JP Aerospace is an interesting company - in Sacramento, California, JP Aerospace, America's OTHER Space Program. Their aim is to develop ways to send airships up into the stratosphere - and more controversially, all the way to orbit with their "Orbital Airships" vision. The airships would accelerate very slowly, at a rate of perhaps a few centimeters per second increase n speed every second, over several days, until they reach orbital velocity.

I will start by explaining the origins of the company - and some of the things we know are possible. For instance if you do it the other way, build airships to re-enter Earth's atmosphere from orbit, then this is much more widely accepted to be possible, with many scientists exploring plans such as the VAMP proposal for atmospheric re-entry for Venus, Titan and Earth by an airship that inflates as it re-enters, and slows down because it presents such a large surface area to the atmosphere. Also there was a 1964 test of a small inflated paraglider that achieved hypersonic speeds of over Mach 3 at a height of 400,000 feet, though only for minutes. So hypersonic flight by airships does seem to be feasible in principle at those heights, but how fast and for how long? Throughout this article, page numbers refer to John Powell's book "Floating to Space, the Airship to Orbit Program".

AIRSHIPS TO ORBIT CONTROVERSY

The most controversial part is their idea of slowly accelerating to orbit. These airships would be constructed and inflated at an altitude of 140,000 feet on a high altitude platform, his "Dark Sky Station" so called because it is so high in the atmosphere that the sky there is dark, just as it is when seen from space, even at midday. They would be far too flimsy to survive at ground level, but would be fine for flight at that height above all the weather in our atmosphere. Passengers would travel up to this platform in a more conventional stratospheric airship, then transfer to the orbital airship for the final stage of their journey. They then slowly accelerate to orbit over a time period of several days.

Most physicists I've talked to say these orbital airships are impossible. If so - how far can he get? Can he achieve airships that fly several times faster than the speed of sound in the high upper atmosphere like the 1964 inflated paraglider? What about his "Atmospheric escape airship?" Can these airships launch from the Dark Sky Station and take passengers up to heights of 200,000 or 300,000 feet? What about his Mach gliders? Those at least should work, based on the 1964 experiment, and could be of scientific interest in themselves, hypersonic inflated gliders traveling in the upper atmosphere until they get too low to fly..

He is not suggesting any new physics like the EM drive, so it's not controversial in that sense. Rather, it's because we have almost no practical experience of huge airships traveling at hypersonic velocity in a medium to hard vacuum to draw on.

There's that one inflatable paraglider test from 1964, and that's it. Nobody has ever tried it since then. He is doing a lot of extrapolation on the basis of his own wind tunnel experiments and rather limited data. So, what makes it so controversial is that this is a different regime from any current experience of ordinary flight. He is talking about kilometer scale aiirships in a near vacuum that stay aloft through a combination of buoyancy and aerodynamics, and eventually also through ballistic motion as they approach orbital velocity. Meanwhile, apart from that 1964 test, which was not powered flight, we don't have any examples yet of airships that can reach speeds anywhere near to breaking the sound barrier. .

It is possible for an airship to have aerodynamic lift. Some hybrid airships are heavier than air, and depend on aerodynamics combined with buoyance to stay afloat. The Lockheed LH-1 is a heavier than air hybrid airship which is going to be used to move freight and personnel to remote areas of Alaska and Canada. 

Still, though these hybrid airships do depend on aerodynamic lift, they still stay up mainly on the basis of buoyancy. Also they could not travel anywhere close to the speed of sound without breaking up.

Meanwhile, conventional planes, can fly at supersonic and even hypersonic speeds (some of them). However, they are normally heavier than air, and are unable to fly higher than the Karman line. This is at 330,000 feet, and above this height a heavier than air airship has to travel faster than orbital velocity to generate enough aerodynamic lift to support its weight.

ESA invests in 4,000mph hybrid rocket jet engine firm, a Mach 5 airplane. Any heavier than air plane like this will be restricted to flying below the Karman line at 330,000 feet, the height at which you need to go faster than orbital velocity to achieve enough lift to hold up the mass of your plane against gravity.

JP Aerospace hope to go above this height using airships balanced to be neutrally buoyant at up to 180,000 feet, and then to fly higher than that through a combination of aerodynamics and buoyancy. In this way, by making their plane much lighter, they plan to "beat" the Karman line restriction.

However, that's for heavier than air vehicles. What happens when you combine buoyancy with aerodynamic flight, at hypersonic speeds, and what's more, do it in conditions that would count as a hard vacuum in a laboratory, at a height of 300,000 feet or more?

Buoyancy changes everything here. If we had the materials to do it, then we could float a sufficiently huge balloon above the denser part of our atmosphere even at the height of the ISS. So long as there is hydrogen inside, and higher molecular weight gases outside such as nitrogen and oxygen, it doesn't matter how thin the vacuum is. The principles are the same, and a balloon will still float, so long as there is some atmosphere, even if it counts as a medium to hard vacuum, for it to float in..

We don't have the capability to do that as even the thinnest materials would be too heavy for a balloon at the height of the ISS. But what is the highest point at which a balloon can float?

Well the world record so far is the JAXA BU60-1 experiment which was 74.5 meters in length, 53.7 meters in diameter and weighed a total of 39.77 kg including instruments. It reached an altitude of 53 km, or around 174,000 feet. This is just short of the height where JP Aerospace eventually plan to build their Dark Sky Station, where passengers will disembark to transfer to their orbital airships.

The BU60-1 balloon, when fully inflated, reached a height of 174,000 feet, launched by the Japanese space agency JAXA.

However, it is one thing to send a balloon that high. Is it possible to design airships and a "Dark Sky Station" balanced to float at 180,000 feet or so as he suggests? Well JP Aerospace has got to 104,000 feet with an airship.

I've not designed V shaped airships or done near vacuum wind tunnel tests, or flown balloons to high altitude. So, this article is not based on my own experiments of course, but on what he says he has done, and the earlier experiments he links to. So far, everything he has said that I can check out, checks out to be true. He also seems to be a person of integrity and he is the only one in the discussions who has actually done wind tunnel tests for his ideas as far as I know. He also has experience of taking the first steps towards his goal, with high altitude balloons, and he continues to think it is feasibleWhen I check out the things he said, that I can check out, they all turn out to be true. So he seems to use his sources carefully, he labels his ideas clearly when he is extrapolating beyond what is currently known,

Many physicists seem certain that these airships are impossible. JP himself thinks they might be possible. I sometimes infuriate physicists when they find themselves unable to convince me of their arguments that this project is impossible. But after taking into account everything they say, and also taking account what John Powell says in his book and talks, I remain  persuaded by JP's arguments that so far, it remains a possibility that these airships just possibly might be able to get us to orbit. I don't think even the most enthusiastic supporter of his ideas would go much further than that.

David Livingston asls of he still thinks they can do it, 22 minutes into this interview. He answers that it's really hard stuff, but that nothing suggests they can't keep going and keep doing the research and figuring it out.

I thought it might help to set out the reasoning in an article like this and invite comment. I have no connection with the company at all, and am writing this as an independent science blogger. I will state the objections of the physicists as clearly as I can as well as his responses to them.

It's clear also to anyone, John Powell not excepted, that the final goal of airships to orbit is a major engineering challenge. We don't yet have airships able to operate up to the site of his proposed "Dark Sky Station" at 140,000 feet, so we are a long way at present from orbital airships, if they are possible at all. It's worth a punt though, if there is any possibility of it working, especially since it leads to so much interesting science along the way. And if it turns out to be impossible, then that's worth knowing also, and I'd support him for all the interesting things he will do by going as close to this goal as possible. While, if he can achieve his goal, it would be a major accomplishment.

Please have a read and see what you think, and comment,. Do explain what I am missing here, if you are one of those physicists who are sure that his idea is impossible.

Anyway let's start with an introduction to the company, and with the much less controversial idea of airships re-entering our atmosphere from orbit. It's easy to see how an airship can achieve re-entry, as you will see, and I think just about everyone is agreed on this point, including scientists who plan to use such airships to explore the Venus and Titan atmospheres (do of course comment if you think they can't). The tough thing is to see how they can accelerate to orbit.

INTRODUCTION TO JP AEROSPACE

Their idea is that they don’t do any big expensive “succeed or go bankrupt” type tests like SpaceX did in their early years. Instead every stage along the way pays for itself. At present they pay for the tests through pongsats and other ways to lift material to the edge of space. Their tests involve high altitude balloons, and V shaped airships rated for the lower atmosphere. They have also tested a high altitude balloon based airship design.

JP Aerospace hold the altitude record for an airship, propeller driven, remotely controlled from the ground, and flying at a height of 95,000 feet above sea level.

Later on they plan a “dark sky” station at the edge of space which will be of a lot of interest for itself both scientifically and for tourists. It gets the name because at that height the sky will be dark even in daytime, as for the Moon. Next, they plan small airships doing test hypersonic glides back to Earth. Finally they do test flights to orbit with smaller airships, then the first human pilots to orbit, and then huge orbital airships with passengers and cargo.

The idea started off as a US Airforce contract for a near space reconnaissance airship. But the US canceled the contract in 2004 or 2005 after first persuading them to attempt to launch one of their prototypes for a lower atmosphere airship in a 50 mph wind (which would count as a “strong gale”). It was only rated as sturdy enough for launch in a 2 mph wind at the time (an airship is particularly vulnerable in the short time it takes to launch it from the ground). They did this with some reluctance - and it blew apart in the strong winds, causing some minor injuries. The inventor himself sustained three broken ribs. That was enough for the US Airforce to cancel the contract.

JP Aerospace have now solved the problem and can launch their lower atmosphere V shaped airships in any wind conditions. You can read their account of this story here. It’s now a civilian company entirely self financed, and they are not interested in any more such contracts, naturally enough.

It’s probably going to take them a fair while, with this approach, maybe decades but it’s interesting: “watch this spot”.

ORBITAL AIRSHIP CONSTRUCTION

It has no internal girders. Its outer shell covers an interior of many large bags of hydrogen to give it rigidity and to stop the gas bunching up at its nose. It also has inflatable trusses, with nitrogen filling the gaps in between these components. The nitrogen is vented if necessary and then replaced from liquid nitrogen tanks.

Note the use of airbeams - at this altitude they would consist of very thin materials, that nevertheless give it some strength because of the cylindrical shape.

It is balanced to float at anywhere between 140,000 and 180,000 feet altitude in the atmosphere. But since it is aerodynamic, it also behaves like a glider when descending. It doesn't look much like a glider to our eyes perhaps, but that big voluminous V shape makes a great glider in the very tenuous upper atmosphere during re-entry.

So what keeps it up is partly aerodynamic lift and partly buoyancy. As it descends from orbit, then to start with it is kept up mainly through aerodynamic lift, as it slows down on its long glide through the upper atmosphere. The aerodynamic effects keep it higher in the atmosphere for longer, and so keep it cooler on the way down. As it slows down to a halt in the atmosphere, it’s finally kept up by buoyancy.

Many details of the design are given in their Floating to Space: The Airship to Orbit Program. They don’t actually give expected skin temperatures. But the design uses nylon rip-stop polyethylene (page 111) which suggests that they expect external skin temperatures well below 100 °C (212 °F) for continuous use.

(Most commercial grade Polyethylene starts to soften at 60 °C (140 °F) and has a maximum continuous use temperature of 65 °C (149 °F), High Temperature Polyethylene can retain its properties up to 100 °C (212 °F) )

On page 109 they say

"By losing velocity before it reaches the lower thicker atmosphere, the reentry temperatures are radically lower.... This makes reentry as safe as the climb to orbit"

You might wonder what happens if the airship is hit by a meteorite or orbital debris. From page 112 of the book:

"One of the most common questions asked about ATO is about meteorites. "What happens if a meteor popped the airship?" The answer is very little would happen. A balloon pops because the inside is at a higher pressure than the air on the outside. The inner cells of the airship are "zero pressure balloons". ... There is no difference in pressure to create a bursting force. All a meteorite would do is to make a hole. The gas would leak out staggeringly slowly... "

To find out more about this see their book Floating to Space: The Airship to Orbit Program

The JP Aerospace orbital airships are so lightweight they could never survive at ground level. The slightest wind would tear them apart. So in their plan, they have conventional airships that take passengers up to a docking station in the upper atmosphere, the “Dark Sky Station”, where they then transfer to the orbital airships.

You might wonder how they could ever manage re-entry from orbit, such thin flimsy seeming things. After all the Space Shuttle heats up to high temperatures at around the same altitude that these airships would dock with the high altitude space station. Well the answer is that it slows down much much higher in the atmosphere.

USING THE UPPER ATMOSPHERE AS A BRAKE - SPACE SHUTTLE

This is the way it is done today, to use the upper atmosphere as a brake, then slowly parachute to the surface or glide down in the lower atmosphere. How easy that is to do depends on the spacecraft.

If it is a heavy one like the Space Shuttle (now retired of course) then it can only slow down deep in the upper atmosphere, where it is dense. So it gets very hot. That’s why the Space Shuttle had to have ceramic tiles able to withstand temperatures up to 3,000 °F (1,650 °C)

Space Shuttle Enterprise banking on its second approach and landing test, during early flight tests.

NASA artwork for Space Shuttle re-entry - it’s high density, so can only slow down deep in the upper atmosphere, and gets very hot during that stage of its flight

LOWER TEMPERATURE REENTRY - SKYLON

Skylon is a plane being developed by the British company Reaction Engines with funding from the UK government and ESA. It will be able to fly to orbit from a conventional runway (though reinforced to carry the extra weight of all the fuel), return back to Earth, and then take off again within a couple of days with a crew of 200 to assist.

Its design is much lower in density than the space shuttle, once it has used up its fuel to get into orbit. So it slows down in the atmosphere at higher altitudes on the way down.

What really matters is the mass per cross sectional area it presents to the atmosphere or more exactly, its ballistic coefficient. Skylon could slow down even higher in the atmosphere if it presented a large blunt face like an aeroshell, but it has to be streamlined for the other stages of its flight. However it is also able to compensate for that to some extent by steering during the early part of the flight to slow down more quickly.

Skylon (future design being developed by UK / ESA). It flies to orbit from a normal length runway, reinforced to take the weight of fuel on lift off and may fly in the 2020s. It is heavy when it takes off, but during the landing, having used up most of its fuel, it is low density and so slows down much higher in the atmosphere than the Space Shuttle

As a result, it will reach lower temperatures than the Space Shuttle on re-entry though higher than a supersonic jet at Mach 3. Here are a few figures for skin temperatures for comparison, hottest first. These are the figures for the hottest parts of the spacecraft or plane:

SKYLON’S ZEPPELIN-LIKE TRUSS CONSTRUCTION, WITH A REINFORCED GLASS CERAMIC AEROSHELL

Modern planes have “stressed skin” structures, where the skin of the plane itself takes up all, or most of the external load from the wings, tail, other stabilizing structures and heavy components such as the engine (See fuselage for details). But the Skylon uses a structure much more like a zeppelin or a small plane. It’s girder-like with a thin glass ceramic outermost shell, which is just a heat resistant covering and doesn’t take any stress at all.

Structure of the Skylon - internal truss framework made from carbon fibre reinforced plastic composite held together with Kevlar ties. It has aluminium propellant tanks suspended inside it. Covering that, it has a thin outer aeroshell of a high temperature silicon carbide fibre reinforced glass ceramic material. For details see page 2 of this report

This ceramic outer skin is black, which is why Skylon is shown that colour in most of the artist renderings. This is an animation to show the concept for a mission to orbit, and back, by Reaction Engines who developed the idea. Re-entry starts about seven minutes into the video

LOW TEMPERATURE RE-ENTRY - ORBITAL AIRSHIPS

So with that background, now let's get back to JP Aerospace. Since their kilometer scale orbital airship is filled mainly with hydrogen, it’s not only lower density than a plane, and the Space Shuttle, and lower density than the Skylon. It’s also much lower density even than a normal airship. It also has a huge cross section which it presents to the atmosphere.

This spaceship design consists of a near vacuum of hydrogen floating in a near vacuum of normal air. If they succeed in building it, then it will be able to slow down just through friction in the very tenuous upper atmosphere. By the time it gets to levels dense enough to heat the skin significantly it’s already slowed down hugely, so the temperature of the skin during re-entry is much less of a problem.

JP Aerospace orbital airship - kilometer scale, extremely low density - this has the least temperature of any spaceship during re-entry, because it is so lightweight and large, has a low ballistic coefficient.

If it works out, the cost per kilogram to get cargo and passengers to orbit would be far less even than the space elevator ($500 per kilogram to GEO for the space elevator, and JP Aerospace’s estimate for orbital airships is $310 per ton to GEO, so 31 cents per kilogram), and it has much less development cost. It would be a leisurely journey as you would get there slowly over several days.

Although it may not look it, its huge V shape is designed to be aerodynamic at hypersonic speeds in the near vacuum upper atmosphere. They have done modeling, calculations and wind tunnel tests with scale models to test this.

ATMOSPHERIC RE-ENTRY FOR VENUS AND TITAN

There are several other places in our solar system with thick atmospheres like Earth, including Venus, and Saturn’s moon Titan. Mars also has a very thin atmosphere. The gas giants have thick atmospheres too (with no solid surface).

JP Aerospace hope the same idea can be used for Venus, with a high altitude staging post again, this time of course in the Venus atmosphere. The aim wouldn’t be to land on the surface, which is incredibly hot and high pressure, but to go down to the Venusian cloud tops to study them and perhaps build habitats there.

Perhaps they could use it for Mars too. The atmosphere of Mars is so thin that you could land an orbital airship like this on the surface. The strongest winds on Mars would only barely move an autumn leaf, fast though they are.

Though this prospect of JP Aerospace landing on Mars or descending into the Venus or Titan upper atmosphere is likely to be decades away, if they do achieve their dream of orbital airships - it could happen much sooner than that with VAMP.

VAMP ORBITAL AIRSHIP RE-ENTRY - FOR VENUS AND TITAN, ALSO EARTH

If you want to fly all the way down to ground level on Earth in one go, then you need a more massive airship. Northrop group’s “VAMP” project to study the Venus atmosphere uses an airship design like JP Aerospace, and they would inflate it outside of the atmosphere, so again that’s very like the JP Aerospace idea. It enters the Venus atmosphere already inflated, and because it is so large (55 meters in diameter) and low density, it doesn’t need an aeroshell.

However, unlike the JP Aerospace design, it’s able to fly in an Earth pressure atmosphere, so it’s not nearly as low density as an orbital airship. It still gets quite hot during the descent.

It would only descend as far as the Venus upper atmosphere, at the cloud tops, where temperatures and pressures are the same as for Earth. The cloud tops also have natural protection from cosmic radiation, and nearly all the ingredients for life. Indeed there are suggestions that it could be a good place for humans to settle outside of Earth. See my Will We Build Colonies That Float Over Venus Like Buckminster Fuller's "Cloud Nine?". Some astrobiologists think there may be life in the upper Venus atmosphere, already, which could have migrated there long ago when Venus was more habitable. The Russians are interested to search for this life, and may include an unmanned aerial vehicle, possibly VAMP in their Venera D mission to Venus in the mid 2020s.It inflates before it enters the atmosphere (see patent for details), and rather similarly to the JP Aerospace idea it decelerates slowly in the upper atmosphere, so generating much less heat, because of its low ballistic coefficient. So it doesn’t need an aeroshell, though because its designed to operate right down to the equivalent of ground level on Earth, its denser and its outer envelope is reinforced to withstand up to 1,200 °C (2,192 °F) along leading edges

They hope it can be used for Venus, and also Titan, and possibly Mars.

The first tests of VAMP would use the Earth’s atmosphere. So it could also be used for Earth re-entry. It might be useful for surveillance, photographing the Earth from above, and also for scientific studies of the upper atmosphere.

The same ideas could also be used for Titan - a moon of Jupiter with an extremely cold atmosphere at -180 °C, but it’s also dense, with the same pressure as Earth’s. This means that humans could go out of doors there, without needing a pressurized spacesuit. Of course they would need protection from the extreme cold and they would need air to breathe, so you are talking about warm clothing, as for Antarctica, perhaps heated clothes, and an oxygen mask.

However, they could get the oxygen to breathe by splitting water ice from Titan, and then burn the methane from Titan in that oxygen, a process that, rather neatly, creates an excess of energy which could then split more water, generating more oxygen for heat, and also for the colonists to breathe. The habitats could be built like many modern Antarctic bases, on legs to hold them above the cold surface. Since the air pressure is the same inside and out, the air could be kept in using double doors in a building of normal construction, again like an Antarctic base. See Let's Colonize Titan, and there are more details in their Beyond Earth: Our Path to a New Home in the Planets.

VAMP flying over Titan to sample and explore the upper atmosphere - Titan’s atmosphere is similar in pressure to Earth’s at ground level, though much colder, so you have similar methods for re-entry for Titan and for Earth. Though its gravity is much less - indeed a human falling from a plane or aerostat on Titan would easily survive the landing without a parachute.

JP AEROSPACE'S IDEAS AGAIN

So the descent from orbit of the airships doesn't seem so problematical. At least, VAMP is seen as plausible by most scientists.

It's really the ascent to orbit that's the most challenging part of their plans. On the way up it gradually accelerates to supersonic speeds, then to hypersonic speeds (by which time it is already in a near vacuum). There are several issues with this including power requirements (which I'll come to later). But first - wouldn't it just break up at such speeds, a hypersonic airship?

So now let's look at this a bit more closely.

1964 MACH 3 INFLATED PARAGLIDER

This is the only data we have for hypersonic flight with a V shaped inflated paraglider. He mentions it in his book (see page 56). It was release in a suborbital flight and inflated, and at its fastest, on re-entry, flew at a speed of about Mach 3 at a height of over 100 km, so over 300,000 feet, launched in 1964.

This is what it looked like

It was expected to reach high temperatures during re-entry. The tests of the materials involved a 60-second temperature rise to 620' C, a 20-second exposure at this temperature, anda 60-second cooldown, see page 14 of this article.

It was deployed at 96 seconds and collected data until 306 seconds, so for three minutes, thirty seconds.

This is a long way from sustained hypersonic flight of course.

Before his orbital airships, he plans to test hypersonic inflated airship type gliders like that himself, flying Mach gliders downwards from 140,000 feet, at supersonic speeds, then from a height of 400,000 feet, this time launched in rockets to reach that height like the original 1964 experiments (page 119).

If he does succeed in getting his Mach gliders to work, this would answer quite a few of the concerns that physicists have raised. After all in the 1964 experiment the Mach glider got very hot, projected to reach 620 C, for twenty seconds or so, though it stayed at hypersonic speeds for probably a minute or two. What happens to his, exposed to hypersonic flight?

This is a point where many physicists will already put their hands up and say "Whoa, that's a step too far". Still, it is possible to have hypersonic airships for at least a minute or so, from the 1964 experiment. That much we know we can do. And after all, if you can go high enough, then the VAMP airships also would be expected to do hypersonic re-entry until eventually they slow down enough to go supersonic and then subsonic.

So the main question he has to answer here are, can we have sustained hypersonic and supersonic flight in an airship, for days on end, during re-entry, at enough altitudes? How long can it remain at hypersonic and supersonic speeds, at what altitudes? Can flight at such altitudes even at hypersonic speed generate the lift it needs to return to the upper atmosphere Dark Sky station as a glider?

And before that he needs to show that his airships can achieve supersonic and hypersonic flight in the upper atmosphere, and can achieve enough aerodynamic lift to rise up through the atmosphere, when combined with the buoyancy of his airships, to above the Karman line.

What do you think? How much of this do you think he can achieve?

TRANSATMOSPHERIC AIRSHIP

Then after that he has a crewed version, the suborbital Transatmospheric Airship which will test the idea of using propulsion to actually leave the denser part of the Earth's atmosphere and return to it again (page 122). It's not zero g flight of course so the "sub orbital" may be a bit confusing. It's still relying on buoyancy together with aerodynamic lift to get to that height, first at 200,000 feet then in later experiments, to reach over 300,000 feet.

Eventually he anticipates that it would be able to reach Mach 10, and to be useful for rapid transport of cargo around the world.

What do you think, is a Mach 10 transatmospheric airship possible?

ACCELERATING TO ORBIT

Since VAMP should be able to achieve hypersonic re-entry of an airship into our atmosphere - why is it so problematic to do this in the opposite direction? Well it's mainly a matter of the power levels available, and whether it can generate enough lift, in the opposite direction from 200,000 feet back to orbit again. Also the amount of time it would need to spend at supersonic and hypersonic speed, not just minutes, or hours, but days, though at a much higher altitude of course than for VAMP.

An ion engine accelerates the ions to a high velocity, so can make velocity changes, eventually, for small amounts of fuel. But the problem is that the thrust is so small, it wouldn't be able to overcome drag. It could be operated up there but just would never be able to get the airship moving or keep it moving. While a chemical rocket would use far too much fuel. 

The engine they use is what they call a "mixed gas plasma" which doesn't have to create the plasma from scratch, which is what makes ion thrusters so demanding of electricity. It's in between a rocket engine and an ion thruster - needs more fuel than an ion thruster but less power - and much less fuel than a rocket engine but needs electrical power to accelerate the rocket fuel to higher speeds. It has 2,000 ISP,  They call it the "symphony engine" but though they are actively developing it and doing many tests internally, they haven't published any papers on it, so I can't link to a detailed description of how it works. But basically they are accelerating the ions in the plasma, much like the way you accelerate materials in a rail gun - and this indirectly accelerates the remaining unionized gas along with them. The fuel he uses to create the plasma is a magnesium parafin lox hybrid. So he is using chemical reactions to create the plasma, not relying on electricity to do that like a conventional ion thruster. He talks about it 74 minutes into his Spaceshow guest appearance.

Also 80 minutes in where he explains that they need their engine to burn the fuel more slowly than a conventional rocket, but to have more thrust than an ion thruster and lower electrical power requirements enough so they can run on solar power and batteries. So that's the big challenge, to do 100% of the plasma creation through a chemical process.

Note, that may seem exotic but all he is talking about here is combustion. Fire is a plasma.

The acceleration is very slow. He says it would take several days to get to orbit (page 16 of "floating to space"). Not just minutes or hours.

He doesn't give details of the acceleration as far as I can see (may have missed it) but can work it out easily enough. With the ISS velocity of 7.66 km/s then if it took three days (say) to get to the orbit of the ISS at constant acceleration, the acceleration would be 1000*100*7.66/(24*60*60*3), or very roughly, 3 cms per second per second.

At that rate of acceleration, which is just an example, then after one hour it would be traveling at 108 meters per second, or 389 kilometers per hour. It would take over three hours to accelerate to supersonic speeds and many more hours to reach hypersonic speeds.

All this time it is also ascending higher in the atmosphere.

Note, that the Space Shuttle was flying at far faster than hypersonic velocities when it burnt up, at a speed of Mach 22.8 and altitude of 230,200 feet, or about 28,000 kilometers per hour. His airships would reach that speed towards the end of the third day of acceleration if it's a three day flight to space.

Of course, he can't have it going at kilometers per second at the altitude where the Space Shuttle broke up. But he has buoyancy going for his airship, as well as aerodynamic lift. So it's not a priori impossible for him to get to high enough altitudes for hypersonic speed in the hours it will take to reach that speed

This calculation depends what he means by his rather vague "several days" - if he means six days it would be only 1.5 cms / sec / sec and it would take over six hours to reach supersonic speeds.

POWER FOR THE FLIGHT TO ORBIT

Potentially a large airship could have vast amounts of solar power available if it can use thin film solar cells - a film only a few nanometers in thickness. That is if he can succeed in integrating them into the skin of his airship. Such thin film solar cells have been integrated for instance into glass windows, where the layer is so thin that the window remains transparent.

He doesn't give a lot of figures, but you can work out some of them to fill the gaps. For instance the surface area of his giant airship would be square kilometers. If you have, say, 100 watts per square meter (probably would be more than that), that's a hundred megawatts per square kilometer. That's as much power as a small power station. So if he can achieve thin film solar power as an airship cover material - then he will have of the order of hundreds of megawatts of power at his disposal. Whether that's possible is then an engineering problem rather than fundamental science. But in those thin conditions with no winds, it will be much easier to have gigantic thin film solar arrays than on the Earth's surface.

He has already flown ultra thin film solar cells three times (82 minutes in here) on their balloon platforms. You get a lot more power out of them at 100,000 feet than at sea level. Their manufactures are now coming out with another lighter even higher powered version.

However here, 64 minutes in, he says that they could alternatively use the electrical power from the exhaust of the fuel itself, using magnetohydrodynamics. As he explains it, they use the ions generated in the exhaust of the rocket through combusion, as a source for power, and use that to drive the acceleration of the fuel, so making the rocket more efficient, so it gets more thrust fro the same amount of fuel. He says they swing back and forth, depending on the current level of development of technology, between using this method and using solar cells that cover the airship.

STORING THE POWER DURING PERIODS OF DARKNESS

Solar power is fine so long as you have sunlight. But as his airships travel to orbit, they will encounter periods of darkness. So what do they do at night?

He looks into many ideas for storing power. All of them require advances. But one of the most promising is to use flywheels, because large diameter flywheels are amongst the most dense methods of energy storage available in terms of stored power per unit mass, with far more power per mass than a battery. Or to put it the other way around they have much less mass density for the amount of power stored - they can be much more lightweight.  They would also be in a reasonably hard vacuum already at such altitudes, inside the airship. The larger the diameter of the flywheel, the more energy you can store. With such large airships, potentially, they could be even tens or hundreds of meters in diameter. Normally flywheels are not built to such a large scale because they operate in a vacuum so you would need to evacuate a large volume in order to house such a huge flywheel. But in the orbital airships, the flywheels would already be operating in a vacuum.

Modern flywheels for energy storage normally operate at between 0.1 and 100 Pa. The top of the mesosphere at about 85 kn or 280,000 feet has a presure of about 0.5 Pa. So it would seem that flywheels in the orbital airshis would be able to operate without a vacuum housing, especially above 300,000 feet, and the higher it gets, the longer it will be able to store energy in flywheels.

He suggests several other ideas on page 118, including conventional lithium ion batteries and nuclear micro batteries. But he says

"For raw power storage, nothing can beat a Maglev flywheel. The volume inside the airship allows for flywheels of truly tremendous size. With a large diameter of flywheel, the mass density can be lower. Experimental city buses are now being run on these flywheels. More study is needed to see if this is a practical power source."

IDEA - EARLY STAGES OF THE FLIGHT IN CONSTANT SUNLIGHT?

Whether he can get enough power density for his batteries or not I don't know. How about this idea though, would it work? He suggests putting his Dark Sky Station in the polar vortices, which are at a latitude of 60 degrees. 

That's close enough to the Arctic circle so that in summer they would have only five hours of darkness a day. Also the elevation of 140,000 feet will help make the nights even shorter. As the airships head off to orbit, if they fly west instead of east, they could even keep up with the sun more or less for the first day. After 24 hours they would have gone around the Earth 1.4 times and by then would be traveling at 1.3 km / sec. or about Mach 3.8. So, if you timed it carefully, so that when the airship reaches 60 degrees south in that first orbit, it is there just as that part of Earth comes into sunlight, perhaps you could arrange for the entire first 24 hours to be in sunlight?

By the end of the second day they have gone around the Earth five times. At this point, then the day / night cycles have decreased to a bit over four hours and they are traveling at 2.6 km / sec. They would of course eventually need storage for power for the night - but if you can do that at a later stage, then maybe you need power only for a couple of hours rather than twelve hours or more. Also his airship is after all a glider. He anticipates that the glide back to orbit would take several days.

So when there is no battery power available, it can glide back down again, a bit like solar powered airplanes circling the globe, but in this case an airship balanced to an equilibrium height of 200,000 feet, so there is no risk of it getting lower than that. It would rise under solar power in the day time and glide down at night. So long as he has a good head start, rising for maybe 24 hours or more in constant sunlight, maybe that can then work for the rest of the way into orbit.

When higher in the atmosphere, the vacuum is harder too, so flywheel storage of power would be more efficient without a need to pump out a vacuum around the rotors. It's just an idea and of course lots of details to flesh out. Surely, power storage for night time use is a significant issue.

Just a suggestion, I wonder, what about beamed power from the Earth's surface, in the form of laser or microwaves. Could these fill in useful gaps with strategically placed base stations for the night time flight?

With such large airships, there would be plenty of space to add a rectenna to receive beamed microwaves from Earth.

DAMAGE BY METEORITES

This doesn't 'seem likely to be an issue because the inner cells are "zero pressure balloons". He says:

"There is no difference in pressure to create a bursting force. All a meteorite would do is to make a hole.The gas would leak out staggeringly slowly..."

(Page 112)

That seems reasonable to me, I don't see meteorite damage as being an issue. What do you think?

TRANSITION THROUGH THE SOUND BARRIER AND HYPERSONIC FLIGHT

He says in this recent SpaceShow guest appearance that it gets to 180,000 feet through buoyancy but doesn't reach Mach 1 until around 240,000 feet (56 minutes in to the talk). He thinks that they may be able to achieve buoyancy up to 280,000 feet here (53 minutes in). The Japanese think 300,000 feet. But for practical purposes they think 250,000 feet is the end of buoyancy. By 320,000 feet then they are using aerodynamic lift only.

FIRST STAGE AIRSHIP

Before he can do any of this, apart from the Mach glider tests, he needs a way to get from the ground up to those altitudes of 140,000 feet to build his orbital airships neutrally buoyant at that height. These high altitude airships can't be built on the ground because their thin film skin would be so lightweight that they would break apart with the slightest breeze of wind.

So he needs to build a first stage airship. This already is a major challenge, an airship able to get to a height of 140,000 feet. The German dirigibles could fly up to 24,000 feet. In 2005, Raven Industries demonstrated powered flight with a five pound payload for five hours at 74,000 feet.

The StratoBus project led by Thales Alenia Space in Europe plans to send a dirigible able to carry 200 kilogram to a height of 20 km, or about 66,000 feet. From this you can see that JP Aerospace's plan of an airship able to travel from ground level up to 140,000 feet is rather ambitious. But he has already achieved flights up to 104,000 feet with his prototype ascenders, as he mentions in this program from The SpaceShow.

Artist's impression of the Stratobus, which will be able to carry a payload of 200 kg to 66,000 feet, half way between a drone and a satellite in its capabilities.

As I mentioned above, JP Aerospace do hold the record for powered flight -just a propeller attached to balloons and a framework but they have flown their Tandem unmanned twin balloon airship to 95,085 feet.

They are also working on the actual V shaped airships that they hope eventually to send up to these heights from ground level. They have flown them to several thousand feet so far in unmanned flights. This shows that their V shaped design works as an airship. It also gives them experience in launching them, which they can now do even in windy conditions. Here is one of the arms of their hundred foot Ascender 6 which they plan to test later this year, in an inflation test

And from inside

These are low altitude vehicles so far. He says in this guest appearance to the SpaceShow (56 minutes in) that the ones they built for the USAF were designed to fly at 100,000 feet but were not actually tested because they didn't get that far before the USAF pulled out of the project. So, their only high altitude experience so far is for the tandem design at 95,000 feet, a propellor attached to a framework kept aloft by balloons. So far they are using much smaller ascenders, all "subscale", only 26 feet for Ascender 26 for instance. He explains in that Spaceshow guest appearance that his aim is not to try to get to the desired height but to work on integrating all the systems and refining the basic V shaped design airship, which later they scale to larger and larger vehicles to get to higher altitudes. It's a lot cheaper to do that on smaller scale vehicles, and they flew it to 6,000 feet. Next was the ascender 36, which they flew to 15,000 feet in 2016 on its first flight. They are half way through the Ascender 100 which will fly to 45,000 feet. Then probably early September they will do a 175 foot vehicle which will be a 65,000 to 75,000 foot vehicle.

The early USAF designs which were designed to fly to 100,000 feet look superficially similar, gigantic V shaped designs. Internally the new ones are very different with many improvements which is why they have gone back to smaller models again to work on the design for the new vehicles. So, they probably won't get ascenders crossing 100,000 feet until towards the end of 2018.

DARK SKY STATION

This is so called because the idea is that it would float at such a height that the sky would seem black in daytime just as it does from space or for the astronauts on the Moon. You might think it is impossible to have a structure of any size floating at a height of 140,000 feet. But this is easier to achieve the larger the structure, because of the way the mass per volume goes down as the structure gets larger, so long as the envelope for the structure contributes most of its mass.

For instance, Buckminster Fuller's "cloud nine" was a design for an entire city, one kilometer in diameter, floating in the atmosphere. A sphere as large as that would be so low in mass, if constructed as a tensegrity sphere, relative to the mass of the atmosphere that just a one degree increase in temperature would be enough for it to float. As a tensegrity sphere it would also be very robust in any weather conditions. There's never been any need to build such a structure, and maybe there never will be, nor did he expect there to be, but it seems generally agreed that the engineering for it is sound. He thought of them only as an "exercise to stimulate imaginative thinking".

So, going on from that, there was a serious proposal in 1980 by doctors Ernst Okress and Robert Brown of the Franklin Institute to build a kilometer scale platform called STARS as an upper atmosphere research station, half a kilometer or one kilometer in diameter. See Solar Thermal Aerostat Research Station (STARS) and the news story about it in the Washington Post:


"Solar Powered Balloon Station Proposed For the Edge of Space".

For an artist's impression of STARS, see Peter Elson's "Orion Shall Rise" painting, an illustration from Poul Anderson's novel of the same name, Orion Shall Rise, which features the STARS aerostat.

This construction would have flown at a height of about 100,000 feet. And it would have been kept aloft only by the heat of the air inside it, like Buckminster Fuller's "cloud nine", not needing hydrogen or helium or any kind of lifting gas.

With that as background, perhaps JP's idea of a dark sky station, with use of hydrogen for lift,  is not so impossible?

The dark sky station would be starfish shaped and use lots of large gas bags along each of the five arms, and not one huge spherical one. This is a very stable configuration.


Artist's impression, shows the Dark Sky Station at 140,000 feet. It would be visited by airships from below and could be used as a launch complex to launch rockets to orbit, which then would not have to push their way through the dense lower atmosphere. This much could be achieved without orbital airships.

Again he goes into a fair bit of detail. The lifting bags would be damaged by radiation and would be replaced every 100 days (page 88) at least unless we can develop new materials to prevent that - and he sees that as part of a continual maintenance cycle, with old bags deflated, replaced and the new ones reinflated with the lifting gas. Instead of trying to get exotic materials, he uses larger (see 94 minutes into the interview). He's already done a balloon swapout in flight at 50,000 feet on his away 6 mission and continued up to 100,000 feet..

He would bring hydrogen up to the dark sky station in the form of liquid helium, something that has already been done in a high altitude helium balloon flight in 2002 by Julian Nott, and liquid hydrogen and use this to keep the bags inflated.

He would use superpressure balloons like the NASA big pumpkin (page 91) so that they stay in the same altitude in the sky and don't rise and fall as the temperature changes. He would put it in the polar vortices, so that it travels around the Earth once every 14 days (page 90). His station would be a starfish shaped structure with five arms for stability (page 85). They have done experiments with balloons attached to struts for an early first try at the configuration of a dark sky station, with success (page 97).

WORK AROUND - IF HE CAN'T ACHIEVE ORBITAL AIRSHIPS, PERHAPS HE CAN RENDEZVOUS WITH A LIFT TETHER SYSTEM?

This is my own suggestion here. It's based on the lift tether system, which is an idea which has been investigated for an easier way to get into orbit, related to the space elevator. We don't have materials to make the space elevator, which is also a massive construction. So, until we have those materials, we need to use a “watered down version” which is not able to hover stationary over the Earth’s surface. However, it would still be enough to make a difference. Normally, you need to travel at about Mach 20-25 to go into low Earth orbit (depending on how high the orbit is). The launch assist tether reduces that to Mach 12 or less.

From: Hypersonic Airplane Space Tether Orbital Launch (HASTOL) System.

This video explains it well:

For more details, see Launch Assist Tethers. You could use the same process in reverse to de-orbit a spacecraft to Mach 12 in the upper atmosphere, and then it glides down from there.

So this would give you a way to slow down your orbiting spacecraft to Mach 12 instead of Mach 20 upwards, which would be quite a plus.

That’s still very fast. It’s four times the speed of the Lockheed SR-71 Blackbird supersonic spy plane, or Virgin Galactica’s SpaceShipOne (Mach 3.09), and more than twice the speed of the ESA’s projected Mach 5 aircraft:

However it's not far off the speed of JP Aerospace's Mach 10 transatmospheric airship, so it may be a way for them to get into orbit if they can't make the last stage of the orbital airship to get all the way to orbit by itself.

SO WHAT DO YOU THINK? HOW FAR COULD THEY GET?

This debate can get so polarized, if you ask the question "Can they do it or can't they". But perhaps we can defuse this a bit by asking a more nuanced question - "How far could they get?"

To get the debate started, here are a few possibilities to think about. Could JP Aerospace

Also what are your thoughts about re-entry of really large kilometer scale airships? Or the smaller ones for VAMP in the Titan, Venus and Earth atmospheres? And what about accelerating to orbit? Is it a problem crossing the sound barrier for instance at such high elevations in a near vacuum?

It will be interesting to see what the range of views is of physicists on this matter. I will surprised if they all agree on how far he could get. So often it is presented as black or white "Will they do it" or "will they not". Do say what you think in the comments area below. Also, if I have missed out anything significant in my presentation of JP's ideas do say. 

COMMENTS

What do you think? Do say in the comments. Be sure to say if you spot any mistakes in what I've said here, thanks!