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#660
by
Kabloona
on 18 Oct, 2013 21:50
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How many times does it need to be said... it was an obvious error in the video. Let it go.
Done.
I was merely answering the question from aero and others where the 20% number came from. On to other subjects...
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#661
by
Lar
on 18 Oct, 2013 21:52
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How many times does it need to be said... it was an obvious error in the video. Let it go.
Sure. Most knew it as soon as they saw it. But it's a fun calculation and I was pleased to be along for the ride
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#662
by
Comga
on 18 Oct, 2013 23:19
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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.
I think Jim has said that all they have are indicators that the fuel and oxidizer are full or empty. It would not be possible to fuel it partially with precision. The logical result is that SpaceX launched with a full fuel load, throttled down based on measured acceleration, and cut the engines upon achieving the proper velocity for staging.
We (Royal we! Where is modemeagle? ) could use the rule of thumb that a kilogram of payload is equivalent to ten kilograms of first stage mass.
Note the payload capacity of F9 V1.1
Calculate the combined mass of CASSIOPE and other elements of the payload
Take the difference.
Multiply it by ten. (Or a better value derived from analysis)
Add it to a reasonable fuel reserve. (Someone here has good insight from experience.)
That should give us a decent guess as to the fuel that remained before ignition of the three engines for the braking maneuver.
Someone (someone I say!) could even calculate how much fuel would be used to halt the velocity at stage separation, the now infamous 6,814 m/sec. This would leave a good guess for the fuel load when the stage starts falling towards the surface of the ocean.
That would tell us (with great uncertainty) the acceleration expected for landing.
Combined with an estimate of terminal velicity, the ignition altitude can be derived.
Sounds like fun. Just have to find the values to plug into the equations.
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#663
by
aero
on 18 Oct, 2013 23:44
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I think Jim has said that all they have are indicators that the fuel and oxidizer are full or empty. It would not be possible to fuel it partially with precision. The logical result is that SpaceX launched with a full fuel load, throttled down based on measured acceleration, and cut the engines upon achieving the proper velocity for staging.
That makes sense. We know that they top-up to replace LOX boil off, which would be very hard to control with a partial LOX load. Full LOX implies full RP-1, so the tanks were full.
Most of the aero and gravity drag was incurred before staging though, so we can't use the rocket equation to accurately calculate the fuel burned to reach 6,814 m/sec.
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#664
by
Comga
on 19 Oct, 2013 02:03
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I think Jim has said that all they have are indicators that the fuel and oxidizer are full or empty. It would not be possible to fuel it partially with precision. The logical result is that SpaceX launched with a full fuel load, throttled down based on measured acceleration, and cut the engines upon achieving the proper velocity for staging.
Most of the aero and gravity drag was incurred before staging though, so we can't use the rocket equation to accurately calculate the fuel burned to reach 6,814 m/sec.
You missed my point.
We (modemeagle or other clever calculater) can work the problem backwards and ignore drag.
(except for the terminal velocity of descent for which someone did a quantitative estimate of that and got 180-200 m/sec.)
Anyone want to try that calculation? (Or supply numerical inputs?)
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#665
by
cambrianera
on 19 Oct, 2013 11:00
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Anyone want to try that calculation? (Or supply numerical inputs?)
I did it some time ago:
http://forum.nasaspaceflight.com/index.php?topic=31734.msg1083622#msg1083622 Trying some quick and dirt calculation:
first stage 22000 kg dry, plus 2000 kg propellant for landing (6-7 s plus 2 s contingency) that's 24000 kg after the boostback;
assuming 2000 m/s for the boostback from the rocket equation you need an amount of propellant about the same as your residual mass (then 24000 kg).
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#666
by
Perchlorate
on 19 Oct, 2013 14:44
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Looking at the last photos in the recent SpaceX.com article about this flight...the side-by side photos, where the one on the left shows the first stage descending with 3 engines running...
Exactly what are we seeing in the right photo? It's obviously long-range, with rather low resolution. Is the stage in mid-air, at some significant altitude, and, if so, what is the white "donut" of water vapor? Or, is the stage just above the ocean surface with the "donut" being spray kicked up off the water by the exhaust plume?
I apologize in advance if this is already being discussed, or has already been discussed, elsewhere.
I'm guessing that the blue background field is sky, not water, and my first possibility is the case. From earlier reports, AIUI, the second, one-engine relight wasn't of sufficient duration and stability to get them that close to a "successful" simulated landing.
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#667
by
mlindner
on 19 Oct, 2013 14:46
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Looking at the last photos in the recent SpaceX.com article about this flight...the side-by side photos, where the one on the left shows the first stage descending with 3 engines running...
Exactly what are we seeing in the right photo? It's obviously long-range, with rather low resolution. Is the stage in mid-air, at some significant altitude, and, if so, what is the white "donut" of water vapor? Or, is the stage just above the ocean surface with the "donut" being spray kicked up off the water by the exhaust plume?
I apologize in advance if this is already being discussed, or has already been discussed, elsewhere.
I'm guessing that the blue background field is sky, not water, and my first possibility is the case. From earlier reports, AIUI, the second, one-engine relight wasn't of sufficient duration and stability to get them that close to a "successful" simulated landing.
It's been discussed multiple times in this topic and others.
Read this and see if it answers your questions:
http://www.newspacejournal.com/2013/10/18/spacex-wrapping-up-falcon-9-second-stage-investigation-as-it-moves-on-from-grasshopper/Is the stage in mid-air, at some significant altitude
No its near the ocean, 3 meters above.
Or, is the stage just above the ocean surface with the "donut" being spray kicked up off the water by the exhaust plume?
Near the ocean yes, unclear how the spray was kicked up or if the engine was firing at or shortly before the picture was taken.
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#668
by
Perchlorate
on 19 Oct, 2013 17:18
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Thank you, sir. I try to check the site 2-3 times a day, but was slammed Wednesday and missed it.
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#669
by
blazotron
on 19 Oct, 2013 17:30
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I think Jim has said that all they have are indicators that the fuel and oxidizer are full or empty. It would not be possible to fuel it partially with precision. The logical result is that SpaceX launched with a full fuel load, throttled down based on measured acceleration, and cut the engines upon achieving the proper velocity for staging.
That makes sense. We know that they top-up to replace LOX boil off, which would be very hard to control with a partial LOX load. Full LOX implies full RP-1, so the tanks were full.
Most of the aero and gravity drag was incurred before staging though, so we can't use the rocket equation to accurately calculate the fuel burned to reach 6,814 m/sec.
We know SpaceX uses a propellant utilization system, where they try to burn out both propellants at the same time. You can't do that (very well, at least) without knowing how much propellant is left in the tanks during the burn, which implies that they have more than just full/empty sensors.
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#670
by
Jason1701
on 19 Oct, 2013 17:43
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I think Jim has said that all they have are indicators that the fuel and oxidizer are full or empty. It would not be possible to fuel it partially with precision. The logical result is that SpaceX launched with a full fuel load, throttled down based on measured acceleration, and cut the engines upon achieving the proper velocity for staging.
That makes sense. We know that they top-up to replace LOX boil off, which would be very hard to control with a partial LOX load. Full LOX implies full RP-1, so the tanks were full.
Most of the aero and gravity drag was incurred before staging though, so we can't use the rocket equation to accurately calculate the fuel burned to reach 6,814 m/sec.
We know SpaceX uses a propellant utilization system, where they try to burn out both propellants at the same time. You can't do that (very well, at least) without knowing how much propellant is left in the tanks during the burn, which implies that they have more than just full/empty sensors.
They use differential pressure transducers, the standard way of measuring propellant levels.
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#671
by
Comga
on 19 Oct, 2013 20:13
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They use differential pressure transducers, the standard way of measuring propellant levels.
So I was wrong about the sensors, but does anyone think the rocket flew with less than a full load of fuel and oxidizer?
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#672
by
Hooperball
on 19 Oct, 2013 21:44
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I think Jim has said that all they have are indicators that the fuel and oxidizer are full or empty. It would not be possible to fuel it partially with precision. The logical result is that SpaceX launched with a full fuel load, throttled down based on measured acceleration, and cut the engines upon achieving the proper velocity for staging.
That makes sense. We know that they top-up to replace LOX boil off, which would be very hard to control with a partial LOX load. Full LOX implies full RP-1, so the tanks were full.
Most of the aero and gravity drag was incurred before staging though, so we can't use the rocket equation to accurately calculate the fuel burned to reach 6,814 m/sec.
We know SpaceX uses a propellant utilization system, where they try to burn out both propellants at the same time. You can't do that (very well, at least) without knowing how much propellant is left in the tanks during the burn, which implies that they have more than just full/empty sensors.
They use differential pressure transducers, the standard way of measuring propellant levels.
How do you know this? do you have a source?
I would assume radar level gauges to be more accurate over pressure transducers for measuring fluid levels as they are not effected by tank pressure, do not need a condensate filled static and dynamic leg to correct for tank pressure, and they do not need an accelerometer to correct for changes in pressure of a column of liquid due to acceleration of tank and liquid.
S
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#673
by
Antares
on 19 Oct, 2013 22:25
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Bad assumption. All rockets already have sensors for those things and can put them into the propellant control loop, since they are already using them for pressure control and flight control.
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#674
by
SaxtonHale
on 20 Oct, 2013 01:42
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How much did the chutes on 1.0 weigh?
If this was able to get through the worst of the atmosphere without ripping apart, couldn't a drogue have gotten rid of low-rpm procession (precession?) and possibly whatever roll messed with the fuel? Then a Soyuz-style soft landing to ensure bigger pieces recovered.
Or, would bigger RCS tanks solve some of the problems instead?
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#675
by
Kabloona
on 20 Oct, 2013 01:57
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How much did the chutes on 1.0 weigh?
If this was able to get through the worst of the atmosphere without ripping apart, couldn't a drogue have gotten rid of low-rpm procession (precession?) and possibly whatever roll messed with the fuel? Then a Soyuz-style soft landing to ensure bigger pieces recovered.
Or, would bigger RCS tanks solve some of the problems instead?
RCS plus deployable legs plus maybe some aero tweaks will deal with the roll issue. Chutes are an unnecessary complication.
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#676
by
meekGee
on 20 Oct, 2013 03:20
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... and in a couple of years, Elon will be describing the next rocket, and will comment on the F9R - "sure, back then we hardly knew what we were doing, so we just went with a simple brute-force design, we just wanted to show that it can be made to work".
There's plenty of room for aerodynamic tweaks to reduce propellant consumption, and maybe fabrication technology to reduce weight - but these will require time and R&D, and there's no reason to get the first reusable design to be 100% optimal.
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#677
by
llanitedave
on 20 Oct, 2013 04:28
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What's important is that the design be extendible, so that adding optimizations doesn't require a major rework. If it's tweakable, the F9 could become the next DC-3.
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#678
by
douglas100
on 20 Oct, 2013 23:32
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What's important is that the design be extendible, so that adding optimizations doesn't require a major rework. If it's tweakable, the F9 could become the next DC-3.
I would expect them to continue to upgrade F9 of course. It's what all other launch providers do, after all. But the main priority is to prove the reliability of the new design and fly the manifest. I wouldn't expect them to make large design changes while establishing v1.1.
I remember the Shuttle being compared with the DC-3 in the early days. I think F9R has a good chance of being commercially successful, but comparing it to the DC-3 is not useful. Spaceflight and aviation are too different.
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#679
by
Antares
on 21 Oct, 2013 01:33
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I would expect them to continue to upgrade F9 of course. It's what all other launch providers do, after all.
Careful. That needs to be conditional. Experience needs to be developed. Repeatability and consistency is important to customers. That the flight hardware has worked and done so together many times before is important. Several major changes bundled together doesn't make customers happy. It tends to reset the counter on the number of successful launches of a type.
I was merely answering the question from aero and others where the 20% number came from. On to other subjects...
