totm nov 2023 SpaceX Discussion Thread

[Green Baron]

Thanks for the forecast.

Question: how risky is just rain ? Or is it more gusts or the chance of a lightning strike that they are afraid of during rocket launches ?

 

[Just Jim]

18 minutes ago, Green Baron said:

Thanks for the forecast.

Question: how risky is just rain ? Or is it more gusts or the chance of a lightning strike that they are afraid of during rocket launches ?

 

Mostly it's the lightning. Unfortunately, this time of year we get what are called "Pop-up storms" that can literally form overhead in less than an hour, and these can have some serious lightning. That's what happened yesterday, the storms began forming in the afternoon, and 25 minutes before the launch there was a lightning strike nearby. Didn't hurt anything from what I can tell, but it was within the safety zone, which immediately scrubbed the launch.

The problem with pop-up storms, in a nutshell, is they're so unpredictable. Where I am in Florida, and so is NASA, we live on basically a huge sandbar in between the Atlantic Ocean and Gulf of Mexico, which are super warm right now. Seriously, if you go to the beach, which is about 5 minutes from here, the Gulf water feels like a bathtub. It's amazing. But unfortunately, in the brutal summer sun, the water evaporates at a staggering rate, and is pouring into the atmosphere both over the Gulf and Atlantic. And this causes the sea breezes, which sweep across the state, especially in the afternoon, and pump in all that hot, wet air over land. The sea breeze direction just depends on which side of the state has the higher air pressure... but most often this air collides somewhere in the middle of the state... and that's where the T-storms will "pop-up". And when they do, it's amazingly fast.. I've seen huge anvil clouds form up in less than an hour right over my head.

Now, granted, this is a super simplified, "Readers Digest condensed version" of what happens... but I think it's close enough to illustrate what poor NASA has to deal with as far as the screwy weather down here.

Edited June 2, 2017 by Just Jim

[tater]

A hiking buddy of mine is a lightning physicist (used to be at the lightning observatory down in Socorro), and we get the same kinds of storms here in NM. I want to say he told me the characteristic rise time is 15-20 minutes. We see a puff, then a cumulous, next thing you know it's an anvil and hailing on us. What we don't have is sea breezes, so predicting their movement is a little easier  .

[Just Jim]

5 minutes ago, tater said:

A hiking buddy of mine is a lightning physicist (used to be at the lightning observatory down in Socorro), and we get the same kinds of storms here in NM. I want to say he told me the characteristic rise time is 15-20 minutes. We see a puff, then a cumulous, next thing you know it's an anvil and hailing on us. What we don't have is sea breezes, so predicting their movement is a little easier  .

That sounds about right... and you're right, the biggest problem here with the sea breeze is figuring out what direction they're going to go... I've seen them go shooting from one side of the state to the other in either direction in a matter of hours, or just form and sit where they are... those can potentially be the worst.

And we do occasionally get waterspouts and small tornadoes... those are all sorts of fun... not.

 

[tater]

Lightning is a huge concern at NASA, I know. My friend told me that the lightning guys have instruments there since there are so many strikes---NM is high in that regard as well, another friend (a EE) worked on isolating the weather radar here from lightning strike related problems since NOAA apparently told them that our among the most knocked out stations in the country from that).

On topic, weather delays are likely to really mess up the 2 week launch cadence.

[Just Jim]

41 minutes ago, tater said:

Lightning is a huge concern at NASA, I know. My friend told me that the lightning guys have instruments there since there are so many strikes---

On topic, weather delays are likely to really mess up the 2 week launch cadence.

yeah... best we keep it on-topic. Why I brought the subject up is I've been down here nearly 20 years now, and this happens every summer, especially during afternoon launches. I've seen way more launches scrubbed for weather, either lightning or high winds, than I have for technical problems.

I just wanted to give anyone that isn't familiar with central Florida some insight into the problems NASA has concerning the weather and launches like yesterday, and why they can be scrubbed so often this time of year. 

Edited June 2, 2017 by Just Jim

[tater]

Do they make an effort to aim for mornings as a result?  Obviously this would be predicated on the orbital mechanics, but there must be launch windows that occur at better times of day.

Summer pop up storms are powered by sunlight, which is why we see them in the afternoon. If you climb something here in the west, your goal is summit and otw down by noon, since after that you will face storms.

[kerbinorbiter]

well if spaceX has a SCE to AUX button they would be fine right?

[tater]

Chance of a violation Saturday is 40%, and Sunday it's 50%.

 

[IncongruousGoat]

All this talk about the weather brings up an interesting point: If Musk wants to substantially increase launch quantity, he's going to have to find some way for the weather to matter less than it does now. Going back to the ever-popular airline comparison, airlines wouldn't be as effective if every airport had to shut down completely every single time it rained.

[CatastrophicFailure]

7 minutes ago, IncongruousGoat said:

All this talk about the weather brings up an interesting point: If Musk wants to substantially increase launch quantity, he's going to have to find some way for the weather to matter less than it does now. Going back to the ever-popular airline comparison, airlines wouldn't be as effective if every airport had to shut down completely every single time it rained.

That's probably one of the reasons they're building in Brownsville, tho that's got its own share of problems too. Again nodding at the airplane thing, perhaps if they can get the reliability high enough they can move inland. Any place on the east coast at lower latitude is gonna be subject to some nasty weather. 

[Just Jim]

1 hour ago, tater said:

Do they make an effort to aim for mornings as a result?  Obviously this would be predicated on the orbital mechanics, but there must be launch windows that occur at better times of day.

I had to go double check quick, but this rocket is rendezvousing with the ISS, and getting really game related, I've learned the best time to launch if you're chasing a space station is just after it passes overhead... The Earth being so much bigger, I'm afraid this probably gives them a very narrow window to launch and catch up to the ISS.

[CatastrophicFailure]

1 minute ago, Just Jim said:

I had to go double check quick, but this rocket is rendezvousing with the ISS, and getting really game related, I've learned the best time to launch if you're chasing a space station is just after it passes overhead... The Earth being so much bigger, I'm afraid this probably gives them a very narrow window to launch and catch up to the ISS.

I think it's more the inclination, in this case. They only get two (very short) windows a day when the orbital plane passes overhead, so like you said, the mechanics of one are probably better than the other.

Or... can they launch 51* southward from the Cape? Would that pass over land too soon? If not, that's only one usable window a day.

[IncongruousGoat]

2 minutes ago, CatastrophicFailure said:

I think it's more the inclination, in this case. They only get two (very short) windows a day when the orbital plane passes overhead, so like you said, the mechanics of one are probably better than the other.

Or... can they launch 51* southward from the Cape? Would that pass over land too soon? If not, that's only one usable window a day.

51 degrees south would leave you dumping boosters on Brazil. So, no. You can't launch at that inclination from Canaveral.

[Just Jim]

Just now, CatastrophicFailure said:

I think it's more the inclination, in this case. They only get two (very short) windows a day when the orbital plane passes overhead, so like you said, the mechanics of one are probably better than the other.

Or... can they launch 51* southward from the Cape? Would that pass over land too soon? If not, that's only one usable window a day.

I don't know for sure... all I know is it's much easier in KSP than in R/L... 

18 minutes ago, IncongruousGoat said:

All this talk about the weather brings up an interesting point: If Musk wants to substantially increase launch quantity, he's going to have to find some way for the weather to matter less than it does now. Going back to the ever-popular airline comparison, airlines wouldn't be as effective if every airport had to shut down completely every single time it rained.

Yes, exactly! I know they originally choose Florida because it's so far south, and you can launch over the Atlantic... but the weather here in the summer can be terrible. And the real fun hasn't even started! Wait until Hurricane Season hits... 

Musk better give some serious thought and consideration... and respect... and fear... to those monsters... One direct hit and that's it.

[tater]

Ninjaed. I was just about to wonder if the only window was NE during a pass.

[CatastrophicFailure]

aaaaand just like that I'm out of likes for the day. 

 

3 minutes ago, Just Jim said:

I don't know for sure... all I know is it's much easier in KSP than in R/

Play from an off-equator launch site for a while, you'll feel their pain. 

[Nothalogh]

1 hour ago, tater said:

Ninjaed. I was just about to wonder if the only window was NE during a pass.

So, what would it take to assure all weather launch capabilities?

Obviously ICBMs from the Titan II onward were capable of this, no?

[Ten Key]

5 hours ago, Green Baron said:

Question: how risky is just rain ? Or is it more gusts or the chance of a lightning strike that they are afraid of during rocket launches ?

It's a factor. While rain itself is not normally a problem, if the cloud tops get high enough the water particles will start to freeze. If your rocket picks up speed and then flies through that, it's a bad day.

https://www.nasa.gov/pdf/649911main_051612_falcon9_weather_criteria.pdf

 

1 hour ago, Just Jim said:

Yes, exactly! I know they originally choose Florida because it's so far south, and you can launch over the Atlantic... but the weather here in the summer can be terrible. And the real fun hasn't even started! Wait until Hurricane Season hits... 

Musk better give some serious thought and consideration... and respect... and fear... to those monsters... One direct hit and that's it.

Brownsville sees its fair share of hurricanes. 

[KSK]

6 minutes ago, Nothalogh said:

So, what would it take to assure all weather launch capabilities?

Obviously ICBMs from the Titan II onward were capable of this, no?

I'm not so sure they were - you'd think that ability would have found it's way into launch vehicles too by now. Pure guesswork here but I'm thinking that if you're in a place where those ICBMs are flying then losing one or two to weather probably isn't going to change your day very much anyway.

 

[Nothalogh]

Just now, KSK said:

I'm not so sure they were - you'd think that ability would have found it's way into launch vehicles too by now. Pure guesswork here but I'm thinking that if you're in a place where those ICBMs are flying then losing one or two to weather probably isn't going to change your day very much anyway.

 

The problem is a statistical loss calculation on launch vehicles will greatly affect the statistical accuracy of warheads on target.

It roughly works like this:

1) ascertain how many kilotons it will take to assure target destruction

2) figure out your CEP based on throw weight and range of target based on launch vehicle and payload

3) allocate as many warheads as necessary to get the kill radius inside the CEP, statistically speaking

 

So if weather factors in to the the reliability of your launch vehicles, you'll need to increase the number of launches per target by at least the number of projected losses due to weather.

As you can see, this spirals out of hand rapidly.

[KSK]

Hmmm,

Good points well made. Next bit of random speculation then - what happens if a rocket gets hit by lightning? I don't imagine it does any electrical systems much good (it certainly did a number on Apollo 12) but how important is that for an intercontinental ballistic missile compared to a launch vehicle flying a relatively complex trajectory to orbit? Honest question - can you just point an ICBM in the right direction off the pad (or at least once it's clear of the silo) and then just let it burn till it runs out of propellant? Because if you could, then frying your guidance system halfway through the launch won't matter that much.

Genuinely curious, because if ICBMs are indeed all weather launch vehicles, what's so special about them (in broad strokes if not exact engineering details  ) compared to space launchers and why doesn't that technology transfer across?

[IncongruousGoat]

1 minute ago, KSK said:

Hmmm,

Good points well made. Next bit of random speculation then - what happens if a rocket gets hit by lightning? I don't imagine it does any electrical systems much good (it certainly did a number on Apollo 12) but how important is that for an intercontinental ballistic missile compared to a launch vehicle flying a relatively complex trajectory to orbit? Honest question - can you just point an ICBM in the right direction off the pad (or at least once it's clear of the silo) and then just let it burn till it runs out of propellant? Because if you could, then frying your guidance system halfway through the launch won't matter that much.

Genuinely curious, because if ICBMs are indeed all weather launch vehicles, what's so special about them (in broad strokes if not exact engineering details  ) compared to space launchers and why doesn't that technology transfer across?

As far as I know, ICBM's steer themselves while well into flight to compensate for things like wind. I seem to remember hearing that Titan II especially would constantly adjust its trajectory-much to the amusement of the Gemini astronauts, who likened it to a dog sniffing around for the right flight path.

[CatastrophicFailure]

ICBMs, at least the more recent ones, carry 6+ warheads that are independently targeted and maneuver on their own for terminal guidance, so "close enough" is probably, well, close enough for the initial lob. 

[Nothalogh]

14 minutes ago, KSK said:

Honest question - can you just point an ICBM in the right direction off the pad (or at least once it's clear of the silo) and then just let it burn till it runs out of propellant? Because if you could, then frying your guidance s

The last US ICBM that flew that way was the Atlas, and by the inaccuracy inherent in that flight mode, required rather large yield warheads to compensate 

12 minutes ago, CatastrophicFailure said:

ICBMs, at least the more recent ones, carry 6+ warheads that are independently targeted and maneuver on their own for terminal guidance, so "close enough" is probably, well, close enough for the initial lob. 

Not really, they've gotta get the apoapsis to the correct window in space for any kind of terminal maneuvering to be useful