Could someone address succinctly the issue of why (modern) guidance algorithms can't handle wind shear?It can't really be a structural issue, can it? Just keep the pointy end into the (local relative) wind!?
F9v1.1 and FT have a very high fineness ratio. So this vehicle may be more susceptible to structural wind shear effects compared to others.
Quote from: deruch on 03/02/2016 12:47 amF9v1.1 and FT have a very high fineness ratio. So this vehicle may be more susceptible to structural wind shear effects compared to others.Can you explain? I understand fineness when applied to an airplane, but a rocket is... a cylinder, how can the fineness ratio be so different compared to Falcon 9 v 1.0 or to the ULA rocket?
And is this because the SpaceX company transports rockets by truck instead of ${EXPENSIVE_TRANSPORT} so they have diameter limitation? Or because the higher fineness ratio has intrinsic performance advantages?
I'm struggling to understand the logic that says a multiple day delay is worth it for such a low probability of success for booster recovery. Unless that isn't what's driving the decision here.
Quote from: WHAP on 03/02/2016 02:36 am I'm struggling to understand the logic that says a multiple day delay is worth it for such a low probability of success for booster recovery. Unless that isn't what's driving the decision here.It has nothing to do with booster recovery. It has everything to do with not breaking the vehicle as it flies through high wind shear. Upper level winds are forecast to be too high for the vehicle structure to handle until Friday. And they must have enough confidence in the forecast not to want to waste time and effort on an earlier attempt that would likely scrub.As others have pointed out, F9 has a high fineness ratio compared to other LV's, and so may be more stressed by Q-alpha loading than some of the vehicles you've launched, and thus require a bit more patience for better wind conditions.
Quote from: sdsds on 03/01/2016 09:18 pmCould someone address succinctly the issue of why (modern) guidance algorithms can't handle wind shear?It can't really be a structural issue, can it? Just keep the pointy end into the (local relative) wind!?I don't know this subject well enough to be succint, but here it goes:Strong variations in winds cause turbulence. Most turbulence experienced at high altitude is either caused by this wind shear Musk refers to, mountain wave turbulence (rotors created downwind of mountains) and convective activity (flying above CB/TS clouds). That critical altitude (32000ft) all of us have flown through with turbofan airliners.
Most recent scrub due to high-altitude winds was, I believe, SMAP on the Delta II (another rather spindly rocket): http://spacecoastdaily.com/2015/01/upper-level-wind-shear-scrubs-smap-launch/So yes, it happens on occasion, just another weather constraint to take into account.
Quote from: Kabloona on 03/02/2016 03:01 amQuote from: WHAP on 03/02/2016 02:36 am I'm struggling to understand the logic that says a multiple day delay is worth it for such a low probability of success for booster recovery. Unless that isn't what's driving the decision here.It has nothing to do with booster recovery. It has everything to do with not breaking the vehicle as it flies through high wind shear. Upper level winds are forecast to be too high for the vehicle structure to handle until Friday. And they must have enough confidence in the forecast not to want to waste time and effort on an earlier attempt that would likely scrub.As others have pointed out, F9 has a high fineness ratio compared to other LV's, and so may be more stressed by Q-alpha loading than some of the vehicles you've launched, and thus require a bit more patience for better wind conditions.Anecdote: In 2005, a long time friend and senior NASA guy at JSC (who shall remain nameless) took me aside at an AIAA conference and said "...von Braun used to say to me – never build a rocket with a fineness ratio greater than 10!"At the time, he was criticizing Ares I, but the words apply to the current F9, too. And to the old Titan IV, which would occasionally have to wait on the pad at WTR waiting for a break in the high altitude wind shear to be able to fly safely.
Quote from: WHAP on 03/02/2016 02:36 amI'm struggling to understand the logic that says a multiple day delay is worth it for such a low probability of success for booster recovery. Unless that isn't what's driving the decision here.It has nothing to do with booster recovery. It has everything to do with not breaking the vehicle as it flies through high wind shear. Upper level winds are forecast to be too high for the vehicle structure to handle until Friday. And they must have enough confidence in the forecast not to want to waste time and effort on an earlier attempt that would likely scrub.
Quote from: HMXHMX on 03/02/2016 03:30 amQuote from: Kabloona on 03/02/2016 03:01 amQuote from: WHAP on 03/02/2016 02:36 am I'm struggling to understand the logic that says a multiple day delay is worth it for such a low probability of success for booster recovery. Unless that isn't what's driving the decision here.It has nothing to do with booster recovery. It has everything to do with not breaking the vehicle as it flies through high wind shear. Upper level winds are forecast to be too high for the vehicle structure to handle until Friday. And they must have enough confidence in the forecast not to want to waste time and effort on an earlier attempt that would likely scrub.As others have pointed out, F9 has a high fineness ratio compared to other LV's, and so may be more stressed by Q-alpha loading than some of the vehicles you've launched, and thus require a bit more patience for better wind conditions.Anecdote: In 2005, a long time friend and senior NASA guy at JSC (who shall remain nameless) took me aside at an AIAA conference and said "...von Braun used to say to me – never build a rocket with a fineness ratio greater than 10!"At the time, he was criticizing Ares I, but the words apply to the current F9, too. And to the old Titan IV, which would occasionally have to wait on the pad at WTR waiting for a break in the high altitude wind shear to be able to fly safely.Both Atlas V and Delta IV also have fineness ratios greater than 10. Without knowing von Braun's age at the time of the statements, I hesitate to invoke a bastardized form of Clarke's first law, but, while the challenges and hazards of successfully building/launching rockets with fineness ratios greater than 10 are undoubtedly the same as they were in his day, great improvements since then in materials science, fabrication methods, computer modeling, and raw computing power for guidance have likely done much to reduce or eliminate them. This is not to say that it's easy/simple to do it today, only that some of the foundations upon which von Braun's concerns were built should be less formidable obstacles to today's rocket designers/engineers.
Quote from: Kabloona on 03/02/2016 03:01 amQuote from: WHAP on 03/02/2016 02:36 amI'm struggling to understand the logic that says a multiple day delay is worth it for such a low probability of success for booster recovery. Unless that isn't what's driving the decision here.It has nothing to do with booster recovery. It has everything to do with not breaking the vehicle as it flies through high wind shear. Upper level winds are forecast to be too high for the vehicle structure to handle until Friday. And they must have enough confidence in the forecast not to want to waste time and effort on an earlier attempt that would likely scrub.I never suggested that SpaceX should launch if the conditions exceeded the capability of the vehicle. I questioned SpaceX's rationale for not making an attempt.Subsequent posts provided supporting evidence for my argument. The examples given were vehicles that tried to launch on a given day - including Falcon 9. They didn't use forecasts, they used actual data on launch day to determine if they could meet their criteria.