dbartos píše:... jsem nalezl tyto stránky:
http://www.flightclub.io/results.php?id ... &code=OG22
Když se na to kouknete, uvidíte úžasné grafy zaznamenávající různé hodnoty při letu, a to jak u boosteru tak u horního stupně. Obzvlášť mě zaujal ten graf, který ukazuje hodnoty aerodynamického tlaku. Chápu to dobře, že aerodynamické namáhání bylo mnohem větší těsně před brzdícím zážehem než při oddělení boosteru od horního stupně?
1) FlightClub stránky se mi taky moc líbí, ale je třeba je brát s rezervou. Jejich tvůrce Declan Murphy je sice velmi šikovný fyzik a programátor, nicméně v tomto simulátoru vidíme pouze jeho nejlepší odhady, vycházející z veřejně dostupných dat o daném letu. Nejsou to "tvrdá data" od SpaceX.
2) Pro správné pochopení grafu Aerodynamic pressure je třeba se podívat také na graf Booster velocity. Pak je zřejmé, že k nejvyššímu aerodynamickému namáhání při návratu dochází někdy v T +550 s, což je okamžik, kdy začíná poslední brzdicí/přistávací zážeh.
Jak jsem psal, je třeba brát tyto hezké grafy s rezervou... sám autor mi o nich napsal toto:
Q1 : I'm wondering what's your data source for each Falcon flight. Do you have some direct source from SpaceX or you mostly calculate values from publicly known flight parameters/flight videos?
A1 : My data source is mostly my own head actually
The publicly known flight parameters are a huge help, but they rarely paint a full picture - usually you can get MECO and second stage ignition from the webcasts, but that's about it. Most missions will publish the target orbit and the payload mass, which is another huge help. After that it's trial and error - I have faith the FlightClub is an accurate physics engine which will realistically do what the user tells it to do.
Some missions have a very public flight profile for whatever reason (Chris B from NasaSpaceFlight forums did a very detailed summary of the booster stage landing burns for CRS-6) - this is great because the landing burns seem to all follow roughly the same pattern, so this gives a nice template.
I imagine you were hoping for a better answer with some hard sources - but when it boils down to it, SpaceX mission profiles are a trade secret that they don't want publicly known. What you see on FlightClub is just a best guess.
Q2 : ... I'd really like to know how did you come to some values like retro burns fuel quantities or down range by boost stage, etc.
A2 : All trial and error. I built the physics engine myself (that was the easy part. Found NASA data for atmospheric modelling). Then spaceflight101 had a great resource for the vehicle properties like dry mass, fuel mass, thrust, Isp, etc. Then we get target orbits and inclinations, so I know where I need to end up. Then we get hazard maps before each flight so I know how much the first stage needs to pitch at the start of the launch.
Then the rest is trial and error. Too far downrange? Do a longer boostback. Aerodynamic pressure too high on reentry? Start the entry burn sooner. Hitting the water too fast? Longer entry/landing burns. Orbit too eccentric? Insert some guidance sooner in the second stage flight.
And so on and so forth. When I say "best guess" what I really mean is "best very educated guess with each number having a specific purpose". I would like to be able to build a complete solver that would do all of this for me - maybe a genetic algorithm or something to find the most efficient path. But not yet.
