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13 hours ago, wumpus said:

Can anyone confirm just how many H-bombs it would take to get an Orion up to .1c?  That's the number that gets thrown around, but I can't imagine how a H-bomb is supposed to get an Isp in the millions or so.  Note that H-bombs emit most of their energy as photons, so that's a lot of momentum that doesn't otherwise require mass, but photons are typically an inefficient means of accelerating spacecraft.

Every time I plug the numbers into the rocket equation I suspect that Dyson was pulling a fast one.

I believe that the pusher plate was supposed to ablate, providing more superheated reaction mass than just the vaporized bomb casing

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On 12/31/2018 at 6:10 PM, wumpus said:

Note that H-bombs emit most of their energy as photons, so that's a lot of momentum that doesn't otherwise require mass, but photons are typically an inefficient means of accelerating spacecraft.

Orion didn't use photons, it used accelerated cores of a thin membrane on top of the charge.

On 1/1/2019 at 7:15 AM, StrandedonEarth said:

pusher plate was supposed to ablate

Only as an undesired parasite effect.

It should be being oiled like a pan iirc.

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6 hours ago, kerbiloid said:

Orion didn't use photons, it used accelerated cores of a thin membrane on top of the charge.

Fusion nuclear explosions emit a lot of photons (possibly the majority of their energy.  But certainly a lot of photons).  I'm not sure that H/N-bombs have enough Isp/mass efficiency vs. classical atom bombs (they are supposedly less efficient, but scale up bigger) so I'm not sure which type were planned.  I've always assumed that they would use H-bombs for cost reasons (or possibly neutron bombs for better control of what gets emitted).

I'd also assume that the "oiled like a pan" is to ablate the oil.

Finally, the whole point of the plunger appears to try to capture as much of the momentum as possible and transmit it to the spacecraft over a wider span of time.  Supposedly it made a huge improvement on the momentum side of things (which is what the rocket equation is all about), but a solid plate had a better energy transmission.  Since momentum is the key to space, the plunger plate won out (I haven't done the math and was always weak on the momentum side of things, but that's what I've heard).

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(I hope, we're speaking about the same Orion, the Dyson's one.)

On 1/4/2019 at 12:03 AM, wumpus said:

Fusion nuclear explosions emit a lot of photons (possibly the majority of their energy.  But certainly a lot of photons).  I'm not sure that H/N-bombs have enough Isp/mass efficiency vs. classical atom bombs (they are supposedly less efficient, but scale up bigger) so I'm not sure which type were planned.  I've always assumed that they would use H-bombs for cost reasons (or possibly neutron bombs for better control of what gets emitted).

They weren't pushing the plate with the explosion directly. The explosion was used to accelerate the intermediate layer of matter hitting the plate.

They had discovered that if vaporize a metal membrane, the gas cloud stays flat while moving in a desired direction. The flatter is membrane - the better it works.
So, they came to the idea of a directed strength explosion and decided to use also for the propulsion.

A cylindric charge with thick metal walls was opened from one end, having a wide axial conical channel with a nuke at the bottom of the channel, so in the middle of the charge. 
From the end the channel was closed with a thin metal membrane (tungsten, iirc, as it should effectively absorb the Xray photons) and filled with plastic (to absorb neutrons)
Upd: filled with beryliium oxide (see the link below).

The vaporized membrane became a disk-shaped gas cloud, moved towards the plate and hit it pushing forwards.
To decrease its erosion, the plate had a set of injectors spreading a protective liquid (basically, water) on the plate, to form a gaseous protective layer between the plate and the vaporized metal cloud.

As the direct hit was causing ~10 000 g acceleration of the ship. the plate was mounted on a two-stage cascade of plungers. Each cascade stage was decreasing the acceleration ~100 times, so the cabin received just 1 g.

Similar charges they were going to use as ammo for the board cannons (Casaba howitzer), so unlikely we'll know much about them soon.
(Still can't get why howitzer when it shoots directly).

UPD.
http://toughsf.blogspot.com/2016/06/the-nuclear-spear-casaba-howitzer.html

Edited by kerbiloid

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Yeah, that really does not make that much sense science wise. They'll never achieve the energies even of the LHC. Better join LHC/FCC !

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7 hours ago, Green Baron said:

Yeah, that really does not make that much sense science wise. They'll never achieve the energies even of the LHC. Better join LHC/FCC !

In a lot of ways I want to agree, especially because CERN pays half my bills! But myself and many of my workmates really like the ILC proposal as well. I can understand why Japan doesn't want to foot the bill solo, of course.

Anyways, cheerful scientific facts! ILC would work using an electron/positron rather than a pair of protons like LHC, which gives it two advantages. The first advantage is its reactions would be a heck of a lot cleaner! It's funny to think about it, but since protons are made up of quarks, those quarks that didn't directly collide apparently wind up getting flung around, sometimes making jets, and generally making a mess of trying to observe the actual things we're interested in. One of my jobs is to help cram electronics into the LHC detector upgrades specifically to help with this problem. As it was explained to me, the ILC has an advantage in that it can make a pinpoint little glob of pure energy because the positron and electron annihilate on contact, making for generally cleaner reactions.

The second advantage is that if the total energy of the electron-positron annihilation (mostly relativistic mass)  is ~240GeV, you apparently get these beautiful clean reactions where you 'commonly' get a Higgs and a Zboson, which itself acts as a nice marker. 240GeV is pretty darn low energetically speaking, but it's the optimum energy for this awesome reaction. Apparently the ILC could spit out Higgs like a firehose. Would have loved seen it... If only I was a multi-billionaire!

I'm happy to hear about the FCC as next steps though for CERN. In the meantime, LHC for the win. :cool:

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Thanks for the explanation :-)

If i understand it correctly there is nothing clear about financing / construction of the FCC yet. Let us hope they find a few of the billions they pump into banks and state finances every month somewhere lying by the side of the road ...

Oops, was that political :cool:

 

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Why did they build their Switzerland right above the particle accelerators? Didn't they have another place?

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For your reference, an opinion (from a physicist) about why pouring billions into a giant supercollider might not be such a great idea. [1]

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1 hour ago, kerbiloid said:

Why did they build their Switzerland right above the particle accelerators? Didn't they have another place?

They didnt have a choice, if you dig deep enough anywhere, its just layer after layer of supercolliders, most are left over from the Roman Empire.

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Adding to the discussion linked by @Steel

Putting something on hold for 20 years will not advance things, and getting rid of 90% of particle physicists because 10% would accomplish the same work does not sound like an argument to me, rather like a rant. Anyway 20 billion euro is not that much, it fits perfectly in the range of the big infrastructure projects planned or under construction.

I am pro :-)

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@Green Baron The author herself has some more thoughts [1].

Personally, my view is that the money could almost certainly be better invested in several, less expensive projects with defined goals and targets (which the FCC doesn't really have).

Edited by Steel

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Well, long live the multitude :-)

It is certainly necessary to discuss and weigh alternatives and see if there are more effective and less costly ways.

I must admit that my opinion is influenced by the constant cost explosion and delays of some of those infrastructure projects.

 

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33 minutes ago, Green Baron said:

...constant cost explosion and delays of some of those infrastructure projects.

This is my worry. 20bill seems like a massively lowball offer for this new collider.

Crossrail (http://www.crossrail.co.uk/) for example, has so far overran its 15bill budget by 600mil, and that is mostly overground, extremely mature off-the-shelf technology, and extremely similar to things that have been built countless times.

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A group of scientists from the University of Cambridge and the American University of Beirut (Lebanon) stated that the likely ninth planet of the solar system may be an unusual disk consisting of small ice bodies. This is what arXiv writes about in an article in the Astronomical Journal.

It is known that transneptutonic objects (celestial bodies orbiting around the sun), which are deflected from their orbits, became the reason for the assumptions of the presence of the planet. This is due to the influence of gravity of a large, as yet undetected object.

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On 1/22/2019 at 10:03 AM, Green Baron said:

Well, long live the multitude :-)

It is certainly necessary to discuss and weigh alternatives and see if there are more effective and less costly ways.

I must admit that my opinion is influenced by the constant cost explosion and delays of some of those infrastructure projects.

This argument comes up a lot in manned vs. unmanned space exploration.  The "moar science for cheaper" arguments of the unmanned contingent quietly ignore that you could probably get even more science done by paying a for a bunch of post-docs to do bench work somewhere involving science that doesn't need any rockets: studying frogs or whatnot.

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2 hours ago, wumpus said:

This argument comes up a lot in manned vs. unmanned space exploration.  The "moar science for cheaper" arguments of the unmanned contingent quietly ignore that you could probably get even more science done by paying a for a bunch of post-docs to do bench work somewhere involving science that doesn't need any rockets: studying frogs or whatnot.

Oh, I absolutely advocate manned space exploration (once it can be done and makes sense, for now probes can pave the way for later direct viewing, e. g. on Mars). And i personally think that, even if a few magnitudes of energy levels are still missing, the FCC should be built. Because we are talking about the Lorentz term, we will always be several magnitudes away, no matter (haha) what.

JWST is at 8⁹ funds now, the ground telescopes that are being built are comparably peanuts (1-2⁹ funds), the FCC proposal sums up to 9-20⁹. This is absolutely in the range of big infrastructure projects, maybe higher.

I only wanted to express that i can understand that people discuss the pros and cons, but of course i hope that one day there will be a go or a proposal for a better version without having to wait 20 years. Better sink the money there than ... elsewhere ;-)

Edited by Green Baron

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Krakatau - Before & After

... going back to Danan & Perboewatan ?

Edited by YNM

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Just now, Green Baron said:

Certainly a dramatic change.

Yeah... my concerns is that the eruption pattern might go back to the old less frequent, larger explosive eruptions; Anak Krakatau so far only had frequent small eruption, not a single instance. Plus, being shorter that it is now, one large eruption might be enough to make the whole thing go kaboom from phreatic reaction...

But yeah, perks of living on the Ring of Fire I guess.

Edited by YNM

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A magma chamber exposed to seawater like 1883 ? That in today's densely populated world ? Hopefully not. People near Etna have the same preoccupation, Etna's eastern flank was reported to be moving, but it is not clear whether it settles or may one day give in to gravity, if the cause is pressing magma or crustal subsidence.

Edited by Green Baron

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