Hello everyone, this is my first post here. I'm working on a
Masters at University of North Dakota and would like to ask a
question and possibly open a debate.
generation in space. Viewed from the perspective of supporting human
life, space is a difficult and dangerous place. However, viewed from
the perspective of generating energy, space may be a very fertile
environment. What I would like to propose is that we do some
unconventional thinking, look past the well-known SPS concept, and
list some other possibilities. What else is there? What ideas need to
be revisited? What new concepts are emerging? Is there a convergence
between near-term lunar exploration and the capacity to
construct any form of power generation plant in space in the next 20
years? I would ask that we list the possibilities, and speak to the
near-term potential for implementation.
Let me start by throwing out two:
1. Large scale photovoltaic SPS in orbit, beams power to rectenna on
Earth's surface. Tends to be very large, difficult to assemble,
suffers from heavy on-board power transmission. Elegance of direct
solar power to electricity is limited by today's low-efficiency
photovoltaic technology.
2. Helium 3 derived from the Moon to power fusion generators on
Earth. Great fuel, but you need working fusion plants, which we
cannot expect for decades.
So, here's your chance - especially those of you with advanced
degrees. What else is there? If you had the opportunity to advise the
nation on how to exploit the space environment to offer a credible
energy alternative, what would you suggest?
> What I would like to propose is that we do some unconventional
> thinking, look past the well-known SPS concept, and list some
other > possibilities. What else is there?
along. But first, don't neglect the SPS thermal proposals which don't
use PV cells.
Thinking outside of the box, we could tap electrostatic field
differentials but I think they are stonger in LEO than at GEO.
We could also seek to tap into the Earth's momentum as a source of energy.
That taps me out for the moment. I still think that these sources are
a bit of a reach when we consider that the Sun is pumping out all of
that energy, so no need to rob the Earth of its spin to provide us power.
As for He3, Andrew Case, one of our list members provided us with a
very thorough explanation about the difficulties involved, and in fact
his post was prompted by a request from another student in your
program. See here:
TangoMan
Probably a more cost effective and more or less off the shelf solution is
using a turbine generator to produce the electricity. By using a light
weight mylar reflector to direct sunlight onto a surface to heat whatever is
used as the system fluid. I have seen some articles about using Helium.
Photovoltaics is not required. Turbine design is well understood. left
requirements for a "mylar mirror" is going to be quite a bit less than
Photovoltaics or their related production equipment if you produce them in
orbit.
Kent
> Probably a more cost effective and more or less off the shelf
> solution is using a turbine generator to produce the electricity.
> By using a light weight mylar reflector to direct sunlight onto a
> surface to heat whatever is used as the system fluid. I have seen
> some articles about using Helium.
from Earth (or dig it out in PPB from Lunar regolith). How about
oxygen instead?
There are two MAJOR problems that attend the use of
turbines in hard vacuum and orbit.
1) They are machines with moving parts that must be
lubricated and replaced on a regular basis. The
failure rate of mechanical devices, regardless of
environment, is easily 10,000 times more likely than
the failure rate of solid state devices.
2)For a turbine to function, it must have a heat sink
somewhere, which necessitates the building of a LARGE
radiative surface to dump the residual heat of
operation. No such requirement for the solor cells
themselves, though the conversion to micro waves would
have some residual waste heat, I doubt it would be as
significant as that from a heat engine such as
turbines.
I have always had a problem with turbines that I have never seen brought
up as a reason for not using them and that is that they are rotating
machinery. When one piece of a machine turns in space then the rest of
the machine has to turn in the opposite direction with the same
rotational energy. Now you could have a turbine pair that rotated in
opposite directions connected by a solid structure then as long as the
torques were equally matched the structure could remain stationary (a
long list of assumptions). (I really would like to see somebody do this
while generating electricity under varying load.) No machine runs
forever. It is just a question of how it is going to fail. So a
bearing freezes on one of the turbines and all of the rotational energy
is quickly transfered to the structure. In my mind something turning
fast enough to generate a usable voltage is going to transfer enough
energy to do a good job of trashing the overall structure. This
structure is going to be designed for minimum weight not maximum strength.
what happens in failure mode overrides what they remember when
everything is working correctly. To me the failure modes associated
with rotating machinery in space out weigh anything else.
Mitchell James
Mitchell James wrote: I have always had a problem with turbines that I have never seen brought
up as a reason for not using them and that is that they are rotating
machinery. When one piece of a machine turns in space then the rest of
the machine has to turn in the opposite direction with the same
rotational energy. Now you could have a turbine pair that rotated in
opposite directions connected by a solid structure then as long as the
torques were equally matched the structure could remain stationary (a
long list of assumptions). (I really would like to see somebody do this
while generating electricity under varying load.) No machine runs
forever. It is just a question of how it is going to fail. So a
bearing freezes on one of the turbines and all of the rotational energy
is quickly transfered to the structure. In my mind something turning
fast enough to generate a usable voltage is going to transfer enough
energy to do a good job of trashing the overall structure. This
structure is going to be designed for minimum weight not maximum strength.
what happens in failure mode overrides what they remember when
everything is working correctly. To me the failure modes associated
with rotating machinery in space out weigh anything else.
Mitchell James
> There are two MAJOR problems that attend the use of
> turbines in hard vacuum and orbit.
> 1) They are machines with moving parts that must be
> lubricated and replaced on a regular basis. The
> failure rate of mechanical devices, regardless of
> environment, is easily 10,000 times more likely than
> the failure rate of solid state devices.
> 2)For a turbine to function, it must have a heat sink
> somewhere, which necessitates the building of a LARGE
> radiative surface to dump the residual heat of
> operation. No such requirement for the solor cells
> themselves, though the conversion to micro waves would
> have some residual waste heat, I doubt it would be as
> significant as that from a heat engine such as
> turbines.
>
> Gary 7
What if the turbines were mounted on the lunar surface? Let's say you had multiple turbines, working independently of each other to isolate any failures and allow for periodic maintenance. Transfer all reactions to the planet. Mechanical and rotary systems are all prone to failure and require maintenance, but we do have a long experience base with the technology, and a base on the Moon would allow tending of the machinery. Is this preferable to a more exotic technology?
Andy
Mounting mechanical devices on a large body such as
the moon would be useful IF you can have a human
presence in place to maintain them. Solar cells, with
their four orders of magnitude greater reliability,
require very little human intervention, a great big
plus in geo sync orbit or anywhere humans are not
available. Teleoperated robots are feasable in geo
sync orbit but not at the distance from earth to luna.
WAY too much lag time,,,
What if the turbines were mounted on the
lunarsurface? Let's say you had multiple turbines,
working independently ofeach other to isolate any
failures and allow for periodic maintenance. Transfer
all reactions to the planet. Mechanical and rotary
systemsare all prone to failure and require
maintenance, but we do have a longexperience base with
the technology, and a base on the Moon would
allowtending of the machinery. Is this preferable
to a more exotictechnology?
Andy
Science education
History of space
exploration My
Space exploration
these 2 major problems can be solved by the following, use a lubrating working fluid. like refrigators use freon. recently mini-gas turbine have been built with air bearing. the good thing about the heat sink you can sent heat out to the cold of space which is about 4 K
turbines in hard vacuum and orbit.
1) They are machines with moving parts that must be
lubricated and replaced on a regular basis. The
failure rate of mechanical devices, regardless of
environment, is easily 10,000 times more likely than
the failure rate of solid state devices.
2)For a turbine to function, it must have a heat sink
somewhere, which necessitates the building of a LARGE
radiative surface to dump the residual heat of
operation. No such requirement for the solor cells
themselves, though the conversion to micro waves would
have some residual waste heat, I doubt it would be as
significant as that from a heat engine such as
turbines.
Gary 7
Regards,
Mike Combs
I understand that the focus of this discussion group is to focus on
"practical" technologies for realizing O'Neill's vision, but what about
considering technologies that may not currently exist but might be
worthy of exploration. In this regard, might frictionless bearings,
slip rings, couplings, etc. based on employing magnetic fields, (such as
is used by Maglev) be possible?. It seems to me that frictionless
couplings would have a considerable impact on the maintenace
requirements of turbines, rotating/non-rotating aspects of a space
habitat, storing energy via flywheels, etc.
> Behalf Of Andrew Daga
>
> > What if the turbines were mounted on the lunar surface?
> > Let's say you had multiple turbines, working independently
> > of each other to isolate any failures and allow for
> > periodic maintenance. Transfer all reactions to the
> > planet.
>
> The minor advantage of being able to transfer reactions to the surface
> would not make up for the major disadvantage of being blocked from the
> energy supply 50% of the time (for 2 weeks at a time).
>
> Regards,
>
> Mike Combs
>
education
History of space My first Space exploration
What if the turbines were mounted on the lunar surface?
times as expensive per kg than putting them in a Lagrangian orbital
location in the lunar vicnity.
Other issue with solar dynamics (SD):
accurate focus.
If a PV array drifts off a few degrees, the power level drops a few
percent.
If a SD array drifts off a few degrees, the power level drops off to
zero.
>
> Probably a more cost effective and more or less off the shelf
solution is
> using a turbine generator to produce the electricity. By using a
light
> weight mylar reflector to direct sunlight onto a surface to heat
whatever is
> used as the system fluid. I have seen some articles about using
Helium.
>
about He, I have not heard about this in any spacecraft type
application.
For any energy system in space, the requirements is to get maximum
energy efficiency per kilogram of system weight.
Here is the main NASA web site on the subject:
http://www.grc.nasa.gov/WWW/tmsb/dynamicpower/doc/adv_sd_tech.html
NASA continues to focus their SD R&D efforts on Brayton cycle
engines using molten salts, because these give much higher
performance per kg than Stirling type systems.
Thanks for pointing that out, Charles.
Soft landing hardware from Earth on to the lunar surface is about ten
times as expensive per kg than putting them in a Lagrangian orbital
location in the lunar vicnity.
Where does this claim of 4 orders of magnitude increase in reliability
come from? I know that generators normally get preventive maintenance
once every year on average, so who was building solar cells 10 000
years ago to validate this claim.
Also don't underestimate a gas turbine system. A 1 megawatt generator
is actually quite small and compact, much smaller than the equivilent
amount of solar cells and when everything is miscellaneous cost
compared to the launch cost one should seriously look at such options.
Now to another point. Did anyone mention simply mount light weight
alunium mylar mirrors and pointing the sunlight the reflect down to a
place where it can be used on the ground. They may be used to extend
growing seasons in cold countries or provide reliable 24/7 sunlight to
ground based solar cells.
Also lets talk about heat instead of electricity. Using concave
mirrors to focus sunlight in space to be used by industrial processes
directly instead of going through the intermediate electricity stage.
This would be used in space, but that doesn't matter.
This may not be considered energy but mining and returning fissionable
elements from asteroids or the moon or mercury might also be a
possibility.
Helium 3 is always talked about but few people understand the reason
we want helium 3 is that it is a key fuel element in fusion research
and presumably if fusion ever happens a major fuel element.
This may be considered energy storage not energy production but refine
high reactive elements such as sodium, lithium, and potassium and use
them to produce rechargable batteries to be kept in space with the
power beamed down to cover electrical peaks.
Bill
--- In ssi_list@... GARY ANSORGE
Yo, Bill, understand, ANY evice built to have moving
parts is inherently less reliable than a solid state
device, measurable in orders of magnitude
improvements. Don't know where the 10 year figure came
from for solar cells, but that's in an atmospheric
environment, with wind, rain, dirt, kids, dogs, etc,
etc.
sunlight to earth, by passing electrical generation.
Unfortunately, the particular mix of frequencies of
solar radiation result in scattering, reflection and
absorbtion of that light before it reachs the ground.
IE. approximately 80 % never gets to the earths
surface. The only advantage is the 24 hour
availablility factor, and you still have to move the
really big collectors to capture and reflect the
sunlight. With short wave transmitters we get to
choose the frequency best suited to passing thru
earths atmosphere unimpeded with a smallish
transmitter vs a large collector. Small transmitter
equals easier realignment for transmission and you
only have to worry about transmitter direction, not
balancing the collector angle at the same time.
,,,and yes, Dr. O'Niell discussed the direct use of
solar heat for industrial processes.
Gary 7
--- In ssi_list@... GARY ANSORGE
>
> Yo, Bill, understand, ANY evice built to have moving
> parts is inherently less reliable than a solid state
> device, measurable in orders of magnitude
> improvements. Don't know where the 10 year figure came
> from for solar cells, but that's in an atmospheric
> environment, with wind, rain, dirt, kids, dogs, etc,
> etc.
>
be more reliable in space than on earth. In space they will have to
deal with damaging electromagnetic radiation, electron bombardment,
and ionizing radiation. I can specifically speak about electron
bambardment because this was the topic of a friend of mines thesis 15
years ago and I have heard much about it. Electron bambardment causes
damage to the crystal structure and accelerates the diffusion rate of
negative ions across the potential barrier (the pn-junction that is
used to produce the electricity). The diffusion renders the built in
potential of the pn junction smaller and smaller that causes a
decrease in voltage in time, and a bigger decrease in electron flow
because the electron back diffusion across the junction increases
exponentially with lower voltage. Furthermore because these are
devices that when functioning have a positive surface, every free
electron around them will start accelerating towards that surface.
A typical silicon polycrystalline cell lasted hours not years in low
energy electron bombardment. Other materials he tested were gallium
arsnide, sapphire, and germanium all with similar results.
The 10 years comes from the box I was looking at a Canadian Tire I had
visited about a couple of hours earlier. This is the rated life time.
You might expect a multiple of three as the real lifetime of the
product. Yes that does include important terrestrial only problems
that will shorten the life span of the product.
The point I was trying to make and was brushed aside was that
believing that space infrastructure will be maintenance free is wrong.
Even if we could create things with 10 000 year lifetimes,
unforseeable events can shorten the lifespan of everything. The
attitude that we can fire these things off into space and forget about
them while reaping in the benefits is wrong. Everything people have
built needs active maintenance, either preventive maintenance, or
maintenenace on demand.
Bill
Well said. Your point on maintenance is also quite right too. These are fundamental issues.
Andy
Bill wrote: --- In ssi_list@... GARY ANSORGE
>
> Yo, Bill, understand, ANY evice built to have moving
> parts is inherently less reliable than a solid state
> device, measurable in orders of magnitude
> improvements. Don't know where the 10 year figure came
> from for solar cells, but that's in an atmospheric
> environment, with wind, rain, dirt, kids, dogs, etc,
> etc.
>
Actually there is no reason to believe that solid state devices will
be more reliable in space than on earth. In space they will have to
deal with damaging electromagnetic radiation, electron bombardment,
and ionizing radiation. I can specifically speak about electron
bambardment because this was the topic of a friend of mines thesis 15
years ago and I have heard much about it. Electron bambardment causes
damage to the crystal structure and accelerates the diffusion rate of
negative ions across the potential barrier (the pn-junction that is
used to produce the electricity). The diffusion renders the built in
potential of the pn junction smaller and smaller that causes a
decrease in voltage in time, and a bigger decrease in electron flow
because the electron back diffusion across the junction increases
exponentially with lower voltage. Furthermore because these are
devices that when functioning have a positive surface, every free
electron around them will start accelerating towards that surface.
A typical silicon polycrystalline cell lasted hours not years in low
energy electron bombardment. Other materials he tested were gallium
arsnide, sapphire, and germanium all with similar results.
The 10 years comes from the box I was looking at a Canadian Tire I had
visited about a couple of hours earlier. This is the rated life time.
You might expect a multiple of three as the real lifetime of the
product. Yes that does include important terrestrial only problems
that will shorten the life span of the product.
The point I was trying to make and was brushed aside was that
believing that space infrastructure will be maintenance free is wrong.
Even if we could create things with 10 000 year lifetimes,
unforseeable events can shorten the lifespan of everything. The
attitude that we can fire these things off into space and forget about
them while reaping in the benefits is wrong. Everything people have
built needs active maintenance, either preventive maintenance, or
maintenenace on demand.
Bill