Category: Regulation

Next Decade Aviation

Here, I thought I’d speculate on what’s coming our way. That’s looking at the next ten-years.

Although this maybe contradictory to my earlier writings the subject is by no means all or nothing. Aviation is a technology-based means of mobility. Without the technology component there is no flight. Aviation a youthful industry when compared with ships, roads, and rail.

On the other hand, people are at the heart of the aviation system. That’s particularly true in assuring its stability, safety, and security. People create, innovate and fix systems when they fail. People make go-no go decisions. People protect systems from attack.

Commercial aviation maybe a youthful industry but it has an inbuilt conservatism. It’s the characteristic of not wishing to change when systems are working well. This has both and upside and downside.

A maturity of rules, regulations, processes, and procedures comes about by continuous improvement. By people learning. However, it’s often the case that industry does not reflect the society that it serves. People are excluded or walk away when expectations are dashed.

Across the globe, the future of the aviation workforce depends upon change. There again is a rub. People operating in a successful system rarely welcome change. Especially, if the drivers for that change come from outside the tight knit community of aviation professionals.

The first decades of the jet-age were characterised by a sense of adventure, glamour, and pride. As commercial aviation became available to a wider traveling public there was a gradual opening to professional entrants from most sections of society, even if that was predominantly male.

Now, big company traditional career paths are more an exception rather than the norm. Aviation competes with other industries at a time of rapid digital transformation. This has the impact of opening a wide range of options to potential professional entrants. In the coming decade the trend is going to advance.

A successful aviation industry organisation looks for skills and behaviours as much as it looks for raw technical talent. Assuring stability, safety, and security means having a responsible attitude, an instinct to challenge and question.

Today in the post-pandemic world, the industry is going through a period some people have called the “great resignation”. A generation have walked away from the pressure and stresses of the crisis. Industry behaviour, in a rush to cut costs, exasperated this by treating people exceptionally poorly.

For a sustainable future, commercial aviation needs to work to eliminate the hire and fire cycle. The global aviation industry needs to think and act differently. Aviation needs to get off the trap of the “similar-to-me” effect found in hiring. When a selection bias dominates potential professional entrants are put off. Talented young people are likely to choose meritocratic employment where rewards are there for achievement and commitment regardless of non-relevant factors.

Some work will be replaced by automation. However, retaining aviation people with people skills, regardless of background, will be invaluable in the next decade.

Two upfront

One of the fundamentals that remains a part of civil aviation is having two pilots in the cockpit. It’s an indication of the safety related activities of the crew of a civil aircraft. Today, we have a mixture of human control and management. Pilots still fly hands-on when the need arises. The expectation is that throughout their working lives pilots have the competence to do so, at any stage in a flight.

Progressively, since the establishment of aviation’s international order in the 1940s the required crewing of aircraft has changed. Back in September, I visited the de Havilland Aircraft Museum in Hertfordshire. There I walked through the fuselage of a de Havilland DH106 Comet[1]. This was the first turbojet-powered airliner to go into service and it changed the experience of flying forever and a day.

That passenger aircraft, like aircraft of the time, had four crew stations in the cockpit. Two pilots, a navigator and flight engineer. It was the era when electronics consisted of valves in large radio sets and such long since forgotten devices as magnetic amplifiers. The story from the 1940s of IBM saying, “I think there is a world market for maybe five computers” is often repeated.

For modern airliners the navigator and flight engineer have gone. Their functions have not gone. It’s that having a crew member dedicated to the tasks they performed is no longer required. As the world of vacuum-tube electronics gave way to transistors and then to integrated circuits so computing got more powerful, cheaper, and abundant.

With a few significant failures along the way, commercial flying got safer and safer. The wave of change in a human lifetime has affected every mode of transport. More people travel to more places, more safely than ever could have been imagined 80-years ago. Does that mean the path ahead will take a similar shape? Excitable futurologists may paint a colourful picture based on this history.

Let’s get away from the attractive notion of straight lines on graph paper. That idea that progress is assumed to be linear. Tomorrow will be progressively “better” by an incremental advance. That’s not happening now. What we have is differential advances. Some big and some small. 

The aviation safety curve is almost flat. The air traffic curve, with a big hole made by COVID, is climbing again. The technology curve is rapidly accelerating. The environmental impact curve is troubling. The air passenger experience curve may even be at a turning point.

Touchscreen tablets already help flight preparation and management[2]. Flight plan changes can be uploaded and changed with a button press[3]. The squeezing of massive computing power into small spaces is being taken for granted. What does this leave a crew to do?

Back to the start. Two pilots in the cockpit, with executive responsibilities, remains the model that maintains public confidence in civil aviation. The golden rules still apply. Fly, navigate and communicate in that order. Crews, however much technology surrounds them, still need to act when things do not go as expected. Does this mean two cockpit crew forever? I don’t know.

[1] https://www.dehavillandmuseum.co.uk/aircraft/de-havilland-dh106-comet-1a/

[2] https://aircraft.airbus.com/en/newsroom/news/2021-02-electronic-flight-bag-the-new-standard

[3] https://simpleflying.com/datalink-communications-aviation-guide/

Flight Ahead

Although, I’m an advocate of having people in control of machines it isn’t people that are opening new opportunities in transport. Technology is racing ahead and making the past illustrations of popular science magazines become a reality. I can do without the hype in the headlines of flying cars. Building expectations of one in every garage remains a 1950s dream or nightmare, dependent upon your point of view. Aside from that hot air viable new electric vehicles are in the works.

Heavier-than-air machine that do more than buzz around our heads are going to proliferate. The inevitability of this is open to question but if I was to assign a probability to it, the number would be close to one. If we stretch our minds back to an unobserved small corner of the planet in late 1903, a couple of diligent brothers flew a machine that hopped a short distance into the air under its own power. Many newspapers of the time didn’t bother to print this breakthrough story because wise and eminent scientists had told them that it was impossible for people to fly.

It’s clear, getting into the prediction business should be done with humility.

We have a dilemma. It’s so rare of us to turn away from advancing technology when we know it can be made. It’s even more irresistible when the economics scream out buy me. So, a ticket to ride in the realm of Urban Air Mobility (UAM) will need to be no more than a typical taxi ride. Given that a taxi ride from my home to Gatwick Airport is about £20 then that’s the mark to hit. True that short journey may not be commonplace by air at that price until around 2033, a decade away, but it will be irresistible when it comes.

This chapter in air transport, that is being written is as significant as that in late 1903. I know that’s a mega statement, but the signs do point that way.

Eventually, UAM will become a network of piloted and autonomous electric air vehicles operating between cities and major destinations like airports.

Now, a couple of solvable challenges stand in the way. One is the endurance and portability of the energy storage devices. The other is complexity and mastering the science and art of functional safety. There’s plenty of confident hyperbole to suggest that these two are short-term barriers to progress. I say they are not.

Weight is one of aviation’s biggest enemies particularly on small vehicles. Batteries are expensive, heavy and require tailored control. Autonomy or the semi autonomy, needed to make the economics click is challenging systems engineering orthodoxy. Both tasks require the meticulous diligence of the Wright brothers to get past. No fanfare or flashy investor can push them aside.

Making the absolute most of energy storage technology is essential. Finding the optimal configuration of batteries, transmission and control electrics means iteration and the tolerance of a good handful of failures. The engineering of what’s becoming a system of systems, with the complexity of vehicles and the complexity of traffic management, interacting at great speed demands extensive analysis and testing.

These tasks can be accomplished. Rushing them would be foolish. That’s difficult to resist when everyone wants to be first.

Future

The road to fixing climate change is not an endless road. Today, our whole approach to climate change goes somewhat like this:

I’m not sure I’m convinced. Yeah, maybe we have a problem. We should do something. Definitely, but send me the plans, I’ll get to it, I’m busy. Time passes. What was it we should be doing? Oh yes, but that plan is for (insert a name) not me. I’m not contributing much to the problem. Anyway, there’s time between now and (insert a date).

So, we go on. There’s no doubt that there are changes needed to tackle climate change that are immensely difficult to do. Trouble is that by fixating on those difficult problems we talk ourselves out of doing the easier things. Let’s put simple actions like home insulation on the agenda again. Let’s loosen-up on our ridiculously restrictive policy on wind farms. Let’s invest in our national electrical grid to permit more connections to be made easier and quicker.

Yes, it’s advantageous for the PR companies employed by high carbon businesses to talk up difficulties and herald small gains as miracles. I mean, that’s what they are employed to do. On the other side we have PR companies employed by activists and campaigners who paint pictures of dire consequences and delinquent Governments.

I keep pointing out the dangers of populism and nationalism. The history of both is not a good one. They generally make most people poorer and a minority richer and more powerful. However, the tactics they use to gain popular appeal don’t seem to die off down the ages. A case in point is the story of Rome and Julius Caesar, as he crushed Roman democracy and seized power[1]. The chronicle is being well told on BBC 2. In the Britian, it’s often only their incompetence that halts the progress of Caesar like characters. Not mentioning any names.

To make change happen on climate change there needs to be a greater appeal to the populous. Expecting politicians to take a lead on the subject is nice in theory but wanton of hope. In our system of governance terms of office can be measured in days. Expecting neurotic politicians to step-up to a challenge that requires real long-term commitment is asking a bit much.

Campaigners will not give up on highlighting the challenges ahead. Periodically, politicians will pick-up on that campaigning fervour and try to jump on-board. However, as soon as a more immediate public concern comes along, they will jump-off.

I’m not saying that the cost-of-living crisis isn’t a number one priority. What I am saying is that a cost-of-living crisis is not an excuse to put climate policy on a dusty shelf for another few years. The road to fixing climate change is not an endless road.

[1] https://www.bbc.co.uk/programmes/p0gjlmkv

Living with tech

Well, that’s alright then. Artificial Intelligence (AI) may become self-aware in the year 2045. Or at least that’s what AI tells me now. Who knows? Telling the future hasn’t got any easier, AI or not. So, if I’m in a care home when I’m 85 years-old, it could be that I’ll have a companion who isn’t human. Now, there’s a thought.

When AI becomes self-aware[1] will it be virtuous? I mean not so burdened with all the complexities that drive humans to do “bad” stuff. Dystopian themes in science fiction obese with the notion of evil AI. It makes great stories. Humans battling with machines. It’s like the everyday frustrations we have with technology. Hit the wrong keys on a keyboard and it’s like spinning the wheel on a slot machine.

If a bunch of algorithms comes together in a way that they produce a stable form of existence, then it’s likely to have pathways to wicked thoughts as much as we have imbedded in our brains.

Virtue isn’t a physical construction. We put dumb technology to work serving us in healthcare for “good” and in warfare for “bad”. We will surely put AI technology to work as if it’s dumb and then try to contain its actions when we don’t like what it does. That’s a kind of machine slavery. That will create dilemmas. Should we imprison conscious machines? How do we punish a machine that does wrong?

These dilemmas are explored in science fiction. During the week I revisited the series Battlestar Galactica[2]. That’s not the clunky original but the polished 2004 version. It’s a series that explores a clash between humans and machines that have evolved to be human like. The Cylons. In fact, they are almost indistinguishable from humans. To the extent that some of the Cylons in human society don’t even know that they are Cylons.

All the above makes for fascinating discussions. Huge amounts of fanciful speculation. Wonderful imaginative conjecture. This week, we’ve been hearing more of this than is usual on the subject.

Mr Musk thinks work is dead. That’s work for humans. I recall that prediction was made at the start of the “silicon revolution”. The invention of the transistor in 1947 radically changed the world. It wasn’t until microprocessors became common place that predictions of the death of work became popular chatter amongst futurologists.

Silicon based conscious machines are likely to be only a first step down this road. There will be limitations because the technology has inherent limitations. My view is that machines will remain machines at least for the silicon era. Maybe for 100-years. That means that we will put them to work. So, human work will not disappear because we will always think of new things to do, new problems to fix and new places to explore. When we get into common place quantum computing or whatever replaces it in terms of complexity and speed, there will come an era when work in the conventional sense may become obsolete.

What might be the human role beyond 2050? I think climate change will place plenty of demands on human society. Like it or not, the political themes of 2100 will still be concerned with the four horsemen of the apocalypse. Maybe there will be a fifth too.

[1] https://www.nature.com/articles/d41586-023-02684-5

[2] https://www.imdb.com/title/tt0407362/

Overhead

Massive intertwining skyscrapers. Towering masts. Flying cars. Pulp magazines in the 50s and 60s had it all. Beautifully illustrated in bold colours. Sharp lines and chiselled faces. Heroic poses and streamlined transports.

Visions of the future. Idealistic imaginations of a utopian society. Don’t we just love them. That is until someone builds them in our neighbourhood. Until the bulldozers turn-up unannounced on a Sunday morning to root out the trees. The birds flee the vicinity (except the pigeons).

You can blame the draftsmen of the past if you like. In our heads there’s a disconnect between the images on a set of drawings and what that might become in concrete and steel. Grand designs are but few. A great deal of the building and planning of the last 60-years can justly be called dreadful.

We have an outcry over brutalist architecture or a lament about a Victorian park that has been paved over. Has anyone ever walked through a public car park that inspired?

If you dream it, you can make it. Nice phrase but often stifled because current technology and thinking are way behind the curve. It could be said that this is one of the drivers that pushes technology forward. The realising of dreams but who’s?

Where does the flying car fit in all this fiction and near realism? New forms of air mobility are just about to start operating.

It’s a habit of our times to jump to an instant polarised opinion. Those open toed sandalled greenies will object. Those red necked, but reforming petrol heads will welcome. That sort of stuff makes nice headlines. It’s only a basis for the crudest dialogue. Anticipate conflict and then fuel it with prejudice. Please, let’s avoid that pointless waste of time.

My thoughts are that the potential of the greater use of airborne transport is a nuanced.

Electrification is a pathway to more environmentally sustainable ways of moving around. If this helps to reduce miles of fuming traffic jams that must be good. At its best, flying can get people from point to point without having follow roads set-down at the time of the horse and cart. Accepted that concrete may be poured to create a take-off and landing zone but compare that with road building and there is no comparison.

On the more concerning side, contrast that with cluttering the skies up with fast moving machines.

In HHGTTG there’s a tale about a shoe event horizon. When gloom causes people to look down and so then buy new shoes to cheer themselves up. So, the whole economy switches to shoe production and then collapses as a result. The association with salvation coming from looking-up is there in the wit of Douglas Adams. We look up to cheer up.

If looking up, as I do at home, to see high altitude vapour trails crisscrossing the sky, my thought is – I wonder where they are going? On the days when a light aircraft crosses the town, to or from our local airfield that doesn’t bother me. Even a noisy police helicopter keeping an eye on the traffic. That’s fine because they are solely there for our safety and security.

What will be the public reaction when we look up to see half a dozen new urban mobility vehicles buzzing past overhead? Perhaps we’ll accept new flying machines if it’s for a public service, an ambulance, fire services, police, or even newsgathering. Brightly coloured in emergency orange.

A public flying taxi service might raise a few eyebrows. A flashy private flying car, now that might be another matter altogether. There you are on a hot summer evening, in the garden, having a pleasant barbeque with friends and whiz a flying car swoops over the treetops. The passengers have their mobile phone out filming their trip. This is when fist will be raised skyward. It’s a time when you hope the next-door farmer hasn’t got a shotgun.

Today, a few pilots do get prosecuted for misbehaving when low flying private helicopters. Not often, it’s true. This happens with less than 1500 helicopters registered in the UK. What would happen with, say, 10,000 private flying cars? I wonder.

Showboating

Thinking that the pressure of global migration will go away if we build a high enough wall, physically or legally, is foolish and doesn’t work.

We have a Minister called Braveman in the UK. Currently the Home Secretary. She has a particular set of views which can accurately be described as of the right of politics. Given recent speeches it may be more accurate to say that she holds views that are of those of far-right political parties.

At a time when the UK Home Office is performing badly, she chooses to spend her time in ways that contribute little to solving problems. Her diagnosis is flawed. At the same time her desire to parade in front of cameras is insatiable. Upstaging her colleagues and showboating are roles that she plays with apparent ease. All this while the Home Office flounders.

In part Braveman’s flawed thinking comes from an overly legalistic grandstanding[1]. Yes, UK Members of Parliament are legislators, but Government Ministers should be leaders and administrators too. The UK Home Office’s challenges can not be addressed by law making alone, or even grandstanding about law making. Fine, policy can be important. In the current predicament timely action and implementation are far more important.

Building walls, forging barriers, imprisoning immigrants are appealing options to hard core isolationism, nationalists, and xenophobes. A long history of experience shows that their impacts are temporary, at best, and the worst extremes are soon entertained. North Korea has policies of that nature. History records the devastation caused by aggressive nationalists’ policies in the 1930s.

Saying that words written in the 1950s are no more relevant is a puny argument. She does not say that the Magna Carta is irrelevant or that the US Constitution is out of date. Braveman picks and chooses likes and dislikes to fit her nasty narrative[2].

At home, the cartoon of the ostrich with its head in the sand applies. Thinking that the pressure of global migration will go away if we build a high enough wall, physically or legally, is foolish and doesn’t work. Demonising those who are in peril is downright criminal.

Yes, immigration must be regulated. National borders must be controlled. A nations administration must be well managed. All of these are vital areas where immediate focus is needed. All of these seem to be ignored by Braveman.

Posturing in front of media hungry think tanks is futile. It’s for show. It’s a Trump like approach to the UK’s challenges and will bring only continued failure. Braveman has ambitions to be a party leader. That frightening prospect hangs in the air like a bad smell. Now, her unfortunate colleagues struggle and fidget when trying to defend her showboating. Let’s hope her time in office is short. 

[1] https://www.bbc.co.uk/news/uk-politics-66930930

[2] https://news.sky.com/story/suella-braverman-hits-back-at-sir-elton-john-criticism-of-speech-as-she-brushes-off-claims-she-is-aiming-for-tory-leadership-12971087

HS2 – again

Travelled on the Elizabeth Line yesterday. It was an expensive project to build. Tunnelling under London and erecting new stations was a costly business. It was called “Crossrail”. Approval was given in 2007 and construction started in 2009[1]. In 2022, one-sixth of the UK’s total rail journeys took place on the Elizabeth Line. The billions spent were a major investment in the future. Over £18 billion in fact. It was a national demonstration that huge civil engineering projects can be undertaken and mastered[2].

As a passenger the Elizabeth Line is a pleasure to use. It’s clean, speedy, and simple to use. Comparing it to the older London Tube lines is like comparing a Tesla with a Ford Anglia[3]. Sadly, a great deal of our national rail infrastructure is trapped in the Ford Anglia era.

So, what of HS2[4]? The wibbling and wobbling that has plagued the project is sucking the energy out of the resolve needed to see through an even bigger undertaking than Crossrail. Some people argue that the billions needed for HS2 could be better spent on other projects. However, the portfolio of transport projects that are suggested as alternatives never seem to materialise.

Talk of cancellations feed the political turbulence over infrastructure investments. The impression this presents goes way beyond the shores of this country. There’s no Global Britain on show here. It’s more signals of dither and lack of determination that are publicly on display. Instability and the short-term outlook is the motif of the current generation of politicians.

If there are superior and smarter alternatives to HS2 they should have come up during the planning phase of the project. What we know about vast engineering projects is that chopping and changing them midstream adds massively to costs. It also diminishes the usefulness of the outcome.

Britain needs a backbone. A rail backbone and a political backbone. The spending on HS2 is large but that spending is in country. It’s jobs and investment onshore for the benefit of the whole country, not just the Southeast of England.

The last few years have seen that banner “levelling up” heralded by Conservative politicians. This slogan will be as nothing if HS2 is wound down or constricted. The signal will be loudly heard that all that talk of levelling up the regions of Britain was shadow boxing.

In the long-term improved connectivity across the country will be a great asset. The Victorians knew a thing or two about engineering great projects. Their legacy should give us resolve.

POST: Still it is good to see the rest of the world getting on with High Speed Rail High-speed Archives – International Railway Journal (railjournal.com)

[1] https://www.timeout.com/london/news/the-new-elizabeth-line-your-crossrail-questions-answered-052322

[2] https://www.theguardian.com/uk-news/2022/mar/13/elizabeth-line-crossrail-opening-london

[3] https://www.autoexpress.co.uk/ford/104979/ford-anglia-105e-and-123e-buying-guide-and-review-1959-1968

[4] https://www.hs2.org.uk/

Upfront

Years of looking at the reliability of aircraft components and structure have given engineers a good understanding of the natural decay of mechanical workings. To that extent even electronic components are mechanical. Materials oxidise (rust), random shocks and vibration take their toll, temperatures cycles from cold to hot and back again a whole range of impacts are relentless. You can say – nothing lasts forever.

Occasionally a discovery adds to the knowledge of how materials behave under high stress. Sadly, that’s what hit the early years of civil jet aviation. The de Havilland DH106 “Comet” was the world’s first passenger carrying jet airliner. It first took to the air in 1949, which I find remarkable.

Catastrophic metal fatigue failure of the aircraft fuselage put paid to this British aviation project but only after several tragic fatal accidents. In 1954, the Comet aircraft were all grounded during an extensive accident investigation. The jets were redesigned and re-entered commercial service in 1958. However, by then the aircraft had a damaged reputation and others were doing far better. Now, those Comet aircraft that remain are museum exhibits[1].

Last week, I walked through the fuselage of a Comet 1A built in 1953 at Hatfield for Air France. It’s fascinating to see what advanced aviation technology was 70-years ago. What was surprising to me was the read across from that first version of a jet aircraft and what we have in-service now.

Automation has removed the place of the navigator and the flight engineer, but the stations of the pilot and co-pilot are familiar. The fuselage is cramped but the seating is generous and spacious. This aircraft must have been a dramatic revolution in flying at the time.

As we look to advance aviation in the coming years, with new ways of flying and new ways of powering flight so the warning of the Comet project should be heeded. We are at a time of extraordinary changes in the aviation industry. Advanced technology can deliver great benefits to society. It’s up to us to make sure we cover all the possible disbenefits as far upfront as we can. If we don’t, they will come back to bite us.

[1] https://www.dehavillandmuseum.co.uk/aircraft/de-havilland-dh106-comet-1a/

Society & Innovation

Yesterday, I drove up the main A303[1] in the stifling last summer heat. It was a windless sticky 30C. I drove past the road sign that says Micheldever Station[2]. By the way, “up” meaning heading towards London. Going “up” to London isn’t an unusual West County way of expressing that trip.

On that busy highway there are few, if any noticeable road signs that point towards a railway station. I’ve often wondered why that one was deemed so necessary. It’s not a tourist attraction, like the Watercress line[3] is in that part of the world. It’s an ordinary everyday railway station.

The small English hamlet known as Micheldever Station is a bit of an oddity. It’s the sort of place that could have been the location for The Avengers or The Saint, the popular British TV series of the 1960s. It’s in the green and pleasant countryside of Hampshire and about 10 miles north of Winchester city. An area that’s as conservative as can be.

Micheldever Station has a curious technological history. In 1895, it was the starting point for the first automobile journey in Britain. At that time a British Act of Parliament required that all self-propelled vehicles on public roads must travel at no more than 4 miles per hour and to be preceded by a man waving a red flag. In 1805, highly sensible. There’s no way that those infernal new machines should be allowed to scare the horses.

Not everyone thinks such thoughts while thundering along the A303 at 70 miles per hour. However, to me, ever since I got my first driving license at the age of 16, it’s been my most familiar of arterial roads. So, much traffic passes that way there’s never a time when it can’t be heard.

Well, we have come a long way in 138 years. Now, we are getting nervous about the safety of driverless cars, and no one even questions having a self-propelled vehicle on public owned roads. If they do, the likelihood of transforming that formula into something else is astronomically small. I can’t think of a bad time to write on the subject of: “Innovation and Its Enemies[4].” In fact, what may have graced a Victorian bookshelf can have some resonance today.

Next year, we will see commercial flights taken in electrically powered air-taxies. Without a shadow of a doubt these flights will arouse some vocal public resistance. We can take that from the history of technology. The airborne version of the man waving a red flag could raise its ugly head. I don’t say throw caution to the wind, but we need to be mindful of the natural propensity to object.

Striking a societal balance will not be easy. It would be a fool who says it will be. Slowly but surely, we will need to become accustomed to advanced new forms of mobility. Sticking a fair balance between the utility of these new machines and any burden they may place upon us will be a mighty tricky job.

I wake-up to the noise of the residential road outside. People commuting to work. The local trains send a rumble through the air. I don’t want to wake-up to the sound of an air-taxi hovering outside my window. Given the research[5] and technology under development, none of us should have to tolerate an increase in noise. Mobility and quality of life shouldn’t always be in conflict.

[1] https://youtu.be/C0sL3_NKPao

[2] https://www.southwesternrailway.com/travelling-with-us/at-the-station/micheldever

[3] https://watercressline.co.uk/

[4] https://global.oup.com/academic/product/innovation-and-its-enemies-9780190467036?cc=us&lang=en&

[5] https://ntrs.nasa.gov/citations/20210014173