Space Forum / Space Flight / March 2006

Sounds like we need to make flywheels from lunar glass fibers.  I have
the impression that glass can be quite strong if made in an anhydrous
environment, which Luna certainly is.  Has anyone tried melting lunar
simulant (maybe with most of its metal contamination removed) in a
vacuum to make glass, then strength-tested the glass while still in a
vacuum?

In sci.space.tech, on Wed, 15 Mar 2006 19:40:54 -0000,
David M. Palmer <dmpalmer@email.com> sez:

` In article <1139929076.495105.80440@g43g2000cwa.googlegroups.com>,
` <wbogen@visteon.com> wrote:

` > Flywheel energy storage has been suggested for use on the Moon (see
` > http://www.asi.org/adb/04/03/03/flywheel-energy-storage.html ).  But I
` > haven't seen a proposal to use lunar materials in the systems to reduce
` > cost.  I suggest that we import bearings, generator/motors, and carbon
` > fiber or Kevlar arms/containers from Earth to the Moon.
` > ...have two 10m arms tipped
` > with sacks or containers for 100kg of regolith, and would spin at 3000
` > rpm.  Perhaps 90% of the total mass could be regolith.

` At least to first order, the limit on the amount of energy that a
` flywheel can store before tearing itself apart is set by the physical
` strength of its construction materials.

` If you spin two long strong arms that have sacks of dirt at the end,
` the arms will break at about the same rotational energy (but different
` speeds) whether the sacks are full or empty.  (Both the tension on the
` arms and rotational energy go proportional to m v^2 .)

` If you aren't running the flywheel fast enough to almost fly apart,
` then you are probably wasting expensive Earth-manufactured mass.

` Indigenous material is only a win if it provides structural strength
` (and the strength doesn't have to be nearly as much as carbon fiber, if
` you  can get the local/imported mass ratio high enough).

What about wear on the bearings? With higher mass you get lower
rotational velocity at the same stored energy, ...let's see,
half the mass is sqrt 2 times v for the same energy, so force
is sqrt2/2 ie less for the lighter case. How does bearing wear
relate to force and angular velocity?

Michael Smith,
Your "large semi-autonomous rover" is a good idea, perhaps as a lunar
metro bus(LMB-1) that can even weigh as much as 600t, which equals just
100t on the moon, as per assembled on location plus locally applied
with loads of extra reinforced basalt fiber and JB-WELD to being
sufficiently robust and fully capable of accommodating a dozen folks
with lots of gear and technology for assisting their task.  With 200 m2
of track drive gets the surface loading down to 500 kg/m2 (50 g/cm2),
that which in places is fairly certain to sink to whatever's the
hard-rock bottom of that otherwise light and fluffy moon dust.

Perhaps you'll also need to consider having a good nuclear reactor
nearby, for accommodating 10 kw/person at your lunar bus depot.
Whereas I'm thinking this item should be of not greater than 60t for
providing 120 kw, thus a mere 10t as situated upon the lunar deck seems
perfectly doable.  Unlike terrestrial applications, the reactor as
intended for the moon need not be all that shielded.

Small Nuclear Power Reactors
http://www.uic.com.au/nip60.htm

This is what I'd recently contributed to "Geoffrey" within the topic of
"Moonbase Power".
http://groups.google.com/group/sci.space.policy/browse_frm/thread/ef1749afd956a8
53/2522cb00f9b37060?lnk=st&q=%22of+what's+similar+to+PVs+is+the+prospects%22&rnu
m=1&hl=en#2522cb00f9b37060

I believe the solar wind driven moon dust is going to represent enough
of a compromise to the life and/or serviceability of those PVs,
especially as such moon dust being of carbon/soot coated elements of
salt, iron, titanium and of whatever's within basalt plus the vast
remains of countless meteor impacts and of their secondary shards
contributing that of just about everything imaginable including the
kitchen sink, along with most everything being so electrostatic charged
to the max.  A mechanical wiper or perhaps a central spinning element
if not having the entire array kept as spinning should help keep the
lens clear enough, unless the harsh abrasive aspects of that nasty
moon-dust is simply too aggressive, although a diamond coated PV lens
might resolve that issue.

Of robust PVs or not, I'd still have to vote for the compact and much
greater energy density of having a small and reliable 24/7/365 reactor
as my resource of nearby energy (10+kw/brave soul), as perhaps not
situated quite so nearby if there's ever a problem of leakage and
you're situated downwind of that reactor as it's going postal.  It
seems being north or south of that sucker by a km should be more than
sufficient.

However, of what's entirely similar to PVs is the prospects of having
the physically robust nature of a hermetically sealed solar-stirling
method of a moon based energy producing unit, that's roughly better off
than twice as good of energy conversion efficiency/m2 than of PVs, and
unlikely to stop ticking unless directly impacted by one of those
incoming or that of a high velocity item as passing near the surface,
such as a fairly common cm3 size of meteor that's going to do a real
number upon anything that's naked upon the lunar surface, whereas even
the secondary impact shards are going to be damn nasty if not lethal to
all but the most robust of applied technology.

Obviously the solar-stirling alternative is considerably more massive
than of those wussy solar-PVs that'll take up a great deal of volume
and otherwise proceed to die-off by at least 10% per year (up to as
much as 25% per year), but perhaps still sufficiently less massive than
the nuclear reactor option.  Of course, with using the LSE-CM/ISS
tether elevator as the method of deploying man and machine to/from the
lunar surface, as such there's no longer a limitation as to the given
tonnage that can be safely and efficiently managed.  What do you think
about the solar-stirling alternative?
-
Brad Guth

Given that better than space quality vacuum can be created here on
Earth, Flywheels ought to be a realistic proposition for stationary
energy storage -  but they haven't taken off. Cost?  As for the moon,
seems to me putting your base at one of the poles and using PV raised
up on trackers you could get constant electricity 708hrs a day. I doubt
I'm the first to suggest it. Not that there wouldn't be need for
storage both for vehicles and for intermittent high energy
applications. Meanwhile battery technology isn't standing still, with
some promising applications of  nanotech materials showing potential
for some serious improvements in energy density and charge/discharge
rates. Never assume that the technology current today is the last word
- particularly when speculating about something so reliant on advances
in technology as settlements on the moon! Whilst a future lunar colony
would benefit from such advances the vast majority of humanity here on
Earth could do with some serious improvements in energy storage
technologies right now. Prof Smalley, nanotech pioneer, has proposed a
"manhattan" style project to develop the kinds of energy technologies
without the deleterious side effects, to carry a growing human
population into the future. Seems to me it would be a worthwhile
effort.
Ken
ps a previous post of mine failed to appear here.

Colonise the poles and put up solar panels on trackers into permanent
sunshine . Still we desperately need good batteries ( high energy
density, fast charging, long service life, reusable materials, low
cost) down here so lets hope we are yet to see the best of energy
storage systems given that most of humanity will be living here on
Earth for the forseeable future and our need for them is immediate.
Ken.