31

SpaceX Super Heavy/Starship (BFR/BFS) - Earth to Deep Space / Re: SpaceX Starship : Texas Prototype(s) Thread 24 : Discussion

« Last post by eriblo on 01/30/2023 08:54 pm »

Here is my attempt at some (mostly upper) bounding numbers for the Potentially World Ending Methane Vents of Doom:

I am using WolframAlpha for physical properties/calculations and some rough pixel counting from the NSF livestream. Please feel free to find mistakes.

Two vents, total ~140 s.
IIRC temperature was 19 °C with a dew point of 13 °C. This  means air is 1.2 kg/m³ with 10 g/kg of water.
Wind speed from the plume movement on the South/North views: 7m/s.
Average specific heat capacity of air is 1.0 kJ/kg.
Average specific heat capacity of methane (gas) is 2.2 kJ/kg.
Specific heat of vaporization of methane is 510 kJ/kg.


Vent opening
The vent has a plate welded on with a smaller hole that looks to be ~13 cm diameter. Assuming John's maximum ullage pressure of 6 bar absolute from above :

Venting gas, worst case: Choked flow at opening, methane at 6 bar, 150 K is 34 kg/s, total 5 t.

Venting liquid, worst case: Bernoulli equation for methane at 95 K and 5 bar pressure drop gives 280 kg/s, total 40 t.


Vent size
The air flow across the initial vent plume is enough to mostly vaporize any liquid content (as we do not see the plume bending significantly downwards under gravity). Estimating the vent cross section to the wind is hard due to the rapid expansion downwind but I get range of 30 m² - 70 m². Note that most of the liquid in the plume would likely evaporate well before it starts to be deflected.

Using 0.5 kg methane per m³ of air and 7 m/s wind gets a range of 100 kg/s - 250 kg/s or a total of 15 t - 35 t

Any vented gas would at most be a few t.


Final plume size
Comparing to the stack the downwind plume expands to a diameter of ~50 m and then disperses (hard to tell because it interacts with the ground and extends beyond most video views).

At this point it has a flow of 12000 m³/s (neglecting wind gradient) and has warmed enough that all the water evaporates, i.e. 6 K below ambient.

Venting gas at boiling point (400 kJ/kg): 250 kg/s, total 35 t.

Venting liquid at boiling point (910 kJ/kg): 110kg/s, total 15 t.

This assumes a homogenous plume and should be an upper bound.


Conclusions
It looks like both plume appearance and size is inconsistent with the maximum gas vent rate, not to mention the amount of ullage gas available (even with rapid boiling).

My guess is a spray with significant liquid content totaling towards the lower range (i.e. on the order of 10 t).

Six bar is the tank rating. At the tank bottom it is the sum of methane weight and ullage pressure. IIRC, John calculated the liquid methane to contribute 3.99 bar at full tank. That leaves ullage at ~2 bar max.

This needs a sanity check as I can't find the referenced post and could easily have LOX and LCH4 switched.

Anyway, I did this screen grab from the NSF feed. It shows both tanks venting at the same time - something that SX should be allergic to. Either this vent was unplanned or had an inert component. I found this while searching for a video I saw showing the beginning of the vent. Didn't find it.

At vent initiation there were a few gobs spewed out that fell in a manner consistent with liquid. Not much, and for less than a second. This doesn't mean that there wasn't more liquid than initially apparent. More could have been hidden in the gaseous plume - or not.

We need Elon to step up and put us out of our misery.


Edit: found it and yes, I did booger the numbers. LCH4 ullage pressure should range between 2.4 and 4.9 bar.

Yes I used the 4.9 bar max rounded to 6 bar absolute.

While not optimal I do not think there is an absolute inhibit for venting both tanks simultaneously. You still want to control the pressures and that vent will not increase oxygen concentration but that much. If both vents were low velocity liquid it would be more of a concern 

32

Advanced Concepts / Re: Realistic, near-term, rotating Space Station

« Last post by Coastal Ron on 01/30/2023 08:53 pm »

NN GNC in the field

2D navigation in crowded conditions is not relevant to realistic, near-term, rotating space station.

And if you look at the chart of how much human intervention Tesla FSD needs (starting at 2:20), you'll see that it is still nowhere close to be reliable.

But again, Tesla 2D driving software is not relevant to this topic, because EVERYONE knows that computer systems can do navigation tasks in the right conditions - commercial airliners can take off, fly a route, and land on their own with no human intervention. So this is not new, or news.

33

Other US Launchers / Re: US Launch Schedule

« Last post by zubenelgenubi on 01/30/2023 08:49 pm »

Cross-post:

I've mostly seen V-001, V-002, etc. but an occasional VC- (which I don't this is correct)
Configuration naming is VC0S, VC2S, VC4L, etc., where S is short (51 ft) PLF and L is long (70)

The V-xxx number is the mission number. The short serial numbers (tail numbers for each cryogenic stage will normally equal the mission number unless stage shuffling occurs).
The typical short format starts with the payload manifest then the VCXX configuration designation identification followed by the V-xxx number. Note that the PLF's where S is standard (51 ft) PLF and L is long (70), our the initial baseline product launch options (Standard was previously the Medium PLF during VC R&D). At a TBD later date other PLF lengths i.e. XS, Short and custom will be made available upon customer request with advanced long lead notice with customer supporting the initial production cost. As for Centaur there is the baseline Standard and Long DEC-V as product launch options. The Short and Extra Long DEC-V versions will be released upon will be made available upon customer request with advanced long lead notice with customer supporting the inital production cost. Note that the SEC-V versions have been shelved until further notice.
SEC-V = Single Engine Centaur-V (Shelved)
DEC-V = Dual Engine Centaur-V (Active Production)
TEC-V = Three Engine Centaur-V (Shelved, Trade Study)
FEC-V = Four Engine Centaur-V (Shelved, Trade Study)

34

Advanced Concepts / Re: Realistic, near-term, rotating Space Station

« Last post by LMT on 01/30/2023 08:45 pm »

NN GNC in the field

35

ESA Launchers - Ariane, Soyuz at CSG, Vega / Re: Ariane 5 VA260 - JUICE - April 2023

« Last post by TheKutKu on 01/30/2023 08:42 pm »

Will JUICE be the next orbital launch from French Guiana?

Yes

36

SpaceX Super Heavy/Starship (BFR/BFS) - Earth to Deep Space / Re: Power options for a Mars settlement

« Last post by daveglo on 01/30/2023 08:40 pm »

The study forgets that Americans eat food.  America has 157 000 000 Ha of arable land, to feed 350 000 000 people, or 2 people per hectare.  Or in other words 5000 m2 of land is required to feed one person.  {snip}

Your math is WAY off. 

Firstly, land in farm production in the US is 895,300,000 acres (362,310,000 Ha), not the value you quoted.

Second, the US feeds far more than it's own population.  Bulk exports of raw products exceed imports by a ratio of almost 40:1.

The reality is that the number you're looking for depends in large part on what you can get away with.  A more general estimate using quality soils would be 1 acre (0.4 Ha) per person.  But of course, the soils on Mars are going to be much more of a challenge, just because of the volume of fertilizer needed to make it suitable for food production.

I would agree that power requirements are going to be a top issue.  The big question is how much power to do you need to get water, oxygen, methane, and nitrogen out of the martian environment?  THAT's the number you're really looking for.

37

ISS Section / Re: Expedition 68 Thread

« Last post by ddspaceman on 01/30/2023 08:39 pm »

https://twitter.com/Space_Station/status/1620171235782201346

38

SpaceX Missions Section / Re: SpaceX F9 : Amazonas Nexus : CCSFS SLC-40 : 5 February 2023

« Last post by Ken the Bin on 01/30/2023 08:36 pm »

The standard time for launching satellites to geosynchronous transfer orbit is overnight, yes?  Backtracking from the need to start drawing electricity from the solar panel(s) ASAP in daylight, so as to avoid running down the battery?  (Of course, there are exceptions.)

Here's what the FAA ATCSCC Current Operations Plan has:

SPACE X AMAZONAS-6 CAPE CANAVERAL SFS, FL
PRIMARY:        02/05           2232Z-0319Z
BACKUP:         02/06           2232Z-0319Z
                02/07           2232Z-0319Z
                02/08-10        2222Z-0309Z

https://www.fly.faa.gov/adv/adv_spt.jsp

39

SpaceX Super Heavy/Starship (BFR/BFS) - Earth to Deep Space / Re: The Air Force has big plans for starship

« Last post by zubenelgenubi on 01/30/2023 08:35 pm »

Moderator:
The thread went WAY off-topic; over the river 🌉 🌁 💦 ♒️ and through the woods 🌳 🌲 🌴 to the dismal Land of Thread-Lock.  Not to grandmother's house. 🏡

Thread locked. 🔒 ✨️

40

SpaceX Facilities and Fleets / Re: SpaceX Texas launch site Discussion and Updates - Thread 12

« Last post by alugobi on 01/30/2023 08:31 pm »

Yeah, really, how did he come up with that.