* Posts by cray74

1081 publicly visible posts • joined 29 Nov 2011

Zombie … in SPAAACE: Amateur gets chatty with 'dead' satellite

cray74

Re: That's pretty nifty!

Well if it fights back, of course...

Doesn't anyone remember the lesson of the Soviet Venus probe!? It's not everyday you have a bionic astronaut handy to defeat those things, so shoot first and shoot often!

PACK YOUR BAGS! Two Trappist-1 planets have watery oceans, most likely to be inhabitable

cray74

Re: Comment about the artwork...

Addendum: the article's depiction of Trappist-1 does fall prey to the common mistake of "red dwarfs must appear dim and red in the sky." In fact, a 2500K light source is going to appear fairly white. The surrounding sky and landscape might take on a different, dawn/dusk-like color, but the star itself will look white to human eyes. The following link is an excellent depiction of a red dwarf and its impact on landscape lighting, as well as having a good discussion and supporting references:

GJ 667Cc

cray74

Re: Comment about the artwork...

Take this one, you see a rather big planet right up the sky. Even though the star they orbit is comparable to our sun in size and the distance idemditto. So there's no way you'd get to see the sun as shown in the image shown in the article, yet here we are.

The planets depicted in the art fall between the foreground planet and Trappist-1. The supposedly habitable-ish planets identified by this study are Trappist-1d and -1e. Therefore, the extreme scenario for the artwork would be an observer on the surface of -1e looking at potentially Trappist-1 and the planets -1b, -1c, and/or -1d.

**Trappist-1, a tiny M8V dwarf, is 0.121 times the diameter of the sun.

**Trappist-1b is 0.011AU from the star and 1.13x Earth's diameter (with rounding on both values)

**Trappist-1c is 0.015AU from the star and 1.1x Earth's diameter

**Trappist-1d is 0.021AU from the star and 0.788x Earth's diameter

**Trappist-1e is 0.028AU from the star, diameter irrelevant since I'm positing the observer is on the surface

For someone on -1e, the star Trappist-1 is 0.121 times Sol's absolute diameter but 35.7 times closer in the sky. Approximately speaking, Trappist-1 will appear (0.121 x 35.7) = 4.3 times larger in diameter than Sol and cover 18.7x more area. It will be a big globe in the sky, quite a bit larger than Sol or Luna. On the horizon, as depicted in the article's artwork, it could appear that big due to the moon illusion. Since the surface temperature is 2500K, it will be fairly easy to stare at, too, a modest "warm, soft white" color that invites lots of naked eye observation while the excess infrared light burns your retinas.

Meanwhile, the planets -1b, -1c, and -1d could appear sizable, too.

1b: Since the world is between the star and foreground planet, which I'm assuming is 1e, the distance is about 0.028 - 0.011 = 0.017AU. This is about 2.55 million kilometers, or 8 times the Earth-moon separation. 1b is, however, 1.13x Earth's diameter and 4.14x Luna's diameter. In this scenario, 1b could appear up to 4.14 / 8 = 0.51 times Luna's diameter in the sky - a distinct globe, but smaller than Luna. One notes the transiting planet is quite small compared to the star.

1c: From 1e, planet 1c would be 4.875x as distant as Luna but 4.03x as large. 1c could appear about 0.8x as large as Luna.

1d: From 1e, planet 1c would be 2.625x as distant as Luna but 2.9x as large. 1d could appear about 1.1x as large as Luna.

The star and two planets in the artwork fit within those proportions: 4.3x as large as Sol (or Luna), and 0.5 to 1.1x as large as Luna. The artist took some care with the proportions.

If the foreground planet is 1d, Trappist-1 would appear 5.76x Sol's diameter, and there'd still be 2 planets that could appear in the sky as depicted.

Overall, I'm going to say the artist wasn't too far off, especially if the Moon Illusion is applied.

Mass limit proposed so boffins can tell when they've fingered a brown dwarf or a fat planet

cray74

Re: Firing up

Seems to me that the critical distinction should be whether the core is, or has ever been, capable of starting nuclear reactions,

Agreed, but that's harder to verify for borderline cases. Mass is relatively easy, especially if an exoplanet/brown dwarf was spotted by the Doppler effect.

All aboard the Vomit Comet: Not the last train to Essex, but a modded 727 for weightless flight

cray74
Thumb Up

Event Horizon

The space sequences in the (excellent) film "Apollo 13" were all filmed aboard one of these ...

Oddly, I only learned about Apollo 13's real free fall sequences from the bonus features on the DVD for Event Horizon (the movie's a guilty pleasure of mine). The Event Horizon actors were complaining about the wedgies and general discomfort they experienced being in harnesses simulating free fall, and added a comment to the effect of, "We didn't have the budget of Apollo 13 to film the sequences in a Vomit Comet."

The next time I watched Apollo 13 I realized you could spot the free fall sequences: they're never more than 25-30 seconds long before the camera switches to another view. Those Vomit Comet parabolas only give you that much free fall if you want to avoid a vigorous lithobraking maneuver.

China's first space station to – ahem – de-orbit in late March

cray74

Re: Coming home

I'm pretty sure it will all make it to Earth, one way or another. Where else can it go?

Since you asked...

Given that:

1) Tiaingong-1 is made of a variety of materials, including polymers. The material that's vaporized will generally be converted to oxides. In the case of polymers, that's mostly carbon dioxide and the horribly dangerous dihydrogen monoxide. Those oxides will disperse into Earth's atmosphere, while other oxides (like aluminum oxide) and debris will continue to Earth's surface. And,

2) Earth's escape velocity is sufficiently high to retain most of its atmosphere over geological timescales, unlike Mars, but there is ongoing loss of light elements, particularly hydrogen. (Earth is currently losing about 3kg of hydrogen per second from its atmosphere.) And,

3) Water is mildly susceptible to photolysis (sp?) from high energy UV above the ozone layer, freeing hydrogen to the exosphere, then

...some of Tiaingong-1 will escape into space after vaporization. A quick back-of-the-envelop calculation making unsubstantiated estimates of Tiaingong-1's polymeric mass fraction concludes several bajillionths** of a gram will escape Earth into space.

**My 5-year old niece assures me this is a valid measurement for small quantities.

Dark matter on the desktop: Dark Energy Survey publishes data

cray74

Re: That DES footprint

"Dark energy tank." You could milk that for a couple of military scifi short stories or some SBIR Phase I funding from the Pentagon.

Mystery surrounds fate of secret satellite slung by SpaceX

cray74

Re: the 45th Space Wing?

So cray74 is not necessarily the 74th cray then? Is that what you are saying?

I'm not certain of the logic that resulted in the "74" suffix in my handle. In a prior millennium, I signed up for a Hotmail account while attempting to retain my dial-up BBS handle of "Cray" and was informed that plain "Cray" was taken. Since I was in a hurry to forward an amusing ASCII artwork message by that new-fangled internet email thing, I didn't bother exhaustively evaluating the availability of email addresses from cray1 to cray73 but rather immediately accepted Hotmail's suggested "cray74."

I usually attempt to use "cray" when signing up in internet forums but when that isn't available I next try "cray74." After 20+ years of usage, "cray74" is easy for me to remember even if I don't know the algorithm that appended the 74 suffix to "cray."

Therefore, I cannot say for certain that cray74 is or isn't the 74th cray, and the answer to your first question is, "Yes." The answer to the second question is also "yes."

cray74

Re: the 45th Space Wing?

How big is a "Space Wing" that they have at least 45 of them?

45? There's also a 460th Space Wing. A quick browse through the USAF Space Command org chart shows:

The 460th Space Wing,

The 233rd Space Group (Colorado Air National Guard),

21st Space Wing,

310th Space Wing,

50th Space Wing,

30th Space Wing,

And two full Air Forces involved in the USAF Space Command:

14th Air Force, and

24th Air Force

Reading all this just makes me realize I know very little about USAF organizational standards. I don't know a group from a wing; I don't know why there are the 21st, 30th, 50th, 310th, and 460th Space Wings, but not a 1st, 2nd, 3rd, 4th, and 5th Space Wings; and I don't know why the USAF Space Command got tasked with running the USAF's IT department ("Air Force Informational Network," which I'm probably misunderstanding, too.) Much more reading to do...

Astroboffins say our Solar System is a dark, violent, cosmic weirdo

cray74

Re: Titius–Bode law

Any hint in the data as to whether the planets in other solar systems obey the Titius–Bode law?

A 2014 analysis of Kepler data says, "No," and other attempts to say this or that system follows a Titius-Bode pattern have been "controversial."

https://academic.oup.com/mnras/article/442/1/674/1253671

Elon Musk lowers his mighty erection for test firing: Falcon Heavy preps for maiden voyage

cray74

Re: Kiss goodbye to that roadster

Is he sending the batteries as well?

I had some questions along those lines, which could be summarized as "What modifications have been done to the Tesla Roadster, if any? Got a link?"

So, yes, was the battery pack removed? If it's only going to orbit, an overheated, giant lithium battery back could produce a lot of debris as it melts down, and removing it would simplify any stress calculations for the team who had to design the launch adapter. (I'd love to be a fly on that wall. "So, team, you've been assigned to design a launch adapter for the boss's car...")

Were any solar panels, beacons, and/or transponders attached to the car? Will there be a SpaceX website letting you track the Roadster as it zips by Mars?

Did the car get any slightly scientific payloads, like a webcam or some Mars-targeted Cubesat's sensors? ("Hey, University X, I heard you were launching a Cubesat to Mars 2020. We've got a spare glovebox and are launching two years sooner. Want to go with us?")

RIP John Young: NASA's longest-serving 'naut explores final frontier

cray74

5 space vehicles, 6 flights, 7 launches, and a space smuggler...

A summary of John Young's career:

1) Operated the largest number of vehicle classes in space:

--Gemini capsule (Gemini 3, 10)

--Apollo capsule (Apollo 10, 16)

--Apollo lander (Apollo 10, 16)

--Apollo rover (Apollo 16)

--Shuttle (STS-1, STS-9)

2) First human to make six space flights (2 Gemini, 2 Apollo, 2 shuttle)

3) First human to make seven launches into space (Apollo 16 featured launches from the Earth and moon)

4) Longest astronaut career

5) Possibly the first space smuggler

His Naval aviation career also garnered recognition at high levels. ("I got a telegram from the Chief of Naval Operations asking me not to do this anymore." — Young, describing an air-to-air missile test in which he and another pilot approached each other at Mach 3, risking destruction of both aircraft.)

Big shock: $700 Internet-of-Things door lock not a success

cray74

Hhmm... that reminds of a story about Apple and the trick they pulled on a saphire glass manufacturer a few years ago. The glass manufacturer went broke shortly after being approached with an offer from Apple.

Sort of?

There were outstanding industrial and technical mistakes on the part of GT Advanced Technologies regardless of Apple's contractual shenanigans. To begin with, GTAT's past was a manufacturer of the furnaces used by other companies to grow artificial sapphire - GTAT didn't itself manufacture sapphire and yet suddenly tried to do so on an epic scale. It failed repeatedly to produce good sapphire boules for reasons ranging from a new, unproven furnace design (a dramatic scale-up from 100kg boules to 262kg boules) to impure feedstock, to poor temperature control, to poor power supplies, to operator fatigue and inexperience. Every furnace run took about a month and there was no in-process monitoring for the defects that could ruin an entire boule.

When GTA needed more money to overcome those problems, Apple said "No." GTA was then caught by a contract that said Apple wasn't obligated to give it any money, and terms that prevented GTA from selling sapphire to other customers. So, GTA went bankrupt. Apple then liquidated GTA's assets to recover its losses, turning the sapphire factory into a server farm and selling off** most of GTA's shiny, barely-used furnaces.

Anyway...Otto's situation is similar in that it was dependent on an outsider buyer who imposed competitive restrictions without legal commitment for funding. However, if I haven't misread the background, Otto wasn't hindered by crushing technical problems to the extent that GTAT was. Otto's not-so-angelic investor was thus actually more of a jerk than Apple.

(**The fire sale of GTA's furnaces and personnel has been a boon for one of my suppliers, who transformed overnight into a sole-source, vertical monopoly for sapphire windows. This news produced much screaming and gnashing of teeth from my procurement department.)

Soz, guys. No 'alien megastructure' around Tabby's Star, only cosmic dustbunnies

cray74

Re: Occam's Razor

Occam's Razor would have saved them $107k!

There are dumb ways to spend large amounts of crowdfunding, like a $55,000 bowl of potato salad, an $8,000 Lionel Richie head, or a $107 million presidential inauguration. $107,000 on an astronomical research project, even if it has a predictable answer, seems comparatively sensible.

'I knew the company was doomed after managers brawled in a biker bar'

cray74

Re: 'gloves were forbidden'

"My boss used to say that it cost about the same as milk."

Liquid nitrogen can be cheaper than milk. When liquid nitrogen is delivered in small Dewar flasks it runs about $0.50 per liter, which is reasonably milk-like in price. However, bulk LN2 deliveries by tanker truck are about $0.10-$0.15 per liter.

Millions of moaners vindicated: Man flu is 'a thing', says researcher, and big TVs are cure

cray74

Britishese to Americanese

Alright, my vocabulary in the Britishese** dialect of English has been corrected. From context, I'd previously interpreted "man flu" to mean "claiming illness for a day off when actually hungover."

**I know, I know, "Britishese," "Americanese," "Australianese" and other English dialect terms haven't been fully embraced by the World English Approval Center. I keep writing them with helpful new words, but I think they're just intimidated about the enormous task of adding new words to English. Instead, when they bother to reply it's always "Cease and desist" this and "We're the Times Square McDonalds, stop bothering us" that.

YouTuber cements head inside microwave oven

cray74

Holy crap. That poor kid. :(

Gah, and there were pictures of her hands.

Now I'm wondering why the YouTube rocket scientist didn't bake his head with the plaster. Better heat transfer with the head's large blood supply?

Opportunity rover survives Martian winter for eighth time

cray74

Re: Will Opportunity outlive Curiosity?

When Curiosity's nuclear battery runs out.

RTGs generally deliver useful power for decades, based on the Pioneer 11-12 and Voyager 1 & 2 examples. I'd expect something else would give out on Curiosity first, like its wheels, batteries, or flash memory.

cray74
Headmaster

Re: Martian Winter

For those readers younger than us

Or born on the wrong side of the Atlantic. ;) Thank you for the link, I'm now more educated in Cadbury products and extraterrestrial advertising campaigns.

cray74
Joke

Re: Martian Winter

Martians have a much more advanced cuisine.

I dunno. Expedition reports suggest that of all possible food crops, Mars' greatest botanist selected potatoes. With a side of ketchup.

Voyager 1 fires thrusters last used in 1980 – and they worked!

cray74

Re: Ancient assembler code checked out

....Why the surprise that code worked?

Because the modern users are unfamiliar with decades-old software and could screw it up?

Russian rocket snafu may have just violently dismantled 19 satellites

cray74

Does someone really have to mention bloody kerbels every single time any aerospace topic is being discussed?

There's few better ways to gain a visceral understanding of rocket failures and orbital mechanics than Kerbal Space Program. In this case, staging errors due to incorrect flight controller programming are common in new Kerbal booster design.

Every time someone relates something in the real world to a game

Aladdin Sane's XKCD reference is worth a look.

Give 1,000 monkeys typewriters, they'll write Shakespeare. Give them robot arms, and wait – they actually did that?

cray74

Re: WTF happened to these monkeys

But the monkeys have learned to control robots with their brains and humans haven't, and revenge will be theirs when the rise of the robots actually happens.

There's no way this could end well.

Forget Sesame Street, scientists pretty much watched Big Bird evolve on Galápagos island

cray74

Re: Without a robust definition of species

Looks like the arrogant jumped-up scienticians lose again.

David Wolfe, is that you?

How is 55 Cancri e like a Sisters of Mercy gig? Astroboffins: It has atmosphere

cray74

Re: "It has a mass of about eight Earths and radius of about two so it's no golf ball."

I don't think any SF writers ever thought of humans inhabiting planets of more than about 3g.

Well, Orion's Arm is a web group that generates modest profits from its anthologies, so it probably counts as "SF writers," and it does address high-gravity worlds with human (and modestly to greatly genetically enhanced human) occupants. OA's peak planetary gravities do tend to top out at 2-2.5Gs because it's difficult for rocky worlds to exceed that G-level without getting wrapped in super-thick atmospheres (1000+ bar of hydrogen and helium), but there are examples of more than 3Gs.

Superterrestrial worlds in OA

High gravity human "tweaks"

cray74

You keep using this word "Earthlike..."

"A new physical model has added more support to the theory that the large exoplanet 55 Cancri e has an Earthlike atmosphere."

55 Cancri e has an average daytime temperature of 2300C and an average minimum temperature of 1340C, which has me wondering if exoplanet studies are now using a rather broader definition of "Earthlike" than the (admittedly fiction-based) sources I followed in my childhood. What exactly is Earthlike about the planet's atmosphere other than being similar in pressure at 1.4 bars?

From Vega with love: Pegasus interstellar asteroid's next stop

cray74

Anyone know how the axis is oriented relative to the tube?

Just on principles: A highly elongated structure is generally more stable tumbling end over end rather than around one of its minor axes.

Chainmail tires re-invent the wheel to get future NASA rovers rolling

cray74

NASA used similar tech (without the titanium) on the lunar rovers.

Nitpick: the Apollo lunar rovers did use titanium. The steel wire mesh had about 50% coverage with titanium slats for traction.

cray74

Re: So how do you heat it?

The "shape recovery" magic property of of titanium alloys needs heat. The alloy has two temperatures:

True, the *shape memory* effect of the Nitinol family happens with heating. However, the alloys have another useful property: a huge elastic range, called superelasticity or pseudoelasticity. Most normal metals can stretch 0.2% of its original length and snap back to their original shape ("elastic deformation"), and any greater stretching results in permanent shape change ("plastic deformation"). Nitinol and friends can exhibit elastic deformations of up to 6%, or 30x that of other metals. This has nothing to do with the shape memory effect.

Hence Nitinol is used in eyeglass frames, bra underwires, and (now) space tires.

cray74

Have these types of wheels ever been implemented on any terrestrial form of transport?

No, because they have very short lives. The original Apollo rover tires had, as I recall, a life of some tens of miles. It was an award-worthy breakthrough in 2009 to develop similar tires with a range of several thousand kilometers. Which is still rather short compared to the life of a modern car tire (on paved roads.)

These metal tires are handy in space because they work over a wider temperature range than rubber. While there are polymers with very wide usable temperature ranges (I work with silicones and fluorosilicones used from -60C to +250C), their mechanical properties shift significantly. Rubber at -60C has quite different behavior than the same at 150C, even if you formulate them to avoid a ductile-to-brittle transition at the low end. Metal wires don't experience that change. (Before anyone says it, vacuum is not an issue for rubber tires. It's just a difference of another 14.7psi. The shuttle tires were kept in unpressurized bays while in orbit. Compared to their ~300psi operating presure, vacuum was a rounding error.)

On the other hand, metal tires experience wear and damage that would just bounce off (har har) a rubber tire. If you CAN use rubber tires because you're in a narrower temperature band (like on Earth), they're a superior option for durability and - usually - traction and ride compared to metal tires. There's just not many reasons to use metal tires on Earth.

Teensy weensy space shuttle flies and lands

cray74

Re: encountering just 1.5 times Earth gravity

Survivable? By what prithee tell...

20Gs is the norm for many current model ejection seats. It's tolerable for carefully seated and supported personnel for a fraction of a second. The ACE II seat supposedly only produces back injuries in 1% of ejections.

Metal 3D printing at 100 times the speed and a twentieth of the cost

cray74

As an engineer, I'd be very interested to know the material properties of the printed metal parts. (i.e. the tensile strength, shear strength, compressive strength, and the typical failure strains.)

My employer is just wrapping up some long-winded evaluations of 3D printed aluminum, titanium, and stainless steel, each of specific alloys from a specific 3D printing machine. (Each alloy, printer, and process technique gets somewhat different results.)

Generally speaking, a given 3D printed alloy will fall into the same vicinity of strength, elongation, hardness, etc. as the same alloy produced by other means (billet, bar, casting, etc.) If you 3D printed Ti-6Al-4V powder, it can have about the same properties as billet Ti-6Al-4V, give or take a bit.

However, there tends to be more scatter in properties in 3D printed parts. Even after trying treatments like hot isostatic pressing and tempering/stress relief/aging/annealing, etc., you get more scatter. The major reasons for the scatter are:

1) There's always more porosity in the final part than a conventional stock metal because you're welding together powder, and

2) You're basically working with a big piece of weld metal

Prior to heat treatment, there's also some variation in strength by direction. A specimen is stronger along the direction of deposition than across layers. My experience is that there's much less anisotropy in 3D printed metals (a few tens of MPa difference) than in 3D printed plastics (factor of 2 tensile strength difference between longitudinal and transverse directions), but that's speaking to specific 3D printing techniques. You can't fix the 3D printed plastics, but heat treating, especially HIPing can help metals.

There's also surface finish to consider. None of our evaluation parts went straight from 3D printer to Instron tensile tester or Charpy impact tester. The exterior was so rough that it was basically a stack of weld beads. So it went from 3D printer to CNC machine tool to finish the test specimen and then into the test rigs. Using the raw, printed metal would've had different properties before the polishing and prettying.

Basically, treat a 3D printed metal part with the care and concern you'd give a weldment or thick casting of the same material. It's more likely to have flaws, brittleness, and reduced elongation compared to properly worked billet material, but none of that means it's unusable and uncorrectable. With a good testing program, you can get A- and B-Basis mechanical properties for 3D printed metals that your designers can depend on.

And results are improving steadily - the 3D printed metals today are nothing like the porous, brittle crap from the 1990s.

Imagine the candles on its birthday cake: Astro-eggheads detect galaxy born in universe's first billion years

cray74

Re: Big, yeah but not the biggest ...

Arecibo Observatory 305m diameter.

Shirley you meant the 500-meter Aperture Spherical radio Telescope, FAST? Assuming you don't count the unfilled aperture 600-meter RATAN-600.

NASA reveals Curiosity 2020's 23-camera payload

cray74
Facepalm

23 cameras and yet...

NASA will still have to explain how the rovers can take a selfie. Five years on and every NASA Facebook rover selfie post still has someone screaming, "Fake! It's from outside the rover and no one else is there!"

C'mon, edgelords: The APIs are ours to command – do we do good or evil?

cray74

Re: Or...

You don't drive through twisty bits of city at 60kph...

Indeed. 100-120kph seems to be the local norm for the twisty bits with blind curves. 60kph on those roads is an invitation to have other cars park in your back seat.

cray74

Re: Errm, Cloudy Thinking ?

No sane automotive control unit developer would farm any life-critical function out to the "cloud".

"Hold my beer and watch this..."

Overheard at 2021 automotive developer's meeting, preceded immediately by the words, "We can get a 0.01km/L increase in efficiency if we move the weight of the control systems to the cloud."

Chinese whispers: China shows off magnetic propulsion engine for ultra-silent subs, ships

cray74

MAD!

Wouldn't magnetic anomaly detectors have a rather easy time spotting this sort of thing, or is there a submarine-friendly way to shield giant magnetic fields? Lots of mu metal?

Interstellar space rock screams through Solar System

cray74

Re: Interstellar space rock screams through Solar System

OK, but did anyone actually hear it?

Hubble got a pretty good shot of the bridge. No sound, but guesses can be made.

Li-ion batteries blow up because they breed nanowire crystals

cray74
Boffin

I think this discussion thread has more materials engineering data than my latest Advanced Materials & Processes journal. Thank you for an enjoyable lunchtime read.

cray74

Re: A double-whammy of success

So, not only do they now know how to view them, they also know how to prevent dendrite problems occurring.

If you include an electron microscope in every battery, sure. ;)

Curiosity rover gives Mars the middle finger, prepares to get drilling

cray74

I asked the tour guide at JPL why NASA seemed consistently to massively underestimate project lifetimes, including basing future expectations on past performance,

It's hard to make comparisons to past performance when most NASA probes are not duplicates of prior hardware. Each probe, or pair of probes, usually has a lot of new hardware that hasn't operated in the novel situations NASA throws them into. You couldn't use (for example) Voyager's performance to predict anything about the Curiosity rover, which differs in everything from RTG to computers to operating environment.

An example of the risk in estimating lifetime is found with Opportunity and Spirit. NASA estimated, based on Sojourner's quick demise due to electrostatic accumulation of dust on solar panels, that 90 days would be a reasonable lifetime for Spirit and Opportunity. They had clear past performance to guide this calculation. However, the Mars Exploration Rovers did not accumulate dust as fast as expected because they were taller than Sojourner. Further, Sojourner's short life did not give NASA the chance to experience the "cleaning events" that blow dust off MERs' solar panels and helped extend their lives by years.

In the opposite direction, Curiosity based its wheel design on the proven engineering lineage of Sojourner's and MERs' aluminum wheels. However, this design proved inadequate in the case of the much larger Curiosity, which is battering its wheels badly. While NASA had worried about dust wear at the hubs (addressing that concern delayed Curiosity's flight by two years), it didn't consider the rapid demolition of the wheels themselves. After all, they were well-proven by past performance.

I can make a guess what's going on with NASA's estimates for probe lifetimes: they're padding their estimates with factors of safety but only using the un-padded value. For example, I'm currently working on a team to develop an adaptor that will mate some underwing hardware to an aircraft that makes carrier landings. We have to certify the adaptor will endure a worst case carrier landing G-load of X G's, where X was given to us by the aircraft maker and US Navy. There's a minimum factor of safety in strength (x2.5) we could use if we put a prototype adaptor on a plane from the Boneyard and (in a quantified, scientific manner) tear it off the airplane. But that's a bloody expensive test, so instead we're using a larger safety factor (x3.75). There's also safety factors for the use of the large billet of metal (the interior properties of thick-sectioned metal drop compared to thinner material), the manner of assembly (e.g., welding knockdowns), and so on. By the time it's done, I'm fairly certain the adaptor could hold the hardware if the plane was flying in the clouds of a 75G brown dwarf star but we're only going to say, "Yes, we'll warranty this for X Gs."

NASA was probably hoping for years of service out of its MER rovers, but it had no prior examples of those exact models of rovers operating in Mars' environment. So, it was only going to guarantee and plan around 90 days of service, and set minimum success targets of 30 days. It got a little more hopeful with Curiosity (2-year target lifespan) but, again, it hasn't deployed anything like Curiosity before.

Hate to break it to you, but billions of people can see Uranus tonight

cray74

Childish Name

Are we really going to have to wait until 2620 for astronomers to rename Uranus to something less open to childish jokes, like Urrectum?

Please replace the sword, says owner of now-hollow stone

cray74

Re: I prefer the more mundane explanation ...

They're forged from metal bars heated, beaten and folded many times

Some swordmakers do that, especially the Japanese, who had to work with pretty crappy steels and the folding process helped blend the properties of hard, brittle steel and soft iron. Other swordmaking techniques welded together pieces without folding - an iron core, high carbon steel edges, and medium carbon skins. The Japanese did that, using their folded billets for parts but not all of the blade.

What does the Moon 4bn years ago and Yahoo! towers this week have in common? Both had an awful atmosphere

cray74

Re: Fly me to the Moon

The US spending hundreds of billions on the military budget whilst starving education and other social services certainly hasn't helped the economy, overall;

Please note that the US Department of Defense ($700 billion/year) is only the third largest department in the US federal government. It is smaller than two social service departments, Department of Health and Human Services ($1 trillion per year) and the Social Security Administration ($900 billion per year).

Overall, defense and security spending in the US amount to 17-18% of the federal budget (the total budget, not that "discretionary spending" pie chart circling teh interwebs). If you think that taking every penny out of defense for social services is going to fix the US's social problems, then you haven't looked at the shambolic state of the US's social services and what they're doing with more than $2 trillion a year, currently.

After seven-hour operation, the ISS has a new 'hand'

cray74

Re: 400 operations

surely at that price it is possible to provide a mechanism which survives more than 400 operations?

The second one, certainly. But you have to learn somehow and there haven't been space-based robotic arms that've gone through 400 wear cycles like this before.

NASA tests supersonic parachute, to help us land on Mars

cray74

Re: But how...

Would opening the chute at x miles up accurately replicate the conditions?

Yes, and it would do so better than a wind tunnel. NASA has had difficulties testing Martian parachute designs in wind tunnels because of difficulties matching Martian conditions.

Computers4Christians miraculously appears on Ubuntu wiki

cray74

Re: Direct link to Deity

Why do "believers" need computers ? Doesn't their Deity already provide them with a direct link to all that they need to know ?

In some cases the two are not mutually exclusive, at least in the mind of the believer. TempleOS is an interesting story, both as a retro computing exercise and of the person behind it.

(Terry Davis)'s done this work because God told him to. ​According to the TempleOS charter, it is "God's official temple. Just like Solomon's temple, this is a community focal point where offerings are made and God's oracle is consulted." God also told Davis that 640x480, 16-color graphics "is a covenant like circumcision," making it easier for children to make drawings for God.

The article goes into some depth about how Davis developed schizophrenia in adulthood, thought oil companies and men in black were following him, and eventually decided God was talking to him. God wants an operating system for direct consultations with his believers, and also likes beamers and the Beatles.

Musk: Come ride my Big F**king Rocket to Mars

cray74

Re: even if the price is possible - how much fuel would this lot need for mass transport

Would that not mean a PHENOMENAL amount of fuel? we may or may not have global warming now, but to burn methane to get lots of these rockets into orbit every day would surely be Huge

Given the limited size of the market for international, really fast flights that cost $10,000 or more, fuel consumption would not be large compared to the rest of the transportation industry. Airlines alone are using about $190 billion in fuel a year (ignoring the early 2010s spike), while a few rocket flights per day (at guestimated $10 million in fuel per flight) would only add a small percentage to that.

Hotter than the Sun: JET – Earth’s biggest fusion reactor, in Culham

cray74

Re: final PACER reactor concept was: make a big cave

Did Footfall inspire Orion or vice versa?

Project Orion started almost 30 years before Footfall was published.

Niven and Pournelle "Footfall": 1985

Freeman Dyson, "Project Orion": 1958

cray74
Mushroom

Re: We've already cracked fusion

...it's called a H-Bomb, we just haven't found a way to slow down time.

Yes, we did. You just need some mass to soak the heat from a fusion explosion, which leads to the PACER fusion reactor concept. Magnetic containment is for nerds. Real fusion reactors use concrete and steel walls. ;)

The final PACER reactor concept was: make a big cave, preferably in hard granite; pre-stress the rock with gigantic rock bolts; line the cave with ludicrous amounts of concrete and 4 meters of steel; and partially fill the cave with molten salts to about 30 meters depth. Begin circulating the salts into giant waterfall curtains to protect the walls. Drop in a fusion bomb, detonate. Circulate super-heated molten salt through steam generators, which drive dynamos. Repeat with another fusion bomb every 45 minutes.

Fusion bombs release a lot of energy, but it is a limited and calculable amount of energy. Muffle the bomb with enough mass and the mass will be heated to manageable, useful temperatures, and then you can extract the bomb's released energy in convenient time frames with conventional power generation hardware.