Quote from: LouScheffer on 05/01/2017 11:50 am Terminal velocity looked like about 300 m/s. This is about as expected from something of that size, shape, and mass.Interesting. That terminal velocity is 2x the 150 m/sec terminal velocity observed on the first F9 landing at the Cape. F9 has bulked up since then...http://forum.nasaspaceflight.com/index.php?topic=39100.msg1465116#msg1465116
Terminal velocity looked like about 300 m/s. This is about as expected from something of that size, shape, and mass.
Quote from: Oersted on 05/01/2017 01:13 pmQuote from: Phil Stooke on 05/01/2017 01:05 pm"...the execution of 100s of people at SpaceX "I had heard that this approach was used in North Korea to encourage hard work among the survivors, but I didn't expect it to be used in the USA as well. Still, these days, who knows?Haha, I lol'ed... :-)Amazing footage indeed. Would have loved a closer ground-to-booster view on landing but that's my only quibble.Congrats to the NRO on being able to snoop even more on all of usElon just posted a nice view on Instagram.
Quote from: Phil Stooke on 05/01/2017 01:05 pm"...the execution of 100s of people at SpaceX "I had heard that this approach was used in North Korea to encourage hard work among the survivors, but I didn't expect it to be used in the USA as well. Still, these days, who knows?Haha, I lol'ed... :-)Amazing footage indeed. Would have loved a closer ground-to-booster view on landing but that's my only quibble.Congrats to the NRO on being able to snoop even more on all of us
"...the execution of 100s of people at SpaceX "I had heard that this approach was used in North Korea to encourage hard work among the survivors, but I didn't expect it to be used in the USA as well. Still, these days, who knows?
Massive bow shock on three engines.some studies have shown that a large bow is easier to maintain, and probably more efficient on multiple engineson one engine you may "pierce" the arc more easily, it's a balance between thrust and air pressure, takes time to fine tune it.
Because we know that the boostback burn is always going to be just about perfectly horizontal (as anything off-horizontal is going to waste propellant), we can now determine for the first time with reasonably good accuracy exactly what the trajectory was at MECO, based on separation altitude vs apogee.Separation: 1.68 km/s at 69.6 km altitude, T+2:23Apogee: 0.293 km/s at 166 km altitude, T+4:46
Quote from: Kabloona on 05/01/2017 01:26 pmQuote from: LouScheffer on 05/01/2017 11:50 am Terminal velocity looked like about 300 m/s. This is about as expected from something of that size, shape, and mass.Interesting. That terminal velocity is 2x the 150 m/sec terminal velocity observed on the first F9 landing at the Cape. F9 has bulked up since then...http://forum.nasaspaceflight.com/index.php?topic=39100.msg1465116#msg1465116I'm very suspicious of that 150 m/s number. If we plug in what we know of the booster (mass = 30t, from Hans), cross sectional area of 10 m^2 (known), coefficient of drag of a cylinder end on (0., density of air at 4000m (0.8 kg/m^3), we get a terminal velocity of about 300 m/s. None of these figures seems uncertain enough to get the terminal velocity down to 150 m/s.
Quote from: sevenperforce on 05/01/2017 01:24 pmBecause we know that the boostback burn is always going to be just about perfectly horizontal (as anything off-horizontal is going to waste propellant), we can now determine for the first time with reasonably good accuracy exactly what the trajectory was at MECO, based on separation altitude vs apogee.Separation: 1.68 km/s at 69.6 km altitude, T+2:23Apogee: 0.293 km/s at 166 km altitude, T+4:46Hans Koenniggsman has talked before about using the boostback burn to lower the apogee by aiming below the horizon and thereby reducing upward velocity, etc. So, while it may be fine as a rule of thumb, I wouldn't necessarily rely on that as 100% set in stone. Plus it may change on a launch by launch basis. Or, since he made those statements quite a while ago, they may no longer be doing this.
Quote from: sevenperforce on 05/01/2017 02:00 pmQuote from: Oersted on 05/01/2017 01:13 pmQuote from: Phil Stooke on 05/01/2017 01:05 pm"...the execution of 100s of people at SpaceX "I had heard that this approach was used in North Korea to encourage hard work among the survivors, but I didn't expect it to be used in the USA as well. Still, these days, who knows?Haha, I lol'ed... :-)Amazing footage indeed. Would have loved a closer ground-to-booster view on landing but that's my only quibble.Congrats to the NRO on being able to snoop even more on all of usElon just posted a nice view on Instagram.Something like six seconds from start of leg deployment to landing. How does that compare with previous landings?
Quote from: deruch on 05/01/2017 02:26 pmQuote from: sevenperforce on 05/01/2017 01:24 pmBecause we know that the boostback burn is always going to be just about perfectly horizontal (as anything off-horizontal is going to waste propellant), we can now determine for the first time with reasonably good accuracy exactly what the trajectory was at MECO, based on separation altitude vs apogee.Separation: 1.68 km/s at 69.6 km altitude, T+2:23Apogee: 0.293 km/s at 166 km altitude, T+4:46Hans Koenniggsman has talked before about using the boostback burn to lower the apogee by aiming below the horizon and thereby reducing upward velocity, etc. So, while it may be fine as a rule of thumb, I wouldn't necessarily rely on that as 100% set in stone. Plus it may change on a launch by launch basis. Or, since he made those statements quite a while ago, they may no longer be doing this.Welsh Dragon's altitude vs. time plot upthread shows nicely that the boostback burn was entirely horizontal, because the altitude vs. time curve during the boostback burn has the same shape as the corresponding period during the "free fall" period on the other side of the curve...ie, going up with (horizontal) boostback is the same as going down under gravity alone, as far as altitude vs. time is concerned.
A few observations from this wonderful footage:There is a "heartbeat" like glow (not the nitrogen thrusters) at the base of the rocket every few seconds. My guess is that they are releasing pressure through the engines so (as opposed to the vents) so they don't upset the attitude.The jets are navigating in 3d,not just two. You can see them thrusting fore and aft as well as sideways.
Quote from: deruch on 05/01/2017 02:26 pmQuote from: sevenperforce on 05/01/2017 01:24 pmBecause we know that the boostback burn is always going to be just about perfectly horizontal (as anything off-horizontal is going to waste propellant), we can now determine for the first time with reasonably good accuracy exactly what the trajectory was at MECO, based on separation altitude vs apogee.Separation: 1.68 km/s at 69.6 km altitude, T+2:23Apogee: 0.293 km/s at 166 km altitude, T+4:46Hans Koenniggsman has talked before about using the boostback burn to lower the apogee by aiming below the horizon and thereby reducing upward velocity, etc. So, while it may be fine as a rule of thumb, I wouldn't necessarily rely on that as 100% set in stone. Plus it may change on a launch by launch basis. Or, since he made those statements quite a while ago, they may no longer be doing this.Welsh Dragon's altitude vs. time plot upthread shows nicely that the boostback burn was entirely horizontal, because the altitude vs. time curve during the boostback burn has the same shape as the corresponding period during the "free fall" period on the other side of the curve...ie, going up with (horizontal) boostback is the same as going down under gravity alone, as far as altitude vs. time is concerned.Which makes sense, now that they've recovered several stages and proven that the stage can survive "falling" from apogee with an entry burn of reasonable duration.
Both yesterday and again today, the presenter of the webcast stated that the Falcon 9 is 12m in diameter. I am right that he is confusing the F9 - which I thought is 3.6m in diameter - with the Falcon Heavy, correct?
Quote from: M.E.T. on 05/01/2017 11:08 amBoth yesterday and again today, the presenter of the webcast stated that the Falcon 9 is 12m in diameter. I am right that he is confusing the F9 - which I thought is 3.6m in diameter - with the Falcon Heavy, correct?The presenter said 12ft (at about 15:50 into the webcast replay) which is close enough with rounding.
Looks like aerodynamic braking is pretty strong, as expected. After the entry burn, it accelerated for a while in the thin air, then decelerated at about 2G. Terminal velocity looked like about 300 m/s. This is about as expected from something of that size, shape, and mass.