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foamyesque

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Posts posted by foamyesque

  1. On 7/1/2022 at 4:20 PM, Ultimate Steve said:

    Here is 620kg:

    MMpVRPB.png

    A small nose cone, an OKTO 2, 2 Oscar Bs, with one of them having one tick of fuel drained, a Spark, and another small nose cone on the back to reduce drag, clipped upwards so it doesn't obstruct the engine.

    UrxwcIy.png

    Liftoff! Ascent profile is very aggressive due to the high TWR, we hit 45 degrees of pitch at around 2.5km altitude. From there, SAS prograde is chosen, and when the apoapsis nears space, the engine is throttled down but kept just barely on to maintain SAS prograde. This is done because in an earlier attempt, I just cut off the engine and due to the drag losses of tumbling around, I didn't make orbit.

    BSWyBhm.png

    KBAkTMI.png

    Throttling down.

    21OJJKN.png

    Complete cutoff. The probe core is placed in hibernation mode during the coast to the apoapsis.

    f1Cm6y6.png

    Nearing apoapsis.

    x9C54bt.png

    Due to concentration and the short burn I forgot to take a screenshot during the burn, but due to burning slightly too early/off prograde, we are not in orbit, but we have 15m/s left to try to circularize at apoapsis. Hibernation is turned on again.

    KXy1sfl.png

    And, successfully in orbit with just a hint of electric charge left!

     

    I'm impressed! I didn't think the Spark could do it without staging. On the other hand, I don't like the nose-cone-clipping technique for drag reduction much. But even with that said, I believe you're the first person in five years to beat my design, so very well done. :)

  2. On 12/11/2020 at 2:50 AM, Helvica_Ring_Scientist said:

    ...what'll you do? What will be the components of your ship? Will you do gravitational assists? Your choice. :wink:

     

    Load up the torchship I used to insert into a retrograde Kerbin orbit, wait for Kerbin to rotate to the correct angle, then launch more or less straight up. When you have 22km/s of 1+g thrust you don't need precision.

    93C324CFAE2F7506DAD18D66F07731AA581ED04A

     

    I might be caught by the game having to slow down during the launch sequence, though.

     

     

  3. Yeah, about the only structural failure you can reliably get any more is ripping wings off when executing 40g manouvers in the atmosphere. Nobody used to modern KSP has any idea what Wobbly Rockets(TM) used to be like. I bent some rockets into a clean horseshoe in days gone by.

  4. 5 hours ago, jimmymcgoochie said:

    I was referring to using engine gimbal to point the spacecraft in the direction of the burn while the engine was on, rather than using RCS or reaction wheels to do it- during a burn gimbal is the best way to do it, but only once you’re pointing the right way. Firing the engine when you’re pointing in any random direction and relying on the gimbal to turn the ship around to point the right way is farcical.

     

    It's actually something I do all the time. Engine gimbals give you enormous torque compared to basically anything else, excepting reaction-wheels on small ships and appropriately sited aerodynamic control surfaces. With particularly large craft I will often crack the throttle in order to align, and then zero out the (minor) translation drift over the course of the burn. And with small craft I begrudge any pennysworth of mass not strictly dedicated to the mission :p

  5. 10 hours ago, jimmymcgoochie said:

    The idea of using nothing but engine gimbal to control attitude for a burn fills me with horror; there’s always a better way, whether that’s reaction wheels (even in RP-1 there are reaction wheels good enough for pointing small probes) or RCS thrusters.

     

    Gimbal control is by far the most effective way to perform attitude control in a burn, excepting perhaps atmospheric control surfaces. It's non-burn attitude control that it struggles with, since any rotation inevitably requires some translation if you're using gimballing, whereas RCS can null out and reaction wheels don't produce thrust as such (although they do generate angular momentum from nowhere, which means you can build some interesting contraptions).

  6. Your issue is the addition of the radiator and the removal of the fins. Radially attached parts have significant drag (and, if asymmetric, can also cause a torque), and because you've put it at the top of your rocket, you've moved your center of aerodynamic force upwards. At the same time, you've eliminated the fins at the bottom that would've moved the center of aerodynamic forces back down. For a rocket of that size the capsule would provide entirely adequate steering otherwise. The heat shield's probably also unnecessary for an LKO machine like this appears to be, but if it's in the stack it shouldn't be causing aero issues.

    My suggestion would be to eliminate the radiator -- I don't see anything on the rocket that would require it -- and, if that's not enough, putting the smallest fins on the second of the solid stages. First one won't get you going fast enough for aero instability to be an issue, but the first Hammer will.

    Note: The above is trying to work with your extant rocket. My own preference for using solids for launchpad kick is to radially mount them and co-fire them with a gimballing liquid engine; the liquid will give you a bunch of control authority and with its likely higher efficiency is better at sustaining your flight, but the solids will shove you up to working speed much faster and cut back on your gravity losses significantly since you don't have to painfully crawl up at 1.1 TWR or what not. By the time they fall off you'll have burned enough liquid fuel, and gained thrust by getting into thinner air, that the liquid engine can now propel you just fine on its own. In addition, because they're a radial attachment at the bottom of a rocket, they can -- it depends on the weight distribution of the rest of the rocket -- act to stabilize you aerodynamically as they burn.

  7. 5 hours ago, RealKerbal3x said:

    No, I think it was just a visual indication that the throttle was at 100%. It was a bit redundant and was removed in a later version.

    It wasn't tied to the throttle; you can see mine is set at zero. As far as I know it was completely meaningless, and I don't remember at this remove what made it light up or not.

    My favourite part about picture is that you can clearly see the great big divot I had to make in order to avoid crashing into the old launch gantry :D

  8. Rockets flip for one of (usually) two reasons:

     

    1. A center of mass that has moved below the center of aerodynamic pressure, causing aerodynamic instability;

    2. A center of mass that has moved out of alignment with the center of thrust, which will induce a torque, and that torque becomes larger than your ability to counteract it.

     

    A picture of the rocket would be useful in figuring out the cause. It's usually aerodynamics if you're in an atmosphere, since engines are heavy and so fuel draining will tend to move the CoM down over a given stage's burn if you have them at the back (as is usual). One of the advantages of a staged design is that the mass of the next stage up helps to counteract that.

  9. 1 minute ago, king of nowhere said:

    yes, that works for launch, but hope you never have to make manuevers again. i suppose you can do it for some relay satellites

     

    Nah, I've used it for orbital manouvers too. When you're that light you have all the dV in the world, if you want it. Nulling out any unwanted translation isn't difficult unless you're trying for extreme precision. This is especially so if you've got a pair of engines; you can roll trivially, toggle engines on and off with action groups, and flip end-for-end with just the barest puff of propellant and barely any translation.

    You should try it sometime. It's a whole new way to fly.

     

  10. 2 minutes ago, king of nowhere said:

     how can you not have attitude control on a ship? if you must point your rocket in one direction, and you are not and have no reaction wheels, are you going to turn on the rocket in the wrong direction and use gimbaling to eventually move it right? i can't believe this can work.

    Yup. Can, have, and might well do so again. :p

    I prefer to use something like RCS or torque wheels on larger craft, but on a tiny probe, you get by far the best attitude-control-for-mass from a gimballing engine. Went to orbit on 670kg that way :p

  11. 11 minutes ago, Corona688 said:

    Unless you're using modded parts, reaction wheels are so ubiquitous it's pretty hard to make a probe without one.

    The OCTO-2 specifically, as the lightest probe core and the one that you'd probably use on anything that actually would mount an Ant in the first place, does not. Nor do lawnchairs, if you're building some kind of lightweight Kerbaled craft.

    11 minutes ago, Superfluous J said:

    Unless your probe core has reaction wheels, or you're using a Octo-2 for which the smallest reaction wheel and it combined are lower mass than all probe cores with reaction wheels.

    Those would be the very supplemental control systems I am talking about. And their mass is poison for lightweight design.

    The smallest reaction wheel has a mass of 0.05t and is, in addition to being way more control authority than something using an Ant could possibly need, shoots the TWR in the foot. A pair of Spiders provides twice the thrust at under two thirds the weight of an Ant + wheel combination. And doesn't need electrical power, to boot. The (slight) vacuum Isp difference is more than made up for by the weight savings on these kinds of microsats. This is even more true if you're going really lightweight and using a single Spider through the use of the translate tool.

  12. 4 hours ago, Corona688 said:

    The ant engine is amazing for what it's designed to do.  Unfortunately they shoved it into the tech tree at such a late point that by the time you unlock it you're already done doing flybys.

     

    The Ant engine has no gimballing, though. It'd be wonderful otherwise, but the absolute requirement to spend additional mass on a supplemental control system means it is heavier than a Spider.

  13. 6 hours ago, king of nowhere said:

    was it even worse than the current magic wings made with thermal shields and "planes" that are a flat forward surface clipped on itself and somehow have no drag?

     

    Oh yeah. I built a plane I couldn't get to stop, even with a parachute, by accident.

    mayBj4j.png

    And the souposphere was improvement over what came before it, what I call in retrospect the brickosphere. At least the souposphere faded gradually as you got higher. The brickosphere was a brick wall at 35km altitude, and vacuum beyond.

     

     

  14. 2 hours ago, Spricigo said:

    It amuses me how often, when it comes to spaceplanes, someone will state a preference for X over Y because they are better in some aspect just for the next guy tell is the other way around in his experience.

    ...and I suppose now I, the "next guy", don't need to even tell what my preference is. :P

     

    Heh. It's true, they are a subject of debate! On non-delta designs, where your CoP naturally tends towards the midbody, you can build a tail out and have it work fine, using a couple of all-moving pitch control surfaces, maybe some autostruts to make sure they actually move the ship instead of just the tail.  Deltas, though, tend to put the CoP far to the back, and if you want a CoM that doesn't shift, it usually means it's further forward. Canards are very helpful there.

     

    Sometimes I even use both. The alterations in drag between the nose and tail can give you significant control authority even in a stall situation, allowing you to force the nose down to get out of the stall, and reducing the strain on any supplemental control systems (RCS, wheels).

     

  15. I'm pretty sure stock aero models a drag shift, yeah. It definitely models a drag spike through the supersonic region. I've had spaceplanes that have been completely uncontrollable through 90% of their entry suddenly flatten out and fly smooth as silk once I drop out of high transsonic, then turn to lawndarts in the subsonic area.

    If your plane is tumbling on re-entry you have a CoP/CoM inversion, there's no question there, but the cause can sometimes be tricky to diagnose. KSP stock aero does model stalls these days; if you turn on the aero overlay and generate enough angle, you will see the blue arrows from your wings disappear and red arrows spawn. If *some* of your surfaces are stalled out, and others not, your CoP can move around significantly, a situation that not only is very likely to occur in a tumble, it can make the tumble worse. In addition, stalled out control surfaces are dramatically less effective at actually steering your ship; you can pilot a nearly-unstable craft reasonably easily if you have good control authority, but if it jams up on you things will rapidly go downhill.

    As a general preference -- and particularly when working with a delta design as yours is -- I tend to use canards over tail-mounted elevators. It makes it easier to get a CoP nicely centered (which in turn makes centering the CoM on it easier), and they behave better in high-angle flight. It is also generally a good idea for anything going supersonic to use all-moving control surfaces, as real supersonic planes tend to.

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