Posts by Mike Hewson

11) Message boards : Cafe Einstein : SpaceX Dragon scheduled for 12/19 (Message 141660)
Posted 9 days ago by Profile Mike Hewson
Department Of Thinking Out Loud : I reckon there's a few reasons to do another barge landing attempt.

- to prove it can be done. SpaceX has got to be populated by type-A personalities.

- SpaceX may not have FAA approval for a land return as yet ie. they might need to prove to a harder standard with the barge business. Once certified by actual demonstration ( times N ) then they may get approval for return to launch site flightplan.

- it will always be incredibly valuable to have an offshore return option succeed. Not just for Falcon 9 in the near term but as a generic methodology for way into the future. If this is to apply to the Falcon Heavy then there's a gaggle of components to recover after each launch. It has already been demonstrated to land beautifully on target but into waves .... we want the dry landing bit. Most of the world's surface is water and thus unlocking this method has got to be an enormously useful breakthrough.

On that last point it may be even more energetically favourable ( I'll have to think about this ) to not do a boost back. Just go further downrange and land quite distally. To be effective that would need a longer upper atmosphere phase to bleed more kinetic energy though. I think there is design room to put in a purely drag type drogue device ( not necessarily a chute ) on top of the 1st stage ie. packed just under the interstage. Deploy it first up at hypersonic speed but before the fin usage, and then toss it.

Cheers, Mike.

( edit ) Drogues work like a 'sea anchor' ie. doesn't hook into the seabed. It can be as simple as a large bag full of sand on a rope say, and slows the drift simply by resisting motion through the water. Blue water fishermen occasionally use their fishing nets in a drogue like fashion.
12) Message boards : Cafe Einstein : SpaceX Dragon scheduled for 12/19 (Message 141658)
Posted 9 days ago by Profile Mike Hewson
The goal, SpaceX wrote, was not to "just to produce cool videos" but to "radically reduce the cost of accessing space by producing a fully and rapidly reusable rocket system."


Touche ! :-) :-)

Cheers, Mike.
13) Message boards : Cafe Einstein : Cafe Einstein: LPTP # X V (Message 141656)
Posted 9 days ago by Profile Mike Hewson
Several years ago when I was in the outback I seem to recall that Toyotas were quite popular with the requisite "roo" catchers.

The Hilux utes still are particularly loved and they are so rugged as demonstrated by TopGear say. You can armour them with bullbars and whatnot and slip on nearly anything useful in the back tray. In Australia they are the commonest small unit bush firefighting vehicle for instance. In some areas more than every second farm property will have one. They can be fitted with winches, all manner of trade implements and I've even seen one with a large saw-bench. They are still used in some war zones as mobile 50 cal mountings. It has really fulfilled the 'utility' title well.

Cheers, Mike.
14) Message boards : Cafe Einstein : SpaceX Dragon scheduled for 12/19 (Message 141653)
Posted 9 days ago by Profile Mike Hewson
And another article from the Planetary Society

I hadn´t seen the distant tracking cam footage before... amazing perspective.

Jeez Louise ! Absolutely ! Thanks for sharing that. In under a minute it transitions to subsonic and then lands with a gentle nudge. That puts the task in good perspective and makes the ...... nearly, nearly, nearly .... bit all the more impressive.

Cheers, Mike.
15) Message boards : Cafe Einstein : hyperloop (Message 141652)
Posted 9 days ago by Profile Mike Hewson
Oh cor blimey, I got a bit lost there.

Slaps oneself around the face (slap slap) OK brain in gear.

Ummm, can I take a rain check on that?

Sorry Chris, I was working off Elon's document which seemed to leave a few issues begging for detail. The basic idea of the hyperloop is to get air out of the way in order to go fast. So for me at least the initial point of discussion has to be the fluid in which the vehicle sits.

Cheers, Mike.
16) Message boards : Cafe Einstein : Cafe Einstein: LPTP # X V (Message 141650)
Posted 9 days ago by Profile Mike Hewson
We have a Chevrolet Matiz hatchback, is that the same vehicle?

Probably not in actuality. Daewoo has co-produced/licensed/badged designs with many manufacturers in many countries outside of Korea. The quality varied alot in the years 2000 - 2004, when there were a lot of recalls for big items like clutch and brake. You should be OK if bought in the last five years or so. DownUnda they're a bit of a joke on account of the earlier problems. The roadside one was of that significant vintage.

DownUnda the current phase of lemon is pushed with the catchphrase 'I bought a Jeep!'. After just two years they are now flooding the resale markets. On the upside there should be plenty of spare parts around to make up a single good one if needed. :-)

Cheers, Mike.
17) Message boards : Cafe Einstein : Cafe Einstein: LPTP # X V (Message 141637)
Posted 10 days ago by Profile Mike Hewson
Here 's a laugh : there's been an abandoned Daewoo/GM Matiz hatchback on the roadside out of town, for about three weeks. It's been untouched and I mean not stripped at all, nothing smashed, nothing missing. Nada. No one could even be bothered striking a match against it. But last night the plates were stolen. They took the most valuable bit ... :-)

Cheers, Mike.
18) Message boards : Cruncher's Corner : GPU computing benchmark site tip? (Message 141636)
Posted 10 days ago by Profile Mike Hewson
FWIW here is a reasonably current schemata. Doesn't mention CUDA per se, but probably represents the relative rankings well. It shows an interesting range of devices, OS's, test types, architectures etc. Was that what you had in mind ? :-)

Cheers, Mike.
19) Message boards : Cafe Einstein : hyperloop (Message 141634)
Posted 10 days ago by Profile Mike Hewson
This is one of those 'space elevator' type ideas : very expensive to setup but once done is relatively cheap to run. The main setup cost here - believe it or not - is the creation of the vacuum. Not only the energy required to evacuate some volume but the structural integrity required everywhere to keep it that way. This makes an equivalent stretch of highway look cheap, at least in the short term which is alas going to be the probable investor timeline.

As Elon points out in the embedded video the market currently has no price signal for pollution or like downsides - the tragedy of the commons writ large - and thus the ultimate costs of alternatives are poorly estimated. But this also applies to the hyperloop itself and not just the existing paradigm. High grade metals* are very expensive and dirty to make. What electricity generation mode is going to drive the pump-down of the tube ? You can't grant the likes of hyperloop a free ticket on these analyses just because it is different/new or apparently cleaner. It could be the same error in disguise.

But it's technically do-able at least. I think the best payoff however would be in freight movement** rather than people. Vacuum is dangerous for people. Lack of fresh air kills. Somewhat akin to climbing a ladder a vacuum represents an immediately accessible energy differential which can be suddenly equalised. Many transportable goods are largely indifferent to this risk. Like the Hindenburg a single accident will destroy usage ( and yet we tolerate the daily maiming with our cars, go figure ).

Cheers, Mike.

* Think of it like an unterseeboot : a non-trivial exercise in keeping separate fluids with radically different densities. With the people on the inside.

** One would prefer high volume, low speed and low drag transport methods for that. Errr .... don't we have two of those three already ? :-) :-) I recall the research effort to make & maintain laminar flow on aircraft wings down to the scale of the otherwise static layer adjacent to the metal skin, by pulling air through small holes in the upper wing surface. This did work and reduced drag nicely. Only the energy cost of the system to do exactly that exceeded the gain from drag reduction. Hence a plane with that facility installed used more fuel when the laminar flow device was operating than when turned off. Oh well .....

( edit ) One could reduce the strain on the containment vessel while also having good flow characteristics for movement within by having a working fluid with low density for a given pressure ( at ambient conditions ). That would be .... wait for it .... drum roll .... hydrogen gas! So you put that in the tube and for much the same reasons as we put it in balloons too. But I'm sure someone already knows that. Hopefully not Hindenburg redux ...

( edit ) Well lookie here. The speed of sound in H2 gas is 1270 m/s ( 1 atmosphere @ 20 C ) ie. four times that of air. This indicates that the various instabilities and turbulence at speed etc will be rather reduced and also the H2 is far easier to shove around through fans etc ( low Reynold's number ). The solar cells could make and maintain the hydrogen in the tube.

( edit ) The Reynold's Number is dimensionless and basically represents the tendency to transfer momentum from some large scale object of interest ( wing, fan blade, soup spoon ) to that of the molecules in the surrounding fluid. Sort of a viscosity measure that encodes the scale of the system in question too. Here we want a low value, but in other circumstances you might want it higher eg. mixing the components of chocolate. :-)
20) Message boards : Cafe Einstein : SpaceX Dragon scheduled for 12/19 (Message 141632)
Posted 10 days ago by Profile Mike Hewson
I follow SpaceX Stats which I believe is an un-affiliated site run by fans of SpaceX and Mr Musk. I don't know where they get their information but it's been quite right thus far. The upcoming launches page is helpful with the specific launch mentioned here.

I think another attempt at a 1st stage landing is implied, but I vaguely recall that being a land return and not to the drone ship. I think that was proposed after the last RUD. Probably SpaceX is not wanting to ramp up expectations again. UTC of 14:21 puts it just after midnite DownUnda ( ie. early Monday of the 29th for me ). I'll be up and watching ! :-)

Cheers, Mike.


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This material is based upon work supported by the National Science Foundation (NSF) under Grants PHY-1104902, PHY-1104617 and PHY-1105572 and by the Max Planck Gesellschaft (MPG). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the investigators and do not necessarily reflect the views of the NSF or the MPG.

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