ApolloHoax.net
Off Topic => General Discussion => Topic started by: bknight on June 25, 2023, 09:03:32 AM
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In a recent interview Musk has stated that a hot start of the second stage while still attached to the first stage will "conservatively result in 10% more payload into LEO. Is this correct?
https://twitter.com/i/spaces/1OyJAVEdkMaxb (https://twitter.com/i/spaces/1OyJAVEdkMaxb)
Note this is a 49 minute interview and there were sound issues for the first 16:30 . Skip ahead, if you are listening.
Now I realize that shutting down the first stage and letting the vehicles separate prior to second stage results in the second stage decelerating until it begins to accelerated again. So hot starting will result in more payload to LEO, but 10%? SpaceX is installing an extension to the inner stage and beefing up the first stage to prevent damage to the first stage.
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Not sure of the engineering calculations, but it sound reasonable. The payload only comprises a relatively small percentage of the second stage mass. Here are some figures for Falcon 9, non-expended
Empty Mass:... 3900 kg
Propellant:.... 92,670 kg
Payload:....... 22,800 kg
--------
Total.... ..... 119370 kg
The payload is 19% of the total mass of the second stage at firing
Increase the mass of the payload by 10% = 25080 Kg
Empty Mass:... 3900 kg
Propellant:.... 92,670 kg
Payload:....... 25,080 kg
--------
Total.... ..... 121650 kg
The payload is now 21% of the second stage at firing
So in reality, there is only a 2% increase in mass to orbit
(provided my back-of-the-envelope math is correct)
ETA: Of course, this is very simplified. I have take no account of the reduction in overall mass as the propellant is burned, but it doesn't seem unreasonable to me that firing the second stage engine a few seconds early, and before it has a chance to start to decelerate might allow a couple of additional % points of mass to LEO.
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Well I created a velocity spreadsheet for A11 with the help of BobB a few years ago and the numbers seem more like your 2% that 10%. And remember he said conservative 10%. I posted part of the spreadsheet in CQ, and I have shut it down currently and will be back tomorrow and post it here.
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Fair enough, and if Musk is making exaggerated claims, well, it wouldn't be the first time, would it?
I'm just pointing out that a 10% increase in payload is a significantly less than that in overall second stage mass. Remember that the second stage goes all the way to orbit with the payload, and in the case of Falcon 9 and Falcon Heavy, carries some extra fuel for a de-orbit burn.
Also, any mass you can strip from the second stage can go to payload. For example, when Rocketlab's Electron made its first flight six years ago, it had a maximum payload to LEO of 225kg. This has gone up to 300 KG, because in the intervening six years, the lithium polymer batteries they use to drive the fuel pumps have gotten smaller and lighter while still delivering the same capacity.
In the case of Falcon 9, with a "hot start" on the second stage, the fact that it will be traveling at a higher velocity might mean it needs to carry less fuel... which equals less mass. I just had a quick look at a Starlink launch - at MECO (2m33s) the whole stack is traveling at 8184 km/h, and drops to 8057 km/h at the moment of stage separation. When SES happens, the second stage does not get back up to 8187 km/h until 2m 49s.
PS: Its worth noting that the Russians have used hot staging on their rockets since the late 1050s. India and China also use it.
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Fair enough, and if Musk is making exaggerated claims, well, it wouldn't be the first time, would it?
I'm just pointing out that a 10% increase in payload is a significantly less than that in overall second stage mass. Remember that the second stage goes all the way to orbit with the payload, and in the case of Falcon 9 and Falcon Heavy, carries some extra fuel for a de-orbit burn.
Also, any mass you can strip from the second stage can go to payload. For example, when Rocketlab's Electron made its first flight six years ago, it had a maximum payload to LEO of 225kg. This has gone up to 300 KG, because in the intervening six years, the lithium polymer batteries they use to drive the fuel pumps have gotten smaller and lighter while still delivering the same capacity.
In the case of Falcon 9, with a "hot start" on the second stage, the fact that it will be traveling at a higher velocity might mean it needs to carry less fuel... which equals less mass. I just had a quick look at a Starlink launch - at MECO (2m33s) the whole stack is traveling at 8184 km/h, and drops to 8057 km/h at the moment of stage separation. When SES happens, the second stage does not get back up to 8187 km/h until 2m 49s.
PS: Its worth noting that the Russians have used hot staging on their rockets since the late 1050s. India and China also use it.
That observation (16 sec) seems a bit slow, but your eye not mine, just saying.
Vehicle Mass Acceleration Space-fixed velocity
Time Dry Fuel Total Flow Thrust ISP Throttle Pitch g Horz. Vert. Load Horz. Vert. Total f
(s) (kg) (kg) (kg) (kg/s) (N) (s) (%) (deg) (m/s2) (m/s2) (m/s2) (g) (m/s) (m/s) (m/s) (deg)
161.63 242186 577266 819452 10716.83 27808451 304.0 100% 70.14 9.650 31.632 2.716 3.46 2339.6 673.1 2434.5 16.05
162.00 242186 575284 817470 0.00 0 0.0 0% 70.25 9.650 -0.285 -8.807 0.00 2345.4 671.9 2439.7 15.99
162.11 242186 575284 817470 0.00 0 0.0 0% 70.28 9.649 -0.284 -8.807 0.00 2345.3 671.0 2439.4 15.97
162.30 242153 575284 817470 0.00 0 0.0 0% 70.34 9.649 -0.283 -8.807 0.00 2345.3 669.3 2438.9 15.93
163.00 109139 550330 817470 0.00 0 0.0 0% 70.55 9.648 -0.268 -8.801 0.00 2345.1 663.1 2437.1 15.79
164.00 108963 550330 816857 1225.45 5104333 427.7 100% 70.84 9.646 5.639 -6.746 0.63 2347.8 655.4 2437.5 15.60
165.00 108786 549105 815631 1225.45 5104333 427.7 100% 71.14 9.644 5.662 -6.767 0.64 2353.4 648.6 2441.2 15.41
165.61 108678 548357 814884 1225.45 5104333 427.7 100% 70.82 9.643 5.658 -6.727 0.64 2356.9 644.5 2443.4 15.29
166.00 108678 547879 814406 1225.45 5104333 427.7 100% 70.61 9.642 5.656 -6.702 0.64 2359.1 641.9 2444.9 15.22
167.00 108678 546654 813181 1225.45 5104333 427.7 100% 70.08 9.640 5.649 -6.638 0.64 2364.7 635.2 2448.6 15.04
168.00 108678 545428 811955 1225.45 5104333 427.7 100% 69.55 9.638 5.641 -6.574 0.64 2370.4 628.6 2452.3 14.85
169.00 108678 544203 810730 1225.45 5104333 427.7 100% 69.03 9.636 5.632 -6.510 0.64 2376.0 622.1 2456.1 14.67
170.00 108678 542977 809504 1225.45 5104333 427.7 100% 68.50 9.634 5.623 -6.446 0.64 2381.7 615.6 2459.9 14.49
171.00 108678 541752 808279 1225.45 5104333 427.7 100% 67.97 9.632 5.613 -6.382 0.64 2387.3 609.2 2463.8 14.31
172.00 108678 540526 807053 1225.45 5104333 427.7 100% 67.44 9.631 5.603 -6.318 0.64 2392.9 602.8 2467.6 14.14
173.00 108678 539301 805828 1225.45 5104333 427.7 100% 66.91 9.629 5.592 -6.255 0.64 2398.5 596.5 2471.5 13.97
174.00 108678 538076 804602 1225.45 5104333 427.7 100% 66.38 9.627 5.580 -6.191 0.65 2404.1 590.3 2475.5 13.80
175.00 108678 536850 803377 1225.45 5104333 427.7 100% 65.86 9.625 5.568 -6.127 0.65 2409.6 584.1 2479.4 13.63
176.00 108678 535625 802152 1225.45 5104333 427.7 100% 65.33 9.624 5.555 -6.064 0.65 2415.2 578.0 2483.4 13.46
177.00 108678 534399 800926 1225.45 5104333 427.7 100% 64.80 9.622 5.541 -6.001 0.65 2420.7 572.0 2487.4 13.29
178.00 108678 533174 799701 1225.45 5104333 427.7 100% 64.27 9.620 5.527 -5.937 0.65 2426.3 566.0 2491.4 13.13
179.00 108678 531948 798475 1225.45 5104333 427.7 100% 63.74 9.618 5.512 -5.874 0.65 2431.8 560.1 2495.5 12.97
180.00 108678 530723 797250 1225.45 5104333 427.7 100% 63.21 9.617 5.497 -5.811 0.65 2437.3 554.3 2499.5 12.81
181.00 108678 529497 796024 1225.45 5104333 427.7 100% 62.68 9.615 5.481 -5.748 0.65 2442.8 548.5 2503.6 12.66
182.00 108678 528272 794799 1225.45 5104333 427.7 100% 62.16 9.614 5.465 -5.685 0.65 2448.3 542.8 2507.7 12.50
183.00 108678 527046 793573 1225.45 5104333 427.7 100% 61.63 9.612 5.448 -5.622 0.66 2453.7 537.1 2511.8 12.35
184.00 108678 525821 792348 1225.45 5104333 427.7 100% 61.10 9.610 5.430 -5.560 0.66 2459.2 531.6 2516.0 12.20
185.00 108678 524596 791123 1225.45 5104333 427.7 100% 60.57 9.609 5.412 -5.497 0.66 2464.6 526.0 2520.1 12.05
186.00 108678 523370 789897 1225.45 5104333 427.7 100% 60.60 9.607 5.425 -5.489 0.66 2470.0 520.5 2524.3 11.90
187.00 108678 522145 788672 1225.45 5104333 427.7 100% 60.63 9.606 5.437 -5.482 0.66 2475.4 515.0 2528.4 11.75
188.00 108678 520919 787446 1225.45 5104333 427.7 100% 60.66 9.604 5.450 -5.474 0.66 2480.9 509.6 2532.7 11.61
189.00 108678 519694 786221 1225.45 5104333 427.7 100% 60.69 9.603 5.462 -5.466 0.66 2486.3 504.1 2536.9 11.46
190.00 108678 518468 784995 1225.45 5104333 427.7 100% 60.73 9.601 5.475 -5.459 0.66 2491.8 498.6 2541.2 11.32
191.00 108678 517243 783770 1225.45 5104333 427.7 100% 60.76 9.600 5.487 -5.451 0.66 2497.3 493.2 2545.5 11.17
192.00 108678 516017 782544 1225.45 5104333 427.7 100% 60.79 9.598 5.500 -5.444 0.66 2502.8 487.7 2549.9 11.03
192.30 108678 515650 782177 1225.45 5104333 427.7 100% 60.80 9.598 5.504 -5.441 0.67 2504.4 486.1 2551.2 10.98
Pasting spreadsheets to forums is not good. Anyway this in A11 and the velocities are space fixed.
For reference:
161.63 OESC S1
162.3 Stage separation.
164 ESC S2.
You can see the acceleration drops from 2.76 m/s at OESC to Earth's gravity. That continues for ~ 2 sec. Then S2 ESC. In this scenario the total velocity meets/exceeds first stage total velocity in ~3.5 sec. 161.63-165. Note most of the acceleration is going into horizontal velocity also Earth's gravity effect is diminishing. I realize that the trajectories will be different so a one to one comparison is not valid.
Note that the speadsheet averages every one second(or one row) but it is a close approximation. BobB's sheet and mine are very similar, he helped a lot and I give him credit for sticking with me during the development.
Note also the total velocity never decreases, just slows from the vertical gravity effect, horizontal was only slowed by the atmosphere.
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Fair enough, and if Musk is making exaggerated claims, well, it wouldn't be the first time, would it?
I'm just pointing out that a 10% increase in payload is a significantly less than that in overall second stage mass. Remember that the second stage goes all the way to orbit with the payload, and in the case of Falcon 9 and Falcon Heavy, carries some extra fuel for a de-orbit burn.
Also, any mass you can strip from the second stage can go to payload. For example, when Rocketlab's Electron made its first flight six years ago, it had a maximum payload to LEO of 225kg. This has gone up to 300 KG, because in the intervening six years, the lithium polymer batteries they use to drive the fuel pumps have gotten smaller and lighter while still delivering the same capacity.
In the case of Falcon 9, with a "hot start" on the second stage, the fact that it will be traveling at a higher velocity might mean it needs to carry less fuel... which equals less mass. I just had a quick look at a Starlink launch - at MECO (2m33s) the whole stack is traveling at 8184 km/h, and drops to 8057 km/h at the moment of stage separation. When SES happens, the second stage does not get back up to 8187 km/h until 2m 49s.
PS: Its worth noting that the Russians have used hot staging on their rockets since the late 1050s. India and China also use it.
That observation (16 sec) seems a bit slow, but your eye not mine, just saying.
Vehicle Mass Acceleration Space-fixed velocity
Time Dry Fuel Total Flow Thrust ISP Throttle Pitch g Horz. Vert. Load Horz. Vert. Total f
(s) (kg) (kg) (kg) (kg/s) (N) (s) (%) (deg) (m/s2) (m/s2) (m/s2) (g) (m/s) (m/s) (m/s) (deg)
161.63 242186 577266 819452 10716.83 27808451 304.0 100% 70.14 9.650 31.632 2.716 3.46 2339.6 673.1 2434.5 16.05
162.00 242186 575284 817470 0.00 0 0.0 0% 70.25 9.650 -0.285 -8.807 0.00 2345.4 671.9 2439.7 15.99
162.11 242186 575284 817470 0.00 0 0.0 0% 70.28 9.649 -0.284 -8.807 0.00 2345.3 671.0 2439.4 15.97
162.30 242153 575284 817470 0.00 0 0.0 0% 70.34 9.649 -0.283 -8.807 0.00 2345.3 669.3 2438.9 15.93
163.00 109139 550330 817470 0.00 0 0.0 0% 70.55 9.648 -0.268 -8.801 0.00 2345.1 663.1 2437.1 15.79
164.00 108963 550330 816857 1225.45 5104333 427.7 100% 70.84 9.646 5.639 -6.746 0.63 2347.8 655.4 2437.5 15.60
165.00 108786 549105 815631 1225.45 5104333 427.7 100% 71.14 9.644 5.662 -6.767 0.64 2353.4 648.6 2441.2 15.41
165.61 108678 548357 814884 1225.45 5104333 427.7 100% 70.82 9.643 5.658 -6.727 0.64 2356.9 644.5 2443.4 15.29
166.00 108678 547879 814406 1225.45 5104333 427.7 100% 70.61 9.642 5.656 -6.702 0.64 2359.1 641.9 2444.9 15.22
167.00 108678 546654 813181 1225.45 5104333 427.7 100% 70.08 9.640 5.649 -6.638 0.64 2364.7 635.2 2448.6 15.04
168.00 108678 545428 811955 1225.45 5104333 427.7 100% 69.55 9.638 5.641 -6.574 0.64 2370.4 628.6 2452.3 14.85
169.00 108678 544203 810730 1225.45 5104333 427.7 100% 69.03 9.636 5.632 -6.510 0.64 2376.0 622.1 2456.1 14.67
170.00 108678 542977 809504 1225.45 5104333 427.7 100% 68.50 9.634 5.623 -6.446 0.64 2381.7 615.6 2459.9 14.49
171.00 108678 541752 808279 1225.45 5104333 427.7 100% 67.97 9.632 5.613 -6.382 0.64 2387.3 609.2 2463.8 14.31
172.00 108678 540526 807053 1225.45 5104333 427.7 100% 67.44 9.631 5.603 -6.318 0.64 2392.9 602.8 2467.6 14.14
173.00 108678 539301 805828 1225.45 5104333 427.7 100% 66.91 9.629 5.592 -6.255 0.64 2398.5 596.5 2471.5 13.97
174.00 108678 538076 804602 1225.45 5104333 427.7 100% 66.38 9.627 5.580 -6.191 0.65 2404.1 590.3 2475.5 13.80
175.00 108678 536850 803377 1225.45 5104333 427.7 100% 65.86 9.625 5.568 -6.127 0.65 2409.6 584.1 2479.4 13.63
176.00 108678 535625 802152 1225.45 5104333 427.7 100% 65.33 9.624 5.555 -6.064 0.65 2415.2 578.0 2483.4 13.46
177.00 108678 534399 800926 1225.45 5104333 427.7 100% 64.80 9.622 5.541 -6.001 0.65 2420.7 572.0 2487.4 13.29
178.00 108678 533174 799701 1225.45 5104333 427.7 100% 64.27 9.620 5.527 -5.937 0.65 2426.3 566.0 2491.4 13.13
179.00 108678 531948 798475 1225.45 5104333 427.7 100% 63.74 9.618 5.512 -5.874 0.65 2431.8 560.1 2495.5 12.97
180.00 108678 530723 797250 1225.45 5104333 427.7 100% 63.21 9.617 5.497 -5.811 0.65 2437.3 554.3 2499.5 12.81
181.00 108678 529497 796024 1225.45 5104333 427.7 100% 62.68 9.615 5.481 -5.748 0.65 2442.8 548.5 2503.6 12.66
182.00 108678 528272 794799 1225.45 5104333 427.7 100% 62.16 9.614 5.465 -5.685 0.65 2448.3 542.8 2507.7 12.50
183.00 108678 527046 793573 1225.45 5104333 427.7 100% 61.63 9.612 5.448 -5.622 0.66 2453.7 537.1 2511.8 12.35
184.00 108678 525821 792348 1225.45 5104333 427.7 100% 61.10 9.610 5.430 -5.560 0.66 2459.2 531.6 2516.0 12.20
185.00 108678 524596 791123 1225.45 5104333 427.7 100% 60.57 9.609 5.412 -5.497 0.66 2464.6 526.0 2520.1 12.05
186.00 108678 523370 789897 1225.45 5104333 427.7 100% 60.60 9.607 5.425 -5.489 0.66 2470.0 520.5 2524.3 11.90
187.00 108678 522145 788672 1225.45 5104333 427.7 100% 60.63 9.606 5.437 -5.482 0.66 2475.4 515.0 2528.4 11.75
188.00 108678 520919 787446 1225.45 5104333 427.7 100% 60.66 9.604 5.450 -5.474 0.66 2480.9 509.6 2532.7 11.61
189.00 108678 519694 786221 1225.45 5104333 427.7 100% 60.69 9.603 5.462 -5.466 0.66 2486.3 504.1 2536.9 11.46
190.00 108678 518468 784995 1225.45 5104333 427.7 100% 60.73 9.601 5.475 -5.459 0.66 2491.8 498.6 2541.2 11.32
191.00 108678 517243 783770 1225.45 5104333 427.7 100% 60.76 9.600 5.487 -5.451 0.66 2497.3 493.2 2545.5 11.17
192.00 108678 516017 782544 1225.45 5104333 427.7 100% 60.79 9.598 5.500 -5.444 0.66 2502.8 487.7 2549.9 11.03
192.30 108678 515650 782177 1225.45 5104333 427.7 100% 60.80 9.598 5.504 -5.441 0.67 2504.4 486.1 2551.2 10.98
Pasting spreadsheets to forums is not good. Anyway this in A11 and the velocities are space fixed.
For reference:
161.63 OESC S1
162.3 Stage separation.
164 ESC S2.
You can see the acceleration drops from 2.76 m/s at OESC to Earth's gravity. That continues for ~ 2 sec. Then S2 ESC. In this scenario the total velocity meets/exceeds first stage total velocity in ~3.5 sec. 161.63-165. Note most of the acceleration is going into horizontal velocity also Earth's gravity effect is diminishing. I realize that the trajectories will be different so a one to one comparison is not valid.
Note that the speadsheet averages every one second(or one row) but it is a close approximation. BobB's sheet and mine are very similar, he helped a lot and I give him credit for sticking with me during the development.
Note also the total velocity never decreases, just slows from the vertical gravity effect, horizontal was only slowed by the atmosphere.
That is very interesting Mr. Knight. Looks like a lot of work went into that.
IIRC, Saturn V staging involved retro-rockets (eight IIRC, fitted at the base of each of the outer F-1 engines - two each engine). They were fired for about a second, and actually decelerated the first stage during staging. Same again for second stage staging using four solid-fueled retro-rockets located in a conical adapter at the front end of the second stage. They did this because they were worried about the discarded stages running into the back of the next stages as they slowed down after engine cut-off. Clearly, stages slowing on MECO and SECO was an issue that needed to be dealt with. The Russians dealt with it by using open frameworks to connect stages and hot starting the stages.
The question for me is, does that slowing down impact the dynamics sufficiently to affect payload in any significant way?
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I am not an engineer and I do not have the ability to run the numbers on this.
Hot staging means that the number of seconds where the stack is in a ballistic curve is reduced. Which means that you are not losing the momentum that the first stage has built up up to the point of MECO prior to normal staging. As soon as those engines cut off gravity will start to do it's work and reduce the momentum that the booster has achieved. This is work that has to be recovered by the second stage. Bear in mind that the second stage has to recover this work using Vacuum Raptors which are then operating in atmosphere, so not at their peak efficiency. I think that this might be the key to it.
Of course, there may be a weight penalty by having to add extra shielding to the booster? And you are burning the booster a little bit longer will mean that more fuel is consumed
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Another thought....how does Starship manage ullage prior to vacuum Raptor ignition? Hot staging removes the need for any ullage motors (or firing of the reaction controls for ullage purposes), so their is a weight saving there.
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Fair enough, and if Musk is making exaggerated claims, well, it wouldn't be the first time, would it?
I'm just pointing out that a 10% increase in payload is a significantly less than that in overall second stage mass. Remember that the second stage goes all the way to orbit with the payload, and in the case of Falcon 9 and Falcon Heavy, carries some extra fuel for a de-orbit burn.
Also, any mass you can strip from the second stage can go to payload. For example, when Rocketlab's Electron made its first flight six years ago, it had a maximum payload to LEO of 225kg. This has gone up to 300 KG, because in the intervening six years, the lithium polymer batteries they use to drive the fuel pumps have gotten smaller and lighter while still delivering the same capacity.
In the case of Falcon 9, with a "hot start" on the second stage, the fact that it will be traveling at a higher velocity might mean it needs to carry less fuel... which equals less mass. I just had a quick look at a Starlink launch - at MECO (2m33s) the whole stack is traveling at 8184 km/h, and drops to 8057 km/h at the moment of stage separation. When SES happens, the second stage does not get back up to 8187 km/h until 2m 49s.
PS: Its worth noting that the Russians have used hot staging on their rockets since the late 1050s. India and China also use it.
That observation (16 sec) seems a bit slow, but your eye not mine, just saying.
Vehicle Mass Acceleration Space-fixed velocity
Time Dry Fuel Total Flow Thrust ISP Throttle Pitch g Horz. Vert. Load Horz. Vert. Total f
(s) (kg) (kg) (kg) (kg/s) (N) (s) (%) (deg) (m/s2) (m/s2) (m/s2) (g) (m/s) (m/s) (m/s) (deg)
161.63 242186 577266 819452 10716.83 27808451 304.0 100% 70.14 9.650 31.632 2.716 3.46 2339.6 673.1 2434.5 16.05
162.00 242186 575284 817470 0.00 0 0.0 0% 70.25 9.650 -0.285 -8.807 0.00 2345.4 671.9 2439.7 15.99
162.11 242186 575284 817470 0.00 0 0.0 0% 70.28 9.649 -0.284 -8.807 0.00 2345.3 671.0 2439.4 15.97
162.30 242153 575284 817470 0.00 0 0.0 0% 70.34 9.649 -0.283 -8.807 0.00 2345.3 669.3 2438.9 15.93
163.00 109139 550330 817470 0.00 0 0.0 0% 70.55 9.648 -0.268 -8.801 0.00 2345.1 663.1 2437.1 15.79
164.00 108963 550330 816857 1225.45 5104333 427.7 100% 70.84 9.646 5.639 -6.746 0.63 2347.8 655.4 2437.5 15.60
165.00 108786 549105 815631 1225.45 5104333 427.7 100% 71.14 9.644 5.662 -6.767 0.64 2353.4 648.6 2441.2 15.41
165.61 108678 548357 814884 1225.45 5104333 427.7 100% 70.82 9.643 5.658 -6.727 0.64 2356.9 644.5 2443.4 15.29
166.00 108678 547879 814406 1225.45 5104333 427.7 100% 70.61 9.642 5.656 -6.702 0.64 2359.1 641.9 2444.9 15.22
167.00 108678 546654 813181 1225.45 5104333 427.7 100% 70.08 9.640 5.649 -6.638 0.64 2364.7 635.2 2448.6 15.04
168.00 108678 545428 811955 1225.45 5104333 427.7 100% 69.55 9.638 5.641 -6.574 0.64 2370.4 628.6 2452.3 14.85
169.00 108678 544203 810730 1225.45 5104333 427.7 100% 69.03 9.636 5.632 -6.510 0.64 2376.0 622.1 2456.1 14.67
170.00 108678 542977 809504 1225.45 5104333 427.7 100% 68.50 9.634 5.623 -6.446 0.64 2381.7 615.6 2459.9 14.49
171.00 108678 541752 808279 1225.45 5104333 427.7 100% 67.97 9.632 5.613 -6.382 0.64 2387.3 609.2 2463.8 14.31
172.00 108678 540526 807053 1225.45 5104333 427.7 100% 67.44 9.631 5.603 -6.318 0.64 2392.9 602.8 2467.6 14.14
173.00 108678 539301 805828 1225.45 5104333 427.7 100% 66.91 9.629 5.592 -6.255 0.64 2398.5 596.5 2471.5 13.97
174.00 108678 538076 804602 1225.45 5104333 427.7 100% 66.38 9.627 5.580 -6.191 0.65 2404.1 590.3 2475.5 13.80
175.00 108678 536850 803377 1225.45 5104333 427.7 100% 65.86 9.625 5.568 -6.127 0.65 2409.6 584.1 2479.4 13.63
176.00 108678 535625 802152 1225.45 5104333 427.7 100% 65.33 9.624 5.555 -6.064 0.65 2415.2 578.0 2483.4 13.46
177.00 108678 534399 800926 1225.45 5104333 427.7 100% 64.80 9.622 5.541 -6.001 0.65 2420.7 572.0 2487.4 13.29
178.00 108678 533174 799701 1225.45 5104333 427.7 100% 64.27 9.620 5.527 -5.937 0.65 2426.3 566.0 2491.4 13.13
179.00 108678 531948 798475 1225.45 5104333 427.7 100% 63.74 9.618 5.512 -5.874 0.65 2431.8 560.1 2495.5 12.97
180.00 108678 530723 797250 1225.45 5104333 427.7 100% 63.21 9.617 5.497 -5.811 0.65 2437.3 554.3 2499.5 12.81
181.00 108678 529497 796024 1225.45 5104333 427.7 100% 62.68 9.615 5.481 -5.748 0.65 2442.8 548.5 2503.6 12.66
182.00 108678 528272 794799 1225.45 5104333 427.7 100% 62.16 9.614 5.465 -5.685 0.65 2448.3 542.8 2507.7 12.50
183.00 108678 527046 793573 1225.45 5104333 427.7 100% 61.63 9.612 5.448 -5.622 0.66 2453.7 537.1 2511.8 12.35
184.00 108678 525821 792348 1225.45 5104333 427.7 100% 61.10 9.610 5.430 -5.560 0.66 2459.2 531.6 2516.0 12.20
185.00 108678 524596 791123 1225.45 5104333 427.7 100% 60.57 9.609 5.412 -5.497 0.66 2464.6 526.0 2520.1 12.05
186.00 108678 523370 789897 1225.45 5104333 427.7 100% 60.60 9.607 5.425 -5.489 0.66 2470.0 520.5 2524.3 11.90
187.00 108678 522145 788672 1225.45 5104333 427.7 100% 60.63 9.606 5.437 -5.482 0.66 2475.4 515.0 2528.4 11.75
188.00 108678 520919 787446 1225.45 5104333 427.7 100% 60.66 9.604 5.450 -5.474 0.66 2480.9 509.6 2532.7 11.61
189.00 108678 519694 786221 1225.45 5104333 427.7 100% 60.69 9.603 5.462 -5.466 0.66 2486.3 504.1 2536.9 11.46
190.00 108678 518468 784995 1225.45 5104333 427.7 100% 60.73 9.601 5.475 -5.459 0.66 2491.8 498.6 2541.2 11.32
191.00 108678 517243 783770 1225.45 5104333 427.7 100% 60.76 9.600 5.487 -5.451 0.66 2497.3 493.2 2545.5 11.17
192.00 108678 516017 782544 1225.45 5104333 427.7 100% 60.79 9.598 5.500 -5.444 0.66 2502.8 487.7 2549.9 11.03
192.30 108678 515650 782177 1225.45 5104333 427.7 100% 60.80 9.598 5.504 -5.441 0.67 2504.4 486.1 2551.2 10.98
Pasting spreadsheets to forums is not good. Anyway this in A11 and the velocities are space fixed.
For reference:
161.63 OESC S1
162.3 Stage separation.
164 ESC S2.
You can see the acceleration drops from 2.76 m/s at OESC to Earth's gravity. That continues for ~ 2 sec. Then S2 ESC. In this scenario the total velocity meets/exceeds first stage total velocity in ~3.5 sec. 161.63-165. Note most of the acceleration is going into horizontal velocity also Earth's gravity effect is diminishing. I realize that the trajectories will be different so a one to one comparison is not valid.
Note that the speadsheet averages every one second(or one row) but it is a close approximation. BobB's sheet and mine are very similar, he helped a lot and I give him credit for sticking with me during the development.
Note also the total velocity never decreases, just slows from the vertical gravity effect, horizontal was only slowed by the atmosphere.
That is very interesting Mr. Knight. Looks like a lot of work went into that.
IIRC, Saturn V staging involved retro-rockets (eight IIRC, fitted at the base of each of the outer F-1 engines - two each engine). They were fired for about a second, and actually decelerated the first stage during staging. Same again for second stage staging using four solid-fueled retro-rockets located in a conical adapter at the front end of the second stage. They did this because they were worried about the discarded stages running into the back of the next stages as they slowed down after engine cut-off. Clearly, stages slowing on MECO and SECO was an issue that needed to be dealt with. The Russians dealt with it by using open frameworks to connect stages and hot starting the stages.
The question for me is, does that slowing down impact the dynamics sufficiently to affect payload in any significant way?
You are correct, except for A15, when they reduced the number to four to attempt to save weight as they were carrying the rover for the first time. S2 more or less destroyed S1 when ESC occurred, because it did not slow as much as the engineers/computers projected. The four where re-installed in both A16 and A17, IIRC.
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Another thought....how does Starship manage ullage prior to vacuum Raptor ignition? Hot staging removes the need for any ullage motors (or firing of the reaction controls for ullage purposes), so their is a weight saving there.
I asked that over at CQ and IIRC the answer was hydraulic/mechanical.
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Another thought....how does Starship manage ullage prior to vacuum Raptor ignition? Hot staging removes the need for any ullage motors (or firing of the reaction controls for ullage purposes), so their is a weight saving there.
I asked that over at CQ and IIRC the answer was hydraulic/mechanical.
Interesting! How does that work? On the Falcon 9 there is a "pole" that reaches up into the bell of the 2nd stage motor. I believe that it uses pneumatics to stage, presumably compressed gas to actuate a piston that shoves the stage away from the booster.
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Well, the hot staging seemed to work.
I switched it on barely a minute before launch, and I think it was a pretty impressive sight. A shame that both stages failed, but the launch as a whole worked a lot better than last time.
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Well, the hot staging seemed to work.
I switched it on barely a minute before launch, and I think it was a pretty impressive sight. A shame that both stages failed, but the launch as a whole worked a lot better than last time.
For the second stage, but not much for the first stage. I agree this launch was much better than the first, all the engines ignited and lifted the vehicle off the pad much faster than in April.
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At this stage of development (pun intended), that was an impressive flight.
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A very impressive sight!
The booster flip looked very energetic. I wouldn't be surprised if the motors ingested gas at start-up hence the RUD. Musk reckons that they could be ready of another flight in 3-4 weeks Musk time notwithstanding). I bet that the next one will be another step forward.
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The ignition after the flip was suspicious. I believe that they only did it once with starship so in my mind the startup procedure needs to be refined IMO>
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A video recorded in Florida of the flight from the point of the Starship explosion (visible in top left), showing remnants.
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A video recorded in Florida of the flight from the point of the Starship explosion (visible in top left), showing remnants.
Only one comment. It appears that the vehicle is tumbling and yet from BC vantage no tumbling was observed.
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A video recorded in Florida of the flight from the point of the Starship explosion (visible in top left), showing remnants.
Only one comment. It appears that the vehicle is tumbling and yet from BC vantage no tumbling was observed.
Sorry, not sure I follow. I didn't know there were post-explosion videos of Starship from Boca Chica.
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A video recorded in Florida of the flight from the point of the Starship explosion (visible in top left), showing remnants.
Only one comment. It appears that the vehicle is tumbling and yet from BC vantage no tumbling was observed.
Sorry, not sure I follow. I didn't know there were post-explosion videos of Starship from Boca Chica.
Look at a video more closely you will see the apparent FTS explosion at the back of the stage and then nothing.
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I haven’t really followed Starship development. But it clearly won’t be ready for a nominal 2025* lunar landing mission. In addition to the vehicle accomplishing the controlled flight profiles that will be necessary, the crew systems will all need to built, integrated, and tested - I have no idea of their development status, but the execrable safety record of Musk-run companies, and my general contempt for Musk as a human being in general and an American in particular, likely colors my uninformed viewpoint.
*I don’t know if that’s still the advertised date. I’ve been more in the line of discouraging (rather assertively) things from flying, rather than encouraging them to do so, lately.
P.S. (waves) Hi, everybody.
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A video recorded in Florida of the flight from the point of the Starship explosion (visible in top left), showing remnants.
Only one comment. It appears that the vehicle is tumbling and yet from BC vantage no tumbling was observed.
Sorry, not sure I follow. I didn't know there were post-explosion videos of Starship from Boca Chica.
I saw somewhere (on Youtube but I cannot remember which channel) that this is a video taken after the RUD not before it, of only part of the top half of the second stage, a piece which survived the explosion, flipping over and over as it fell out of the sky.
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A video recorded in Florida of the flight from the point of the Starship explosion (visible in top left), showing remnants.
Only one comment. It appears that the vehicle is tumbling and yet from BC vantage no tumbling was observed.
Sorry, not sure I follow. I didn't know there were post-explosion videos of Starship from Boca Chica.
I saw somewhere (on Youtube but I cannot remember which channel) that this is a video taken after the RUD not before it, of only part of the top half of the second stage, a piece which survived the explosion, flipping over and over as it fell out of the sky.
If the RUD was a result in the FTS, then that didn't work so well. Scott Manley suggested in one of his videos, that there may have been a leak in the oxygen system, look at the oxygen and methane graphs closely, oxygen is GT methane up until almost the RUD, then there was the RUD with oxygen below methane, seemed like a leak fueled the RUD. But the "upper" portion of the starship seems reasonable. thanks
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And now the fourth flight made it all the way through re-entry to splashdown.
Watching that fin actuate having been essentially burned through was one of the most amazing things I've ever seen - until I saw the telemetry indicated it had splashed down.
I think the last time I was so emotionally affected by something in space and rocketry was the launch of the first Falcon Heavy.
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And now the fourth flight made it all the way through re-entry to splashdown.
Watching that fin actuate having been essentially burned through was one of the most amazing things I've ever seen - until I saw the telemetry indicated it had splashed down.
I think the last time I was so emotionally affected by something in space and rocketry was the launch of the first Falcon Heavy.
Epic, wasn't it?
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I've never before seen anything that so clearly expresses the sheer brutality of re-entry. And yes, I too had an uh-oh moment when I saw the fin root starting to break up. At that point, normally, you just hope it breaks cleanly away and leaves you with a reasonable fallback control regime. To have it still continue to steer the ship as it's falling apart is a testament to robust engineering.
The commentary from our fluid dynamics wonks also included marveling at how uniform the flow was during entry interface. It's just sobering to see in 4K what normally you see only in computer-generated isolines or through tiny windows in hypersonic wind tunnels.
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I've never before seen anything that so clearly expresses the sheer brutality of re-entry. And yes, I too had an uh-oh moment when I saw the fin root starting to break up. At that point, normally, you just hope it breaks cleanly away and leaves you with a reasonable fallback control regime. To have it still continue to steer the ship as it's falling apart is a testament to robust engineering.
The commentary from our fluid dynamics wonks also included marveling at how uniform the flow was during entry interface. It's just sobering to see in 4K what normally you see only in computer-generated isolines or through tiny windows in hypersonic wind tunnels.
It's fascinating to read comments like this from someone who works in the field. Thank you for sharing!
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I've never before seen anything that so clearly expresses the sheer brutality of re-entry. And yes, I too had an uh-oh moment when I saw the fin root starting to break up. At that point, normally, you just hope it breaks cleanly away and leaves you with a reasonable fallback control regime. To have it still continue to steer the ship as it's falling apart is a testament to robust engineering.
The commentary from our fluid dynamics wonks also included marveling at how uniform the flow was during entry interface. It's just sobering to see in 4K what normally you see only in computer-generated isolines or through tiny windows in hypersonic wind tunnels.
Clearly, they are going to need additional heat shielding in that rear area of the flap.
I am pretty sure the fact that flap survived would mostly down to the fact that SpaceX made the decision to build Starship using 304L stainless rather than the usual aluminium alloys. SpaceX are apparently going to shift the forward flaps leeward "to help improve reliability and ease of manufacturing". I do wonder what effect a change like that would have on control authority, both during launch and ascent, and during the flip maneuver during the landing.
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The hinge was an expected trouble spot. It'll be interesting to see how they change the design to cope with it.
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Discontinuities tend to create hot spots. Wing roots on supersonic aircraft are notorious for this. Sometimes using more robust materials is the answer, such as RCC for the space shuttle leading edges. But more often you can fix it by rearranging the geometry. Moving the flaps is definitely worth investigating, with the noted caveats that handling characteristics will change.
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Here is an interesting video - an interview of Elon Musk by Tim Dodd (Everyday Astronaut YT channel) at Starbase on a tour of the facility.
This was all filmed before Test Flight 4 and Musk talks about the issues with heat shielding and some of the measures they have been planning, specifically around the flaps and their hinge points, so its clear they did have some concerns about that before the flight.
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Well they should, any moving parts by necessity leaves gaps however small they may be. Gaps lead to plasma moving through those gaps as we viewed on the video of the reentry of Starship. As stated earlier it was amazing to me that they still functioned after all that and oriented the vehicle vertical so the engines could light. Not a perfect "landing", but progress.
Now they need to design the booster engines so that atmospheric drag doesn't tear them apart and they should have a catch by the tower.
I found that the second tower at Boca will be taller than the first allowing stacking/catching the newer version which is taller.
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I wonder if looking at how they armoured knee joints in plate armour might help. Both have the goals of coverage while maintaining flexibility. Middle Ages and Renaissance armours didn't have to contend with thousands of degree plasma, mind you.
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And now in flight 5 they caught the damn first stage, and videoed the splashdown of the second stage...
That suggests some pretty spectacular aiming.
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And now in flight 5 they caught the damn first stage, and videoed the splashdown of the second stage...
That suggests some pretty spectacular aiming.
Yes they had a very good flight and the FAA says no investigation warranted after the flight, onward and upward.
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Long road still, there's a lot of damage to the vehicle that's going to impede rapid turn around as is stands, but getting that catch on the first try is damn impressive.
Come a long way from the Grasshopper, that's for sure, hanging "in the sky in much the same way that bricks don't."
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It was one hell of a test flight! Looks like there's a lot to do with the heatshield and preventing flap damage.
Also, time to stop funding the boondogle that is SLS? (not going to happen though...pork barrel politics and all that).
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Also, time to stop funding the boondogle that is SLS? (not going to happen though...pork barrel politics and all that).
We get the government we deserve. If the American people could stop treating politics as reality TV and electing clowns, grifters, criminals, and fossils to Congress, mistakes like SLS wouldn't happen (as often).
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Long road still, there's a lot of damage to the vehicle that's going to impede rapid turn around as is stands, but getting that catch on the first try is damn impressive.
Come a long way from the Grasshopper, that's for sure, hanging "in the sky in much the same way that bricks don't."
One of the other things which was pointed out in one video was how the chopsticks moved the booster laterally so that it was positioned above the launch pad. I mean, I knew there was no way the booster would be able to land directly above the pad, but I hadn't bothered to think through what would be involved in the repositioning process.
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Long road still, there's a lot of damage to the vehicle that's going to impede rapid turn around as is stands, but getting that catch on the first try is damn impressive.
Come a long way from the Grasshopper, that's for sure, hanging "in the sky in much the same way that bricks don't."
One of the other things which was pointed out in one video was how the chopsticks moved the booster laterally so that it was positioned above the launch pad. I mean, I knew there was no way the booster would be able to land directly above the pad, but I hadn't bothered to think through what would be involved in the repositioning process.
As far I can see, this may always be necessary as the booster will not always approach the launch tower from the exact same direction. There will be variations depending on the orbital inclination of the launch.
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Can be that they guide the booster in using waypoints, so the final few kilometers is the same each time. By doing that, they ensure the booster can fail safely in a predetermined path, if the engines go away.