omenti

green flight

Two years ago the Environmental Protection Agency reported aviation accounted for about three percent of the nation's CO₂ emissions, or about twelve percent of transportation.  The international figure is about two point five percent.  These may not seem huge, but they've been growing steadily and, post pandemic, should continue their growth.  Making matters worse is the global warming contribution from the cloud-like contrails produced by the jet engines at altitude.   It's difficult to study, but indications are the contribution may double the global warming impact. 

 

A number of approaches have been suggested and are in various stages of testing.  Moving to bio-fuels isn't the greatest solution as growing and producing biofuels has issues and you're still producing contrails.  In the short term some airlines will move to it, but that may be part a PR and carbon credits game as much as anything. 

 

Electric airplanes exist and there are even a few (very) sort haul commercial flights.  The problem is the specific energy of the battery - how heavy is a battery per unit of energy storage.   Turbine fuel stores about eighty times as much energy as a safe lithium-ion battery of the same weight.  Airplanes frequently carry large amounts of fuel - the weight of fuel burned on a cross country trip is greater than that of the the passengers and crew.  The range of a battery powered airplane is severely limited even after accounting for the great efficiency of an electric motor.   We could get a lot closer with exotic batteries that aren't anywhere close to reality, but even then you're talking about a propeller driven (slower) aircraft. 

 

Hydrogen often comes up as the perfect clean fuel - the combustion product is just water.   Although it's the most common element in the universe and accounts for most of your body's atoms, we need hydrogen gas and that's extremely rare on Earth.  Hydrogen gas (H₂) must to be produced and it takes a lot of energy to create it - more than you can get out of it.  Most of it is produced from a petrochemical process that involves carbon emissions.  This is called black or grey hydrogen and, if you manage to capture most of the carbon emissions it's called blue hydrogen.  What you want is green hydrogen - hydrogen produced using electrolysis with electricity from wind, solar or nuclear power.  That seems like a nice use of excess intermittent power. 

 

It's important to think of hydrogen as an energy storage medium - a non-rechargeable battery of sorts.  It has a very low - essentially unusable energy density at atmospheric pressure.  You'd need impossibly large tanks (think about Hindenburg sized tanks) or you can compress it or liquify it and shrink your tanks to something more manageable.  In gas form at a very high but probably safe pressure it needs about five to ten times the volume of  jet fuel. Liquid hydrogen gets you down to about three and a half times the volume.  

 

Engineering is all about finding an optimal solution to several problems that generally interact.  You could convert a turboprop or turbofan to burn hydrogen and see where that takes you.  Turboprops seem to be workable on short haul routes (1,000 km or less) with small passenger loads (under 100 passengers).  They'd be slow and fly at lower altitudes than today's jets.  Turbofans present a number of problems - at altitude they're making contrails and the range and payload isn't great.  One needs to think a bit out of the box.   

 

You might use a hybrid jet fuel/hydrogen engine that climbs to cruising altitude on jet fuel as fuel consumption is much greater in that phase. Then the switch to hydrogen fuel is made when the engines are throttled back at cruise altitude.  You could also design a lifting body aircraft that has a lot of internal volume for liquid hydrogen fuel tanks without being too large for conventional airports.  Tricks might get you across the US with a few hundred passengers, but flights across the Atlantic or Pacific would require something more. 

 

The prop-driven airplanes present other opportunities. A fuel cell converts hydrogen to electricity and electric motors are more efficient that jet engines.  There are a number of little problems that can be overcome, but a fuel cell propeller airliner may just be a short to medium range solution.

 

I didn't go into the NOx problem.  The high heat of combustion in a jet engine creates nitrous oxides when the nitrogen in the air is heated to high temperatures.  That's a problem - particularly at the high altitudes jets fly at and burning hydrogen won't fix it.  The way around it is to use fuel cells and electric motors, but that's for lower altitudes and slower speeds.  There isn't an ideal solution - you just hope to reduce as much as you can.  

 

Airbus is working on the problem - or at least they were before the pandemic.  I can believe the target date for the propeller aircraft, the lifting body is probably more than fifteen years out.

There may be a near term niche for hydrogen powered flying vehicles.  Agricultural and inspection drones are much larger than hobbyist drones.  They're limited to half hour flight times with batteries, but new fuel cell drones with small high pressure hydrogen tanks have appeared in Korea.  They can fly for hours and that may be the first practical opening for aerial hydrogen.

 

why you can watch I Love Lucy

A few days ago Om and I were talking about some technologies.  I mentioned I sort of predicted one with reasonable confidence about twenty years out.  It seemed a bit too scifi on the surface, but other people in research agreed it could happen if a lot of money was spent.  It seemed desirable, so why not?  There was only one major roadblock and that turned out not to be roadblock at all.  It needed a much better battery than anything we knew about.  A lithium-ion battery was in the ball park at the time, but we had no idea Sony was playing with the technology at the time. We were equally unaware of the fundamental work in university labs two decades before.  

 

It's interesting to think about areas of technology under rapid development and the importance of missing technologies. Television is a great example.

 

Television has been around for a long time.  Philo Farnsworth's all electronic television in the 20s was probably the most important breakthrough.   The lens of a camera focued an image on a photosensitive plate while an electron beam was scanned row by row across the imaged area.  A signal of strength that varied with the brightness of the region the beam was on would be transmitted as a radio signal to a television receiver.  The receiver had a cathode ray tube that, in lock-step with the beam in the camera,  scanned a piece of glass coated with a phosphor that would glow when the beam hit it with a brightness that changed as with the signal the camera was sending. All of this was done at about thirty frames a second - good enough that your mind perceives motion.

 

Television was such a great name - viewing a moving scene at a distance as it happened.  Shortly after WWII a few television networks sent their television signals between cities and then across the country.  Even though the receivers were expensive it quickly caught on and the networks were spending serious money on production. But there was this problem with time zone.  You put a program on at 6 PM in New York City and the television receivers in Los Angeles would display the image at 3 PM.  Not exactly good for creating the largest potential audiences.

 

Electronic recording would fix the problem, but wire and tape recorders were just getting good enough for audio and television signals had about a thousand times as much information.  It just wasn't possible.   The solution seems a bit crazy now - point a film camera at a television monitor and immediately develop the film. Eastern and Central time zones were live, Mountain and Pacific were delayed by two hours.

 

At first these kinescopes used  16mm film.  Once used most of the film was thrown away it degrades and is a fire hazard..  By 1954 television kinescope delayed broadcast became the largest consumer of movie film eclipsing Hollywood and the home movie markets combined. A bit before  I Love Lucy became a huge hit show.  Lucile Ball demanded higher quality so a switch was made to 35mm.    The larger format was so expensive and had to be stored in newly constructed fireproof facilities.  An archive began to emerge. 

 

A few years passed and Ampex came out with a video recorder able to handle the flood of information. - a monster that used two inch wide tape.  An expensive and initially temperamental monster that used two inch tape, but dirt cheap compared to the  kinescope process.  It quickly became the standard for time zone delay. The curious thing is that the television people didn't see tape as an archive medium.  For a few years none of the tape delayed shows remain as the expensive tapes were reused until they wore out.  No one thought long term storage was important.

 

The last part is interesting.  We don't think of television as remote viewing - rather it's a video stream that might be live, time delayed, manipulated,  archived, or all of these. 

 

Oh .. the prediction from 1993?   You will take a flat piece of glass out of your pocket and have a video conversation with a relative in India and the "call" won't cost anything.  We knew how to code video, mobile radio would easily have the bandwidth in 15 or 20 years, multi-touch screens were in the labs, lcd color screens and lcd cameras were only going to get better, the price of bandwidth was going to crater (our corporate management didn't like that message) ... Moore's law on everything but the battery.   Note:  I've made a few good predictions, but looking back at my old lab books can be an embarrassment - you tend to forget the dead ends.  

 

 

checking out your neighborhood

minipost and recommendation

The books you wore out when you were fourteen or fifteen are probably serious hints about your dreams and direction.  One of the two I wore out was a Norton's Star Atlas and Reference Handbook.   Beautiful, wonderful star charts to find your way around the night sky.  The graphical design was (and still is) stunning and it just works.  It cost a fortune in the day, but so wonderful.

 

Every now and again someone publishes a survey that claims only a small fraction of Americans under 30 or 35 have seen the Milky Way. That's a shame.  On a sufficiently clear dark night it's about as beautiful as anything I've seen in Nature.  Light pollution has largely taken it from us.

 

But even in suburban areas you can still see some stars and planets and the Fall in much of Europe and North America offers crisp clear skies.  Checking out our stellar neighborhood is much more inspiring than watching TV, but you need a guide to make any progress. Although I still love my Norton's (I've been through several editions), the better entryway is to use an app.  At least a dozen exist.  My clear favorite on iOS is Sky Safari at about three dollars on the App Store.  (they also have an Android version, but I haven't used it).  Go for the low-end version - currently Sky Safari 6 AR - the more expensive versions are used to drive computerized telescopes.

 

The beauty of apps like this is they know location and the time of day.  Then, using the phone or pad's compass and gyroscope, they calculate and display the section of sky you're pointed at.   Change the display magnification to roughly match the sky and it's sort of augmented reality. You can identify stars and planets as well as search for them and learn the constellations. Playing around with the settings is useful (particularly turning off the background music), but the defaults for star brightnesses displayed roughly matches the human eye in a semi-dark area.  You can also turn off the compass and gyros and explore the sky indoors.

 

If you get hooked the next thing would be a good pair of binoculars .. stay away from telescopes for awhile. 

 

 

 

in praise of techs

mini post

1874 saw the opening of the most important inventions of the 19^th century - The Cavendish Laboratory at the University of Cambridge.  Serious science began to take off in the 1850s in universities.  It was mostly applied and work aimed at solving the problems of the day - railroads and telegraph.  Cambridge was late to the game, but their approach was revolutionary.  Apparatus and expertise were concentrated at one location.  Research cultures emerged. Not only was this cost effective, it freed up researchers to explore new classes of problems - not only hypothesis based and applied work, but true exploration.  That turned out to be the fuel of scientific and technological change in the following century. 

 

The model spread and by the 1890s and areas of deep expertise began to appear.  A dramatic example is the race to zero - how experimentalists tried to achieve the lowest possible temperatures.  Three institutions were deep into the game, but success and failure came down to who had the best apparatus and laboratory technicians. The experiments had become so difficult that expert technicians who built, understood and modified the experimental apparatus made all the difference. 

 

The public often sees science as the quirky theorist standing at her slate board and, chalk in hand and on her shirt and pants,  having deep thoughts. In fact most of it is very careful labor that can consume a small army of people for years to get a result that something didn't exist (that's as important as finding something!)  The Nobels celebrate the principal scientists and praise is warranted, but it often misses the supporting staff. (I think the Nobels have their place as they tend to focus on the frontier rather than hypothesis driven work.  I wish they were more inclusive, but another story)

 

Here's a short video on a tech at EGO-Virgo - the gravity wave observatory near Pisa, Italy.  Three such instruments exist with a forth coming online in Japan soon and a fifth under construction in India.  Able to measure distortions more than ten thousand times smaller than the diameter of a proton, these are far and away the most precise instruments ever built.  The technicians responsible for various bits and running them made it all possible.  I've worked with people like this - they're among the greatest craftsmen and women in the world.