SpaceX (Vol. 2)

[ridds]

Talksteer said:

ridds said:

Talksteer said:

Timothy Bucktu said:

Not for the fanboys, but interesting take if you have an open mind...
https://youtu.be/nxG0WAwwrGk?si=5XSKp3KZNQdGZdCR

1. triggered

Thunderfoot hasn't done a day of engineering in his life and gets very basic things wrong about physics, scaling and the engineering process. He pompously laughs at prototypes and subscale tests for not being finished products and generally does straw man arguments which boil down to not understanding the process of technology development ergo railing against stuff for not existing.

He also doesn't appear to realise that just because a start-up is bullsting or giving an incomplete picture doesn't mean that they might be aware of all the "issues" that you've discovered in your casual guidance at their technology and might have a plan to do something about it.

The fact that he occasionally targets actual bullst products doesn't mean he's worth listening to.

My general advice is not to both watching any of his content if you want insightful coverage there are much better options with a much better ratio of signal to noise.

1. Hyperloop....? Yep, he was totally wrong calling that one out.

Which "basic Physics" things has he got wrong? I'm curious to know.

There are a few videos going scene by scene which will catalogue all the mistakes on the hyperloop videos but from my background in aero engines I can tell you he hasn't go the faintest clue about pressure ratios in compressors and how they actually work. (it's the whirl velocity that you keep constant hence little ones with small diameters spin fast and big ones spin slow)

He does a whole load of "experiments" with vacuums which show he has no idea of scaling, he claims if the tube is breached you'll have a shock wave progressing down the tube for hundreds of miles causing devastation. In fact what you get is pressure loses (due to air flowing rapidly inside the tube) in the tube resulting in that sonic shockwave rapidly diminishing in pressure. This would mean that an oncoming pod would meet a much lower pressure shockwave followed by a gradual ramp up in air pressure. Provided the pod is aerodynamic the net result of encountering the oncoming air is likely to be more like being in a plane at 600mph and then switching off the engine than crashing into a brick wall.

He's also obsessed with the "mighty power of the vacuum" as if engineers aren't capable of designing pressure vessels that can resist negative 1 bar. You just over design it so that it won't fail if part of the tube gets ovalised. We routinely design large pipes with anything up to 1000 bar of pressure resistance, a vaccum is relatively trivial. Hyperloop 1's test tube was designed to ASME standards and was about 15mm thick.

His claims around thermal expansion just basically show that he doesn't know anything about it, from a mass per length basis a hyperloop tube uses about as much steel as there is in 6 railway lines. Ergo you could just tension the tube (or heat it to max operating temp) before you weld it and fix on new sections. This is what they do with rail tracks. He literally talks about differential heating (top in the sun bottom in shadow) causing a hyperloop tube to bend and buckle while stood next to a rough ass prototype tube which isn't doing either of those things because 1: differential heating of conductive steel is difficult and 2: the stresses imposed are less than those imposed by the tubes own weight so it goes nowhere. Personally I'd just fit the tubes loose like a water pipe and then use a welded bellows seal between each section would take about 5 minutes to fit.

For all the invective around Hyperloop it's notable that Elon Musk didn't start developing it he just threw the idea out to try and get people to work on it. He was perfectly up front that the end product wouldn't look anything like what was initially proposed.

The Hyperloop 1 demonstrator and the student competitions made meaningful progress in inductrack maglev designs and there are now new companies working to make that system backwards compatible with conventional rail. Those demonstrations also showed that the vehicle itself was eminently feasible. The issue was that the requirements for straightness of the track plus the plus the potential for naughty people to attack it means that its probably best to stick the thing under ground (unless you have a massive empty desert like the likely first customers will have). Hence the place Musk put his own money was into tunnelling.

Just because the early crazy money has run out doesn't mean that nobody is working on this or that it won't happen. You still get lots of rail fans making straw man arguments that the system won't work because the pods are small (chain them together if you must) or because trains must not travel within the stopping distance of another train so must Hyperloop pods and therefore the capacity of the system would be small. In practice I suspect the system would have a safety case more like a roller coaster than a railway line.

The physics are fine and most of the complaints are like someone stating that commercial jetliners aren't possible in 1945 because current planes are dangerous, noisey and slow.

Edited by Talksteer on Wednesday 24th April 12:30

I think a lot of it boils down to what is defined as a "vacuum" and what Hyperloop would actually need to run in to be able to achieve the claimed speeds.

I've delved into Turbomolecular Vacuum Pumps and it is a world away from vac filling your car engine with coolant for example. That last few percent is incredibly hard to achieve.

Containing air under extreme pressure or vacuum is very hard and very dangerous. I try and keep as far away as possible from either.

In terms of risk, I'm not sure it's overly different to High Speed Rail. TGVs in France and the Shinkansen in Japan regularly run at speeds that would result in a very nasty events if someone were to attack it. At least Hyperloop would have been in a steel tube.

I think the real issue is the power needed to achieve the required vacuum, how you transition the pod into said tube and the cost associated with maintaining the integrity of the tube over massive distances, including coping with thermal expansion/contraction.

Then add in the power for the MagLev (if that's the motive system of choice). There's a reason there's only a few operational transport systems using this tech across the world.

[Beati Dogu]

Falcon 9 B1060 will soon launch for its 20th and final time. It is being expended to get two Galileo-L12 Satellites up to their desired orbit. They were originally going to fly on Ariane 6, but that is still delayed.

[Beati Dogu]

^ That one went off ok. Satellites delivered and 20th flight booster now giving the Atlantic sea life something to check out.

This launch was also the 200th mission to use flight-proven fairings. Quite a revolutionary cost saving it its own right.


SpaceX also said:

"We’re working toward qualifying our fleet of Falcon boosters and fairings to support 40 missions each. Increasing Falcon's flight count provides valuable information on repeated reuse, a critical element for making life multiplanetary with Starship"

40 flights per booster? That just happens to be one more than Space Shuttle Discovery's record.


Meanwhile the CRS-30 Cargo Dragon has left the ISS after about 5 weeks. It is due to splash down on Tuesday.

[Dog Star]

Toaster said:

Are we there yet...I mean hundreds and hundreds of posts and still we are not there......Makes NASA and Apollo look an absolute brilliant achievement. They not only had to design and invent new technologies but the Math that went along with with it. They also had to invent the computers as they went along. This bunch have the technology the Math and previous experience so I will ask again are we there yet

How much did Apollo and a Saturn cost to develop? Was it even partially reusable and designed from the outset to be reusable? All the got back was a charred CM. That’s the lot from a 363’ stack.

Not even a valid comparison. If SpaceX were just building some huge, dumb, expendable rockets they’d have done so years ago and they’d probably cost 30p each.

Few posts above that one “they’re having trouble with Starship re entry”. Eh? They’ve had one single shot at it with IFT3 and what was clearly no attitude control, so in fact they didn’t even get a proper go. I think it will be very difficult and a flip and soft can “landing” won’t be this year. I hope it is though.

I think they’ll have the booster sorted in the next couple of flights; they’re masters at this, it’s just scaled up and getting the Raptors to relight and survive that descent.

[Arnold Cunningham]

His post was clearly just trying to evoke a response.

[MartG]

Arnold Cunningham said:

His post was clearly just trying to evoke a response.

Yes - unfurtunately he pops up every so often with his jaundiced view of the world

[hidetheelephants]

Dog Star said:

How much did Apollo and a Saturn cost to develop? Was it even partially reusable and designed from the outset to be reusable? All the got back was a charred CM. That’s the lot from a 363’ stack.

Apollo required ~5% of the US GDP for a decade-ish. Mental amounts of money.

I thought that seems a bit large on reflection and having factchecked myself it is; spending peaked around 1965 at 5% of govt spending or about 0.66% of GDP, ~$5bn with total expenditure on spaceflight to 1972 being ~$30bn. Still a mental amount of money.

Expenditure on the Vietnam war over the same period was $178bn, although subsequent cost of pensions, veteran treatment and disability payments etc is $270bn. War; what is it good for? Profit for the MIC, who also did well out of Apollo contracting.

Edited by hidetheelephants on Monday 29th April 23:03

[Beati Dogu]

At the height of the Vietnam War as well.

[Talksteer]

ridds said:

I think a lot of it boils down to what is defined as a "vacuum" and what Hyperloop would actually need to run in to be able to achieve the claimed speeds.

I've delved into Turbomolecular Vacuum Pumps and it is a world away from vac filling your car engine with coolant for example. That last few percent is incredibly hard to achieve.

Containing air under extreme pressure or vacuum is very hard and very dangerous. I try and keep as far away as possible from either.

In terms of risk, I'm not sure it's overly different to High Speed Rail. TGVs in France and the Shinkansen in Japan regularly run at speeds that would result in a very nasty events if someone were to attack it. At least Hyperloop would have been in a steel tube.

I think the real issue is the power needed to achieve the required vacuum, how you transition the pod into said tube and the cost associated with maintaining the integrity of the tube over massive distances, including coping with thermal expansion/contraction.

Then add in the power for the MagLev (if that's the motive system of choice). There's a reason there's only a few operational transport systems using this tech across the world.

His original comments were on the "V1" design that SpaceX proposed. In that there was a fan on the front of it which was intended to allow the tube to be smaller and also power the vehicle once it had been accelerated to speed. This removed the need to electrify the whole tube. In this circumstances the pod would essentially be "flying" at about 130,000ft the compressor would work essentially like an electric powered jet engine with a relatively low pressure ratio. No cleverness would be required for this compressor.

In practice once teams started looking at the idea most of them went with a slightly larger tube and maglev propulsion all the way. The compressor idea needed each pod to have water/steam cooling board to stop the air in the tube heating up excessively.

As for maintaining the vaccum, the use of the word is highly dependent on what you are doing with it. In the case of human health anything above the Armstrong limit is basically the same, in the case of vacuum vessel structural design they are all the same. However as far as the pods go they are essentially travelling in something akin to high altitude flight and as far as the vaccum pumps go the difficulty pretty much doubles every time you halve the pressure. Ergo 0.1% atmosphere is ~3x more difficult to maintain than 1% atmosphere.

The choice of vacuum pressure for most systems concepts is basically trade between energy usage for moving the pods and cost of generating the vaccum. The pump units have been built and tested for representative scale systems. Those wouldn't be where I'd look for the maximum technical risk. The same would go around expansion, there are solutions the fact that Thuderfoot doesn't understand them is why he's making essentially a straw man argument. The big issue with the above ground solution is that due to the speed its likely that a real system would have to be so straight as to make the civil engineering excessive expensive along with the planning and land acquisition.

Regarding the ends of the line for a high capacity system I would assume that they will end up looking something like the breach of an automatic firearm. The pod gets encapsulated in a space filler that makes it a near perfect cylinder and excludes most of the air before it gets loaded into a "cartridge", residual air is removed in the cartridge (this may not be necessary). The cartridge gets loaded onto the end of the system and the pod passes through an pressure door. The encapsulation is then removed and sent to be placed around a departing pod which reverses the process. There is no reason why multiple breaches couldn't serve a single tube.

The issue with 99% of commenters on the Hyperloop is that they are looking for some sort of "gotcha". There isn't one, there is nothing wrong with the concept from a physics basis, people will then generally try to find some sort of "gotcha" from an engineering basis which generally take the form of picking on a novel bit of it throwing a rubbish semi analogous solution at it and then saying it can't work. The people working on it aren't idiots and have spent longer thinking about solutions than the commentators.

What is a lot more reasonable is to say that the cost of developing a viable solution is currently unknown (it is higher than the early developers thought hence the bankruptcies), there are relatively few bodies who are in a position to fund development on that basis.

However given that such a system is basically a teleporter there is a good argument for people to be working on such a system as well as trying to make commercial products that utilise some of the technological building blocks. Specifically improvements in tunneling and backwards compatible maglev for existing rail.

Looking a previous technology adoption is likely that early adopters will be left with something which is incompatible with later systems, is difficult to maintain in the long term and will be unreliable initially. Finding a client who is ok with that in the public transport realm is likely to be difficult which is why the first ones will likely be built in either China or the Gulf.

[skwdenyer]

Splendid post.

I recall a book I had as a child: “Spacecraft 2000 to 2100 AD.”

amongst the “spacecraft” was a trans-Atlantic evacuated tunnel, featuring a craft riding (or rather, levitating) on 3 rails (at approximately 120 degree angles). I’ve wondered if Musk read the same book?

It turns out the Internet Archive has the book at https://archive.org/details/terrantradeauthorityha... from which we find:

[RustyMX5]

It's been a significant number of years since I did anything in fluid mechanics but I wonder if the goal of pressure reduction rather than creation of a vacuum within the tube might be a sensible alternative. Just a thought.

[C n C]

skwdenyer said:

Splendid post.

I recall a book I had as a child: “Spacecraft 2000 to 2100 AD.”

amongst the “spacecraft” was a trans-Atlantic evacuated tunnel, featuring a craft riding (or rather, levitating) on 3 rails (at approximately 120 degree angles). I’ve wondered if Musk read the same book?

It turns out the Internet Archive has the book at https://archive.org/details/terrantradeauthorityha... from which we find:

Sorry it's O/T but it reminds me of this toy I had many, many years ago..

[Arnold Cunningham]

I had one too! Dinky toys were cool.

[Hill92]

SpaceX have revealed their Extravehicular Activity (EVA) space suit to be used on by the astronauts on Jared Issacman's Polaris Dawn flight:

https://twitter.com/SpaceX/status/1786759044948189...

https://twitter.com/PolarisProgram/status/17867603...

SpaceX on X said:

At ~700 km above Earth, the EVA suit will support the @PolarisProgram’s Polaris Dawn crew in the vacuum of space during the first-ever commercial astronaut spacewalk.

Evolved from the Intravehicular Activity (IVA) suit, the EVA suit provides greater mobility, a state-of-the-art helmet Heads-Up Display (HUD) and camera, new thermal management textiles, and materials borrowed from Falcon’s interstage and Dragon’s trunk.

Building a base on the Moon and a city on Mars will require millions of spacesuits. The development of this suit and the execution of the spacewalk will be important steps toward a scalable design for spacesuits on future long-duration missions as life becomes multiplanetary.