Jump to content

inflatable orbital refueling


farmerben

Recommended Posts

 

We need refueling capabilities in LEO.  We are switching to methane, which is easy to transfer as a gas and compress into a liquid without cryogenics.  Nitrous oxide is similarly easy to handle.  Its also easy to decompose so the fuel station could sell nitrogen and oxygen separately, whatever the customer wants.  

The lightest cheapest material that can separate these gases is polyethylene.  The lightest cheapest way to run tubing is a fractal, just like human lungs and trees.  

A Rubix cube has 27 cubes, and 54/162 squares have color.  If all squares can hold 10 pounds, and the colored squares can hold 20 pounds, then the center cube may be pressurized to 30 pounds.  102 squares are completely redundant, and may be reduced or eliminated.  

The mass of the space shuttle big orange tank is the same as the mass of heavy duty garbage bags 30-50 times the volume.  Of course, gas is 1000 times less dense than liquid, and its safer to go 10-100 times lower pressure in vacuum.  But I don't think its impossible to get >10,000x improvement over garbage bags using the exact same material.  It involves larger thinner higher pressure balloons near the center, smaller tougher lower pressure ones going out.  And in it's own shadow we can liquefy the gases on one side.  Mylar is only slightly heavier and offers several advantages for the exterior.  

Check valves?  Polyethelene about the size of a shirt button.

Tubes?  None, just extra seams in the poly.

A giant lung in LEO would intercept more gas and debris than any other satellite.  So it consumes fuel to stay aloft, and burns up in the atmosphere if damaged or neglected.  Debris kinetic energy is mostly absorbed by gas, reducing shrapnel.  Polyethylene mostly tears rather than shatters, so its pretty unlikely to produce shreds of plastic at inclined orbits.  The exception to that would be a chemical explosion within the tanker.  This is a potential problem for any tanker.  A solution is to separate the fuel and oxidizer, either by having two lungs in vacuum, or 3-4 lungs one of which is inert nitrogen, which will eventually be worth a lot for fertilizer.  

Edited by farmerben
Link to comment
Share on other sites

The moon gets -173 C and it has thermal mass.  So a shade can make things colder.

-183 C is the boiling point of oxygen, just barely within reach.  But that is the freezing point of methane, which boils at -161 C.  So methane does not need insulation, only shade.  

Liquids are pretty tricky at low pressures though....  We only require liquids for transfer to other vehicles, and that requires a small compressor near the hardpoints.  

Nitrous oxide and ethane can exist as solid ice in LEO if they have enough shade.

Edited by farmerben
Link to comment
Share on other sites

What happens when a 1 gram bit of rock or old space-grade aluminum hits your polyethylene bag at LEO velocities?  Even if the impact is non-catastrophic, its still going to put 2 holes in the lung.  This would require a full-time EVA team on standby to prevent significant loss in event of a strike.  You're at least going to want a layer around it to act as a whipple shield to mitigate damage. But I don't really see the need for an at-scale LEO fuel dump until we get fuel from the moon or NEAs. At first, your mission schedule is going to be pretty sparse, so there's plenty of time between missions to take a few months/launches and just directly refuel whatever your vehicle is. At most, you keep enough propellant on-site to fuel up the ship once, and only start filling that from the ground when absolutely necessary - it spends most of its time empty rather than full.

What you really want to do is ship up and store water, and then electrolize it into LH2 and LOX using free solar power or an onboard nukie when you need it. Water is way more dense than either propellant, so you can fit way more into a payload fairing.  When you get it to the depot, just let it freeze into a block and be done with it. Sure, the electrical overhead is significant to melt and then convert it (water has a stupid high specific heat and enthalpy of fusion, but waste heat from the nukie and solar heating can help), but you're basically immune to propellant loss due to impact, and you don't have a constant need for cryocooling.  This makes sense for a lung - when your new propellant arrives in a fluid state, pump it around the outside of the current icecube and let the bag expand. Once it freezes, forget about it. Before the next shipment arrives, send an EVA team to patch all the holes.

Best part is, the crew (if the station is crewed, which is probably should be for maintenance purposes) gets free ox and drinking water from the propellant store. Centrifuge gravity would also help with managing the fluids, but that would be hard to manage when your mass is constantly changing.

Edit: methane is only in vogue right now because Mars has CO2 in spades and a Sabiter reactor is practical. Any other destinations and you're going to want water derivatives (i.e. hydrolox).

Edited by natsirt721
Link to comment
Share on other sites

Are there many satellites with the provisions to be refueled, the ability to manoeuvre enough to travel to the refueling point and the useful potential lifespan to warrant it? I’d dare say an extremely small number of current satellites would make use of a refueling station. 

BTW who is we, when you say we are switching to methane? Starship will use methane due to the specifics of its ultimate purpose, and will also have it’s own re-fueling tankers for LEO. Besides them who else is using methane? All the Lunar stuff I’ve seen will use either hypergolics, Xenon or Hydrogen/Oxygen. 

The idea of storing large amounts of cryogenic fuels in orbit for long periods isnt a good practice imo...

Edited by Guest
Link to comment
Share on other sites

9 hours ago, farmerben said:

to methane, which is easy to transfer as a gas

?

9 hours ago, farmerben said:

and compress into a liquid without cryogenics

Having a tank with strong walls. Like any tank for pressure-fed engines.
So, a small sat should contain tanks heavier than itself, docking port, docking optic or radio system, and a full set of engines for docking.
Better send a new sat.

9 hours ago, farmerben said:

Nitrous oxide is similarly easy to handle.  Its also easy to decompose so the fuel station could sell nitrogen and oxygen separately, whatever the customer wants.  

Why should why need as much N as O? What will they do with the excess of N?
And all oxygen-rich and easy-to-decompose compounds are well known propellant oxidizers: tetroxide, peroxides, perchlorates, permanganates.

9 hours ago, farmerben said:

The lightest cheapest way to run tubing is a fractal, just like human lungs and trees.  

Lungs weight ~1.3 kg. They hold up to 6 l of air, i.e. ~7 g.
Construction-to-fuel ratio is ~200. That's the price of any fractality. Wall surface grows much faster than volume.

9 hours ago, farmerben said:

A giant lung in LEO

With a giant eye and giant jaws. In the night sky this will be looking unforgettable.

Link to comment
Share on other sites

2 hours ago, Dale Christopher said:

Are there many satellites with the provisions to be refueled, the ability to manoeuvre enough to travel to the refueling point and the useful potential lifespan to warrant it? I’d dare say an extremely small number of current satellites would make use of a refueling station. 

BTW who is we, when you say we are switching to methane? Starship will use methane due to the specifics of its ultimate purpose, and will also have it’s own re-fueling tankers for LEO. Besides them who else is using methane? All the Lunar stuff I’ve seen will use either hypergolics, Xenon or Hydrogen/Oxygen. 

The idea of storing large amounts of cryogenic fuels in orbit for long periods isnt a good practice imo...

This type of station probably wouldn't be for satellite refueling. It would be for launcher fueling. For example you launch into a rendezvous orbit with minimal fuel left, dock, refuel and then continue to GEO, Lunar, or Mars orbit. This exponentially decreases the size of your rocket (or exponentially increases your payload capacity). If you did want satellite refueling, NASA has researched refueling satellites before and they did operate on the assumption that they wouldn't be provisioned for refueling which was proven to work on an ISS mission (Robotic Refueling Mission), though it wasn't a real satellite just a representative example. Chances are you wouldn't have the satellite come to you, but instead send out a tug with just as much fuel as you need to resupply it (see Space Infrastructure Servicing).

Methane will be used by Vulcan's first stage (ULA), New Glenn's first stage (Blue Origin), and of course Starship (SpaceX). However, you do have a point since only Starship's orbital stage is methane so only it could benefit directly from methane in orbit. Having said that generating hydrogen from methane is relatively easy (pretty much all commercial hydrogen is produced this way anyway). You would need to liquefy it, which is difficult, but if you have the lead time, power, and cooling systems entirely doable. ULA's ACES upper stage is planned to have refueling provisions which would be able to benefit from a hydrolox refueling station.

A fuel depot can afford the extra mass for active cooling, because they don't need to worry about their dry mass/wet mass ratio to the extent a spacecraft maximizing delta-v needs to.

The real problem a fuel depot needs to overcome is economic. They need to have enough clients to justify the large up front cost and ongoing overhead. This means either it needs to be cheap to launch and operate or you need a high volume. If we go to the moon and stay for a prolonged period (or even just have an active tourist industry) you probably have the volume to justify it, but until then there probably isn't enough GEO, Lunar, Mars orbit launch volume to make this economically viable (ignoring the case where it is heavily subsidized, which it probably could be).

Link to comment
Share on other sites

The bigger glass - the higher orbit.
The higher orbit - the less drag.
The less drag - the less fuel.

The bigger glass - the bigger sat.
The bigger sat - the more sense in its personal refueling.

So, probably huge armored sats in 1000 km orbit with periodically sent tankers, solve the logistics problem.

Enough huge sats with thick armor in 25 000 km orbit need even less fuel.

So, just make bigger rockets and make the LEO clean again..

Edited by kerbiloid
Link to comment
Share on other sites

@satnet

oh I didn’t even know Vulken and Glen’s first stages would be methane! That seems weird to me! 

The thing about having a fuel station reducing the size of the rocket needed to launch missions etc... it might at that but still necessitates multiple launches in the place of one. Someone is after all launching the fuel up there as well albeit separately. 

But like you said it depends on the market I guess, if there are a heap of launches heading out of LEO it might turn out to be a good idea. (Though I’m sceptical)

 

Link to comment
Share on other sites

Martian ships need a lot of fuel and water at once, in expendable package.
Lunar base need a lot of fuel and water at once, and the package can be expendable reusable by the lunar rednecks for needs.
Big orbital base needs a lot of fuel and water at once, you don't need split it into small portions.

So, just avoid small forms, and the bigger is the better.

Spoiler
5 minutes ago, Dale Christopher said:

Vulken and Glen’s first stages would be methane!

After KSP the mankind will never stay the same.

Everyone who tried ISRU in KSP will prefer low-level compounds.

So, we can presume that Musk and Bezos first try their projects in KSP.

 

Edited by kerbiloid
Link to comment
Share on other sites

5 minutes ago, kerbiloid said:

 

  Hide contents

we can presume that Musk and Bezos first try their projects in KSP.

 

Musk totally does. I’d bet money on it XD

Edited by Guest
Link to comment
Share on other sites

Methane is the fuel of choice for the next decade or two of Moon and Mars explorations.  What I've heard is that Elon will refuel starship twice in LEO before heading to Mars.  Zubrin wants to start using lunar ice to fuel Moon transport right away.  But, the other plans call for a gateway in lunar orbit or in LEO with at least one refueling in space for every trip from the Moon to Earth.  

It's easy to get water from our fuels by burning them.  It is easier to make H2 from methane than the other way around.  So in the interests of keeping the fuel station simple, we want to haul more complex molecules from earth which can break down exothermically into the other molecules we might want.  Nitrogen will be needed for habitation, fertilizer, and cold gas thrusters.  The ability to store and liquefy these materials in plastic bags, without any insulation or heat pump, makes up for the fact that they are heavier than alternatives like O2.   One day we might need to haul ammonia from the outer solar system to Mars and the Moon, but at first we will depend on Earth supplies.  

A conventional fuel tank requires high fuel density and insulation to get through the Earth's atmosphere.  Once outside the atmosphere, those constraints are gone.  

In LEO, debris is a leading concern.  The idea is not to shield bags of gas from debris.  The idea is to use bags of gas as shields for everything else.  A percentage of bags can be sacrificed or recycled.  The valves we need to isolate bags are lighter duty than the type found on pool toys.  

 

Once we build greenhouses and domes on the surface of other worlds we will need to insulate and protect them.  Nitrogen gas in clear tubes is a good way to go.  If water vapor gets in there and forms condensation or frost, then we know the primary dome has a leak.  Whereas if we are just monitoring the pressure in the primary dome, small leaks are hard to detect.  

Edited by farmerben
Link to comment
Share on other sites

Spoiler
3 hours ago, farmerben said:

Whereas if we are just monitoring the pressure in the primary dome, small leaks are hard to detect.  

A leak tracker.

Spoiler

PINNY-Buddha-Stick-Ceramic-Incense-Holde

 

Upd.
I'm afraid, dome mass/surface area of glass domes exclude any possibilityof the greenhouses under domes.

Edited by kerbiloid
Link to comment
Share on other sites

2 hours ago, kerbiloid said:

Upd.
I'm afraid, dome mass/surface area of glass domes exclude any possibilityof the greenhouses under domes.

Drone-Best1-resized.jpg

 

If this works on Earth, why not on other worlds?  Only tensile strength is necessary no compression or shear strength is required for this type of structure.

Polyethelene is weak compared to other materials, but it permits embedded fibers or surface coatings just fine.  Polyethelene films 6 mils (.006 inches) in thickness burst between 20-60 psi.  1 acre of 6 mil polyethylene film weighs 200 lbs on Earth.  

 

 

Even 1 mil will stop water vapor and carbon dioxide.  Putting a greenhouse inside a greenhouse raises temperature by about 10 C per layer, according to Elliot Coleman who grows in Maine during winter.  So we definitely could have inflatable greenhouses on Mars.  

Would you rather grow corn in underground tunnels, or would you rather use inflatable structures?  Something like this would represent enough food for 10 people per year.  Say 5 tons of food and 25 tons of low value material and 20-30 tons of gas protected by less than 1 ton of plastic

 

 

 

 

Link to comment
Share on other sites

53 minutes ago, farmerben said:

If this works on Earth, why not on other worlds?

Nice picture. One human requires ~1 hectare of plowland for comfortable life, and ~0.1 for poor one.
On Mars there is twice less sun and no soil.

53 minutes ago, farmerben said:

Would you rather grow corn in underground tunnels, or would you rather use inflatable structures? 

I would grow unicellular cultures to make food pastes.
In multistorey vaults powered with an energy source like a reactor.

Edited by kerbiloid
Link to comment
Share on other sites

3 minutes ago, kerbiloid said:

Nice picture. One human requires ~1 hectare of plowland for comfortable life, and ~0.1 for poor one.
On Mars there is twice less sun and no soil.

I would grow unicellular cultures to make food pastes.

Plowland will not be available for a long time.  ~0.1 hectares per person is about what Chinese farmers have used for the past 4000 years.  It is possible to increase plant yields about 10x with every trick in the book.   Rabbits and fish can recycle nearly all of the plant waste without competing with humans for carbohydrates.  So Martians should be able to eat meat several times a week.

 

Link to comment
Share on other sites

1 hour ago, farmerben said:

~0.1 hectares per person is about what Chinese farmers have used for the past 4000 years.

This inspires. Living like an ancient Chinese farmer is really a success.
Btw they also have soil and fishes on their plowland.

1 hour ago, farmerben said:

Rabbits and fish can recycle nearly all of the plant waste without competing with humans for carbohydrates. 

Then we can first try this in Sahara. Sun, sand, and much warmer.

1 hour ago, farmerben said:

So Martians should be able to eat meat several times a week.

Yes, they should.
https://en.wikipedia.org/wiki/Cultured_meat

 

Link to comment
Share on other sites

14 hours ago, kerbiloid said:

This inspires. Living like an ancient Chinese farmer is really a success.
Btw they also have soil and fishes on their plowland.

Then we can first try this in Sahara. Sun, sand, and much warmer.

Yes, they should.
https://en.wikipedia.org/wiki/Cultured_meat

 

An ancient Chinese unit is the "mu" = 0.165 acres, and a Japanese "tan" = 0.24 acres.  Each is reckoned to feed one person for a year.  A typical senior farmer with access to child labor usually managed more than 3 acres.  

Growing food in the Sahara is easy, just look at the Nile valley.

It is necessary to have CO2 emitting organisms to recycle plant materials, including bacteria and worms.  Theoretically, Mars could have any type of livestock.  I just think fish and rabbits are particularly good.  Rabbits can deposit their poop and food waste directly through wire mesh flooring into a fish tank.  The water is fertilized and balanced for direct application to hydroponics.  The organic sludge at the bottom of the tank, is easier to handle and superior to human poop.  The sludge can be mixed with inert sand and used immediately to grow plants.  Human poop must be heat sterilized and then recolonized by bacteria.  Initially human poop is a hot manure, like chickens, pigs, horses... nutrients come too much too fast, this requires them to be aged by bacteria before use on plants.  

If we had more startup capital than a Chinese peasant, there are several things we could do.

1. Grow 365 days per year.

2.  Provide daylight >20 hours per day in the early stages of plant growth.  In some cases reducing light promotes faster ripening.  

3.  Boost CO2 levels to 4x normal.  Provide optimal temperature and moisture at all times.  This provides about 25% boost over a "good season" on Earth.  

4.  Use shelves or hanging baskets to multiply surface area.

5. Gain 100% control of weeds, pests, predators, etc using airlocks and/or radiation.

6. Food irradiation technology allows indefinite storage.  Similar technology can be used to kill human pathogens in human poop, etc.  Cesium 137 under glass in a device that looks like the scanners at supermarkets can do this. 

7. Intense cultivation of crops like manioc and sweet potato produces about 10x more starch than grains.  The New Guinea highlands were more densely populated than Chinese valleys.   Tomatoes and melons probably give an equal yield, but they don't count for a huge amount of traditional diets because they spoil in a few days under traditional circumstances.  

8.  Martians should not be limited to a narrow staple diet.  I'm just saying, I think yields can be pushed way more than the traditional Chinese yield for certain things.  Spaghetti with manioc noodles and rabbit meat, or sweet potatoes and tilapia, could be available for 50-100 people per acre.

Link to comment
Share on other sites

37 minutes ago, farmerben said:

An ancient Chinese unit is the "mu" = 0.165 acres, and a Japanese "tan" = 0.24 acres.  Each is reckoned to feed one person for a year.  A typical senior farmer with access to child labor usually managed more than 3 acres.  

Yes, I mean quality of life, not the possibility to survive.
Except food itself, currently a human spends several times more food plants or grown instead of food to produce things.

37 minutes ago, farmerben said:

Growing food in the Sahara is easy, just look at the Nile valley.

I'm afraid, Nergal Valley of Mars is a little drier than the Nile Valley.
And almost all Mars is as dry as Sahara beyond this green zone.

37 minutes ago, farmerben said:

I just think fish and rabbits are particularly good. 

Maybe fish but unlikely rabbits. Their motto is "Live fast, die young". They mass born and mass die, so their population is highly unstable for a limited ecosystem. They need a lot of grass and a lot of expendable predators like foxes, so they are for a green planet.

Also don't forget that the smaller is a pet, the more it eats per kg of future meat. Because of surface/volume.
A pig is the best in sense of food/product + rate of growth + omnivorous. Up to 2.5 t of meat from 1 pig per year.

(Unless they name a pig "giant round-eared rabbit" for cultural reasons)

37 minutes ago, farmerben said:

Rabbits can deposit their poop and food waste directly through wire mesh flooring into a fish tank.  The water is fertilized

with dead plants and fishes.

No mammal manure should be used directly (except for strawberries), it should first rot together with straw in a compost pit.

37 minutes ago, farmerben said:

The organic sludge at the bottom of the tank, is easier to handle and superior to human poop. 

A mass genocide of plants and fishes.

37 minutes ago, farmerben said:

Human poop must be heat sterilized and then recolonized by bacteria. 

An overkill with same result. Plants aren't afraid of human deseases. Just put it into compost.

37 minutes ago, farmerben said:

Grow 365 days per year.

Warming it with a nuke reactor because there is -100°C outside.
And making the light same way if the farm is placed next to a polar cap (where there are both water ice and polar night).

37 minutes ago, farmerben said:

4.  Use shelves or hanging baskets to multiply surface area.

making a deep shadow behind the vertical shelved greenhouse.
When a 10 m high greenhouse makes next 30x20 m a shaded plowland-free zone when the sun is not above the head.

37 minutes ago, farmerben said:

7. Intense cultivation of crops like manioc and sweet potato produces about 10x more starch than grains. 

And depletes the soil, and feeds the insects, so a typical rotation sequence for the potato field is something like:
potato - crops - crops - corn or beans or sugar beet - crops - crops or beans - potato - ....

So, the potato is by no means a panacea, like any other plant.
Cereals are a nice estimation what you can get from the field. Any other plant can only appear between them.
See crop rotation.

Edited by kerbiloid
Link to comment
Share on other sites

The power demands of indoor agriculture are about 600W/m2.  This means that on the Martian equator at noon, lighting is almost perfect.  The rest of the time we can use as much as 2.4 MW / acre electrical.  It makes sense to have 90% of the total mass of the system be warm water.  

The TRIGA only works with liquid water as a moderator, it automatically shuts off before the water boils, and requires ice to be thawed to start.  3-5 MW thermal per acre of warm water is a good radiative balance with the outside.  

10 psi of atmosphere is fine for the working level.  It can be insulated by carbon dioxide at 5 psi or less.  Without electrical power a ten layer greenhouse might almost survive the Martian night without frost.  With power anything more than 3 layers will provide control.  Even at 1 psi a structure would have considerable lift on Mars.  It might need seams like a soccer ball of higher pressure tubes.  

1/2 MW per person of nuclear power seams reasonable for a settlement on Mars, not including their fuel and metal production.  

Link to comment
Share on other sites

On 6/22/2019 at 8:47 PM, natsirt721 said:

What happens when a 1 gram bit of rock or old space-grade aluminum hits your polyethylene bag at LEO velocities?  Even if the impact is non-catastrophic, its still going to put 2 holes in the lung. 

This happens to the ISS as well.  You only get one hole, as anything making the first hole is vaporized on impact.  The solution is to make a somewhat larger if thinner polyethylene bag around your gas tank, fill it with .01bar whatever (presumably He to reduce launch costs) and let it take any hits coming its way (so your 'real gas bag' gets hit with dispersed vapor), and patch as necessary (you'd think a patching robot would be possible, but I suspect that it would require astronaut visits a couple of times a year).

Link to comment
Share on other sites

A whipple shield is made of kevlar and nextel ceramic.  It has extremely high strength and insulation value.  Very thin fibers allow most of the space to be filled with vaccuum.  Incoming projectiles hit multiple threads of whipple shield, ionizing them.

Say a 1 gram rock ionizes 1 gram of whipple shield, before it's sufficiently dissipated for the hull.

On the other hand, we could ionize 1 microgram of plastic and 1 gram of gas.  The heat then rapidly disperses through several hundred kilograms of gas.  

A robot comes over and sprays polyurethane over the leak.  

Link to comment
Share on other sites

23 hours ago, wumpus said:

The solution is to make a somewhat larger if thinner polyethylene bag around your gas tank, fill it with .01bar whatever (presumably He to reduce launch costs) and let it take any hits coming its way (so your 'real gas bag' gets hit with dispersed vapor), and patch as necessary

 

22 hours ago, farmerben said:

On the other hand, we could ionize 1 microgram of plastic and 1 gram of gas.  The heat then rapidly disperses through several hundred kilograms of gas.  

A robot comes over and sprays polyurethane over the leak.  

The reason the whipple shield works is because each layer has enough mass per unit area to vaporise the impactor before it passes through. 1 gram/cm2 in spaced layers is sufficient, but a few milligrams of plastic is not going to cut it.  For the same reason, the gas will likely be as ineffective as the plastic for stopping impactors.

For smaller objects like dust or paint chips the plastic might be effective (if deployed in spaced layers), but anything else is going to go clean through.

You can make whipple shields out of pretty much anything because again, it's about mass per unit area and spacing that makes it effective.  For something sacrificial like a whipple shield, I would probably use something like aluminum thats cheap to replace. 

Edited by natsirt721
Link to comment
Share on other sites

29 minutes ago, natsirt721 said:

 

The reason the whipple shield works is because each layer has enough mass per unit area to vaporise the impactor before it passes through. 1 gram/cm2 in spaced layers is sufficient, but a few milligrams of plastic is not going to cut it.  For the same reason, the gas will likely be as ineffective as the plastic for stopping impactors.

 

So you want 10 kg of shielding for 1 m2 of surface.  Is that just for the pilot's chair?  Or for all the fuel tanks as well?

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...