that effort). Let me try this again, and please accept my advance apologies for anything that repeats what was said above. My full reply is quite long, so I put a lot of it in spoilers: Of course, when you remove engines, there's a difference in thrust and attendant burn time, as you well noted. Part of our misunderstanding, I think, is the fact that the various staging options are generally regarded as launch configurations. Technically, I understand that long, thin rockets are the best designs for any situation with an atmosphere, provided that they will do the job. You may feel free to launch pancake rockets to your heart's content on Minmus and other airless bodies where drag does not exist. But long, thin rockets are not a balm for every situation, either, because: That is exactly right. Eventually, you will reach the limit of what one engine can do. Even a Mammoth, with its 4,000 kilonewtons of thrust, won't lift a rocket that weighs 4,001 kilonewtons (until it drains that kilonewton of fuel, that is). Clustering can assist with this, but there's only so much room for that. The only true solutions are either to cut the payload to manageable pieces and assemble it in space, or to accept that the limitation of thrust is an inherent trade-off of inline staging and that to get anything larger into orbit, you'll need a different scheme. The amount of delta-V lost to drag depends on the cross-sectional profile of the rocket, its orientation into the air stream, the thrust with which it attempts to plough through the atmosphere (airspeed, essentially), and the pressure and density properties of the atmosphere itself. There are probably other elements, as well. Drag's importance is less of an issue for delta-V and more a matter of balancing the forces on your rocket. If you imagine the thrust from the engine acting as a lever that works through the rocket's centre of mass, then you'll see that it is necessary for that thrust to point directly through that centre to keep the rocket from spinning out of control. Since you've been moving asteroids about, you've experienced this first-hand. The forces involved in that do not need to be large: most engines that gimbal have a gimballing range of less than five degrees. For longer rockets, five degrees is too much. In like fashion, tiny drag forces can cause a rocket to flip out of control; this is why fins at the fore are normally a bad idea. Fins at the rear can help keep a rocket stable, but there is also such a thing as too stable, because too much stabilising drag can make the rocket difficult to turn. Under the old (pre-version 1.0) aerodynamics, drag was so much worse that it cost over a thousand more metres per second just to reach orbit (roughly 4,500 m/s versus the present roughly 3,400 m/s). Furthermore, it was practically necessary to lift off vertically for the first ten kilometres and then make a sharp turn to forty-five degrees. You cannot do that with a current-version rocket and expect not to flip out of control and crash. But this is also the reason why so many posts and threads (especially old ones) sing the praises of asparagus staging: under that aero system, a staging scheme that had high thrust and kept high mass ratio was the best way by far to plough through the atmosphere and still have enough fuel to get to orbit. Under the current system, it is not that asparagus staging is bad, but rather that it is reduced to an equal footing from its original status as the clear winner over everything else. I'm guessing that you mean fifty tonnes of payload delivered to space, not on the pad. If so, then yes, that's a lot of Skiffs! Consider looking at the Twin Boar; I think that it unlocks in the same node as the Skiff. It's expensive, but it provides a lot of rocket for the price. If it's a mission or a challenge to do it with only Skiffs, then you may consider clustering. Do Skiffs surface attach?
  3. @Aegolius13 did a good job of explaining the rationale; I'll just give you some basic categories. As a very rough thumb rule, engines with an atmospheric (not vacuum, for once!) Isp of less than 250 seconds are usually vacuum engines. Engines with atmospheric Isp greater than 275 are usually good sea-level lifting engines, and engines with atmospheric Isp between 250 and 275 can fit either role, albeit not necessarily so well as more specialised engines. To refine that, if an engine has a vacuum (note that this time, it's vacuum, not atmospheric) Isp greater than 320, then it is probably a good choice for space. If you want to pick an engine with an eye specifically for launching, then try for one that has an atmospheric thrust of greater than 100 kilonewtons (kN). The Thud is arguably the worst choice that still follows this rule, the Rapier is a niche engine, and the Rhino is actually best in vacuum (you can tell because its atmospheric thrust is about 60% of its vacuum thrust, whereas most launching engines have between 85% and 90% of their vacuum thrust at sea level), but it has good properties on the ground, too. The others all are good choices for launch stages. SRBs don't follow the Isp rule: they have low Isp in any situation, and are best suited to the launch stage. Don't attempt to use jets in space. You can try, but you'll be disappointed. That's not to say that many of the remaining engines do not have specific niche applications that defy these rules, but the rules will probably get you to your destination with a minimum of trouble. Concerning thrust-to-weight ratios, it depends on the celestial body. More is often better, but when an atmosphere is involved, you need to consider drag (usually not a problem unless your rocket is not streamlined) and heating. For rockets launching from Kerbin, I typically design for a TWR of between 1.3 and 1.6. You can get away with anything from 1.2 to 2.0 provided you design the rocket well. TWR values under 1.2 take too long to get up to speed (and they waste too much fuel fighting gravity during that time), and values over 2.0 tend to get too hot in the lower atmosphere. For airless bodies, it's simpler: I generally try for a TWR of more than 2 for the body I'm landing on. Remember that a rocket weighs less in weaker gravity, but an engine's thrust is constant for a given throttle setting: a TWR of 1 on Kerbin can be 6 on the Mun. SRBs are terrible engines insofar as efficiency is concerned, but they are the cheapest engines available. Use them in the launch stage, either on their own or as a low-cost way to increase your rocket's TWR without resorting to a complete redesign. When you have a choice of engines, the usual method is to burn your least efficient engines first and go in order from there, and SRBs are no exception. When designing your initial launch stages, don't neglect the Twin Boar. It is also extremely cost-effective for the thrust that it delivers, and unlike SRBs, it isn't utter rubbish in the upper atmosphere.
  4. But the rigid part of the pendulum--the steel bar--is still free to rotate about the fulcrum on the bearing. That rotational degree of freedom is the necessary part. My apologies if that was unclear; I cited flexible cables specifically because that's what real sky cranes use.
  5. It's not a fallacy when it's an actual pendulum. The reason that the pendulum fallacy is a fallacy is because it involves the idea that a rocket essentially dangles from its tip because of gravity. Aside from having no answer for what to do once it reaches free space where gravity is effectively nil and the concept of dangling needs to be redefined, there is the problem that a rocket is a rigid body, but a pendulum is not. In order to work, a pendulum must hang freely from a fulcrum and be subject to forces external to itself--specifically, forces that are transmitted through the fulcrum one way or the other. Normally, that's gravity on the pendulum and a normal force transmitting through the fulcrum, which is to say that the fulcrum holds the pendulum up against the pull of gravity with an equal-and-opposite force. While it is true that a rocket is subject to gravity, it's also true that both the gravity and its own force of thrust work through the rocket's centre of mass (meaning that they work on the rocket in its entirety), and that it dangles from nothing. In like fashion, a fulcrum under thrust or acceleration of some kind can be the fulcrum for a pendulum provided that the force on the fulcrum is transmitted through it to the pendulum. A force that operates equally on both won't work, which is why a pendulum-driven clock won't work in free fall--the force is not being transmitted through one to the other but instead acts on both fulcrum and pendulum directly. The technical term is restoring force and it refers to the tendency of a pendulum to hang along the gravitational pull so as to minimise its potential energy--i.e., the swinging action restores it to vertical. A hanging object that generates its own force is no longer a pendulum, because the direction of the force changes orientation as the object does; it's no longer restorative. A sky crane, on the other hand, is an actual pendulum because the rover hangs by a flexible cable and the force behind the hanging is gravity or an acceleration generated somewhere not on the payload, but still transmitted to the payload through the cable. It's either from the rockets on the sky crane (which would be a pseudo-gravitational acceleration that impels the payload to hang) or it would be gravity itself if the crane is landing the payload on the surface of some other body and there is a hovering element involved in the landing. On the gripping hand, a pendulum-like rocket would work just fine if the payload hung from the force generator by a flexible attachment and the force generator kept its orientation in despite of any motion of the payload. That's the operating theory behind Medusa rockets (they're like Orion, but with the nuclear bombs going off in a sort of shroud in front of the rocket), or, for that matter, parachutes.
  6. For your information, I never lean out the window in space. I'd get my helmet stuck on the frame! Theoretically, the limit for a rocket with infinite fuel in KSP tanks and a massless payload is 6,895.2 m/s of delta-V, to be exact. Also, I made no provisions for your choice of transfer trajectory or destination; my theoretical rocket can't lift off from Eve, either. That wasn't really the point. Neither was my point to say that staging has no value in the face of larger tankage. My point is that larger tankage, in space, solves the same problem that asparagus staging solves on (or very near to) the ground: making more propellant available to the engines. I treat the asparagus-stage need for more engines, as well, to be a specific use-case application of drop tanks in a gee field too strong to otherwise support the increased fuel load. That said, drop tanks, as I indicated, do have a use, and they work very nicely in those applications where manipulation of the dry mass portion of the mass fraction of the rocket is necessary to achieve a desired outcome--namely, the one where every element of the payload is essential across two or more stages. Being able to remove dry mass from a rocket is the only way to overcome the problem of diminishing returns: you diminish the rocket, instead. Nevertheless, the point is well taken; I will endeavour to be more precise in the future. It's more that asparagus staging isn't necessary in space. You don't need fuel lines and you definitely don't need extra engines because you're not trying to go straight up against gravity. If you were seeing bad results from the nuke engines, then there are two likely reasons for that. First is that your rocket was too light--three tonnes of engine on one tonne of payload is a lot. Three tonnes of engine on thirty tonnes of payload is a lot less of a dry mass penalty, and gives the nuke a chance for its higher efficiency to work for you. Second is that you were using rocket propellant tanks instead of liquid-fuel-only tanks. That not only gives you a reduced fuel load, but also several tonnes of dead weight in oxidiser. Even draining the oxidiser would still leave you with less than half the fuel in a too-large tank. Let me ask you this: are you asparagus-staging rockets that have only two or three stages, or are you speaking of a ten-stage monstrosity? Every staging scheme has its benefits and its costs. Traditionally, there are inline staging and side-along staging. There are some variants such as onion staging, and asparagus staging is a sort of hybrid. Inline staging (like the Saturn V) has the benefit that when each stage empties and is jettisoned, the remaining upper stage is fully-fuelled. This works well for the Saturn V because it gives the benefit of full burn time for each booster but at a cost of reduced thrust on each stage. However, the reduced thrust is okay because the upper stage engines are optimised for the region of the atmosphere in which they were meant to work; there is no benefit from burning all of the stages at once (assuming that it could be done without rapid unplanned disassembly). Side-along staging (like the Delta IV Heavy) has the benefit that all of the engines (core and two boosters), burn at the same time, which increases thrust (by about three times, assuming my arithmetic is still good). Putting aside the throttle trickery used by the actual Delta IV Heavy, the net effect is that when the boosters empty and stage away, the core is left partially empty and thus suffering from both a higher dry mass in the mass fraction and reduced burn time because of the lack of fuel. Onion staging (I don't know of any rockets that actually use this, but I don't think there's any reason they can't) is actually a variant of inline staging. Envision a rocket like the Delta IV Heavy, but instead of lighting all three engines, imagine that only the outer two are lit, and when they are empty, they stage away and the core is lit. The name comes from the idea that the outer boosters fall off and leave the inner ones to burn anew, much like peeling layers of an onion. Note that it looks the same as the side-along-staged Delta IV Heavy, but it merely appears similar to side-along staging because strapping the boosters to the sides helps with symmetric thrust. You get the same result when you attach the boosters to a bicoupler or the like and achieve a more inline look. In essence, we can even go so far as to say that inline staging is the degenerate case of onion staging when there is only one additional booster in each stage. Its benefits and costs are the same as for inline staging, except that when there are multiple outer boosters, they do have the advantage of some increased thrust (though technically the same effect can be achieved with clustering and taller or more numerous propellant tanks). Asparagus staging works by the boosters sharing their propellant with all engines inward from them. Practically, it is a series of powered supplementary propellant tanks--meaning that the tanks lift their own mass against gravity rather than your core stack needing to lift their mass in addition to the rest of the rocket. This means that, in the Delta IV Heavy example, all three engines are lit at the start, but you'd see the outer side boosters stage away much sooner. The core engine, however, would have the benefit of full burn time because until that point, it would be running on propellant flowing in from the outer boosters rather than in its own tank. In this way, it combines the advantages of high thrust and high second-stage mass fraction, but at the cost of increased drag (there's no inline form) and much-reduced stage burn time. Because the core stage burns (usually with a full propellant load) the entire time, this is a problem with efficiency in the new aerodynamics model because first-stage engines get to be quite inefficient compared to their vacuum-rated counterparts once they get over ten kilometres. The old model had an atmosphere thick enough to require high-thrust engines quite a long way, and it also calculated drag in a weird way that actually justified pancake-shaped rockets (drag was calculated per-part and paid no attention to orientation, so nosecones, for example, increased the part count and thus increased drag). It made sense in some cases to have many-stage rockets that were wider than the launchpad just to get to orbit. Now, the atmosphere is thinner (such it takes 1,000 m/s less delta-V to reach orbit), and the aerodynamics reward long, thin rockets. If you need extra thrust in the first stage, then solid rocket boosters provide that at a bargain. Asparagus staging, on the other hand, requires a wider rocket and involves extra parts that are also extra-draggy parts. It still has applications (Darts enjoy good efficiency from the surface to orbit, and high thrust, high second-stage mass-fraction rockets are a practical application for a lot of situations--Eve ascent is the crown of them all), but it is no longer the champion Über-rocket that it once was. However, in space (which was your original question) it is normally a waste to haul engines that you do not absolutely need. As with anything, there are applications, but few to none for asparagus staging once in orbit.
  7. Not as such, no. Putting aside the question of how you get an asparagus-staged rocket to space in the first place, once you are there, the rules are a bit different from the situation that would necessitate asparagus staging on the ground. The main advantage of asparagus staging is that it was essentially a way to run the core along with the boosters while still expending only booster propellant. This does two things: it gives a lot of thrust, and it also leaves you with full propellant tanks after each staging event. In space, there is little need for high thrust. It helps in certain applications--the Rhino is a vacuum-rated engine and it has a proper niche--but it's not strictly necessary in the way that it is necessary to have high thrust to get off the pad at launch. However, having full propellant tanks after each staging event (or, more accurately, staging away empty tanks rather than carrying the tankage dead weight) is useful in space. That's already a concept; it's called drop tanks. The idea is that you have one engine (or cluster, or however you're moving your rocket) feed from a series of tanks, and as each tank empties, you stage away the empty dead weight. This works in applications that need it, but in many cases, it's just not necessary. Part of the reason for that is that it doesn't take a literally astronomical amount of propellant to get anywhere in KSP. Another part is that staging away the empty tank improves your mass fraction by the mass of an empty tank--i.e., not much if it's a large rocket. Small rockets benefit more, but in those cases, it's trivial to add significant propellant mass fraction. A small probe on an FL-T800 tank with a Spark engine can go nearly anywhere. The same probe on an S3-14400 tank can go anywhere ten times. There's no need for staged tanks when you can simply use a larger tank.
  8. Goddard himself built the first liquid-fuelled rocket with the engine on top and the tanks on the bottom. When it comes to making mistakes with rockets, you're in good company.
  9. The Avionics Hub gives the full suite of SAS options (referring to prograde/retrograde, target/anti-target, manoeuvre node holds, &c.) but it is not a probe core, so though it offers SAS capability, it does not offer control. In other words, the Avionics Hub is almost a sort of upgrade so that your untrained pilot, non-pilot, or low-grade probe core can use all of the SAS options, but it cannot use those options itself.
  10. Remember that in general, the rule here is that the amount of delta-V that works is the 'right' amount. That's most likely because people don't generally single-stage a Mun rocket to orbit. They usually reach orbit in two, or possibly three, stages. Thus, aside from the usual advice that the initial stage should have between approximately 1.2 and 2.0 thrust-to-weight and each stage should have approximately two minutes' burn time, there really isn't much. That being said, if you want to optimise your rocket to the fullest extent possible and reach the absolute minimum required delta-V, then I think it can be done with 2,800 or 2,900 m/s. However, I believe that the rockets that accomplished this had almost no payload; that's not an option for a Mun rocket. The general advice of 3,400 m/s is about the best that you'll get.
  11. You've got my respect for the level of difficulty you've assumed for this. It may also be advantageous to change some or all of the landing gear to a heavy-duty version; it may be ugly, but it's much more ugly to have your vessel in pieces strewn about Minmus's surface. Furthermore, I think that you may have some success with a reverse-tricycle design, also known as a tail-dragging plane, where you have the dual landing gear in the front and a single gear in the back. When you touched down, you had a slight sideslip that, on braking, caused you to flip over to the oblique right. Overcorrection (which is stupendously easy at 160 m/s) caused you to flip out of control. This is a problem with any tricycle; deceleration on braking tends to shift the weight forward, and if that weight goes even slightly to the side, then it can cause your vehicle to flip over the leg of the triangle between your contact points--i.e., the wheels on the ground--because those front legs tend to come very close to the centre of mass. Remember that Minmus's surface acceleration is a little under half of a metre per second squared; most of the force on your craft will be from the deceleration in the forward direction, not the gravity pulling you down, and that makes it easier to flip. You can change that by reducing your horizontal velocity, but I think your choice of orbit has reduced that to the lowest point possible without a retroburn. The only other possibility I can think of involves landing in the highlands, not the flats, where you're closer to your apoapsis and thus slower, but of course that appears to save only ten metres per second and further requires you to land on a rougher surface. With a reverse-tricycle, the centre of mass is much farther away from the front leg of what I will call the 'contact triangle' with the wheels at the vertices, and a slight sideslip won't cause you to flip to the right or to the left, because it still has to flip over the front. It may, however, still flip over the front. Any vessel on the ground can spin out of control. But I hope this helps you.
  12. Exactly! I certainly am not suggesting that your approach is the wrong one. In fact, I follow the same philosophy overall--I don't want to spend my time making tiny changes just so I can reach orbit when there's so much more to do and see. As the saying goes, once you can reach orbit, you're halfway to anywhere--well, I want to explore that second half. Since my rockets all have nearly the same design, I only need to know one optimal trajectory. Honestly, it appears that we have arrived at the same solution, but came to that solution from opposite ends of the problem. You took the precalculated trajectory and designed your rockets to fit, and I designed the rocket and adjusted the trajectory to fit. Either way, we get where we want to go, so that looks like success to me.
  13. Don't forget that the spacecraft itself is a variable. Unless you fly essentially the same design to orbit again and again, expect that the correct values for one rocket will not work for another. That being said, I tend to build rockets that are variations on a consistent theme, and I usually tie my launch scripts to the altitudes rather than the apoapsis--but I just about always launch to an 80 km parking orbit before I do anything else. If you're changing your target apoapsis, then that modifies the shape of the launch--but on the other hand, it shouldn't change the shape too much considering that your flight path is a (hopefully smooth) transition from a radial starting orbit to a circular final orbit. On the gripping hand, that shape is going to change the most in the atmosphere, where drag is going to fight whatever you do. It may be ultimately cheaper to launch directly to the target apoapsis, but traditionally, cost is in third place among rocket designers' design priority philosophy. Your thought on sampling data is a good one. I don't know what you're trying to optimise, though. Is it fuel consumption? Flight time? Ratio of crashes to successful launches? @VoidSquid: MechJeb includes a preset trajectory shape that works most, but not all, of the time. Since MechJeb doesn't know what you're launching, it has to use a one-size-fits-all approach and essentially tries to force the rocket to fit the ascent path, so it's not optimised at all--the mod for that is GravityTurn Continued. There's a discussion of the difference between GravityTurn and MechJeb in the first few posts of the GravityTurn thread, if you're interested. It's not technical, but it is correct. In essence, good gravity turns do look a lot alike because however the rockets fly, they all need to ascend out of the same atmosphere and in the same gravity field. But the subtle differences still count for a lot of efficiency. @dire: The pdf was a good read; thanks for sharing! Since it covers the Apollo lunar module ascent from the Moon and not the Saturn V ascent from Earth, I don't think it will completely solve the launch problem, but it does show some interesting ways to look at it. There are definitely some good ideas there.
  14. Indeed; that was the image I wanted to conjure with my analogy about revving the engine in neutral. Another similar situation is not staging the launch clamps, which gives me leave to ask whether you've left the parking brake on.
  15. Welcome to the happy little group! Others have given good answers to your other questions, but I wanted to focus on this one: ... Because there's a bit of nuance to it. On the one hand, yes, if you can land the booster safely, then you can recover part of the cost, and parachutes do help boosters to land safely. Also, you recover part of the cost of the parachutes, too, so there is a point to doing so. However, there are a few ways for that to go wrong. For example, the parachutes may have the booster falling too slowly, so while you're following it down, the vessel that you want to get to space can reach a critical part of its orbital insertion completely uncontrolled. There are other options: I have used it, and I will say that the primary purpose of it is not to save money; it's to save time: Stage Recovery is meant to be used with Kerbal Construction Time (a mod that causes rocket construction to take in-game time) and provides a pool of already-built rocket parts so that rockets can be constructed more quickly. That said, Stage Recovery will recover your parts, science, and Kerbals, provided that the stage that they are in is capable of landing safely (safely in this case is defined as reducing its speed to a specific value so it doesn't crash). There are a few ways to do that, but they all have a trade-off cost, and it is important to know that it doesn't always work: sometimes, a booster is moving too quickly and the mod assumes that it burned up in the atmosphere rather than safely recovered. Think about the risk before you send a crewed pod full of experiments on a fire-and-forget recovery insertion. I will say that unless you are specifically looking for what Stage Recovery (and by extension, Kerbal Construction Time) offers, you are probably better off not using it. Of course, that's true of any mod, so I haven't really told you anything you didn't already know. Instead, to answer for your original use case of dropping a Science Jr. while underway, I will suggest that you take your science experiments and storage modules to space with you: get the vessel in a stable orbit, do the experiments (or transfer your high-flying science into a container for it), decouple a science pod that contains the experiments and recovery equipment, and then you can follow it down to the surface without needing to worry about the vessel in space. I've used these sorts of 'drop pods' to good effect; they let me make a multipurpose mission very cheaply, but I also get to keep the full science value of the experiments because they are recovered rather than transmitted, and I can do so while the main vessel stays in space, ready to go wherever I mean to send it. If you are flying a plane and not a spacecraft, on the other hand, then why not just land it--on the runway, even, where you get full recovery value? Science experiments are expensive; if you're going to recover them, then recover as much as you can.