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SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Not sure about the recovery test (121 comments)

Those boosters were hollow steel tubes, open at the back. Seawater partially flooded them, that's why they popped up. The Falcon 9 first stage is mostly empty tanks that aren't going to flood (barring severe damage from the waves). If held vertical, the weight of the entire stage wouldn't push it down even two meters into the water...its diameter is greater than that. The engines aren't that heavy, half the mass of the vehicle is in those very long tanks...it's going to float very high in the water, on its side.

yesterday
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SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Cost breakdown (121 comments)

NASA is paying for Dragon missions to the ISS, not just mass to orbit. They're getting a lot more than the launch: delivery of a Dragon loaded with supplies to the ISS, a brand new man-rated spacecraft that people will be working inside while it's at the ISS, return of more payload to Earth than any other option currently available, and operations in orbit and recovery. And probably also various other expenses and extra work involved in working with NASA and the other ISS partners. Their defense launches are also priced higher for the same reason, working with the DOD involves extra work that the customer demanding it has to pay for.

yesterday
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SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Not sure about the recovery test (121 comments)

It doesn't need to brake to a complete stop and then retrace its outgoing path, it needs to bend it's largely-upward trajectory into one that comes back down over the landing site, and manage its velocity so it doesn't go too high and hit the atmosphere too fast on the way back down. As for the difference in separation speed, the flight profile for the reusable flights may very well take a more vertical trajectory during the first stage burn, the first stage taking on more of the gravity losses and going more for altitude rather than speed, and the ratio of propellant loading between the first and second stages may be different for reusable flights...they could oversize both at a minor cost in mass and tweak the ratio to suit the launch, the maximum loading being set by the first stage thrust rather than the total tank capacity.

yesterday
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SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Not sure about the recovery test (121 comments)

It got up there while carrying a lot more propellant and a whole second stage. The braking burn uses only 3 engines to limit the acceleration and ends with just enough propellant left to stop it when it reaches the ground. On top of this, it gets passive aerodynamic braking the whole way down.

The mass ratio for the first stage burn, burdened with the second stage and braking propellant, is probably around 4, and a braking burn with equal delta-v would need the same mass ratio, except with no second stage and ending with the rocket empty. The overall first stage mass ratio is around 30, so all else being equal, a return would take around 3/29 = 10% of the propellant on the first stage. But all else is not equal, the returning rocket is mostly empty tanks descending through a thick atmosphere that provides plenty of braking, so the final burn only has to bring it to a halt from terminal velocity, and I omitted the second stage propellant. Overall, 4% sounds quite reasonable.

2 days ago
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SpaceX Launches Load to ISS, Successfully Tests Falcon 9 Over Water

cjameshuff Re:Not sure about the recovery test (121 comments)

They're already doing precision landings with the Grasshopper vehicles. The only splashdown landings are going to be tests of the vehicle control, like this one, where the vehicle is not intended to be reused.

2 days ago
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Ask Slashdot: Why Are We Still Writing Text-Based Code?

cjameshuff Re:Because we are stuck in an imperative paradigm (876 comments)

"For example, consider a system that is designed completely around events. If one can visualize the inter-connection of components, and one annotates each component with the types of events that it generates (perhaps using expressions), one can easily grasp the overall behavior much more easily than one could if that same design were expressed textually. Thoughts?"

You're making a big assumption that has been contradicted by actual real-world examples. Complexity is hard, and the difficulty has nothing to do with it being in text form. A screen filled with an easy to understand graphical representation is easy to understand because the representation is simple enough to fit on a single screen, not because it's graphical. The systems best able to cope with complexity are textual.

Hardware is also much simpler than software, and it still has bugs. You'll have a hard time finding a complex part that doesn't have an errata sheet. It's also harder and more expensive to debug and test, and typical VHDL makes heavy use of testbenches and simulation to verify individual modules. Conventional software often isn't tested this way. If you want to improve software, encourage adoption of methodologies like unit testing.

about 2 months ago
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Ask Slashdot: Why Are We Still Writing Text-Based Code?

cjameshuff Re:Because we are stuck in an imperative paradigm (876 comments)

You've got a powerful text based language for the actual implementation. Why go to a limited, clumsy graphical program for the high level stuff? "It's simple enough you can do it graphically" isn't a compelling reason. Why do you want to do it graphically? Simple, easy to read diagrams are easy to read because they are simple, not because they are graphical. They have use in education, but need to be kept simple to stay meaningful. The people selling these tools love simple examples. Complex ones look very impressive at a glance and give the illusion of being more comprehensible than a similar view of code, but aren't actually very useful, so the salesmen don't dwell on them for long.

You're just giving yourself headaches when things inevitably grow beyond the limitations of the tools, and you have a huge mess of connected boxes that you have to refactor or rewrite in text format. Not to mention having to wade through reams of near-unreadable machine-generated code when stuff goes wrong, or constantly having to refer to diagrams and models in a separate tool when dealing with the interface between the two.

about 2 months ago
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Ask Slashdot: Why Are We Still Writing Text-Based Code?

cjameshuff Re:Because we are stuck in an imperative paradigm (876 comments)

It's quite true. Logic circuits of any complexity is generally done in a HDL, checked in simulation, and prototyped on FPGAs before being put in silicon. Designs are sold or licensed as Verilog or VHDL. Layout may be manually tweaked graphically (especially for particularly timing-critical things), but that's because the restrictions of a 2D graphical representation closely match the restrictions of a largely 2D integrated circuit.

You can express in a few lines of code what would take pages of gate-level schematics. You can easily parameterize components for reuse. You can separate implementation details from from intent and let the synthesizer find opportunities to reuse logic or adapt implementation details to the situation. You don't have to pore over multi-sheet hierarchal schematics tracing signal lines. And you don't end up finding that stuff that looked connected actually wasn't.

cjonslashdot's comment about symbols was particularly off the mark. Large schematics involve *lots* of named signals. Often actually connecting things with a line would make the schematic hopelessly unreadable, and they actually terminate in a little tag with the signal name, leaving you to hunt for the other end in a haystack of lines and symbols...but it's still an improvement over the impenetrable tangle of lines you'd have otherwise.

about 2 months ago
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Intel Puts a PC Into an SD Card-Sized Casing

cjameshuff Re:So do WiFi cards (219 comments)

For which? The 400 MHz ARM that's been out for a few years already, or the 400 MHz Intel that's just now being put in this form factor?

about 3 months ago
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Intel Puts a PC Into an SD Card-Sized Casing

cjameshuff Re:So do WiFi cards (219 comments)

The Quark is a 400 MHz part designed for deeply embedded applications with low power consumption. It's not going to provide the power of a desktop system just because it's an x86. Specs are comparable, and probably in ARM's favor, particularly in terms of performance per watt.

about 3 months ago
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Orbital Sciences Cargo Test Mission To ISS Launches Successfully

cjameshuff Re:Congratulations to Orbital Science (39 comments)

Two prominent ones come immediately to mind, not at all an exhaustive list:
Destroyed shortly after launch due to an cracked casing in a "so reliable they don't need to be test fired" GEM-40 booster:
http://en.wikipedia.org/wiki/GPS_IIR-1

Blew up on the pad as people were working on it, leveling the pad and killing 21 people (they seem to have moved on to largely liquid-fueled systems now):
http://en.wikipedia.org/wiki/VLS-1_V03

Manufacturing solids is a hell of a lot more than "a giant Magimix with extra safety precautions", it requires extremely good process control and very detailed inspection of the end product with a lot of expensive equipment, and entails a tricky disposal issue with all the castings that fail QC and huge amounts of hazardous materials to handle all along the supply line.

Ares was canceled, in large part due to being unaffordably expensive yet underperforming. Epsilon and Vega are tiny, Ariane 6 is a big step back in capability and not particularly cost competitive, and there's a lot of industry support for a change in direction to liquids. The Russians and Chinese primarily use liquid boosters, there were proposals to replace the Shuttle's solid boosters with higher-performing liquids (the performance benefit is actually quite substantial, this being the reason almost all launchers use liquids), and Aerojet is developing liquid boosters for the SLS Block IA and Block II as an upgrade from the Block I's Shuttle-derived solids (which may see use as launchers themselves, as the Energia's Zenit boosters have).

And again, SpaceX keeps demonstrating the advantages of liquids: the vehicle is safer to work on, engines can be properly tested prior to use, the vehicle can be shut down on the pad after ignition if problems are found, it can continue on to orbit even after losing an engine in flight...and there's just no way a solid first stage can come back and land for reuse like the Falcon 9-R. Liquid systems easily beat solids in cost, SpaceX's Falcon 9 is far cheaper than any solid system even without reusing the first stage.

about 7 months ago
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Next Chapter In the Leap Second Story

cjameshuff Re:Double time (68 comments)

It's not even helpful to astronomers. Your telescope's direction will jump by 15 arcseconds for every leap second applied. If you want precise pointing, you'll use a rotation model based on more detailed data on Earth's rotation with a timebase that's actually real time, not some mostly-increasing number with arbitrary jumps forward and back.

about 7 months ago
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Without Plutonium, Deep-Space Probe Missions May Sputter Out

cjameshuff Re:Why are nuclear fission systems too heavy? (268 comments)

As others point out, things don't lose their mass just because they're in space.

However, the problem with reactors isn't that they're "too heavy", they're lighter than an RTG with equivalent power output would be. The problem is that they're too big. An RTG is a lump of passively decaying material surrounded by thermoelectric converters and heat sinks, there's no hard lower limit in size. A reactor has to have enough material to sustain a chain reaction, which imposes a stricter minimum mass.

If your mission's big enough to use one, a reactor makes much more sense than an RTG, but they only make sense for big missions. One example is the SAFE-400, which masses 512 kg but puts out 400 kW thermal and 100 kW electrical. A GPHS-RTG masses 57 kg and produces 4.4 kW thermal, 300 W electrical at the start of the mission. The reactor's a lot lighter for its output, but if you need 1 kW, what do you choose?

about 7 months ago
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Orbital Sciences Cargo Test Mission To ISS Launches Successfully

cjameshuff Re:Congratulations to Orbital Science (39 comments)

And if they'd been using a solid? They'd have been unable to do a hot fire test, and might have attempted to launch with a faulty vehicle, leading to a messy failure rather than a 2 week delay due to range contention. They've repeatedly demonstrated the benefits of being able to shut the vehicle down on the pad, among other advantages of liquids. (You can't make a launcher with engine-out capability using solid rockets, for example.)

Solids are a lot more trouble to manufacture, transport, and work around, can't be test fired or shut down when problems are encountered, have a nasty habit of exploding, are very difficult to scale up, and their performance sucks. In addition, just try restarting a solid and performing a precision landing as SpaceX intends to do with the Falcon 9-R. Even without that, SpaceX is launching for far lower prices than those other rockets.

Launch vehicles based on solid rockets are a dead-end carried over from and kept on life support by the ICBM industry, where they are required for their ability to sit in a silo for years and be ready to fire.

about 7 months ago
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Suborbital Spaceflight Picks Up Speed

cjameshuff Re:Layman here... (51 comments)

In fact, 1 billion dollars would fuel around 5000 Falcon 9 launches, each lifting 13 metric tons of payload to LEO, for 65000 metric tons total. For the Falcon 9 (one of the lowest cost launchers), propellant is about 0.4% of the launch cost.

The real costs are in the hardware and in operations. The problem is that there really hasn't been a huge amount of incentive to reduce costs. Especially in NASA's launcher programs, where things like Constellation and the SLS are specifically intended to keep Shuttle personnel employed and funds going to the important Congressional districts. This is just not an approach that will reduce costs.

The COTS effort is shaking things up a bit. SpaceX's prices are a lot lower than the competition's, and they are working on recovery and reuse of as much of the vehicle as is economical.

about 7 months ago
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Future Astronauts Must Deal With Toxic Chemicals In Martian Soil

cjameshuff MInor detail, not a problem (117 comments)

Perchlorate is a reactive and unstable anion that can easily be washed out of regolith, thermally decomposed by baking in an oven, or removed using chemical or microbial treatments. Similar treatments are likely going to be required anyway if you're going to be growing plants in it.

It's also not actually all that toxic. The thyroid absorbs it in place of iodine, reducing the amount of iodine absorbed...it has no other effects, and the iodine uptake interference stops when exposure to perchlorate stops...chronic ingestion is required to make it a problem, an acute exposure will only have a brief effect.

Basically: don't make a habit of eating untreated dirt, and monitor drinking water contaminants. Nothing they shouldn't already be doing. Iodine supplements might be a good idea in case drinking water becomes contaminated and it takes some time to correct.

about 10 months ago
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Mars Explorers Face Huge Radiation Problem

cjameshuff Re:Hitch a ride: (283 comments)

You're missing the point. You have to make basically the same velocity change (somewhat more to actually rendezvous), but *you don't have to carry your radiation shielding while doing so*. A "cycler" carrying equipment and shielding only needed for the long duration port of the trip would only have to make minor maneuvers to maintain its orbit, the craft traveling to and from it could be much lighter because they only need to support their passengers for a relatively short trip.

about a year ago
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Mars Explorers Face Huge Radiation Problem

cjameshuff Radiation exposures not "huge" (283 comments)

"astronauts on even the shortest roundtrips to Mars would get radiation doses of about 662 millisieverts"

That is simply *not* the "huge amount of radiation" the article claims. It won't even cause any effects that can be tied to the radiation...it'll increase the long-term risk of fatal cancer by a few percent (for the 1000 mSv, 5% increase in cancer risk limit, that means you're still 20 times more likely to die of cancer from something else), provided the models are even accurate for such low exposures. Radiation exposure is something we'll obviously want to minimize, but this article is just radiophobic fearmongering.

about a year ago
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Plug Into a Plant: a New Approach To Clean Energy Harvesting

cjameshuff Re:Isn't there an obvious flaw? (80 comments)

They grind the plants up, extract the thylakoids from the chloroplasts in the plant's cells, and somehow bind them onto a base electrode covered in carbon nanotubes (it's not clear where the other electrode is). So no, the plant is not going to be doing anything with the energy produced. It's also not going to be doing any repair or replacement work on those extracted bits of cellular machinery, or reproducing, etc.

about a year ago

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