totm nov 2023 SpaceX Discussion Thread

[kerbiloid]

5 minutes ago, Nibb31 said:

Aligning 4 points or 1 is exactly the same mathematical problem. You need to align X, Y, Z and rotation in exactly the same way.

If your ship is an ideally hard mathematical point.
Why do other ships and station modules use a single node?

8 minutes ago, Nibb31 said:

You need fluid and venting: fluid goes one way, helium or filler gas goes the other.

Filler gas goes out. You need one pipe per a component, one hole to outside and one balloon of liquid nitrogen (or helium) as a filler gas.

[Nibb31]

Just now, kerbiloid said:

If your ship is an ideally hard mathematical point.
Why do other ships and station modules use a single node?

It's still a single node. Just bigger.

Just now, kerbiloid said:

Filler gas goes out. You need one pipe per a component, one hole to outside and one balloon of liquid nitrogen (or helium) as a filler gas.

Fuel that comes out of the source tank needs to be replaced with filler gas. Filler gas is vented from the destination tank. It's simpler to just recirculate the filler gas from destination tank to the source tank and let acceleration (or gravity ;)) do the rest.

[tater]

Other docking uses a single node, because the entire point is a door in the middle, not 4 doors. Any docking ring that includes power, and liquid pipes has as many "nodes" as connections, it just has one big node in the middle. 

[Mitchz95]

Elon mentioned that the docking mechanism is also what holds the booster and ship together during launch (kinda like using docking ports as decouplers in KSP ) Has that been done before? What are the challenges, if any, about doing it?

Edited September 30, 2017 by Mitchz95

[Nibb31]

9 minutes ago, Mitchz95 said:

Elon mentioned that the docking mechanism is also what holds the booster and ship together during launch (kinda like using docking ports as decouplers in KSP ) Has that been done before? What are the challenges, if any, about doing it?

It hasn't really be done before because it hasn't really been needed. I don't see it as a huge problem as long as the system is designed for the appropriate structural loads. F9 already uses mechanical latches for attaching the first and second stage.

It has to be super reliable though, especially with the BFR architecture, because if a latch fails to disengage, you risk losing both vehicles.

Edited September 30, 2017 by Nibb31

[Ultimate Steve]

10 minutes ago, Mitchz95 said:

Elon mentioned that the docking mechanism is also what holds the booster and ship together during launch (kinda like using docking ports as decouplers in KSP ) Has that been done before? What are the challenges, if any, about doing it?

Elon: Alright, we need to design something complicated to cut the rocket in half, any ideas?

Random dude: Right click, decouple node.

[ModZero]

3 hours ago, Pipcard said:

23:30 - BFR spaceships will dock end-to-end and use milli-g thrusts to settle the methalox propellant during transfer.

*PowerPoint animation* *Applause*

I feel a sudden urge to start linking Star Citizen spaceship presentations in this section.

[regex]

25 minutes ago, Nibb31 said:

It has to be super reliable though, especially with the BFR architecture, because if a latch fails to disengage, you risk losing both vehicles.

Or a backup shear mechanism so you can at least recover both craft for repairs rather than lose both of them.

[Cunjo Carl]

I was presently surprised about how open Elon was with his long-term goals! He always has been, but it still surprises me- one of the advantages of a private company, I guess! I still can't believe it though- Despite just getting the falcons online and primed as one of the world's more attractive launch platforms (read: steady money influx) he's gonna call them obsolete to his next great adventure... If anyone can do it it's them, but they're putting the whole company on a double-down that they can stockpile and reuse the falcons, and then another double-down that they can have the Big Falootin' Rocket up and running before their money runs dry. What a risk! What a reward! I feel like the whole company has just been wagered on 00 at the roulette table.

I think my favorite moment of the presentation was when Elon said wistfully and longingly (paraphrasing) "I.... I wanna terraform mars...", and someone from the crowd shouted reassuringly "You can do it, Elon!" That made my day!

On a practical standpoint, I really hope they think about maintenance on the Big Falootin' Rocket they have in mind. Just thumb in the wind guessing, on a build-a-dozen basis, it looks like they might be one to several $B each to build primarily in house. He was saying he could get the per-launch cost down below a rocket that looked like it might have been a couple $M on a build-a-dozen basis.

How much of this ~$2M goes to fuel, and how much to logistics/maintenance?

All of this being very-rough-estimate, of course... If you have onsite liquefaction, LOX is ballpark a few tenths of a penny per cuf. From what I hear from my LN delivery guy, pipeline/import-tanker LNG is about at that cost too these days, which makes things convenient to estimate. The Big Falootin' Rocket first stage body is about 30ft Dia, and 200ft tall (eyeballing an aspect ratio ~6.5). Doing a high-side estimate we'll call it all tank so the volume is pi/4 D^2*H = ~~150,000 cuf. That comes to ~~$500-$1000 per 1st stage tank fill on raw material. Of course they'll need to pay more if they need unusual purity (factor 10), or if they need truck-delivery (factor 3), and for their sub-cooling (no idea), but all told, I'm convinced they won't need to spend appreciable money on the fuel itself. A couple k$ is hardly a drop in the bucket *cough*.

So very little cost in fuel.

Aside: Compare this to jet fuel, which is (I just looked up) more like $40/cuf! That's something on 5000-fold more expensive by mass and so ~1000-fold more expensive by Joule (intentionally ignoring the factor-20 better Isp from bypass and factor-20 L/D from wings to make a point). Yowza! Coach class P2P here we come (joking)

That leaves them a couple million maintenance per launch... That's good- I think they'll need it and then some! I do worry about reuseability. Things wear out and can be fixed for 2M per launch. I don't doubt that. I worry they won't be able to _find_ the problems and fix them for less than 2M per launch. I've done some work in that field... it's not trivial to find a microfissure in 18,000 ft^2 (a half-acre!) of rocket. And it's not trivial to find a propellant valve that's getting sticky or a seal that's starting to fatigue when you have a few dozen engines! How will they do it? I only hope they give themselves enough time to figure out . I'm completely rapt with excitement.

[tater]

The BFS (crew version) carries 240 tons of CH₄. 

That's ~$150,000. LOX is practically free.

Haven't seen tankage numbers on the booster, but propellant costs are, in the world of spacecraft, virtually free. Looks like the numbers for operational costs SpaceX posted for the original ITS in fact include fueling. 200k for the spacecraft, and 700k for the booster. So under 1M$ for the current version. Even if the craft only flew 10 times, and cost (booster and spacecraft combined) 300M$ to fabricate, the per launch cost would be 31 million $ for 150 tons to LEO.

If they can fly 100 times, then 4M$/launch.

Might as well send the tanker, and fly the sat to GEO, and upper stage might cost more than the 4M$ cost to send the tanker. Reuse really does change everything if it can possibly be made to work.

 

 

[Spaceception]

Ok, so, assuming 4 million a launch, divided up by 100, is $40,000 a person. Minimum (But that's grossly unrealistic).

So, crunching some numbers (Not that hard though hah), that's 48 million (480k a person) for all 12 launches dedicated to 1 crew (1 crewed, 1 cargo, 10 refueling) that will be spread across 100 people. 500k a person is pretty good.

And I'm guessing the lower the price, the more crowded the rocket. Be sure you want economy style before you book your trip

 

Edited September 30, 2017 by Spaceception

[magnemoe]

3 hours ago, kerbiloid said:

If your ship is an ideally hard mathematical point.
Why do other ships and station modules use a single node?

Filler gas goes out. You need one pipe per a component, one hole to outside and one balloon of liquid nitrogen (or helium) as a filler gas.

Suspect that BFR uses LOX and methane as filler gas, much like the planned centaur replacement will use LOX and H2, it should be possible to cool and reuse most boil off. 

During fuel transfer you get some but can use this to generate trust during transfer, you would also need pumps the trust is just to settle fuel in bottom of tanks same as you need before any second stage burn. 

2 hours ago, regex said:

Or a backup shear mechanism so you can at least recover both craft for repairs rather than lose both of them.

Makes perfect sense.

Lack of LES on BFR is more of an issue. Yes you could put one on top, you also want all into acceleration chairs during takeoff and landing, putting this on top and you could make an simple pod out of it, Simple as in pressurized, rockets to separate and parachutes, no heat shield, not 15g trust but you have all the cargo and living space between you and upper stage tanks. 
This is another nail in the coffin for the passenger ICBM who was not very practical in the start  

[tater]

Shuttle had no LES, either. Part of the rationale for a cargo version first (100% automated) is that they can test many launches and landings before even trying crew. Perhaps the first crew version could have a crew capsule at the top with LES, again, just to establish reliability.

Bottom line is that for large craft, safety needs to be the craft itself. You're always just going to have to trust it for landing.

[mikegarrison]

Stuff that is supposed to be reusable doesn't always stay that way.

https://twitter.com/jacobsoboroff/status/914228840708186112/photo/1

[magnemoe]

10 minutes ago, mikegarrison said:

Stuff that is supposed to be reusable doesn't always stay that way.

https://twitter.com/jacobsoboroff/status/914228840708186112/photo/1

Engine lost its fairing, I guess its pretty easy to remove to make engine inspection easier and someone messed up putting it together. 
Main issue would be part of it ending into the fans or it ripping critical stuff off then snapping. 

Anyway its an four engine plane:
An B52 had an engine out during an large air force exercise, it then requested prioritized landing because of engine out. 
An fighter pilot who probably needed to go to the bathroom had an salty comment on radio: one of the dramatic 7 engine emergency landings 

[mikegarrison]

14 minutes ago, magnemoe said:

Engine lost its fairing, I guess its pretty easy to remove to make engine inspection easier and someone messed up putting it together. 
Main issue would be part of it ending into the fans or it ripping critical stuff off then snapping. 

No, the whole fan is gone. Most likely the disk failed.

[magnemoe]

1 hour ago, mikegarrison said:

No, the whole fan is gone. Most likely the disk failed.

That one is very bad, scary so, as I understand the fan blades holds an significant energy the fairing has to be armored to catch blades who might hit wing, fuselage or other engines. 
On the other hand the armor only have to stop them, not survive the event, still the drive shaft for the fan should have survived 
 

[kerbiloid]

4 hours ago, magnemoe said:

Suspect that BFR uses LOX and methane as filler gas

Wouldn''t matter, as the filler gas mass is anyway much less than the fuel mass.

[sevenperforce]

The acceleration is needed because pressing with nitrogen or any other gas doesn't necessarily force the liquid in the desired direction in microgravity.

[NSEP]

On 30/09/2017 at 1:06 AM, YNM said:

Regarding BFR Earth-to-Earth concept...

 

So, how do we differ a BFR from an ICBM, again ?

The BFR is Cryogenically fueled, meaning that you need to refuel it right before launch before it warms up and boils off. Refuelling such a thing takes up quite a bit if time, so if you were to strike back, there is a big chance you will be late. Also, ICBM's are usually made to be small, compact and have the ability to launch anytime. So using the BFR as ICBM is as practical as sending 150 Ford Fiestas into space. Just because you can does not mean its practical.

[Nibb31]

22 minutes ago, NSEP said:

The BFR is Cryogenically fueled, meaning that you need to refuel it right before launch before it warms up and boils off. Refuelling such a thing takes up quite a bit if time, so if you were to strike back, there is a big chance you will be late. Also, ICBM's are usually made to be small, compact and have the ability to launch anytime. So using the BFR as ICBM is as practical as sending 150 Ford Fiestas into space. Just because you can does not mean its practical.

If people can use trucks and airliners as weapons, I don't see why this doesn't have the potential of be used as a weapon too.

But the question was rather how does a country's defense system distinguish an incoming passenger flight from an incoming ICBM. A lot of people won't be too keen on seeing suborbital hypersonic projectiles coming down on major cities.

The question is moot though, because there are so many impracticalities that it will not happen in any foreseeable future, and certainly not in the form that was presented in the CGI videos. Musk presented this for its clickbait value, and a lot of people are focusing on it as if it was the big news of the presentation. It wasn't. It's just an afterthought.

[kerbiloid]

12 minutes ago, Nibb31 said:

But the question was rather how does a country's defense system distinguish an incoming passenger flight from an incoming ICBM.

Is it much bigger, it speaks to the ground control, flies on schedule, and follows its official route

Spoiler

from Pyongyang

 

[ModZero]

8 minutes ago, kerbiloid said:

Is it much bigger, it speaks to the ground control, flies on schedule, and follows its official route

No it doesn't, because the only customer willing to pay for the service is the army.

EDIT:

28 minutes ago, Nibb31 said:

Musk presented this for its clickbait value, and a lot of people are focusing on it as if it was the big news of the presentation. It wasn't. It's just an afterthought.

Well, it was a high-point of the presentation from the humorous perspective.

I think you can put the barge in the Zurich lake?

Edited October 1, 2017 by ModZero

[kerbiloid]

4 minutes ago, ModZero said:

the only customer willing to pay for the service is the army.

Then the question is not "how to distinguish?", but "how far is the open-fire range?".

Upd.
And "how high", too.
150 (or how much?) tonnes of payload = ~1000 Mt. Low orbit also should be prohibited.

Edited October 1, 2017 by kerbiloid

[Spaceception]

3 hours ago, Nibb31 said:

The question is moot though, because there are so many impracticalities that it will not happen in any foreseeable future, and certainly not in the form that was presented in the CGI videos. Musk presented this for its clickbait value, and a lot of people are focusing on it as if it was the big news of the presentation. It wasn't. It's just an afterthought.

I agree, it seemed more like a cool what if thing to me. The cinematic was cool at least.