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#140 by Comga on 14 Nov, 2019 00:49
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This launch was to a 280 km injection orbit, but the first went to 440 km.
Not only does the lower orbit support greater payload capacity, but if the plan is to deploy to 3 planes, it's much quicker from this lower orbit.
What is the expected passive time it would take for a dead satellite to de-orbit from the 280 km injection orbit?
For 350km they said a couple weeks to 8 months depending on the solar cycle. I don't think they've said numbers for 280km.
A crude rule of thumb says that the atmospheric density doubles or halves every 20 km. So the orbital lifetime does the same in reverse.
Because we are in an incredibly weak solar cycle (Did you see the sunspot-less solar disk for the Mercury transit?) the 8 month upper end of their estimate is more likely.
So 8 months divided be 2^3=8 to 2^4=16 would be 2-4 weeks.
Pretty short orbital lifetime. -
#141 by sferrin on 14 Nov, 2019 11:20
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Any word on Flights 2 & 3? They're still scheduled for this year over on Spaceflight Now.
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#142 by ZachS09 on 14 Nov, 2019 12:16
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Any word on Flights 2 & 3? They're still scheduled for this year over on Spaceflight Now.
My best guess is that they’re now scheduled for 2020, although it’ll take time for SFN to update their launch schedule. -
#143 by crandles57 on 14 Nov, 2019 15:36
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Any word on Flights 2 & 3? They're still scheduled for this year over on Spaceflight Now.
My best guess is that they’re now scheduled for 2020, although it’ll take time for SFN to update their launch schedule.
SLC launches Dec 4 and 16. If a minimum of a week before Dec 4, we would know about it by now. Insufficient time between 4th and 16th. So earliest possible opportunity from SLC 40 would be about Dec 28. Another from LC-39A a couple of weeks after in flight abort so before end of year is just about possible... but with such little leeway and Christmas interfering with those timescales, I agree the smart money would be on 2020 rather than 2019. -
#144 by bobaroony on 14 Nov, 2019 18:51
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photo cut from spacex starlink live video at 23:56
looks like almost empty tank right after landing on barge
RP1 or LOX mabe ... i wonder
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#145 by gongora on 14 Nov, 2019 19:32
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photo cut from spacex starlink live video at 23:56
looks like almost empty tank right after landing on barge
RP1 or LOX mabe ... i wonder
That should be the second stage LOX tank. -
#146 by CyndyC on 14 Nov, 2019 22:03
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photo cut from spacex starlink live video at 23:56
looks like almost empty tank right after landing on barge
RP1 or LOX mabe ... i wonder
That should be the second stage LOX tank.
There are too many reasons to think it's the 1st stage RP1 tank. The video flashed to it directly from the landing shot and then went directly back to the landing shot. Even though Lauren & the timeline ref'd SECO about the same time, both 2nd stage tanks are monocoque. The 1st stage LOX tank is also monocoque, but the 1st stage RP1 tank has "a stringer and ring-frame design that adds strength to the vehicle" (SpaceFlight101.com), exactly what is pictured in the video. Also, where's a vent pipe like that going to go from the 2nd stage LOX tank, into the payload? Below is a photo by SpaceX of inside the 2nd stage LOX tank, and it's not the same tank that was in the video.
Incidentally, Spaceflight101 also reveals the FT 1st stage under full performance has to achieve MECO in 150 to 170 seconds after lift off to be able to land, and according to the press kit this burn was 153 seconds,so that's about 17 seconds of fuel remaining.
Edit: My thinking on remaining fuel wasn't quite right. The 1st stage can burn up to 195 seconds without a landing, so that was about 42 seconds of fuel remaining.
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#147 by whitelancer64 on 14 Nov, 2019 22:30
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photo cut from spacex starlink live video at 23:56
looks like almost empty tank right after landing on barge
RP1 or LOX mabe ... i wonder
That should be the second stage LOX tank.
There are too many reasons to think it's the 1st stage RP1 tank. The video flashed to it directly from the landing shot and then went directly back to the landing shot. Even though Lauren & the timeline ref'd SECO about the same time, both 2nd stage tanks are monocoque. The 1st stage LOX tank is also monocoque, but the 1st stage RP1 tank has "a stringer and ring-frame design that adds strength to the vehicle" (SpaceFlight101.com), exactly what is pictured in the video. Also, where's a vent pipe like that going to go from the 2nd stage LOX tank, into the payload? Below is a photo by SpaceX of inside the 2nd stage LOX tank, and it's not the same tank that was in the video.
Incidentally, Spaceflight101 also reveals the FT 1st stage under full performance has to achieve MECO in 150 to 170 seconds after lift off to be able to land, and according to the press kit this burn was 153 seconds,so that's about 17 seconds of fuel remaining.
Edit: My thinking on remaining fuel wasn't quite right. The 1st stage can burn up to 195 seconds without a landing, so that was about 42 seconds of fuel remaining.
Kerosene is naturally colorless, and standard RP-1 is dyed red.
LOX is naturally a pale blue. This is LOX. -
#148 by CyndyC on 14 Nov, 2019 22:52
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photo cut from spacex starlink live video at 23:56
looks like almost empty tank right after landing on barge
RP1 or LOX mabe ... i wonder
That should be the second stage LOX tank.
There are too many reasons to think it's the 1st stage RP1 tank. The video flashed to it directly from the landing shot and then went directly back to the landing shot. Even though Lauren & the timeline ref'd SECO about the same time, both 2nd stage tanks are monocoque. The 1st stage LOX tank is also monocoque, but the 1st stage RP1 tank has "a stringer and ring-frame design that adds strength to the vehicle" (SpaceFlight101.com), exactly what is pictured in the video. Also, where's a vent pipe like that going to go from the 2nd stage LOX tank, into the payload? Below is a photo by SpaceX of inside the 2nd stage LOX tank, and it's not the same tank that was in the video.
Incidentally, Spaceflight101 also reveals the FT 1st stage under full performance has to achieve MECO in 150 to 170 seconds after lift off to be able to land, and according to the press kit this burn was 153 seconds,so that's about 17 seconds of fuel remaining.
Edit: My thinking on remaining fuel wasn't quite right. The 1st stage can burn up to 195 seconds without a landing, so that was about 42 seconds of fuel remaining.
Kerosene is naturally colorless, and standard RP-1 is dyed red.
LOX is naturally a pale blue. This is LOX.
They have good reasons to stabilize the RP1 tank basin with that extra structure since it's directly over the octaweb, but not as much reason to add the same structure to the shorter LOX tank above the RP1 tank, as that idea would imply they did so later or that Spaceflight101 was incorrect. It's possible SpaceX doesn't pay the extra cost of red dye in their RP1, which wouldn't be a trivial amount, and that the blue tint of the basin is shining through. It would be a lot easier to just ask someone at SpaceX. -
#149 by whitelancer64 on 14 Nov, 2019 23:03
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Kerosene is naturally colorless, and standard RP-1 is dyed red.
LOX is naturally a pale blue. This is LOX.
They have good reasons to stabilize the RP1 tank basin with that extra structure since it's directly over the octaweb, but not as much reason to add the same structure to the shorter LOX tank above the RP1 tank, as that idea would imply they did so later or that Spaceflight101 was incorrect. It's possible SpaceX doesn't pay the extra cost of red dye in their RP1, which wouldn't be a trivial amount, and that the blue tint of the basin is shining through. It would be a lot easier to just ask someone at SpaceX.
RP-1 is dyed red by the manufacturers, not by SpaceX, and it doesn't cost extra. It actually costs more to get RP-2, which is further refined to be lower in sulfur content and is not dyed red. RP-1 is dyed red to comply with federal law regarding tax-exempt status for non-road-grade kerosene. Locomotive diesel fuel is dyed red for the same reason.
Picture of standard RP-1
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#150 by ejb749 on 14 Nov, 2019 23:13
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Quote
They have good reasons to stabilize the RP1 tank basin with that extra structure since it's directly over the octaweb, but not as much reason to add the same structure to the shorter LOX tank above the RP1 tank, as that idea would imply they did so later or that Spaceflight101 was incorrect. It's possible SpaceX doesn't pay the extra cost of red dye in their RP1, which wouldn't be a trivial amount, and that the blue tint of the basin is shining through. It would be a lot easier to just ask someone at SpaceX.
https://twitter.com/elonmusk/status/1116479251669078016
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#151 by LouScheffer on 14 Nov, 2019 23:52
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This is surely the second stage LOX tank. We can determine this from the sloshing of the liquid and the amount remaining, in addition to the color above.
We see it slosh from one side to the other, and it does not complete even half a cycle in two seconds. So the slosh rate is very slow, meaning low acceleration. Under 1 g after landing it would be much faster. Next, the landing was a 8:26, and the sloshing shown at 8:54, almost 30 seconds later. Any remaining slosh in the first stage would have already almost died out. Finally the surface of the sloshing liquid is nowhere near flat. This can only happen in (much) reduced gs. So this is the second stage.
Next, how much liquid is shown? The puddle covers about 1/2 the diameter. The dome (from SpaceX pictures) looks like it is about 1 meter deep. We can crudely approximate the liquid volume as a cone of height 1/2 meter and a radius of 1 meter. Using V = 1/3*pi*r^2*h, we get about half a cubic meter. That's roughly 500 kg, using a density of 1 (good enough for both LOX and kerosene for the accuracy needed here.)
Now an Merlin engine eats about 288 ks/sec at full throttle. (981,000 N /348 (ISP) / 9.8 = 288 kg/sec). Of this 208 kg/sec are LOX and 80 kg/sec are kerosene, assuming a mixture ratio of 2.6. This then represents 2.5 seconds worth of LOX (plus whatever is in the piping), or 6+ more seconds of kerosene. This makes sense for LOX, which just needs a 1 second circularization burn (likely not at full throttle) but would be a crazy amount of kerosene to have left over after landing, or for the remaining second stage burns.
So, this can only be the second stage LOX tank.
EDIT: fix typo -
#152 by Gliderflyer on 15 Nov, 2019 00:03
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In addition to all these good reasons that this is the LOX tank and not the kerosene tank, the kerosene tank has giant LOX transfer tube running down the middle, which this image lacks.
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#153 by bobaroony on 15 Nov, 2019 00:11
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re: the sloshing, after 30 seconds from landing on barge, the ocean action on the barge would be reflected in the 1st stage lox tank sloshing at low freq.
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#154 by CyndyC on 15 Nov, 2019 01:50
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.......This then represents 2.5 seconds worth of LOX (plus whatever is in the piping), or 6+ more seconds of kerosene. This makes sense for LOX, which just needs a 1 second circularization burn (likely not at full throttle) but would be a crazy amount of kerosene to have left over after landing, or for the remaining second stage burns.
So, this can only be the second stage LOX tank.
Did you really mean to say a crazy amount left for either stage, before concluding this was the 2nd stage tank? They still had a 2-second 2nd stage burn left to go for insertion, and it occurs to me I don't know if they burn again for de-orbit. They HAVE cut it that close for a landing before, if you recall the one heading for the drone ship and it dropped short into the ocean.
At least we can be certain it's LOX now, but I would like to leave my suggestion on the table to save some fuel costs by leaving the dye out of processing RP1, for non tax-exempt launches I'll add now thanks to Whitelancer's input. A major business lesson I learned during a stint in newspaper logistics is how fast fractions of a cent can add up, and we all know a launch uses millions of gallons, and Elon Musk has shared that the biggest cost of any rocket launch is the fuel. You heard the rest here first -
#155 by Robotbeat on 16 Nov, 2019 03:28
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Looks like they're raising by a little under 5km a day. (Attachment is an animated gif)
Except STARLINK 1040, which looks to be decaying 1km/day. -
#156 by Yazata on 16 Nov, 2019 07:26
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So why would they install a camera and lights in the second stage LOX tank? Presumably the SpaceX engineers want more information on how liquid behaves in there.
How do they prevent the remaining liquid in mostly empty tanks from forming into floating fluid balls when the engines are off and the vehicle is coasting? Is fuel and oxidizer in the lines sufficient to restart the engines and produce enough acceleration to corral the remaining fluid at the bottom of the tanks? Does Falcon 9 have headers? -
#157 by ugordan on 16 Nov, 2019 08:02
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They use cold N2 thrusters to settle the propellant in addition to attitude control.
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#158 by smoliarm on 16 Nov, 2019 08:31
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So why would they install a camera and lights in the second stage LOX tank? Presumably the SpaceX engineers want more information on how liquid behaves in there.
...
Well, I guess they do it by the same reason such cameras are installed in some regular/industrial LOX or LN2 tanks - for monitoring cryogenic liquid and the insides of the tank.
It's really very handy thing - you can detect visually (and - immediately!) almost all typical troubles which may happen during tanking/detanking cryogenic liquid. E.g., you can easily SEE any crystal build-up, and even tell apart water and CO2 crystals.
Thus you can identify the problem and, sometimes, even locate the faulty gasket.
And BTW they told me there are no "lights" - such monitoring systems utilize some cheap IR-cameras which give "illumination" of its own. So it's a sensor and a lamp - at the same time.
And (AIUI) the bluish picture is a result of false-color conversion of IR-picture to "RGB". At least from what I saw - LN2 on these monitors looks the same color as LOX. -
#159 by Danderman on 16 Nov, 2019 15:23
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Turns out Thomas Burghardt of NSF and Stephen Clark of SFN both reported the lower insertion was to check out and de-orbit improperly functioning satellites from a lower altitude. They'll actually be drifting to their respective planes farther up if they check out, at 350km/217mi, but still lower than the previous insertion at 440km/273mi. Operational orbit will remain the same at 550km/342mi, although previously lowered right before the test launch with FCC approval in April.
From Thomas Burghardt's article at https://www.nasaspaceflight.com/2019/11/spacex-cape-return-first-operational-starlink-mission/:QuoteAfter launch, SpaceX will establish contact with each satellite and confirm each spacecraft’s health before maneuvering them to 350 kilometer orbits. Any satellites not functioning properly after launch will be left in the initial 280 kilometer orbit to naturally deorbit. Satellites that pass their health checks will use the 350 kilometer orbit to drift to their orbit planes, where they will then maneuver up to their operational altitude of 550 kilometers.
From SFN in the next to last paragraph at https://spaceflightnow.com/2019/11/10/spacex-readies-upgraded-starlink-satellites-for-launch/:QuoteSpaceX says injecting the satellites into a lower orbit at an altitude of 174 miles will allow time for checkouts before orbit-raising. The Starlink satellites launched in May were deployed in a higher orbit at an altitude of around 273 miles (440 kilometers).
What is the original source reporting that these satellites will deploy to more than one plane?
