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Solar-powered aircraft flown for nearly three weeks without landing (theiet.org)
379 points by OJFord 53 days ago | hide | past | favorite | 217 comments

This is great and points to how solar in some cases already can facilitate continuous operation without the need for refueling of planes, boats, cars, you name it. Expect this to grow as battery and solar cell tech develops further.

My favorites atm are the yachts that are capable of sailing just about anywhere in the world without a drop of fuel. The price is prohibitive, but considering that you might not need a house anymore it is actually getting close to possible for a reasonably senior tech employee.

[full disclosure: no affiliation]



I've always been kinda fascinated by this solar yacht concept.

I wonder now with post-covid remote working options and starlink if you could actually make it work.

I do wonder though if sailing the ship is basically a full-time job in itself (navigation channels? Docking at foreign countries? Getting food etc?).

I have a 38' steel sloop with 400w of solar + a wind generator on-board.

I'm not a full-time liveaboard, but I have been on-board for the last couple of months and you can definitely make it work.

Sailing is labor intensive, but not in the ways you imagine. Navigation, docking and provisioning are all straightforward.

Where it can sometimes feel like a full-time job is maintenance. Everything on a boat wants to break all the time. Doesn't matter if the vessel is brand new or 40 years old; finding a balance between maintenance and life is difficult.

I learned a few years ago about barnacles, which by virtue of being unaerodynamic and super heavy if you let them form huge colonies on the bottom of your ship, can decrease fuel efficiency severely. I saw how much work maintanence was, I said 'nope!' I guess a house is similar in some ways. Shingles don't last forever, pipes get corroded. The salty sea though, it's a bit more unkind to things, aye?

If you use anti-fouling bottom paint and either a) live in a region where it's pleasant to dive and scrub your hull, or b) can pay a service to do it for you, either way it's only a once a month thing, and a haul out ever couple of years. Although I can't speak to steel hulls, with fiberglass water can get into the fiberglass causing blisters that have to be ground out and epoxied in, which is precisely as annoying and expensive as it sounds.

Compared to a house an ocean going (so salt water) sailboat disintegrates while you're looking at it. A sweet water boat a bit less fast but still quite fast. GP has it right: the maintenance is where the work and the money goes. The proverb is "a boat is a hole in the water that you throw money in".

At least with a house the timeline is long and it's easy to hire someone to do it for you. Even galvanized pipes last 40-50 years without much problem, and newer pex pipes may last indefinitely. Roofs are 25+ years.

Not soaking your house in salt water really helps with longevity I've found

For sure. Even then, the techniques used by builders at the beach seem to allow houses to endure a long time.

You’ve gotta replace some stuff yearly on those houses by ocean spray, it’s actually a bigger problem than it might seem

Absolutely. I once looked at an apartment on IJmuiden beach, it was only a few years old and it looked as if it was 50 years old (and had not been maintained in those 50 years).

I don't get why US houses are still built with shingles, they don't seem to last at all. Our houses are generally built with roof tiles (not mine, I've got a flat roof which will need to be redone every 25-30 odd years :/ ) which last for decades and generally only need a few replaced after heavy storms, maybe cleaned up if they look grimy.

Pipes are made from plastic and last decades, but they're generally not too hard to replace though.

I'd argue the biggest maintenance jobs to a house is keeping everything clean, basically the same as a boat. The other one would be painting every couple of years, and of course garden maintenance.

When I lived in southern California, roof tiles were very common but in the eastern US, it's mostly shingles. I hate to think of what a hailstorm would do to a roof full of tiles. Hail can cause significant damage to a shingled roof but it's much less expensive to replace.

Boats also have critical systems such as engines that need maintenance and despite that break often. Esp. on a sailboat, there's nothing more important than the engine and these are usually cooled by salt water.

Yachts don't rely on solar. Sometimes they have solar but only as a small auxilary system. They primarily rely on propeller regen where the prop flips into drag mode stealing a fraction of a knot from the sail-driven ship. I've seen some yacht owners try to install a small wind turbine but it's not worth the trouble because of the noise it creates. They also tend to have at least one gas generator as an emergency backup.

I thought starlink didnt work for mobile connections? I.e. that it had to be registered and operated at a fixed address.

That said, unless you are able to drop anchors, I am guessing that you would spend most of your working hours at a dock or with a partner piloting instead.

I believe this is only temporary and SpaceX has announced plans to roll out different subscription plans (including roaming) in the future.

They've said that the base station will be able to roam at some point in the future and right now it's because they don't schedule the service on an ad-hoc basis so if you're base station isn't in it's expected area it won't get service.

Starlink has to abide by the laws of whatever jurisdiction you are in. There's not many technical reasons why they can't provide roaming service on the seas but there are issues such as if you dock in a country that prohibits Starlink service, they're going to want some system in place to reject your packets. That shouldn't be too difficult but resources must be allocated to making it happen. They probably have other things on their plate now that are a higher priority.

> I thought starlink didnt work for mobile connections?

It will not work either far away from the shore.

Again I have to believe this is only a temporary restriction.

SpaceX are launching satellites with ("frickin") lasers now. So, if you are in the middle of the ocean, your packets step between satellites on the same orbit, forward or back, until they get in range of a node. First actual use is for polar service.

On certain routes, packets will be artificially delayed so that high-speed traders can pay big bucks to get their packets through first, ahead of fiber. And, maybe pay even bigger bucks to prevent their competitors from getting their packets through as fast. Imagine tiered pricing, where each millisecond ahead of the rest of the pack is ten times the price.

So, for example, orbits inclined near 70 degrees pass near New York and London/Frankfurt. Packets going by satellite laser links can get there many milliseconds ahead of those poking along on subsea fiber. Somebody in London who finds out 10 ms before everyone else about a price change in New York gets to make a killing trading on the exclusive information.

There is a whole world there I do not know and don't really want to. What a strange world we live in.

Yes. You can think of it as automated stealing. Much of the inequity could be eliminated by imposing a per-transaction tax.

Then you get more smart people being pointed at "minimising the tax burden" instead of "doing things faster/better".

Or you can think of it as HTF trading firms subsidizing 20-60ms internet for the common user. The last couple ms probably mean nothing to you but they mean a lot to them. I guess it depends on what your world view is.

Somehow, I foresee SpaceX just pocketing the extra money, not reducing the little peoples' prices. Have you seen any reason to expect different?

The extra money is probably needed to make the whole thing viable. SpaceX probably has a goal price for consumer plans and they are just trying to hit that price.

Regardless I just don't see SpaceX as the company that doesn't evolve with times tbh.

I do not understand that reasoning at all, where there is any.

"Evolve with times" does not seem to mean anything. In markets where Starlink is viable, they have no effective competition, and can charge as much as the market will bear. As long as they have more potential users than bandwidth to sell them, they are under no pressure to reduce prices or give up profit. A goal to subsidize Martian colonization provides a very strong incentive to maximize income. We should expect to see very high gross margins until other constellations begin to compete.

Yea let's not serve an area because their only option could potentially overcharge them! Completely ignoring the fact that you can't define an overcharge without alternative options. Current sat internet is orders of magnitude more expensive for a much worse service. Starlink is literally breaking monopolies and your worry is that it's going to be a monopoly itself.

I suspect this is why starlink has some base station licenses in eastern parts of Newfoundland. It’s the closest you can get to London before swimming from Contiguous North America.

They also need them there for current architecture up and back service to rural Atlantic Canada.

You’d build more central for that though, no? Otherwise you’re just covering a lot of ocean (until inter-sat links are up and running).

You would cover a lot of ocean but you'd also cover all of rural Newfoundland. I believe there's also a site somewhere in Nova Scotia. Dozens of starlink earth stations are now up and running.

Is there any real world test data out for going over the laser interlinks yet? I know there have been Elon Musk tweets on the topic, but he tends to tweet from a spherical cow engineering world when looking at future specs. From very early on the "much lower latency due to the speed of light in a vacuum" posts have been repeated but there is a non negligible number of routing decisions and hops in the starlink mesh and the additional 1100-2200km entry/exit, as well as bandwidth and handover limitations.

London/New York doesn't seem like the distance that there is going to be huge wins for back bone connected entities. But I guess that even if you can land a percentage of packets quicker via starlink, then there is some value in the trading world?

Let's look at numbers. NYC->LDN great-circle distance is 5576 km. At altitude, that is (3959+547)/3959 * 5576 = 6346 km. Idealized path is thus 547 * 2 + 6346 = 7420 km. (Actually a bit less because the path is part of a polygon, not an arc.) Non-ideal path, for satellites not directly overhead, is more like 7900 km, worst case more. Still, transit time, light through vacuum, is <28 ms.

Compare to fiber. Best ping time is 76 ms, or 38 ms one way. So, our budget margin is 10 ms. Suppose, instead of a direct downlink, packets are dumped to a nearby hub and carried via 1000 km of fiber to the destination, with various routing delays, adding 5 ms, leaving a 5 ms lead, 5000 microseconds.

In finance, we say a microsecond is an eon, a millisecond an eternity. That is because in a microsecond we can do >1k multiplications. 5 ms is time for >5M multiplications, many more than needed to evaluate a position and choose a response.

The only routing choices are which satellite to uplink to, and whether to forward or downlink each packet. Whatever choices are made don't need to be re-evaluated more than per second. Packet queuing delay can be negligible; modern switching equipment will start forwarding a packet while the rest is still arriving; this would happen when forwarding via laser link.

The latency advantage for New York/London/Frankfurt <-> Singapore/Tokyo/Hong Kong would be even more compelling.

that crap should be banned... if only rich folk can do these trades it is not fair for everyone else.

Who ever said it is fair?

There are many things rich people can do, poor cannot. You gotta have money, to make (real) money. Thats the harsh truth and most of us who do not have it, have to struggle hard, to make some wealth and very, very hard and be very lucky and gifted, to get rich by it (without negating all ethics).

Isn't some of the futility if that struggle due to the theft-by-design that central bank led inflation causes, along with their reliance on the government education systems continuing to fail to educate people on his money actually works?

That’s what public companies are for. Lots of not necessarily rich people pool their money to become one very rich entity

Or anyway taxed.

The profit from trading securities is definitely already taxed.

> I do wonder though if sailing the ship is basically a full-time job in itself

Someone should always be on watch if possible. It doesnt always happen as people do solo voyages. Open ocean most vessels would have transponders but if you're anywhere coastal you couldn't take the chance as smaller vessels don't always have and you can't rely on radar either.

I do think you could make it work though. Similar to van living. Plan your legs based on availability. You down time will be part maintainance etc.

Why wouldn't you use the wind energy also? It's a lot of fun, readily available and a lot cheaper…

Sails have several major downsides, most notably they take up a lot of deck space and cause a boat to tilt to the side. If you’re regularly sailing long distances it’s much faster but top speed isn’t that big of a deal when your living on the boat full time.

Other options like kites and wind turbines can work well but they all all significant upfront costs as well as ongoing maintenance issues. Spending that same money on a bigger boat gets you much more space, and of course a generator can give you redundancy or higher top speeds.

…cause a boat to tilt to the side…

This is a net positive. The alternative is to roll back and forth with the waves. It’s much nicer with the sail up and ata bit of a heel.

Also, just to throw this in, one of the world cruising sailing couples which wrote for the magazines switched to a diesel powered boat as they aged and found that they spent less of fuel than they had on new sails. Sails are consumables if you care about performance.

The alternative is a catamaran.

Your point on the diesels still stands. Properly designed cats are unsinkable and don't readily capsize, but not weathering a storm is worth every penny invested in diesels. Besides one needs them in marinas anyway.

Electrical engines are more and more becoming a thing, especially for sail boats, where they server more for harbor and anchoring than covering distances.

Interesting last point...curious why is that? Do they get battered from weather and physically tear, or do they just stretch/thin over time?

Racers use very thin, light, and stiff sails made from mylar or similar materials. They are typically very expensive and want to be changed as often as possible, at least once every racing season. Modern small pleasure yacht cruising sails "canvas" is laminated polyester, aka dacron, which is far thicker, more durable, springier, and more common than mylar.

It's an interesting question, where does the wear come from. But sails are a very active part of the boat; every tack is going to drag the sail across the deck of the boat, rub against fittings. When a sail luffs, head-to-wind it's whipping around with the weight of the sheets (control lines), and then when you're taking the sail down it's getting folded (best case) or stuffed into a bag (worst case) [EDIT: some sail materials like being shoved in a bag!]. And of course even when a sail is just sitting there powering the boat it's under a tremendous amount of force, which stretches it over time.

Sails do fail, and yes often by ripping in half. I've personally never heard of a sail failing at the control points (e.g. the tack of a jib), probably because those areas are heavily reinforced.



This is all spot on. Sails fail due to wear of the fabric itself, because a seam failed, from rubbing, repeated stretching and releasing (you can tell an older sail because it will bulge more as a result of this) or because it got over-stressed. Salt water obviously also doesn't help with sail fabric longevity, as does UV influence all of which will age a sail (check the color difference on spare sails that have been bagged vs the ones in use or, check the first strip of a roll-up sail to see how much that can affect the fabric).

Those areas where the sail needs to be strongest is where they are re-inforced doubling up the layers (and not just 'two', a corner can easily be 10 ply or more thick), on older boats further re-inforced with leather or heavier grades of fabric. The panels are carefully laid out so that the highest stress aligns with the warps. A large sail can be made up from many 10's of panels, which are joined in a variety of manners (glue (typically for very fast boats or as re-inforcement of stitching), stitching, sometimes ultrasonic welding for special applications). On the very high end there are even laminated custom laid out fibre pattern sails (for instance: a sandwich of Kevlar wire between two layers of bonded fabric or plastic).

At one time I worked for a competitor of North Sails, who by the way were pioneers in the digitization of sail manufacturing.

Thanks. As someone who has never and doesn't ever plan to sail, this taught me lot.

They lose their ability to hold their "shape" and become less efficient. This is primarily a concern for people that want to go as fast as possible. I've been perfectly happy with sails after 20 years of light use. I mean, I can see that they don't really have the best shape, but I'm still sailing so all is good.

It really depends on the type of sails you buy.

The cheapest ones last the longest but offer the worst performance.

>top speed isn’t that big of a deal when your living on the boat full time.//

If you're living on your boat 365 then I imagine avoiding severe weather becomes more important?

This is the reason Weather reports and forecast are so important for people on boats.

Most people living in boats actually live on ports and don't get very far from the coast most of the time.

You are right but it depends on the skillset and general lifestyle needs of the person. I've watched (a little) some of the sail around the world channels on YouTube and one couple moved to a performance trimaran, the guys reasoning was that he wanted to have speed to get out of the way if the weather changed.

For those that do not really stray far from the shore or who are willing to take more risk for more comfort, they use a slower boat.

On average liveaboards are sailing around 10% of the time. Most of the time if bad weather is approaching they will just stay in a safe location.

> Sails have several major downsides[..]

Yes, but it makes less noise.

Also less disturbing to the ecosystem below than a prop.

a sail (especially when luffing) is really f**ing loud

From the images on the site it looks like it deploys a sailing kite in addition to the solar powered engines.

Oh hi jjcim. Another cool research project from where I used to work. [0] Back in the day, the development building had a great view of the runway during the Farnborough air show and my pals on the Zephyr project would give me a shout if anything interesting was taking off.

[0] https://en.wikipedia.org/wiki/Airbus_Zephyr

The second link of the parent comment describes a optional automatic parasail tug.

Most sea going sailboats, and many others, are perfectly capable of sailing around the world, without any fuel. Solar panels are only needed to charge batteries, that are only needed if you want the extras: GPS, radio, other communications. 2 panels and 2 batteries are good enough for most boats, for 1 to 4 persons, traveling for anywhere around 1-2 months across the seas. The limitations are water, and food storage. The solar and batteries are good for years, easily up to 5 years. Humans need other things though. It's not the boats or the technology its the price that limits. (You can buy an ocean cruising bust for 20k USD, easy.) But, it is a life style commitment!

That's the entry fee. And then the real cost starts to roll in. There is a reason so many Youtube channels and Patreon accounts are being used to fund otherwise unviable life-styles of people sailing full time.

Food can be stored longer by refrigeration, which requires power. Similarly water can be desalinated, which again requires power. Solar & batteries can help with both of these.

On a typical sailboat space is very much at a premium, even de-hydrated foods occupy quite a bit of room.

Wow, the "Silent Yachts" one has a "fully automated towing kite"! That's not something I've ever encountered before, very clever. Removes the need for an annoyingly tall mast and probably saves a lot of weight as well.

A mast provides a predictable center of lift in the boat on two axes, easy to control, handles high winds elegantly. Kite? Not so much. Also, try sailing in to the wind with a kite. May be possible, but very, very slow going. Traditional sail plans strike a balance between functionality at all points of sail, ease of handling and safety. They also have downwind sail options.

One advantage of a kite sail is you have more surface area for solar panels and those panels are not going to shaded by the sail while underway.

I find it quite strange that on the Azura landing page they don't have even one photo of a yacht. Just renderings.

They also have a price, which was nice.

It looks like shit though. The other yacht looks much nicer.

These guys spent the night on the Silent-Yachts one a ~month ago. https://www.youtube.com/watch?v=iIte4FNI0U0

anyone else think it would be super damn fun building solar floating homes like this?

A local company does this, but they are intended to be mostly stationary.


I’m waiting for the floating cities. Sounds incredibly fun.

I'd be down haha - When do we start?

You definitely want to try an English narrowboat before you start. I know people that have done this; it's romantic, but at its least romantic you're living in a not very well insulated damp trailer.

I'm on board mine now! I guess the theoretical benefit of the seagoing version is your roof space isn't constrained by the size of English locks so you might actually be able to fit enough solar to power the vessel. That and find good weather...

If sea levels keep rising a lot of coasting could be like this.

In the netherlands they have flaoting houses in the canals, but stationary AFAIK

There's a couple living on a cheap ass floating tent/home (it literally uses barrels to float) in Sweden I think. Pretty cool. Also narrow boats in England are cheap and rather nice. Could start there.


You know, sailing catamarans are a thing, right?

Wind is more consistent than sunshine.

Sure, I know sailing catamarans well (via Youtube vids mostly admittedly). But I switched drooling focus when these things started appearing- I suspect they will eventually displace many if not most other boat types (albeit not in my lifetime), possibly using hydrogen (not battery packs) as energy storage. Sunshine is not required if I understand it correctly. No wear and tear on the sails, not dependent on winds to go from point a to b, more like driving than sailing, except no pollution, no noise.

Solar yatchs are cool!

Considering loitering is a very important goal for military drones, I expect them to be using solar power extensively too.

For those curious about the physics of these aircraft, here's an analysis I did of the same concept. The goal is to determine the smallest aircraft configuration that can indefinitely sustain flight: https://github.com/gusgordon/atmospheric_satellite#readme

Is there a reason you optimized the amount of starting energy in the battery? I know basically nothing about how solar power works, but surely you'd just fill the battery up to 100% with an extension cord on the ground before launching it?

Good question. One requirement for the aircraft in this optimization is that they must have more energy in the battery than they did 24 hours prior. If the aircraft started at full energy, they wouldn't ever be able to satisfy this requirement, so that's why it's an independent variable.

For example, an aircraft could "start" at 50% battery state of charge, then charge to 95% over the course of the day, then come back 24 hours later at 51%, and that would be valid. There are other ways around this, but this is what I came up with at the time.

This is similar to why the starting altitude is allowed to float. The gravitational potential energy of the aircraft can be used as another "battery", but the aircraft is only a valid solution if it's not losing altitude over the course of 24 hours.

Maybe it helps surface how much charge is required to climb to altitude vs how much charge is required to sustain it? This may also help surface how much of a buffer you may have in takeoff time in order to survive night. E.g. if you require 100% charge then it's likely you have to take off at a fairly specific time of day.

The battery is too heavy if it's fully charged.

There are actually electrochemical cells which do change mass as they charge and discharge, metal-air batteries. In these, oxygen from the air is the cathode used to reduce the metal anode. But mass gain goes the opposite direction: the batteries are actually heaviest when discharged.

Various metals can be used. Iron is cheap, whilst aluminium-air cells actually offer some of the best performance in kWh/kg of available materials, exceeding that of LiON cells.


Batteries are heavier when fully charged. Takeoff weight matters. It's not much heavier, but it might be enough to affect things at this scale.

edit: remember the context. This is about an abstract optimization to find the minimum viable aircraft.

I can't tell if you're being serious. You are technically correct, but also incredibly wrong in suggesting that the increased weight would be substantial enough to impact anything measurable. Depending on the size and capacity of the cell, you might see a difference due to general relativity on the order of nanograms.

see: https://physics.stackexchange.com/questions/34421/does-the-m...

A nanogram saved is a nanogram earned.

I can't tell if this is satire or not, but taken in good faith, how?

A fully charged battery would necessarily have more mass than a fully depleted battery, but the difference should be so tiny as to be immeasurable. Or am I wrong? We're essentially talking about the sum weight of a bunch of electrons, which are extremely light. There's no other exchange of matter going on when charging/discharging a battery, just the creation/destruction of chemical bonds, and associated movement of electrons.

A battery doesn't have a static charge. When it discharges, electrons move from one side to the other, then back through the batter, and you modify which atoms have which elections. But it continues to have no static charge.

However it has less potential energy. And therefore you change mass by the mass associated with that potential energy.

what kind of batteries are meaningfully heavier when charged? are you just talking about like E/c^2?

A water/gravity battery comes to mind. Definitely not the answer you are looking for, but an answer none the less.

Depends on your definitions. Is the water pumped considered part of the battery before it’s elevated?

The pumping of the water would be "charging" the barrel of water, I guess.

I'm sure this will work great for powering an aircraft, too. You could just let it all hang from an anchor at the highest point in the battery :-P

Gas tanks :D

nice analysis

Is it feasible to operate these at lower altitudes?

e.g. can we have solar/air drones posted every 100 miles of interstate highway?!

Yes it's a lot easier at lower altitudes since you can get more lift, but you might run into some extra regulatory issues with that :)

> e.g. can we have solar/air drones posted every 100 miles of interstate highway?!

What's the usefulness of this or was it just a random example?

As someone who lives somewhere with photo radar, I assume photo radar.

Nobody likes photo radar.

In 1958 two guys flew a Cessna 172 nonstop for 64 days without landing. They refueled mid-air via a truck that drove under them during a low pass.

I had never heard of this record until now. Cross-country flying in small planes like this can be incredibly tedious and the refueling sounds very dangerous. I can't imagine doing it for this long. Apparently, neither can the guy who did it:

> When asked by a reporter if he would ever replicate the stunt, Cook replied: “Next time I feel in the mood to fly endurance, I’m going to lock myself in a garbage can with the vacuum cleaner running, and have Bob serve me T-bone steaks chopped up in a thermos bottle. That is, until my psychiatrist opens for business in the morning.”

Source: https://www.airspacemag.com/daily-planet/airborne-for-64-day...

Good Lord, what an adventure! Thank you for posting!! I had no idea about this flight.

Here's an account that popped up on Google.


Even more impressive, they did it before audiobooks!

how did they um...."defuel" their bodies and such in the air?

Summary: they pooped into plastic bags and tossed them overboard.

Probably/unfortunately not really a Starlink competitor, right?

They don't specify the "cruising" altitude, but I assume it's ~10 kilometers at most, probably less?

Airbus would need quite a few of these in order to build a global internet connectivity service then.

Edit: https://en.wikipedia.org/wiki/Airbus_Zephyr says ~20 km.

Starlink sats (will) operate at ~540-570 km:


[EDIT] remove redundant info

> Airbus would need quite a few of these in order to build a global internet connectivity service then.

Yes it would require more units, but with a much smaller cost per unit for build, launch and maintenance. That's where it will start to get interesting: Which will have the lowest cost per GB, per user, per square km of coverage etc?

I suspect even if it's cheaper it would still remain less global, since having massive swarms of these would probably be even more of a logistical nightmare than starlink. i.e they would supplement other technology... which is pretty much what Airbus is quoted suggesting in the article.

> with a much smaller cost per unit for build, launch and maintenance

Somebody further down in the comments estimates $250k in launch costs for each Starlink satellite^[1]. Elsewhere, I found a claim that SpaceX execs said in 2019 that the per-satellite cost was "well below" $500k^[2]. So let's say $400k per satellite including manufacturing and launch, just to pick a number.

Once it's in orbit, you need to pay for operations, but not maintenance (except on your ground-based infrastructure). And multiple factors (e.g. cheaper launch) stand to bring that price down.

Realistically, how much do we expect one Starlink satellite's worth of telecom UAS to cost on an ongoing basis, including the maintenance and operations costs that don't apply to Starlink? Where is the analysis? OP's article makes the "cheaper" claim with (AFAICT) absolutely nothing to back it up, and the fact is that full size aircraft are not cheap.

The service density flexibility and possibility for additional radio bands Starlink can't provide might be a good argument for this system to exist, but all this talk of it being cheaper seems very vague and presumptuous. What am I missing?

^[1] https://news.ycombinator.com/item?id=28832257

^[2] https://www.teslarati.com/spacex-starlink-satellite-launch-s...

> OP's article makes the "cheaper" claim with (AFAICT) absolutely nothing to back it up, and the fact is that full size aircraft are not cheap.

It's not a full sized aircraft. 1 small autonomous plane is cheaper than 1 small satellite in general - in almost all respects. The article didn't claim anything beyond this:

> The unmanned glider [...] is cheaper and more environmentally friendly than a satellite.

This is fairly obvious and uninteresting, what is interesting is cost per GB/user/km2, in other words the end result, which is hard for anyone to say with much certainty at this point even with a thorough analysis because nether business has reached scale yet.

> It's not a full sized aircraft. 1 small autonomous plane is cheaper than 1 small satellite in general - in almost all respects. The article didn't claim anything beyond this:

From the picture in the article I'm not sure what else to call it other than "full size". Wiki claims it has a ~90 foot wingspan^[1]. Wiki also claims it has an 11 lb payload capacity, so one imagines a practical version of this concept would need to be be substantially larger in order to carry a useful telecom payload.

(A Starlink satellite is a couch-sized slab weighing over 500 lbs, and one can only assume how much of that is telecom equipment, but it's probably a lot more than 11 lbs. So it seems plausible that you'd need on the order of 10 aircraft of this size, or a single much larger and much more expensive aircraft, to equal the throughput of a single Starlink satellite. None of that sounds cheap.)

Being a UAS doesn't necessarily make it cheaper, either. The MQ-1 Predator, a borderline obsolete ~1500 lb airframe pushed by a ~100 hp air-cooled Rotax, seems to cost governments on the order of 10 million dollars to procure. I'm sure there's a lot of pork in there, but it seems far from obvious that relatively exotic UASs like this one can be procured and pressed into production use for, say, two orders of magnitude less than that.

> This is fairly obvious and uninteresting, what is interesting is cost per GB/user/km2, in other words the end result, which is hard for anyone to say with much certainty at this point even with a thorough analysis because nether business has reached scale yet.

Starlink is already a service you can buy and use, subject to whatever "beta" rollout scheme they're using. They still have a long way to go to realize their scale ambitions, but I think their economics are far more settled than other schemes (like this one).

I do agree that cost per user is the interesting number here, but--as above--it seems far from obvious that this UAS scheme can even be competitive with Starlink, let alone cheaper in any reasonable sense.

^[1] https://en.wikipedia.org/wiki/Airbus_Zephyr

These planes can compete with Starlink in certain scenarios, for example you can launch them in the event of floods that knock out the regular telecommunications infrastructure.

With Starlink soon having ~global coverage, why bother transporting, launching and servicing these aircraft for a one time thing? I don't see the benefit. Will also be really hard to reach low prices for end user terminals with this approach.

Very high quality visual/signals surveillance seems like a much more obvious market fit.

First, Starlink has limited bandwidth per square mile. Therefore it cannot conceivably provide telecommunications for densely populated areas.

Second, all you have to do is make these aircraft compatible with cell phones. So your target population already has "end user terminals" literally in hand.

Third, this is not a one-time need. Local disasters happen fairly regularly, and sometimes can be predicted in advance. (For example hurricanes.) There is real value to an instant telecommunications network that can be deployed on short notice.

Now I don't claim that this is actually economically viable. But it is not exactly crazy, either.

Pretty good points. Starlink can't do 2G/3G/4G/5G with mobile phones on the ground, ~550+ km away, of course.

They should probably look into partnering with e.g. Ericsson Response (https://www.ericsson.com/en/about-us/sustainability-and-corp...).

> Very high quality visual/signals surveillance seems like a much more obvious market fit.

Oh, yeah, there are already companies the provide complete surveillance of cities or large areas of cities so that even if a crime scene is discovered hours or days later, they can just go back to that time and track vehicle movement to and from the crime scene to wherever it ends up as long as it's in the same (large) area.

Reducing the cost of the equipment that does the recording of the area will only make it more accessible to more police departments, for better or worse.

For starters, all network participants need an expensive, large and power hungry Starlink antenna. An airplane could work with smaller devices as endpoints, such as phones.

They would have the advantage of variable density based on demand, i.e. more of them over population centers and none over oceans, whereas LEO satellite constellations are pretty uniformly distributed because they're orbiting.

It's sort of in between a stationary cell tower and LEO satellite constellation.

But then you have to worry about them failing and hitting those population centers, whereas satellites deorbit slowly and usually burn up completely.

You wouldn't need that many. The line of sight area has 300 km radius. There's even a precedent. https://en.wikipedia.org/wiki/Stratovision

The U2 operated at over 20km, so maybe the altitude is higher.

I suspect the greater issue is vehicle cost, lifetime, and safety. A starlink satellite is much smaller (and as result cheaper) and is rumored to have a 5+ year lifetime. Also, at end of life it burns up in the atmosphere. No worry about pushing the life on a component and having it crash and kill someone as a result.

I’m a bit puzzled by the economy here. Is creating, lunching and orbiting a satellite really cheaper then flying an airplane? Is it really cheaper to have a decommissioned satellite totally burn up in the atmosphere then reusing parts of an airplane to fix another, recycle unusable parts and put the rest in a landfill?

The economics here just seem wrong.

USD2021$15M per Falcon 9 launch (re-used, assuming first launch was paid for by a customer) [0]

60 Starlink satellites per Falcon 9 launch [1]

= + USD2021$250,000 in launch costs per satellite (+ manufacturing / ops costs)

[0] https://www.elonx.net/how-much-does-it-cost-to-launch-a-reus...

[1] https://space4peace.org/starlink-gears-up-to-launch-nearly-1...

As a reference a new Cessna 172 is $432,000 [1] and that is not a high tech aircraft.

[1] https://www.forbes.com/sites/erictegler/2021/04/28/prices-fo...

This feels like comparing potatoes and pineapples.

A new Cessna vs a used Falcon 9 launch hardly seems like a fair comparison. The cost of the rocket is written off as externalized. The actual satellites are not factored in at all. Really what we are comparing here is the cost of an operation vs the cost of an airplane. The economics still seem dubious.

And a Cessna 172 has to be human safe.

Indeed, and the $432,000 is the price on the consumer market. A mass order of Zephyrs by, say, the British Government is sure to land a much smaller price tag per unit then a lone hobby pilot can expect when buying a single airplane.

On top of this, if Starship is successful ("fully and rapidly reusable") it could bring the launch cost down another order of magnitude.

And because Starlink is building thousands of satellites it has economies of scale that no previous satellite/spacecraft had.

If Airbus is successful, you'd have to compare SpaceX's scale to a similarly massive manufacturing operation of solar-powered aircraft. And you could theoretically make money from multiple sources since the aircraft could carry multiple pieces of equipment. You could make money from being an ISP and from selling imaging services.

Glide based efficiency crafts absolutely need thick atmosphere. They don't have supersonic jets.

The U2 was subsonic. Also, un-powered gliders can get up to impressive altitudes.


> The unmanned glider, which is powered by two small propellers,

I’m confused by the article and the above comment. Isn’t a glider by definition unpowered?

Checkout [1]. Easier to say "motor glider" or "powered glider" than "powered airplane with glider like configuration".

[1] https://en.wikipedia.org/wiki/Motor_glider

Unfortunately the first commercial application of this is likely to be helping loitering munitions stay aloft longer, to lethally target humans.


Funny how tech these days end up majority in use either for targeting Ads or warfare or surveillance.

They're hoping to get six months flight eventually out of a propeller craft. I can't help but wonder what we could eventually get out of a solid state craft.[1] They mention batteries in this article when referencing that six months target, but I have to assume servicing the propellers is important as well.

1: https://www.engineering.com/story/how-the-worlds-first-solid...

You got a small typo there.

Lol, thanks. :)

Not mentioned in the article, but the li-ion batteries onboard the aircraft have a silicon nanowire anode thus achieving amazing energy density:


Do you know what sort of density and discharge rates they're talking?

Only the company's own marketing materials, but as a data point six years ago they partnered with a Chinese phone manufacturer to create a device with an absurd (at the time) 5800mAh battery:


They've made some improvements since, but the exact parameters haven't been disclosed.

Hmm, that seems interesting, but it's not very specific (Ah/g), so who knows what the actual capacity is... They do mention a 1.25A discharge rate, at least.

“ It is a sustainable, solar-powered, ISR and network-extending solution that can provide vital future connectivity and earth observation to where it is needed”

This military-industrial style of English always sounds very odd and is ubiquitous with these companies. Is it because they’re selling to Military buyers?

To fly through the night, you need energy. I'm wondering if it's more efficient to store it in the batteries, or as stored kinetic energy by flying to a high altitude and descending through the night.

It's a good idea, in principle. But according to the sources I could find, to get enough gravitational potential energy to equal the electrical capacity of Zephyr's batteries, you'd have to lift the entire craft by about 70km.



I can imagine you'd want to take advantage of gravity to a certain extent, but it seems a bit tricky to estimate how much. Presumably there's a particular altitude at which the aircraft's overall efficiency is at a maximum. Deviating from this altitude allows you to store a bit of extra energy (which means you can get away with a smaller battery) but you don't want to deviate too far, or you'll lose more energy to various inefficiencies than you're saving. And you probably need to keep some electrical reserve power anyway, in order to be able to actively navigate away from unfavorable winds.

There's also the fact that this is optimizing for power usage in the air, when really what we'll want to optimize for most likely is power usage while doing some specific task in the air, and that task may necessitate specifics of what altitudes it can function at.

That's the real challenge. Being able to, for example, loiter over a suspected clanlab 24/7 for a month to gather evidence is far more taxing than flying an optimized route.

Assuming you didn't care about the path, could you also take some optimal path where you go east to west to prolong the days, then go west to east to shorten the nights. Could probably play with south/north too depending on the time of the year to get longer days. Or maybe you can go far enough to the pole where it's always day.

If you fly fast enough you can outrun the night, but that opens up a whole new set of problems.

Also, if you raise altitude high enough, you also can get rid of air resistance, so you won’t need to spend any energy to maintain altitude.

What's the benefit over something like a weather balloon?

Pretty interesting thought, tape a few hundred micro SD cards to it and you've got some impressive bandwidth.

You can tell this where to go - weather balloons are utterly beholden to the whim of wind patterns.

And this is more than a theoretical risk...


¿Por qué no los dos?

It looks like solar-powered zeppelins are a thing, although with the brief googling I did it looks like nothing really exists just yet.

Yea I guess I was more thinking of a kind of blimp, where it still has some solar to allow it to maneuver around, but not to actually stay up.

If the aircraft needs to stay in one place maybe that would be less efficient though, since it would be harder to fight winds.

You're basically describing the JLENS program, though the lighter-than-air craft was tethered, not free-flying.


I thought that you could somewhat control a balloon by using different wind patterns in different elevations.


Google's Titan project was going to deliver internet service (... before it got strangled in the womb grumble grumble ...). LTE from aircraft to client, and a dedicated point-to-point radio from aircraft to backbone.

"Airbus ultimately believes that the aircraft could remain airborne for “months at a time” and could provide internet to both commercial and military customers."

What sort of power requirements would this bring? I assume that it would be more sophisticated than just dumping RF energy indiscriminately across a huge area.

Complete outsider doubt: Does this has the potential to replace satellites? Or, why did google project loon failed?

A craft like this is more likely to serve predator/reaper/sentinel missions. Particularly ones in locations you don't want the aesthetics of full state surveilance but still want the same operational capacity.

I envision more unarmed uses. I live in Washington DC, where the aesthetics don't matter as much as the operational capability. We're so used to helos flying around that spotting them has become a game: https://twitter.com/HelicoptersofDC

When a bank teller says "The robbers drove away in a blue car," the police want the ability to roll back the tape and find all the blue cars that left the bank in the past hour and see where they are now.

I think it would complement, not replace. There are missions that nicely fit the capabilities of UAS, there are missions that nicely fit the capability of satellites, and there are in-between missions that could benefit from long-duration aircraft like this. I live in the east side of Washington DC. We regularly have police helos flying overhead. I wonder if this kind of platform could supplement their efforts for things like tracking escaping vehicles when the police call off pursuit (car chases are frowned upon here due to the fact that they're so dangerous).

Cherry picking examples, UAS will always be best for a construction manager looking at the progress of a highrise, and there's no way an atmospheric vehicle would host a world class space telescope. But things like monitoring deforestation could benefit from a vehicle that can take high-res photos day after day without needing a lot of maintenance and then be packed up and shipped to the arctic to estimate sea ice. A single satellite would have trouble performing both missions.

I love that these aircraft are built so lightly and fly so high. They are probably cheaper than any missile capable of shooting them down. They could operate over enemy territory without much worry. Send dozens. Shooting them down will cost more than their replacement.

Wasn't Facebook working on a similar project (Aquila)?

Related (in at least one dimension): https://www.airspacemag.com/daily-planet/airborne-for-64-day...

Cessna 172 flown for 64 days, 22 hours, 19 minutes and 5 seconds.

> When asked by a reporter if he would ever replicate the stunt, Cook replied: “Next time I feel in the mood to fly endurance, I’m going to lock myself in a garbage can with the vacuum cleaner running, and have Bob serve me T-bone steaks chopped up in a thermos bottle. That is, until my psychiatrist opens for business in the morning.”


I think he sums this up nicely. What a feat!

You can see the aircraft used at the Las Vegas airport. It says "Hacienda Hotel" on the side and I think it's hanging over baggage claim.

https://en.wikipedia.org/wiki/Cessna_172 :

"From December 4, 1958, to February 7, 1959, Robert Timm and John Cook set the world record for (refueled) flight endurance in a used Cessna 172, registration number N9172B. They took off from McCarran Airfield in Las Vegas, Nevada, and landed back at McCarran Airfield after 64 days, 22 hours, 19 minutes and 5 seconds in flight. The flight was part of a fund-raising effort for the Damon Runyon Cancer Fund.[14][15]"

Was the engine oil okay for that long continuously? I mean I guess obviously it was but is that ok?

according to the airspacemag.com link in other comments, they replenished the engine oil in flight.

The linked article on that page is broken. I’m guessing he somehow refueled in flight?

Yes. They flew low and slow over a long, straight road and refueled from a truck that kept pace with them.


> A Ford truck, donated by Cashman Auto in Las Vegas, was outfitted with a fuel pump, tank, and other paraphernalia required to support the aircraft in flight. When fuel was required, a rendezvous would be arranged on a stretch of straight road in the desert near Blythe, California. An electric winch lowered a hook, the fuel pump hose was picked up, and Timm or Cook inserted it into the belly tank. It took a little more than three minutes to fill the belly tank.

> The total fuel capacity of the airplane was 142 gallons. Plans called for refueling twice daily. Sometimes weather or the inevitable glitches upset the schedule, and a new rendezvous was worked out by radio. This activity was repeated more than 128 times.

The whole article is worth a read; it was quite the hairy sounding endeavour. Two months in a C-172 would kill me, I'm quite certain.


Haven't read it to find the answer to your question yet, but bless the Internet Archive

Yes. Also added oil.

Neat - but not interesting from a technological stand point.

Over 1500 hours of continuous operation is quite a feat. Components like magnetos have service schedules much shorter than that.

This also ignores all the unexpected issues that pop up in aviation. My only experience with Cessna 172s are rentals which are treated like crap - those planes need something looked at like every 50 hours.

Is it not? I don't imagine such sustained flight, continuous operation of all the equipment and engine for so long, would've been a design consideration.

Presumably there's a number, I just doubt it's tens of days, so isn't it interesting that it was achieved?

This record was set ~3 months after someone else did it for 50 days.

From an engineering stand point, performance of components or materials are always assumed to be much worse than actual and the forces / conditions they are subject to overestimated, with further factors of safety applied on top. This is how it should be. It also means properly designed things will carry on working better than you expect (on average).

It’s not interesting (to me) from a technological stand point compared to the solar UAV because flying up and down the same road with a truck refuelling you is not useful, and if others (e.g. Military, NASA) could be bothered to do it - they would probably do a better job relatively easily.

To me - It’s the same as building the worlds longest domino trail. You could beat the previous record by 1 million dominos which is neat but.. what have you proven, and why does it matter ?

> This record was set ~3 months after someone else did it for 50 days.

Fair enough, I didn't know about that, I'd have been as interested to hear about either of them first, and like you not so much the other second. (And I doubt the commenter that shared it meant it as 'wow look 64 compared to 50' either.)

I like the optimism of the article but I can't help but believe that the primary purchasers of this capability will be armies and spies.

Isn’t taxi-takeoff-landing what consumes the most energy? It’s often 10% to 25% of the total flight consumption for supersonic planes like the Concorde (but not for the SR-71, since they refueled in-flight to fill the rest with inert gas https://theaviationgeekclub.com/former-sr-71-driver-explains... ), and still a lot for the other planes.

Based on your percentages then, I think you mean most per unit time? So then, given three weeks far exceeds normal flight time (by more than 1/25%)...

With a cruise speed of 30kn, better hope its not too windy wherever you are flying, winds aloft can often be much higher than this

That's a definite problem for ISP duties. Law enforcement is used to "sorry no air support tonight, it's windy."

I would love a low cost electric ultralight.

I wonder how the engine can keep operating for such long periods of time without maintenance!

This stuff is pretty sturdy. The lifetime of brushless electric motors used in this kind of dirtless environment is basically the lifetime of the bearing used and can usually be measured in years of nonstop operation without any modification already.

Doesn't appear to have a payload in the picture. That would add weight & power draw.

Proving the concept is huge, since this is an idea that's at least as old as satellites. Once they have the proof of concept, I see three additional hurdles: 1. Safety. Prove you can keep these things in the air for months at a time without any of them crashing. 2. Payload. Exactly what you point out. 3. Operational usefulness. Can this thing stay in the air for months while flying the routes necessary to complete its mission?

I really hope Airbus and others are able to make this concept work. It would be nice to have an in-between option between UAS and satellite.

First communications satellites were just passive reflectors. They were just big inflated balloons made with reflective material.

Same idea could work with solar powered aircraft.



Why use a solar powered plane and not a solar powered airship?

Looks more like a drone to me (ie, there's no useful load).

> "which is designed to stay airborne for weeks at a time in order to provide internet to users on the ground"

The hardware for this purpose doesn't require a heavy aircraft, I suppose.

The wing tips look wicked, not sure if necessary

It’s so depressing to read that one proposed mission for this plane is…monitoring oil spills.

I worked on a satellite imaging startup. For this kind of stuff usually oil and gas and large scale agriculture are the first ones to show interest. They don't need great resolution or revisit times and their assets span over very big areas so monitoring from the ground/sea or with small drones is really expensive.

Depends on the appplication. An NDVI analysis or determining vast crop / growth problems yes but if you want to check for disease this is often done by drones to have higher resolution. I could imagine doing regular field visits with these planes and avoid the high labor costs of drone management/flying.

Sources: I work in a big agtech company with satellite imagery. PS: We should connect.

Why is that depressing? Unless you have some silver bullet to remove the need for oil or prevent any future oil spills it seems like creating innovative technologies to detect them as soon as possible is a good thing.

It would be like if someone developed a cheap, non-invasive technology that could detect cancer extremely early, and then you complained because they hadn't cured cancer instead.

But there is starlink for internet in rural areas

Sure, but even if these planes managed to somehow cost as much as a starlink satellite, it'd still be cheaper to do it this way because having some dude toss it up into the air for takeoff is basically free compared to even a fully reusable Starship flight.

Plus it can be deployed on an as-needed basis. Large concert in a rural area? Hurricane destroy your city's infrastructure? Toss up a few planes and get the service you need for a week or month until the situation is resolves. (At least that's the theory... I hope this technology works as planned.)

I'm assuming the flights were achieved mid summer when they days are longest and it can't yet operate outside this window.

If this is the case, shame they don't just admit this up front

They ran the 18 day flight test in September, so not the dead of winter, but also not on the longest summer days:

A solar-powered aircraft has completed an 18-day test flight offering hope it could be used to create internet access for billions of unconnected people around the world...The test flight touched down in Arizona on September 13.


Phoenix has about 12.5 hours of daylight on Sept 13th. (compared to ~14.5 hours on June 21st, ~10 hours on Dec 21st.

All of this comes with a big "Work in progress" caveat. Still, this type of technology has been theorized for decades so it's nice to see Airbus making progress. Let's see if they can get it to the point of commercialization.

Perhaps they are aware of eatrh's axis and will move operations to the southern hemisphere? Or adjust the drone's speed to stay in sunlight?

> Or adjust the drone's speed to stay in sunlight?

Depending on altitude, that would require an awfully fast aircraft.

no mention of their recent faults too... (https://www.reuters.com/article/airbus-zephyr-idUSKBN26J0NU)

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