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Comment: Simply to avoid confusion. (Score 2) 127

by robbak (#49626621) Attached to: Opportunity Rover Reaches Martian Day 4,000 of Its 90-Day Mission
If they called it a 'day', they wouldn't have known if it was an Earth day or a Mars day. If they relied on calling them 'Mars Day' or 'Earth Day', soon someone would have forgotten to maintain the prefix.

So they coined a new word to use for a Martian Day, and stuck to it.

For other planets, I expect that the same term will be used. 'Day' for time on Earth, 'Sol' for time on the planet. That said, we don't have all that many things that would have usable 'Sols'. Mercury's days last for months, Venus' day last for longer than its year. Maybe probes on minor planets, which look like they have days around 8 hours long.

Comment: Google is fixing the Updates problem, effectively. (Score 1) 343

by robbak (#49626511) Attached to: Google Can't Ignore the Android Update Problem Any Longer
Google is fixing the updates problem. While the best way to fix it would be to somehow get device makers to provide them (How? This is never addressed!), Google has moved to resolve this another way.

And that is moving more of the operation from Android to the Google Play services, and Google - sourced apps on the store. These are regularly updated, and updates are pushed out through the play store in the usual manner. This allows most security issues to be rectified or worked around.

Personally, I'd like a different solution - requiring source drivers for everything and unlockable boot loaders, so Google or someone else can provide updates even if the manufacturer defaults - but I'll live with what I have. (What I actually live with is an old Moto Defy running 4.4.4 from CyanogenMod.)

Comment: Neither do I... (Score 4, Informative) 157

by robbak (#49231383) Attached to: Strange Stars Pulse To the Golden Mean
Golden ratios emerge wherever you have a relationship of T(n)=T(n-1) + T(n-2). Where the first two terms are 0 and 1, you have fibonacci numbers: but no matter what your starting numbers are, the ratio between T(n) and T(n-1) will approach phi (as demonstrated with 'brady numbers').

So it is not at all surprising that phi might crop up in seemingly strange places.

Comment: "Getting into orbit" requires a big rocket. (Score 5, Interesting) 282

by robbak (#48949751) Attached to: NASA Looking At Nuclear Thermal Rockets To Explore the Solar System

That big rocket is mostly just to put the payload into orbit. Once in a low earth orbit, it doesn't take that much more to take it from there to a different orbit.

This xkcd is probably the best way to grasp the difficulties of 'getting into space".

Comment: This is the second best solution. (Score 1) 265

The best solution, and this is in our grasp, is to modify mosquitos so they will produce healthy male mosquitos that carry the modification, and either no female offspring, or sterile female offspring. This will rapidly eliminate a population.

The problem is that you would not be able to contain it - your modified males would spread uncontrollably. Do it worldwide, and we could drive aedes aegypti and the problematic Anopheles species to extinction. The only question left is should we?

Comment: Re:Wait a minute (Score 1) 248

by robbak (#48872663) Attached to: SpaceX Landing Attempt Video Released

Because any electric hydraulic pump is going to be slow at pumping fluid, you still need the pressurized accumulator, so you can move your control surfaces quickly when you need to. So the reservoir, pump and the batteries are an additional weight, that you would want to omit if you could.

The reason why you have never seen a total loss pressurized system is that the conditions that call for it are ones that you rarely see - a strong mass constraint (which has to include the power source), and a short time period when it is required. Your plane's system needs to operate over a period of many hours, there is normally a power source on hand (the engine's alternator), and the mass is not really that constrained. Really, a rocket is the only place where a pressurized total loss hydraulic system makes sense.

(Note that this crash could probably have been avoided with more complex programming. The programming could have kept count of how much hydraulic fluid it was using, and driven the fins to neutral before it ran out. This sort of capability - or even just a fluid level sensor - will doubtless be added before the landing system leaves the testing stage. If dealing with early exhaustion of fluid does turn out to be this easy, then the need for the extra mass completely disappears.)

Comment: Re:The problem was the control fins. (Score 1) 248

by robbak (#48842777) Attached to: SpaceX Landing Attempt Video Released

The rocket decelerates quickly during quite a short landing burn, so they would have had a strong effect until the last few seconds. Indeed, the loss of that force as the rocket comes to a stop would have been an important part of the crash - the rocket would have been countering the influence of the grid fins pushing the top of the rocket away from the camera, while tilting the rocket toward the camera to get it back to the platform. Then the rocket slows and that force dies away. Now the rocket has to go from working hard forcing the rocket to tilt toward us against that force, to trying to push it back upright with that force suddenly gone. You can see that it was trying, because the rocket flame is directed away from us, illuminating the far side of the rocket, leaving the near side in darkness.

Nope. Grid fins explain what we see very well.

Comment: The problem was the control fins. (Score 1) 248

by robbak (#48838347) Attached to: SpaceX Landing Attempt Video Released

The fault that caused this failure was the control fins running out of pressurized hydraulic fluid. When this happened, they were driven fully to one side, pushing the rocket over. The engine tried it's best to counter that, but it didn't have a hope.

A fellow fan tried something similar in the Kerbal Space Simulator. I imagine the real flight was very much like this:

Comment: Solid boosters vs. liquid rockets. (Score 1) 248

by robbak (#48838329) Attached to: SpaceX Landing Attempt Video Released

Solid booster casings are a very different beast. A solid booster rocket needs to be very strong, because the combustion chamber of a SRB is literally the entire rocket. The whole thing needs to withstand combustion chamber pressure. So it is strong, tough (and heavy), so you can do what you like with it.

A liquid fuel rocket is a much more fragile beast. If allowed to tumble through the atmosphere, or hit the water at parachute speeds, it would be totally destroyed.

Failure is more frequently from want of energy than want of capital.