* Posts by cray74

992 posts • joined 29 Nov 2011

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Russia admits, yup, the Americans are right: One of our rocket's tanks just disintegrated in Earth's orbit

cray74

Re: Hopefully time limited

The main "could be worse" factor is that the perigee is quite low, so the orbit should decay reasonably fast.

Not as fast as a 400km circular orbit, unfortunately. With only brief dips to 400km, that second stage and its debris field could last decades. Recent Western practices for second stages are to get their perigees a bit lower or actively deorbit them (SpaceX) after payload release.

A nice database of debris entries and initial launch dates can be found here. Too many of those upper stages last decades in GTOs.

World's smallest violin to be played for opportunistic sellers banned from eBay and Amazon for price gouging

cray74

Re: Price Gouging: the free market libertarian perspective

when faced with a crisis the response is universally - for lack of a better word - socialist.

Indeed. On that note, there have been some excellent arguments for national healthcare and mandatory paid leave in the US based on the COVID-19 response. It's a lot easier to stay at home when you're not losing your job, and it's easier to get treated if you won't go bankrupt visiting the emergency room.

cray74

Price Gouging: the free market libertarian perspective

I saw an interesting argument to allow price gouging. To me, this argument sounds like a good way to encourage robbery and shopflight, but I'd love to hear more nuanced takes on this theory:

"Anytime you have a sudden huge increase in demand, like for toilet paper or hand sanitizer recently, the price must rise to reflect that. If it doesn’t, there will be shortages and empty shelves. We can whine on social media all we want, but this will ALWAYS happen if prices aren’t allowed to rise. Which they aren’t allowed to, because we have “price gouging” laws and social media scolds which will severely punish retailers who raise prices above some arbitrary metric.

"The reason for the inevitability of hoarding and empty shelves is because the market value of the toilet paper or hand gel is suddenly far higher than what it’s being sold for. Thus, there’s no penalty for hoarding and over supplying, because even if the hoarding isn’t ultimately needed, no one has overpaid for the product, and can just use the toilet paper in the future. So you have a prisoner’s dilemma-type situation. Everyone can scoff at each other for hoarding and say it’s unethical, but the first person who hoards benefits tremendously by buying goods at way under market value. ...

"What “price gouging” does is to raise the cost of the good to the market clearing price, which is critical because it lets everyone know what the actual value of the good is, and sends the proper price signal to consumers and producers. With higher prices, if you hoard you are paying a huge penalty for doing so and taking a huge risk, because if prices drop in the future you’ll be a giant loser. Few will stock up on gallons of hand sanitizer or pallets of TP if it costs them a fortune. Additionally, it sends a signal to conserve those valuable resources and shift behavior if possible.

"The other benefit to price gouging is to give producers a huge incentive to produce more. Ramping up hand sanitizer gel production is now much more lucrative than producing hair gel, for instance. Allowing prices to function allows the market to allocate resources to their most productive use, which is what we want, particularly in dire situations. We want producers to up the supply and drive the price back down. If no price signal is given, there’s little incentive to do so.

"Whining about and prohibiting price gouging does two things; it guarantees shortages and hoarding, and lessens the incentive for producers and retailers to bring more product to the market."

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Billionaire Bezos unveils plans to land humans on Moon, with a little help from some old friends

cray74

While everyone else is futzing about and getting nothing done, Space X is eating their lunch and actually launching rockets and all the other amazing stuff they do.

SpaceX does have fantastic public relations to go with their amazing hardware.

While SpaceX has been futzing around with its Starship to the point one of its customer had to yell at it to pay attention to its Dragon 2 contract, other companies...

1. Have won NASA's CATALYST contract for commercial cargo deliveries to the moon (Astrobotics, Intuitive Machines, and Orbit Beyond - not SpaceX)

2. Are developing and testing commercial lunar landers without NASA funding (Moon Express & Rocket Lab, the latter of which flies the proven Electron rocket)

3. Have been launching Atlas V rockets, testing the Orion capsule (in the atmosphere), and bringing in 4-5x SpaceX's revenue in the space industry

4. Have been launching Delta IV rockets, maintaining the ISS, developing the SLS, testing the CST-100 Starliner, and bringing in 6-7x SpaceX's revenue in the space industry

5. Have been launching Antares rockets and delivering cargo to the ISS with the Cygnus

6. Have been developing a new spaceplane for reusable orbital cargo delivery, the Dream Chaser

SpaceX is impressive, but it's a small company that represents a small part of the current aerospace market. Don't overlook the leviathans and upstarts around it, there's some fascinating stuff happening in aerospace right now and it's not all about SpaceX.

cray74

Re: The Future’s Bright

I suppose the silver lining is they are doing it under contract with NASA, not going the entirely lone way of Musk or Branson.

Musk has been raking in a fortune from NASA. When SpaceX was staggering after the near-failure of the Falcon 1 and was trying to develop the Falcon 9, NASA offered SpaceX the COTS contract for cargo delivery to the ISS. NASA flew the DragonEye docking system on the shuttle to test it out for SpaceX (missions STS-127, STS-129, and STS-133). The Crew Dragon / Dragon 2 is also dependent on NASA funding.

SpaceX is just following a long line of private companies in lining up for NASA's contracts. NASA doesn't have a rocket factory, so whether it was flying a Mercury-Redstone (Mercury capsule: McDonnell Aircraft Company, Redstone rocket: Chrysler Aerospace) or landing an Apollo LM (Grumman) on the moon, NASA has depended on private contractors.

Two astronauts conduct a successful spacewalk, world+dog lose minds

cray74

Re: Sorry Richard, you blew it

One of them decided WHEN IN SPACE ALREADY that she preferred the fit of a different size suit than the one she had chosen on the ground.

It is normal for astronauts to gain about 3% in height after some days in zero-G. An astronaut on the borderline between suit sizes might well gain a size when they're in orbit. That's not "a decision," it's a physiological change involving a stretching spine.

The small number of suit pieces on the ISS does represent a "parlous state" if NASA isn't accommodating that known effect on humans.

Oh chute. Doubts cast on ExoMars lander's 2020 red planet jaunt after another failed test

cray74

Curiosity

The Curiosity Rover also ran into parachute testing problems.

"And the parachute blew apart basically. So the [wind] tunnel is fine, but the parachute, uh, it's a loss." --Doug Adams (the other one).

The Curiosity team - which also assembled a team of Martian parachute experts - eventually decided that they were incapable of simulating Martian conditions in the wind tunnel. The air was just too dense and the parachute would work fine on Mars, but not terrestrial wind tunnels.

cray74

Re: Propulsive landing for the win

It beats me why NASA love parachutes so much. ESA's problems here highlight how unreliable they are.

NASA's track record highlights how reliable parachutes are. Parachutes worked successfully at Mars on Viking, Pathfinder, MER, Curiosity, Phoenix, and Insight.

As I recall, NASA's never had a failed mission because of the parachutes themselves unless you count Genesis, which was a sensor failure (acceleration sensor installed during test). They've certainly had failures during testing - Orion and Dragon both have had recent parachute test problems, as did Curiosity - but beyond Genesis I can't think of a NASA mission scuppered by its parachutes.

Rival rocketeers SpaceX and ULA make oblations to weather gods ahead of double-launch action

cray74
Pint

Atlas V Launch

Nice dawn launch. I saw it from about 100km due west of the Space Center. Perfect viewing conditions - I couldn't see the ISS flyover last night because of clouds, but the sky was completely clear this morning. In those conditions, you can see the exhaust plume really expand in vacuum as the rocket starts dropping toward the horizon. The boosters were visible as sparkling red dots as separation.

I wasn't able to get a clear shot, but I have snagged a few from teh interwebs:

Launch Shot Before the Space Whale Arrived

The Space Whale is Born

("Space whale" isn't my first choice of description, but I'm not sure how The Register would react to me comparing it to while, tadpole-like male germ cells.)

Bad news. Asteroid 1999 KW4 flew by, did not hit Earth killing us all. Good news: Another one, Didymos, is on the way

cray74

Have these people never played Asteroids? You always die in the end!

Only when I got bored of flipping the score over and over.

It's 50 years to the day since Apollo 10 blasted off: America's lunar landing 'dress rehearsal'

cray74

Challenger was not a failure of Congress

The root cause goes back to Congress on several levels. For example, during the 1970s four bids were submitted on the shuttle booster, with Morton-Thiokol's bid winning. NASA ranked Utah-based Morton-Thiokol's fatal booster design as fourth out of the four bids on technical merits and cost. Other designs, like Aerojet's monolithic boosters, entirely avoided risks present in the Thiokol booster.

However, Senator Frank Moss (Utah) was Chairman of the Committee on Aeronautical and Space Sciences, and controlled NASA's purse strings. Morton-Thiokol won the bid.

Three planets and two stars adds up to one research team made very happy by Kepler's unique discovery

cray74

Goldilocks screwed up a good deal, too

Habitable?

Just because a planet shows up in a "Goldilocks" zone doesn't mean it's automatically habitable. Venus and Mars are in (or near) Sol's habitable zone but screwed up their chances to be infested with humans due to poor choices.

Astroboffins spot hefty pair swinging together. What? Um, we're talking about record-breaking massive binary stars...

cray74

It did require some digging. Even the article with distance information buried it.

http://www.leeds.ac.uk/news/article/4379/massive_twin_star_snuggles_close_to_its_stellar_sibling

NASA pops titanium tea cosy over Martian InSight probe instrument

cray74

Re: Tea cosy hat

> They don't drink tea in France (or America)

My US employer's on-site mini-convenience store has a dozen different types of tea bags available, and the cafeteria serves 8 different flavors of sweet and unsweet teas. Since any size cup of tea is $1.00 I often avail myself of the 32oz/1-liter cups. That's enough calorie-free caffeine to get me started in the morning.

Boffins debunk study claiming certain languages (cough, C, PHP, JS...) lead to more buggy code than others

cray74

Re: poor tools can't be blamed?....sure, sure, suurrrrre

Going off on a materials science tangent...

> But that'd be like complaining that a vice designed to be sold cheap to mugginses-in-a-shed to generate business-profit, fell apart in the hands of people trying to do professional high-pressure high-temperature work

If the prior poster's claim that the vise had an ultimate tensile strength of 3,000psi is correct then the vise would fail in common, everyday use, not "high pressure, high temperature work."

3,000psi is the realm of unreinforced plastics. The softest aluminum alloys barely drop below 10,000psi (10ksi); 30-45ksi is typical and over 75ksi possible. Cheap, mild steels and cast irons you'll encounter daily in cars, steel cans, and fence posts should be 35ksi - 60ksi, while alloy steels like 4340 can nose past 200ksi and ubersteels like Aermet 340 perform above 300ksi. Not that titanium (Hollywood's darling) would show up in a vise, but common titanium alloys are in the 140-160ksi range, with some 21st century exotics broaching 200ksi.

Point being: 3ksi from a vise's steel ain't right. Some foundry screwed up in an extra special way to make that metal.

Japanese astronomers find tiniest Kuiper Belt object yet – using cheap 'scopes and off-the-shelf CMOS cameras

cray74

Epic find, but...

...for their next feat of perception can they find the sock that went missing in my last load of laundry?

Killer superbugs in space... are something astronauts on orbiting science lab don't have to worry about right now

cray74

Mir

Not a mention of Mir's slime-mold-bacteria problems, or did I skim too fast? Mir had mold growing across its windows until they were unusable and blackening insulation. It was a seriously unhealthy space station in its last years.

New Horizons snaps finish buffering: Ultima Thule actually two dust bunnies that got snuggly 4.5 billion years ago

cray74

There was a time about 50 years ago when a modem with that speed was considered almost impossibly fast.

Heck, I irritated friends by bragging about a 2400-baud modem in the late 1980s. It gave me a serious advantage over their 1200- and 300-baud modems when playing the text-based Galactic Empires on BBSs.

A few reasons why cops haven't immediately shot down London Gatwick airport drone menace

cray74
Paris Hilton

Re: How about a high power laser burst ?

The Mercians have been bombing Afghan weddings from the comfort of the American midwest.

I thought the Danes took care of the Mercians a bit before drones became a common element in warfare or lodging stern objections to weddings.

The Palm Palm: The Derringer of smartphones

cray74

Re: "useless coin pocket" ?

a naildriver, because it does everything you could possibly want to do

If you have a moment, would you mind sharing the make and model of the naildriver? I've gone through a lot of pocket tools and settled on, basically, a folding knife because most of the others weren't useful. Something less stabby and alarming to coworkers would be appreciated.

Astroboffins spy a rare exoplanet evaporating before their eyes

cray74

If you could bottle that...

Several billion years to evaporate down to its rocky core? That's still faster than my diet.

Falcon 9 gets its feet wet as SpaceX notch up two more launch successes

cray74

Re: NASA has concerns over SpaceX culture??!?

but they've sat on their ass and not done any significant basic rocket research since the '70s WHICH IS THEIR JOB

What do you define as "significant basic rocket research?"

NASA has been steadily testing rocket engines, propellants, and structures since the 1970s. Aerospikes, composites, exotic propellants, new engine cycles - they all get tested at NASA. And it hasn't ignored the atmospheric side, either. Whether it's looking into quiet supersonic transport or more efficient jet engines, aircraft and engine makers benefit strongly from NASA's ongoing research.

But then there's that valley of death in implementation. A new rocket is billions of dollars of investment, so how is NASA supposed to apply some great innovation if the commercial world doesn't want to spend $5 billion on a new model rocket and the White House or Capital Hill deletes the moon/Mars/space base program that needed the rocket?

They've talked about recovering boosters FOREVER and not done it.

NASA recovered very large boosters over 130 times. I work with some of the team members that cleaned up and prepped those recovered boosters for the next launch. If you want NASA to build additional recoverable boosters of some new form, then I'd suggest:

1) Get Congress to secure several billion in funding

2) Get a commercial partner to build the boosters, because NASA never had a significant rocket factory

3) Get Congress to not cancel the years-long contract after the next election

All NASA can do in such an organization is lobby, plead, and argue for money. It doesn't set the federal budget that decides how it can innovate.

And Gemini was supposed to be recovered by parasail, and they bottled out again.

The short version is that Gemini's Rogallo wing development was slower than the rest of the program. They had a spaceship ready to fly while the Rogallo wing was still failing. Rather than let that hold up the program, NASA "got'er done" with plan B: parachutes.

The longer version is that while the Gemini capsule developed rapidly the Rogallo test vehicle ("Parasev") handled poorly in the air, crashed, and had a steep learning curve. (Gemini wasn't using proven commercial Rogallo hang glider technology. Instead, it was developing the technology that would lead to Rogallo wings in hang gliding use.) And just as the Parasev started working well, the Rogallo wing-equipped Gemini capsules were running into problems. Wind tunnel tests showed the capsules' wing liked to disintegrate in adverse landing conditions. (Solution: only land in nice weather.) Beyond the wind tunnel tests, there were problems with deploying the wing in real world conditions, which led to destruction of test vehicles.

Instead of spending another couple of years ironing out the Rogallo wing, NASA launched the Gemini capsule with parachutes and the USAF looked into "Winged Gemini." It was a get'er done attitude that didn't let technological setbacks or paperwork hold up the program. Speaking of which...

Commercial crew is ready to go, except NASA can't get the paperwork together.

NASA has the blood of 17 astronauts on its hands from other times when it decided to ignore the paperwork and just go ahead with the test or launch. Apollo 1: rushed too fast, numerous deficiencies in blueprints, testing and safety, three dead astronauts. Challenger: ignored the flight data that said the SRBs had a leakage problem and ignored the spaceship's manufacturer's paperwork that said, "Shuttles are not meant to launch in this weather," seven dead astronauts. Columbia: smoothed over safety briefings identifying risks in heat shield damage, seven dead astronauts.

Now, NASA is responsible for vetting US-built spacecraft as safe for human flight. It probably is going to go a bit slowly.

cray74

Re: Bowl of Rice?

Seriously, have you looked at that URL you pasted?

Apparently not the way you meant. The chain was:

Google Image Search: Bowl of Rice SpaceX

Look for the amusing pic found on Facebook of a Falcon 9 in rice: no luck

Look for another pic of tech in rice: found many

Look for page not flagged by security: found some

Look for short-ish link that isn't 7 lines of text long: found several

Paste in to Register post with bits of code

Test link when Previewing message: opens without problem, pop-ups, or security warnings

Submit

cray74
Headmaster

Gruesome Post-Mortem

While SpaceX is interested in the failed hydraulic pump on the grid fin, I would love to see what happened to the single engine that was running when the Falcon 9 stage dropped into the water. The thermal shock, hot corrosion, unplanned back pressure - that'd make for an interesting materials failure analysis.

Naked women cleaning biz smashes patriarchy by introducing naked bloke gardening service

cray74

Re: Doesn't everything green have thorns in Australia?

What kind of gardening are they doing, trimming some bushes and plucking some fruits?

My brother runs a lawn care service on the side in Florida. It is a dirty, sweaty job that is the antithesis of sexy. Just normal mowing, even with a catcher bag, produces a cloud of dust and grass duff that gets everywhere. The cloud of lawn shrapnel gets more exciting when the yard's owner has a dog, which tend to leave fragrant landmines for the mower to trigger.

And sweat - it was cost effective for him to buy a hotel-scale ice maker to fill his ice chest rather than collecting drinks and 10 pounds of ice from a store every morning.

FYI: NASA has sent a snatch-and-grab spacecraft to an asteroid to seize some rock and send it back to Earth

cray74

Re: Serious Question

Care to explain how much gravity that 500m diameter accretion of dust and mystery is generating,

10 micro-Gs according to Wikipedia's physical characteristics panel on Bennu. It also has density and mass values.

and how much effect that will be having at 7 kilometers distance ?

Not much. Wellyboot already provided the reference showing Osiris is in orbit around Bennu, but there are times where the various asteroid and comet chasing probes aren't so much "orbiting the object" as "strolling around the sun beside it." Hayabusa hovered beside Itokawa for a while, and Rosetta hovered off 67P/Churyumov–Gerasimenko before some of its orbital operations.

cray74

It won't contain any clays unless I'm more out of touch with notions on how bodies form from a stellar accretion disk than I realised.

Asteroidal clay has been proposed for radiation shielding. Unfortunately, my lackadaisical search didn't find any substantial papers on clay and asteroids, just discussions that assumed the clay existed.

cray74

there is less than a 1 per cent chance of that happening, based on current data

So you're telling me there's a chance!

NASA's Mars probe InSight really has Mars in sight: It beams back first pic after touchdown

cray74
Trollface

Re: I Am Spartacus

3. the image was *embedded* *in* *the* *story*.

So, wait...where can I find these images you're talking about?

cray74

Re: Well done

They keep a lens cap on to protect the under-deck camera from the dust that blown up during landing.

The rockets are no joke. Despite all the efforts to protect Curiosity, including using the "sky crane" design, Curiosity's wind sensors were damaged by flying debris during landing.

What the #!/%* is that rogue Raspberry Pi doing plugged into my company's server room, sysadmin despairs

cray74

Re: easy pickings

My email (username) and password still worked.

Wow. At the other end of things, when a downsizing caught me my access was cut-off mid-email the morning I was booted out the door. While I was getting the bad news from HR (over the phone, because the local HR rep had been laid off before me), I had been trying to email coworkers to pick up my remaining tasks and notify customers. But IT had deadlines to cut access and happened in the middle of the call.

Since the company had been shriveling for some time they had apparently dealt with a number of emails from terminated employees that contained less-than-professional departing comments, hence the hurry to cut access.

Subsequent emails from the company, such as for termination benefits, went to my personal email address.

Big Falcon Namechange for Musk's rocket: BFR becomes Starship

cray74

Re: You'd have to be a Dummy,....

DC-X was demonstrating vertical rocket landing in 1980s

The DC-X first flew, for 59 seconds, on 18 August 1993.

and still need be completely disassembled and rebuilt after landing.

The DC-X, Falcon 9, and New Shepherd all reuse(d) engines without significant rebuilds between flights.

cray74

Re: You'd have to be a Dummy,....

SpaceX - we took nine exactly same rocket booster NASA designed in 1960 for Lunar module

Saying the Merlin is exactly identical to a LEM engine is like confusing the 5.2 L Aston Martin AE31 twin-turbocharged V12 for a VW Bug's 1100cc H4 because they both use pistons. Yes, it's true, they're both piston engines. They're not exactly the same, not even the piston design.

Specific to the rockets, a few points:

1) The Apollo LEM's descent propulsion system was developed by the private company Space Technologies Laboratories (TRW), not NASA.

2) The SpaceX Merlin engines shared the same style of propellant injector, a pintle injector, as the LEM's descent propulsion system, but SpaceX's injectors differ in alloy, size, shape, and design.

3) Merlin engines use different propellants than the LEM's descent propulsion system

4) Merlin engines have vastly more thrust than the LEM's descent propulsion system

5) Merlin engines use turbopumps to deliver propellants, which differs from the pressure-fed LEM descent propulsion system

6) Merlin 1C and later engines are regenerative cooling, which differs from the ablatively-cooled LEM descent propulsion system

7) Merlin engines use a different combustion chamber design than the LEM's descent propulsion system

8) Merlin engines use a different nozzle design than the LEM's descent propulsion system

9) Merlin engines use different alloys than the LEM's descent propulsion system

The Merlin engine shares a single general detail with the LEM's engine, which is a pintle-type injector. It differs in all other major aspects of rocket engine construction: thrust, propellants, pumping method, cool design, and construction techniques.

Holy moley! The amp, kelvin and kilogram will never be the same again

cray74

Re: Sad case of science ignoring the evidence

Except both platinum and iridium are more expensive than gold.

Now, yes. However, platinum used to be considerably cheaper than gold.

cray74

Re: @A.P. Veening Economists - In 1889?

But the ideal keel material would be osmium.

Osmium oxidizes too easily and its common tetroxide is poisonous. It also only offers a slight density gain over platinum, which is more common and better behaved chemically, and only a modest gain over tungsten and uranium.

Another approach to enhance sailboat performance is switch to a multi-hull so you're not burdened with a heavy keel.

cray74

Re: @A.P. Veening Economists - In 1889?

If I was a billionaire, I think I'd have a boat with the heat exchangers made out of platinum iridium alloy, because I could. No corrosion worries.

If the rest of the boat is made of non-platinum group metals then you'd need to be careful of galvanic (dissimilar metal) corrosion. Platinum's at the far end of the galvanic series so it's a threat to most other metals. It's relatively easy to address if you can separate the metals with non-conductive barriers (e.g., paint), but I wouldn't say "no worries."

Douglas Adams was right, ish... Super-Earth world clocked orbiting 'nearby' Barnard's Star

cray74

Re: As for ion drive, where do you propose to get the energy from?

If you can use a planet's gravity to slingshot (i.e. accelerate) a probe, why couldn't you use one to slow it down too?

Periapsis burns are standard practice for capture. Cassini and Galileo both depended on planetary gravity to help their captures.

Rocket Labs mean business, Brits stick pin in Mars map, and Japan celebrates HTV-7’s dive into the atmosphere

cray74

Re: Hippy-friendly hybrid-electric rocket motors

and as each one is depleted it is jettisoned

Cool, I didn't know that.

cray74

Hippy-friendly hybrid-electric rocket motors

I'm still boggling at the use of electric turbopumps on the Rocket Lab's Electron, but if you only need 1 megawatt (those 9 engines are tiny) for about 2 minutes then that's about 33kWh and not too bad.

The engineering and development advantages are interesting. You entirely eliminate all the turbomachinery of the fuel pumps, so that makes development easier. You're not diverting propellant to run turbines, so the engine can gain efficiency without the plumbing complications of a staged combustion engine.

The drawback is a heavy battery pack, but it'll be lighter than an electric car's because you don't care about reusability and good recharging characteristics.

I wonder how electric pumps would scale to larger rockets that use turbopumps in the tens of megawatts.

I found a security hole in Steam that gave me every game's license keys and all I got was this... oh nice: $20,000

cray74

Re: Tsk tsk tsk

Elimination of intellectual property law equals life upgrade for the entire world

Or quick development of coercive monopolies. If you take regulations out of the picture, then historically the groups that tend to profit the most are those who have lots of money and legal clout to make their own rules.

In news that will shock absolutely no one, America's cellphone networks throttle vids, strangle rival Skype

cray74

A couple of Net Neutrality questions from a non-IT sort:

1) Is throttling or blocking allowed for an infected device spewing malware under the US's Net Neutrality rules?

2) What is the UK equivalent of the US's Net Neutrality regulations?

FYI NASA just lobbed its Parker probe around the Sun in closest flyby yet: A nerve-racking 15M miles from the surface

cray74
Paris Hilton

Re: Glad they got there OK

I was worried they were going the wrong way when they launched it at night.

If they had really sent Parker to the sun at night then couldn't they have done away with all that heavy heat shield mass?

.

.

.

I will forever regret not using that question at a Q&A with a representative of the ESA's Solar Orbiter team.

cray74

Re: So what I'm wondering now...

But is velocity still a Constant in these circumstances?

No. As you noted, the probe accelerates (changing speed and heading of the velocity vector). From this plot of Parker's course, you can see how the time intervals change with position. It takes longer to cover the same distance when further from the sun - Parker slows down. Another plot also shows distance (in solar radii) and time, with zoomed in section of the closest approach.

And as noted in the font of all human knowledge, Parker is barely puttering along at Venus (26km/s) but accelerates to 120km/s near the sun.

So, in short: Parker moves much faster at periapsis (the close point to the sun) than at apoapsis (furthest point).

Astroboffins spot one of the oldest, coolest stars in the universe lurking in the Milky Way

cray74

Re: Hydrogen is a *good* coolant

because its low density, high specific heat, and high thermal conductivity make it a good coolant.

I was going to say the same thing. I wonder what makes hydrogen a poor coolant in space.

Dawn of the dead: NASA space probe runs out of gas in asteroid belt after 6.4 billion-mile trip

cray74

Re: Dear NASA

Satellites could use a backup Electro-Magnetic drive to putter back to Earth orbit.

Nope, since the electromagnetic drive has been debunked.

cray74

Re: This seems like a good argument for ion drives

What I'm curious about is whether it also has reaction wheels or similar for attitude control, whether those had also failed.

Yes, and yes.

The third of four reaction wheels failed in 2017. Dawn has had reaction wheel failures throughout its mission. At Vesta, wheel failures led to "hybrid" thruster/wheel operations, and the approach to Ceres was an odd overshoot-and-return because Dawn couldn't perform a typical spiraling ion engine capture orbit with (then) two functional reaction wheels.

Core-blimey! Riddle of Earth's mysterious center finally 'solved' by smarty seismologists

cray74

Re: out of curiosity

carbon steel is a completely different beast to iron and only has 2% carbon in it

Nitpick: the vast and varied family of alloys known as "carbon steel" covers steels with 0.05 to 2.1% carbon. With more carbon they're called "cast iron" and below that they're just iron...or steel. Some steels (especially some of the stainless family) hate carbon and try to exclude it.

More on topic: While the many other elements in the core are worth considering, it is hard to do so. Even for a fixed alloy composition, mechanical properties, magnetic properties, and even chemical properties will vary by temperature, pressure, and time, hence the T-T-T (Time-Temperature-Transformation) diagrams used in metallurgy for plotting heat treatments. You can get substantially different properties for an alloy held at high temperatures because of different crystal structures, different amounts of segregation of alloying elements, and other microstructural changes.

The problem with estimating the impact of other elements on the core's properties is that a) the exact composition is unknown and variations smaller than 0.1% can be significant; b) the core sits at a combination of temperature and pressure way off the usual metallurgy charts; c) it's hard to even simulate the core's conditions for more than a fraction of a second in diamond anvils or nuclear explosions, which makes normal metallurgical tests** challenging; and d) there are probably regional variations in composition just like the crust and mantle, and there are certainly temperature and pressure variations across the core's radius.

So it'd be hard to fault geologists for approximating the core as a big lump of nickel-iron. They do, on occasion, allow for the presence of uranium and potassium-40 to help estimate the radioactive heat budget of the core.

**My lab's Instron tensile test rig has a small environmental chamber fit for -100C to +600C at one bar of pressure (air or clean, dry nitrogen). There might be error if its results were extrapolated to the core's conditions.

Leaked memo: No internet until you clean your bathroom, Ecuador told Julian Assange

cray74

The US has the highest incarceration rate of any country in the world yet also the highest crime rate in the OECD

Crime RATES or total number of crimes? The US undoubtedly has higher murder rates (absolute and per capita) with only the OECD's Turkey giving it a challenge on a per capita basis, but its rates of property crime (burglary, mugging, theft) and assault are less exceptional on a per capita basis. The UK, for example, has higher burglary and robbery per capita than the US.

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