totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

18 hours ago, Goaty1208 said:

Watched Space X launch fail

Really a big fail. Well, hope it goes better next time.

This feels troll-y.

[tater]

 

6 hours ago, Goaty1208 said:

Yep, I knew that I needed to specify. They were right to postpone the launch for weather, because, who knows, maybe the rocket could have had problems. What I meant is: Nasa has a lot of weather satellites, now also Space X have some, and when they did some hours before the weather check they couldn't know that? Well, hope Sunday goes better though. 

Weather commit criteria were almost met. Had the window been 15 minutes instead of instantaneous, they likely could have flown. There is no way to predict thunderstorms that accurately, ever. The characteristic rise time of a puff of cloud to a cell is 15-20 minutes (hiking buddy of mine is a lightning physicist). You could have a puff of cloud to the west, and 25 minutes later it's over you, with hail pouring out of it.

[sevenperforce]

6 hours ago, Goaty1208 said:

Nasa has a lot of weather satellites, now also Space X have some, and when they did some hours before the weather check they couldn't know that? Well, hope Sunday goes better though. 

SpaceX does not have weather satellites, but that's minor pedantry.

I have to wonder -- were you actually watching and paying attention? Throughout the entire process, they repeated over and over that the mission was a no-go for weather constraints, but that range predicted a weather clear-up by the scheduled launch window. That prediction became more and more marginal over time and finally it was discounted once it was too close to have any possibility of coming true. This is exactly what the system is designed to do.

That's like saying someone "failed" their driving test because the brakes worked properly when they had to stop short due to a deer jumping out in the road.

6 hours ago, Goaty1208 said:

 I heard that the Apollo 12 got struck by a lightning and well, the mission didn't go really badly. They just landed on the moon.

The two lightning strikes on Apollo 12 shut down the entire control system, erased the gyroscopes, and torched two of the three fuel cells in the CSM. They also very nearly killed the electrical switches that would trigger the chutes on return. The crew was very, very lucky.

11 minutes ago, tater said:

Had the window been 15 minutes instead of instantaneous, they likely could have flown. There is no way to predict thunderstorms that accurately, ever.

Technically the launch window is like 13 minutes long, with lowest prop consumption (and best dV margins) smack dab in the middle. But because Falcon 9 uses subcooled props, it has to target a specific launch moment half an hour in advance and can't recycle within a 13-minute window.

But yes, there is no way to predict that accurately.

[mikegarrison]

6 hours ago, Goaty1208 said:

Yep, I knew that I needed to specify. They were right to postpone the launch for weather, because, who knows, maybe the rocket could have had problems. What I meant is: Nasa has a lot of weather satellites, now also Space X have some, and when they did some hours before the weather check they couldn't know that? Well, hope Sunday goes better though.

1. The next window is Saturday.
2. If the weather had been hopeless, they would not have tried. But the weather was not hopeless -- it was close enough to try.

I used to do airplane noise, and we have strict weather windows on our tests. I can't tell you how many times I've sat at a test site, watching the weather station output, waiting for what might be a 45 second window to open up so we can take the data. It's THE WEATHER. Literally the best example ever of "things out of your control". Plenty of times we got up in the morning, looked at the forecast, and said "well, we're not testing today". But also plenty of times we got up in the morning, looked at the forecast, and said, "let's set up for the test -- we *might* get some test points in today". Airplanes (and spacecraft) are expensive, and you don't just let them sit around waiting for that golden clear day when you know for sure the weather will be fine.

[YNM]

57 minutes ago, Geonovast said:

I, for one, was glad to see a scrub.  Those lives are more important than "But I wanted to see a rocket launch today".

Apollo 12 and Challenger are fairly harrowing examples of what could happen if you push it outside the boundary set by nature.

6 hours ago, Goaty1208 said:

when they did some hours before the weather check they couldn't know that?

Exact weather in an instantaneous window is almost impossible to tell days or even hours or tens of minutes before. Given that the baseline predictions was pretty high anyway (40% is still somewhat hopeful), it's better for them to risk having a scrub rather than missing out a window at all by not even preparing for it. If there was a tropical storm over the launch site obviously they wouldn't even try to prepare, but if it's only somewhat overcast, who knows ?

Although I'll say that, given these experiences, NASA might make a new guideline for when one can launch based on forecast percentages. Falcon 9 is not Space Shuttle that has a lot more tolerance on the launch window.

Edited May 28, 2020 by YNM

[Starwaster]

@sevenperforce I can’t imagine any definition for ‘torched’ which corresponds to all three fuel cells successfully being reconnected to the power bus and functioning normally for the remainder of the mission. What happened (according to the official report) is that they were disconnected from the system to protect them. Automatically. 
 

Also it is an exaggeration to say the entire control system was shut down. It’s true that the command module computer was down but actual control of the launch vehicle is from the instrument unit in the S-IV-B with the command module computer taking over the launch if the instrument unit fails. 
 

 

[tater]

 

SN4 gonna put on a show later, perhaps.

[CatastrophicFailure]

2 hours ago, tater said:

SN4 gonna put on a show later, perhaps.

So it would seem. Except not perhaps the right kinda show... 

 

[tater]

Static fire!

[Jacke]

3 hours ago, Starwaster said:

@sevenperforce I can’t imagine any definition for ‘torched’ which corresponds to all three fuel cells successfully being reconnected to the power bus and functioning normally for the remainder of the mission. What happened (according to the official report) is that they were disconnected from the system to protect them. Automatically. 

Also it is an exaggeration to say the entire control system was shut down. It’s true that the command module computer was down but actual control of the launch vehicle is from the instrument unit in the S-IV-B with the command module computer taking over the launch if the instrument unit fails.

Glad you pointed these out, @Starwaster.  As far as I know, the Apollo SM fuel cells could only be started on the pad prelaunch and even if fundamentally unharmed, shutdown of even one prior to Trans Lunar Injection would lead to a mission scrub and abort reentry and after to some variant of mission abort.  It's why there's a mission controller (traditionally RETRO) who's job it is to know all planned abort procedures and how they change in flight.

And real-life launch vehicles are very much actively guided by machine while under thrust.  For Apollo, loss of both IU and CM guidance would quickly lead at low altitude to sufficient angle-of-attack to cause vehicle departure and breakup and a launch escape abort, while at high altitude almost certainly require a CSM separation abort.

These issues are still current for all space missions, including everything SpaceX flies.  To get a feel of how close things came in Apollo 12 and how the crises were salvaged, the section in the Wikipedia article has lots of details.

https://en.wikipedia.org/wiki/Apollo_12#Launch_and_transfer

Spoiler

Apollo 12 launched on schedule from Kennedy Space Center, under completely overcast rainy skies, encountering wind speeds of 151.7 knots (280.9 km/h; 174.6 mph) during ascent, the highest of any Apollo mission.^[10]

Lightning struck the Saturn V 36.5 seconds after lift-off, triggered by the vehicle itself, discharging down to the Earth through the ionized exhaust plume. Protective circuits on the fuel cells in the service module (SM) detected overloads and took all three fuel cells offline, along with much of the command and service module (CSM) instrumentation. A second strike at 52 seconds knocked out the "8-ball" attitude indicator. The telemetry stream at Mission Control was garbled. However, the Saturn V continued to fly normally; the strikes had not affected the Saturn V instrument unit guidance system, which functions independently from the CSM.

The loss of all three fuel cells put the CSM entirely on batteries, which were unable to maintain normal 75-ampere launch loads on the 28-volt DC bus. One of the AC inverters dropped offline. These power supply problems lit nearly every warning light on the control panel and caused much of the instrumentation to malfunction.

Electrical, Environmental and Consumables Manager (EECOM) John Aaron remembered the telemetry failure pattern from an earlier test when a power supply malfunctioned in the CSM signal conditioning electronics (SCE), which converted raw signals from instrumentation to standard voltages for the spacecraft instrument displays and telemetry encoders.^[11]

Aaron made a call, "Flight, EECOM. Try SCE to Aux", which switched the SCE to a backup power supply. The switch was fairly obscure, and neither Flight Director Gerald Griffin, CAPCOM Gerald Carr, nor Mission Commander Pete Conrad immediately recognized it. Lunar Module Pilot Alan Bean, flying in the right seat as the spacecraft systems engineer, remembered the SCE switch from a training incident a year earlier when the same failure had been simulated. Aaron's quick thinking and Bean's memory saved what could have been an aborted mission, and earned Aaron the reputation of a "steely-eyed missile man".^[12] Bean put the fuel cells back on line, and with telemetry restored, the launch continued successfully. Once in Earth parking orbit, the crew carefully checked out their spacecraft before re-igniting the S-IVB third stage for trans-lunar injection. The lightning strikes had caused no serious permanent damage.

Initially, it was feared that the lightning strike could have caused the explosive bolts that open the Command Module's parachute compartment to fire prematurely, rendering the parachutes useless which would have made safe return impossible. The decision was made not to share this with the astronauts since there was little that could be done to verify or resolve the problem if it existed. The parachutes deployed and functioned normally at the end of the mission.^[13]

After LM separation, the S-IVB was intended to fly into solar orbit. The S-IVB auxiliary propulsion system was fired, and the remaining propellants vented to slow it down to fly past the Moon's trailing edge (the Apollo spacecraft always approached the Moon's leading edge). The Moon's gravity would then slingshot the stage into solar orbit. However, a small error in the state vector in the Saturn's guidance system caused the S-IVB to fly past the Moon at too high an altitude to achieve Earth escape velocity. It remained in a semi-stable Earth orbit after passing the Moon on November 18, 1969. It finally escaped Earth orbit in 1971 but was briefly recaptured in Earth orbit 31 years later. It was discovered by amateur astronomer Bill Yeung who gave it the temporary designation J002E3 before it was determined to be an artificial object.^[14][15]

 

Edited May 28, 2020 by Jacke

[tater]

 

[Jacke]

6 hours ago, YNM said:

Ah ok, so they do avoid to overfly Haiti / Dominican Republic and the NE coasts of South America. An SE launch to ISS inclination would have to launch at ~135° azimuth, which is well outside the approved azimuth range or requires significant dogleg. (they should launch NE to ~45° azimuth assuming no doglegs.)

Apparently now with the new Autonomous Flight Termination system at the Eastern Range, the azimuth angles are being broadened, especially for special dogleg launch trajectories.  From the Wikipedia article's source:

https://www.floridatoday.com/story/tech/science/space/2017/12/31/southbound-cape-rockets-may-fly-new-path-toward-poles/975027001/

this includes up to polar launches that pass just east of Miami with potential first stage impact just north of Cuba.  That's not been used since 1960 and has yet to be used, but remains a possibility.

[YNM]

10 minutes ago, Jacke said:

this includes up to polar launches that pass just east of Miami with potential first stage impact just north of Cuba. 

Well it'd mean they'd overfly straight through South America, but I guess by that point it's just the 2nd stage most of the time.

[Jacke]

10 minutes ago, YNM said:

Well it'd mean they'd overfly straight through South America, but I guess by that point it's just the 2nd stage most of the time.

Would all be 2nd stage and post-SECO coasting.  Certainly Central America, probably over Panama, and maybe Ecuador and Peru, but could be west of them, as South America is very much farther east than North America.

[YNM]

2 minutes ago, Jacke said:

Certainly Central America, probably over Panama, and maybe Ecuador and Peru, but could be west of them, as South America is very much farther east than North America.

True for the slightly retrograde orbits, but ISS launches to the SE would go right over Brazil.

[tater]

 

[Jacke]

39 minutes ago, YNM said:

True for the slightly retrograde orbits, but ISS launches to the SE would go right over Brazil.

Good point.  When expanded, there are likely azimuth angles from the Eastern Range that are dicey for abort, especially crewed abort.  Near-polar orbits like Sun Synchronous have fewer issues.  A SE launch to the ISS would likely have too many abort landing zones in or too close to many Caribbean islands or the South American continent to be used.

Look on a small-scale Mercator map.  Draw a line from KSC to Newfoundland; I think that's the rough ground track of the NE launches to the ISS.  Now mirror that line at the same angle to the south.  The southern track will pass closer to and even over land a lot more, which complicates recovery.

Edited May 28, 2020 by Jacke

[Wjolcz]

On 2/26/2020 at 11:31 AM, Wjolcz said:

Remember when I said it's going to fly in late spring?

 

[sevenperforce]

1 hour ago, tater said:

 

This appears to be an open-ended, blanket permit for all future suborbital Starship test flights, with no altitude limit and only a three-day notice requirement.  

[tater]

 

Edited May 29, 2020 by tater

[tater]

So maybe another SN4 test today?

Also, rumor mill has it that Elon is there today... Hop?

[Shpaget]

A high pucker factor hop a day before Dragon launch? Nah, I think they'd prefer to see the Dragon safely attached to ISS before risking bad press.

[magnemoe]

58 minutes ago, Shpaget said:

A high pucker factor hop a day before Dragon launch? Nah, I think they'd prefer to see the Dragon safely attached to ISS before risking bad press.

Yes other has stated this. Yes for SpaceX blowing up SN4 is kind of destructive testing. You need to expend 3-5 in 1000 of your artillery shells or air bags so we see they work. 
Public don't see it that way. 
No parachute manufacturer will detail their development outside of we did  20.000 test drops. That the first 15K mostly impacted and also was an environmental hazard outside of hitting an poor duck or rabbit

[Jacke]

44 minutes ago, magnemoe said:

No parachute manufacturer will detail their development outside of we did  20.000 test drops. That the first 15K mostly impacted and also was an environmental hazard outside of hitting an poor duck or rabbit

As you said, they don't detail what actually happened.  But because the science and engineering are well known, it's more likely those drop tests mostly succeeded.  What they're looking for is details on how well the parts deployed and opened and afterwards the wear and tear on the 'chute by examining it and taking it apart.

I also think SpaceX is unlikely to tempt bad news right before a very important launch window.

[sh1pman]

 

Holy cow, that fireball!!! RIP SN4, but that explosion was spectacular!

Edited May 29, 2020 by sh1pman