totm nov 2023 SpaceX Discussion Thread

[Green Baron]

22 minutes ago, KSK said:

... what happens if a rocket gets hit by lightning?...

You switch SCE to AUX :-) (Apollo 12)

It is probably anything between nothing happens, the charge just flows off, and an rud because of multiple breeches and holes welded in the hull by the strong current. Like with aircraft, mostly nothing happens, but sometimes things go bad.

Lighting is unequal to lightning, and depending on weather conditions the charge can dissipate, collect over the surface, weld it's way in the interior, destroy electronic equipment ... whatever you want.

 

[HebaruSan]

Dialing it back from lightning to mere weather for a moment, since ICBMs don't have to go to orbit, their payload fraction is higher, so in principle they have the option to include more maneuvering fuel for correction burns. I doubt there are public stats available for ICBMs, but using the V-2 as a proxy:

https://en.wikipedia.org/wiki/Payload_fraction

Vehicle	Payload fraction
Ariane 5 (vehicle + payload)	2.506%
Soyuz-2.1b	2.63%
Soyuz-2.1a	2.25%
Saturn V	4.33%
Space Shuttle (vehicle + payload)	6.49%
Space Shuttle (payload only)	1.41%
V-2	25.97% [6]

[KSK]

2 minutes ago, Green Baron said:

Lighting is unequal to lightning, and depending on weather conditions the charge can dissipate, collect over the surface, weld it's way in the interior, destroy electronic equipment ... whatever you want.

Turn your eyes to steel?

 

[Nothalogh]

1 minute ago, HebaruSan said:

since ICBMs don't have to go to orbit

Most could probably put their payloads on escape trajectories.

They tend to fly a high elliptical trajectory rather than a low circular one, this is for two reasons.

1) steep reentry angle reduces accuracy loss due to atmosphere

2) plane change maneuvers at apoapsis are easier

[DerekL1963]

9 hours ago, Nothalogh said:

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 

NO US ICBM (or IRBM, or SLBM) has ever flown 'that way' (simply point in the right direction and burn till fuel exhaustion).   All of them have either used some form of thrust termination or flew a shaped trajectory that brings the point of exhaustion and the desired velocity to equality.  (Trident -I and -II use a method known as "Generalized Energy Management Steering" to accomplish the latter.)

Atlas flew on the sustainer until it was just short of the desired velocity, and the sustainer was shut down.  (The high t/w ratio and the uncertainty of thrust decay of the big engines made it impossible to shut them down precisely on time with proper velocity with the technology of the day.)  Those two itty-bitty LR-101 verniers (1000lb thrust) then propelled the vehicle to the desired final velocity, then they shut down and the warhead separated.
 

9 hours ago, Nothalogh said:

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

All available information indicates that powered flight [for ICBM's] is over long before apoapsis.  (Which makes sense - the earlier a velocity increment is applied to a RV, the bigger the difference at the end of the trajectory.)

Edited June 3, 2017 by DerekL1963

[Nothalogh]

2 hours ago, DerekL1963 said:

NO US ICBM (or IRBM, or SLBM) has ever flown 'that way' (simply point in the right direction and burn till fuel exhaustion)

Should have specified, what I meant is they flew via pre programmed on board instructions, unique to each launch site and target, unlike the Titan which brought the star tracker and inertial guidance into play.

Makes me wonder, how many feet of punch tape had to get trucked out to each silo each time you put the wing on alert.

[CatastrophicFailure]

Just now, Nothalogh said:

Makes me wonder, how many feet of punch tape had to get trucked out to each silo each time you put the wing on alert.

Weren't they constantly on alert? At least, most of the years they were active?

[Nothalogh]

10 minutes ago, CatastrophicFailure said:

Weren't they constantly on alert? At least, most of the years they were active?

No, the Atlas being kerolox and surface launched but stored in silos, meant that there was a limited alert window within which they could be fired, about three hours long, preceded by about a three hour process of raising the missile, fueling it, and feeding the target specific flight program into it.

There's a good reason their service life was short.

 

Fun fact, we've still got the old silos up around my area.

Swanton, Alburg, Champlain, Ausable, I swear there was one other but I can't remember the town.

It was all run out of the old Plattsburgh AFB 

Edited June 3, 2017 by Nothalogh

[Mighty1]

15 hours ago, Just Jim said:

 

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

Soon Musk will start a new company called "The weather company" with the goal of making a weather controling machine.

[Codraroll]

16 hours ago, CatastrophicFailure said:

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

They should just pack up and start constructing a launch pad in Mogadishu already.

Seriously, while Somalia has a few too many problems and then some today, if/when the dust settles they've got the perfect location for a spaceport. Not much room for launches inclined to the north, but they've got almost the entire south-east quadrant completely free of places that would mind a booster falling down on it. Apama, Brazil, has its north-east quadrant free, so with some cooperation, the two locations could handle all kinds of launches along the equator plane.

[K^2]

1 hour ago, Nothalogh said:

Should have specified, what I meant is they flew via pre programmed on board instructions, unique to each launch site and target, unlike the Titan which brought the star tracker and inertial guidance into play.

Makes me wonder, how many feet of punch tape had to get trucked out to each silo each time you put the wing on alert.

Absolutely all of them had inertial navigation of some sort. Even the olden-days ballistic missiles didn't execute the program on the clock. Instead, they had series of gyro-integrators that would help keep rocket on course, pull the program tape or equivalent, and be capable of triggering warhead or self-destruct as necessary. Soviets stuck to that very heavily until the end, while US has added more and more electronic components in later models.

And while some rockets weren't stored fueled, as far as I know, they were all stored pre-programmed with targets. Targeting information was just too sensitive to truck it out to the rocket at the last moment. Of course, modern computers made that bit entirely redundant. Still, I'm not sure if Russia ever switched over to computer guidance. Back in the days of Cold War, Soviets considered electronic components a weakness, potential for an attack, and avoided them even when ICs became available. There wasn't even a radio on board. Once it lifted out of silo, it was heading to its target and that's that. Part of me wouldn't be surprised if Russian ICBMs currently deployed still use punch tape with mechanical gyro-integrators.

[Scotius]

52 minutes ago, Codraroll said:

They should just pack up and start constructing a launch pad in Mogadishu already.

Seriously, while Somalia has a few too many problems and then some today, if/when the dust settles they've got the perfect location for a spaceport. Not much room for launches inclined to the north, but they've got almost the entire south-east quadrant completely free of places that would mind a booster falling down on it. Apama, Brazil, has its north-east quadrant free, so with some cooperation, the two locations could handle all kinds of launches along the equator plane.

You mean Kenia? Equatorial country, nothing but wide ocean east of the coastline, decent industry and infrastructure for an African country. And infinitely more stable than Somalia which suffers from near constant civil war, lack of central government and piracy problem (of the "Arrr! Prepare to be boarded!" variety).

[Spaceception]

Back up, 9 hours to go

 

Edited June 3, 2017 by Spaceception

[Scotius]

Fingers crossed. Hopefully SpaceX will uphold their long standing tradition of launching without a hitch on second attempt

[Just Jim]

7 minutes ago, Scotius said:

Fingers crossed. Hopefully SpaceX will uphold their long standing tradition of launching without a hitch on second attempt

Well, hopefully I'm not jinxing anything saying this, but I checked the local weather, and what rain is out there now is far to the south of NASA.... and no where near as heavy as the other day. I'll check it again in a few hours.

[DerekL1963]

4 hours ago, Nothalogh said:

Should have specified, what I meant is they flew via pre programmed on board instructions, unique to each launch site and target, unlike the Titan which brought the star tracker and inertial guidance into play.

Atlas-D used ground controlled radio guidance, subsequent versions used fully self contained inertial guidance systems.  Neither Titan -I or -II used a star tracker.  The first operational US strategic ballistic missile to use a star tracker was Trident-I.  (Poseidon was slated to be upgraded to stellar-inertial guidance, but the program was cancelled by President Nixon (IIRC) because the increased accuracy was considered 'too provocative to the Soviets'.)
 

5 hours ago, Nothalogh said:

No, the Atlas being kerolox and surface launched but stored in silos, meant that there was a limited alert window within which they could be fired, about three hours long, preceded by about a three hour process of raising the missile, fueling it, and feeding the target specific flight program into it.

While time varied between launching system, prep time (that time between receipt of the launch order and missile away) never appears to have exceeded an hour.  (Down to 15 minutes in the later versions.)

In the parlance of US strategic weapons 'Alert' means "ready to accept the launch order", not "ready to launch".  While Atlas (and Titan-I) had a limited ability to hold between being prepared to launch and actually launching, that capability does not appear to have ever been used operationally.  The concept was to proceed to directly to launch on receipt of the launch command.

[wumpus]

4 hours ago, Scotius said:

You mean Kenia? Equatorial country, nothing but wide ocean east of the coastline, decent industry and infrastructure for an African country. And infinitely more stable than Somalia which suffers from near constant civil war, lack of central government and piracy problem (of the "Arrr! Prepare to be boarded!" variety).

I still favor Ecuador, although you need to vastly more careful about where the stages come down.

[Streetwind]

Could you guys take your multiple pages worth of ICBM discussions to a thread of its own, please?

[StupidAndy]

I see only cloudy weather, 80*(F, not C, if it was C we would all be dead)

of course this is a simple BING search

of course I probably trust @Just Jim's power of actually being there

 

Edited June 3, 2017 by StupidAndy

[Just Jim]

4 minutes ago, StupidAndy said:

I see only cloudy weather, 80*(F, not C, if it was C we would all be dead)

of course this is a simple BING search

of course I probably trust @Just Jim's power of actually being there

Here's the link to our local radar, in real time (more or less) so you can actually see what direction the storms are moving across Florida. This is what I'm going by.

http://www.baynews9.com/content/news/baynews9/weather/klystron-9-radar/local.html

Edited June 3, 2017 by Just Jim

[tater]

Not new, but interesting (and the old thread was destroyed  ):

 

 

[NSEP]

Got to wait another midnight untill CRS-11. Time flew by fast though.

[StupidAndy]

1:37 until T-0?

T-1:37:00?

Edited June 3, 2017 by StupidAndy

[Just Jim]

1 hour ago, StupidAndy said:

1:37 until T-0?

T-1:37:00?

Possibly... Weather's looking a lot better today!

[TheEpicSquared]

90% chance of acceptable weather according to SFN