
Aviation Is on a Low-Carbon Flight Path - flip8
https://www.scientificamerican.com/article/aviation-is-on-a-low-carbon-flight-path/
======
maliker
Electric aviation for aircraft larger than 4 passengers is extremely hard.
Batteries don't have the energy density needed, and fuel cells are barely at
the prototype stage for aviation. ARPA-E has been looking at this for while,
see slide 6 in [1] for an overview of payloads by energy storage medium. If
you read a little more through the deck you'll see there are also issues with
power output of electric motors in this application.

I'm much more optimistic about low-carbon jet fuels. Biofuel options here have
already been trialed successfully. And some new synthetic fuel companies [2]
that use direct air capture CO2 are looking promising.

[1] [https://arpa-e.energy.gov/sites/default/files/Grigorii-
Solov...](https://arpa-e.energy.gov/sites/default/files/Grigorii-Soloveichik-
Fast-Pitch-2018.pdf) [2]
[https://en.wikipedia.org/wiki/Carbon_Engineering](https://en.wikipedia.org/wiki/Carbon_Engineering)

~~~
mikepurvis
It's also hard because batteries don't get lighter as they deplete, so you're
landing a plane with the exact same weight as what you took off with, meaning
you need much more rugged (and heavy) landing gear. This is extremely
significant when you consider that a fully loaded 747-8 is 970,000 lb, of
which up to 326,000 lb is fuel (per Wikipedia's numbers).

It's a hard problem, and most proposed solutions are extremely novel and
risky, like having an all-battery tugboat that tows the plane up to cruising
speed/altitude before returning to the airport to charge or get a battery
swap— obviously bad because risky, also adds 50% to runway capacity to land
all the tow planes.

~~~
kuu
Just drop them before landing... There could be a batteries landing place
where they'd be collected.

Is it too crazy?

~~~
mikepurvis
Since a big chunk of the power is expended on takeoff, the ideal would be to
drop part of your battery then rather then waiting until after landing. But
either way, you're stuck with the significant complexity and expense of having
to prepare a parachute and landing gear specifically for the battery on each
flight, plus having to collect and charge those batteries.

~~~
SupersonicScrub
There's a better electrically driven solution that takes advantage of the fact
that take-off and climb-out requires the most power.

Maximum power requirements come from take-off and climb-out, so the engine
size is designed around the max take-off power. This means that the engine is
over-designed and less-efficient for the majority of the flight.

By implementing a hybrid engine, the gas-powered component and the electric
powered component work together to provide take-off power requirements. By the
time the aircraft reaches cruising altitude, the batteries are dead, and the
gas-powered component works alone. This allows the engine to be designed for
the cruise power requirements, which results in a much more efficient engine.
UTC is currently experimenting with this concept.

[https://www.flightglobal.com/news/articles/utc-to-test-
hybri...](https://www.flightglobal.com/news/articles/utc-to-test-hybrid-
electric-propulsion-system-on-da-456942/)

Yes it's not carbon neutral, but it's a step in the right direction.

~~~
iguy
Not just for take-off, but for the possibility of finishing the take-off with
one engine failure. That's quite a bit of spare capacity.

However I also wonder why, if electric motors are a solution here, there
hasn't been a comparable fuel-powered extra-takeoff-engine. Why would this not
have the same benefits? Or are extra engines simply too complicated
mechanically unless they are motors?

(The liked article is about modifying a Dash 8, which is a turboprop, and
perhaps it's easy to have oversize propellers for takeoff, and just connect a
motor to the same gearbox.)

~~~
mikepurvis
Probably because a jet engine costs like $30MM. It may well be that the
incremental cost ($, weight, complexity) of adding an electric booster to an
existing engine design is much more practical than just adding more engines.

------
spodek
I challenged myself to go a year without flying for climate reasons. I thought
I would hate it. Work, family, and lifestyle depended on it.

It turns out it was one of the best things I've done. Experience taught me
what I never could have imagined -- how much my life improved. Like dropping
Facebook on steroids. What I expected to miss I got more without flying, plus
improved relationships, community, and connection.

A few months in I decided to go for a second year. I'm 4.5 years in now. I may
fly again, I don't know, but I want to less and less.

EDIT: Amazingly, my TEDx talk on this experience went live minutes ago:
[https://youtu.be/sTYiHr1lu10](https://youtu.be/sTYiHr1lu10).

~~~
mhb
This doesn't seem very hard to believe. Flying is a miserable experience.

~~~
jml7c5
If you're a die-hard reader and always have a book in hand, it's actually not
that bad. You just happen to stand in line to read, rather than lounge or lie
down to do so. Granted, obtaining and arranging accessories (pillows etc.) so
as to sit comfortably in the seats does take some trial and error.

~~~
AnimalMuppet
Or I could just stay home, and read in a more comfortable seat...

------
criddell
Recently there has been some talk about banning air miles programs and
actually flipping the incentives. Because you have to fly under your
government ID it wouldn't be out of the question for people who fly a lot to
pay more per mile in taxes.

I've been thinking about this a lot trying to root out the unintended
consequences of such a plan, but I can't think of any.

~~~
t34543
This is a terrible idea. Some people have no choice but to fly. Say what you
want but air travel is efficient.

~~~
MauranKilom
Pretty sure it doesn't take a literal ton of fuel to move me across Europe in
a train. In an airplane, it does.

~~~
t34543
Time is more valuable.

~~~
esotericn
Indeed it is.

There'll be time after us.

------
cagenut
Its important to remember the time constraint in these conversations.
Engineering is about constraints, and if you simply remove the biggest one
(time) it becomes facile and easy to endlessly talk about future,
hypothetical, optimistic "someday" solutions. It is vapid empty happy-talk.

When you factor in the time constraint, specifically the timeframes outlined
in the IPCC SR 1.5 report, then you simply cannot claim that direct air
capture fuels are a meaningful part of the conversation of what to do with air
travels footprint.

I am 100% in favor of continued _and_ _increased_ investment in R&D for DAC. I
am 0% delusional that it will be a viable solution in the timeframe we need it
to be (same goes for thorium and fusion).

If you're not solving for the time constraint and the curve shape in this
graph, you're not talking about "solutions" you're just chit chatting about
(cool) tech:
[https://www.ipcc.ch/site/assets/uploads/sites/2/2019/02/SPM3...](https://www.ipcc.ch/site/assets/uploads/sites/2/2019/02/SPM3a.png)

~~~
thinkcontext
Airplanes are not going to stop flying. We can try raising the price to make
them fly less than they would otherwise but there will still be a need to
lower the carbon footprint of flight. Synthesizing fuel from captured CO2
seems like a much better pathway than batteries. Also, I don't think its valid
to compare it to thorium or fusion. We can make synthetic fuel from captured
CO2 today whereas those are science projects. Synthetic fuel isn't cost
effective given economic and political realities but its likely this will
occur within the next 10 years in at least some places.

Minor point, people seem to marry DAC with synthesizing fuel, probably because
Carbon Engineering has gotten a lot of press. Fuel can be synthesized from CO2
from any source. It is my understanding that DAC is currently more expensive
than capturing from a point source, like a natural gas power plant. This is
due to CO2 being such a small percentage of the atmosphere vs 10%+ from plant
flue gases. So, while DAC is more expensive and there are still substantial
point sources of CO2, fuel made from DAC will be more expensive from point
source capture.

~~~
cagenut
point source capturing co2 from burning fossil fuels and then turning it into
more liquid fuels that you then burn again is _madness_. you get that right?
it makes _less sense_ than simply saying "fuck it" and pumping the same amount
of fossil fuel up. at least then you don't have to pay the energy cost of the
transitions.

this kind of high-anxiety circular reasoning is hopefully the 'bargaining'
phase before you move onto acceptance.

~~~
thinkcontext
I don't get that because its not true. In both scenarios after the energy
consuming activities are done the same amount of CO2 is in the air (ignoring
operational efficiency). One just costs more than the other because a more
difficult path of capturing the CO2 is chosen.

~~~
cagenut
oh well if we just ignore efficiency and cost!

you are living in a world of spherical cows, not in the reality of the climate
emergency.

please understand that as the body counts rise this level of "technically
correct" pedantry will be seen for the rather gross complicity it is.

~~~
thinkcontext
The operational efficiency of both is probably within 10% of each other, so
not that significant compared to the big picture of what we are discussing. My
guess is that DAC actually fares worse because you have to run an enormous
bank of fans to suck in all that air which is why it costs more.

As for cost, I'm not ignoring it, it was my point. Fuel from one pathway costs
more from another pathway. High cost is a barrier to taking a solution out of
the lab and actually putting it into action to causing less CO2 to be emitted.
If 2 fuel pathways have the same carbon footprint but one costs less than the
other why would you choose the one that costs more?

I'm willing to listen if you would like to explain why you think DAC is better
but so far you haven't done that, you've just been insulting which I don't
get.

~~~
cagenut
I have no idea how you got it in your head that i'm advocating for DAC. I not
only did not do that, I specifically did the opposite by saying I have "0%"
hope for it. The fact that you've twisted this around now into trying to get
me to defend it is an example of why i'm being insulting to you. Your behavior
is bad, and I hope you feel bad about it. Why should I treat you with respect
when you're ignoring the context of the conversation in order to correct
internet strangers with your tangential distraction of a point? What makes you
feel entitled to other people being graciously receptive to that?

The actual topic at hand here is the GHG footprint of air travel (see topic,
OP). My comment was about the time constraint provided by the IPCC that people
fail to include in their analysis. Here you are 5 replies deep twisting my
arguments into their opposite while failing to even address, let alone refute
or propose your own alternative for the central point.

On a micro level your behavior is just garden variety piss poor social skills
(can't say i'm the best either!). On a macro (and specific to this topic,
climate change) level your behavior is the sand in the gears that keeps any of
the rest of us from discussing this challenge in good faith and reaching
rational conclusions. You are poisoning the well. You are pissing in the pool.
Please stop.

~~~
dang
Personal attacks and flamewar like this will get you banned here. Please
review
[https://news.ycombinator.com/newsguidelines.html](https://news.ycombinator.com/newsguidelines.html)
and don't do this on HN again.

~~~
cagenut
hi dang

which side are you on?

[https://www.theguardian.com/environment/2019/nov/05/climate-...](https://www.theguardian.com/environment/2019/nov/05/climate-
crisis-11000-scientists-warn-of-untold-suffering)

the bodies are piling up. are you a polite german or a rude one?

i'm a rude one.

~~~
dang
If your internet comments are coming from a noble place, you should be able to
make them without taking cheap shots or attacking people personally.

~~~
cagenut
you have made a category error if you truly believe that

------
burlesona
A quick google suggests that aviation accounts for 2% of global carbon
emissions.

Everyone in this thread is pointing out how difficult the engineering is to
convert aviation to something emission-free.

To me it seems obvious that we should focus on shrinking the 98% as fast as we
can. While we should also work on decarbonizing air travel, I am pretty sure
that if we decarbonized everything _else_ that the environmental impact of air
(and space!) travel would not be enough to fuel global warming on its own.

Further, because the impact is so much smaller, it might be more feasible for
air travel to eventually be required to perform offsetting direct carbon
capture than to replace jet fuel with an alternative. That would make flying
more expensive, which I think is fine, but it wouldn’t make flying
_impossible_ which I think is at least highly undesirable.

~~~
Scramblejams
Nearly every article I've seen on this subject conveniently omits the
proportion of aviation's contribution to global carbon emissions.

I'm starting to think it's intentional, and it's instructive to ask _why_.

~~~
p_l
A lot of railway-related lobbying, at least in western europe.

~~~
nexuist
The submarine:
[http://paulgraham.com/submarine.html](http://paulgraham.com/submarine.html)

------
0x7265616374
Clickbait title. Read the article hoping for great news in the emerging
aerospace sectors. What I actually found was a rather large serving of
humblebrag with a generous side of monetary privilege.

~~~
stevenwoo
Based on past decisions, it's going to take some revolutionary technology that
is cheaper than avgas fuel/engines. Isn't the USA is the largest and last
major country that uses leaded fuel for small planes. We'll do almost anything
to save small plane owners the cost of upgrading.

~~~
bdamm
Mainly because avgas is not a meaningful contributor to climate change or
environmental lead. It's a pittance when compared to anything else; commercial
aviation all sources, DoD, road transport for GhG and piping, paint, and
industrial sources for lead.

~~~
stevenwoo
I should have been clear I was not comparing greenhouse emissions of avgas to
replacement but that contributing more lead in any amount to the environment
is pretty terrible since we all pay for the effects, even considering
whataboutism of all other human lead pollution. The forever persistence of
lead and ready bioavailability makes it special.

------
rcMgD2BwE72F
>Aviation Is on a Low-Carbon Flight Path

Really? The article just says its author hope for a low-carbon future for the
air transport, and mentions some tiny plans by jet makers and early startups
to plan to 'hybridify' airplanes.

How much low-carbon would that be? As far as I could read, the author does not
even try to evaluate that and blindly hope that it should be helpful, somehow.
As if he can't bear flight shame, and tries to share/sell some "hope" to cope
with that.

~~~
ekianjo
There's always the possibility of hydrogen-powered planes.
[https://en.wikipedia.org/wiki/Reaction_Engines_A2](https://en.wikipedia.org/wiki/Reaction_Engines_A2)

~~~
sokoloff
Energy density of hydrogen by mass is excellent (about 3x that of gasoline/jet
fuel), but much worse by volume (about 1/4 of gasoline/jet fuel).

Finding a way to store liquid hydrogen in 4x the volume (plus any required
cooling/insulation and safety systems) might be a challenge for long-haul
flights.

~~~
revax
Also the production of hydrogen is far from being low-carbon.

Yes there are some ways to produce hydrogen from electricity with electrolysis
but at the moment 90% of hydrogen use natural gas or other hydrocarbons and
release enormous amount of CO2.

~~~
davedx
You can say that about everything (except maybe nuclear) right now. This
morning I had a discussion with someone on Twitter about windmills, and he
said "yeah but they're still manufactured with carbon based processes, cement
and steel are made using fossil sources".

Hydrogen production _can_ be clean though.

[https://www.cleanenergywire.org/news/hamburg-and-
fukushima-c...](https://www.cleanenergywire.org/news/hamburg-and-fukushima-
cooperate-wind-power-and-hydrogen-production)

~~~
revax
It can be, but it in fact not. And if it is, at what price?

Don't misunderstand me, I want a low-carbon aviation, I'm all for it. But even
if you cut the emissions by a factor 2 of each newer aircrafts, what's the
point? The numbers of flights is expected to double in less than 20 years.
Global emissions won't reduce at all.

[https://www.iata.org/pressroom/pr/Pages/2018-10-24-02.aspx](https://www.iata.org/pressroom/pr/Pages/2018-10-24-02.aspx)

IMHO, we need more regulations (e.g. ban domestics flights if high-speed
trains are a viable alternative) rather than technological solutions.

~~~
netcan
There needs to be some middle ground in these discussions.

Yes, it's silly to ignore realities like "how was the electricity powering
this car produced?" OTOH, since we're talking about _potential_ future
solutions to a hard problem (hard relative to cars, for now)... you kind of
need to dismiss current issues if they're solvable to in theory.

Price of electrolysis hydrogen now, when we're not using that much of it is
not necessarily indicative of potential prices at scale.

To me, I think we need to focus regulation that gets high potential
technologies (eg electricity production and electric transport, atm) past the
point on their learning curves where ordinary price economics and/or bans on
carbontech can take over.

The problem with marginal mitigation like discouraging flights or large ICE
engines is that gains are one-off, and not en route to bigger solutions.

I agree that commercial flight is a big problem. I'm just skeptical that
carbon austerity can amount to more than a rounding error in the long term.

------
nradov
There are electrification gains to be made on the ground. Aircraft
manufacturers are already experimenting with using electric motors for taxiing
so that they can wait to start the turbines until close to the runway.

[https://en.wikipedia.org/wiki/EGTS](https://en.wikipedia.org/wiki/EGTS)

And longer term, electromagnetic catapults embedded in runways can be used to
launch aircraft using renewable power. The engineering challenges will be huge
and a new generation of airliners will be needed to make it work, but the
concept is technically feasible.

[https://www.theregister.co.uk/2012/09/07/airbus_smarter_skie...](https://www.theregister.co.uk/2012/09/07/airbus_smarter_skies/)

------
brianbreslin
I'm curious if anyone here can answer this: what part of flight consumes the
most energy/fuel? Is it the take-off? Landing? Cruising? So would a hybrid
model plane make sense to use jet fuel or equivalent for the most energy
consuming part, then electric batteries for the least intensive parts?

~~~
Robotbeat
For long-haul, it's cruise. And the energy required can thus be improved
directly proportional to lift to drag ratio. What I find promising is work
NASA is doing and has done on truss-braced wings to enable a ~doubling of
current transonic lift to drag ratios by using an extremely high aspect ratio
wing.

~~~
yboris
Truss-braced wings seem really cool!

[https://en.wikipedia.org/wiki/Boeing_Truss-
Braced_Wing](https://en.wikipedia.org/wiki/Boeing_Truss-Braced_Wing)

------
aaron_m04
Why not use renewable energy to synthesize the regular airplane fuel? That
would be carbon neutral, and it would avoid all the issues with heavy
batteries and upgrading or replacing existing planes.

~~~
AWildC182
It likely wouldn't be Jet-A that's synthesized, it would be some sort of bio
diesel that would have to get approval. GA still uses leaded gas because the
industry is so slow to change and everyone is terrified of having to re-
certify (STC) existing aircraft or add additional fueling infrastructure. It's
a far more complex issue than I can describe here but it works as a useful
analogy.

Electric aircraft, however, sound really good in a boardroom because the
logistics are "simpler" (disregarding the issue of charging gigawatt-hour
batteries somehow).

------
geogra4
No discussion of Synthetic Natural Gas => LNG powered jetliners? To me that
seems a lot more realistic than banning flight altogether or battery/electric
powered aircraft.

~~~
jackdeansmith
My bet is that if you're making synfuels, it makes more sense to take the
efficiency hit and go for long chain hydrocarbons instead. Even if LNG is the
technically superior fuel, planes last a long time and compatibility with
existing equipment is worth a lot.

------
buboard
What if we work to make air travel less useful. Find reasons why people air
travel and eliminate them. For example, conferences where a whole lot of
nothing happens - and they 're usually seen as an excuse for mini vacation.
Business travel is often a game of persuasion that should be done over skype.
Apparently the #1 reason people travel is education & training.

The idea of a battery plane sounds too good to be true , and it 's probably
decades away

~~~
choeger
> What if we work to make air travel less useful.

Air travel is (for a certain distance) the most efficient way to travel. No
infrastructure needed along the way (if you discount the air ports used as
emergency targets), fast, and quite flexible. Trying to ignore that is futile.

We should simply mandate a growing percentage of carbon neutral fuels for all
aircraft traveling to and from our countries. Start with 1% next year, it
should be easy to implement and then increase every 2 years by another
percentage point.

~~~
buboard
how is that better than not needing to travel at all?

~~~
choeger
Because most people _like_ to travel. Any policy that makes people happy is
intrinsically better than one that makes them angry or sad. Weird that I have
to tell you that.

------
raxxorrax
With the weight of batteries it would definitely be a challenge. Fuel is heavy
too, but there is still a factor between their energy density that is close to
100.

Owners of electrical drones know that the fun often ends after around 20
minutes with the battery being the heaviest part by far. I remember there
being a drone that could fly for 2 hours with the whole body basically being
the battery.

------
starpilot
Is this really more environmentally friendly if the electricity comes from a
coal plant driving a turbine? With a gas aircraft, it's still fossil fuels
driving a turbine. Sometimes they're very similar turbines:
[https://www.ge.com/power/gas](https://www.ge.com/power/gas).

~~~
gumby
The Carnot efficiency (and joules/“unit pollution”) go up dramatically at
scale (one of the reasons the 737 MAX was designed for such huge engines). So
yes, a vehicle powered by a coal plant could pollute a lot less than a vehicle
burning melted dinosaurs at the point of use.

In addition some of the other pollution (NOx, particulate etc) could be more
manageable when coming out of a large smokestack in a desert vs in the cramped
spaces of a city (car) or upper atmosphere (plane).

I’m definitely not defending coal! Just saying the calculus is complex and
multi factor.

------
dzhiurgis
Hmm, when fuel is around 5% of your total ticket cost, something says that
there are much more inefficiencies to solve than just the flight itself.

Being forced into security theatre, not allowed your drink or food, forced to
overpay in airport... Smells a lot like how housing market is regulated by
councils or NY trains having higher carbon emission than Prius due to admin
costs...

Most of stewardess could be replaced with a vending machine. Bunk beds made
using compliant mechanisms. Tax charge passengers by weight, not by height.

Here's something even more ambitious - it's really bizarre that airlines buy
airplanes and then decide to skimp on maintenance. They should really be
leasing them from manufacturer who does all the maintenance. Same with pilots,
but perhaps they could be airport staff (especially crew). Airline should only
focus on ticketing and routing (similar to how energy and telco markets are
"deregulated" in some countries).

~~~
xyzzyz
The planes themselves are also pretty expensive. New Boeing 737 costs $120M.
Maintenance also costs money. You need to recover all these costs too.

------
AtlasBarfed
Biofuels or fuels made by excess wind/solar seems the way forward. Carbon
neutrality should be the immediate goal.

All electric will require lower speeds and probably a hybrid airship airwing
design

------
GhettoMaestro
We just need someone to develop an air-to-air battery replenishment system
(same theory/model that you see in use with military tanker aircraft for air-
to-air refueling).

I can see it now. Max weight/batteries on take off. Controller to drain
batteries serially, and as each one is exhausted, chuck it out the bottom of
the plane (with some kind of landing/recovery mechanism). When you start
running low on batteries, re-fuel at the nearest tanker.

Obviously I'm kidding. The tanker model is ridiculously expensive. That's why
you only see it used for extremely critical things (military).

------
cagenut
couple of key points here:

#1 - this article is a great example of how the conversation is shifting, but
the mid-point we're at now is a wasteland of nonsense and cognitive
dissonance. the text of the article is about the truth of what things matter
to reduce your footprint (kids, flying, cars, beef), but the tone of the
article and the headline is one of "things are gonna be fine because the whiz
kids are working on it" soft-denialism.

#2 - the co2 footprint from jet travel is somewhere between half and 1/4th of
the overall greenhouse gas emission footprint of flying. this is because
nitrogen oxide and water vapor are also greenhouse gasses (particularly at
altitude). It gets very complicated to factor, but at a high level you should
simply 3x the carbon cost of flights for the "CO2e" total:
[https://en.wikipedia.org/wiki/Environmental_impact_of_aviati...](https://en.wikipedia.org/wiki/Environmental_impact_of_aviation#Total_climate_effects)

#3 - the electrification of air travel is very well under way. it will not
replace trans-oceanic flights in our lifetimes, but it can replace a massive
amount of regional travel, and customers can be forced to adapt to a multi-hop
world (jfk <-> ord <-> den <-> sfo). If you'd like to learn a ton about the
state of the art 1 year ago, check out this playlist from the Sustainable
Aviation Summit last year:
[https://www.youtube.com/watch?v=6LDU0Wgn0Lk&list=PLWUnMAqjJ9...](https://www.youtube.com/watch?v=6LDU0Wgn0Lk&list=PLWUnMAqjJ9CAue9jS0osS5i-QQF8X6Q-l)

~~~
sokoloff
Given that we already have private jets flying routes that are directly served
by airlines non-stop, I doubt how much you can impact business travel.

You can stop kids from seeing their grandparents quite easily by raising
ticket prices or taxing jet fuel. I’m not so sure that’s going to keep
airlines from serving JFK-SFO direct for business travelers.

~~~
cagenut
you are correct that marginal pricing mechanism are no longer enough to solve
this problem. we have moved on to the legislative phase.

~~~
sokoloff
I guess I’ll believe it when I see private flights banned or airlines banned
from running SFO-JFK direct flights.

I don’t expect to see that in my lifetime (next 40 years).

~~~
cagenut
Yes, the number one problem we have right now is neither technological nor
scientific. Its the self defeating circular reasoning of normalcy bias and
projecting your unwillingness to change on everyone else.

~~~
sokoloff
It costs me $2500 or so to fly to Europe and stay for a week. Maybe $4K in a
high week.

I can steer or create a significant _multiple_ of that value by visiting my
teams for a week. There’s massive financial incentive for me to take that
trip.

~~~
cagenut
yes when the cost of carbon is not accounted for then it creates financial
incentives to not just ignore but actively exploit that externality.

------
sailfast
Didn't see it listed as an option here, but are the travel-via-ICBM options
that SpaceX has been touting going to actually be cleaner options than burning
jet-fuel? If you remove the cruise speed requirements for longer-haul flights
and put them in space, maybe that helps? Hard to say without any real numbers
out there (and even if I had real numbers I'm probably not in a position to
synthesize them vs. aircraft)

~~~
FlyingAvatar
Judging by the amount of volume of a rocket or ICBM that is consumed by its
fuel, I would have to venture that it's nearly impossible that it's cleaner.

~~~
Ottolay
I would love to see the numbers for this.

A significant part of the volume in a ballistic rocket is oxidizer which a jet
does not need to carry. Liquid methane is much less dense than jet fuel, so it
makes sense it would take up much more volume. Also, methane has less carbon
in it than jet fuel on a per energy basis.

Still suspect you are right.

------
jellicle
Probably the best way to cut air travel pollution is with a combination of
high-speed electric trains between all major cities (make it convenient to get
around without flying) along with a ration book for air travel - everyone is
allotted one trip per year, second trip has a surcharge, third and subsequent
trips have massive surcharges growing to astronomical numbers.

The average person does not fly in a given year. Those that do fly tend to
take no more than one trip. A very small percentage of frequent flyers account
for the bulk of air travel. An explicit rationing system would allow "regular"
people to still fly occasionally and would have huge benefits for cutting air
travel overall while impacting only the frequent flyers. People would be
forced to ask if they REALLY need to fly out to NY for that meeting.

The boosts to the VR/Skype/virtual presence/hologram/conferencing field would
be enormous.

~~~
0xffff2
As a California resident, this reads like a fantasy novel. Sure it would be
great to have high-speed trains linking every city, but we cant' even link the
two biggest cities in California.

Maybe I'm not as typical as I think, but all your proposal has done is cause
me to drive to the one or two conferences I go to each year. Probably not a
win at all since I don't drive and EV.

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notatoad
The most interesting part of this article to me is that carbon offsets to
cover 12T of CO2 emissions comes out to only $10/month. I've never looked into
personal carbon offsets before, but that seems really cheap.

~~~
staticcaucasian
For less than you might pay for a car, or a year of college, or heck, what you
might put into your 401k for the year, you can offset effectively your entire
life at $16,000. (80y lifespan * 20T/year typical American emissions * $10/ton
current price). I am expecting my first child and I've thought about
registering for carbon offsets in his name instead of a typical baby registry.

Unfortunately of course, that will only do so much, because the growing global
demand for things like air travel, personal car ownership, meat in diets, or
air-conditioning mean the numbers on this chart will start to get uglier:
[https://en.wikipedia.org/wiki/List_of_countries_by_carbon_di...](https://en.wikipedia.org/wiki/List_of_countries_by_carbon_dioxide_emissions_per_capita)

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elif
The safety benefit of removing the concern of fuel fouling will be a
revolution for air travel.

I just hope they don't end up more exposed to bird strike due to bigger more
efficient turbines with more composite components.

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iandanforth
As a thought experiment if you could produce jet fuel using carbon captured
from the atmosphere (and energy from zero-carbon sources) what other negative
externalities would remain from burning it in planes?

~~~
elihu
I would expect the biggest one to be the opportunity cost of what you could
have done instead with that electricity besides make fuel.

For instance, if, say, converting natural gas heating to electric is a better
use of energy in terms of reducing greenhouse gasses, then maybe we should do
that first.

In the end, a lot of these sorts of proposals depend on cheap renewable
energy, and if we can get enough solar and wind power installed then other
goals become feasible. Fuel production is an interesting case because you can
use surplus energy at times of low demand.

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frankus
Some air-breathing batteries can apparently roughly match liquid fuels for
specific energy, but they're not rechargeable so much as recyclable, and they
also get heavier as they discharge.

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clueless123
Doing my part to solve the issue :)

[https://www.youtube.com/watch?v=HBTZG1qkH5s](https://www.youtube.com/watch?v=HBTZG1qkH5s)

~~~
raquo
Hey, nice! What kind of components are you using? Engine, batteries, etc.? Did
you pick those yourself, or borrow the design from an existing system like the
e-help for hang gliders?

~~~
clueless123
Motor: [http://www.freerchobby.cc/](http://www.freerchobby.cc/) 202/80 27
brushless motor with hall sensor

Controller: [https://kellyev.com/shop/khb/](https://kellyev.com/shop/khb/) KHB
- High Power Opto-Isolated Brushless Motor Controller With Regen (72V-144V)
(400A) * must choose high speed option controller to get more than 2000RPM !

Batteries : 6 * CNHL 8000MAH 22.2V 6S 30C LIPO BATTERY Propeller: Wood 49"
Pitch 30

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JumpCrisscross
What's the advantage of this over using clean energy sources to synthesize jet
fuel?

------
_pmf_
Electricity == low carbon

Not a good starting point for a discussion.

~~~
Robotbeat
It actually is. Super easy to clean the grid; many grids are extremely clean
already.

