Dirigibles on Mars - A practical means of transport?

tahanson43206 · 2019-12-31 19:07:05

For SpaceNut re #99 and #100

It is good to see such well done visualizations!

The vacuum idea is interesting, from the standpoint that the author asserts that the crushing effect is so much lower on Mars that a physical shell might survive evacuation of the Martian atmosphere.

I'm somewhat skeptical that particular idea will be realized anywhere in the Solar System but I'm pretty sure it is not forbidden by physics, so someone might be able to pull it off at some point.

On the other hand, your idea of heating a balloon (I'm presuming one filled with Hydrogen) certainly makes sense. What is more, it could be tested on Earth, either inside an evacuated chamber with conditions matching those of Mars, or (perhaps) at the elevation in Earth's atmosphere which matches Mars.

I asked Mr. Google for help comparing the atmosphere of Mars with that of Earth, and found this:

https://www.mathscinotes.com/2012/10/ea … e-to-mars/

Analysis
The quickest (and cheapest) way to find the altitudes we want is to go out to NASA's web site and download a table. Using this table, we can look up the altitudes that correspond to pressures of 0.3 millibars and 11.5 millibars. Those altitudes are:
11.5 millibars ⇒ 30.125 km = 98,350 feet
0.3 millibars ⇒ 57.150 km = 187,500 feet
Conclusion
The surface pressure on Mars is equivalent to the range of pressures on Earth at altitudes between ~30 km and ~60 km. That seems like pretty thin atmosphere. Since humans require pressure suits for altitudes above ~19 km (called the Armstrong limit), it looks like people will always be wearing pressure suits while walking about Mars. Too bad -- I actually kind of liked the scenario shown in the movie Robinson Crusoe on Mars (Figure 2).

Next, I asked Mr. Google about the greatest altitude reached by a balloon:

Search string: maximum elevation achieved by balloon on Earth

A satisfying array of citations appeared, confirming that balloons HAVE flown above the altitude of 30 km shown as the best condition on Mars.

Here is one: https://www.space.com/41791-giant-nasa- … ecord.html

NASA officials said the Big 60 set a new sustainable-altitude record by reaching 159,000 feet (48,500 m) during an 8-hour flight on Aug. 17, traveling into Earth's stratosphere and ascending about 5 miles (8 km) higher than the next-largest balloon prototype.

These experiments confirm that balloon operation is possible on Mars.

What the facts of the Mars environment confirm as well, is that the balloon operator will be starting at what amounts to a VERY high altitude on Earth.

And this entire chain of thought brings me to a recollection that there is a gent attempting to put a balloon into orbit.

John Powell is the gent, and the company is JP Aerospace.

Wikipedia has an article about a flight in 2011:

The JP Aerospace Twin Balloons Airship is an unmanned airship comprising two balloon envelopes side by side, with twin electric-powered propellers mounted midway along the connecting boom. On October 22, 2011 it is claimed to have flown to 95,085 feet (ca. 28,982 m), nearly 4 miles higher than any airship before.

Mr. Powell was a guest on The Space Show on multiple occasions, so any forum reader interested can search TheSpaceShow.com archive to find the interviews.

And ** that ** recollection leads me (inevitably) to the realization that if Mr. Powell can get his concept to work on Earth, then it certainly would work on Mars, to gently lift payloads up to orbit.

Reading further down the Google citation list brings up this important quotation:

www.jpaerospace.com › atohandout
JP Aerospace is developing the technology to fly a balloon-or more accurately, their relative, the airship-directly to orbit. Flying an airship directly from the ground to orbit is not practical. An airship large enough to reach orbit would not survive the winds near the surface of the Earth.

I had forgotten that detail from the John Powell interviews ... the STARTING conditions on Mars might just be close enough to those required for a vehicle designed to fly directly to space!

For any forum reader who is so motivated by this post, a pdf handout is available:
http://www.jpaerospace.com/atohandout.pdf

SpaceNut ... I started this post in a skeptical frame of mind, but now I'm cautiously optimistic that you may be on to something.

SpaceNut ... if you find yourself in a mood of inquiry, here is the email address for Mr. Powell, given at www.jpaerospace.com

jpowell@jpaerospace.com

(th)

Last edited by tahanson43206 (2019-12-31 19:11:10)

SpaceNut · 2019-12-31 19:28:31

I believe that we do have the company and its attempts to gain orbit with a Balloon by them shaped like a V. Its earth greater gravity that is the issue and not so much the lift of the gas used. as of the last post which I did update for somemore details and graphics the design is made from strong but light weight materials. As you noted even atom of a specific type matters for the lift capability to move mass on mars.

The atmosphere of Mars is the layer of gases surrounding Mars. The atmospheric pressure on the Martian surface averages 600 pascals (0.087 psi), about 0.6% of Earth's mean sea level pressure of 101.3 kilopascals (14.69 psi)...

tahanson43206 · 2019-12-31 19:38:18

For SpaceNut re #102

Thanks for confirming JP Aerospace may be in the forum archive.

I am confident NO ONE in this forum has considered the possibility the JP Aerospace concept might work BEST on Mars, and provide a way to reach orbit without having to operate a rocket.

If you (or anyone in the forum community) is interested, the email address for Mr. Powell is available.

It should be noted that if a JP Aerospace vehicle can REACH orbit on Mars, then it certainly can provide a gentle, terror-free method of landing critical items, such as people.

(th)

SpaceNut · 2019-12-31 21:06:45

Balloons to Space

Airship to Orbit?

Orbital hydrogen balloon impacts with suborbital craft

Airship part-way to Orbit

Calling our technical experts - Any chance this thing works? JP Aerospace has a novel idea for Earth to LEO - - airships to orbit:

Inflatable space parachute or escape pod - Just another use inflatable technology?

Is this a new idea for getting to LEO? - A possible efficient way to get to LEO?

kbd512 · 2020-01-05 19:19:52

One of the simplest and most energy efficient ways to obtain both water and carbon dioxide might be to send autonomous airships to the polar regions to collect H2O and CO2 in tanks that are then pumped into Starship's holding tanks upon return to the equator. A polar lander with a fission reactor could supply the thermal power necessary to melt water and liquefy CO2. Significant power would still be required for the Sabatier reactor, but obtaining pure water and CO2 from those polar ice deposits would drastically simplify the operation.

SpaceNut · 2020-01-05 19:29:33

Seems that a good landing with a kilowatt reactor would be just about right as its going to waste 30kw in heat to make 10 kw for each unit of electrical...

SpaceNut · 2020-07-27 21:30:56

blimp by another name

tahanson43206 · 2020-07-28 06:19:37

For SpaceNut re #107

There are significant differences between blimps and dirigibles.

The outward appearance is so similar that uninformed observers might not be aware of the differences.

So while I can understand the confusion due to similarity of outward form, I'd like to invite you to go back to #107 and add details so that readers of the forum who do not have the background necessary will not come away thinking the two words are synonymous.

The words are different because the machines are different.

(th)

Last edited by tahanson43206 (2020-07-28 06:20:06)

Calliban · 2020-07-28 07:10:43

tahanson43206 wrote:

For SpaceNut re #107
There are significant differences between blimps and dirigibles.
The outward appearance is so similar that uninformed observers might not be aware of the differences.
So while I can understand the confusion due to similarity of outward form, I'd like to invite you to go back to #107 and add details so that readers of the forum who do not have the background necessary will not come away thinking the two words are synonymous.
The words are different because the machines are different.
(th)

I take it you are talking about the difference between rigid and non-rigid airships.

Typically, rigid has better aerodynamics, but at the expense of higher frame weight. The gas cells within the frame are non-pressurised and are fitted with valves that lift if there is any significant differential pressure between the gas cell and the atmosphere. No airships of this type have been built since the 1930s. The high frame weight would make it exceptionally difficult on Mars. It would be the airship of choice on Titan. If we were ever to get back to hydrogen filled airships on Earth, they too will probably be rigid, as they would need to fly at speeds of 100km per hour and often against the wind. The hydrogen gas cells would need to be surrounded by nitrogen within the external envelope.

Last edited by Calliban (2020-07-28 07:13:01)

tahanson43206 · 2020-07-28 08:32:30

For Calliban re #109

Thank you for helping to clarify the difference between the topic title "dirigible" and SpaceNut's humorous remark about the similarity of appearance of the two vehicles.

It is possible (with so much new information flooding in constantly and from all directions) you may (must?) have missed developments in dirigible technology since the 1930's. In fact, just recently there was a dirigible operating for excursion flights along the west coast of the US. It employed helium as the lifting agent.

In England, right now (at this very moment) the famous "bum" design is in development and testing. This is NOT a blimp, and it might not seem equivalent to the 1930's design for a dirigible, but that seems understandable, because decades have gone by.

Here is where the talents of SpaceNut can help, if he has the time and opportunity.

This topic is about Dirigibles and NOT Blimps.

On the other hand, (I think it was Calliban) one of the forum contributors has been making (renewing) a case for a solar cell covered blimp that would tow behind a ground vehicle to provide power. I think that concept deserves its own topic, and hope someone sets one up.

That concept on its own could lead to a business on Mars, making the equipment and providing the gases for lift, as well as providing field support as needed by customers.

I'm not ready to set this up as a business in My Hacienda, but it is definitely a candidate.

Edit#1: I asked Google about the Goodyear Blimp, and found that confusion exists at Wikipedia:

The Goodyear Blimp is any one of a fleet of airships or dirigibles operated by the Goodyear Tire and Rubber Company, used mainly for advertising purposes and capturing aerial views of live sporting events for television. Wikipedia

For SpaceNut .... this situation is calling for your skills to provide clarification. Language can be (and often is) corrupted by constant misuse of a word, until it loses its original meaning and even becomes interpreted as the opposite.

Edit#2: Pending SpaceNut's clarification, my understanding of the difference between the two vehicle types is where the structure is defined.

A Blimp is like a shelled creature, whose structure is carried in the shell.

A dirigible is like a mammal, which has a skeleton upon which the components of the structure are "built". The outer skin of a dirigible (as Calliban pointed out) does ** not ** contribute to the structural function of the vehicle.

In a blimp, the payload is carried by the gas bag.

In a dirigible, the payload is carried by the internal frame.

Edit#3: I am sorry to see this venture closed operations. It was in business for several years in the US, and customer testimonials show how enjoyable the experience of flying with them was.

To the point of this topic... this vehicle was described as a Zeppelin class vehicle. However, observers thought it was a blimp. It would have looked like the Goodyear Blimp.

https://www.airshipventures.com/

AIRSHIP VENTURES HAS CEASED FLIGHT OPERATIONS
As of November 14, 2012, Airship Ventures ceased flight operations.
Airship Ventures proudly operated America's first commercial passenger Zeppelin airship, "Eureka", from October 2008 to November 2012. Over 20,000 passengers were introduced to the wonder and joy of travel by airship, floating serenely over California and beyond. We provided unique 'flight seeing' tours, televised coverage of events, a stable aerial platform for scientific research & development, set aviation records, performed at air shows and produced a number of weird and wonderful skydiving stunts. We ceased operations due to lack of a major/title advertising sponsor, a necessary part of the revenue mix. The Zeppelin was disassembled and has been returned to her place of manufacture in Germany.
You can read a running diary of the history of our company and operations on our blog, and you can also find people talking about us and sharing their memories and experiences on our Facebook page.
CONTACTING US
If you need to contact us, please do so by sending an email to info@airshipventures.com.

(th)

Last edited by tahanson43206 (2020-07-28 09:17:34)

Calliban · 2020-07-28 09:42:08

Tahanson, there is an intermediate class known as semi-rigid. This is a flexible envelope, which is mounted onto a frame, which runs along the bottom of the envelope. It provides stuctural reinforcement, but is not a rigid airship in the historical sense, as it does not have gas cells within a rigid frame. I believe this is what Zeppelin have been building in recent years.

I don't know why Americans call these things 'dirigibles' or 'blimps'.

Last edited by Calliban (2020-07-28 09:42:57)

SpaceNut · 2020-07-28 18:45:32

Just think this all started with a hot air balloon.

The structure/ framing is more about holding shape and to create support for the attachment.

Harder materials would do a simular function without the internal ribs.

Also once we get to metals that are semi ridgid we are looking at a balloon fuel tank.

tahanson43206 · 2020-07-28 20:44:14

For Calliban re #111

Thanks for the tip for a direction to focus reading ...

For SpaceNut ... The flights of the first hot air balloons were a wonder to behold in their time, and (from my point of view) they would still be so today.

The first flights (as I vaguely remember the accounts) involved burning fuel in the framework under the balloon.

My recollection is that the envelope of the balloon for those first flights was made of paper. Again, working from memory (which is likely to be hazy) I think the inventors were in a position to make the balloon envelope of paper because they were members of a family who had a paper making operation.

So (if memory serves) you had a live fire under a paper envelope. Gutsy!

(th)

kbd512 · 2020-07-29 15:17:26

tahanson43206,

The figures of merit here are horsepower per ton (or kilowatts per kilogram), center-of-gravity (load distribution on the complete ready-to-run vehicle at maximum design weight when loaded with the maximum tonnage of cargo permitted by vehicle load restrictions), and traction (the ability to transmit power to the ground, or to produce motive force, in the direction you wish to travel). We don't have a usable atmosphere to work with for combustion of liquid hydrocarbon fuels and the dynamic force applied by the Martian atmosphere to even a multi-hundred-kW array is negligible. It doesn't have to be a simple sphere. It can be a torus with a solar array draped over the top of it. A multi-point connection system or bridle can also be used and connected to the tether that the vehicle ultimately controls. We have very rough terrain, not a single road on the entire planet, the regolith is often quite sandy in places, and those factors tend to favor a tracked vehicle that has a very large contact area with the ground and low-CG, as compared to a wheeled vehicle purely using onboard battery power.

As stated before, each and every time the US Army conducts a new mobility study they "rediscover" that tracked vehicles are roughly 28% lighter for a given payload capacity when the vehicle is primarily used in an off-road environment. The Army puts armor / fuel / weapons on their vehicles, we need radiation armor / an extremely efficient form of "fuel" (electrons) that we don't have to carry with us / consumables (air / water / CO2 tanks for powerful yet simple air-powered tools for maintenance) / scientific instruments on our vehicle. We have roads in lots of places where fighting occurs here on Earth, hence the desire to appropriate wheeled armored vehicles and to accept or design around the inevitable load restrictions, but nothing of that sort exists where we're going. Thus, we don't need to design for scenarios that don't exist in our operating space. Sure, tracks are heavier and have more parts than wheels, but in practice the suspension systems required for heavy wheeled vehicles are every bit as complex as tracks with torsion bar suspension systems and then some. In short, physics won't change to suit the desire boys have to play with their trucks. The 38% gravity is a bonus, but that means we use that to design lighter vehicles that are easier to transport to Mars.

For a pair of astronauts wanting to transport heavy cargo overland, perhaps to resupply a remote geology output hunting for resources, a 100kWh 1,500kg battery (includes all plumbing and radiators for thermal regulation) from an EV would approximate the weight of a tank engine (less transmission) and could provide life support for multiple days if the vehicle suffers a mechanical failure during a dust storm. My thought process is that life support / thermal regulation / communications and navigation electronics will account for something like 2kWh per hour and the tethered array will easily be capable of recharging that battery within a couple of hours of sunrise. The rest of the daylight hours can then be devoted to travel, if so desired. I estimate that an electric motor and non-contact (permanent magnet) transmission / gearing system would weigh somewhere in the 500kg range. Since we're already experimenting with these for helicopter power transmission systems here on Earth, I presume they're mature enough for use in a land vehicle on Mars.

Incidentally, a Pu238 powered 2kWe RTG would have a mass of 900kg and require an array of 20 MMRTGs. It's possible to do, but seems impractical. The defunded ASRG design would've been substantially better. As you pointed out, it may be better to directly convert thermal power into mechanical power to drive an electric generator. The as-designed ASRG was 32kg vs the MMRTG at 45kg, and produced 130We from 500Wth (1.2kg of Pu238 per unit), as compared to the MMRTG's 125We from 2,000Wth (4.8kg of Pu238 per unit). ASRG is approximately 1/4th of the Pu238 consumption for the same electrical output. The conceptual eMMRTG produces 145We and is 8% efficient vs MMRTG being 6% efficient, and therefore 3.6W/kg vs 2.8W/kg. ASRG is still 4W/kg. You'd need 16 ASRG's to produce the same output as a single MMRTG, for a total mass of only 512kg. Overall, this solution would provide guaranteed life support power for at least a decade or three and is approximately equivalent in weight to a bleeding edge 100kWh battery that supplies 4 days of life support power. As actual operational experience on Mars has shown, it's completely unaffected by atmospheric dust. If it was purpose built for backup power as a single unit, it could be much lighter and more compact. The environmental packaging accounts for nearly all of the mass and the 19.2kg of Pu238 is negligible. The figure presented was for a redundant array of 16 "as-designed" ASRG devices. MMRTG's Aluminum cooling fin root temperature is 157C/315F, so you need to steer clear of them to avoid thermal burns.

The nuclear part of the device I envisioned was a removable / storable core that can be exchanged or transferred to other vehicles and structures, as required. The rest of the power takeoff (both thermal and electrical) would be built into the vehicle or structure. Imagine you have an always-on life support backup, like a nuclear powered uninterruptible power supply. Two "slots" or "bore holes" in the vehicle or structure are reserved for nuclear heat sources and drive CO2 powered turboelectric generators (Stirling engines) using radiated thermal power transferred from the thermally "hot" nuclear power core, as a sort of "closed loop" secondary / backup life support system. The rest of the cylindrical slots or bore holes are reserved for batteries or super capacitors. Since the power supplies have the same form factor, they're interchangeable, after a fashion. The nuclear core is there to supply thermal and life support power, the super capacitors supply surge power, and the batteries supply moderately variable power. Between those power cores and the floating solar array, we have a complete power solution that doesn't come with design limitations that inhibit our ability to explore or construct habitation for future colonists.

Anyway, all of those factors and figures of merit favor a different type of power provisioning system that isn't limited to the weight of oxidizer and fuel or a giant battery that a vehicle might otherwise be forced to carry with it. A range-limited combustion engine powered rover was simply the best we could do using 1980's technology, but technology has moved on since then. Thin film solar and advanced materials like CNT make this feasible. Otherwise we end up with a giant battery on wheels or a giant cryogenic gas tank on wheels if we want to, say, cover 500km prior to returning to the base or settlement.

SpaceNut · 2020-07-29 17:14:13

I work in a group 2004 that used magnetic coupling of a single shaft that turn the air conditioning unit and cooling fluid exchanger at different rates.

SeaDragon · 2020-08-11 14:10:15

OK, upon further reflection, I'm now of the opinion that dirigibles might actually be a good way to transport freight after all.

Subject to the following assumptions:
- The wind is reliable enough that it can be ridden to the intended destination with relatively little steering (jet streams and so on may be of great help),
- The airship can get away with only operating during daylight hours, gently landing and loitering near the ground for the cold and lightless nights,
I present the following design for a Martian airship:

Starting from the centre, the payload to be transported is slung directly under the airship. Interior atmosphere is nitrogen, giving about 1/3rd the weight of CO2 displaced as lifting force. This is way worse than H2 but it's way easier to keep inside the ship (even very thin plastic can be made to leak N2 far slower than H2), much cheaper to replace and can even be replenished in-flight.

Propulsion
This ship must be far too big and low density to be effectively propelled by anything but natural Martian wind. It has the ability to steer (to one degree or another) and to increase or decrease the push from wind by rotating its structure to be perpendicular to the wind (to increase wind force and speed up) or remain parallel to it (decreasing wind force and slowing down).

Buoyancy
Two ballast tanks either side of the centre, here shown partially inflated, can be filled with N2 to increase buoyancy or deflated to decrease it. I want to keep pressure differences as low as possible so that the forces acting on the numerous inflatable structures of the ship are as small as possible. The two main ellipsoidal balloons front and aft of the centre are transparent. They have inflatable cylinders within that are half silvered with aluminium on the outside but coated with carbon black on the inside. With the slivered side facing the sun almost all light is reflected and the cylinder remains cool, but if it rotates to expose the carbon black coating it will instead absorb almost all of that light and heat the interior air. In this way, the temperature of the interior can be carefully controlled in flight adjusting buoyancy accordingly.

Steering
This is provided for by 3 inflated vertical cylinders capable of being rotated by electric motor rapidly about their vertical axes. The point of this is the Magnus effect: a spinning cylinder deflects oncoming air proportional to its speed and the direction of the rotation. In this way, small sideways forces can be generated that act to steer the ship. Of course, they are acting quite a way vertically upwards from the ship's centre of mass but the combination of strong buoyancy forces and the ship's mass being concentrated with the underhanging cargo make it relatively stable against being toppled.

Power
In the furthest fore or aft spherical balloons are found central inflatable cylinders (resting on smaller spherical balloons) that can be rotated 360* about their central vertical axis. These are cylindrical solar concentrators that are half silvered (my favourite trick!) and, by correct orientation to point directly at the sun, can focus light onto silicon carbide solar cells at their centre. This might give 1 kW per square metre of solar cell simply radiating away waste heat by operating at high temperatures, a feat which SiC can accomplish without debilitating loss of efficiency. This goes a long way towards getting good power to weight ratio.

I've not decided on the size yet, suffice to say that every cubic metre of N2 gives ~10 grams lifting capacity near the Northern Martian surface so that a cylinder 500 m long and 150 m tall could lift some 80 tonnes total. For very thin composite polymer fabric or going even bigger than this (hopefully big surfaces but thin skins aren't so bad as they sound) this may thus present a potential option for transporting good across long distances at reasonable speeds.

Can anyone see issues I've missed? Ideas, critiques and analyses welcome.

Last edited by SeaDragon (2020-08-11 14:12:36)

tahanson43206 · 2020-08-11 17:28:26

For SeaDragon re #116

Bravo! Nicely done! Terrific sketch and supporting text!

You are the first person (I'm aware of) who suggested Nitrogen as the lift gas.

Hopefully you'll receive some feedback from others here in the forum. You've made some assumptions that may (or may not) match up well with the reality of Mars.

I also recognize you've not had the time to read from the many posts that deal with this subject. Many are scattered around the archive in topics that have nothing to do with balloons.

(th)

SpaceNut · 2020-08-11 19:29:28

Lets if i have a search to fill in any knowledge not stated thus far.

Bouyancy and ballast using free nitrogen not possible for mars but co2 is and can vent for a rise and pumped into stores will allow it to sink.
Co2 = 12 + 2(16) = 48 mole mass
N2 = 2(14) = 28 mole mass

Of course the only element that could be from Mars is in the water as H2.
Then again any of the ane's will work from carbon and hydrogen.

This submittal is for a mobile rigid airship Mars base. For the 2014 NASA Mars base challenge.
Mars airship

If you throw a less dense gas than CO2, say hydrogen into a balloon on Mars, the balloon will expand until pressures are approximately equal, and the balloon will have some small lifting force on it. Just like a helium balloon in the earth's primarily nitrogen atmosphere.

Scratch numbers on page

Geometrical layout of a Mars balloon and precalculation of the thermal control system

https://en.wikipedia.org/wiki/Lifting_gas
https://infogalactic.com/info/Lifting_gas

https://edition.cnn.com/2020/07/27/us/n … index.html

http://www.elementalmatter.info/mass-numbers.htm

By the way multiple linked section seem to be the possible max lift to flight control.

tahanson43206 · 2020-08-11 20:02:09

For SpaceNut re image in Post #118 ... did you notice the image is from Thingiverse? I thought the style of the image looked familiar.

For SeaDragon ... I appreciate SpaceNut commenting on Nitrogen as a lifting gas, but he dismissed your idea pretty quickly.

I'm hoping you will extend your thinking a bit to help us understand where you were planning to acquire the volumes of Nitrogen needed.

We need lots of Nitrogen for plants, so wherever you're going to find Nitrogen will be welcome news to growers!

Edit#1: Since you are still learning how to get around in the NewMars archive, a search for posts that contain nitrogen will reveal the great variety of inputs to the collection accumulated over 20 years.

(th)

Last edited by tahanson43206 (2020-08-11 20:03:27)

kbd512 · 2020-08-11 22:25:34

SeaDragon,

Have you ever heard of a super-pressure blimp? There are 2 layers of fabric with a gas trapped between them and the center of the balloon is evacuated. That might be one way to obtain more lifting force from less gas. The atmospheric pressure is far lower on Mars compared to Earth, so comparatively less strength is required from the membrane. I haven't done the math on this to determine how well it would work or if the second layer of fabric eats up all of our payload mass.

Mars atmospheric density is ~0.015kg/m^3.

10 micron Mylar is 13.6g/m^2, so 42.704g for a 1m sphere. Well... That idea was done pretty quick.

CNT tape on the other hand, is only 0.1g/m^2. If you had 2 layers of tightly woven CNT fabric, could a gas with larger molecules, maybe Argon, be trapped in it?

tahanson43206 · 2020-08-12 06:21:59

For kbd512 #120

Thanks for mentioning this idea to SeaDragon. It is one of many examples of knowledge/insight that are present in the NewMars archive.

I've looked at the idea, and posted an observation (somewhere in the archive) that there is tension between the outer layer of fabric, and the inner layer of fabric which is exposed to vacuum.

Threads would (presumably) carry tension between the outer layer and the inner layer.

Those threads will bear the load.

That load would consist primarily of the gas pressure inside the separated layers. Another component of the load would be the pull of gravity of Mars on the entire structure, including payload.

On the inside of the layers would be vacuum, and on the outside is the near vacuum of Mars.

It should be possible to compute the pressure that would be required between the layers to sustain the shape desired, and from that deduce the number of threads that would be needed to carry the load.

Kevlar #92 thread can (according to the sales text at an online distributor) carry 30 pounds or 13 Kg without breaking.

I would ** really ** like to see an analysis of what this concept would look like if an attempt is made to put it into practice.

Design of this vehicle would (presumably) include planning for rip-stop capability. The pressure between the layers would (presumably) be high, so any penetration of the outer layer by a flying object (such as debris from a landing space probe) would provide an escape opportunity for the gas under pressure there. A honeycomb design might be the answer.

In any case, I am glad to see the idea brought forward again.

(th)

Last edited by tahanson43206 (2020-08-12 06:26:55)

SeaDragon · 2020-08-12 14:58:42

SpaceNut,

I see where you're coming from but I think it's going a little too far to dismiss N2 just on one figure of merit (lifting ability) and by my analysis it certainly is a lifting gas. Let me show you my thought process:

As you say, N2 has a mass 28/44 ~ 2/3rds the mass of CO2, hence @ Acidalia Planitia's 1KPa surface pressure and air density of 0.03 kg/m^3, 100 cubic metres of enclosed N2 will lift 1 kg of blimp mass. Very true, it's not nearly as good as H2, where 100 cubic metres lifts almost 3 kg of blimp mass but it does provide lifting force and it has other advantages.

One of which is cost - I contend that it is possible to gather N2 for far lower energy expense than production of H2. As in "The Case For Mars", zeolites (basically clay boiled in sodium hydroxide, relatively easy to make) absorb CO2 very strongly when cooled and reject it again when heated. At its simplest such a system could take the form of a large fan feeding a series of pipes filled with zeolite and kept in the shade behind a large silvered curtain during the day. As the pipes cool from the shade the zeolite inside pulls air through and sequesters the CO2 component. Since the air is pushed via the fan, a mixture of N2, argon and other trace gases (whatever isn't CO2 or H2O) leaves the other side of the pipes to be collected in a balloon for later purification by compression through a membrane system.
When the zeolite is saturated one simply turns the fan off and lifts the curtain, exposing the pipes to sunlight and purging CO2 from the heated zeolite (which soaks up a lot of heat in the process). There's plenty of N2 in Mars' atmosphere.

How much heat is needed?

H2 production takes realistically something like 200 MJe per kg of H2 gas produced. By contrast, N2 production only requires heat input in the first phase and the hassle of heat rejection in the second.
For the zeolite process above, taking as a maximum energy requirement for sequestering of CO2 the latent heat of sublimation (I don't have the figures for heat released by a zeolite during absorption but it's this or lower) gives 25 KJ/mol ~ 570 KJ/Kg CO2 sequestered
(Data from eg https://en.wikipedia.org/wiki/Enthalpy_of_sublimation )

Since only 2.6% of the atmosphere is N2 we need to sequester some 60 kg of CO2 for every 1 kg of N2.
This takes ~0.57MJ/kg*60kg ~ 34 MJ of heat first rejected then added to collect 1 kg of N2 from Mars' atmosphere. The harder thing, of course, is separating N2 from argon. This could be done using a bus of membranes that allow argon through but not nitrogen or vice versa. Alternatively, there are some zeolite compositions that will soak up both nitrogen and argon but at different rates (eg https://link.springer.com/article/10.10 … 1529328878 ). Using a system like this, multiple refluxes eventually separate argon and nitrogen enough to get N2 as a lifting gas. Either way, even assuming many consecutive passes are necessary it can't possibly cost more than the heat required to sequester the CO2 in the first step so doubling that energy bill gives ~70 MJ heat for 1 kg N2 separation.

Overall: accounting for differences in density, 40 kg N2 lifts as much as 1 kg H2
40 kg N2 needs pessimistically ~ 2.8 GJ heat to produce, 1 kg H2 needs ~ 200 MJ electricity to produce
Even at its most naïve this setup makes N2 competitive with H2 as a lifting gas because heat is so much cheaper than electricity on Mars but if you treat the zeolite sequestering process as an excuse to produce high pressure CO2 and as a free heat sink you might well be producing an N2:Ar mix as a happy biproduct of what you were already doing.

As for ballast, putting balloons on the side that can be filled with CO2 does not affect buoyancy: a balloon filled with air on Earth exerts a weight exactly the same as the balloon does when uninflated (excluding the tiny amount of compression needed to fill it). An internal ballast tank filled with CO2 when you want to go down would work by displacing the interior balloon volume and hence decreasing the total lifting gas volume. By having balloons on the exterior that can be inflated when you need to go up and deflated when you need to go down you get more total potential lifting volume for your effort: they're not ballast tanks really, just extra balloons you can inflate to go higher if you need to. I call them ballast tanks simply because that name is indicative of their role. I suggest heating the interior gas using the interior swivelling cylinders silvered on one side and black on the other as illustrated, turning the black side towards the sun when you want more heat hence pressure to inflate your ballast balloons and away from the sun when you want less heat and hence for your ballast balloons to be deflated.

My main problem with H2 is its greatest strength: it's a very light molecule. It leaks through barriers very rapidly, which is a big problem if you need your airship skin to be so thin as is needed to work on Mars. It takes a lot of electricity to replace any lost H2 gas.

If we really must have better lifting performance than N2 I put methane forward as an alternative: its molecular mass of 16 means 1 kg methane displaces 44/16 ~ 3 kg CO2, hence 1 kg methane lifts ~ 2 kg of airship mass. It's even more electricity intensive than H2 to produce but at least it is bigger and hence less inclined to leak through the airship.

Interesting link for the mobile base btw, I was thinking something far bigger with almost no rigid supporting structures: only its own inflation pressure and tensile cables keeps it together, which is by far the lightest approach to airship engineering.

tahanson,

Hopefully this approach for N2 separation from the atmosphere gives ample cheap N2 for ammonia production and all the fertiliser our farmers will need!

Last edited by SeaDragon (2020-08-12 15:27:03)

SeaDragon · 2020-08-12 15:21:24

kbd512,

Interesting idea - with tahanson's suggestion (which matches what I was thinking!) of using a higher pressure in the cushion gas between both layers and connecting the outer layer to the inner layer by cables or other tensile members so that the tendency of the interior to collapse in on itself can be countered by purely tensile forces in the outer skin layer connected by strings this may well be workable. If the interior layer is not reinforced in this way it must contend with a very large compressive force pushing it inward which, being so thin, causes highly destructive buckling forces as per https://en.wikipedia.org/wiki/Vacuum_airship#Buckling

Haha, CNT, you love this stuff!
Since you introduced CNT yarn to me a few weeks back I've grown quite partial to it myself - with its excellent tensile strength to weight ratio it might well be the best choice for connecting the compressed interior balloon of a vacuum airship with the stretched outer balloon as above as well as reinforcement for the balloon skins themselves.

Still, while the advantages of lower H2 production costs (since a vacuum airship doesn't need any!) and very slightly greater lifting ability must be considered a vacuum airship requires at least twice as much airship skin, possibly upwards of 3 times as much for the same total enclosed volume as a normal airship (accounting for both the vacuum portion and the cushion of gas between both layers).

Last edited by SeaDragon (2020-08-12 15:28:16)

SpaceNut · 2020-08-12 16:46:29

SeaDragon thanks for your post #122
Mars carbon dioxide rich atmosphere has about 1.9 percent of nitrogen as N2. fractional distillation via night temperatures with a chiller but.
https://nigen.com/how-separate-nitrogen … -nitrogen/
seems there is a low energy compression through a membrane for seperation.

SeaDragon · 2020-08-13 18:05:21

SpaceNut,

Yes indeed, membrane separation is a good option if you can find the right membrane materials for the N2-Ar system, probably more scalable and far less energy intensive than alternatives. The issue is just that compression requirement, which I'd prefer to live without if possible: I want systems with basically no moving parts if I can get them, hence my preference for what amounts to pressure swing absorption even if it costs extra heat. I've seen general literature say that PSA is more expensive than membrane separation though, not sure why or how, it may be that even with a rotating compressor membranes just make more sense.

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