totm nov 2023 SpaceX Discussion Thread

[softweir]

58 minutes ago, Spaceception said:

Less than a minute for second stage engine restart!

What flew off the engine when it ignited?

It's a ring of stiffening material that keeps the second-stage engine bell in shape during launch. The engine bell is made of very thin, high-temperature alloy that could fold up under launch accelerations. Once the S2 engine is lit the pressure of expanding gasses holds it in shape, while it is coasting there are no vibrations or acceleration to damage the bell.

Fun fact: they glue the stiffener on with a material that melts when the engine bell heats up, releasing the stiffener.

[CatastrophicFailure]

Re: that "flimsy" paper-thin engine bell:

There's a long metal dingus that goes up inside the second stage engine, possibly a separation pusher someone said. Seems likely to damage that fragile engine bell if there were a torque on the booster at exactly the wrong moment during staging. 

If the bell did get torn, what would realistically happen? Would it rip itself apart or could the upper stage potentially limp into space?

[Mitchz95]

2 hours ago, Spaceception said:

Which one was that? Could you give the link?

SES-9.

 

[StupidAndy]

3 hours ago, cubinator said:

10 minutes ago, Mitchz95 said:

SES-9.

 

Also, do you think that when Crew Dragon is operational they'll show the crew portraits in the bottom right?

oh that is the funny thing I would like to see!

[CatastrophicFailure]

Also, can we just get a round of grins for the fact that SpaceX just launched three rockets in twelve days?

May not be a record, but it's the first time it's happened in my useful memory at least. Which is, admittedly, rather short, despite being an old... er, what was I saying? 

[KSK]

Donating a big grin right here. I, for one, welcome our improved launch cadence Spaaaaaace Overlords!

[Steel]

7 hours ago, CatastrophicFailure said:

If the bell did get torn, what would realistically happen? Would it rip itself apart or could the upper stage potentially limp into space?

Oh it would absolutely rip itself apart. Of course an engine doesn't actually need the bell to function, but it would severely impact the performance of the engine, probably to the point where it wouldn't have the dV needed to reach orbit

Edited July 6, 2017 by Steel

[TheEpicSquared]

https://twitter.com/elonmusk/status/882761133177790464

Sorry, can't embed tweets due to mobile, but 43,000km! Wow 

[sevenperforce]

12 hours ago, Ultimate Steve said:

I'm not sure if this is what you're talking about, but there is a ring of stuff at the base of the nozzle (not sure of the purpose) that falls off that I've noticed before.

Also, you're above 3000 rep!

Everyone asks this once, haha. The niobium-alloy engine bell is so thin at the base that it can easily be bent during transport, ascent, and staging. Only once the MVac is at full throttle is the exhaust pressure high enough to keep the engine bell perfectly round. So SpaceX attaches a circular stiffener ring to the edge of the engine bell to ensure it maintains its shape until the MVac throttles up, at which point the heat and expansion breaks it off and sends it flying.

12 hours ago, Just Jim said:

OK, admit it y'all... am I the only one that's tried to spin the live-feed map-view around in different directions??? 

Every gorram time.

10 hours ago, CatastrophicFailure said:

Re: that "flimsy" paper-thin engine bell:

There's a long metal dingus that goes up inside the second stage engine, possibly a separation pusher someone said. Seems likely to damage that fragile engine bell if there were a torque on the booster at exactly the wrong moment during staging. 

If the bell did get torn, what would realistically happen? Would it rip itself apart or could the upper stage potentially limp into space?

The metal pusher extends straight up the center of the engine bell and presses against the throat, which is by far the strongest part of the engine bell. Honestly, it's one of the strongest components on the entire second stage, probably second only to the payload adapter. 

If the edge of the bell clipped the interstage during separation and was just slightly bent, then the exhaust pressure would straighten it back out. If its structural integrity was breached, even slightly, then it would rip itself apart on ignition.

I wonder if the nozzle extension is frangible enough to separate completely if that happened, essentially leaving behind an underexpanded SL Merlin. Reduced thrust and isp but perhaps enough to reach a lower orbit.

2 hours ago, TheEpicSquared said:

43,000km! Wow 

Holy crap! That's impressive.

I wonder if it would've had enough margin for S1 recovery...or at least a recovery attempt.

[Scotius]

I just got back from work and watched the replay on YT. Holy vista Batman! Weather was perfect. Then i imagined how RTLS landing would look in such beautiful conditions We would be able to see EVERYTHING! Alas, not this time...

[KSK]

1 hour ago, sevenperforce said:

Holy crap! That's impressive.

I wonder if it would've had enough margin for S1 recovery...or at least a recovery attempt.

Heh - this is one question where KSP does give you a reasonable real world answer.  Or at least a feel for that answer.

Any KSP novice (cough) who's put a ship into a horribly eccentric orbit will know that a little bit of delta-V (relatively speaking) can result in a significant increase in apoapsis. So they wouldn't have had enough margin to recover S1 and put the payload in their contracted minimum transfer orbit.

[RCgothic]

Can we back calculate what the maximum payload to the minimum GTO is and compare it to Spacex's stated values?

[CatastrophicFailure]

5 hours ago, TheEpicSquared said:

https://twitter.com/elonmusk/status/882761133177790464

Sorry, can't embed tweets due to mobile, but 43,000km! Wow 

"Hi, Intelsat? This is Elon. I'm not sure how to tell you this, it seems our second stage was a bit peppier than we thought and we just sent your satellite to the Moon. But if you give Jeff Bezos a call he might want to buy it at a fair price."

[TheEpicSquared]

3 minutes ago, CatastrophicFailure said:

"Hi, Intelsat? This is Elon. I'm not sure how to tell you this, it seems our second stage was a bit peppier than we thought and we just sent your satellite to the Moon. But if you give Jeff Bezos a call he might want to buy it at a fair price."

Speaking of which, are there public figures on how much F9 can take to TLI?

[sevenperforce]

1 hour ago, RCgothic said:

Can we back calculate what the maximum payload to the minimum GTO is and compare it to Spacex's stated values?

That's the sort of question I like!

2 minutes ago, TheEpicSquared said:

Speaking of which, are there public figures on how much F9 can take to TLI?

They haven't published one, to my knowledge, but if it can take 8.3 tonnes to nominal GTO (2.5 km/s out of LEO) then it can take at least 3.4 tonnes to TLI (4.1 km/s out of LEO). And they're claiming 4 tonnes to trans-Martian injection.

[Brotoro]

I'm still waiting on seeing the on-barge landing footage from the Bulgariasat flight. Come on, SpaceX.

[sevenperforce]

6 hours ago, RCgothic said:

Can we back calculate what the maximum payload to the minimum GTO is and compare it to Spacex's stated values?

Coming back to this...

According to the Intelsat 32e webcast, second-stage startup took place at 9,384 km/h and 82.7 km. SECO-1 took place at approximately 26,857 km/h and 164 km. Restart took place at 26,502 km/h and 248 km. SECO-2 took place at 35,478 km/h and 262 km. Intelsat-35e massed 6,671 kg. Our best figures on the Falcon 9 FT (from here) are a 4-tonne upper stage carrying 107.5 tonnes of propellant and a 22.2-tonne first stage carrying 411 tonnes of propellant.

Now if I can just crunch some numbers...

[magnemoe]

5 hours ago, CatastrophicFailure said:

"Hi, Intelsat? This is Elon. I'm not sure how to tell you this, it seems our second stage was a bit peppier than we thought and we just sent your satellite to the Moon. But if you give Jeff Bezos a call he might want to buy it at a fair price."

LOL, however the first satellite in solar orbit was an soviet moon mission who missed. 
But why put Ap at 48K km? its higher than GEO, from my experience in KSP it would make it more expensive for satellite to circulate.
Raising Pe will help. 

[sevenperforce]

5 minutes ago, magnemoe said:

LOL, however the first satellite in solar orbit was an soviet moon mission who missed. 
But why put Ap at 48K km? its higher than GEO, from my experience in KSP it would make it more expensive for satellite to circulate.
Raising Pe will help. 

IIRC, raising the apogee higher places the satellite's period as close to 24 hours as possible. This is known as a "supersynchronous" orbit. This way, the satellite does not have to alter its orbital period; it can simply alter its Pe and Ap as gradually as it needs to. Lowering the Ap and raising the Pe while keeping orbital period constant (or only needing to increase it slightly) is more efficient than having an Ap exactly at GEO altitude, because any burn that isn't exactly at Ap will reshape the orbit, and no satellite has enough thrust to go from GTO to GEO instantly.

[RCgothic]

I think there's also a slight plane change manoeuvre required, which is cheaper at higher apoapsis.

[CatastrophicFailure]

Just now, RCgothic said:

I think there's also a slight plane change manoeuvre required, which is cheaper at higher apoapsis.

Slight? It's more like 23 degrees.  Which yes, is much cheaper with your apoapse as high as you can possibly get it. That's probably where much of the delta-V savings is coming from from the higher orbit.

Also, due to LOX boiloff, batteries, and and comm limits, the F9 upper stage can't relight at GS altitude, so everything it's gotta give has to be given down low, and soon after liftoff.

 

[sevenperforce]

17 minutes ago, CatastrophicFailure said:

Slight? It's more like 23 degrees.  Which yes, is much cheaper with your apoapse as high as you can possibly get it. That's probably where much of the delta-V savings is coming from from the higher orbit.

Also, due to LOX boiloff, batteries, and and comm limits, the F9 upper stage can't relight at GS altitude, so everything it's gotta give has to be given down low, and soon after liftoff.

 

This is also why the Falcon 9 always needs a coast period for GTO missions.

 

[DVDRW]

22 hours ago, CatastrophicFailure said:

Also, can we just get a round of grins for the fact that SpaceX just launched three rockets in twelve days?

May not be a record, but it's the first time it's happened in my useful memory at least. Which is, admittedly, rather short, despite being an old... er, what was I saying? 

Nice, but next launch will be over a month. Hoping they now have time to fix LC-40 sooner.

[CatastrophicFailure]

7 minutes ago, DVDRW said:

Nice, but next launch will be over a month. Hoping they now have time to fix LC-40 sooner.

The downtime is due to the USAF closing the entire eastern range for maintenance,  nothing SpaceX can do about it. Hopefully they'll put it to good use. 

Also, I wonder if maybe the Air Force is taking steps to integrate that new automated FTS system that promises quicker turn arounds...

[magnemoe]

9 hours ago, sevenperforce said:

IIRC, raising the apogee higher places the satellite's period as close to 24 hours as possible. This is known as a "supersynchronous" orbit. This way, the satellite does not have to alter its orbital period; it can simply alter its Pe and Ap as gradually as it needs to. Lowering the Ap and raising the Pe while keeping orbital period constant (or only needing to increase it slightly) is more efficient than having an Ap exactly at GEO altitude, because any burn that isn't exactly at Ap will reshape the orbit, and no satellite has enough thrust to go from GTO to GEO instantly.

 

9 hours ago, CatastrophicFailure said:

Slight? It's more like 23 degrees.  Which yes, is much cheaper with your apoapse as high as you can possibly get it. That's probably where much of the delta-V savings is coming from from the higher orbit.

Also, due to LOX boiloff, batteries, and and comm limits, the F9 upper stage can't relight at GS altitude, so everything it's gotta give has to be given down low, and soon after liftoff.

 

Understand at it makes sense.