Wikipedia:Reference desk/Archives/Science/2017 January 3

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January 3

Why don't they just put parachutes on rocket stages to make them reusable?

I'm aware this used to be done with the Space Shuttle's solid-rocket boosters, and was proposed for SpaceX's Falcon 9's first stage before they decided that it wasn't feasable (apparently the stages sank to the bottom of the sea) and instead would land the first stages on barges (with interesting names to boot). Why don't they just improve the parachutes or the designs of rockets so that they could easily be reused through splashdowns in the ocean? If it could be done for the Shuttle SRBs, why can't it be done for other rockets like the Atlas and Delta rocket families? Narutolovehinata5 ^tccsdnew 03:01, 3 January 2017 (UTC)

• I speculate here. The shuttle boosters were extremely simple solid-fuel rockets with essentially no moving parts, and thus much affected by immersion in salt water. SpaceX uses liquid-fueled rockets, with complicates pumps that may be difficult to engineer for salt-water immersion. In addition, it's not clear that shuttle booster reuse was actually cost-effective: it was basically a stunt to make the system appear to be more "reusable" than it actually was. the origina goal of the system was total reuse, for example by using a manned first stage which could be landed and re-used. -Arch dude (talk) 03:38, 3 January 2017 (UTC)

Also, for second and subsequent stages, the speeds and altitudes they attain become a problem for their reuse -- they fall through essentially the entire atmosphere (therefore part of their fall is equivalent to an atmospheric reentry), and at such high speed that kinetic heating becomes extreme. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 05:12, 3 January 2017 (UTC)

Kenneth W Gatland covers this very subject in one of his books (either Frontiers Of Space or Manned Spaceflight). The idea was mooted by NASA after a large chunk of one of the Gemini rockets was found floating. NASA came up with several proposals for the Saturn series, involving both water and land landings. The addition of parachutes, heat shields, landing floats, landing bags, etc all reduced the useful payload of the mission. The extra monetary cost was a factor too. Check back in a couple of days and I'll dig the exact book out. --TrogWoolley (talk) 12:23, 3 January 2017 (UTC)

OK, so I've found the book. In Frontiers Of Space (Philip Bono & Kenneth Gatland), page 153/4 "Some time ago, after the launching of a Gemini spacecraft, a 24 ft (7.3 m) section of the Titan II rocket, weighing 1,500 lb (680 kg) was discovered floating in the Atlantic. It was the first major section of a space booster to be inadvertently recovered in reasonably good condition." This is probably what spurred NASA into considering recovering boosters.

The book goes on to say "During the first phase of the flight-test program, a minimum-weight ocean-recovery system for the S-IVB would incorporate a modification kit weighing 6,500 lb (2,960 kg). The scheme is illustrated on pages 60-61. Included in this kit would be propulsion for stabilizing the stage in orbit, retro-rockets for the de-orbit manoeuvre, a heat shield for protection during re-entry, and three 80 ft (24.4 m) parachutes to ease the 58 ft (17.7 m), 15 ton (13,600 kg) stage into the sea."

Obviously the recovery kit means less useful payload to orbit. The book also mentions salt water contamination of the recovered stage adding to the cost of reconditioning. The book describes a land recovery system too, consisting of retro-rockets (2,950 kg) 8.5 m ballutes, heat shield, three 37.8 m parachutes, a crushable aluminium honeycomb 'bumper' fitted behind the heat shield and four extensible legs to prevent the booster tipping over on landing. All up weight of this kit, 3,580 kg. --TrogWoolley (talk) 22:54, 5 January 2017 (UTC)

Hex bar

In what sizes (thicknesses) are stainless steel hex bars commonly available here in the USA? (Also, would that be measured by edge length or by diameter of circumcircle?) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 06:08, 3 January 2017 (UTC)

Here Fastenal's online catalog says "Hexagonal bars are measured by the distance across the flats" (see also their product spec) and lists various grades of stainless steel hex-bar stock with diameters ranging from 1/4" to 1-1/2" in various increments[1]. DMacks (talk) 06:20, 3 January 2017 (UTC)

The cited specification sheet describes a bar in low carbon not stainless steel and the drawing suggests the bar circumcircle diameter "A" is measured not the width across flats. Another supplier OnlineMetals offers a range of stainless steel grades and hex bars in a range of sizes measured across the flats (example) in inches or millimeters. For some purposes a stainless steel long nut may serve; here are examples which are widely available in all common nut sizes. Blooteuth (talk) 11:29, 3 January 2017 (UTC)

Thanks! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 11:42, 3 January 2017 (UTC)

I'm not here to draw judgement about contractory or mis-linked content from within a company's own catalog site:) DMacks (talk) 19:28, 3 January 2017 (UTC)

Why use less paper and more eletricity is good for earth?

People always say use less paper to save trees. End up use computers, iPads and phones to read and write. Why is good for Earth? Maybe cause eletricity can get from sun, water and wind? --Curious Cat On Her Last Life (talk) 12:28, 3 January 2017 (UTC)

We may be forced to use paper in the not too distant future. Here's why:[2]. 2A02:C7F:BE2B:5600:2406:BE05:ECF1:D323 (talk) 12:35, 3 January 2017 (UTC)

I think it's so that spies could more easily find out what they want to know about you, simply by hacking into your computer and stealing your documents (as opposed to going to all that trouble with physically going to your home or office, picking locks, cracking safes, taking photos of your documents, etc., etc. -- which is both time-consuming and risky). Same for the whole brouhaha about "cloud computing" -- it's easier (and more productive) to hack into a big public server than into someone's own personal computer, no? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 13:03, 3 January 2017 (UTC)

There is much truth to that now, but the drive to "go paperless" strikes me as a 90s thing, long before the records were readily accessed remotely. (I mean, hacking into someone's modem to get at data on a floppy disk can't be done 24/7 at least) I think it started off more as a feel-good sales tactic made by people who knew all the nasty bits described at computer recycling (and had no intention to recycle) but knew how to make customers feel proud of themselves. And, yes, it also really does let businesses get rid of their filing rooms and have a smaller, cheaper footprint that is easier to close out after some competitors duplicate it all in Guangdong. Wnt (talk) 13:36, 3 January 2017 (UTC)

The cloud is totally safe, as long as the only stuff you put there is stuff you would be happy for everyone in the world to have a copy of. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:02, 3 January 2017 (UTC)

The push to use less paper began in the 60s. A famous song of the time claimed that it wouldn't be long that the last trees would be cut down and you'd have to go to a museum and pay if you wanted to actually see a tree. 209.149.113.5 (talk) 14:23, 3 January 2017 (UTC)

• The above replies look offtopic, as the original question seems to be about which is the most environment-friendly, of paper or numerized storage. Surprisingly, the internet does not seem to have a ready-to-go answer, so here we go.

First of all, there are as usual a lot of tricks to this comparison. For instance, paper requires trees to be cut; that is not a problem if they are grown again in a well-managed forest, but deforestation is a real issue in other places (see this WWF report, even if it is not a neutral source). The electricity in use for the computer option could come from lignite (lots of CO2), or solar power (not much CO2, but depending on the technology, uses a lot of rare earths extracted in non-green conditions), or nuclear power (not much CO2, but radioactive waste, and unhappy neighbours). Also, depending on which type of information you want to store, a computer format can be efficiently compressed. It is easier to copy-paste one gigabyte of data on your external hard drive than to photocopy a full dictionary, so you might be more liberal with digital copies and make - say - 5 copies of the same file for backups - hence, you "pay" the storage costs 5 times compared to the paper alternative, but that's for a useful function: should the cost be multiplied by 1, 5, something in between?

With that in mind, let's talk purely in CO2 emissions, based on the average for everything.

Wonk alert: calculations

[3] has numbers, but for India (see table ES.5). For 8Mt of CO2 released in the atmosphere, we get 12 Mt of paper-y production (including things like cardboard, but they are counted in the emissions as well). I have no real idea whether India's paper production is efficient or not compared to other countries, but let's go with 1.5 paper to CO2 mass ratio. Per ISO_216#History, Since an A0 sheet has an area of 1 m2, its weight in grams is the same as its grammage, and Grammage, let's assume 80g per A0 sheet, or 80g/(2^5) = 2.5g per A4 sheet. Being generous and rounding down 2.5/1.5 to 1, we get a nice and round estimate of 1 g of CO2 per sheet of paper. Finally, going by [4] and assuming 4000 characters per sheet (generous), we get 250g of CO2 to store 1MB of data in paper format. Remember that this includes only the emissions associated with the production process, not transport, ink printing, etc., but it seems that it is the main emission center for the paper life cycle. On the other hand, how much CO2 does our computer solution use? [5] estimates that the average energy cost to transfer 1MB over the internet is around 3 watt-hour (III.A, "energy intensity" between 2.17 kWh/GB and 3.61 kWh/GB). [6] gives the electricity-to-carbon conversion under various assumptions; let's take (fig 1) dirty coal at 1 gCO2 / Wh, this gives 3g of CO2 to transfer 1MB of data over the internet. That is a one-time (or maybe two, three-times) carbon cost, not a recurring one, and it is fairly negligible compared to the paper solution. If you transfer the files locally, it should also be better energy-wise than packets hopping all around the Web where multiple servers have to stay up and running (modern external hard drives I found online indicate a few watts of consumption in full use, and take at most a few seconds to transfer 1MB, so a factor of 1000 sounds plausible.) As for the carbon cost of producing the hard drive (or whatever support) that holds the files, I could not find any plausible number. If I use [7] (seemingly not a reliable source, in French), it gives (§6) the number of 0.04gCO2/MB/year for the storage on an email server. That number probably assumes a big data center at a large scale (hence, better efficiency) but also "accessible at any time"; if that number is correct, then the cost of storing itself is fairly low. It means that in 100 years' time, the storage will have costed in emissions about as much as the initial transfer; although paper is "free" to store emission-wise, at that timescale it will surely start to degrade.

So, all said and done, computer storage seems to be better by two orders of magnitude, with around 5gCO2/MB vs. paper's 250gCO2/MB. But again, it depends on a lot of hypotheses. Tigraan^{Click here to contact me} 18:18, 3 January 2017 (UTC)

You may want to skim the review article I link below. While your WP:OR analysis seems reasonable, it is very simplistic, compared to what researchers in the field are doing. Also, please follow WP:INDENT and WP:THREAD. Since your first-level comment was posted after my first-level comment, it should have been placed below. I'd move your comment to fix it, except that my answer is well-referenced and on topic ;) SemanticMantis (talk) 18:49, 3 January 2017 (UTC)

That was weird. Your comment is indeed timestamped well before mine, yet I did not get the usual "edit conflict" warning (nor did I overwrite it, even though I started typing before yours was posted).

I did skim the review article, but (unsurprisingly) the conclusion is "it depends on a lot of assumptions". Tigraan^{Click here to contact me} 08:57, 4 January 2017 (UTC)

It's not that simple. Some paper can be grown sustainably. See sustainable forestry. Some electricity can be generated sustainably see sustainable energy. While sustainability is not exactly the same as "good for earth", it's closely related. To really get at the net result, and environmental impacts, we need to look at life cycle analysis (LCA). Often, as a proxy for all the other impacts, researchers look at carbon footprint. Here are a selection of research articles that discuss how paper and digital technologies affect the environment [8] [9] Here [10] is review article that summarizes many LCA studies that compared digital to paperless processes. Hope that helps, SemanticMantis (talk) 17:39, 3 January 2017 (UTC)

To complicate it more, an anecdote... Wesvaco suffered through the 80s as the paper reduction efforts gained steam. They were eventually purchased by Mead. Then, the paper reduction efforts increased more, and Mead was suffering. Then, the Internet became a thing and newspapers began suffering, which directly causes problems for the paper industry. Then, Mead-Wesvaco began selling off large chunks of their forests that they use for paper. The trees were cut down and the land was developed. So, the "save a tree" movement caused deforestation by not supporting the purpose of the paper forests. I'm sure there are more anecdotes that both support and contradict this series of events, but I just want to point out that it is very complicated. Using less paper does not necessarily save any trees. 209.149.113.5 (talk) 18:33, 3 January 2017 (UTC)

• The cost must include the cost of physical storage. If the data is fairly ephemeral, the paper's life is short (e.g., a newspaper delivered to a home.) If long term (e.g., a hardbound book in a library, business records or vital records) the storage costs are large. A big book might have 1000 pages of 1000 characters, or 1MB, so you can store a million books on one 1TB hard drive. a million books or equivalent for other records therefore takes a medium-sized wharehouse, which must be kept at the correct temperature and humidity, which takes quite a bit of energy. To be useful, this information must be retrievable. This is quite expensive, especially if it is to be accessed from multiple locations. You must either replicate the physical warehoused in multiple locations, or you must allow for scanning and electronically transmitting the images, which sort of defeats the purpose. On a personal level, I had a 30'x30' library in my old house. My new house has a total area of less than twice that. The cost of that extra 1000 sq.ft must be treated as the extra cost of paper storage. -Arch dude (talk) 21:24, 3 January 2017 (UTC)

Then also we must note that paper can do fine on its own for centuries, whereas digital data takes lots of manpower to maintain integrity and accessibility on the scale of decades. All that manpower costs money and carbon footprint too. (Has anyone recently accessed a floppy disk written in 1992 then left on a shelf? I read books printed before then all the time :) SemanticMantis (talk) 22:48, 3 January 2017 (UTC)

Some forms of paper can "do fine for centuries" under some conditions. Other papers under other conditions cannot. You can recopy a 1TB HDD for less than $100, using less than $50 of labor, and it will last at least 5 years: call it $100/yr, total, to be generous. Maintaining a million books in an adequate environment will cost you a whole lot more than that. Just as with your floppy disk example, we have lost a lot more thant that when it was stored only on paper. See, for example, the National Personnel Records Center fire. Yes, floppies (and lots of other offline media) were vulnerable, but any more modern system allows for trivial automated backup. Another counterexample is color photographs. Your pictures from the 1970's are fading and losing color, while your digital photos are not. -Arch dude (talk) 02:00, 4 January 2017 (UTC)

Call me when you access a 50 year old digital photograph that has had no yearly preservation. See also data curation, data degradation, and data steward. If you want your great-grand children to see your photos, you are far better off printing them on acid-free paper with a good printer, then putting them on the shelf, because if you do that no other action is necessary, but if you put them on a hard drive, you'd have to ensure time and money of future generations is spent. SemanticMantis (talk) 15:32, 4 January 2017 (UTC)

Err, that is a bit unfair; digital photographs did not exist 50 years ago. You may have a point that digital data is more degradable than its support though. If late 2013 counts as "recently", I did read a floppy disk back then, which had been left at the back of a garage, and its files were intact as far as I could tell (I cannot tell the date of writing either, but it was a floppy disk, so likely pre-2000); however, that is an anecdote, I may just have been lucky.

On a side note, I have not redone my calculations above, but photographs are a waaaay bigger "disk space per A4 paper" ratio than text (and still lower than videos, since individual frames of a video are highly correlated, there are brutal compression algorithms). So I would expect paper to beat computer in that area, from a strict carbon-footprint point of view. Tigraan^{Click here to contact me} 16:50, 4 January 2017 (UTC)

Russell A. Kirsch would argue about the existence of digital photos more than 50 years ago. 209.149.113.5 (talk) 20:11, 4 January 2017 (UTC)

Digital dark age is a known problem. That article discusses an actual example, and the cited NYTimes ref goes into lots of detail of various aspects of the problem of inaccessibility. The cost of storage of "data" might be comparatively low, but if you eventually need it, the cost of figuring out how to extract it seems like it can be enormous. DMacks (talk) 20:07, 4 January 2017 (UTC)

There are good and bad ways to store digital data, and good and bad ways to store paper. Best practice for color images on paper is quite expensive and I doubt most casual photographs would ever be stored this way: acid-free paper, high-quality ink, environment with good temperature and humidity control, and replicated off-site (under the same conditions) to ensure against fire/earthquake/etc. Best practice for digital is also expensive, but the expense is more easily amortized over larger data sets. It includes storage in open-source formats, storage with the source code of the retrieval software together with its development environment, and robust replication at multiple sites. -Arch dude (talk) 05:31, 5 January 2017 (UTC)

The answers about "cost of physical storage" not clear about which storage is good for earth. Thanks to Tigraan for the maths and SemanticMantis for the links. --Curious Cat On Her Last Life (talk) 06:49, 7 January 2017 (UTC)

Oldest dolphins?

Granny, the oldest known orca, is believed to have recently died at an estimated age of 105. I know that some baleen whales are believed to live longer than this, but I am wondering, are orcas the longest lived of the oceanic dolphins? Dragons flight (talk) 14:31, 3 January 2017 (UTC)

Possibly. According to This the oldest dolphin in captivity, a common bottlenose dolphin, died in 1994 at the age of 61. I can't find any information on any dolphins living longer. Other toothed whales don't seem to live as long even, the oldest beluga whale died at 46: [11]. However, the oldest narwhal may have been 115: [12]. --Jayron32 14:51, 3 January 2017 (UTC)

This book: [13] notes the oldest harbor porpoise only lived to 23. --Jayron32 14:53, 3 January 2017 (UTC)

According to this report (Table 1) there are some dolphins that have older ages than the orca for the oldest known reproducing female, which suggests that the Northern right whale dolphin may live longer. Mikenorton (talk) 15:16, 3 January 2017 (UTC)

Interesting. I know that orcas are famously one of relatively few species that definitively experience menopause and have a distinct post-reproductive phase of life. For many of the other cetaceans we don't really have enough evidence to know whether or not they experience menopause; however, if it is uncommon among other cetaceans, then a focus on the oldest reproducing female might give misleading results. I tried searching for oldest "northern right whale dolphin" but didn't find much more than that their average lifespan is 40-50 years, which says nothing about the longest lived members. Dragons flight (talk) 15:57, 3 January 2017 (UTC)

Jayron, thanks very much for those references. The published paper on the narwhals can be found here[14]. I have some problems accepting that a female lived to 115 years of age. First, this is 3 times the average age of the narwhals sampled. If I had collected data such as this, I would discount it as an outlier. Second, for this individual female, the authors give an SE (standard error) value for her age. I can not find how they have managed to get an SE from a single data point - unless this is for measurements on both eyes, but this is still misleading. DrChrissy ^(talk) 17:48, 3 January 2017 (UTC)

You are I think reading 'average age' as 'average life expectancy'. The average age of humans currently is probably something like 32 years. Dmcq (talk) 16:55, 4 January 2017 (UTC)

Not just something like 32 years, just a shade under 32 years. Good guessing! Reference: [15]. --Jayron32 18:34, 4 January 2017 (UTC)

@Dmcq No, I did not make that mistake. The Narwhals were from a cull. The figure shows a highly skewed distribution whereas if it was "life expectancy", we would be expecting a normal distribution. Possibly, with age, the narwhals learn to avoid culls, or maybe their population is naturally skewed. Anyway, enough guesswork from me. DrChrissy ^(talk) 20:02, 4 January 2017 (UTC)

It says here[16] that the average lifespan of a narwhal is 40 yrs. Here[17] it states "Maximum life span expectancy was found to be approximately 100 years." DrChrissy ^(talk) 20:58, 4 January 2017 (UTC)

Damn it - I have just realised the lead author and some of the others are the same as on the paper cited by Jayron. I was hoping there might be independent corroboration. DrChrissy ^(talk) 21:09, 4 January 2017 (UTC)

Blu tak-- thermal conductivity

Anyone know the thermal conductivity of Blu tak?--86.187.169.30 (talk) 23:36, 3 January 2017 (UTC)

Blu-Tack is a sticky synthetic rubber resembling chewing gum. This reference lists thermal conductivities of various rubbers from 0.09 to 0.63 W/mK. Here is an article on measurements on raphia gum (from the West African palm Raphia vinifera) whose thermal conductivity varies from 0.0164 to 0.403 W/mk. Blooteuth (talk) 13:14, 4 January 2017 (UTC)