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Comment Re:Would be nice... (Score 1) 75

It also depends on the way the helium is expanded. In free expansion, it'll cool and gain a large amount of kinetic energy. If expanded through an insulated porous plug, it'll gain a small amount of kinetic energy but heat up. It's basically down to where the energy released in the expansion ends up.

As the helium swirls around the tank, turbulence and friction will convert the kinetic energy it gained in expanding into the tank to random heat. However, when it is released into the tank, I'd expect it to cool due to experiencing more or less free expansion, so while the average temperature of the tank may rise, cold spots seem likely.

Comment Re:Not Harvard architecture? (Score 1) 101

It runs at 160 MHz. Processors that run directly from flash are much slower (around 32-48 MHz...ST's Cortex M0 processors run at 48 MHz). The only flash-based processors that run at comparable speeds do so with complex hardware to read instructions ahead of time in large chunks, storing them in SRAM until the processor requests them (ST's ART Accelerator, for example)...which can result in difficult to predict variations in execution speed when branches result in the needed code being something other than what was preloaded. Luis mentioned working on some method to "virtualize RAM" in the other reply, which might be a somewhat similar system, which again would sacrifice determinism for speed.

Comment Not Harvard architecture? (Score 2) 101

The high speed is because they currently don't have any on-chip flash (flash being slower to access than SRAM, and typically being what slows 32-bit microcontrollers down). That means this isn't a single-chip solution like most microcontrollers, though they are working on changing that.

Instead of flash, they store their program in the same SRAM used to store data (which makes that 8 kB of SRAM a lot more limiting than it would be on a Cortex M0 with the same amount of SRAM plus 16-256 kB flash). Most microcontrollers use a Harvard architecture with separate program and data memory, allowing instructions to be fetched from flash while performing reads from and writes to SRAM. If they don't do this, I wonder what sort of performance they'll see when they have to make regular reads from a slow flash memory in between SRAM accesses. Or will they just load the entire program into SRAM? That's not going to be ideal in terms of power consumption, requiring a much bigger memory array than they'd otherwise use, something that's going to get worse as they try to compete with larger microcontrollers.

Also, the Harvard architecture has some advantages in security: things can be set up so a very specific sequence of actions has to be performed to enable writing to program memory. With IoT devices, this sort of thing is becoming more important...not an issue at present, with their 8 kB memory, but something to consider when thinking about this thing's future.

Comment Re:The 90's called.. (Score 2) 121

Current satellite internet is that way because all the data is funneled through a handful of satellites up in geostationary orbit. This system uses a much larger number of much closer satellites, so latency's far lower, signal levels and link bandwidth are higher and you don't need a big dish to make your link budget work, and system bandwidth is orders of magnitude higher.

Comment Re:Can someone explain this to me? (Score 4, Informative) 99

It's just a really, really terribly written article.
There is a theoretical object called a "naked singularity", a black hole without an event horizon, which stuff actually would be able to escape from. This isn't one of those. The author's calling it "naked" because it doesn't have any of the usual stuff around it...except it's not even that. It's the remnants of the core of a galaxy: a few thousand stars, some gas, and a black hole. The x-rays come from surrounding debris falling into it, not the black hole itself. The black hole isn't hemorrhaging anything, the gas is just debris that the core wasn't able to hold onto after the collision that stripped most of the rest of its stars and gas away. It doesn't even mean anything to say "it may never stop"...stop relative to what?

It's just sensationalized gibberish.

Comment Re: Good attitude (Score 1) 98

Astronomy is better done away from the gravity, dust, and temperature extremes and without the obstruction of half the sky by a giant ball of rock. Power generation is better done in open space where you can have constant direct sunlight. And semiconductor fabrication can be done at whatever effective gravity you desire in orbit.

The biggest reason to go to the moon is to study the moon. When space infrastructure and technologies are more advanced, it'll be a useful source of raw materials in Earth orbit. But at the current early stages of actually developing that infrastructure and technologies, it's an expensive distraction.

Comment Re: Good attitude (Score 1) 98

You could use a silicone binder. Primarily silicon and oxygen, neither of which is exactly scarce. Major downsides include being yet another fuel with solid combustion products (and a pretty terrible fuel apart from that), and requiring a rather complex chemical industry to produce.

And all of these options have the really major downsides of very poor performance, the complexities of producing large solid fuel cores, and inability to refuel the craft landing on the moon. If you want to reuse the same craft for multiple trips, your task is much, much easier on Mars.

Comment Re: Good attitude (Score 1) 98

It's enough atmosphere to be a substantial assist in landing mass on the surface, and actually does provide significant radiation protection while also moderating temperatures. The perchlorate issue is massively overstated: they are not that toxic, and are easy to remove, and there's entire glaciers of water on Mars.

Comment Re: Good attitude (Score 1) 98

The need for huge energy storage systems or nuclear power from the very start is a significant problem for the moon. The game-breaker though is ISRU propellant production. Getting enough water on the moon to supply return craft will require large scale mining and regolith processing facilities...meaning any return propellant will have to be imported until the colony is well established. On Mars, it should involve little more than drilling into a glacier and lowering a heat source to sublime the ice, which makes it a lot easier to get your spacecraft back so you can use it on another trip. The relative ease of delivering mass to Mars and greater proportion of the delivered mass that can be productive colony hardware can do a lot to compensate for the greater distance and travel time.

Comment Re:I'd rather see (Score 1) 348

Lunar helium-3 mining has always been about as plausible a suggestion as strip-mining the moon for green cheese. Helium-3 is a byproduct of storage of the tritium that 1st generation fusion will breed for fuel, and if you can do He-3 fusion, you can do p-B11 fusion. So: by the time we can make use of it, we'll be able to mass produce it far more easily than we could mine it, and we probably won't even bother with it due to availability of far more abundant fuels.

Comment Re:Perpetual motion machine of the first type (Score 1) 532

A "working EmDrive" would be a reversible electromagnetic machine, functioning equally well as a motor or a generator: (page 6, ironically titled Conservation of Energy)

If allowed to accelerate, the microwaves in the cavity would red-shift and lose energy, if accelerated in the other direction, they would blue-shift and gain energy. A "working EmDrive" placed on one end in Earth's surface gravity would thus either continuously create or destroy energy.

The reasonable conclusion is that there is no such thing as a "working EmDrive".

Comment Re:Perpetual motion machine of the first type (Score 1) 532

He claims that, but his analysis is based on velocities relative to a fixed universal rest frame, which he seems to believe is the same reference frame as Earth's surface. For example, he says that it produces thrust most efficiently if "stationary", and is best used to counter gravity and allow a craft to hover, with jets and rockets being used for propulsion (he seems unaware that a hovering craft is one that is accelerating upward at a constant 9.8 m/s^2).

If you really take Shawyer's math and vehicle concepts seriously, he's apparently a stationary-Earth geocentrist. More likely, he's just clueless about physics.

Comment Re:Perpetual motion machine of the first type (Score 1) 532

The confusion is yours: you can't violate just conservation of energy or conservation of momentum. And it's trivial to show that the claimed behavior of the EmDrive violates conservation of energy: a working EmDrive placed on one end on the ground would turn gravitational acceleration into an infinite source or sink of energy, depending on which end was up.

Comment Re:Sixty Years Ago... (Score 1) 55

For what?

For operating a vehicle in atmosphere, which occurs at two critical stages of a spacecraft's mission.

That doesn't answer the question. Spacecraft spend only a tiny fraction of their lives in the atmosphere, and sustained aerodynamic flight is not a requirement during their short passages through it during launch and landing. So what do they need wings for?

No. That is specifically the design I am arguing against. Please check my post again and you will see I deliberately *exclude* the mass of the engines.

Engines using diluted low-pressure gaseous ambient oxygen as an oxidizer have poor thrust to weight ratios, and wings are generally used to make up for that, making it possible for a craft with underpowered engines to accelerate early on, though at a cost in aerodynamic drag and sustained heating. If you're *not* using air-breathing engines, you can just fly a near-vertical trajectory that quickly exits the bulk of the atmosphere, without having to deal with aerodynamic drag and heating. As for the return, where are you trying to go between reentry and landing? What do you need wings for?

(Note: "to operate from an airport" is not an answer. Needing a reinforced extra-long runway in addition to all the usual pad infrastructure is a cost, not a benefit.)

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