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# Why did thethis fairing separation happen at such a high altitude? (SpaceX Iridium-6/GRACE-FO)

I noticed in the video of the recent Iridium-6/GRACE-FO launch that the fairing separation happened at an altitude of about 147143 kilometers. This is significantly higher than any altitude I can remember. I first started watching this last year and noted the altitude for several launches here.

After seeing the 147143 km, I went back and checked several more recent SpaceX launches and compiled more numbers that can be compared with the table in the previous question. It seems Iridium-6/GRACE-FO stands out with a uniquely and significantly higher altitude for fairing separation than any other recent launch as well, including two other Iridium launches.

MISSION                speed  altitude  post 2nd stage
km/hr    km      ignition (sec)
-------                -----    ----    --------------
Iridium-6/GRACE-FO     8754     147143          28
Bangabandhu Sat- 1     8978     111          53
TESS                   7055     107          24
Iridium-15             8052     110          42
HISPASAT 30W-6         8979     111          48
PAZ Mission            6509     119          20
CRS-14                 8158     115?         29
GovSat-1               9222     111          52
FH Test Roadster      10196     115          28
Iridium-4              7578     111          30
CRS-13                 5982     106?         32


# Why did the fairing separation happen at such a high altitude? (SpaceX Iridium-6/GRACE-FO)

I noticed in the video of the recent Iridium-6/GRACE-FO launch that the fairing separation happened at an altitude of about 147 kilometers. This is significantly higher than any altitude I can remember. I first started watching this last year and noted the altitude for several launches here.

After seeing the 147 km, I went back and checked several more recent SpaceX launches and compiled more numbers that can be compared with the table in the previous question. It seems Iridium-6/GRACE-FO stands out with a uniquely and significantly higher altitude for fairing separation than any other recent launch as well, including two other Iridium launches.

MISSION                speed  altitude  post 2nd stage
km/hr    km      ignition (sec)
-------                -----    ----    --------------
Iridium-6/GRACE-FO     8754     147          28
Bangabandhu Sat- 1     8978     111          53
TESS                   7055     107          24
Iridium-15             8052     110          42
HISPASAT 30W-6         8979     111          48
PAZ Mission            6509     119          20
CRS-14                 8158     115?         29
GovSat-1               9222     111          52
FH Test Roadster      10196     115          28
Iridium-4              7578     111          30
CRS-13                 5982     106?         32


# Why did this fairing separation happen at such a high altitude? (SpaceX Iridium-6/GRACE-FO)

I noticed in the video of the recent Iridium-6/GRACE-FO launch that the fairing separation happened at an altitude of about 143 kilometers. This is significantly higher than any altitude I can remember. I first started watching this last year and noted the altitude for several launches here.

After seeing the 143 km, I went back and checked several more recent SpaceX launches and compiled more numbers that can be compared with the table in the previous question. It seems Iridium-6/GRACE-FO stands out with a uniquely and significantly higher altitude for fairing separation than any other recent launch as well, including two other Iridium launches.

MISSION                speed  altitude  post 2nd stage
km/hr    km      ignition (sec)
-------                -----    ----    --------------
Iridium-6/GRACE-FO     8754     143          28
Bangabandhu Sat- 1     8978     111          53
TESS                   7055     107          24
Iridium-15             8052     110          42
HISPASAT 30W-6         8979     111          48
PAZ Mission            6509     119          20
CRS-14                 8158     115?         29
GovSat-1               9222     111          52
FH Test Roadster      10196     115          28
Iridium-4              7578     111          30
CRS-13                 5982     106?         32

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# Why did the fairing separation happen at such a high altitude? (SpaceX Iridium-6/GRACE-FO)

I noticed in the video of the recent Iridium-6/GRACE-FO launch that the fairing separation happened at an altitude of about 147 kilometers. This is significantly higher than any altitude I can remember. I first started watching this last year and noted the altitude for several launches here.

@awksp's excellent answer explains the relative constancy of the altitude as likely originating from a standardized spec. The answer is thorough and worth reading, but here is a snippet from there:

...after the 3-sigma high theoretical free molecular heating for a flat plate normal to the free stream drops below 1135 W/m$$^2$$ (360 Btu/hr ft$$^2$$) based on the 1962 United States Standard Atmosphere.

After seeing the 147 km, I went back and checked several more recent SpaceX launches and compiled more numbers that can be compared with the table in the previous question. It seems Iridium-6/GRACE-FO stands out with a uniquely and significantly higher altitude for fairing separation than any other recent launch as well, including two other Iridium launches.

Question: Why did the fairing separation here happen at such a high altitude compared to so many other SpaceX launches? Solar activity-induced atmospheric heating? Abundance of caution for this payload combo? Anomaly? Just to see if we're watching? Something else?

MISSION                speed  altitude  post 2nd stage
km/hr    km      ignition (sec)
-------                -----    ----    --------------
Iridium-6/GRACE-FO     8754     147          28
Bangabandhu Sat- 1     8978     111          53
TESS                   7055     107          24
Iridium-15             8052     110          42
HISPASAT 30W-6         8979     111          48
PAZ Mission            6509     119          20
CRS-14                 8158     115?         29
GovSat-1               9222     111          52
FH Test Roadster      10196     115          28
Iridium-4              7578     111          30
CRS-13                 5982     106?         32


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