SpaceX Starship : First Flight : Starbase, TX : 20 April 2023 - DISCUSSION

[frogamazog]

Seems unlikely to me that Miazawa misspoke. More likely they are using some simplifying approaches in this first flight that they may hope to move beyond in future flights. Going with helium pressurization in the booster would seem like a reasonable “simplification” in early prototype tests.

[frogamazog]

Seems unlikely to me that Miazawa misspoke. More likely they are using some simplifying approaches in this first flight that they may hope to move beyond in future flights. Going with helium pressurization in the booster would seem like a reasonable “simplification” in early prototype tests.

[lrk]

One of the objectives for the long-duration Booster static fire they did a month or two ago was testing autogenous pressurization.  It may be that they use autogenous in flight, but pressurize with helium on the ground before launch.  That would simplify the GSE needs for this initial test by avoiding the need to supply high-pressure gaseous CH4 and O2.  Probably something they would like to eliminate long-term.

[rsdavis9]

Didn't we see helium on the qd pinout pics?
Quick Disconnect for both ship and booster.
SQD and BQD respectively.

[envy887]

One of the objectives for the long-duration Booster static fire they did a month or two ago was testing autogenous pressurization.  It may be that they use autogenous in flight, but pressurize with helium on the ground before launch.  That would simplify the GSE needs for this initial test by avoiding the need to supply high-pressure gaseous CH4 and O2.  Probably something they would like to eliminate long-term.

It will be difficult to eliminate He pressurization on the upper stage during boost, because the subcooled props will really tend to condense out the gaseous autogenous pressurants, especially when agitated during flight.

They could get around that issue by using the booster to supply hot gaseous pressurants to the upper stage in flight, or by running a heater or APU on the upper stage.

[Alberto-Girardi]

One of the objectives for the long-duration Booster static fire they did a month or two ago was testing autogenous pressurization.  It may be that they use autogenous in flight, but pressurize with helium on the ground before launch.  That would simplify the GSE needs for this initial test by avoiding the need to supply high-pressure gaseous CH4 and O2.  Probably something they would like to eliminate long-term.

It will be difficult to eliminate He pressurization on the upper stage during boost, because the subcooled props will really tend to condense out the gaseous autogenous pressurants, especially when agitated during flight.

They could get around that issue by using the booster to supply hot gaseous pressurants to the upper stage in flight, or by running a heater or APU on the upper stage.

Great point. We know that there is no connection (not even eletrical, only a wireless data one, IIRC) between the two stages, so this might be true.

But wasn't the problem on the booster? edit: NO, we do not know where the problem was, sorry for the error

[envy887]

One of the objectives for the long-duration Booster static fire they did a month or two ago was testing autogenous pressurization.  It may be that they use autogenous in flight, but pressurize with helium on the ground before launch.  That would simplify the GSE needs for this initial test by avoiding the need to supply high-pressure gaseous CH4 and O2.  Probably something they would like to eliminate long-term.

It will be difficult to eliminate He pressurization on the upper stage during boost, because the subcooled props will really tend to condense out the gaseous autogenous pressurants, especially when agitated during flight.

They could get around that issue by using the booster to supply hot gaseous pressurants to the upper stage in flight, or by running a heater or APU on the upper stage.

Great point. We know that there is no connection (not even eletrical, only a wireless data one, IIRC) between the two stages, so this might be true.

But wasn't the problem on the booster?

I don't know which stage had the issue yesterday, or whether it was even a issue on the vehicle or GSE.

But the consumables cost for the He to press only the ullage space before liftoff is very small, probably only a few thousand dollars. If it saves any complexity, that's a good trade until flight rates are quite high.

[rdale]

they rely on National Weather Service entirely.

That's a new one for me - that would be highly unethical for the NWS to be their sole weather provider, plus that would mean their weather criteria are available for public viewing and we know that's not the case

Where have you seen that publicized?

[kraisee]

Given that the propellant liquids are super chilled, using GOX or GCH4 in the ullage space would cause much of the gas to condense into liquid. He won't condense at these temps, so it is used to keep the pressure stable initially. Once the engines start, the autogenous system takes over.

He may also be used for purging lines, though N2 is probably sufficient for most instances.

I'm not sure; is He used to initially spin any of the Raptor 2 turbopumps too?

Ross.

[joek]

...
But wasn't the problem on the booster?

Do not think that was stated-confirmed? Do we have a reference?

In any case, need to be careful speculating about what we are see now vs. what is likely in the future. SpaceX appears to be taking some short term tactical steps in order to buy down (or gain more knowledge of) longer term strategic risks. Not unusual given their MO.

[xvel]

On spacex stream was clearly stated multiple times that it was "first stage issue"

[joek]

they rely on National Weather Service entirely.

That's a new one for me - that would be highly unethical for the NWS to be their sole weather provider, plus that would mean their weather criteria are available for public viewing and we know that's not the case

Where have you seen that publicized?

They do not rely on NWS exclusively for local launch conditions, as clearly stated in the PEA/WR:

Prior to launch, SpaceX will deploy weather balloons to measure weather data. ...

Not sure about reentry conditions; PEA is vague on that, but implies USCG data (which presumably is better than NWS public data?):

Weather and ocean current data would be used to further characterize the debris field as the operation is conducted. During the operation, SpaceX would coordinate findings and action items directly with the USCG Sector 14 to ensure all of the requirements of the Letter of Intent are met.

[cuddihy]

Sorry, wasn’t trying to imply they don’t use multiple sources, just reiterating that as far as I know the only government entity supporting weather for them in Texas is the NWS, not the USSF.

[Jcc]

Given that the propellant liquids are super chilled, using GOX or GCH4 in the ullage space would cause much of the gas to condense into liquid. He won't condense at these temps, so it is used to keep the pressure stable initially. Once the engines start, the autogenous system takes over.

He may also be used for purging lines, though N2 is probably sufficient for most instances.

I'm not sure; is He used to initially spin any of the Raptor 2 turbopumps too?

Ross.

I think N2 is supplied from GSE to spin the outer 20 engines, and the externally mounted copvs (covered up) contain N2 to spin the inner engines and for restart. I think N2 is also used to pressurize empty stages for transport. To pressurize full tanks before engine start maybe they do need a heater for the propellant and do that outside the tank.

[clongton]

I don't think there is a 37th Space Wing? They have their own meteorologists.

Can you provide an update on the potential for shear at high altitude? AIUI, that is/was the main concern for a Thursday launch.

[Jim]

Prior to launch, SpaceX will deploy weather balloons to measure weather data. ...

That is for winds aloft and not local conditions.

[Jim]

Weather and ocean current data would be used to further characterize the debris field as the operation is conducted. During the operation, SpaceX would coordinate findings and action items directly with the USCG Sector 14 to ensure all of the requirements of the Letter of Intent are met.

That would be for the sea conditions and not weather.

[Jim]

they rely on National Weather Service entirely.

That's a new one for me - that would be highly unethical for the NWS to be their sole weather provider, plus that would mean their weather criteria are available for public viewing and we know that's not the case

Where have you seen that publicized?

How so?  NWS can supply the data.  It is up to SpaceX to determine the criteria and it doesn't have to share it.

[joek]

That is for winds aloft and not local conditions.

They have other sensors for that. Did not think it was worth mentioning, but, from the previous PEA:

SpaceX plans to use a portable sound detection and ranging (SODAR) device to collect weather data needed for launch and landing. The SODAR sends out a short sonic pulse every 15 minutes that can reach 92 decibels (dB) at the source and dissipates to 60 dB within 100 feet. The SODAR would be located on a SpaceX private parcel in the production and manufacturing area, north of the solar farm.

[clongton]

All this discussion about He vs. autogenous begs the question - how are the propellants going to be pressurized for engine restart on the surface of the moon or Mars?