HOME | DD

Eagle1Division In reply to Jerzy232 [2011-08-16 03:06:43 +0000 UTC]

Lol. It gets a lot worse!
And you can skip the math if you want...
But did you get it?

I need to learn how to do animated images, and make one about this. I think that would help a lot

👍: 0 ⏩: 1

Jerzy232 In reply to Eagle1Division [2011-08-16 06:44:37 +0000 UTC]

I got it, because I play Orbiter. But its complicated. Explains the world in numbers xD

👍: 0 ⏩: 1

Eagle1Division In reply to Jerzy232 [2011-08-17 00:12:32 +0000 UTC]

You play orbiter and you consider it complicated?

👍: 0 ⏩: 1

Jerzy232 In reply to Eagle1Division [2011-08-19 08:22:58 +0000 UTC]

Yeah, I like it since some addon makers stopped thinking "let's enhance game realism and fly to the Moon in a red square..." and made things like Arrow Freighter or Ravenstar...

I can't do maths at all.
At all.
I just... fly Orbiter. And I have success.

👍: 0 ⏩: 1

Eagle1Division In reply to Jerzy232 [2011-08-20 03:19:18 +0000 UTC]

Lol, yeah, I've been working on it for a long time, without much success. But still there's some, however slowly it comes: [link]

I know the mathematical basis, equations for orbital velocity, gravity, escape velocity, Delta-Vee for hohmann transfers... But still just a little too little to do anything really extreme like interplanetary transfer, TLI, or atmospheric ascent profile. I can get a pretty close estimate on a lot of things, but my speed at my lunar approach was ~2,700 m/s, and I calculated it at around ~2,500 m/s :/

It's annoying. I know almost enough but not quiet enough to make a spaceship...

I wouldn't call the Arrow or Ravenstar realistic (at least not in terms of engine performance...) If you want realism then try Project Gemini, the Dragonfly (which doesn't work on my Orbiter ) or Apollo
But they (Ravenstar, Arrow Freighter) do have a lot of depth, and are very well made.

Have you heard of Atomic Rockets/Project Rho?

👍: 0 ⏩: 1

Jerzy232 In reply to Eagle1Division [2011-08-20 07:18:23 +0000 UTC]

Well, that's exactly why I recalled Arrow and XR-2 - they put too much realism to Orbiter, so you can fly to the Moon in a red square. Thanks to Arrow and XR-2, that is not necessary, and we have some nice ships.

But these are space planes. It is realistic, isn't it? I thought it's better to use such than rockets...

👍: 0 ⏩: 2

Eagle1Division In reply to Jerzy232 [2011-08-23 03:12:23 +0000 UTC]

I should do the next tutorial on introduction to rocket science, instead of orbits . I could alternate in-between the two subjects

You just got the crash course though. That skimmed over the basics and shot straight for the complex stuff, like waste heat and kinetic energy

👍: 0 ⏩: 1

Jerzy232 In reply to Eagle1Division [2011-08-23 04:05:52 +0000 UTC]

Heat. You should make a reentry tutorial. That would be really useful |D

👍: 0 ⏩: 2

Eagle1Division In reply to Jerzy232 [2011-08-23 05:17:11 +0000 UTC]

Actually, now that you mention it, I haven't. I should make a playback with those, with the things I mentioned

👍: 0 ⏩: 1

Jerzy232 In reply to Eagle1Division [2011-08-30 10:34:05 +0000 UTC]

XD

👍: 0 ⏩: 0

Eagle1Division In reply to Jerzy232 [2011-08-23 05:11:45 +0000 UTC]

LOL! I have!

Requires:
XR-2 Ravenstar (I used 1.2, I only hope later versions will work )
Shuttle Fleet 4.5 (4.7 may work, I don't know on that one. But GPC MFD mode OPS 3 has to work for the XR2, and I know in 4.5 OPS1 works for any vehicle but in 4.7 OPS1 only works for the shuttle )

Argh. I wish I could rewrite that readme. I should've mentioned it's a "pack" of 7 scenarios, each during a different phase of re-entry. You can play the last and just land, or start from the beginning and go from first re-entry to wheelstop.
[link]

It's strictly re-entry. No de-orbit burn . To do those, just do a burn to get your periapsis ~57km somewhere over the western U.S. to land at the KSC. Once you get around 100 km altitude, use Surface MFD and OPS 3 to guide in. If you don't see yourself on the OPS 3 and it's on trajectory 1, then try to use lift to hold altitude, you're too far out. This is usually what happens.

(I get my periapsis over the west coast, and I almost always end up having to hold my altitude at ~100 km for about 1/3rd of the entire pacific, which means I re-enter too far from Kennedy, so putting your periapsis at about the midwest USA should be right.)

Tell me how it goes

Oh, and one thing I forgot to mention is that as you get close to the KSC, the aerodynamics seem to try to suck your nose down to level horizon, and will do so if you drop below 25* AoA. It's not much of an issue, since you're already mostly done with re-entry, but if you want to fly it like the shuttle then make sure not to drop below 25* AoA until you're ready to glide in on OPS 4.

👍: 0 ⏩: 0

Eagle1Division In reply to Jerzy232 [2011-08-23 03:10:56 +0000 UTC]

Yeah, in reality space planes are a lot more complicated, though, esp. in terms of controlling them. And any vehicle that reaches orbital velocity will have to have many times it's own mass in fuel in order to do so.
The Rocket Equation:
Dv = Ve * ln[R]

Dv is the Delta-Vee of a rocket, the total speed it's capable of.
Ve is the exhaust velocity of the rocket engine.
R is the mass ratio, Mass of the vehicle fully fueled divided by the mass of the vehicle with an empty fuel tank.

To reach orbit, you'll need ~7,800 m/s, an extra ~3,000 m/s to overcome gravity during the run to orbit, and ~300 m/s for atmospheric drag, for a total Delta-Vee of about 11,000 m/s. It's ballpark, since different vehicles with different stage arrangements, thrusts, ascent profiles, etc. will change it a good deal, but ~11 km/s is normal, I'll guess about 9 km/s is the lowest it'll go. (~1,000 m/s to overcome gravity if you accelerate 3x as fast.)

So that's your Delta-Vee. Now Exhaust velocity. The most fuel-efficient, high-thrust rocket engines that exist will give you ~4,400 m/s. (I say high-thrust, because Ion engines and VASIMR will give you up to ~200,000, but they don't have enough thrust to lift themselves, nevermind themselves and a vehicle, so for now we're focusing on chemical rocket engines).
These efficient rockets will use LOX/LH2. A better choice might be LOX/RP-1, which is liquid oxygen (LOX) and Rocket-Propellant 1, which is just kerosene. It will give a Ve in the range of ~2,650 m/s to ~3,200 m/s, but the fuel is more dense and easier to work with than LH2 (Liquid Hydrogen), so it's much easier to get a higher mass ratio.

Now, to find the mass ratio:
Dv = Ve * ln[R]

R = e^(Dv/Ve)

Using the real, above numbers, you'll find that no rocket can reach orbit with anything less than about ten times it's own weight in fuel. That's just the basic math. The space shuttle uses solid rocket boosters in order to get the tremendous amount of thrust needed to climb right at first, solid rockets only have a Ve around ~2,600 m/s, so it has a mass ratio ~16. And as you make the fuel tanks larger, they also get more massive, so there's an engineering limit to what mass ratio you can get, and the best rocket engines give a limited Ve, so actually, we end up losing the rocket equation and it's impossible to reach orbital speed. BUT, if you make the fuel tank two parts, and once one part is empty, you drop it to get rid of dead weight, then it's possible. This is staging, you essentially throw away half a rocket every time, but orbit has never been reached without it. For example, the shuttle's reusable, but it jettisons the SRB's, and the External tank goes to waste every time.

Going to orbit without using staging, like those spaceplanes, is called SSTO, Single-Stage-To-Orbit. Many think it would completely revolutionize spaceflight, to the point where it's cost would be in the range of airline flight. I don't think so, but I do think it would drastically change everything, in that direction.

The biggest, most exciting SSTO project was the Venture Star. But Congress couldn't spare a few billion of it's many thousands to revolutionize the world, so it got cancelled because some of the engineers gave up . [link]


In other words... They don't have enough fuel . I guess just saying that would be much simpler than that huge explanation, but if you're anything like me you wouldn't mind

And any futuristic engine that does have high enough Specific Impulse (Specific Impulse is another way to express Ve. Except it's measured in seconds, in G's. So 1 ISP = 9.8 m/s, or 32 ft/s.), and enough thrust to lift the spaceship, will produce a tremendous amount of waste heat. This is because rockets work by kinetic energy, KE = 1/2mv^2, to double the speed, you have to quadruple the energy. This is fine when there's only a few million atoms at a time for an extremely low-thrust engine, but when you need enough atoms, enough mass being thrown out the back, to produce enough thrust to fight gravity, the kinetic energy requirements are absolutely perposterously enormous. It's extremely difficult to imagine a design that wouldn't vaporize the rocket with waste heat.

Not that it's impossible. It's just I'd expect very large fuel tanks, and some major technology to address the heating issue. Not to mention starting, thrusting, or cutting off an engine that advanced would be far, far more complicated than it's depicted .

👍: 0 ⏩: 0