Read my post. Hydrogen as energy transmission is a dead end physics wise. Use the electrical grid and get 90%+ effiency, or use hydrogen and lose most of your energy. Electrolyzing water is, and always will be very inefficient. It will not, cannot reach the efficiency of the grid.

This is why I think electric vehicles have an advantage...you can put the charging station at your residence. All it needs is a wire. The infrastructure is already there, and can be expanded with relatively little expense. I can imagine charging stations everywhere one parks one's car. We all park our cars at some point, so we will all be able to charge our battery cars enough to make them usable, especially if the charging stations are high capacity.

In addition I think that in terms of space and expense, the potential power output of batteries is far larger than for fuel cells. I picture fuel cells as being finicky and complicated. If I am wrong, please correct me. However I have trouble imagining 800hp output (like the latest Tesla) from a fuel cell. My suspicion is that such a powerful fuel cell would be a Rube Goldberg machine.

Finally, and I think this is the real nail in the coffin for hydrogen as an energy source, is energy efficiency. Creating hydrogen from water, or from whatever other source you have takes a fairly large amount of energy. Let's say we take our hydrogen from water. How much of that input energy will actually make it to the fuel in terms of chemical potential energy? Some of the energy will be put into the O2 bond, which will not be transferred as fuel. Some (most) of the energy will be lost as thermal energy. Only a relatively small amount of the input energy will make it into the fuel. I would be surprised if it was even 20%, and I suspect it is less.

Compare this with gas turbine generators, that can have efficiencies well over 50%. So, you use your natural gas to generate electricity, in which you lose half of your energy already. Now you have a choice: you can use that electrical energy to electrolize water and lose 80% or more of that remaining energy. Or you can use the electrical grid to transfer the electricity directly to the car and lose only about 5% of the energy to the electrical grid.

The laws of thermodynamics are against the use of hydrogen is a fuel. Unless we can find a way of electrolyzing water that has an efficiency equivalent to the electrical grid (more than 90% - and such a process would violate the laws of thermodynamics), hydrogen as a fuel is an obvious dead end. If only the people who ran these companies knew a little bit of physics. I'll take a BSc in Physics any day over an MBA.

Here is a twitter discussion with Musk and Carmak that gives some reasons for using the fins. To quote:

My suspicion is that there will be a degree of unpredictability for this flight as they refine the control characteristics of these fins. Thus Musk was quoted as saying that the success probability was 50/50 for this landing.

This is a quote from Elon Musk on what he thinks about "process":

This just about nails it for me.

I forgot to mention...what I describe above is called learning by induction. Which is a form of probabilistic learning.

Perhaps I am not using the correct terminology. And I am not an expert...this isn't really my field. But I have seen neural network simulations which, for example recognize handwriting. You show the program many variations on the letter F, and the computer then learns to take symbols that look like the letter F and put them into that group. One can imagine that the brain is made up of many such processes. It certainly sounds like the way that I learned. See a spoon, see mommy using it to feed me, see mommy using it to feed herself. They are all different spoons, but they look similar and they seem to be used to move food from a bowl to a mouth. In a way it isn't that different than taking similar shapes and calling them a particular hand-written letter. It's just that we do this categorization at a myriad of levels on a myriad of objects and eventually of ideas themselves.

I suppose what I think might happen is that instead of building simulations of neural networks, that we will build actual neural networks using some form of electronic system. I don't know what that will look like exactly, but I suspect it is quite possible. After all, nature has already done it.

If we can make a human level brain, then we can make something much smarter as well.

There is the problem...I think that CPU's are the wrong tool. The problem needs to be re-framed. Perhaps we need synthetic neurons. Then we will need precisely one synthetic neuron to simulate a real one. I know...easier said than done. But we do know the basics of neuron function. Why can't we make a single electronic element that does something very similar?

Neurons can typically fire at a rate of 250Hz. There are about 100 billion neurons in a typical human brain. These neurons are networked in an extremely complicated and changeable parallel network. This network of neurons can be powered for reasonably long time with the energy contained in a bowl of oatmeal. Surely we will at some point be able to create a similar device, and one that doesn't require most of the world's computing power to run.

I suspect the breakthrough will come with a new computing paradigm, one that is based on massive parallelism. Perhaps it will consist of a silicon based device that mimics the network and function of neurons. I suspect it will be based on probabilistic computing, similar to how our own brains work. It will be taught rather than programmed. Perhaps there will be more states than merely 0 and 1.

I think that this is coming, because our brains are already doing it. And with incredible efficiency. Once we saw birds fly, and so we tried to do it ourselves. Eventually we figured it out. I think it will be the same with AI. We will copy nature, learn its principles, and then we will create our own version. And in doing so, I suspect our ideas of what intelligence is will fundamentally change.

There is a BBC documentary film maker named Adam Curtis who makes some fascinating and disturbing videos about society and control. He has access to the BBC film archives, and uses historical footage extensively. The assertions made are extensively documented and the interviews of powerful people are extremely interesting. I think that this video, The Engineering of Consent, is relevant to this discussion. It is one hour, and quite "stream of consciousness", but worth watching. It is the second episode in a series called The Century of the Self.

From the wikipedia summary:

I have been reading lately that there has been serious concern about the liquid-solid hybrid engine used in Spaceship 2. In 2007 there was a nitrous oxide explosion that killed three people.

parabolicarc.com is a pretty good source of information on New Space. Here are some tweets:

I am a huge supporter of commercial space, most especially Space X. But I think that accidents like this give the whole sector a bad name. Virgin Galactic/SC have been building this ship for 10 years, and they still don't have a viable engine. That is not a good sign.

Contrast that with Space X, which in about the same amount of time has built the Falcon 9, which has a string of 13 straight successes (touch wood). It seems to me that not all space companies are created equal.

My guess is that it was a turbo-pump that failed. Those are a part of this Soviet engine, and were also likely made in the 1960's.

Elon Musk called it two years ago in this interview.