Space Towers and Skyhooks

kbd512 · 2018-10-02 14:35:51

Josh,

I'm looking forward to seeing what you've come up with. I tend to think that megastructures in space are a little beyond our current capabilities, but I could always be wrong. I hope BFR will start to change that, but it needs to fly first.

tahanson43206 · 2018-10-12 12:06:43

For Josh: #1 ...
Your vision of an inflatable tower inspired me to look around a bit to see what might already exist. I found a commercially available Ham Radio field antenna tower that inflates to a height of 30 feet. It is held in place with a steady flow of air from a small gas engine powered air pump.

From past camping trips, I remembered that there are collapsible cups, so I ordered a couple to see how they are made. The cups arrived yesterday. One is made of metal and the other plastic. Both achieve water tight seals through (what I assume is) cohesion between the (nearly perfectly) smooth surfaces of the ring walls of the cups. However I note that the commercially supplied cups could not be inflated because the wall seal does not occur until the sections have been physically brought into firm contact.

In reviewing this before posting, I noted that it is not clear that the intention is that the hooks shown in the diagram are intended to push against the wall adjacent to them, to create a seal at inflation time. The vertical pressure of the inflated tower should provide a seal as the lips come into firm contact with each other.

In thinking about how the collapsible cup idea might be adapted for an inflatable tower with metal walls, I offer this little doodle for consideration.
Hopefully Dropbox's link below is available to anyone who might wish to open it.

(th)

https://www.dropbox.com/s/40ysvk22xr9tm … l.pdf?dl=0

SpaceNut · 2018-10-12 17:50:37

The cone up approach would be folded in on its self for each section of flexing fabric, with the limiting diameter of the ground section being the largest and would be related to the wall thickness of the materials used. The mass of the material would change with diameter as it rises and so would the air pressure.

only upside down

JoshNH4H · 2018-10-16 17:40:06

tahanson43206 wrote:

For Josh: #1 ...
Your vision of an inflatable tower inspired me to look around a bit to see what might already exist. I found a commercially available Ham Radio field antenna tower that inflates to a height of 30 feet. It is held in place with a steady flow of air from a small gas engine powered air pump.
From past camping trips, I remembered that there are collapsible cups, so I ordered a couple to see how they are made. The cups arrived yesterday. One is made of metal and the other plastic. Both achieve water tight seals through (what I assume is) cohesion between the (nearly perfectly) smooth surfaces of the ring walls of the cups. However I note that the commercially supplied cups could not be inflated because the wall seal does not occur until the sections have been physically brought into firm contact.
In reviewing this before posting, I noted that it is not clear that the intention is that the hooks shown in the diagram are intended to push against the wall adjacent to them, to create a seal at inflation time. The vertical pressure of the inflated tower should provide a seal as the lips come into firm contact with each other.
In thinking about how the collapsible cup idea might be adapted for an inflatable tower with metal walls, I offer this little doodle for consideration.
Hopefully Dropbox's link below is available to anyone who might wish to open it.
(th)
https://www.dropbox.com/s/40ysvk22xr9tm … l.pdf?dl=0

Hey Tahanson,

This seems super interesting and just the sort of thing we might look to when the time comes to build the actual tower. Because we'd be operating at a much larger scale we might choose to go for some sort of winch/hook assembly that operates on each level with a temporary seal over the top of the cup while lifting

tahanson43206 · 2018-10-19 09:28:19

Thanks to Josh in #29 for taking a look at the idea of using metal walls for an inflatable tower.
Thanks to SpaceNut in #28 for finding that neat image of a collapsible cup

Updated 2019/07/22

SearchTerm:blender

https://www.dropbox.com/s/fjrc0yb3mr29u … blend?dl=0

The link above points to a Blender drawing file which may be of interest to someone in the forum.
Blender is a free software package designed to make animated movies, but it works just fine to create 3D printer models.
The file at the link above shows a set of shapes that I am intending to use to create an S "ess" shaped wall section for a metal inflatable lift

While a tower such as Josh originally described is something for the future, it is perfectly reasonable to design a pneumatic lift for use in today's world, let alone Mars. What I have in mind is a "collapsible" "cup" able to support a worker doing maintenance at home or in an industrial setting. The 3D printer design I am considering would be scalable from what can be printed on a consumer 3D printer, to a full sized lift able to carry 200 pounds up 20 feet.

Unlike the Ham antenna fabric design referenced earlier, I am hoping that a metal design would have very little loss and that the structure could be maintained for a reasonable period without a constant flow of volumes of gas.

An advantage which might be realized would be the ability to lift a worker smoothly and rapidly (and safely) to a work site, and then to lower the worker smoothly, safely and rapidly back to the ground.

For Mars, it seems (to me) reasonable to suppose that the design could be used for access to the elevated port of a landing craft, in order to lower mass to the ground or to carry it up to the port.

The proof of concept would be a working 3D Printed plastic model.

For anyone who may be unfamiliar with 3D printing design processes, I think it is fair to say that a person with computer programming experience and some mechanical shaping experience would be able to create useful designs after a few weeks of study and experiment.

There are a number of free 3D design packages, and the only reason I recommend Blender is that I went through the learning process and have no reason to change to one of the other packages. However, friends tell me that other packages may be easier to learn and to use.

I can offer a Blender output as an "stl" file, which can then be imported into another package if anyone wants to go that route.

It is not necessary to own a 3D Printer to evaluate designs. Free software packages such as "Cura" allow the designer to examine an "stl" file away from the design software, and to make changes, such as changes in scale.

Finally, again with the view that owning a 3D printer is not necessary to gain some experience, there are 3D Printer service companies which will accept upload of an "stl" file, and which will print the item for you for a fee. I have gone this way and have been impressed by the quality of the product delivered via UPS.

Edit 2018/11/15: The local maker community holds a 3D Printer meeting every 2nd Wednesday. Last night I ran the pneumatic tower idea past members, and came away with several suggestions for designing a Blender configuration to feed into a 3D Printer.

I had originally imagined it might be possible to design the configuration in such a way that the system could be fabricated in a single object with multiple components. Due to the requirement for an air/gas tight seal, I no longer think that is the best way to go.

At this point, I am imagining three print specifications:

1) The platform, to be oriented for fabrication with the platform at the bottom, and the ring wall projecting up from the base.

2) A set of rings, consisting of rings 2, 4 and so on. The rings would not be touching, but the 3D printer can fabricate such a structure in a single print.

3) The second set of rings, consisting of 3, 5 and so on. As above, the rings would not be touching.

Assembly of the system would occur after the prints are completed.

The platform would be set top down, as it was printed. The rings from the even and odd sets would be set around the platform.

With appropriate design specification, the rings should form a gas tight seal with their adjacent rings.

Following assembly, the package would be inverted, so that the platform is now on top.

Testing would consist of:

1) Secure the outermost ring to a base plate, to insure a gas tight seal there
2) Introduce gas below the platform

The expected result is that the platform would rise as gas pressure increases, pulling adjacent rings up as the lips engage with each other.

If the assembly rises as intended, and if the gas seals work as planned, then additional gas pressure can be introduced to allow the platform to carry load.

After a load has been added to the platform, gas can be released from the expanded tower, to facilitate a gradual lowering of the platform, until all gas has been removed, and the platform and the load will have reached the rest state.

Edit: As of 2019/07/21, a complete set of models to make a scale model of the proposed Pneumatic Lift Tower are posted on Shapeways.com

To see the models (and two precursors) visit www.shapeways.com/shops/tahanson43206

Because someone may enter the search term Blender, I've decided to update this post with a few details of the steps performed to make the models.

Blender is a complex package, and I have only learned a tiny part of its capability. The Shapeways exhibit includes a model created by Xen, who is a veteran professional Blender designer. Xen's model uses "Screw" and "Bevel" modifiers. I have not learned those, but I did succeed by using the Spin tool, which I learned about from YouTube video.

I'll save this update and return later to complete my notes.

Edit at 19:45...

2019/07/17

YouTube video on Spin tool for blender

https://www.youtube.com/watch?v=wa6LAidbmHw

Update 2019/07/18

The “secret” for the Pneumatic tube project is to set steps at 64+

Update 2019/07/22 … set steps as needed to close gaps. setting depends on radius.

Set spin at 360 (to complete cylinder)

Set screw angle at 0 (applies to Screw modifier. Not sure about Spin tool)

The result is a cylinder with the shape of the outline.

***
The outline of the cylinder wall was created using a thin cube:

Create cube in empty space >> F6 >> set Y to desired thickness (eg, .05)

Then use boolean logic to extract material from slab leaving desired outline of wall.

Note: Use difference option, and use BigCube as the object to apply in Boolean operation.

Note: Add BigCube to the Slab, not the reverse.

***
I used Cura to verify the stl saved from Blender looked reasonable.

I thin used Sli3er to scale the model from 100 (Blender) to 4100 (for Shapeways)

Note that Sli3er also corrects errors which may exist in the stl coming from Blender.

Finally, extract the scaled model from Sli3er to stl and upload the stl to Shapeways.

(th)

Last edited by tahanson43206 (2019-07-22 17:52:16)

SpaceNut · 2018-10-19 18:18:08

This is a topic that would work very well on the moon or mars as the weight of the atmospheres that would push down on the materials would make the ones we have now a possible for such a tower.

Belter · 2018-10-20 11:09:00

I don't think we want to be taking that much material from the planet to launch into space. Even IF you could get a space hook to work it would take massive numbers of launches to do it and would take massive amount of energy to keep it in orbit. It would also be a gigantic menace that could kill millions of people if it fell. Better to just launch the stuff. A rail gun remains the most possible thing we could do to launch materials from Earth and probably the least expensive. Maybe someday we can figure out how to make a "gravity shield" that interferes with gravity, but it would have to use some sort of energy field to bend gravity or interfere with it somehow, and then turn it off when you hit a high enough orbit for 1000mph to work. But that might be absolutely impossible, along with warp drive, wormholes, teleportation and other nice thing we are shown in sci-fi as plot devices and problem solvers.

I think the reality is, we are going to get 99% of our materials from space at easy, low G locations at some point, no need to launch stuff from Earth and deplete our resources. Once robots take off and can mine and produce materials 24/7, as well as replicate things, sky hooks and space elevators will go back to being quaint ideas from old fiction stories.

tahanson43206 · 2019-02-18 07:48:18

JoshNH4H wrote:

OK, Hypersonic Rotating Skyhooks, let's go:
This is not an original idea from me, but I think it's a very interesting one. The idea is similar to a space elevator: An orbiting tensile structure makes it easier for a payload to get into orbit. The important difference between the space elevator and the skyhook is that the skyhook is orbiting while it rotates, in such a way as the bottom part of the tether has a slower speed than it were if it were simply orbiting naturally.

For JoshNH4H, RobertDyck and others who participated in this topic, and related topics featuring the word "tether"

I scanned for "tether" and while I did not look at every message, I looked at a lot of them, so I may have missed the idea of using a tether to deliver payloads gently to the surface of Mars.

That said, I can see that calculations for Earth oriented tether systems have been worked out in some detail, so I'm hoping what I will propose below will be worth investment of some time to confirm or falsify:

Phobos is a potential resource for gentle landing of payloads on Mars. The moon has an orbital speed (as given by Wikipedia) of 2.138 km/s, which converts to 4474 miles per hours. That is hypersonic on both Earth and Mars, but I am hoping that it is NOT a speed that is out of the question for Mars, since the atmosphere is so much thinner.

Again according to Wikipedia, the average elevation of Phobos above Mars is 6,000 km (3,700 miles).

My proposal then, is to dock at Phobos, attach a payload to a tether, deploy the tether behind Phobos until it is fully extended, and then gently thrust the payload package toward Mars. My expectation (and hope) is that the payload package would engage with the atmosphere and pull the package gently down toward the surface. The payload would be released at some optimum point, and the tether would return to orbit through some mechanism.

In the first instance, it can be imagined that the payload would fly to its destination, perhaps using retrorockets for landing.

However, in the more interesting scenario, similar to the rotating tether concept described by JoshN4NH in an earlier post, the tip of the tether could be "flown" in such a way as to accelerate ahead of the track of Phobos on the ground, and then decelerate so that the package arrives at a velocity of zero with respect to the surface of Mars. The payload would detach from the flight component, and the tether would return to orbit.

I concede that materials may not yet exist capable of performing the flight maneuvers described, at an extension of 6000 kilometers, but I'd be most interested if someone can show how close existing materials might come to achieving the described performance.

Braking to match orbit with Phobos is not the subject of this particular post, but it would certainly become an operational issue if the landing method is seriously considered.

(th)

Last edited by tahanson43206 (2019-02-18 07:52:37)

SpaceNut · 2019-02-18 10:50:42

Lucky for use Phobos is the inner moon circing mars for this to work.

Sort of the SkyCrane delivery system which did work on mars but the moon is moving, atmospheric air drag on the payload and cable which means min altitude is the highest mountain in the orbital path the moon takes around mars.

A forces working on the cable plus payload is air drag, mass of cable mass versus length in the atmosphere will have a force which increase that mass with it being amplified by orbital speed of Phobos making the cable slant relative to the surface of mars at an angle of which if cable is not going to be straight as its flexible.

Phobos, is only 14 miles across (22 kilometers), made up of material that resembles Type I or II carbonaceous chondrites, the substance that makes up asteroids. Phobos is slowly spiraling inward at a rate of 6 feet (1.8 meters) every century, so it will be sensitive to air drag forces on the cable.

1. Phobos orbits 6,000 km (3,700 mi) from the Martian surface which means the cable length needs to be twice that on the spool.
2. Phobos orbits Mars much faster than Mars rotates, and completes an orbit in just 7 hours and 39 minutes or Average orbital speed
2.138 km/s
3. phobos window on landing time rise in the west, move across the sky in 4 hours and 15 minutes or less, and set in the east, twice each Martian day.
4. Phobos Mass 1.0659×1016 kg (1.78477 nEarths) means all forces of air drag must be a few percentage points of it or we will be altering it orbital path.
5. Mars atmosphere has a scale height of 11.1 kilometres with at the tallest mountain pressure being 30 pascals (0.0044 psi; 0.30 mbar) on Olympus Mons's peak Mars atmospheric density equations
6. The volcano has a height of nearly 25 km (13.6 mi or 72,000 ft) as measured by the Mars Orbiter Laser Altimeter (MOLA). which means if we are not timing the drop within the orbital window for the continued drop works out to that being the altitude of retro propulsion point for the payload.
7. Air drag is a mass, surface area and speed equation https://www.grc.nasa.gov/www/k-12/rocket/termvr.html http://www.braeunig.us/space/atmmodel.htm
8. heating as a function of surface to altitude air drag on cable

tahanson43206 · 2019-02-18 13:10:18

For SpaceNut:

First, thanks for your detailed analysis of the proposal, and for the additional information you provided, for anyone who might care to develop the proposal further.

I was taken aback (I'll admit) by your estimate that the cable would have to be twice the distance from Phobos to the surface. My guess is that you are assuming the cable would be so influenced by drag that it would stretch out for a considerable distance to the lee of the moving moon.

I had assumed (admittedly without taking atmospheric drag into account) that the mass of the payload and delivery package would be so great that Mars would pull the tether taut, and that airfoils on the delivery head would be able to maneuver in the atmosphere. In particular, the delivery head would be able to maneuver around mountains or any other obstruction that might impede progress toward the desired destination.

Regarding the deteriorating orbit of Phobos ... I agree this is an issue, and propose that it can be addressed if the moon becomes an economic asset.

It would be necessary (assuming the moon can pay for itself) to generate continuous thrust using solar energy as the source, to counteract both the gravitational drag of Mars itself, and the atmospheric drag of payload tether activity.

Not mentioned in the original post is the (potential) option to pull payloads (such as pods with people) from the surface, or at a minimum, to attach a vehicle maneuvering up from the surface to catch a ride on the tether.

(th)

SpaceNut wrote:

A forces working on the cable plus payload is air drag, mass of cable mass versus length in the atmosphere will have a force which increase that mass with it being amplified by orbital speed of Phobos making the cable slant relative to the surface of mars at an angle of which if cable is not going to be straight as its flexible.
Phobos, is only 14 miles across (22 kilometers), made up of material that resembles Type I or II carbonaceous chondrites, the substance that makes up asteroids. Phobos is slowly spiraling inward at a rate of 6 feet (1.8 meters) every century, so it will be sensitive to air drag forces on the cable.
1. Phobos orbits 6,000 km (3,700 mi) from the Martian surface which means the cable length needs to be twice that on the spool.

Void · 2019-02-18 13:32:24

tahanson43206 and SpaceNut. I will not post against any of the previous. I do feel I can suggest something different.

tahanson43206 has effectively described the momentum of Phobos as a possible resource. Also that person has a desire to get payloads down to the surface of Mars.

I like shorter tethers. Still they must be long enough for the task they might do.

Let me suggest that we might withdraw momentum from Phobos, a loan, and hope to bring Martian atmosphere up to Phobos with a skyhook tether arrangement.

https://en.wikipedia.org/wiki/Skyhook_%28structure%29

In this case I am preferring a non-rotating skyhook/tether system, as it may deliver what is desired, and be simpler than a spinning one.

My intentions are to mine the atmosphere of Mars.

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

And while tethers can be used as propulsion, or to generate electricity, they might also draw molecules up to the top end of them. And that process will draw the tether to a lower orbit. However if you have the momentum of Phobos to draw a loan from, then it could be OK, to serve human purposes.

And if we were to be involved with Phobos, we would be wise to see what we could get insitu from it. One thing I want is habitats with synthetic gravity inside it' presumed rubble.

So, now obviously the bottom end of the tether does not have to go to the Martian surface, just suck atmosphere up electrically like a straw to Phobos. And of course the intentions are to provide service mass for human and machine operation in the Martian orbit. That then will translate to machines and their propulsion mass to travel from the orbit of Mars to the surface and back again. Also perhaps propulsion mass for interplanetary craft.

So momentum of Phobos converted into spacecraft propulsion methods.

One problem to solve is how you extract the molecules collected and convert their phase out of plasma and ions, into something that a rocket can use.

Done.

Last edited by Void (2019-02-18 13:47:04)

tahanson43206 · 2019-02-18 14:07:23

For Void:

Thank you for your helpful contribution to this discussion.

Your suggestion seems (to me at least) to help to answer the question first posed by SpaceNut earlier. Delivery of payloads to the surface of Mars, or retrieval of payloads to be lifted to Phobos, will indeed take out multiple loans against the momentum of Phobos. And those loans would be on top of the incessant drain of momentum by Mars itself.

Movement of payloads would seem likely to occupy the tether for only a small part of the flight time of Phobos. The tether could therefore be deployed for other purposes, such as the one you have proposed.

I will offer this as a question: Could your suggestion contribute to a resolution of the problem of how to pay back the loan?

Energy is supplied to the surface of Phobos while it is not in the shadow of Mars, so the atmosphere you have proposed to retrieve could be collected and processed to yield useful outputs. For one thing, Oxygen and Nitrogen and Argon would all be highly prized for use by visiting spacecraft, or for any habitats that might be constructed on Phobos itself. The Carbon Dioxide might have use as is, but it seems to me a part of that fraction could be split to facilitate propulsion of Phobos to repay the loans of momentum, using solar energy to even the accounts.

Phobos could (presumably) earn its keep as an economic engine, and not just be allowed to deteriorate in orbit as is now the case.

(th)

Void wrote:

tahanson43206 and SpaceNut. I will not post against any of the previous. I do feel I can suggest something different.
My intentions are to mine the atmosphere of Mars.
Done.

Void · 2019-02-18 14:31:15

Well, lets hope we can cheat our way through this. Cheating fate is technically something to admire in my opinion. The lion is about to try to eat you, as it might, but you are too tricky for that. Is that a bad way to cheat reality? I don't think so. We combat cheating in schools and for taxes, as it leads to improper learning/rewards, and load sharing.

But in the end, I do believe our ancestors managed to get us here by being fantastic cheats of the nasty game they were put into.

So, we use everything except the squeal if we can. Well I have some sympathy for pigs. Don't eat that very often. It is not religious, I just think they are too smart and sensitive to be food. Plus, the closer a food is to you genetically the worse the health problems, (Ignoring poison).

So, the reason Phobos will break apart some day, is rubble piles are not very strong. So, take the momentum, and convert the materials into strong structure that can survive at lower orbits. Cheat and win. The universe seems to like it actually A+.

Yes, I intend to stiff the bank, slap their face, and take their cigar. There are no rules you should not seek a fix for as far as the cruelty of reality goes.

Done.

Last edited by Void (2019-02-18 14:37:31)

tahanson43206 · 2019-02-18 15:00:43

For Void:

It it is time for me to remind myself we are in the topic: Space Towers and Skyhooks

So with that reminder, I will follow up on your #38 about cheating fate, by asking if you have a concept in mind for how to strengthen Phobos so that it can safely perform the tasks we have proposed for it?

Also, I remind myself that we have been chatting freely here, for a few hours, but there are others in the forum who have not yet weighed in, and they may well have contributions that will support our initial direction, or correct it as might be needed.

An investor who would pour resources into making Phobos a platform for gentle delivery of payloads to Mars, and to retrieving payloads from Mars in a gentle way, will (it seems to me) expect to derive a return for that investment, and might (it is not inconceivable) lay claim to the entire moon as the price of that investment.

This observation is intended to provoke discussion. I will be disappointed if it does not.

(th)

Void · 2019-02-18 16:01:22

tahanson43206, I would gradually convert the materials of Phobos into space habitats, that by being smaller, and yet being presumed to be made of stronger materials than rocks and dirt, will endure tidal forces. And so a large part of the momentum of Phobos could be harvested to human purposes. If left to nature, then presumably Phobos will split into fragments to form a temporary ring, and that will then fall down to Mars. If we interfere, then the momentum of Phobos can serve humans, and we can make a ring of processed and so stronger materials.

I am not against the notion of a skyhook that reaches into the (Not really) troposphere of Mars, or even the surface. Practice makes perfect. Who can say what the children's, children's, children might do?

https://www.bing.com/videos/search?q=ch … ORM=VRDGAR

Who's gonna own Phobos? Maybe lots of people if it gets shredded into homes in orbit.

Good enough for now,

Done.

Last edited by Void (2019-02-18 16:23:26)

SpaceNut · 2019-02-18 18:02:03

One issue for the tether end in the atmospher and trying to go back up seems lie in it needs to have some sort of lift bouyancy device to keep the momentum of Phobos being reduced over time. So the question is do you leave a fueled device on the end with ability to activate from a remote area of is it manned.

I am thinking like the skycrane jetisoned platform and making it reuseable and for the purpose of course adjustment if we need it for the payload to get to the x on mars correctly.

Vaccumn pumps at the end of a hose that is connected to the cable would allow for atmospher gathering from where its densest to be processed on phobos for crew air and fuels for the tether unit.

Second part of the atmosphere is we can use to to help maintain phobos by use of rocket engines to reboost as we do the ISS.

Last item of focus is after launch from the surface to catch the skyhook device is how would we grab its end of which part of the fact that we would not be able to hover to allow for a hock to fall into the latch location of the ship?

tahanson43206 · 2019-02-18 19:32:24

For Void #40 .... Your vision of Phobos as a big rubble pile is challenging to deal with, if the goal is to render the body sturdy enough to accept the tugs and pushes that I am proposing for an economic engine.

For SpaceNut #41 ... you have a lot going on in this post, and earlier ones.

I'd like to offer a supplement for you to try to work into your set of ideas .... as I am thinking of the tail of the tether (where the payload is attached) I have in mind a kite, or better yet, a sail boat, which can tack in the flow of the atmosphere to maneuver down, up or to the side, in order to intercept an upcoming payload carrier like a refueling jet approaches a tanker. The tanker holds steady, while the boom operator makes fine adjustments. The jet maneuvers so that the socket for the boom is within range of the boom operator. At that point, a refueling jet tries to hold position. In the case of the Phobos tether system, the upcoming payload would lock onto the tether and the upcoming payload carrier would release and fall away.

An even better example might be a sail plane that is secured to a tow plane by a tether. The pilot of the sail plane can maneuver to some extent behind the tow plane, although my observation is that such maneuvers are kept to a minimum to avoid distracting the tow pilot. In the case of a tow from Phobos, distraction of the towing pilot is not likely to be an issue, and I would expect the tether flyer to have quite a bit of freedom of movement.

I like your suggestion of using chemical propulsion to add momentum to Phobos to replenish momentum "stolen/borrowed" by the tether. My idea had been to use ion engines running whenever sunlight is available to power them. The two methods of acceleration are compatible and complementary. Something the size of a moon (even a small one) will require a lot of engines to overcome Mars' drag on top of tether activity.

(th)

Void · 2019-02-18 21:04:28

Quote the "tahanson43206". (Oops! never intended an insult t....) Tired though nite.

For Void #40 .... Your vision of Phobos as a big rubble pile is challenging to deal with, if the goal is to render the body sturdy enough to accept the tugs and pushes that I am proposing for an economic engine.

Per Others/Spacenut, I wholeheartedly bless any thinking they might have on the topic and Space Towers and Skyhooks.

However, you left me with an opening.

Yes, I think what may be real is fabulous.
https://en.wikipedia.org/wiki/Phobos_(moon)
Quote:

Images and models indicate that Phobos may be a rubble pile held together by a thin crust, and that it is being torn apart by tidal interactions.[9] Phobos gets closer to Mars by about 2 meters every one hundred years, and it is predicted that within 30 to 50 million years it will either collide with the planet, or break up into a planetary ring.[6]

Good heavens! Where does the time go? We have 30 to 50 million years!

The reality I think I may see, is that many asteroids are rubble piles. And that can be good. The original parent body had liquid water, and so clays happened. Hydrated minerals. A possibility of water. Phobos resembles a carbonaceous body, and so it may have such as a parental contribution to its current nature.

A possible reality is that we exist as the winners of a lottery. We may live on one of the few habitable planets in this section of the galaxy, where collision has not utterly obliterated the possibility of living things.

While such a reality may, seem like a cruel parent, yet here we are for the moment. And it appears that a lot of our sibling objects may have been ejected from the inner solar system. That suggests hopes. Places far out. That's a good phrase! "Far Out Man!". A long time ago, I am.

Don't be distressed if your Phobose may have already been chewed for you.

And so, by the potential of magnetic fields we may hope to make phobos cling to itself while we would remake it. No need to cry. The human race may be able to capture more moons for Mars from remnant small objects. Try using ballistic capture.

It's looking like a fabulous reality now.

Done.

Last edited by Void (2019-02-18 22:15:26)

tahanson43206 · 2019-02-19 08:36:45

For Void:

I am intrigued by your hint that a magnetic field in or near Phobos could strengthen the rubble pile.

Can you (would you?) expand on that idea?

Void wrote:

And so, by the potential of magnetic fields we may hope to make phobos cling to itself while we would remake it.
Done.

For SpaceNut ...

The model of the proposed tether as comparable to a sail plane hauled along by a tow plane has additional benefits I did not think of yesterday.

For one, the strength of the tether is reduced from what I had originally imagined might be needed. Instead, the tether will be dealing with the drag of the payload vehicle in the atmosphere, and not directly with the pull of gravity on the payload vehicle. I haven't thought through the physics yet, but the principle would be the same as that used by an aircraft. I have never thought about this before, and am feeling my way. There are members of this forum who could provide corrective guidance as necessary.

Let us consider a helicopter transporting a payload (a jeep) suspended from a tether (a cable). In that case, the engine of the helicopter is working against gravity by accelerating matter downward, and the full weight of the jeep is borne by the cable.

In the case of a Phobos Transport Tether, I am anticipating that for much of the flight from orbit to payload dropoff, the payload vehicle would be in freefall, after a starting boost from orbit behind the moon. The load on the tether would consist of an increasing load of drag as the payload vehicle and the tether itself engages with the atmosphere.

However, I would expect that the bulk of the pull of gravity on the vehicle would be borne by wings, and NOT by the cable.

This would be comparable to the case of a sail plane, the greater part of whose mass would be sustained against gravity by the constant acceleration of atmospheric mass downward by the wings.

It seems reasonable to suppose that it would make economic sense to enable a human pilot to operate the payload vehicle, while at the same time anticipating that automation of that capability would be the norm.

***
The issue of boosting Phobos in orbit is one I am not prepared to attempt to deal with. There certainly appear to be members of this forum who could address that challenge, if it is of interest. The mass of the moon is known, the decrease of orbit is (apparently) well characterized, and the amount of solar energy impinging upon the moon should be knowable.

Void has suggested a mechanism for bringing useful mass from the atmosphere of Mars up to the moon, using the tether I had originally proposed for delivery and retrieval of payloads. A mechanism for collecting atmosphere would (could) be a large fabric sock (like a wind sock) that gathers up atmosphere until the head opening is closed, and the tether flies itself back up to orbit behind the Moon.

The mass collected in this manner could be processed at the moon, using solar energy, to most efficiently generate thrust.

SpaceNut has suggested chemical combustion as a thrust producing mechanism. I have suggested using ion engines, while recognizing that the incremental thrust provided by such an engine is small compared to a chemical engine. There may be another alternative not already considered, to generate useful thrust to sustain Phobos in its orbit.

(th)

tahanson43206 · 2019-02-19 08:52:55

For Void ...

Your reminder that Phobos is a rubble pile led me to consider how to secure the (proposed) transport tether to the moon.

It came to me that since the proposed tether is 6000 kilometers long (or more as suggested by SpaceNut), it would be a small investment of cable to simply wrap a loop of cable around the moon.

From: https://en.wikipedia.org/wiki/Moons_of_Mars

Both moons are tidally locked, always presenting the same face towards Mars

Since the moon is tidally locked, the loop of cable can be laid once, secured and subsequently used for multiple deployments of the tether without further adjustment needed to the position of the cable.

Noting that the surface of Phobos is reported to be a layer of fine powder, I expect that the loop of cable will work its way down from the surface until it encounters enough resistance to prevent further progress. At that point the cable should be (???) secure from accident, barring a direct strike by a meteor or similar celestial object.

In an earlier post, SpaceNut suggested using a spool with the tether. I am thinking along the lines of deploying the 6000 kilometers (or more if needed) in the lee of the moon's orbit, and leaving it in place. A second, spooled line could be used to pull payloads retrieved by the tether if that would be more secure than simply accelerating the retrieved payload to the moon along the extended tether. The strength of the retrieval line could be quite low.

***
Topic .... electricity generated by movement of a metal tether through the atmosphere of Mars

In anticipation of this possibility, I would suggest building the main tether in 1 kilometer increments, separated by insulators of sufficient strength to endure whatever compression may be generated by service. Note that I am NOT thinking of using insulators which are themselves part of the stress line. Instead, the cable ends would be looped through each other, separated by an insulator, and then secured back on the main cable line.

The joining mechanism is a point of failure, so a system capable of withstanding the anticipated stress of service will be needed.

(th)

Last edited by tahanson43206 (2019-02-19 09:22:48)

Void · 2019-02-19 11:31:51

Tether projects may be subject to damage from space debris, that is true. The longer the tether the more it is at risk.

Also I have read that Phobos has very high voltage around it caused by the solar wind. And I think that if a tether is not correctly built, it could get zapped with electrical current. I know that they can move up in orbit if provided electric power, and can generate electricity if they allow themselves to move down in orbit.

I actually don't feel I understand them well enough. It would be a very big project, something for later on, but worth learning about now I feel.

Done.

Last edited by Void (2019-02-19 11:37:43)

tahanson43206 · 2019-02-19 12:16:34

Void, thanks for the tip about electrical charge buildup on Phobos!

I found this, asking Google: does phobos have electrical charge

https://www.space.com/38530-solar-wind- … hobos.html

Regarding charge accumulation along a tether ... I asked Google: electrical charge on tether

and got back a large number of related citations, including records of experiments performed with the Space Shuttle.

My proposed defense (until advised otherwise) is to limit the length of a segment to one kilometer, and to separate the segments with insulating devices.

It the post above, I point out that the insulator should operate in compression mode, between loops of the inner and outer segments, to insure that the insulating material does not participate in the stretching that will be felt by the tether material.

One note I came away with, from the article cited above, is that people (and probably vehicles) should perform static discharge actions when approaching other persons or objects which might have a different charge.

(th)

tahanson43206 · 2019-02-19 19:02:33

For Void, #26:

Void wrote:

Tether projects may be subject to damage from space debris, that is true. The longer the tether the more it is at risk.
I actually don't feel I understand them well enough. It would be a very big project, something for later on, but worth learning about now I feel.
Done.

I found some steel cable able to hoist 7,000 pounds on Earth. I have no way of knowing if that strength is sufficient for managing the drag of Mars' atmosphere on a sail plane payload delivery and pickup vehicle. What it allows is a preliminary cost estimate.

Assuming 6000 kilometers plus some spare length to wrap around Phobos and for SpaceNut's slope, I came up with a price of $5.5 billion to put the components of the tether into Earth LEO. That price is for Falcon 9 in today's market, and it seems likely to decrease over time.

Is that a lot, or not? I have no idea, but I am pretty sure that the proposed payload delivery system would be a great deal safer and more reliable than using rockets to deliver people to Mars.

Elon Musk is talking about delivering as many as a million people to Mars. It seems to me that the cost of a tether payload delivery system for Phobos, spread over that many people compared to delivery by rocket, would be competitive.

(th)

SpaceNut · 2019-02-19 19:41:49

The elevator topics have tons of calculations with in them...

I looked a bit with regards to helicopters and it does not seem to be feasible due to how it must be connected to the end of the tether where the blades are.

A glider like unit requires wings that are about 4 times the earth area of surface but it seems possible as all we are doing is making a boom with the struture to support the cable to phobos and the down connection for grappling the returning ship. The wings are motorized for lift and for turning just like a normal plane with a tail rudder that does breaking by spliting just the same as the shuttle.

We can also do a heated balloon between the cabling with it wrapping around the balloon only using it for lift. Provide heat you get extra lift, cool it down and it sags.

One concern is once the payload is released is the cable snap back which will happen from any of the devices that we would place at its end to negate the drag mass products...