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#1240 by TheRadicalModerate on 18 Apr, 2023 23:02
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that sounds sporty for the Raptors.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?
I imagine they will forgo subcooling on Mars. Without subcooling, LOX and LCH4 will self-pressurize while just sitting there, and then once the engines are running add in autogenous.
I think the sportiness is required, unless you're planning on putting big cryocoolers in place from the git-go, along with the heat rejection needed to make them work. Raptors have to be able to restart over a wide range of idle intervals, some of which are too short for active cooling but too long for the prop to remain subcooled on-orbit. (I think most GTO profiles fit this constraint.)
And things are even worse on the lunar and martian surfaces, where you can't play attitude tricks, the sun moves, and you have a quasi-lambertian surface radiating at you from all directions.At mars pressure lox and lch4 are subcooled.
Dropping pressure lowers the boiling point. If you drop the pressure on a boiling liquid, it just boils faster. You can raise the pressure and make it subcooled, though. -
#1241 by kdhilliard on 18 Apr, 2023 23:08
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#1242 by TheRadicalModerate on 18 Apr, 2023 23:14
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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?
Pump liquid (LCH4 or LOX) into a COPV, seal the COPV, and superheat it.
There are a lot of things that need high-pressure gas over the operating regime of a fully functional Starship:
1) Bringing main and header tanks up to flight pressure (~6bar).
2) Providing spin-start gases (>100bar?).
3) Driving cold-to-warm-gas thrusters (6-20bar).
4) Driving combusting thrusters (6-10bar).
My guess is that the current test articles can't do all of these things yet, and the COPVs and heaters are either rudimentary or non-existent. Note that this may be yet another explanation for what Starship is going to belly-flop all the way into the sea: there simply aren't enough COPVs to handle more than the Starship spin-start at stage separation. -
#1243 by alugobi on 18 Apr, 2023 23:20
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Now on the NSF livestream the commentator said the problem was on the booster.
Their source? -
#1244 by kdhilliard on 18 Apr, 2023 23:51
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John Insprucker.Now on the NSF livestream the commentator said the problem was on the booster.
Their source?
See my post 13 above. -
#1245 by sferrin on 19 Apr, 2023 00:02
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A shame some people have NO sense of humor.QuoteThe TFR for a Starship launch attempt on Thursday has been removed. Awaiting an update from SpaceX.
QuoteRight now the next TFR is for a possible launch attempt on April 21.
Poor Elon, he must be soooo disappointed. But I'm impressed that he listened to the team and let it slip past his juvenile joke date.
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#1246 by kdhilliard on 19 Apr, 2023 00:28
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...
I think you and rs are using the term differently.At mars pressure lox and lch4 are subcooled.
Dropping pressure lowers the boiling point. If you drop the pressure on a boiling liquid, it just boils faster. You can raise the pressure and make it subcooled, though.
Yes, a liquid is subcooled when it is below its boiling temperature for its given pressure, but by that standard the LOX in a Falcon 1 tank was subcooled once the tanks were pressurized for flight. SpaceX, when speaking of subcooled propellants, is of course saying that they are densified by being brought below their boiling point at Earth atmospheric pressure (since they are usually stored in bulk near atmospheric pressure, with their temperature maintained through boil-off).
Subcooling methane with respect to Mars atmospheric pressure will be difficult to do given its triple point of 90.69K/0.117bar, well above Mars's atmospheric pressure of 6mbar! Instead, what I believe rs is saying is simply that the densified propellant temperatures that SpaceX calls subcooled on Earth will be that of boiling propellants in an only partially pressurized tank on Mars. -
#1247 by TomH on 19 Apr, 2023 00:51
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Is it me or has bickering about semantics become a trend here? With what "faulty" means, how long 48 hours is, what "orbital" means, and others, going on for pages and pages, it feels like being trolled.
Not just you. It seems like people are often arguing about the definitions of words when it's pretty clear that people do in fact understand each other. It's tiresome, like kids bragging about how much smarter they are than the next kid.
Words and their definitions do matter. If the valve itself is faulty, then it needs to be replaced or redesigned. If the valve froze due to a procedural error, then the procedure is faulty, not the valve.
Chronological measurement matters. While I can see your point regarding the 48 hours, timing is of great importance in such spaceflight.
Unit measurement is also vital. The Mars Climate Orbiter, a $125M craft, was lost due to an error in Imperial/metric conversion.
If one finds intellectual discourse tiresome, the possibility exists that the issue lies with the reader, not the writers.Is it me or has bickering about semantics become a trend here? With what "faulty" means, how long 48 hours is, what "orbital" means, and others, going on for pages and pages, it feels like being trolled.
It is solved on other sites by threading comments, so those who enjoy it can go down their silly rabbitholes but normal people can just skip over those threads. It also makes quoting much less necessary.
Unfortunately this site seems to use technology from the 90s that cannot do comment threads.As someone working in the voice business, I think they should give a bit more thought to which voices they use. Insprucker has a fantastic "1960s rocket engineer" voice. Content-wise he is good and getting better. Most of the others... not great. A California valley girl voice (plus intonation), as well as a high-pitched adolescent boy voice just won´t keep audiences happy. They will get annoyed after a while and turn off the feed.
That was me for one!
I could not continually watch the Spacex broadcast because of those two's voices.
The "boy"'s voice was particularly nasal and jarring, I thought.
Respectfully, I'm going to ask that you reflect on this a little bit. Agreeing with those who think discussion of word meaning is pedantic, then turning around and being critical of someone's voice (and referring to him as a boy) is, at best ironic, and at worst hypocritical. Please think with more discretion before clicking save. -
#1248 by AS_501 on 19 Apr, 2023 05:01
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It will be interesting to see (i.e. "hear") how many decibels this bird generates at liftoff. I think Saturn V was around 120-125, while SLS-1 was 135-140.
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#1249 by chopsticks on 19 Apr, 2023 05:04
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https://twitter.com/elonmusk/status/1648550090330480640
I wonder what these many issues are. Did the WDR do a number on the booster somehow?QuoteThe team is working around the clock on many issues. Maybe 4/20, maybe not.
Edit: oops, I posted to the launch attempt thread, didn't realize it was updates only -
#1250 by Danrar on 19 Apr, 2023 05:54
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That's the FireX. Which also uses LN2. I believe the outer engines spin up the same way the inner ones do they just have simpler drain plumbing being closer to the mount.I think N2 is supplied from GSE to spin the outer 20 engines, ...
Oh, is that what we're seeing in this 2-second shot during the SpaceX Starship livestream intro?
See 3:54.
[The full 80-second into starts at 3:15.] -
#1251 by alastairmayer on 19 Apr, 2023 06:10
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[...]
I wonder what these many issues are. Did the WDR do a number on the booster somehow?QuoteThe team is working around the clock on many issues. Maybe 4/20, maybe not.
Edit: oops, I posted to the launch attempt thread, didn't realize it was updates only
Curious about that too, and made the same mistake. -
#1252 by Danrar on 19 Apr, 2023 06:18
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It's possible they had other issues they were able to work around. Remember they were aiming at 8:00am and it slipped to a slightly later time.
Curious about that too, and made the same mistake.[...]
I wonder what these many issues are. Did the WDR do a number on the booster somehow?QuoteThe team is working around the clock on many issues. Maybe 4/20, maybe not.
Edit: oops, I posted to the launch attempt thread, didn't realize it was updates only
It would be prudent to fix anything they had to work during the previous countdown while handling the blocking issue. -
#1253 by edzieba on 19 Apr, 2023 08:20
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No, it's not the detonation suppression system. Note the jets are of gas rather than water, and originating from the retractable QD couplings for the outer engines and not the suppression system nozzles (which hare fixed and further out on the underside of the OLM ring).
That's the FireX. Which also uses LN2. I believe the outer engines spin up the same way the inner ones do they just have simpler drain plumbing being closer to the mount.I think N2 is supplied from GSE to spin the outer 20 engines, ...
Oh, is that what we're seeing in this 2-second shot during the SpaceX Starship livestream intro?
See 3:54.
[The full 80-second into starts at 3:15.] -
#1254 by RamsesBic on 19 Apr, 2023 08:54
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No, it's not the detonation suppression system. Note the jets are of gas rather than water, and originating from the retractable QD couplings for the outer engines and not the suppression system nozzles (which hare fixed and further out on the underside of the OLM ring).
That's the FireX. Which also uses LN2. I believe the outer engines spin up the same way the inner ones do they just have simpler drain plumbing being closer to the mount.I think N2 is supplied from GSE to spin the outer 20 engines, ...
Oh, is that what we're seeing in this 2-second shot during the SpaceX Starship livestream intro?
See 3:54.
[The full 80-second into starts at 3:15.]
The FireX system uses nitrogen to atomize the water. The nitrogen nozzle is pointing at the water nipple. So we get a mixture of both. -
#1255 by edzieba on 19 Apr, 2023 09:47
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Look at the photo. The spray is from the engine QDs, not the detonation suppression system nozzles. Both are visible in the photo.
No, it's not the detonation suppression system. Note the jets are of gas rather than water, and originating from the retractable QD couplings for the outer engines and not the suppression system nozzles (which hare fixed and further out on the underside of the OLM ring).
That's the FireX. Which also uses LN2. I believe the outer engines spin up the same way the inner ones do they just have simpler drain plumbing being closer to the mount.I think N2 is supplied from GSE to spin the outer 20 engines, ...
Oh, is that what we're seeing in this 2-second shot during the SpaceX Starship livestream intro?
See 3:54.
[The full 80-second into starts at 3:15.]
The FireX system uses nitrogen to atomize the water. The nitrogen nozzle is pointing at the water nipple. So we get a mixture of both. -
#1256 by RamsesBic on 19 Apr, 2023 11:24
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I see. I thought you were talking about the FireX.
Look at the photo. The spray is from the engine QDs, not the detonation suppression system nozzles. Both are visible in the photo.
No, it's not the detonation suppression system. Note the jets are of gas rather than water, and originating from the retractable QD couplings for the outer engines and not the suppression system nozzles (which hare fixed and further out on the underside of the OLM ring).
That's the FireX. Which also uses LN2. I believe the outer engines spin up the same way the inner ones do they just have simpler drain plumbing being closer to the mount.I think N2 is supplied from GSE to spin the outer 20 engines, ...
Oh, is that what we're seeing in this 2-second shot during the SpaceX Starship livestream intro?
See 3:54.
[The full 80-second into starts at 3:15.]
The FireX system uses nitrogen to atomize the water. The nitrogen nozzle is pointing at the water nipple. So we get a mixture of both. -
#1257 by sferrin on 19 Apr, 2023 12:05
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Some of these critiques are starting to sound a little like personal insults. I appreciate the various hosts for their differences, their passion, and the connection they have with SpaceX in addition to just being some "hired newscast blob" but that's all just my opinion and I'll leave it at that.
I'd be surprised if anybody means them as insults. Some people have a "face for radio" and others have a "voice for print". It's just a harsh reality. -
#1258 by kdhilliard on 19 Apr, 2023 12:08
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It will be interesting to see (i.e. "hear") how many decibels this bird generates at liftoff. I think Saturn V was around 120-125, while SLS-1 was 135-140.
Is there a standard distance these are measured at? -
#1259 by Orbiter on 19 Apr, 2023 13:12
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It will be interesting to see (i.e. "hear") how many decibels this bird generates at liftoff. I think Saturn V was around 120-125, while SLS-1 was 135-140.
Is there a standard distance these are measured at?
This article quotes Saturn V as 120 dB from 1.5 km away. The same distance for SLS was recorded at 136 dB.
https://www.bbc.com/future/article/20230306-just-how-loud-is-a-rocket-launch