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Chaos_Klaus

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Posts posted by Chaos_Klaus

    Efficiently using transfer windows

    in KSP1 Gameplay Questions and Tutorials

    Posted · Edited by Chaos_Klaus

    Basically, you just want to do a basic hohmann transfer from one altitude to another. The only difference is that there is a planetary body at both your starting point and destination. These bodies mess up your trajectory.

    You still want to do a hohmann transfer and that means you want your resulting interplanetary orbit to be tangent to Kerbin's orbit. So you want to leave Kerbin's SoI in parallel to Kerbin's orbit ... along Kerbin's prograde.

    To do that, you need to do the ejection burn at the correct ejection angle. It's not sufficient to just burn on the day or night side (depending on your destination). You need to burn earlier. You can see this in an infographic here:

    http://ksp.olex.biz

    The transfer window just tells you when the planets are aligned so that you will get an encounter this way.

    How to achieve good TWR when you need lots of fuel

    in KSP1 Gameplay Questions and Tutorials

    Posted

    Well, by adding more stuff you basically negate your assumtion that your vessel is "mostly fuel". ;)

     

    The rocket equation has an interesting twist. Let's assume your vessel has no payload at all and the engine does not weigh anything. That basically leaves you with fuel tanks only. In KSP, fuel tanks have a wet/dry-mass ratio of 9:1. That's as close to "mostly fuel" as we can get. In this case the rocket equation simplifies to:

     

    delta v = ISP * 9,81m/s² * ln 9

    delta v = ISP * 9,81m/s² * 2,20 

    delta v = ISP * 21,58m/s²

     

    That implies that the maximum amount of delta v depends on ISP only. With a Terrier that would be 7445m/s. With a nuke it would be 17264m/s.

    Now since the natural logarithm in the equations gives us diminishing returns, we have a problem. If we add some payload, we would need an infinite number of fuel tanks to get this maximum delta v. There is a point where adding more tanks just isn't adding enough delta v. To me that point is around 10 * ISP. That is why I tend to build my stages so that each stage has this amount of delta v. With a Terrier that would make 3450m/s. Anything above that and I would actually use staging. 

     

    I think it boils down to how you build your landers in general. I tend to build with 10*ISP in mind. That implies a certain wet/dry ratio. I usually do not put RCS on my landers and have the orbiter do the active docking, by the way.

    Maybe your desings tend to always come out with a certain wet/dry ratio because that's what your intuition tells you. In that case, your rule of thumb would work well for your designs.

     

     

    How to achieve good TWR when you need lots of fuel

    in KSP1 Gameplay Questions and Tutorials

    Posted · Edited by Chaos_Klaus

    There is two things you could maximize with a lander. 

    You could go for a large delta v budget. It is easy to build a lander with conventional rockets that has 3500m/s+. Here I built one that has 4000m/s without staging. It's also hugely overpowered and not a very sophisticated design:

    MurEy0j.jpg

    It takes about 600m/s to land on the mun and another 600m/s to take off again. This thing can land and take off from the mun 3 times. 

     

    The other thing you can maximize is weight efficiency. Build a very light lander. In that case you would design it in a way so it would have no fuel left at all when it got back into munar orbit. 1200m/s of delta v and nothing more.

     

    This design has very little room for error but only weighs 1265kg. It will just barely make it back into orbit with almost no fuel left.

     

    mVWan2K.jpg

    How to achieve good TWR when you need lots of fuel

    in KSP1 Gameplay Questions and Tutorials

    Posted · Edited by Chaos_Klaus

    On 3.1.2016 at 1:53 PM, Plusck said:

    It is extremely disagreeable to contradict someone just for the sake of it, and counter-productive to do it in a thread that is supposed to be a help to other players.

    So I repeat: a rough rule of thumb is that you can get down to Mun surface from a low-ish orbit using slightly less than half of your fuel, and back up to orbit with slightly more than half of what's left.

    And that applies for any LfO-burning lander where most of the mass is in the fuel.

    I would add that it will be very difficult to design a lander that is able to do much better than that for the Mun, and still be useful for doing any of the other things you might want a lander to do (i.e. ferry people, carry scientific experiments, dock with orbiting mothership). The only real way of doing better is to use an LV-N and a lot of fuel, but that makes a very unwieldy craft.

    I'm not contradicting for the sake of it. I'm just saying that that is not true. Landing on the Mun and returning to orbit both takes the same amount of delta v. The same amount of delta v can stand for different amouts of fuel. You can see that your ascent takes less then half of your fuel. The fact that in your case it takes exacly half of the total fuel and you have 1 quater left is purely incidental.

    What portion of your fuel you use, depends on the total delta v budget of the rocket/lander.

    I'm sorry if I upset you. But it is how it is. ;)

    How to achieve good TWR when you need lots of fuel

    in KSP1 Gameplay Questions and Tutorials

    Posted

    1 hour ago, Plusck said:

    To get down to the surface of the Mun, you will generally use a bit less than half of your fuel (assuming your vessel is mostly fuel). Getting back up will generally take a bit more than half of what's left.

    Nope. You will use about half your delta v ... but due to the logarithmic nature of the rocket equation that translates to way more than half of the fuel.

    That thing called drag...

    in KSP1 Gameplay Questions and Tutorials

    Posted · Edited by Chaos_Klaus

    I think you guys are going about this the wrong way. You see a large number of red arrows and assume that there is a lot of drag. Acutally, many of these arrows are quite short. Even with an unaerodynamic rocket that has 4100m/s of delta v, you should be able to reach orbit no matter what. I guess the problem is with ascent profile?

     

    6 hours ago, panzer1b said:

    Drag is now oversimplified

     

    What do you mean ... "now"? Before 1.0 there was no occlusion at all. Every part was subject to drag as if it was flying around alone and the size of the part was estimated by its mass. A full fueltank would cause more drag then an empty one. That's what I call oversimplification.

     

    Instead what you see in the picture is perfectly sane physics. The outer tanks are angled. And the sides of these stacks are exposed to the air stream at an angle. Naturally, this creates drag.

    Drag also occurs with parts that are exactly behind other parts in a stack. That is because drag is induced by all faces that are exposed to moving air. Obviously that applies to faces that are pinted into the airstram, but it also is true for all the faces at the rear of the vehicle. Actually most of the drag we mean when whe say "drag" is actually caused by the low air pressure *behind* the vehicle. Air moving over a surface causes skin drag. That even applies to faces that are perfectly parallel to the airstream.

    Occlusion only happens when two faces are ontop of another. The top face of a tank won't cause drag if it is stacked behind another part of the same size. All the other face will however still create drag.

    It's more complicated then you think and KSP's aero model does a relatively good job. Remember that in real physics we make many seemingly stupid simplifications. Like talking about point masses. But if it works, it works.

    In cases where you clip parts into one another and build things that are not quite so rocket shaped, the model struggles. If you want something more sophisticated, use FAR. But it's more sophisticated and that's the price you pay.

     

    Is it just me or are Liquid Fuel tank masses backwards?

    in KSP1 Gameplay Questions and Tutorials

    Posted

    The Oscar B now uses the same mass fraction as the other LOX tanks.

     

    The other difference is due to the dry mass being rounded to sane numbers.

    Mk1 liquid fuel fuselage weighs 0.25t and holds 2t. --> 1:8

    MK0 liquid fuel fuselage weighs 0.025t and holds 0.25t.  1:10

    It's a little inconvenient. But a dry mass of 0.031t looks kinda silly. The tanks in KSP obviously contain structural elements (since nobody builds cylindrical tanks). Im' fine with that.

    MK3 Tanks are shaped in a completely different way. Makes sense that they don't hold that much fuel. All in all, the differences are minor.

     

    Also: You picture clearly shows that it's not worth staging with 3900m/s of delta v on a Nerva. As a rule of thumb: Stage when your delta v is about 10 times the ISP of the engine. With an ISP of 800s, that means you can go up to 8000m/s until you should stage.

    Can we talk about the new MK I cockpit

    in KSP1 Discussion

    Posted

    [QUOTE][COLOR=#333333]the new Mk1 is a plane cockpit, period. Gorgeous, but it only looks right when flying in an atmosphere, and plain ridiculous on top of a rocket. The old Mk1 was much more... open ended? Short of like the shuttle parts: it is very difficult to use them in a modular fashion like the old aero parts, constricting the kind of designs that you can use and look right, at least in my eyes.[/COLOR][/QUOTE]

    That is all complete crap. Sorry.

    Firstly: [url]http://www.space.com/24902-european-space-plane-eads-images.html[/url]
    New MK1 is totally viable for space.

    Secondly: Did you actually *see* the old MK3 parts? How were those better then the new ones? Modular? I mean there was a tank and a cockpit ... wow.

    New-fangled buoyancy model -anyone know how it works?

    in KSP1 Discussion

    Posted · Edited by Chaos_Klaus

    You should add that to the bug tracker. The volume of the parts is estimated via the drag cubes. So if there is no drag applied (like in a fairing), there might be no buoyancy aswell (by accident).

    For landing on the water:

    Make sure your angle is reeeeally shallow. If you drop below stall speed and lose altitude too fast, you will dip into the water too hard and deccelerate quickly. But I managed a few landings that were very smooth indeed. Even at speeds above 50m/s. The first time, I actually was sure I would crash. ;)

    How make my rocket more stable ?

    in KSP1 Gameplay Questions and Tutorials

    Posted

    go with the solar panels. Nothing worse than running out of power.

    Why are you useing all these FL-T200 tanks when you have the larger FL-T400 tanks unlocked? With the larger tanks you get less stability problems, because the larger tanks will drain as a whole and not shift around your center of mass so badly.

    Part of your instability problem comes from the top tanks draining first, shifting your CoM backwards. At some point it moves behind the center of pressure/drag and your rocket wants to fly backwards.

    Another big problem is really the probecore. It has no stability control and no reaction wheels. Unlocking flight controls would give you a reaction wheel, but without SAS to provide stability control that's basically worthless.
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