Hi! You're both right. There are 45 possible pairs of engines. There are 72 possible ways in which to choose one engine, and then choose another engine.
Quote from: happyflower on 10/08/2012 07:27 pmHow can an engine "explode" and yet still send telemetry to SpaceX? Electronics is placed (due to the high sensitivity of components [mechanical, dirt, water, ...]) into very rigid housings. I guess, that the nozzles of the neighbouring have a higher risk to be damaged by an explosion (if it was one). Also due to vibrations the pcb is typically mechanically seperated by vibration dampers (can be even some special type of foam).If I could ask a question, it would be, what "telemetry was received" means exactly. Where all sensors/actors responding? It might be, that just the engine control computer responded to the guidance computer, but most of the s/a where damaged, not responding or responding of scale.
How can an engine "explode" and yet still send telemetry to SpaceX?
Am I late with this? - http://www.spacex.com/press.php?page=20121008"Approximately one minute and 19 seconds into last night's launch, the Falcon 9 rocket detected an anomaly on one first stage engine. Initial data suggests that one of the rocket's nine Merlin engines, Engine 1, lost pressure suddenly and an engine shutdown command was issued. We know the engine did not explode, because we continued to receive data from it. Panels designed to relieve pressure within the engine bay were ejected to protect the stage and other engines. Our review of flight data indicates that neither the rocket stage nor any of the other eight engines were negatively affected by this event."
Quote from: edkyle99 on 10/08/2012 07:41 pmQuote from: Joel on 10/08/2012 07:30 pmQuote from: ugordan on 10/08/2012 07:26 pmQuote from: Joel on 10/08/2012 07:24 pmJust for my understanding. Does 30 seconds of extra burn roughly equate to 30 seconds of extra gravity losses, or around 300 m/s lost delta-v?Only if you're flying straight up. It's less of an issue if your velocity vector is more toward horizontal. Well... divided by the square root of two if horizontal... But we are still talking about between 200 and 300 m/s lost delta-v?What matters is how much extra time was spent flying up the vertical portion of the ascent vector. The majority of the extra seconds of flight in this case were likely spent flying horizontally in space, during the second stage portion of the ascent. Gravity losses in horizontal flight at orbital altitude are near-zero. Some pitch up gravity losses likely did occur, but I wouldn't as much as expect 200 m/s. - Ed KyleBut remember, that's 200m/s (or 50m/s, whathaveyou) pushing a full Dragon, etc... If the second stage was just pushing the Orbcomm bird, that 50m/s could be much more, perhaps even that whole 100-150m/s needed to push Orbcomm to the desired orbit plus margin.
Quote from: Joel on 10/08/2012 07:30 pmQuote from: ugordan on 10/08/2012 07:26 pmQuote from: Joel on 10/08/2012 07:24 pmJust for my understanding. Does 30 seconds of extra burn roughly equate to 30 seconds of extra gravity losses, or around 300 m/s lost delta-v?Only if you're flying straight up. It's less of an issue if your velocity vector is more toward horizontal. Well... divided by the square root of two if horizontal... But we are still talking about between 200 and 300 m/s lost delta-v?What matters is how much extra time was spent flying up the vertical portion of the ascent vector. The majority of the extra seconds of flight in this case were likely spent flying horizontally in space, during the second stage portion of the ascent. Gravity losses in horizontal flight at orbital altitude are near-zero. Some pitch up gravity losses likely did occur, but I wouldn't as much as expect 200 m/s. - Ed Kyle
Quote from: ugordan on 10/08/2012 07:26 pmQuote from: Joel on 10/08/2012 07:24 pmJust for my understanding. Does 30 seconds of extra burn roughly equate to 30 seconds of extra gravity losses, or around 300 m/s lost delta-v?Only if you're flying straight up. It's less of an issue if your velocity vector is more toward horizontal. Well... divided by the square root of two if horizontal... But we are still talking about between 200 and 300 m/s lost delta-v?
Quote from: Joel on 10/08/2012 07:24 pmJust for my understanding. Does 30 seconds of extra burn roughly equate to 30 seconds of extra gravity losses, or around 300 m/s lost delta-v?Only if you're flying straight up. It's less of an issue if your velocity vector is more toward horizontal.
Just for my understanding. Does 30 seconds of extra burn roughly equate to 30 seconds of extra gravity losses, or around 300 m/s lost delta-v?
Rocket pressure vessels don't develop nice, smooth, symmetrical holes in them, unless some sort of port or fitting that's part of the existing design comes loose. They crack, which creates stress concentrations, which open the cracks quite quickly. EPR and explosion, especially when heat + oxidizer without fuel yields burning metal, are essentially the same.Oh, and the post about dumping fuel inside the stage during shutdown?? If that were the design, how would that work during static fire or an on-pad abort?
Rocket pressure vessels don't develop nice, smooth, symmetrical holes in them, unless some sort of port or fitting that's part of the existing design comes loose. They crack, which creates stress concentrations, which open the cracks quite quickly. EPR and explosion, especially when heat + oxidizer without fuel yields burning metal, are essentially the same.
Oh, and the post about dumping fuel inside the stage during shutdown?? If that were the design, how would that work during static fire or an on-pad abort?
Quote from: Robotbeat on 10/08/2012 07:53 pmQuote from: edkyle99 on 10/08/2012 07:41 pmQuote from: Joel on 10/08/2012 07:30 pmQuote from: ugordan on 10/08/2012 07:26 pmQuote from: Joel on 10/08/2012 07:24 pmJust for my understanding. Does 30 seconds of extra burn roughly equate to 30 seconds of extra gravity losses, or around 300 m/s lost delta-v?Only if you're flying straight up. It's less of an issue if your velocity vector is more toward horizontal. Well... divided by the square root of two if horizontal... But we are still talking about between 200 and 300 m/s lost delta-v?What matters is how much extra time was spent flying up the vertical portion of the ascent vector. The majority of the extra seconds of flight in this case were likely spent flying horizontally in space, during the second stage portion of the ascent. Gravity losses in horizontal flight at orbital altitude are near-zero. Some pitch up gravity losses likely did occur, but I wouldn't as much as expect 200 m/s. - Ed KyleBut remember, that's 200m/s (or 50m/s, whathaveyou) pushing a full Dragon, etc... If the second stage was just pushing the Orbcomm bird, that 50m/s could be much more, perhaps even that whole 100-150m/s needed to push Orbcomm to the desired orbit plus margin.Right. I forgot the changing mass. It all starts to make sense now. The engine out could have eaten up the whole second burn.
http://www.spacex.com/press.php?page=20121008On net I give this release 7 out of 10 possible stars. Because it is essentially complete it gets a base score of 5 stars. It gets 1 bonus point for timeliness. It gets 3 bonus points for the sentence, "We will continue to review all flight data in order to understand the cause of the anomaly, and will devote the resources necessary to identify the problem and apply those lessons to future flights." It loses 1 point for each of the sentences, "It is worth noting that Falcon 9 shuts down two of its engines to limit acceleration to 5 g's even on a fully nominal flight. The rocket could therefore have lost another engine and still completed its mission." 5+1+3-1-1=7.
Why does it lose a point for those? It's technically correct, isn't it?
Quote from: Robotbeat on 10/08/2012 08:31 pmWhy does it lose a point for those? It's technically correct, isn't it?Perhaps. But the first sentence is purely marketing spin; the second involves a hypothetical scenario which did not take place on this mission. "It's worth noting the glacier freezer could have delivered Ben and Jerry's. In which case we would have sent them "Coffee Coffee Buzz Buzz Buzz" flavor.
Quote from: mduncan36 on 10/08/2012 07:37 pmAm I late with this? - http://www.spacex.com/press.php?page=20121008"Panels designed to relieve pressure within the engine bay were ejected to protect the stage and other engines. "Oh, that's interesting. Are they saying that the deliberate ejection of panels is somehow part of their engine protection scheme? I'm having a hard time visualizing how that would work.
Am I late with this? - http://www.spacex.com/press.php?page=20121008"Panels designed to relieve pressure within the engine bay were ejected to protect the stage and other engines. "