SpaceX Falcon 9 : GPS III SV01 : SLC-40 : Dec. 23, 2018 - DISCUSSION

[envy887]

Why is there a dark spot on the tip of the fairing?

[dmc6960]

Extra thermal protection for this launch.

[CorvusCorax]

Why is there a dark spot on the tip of the fairing?

extra thermal protection, was just mentioned in the webcast


on other news, looks like the countdown didn't get to T-1:00, so no scrub due to upper level winds. damn!

[Jcc]

Hold due to LOX thermal limits. Is that too warm for needed performance, or was it a false alarm?

[jpo234]

Was the VP there?

[skymech231]

Did it get to warm or cold?

[RDMM2081]

Was the VP there?

This tweet says yes:

https://twitter.com/SciGuySpace/status/1075031761845919744

Huge launch for SpaceX today. @VP is there. Critical mission for critical customer (Air Force). And its their 21st (!) and final launch of the year. Webcast getting going now:

[jpo234]

Was the VP there?

This tweet says yes:

https://twitter.com/SciGuySpace/status/1075031761845919744

Huge launch for SpaceX today. @VP is there. Critical mission for critical customer (Air Force). And its their 21st (!) and final launch of the year. Webcast getting going now:

Ouch. Not a day you want to have a scrub.

[ugordan]

Was the VP there?

This tweet says yes:

https://twitter.com/SciGuySpace/status/1075031761845919744

Huge launch for SpaceX today. @VP is there. Critical mission for critical customer (Air Force). And its their 21st (!) and final launch of the year. Webcast getting going now:

Ouch. Not a day you want to have a scrub.

Where have I heard that before, go fever for big shots' sake, etc?

[deruch]

Abort with clear audio from countdown net

Very clear audio of the hold call at T-7:01--  "HOLD, HOLD, HOLD.  This is the Launch Director calling a HOLD for 1st stage LOX DP temps approaching thermally compensated limits.  Please proceed into abort."

I'm assuming that DP = Down Pipe.  According to the webcast presentation, the F9 starts the 1st stage engine chill right around the T-7minute mark.  So, right about then would be an appropriate time to encounter an anomalous or out-of-bounds temperature reading in the plumbing between the LOX tank and the engines. 

[Jakusb]

Did it get to warm or cold?

Out of family sensor, could also mean that the reading was not logical and thus false positive?

[codav]

Did it get to warm or cold?

Out of family sensor, could also mean that the reading was not logical and thus false positive?

Wording was "thermally compensated limits", so that means the temperature reading was outside the specification of the used temp sensor. These sensors are built to compensate any errors (e.g. non-linear) changes in the readings for a specified temperature range. If the temp runs outside this window, the value is no longer accurate. Could be a faulty sensor or a temperature too high at the location. That's what SpaceX engineers now need to check. Worst case would be the need to replace the sensor.

[AC in NC]

Ouch. Not a day you want to have a scrub.

Correction.  Not a day you want to blow up a payload.

[jpo234]

Ouch. Not a day you want to have a scrub.

Correction.  Not a day you want to blow up a payload.

That too.

[deruch]

Did it get to warm or cold?

Out of family sensor, could also mean that the reading was not logical and thus false positive?

Wording was "thermally compensated limits", so that means the temperature reading was outside the specification of the used temp sensor. These sensors are built to compensate any errors (e.g. non-linear) changes in the readings for a specified temperature range. If the temp runs outside this window, the value is no longer accurate. Could be a faulty sensor or a temperature too high at the location. That's what SpaceX engineers now need to check. Worst case would be the need to replace the sensor.

I don't think we can say that based on the information currently available.  e.g. If this sensor is in a location which is supposed to be insulated from the cold temps and it suddenly showed as too cold, that could potentially indicate improperly applied insulation or potentially even a minor LOX leak, etc.  Also, the exact call from the LD was for temps "approaching thermally compensated limits."  So, it sounds like at the time of the hold, it might have still been reading within the allowed limits but clearly trending to a violation or possibly violating some rate of change limit (like not actually speeding but accelerating too hard).  All of which is pure hypothetical and just to say that we outsiders don't really know anything and therefore can't say what the worst case might be.

[whitelancer64]

Did it get to warm or cold?

Out of family sensor, could also mean that the reading was not logical and thus false positive?

The phrase "out of family" just means "outside the known range of readings normally gotten from this type of sensor," because you're not going to get exactly the same reading from all sensors.

For example, if you set up ten sensors and put them in the bottom of the same LOX tank, you'll get 10 slightly different readings, but they should all be within an expected range. That's "family."

[LouScheffer]

With the press kit, we can now see the sequence of burns:

Launch into an LEO x 4000 km orbit (about 2 hour period).  Takes LEO + 830 m/s.

Wait one hour until apogee, then go 4000 x 20000 km (6.9 hour orbit) .  Takes 1960 m/s.  Release satellite.

Second stage coasts to apogee (3.45 more hours).   Then a retrograde burn at -480 m/s to a 100 x 20000 orbit (5.8 hour period).   Wait 2.9 hours and re-enter.

Total delta-V is about LEO+3270 m/s, as predicted.  Re-entry at launch + 6.5 hours, as stated.  Satellite needs about 970 m/s to circularize.

4000x35000 is a pretty standard second stage graveyard orbit for centaur, so if the deorbit burn is what pushed this expendable, it seems a bit wasteful...

Maybe this is a way of demonstrating and quantifying their extra performance.  It's minimum risk for the Air Force since they use the extra capacity after the spacecraft release, so all margins are available in case of contingency.  But if it works, maybe next time maybe the AF will allow them to use the margin for recovery instead of de-orbit (for a reduced price, most likely).

[Brovane]

Hasn't it been a while since SpaceX has had a hold like this in the final 10-mins of countdown? 

[Newton_V]

Is the 2nd stage de-orbit a requirement from the USAF, or is it a choice by SpaceX?  (Or something else?)

It's a requirement.

[whitelancer64]

Hasn't it been a while since SpaceX has had a hold like this in the final 10-mins of countdown?

Bangabandhu had a scrub at T-58

But you're right. Nothing else like that in a while.

SpaceX has been in a pretty smooth run.