Do we know which core flew today?
I have the longest boostback, at 45 seconds or longer, taking place during the CRS-9 flight, during which the first stage returned to LZ 1. For some reason, a shorter 33 second burn was used for CRS-10, which also returned to LZ 1. Both of these flights had a 141 second first stage MECO.
I also eagerly await all the smart and informed answers to these questions! Gravity losses and basic orbital mechanics are something I somehow missed out on my space "career"! Thanks everyone!
Quote from: rockettrey on 05/02/2017 12:56 amI also eagerly await all the smart and informed answers to these questions! Gravity losses and basic orbital mechanics are something I somehow missed out on my space "career"! Thanks everyone!I'll catch hell but, whatever ...Just like all NSF-based discussions of spaceflight eventually gravitate toward SpaceX, most SpaceX discussions among uneducated (*) fans eventually turns to Kerbal Space Program. But aside from the snark, if you spend a few weeks with that game and really try to learn it, you'll get a better intuitive grasp of the physics involved than you can get without a multi-year college education.(*) Not an insult; just shorthand to describe those who may lack at least a Bachelor's level degree in aerospace engineering, physics, or something similar.
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: 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.
Well, I learnt something today.I was surprised that even though the main engine cut out at around 65km altitude, the booster gained more altitude AFTER main engine cut out than it had gained for the entire time that the engine was actually burning. This is obviously old news to you experts on the forum, but to me as a layman I just intuitively expected that altitude gains would stop pretty soon after the booster's engine cut out.As it turns out, the booster engine cut out at 65km, but the 1st stage continued up to attain an altitude of 165km or so before it started falling back to Earth.In hindsight it makes sense, as basic physics tells me that vertical speed would only decrease by 10m/s once the thrust disappeared, but it was interesting to see nevertheless. Normally we just see the 2nd stage altitude after MECO.
Once the engine shuts down, gravity would be slowing the stage down 10m/s per second downward (10m/sē) but since the stage is flying horizontally at some good speed, that speed produces a centripetal force with fights gravity on its own.Imagine if the stage were going at orbital velocity horizontally, that speed would be enough to cancel out gravity and keep it in orbit.Half orbital speed would cancel half gravity.1/4 orbital speed would cancel 1/4 gravity.
Wow, there sure were some great close-ups of the returning booster - anybody notice that?
Quote from: macpacheco on 05/02/2017 02:24 amOnce the engine shuts down, gravity would be slowing the stage down 10m/s per second downward (10m/sē) but since the stage is flying horizontally at some good speed, that speed produces a centripetal force with fights gravity on its own.Imagine if the stage were going at orbital velocity horizontally, that speed would be enough to cancel out gravity and keep it in orbit.Half orbital speed would cancel half gravity.1/4 orbital speed would cancel 1/4 gravity.Centripetal acceleration goes like v^2/r, so half orbital speed cancels 1/4 gravity. 1/4 orbit speed cancels 1/16 gravity.So for the speeds reached by the first stage, gravity cancellation is quite a minor effect.
Great Youtube footage with nice close-ups of the landing (Not my video)33 seconds in is my favoritehttps://www.youtube.com/watch?v=GoRKhH8J1YQ#t=75.629688
Quote from: bunker9603 on 05/02/2017 01:36 amGreat Youtube footage with nice close-ups of the landing (Not my video)33 seconds in is my favoritehttps://www.youtube.com/watch?v=GoRKhH8J1YQ#t=75.629688The best footage is from this new Instagram video posted by Elon:https://www.instagram.com/p/BTjVdLVB1bO/
The best footage is from this new Instagram video posted by Elon:https://www.instagram.com/p/BTjVdLVB1bO/
We've come a long way from reconstructing the landing footage of CRS-3, haven't we? Congratulations to SpaceX on their first DoD flight and for a spectacular depiction of how our robot overlords will soon invade us. I, for one, welcome more simulations.
Les Kovacs, ULA: want to throw a wet blanket on concept of reusability. Additional systems needed to land stages comes at cost of payload.
Quote from: M.E.T. on 05/01/2017 05:26 pmWell, I learnt something today.I was surprised that even though the main engine cut out at around 65km altitude, the booster gained more altitude AFTER main engine cut out than it had gained for the entire time that the engine was actually burning. This is obviously old news to you experts on the forum, but to me as a layman I just intuitively expected that altitude gains would stop pretty soon after the booster's engine cut out.As it turns out, the booster engine cut out at 65km, but the 1st stage continued up to attain an altitude of 165km or so before it started falling back to Earth.In hindsight it makes sense, as basic physics tells me that vertical speed would only decrease by 10m/s once the thrust disappeared, but it was interesting to see nevertheless. Normally we just see the 2nd stage altitude after MECO.Once the engine shuts down, gravity would be slowing the stage down 10m/s per second downward (10m/sē)
but since the stage is flying horizontally at some good speed, that speed produces a centripetal force with fights gravity on its own.
Quote from: MattMason on 05/02/2017 07:52 amWe've come a long way from reconstructing the landing footage of CRS-3, haven't we? Congratulations to SpaceX on their first DoD flight and for a spectacular depiction of how our robot overlords will soon invade us. I, for one, welcome more simulations.Nice reminder... CRS-3 was April 18, 2014. Three years to go from seemingly impossible to routine!First half (1y8m) got us to first land landing -- now (1y4m later) a core has been reflown, a handful are scheduled this year, and landing is routine -- though not boring. Final upgrade of F9 is being fab'd to incorporate lessons learned.Brilliant test program. Naysayers... any last words?(other than ULA's 'wet blanket/lost performance' comment yesterday at #ulcats)