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Comment Re:Speaking of delays... (Score 1) 107

ULA's track record with the Atlas V: 100%

Yes, let's take one vehicle in its fifth generation (not counting subrevisions), and ignore its track record with all of its earlier versions that led up to this point and all of their failures, and all of Lockheed and Boeings' other launch vehicles over time, with all of their failures. Lets also ignore that they're going to have to switch engines soon, to an engine with zero track record.

Payloads typically launch on schedule or within a few weeks. .... Some payloads have been waiting literally years due to delays.

Let's totally ignore that Atlas V launches once per two months, while SpaceX launches once per month, and that almost all of the wait time was due to investigation backlog. When it comes to hitting launch windows, SpaceX has a higher average success rate than average than Atlas V

And lets entirely fail to mention the point that ULA charges nearly double what SpaceX does per kilogram. Or that SpaceX is doing everything while rapidly evolving its rocket, to the point that they've basically even switched propellants partway through (denisification radically changes their properties). And while at the same time running an aggressive recovery and refurbishment programme and developing a heavy lift vehicle, with a small fraction as much capital.

Comment Re:What governmen brought to the table (Score 1) 107

As if liquid boosters can't fail catastrophically? Check out SpaceX's last failure. Liquids are hardly immune to catastrophic failure.

And actually more to the point, you've got it backwards. The SRB failure on Challenger was slow, more like a blowtorch. The explosion was when it compromised the external tank (which, obviously, stored liquids).

Solid propellants aren't like explosives. More to the point, you have to keep them under pressure to get the sort of burn rate that is desired for a rocket.

Comment Re:Speaking of delays... (Score 2) 107

Could you remind me how many people SpaceX has killed? Boeing and Lockheed have certainly killed people in the past.

If you're referring to the AMOS 6 ground failure, ignoring that part of the whole point of flying a stack unmanned as much as you can before you fly it manned is to shake out any problems, is that a manned mission would have almost certainly survived that. Unless the launch escape system failed, despite the drama, that was an eminently survivable. How do we know this? Because AMOS-6's hypergolic propellant tanks didn't ignite until the satellite hit the ground. AMOS-6 had the fairing as some extra protection, but on the other hand, the satellite itself isn't nearly as durable as a crew dragon.

The launch escape system ignites within milliseconds of a failure being detected and almost immediately reaches full thrust, accelerating away at 10gs. Here's a graphic of Dragon's abort test superimposed over the AMOS-6 failure. Things like this are the very reason that launch escape systems exist. NASA's last manned space vehicle lacked such a system entirely. And while their design for the Shuttle ultimately wasn't chosen, you know what? Lockheed's proposal didn't have one either. And it had a strong impact on influencing the final Shuttle design outcome.

Comment Re:What governmen brought to the table (Score 1) 107

SpaceX and Blue Origin would not use solids, not because there's something wrong with solids per se, but because they're not "fuel and go", which makes them expensive to reuse - and SpaceX and Blue Origin are all about reuse.

A lack of experience with hydrolox surely factors into the picture for SpaceX and Blue Origin; they'd get significantly higher payload fractions by using a hydrolox upper stage. But they're willing to accept lower payloads in order to simplify their manufacture and ground infrastructure, and in particular because the need their propellants to be storable, and storing LH for long periods is a PITA. Storing methalox is quite difficult, but nothing compared to hydrolox.

Comment Re:What governmen brought to the table (Score 2) 107

Solids really aren't that bad when reusability isn't a concern. They're very high thrust, which is exactly what you want out of a booster, and they're structurally very simple. Their low impulse and high structural mass are not particularly important aspects for boosters. Reuse of solids however gains you very little, because there's so much work in refurbishing them.

Comment Re:What governmen brought to the table (Score 3, Informative) 107

That's not the reason you don't use it for a first stage. The disadvantages of hydrolox (which are numerous) are offset by its incredible specific impulse. But for a first stage, specific impulse doesn't matter that much, while thrust matters a lot. Thrust is in large part proportional to fuel density, as a turbopump sweeps out a fixed volume per rotation, so the denser the fuel, the more mass (and generally all else being equal, energy) it pumps per rotation.

Another aspect is that first stages are big, meaning that cost is more important than specific impulse. By contrast, when dealing with an upper stage, a small increase in mass has a huge increase in first stage size, and since first stages are so large and expensive, that's a big cost. So you generally want a higher ISP upper stage. With the caveat that "storability" requirements for engines that need to restart can shift the balance; because hydrogen is so deeply cryogenic it's difficult to store for protracted lengths of time. Also, the longer you plan to have a stage in usage without maintenance, the more you tend to favour simple propellants over high performing ones, particularly when you're dealing with small, light engines. So for example if you have an interplanetary probe you'll tend to favour a self-pressurizing hypergolic system so that you only have to rely on a couple valves working, even though self-pressurizing propellant tanks are heavier and hypergolics tend to be lower specific impulse. Engines that are smaller still are often monoprops for an even greater degree of simplicity.

Comment Re:Wonder how it compares to Airlander (Score 1) 119

That accident sure was a black eye for them... but the design is now better because of it. Also, gotta love having an aircraft whose crashes are in slow motion ;) "Coming soon on World's Least Dramatic Air Crashes!"

I imagine for the pilot it was sort of like when you're driving down a slope on ice and you lose traction, and you end up skidding down the whole slope at a several kilometers per hour: First, alarm and futile attempts to regain control, followed by acceptance, then "Okay, you can stop any time now...."

Comment Re:Going Howard Hughes... (Score 2, Informative) 119

Airships are not party balloons; they don't "pop" when you make a hole in them. They have low overpressure and a huge volume to surface area, so a "bullethole" is just a slow leak; it's not even a reason to land. A helicopter is far more vulnerable to small arms fire than a helium airship.

As for what it buys over a helicopter, show me a helicopter that can move 50-500 tonnes payload at a per-kilogram rate cheaper than a freight truck while flying halfway around the world without refueling. Because that's what people are looking to build with this new generation of airships. Even Airlander 10, which is just a commercial prototype for the Airlander 50, carries more payload than the largest helicopter used by the US military, the Sikorsky CH-53E Super Stallion.

Comment Re:Going Howard Hughes... (Score 2, Interesting) 119

A common usecase for large airships is remote mining operations. They need big, heavy pieces of equipment brought into places without roads. Currently, the first step is to build a road - which is expensive and environmentally destructive. An airship needs only a clearing - and the "skycrane" variants don't even need that.

Another advantage is that it's much easier to design them to carry "bulky" cargoes than airplanes. Again, especially "skycrane" designs where the cargo hangs beneath.

Comment Re:Wonder how it compares to Airlander (Score 2) 119

Given the fact that it's rigid, and given the size of Hangar Two and the fact that the frame is said to take up much of the hangar, it's probably much larger than Airlander 10.

Probably also doesn't look like a giant rear end ;) Even if it's a lifting body, the fact that it's a rigid airship (from the description) means that they can shape it however they want. So probably something like a flattened teardrop, if they go for the hybrid (lifting body) approach. Which generally seems pretty popular these days, for good reason (lots of extra lift at little cost, higher top speeds because you don't have to have as large of a cross section for a given cargo, etc). But of course there's nothing here to suggest whether it's actually a hybrid.

Comment Re:Money to burn I guess (Score 2) 119

It's easier to hate on?

I'm wondering what the "innovation" is. Because I'm sure that he's not doing this without some angle, something unusual that he's doing with this one vs. other airships. Some sort of wow factor.

Sergei, blow me away with something totally crazy. Like make its skin transparent, fill it with heliox and have people live inside the envelope farming, like an Earth prototype of a Venus colony ;)

But honestly, my expectations are that it's a generic freight carrier, and that the twist would be that it's a rigid lifting body. Maybe if we're really lucky, solar-powered too.

Comment Re:Going Howard Hughes... (Score 3, Interesting) 119

I personally find it very exciting. I knew that Alphabet had rented the Moffett Field hangars from NASA and were rennovating them. But their official stated purpose for doing so was to store a number of company planes. This is the exciting part:

Engineers have constructed a metal skeleton of the craft, and it fills up much of the enormous hangar.

So first off:

1) It's a rigid airship. Which used to be common but is now rare. Zeppelin NT is a semirigid, with a trilobate truss inside, but there's not many other examples. Rigids are favored when you're building something very large, as they reduce the stress on the skin.

2) It's huge. Hangar 2 is 52,1 meters high, 90,5 and 327,7m long.

I hope it's a lifting body! If I'm not mistaken it'd be the world's first rigid lifting body airship (correct me if I'm wrong!). Either way it's yet another sign that we're - at least temporarily - entering a new lighter-than-air renaissance. Who knows whether it will last, but it's great to see so many companies giving it another shot, making use of modern technology and design. Because there have been some huge improvements since the old Akron / Macon days. Also wonder about the fuel. Something like Blau gas, so it's buoyancy-neutral as it burns?

Of course, not everything in the article is exciting or new...

He went on to describe a prototype he was considering of a helium-based craft that appeared to breathe. "And so the way that works is that the helium in the main envelope is taken and stored in bags inside the airship at a slightly higher pressure," he said. "As you do that, air is taken in from the outside into essentially like lungs that are attached in the side of the vehicle. So the analogy of breathing is a good one. And the overall lift of the vehicle is equal to the weight of the air that is being displaced by the helium. And as you change that, you can control the amount of buoyancy that the vehicle has."

Um... yes, that's how lift cells work.... you either use them or you use ballonets, your choice... there's a couple other possibilities, like high overpressure superpressure balloons, or compressors + gas tanks, but the former doesn't scale, and the latter generally comes with too much mass and cost penalties with too poor responsiveness.

BTW, for those not familiar with the Macon and the Akron, I definitely recommend reading about them. They were literal flying aircraft carriers. You know how a landing jet on an aircraft carrier catches a cable with a hook? They did that too, but in the other direction - they caught a "trapeze" on their topside. They were then raised into the hangar, which was designed for five airplanes.

They unfortunately weren't long in service. Both of their losses could have been prevented with any combination of better weather prediction, computer controls, and better lift control. The Macon's loss was also stupid in that they were flying with unrepaired structural damage, out doing fleet maneuvers.

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