18-Apr-2022

Kerbal Space Program 1.0 - Launching Rockets To Orbit

Hello, its Scott Manley here with Verbal space program, 1.0. And I would like to talk about launching rockets into orbit, something which most of you probably already know about, but perhaps of some new people here who are interested, but more specifically I want to talk about how the new aerodynamics affects it. And the best way to find out how the aerodynamics is impacting anything is to use the debug menu. So alt and f12 will bring up the debug toolbar and there are a bunch of buttons here. Your cheats. Obviously gives you infinite fuel and everything, but under physics, you have display aerial forces in flight, and that will apply that'll create these little red velocity, vector or force vectors acting on your spacecraft. You see one here pointing at the back.

This is a drag vector right now, if I turn the rocket just a little, you can see what we've got. We've got forces acting all the way down the rocket. And what I've done by turning too hard is the forces near the front we're greater than the forces. Of the back. So we ended up with a torque pulling the rocket over.

Now, of course, would be cat a strong catastrophic. If you attempted say to perform a gravity, turn at the 10 kilometer mark. This thing is actually fixing itself for the simple reason that we're we're running out of fuel here. And the center of mass of the rocket is moving further forwards.

But if you have said a giant egg-like fairing on the front you're going to find that your Rockets really very much want to fly backwards. Now you can. Fix that by putting on fins at the bottom, but you'll notice that even when SpaceX Falcon is flying, it doesn't have any fins it entirely is controlled through the thrust vectoring in the engine. So lets a revert flight to launch, and we'll talk about how to do a proper gravity. Turn if you have been playing Verbal space program with a stock aerodynamic model for a long time, then you've probably got into some very bad habits and probably launched some very cool things. But we're all about bad habits. So since we're, talking about launch, we're going to go over what the newbies might need to know, press em to go to the map screen at the bottom.

You want to bring up your littler nav ball and the top right of the screen you want to click on this fuel tank. So you can see the fuel you have available right that will show your liquid fuel and oxidizer. So you know, when you're running out press M to come back at T will enable SAS. You want to make sure that light is on and Z or Z. If they're, depending.

Which country you're from will activate 100% throttle and very rarely do you want anything but 100% throttle. Now this whole thing I want to start going up straight away, but within a few seconds we want to turn over by about five degrees of all we're doing is we're putting our velocity vector, slightly sideways. This is important for the people in the pad, because it means that our rocket won't immediately come back down, and you crush them and burn them any giant flaming ball Dan. Now, remember those.

Force vectors that worship we're turning our spacecraft around well, the best way to avoid those force vectors, turning your spacecraft around is to make sure that they are all pushing in the same direction that you have control. So if you keep your velocity vector, right your nav ball, pointing exactly along your velocity vector, then means that the forces are all being applied straight down your spacecraft. And so the amount of torque that's being generated to retain your spacecraft. They might have. Forces trying to turn your spacecraft is being minimized, and hopefully being kept below the limit, which you can control with the various control systems on board know, the gravity turn your can aiming to hit about 45 degrees in the 10 kilometer region, I think I did a pretty good job, or I've accidentally clicked on orbit.

Here, that's, okay, we're going to keep it until we get what we're going to keep in this viewpoint until we run a fuel in this stage and brought this down a bit 30 degrees on the. Horizon here and now switching to the next stage we're high enough up that the aerodynamics are no longer such a concern instead, we want to make sure that we're actually going upwards into a suitable orbit. So this is still looking good we're firing our engine in this second stage here you see is generating a little amount of thrust, but it's enough to be accelerating us. But in the map, we can see the ballistic trajectory, we are going to follow.

And our current Apple apps is about 60 kilometers. That's, pretty good I'm just going to keep this following this. Now, if you find that your velocity vector is starting to get too close to the horizon. You can push your orbit, a little higher if you're going too high. You can push it lower the higher up in the atmosphere. Furthermore, you are the more you can deviate from this velocity vector. It is all kind of complicated, but it will become second nature to you know, we're up to about 95 kilometers, 94, 95 and 697 we're going to burn out at a hundred we're.

Just going to press the X key to cancel our thrusters. So we still have a little of fuel left here, but we're saving that because this orbit is fine, but in fact, it lands back on the surface. What we want to do is turn it into a circle and to turn it into a circle. We have to fire our engines here. So that we turn the thing more circular. If you imagine, what this really is part of an ellipse, the ellipse kind of goes down inside the planet, and then it actually continues to about there. So by.

Accelerating here, we're going to lift this internal one, although you can actually see it here by mousing over it. There is where that orbit actually goes see that how very, very useful for me to show you this. So when we accelerate at the furthest point from the planet also known as Apple apps, we will hopefully lift this up until it ends up outside the planet. And we are saved from falling back and being all sorts of embarrassed. So we just move our time forward until we're about, but 30 seconds away. Or so then turn the spacecraft to point along this.

Now in sandbox mode, you might just be able to click on the pro great button. But that is just fine and then throttle up to 100% by pressing the Z key or the z key, depending upon where you hail from. So look, we can watch this I move using the mouse cursor. We can see this is coming up it's coming up it's coming up it's coming up. And there when we get this about 70, or when these flip then just press X there, we go 111 by 99, 9 is a solid.

Solidly good orbit here, and we have enough fuel left. The important thing is we have enough fuel left to go home. If you can't get up here, and you have no fuel then you're in trouble, because you can't get home, and you need a rescue mission. Anyway, picking the exact gravity turn is actually kind of a hard thing to do unless you have huge amounts of analytical tools.

So I kind of want to show you that it's not disastrous. If you get the wrong, turn selection, right? So this one, as an example of a turn. Which is far too slow, which means we end up going far too quickly into a ballistic trajectory. We have to cut our engine sooner and then spend more time burning fuel up here, circular rising. And thanks to the magic of something called the Berth effect.

This is less efficient, it's actually analogous to instead of walking around a rectangular field walking across the diagonal. Instead, it's, a short, and it's, actually an energetic shortcut, which is offensive. We are saying we are doing something more. Efficiently so yeah, I perform the same action, action as before we circularize the orbit. And we see that we have 34 units of fuel left, which isn't much less than the better trajectory.

I flew for a first estimate. Now here is an example where we overcook the gravity turning early on what I do is I begin to say, oh, this is too steep and try to correct, so I, keep my nose high to try and stop my velocity vector, dropping too low and basically as turning over and crashing into the ocean. If you have fins on. Your spacecraft you may not be able to perform that you may find your spacecraft inexorably, pulling its nose down then diving into the ocean like a ginormous lawn dart. That is where you essentially don't have enough pitch authority to counteract the aerodynamic torque. You've placed on it fancy way of saying, if you put fins on it, then you keep it stable, but you may not be able to pick where stable is pointing while we're burning less fuel in space. We did have to burn a lot more fuel.

Early on. Because we were going edge on into the air stream, but how much did it affect our final fuel bill? Well, not that much as it happens. The point I'm trying to make here is don't agonize over getting the perfect gravity. Turn you're going to get within about 20 to 30% of the best one just by guessing, as long as you keep your rocket stable and don't, have it spinning out of control that's where the major losses are going to happen concentrate instead on building, aerodynamic Rock rockets and making. Sure that they are actually flying in a straight line.

And then of course, try to figure out how to bring them safely back to the surface through the heating effects of the atmosphere until then I'm Scott Manley fly safe.