totm nov 2023 SpaceX Discussion Thread

[Ultimate Steve]

6 minutes ago, tater said:

Range congestion is already an issue, and once Blue starts flying from the Cape as well, it can only get worse. If SpaceX never exceeds their pace for this year (~30), and Blue flies what they claim (12/yr), then the range already exceeds what the AF says they can possibly do in a year (48).

Unless they decide to change the regulations and revamp the range, which is something they are going to have to do eventually, especially if SpaceX plans on flying multiple BFR's a day.

[YNM]

1 hour ago, PB666 said:

a bullet train experiences both compression and inflation forces and the changes occur very rapidly measured in millesonds.

... for moments only.

Try hammer a block of wood.

Now try putting it under a stone and leave for a year.

Despite the (probably) larger force in the first event, the second could be more effective in destroying the wood.

 

There are at least three stress limits :

- Ultimate (proper break)

- Yield (big deformations)

- Fatigue (repeated load).

A reusable rocket needs to avoid all of it.

EDIT : Aditionally, modern train tunnels feature emergency platforms for evacuation, which means plenty of room for air to move about. The tightest fit that I know on Shinkansen is the Seikan tunnel; but the speeds are restricted to 140 km/h (85 mph), not >300 km/h (>185 mph).

24 minutes ago, tater said:

Range congestion is already an issue, and once Blue starts flying from the Cape as well, it can only get worse.

Make a new one ? Wallops ?

Edited April 10, 2018 by YNM

[PB666]

28 minutes ago, tater said:

Range congestion is already an issue, and once Blue starts flying from the Cape as well, it can only get worse. If SpaceX never exceeds their pace for this year (~30), and Blue flies what they claim (12/yr), then the range already exceeds what the AF says they can possibly do in a year (48).

Yeah, its a problem, but Boca Chica might allows more launches. Problem here is that will the F9 launch from BC. But if they had several launch sites spread far enough apart they could launch twice in one day. Rememeber they said they wanted 5/month . . . 60 per year, if thats split between CC and V thats 30 each. So if the USAF is limiting them to 48 that means 18 for non spaceX at CC. They must have some sort of work-around planned.

[ment18]

35 minutes ago, tater said:

Range congestion is already an issue, and once Blue starts flying from the Cape as well, it can only get worse. If SpaceX never exceeds their pace for this year (~30), and Blue flies what they claim (12/yr), then the range already exceeds what the AF says they can possibly do in a year (48).

I think spacex is planning to use sea based launch platforms soon,  before P2P.

These are listed under Launch Engineering:

http://www.spacex.com/careers/position/215429 - Literally Called Naval/Marine Architect

http://www.spacex.com/careers/position/215424 - Experience with shipyard work, experience as ship engineer

http://www.spacex.com/careers/position/215307 - More maritime experience, shipyard

I haven't looked through the whole catalog, but I doubt these are the only ones.

Edited April 10, 2018 by ment18

[tater]

39 minutes ago, Ultimate Steve said:

Unless they decide to change the regulations and revamp the range, which is something they are going to have to do eventually, especially if SpaceX plans on flying multiple BFR's a day.

I'll buy that when/if it's an actual problem, lol.

27 minutes ago, YNM said:

Make a new one ? Wallops ?

Dunno. Boca Chica, as well, with fewer constraints at least---particularly if they launch offshore. ^^^^

Edited April 10, 2018 by tater

[PB666]

18 minutes ago, ment18 said:

I think spacex is planning to use sea based launch platforms soon,  before P2P.

These are listed under Launch Engineering:

http://www.spacex.com/careers/position/215429 - Literally Called Naval/Marine Architect

http://www.spacex.com/careers/position/215424 - Experience with shipyard work, experience as ship engineer

http://www.spacex.com/careers/position/215307 - More maritime experience, shipyard

I haven't looked through the whole catalog, but I doubt these are the only ones.

Even if they choose to launch in the mid-pacific, they still have range issues. Don't forget maritime laws apply to everyone, so if they planned to launch from the mid-pacific then they have to provide their own range officers.

I should also point out that for communication satellites that are LEO (high LEO) they don't really want (need) equitorial launches. The satellites need to be able to cover ranges of latitude relative close to Earths surface. This requires as stated above dozens of orbital planes.

Edited April 10, 2018 by PB666

[Elthy]

14 minutes ago, ment18 said:

I think spacex is planning to use sea based launch platforms soon,  before P2P.

These are listed under Launch Engineering:

http://www.spacex.com/careers/position/215429 - Literally Called Naval/Marine Architect

http://www.spacex.com/careers/position/215424 - Experience with shipyard work, experience as ship engineer

http://www.spacex.com/careers/position/215307 - More maritime experience, shipyard

I haven't looked through the whole catalog, but I doubt these are the only ones.

SpaceX tries to keep the cost down, and land based launchsites are way, way less complicated than those at sea. I think those offerings are maybe for an upgraded barge, one that is a proper remote controlled ship which can travel on its own and is faster than the current solution...

[tater]

3 minutes ago, Elthy said:

SpaceX tries to keep the cost down, and land based launchsites are way, way less complicated than those at sea. I think those offerings are maybe for an upgraded barge, one that is a proper remote controlled ship which can travel on its own and is faster than the current solution...

The coastal waters around TX are quite shallow, and the possibility exists to use an anchored barge, or even something akin to a drilling platform, sunk to the bottom.

Edited April 10, 2018 by tater

[ment18]

1 minute ago, Elthy said:

SpaceX tries to keep the cost down, and land based launchsites are way, way less complicated than those at sea. I think those offerings are maybe for an upgraded barge, one that is a proper remote controlled ship which can travel on its own and is faster than the current solution...

Honestly, not really.  When you want to launch multiple times per day, you don't have a choice.  A conventional launch system will not evolve to that need within a reasonable time.  In addition, these rockets are huge, so the locations where land based launch sites can be is super limited.  Boca Chica is limited to only F9 and FH, 12 per year.  Not even close to BFR, and there are people too close to it to launch BFR.  In addition, how are you going to get approval for landing the BFS at a land based site, it cones from orbit without glide capability, it could miss and hit populated areas.  Also, they dont have to go far, only 10-20 miles off shore and launches won't be heard from shore.  It allows you to choose your launch inclination as well.  There is a huge difference between current rockets where you need to ship in all of the parts of the rocket and the BFR, where the only thing you need it prop (tanker or on site creation), and payload, which is usually prop anyway.

[PB666]

6 minutes ago, tater said:

The coatal waters arounf TX are quite shallow, and the possibility exists to use an anchored barge

They drop at about 5-10 feet per mile east bound. SpaceX does not, as of yet have a port facility in Port of Brownsville which is like 12 miles from their launch site. You could potentially launch from a retired derrick (not quite as many as there used to be). That sea lane shoots out from the Port Isabel jetties due east into the Gulf of Mexico, that is the last Seaway in the continental United States. Its not used like the galveston ship channel, but during the summer you see tankers lined up about 10 miles offshored anchored waiting to get to the port of Brownsville. In fact currently there is not even a road going to BC suitable to carry a BFR, let alone a road going to the Port that could carry a BFR. Boca chica hiway is essentially a park road. So, when are we going to see a SpaceX facility at the Port of Brownsville, not to mention, expansion of the port requires an environmental impact study which takes years to complete.

The ends of the Port Isabel jetties the water is 65 feet deep (20 meters). . . . .tropical marine gulf, and going and coming out of their its has some of the steepest swells in a gulf going trip. I don't see this as a major problem, but during the summer the wind can blow 15 to 25 knots constantly, only quietening for a few hours in the morning and this can go on for days, offshore the wind dies down considerably, their launch site experience some of the highest constant winds . . .in mid summer these tend to blow strait up from Mexico (why S.Texas is semi-arid). Downrange is east, so they will have protracted launch delays due to heavy winds along the coast.  OTOH in the winter a cold-front can pass over, and short of a cloud line and a modest shift of wind its hardly noticeable. In august and september it might actually be easier to launch off-shore from BC.

Edited April 10, 2018 by PB666

[wumpus]

19 hours ago, tater said:

They have 6 years to launch 2,213 of their own satellites.

Mars has nothing to do with it.

367 satellites a year.  One per day (with way too much overtime).

I'd assume that is comparable to shipping 60k Tesla Ss a year, not trying to mass market a Tesla 3.  Mass production is the first thing that made Musk stumble.  I have no reason to suspect that Spacex can't do the BFR.  Judging from the FCC application (and spacex's love of vertical integration) they would be directly responsible for getting all 2,213 birds (initial run is 1,600) manufactured.  It won't be good having two constant sets of crisis going on in the same company (not saying that anything is going *wrong* with BFR, just that it is a major project pushing their limits as a company and is going to have plenty of moments of crisis and handling them).

[DerekL1963]

1 hour ago, PB666 said:

The vibration and stretch forces are quite intense, if you have ridden on these bullet trains you would know this. A 787 only experiences stretching forces relative to ambient along the length, a bullet train experiences both compression and inflation forces and the changes occur very rapidly measured in millesonds. Its not an issue of how much force

Yes, they're intense.  They're also a small fraction of what a booster encounters, and a Shinkansen isn't (as) limited in the structural weight it can devote to resisting those vibrations and forces.  (Nor is a Shinkansen filled with a couple of millions of gallons of cryogenic fluids vibrating in response to those vibrations and forces and thus imposing additional forces.)

And yes, it absolutely is an issue of how much force - because it's force that determines the level of stress that results from the force.  Hang a hundred pound weight from twenty pound fishing line and stand underneath it if you don't don't think force matters.  I'll be over here looking up the number of a good funeral home.

[PB666]

On 4/10/2018 at 2:11 PM, DerekL1963 said:

Yes, they're intense.  They're also a small fraction of what a booster encounters, and a Shinkansen isn't (as) limited in the structural weight it can devote to resisting those vibrations and forces.  (Nor is a Shinkansen filled with a couple of millions of gallons of cryogenic fluids vibrating in response to those vibrations and forces and thus imposing additional forces.)

And yes, it absolutely is an issue of how much force - because it's force that determines the level of stress that results from the force.  Hang a hundred pound weight from twenty pound fishing line and stand underneath it if you don't don't think force matters.  I'll be over here looking up the number of a good funeral home.

Well if you are going to use a 787 as a model, a craft that climbs to 8000 feet before the cabin undergoes pressurization, and gantly climbs over 20 minutes to its cruising altitude with a craft that at maxq traveling 500 m/s nearly vertical to a complete.  A typical descent rate is 3 natical miles per 1000 feet of elevation, essentially 100 meters per 1.8 km traveled. . . . .at 250 knots FL100 trans limit that occurs about 125 m/s and on 10s of meters per second vertical change versus 100s of meters per second, that is a fairly major difference in the rate of pressure change. There is almost no chance at all that a 787s pressure hull will ever fail, there could be other damages that LOAF but gently climbing in and out per standard climbout and descents are not going to be that cause. 

If you [snip] looked it up, you would find that the stretching of a shinkansen as it moves into a tunnel is considerably more than 787 and notable by the passengers,  the vibrational forces per unit of cabin structural mass are also alot greater than a 787 during flight, 787 runs on air, the trains runs on rails. Despite what you bias tells you, a bullet train faces the types of forces per unit of structure mass more comparable to a rocket. 

Edited April 11, 2018 by Vanamonde

[mikegarrison]

8 minutes ago, PB666 said:

787, a craft that climbs to 8000 feet before the cabin undergoes pressurization

This is not correct. Pressurization of the cabin is more complicated than that. Essentially it is a gradual fade from airport ambient to final cruise. The following image is cartoony but roughly correct. Note that the pressurization begins as soon as the doors are closed, and the delta p (the difference between the green and the red) grows as the airplane climbs. It doesn't just follow the red line until it hits the final cabin altitude.

(Also, the cruising cabin altitude on the 787 is 6000 feet, not 8000 ft.)

[Wjolcz]

3 hours ago, ment18 said:

Honestly, not really.  When you want to launch multiple times per day, you don't have a choice.  A conventional launch system will not evolve to that need within a reasonable time.  In addition, these rockets are huge, so the locations where land based launch sites can be is super limited.  Boca Chica is limited to only F9 and FH, 12 per year.  Not even close to BFR, and there are people too close to it to launch BFR.  In addition, how are you going to get approval for landing the BFS at a land based site, it cones from orbit without glide capability, it could miss and hit populated areas.  Also, they dont have to go far, only 10-20 miles off shore and launches won't be heard from shore.  It allows you to choose your launch inclination as well.  There is a huge difference between current rockets where you need to ship in all of the parts of the rocket and the BFR, where the only thing you need it prop (tanker or on site creation), and payload, which is usually prop anyway.

Exactly. There's also the problem of transporting it from sea to land and the other way around. You need a crawler and a huge crane. It's just a waste of time and money. Why not just a  boat/rig-like structure.

Maybe what's happening in BC is just a second Florida-like launch site but only for Falcons? Maybe they aren't planning to transport the BFR/BFSs to Boca Chica at all? What's the point of transporting it there anyway if you can just float the launch pad out into Pacific.

Edited April 10, 2018 by Wjolcz

[CatastrophicFailure]

11 minutes ago, Wjolcz said:

ybe what's happening in BC is just a second Florida-like launch site but only for Falcons? Maybe they aren't planning to transport the BFR/BFSs to Boca Chica at all?

Shotwell has said they’re going to do initial BFGrasshopper testing out of Boca, but just that will probably require pretty minimal support hardware. 

[DerekL1963]

59 minutes ago, PB666 said:

Well if you are going to use a 787 as a model, a craft that climbs to 8000 feet before the cabin undergoes pressurization, and gantly climbs over 20 minutes to its cruising altitude with a craft that at maxq traveling 500 m/s nearly vertical to a complete.

0.o  I'm not the one using the 787 as a model.  I'm one of the ones repeatedly showing how the 787 isn't relative.  What you posted above certainly isn't.
 

1 hour ago, PB666 said:

a bullet train faces the types of forces per unit of structure mass more comparable to a rocket. 

A bullet train neither goes supersonic, not experiences multiple gees of acceleration, nor experiences vibrations of the magnitude of a rocket launch, nor experiences the loads of cryogenic fuels sloshing about inside it...  So, no.  It doesn't experience loads comparable to those of a rocket.  The measure "per unit of structural mass" is nothing but meaningless piffle.

You invoked science, but now shy away from science.  This pretty much ends my interest in the conversation.

[Ultimate Steve]

So, to sum up everyone's arguments, Carbon Fiber Spaceships have at least something to build on - not something too terribly similar, but similar enough and infinitely better than nothing.

[mikegarrison]

21 minutes ago, DerekL1963 said:

The measure "per unit of structural mass" is nothing but meaningless piffle.

I take sort of an exception to this.

For structural loads, it certainly does matter what structure you are applying the loads to. Apply the same load to a massive steel beam or a paper clip, and obviously the paper clip will fail first. This is because the stress level in the paper clip will be much higher than the stress level in the steel beam.

[YNM]

Also, trains are made from aluminum, not carbon fibre...

[tater]

 

[PB666]

3 hours ago, DerekL1963 said:

0.o  I'm not the one using the 787 as a model.  I'm one of the ones repeatedly showing how the 787 isn't relative.  What you posted above certainly isn't.
 

A bullet train neither goes supersonic, not experiences multiple gees of acceleration, nor experiences vibrations of the magnitude of a rocket launch, nor experiences the loads of cryogenic fuels sloshing about inside it...  So, no.  It doesn't experience loads comparable to those of a rocket.  The measure "per unit of structural mass" is nothing but meaningless piffle.

You invoked science, but now shy away from science.  This pretty much ends my interest in the conversation.

Neither does a 787, in fact compared to a bullet train its IAS is actually similar. Since it never gets to Mach Speed, and when it gets close its essentially at 30,000 feet, about 1/3 surface pressure. Niether does it experience the windshere of going in and out of a tunnel at 150+ m/s. But you would know about the difference of both vehicles if you had experienced both, but you haven't.

 

3 hours ago, mikegarrison said:

I take sort of an exception to this.

For structural loads, it certainly does matter what structure you are applying the loads to. Apply the same load to a massive steel beam or a paper clip, and obviously the paper clip will fail first. This is because the stress level in the paper clip will be much higher than the stress level in the steel beam.

And there is not much in the normal structural loading on a carbon fiber hull of a 787 that would significantly age it. Maybe in 40 years, but again judging by some of the DC3 in service currently (i.e. built in 1935), it would generally have to require some unusual service that would cause a 787 hull to experience the type of stress that would be useful (determine the limits of that design).  I would seriously doubt anyone would put the kind of money down on a 787 if its expected life was less than 30 years. BFR is to be designed and completed in 5 . . .its would be rather useless. 

3 hours ago, Ultimate Steve said:

So, to sum up everyone's arguments, Carbon Fiber Spaceships have at least something to build on - not something too terribly similar, but similar enough and infinitely better than nothing.

It means that SpaceX needs to do some stress testing on their own, for example a sounding rocket with lower than expected tolerance in order to see what stress can be observed.

------

I should add to the above that a rocket passing Mach 1 has a boundary layer that separates from the craft the rejoins down the craft, as the speed increases that layer moves down the side of the craft until it surpasses the engines. Its a primary reason you don't want to linger near Mach speed. This is very similar to what happens when a fast train passes into a tunnel. As the train approached the tunnel a pressure gradient builds at the face of a tunnel, which dissipates as it travels into the tunnel, and pressure declines on the skin.

 

Edited April 11, 2018 by PB666

[mikegarrison]

21 minutes ago, PB666 said:

And there is not much in the normal structural loading on a carbon fiber hull of a 787 that would significantly age it. Maybe in 40 years, but again judging by some of the DC3 in service currently (i.e. built in 1935), it would generally have to require some unusual service that would cause a 787 hull to experience the type of stress that would be useful (determine the limits of that design).  I would seriously doubt anyone would put the kind of money down on a 787 if its expected life was less than 30 years. BFR is to be designed and completed in 5 . . .its would be rather useless.

Airplanes usually last forever, unless you crash them. They just get to be more and more and more and more expensive to keep flying.

That being said, comparing the expected life of a 787 (plastic/titanium structure) versus a DC-3 is kind of pointless. And talking about how some DC-3s are still flying ignores that something like 16000 of them were built (mostly for WW2) and probably less than 1% are still flying.

[tater]

Hopefully we'll know more soon enough, when they start to try and break some of them in flight.

[_Augustus_]

9 hours ago, tater said:

 

Why?

F9 has ridiculous margins on this launch - easy to RTLS.......