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#640
by
ugordan
on 17 Oct, 2013 22:16
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Apart from the 1st stage restart video (which was blown up unnecessarily, cropping the 4:3 aspect to fit 16:9 in the process), the mission overview video was pretty disappointing.
Seriously, no tracking camera shots?
There weren't any cameras.
What's this, then? www
.youtube.com/watch?v=WX0Gnid2E0E&t=72
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#641
by
mlindner
on 17 Oct, 2013 22:17
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Apart from the 1st stage restart video (which was blown up unnecessarily, cropping the 4:3 aspect to fit 16:9 in the process), the mission overview video was pretty disappointing.
Seriously, no tracking camera shots?
There weren't any cameras.
What's this, then? www.youtube.com/watch?v=WX0Gnid2E0E&t=72
Video from one of the cameras that wasn't disabled? That was why they didn't have any during launch.
Edit: Do the cameras have on-board storage drives?
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#642
by
ugordan
on 17 Oct, 2013 22:23
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Cameras weren't disabled. What Helodriver reported in another thread was that the antenna that SpaceX apparently used for forwarding camera video was knocked off alignment because it was too close to the pad. The western range obviously had their own links and range recorders.
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#643
by
mlindner
on 17 Oct, 2013 22:26
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Cameras weren't disabled. What Helodriver reported in another thread was that the antenna that SpaceX apparently used for forwarding camera video was knocked off alignment because it was too close to the pad. The western range obviously had their own links and range recorders.
Ah ok, thank you.
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#644
by
Antares
on 18 Oct, 2013 04:35
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I'm a little surprised that we haven't seen photos of some major rocket parts recovered. I guess they broke up and sank.
Blame the FAA.
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#645
by
joncz
on 18 Oct, 2013 11:44
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Someone with a better explanation than a mistake for those two frames showing exactly the same speed?
Possibility:
The first overlay is shown right as the "first stage is relighting..." - so it is continuing to accelerate. By 10 seconds later, the stage has begun to decelerate. The stage's peak speed is somewhere just above 6814 km/hr and occurred between the two screengrabs.
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#646
by
Kabloona
on 18 Oct, 2013 13:55
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Someone with a better explanation than a mistake for those two frames showing exactly the same speed?
Possibility:
The first overlay is shown right as the "first stage is relighting..." - so it is continuing to accelerate. By 10 seconds later, the stage has begun to decelerate. The stage's peak speed is somewhere just above 6814 km/hr and occurred between the two screengrabs.
The probability that the speeds at those two different times and altitudes are identical, to four significant figures, is quite close to zero, IMO. They could be *similar*, but it's the four significant figure identicality that I find highly unlikely, and indicative of the likelihood that someone in the editing room simply forgot to change a number.
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#647
by
kevin-rf
on 18 Oct, 2013 14:09
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Kabloona, It could be a resolution/precision issue. As in the value step's in non even integer steps but outputs to more sig figures than available from the data.
Example, lets say you measure a speed in .41 km/hr increments, so the values you can display are 0.41, 0.82, 1.23 km/hr.
Just a thought.
Edit, problem with that is 6814/2 is 3407, which is prime...
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#648
by
Kabloona
on 18 Oct, 2013 14:44
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Just for fun, I did a few BOTE calcs re that 6,814 km/hr speed number.
Over the 10 second interval from 7:40 to 7:50:
Altitude loss = 11.4 km, which would result in speed gain of 58 m/sec if no retro burn
Assume 20% propellant load
3 engine burn at 100% thrust results in approximately 2 g retro burn
Over 10 seconds, delta V retro is approximately 200 m/sec
Then speed change is approximately 58-200=negative 140 m/sec= negative 504 km/hr
6,814-504=6,310 km hr.
So unless my math and or physics are way off (entirely possible, I admit!) we should see a significant speed decrease after 10 seconds of retro burn, despite the energy gain due to altitude loss.
Ergo, I continue to posit that the speed cannot be 6,814 km/hr both before and after 10 seconds of retro burn, and that the difference is far greater than measurement resolution/precision granularity.
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#649
by
AnjaZoe
on 18 Oct, 2013 14:50
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The explanation offered by "space our soul" is the most likely imho.
Zoe
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#650
by
Lars_J
on 18 Oct, 2013 15:27
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The explanation offered by "space our soul" is the most likely imho.
Zoe
Indeed. It is a video editing error... Not live telemetry. There is no need to go looking for the man on the grassy knoll here.
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#651
by
Jason1701
on 18 Oct, 2013 16:32
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Just for fun, I did a few BOTE calcs re that 6,814 km/hr speed number.
Over the 10 second interval from 7:40 to 7:50:
Altitude loss = 11.4 km, which would result in speed gain of 58 m/sec if no retro burn
Assume 20% propellant load
3 engine burn at 100% thrust results in approximately 2 g retro burn
Over 10 seconds, delta V retro is approximately 200 m/sec
Then speed change is approximately 58-200=negative 140 m/sec= negative 504 km/hr
6,814-504=6,310 km hr.
So unless my math and or physics are way off (entirely possible, I admit!) we should see a significant speed decrease after 10 seconds of retro burn, despite the energy gain due to altitude loss.
Ergo, I continue to posit that the speed cannot be 6,814 km/hr both before and after 10 seconds of retro burn, and that the difference is far greater than measurement resolution/precision granularity.
How did you get 2 g acceleration for the retro burn? I think it would be a lot higher with an almost-empty stage.
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#652
by
Nomadd
on 18 Oct, 2013 17:01
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Just for fun, I did a few BOTE calcs re that 6,814 km/hr speed number.
Over the 10 second interval from 7:40 to 7:50:
Altitude loss = 11.4 km, which would result in speed gain of 58 m/sec if no retro burn
Assume 20% propellant load
3 engine burn at 100% thrust results in approximately 2 g retro burn
Over 10 seconds, delta V retro is approximately 200 m/sec
Then speed change is approximately 58-200=negative 140 m/sec= negative 504 km/hr
6,814-504=6,310 km hr.
So unless my math and or physics are way off (entirely possible, I admit!) we should see a significant speed decrease after 10 seconds of retro burn, despite the energy gain due to altitude loss.
Ergo, I continue to posit that the speed cannot be 6,814 km/hr both before and after 10 seconds of retro burn, and that the difference is far greater than measurement resolution/precision granularity.
How did you get 2 g acceleration for the retro burn? I think it would be a lot higher with an almost-empty stage.
Not that empty with 20% fuel. It would still be about 200 tons of thrust for 20 tons of booster and 80? tons of fuel?
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#653
by
cambrianera
on 18 Oct, 2013 17:05
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Just for fun, I did a few BOTE calcs re that 6,814 km/hr speed number.
Over the 10 second interval from 7:40 to 7:50:
Altitude loss = 11.4 km, which would result in speed gain of 58 m/sec if no retro burn
Assume 20% propellant load
3 engine burn at 100% thrust results in approximately 2 g retro burn
Over 10 seconds, delta V retro is approximately 200 m/sec
Then speed change is approximately 58-200=negative 140 m/sec= negative 504 km/hr
6,814-504=6,310 km hr.
So unless my math and or physics are way off (entirely possible, I admit!) we should see a significant speed decrease after 10 seconds of retro burn, despite the energy gain due to altitude loss.
Ergo, I continue to posit that the speed cannot be 6,814 km/hr both before and after 10 seconds of retro burn, and that the difference is far greater than measurement resolution/precision granularity.
How did you get 2 g acceleration for the retro burn? I think it would be a lot higher with an almost-empty stage.
Assuming 20% residual propellant the acceleration should be about 2g.
I agree with you (Jason1701) that the residual propellant should be much less (around 5%), but in this particular case, commenting the labels of some frames, the BOTE calculation of Kabloona is OK (if anything, strenghtened by a lower propellant residue).
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#654
by
Jason1701
on 18 Oct, 2013 17:27
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Just for fun, I did a few BOTE calcs re that 6,814 km/hr speed number.
Over the 10 second interval from 7:40 to 7:50:
Altitude loss = 11.4 km, which would result in speed gain of 58 m/sec if no retro burn
Assume 20% propellant load
3 engine burn at 100% thrust results in approximately 2 g retro burn
Over 10 seconds, delta V retro is approximately 200 m/sec
Then speed change is approximately 58-200=negative 140 m/sec= negative 504 km/hr
6,814-504=6,310 km hr.
So unless my math and or physics are way off (entirely possible, I admit!) we should see a significant speed decrease after 10 seconds of retro burn, despite the energy gain due to altitude loss.
Ergo, I continue to posit that the speed cannot be 6,814 km/hr both before and after 10 seconds of retro burn, and that the difference is far greater than measurement resolution/precision granularity.
How did you get 2 g acceleration for the retro burn? I think it would be a lot higher with an almost-empty stage.
Assuming 20% residual propellant the acceleration should be about 2g.
I agree with you (Jason1701) that the residual propellant should be much less (around 5%), but in this particular case, commenting the labels of some frames, the BOTE calculation of Kabloona is OK (if anything, strenghtened by a lower propellant residue).
20% residual would let three engines burn for over 100 seconds. The actual residual is probably about 3-5%.
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#655
by
aero
on 18 Oct, 2013 18:06
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yes - I calculate that 20 % fuel would boost the stage 1 by over 14,000 km/hr. so I think 20 % fuel reserve is excessive.
dry mass = 28 tonnes
fuel load = 411 tonnes, 20 % = 82.2 tonnes
reserve for final soft touchdown burn= ~ 2 tonnes, for terminal velocity =200 m/s, from the rocket equation and sea level Isp.
so with vacuum Isp, the rocket equation gives delta V = 3051 m/s* ln(110/30) and that's a lot.
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#656
by
MP99
on 18 Oct, 2013 19:32
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20% residual would let three engines burn for over 100 seconds. The actual residual is probably about 3-5%.
Is that what you'd expect on a routine mission, or do you think they might have left larger residuals for this flight given it's first-of-it's-kind, and such a tiny payload?
I am thinking that SpaceX may have done a burn to a lower final velocity this time, to try to ensure that the stage survived re-entry? Later flights might use a smaller burn, depending on what they learned this time / may learn from future recovered stages.
cheers, Martin
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#657
by
Kabloona
on 18 Oct, 2013 20:07
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yes - I calculate that 20 % fuel would boost the stage 1 by over 14,000 km/hr. so I think 20 % fuel reserve is excessive.
dry mass = 28 tonnes
fuel load = 411 tonnes, 20 % = 82.2 tonnes
reserve for final soft touchdown burn= ~ 2 tonnes, for terminal velocity =200 m/s, from the rocket equation and sea level Isp.
so with vacuum Isp, the rocket equation gives delta V = 3051 m/s* ln(110/30) and that's a lot.
Sorry for the confusion. I was merely trying to prove that it would be virtually impossible for the speed to be 6,814 km/hr at both 7:40 and at 7:50, ten seconds into a retro burn. Earlier in this thread I posited that there must have been an error in the video editing, where someone put the same number (6,814 km/hr) on the screen at two different points in the video.
But some forumites here wondered if, perhaps, that number could be correct at both times, by coincidence, that the gain in speed due to altitude loss might cancel the thrust delta V over that small time interval.
So I pulled some numbers out of the air (e.g. the 20% fuel load) and did the calcs to show that, even with a relatively large (assumed) residual fuel load, there should be a quite significant difference in speed at those two points.
If in fact the correct number is closer to 5% residual propellant load, the change in speed from 7:40 to 7:50 will be even greater...reinforcing my original point that the 6,814 km/hr figure cannot be correct at *both* the 7:40 and 7:50 time marks, and is likely a mere video editing error.
So if the real number is more like 5% residual propellant, I apologize for muddying the waters with the 20% assumed figure I used for my BOTE calcs. But as a limiting case, it proved my point.
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#658
by
aero
on 18 Oct, 2013 20:34
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Yes - your point is proven. Your argument brings up some interesting points though.
Like-
how much fuel did S1 actually use to reach staging altitude and velocity?
Which begs the question of whether of not CASSIOPE launched with a full fuel load.
What was the lift-off mass?
With a little more data we could calculate the actual average thrust of the v1.1.
And how long was the deceleration burn actually?
Did we ever find out what the real value of terminal velocity is?
Answers it would be fun to know.
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#659
by
Lars_J
on 18 Oct, 2013 21:21
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yes - I calculate that 20 % fuel would boost the stage 1 by over 14,000 km/hr. so I think 20 % fuel reserve is excessive.
dry mass = 28 tonnes
fuel load = 411 tonnes, 20 % = 82.2 tonnes
reserve for final soft touchdown burn= ~ 2 tonnes, for terminal velocity =200 m/s, from the rocket equation and sea level Isp.
so with vacuum Isp, the rocket equation gives delta V = 3051 m/s* ln(110/30) and that's a lot.
Sorry for the confusion. I was merely trying to prove that it would be virtually impossible for the speed to be 6,814 km/hr at both 7:40 and at 7:50, ten seconds into a retro burn. Earlier in this thread I posited that there must have been an error in the video editing, where someone put the same number (6,814 km/hr) on the screen at two different points in the video.
But some forumites here wondered if, perhaps, that number could be correct at both times, by coincidence, that the gain in speed due to altitude loss might cancel the thrust delta V over that small time interval.
So I pulled some numbers out of the air (e.g. the 20% fuel load) and did the calcs to show that, even with a relatively large (assumed) residual fuel load, there should be a quite significant difference in speed at those two points.
If in fact the correct number is closer to 5% residual propellant load, the change in speed from 7:40 to 7:50 will be even greater...reinforcing my original point that the 6,814 km/hr figure cannot be correct at *both* the 7:40 and 7:50 time marks, and is likely a mere video editing error.
So if the real number is more like 5% residual propellant, I apologize for muddying the waters with the 20% assumed figure I used for my BOTE calcs. But as a limiting case, it proved my point.
How many times does it need to be said... it was an obvious error in the video. Let it go.