Quote from: CuddlyRocket on 12/31/2015 02:43 amQuote from: Lee Jay on 12/30/2015 11:21 pmQuote from: macpacheco on 12/30/2015 11:19 pmThe stage isn't an airfoil. In fact its the opposite. A round shape does the best job of allowing the wind to flow around the object while generating as little reaction force to wind flow as possible.Not much could be further from the truth.A cylinder like that has a drag coefficient of around 1.2!Ever seen this drawing? This is to scale and both have about the same drag.That's only true for the wind direction indicated. If the wind was 90 degrees to that, the results would be different! Real winds come from all directions and a cylinder is symmetric.Symmetric and very, very draggy.
Quote from: Lee Jay on 12/30/2015 11:21 pmQuote from: macpacheco on 12/30/2015 11:19 pmThe stage isn't an airfoil. In fact its the opposite. A round shape does the best job of allowing the wind to flow around the object while generating as little reaction force to wind flow as possible.Not much could be further from the truth.A cylinder like that has a drag coefficient of around 1.2!Ever seen this drawing? This is to scale and both have about the same drag.That's only true for the wind direction indicated. If the wind was 90 degrees to that, the results would be different! Real winds come from all directions and a cylinder is symmetric.
Quote from: macpacheco on 12/30/2015 11:19 pmThe stage isn't an airfoil. In fact its the opposite. A round shape does the best job of allowing the wind to flow around the object while generating as little reaction force to wind flow as possible.Not much could be further from the truth.A cylinder like that has a drag coefficient of around 1.2!Ever seen this drawing? This is to scale and both have about the same drag.
The stage isn't an airfoil. In fact its the opposite. A round shape does the best job of allowing the wind to flow around the object while generating as little reaction force to wind flow as possible.
Quote from: Rocket Science on 12/30/2015 10:13 pmQuote from: macpacheco on 12/30/2015 07:22 amWhat's the launch wind criteria ?50mph (44 knots / 81 km/h) is a LOT of wind. Ultra rare having even 40 mph winds.Even for ASDS 44 knot wind is a substantial margin.Launch: <20Landing: <50I've asked Chris if he could verify the landing number (we need gust limit as well).That 50mph seems huge in terms of landing controlabity... If true, very impressive... IMO.The stage isn't an airfoil. In fact its the opposite. A round shape does the best job of allowing the wind to flow around the object while generating as little reaction force to wind flow as possible.And the real concern isn't controllability while in flight, but the period between the last second or two before touchdown until a few seconds after, aka the landing flare, and toppling risk (which can't happen while in flight). (Not a rocket engineer, but as a hobbie cat sailor, skydiver and private pilot I know a thing or two about the wind).
Quote from: macpacheco on 12/30/2015 07:22 amWhat's the launch wind criteria ?50mph (44 knots / 81 km/h) is a LOT of wind. Ultra rare having even 40 mph winds.Even for ASDS 44 knot wind is a substantial margin.Launch: <20Landing: <50I've asked Chris if he could verify the landing number (we need gust limit as well).That 50mph seems huge in terms of landing controlabity... If true, very impressive... IMO.
What's the launch wind criteria ?50mph (44 knots / 81 km/h) is a LOT of wind. Ultra rare having even 40 mph winds.Even for ASDS 44 knot wind is a substantial margin.
Hi!I signed up to learn what is the influence of side wind on a rocket in the last seconds of landing. I thought it might be a problem, considering relatively big side surface of the rocket, high air pressure at the sea level or sudden changes in wind speed. Is there a wind speed at which rocket landing is impossible or extremely risky?
So what the heck is the point of your argument? That a stage should have a wing cross section, and rotate quickly to face whatever gusts happen?? C'mon.
Landing Weather Looks good
Up thread it clearly says that the LANDING criteria is <20 knots (this information from SpaceX). Then someone suggests without anything to back them up that it is 50mph and all of a sudden everybody takes this as gospel.>
The complicating issue to that is the desire to have as close to zero horizontal velocity as possible. So there has to be some tradeoff, either accept a bit of horizontal drift due to wind when it gets vertical for touchdown, or keep it tilted a little bit into the wind for zero horizontal drift, so the structure can handle the fact that one or two legs will touch down before the other legs and there will be some acceptable degree of settling-in rocking.
Quote from: mrhuggy on 12/21/2015 10:00 pmLanding Weather Looks goodSee the post above for the SpaceX's "Landing Commit Criteria" in ORBCOMM-2 update thread. It clearly shows that that wind speed limit for landing is 50mph.It is funny but another screen capture here:http://forum.nasaspaceflight.com/index.php?topic=37739.msg1395299#msg1395299entitled: "Launch Commit Criteria" shows item no. 3 - first stage landing (<10ft waves <20 kt winds).It seems to me that the <10ft waves <20 kt winds criteria refer to landing on an ASDS (barging) and <50 mph winds to RTLS type landing. Any better explanation for this discrepancy? It looks like they can tolerate higher winds due to a much bigger landing pad in LZ-1.
It looks like they can tolerate higher winds due to a much bigger landing pad in LZ-1.
Quote from: tleski on 01/04/2016 02:51 amIt looks like they can tolerate higher winds due to a much bigger landing pad in LZ-1.Or because the landing pad itself isn't moving around, no matter how fast the wind.The tighter limits on ASDS landing may be due to the limits of ASDS itself being able to stay stationary and level.
I think it's fairly certain that the latest success is largely due to the landing pad not moving around.
Quote from: CameronD on 01/07/2016 12:37 amI think it's fairly certain that the latest success is largely due to the landing pad not moving around.?A corollary would be that the failures occurred because the barge was moving...And since the corollary is false, then I think the original statement is not very certain...
Quote from: meekGee on 01/07/2016 12:52 amQuote from: CameronD on 01/07/2016 12:37 amI think it's fairly certain that the latest success is largely due to the landing pad not moving around.?A corollary would be that the failures occurred because the barge was moving...And since the corollary is false, then I think the original statement is not very certain...The previous failures occurred for many reasons (perhaps even some we aren't privy to), only one of which being that, during the last attempt, the platform was moving (rocking).. but I guess we have only to wait for the Jason-3 launch to know if SpX can overcome the effect of this in practice.I know from many years of personal experience working with and around floating platforms of all kinds that it's a tough ask, but looking at what they've been able to achieve thus far, if it can be done at all, SpX will do it.
Quote from: CameronD on 01/07/2016 01:10 amQuote from: meekGee on 01/07/2016 12:52 amQuote from: CameronD on 01/07/2016 12:37 amI think it's fairly certain that the latest success is largely due to the landing pad not moving around.?A corollary would be that the failures occurred because the barge was moving...And since the corollary is false, then I think the original statement is not very certain...The previous failures occurred for many reasons (perhaps even some we aren't privy to), only one of which being that, during the last attempt, the platform was moving (rocking).. but I guess we have only to wait for the Jason-3 launch to know if SpX can overcome the effect of this in practice.I know from many years of personal experience working with and around floating platforms of all kinds that it's a tough ask, but looking at what they've been able to achieve thus far, if it can be done at all, SpX will do it. I think that's a stretch... Like an aircraft coming in to land without hydraulic fluid and crashing because of a wind gust.(Some may recognize the aviation scenario)So yeah, the wind gust was a contributing factor, but to claim that it is "certain that it was the lack of wind gusts that made a subsequent landing possible"... Meh. It was the presence of hydraulic fluid....