SPACE

[zip accident]

A so-called planetary nebula: the Southern Owl.

Wow, that's a wierd looking thing, looks like an atmosphere with no planet, but presumably much bigger and not much pressure.

[pogo]

It’s 4 light years across. It’s interesting, and I suppose this is why it’s “planetary”, as we came from something like that. The universe is mostly hydrogen, bare protons with electrons. Other elements are formed in nuclear reactions in stars, but most stars the reactions only produce some of the elements, the lighter ones. Heavier ones are only produced in supernovae. These also do the job of distributing the heavier elements, through the explosion from which they get their name. Eventually these elements can be drawn into the orbit of a new star and form planets and planetoids like around our own sun.

This has a few implications for the search for life in the universe. One is that life is probably a relatively recent innovation, as the first stars and star systems were lacking the heavier elements for life. This may help explain why no-one has visited or contacted us, no one else has been around for very long. There’s no galaxy spanning civilisation or federation as no-one has been around for long enough to establish one.

Another is sometime before the Sun formed one or more supernovae seeded this region of space with lots of heavier elements. This means other stars and star systems around here formed about the same time should have had all the ingredients for life, as well as the hundreds of millions of years we think it needs for life to evolve.

[gumboot]

Looks like something out of 1960s Star Trek.

[zip accident]

Looks like something out of 1960s Star Trek.

Yeah, but it's a lot bigger than it looks.

[F-ZeroOne]

They're "planetary nebulas" because they looked like planets to earlier astronomers.

[merman]

Worth catching up on last night's Horizon on iPlayer, it's called The Trouble With Space Junk.

Especially since they managed to do an hour-long programme without referring to a certain Hollywood blockbuster.

[pogo]

Someone thinks they can build a “Space Elevator”, a 20km tower for take off and landing space craft. So much so they have patented it. The point about patents is they give you an exclusive but only for a very short time, 20 years normally. Which means they must think it’s possible to build one in that time. Really?

Problem with it that I can see is it’s supposed to be a runway in the sky. So how do they build something solid so tall? They don’t it’s a balloon (“pneumatically pressurized”). A balloon will certainly get you 12 miles into space, but with perhaps a GoPro in tow. Not a space rocket/plane, never mind everything you need for take off and landing, such as fuel for refuelling.

Even if you could in theory build one, it would take just one bumpy landing or other accident to blow a hole in it, and you know what happens when you put a hole in a balloon. Being non-solid it would sway like crazy, making landing and taking off a serious challenge. Or a meteor, or lightning, or a hurricane could rip it apart.

http://thothx.com/news-2/

[gumboot]

20km seems kind of low. Is a 20km ascent, minus the cost of the momentum it should have at that point, really 30% of rocket fuel usage?

[pogo]

It would be a win: the atmosphere is thickest at ground level so you have its resistance to overcome. In particular you cannot go to fast, but expend a lot of fuel just staying in place. The lowest low Earth orbit is 160km so it’s 1/8 of that.

But it really does seem all sorts of impossible. My only guess is patenting it is meant to make them look serious enough to attract investment, perhaps from people with a lot of money but a poor grasp of physics.

[gumboot]

One of my earliest thoughts on how to build a space elevator (a proper one; to geostationary and beyond!) was to try to offset as much of the bottom weight as possible with balloons. It didn't seem like balloons would be effective over any meaningful length so I never got as far as doing any arithmetic; but at least it offered some degree of redundancy in case of impact damage (over the short range for which balloons were relevant).

Presumably it's made of lots of individual compartments along its length (like the Titanic). One assumes that the stabilisation technology that compensates for air currents can manage the outflow from one or two of those at a time; and when things really turn to shit the bulk of the material should be held up (or have its descent slowed) by the remaining compantments.

I guess.

[pogo]

Balloons certainly can lift things, even up to 20km and beyond. Their problem is you need a massive balloon to lift even a small payload. As you go up and air pressure thins you need a bigger and bigger balloon. High altitude weather balloons deal with this by expanding to many times their launch size. The bigger it is the thinner it gets until it pops and falls to Earth; great for short term experiments. Although the landing site even in mild weather can be 100km away or more, as the winds high up get quite strong.

So this, 20km tall, would need to be very very big to support any sort of weight. And the bigger it is the wider it is, so the more wind pushes it. You can hardly reinforce it as that would add weight. And anyway even a solid steel reinforced pillar would sway like heck if it were 20km tall (tall buildings today sway noticeably and are only 1/20th the size).

[gumboot]

Isn't the general working principle around these problems that you use a continuous supply of energy to push the tower back into balance against the wind?

Might also want to continuously rotate into the proper orientation, segment-by-segment, to be more streamlined.

Disregard their picture and try to visualise a vertical stack of blimps tethered together so as to keep an internal elevator shaft approximately vertical.

Not actually saying that it's a sensible idea, mind you.

[pogo]

But all that takes mass and energy. Energy is maybe not an issue if it saves you fuel. But mass, for the engines that do the pushing, would need lifting by the balloons.

As for making it more aerodynamic there’s a limit to how much that can be done. The slimmer it is the smaller its volume, which means the less air inside it. You can see this in the design of blimps: a thinner design would be much more aerodynamic but would not be able to lift anything. They trade buoyancy for speed, and can’t go very fast, or withstand very strong winds.

[zip accident]

It looks silly to me.

[gumboot]

I did wonder about the fuel thing. If you use props then you can supply them with electricity; but they might not be much use. Obviously there's something there or there wouldn't be a wind concern and there wouldn't be anything holding them up, but perhaps the feasibility of propellers drops off before the feasibility of balloons, in which case you really do need rocket-powered balloons. On the plus side, you might be able to use waste heat for more lift.

Googling to see whether that even begins to make sense, I find:
http://www.halfbakery.com/idea/Hot_20Helium_20Ship

Looks like fun.

As for volume against aerodynamics. It's a similar problem to boats. For the same load, narrower just implies longer (else you sink!). The length of a boat is limited by the conditions it has to deal with (size of waves and cornering), but that's not an issue here.

There's also hull surface (mass) versus volume... not sure how bad that gets.