Author Topic: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION  (Read 74736 times)

Offline kevinof

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From the ground camera yes, it looks like a significant attitude change , but from the on-board it looks pin straight. I know the on-board shots do lack perspective and it's more difficult to judge but it looked bang to me.

But that angle is a bit deceptive, the extreme telephoto lens makes it look like a larger angle than it is.

To me, it was more the separation of the vapor/exhaust contrail from the S1 cylinder body than the photo angle that made the angle of attack look extreme.   I've watched over & over how the entry burn is straight into the velocity vector of the stage, & today's video coverage shows a pretty significant attitude change within a few seconds of the entry burn shutdown.

Offline deruch

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CRS-12: 3310

The cargo figure you have for CRS-12 is wrong.  Per the NASA mission overview, this dragon is taking 2910kg of total cargo (including ISS-CREAM).  Which fits with the statement during the pre-launch briefing that this was the 2nd heaviest mission so far-- CRS-8 being the heaviest.  So, the total cargo delivered needs to adjusted downward 400kg.

https://www.nasa.gov/sites/default/files/atoms/files/spacex_crs-12_missionoverview.pdf
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Offline Jdeshetler

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Looking side way, looks like 20-25 degree angle of attack.


Offline whitelancer64

Cropped version of SoaceX landing photo. I know the side on angle isn't great, but to me it looks mainly like dirt (sand?) on the pad, the pad paint job seems to have held up pretty well?

The landing pad is concrete. This has been definitively established multiple times. It's surrounded by a ring of compacted dirt.
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Offline abaddon

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Cropped version of SoaceX landing photo. I know the side on angle isn't great, but to me it looks mainly like dirt (sand?) on the pad, the pad paint job seems to have held up pretty well?
The landing pad is concrete. This has been definitively established multiple times. It's surrounded by a ring of compacted dirt.
I believe @FutureSpaceTourist was talking about what looks like a bit of a wash of dirt/sand on the pad, not what the pad is made of, and suggesting that it is in fact dirt/sand and not damage from the rocket plume.  As noted, it is difficult to say for sure due to the angle, but I would tend to agree.
« Last Edit: 08/15/2017 04:00 PM by abaddon »

Offline Rocket Science

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The grid fins seemed to be much more active during the landing sequence, compared to previous missions.
They looked like they were getting a workout and still makes me smile every time... :)
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Offline joncz

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I believe @FutureSpaceTourist was talking about what looks like a bit of a wash of dirt/sand on the pad, not what the pad is made of, and suggesting that it is in fact dirt/sand and not damage from the rocket plume.  As noted, it is difficult to say for sure due to the angle, but I would tend to agree.

Surely so.  They've scarified the nearby surface to remove topsoil in preparation for pouring concrete for the second pad.  They certainly didn't have a water truck active just prior to launch for dust control, and with the wind at the coast, I have no doubt there was a layer of dust and sand across the entire concrete surface.

Offline Basto

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If you compare the landing location on the pad to CRS 11 and you can see that the rocket performed the landing perfectly.

While the AOA looked pretty dramatic, there are not many landings that have had as clear a view of the entire process from the ground. So I am assuming it was not far out of the ordinary. Either that or we were witnessing part a block IV upgrade of some sort.


Offline kenny008

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My understanding is that they target offshore until they are comfortable that the engines are performing properly, then bring it over the pad for final landing.  The AOA maneuver occurred right after the entry burn was complete, so this might be when they are satisfied the engines are working properly and they can then target the pad. 

Not convinced it's any different than previous flights.  Might be just a great view this time.

Offline AlesH

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Where exactly (relative to ISS) is Dragon CRS-12 right now (Tuesday, August 15th, 18:30 UT)? Do you know the times and parameters of Dragon's orbital maneuvers? The officially issued TLE parameters do not make much sense to me, because the arrival to the ISS would be up to August 17th (without very strong and ineffective maneuvers).
« Last Edit: 08/15/2017 07:01 PM by AlesH »

Offline stcks

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you will notice some of the block 4 differences if you have a good eye and watch the flight footage and not all are small differences but most are. I'll leave you with that until launch day.

Well, its the day after and I've looked at tons of pictures and video and I can't find anything different. Care to elaborate?

Offline ppb

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Looking side way, looks like 20-25 degree angle of attack.


Great pix. I'm kind of amazed the little (relative to the body) grid fins have that much control authority. The CG must really be close to the engines at that point.
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Offline LouScheffer

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The takeoff looked quicker to me, but I compared it to CRS-11 and it's almost identical.

Looking at both videos, at the frame where the clock ticks from 6 to 7, the bottom of the booster is about 3 "floors" above the top of the FSS just behind it.  Side by side, it looks exactly the same to me.  The telemetry at this frame shows 53 km/h for CRS-11, and even a little less for CRS-12 (51 km/h).   So certainly a 10% thrust increase is ruled out - that would change the initial acceleration from something like 0.3 G up to 0.4 G up, which would be clearly noticeable.  Instead the two launches look identical to within the accuracy of the webcast.
EDIT: fixed units
« Last Edit: 08/16/2017 12:45 AM by LouScheffer »

Offline stcks

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The takeoff looked quicker to me, but I compared it to CRS-11 and it's almost identical.

Looking at both videos, at the frame where the clock ticks from 6 to 7, the bottom of the booster is about 3 "floors" above the top of the FSS just behind it.  Side by side, it looks exactly the same to me.  The telemetry at this frame shows 53 m/s for CRS-11, and even a little less for CRS-12 (51 m/s).   So certainly a 10% thrust increase is ruled out - that would change the initial acceleration from something like 0.3 G up to 0.4 G up, which would be clearly noticeable.  Instead the two launches look identical to within the accuracy of the webcast.

Yes there were clearly no thrust increases on CRS-12.

Offline Joffan

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The takeoff looked quicker to me, but I compared it to CRS-11 and it's almost identical.

Looking at both videos, at the frame where the clock ticks from 6 to 7, the bottom of the booster is about 3 "floors" above the top of the FSS just behind it.  Side by side, it looks exactly the same to me.  The telemetry at this frame shows 53 m/s for CRS-11, and even a little less for CRS-12 (51 m/s).   So certainly a 10% thrust increase is ruled out - that would change the initial acceleration from something like 0.3 G up to 0.4 G up, which would be clearly noticeable.  Instead the two launches look identical to within the accuracy of the webcast.

I think the difference might just be that the audio count of zero was better synchronized to the hold-down release. Because it looked quicker to me too, but I don't see that on telemetry or visuals.
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Offline envy887

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The takeoff looked quicker to me, but I compared it to CRS-11 and it's almost identical.

Looking at both videos, at the frame where the clock ticks from 6 to 7, the bottom of the booster is about 3 "floors" above the top of the FSS just behind it.  Side by side, it looks exactly the same to me.  The telemetry at this frame shows 53 m/s for CRS-11, and even a little less for CRS-12 (51 m/s).   So certainly a 10% thrust increase is ruled out - that would change the initial acceleration from something like 0.3 G up to 0.4 G up, which would be clearly noticeable.  Instead the two launches look identical to within the accuracy of the webcast.

Assuming the liftoff mass was the same... which it may not have been since it depends on prop temp.

I don't have any evidence that thrust was higher, and I actually doubt that it was, but I'm just pointing out that acceleration depends on more than just thrust.

Offline Steven Pietrobon

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Maybe the thrust increase was for the second stage. CRS-12 second stage burn time was 10 seconds shorter than CRS-11 (6:38 versus 6:48). Of course, different payload mass, orbit and throttling could help to explain the difference.
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Online Bargemanos

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« Last Edit: 08/16/2017 01:53 PM by Bargemanos »

Offline abaddon

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I suppose it is possible that the booster was cleared for higher thrust but the mission profile chose not to use it.  No need for it on this mission and maybe NASA didn't want to be the first guinea pig.

Offline stcks

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Maybe the thrust increase was for the second stage. CRS-12 second stage burn time was 10 seconds shorter than CRS-11 (6:38 versus 6:48). Of course, different payload mass, orbit and throttling could help to explain the difference.

Maybe, but ChrisG specifically said M1D:

Quote
The first Block 4 did make use of increased-thrust Merlin 1D engines. The thrust increase of the Merlin 1Ds is also incremental, with a final thrust increase set to debut on the Block 5.

If there was a thrust increase on the first stage it was so slight as to not be noticeable. There are some really good telemetry graphs and two comparisons between CRS-11 and CRS-12 that can be found on this reddit post. Its quite obvious that, everything else being relatively equal, both CRS-11 and CRS-12 were flown with basically the same thrust (but different max-q throttling).

I'm very curious what was meant by the above quote. Did it just mean that the flown engines were uprated but flown at same thrust levels?

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