A long enough reentry burn is the same as a reentry burn... There's not a sharp line, there.
Great vid! The only minor critique I have is that we're pretty sure that there wasn't a boost-back, just re-entry and landing burns. So, if I was making this video (I'm in no way skilled enough to make one anywhere near as good as your is though), I don't think I would show one even in animation. But this is a fairly minor technical point. Great job!
Quote from: deruch on 07/28/2014 01:06 amGreat vid! The only minor critique I have is that we're pretty sure that there wasn't a boost-back, just re-entry and landing burns. So, if I was making this video (I'm in no way skilled enough to make one anywhere near as good as your is though), I don't think I would show one even in animation. But this is a fairly minor technical point. Great job!Thanks Deruch I also though about that... as well as the animation of the rocket descending and legs opening while still at quite an altitude - when it seems that the actual attempts have opened much lower(?). I think reusability plans have evolved in the last 2 years (the animation still has the square layout of engines too).I wasn't trying to emulate the 2 'land'ings so much as give a good story of the overall process we're seeing developed. It was partly a "side by side" of the 2 successful attempts, and partly an upgrade to the animation via as much real footage as possible - because both of the supplied videos have weaknesses. They're not clear, and too easy for the casual viewer to misinterpret the landing videos as having the engines ignite only at the last second. In the side-by-side I wanted to show the common leg movements, matching flames, and the similar flame activity in the F9R when near real ground (with a linking wide shot for some perspective). But yeah... the purist in me wants to keep it entirely consistent with the OG2!
Anyone know if they are going to do a hover / translation on any of the upcoming flights. (ie, hover then start translating towards the coast.) It seems like that would be a logical step in the test plan. I suppose they would have to do something like this prior to coming onshore to land at the Cape since a boost IIP on the land would be scary. It would be really cool to see!
Quote from: guidanceisgo on 07/28/2014 05:15 amAnyone know if they are going to do a hover / translation on any of the upcoming flights. (ie, hover then start translating towards the coast.) It seems like that would be a logical step in the test plan. I suppose they would have to do something like this prior to coming onshore to land at the Cape since a boost IIP on the land would be scary. It would be really cool to see!I agree it would be cool to see, but hover isn't going to happen on any real flight, because to do that they would have to have enough fuel left over in the rocket to where the T/W ratio is one or less when throttled down to 60%. The only reason the Grasshopper and F9R-Dev1 rockets have been able to hover is because they are ballasted with much more fuel than would be present on a real return from launch.Translation may occur, to a small extent, during the landing burn. Grid fins should have the effect of minimizing this.
I disagree. I thought that was why they were choosing a pad next to the ocean- the return will target a patch of water 200-400 meters offshore and the rocket will use the landing burn to translate to the pad.Otherwise they risk damage to the pad. Bare concrete pads still cost a significant amount of money.
unless Mueller and his staff manage pull a rabbit out of a hat and suddenly discover how to get a Merlin 1D to throttle down more than 50%.Yet another rabbit, that is.
Wasn't that confirmed already at some point? I distinctly remember a quote from Musk about the surprisingly large throttle range of the Merlin 1D (anyone here who can dig it up?).
Quote from: Elmar Moelzer on 07/28/2014 03:09 pmWasn't that confirmed already at some point? I distinctly remember a quote from Musk about the surprisingly large throttle range of the Merlin 1D (anyone here who can dig it up?).If I recall correctly, it was a twitter quote that was much debated. IIRC he said "60% throttle" or some such, and readers were sharply divided over whether he meant "throttle down 60%" (aka, total thrust 40% of maximum) -- which would be surprising -- or "total thrust of 60% of maximum", which would be less surprising.Evidence since then has not supported the surprising interpretation.
What would be acceptable vertical velocity limits for "hovering"? 0 +/- 5 m/s? Can the stage do that by pulsing the engines, or even by slewing the throttle up and down constantly? If the response time of the engine, and the rates are fast enough, then you wouldn't need the T/W to be ~= 1 at all. (Although, obviously that does help). Basically, can they playing a game of flappy bird, with a Falcon?
Quote from: AJA on 07/31/2014 07:49 pmWhat would be acceptable vertical velocity limits for "hovering"? 0 +/- 5 m/s? Can the stage do that by pulsing the engines, or even by slewing the throttle up and down constantly? If the response time of the engine, and the rates are fast enough, then you wouldn't need the T/W to be ~= 1 at all. (Although, obviously that does help). Basically, can they playing a game of flappy bird, with a Falcon?No, because of instabilities with the prop in the engine. Basically the same reason they can't throttle down beyond a certain point- because the propellant has to mix and combust at a certain rate and if it doesn't you might get too little combustion for a brief moment, then a spike in pressure as the buildup of uncombusted, poorly mixed propellant finally combusts. And there goes your engine.I think the dracos can pulse because their fuel is hypergolic.
I think the dracos can pulse because their fuel is hypergolic.