Balloon Landing System from Phobos to Mars

tahanson43206 · 2020-05-18 20:14:14

The image at the link below shows plastic chain, arranged with interlocking links.

This is how Kevlar thread might be interwoven if a material cannot be found to bear the full weight of the tether at the junctions between the links.

Manufacture would involve passing a reel of thread through the open loop of the first segment of chain.

Because metal can handle compression better than tension, it would seem reasonable to place metal guides between the coils of thread, to prevent the threads from interacting with each other directly.

The risk would be that the threads would sever each other if they had direct contact.

SearchTerm:LinksChainYellow
SearchTerm:ChainLinksYellow

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Last edited by tahanson43206 (2020-07-01 10:32:43)

tahanson43206 · 2020-05-19 06:33:56

The quote below comes from GW Johnson's topic on Docking with Phobos. GW Johnson confirmed that the 2% elongation of Kevlar under stress is "mostly elastic" which I interpret as an indication that property of the material can be enlisted to permit laser beam measurement of elongation during system operation, and thus to provide input to control programs able to adjust the load on the system in real time.

tahanson43206 wrote:

For GW Johnson re Post#55
Thank you for the work you put into the study you reported! And thank you for confirming the "mostly elastic" property of the 2% elongation for Kevlar.
This tells me it would be reasonable to anticipate measuring stress on the material in real time using optical instrumentation (ie, lasers) to accurately measure elongation. That information could/would be fed into the control programs for the descent system in the balloon tether topic.
Your work on finding traditional de-orbit approaches for Void's gas-filled bubbles seems (to me at least) quite encouraging. I hope that folks with more education and experience than I can offer will begin to think about the approach you have outlined.
A distinct advantage of the traditional approach you are developing, with refinements for the unique features of Mars, is that the infrastructure required is MUCH less massive. I am arriving at the understanding that the tether approach can be done, but it would require a Normandy Invasion investment to pull it off. Several projects were carried out to fulfill the Normany Invasion. I'm thinking now of the British mobile dock systems, which were built in sections in Britain, towed over the channel and assembled for deployment on the shore and extending out to deeper water for cargo transfer.
A tether appears to be feasible, and it would (apparently) offer gentle dropoff of cargo and personnel above the atmosphere, but the investment would be massive. Per Google >> www.compoundchem.com, and pubchem.ncbi.nim.nih.gov, the formula of Kevlar is C14 H14 N2 O4.
It would be (should be) possible to assemble the components by harvesting asteroids and comets and the occasional moon, without bringing everything from Earth.
In contrast, as I understand your approach after a first reading, investment would be limited to individual vehicles, and therefore the return on that investment could be directly calculated.
If there is someone in the registered forum able to support GW Johnson in exploring this way of delivering Void's bubbles of gas to the surface of Mars, now is a good time to pitch in. If there is someone in the forum audience who can assist in refining this set of ideas, now is a good time to register and help out.
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Last edited by tahanson43206 (2020-05-19 06:36:21)

tahanson43206 · 2020-05-19 07:08:37

Kevlar is under consideration as a material from which the load bearing components of a Phobos Tether might be constructed.

In particular, it was suggested by Hop in a blog post about a tether from Phobos (and other celestial objects). To find the blog post, look for a post by Terraformer which includes the term "Hop".

Today, I'm adding a link to a detailed article about Kevlar.

https://www.azom.com/article.aspx?ArticleID=1992

Polyaramid Polyparaphenylene Terephthalamide ( Kevlar / Twaron ) is an infusible, wholly aromatic polymer that can strictly be described as nylon T,T - but rarely is. Manufactured only as a fibre (by solution spinning), it has a very high thermal stability and temperature and flame resistance.
In contrast to its chemical isomer Nomex®, the tensile properties of Polyaramid Polyparaphenylene Terephthalamide ( Kevlar / Twaron ) are up to an order of magnitude greater than those of normal textile fibres, because of a high degree of molecular orientation resulting from its stiff linear molecules and their propensity for forming liquid crystals in the spinning solution.

The detail I would like to highlight in the quote above is the description of manufacture as a fiber. This is significant in the context of my (slowly) growing understanding of how a working tether might be constructed at Phobos, in real life, by real people, using real materials.

As shown in a recent post in this topic, it is possible to imagine creating chain links of Kevlar thread, by (robotically of course) spinning thread into loops of as many iterations as are needed to achieve the strength required for a particular link in a particular location in a chain comprising the tether.

It seems reasonable to me to imagine (pending correction by those more knowledgeable) that a bumper of soft metal such as Aluminum might be placed between the loops of the Kevlar chain, to prevent the Kevlar threads from coming into contact with each other. That same metal can be fitted with arms that reach out to comprise the attachment points for other components of a working tether. In particular, I am interested in hanging a metal plate that would serve as the target of magnetic flux used to slow the rate of descent of vehicles making the trip from Phobos to a drop off point above the atmosphere of Mars.

It remains to be determined what is the greatest altitude from which balloons covered with suitable fabric can be safely dropped, in order for them to navigate safely through the atmosphere to a customer site on the surface of Mars.

As a reminder, anyone with expertise in any field related to this topic is welcome to register with the forum and help to move the project/vision along.

I am grateful for guidance (and helpful suggestions) provided by already-registered members of the forum.

Edit#1: Aluminum would be under compression in the bumper role described above. It may not have sufficient strength to withstand the enormous pressure that can be expected at the topmost loops of the chain, so another bumper material may be required. However, Aluminum can be procured from the Earth Moon, so it can (and probably will) be used by Solar System builders in the years ahead.

Edit#2: If by chance a college student (or Post-Grad) with access to CFD (Computational Fluid Dynamics) software reads this post, I would greatly appreciate assistance with determining the optimum drop-off altitude for balloon delivery vehicles for Mars. In a parallel topic, GW Johnson is working on a traditional landing approach for balloon vehicles. GW Johnson appears to be optimistic that a traditional landing approach might ** just ** work for ** just ** the right sized ball shaped vehicles with ** just ** the right combination of mass and dimension, and ** just ** the right material to comprise the envelope.

If someone would have the resources to assist GW Johnson in his traditional approach, please register and let him know of your interest.

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Last edited by tahanson43206 (2020-05-19 07:18:08)

SpaceNut · 2020-05-19 07:44:33

The Kevlar chain links would need to be made differently as the link strength is dependent on size to get the ration of large to small at the payload delivery point. Chains also would be complicated for pay out and retrieval as the size shapes would not roll evenly..

The thoughts to add metal and passing thread through the links just adds to the complexity and mass as well as for the manufacturing plus delivery of the system to phobos.

I was thinking that the balloon would be a delivery system that is one way system from phobos to mars and that for the balloon to survive entry heating we would have it in a canister until we are in the atmosphere at which time the container would split into two parts and the balloon would inflate. This would be like the canister that all probes landing on mars would make use of.

The pay out system would operate similar to the sky crane which is used to slow land a probe to the surface but instead to the upper parts of the atmosphere.

tahanson43206 · 2020-05-19 08:16:56

For SpaceNut re #54

Thank you for your continued interest in and support of this topic! I logged in just now to offer something you could help with.

But first, it might help ** you ** help ** me ** if I were more clear about how the vision is shaping up in my mind. That vision is under constant development as you and GW Johnson and others add inputs.

The chain would not move. It would be fixed in place. I was trying to figure out what Hop had in mind with his 11:1 taper idea. You provided a link to a web site that describes how Kevlar thread is made and used, and that gave me the understanding that a link at the top of the chain could be made of multiple loops of thread. In fact, the number of threads in that top loop would be determined by the mass suspended below and the force of gravity of Mars on each segment of the chain, accumulating to the tension on that top loop.

All loops/links of the chain below that point would contain fewer rounds of thread, as the tension they bear is less.

The complexity of making a chain is an interesting observation. Humans have been making chains for a while.

The mass of the tether needs to be great enough to support itself and its planned cargo/passenger traffic, plus a safety margin.

There's no way around that, and it's the price to be paid for the safety, convenience, reliability and ultimately cost effectiveness of the solution.

Insurance costs are going to be a significant consideration for companies offering transport to Mars. I am betting on the tether as the long term winner in ** that ** competition. It's comparable to offering a ride in an ocean liner from Britain to the US, as compared to a sail boat. You ** can ** make the trip in a sail boat, and many folks ** have **, but I'll bet most of them would have traded the safety, reliability and cost effectiveness of the liner if they'd had the choice.

I agree with your concept of the balloon delivery system as one way. That started with Void's Conjecture, which is archived earlier in the forum archive.

In another topic, GW Johnson has shown that a balloon, of the correct size and mass, CAN survive heating by the atmosphere using a carefully chosen grazing trajectory.

The tether concept would reduce the relative velocity of the vehicle at release with respect to Mars to (about) 600 meters per second, which is still a significant number.

It will be interesting (to me at least) so see some serious computation done to show which of these approaches is best for which situations.

My guess is that each will turn out to be best for certain use cases, but that is ahead of us.

Regarding the pay out system ... I've ** just ** arrived at an understanding of how magnetic hysteresis can be enlisted to help with the slowing of the vehicle as it descends the tether. Notes on that are available for review earlier in this topic.

So! I logged in just now in hopes of enlisting your assistance in finding a specialized calculator for use by engineers building structures with chain.

I found this site to get started:

https://itstillruns.com/calculate-chain … 37033.html

This site appears to be about bicycle chains. The authors of ** that ** site would surely be surprised by the idea of making a chain to suspend from Phobos, but with any luck, they might find the challenge interesting.

I'm looking for a calculator that can compute the tension on each link in the (imagined) chain from Phobos to the point Hop identified, just above the atmosphere of Mars.

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tahanson43206 · 2020-05-19 09:28:53

For SpaceNut and All ...

I am delighted to be able to post this reply from the NASA author of the paper/article on a proposal for an experiment package to be deployed on a tether from Phobos.

kevin.s.kempton@nasa.gov

I am not sure if you or your collaborators have rounded up the PHLOTE ConOps and have attached it. I also attached the Mars Ice Home ConOps which was another study I worked on that you may find interesting.
Phobos orbits Mars about every 7 hours so by using a tether and extending payloads toward Mars you could reduce the entry velocity without expending propellant which may help.
Aero-braking over several passes in an elliptical orbit can do the same thing probably more efficiently for most missions.
If one end of the tether is fixed to Phobos and you extend a mass past the L1 point where Mars gravitational force exceeds that of Phobos the system will become stable all the way until you encounter the Martian atmosphere.
Dr. Eugene Levin performed most of the stability analysis for the PHLOTE study.
Interestingly at the Pluto-Charon system, both bodies have synchronous rotation so it would be possible to have a tether connecting the two bodies directly all the way to each surface.
Balloons on Mars are challenging due to the very low atmospheric pressure on Mars. They have to be quite large in order to have significant lifting capacity.
Hydrogen could be obtained from electrolysis from the large quantities of water ice found on Mars. It would likely be easier to produce hydrogen on Mars rather than bringing it there.
Remember even liquid hydrogen requires very large volumes for an equivalent mass.
Titan would be a great place to try out balloons.
NASA is actively looking for more effective ways to land large payloads (40 MT) on Mars. This is a real challenge. A recent NIAC by Bob Moses looked interesting. Your team may want to look at proposing a Phase 1 NIAC study.
They are very competitive but working on a proposal will force the team to really pull their ideas together into a cohesive concept that could be published in a paper and it doesn’t cost anything to submit.
Thanks
Kevin

I would particularly like to call to the attention of the community the encouragement offered in this message, to develop a proposal for a study.

There is a lot of meat in this message from Mr. Kempton, and I certainly hope members of the forum will be inspired to take up individual points.

As a reminder, this forum is in need of a wide variety of expertise, so readers who are not yet registered and who are able and willing to assist are encouraged to do so.

Mr. Kempton's bio from his NASA page is here: http://newmars.com/forums/viewtopic.php … 21#p168221

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Last edited by tahanson43206 (2020-05-19 09:37:42)

tahanson43206 · 2020-05-19 10:23:12

This is for SpaceNut ...

NASA is actively looking for more effective ways to land large payloads (40 MT) on Mars. This is a real challenge. A recent NIAC by Bob Moses looked interesting. Your team may want to look at proposing a Phase 1 NIAC study.

The quote above is from Mr. Kempton's email in Post#56 ... I took a quick look at the reference to Bob Moses and realized quickly Dr. Moses is now and has been for some time a major contributor to research on Mars landing as well as other topics.

Edit#1: The quote above ** also ** sets a target for performance of any landing system: 40 Metric Tons.

That means (in the context of this topic) that the lowest rung of the (proposed) tether needs to be able to hold 40 Metric Tons plus it's own weight, plus a safety margin. I'll set the target capability at 60 Metric Tons for now. The capability of each link above the bottom one will need to include that 60 MT plus its own weight, all the way to the top of the stack, however long it may turn out to be.

Edit#2: The target of 40 MT for the payload package also means that the slowing mechanism needs to be strong enough to hold the package to a steady velocity of something on the order of a few hundred kilometers per hour, including the ability to stop the package entirely at any point if necessary for safety or scheduling reasons. An example of that would be taking the package down to the bottom of the tether, and then holding until the drop off point comes along.

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Last edited by tahanson43206 (2020-05-19 12:26:15)

tahanson43206 · 2020-05-19 14:37:37

Because this topic is generally about balloons, the answer below from StackExchange seems relevant.

I'm hoping someone in the current forum membership will be interested in verifying the ballpark estimate this author provided.

https://space.stackexchange.com/questio … h-this-way

Answer by Hobbes:
NASA is working on an inflatable heat shield. Not quite a blimp, but a heat shield that's inflatable to a size much larger than the probe it's attached to. The extra area helps decelerate the spacecraft. So inflatable structures can be made to withstand the heat of reentry.
Because Mars' atmospheric density is only 0.6% of Earth's, a blimp's lift will only be 0.6% of its lift on Earth.
The Hindenburg could carry 90 passengers on Earth. It weighed about 200 t. It'd be able to carry about 1 passenger on Mars. A blimp would be lighter (Hindenburg was a rigid airship), but you can see you'd need a ridiculously large structure to ensure a soft landing. To compare with current landing methods: one passenger is well within the load capacity of Curiosity's sky crane.
share improve this answer
answered Nov 18 '16 at 14:56
Hobbes

I am reminded of a book I found a while ago, about early experiments with lighter-than-air craft in the 1800's.

Here is a link to an article about that history:
https://www.space.com/16623-first-powered-airship.html

The reason these achievements came to mind is the StackExchange reply quoted above.

I created a mental image of an enterprising passenger steering a Hindenberg sized vehicle through the lower levels of the Martian atmosphere.

However, I suspect the person who created the reply quoted above was off by a considerable amount. The atmosphere of Mars at its most dense is (quoting from memory now) equivalent to about 38 kilometers on Earth. During the peak years of Zeppelin development, a few were flown as high as 20,000 feet (according to Wikipedia) but those were flights in which the engines were enlisted to gain altitude.

The 20.000 foot reference came from this source: https://www.quora.com/Whats-the-highest … in-can-fly

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Last edited by tahanson43206 (2020-05-19 14:39:24)

tahanson43206 · 2020-05-19 14:53:23

Here's another discussion from another forum I'd appreciate someone reviewing:

https://worldbuilding.stackexchange.com … s-zeppelin

This answer was (apparently) provided by a member with the screen name: FoxElemental

Requirement A) Useful Lift Capacity of 50 tons
Given the Atmosphere of Mars is 0.02 kg/m^3 , and the densities of hydrogen and helium being 0.0004kg/m3 and 0.0008kg/m3 respectively*, Helium should lift 25 kilos per Kg of gas(1250m3) on Mars, and Hydrogen 50 kilos per kg of gas(2500m3); making hydrogen the most practical choice (especially since helium is rare on Mars, whereas hydrogen can be extracted from water). This then gives us an airship of 2900000m3 of hydrogen for it's 50 ton load, and using the proportions of the Zeppelin NT, one finds it need 3125000 to carry it's own weight. This results in a diameter of 127.44 meters and length of 675 meters

I was curious to know what the Zeppelin NT might be:

The Zeppelin NT is a class of helium-filled airships being manufactured since the 1990s by the German company Zeppelin Luftschifftechnik GmbH in Friedrichshafen. The initial model is the NT07. Wikipedia

It’s not clear (to me at this point) if the author of the answer was taking the lower gravity of Mars into account. In any case, as a ballpark response, it would appear that a lift capability of 50 tons is feasible on Mars.
That’s a lot of Hydrogen, for sure!

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SpaceNut · 2020-05-19 15:51:01

Repost:

SpaceNut wrote:

Current mars landing from orbit to surface is a 15:1 ratio of hardware, fuel and devices to slow the item down to have a payload that we can use.
So 15 tons of ship on orbit with payload of 1 ton on the surface is where we are for the technology.
We know from aero dynamics that the larger the diameter the heatshield is the more payload we can land.
The same holds true for upping the fuel mass for the engine run time is the other solution to slow a vehicle down for the larger payload.
Bottom line more mass for mars means more mass to launch out of earths gravity well which incurs costs for the mission.

Strictly speaking of landing once well on the way to the surface the skycrane lowered the payload on a crane while slowing to a soft landing for the rover.

The payloads while we want a target value of 40 mt its still will need some fuel and engines to make that soft landing.
Current nasa approaches are with the adapt heatshield, which folds out like the umbrella, which gives the larger value for deceleration.

So lets picture an umbrella that the basket location on a regular balloon of which the payload is in between it and the balloon so as to make use of the large surface to shield the payload and balloon on the hot period of deorbit to the surface.

At some point past the heat we would inflate the balloon and jettison the tank that held the gas we chose for the balloon to reduce mass.

The timing of when to fire the engines and to remove the heat shield will depend on how slow the ship has been slowed on the way down to the surface with the payload we are trying for.

SpaceNut · 2020-05-19 16:03:33

https://physics.stackexchange.com/quest … rk-on-mars

https://www.airships.net/helium-hydrogen-airships/

The Relative Lifting Ability of Hydrogen and Helium
Although helium weighs twice as much hydrogen, because each gas is so much lighter than air helium provides about 93% of hydrogen’s lift at full purity. In practical operation it is impossible to achieve or maintain 100% purity of either gas, reducing helium’s lifting ability to about 88% of the lift of hydrogen.
The actual lifting ability of each gas varies with temperature, pressure, and humidity, and to take account of varying atmospheric conditions and gas impurities airship designers often conservatively estimated helium’s lift at 60 lbs per 1,000 cubic feet and hydrogen’s lift at 68 lbs per 1,000 cubic feet.

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

Balloons for the exploration of Mars

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

http://www.polyhedronlearning.com/see_apps_balloon.html
Mars City—Balloon Physics Challenge

https://www.lpi.usra.edu/meetings/lpsc2006/pdf/1719.pdf
LONG LIFE AND LIGHT GAS BALLOONS WITH ACTIVE ISOLATION ENVELOPE FOR MARTIAN APPLICATIONS

tahanson43206 · 2020-05-19 19:10:38

For SpaceNut re #61

Thanks for your impressive collection of citations!

I like the relative lifting ability summary, although it is (most surely) written for Earth at standard temperature and pressure.

Here is a snippet from the web site you found earlier, about Kevlar thread.

https://www.thethreadexchange.com/miva/ … d_Size_092

KEVLAR THREAD - SIZE 92 / TEX 80 / GOVT. F
Use to sew middleweight fabrics and leather and reinforcing lighter duty belts. Average thickness: 0.29 mm (11/1000 In). Nominal tensile strength: 30 Lbs. Needle sizes: 110/18 to 125/20.

30 pounds converts to 13.6078 kilograms

What I'm planning to do with this is to find out how many windings are needed to make the bottom-most link of the Phobos tether.

Also, by way of clarification of the NASA specification of a need to land 40 Metric tons on Mars .... that would be mass, of course, so the gravitational pull on that mass would be 38% at Mars, so the support capability of the bottom-most link can be reduced accordingly.

I had set it at 60 Metric Tons in Earth gravity, an arbitrary amount to insure a safety factor beyond 40 metric tons.

38% of 40 is 15.2, so the gravitational component of the strain on the chain would be 15.2 MT. However *** !!! *** the mass being slowed would be 40 MT.

I'll have to think about the implications of that. The force exerted by a mass of 40 tons being accelerated by Mars, and decelerated by the tether, will be communicated to the tether.

I'll have to think about that << grin >>

At rest, the strain would be 15.2 MT, but i suspect the slowing force would be exerted against the full 40 MT.

To be on the safe side, I might as well leave the expected demand on the bottom link as 60 MT.

60 metric tons divided by 13.6+ kilograms is 3947 and change.... I'll call it 3948. That means the bottom-most link would be made of 1/2 3948, or 1974 loops.

Now I have to decide on a length for the loop, which will allow estimate of the length of the thread, and from that the mass can be derived.

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Last edited by tahanson43206 (2020-05-19 19:17:32)

SpaceNut · 2020-05-19 19:57:49

The mass (payload) on the phobos moon or high in mars atmosphere is the same mass its the force which is acting on it that changes which should increase as it approached mars.

So the measure of the total length of the cord to high atmosphere must support the mass of the cord and payload for the ratio of 1 and as it gets closer to phobos should get larger.

https://arxiv.org/pdf/cond-mat/0601668
On the strength of the space elevator cable

https://www.sportsmith.com/strength-pro … tegory/674
parts and pieces you might make use of

This what you are looking for...
https://www.engineeringtoolbox.com/cabl … _1816.html
Uniformly Loaded Cables with Horizontal Loads

tahanson43206 · 2020-05-19 21:03:01

For SpaceNut re #63

More ** very ** interesting finds! Thanks!

The space elevator cable was particularly interesting because I saw a few familiar references immediately, so the paper was off to a reassuring start.

The engineering toolbox looks impressive and I'll spend some time with it. The immediate application appears to be for a suspension bridge, which would make sense because there are so many bridges of that type around the world. However, I'm looking forward to seeing what might be available in the toolbox along with that particular tool.

The Phobos Tether would be different from a bridge which has two ends.

I'm thinking of writing a simple calculator program for the special case of the Phobos Tether, if I can't find one already written.

Another detail for planning is how to join two ends of a Kevlar thread. After wrapping the link loops, the two loose ends need to be "welded" together. Ordinary plastic can be joined with glue, or melted together, but Kevlar properties may prevent that.

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Last edited by tahanson43206 (2020-05-19 21:06:13)

SpaceNut · 2020-05-19 21:14:15

Got a few more links and images of Kevlar weaving...and the number of types of kevlar
https://textilelearner.blogspot.com/201 … fiber.html

notice that threads are woven to make larger threads which are finally woven into the cable of larger sizes....

https://www.engineeringtoolbox.com/elev … _2079.html

https://www.engineeringtoolbox.com/cent … _1285.html

Terraformer · 2020-05-20 02:41:54

It’s not clear (to me at this point) if the author of the answer was taking the lower gravity of Mars into account.

Gravity doesn't change the required size of a balloon. You have to displace the same mass of air to lift the same mass, whatever the gravity. To lift 1 tonne on Mars (weighing ~4000 N), 1 tonne of Martian air (~4000 N) must be displaced. To lift 1 tonne on Earth (~10,000 N), 1 tonne (~10,000 N) of air has to be displaced.

The lower the gravity, the more heavier than air flight is favoured. On a "gas dwarf" with a thick nitrogen atmosphere and 1% surface gravity, very small wings/rotors would be required to keep a platform in the air. Conversely, on a very heavy body (say a superjovian), aerostats would be preferred.

tahanson43206 · 2020-05-20 07:44:40

For Terraformer re #66

First, thank you for another neat contribution to this topic!

Second, thank you for the insight about displacement of of one gas by another being independent of gravity.

Upon first reading (by me at least) that insight seems right.

On the other hand, ** this ** topic is managed (by me << grin >> ) as a scientific undertaking, so I invite other members to provide critique if any is called for.

In other words, critical thinking (which I most definitely encourage in ** this ** topic) only works if the brain involved has the supplies on hand to complete the task successfully. In my case, while my first impression is that your insight is valid, I'm soliciting reinforcement to be added to the topic.

The original insight, and any added reinforcement, will become a permanent part of the archive here in the NewMars forum.

SearchTerm:TerraformersLaw
SearchTerm:GasDisplacementIndependentOfGravity

Edit#1: For Terraformer ... would be willing to check to see if you are quoting Boyle's Law, by any chance? I've forgotten what Boyle's law covers.

I think it is still reasonable to give you credit for a component of Boyle's Law, if it turns out Boyle's Law covers that specific rule in addition to others.

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Last edited by tahanson43206 (2020-05-20 07:56:26)

tahanson43206 · 2020-05-20 07:50:01

For SpaceNut re #65

Thank you for that (to my eye) ** spectacular ** image of Kevlar winding!

I've been thinking about the design of a (simple) calculator program to compute the chain links for a tether made of Kevlar.

Overnight it came to me that Calliban's basalt thread might be worth considering as well, so I'm moving in that direction. The distinct advantage of basalt thread is that it appears to be readily available in flying repositories such as Apophis, which I've been hoping Calliban would wrap with the famous and historic "Calliban's Spider".

Now I'm expanding my thought a bit to include (a) wrapping Phobos to hold it together in light of tether stresses and (b) making the tether itself.

Here is information Google came up with for Basalt thread:
Google search: tensile strength of basalt thread
About 112,000 results (0.52 seconds)
Search Results
Featured snippet from the web
Properties
Property    Value
Tensile strength 2.8–3.1 GPa
Elastic modulus    85–87 GPa
Elongation at break 3.15%
Density    2.67 g/cm³
Basalt fiber - Wikipediaen.wikipedia.org › wiki › Basalt_fiber
Feedback
About Featured Snippets
Web results
Basalt Fiberswww.lbie.com › PDF
PDF
... carbon fiber and fiberglass, but basalt has better mechanical properties than ... Tensile strength after heat treatment (%) ... Electric insulation yarns and threads.

Here is what Google came up with for Kevlar Thread:

Google search: tensile strength of kevlar thread

about 3,620 MPa
When Kevlar is spun, the resulting fiber has a tensile strength of about 3,620 MPa, and a relative density of 1.44. The polymer owes its high strength to the many inter-chain bonds.
Kevlar - Wikipedia

Basalt thread seems to compare reasonably well in tensile strength. I'm not clear on other properties.

If someone would like to explore the comparison in more detail I'd appreciate the assistance. I'm planning to focus for the near term on writing a (simple) calculator to show how much Kevlar thread would be needed to make an arbitrary length of tether in an arbitrary gravity field.

The Kevlar thread can be priced (via the web site that SpaceNut found) so I'll be able to deliver a price for materials as well as a total length of thread.

I'm planning to work with the #92 thread shown at the web site, which has a tensile strength of 30 pounds/ 13 Kg.

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Last edited by tahanson43206 (2020-05-20 08:06:20)

tahanson43206 · 2020-05-20 11:44:05

This post is about Basalt thread .... I'm looking for a comparison of this thread with the #92 Kevlar thread which has a tensile strength of 13 kilograms.

The information posted below may provide a way to make a direct comparison, but at this point I don't see it.

From: http://basaltfm.com/eng/fiber/info.html

High durability
Strength-to-weight ratio of a basalt fiber exceeds strength of alloyed steel 2.5 times, strength of fiber glass – 1.5 times.
Tabl.2. Breaking strength-to-weight ratio for CBF various diameters
Continues Filaments’ diameter, µm
5.0 6.0 8.0 9.0 11.0
Breaking strength-to-weight ratio of elementary fibers,kg/mm²
215 210 208 214 212
Tabl.3. Breaking strength of CBF roving type RB-10
Diameter of elementary fibers, µm Tex Breaking strength, N
10 600 400
10 1200 700

40.788 kilograms = 400 Newtons (per Google)

I'm not clear on what how the results above compare to Kevlar thread.

10 micrometers is my understanding of the diameter term given in the table.

The web site gives a price per kilogram of $2.5 USD

I'm not sure what the term "roving type RB-10" means

For comparison, here is the data for Kevlar #92 thread, copied from an earlier post:

KEVLAR THREAD - SIZE 92 / TEX 80 / GOVT. F
Use to sew middleweight fabrics and leather and reinforcing lighter duty belts. Average thickness: 0.29 mm (11/1000 In). Nominal tensile strength: 30 Lbs. Needle sizes: 110/18 to 125/20.

The Kevlar quote seems to show reasonably clearly, that if a 13 kg weight is suspended with a 290 micrometer diameter thread, then the thread will hold.

Per Google, 30 pounds is 13.6078 kilograms.

Edit#1: I started work on a (simple) calculator program for the tether links problem. I can't believe how rusty I've become after having set programming aside for a few months.

(th)

Last edited by tahanson43206 (2020-05-20 20:50:33)

tahanson43206 · 2020-05-21 07:14:52

This is a status report on development of a (simple) calculator to predict the nature of a Kevlar (or Basalt) thread wrapping to deliver a tether for deployment at Phobos.

The GUI and structure are complete. The program executed 1000 steps simulating links in a chain construction sequence, and each link procedure executed 100 steps to exercise the corresponding progress bar.

It became clear overnight that this program will need to run at least twice and quite likely more than twice.

The first pass (as currently planned) will layout individual threads in a cross-section that is held to a square format. At the end of that first pass, we will know the width of the topmost link in the chain. At that point the width can be applied to the links below, which will shrink the length of the chain.

At the same time, Aluminum buffer guides can be added to the design. I'm currently thinking of making the Aluminum buffer thickness equal to the height of the thread at the intersection of two links. This will further shrink the chain.

Depending upon the amount of shrinkage, it may be necessary to extend the top of the chain, and the increased width of the thread winding may need to be propagated down the full chain.

I'd like to invite a forum member who might have a bit of free time to try to find the thickness of a Basalt thread which can hold 13 kilograms in a 1 G field.

My preliminary investigation (reported above) seems to imply a thread of only 10 micrometers diameter can hold a mass much greater than 13 kilograms. That seems so far out of line with the performance of Kevlar (as reported by a commercial site offering Kevlar thread for the industrial market) that I don't trust it.

Today, if plans hold, I'll add code to the (simple) calculator to wrap individual links of the chain.

The procedure should be straight forward. The bottom most link must support 60 metric tons (an arbitrary number based on NASA 40 MT request).

Since the properties of Kevlar thread are known (thanks to the commercial site found by SpaceNut) it will be possible to determine the number of wrappings that will be needed to support the target mass. From the count of windings we can know the thickness of the winding, and its mass.

This information will be fed into computation of the count of wrappings needed for the next link, which must support the link below.

I'm thinking of starting the length of the first loop at 11 meters (from center of the top of the link to the center of the bottom of the link).

Then, at least at this point in planning, I'm thinking of incrementing the length by one meter, so that each link will have a unique length, and thus a unique identity.

In a like manner, I'm thinking of starting the width at 1 meter (diameter of circular cross section of aluminum bumper guide) and then increasing that value as the width of the wrapping increases.

Edit#1: Adding the mass of the Aluminum bumper guides will increase the number of threads needed, and that will propagate changes throughout the structure. The iterations could continue for a while.

(th)

Last edited by tahanson43206 (2020-05-21 07:23:47)

tahanson43206 · 2020-05-21 18:33:14

Because tomorrow (Friday on Earth) I'll be tied up with volunteer duty, here is a status report.

The (simple) calculator has been enhanced to permit interruption of the loop. Because the loops can be expected to consume substantial blocks of time on an ordinary computer, I felt it would be a good idea to implement a Stop capability.

That was completed today. In addition, variables were added for characteristics of the thread which is to be wound to make links.

The starting values will be those provided by the commercial Kevlar sales site ... 290 micrometers diameter, and 16 ounces for 5000 yards, converted to kilograms per meter. That is a very small value, of course.

With a starting length for a link of 11 meters, a starting width of 1 meter, and a required capacity of 60 metric tons, it should be possible for the (simple) calculator to find the length of thread needed to hold that 60 MT, within a few thousand iterations.

Once the first link is completed, the rest of the chain should follow reasonably soon thereafter.

A forum reader with an ordinary calculator (or a pad and paper) should be able to estimate the length of thread needed, because (according to the Kevlar sales site) each thread can hold 13 kilograms with some allowance for additional strain.

60 MT divided by 13 Kg would give you the number of threads. The 11 meters is between the centers of the hubs, so a bit of thread is needed to round the circles at the top and bottom.

(th)

Last edited by tahanson43206 (2020-05-21 18:38:19)

tahanson43206 · 2020-05-22 05:06:23

A tentative plan for "wrapping" thread (for the purposes of calculating length needed) would be to maintain a square cross section.

The algorithm would proceed by laying the first thread, then a thread next to the first one, and then threads on top of the first two to make a square.

The next thread would be laid to the side, then one on top to even the stack, and then a duplicate of the entire set to make a square.

In "real life" the thread would be laid along the entire bottom layer first, but the purpose of the computation is to find out what the width of the bottom should be.

The algorithm to maintain a square cross section is interesting. It will require some nested loops, and some status variables.

(th)

tahanson43206 · 2020-05-22 13:29:34

Here's an engineering question ...

The term "pillow block" is in use for a housing for bearings, usually for a shaft which rotates against bearings which are encased by the "pillow block" structure.

I'm looking for a term for a body of material which would sit between the two interlocking links of a Kevlar chain.

The idea is to insure that the two sets of Kevlar threads never come into contact with each other, but are instead cushioned by the material chosen to accept the compression load that will exist between the links.

An image of plastic links is available in Post # 51

The material I am thinking of (as a first cut) is Aluminum, but it may not have the strength to be able to hold 60 metric tons while being squeezed by two meter wide ribbons of Kevlar thread.

What is the correct term used for a component of a system designed to perform this force distribution function?

Edit#1: Here's a word picture of what I have in mind:

1) Imagine a cylinder one meter in diameter and one meter in length
2) Split the cylinder precisely down the center in the length axis
3) You have two half cylinders 1 meter along the four sides of the cut
4) Place the flat side of one half cylinder against the flat side of the other, and rotate 90 degrees around the axis running through the diameter
5) This is the shape I'm visualizing to take the compression load of two 1 meter wide ribbons of Kevlar thread.

If there is a picture of such a shape, I'd appreciate someone adding a link in a post in this topic.

It is possible to make an image using a design program such as Blender, or Fusion 360, or any of the other free design tools.

What I'd ** really ** like to see is a shape similar to the one described, but with flanges like a spool or reel.

The problem I'm confronting (as I hold a cut wooden dowel up for inspection) is the challenge of designing flanges.

I can visualize a flange on one of the two halves, if that half is shortened, but I'm having difficulty imagining BOTH halves fitted with flanges.

Edit #2: Here is an image of a 1/2 cylinder, but this one is longer than the diameter.

[img]data:image/jpeg;[/img]

That didn't work !!!

Obviously I still don't have the knack for posting image links.

Trying again:

volume-slicing-b-find-volume-half-cylinder-length-12-inches-diameter-10-inches-taking-vert-q19029896

Edit #3: SpaceNut .... the link that worked in #50 ends in jpg.

the links that fail above in this post do NOT end with jpg.

Here comes an attempt with a link that ends in jpg ...

(th)

Last edited by tahanson43206 (2020-05-22 20:09:41)

SpaceNut · 2020-05-22 16:32:26

The posting of images still require the what is between the *http://* in order for it to show.

The pillow for bearings is like a plastic cradle for the metal ball to roll within.

tahanson43206 · 2020-05-22 20:13:18

For SpaceNut ... Please note that (apparently) it is necessary to insure that the link to an image ends in jpg

Post #73 has (finally) been updated successfully to show a half cylinder.

What I would ** like ** to show is an image of a half cylinder arranged as described in Post #73, to provide a compression cushion for the Kevlar ribbon under discussion in this topic.

Such an image may not exist. It is possible to create one using a drawing package.

(th)

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