Posts by cray74

"Well it mentions 128GB storage, and (128 gigabytes) / (1 kbps) = 32.449295 years"

I believe total science data is going to be 8GB, but that's still 2 years. Alright, potentially a bit more than 45 to 90 days. Maybe that's the "cool public interest data" phase.

Re: Cockpit

"None of the huge acerage that the yanks have in the b-52, which makes the black buck missions even more remarkable."

I'll grant the Vulcan's cockpit is smaller, but "acreage?" The B-52H's have a 2-deck compartment for a crew of 5 in survival gear and ejection seats with a cumulative volume similar to a minivan. I'm not tall, but I got leg cramps while touring a B52H that was undergoing maintenance and had its ejection seats removed.

Of course, I'm not a military air crewman so maybe that does count as acreage. The F-4's cockpit in the National Museum of the USAF was claustrophobic. I had to put my camera to my forehead to photograph the control panel while seated in it.

Re: What a shame

"as this most recent failure confirms. Russia and SpaceX are both unreliable sources to supply ISS."

You need several points to plot a trend, but SpaceX has had 1 complete launch failure in 19 Falcon 9 launches. There's no confirmation there.

"Clean, efficient, safe and from what I understand can be used to burn up our existing nuclear waste stock piles."

Fast reactors do better at burning transuranic waste than most molten salt reactors, which tend to be thermal rather than fast. The continuous molten salt reprocessing needed to efficiently produce uranium-233 does give some interesting opportunities for waste "burning" in thorium reactors, though.

Re: jet fuel can't melt

I guess I don't get these "steel melt" memes. Are they saying conspiracy theorists are idiots for thinking the steel melted, or for thinking that the steel did not melt?

There was no need for steel melting in WTC. The temperature of the jet fuel fire was plenty sufficient to heat up the remaining ASTM A36 structural steel in the impact areas to 300-500C, when such cheap steels lose half their strength. Look up a temperature-strength curve for A36 steel. After the hijacked airlines knocked out the other half of the Towers' structural strength, the Towers were well below the strength they needed standing. They originally had a factor-of-2 safety in their strength but were down to 1/4 their original strength, and the remaining beams were experiencing enormous new stresses due to fully-clamped thermal expansion conditions.

References:

1. Journal of Materials (JOM), "Why Did the World Trade Center Collapse? Science, Engineering, and Speculation," Vol. 53, No. 12, p. 8-11.

2. JOM, "The Role of Metallurgy in the NIST Investigation of the World Trade Center Towers Collapse", Vol. 59, No.11, p. 22-30.

[edit] Both articles are fully online if you're bored.

Re: Shame

"I liked the idea of having Rosetta in a parking orbit. "

As I understand it, there isn't a stable parking orbit around the comet. It's too lumpy and too small. Rosetta's sort of been following its solar orbit rather than really orbiting the comet. And what orbiting occurs does so with constant course corrections.

Re: Were Neanderthals really stupid?

"We ascribe stupidity to Neanderthals mainly because they got wiped out."

Or their lack of innovation and lower encephalization?

Neanderthals covering broad swaths of land and time - i.e., multiple cultures - stuck to Mousterian tools for 540,000 years. You only see significant evolution of the Mousterian tools (such as into Emireh culture and maybe Chatelperronian industry tools) c40K-30KBC, by which time there was potential overlap of Neanderthal and modern human populations.

While modern humans weren't leaving proof of being ancestors to rocket scientists prior to c50,000BC, they developed tools and arts more rapidly than neanderthals. For example, the modern human Aurignacian culture (c35KBC) showed innovations that Neanderthals never did*: representational art and ranged weapons like spear throwers and bows. It was recently big news that - maybe - the neanderthals scratched cave walls [1] as art while at the same time modern humans (proto-furries, I guess) made "the lion man" [2] and various Venus figurines. (*Or haven't yet been found to do.)

Which makes sense. Neanderthals' bigger brains showed less encephalization - the larger nerve mass was controlling a larger body [3] rather than getting involved in paleolithic hippy liberal arts. "Ifn uh stone axe wer good 'nuff fer great grandpa then it was good 'nuff for kids these days, none of them foo-foo 'bows' and new-fangled 'spear throwers' for Neanderthals, no sir."

Neanderthals weren't dumb brutes: they had fire, they had stone tools, they buried their dead, took care of their sick, and maybe made musical instruments. But archeologists need some big discoveries to show that Neanderthals had the same range of abstract thinking and intelligence as modern humans. (Or I need to improve my Google searches.)

[1] http://www.bbc.com/news/science-environment-28967746

[2] https://en.wikipedia.org/wiki/Lion_man_of_the_Hohlenstein_Stadel

[3] http://archaeologyinfo.com/homo-neanderthalensis/

Re: Kind of a shame, really...

After Mad Max: Fury Road, any silver food spray on Amazon has awesome reviews, many voted as very helpful.

Re: Question

This new helium went into making new stars which fused hydrogen into helium, and helium into Lithium, then they went bang, ekcetera...

Actually, big stars only use a little bit of their hydrogen fuel because they can only use the hydrogen in their core. Unlike red dwarf stars - which don't supernova - bigger stars don't have convection occurring in their "mantles" that might bring fresh hydrogen to the core.

So bigger stars do produce helium in their core and distribute it when they supernova, and that makes the next generation of stars richer in heavier elements, but they still have a lot of left over hydrogen by the time they blow up. They redistribute a lot more hydrogen than heavy elements. As a result, the next generation of stars starts off burning hydrogen, too.

In fact, all stars start off as hydrogen burners. They have to exhaust the hydrogen in the core before they move on to more difficult fuels like helium.

Re: Remember Iridium?

"That was a multi-satellite cluster (planned 77, launched 66 I think) that lost about $5B from Motorola, etc, because the revenue from it was nothing like enough to cover the costs as by time it was launched.

Sure, but Motorola well and truly amorously assaulted the pooch with its business plan and consumer hardware. The phones were larger, shorter-lived, and had poor indoor reception even by the standards of the time. As you noted, cell phones were already delivering most of the utility of Iridium phones except for users stuck in Antarctica. The plans and phones were very expensive for modest performance and some potential customers have cited poor sales handling.

http://www.cnn.com/TECH/computing/9902/24/iridium.idg/

Is OneWeb making the same mistakes? There's been a lot of examples of failed constellations for investors to learn from.

"It is only going now as the US military bought it from bankruptcy as a bargain and it helps them with world-wide coverage where user revenue is not a concern."

And wasn't that the deal of the century? $35 million to acquire a satellite constellation and related businesses worth $6 billion.

Since then, Iridium is staggering along. It has orbited a total of 95 satellites, has 72 operational (including 6 on-orbit spares), and is planning to volley a replacement set of 66 IridiumNEXT satellites beginning this year (7 SpaceX launches acquired for $490-ish million). Its revenue seems healthy for its expenses and only 23% of its revenue is from government subscribers.

Shuttle's Accidental Thruster Firings

"But 'accidentally' firing the rocket motors on a space capsule attached to the ISS..."

This was a persistent fear about the shuttle on station missions. Apparently, NASA reckoned there was a 1-in-10,000 (or less) chance of the shuttle's thrusters accidentally firing while docked. There had been 5 accidental thruster firings in free space prior to the station missions, where the loud bangs harmed nothing but astronauts' underwear. For Mir missions, astronauts simply de-powered the avionics that controlled the shuttle's thrusters, but there were always windows of opportunity for the thrusters to glitch when they were powered, such as during undocking and docking procedures.

Besides the obvious difference in size and mass between the US shuttle and Rooskie capsule, there's a fundamental difference in philosophy about performance. Russian capsules have always had under-powered thrusters because, as noted in this discussion, they don't need much thrust once in orbit. American Gemini and Apollo capsules and the shuttle have been comparative hotrods with significant design influence from their military test pilots, who wanted responsive vehicles.

This led to NASA's fear about a docked shuttle's motors firing accidentally: the thrusters could tear the shuttle off the station, depressurizing both vehicles and causing a TPK.

http://www.space.com/972-shuttle-thrusters-potential-risk-space-station.html

Re: "Anyone who does not assume that all states do this is very naive"

"40 years ago I worked as a physicist on one of the big MoD research sites. Our security briefings went along the line of "obviously the Russians are hot after military secrets, but the second worst bunch of spies are the Israelis...."

That's still the case in general. I work in an aerospace company and the briefings run to the effect of, "Keep an eye on the allied foreign customers," followed by numerous examples of 'lost' visitors turning up in office areas shortly before there's an outbreak of malware.

I suspect actually spotting skullduggery by visitors will be more difficult than is suggested by the training films, though. I have yet to see a foreign customer show up in a turban or my infected inbox visibly sending emails to Beijing.

Re: How do the manage the fuel

I am amazed to read launched in 1977 and still has years of fuel left. What kind of fuel is used on these craft, is it nuclear or carbon based and how are they actually propelled/steered?

Depending on the application, Voyager has 2 types of fuel.

There's plenty of plutonium fuel left for electrical generation in the radioisotope thermal generator (RTG) until about 2025. The plutonium isotope 238 has an 87.7-year half-life, and Voyager is "only" 37 years old. The 420 watts of electricity from Voyager 2's RTG is down to 258 watts (as of early 2015).

Voyager 2 also had 100kg of hydrazine at launch. This was used sparingly, mostly to set up planetary slingshots where gravity did the most work tossing Voyager from planet to planet. It has used 75kg over 37 years and needs very little to stay oriented in deep space.

"I still want to know why Neptune's orbit isn't as far out as Pluto's average orbital distance: "

See: Nice Model. The planets didn't settle down into a primate-pleasing, mathematically-simple arrangement because they're the result of chaotic collapse of an interstellar cloud of gas and dust. Our pre-solar cloud initially collapsed into a very different pattern than is observed today and the planets gradually migrated into the current configuration.

"this would validate Titius-Bode."

No, it wouldn't. Having the solar system set up in the pattern of Titius-Bode would be a single case of Titius-Bode working - a coincidence not repeated elsewhere. Titius-Bode is not repeated in the moon systems of Jupiter, Saturn, Uranus, Neptune, or Pluto, nor in any of the observed extra-solar planetary systems.

Re: Air cooling has some other problems, too ...

Tin whiskers are a problem in vacuum and air, but may be suppressed with non-ecofriendly options like adding lead to your solder or more environmentally conscious conformal coatings like parylene. Or both.

Re: Relax, it's going to Mars, not to your leaders

Heh. I entered comments just to say, "Why not go to Mars after picking up our leaders?"

"That takes care of this weeks Darwin Awards nomination."

Nope, not qualified. He has offspring.

http://www.huffingtonpost.co.uk/2015/06/01/fisherman-randy-llanes-killed-swordfish-harpooned_n_7482468.html

Re: Why can you install software incorrectly on an aircraft?

"I would have thought that somewhere in millions of quid spent on this a check on having the correct software properly installed would have been built in on boot?"

The test systems for aerospace hardware often contend with different software versions in the gear they're testing. I'm on an aerospace company's program for a targeting system and we have different firmware versions for different customers and legacy versions of the system, which means the test rigs are necessarily flexible - they don't scream if you've got (for sake of argument) v1.01 firmware installed instead of the latest v1.03. And it's real easy to let your eyes glaze over when the boot-up data scrolls past and you've got the chance to spot "v1.01" instead of "v1.03." The real meat of the test data is whether the system works and all the flagged functions say, "pass," "working," and so on.

The A400M's engines go through a lot of tests. I can guess at some of the objective evidence that would be required to make Airbus and Europrop happy. At a minimum:

1) The ECU was tested and certified by its maker before it was sold to Europrop (admittedly probably without the software, which would be Europrop's or Airbus's responsibility to install);

2) Europrop tested the all-up engines on a test cradle before it sold the engines to Airbus;

3) Airbus would've powered up all 4 engines on the A400M long before the plane was allowed to take its first, fatal test flight since big aircraft don't get near a runway until their many systems are tested;

4) On that fatal flight, the engines powered up and made all the blinken lights in the cockpit glow happy colors without spitzensparken

The software that crashed the plane did go through check after check, and it worked. Up until the most important check.

Airbus has noted problems with the A400M program's organization: it treats production, development, and retrofitting as separate programs, rather than an integrated single program. That's an environment where version control problems are going to proliferate. I could very easily imagine the poor bastard who "incorrectly configured" the software was just using an out-of-date manufacturing process plan that said something like, "get the USB stick with software version 1.01" because no one had flowed down process changes to the MPP hardcopy at his workstation to say, "get the v1.03 stick." Or something like that.

@JP19

"You and we don't know that he was. It sounds like he was using media player controls and doing that on your wrist is probably less distracting than doing it on the car stereo."

We know that whatever the driver was doing involved being distracted by his wrist to the extent that someone in another car was able to observe him doing something with his watch. Whether flipping through his mix list, getting directions, or catching on Game of Thrones, by the time other drivers can notice it, it's too much distraction.

The only fast wrist action other drivers tend to notice is when the wrist is deliberately displayed to them, usually surmounted by a closed fist and individually exposed middle finger.

Re: Seems to me that a rarity...

"Even Sylvester Stallone has said the the new Dredd movie was better then his Dredd movie."

Yep. It had one of the best dystopic cities I've seen. I loved it more for the background (and cute telepath) than Dredd.

Re: Sadly no Europa orbit

" Also the proximity of Jupiter would probably make Europa orbits quite unstable too."

Wouldn't the destabilizing factors be Io and Ganymede, not Jupiter?

Re: Orbital factory

"Would need some sort of micro-fabrication facility."

And many other facilities: those to reprocess solar cell materials; the vast and varied chemical facilities to work with the many different battery types in orbit; differing metallurgical facilities to handle the steel, aluminum, magnesium, titanium, and other alloys; the enormously complex facility needed to make microchips from whatever electronic raw materials you find in orbit; something to recycle the composites; and then you'd need several layers of facilities to turn the resulting basic components into finished goods.

The aerospace industry is a complicated web of processes to turn raw ores - or defunct, atomic oxygen-worn, radiation-blasted space hardware - into useful goods.

Re: Relativity

"That is short-lived by stellar life times, still long as measured by our humble time upon this Earth."

The time in these Wolf-Rayet phases is a few thousands of years so you're starting to get into periods that can be described with phrases like "1/70th of humanity's existence" or "on timescales similar to the longest-lived human cultures," so that's not necessarily long compared to our humble time upon this Earth.

Re: It's about time somebody went...

Speaking of manned landings, yes, it's been 42 years (7 Dec 1972). But after Apollo 17, the following lunar landings occurred, skipping orbiters and impactors:

Luna 21 / Lunokhod 2 (1973)

Luna 23 (sample return, 1974)

Luna 24 (sample return, 1976)

Chang'e 3 (lander/rover, 2014)

Skipping orbiters after 1972 leaves out a surprising (to me) number of missions. Workhorses like Clementine and Chang'e 2 tend to be overshadowed by Mars.

Re: Dropping a brick

"It's a 10cm cube & they need to test its aerodynamics?"

It's a 10cm cube with differing centers of mass depending on the exact contents of the Cubesat that might thus twirl or fall in a manner different from a homogenous cube. It is also a 10cm cube that might be placed in an aeroshell.

Re: What is unbelievable..

"They're still pushing for weakenned security because they believe they are in the right , they are justified, they are the white knight protecting us ,and they have absolutly no intention of stopping."

Regardless of motivation, it's also a low-cost option with high payout for a big gubmint agency to pursue legal / regulatory courses of defeating encryption.

1) They have legal staff that will either bill equally for sitting around checking Facebook or for trying to convince the relevant legislature to change the law.

2) There's little social cost to individuals - managers or lawyers - in a large agency for pushing an unpopular law. People generally rage at acronyms, not the people behind them. (You read, "The NSA is such a meanie!" not "Sub-Director 3rd Grade Bob Jones' initiative to hinder superior encryption offends me.")

3) Lawyers are a fiscally sound option: a small army of them is still cheaper than a new code-cracking supercomputer.

Re: Only one Ion Engine?

I understood they worked much better in multiples, usually in a twin arrangement."

The engines don't get any performance enhancement from being mounted in multiples. Instead, multiple ion engines are usually mounted on spacecraft for reliability reasons. They're expected to operate for thousands of hours at high voltages, often with erosive internal conditions. There isn't a normal number, though, two or otherwise.

The Smart-1 probe had a single ion engine, which proved adequate for its full mission. Hayabusa had 4, and all crapped out at some point before remote repairs got at least 1 working for the flight home. Deep Space-1 had a single thruster, which didn't fail; Dawn uses 3 of the same thrusters as DS-1 (no problems to date); the Boeing 702SP uses 4 XIPS engines.

Re: Icehenge

"I thought Icehenge was just a shit Kim Stanley Robinson book. Turns out it was non-fiction."

But still shit. I mean, the book not this finding on Comet 67P, which is cool.

"And the whole precooler idea means they can run on atmospheric oxygen for more of the flight profile, which in turn brings about big savings."

The challenge is that reducing oxygen mass in a single stage to orbit vehicle is NOT a big weight savings by the time you get into orbit.

Yes, oxidizers are the largest fraction of a launcher's mass when it's sitting on the ground. But the thing is, most of that mass goes out the tailpipe by the time you reach orbit. Take a moment to consider the rocket equation (if you'll pardon the simplification):

Delta-V = Exhaust Velocity x natural log (fueled mass / dry mass)

The fueled mass doesn't matter much by itself because an SSTO is going to throw most of that away. More important values are the exhaust velocity (or specific impulse times G, if you prefer) and the ratio of fueled mass to dry mass. An SSTO really wants to have a big ratio between fueled and empty masses and, of course, a high exhaust velocity would be nice.

Skylon claims to achieve a specific impulse in the atmosphere, and I won't question that. So let's look at the ratio of dry to fueled masses for SSTOs. The dry mass consists of frame, oxidizer and fuel tankage, avionics, landing gear, engines, cargo, and anything else that didn't get dropped during flight.

In the case of a rocket, the in-orbit leftovers of the oxygen system are oxygen tanks. Rocket oxygen tanks are light, around 1% or less of the mass of the oxygen they carried. For example, the shuttle external tank's oxidizer tank was about 10 tons for 600 tons of liquid oxygen.

There are heavier bits on a rocket headed for orbit than oxygen tanks. The perennial favorite fuel, hydrogen, needs about 10% of its mass for tankage. The shuttle ET's hydrogen tank was about 15-20 tons and held 100 tons of liquid hydrogen. The dominant factors in tankage mass are volume and pressurization - interestingly, liquids' weights scarcely impact rocket fuel tank design, even when you're looking at the weight at 3Gs. Liquid hydrogen has low density (1/14th of water, 1/16th of liquid oxygen), and its fuel pumps need high tank pressurization to help prime them, on the order of 35psi. That calls for a large, sturdy tank and thus high dead mass per unit of liquid hydrogen.

Engines may be a large part of an SSTO's mass, or not. Dense fuel rockets, like kerosene-oxygen rockets, achieve better than 100:1 thrust to weight ratios, meaning a 1000-ton SSTO requiring a 1.3:1 takeoff thrust only has 13 tons of engines. SpaceX is nosing around 150:1. Hydrogen:oxygen rockets rarely beat 75:1 and tend to be around 40 to 60:1 simply because they need such massive fuel pumps for a given thrust level - fluid pumping horsepower requirements are largely dominated by fluid volume, not mass, but thrust levels are determined by the rate (mass per unit time) you're burning fuel. Dense fuel engines can burn a lot of fuel mass with a light pump; hydrogen/oxygen engines are screwed by hydrogen's low density since they need a big pump to move a little fuel.

Rocket engines aren't the only game in town, as Skylon and scramjet enthusiasts demonstrate. However, airbreathing engines have much worse thrust-to-weight ratios than rocket engines. A good, military, afterburning jet engine manages about 10:1 thrust-to-weight ratio. Scramjets might not break 1:1.

Skylon's SABRE hopes to reach 14:1, which is good for an airbreather. Still, that's a lot of deadweight to carry into orbit just so you can shrink the already-lightweight oxygen tanks.

Skylon's design (and that of other airbreathing SSTOs) runs into other issues. It needs to be sleek and aerodynamic so it can fly at high speeds through the atmosphere. "Sleek and aerodynamic" mean "high surface area for a given volume." That means a proportionally high mass for tankage and frame compared to chunky SSTOs like the Kankoh Maru, SASSTO, or even the VentureStar. The "high speed atmospheric flight" also means "more heat shielding," compounding the surface area issue.

Admittedly, a larger liquid oxygen tank does drive several other weight increases: more heat shielding, larger frame, more engines, etc. However, those are modest increases. Frames, rocket engines, and heat shields are percentages of masses they carry, not multiples.

I'm not saying Skylon's impossible, just that it took the more painful route. The "big savings" in oxygen mass really isn't a big savings since oxygen tanks are so light, and you're getting those oxygen system savings at the expense of enormously heavier engines, more challenging aerospaceframe design, heavier heat shielding, and so on.