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#1 2019-11-08 08:30:05

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 209

Manufacturing Solar Power Satellites within Near Earth Asteroids

I ran a few numbers for solar power satellites.

Northropgrumman manufacture lightweight space solar power systems.
https://www.northropgrumman.com/Capabil … tsheet.pdf

From their graph, an ultraflex system capable of delivering 700kW (presumably in full sun, at Earth orbit) would weigh some 7000kg.  That works out at 100W/kg.  Due to UV light, all panels have a decline rate in power output.  Thicker cover glass reduces decline rate, but also increases weight.  Since I do not know, I am going to model SPS lifetime as 20 years with no decline.  You get the same results if you assume a 40yr lifespan with a linear decline rate to zero after 40 years.

If we assume that the solar power producing elements of a SPS constitute roughly half its mass, and that attitude control, fuel and microwave antenna contribute the other 50%; power density in GEO would be about 50W/kg.  So, a 10,000MWe SPS would weigh some 200,000 tonnes.  It would take several thousand Falcon Heavy launches to deliver it to GEO.

Over a 20 year lifespan, each kg of satellite mass will yield 8766kWh of electricity.  Assuming microwaves are used to transmit power to a ground receiver rectenna; about 50% of the electricity will be lost either as losses in the atmosphere or in power electronics.  So each kg of satellite will deliver 4383kWh into the grid.

Using the Falcon Heavy, launch costs to GEO are about $3000/kg.  So ignoring all other costs, launch costs would be $0.68/kWh of electricity delivered to the grid.  So, Earth launch satellite solar power is not economically competitive and it is very unlikely that it ever will be.  Furthermore, it would be logistically difficult to maintain enough launch capacity to deliver it.

However, SPS is a far more workable option if its heavy components can be manufactured in space, using materials mined from the moon or asteroids.  A single 100m diameter stony NEO, would weigh some 1.4million tonnes.  That is enough material for perhaps 2x 10GWe SPS, each weighing 200,000t and the reaction mass required to deliver them to Earth orbit.  On a neighbouring thread, it was determined that such a body could be enclosed in a polymer net or bag, allowing pressurised tunnels to be excavated within it.  Furthermore, the body could be imparted with a spin, to allow modest lunar levels of gravity within the tunnels.  The restraining bag or net to allow for this would weigh about 100 tonnes for a 100m diameter body– about three orders of magnitude less than the weight of a single SPS.
http://newmars.com/forums/viewtopic.php?id=9110

Presumably, the optimum arrangement would be to ship mining equipment and manufacturing equipment to the NEO and assemble this equipment within the excavated tunnels within the NEO.  It would be necessary to manufacture the SPS in small modular segments, which are then assembled in space into a single large structure.  The required mass of the manufacturing, mining and life support equipment is difficult to determine.  But let us assume that for SPS to be economic, the mass of equipment delivered to the NEO must be 2 orders of magnitude less than the total mass of the two SPS delivered to GEO.  This puts the total mass delivered to the NEO no greater than 4000t.

Could we carry out a NEO mining and SPS manufacturing operation, within a mass budget of 4000 tonnes?  That is an interesting question.  The restraining bag would consume about 2.5% of that mass budget.  We would need all sorts of mechanical and chemical processing of excavated material, to convert it into iron, aluminium and doped silicon, before we would presumably either 3D print or cast the required components.  And of course, we would need crew and habitation space for the crew, along with a vehicle to get them there and supplies to support them for what will probably be a mission lasting several years.  It is an open question.

On the plus side, if an SPS delivers 5000MWe to a ground based grid and the operator is paid a constant $100/MWh; then the SPS will deliver some $87.7bn over its lifetime, or $44,000 per kg of equipment mass delivered to the NEO.  This suggests that finished goods delivered to Earth orbit, are probably a more profitable endeavour than mining platinum.  And most of the mass of those goods is basic elements like iron, aluminium and silicon, which can be found on most asteroids.

Last edited by Calliban (2019-11-08 08:43:51)


Interested in space science, engineering and technology.

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#2 2019-11-08 12:13:09

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,754
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Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

Calliban:

Does anyone yet know how to turn rock rubble into real engineering materials?  If there is,  I haven't heard of it.  Not yet,  anyway.  Mass conservation is not the same thing as materials properties,  even though both start with an "M". 

Just because the atoms are there does not mean you can actually do anything useful with them.  Especially in a vacuum/zero-gee environment.  And anything you do besides simple masonry construction will require massive amounts of energy.  It certainly does here on Earth. 

Typical rocks and rocky materials have compressive strength,  but little tensile strength,  which means they have very little bending strength.  That has driven masonry construction to compression-only structures for millennia now.

For just about any conceivable useful things in space,  you need pressure shells.  Those require materials with at least high tensile strength,  and usually significant bending strength.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#3 2019-11-08 14:00:28

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 209

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

GW Johnson wrote:

Calliban:

Does anyone yet know how to turn rock rubble into real engineering materials?  If there is,  I haven't heard of it.  Not yet,  anyway.  Mass conservation is not the same thing as materials properties,  even though both start with an "M". 

Just because the atoms are there does not mean you can actually do anything useful with them.  Especially in a vacuum/zero-gee environment.  And anything you do besides simple masonry construction will require massive amounts of energy.  It certainly does here on Earth. 

Typical rocks and rocky materials have compressive strength,  but little tensile strength,  which means they have very little bending strength.  That has driven masonry construction to compression-only structures for millennia now.

For just about any conceivable useful things in space,  you need pressure shells.  Those require materials with at least high tensile strength,  and usually significant bending strength.

GW

Unanswered questions I would suggest.  Aluminium and magnesium are produced via electrolysis of molten oxide rocks.  The process requires carbon electrodes and generates CO2, which would presumably need to be recycled back into carbon.  The scale of the operation is intimidating.  Whether it could be done on a more compact scale is questionable.

https://aluminiumleader.com/production/ … _produced/

Typically, about 20kWh of electrical energy is required to produce 1kg of aluminium.  To produce 100,000 tonnes of aluminium would require some 2billion kWh.  Other a nominal five year period (2.3 tonnes per hour), that is equivalent to a constant power of 46MW.  The solar array needed to produce this much power would weigh 460 tonnes.  That is about 11% of the assumed mass budget.

Last edited by Calliban (2019-11-08 14:45:57)


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#4 2019-11-09 07:05:18

tahanson43206
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Registered: 2018-04-27
Posts: 1,615

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

For Calliban re topic ...

Thank you for creating this topic, and for performing the analysis given in Post #1.

While your numbers are sobering, they are useful as a starting point for anyone wanting to determine the viability of SPS after so many decades since they were first imagined.

One number that jumped out at me was "1000", which you provided as the incremental number of Falcon Heavy launches that would be needed if a system were to be built on the Earth.

I suspect that Falcon Heavy is not being manufactured at this point, but your point is helpful for a reader wanting to grasp the scale of the enterprise.

There ** is ** one (potential) driver of an investment on the scale that would be needed ... If the world were to decide to wean itself from fossil fuels in 10 years, then SPS would certainly be in the mix of solutions.

From the earliest days of discussion of SPS, building systems using off-Earth resources has been anticipated and even described to some degree.

The benchmark for that discussion is 1977, the publication date of T.A. Heppenheimer's book on the subject.

(th)

Last edited by tahanson43206 (2019-11-09 07:06:54)

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#5 2019-11-09 10:41:13

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,333

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

This is also the issue for payloads in general including the SLS and Starship as the gravity well of earth is a huge factor in why we are not building in space.
Building in a mudular manner has been shown to be as good of a method with regards to space since we are not capable of tonnage that exceeds a single payload capable ship.
Louis is quite excited at 100 mT but what happens when you need something that pushes that limit even higher to 110 - 150 for a single chunk item? Now we are left to cutting the whole unit into more manageable pieces so as to build it on orbit. Which means solving for what can not be cut up to allow for the mission to build what we want.

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#6 2019-11-10 07:10:10

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 209

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

Asteroid Bennu is a B-type asteroid containing hydrated minerals and its orbital characteristics make it relatively accessible from the Earth.  It is therefore a good candidate for asteroid mining and SPS manufacture.  Its aphelion takes it out to 1.36AU, where sunlight levels are only 54% those at Earth orbit.  So not an ideal destination.

https://en.wikipedia.org/wiki/101955_Bennu

https://en.wikipedia.org/wiki/B-type_asteroid

The presence of hydrated minerals and organic material is of great importance for space manufacturing, because hydrogen and carbon are the two most important reducing agents for iron.

The asteroid is nearly 500m in diameter, so it would not be practicable to enclose the body within a bag shipped from Earth.  Instead, a rotating habitat and factory could be placed at one of the asteroids poles and mounted on thrust bearings.  The gravity of the asteroid is only six-millionths of Earth's; so a habitat massing 10,000 tonnes would weigh only 60kg.  Material could be gathered using robotic handlers and fed into an airlock at the base of the rotating factory.

A solar array could be installed on bearings at the opposite pole and would track the sun to provide continuous electric power.  A solar panel 200x200m in area would weigh 80 tonnes and would provide some 16MWe of power at Earth distance from the sun, but only 8.5MWe at aphelion.  So some high energy tasks must be carried out close to the asteroid's perihelion.

As manufacturing produces waste silicate materials, fibreglass fibres could be woven into rope and used to produce a net which would eventually be of sufficient size to surround the entire asteroid.  At this point, the asteroid would be enclosed by the net and could then be spun up.  At this point, tunnels could be dug into the asteroid, which could be pressurised and would have gravity due to the spin of the asteroid.  Operations could then be expanded, with additional facilities constructed in excavated tunnels.

Last edited by Calliban (2019-11-10 07:18:22)


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#7 2019-11-10 09:04:31

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,615

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

For Calliban re #6 ...

Very nice!  I'll study it.

In particular, thanks for the suggestion of Asteroid Bennu.

I'm (at this point) intending to use it as a focus for exploration of the NASA mission planning site.

The extent of the current orbit is not a show stopper as far as I'm concerned, because the asteroid will eventually return.

My guess is that your concern is that as the object recedes away from the Sun, solar power will become less and less useful for material processing.

However, a nuclear power plant would not be affected by location in the solar system, so an investor group looking at this object might well find the trades between solar power and nuclear power well worth examining closely.

Proper orbital period: 1.19548 yr; (436.649 d)
Did you know: It has a diameter of 492 meters, which is a bit larger than the height of the Empire State Building in New York City, and rotating once every 4.3 hours. spacedaily.com

Heck! That orbital period is quite reasonable.  I was worried that the period might have been several years.

I ** really ** like your rotating habitat on an axle projecting from the axis of the asteroid!  Bravo!

That is MUCH better than my idea, which I won't bother describing because yours is so much better.

The components of the habitat can be delivered as individual packages and assembled at the asteroid.

Not too long ago, someone (probably SpaceNut) posted an image of a design for a rotating habitat made of rocket bodies.  That concept seem eminently practical, with the caveat that (in my opinion) the Bigelow habitat concept would be superior in a number of ways.

It would NOT surprise me at all if some enterprising member of the Bigelow engineering team has already proposed a rotating habitat composed of Bigelow cylinders, connected end-to-end by canted couplings.

In your honor, I will add a search term:
SearchTerm:AxleHabitat

(th)

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#8 2019-11-10 18:18:59

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,333

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

Rocket Propulsion Analysis

RPA is a multi-platform analysis tool for conceptual and preliminary design of chemical rocket engines capable of:

    Engine performance analysis
    Thrust chamber sizing
    Nozzle wall contour optimization
    Thrust chamber cooling analysis
    Engine cycle power balance analysis
    Engine mass estimation
    Scripting utility for development of custom solutions

Trial version... sad

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#9 2019-11-12 13:03:17

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,615

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

For Calliban re #6 and rotating habitat mounted on axle projecting from axis of rotation of asteroid ...

Thank you again for this intriguing idea.  I have seen it nowhere else, and believe it deserves further development.

Please develop the idea further, and add drawings if you have time and the inclination.

There is a way to point to image objects, which you can place on a number of cloud sites.

Enclose the URI in the expressions [i m g] and [/i m g] 
(remove the spaces, which I added to prevent FluxBB from treating them as commands)

What I particularly like about your idea is the fact that it completely eliminates the fuss and bother of trying to make a habitat out of the asteroid, when the object of the mission is to collect its valuables.  The axle insures that the habitat is secured to the asteroid so the two don't get separated until there is nothing left of the asteroid.

(th)

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#10 2019-11-12 19:49:13

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,333

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

The reason for humans to burrow into the asteriod is to shield us from the radiation which we can not tolerate.
Sure AG would happen depending on the spin rate but then you need to design the habitat for doing so.

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#11 2019-11-12 20:35:19

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,333

Re: Manufacturing Solar Power Satellites within Near Earth Asteroids

Here is what was posted in the other topic:

tahanson43206 wrote:

For Louis re topic .... here is a paper from 1979 that appears to use a variation on Calliban's idea of spinning at habitat on an axis that runs through an asteroid.

Please note that the paper includes images that show the proposed propulsion system (for asteroid material to be sent to Earth) running on either (both) end of the axis of the asteroid.

http://www.star-tech-inc.com/papers/ast … eroids.pdf

ASTEROID RETRIEVAL BY ROTARY ROCKET* Jerome Pearson** U. S. Air Force Flight Dynamics Laboratory Wright-Patterson Air Force Base, Ohio 45433

Rather than expending 80% of the asteroid mass to bring back the remaining 20%, it may be more advantageous to launch larger masses with the proper velocity to return directly to the earthmoon system. In this case we might launch only 20% of the mass of the asteroid, but it would all be retrieved for use. This technique would have the advantage of producing the first payload in a matter of a year instead of 4 to 5 years.

I had the opportunity to attend presentations by Mr. Pearson on several occasions.  At the time he was working on tethers, about which he has published several papers.

(th)

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