lunar resources/lava tubes
Allen Thomson
> A couple of suggestions from the discussion about finding
> lava tubes.
>
> Radar satellite come in two varieties. Downward looking and
> sideways looking. Sideways looking radars use the motion of
> the spacecraft to synthasize (sp) a very large antenna in one
> direction. A lunar version of the Earth resources satellites with
> a long slab antenna might be a way to get the resolution required.
> Incidently knowing where the satellite is essential to reconstruction
> of the radar data, so the satellite could also act as a gravity probe.
> However sideways looking radars use back scatter from the surface and
> are not that good at deep penetration surveys, however such a survey
> might reveal the surface signatures (slumping) that indicate a lava
> tube.
[snip]
The Swedes have a long-wavelength synthetic aperture radar (what
you're describing) that achieves a fair amount of penetration: it
has traced a pipeline on the bottom of a freshwater lake.
I disremember the name (Omega??), but it was written up in an AWST
article within the past few years. Maybe something of that sort,
with multiple passes, integration, lots of processing...
Dave Stephenson
lava tubes.
Radar satellite come in two varieties. Downward looking and
sideways looking. Sideways looking radars use the motion of
the spacecraft to synthasize (sp) a very large antenna in one
direction. A lunar version of the Earth resources satellites with
a long slab antenna might be a way to get the resolution required.
Incidently knowing where the satellite is essential to reconstruction
of the radar data, so the satellite could also act as a gravity probe.
However sideways looking radars use back scatter from the surface and
are not that good at deep penetration surveys, however such a survey
might reveal the surface signatures (slumping) that indicate a lava
tube.
A first crack at that problem might be to examine existing photographs
of the Moon close to the terminator and look for shadow lines.
For deep penetration of the Moon you want as much power as possible going
down, so a dish pointed at the surface would be required, synthesis is
not going to get you sensitivity, but some smart electronics. (spread
band, encoded waveforms) will help. Once again it will be essential to
know where the spacecraft is for reconstruction.
As for geophones. You do not need explosives. Do what was done during
the Apollo missions. Bombard the Moon with space junk. If your mission
is not a direct landing on the Moon, but involves a lunar orbit bus,
then once the geophones are in place. Deorbit the Bus, it should make
a very nice bang when it lands. And if more data is required simply
send something heavy to crash on the Moon. This will allow you to
taylor the mission to your budget.
"Look we have a couple of million bucks left in the account, and
the end of the financial year is coming......"
--
Dave Stephenson
Geological Survey of Canada * BEWARE!
Ottawa, Ontario, Canada *
Internet: step...@ngis.geod.emr.ca *Bill Gates is lurking you!
Dave Stephenson
(snip)
: As for geophones. You do not need explosives. Do what was done during
: the Apollo missions. Bombard the Moon with space junk. If your mission
: is not a direct landing on the Moon, but involves a lunar orbit bus,
: then once the geophones are in place. Deorbit the Bus, it should make
: a very nice bang when it lands. And if more data is required simply
: send something heavy to crash on the Moon. This will allow you to
: taylor the mission to your budget.
: "Look we have a couple of million bucks left in the account, and
: the end of the financial year is coming......"
Some second thoughts about explosions for geophones on the Moon.
This would be a good first use of a small mass driver. Use it as
a mortar. Shoot suitably sized 'particles' (I am a physicist) up
wards. They will come down to a precise location with the velocity
they went up with, and bingo a seismic explosion of known intensity.
The advantage of this scheme is that CNH are not required and from
a central location a series of explosions can be arranged all feeding
data to one array of geophones. This will greatly assist the analysis
of the data. Indeed with a suitably powerful mortar impacts on the
other hemisphere of the Moon could be arranged, for research into
the Moon's core (?).
However if the impactors are to be launched from orbit, only
a minimum of fuel will be required as instead of completely de-orbiting
the impactor, it only has to have its perilune lowered until it
hits the surface, and it will impact at orbital velocity. A bus could
contain a dozen or more small impactors and release them as required.
The reaction of releasing the impactors might be arranged to be enough
to cause the impact.
: --
Frank Crary
Dave Stephenson <step...@ngis.geod.emr.ca> wrote:
> As for geophones. You do not need explosives. Do what was done during
> the Apollo missions. Bombard the Moon with space junk. If your mission
> is not a direct landing on the Moon, but involves a lunar orbit bus,
> then once the geophones are in place. Deorbit the Bus, it should make
> a very nice bang when it lands.
Unfortunately, that would only work once. For studies of the
deep interior, that's fine. But the waves that travel for
great distances are long wavelength and insensitive to
small, near surface features like lava tubes. You really
need an energy source close to each, prospective lava
tube (several, if you aren't going to require a network
of geophones.) That's likely to mean dozens of events,
not a single, de-orbited spacecraft.
> ...And if more data is required simply
> send something heavy to crash on the Moon. This will allow you to
> taylor the mission to your budget.
Tailor isn't the word I'd use. Cause a large increase in the
budget would be closer. Causing enough, sufficiently large,
impacts would require alot of mass on orbit. I think using
explosives would be easier.
Frank Crary
CU Boulder
Frank Crary
Dave Stephenson <step...@ngis.geod.emr.ca> wrote:
>Some second thoughts about explosions for geophones on the Moon.
>This would be a good first use of a small mass driver. Use it as
>a mortar. Shoot suitably sized 'particles' (I am a physicist) up
>wards. They will come down to a precise location with the velocity
>they went up with, and bingo a seismic explosion of known intensity.
That would work, but it might not be the most efficient choice.
If the plan is to build a mass driver anyway, then it's a
very good idea. But if a mass driver isn't in the budget,
or there are no plans to build one _first_ (remember, the
lava tube survey is to find a location for the base, so
the mass driver would have to be built before the base)
then you've got a mass problem: A trade off between costs
of importing a few dozen kilos of explosives and of
building a mass driver.
>...Indeed with a suitably powerful mortar impacts on the
>other hemisphere of the Moon could be arranged, for research into
>the Moon's core (?).
Possible, but it would take throwing a very large mass. (You
can't throw it was more than lunar escape velocity and expect
it to hit the surface again, so you'd need mass to give you
the required kinetic energy.) It also might not be necessary.
For deep seismic work, all you need is an impact on the surface
of the Moon. Unlike local surveys, the impact can be anywhere.
So smallish, natural impacts are a good source.
Frank Crary
CU Boulder
doyle@problem_with_inews_gateway_file
s
Explosives were used on Apollo 17 to do active seismic sounding in the
Lunar Seismic Profiling Experiment. lso there was the Active Siesmic
Experiment but I am not sure if that one was actually done.
Karen
doyle@problem_with_inews_gateway_file
> In article <DLL6t...@emr1.emr.ca>,
> Dave Stephenson <step...@ngis.geod.emr.ca> wrote:
> > As for geophones. You do not need explosives. Do what was done during
> > the Apollo missions. Bombard the Moon with space junk. If your mission
> > is not a direct landing on the Moon, but involves a lunar orbit bus,
> > then once the geophones are in place. Deorbit the Bus, it should make
> > a very nice bang when it lands.
I think a satilite which would drop lead balls at specified loctions
would be far better. When a piece of Apollo 13, I believe, was crashed
on the moon it rang like a bell for 3 hours. This is too much noise
for geophones.
> Unfortunately, that would only work once. For studies of the
> deep interior, that's fine. But the waves that travel for
> great distances are long wavelength and insensitive to
> small, near surface features like lava tubes. You really
> need an energy source close to each, prospective lava
> tube (several, if you aren't going to require a network
> of geophones.) That's likely to mean dozens of events,
> not a single, de-orbited spacecraft.
> > ...And if more data is required simply
> > send something heavy to crash on the Moon. This will allow you to
> > taylor the mission to your budget.
If you hard land it you don't want it to be too heavey.
> Tailor isn't the word I'd use. Cause a large increase in the
> budget would be closer. Causing enough, sufficiently large,
> impacts would require alot of mass on orbit. I think using
> explosives would be easier.
> Frank Crary
> CU Boulder
Karen
Thomas L. Billings
Stephenson) wrote:
> A first crack at that problem might be to examine existing photographs
> of the Moon close to the terminator and look for shadow lines.
>
> For deep penetration of the Moon you want as much power as possible going
> down, so a dish pointed at the surface would be required, synthesis is
> not going to get you sensitivity, but some smart electronics. (spread
> band, encoded waveforms) will help. Once again it will be essential to
> know where the spacecraft is for reconstruction.
>
> As for geophones. You do not need explosives. Do what was done during
> the Apollo missions. Bombard the Moon with space junk. If your mission
> is not a direct landing on the Moon, but involves a lunar orbit bus,
> then once the geophones are in place. Deorbit the Bus, it should make
> a very nice bang when it lands. And if more data is required simply
> send something heavy to crash on the Moon. This will allow you to
> taylor the mission to your budget.
>
> "Look we have a couple of million bucks left in the account, and
> the end of the financial year is coming......"
>
>
> --
> Dave Stephenson
> Geological Survey of Canada
> Ottawa, Ontario, Canada
> Internet: step...@ngis.geod.emr.ca
I guess I should jump in here.
Karen was kind enough to reference my paper in JBIS on this subject during
the thread from which this seems to have developed, but I've had some more
thoughts since1990. Dave has mentioned some concepts from which my
present thinking began to take shape.
The basic problems for any radar detection of lunar lavatubes are
resolution, penetration, and signal to noise ratio. (Did I mention
Money?) We MAY have a way to get around all of those at acceptable cost,
but it definitely isn't your standard GPR setup.
My idea evolved from elements of the 2 schemes Dave began mentioning
above, radar and impactors for geophones.
The radar equation describes the signal to noise ratio we'll get from a
radar, with some hard relationships to make work. First is the 4th power
range coefficient in the denominator, a real pain. Second is the fact
that the s/n ratio gets worse with the 2nd power of the frequency. Also,
penetration without massive attenuation pushes us to longer wavelengths.
Of course the rayleigh limit for resolution and the ionospheric limits for
radio frequency require useful wavelengths on the order of a meter, as
Frank Crary has ably pointed out. I should note, however, Dr. Coombs
initial work does seem to indicate some lavatubes much bigger than 200
meters in diameter. Indeed, I remember indications of one tube 500
meters wide by about 7500 meters long and another 1100 meters across.
Nevertheless, frequency/aperture is still a problem for any regular GPR
looking for lavatubes from lunar orbit. :>(
There is also a problem with geophones that I'm unhappily resigned to.
Once again it has to do with frequency and resolution, and in addition,
the state of cooled basalt. According to Steve Gillet, who has posted to
s.s.p. in the past and worked with Oregon L-5's research Team in Bend,
Oregon, when a flow of basalt cools, it cracks. It cracks a lot! Those
cracks will cause signal/noise problems for short wavelength searches with
sound that are far worse than they would be for EMR methods. Reflection
of sound from a crack in vacuum would be total. I believe now that any
wavelengths long enough to avoid attenuation by these cracks may well be
so long that we won't get the resolution needed for even 500 meter tubes.
:>(
However, the use of impactors (I called them "Thumpers") to deliver the
needed energy for geophones stayed with me. I had wanted to put them in
a spacecraft doing figure eight orbits between Earth and the Moon,
dropping them off with a little shove that would put them on an accurate
lunar impact trajectory. Then, someone mentioned to me that tracking
spacecraft by radar is done with a "Cooperative Target" most of the time.
I was feeling sorry for myself that lunar lavatubes didn't "Cooperate" as
well. I had already been looking at doing the job of synthesizing the
radar dish down here, on Earth, using VLBI techniques in my earlier paper,
in order to get better resolution at lower cost. Unfortunately, the
signal/noise ratio for surface work already required 124 seconds of
integration time for each 50X50 meter pixel, and penetration, even on a
dry Moon, would only make it worse.
So, what would happen if we delivered, to the area near a suspected
lavatube, a powerful EMR source of appropiate frequency, to make the
object of desire more "cooperative". Good news! It could have close
range penetrating power! It's equivalent equation to the radar equation
should have only a 2nd power on the range coefficient, thus giving a much
better s/n ratio! Bad News! It would cost like sin to set such a power
source down on the lunar surface by soft landing! I remembered the
"Thumpers". Too bad their K.E. wasn't EMR. It would be like a flashbulb
illuminating a sea bottom, observed from a telescope in an airplane at
night. You could probably "see" reflective voids in the lunar crust for
several kilometers around the impact using the VLBI.
Then I was reminded of homopolar generators. These are neat storage
devices for energy that turn K.E., from gyroscopes on steroids, into
monster electric currents. If we could do, just once and very fast, the
same thing with the linear motion of a compressible impacting "Thumper"
that homopolar generators do again and again with rotary motion, then we
might just have a good source of EMR for a lunar EMR "flashbulb". At 2350
meters/sec. that's a lot of ergs available for conversion into a really
massive radar pulse!
Of course, the current pulse has to be converted into a properly modulated
radar pulse and then directed down into the lunar crust, and all in 1/2350
seconds if the "Thumper"'s linear compressive motion is about a meter
long. Then the Thumper is splattered. That conversion part I'm not
enough of a radar engineer to work out yet. Still, I've been told in
passing by those who are experienced in that field that the idea sounds
"not-impossible". So we may have the elements of a useful search system
for underground lunar phenomena, including lunar lavatubes most
prominently.
These would be:
1.) A VLBI about as large as you can get on Earth. NRAO has made a good
start on this with their currently operating VLBI. We must equip it with
receivers in the appropriate frequencies.
2.) A supply of EMR "flashbulbs" in a useful storage orbit that has low
d/v for impact with a large part of the lunar near side.
3.) Information from Clementine and other lunar probes about where we
could best place these EMR "flashbulbs" for the best chance of
illuminating our desired lavatube features.
As Jeff Greason has noted elsewhere, Oregon L-5 is still struggling with
shoehorning a proper lavatube search of the massive Clementine data set
into whatever private funding we might get.
I hope that someone out there might contribute their knowledge of power
engineering and radar into an analysis of the "flashbulb" and it's
particular problems.
Thanks for any Comments,
Tom Billings
--
Tom Billings, Institute for Teleoperated Space Development
"Minds Wielding Tools, Preparing Our Way Into Space"
http://www.teleport.com/~itsd1/index.html
Dave Stephenson
: I guess I should jump in here.
: These would be:
: Thanks for any Comments,
: Tom Billings
A couple of brainstorm ideas for you emr flashbulbs. One. The
thumper is stablised so that one end hits first. It carries a
magnet that is driven back through a coil of wire by the impact.
This a homopolar generator that makes a big current, that is then
squashed as the tail of the thumper hits the surface. Problem
the current will take time to build up, and the impact will probably
be over before the emr pulse can be created.
Two. The thumper is a hollow light weight container. It is lined
with high temperature superconductor that is kept superconducting.
This forms a resonant uhf/microwave cavity with infinite Q.
While in orbit a microwave generator pumps microwave energy into
the chamber until the fields are just below vacuum breakdown.
Impact this on the Moon. The chamber and the RF fields will be
squashed and the energy dumped in one flash.
!
Personally I think the most sensible way to go is to start at
a collapsed lava tube and trace it from the surface until
you are suitably far from the collapsed part. For this a gravity
survey is probably the best way to go. A small robot rover could
zig-zag across the line of the tube making gravity anomily measurements
This would be slow but reliable and I am looking into the sensitivity
required.
--
Dave Stephenson
Frank Crary
Thomas L. Billings <it...@teleport.com> wrote:
>Karen was kind enough to reference my paper in JBIS on this subject during
>the thread from which this seems to have developed, but I've had some more
>thoughts since1990.
Even so, I have a question about the JBIS paper. You estimate
the signal to noise ratio for a VLBA radar survey, but the
equation you use doesn't seem to account for attenuation
as the radar pulse goes through the regolith. The only
possible place I can see is in radar cross section,
which you give as 50m x 50m x 1E-3. You don't mention where
the 1E-3 comes from, so it might be attenuation from
the regolith. But the Apollo radar experiments found a
50% reduction in power per four wavelengths of depth
into the regolith (Tyler and Howard, Journal of Geophysical
Research, v.78, p.4852, for meter wavelengths, and Phillips
et al., Proceedings of the Fourth Lunar Science Conference,
p. 2821, for 20 and 60 meter wavelengths.) A 1E-3
reduction would be consistent with a 40 wavelength
depth. But you state that the method would work for
as much as 200 meter depth (~300 wavelengths for the
wavelength you assume.) If the 1E-3 in the radar
cross section if from regolith attenuation, then
you are only accounting for a 30 meter depth. If
the 1E-3 comes from some other consideration, then,
by your estimates, you would reach a signal to
noise ratio of one at a depth of a bit over
two wavelengths, or about 2 meters.
>There is also a problem with geophones that I'm unhappily resigned to.
>Once again it has to do with frequency and resolution, and in addition,
>the state of cooled basalt. According to Steve Gillet, who has posted to
>s.s.p. in the past and worked with Oregon L-5's research Team in Bend,
>Oregon, when a flow of basalt cools, it cracks. It cracks a lot! Those
>cracks will cause signal/noise problems for short wavelength searches with
>sound that are far worse than they would be for EMR methods. Reflection
>of sound from a crack in vacuum would be total. I believe now that any
>wavelengths long enough to avoid attenuation by these cracks may well be
>so long that we won't get the resolution needed for even 500 meter tubes.
This might not be a problem. The thickness of the crack matters
much more than its width. Assuming the cracks are no wider
than a few centimeters (typical for terrestrial basalts)
then this wouldn't cause as much of a problem. It would
still cause problems. Larger cracks aren't common, but
they do exist, and range up to meters (these are usually
called faults, not cracks, but...) Also, there is a
projection effect: What matters isn't exactly the width
of the crack, it's the distance the seismic wave travels
in going through it. So a wave traveling nearly
parallel to the crack would have to go a long way
in crossing it. (I.e. the important distance is
w/sin(theta), where theta is the angle between the
wave's path and the direction of the crack, and
w is the width of the crack.) That might cause
reflection problems, even for a narrow crack.
>So, what would happen if we delivered, to the area near a suspected
>lavatube, a powerful EMR source of appropiate frequency, to make the
>object of desire more "cooperative". Good news! It could have close
>range penetrating power! It's equivalent equation to the radar equation
>should have only a 2nd power on the range coefficient, thus giving a much
>better s/n ratio! Bad News! It would cost like sin to set such a power
>source down on the lunar surface by soft landing! I remembered the
>"Thumpers"...
>Then I was reminded of homopolar generators. These are neat storage
>devices for energy that turn K.E., from gyroscopes on steroids, into
>monster electric currents. If we could do, just once and very fast, the
>same thing with the linear motion of a compressible impacting "Thumper"
>that homopolar generators do again and again with rotary motion, then we
>might just have a good source of EMR for a lunar EMR "flashbulb". At 2350
>meters/sec. that's a lot of ergs available for conversion into a really
>massive radar pulse!
It might work. But I've got a frequency problem. I'm not sure
how homopolar generators work, but just on a basic, mathematical
level, it's very hard to get a low frequency wave from a
short event. The even will produce waves of all frequencies,
but most of the energy is at frequencies higher than
1/t, where t is the duration of the event. You can play
some tricks to alter this somewhat, but not by much
(e.g. you can arrange things so that most of the energy
goes into some frequency which is below 1/t, or
so that more energy goes into higher frequencies.)
For a penetrator, the impact velocity is over 200 m/s
and the prentrator stops after traveling a meter or so.
So the impact would take about 5E-3 seconds and most of
the energy would go into 200 Hz and greater frequencies.
Now that I've typed that, I see that this would not
be a problem. You want energy in frequencies
energy would go into frequencies above 200 Hz,
and even if the impact were at 20,000 m/s, it's
still putting most of its energy into 20 kHz
and higher frequencies, which is fine. We're
talking about over 30 MHz or higher for Earth-based
measurements. Of course, there is an efficiency
problem. It's quite possible less than one part
in a thousand of the impact energy could be
converted to radio signals. But for a realistic
sized penetrator (of order 1 kg or more), and
a 5 km/s impact, the energy is of order 2.5
million Jules. Given the Earth-Moon distance,
about 1E-17 of that would reach an Earth-based
telescope (1 meter diameter), with inefficiencies
perhaps no more than 1E-20 or 1E-23 or something.
But astronomical radio gear can easily pick
up a 1 Jansky signal (1E-27 W/m^2/Hz) so this
would be a very detectable signal.
>Of course, the current pulse has to be converted into a properly modulated
>radar pulse and then directed down into the lunar crust, and all in 1/2350
>seconds if the "Thumper"'s linear compressive motion is about a meter
>long.
That might not be a problem. A very hot, vaporized material
_will_ generate strong radio signals, and send them out in
all directions. That's what produces static from lightning
or the EMP from nuclear blasts. Such an explosion has
a very wide bandwidth, the radio waves go out in all
directions, and the efficiency of producing radio waves
is very low. But an impactor could have energy to waste,
and still produce a detectable signal. You might want
a system as simple as a solid mass of an easily
ionized material (e.g. a cesium "bomb").
>As Jeff Greason has noted elsewhere, Oregon L-5 is still struggling with
>shoehorning a proper lavatube search of the massive Clementine data set
>into whatever private funding we might get.
This is totally irrelevant, but one question that occurred to
me reading your JBIS paper: Why do you think lava tube is
a single word?
Frank Crary
CU Boulder
Thomas L. Billings
Stephenson) wrote:
> Thomas L. Billings (it...@teleport.com) wrote:
SNIPPED all the build up to the "flashbulb concept"
> : Then I was reminded of homopolar generators.
If we could do, just once and very fast, the
> : same thing with the linear motion of a compressible impacting "Thumper"
> : that homopolar generators do again and again with rotary motion, then we
> : might just have a good source of EMR for a lunar EMR "flashbulb".
> : Of course, the current pulse has to be converted into a properly modulated
> : radar pulse and then directed down into the lunar crust, and all in 1/2350
> : seconds if the "Thumper"'s linear compressive motion is about a meter
> : long. So we may have the elements of a useful search system
> : for underground lunar phenomena, including lunar lavatubes most
> : prominently.
> A couple of brainstorm ideas for you emr flashbulbs. One. The
> thumper is stablised so that one end hits first. It carries a
> magnet that is driven back through a coil of wire by the impact.
> This a homopolar generator that makes a big current, that is then
> squashed as the tail of the thumper hits the surface. Problem
> the current will take time to build up, and the impact will probably
> be over before the emr pulse can be created.
This has generally been the concept I've tossed around, basically two
concentric cylinders, one of which strikes the ground first and is driven
down the axis of the other. The largest losses and delays of current
build-up I can remember from my old circuits courses would be from
inductance. The most I can think of is to balance this off with is a BIG
capacitance supplied by the types of lightweight capacitors developed at
Sandia for very fast circuits, like bomb triggers.
> Two. The thumper is a hollow light weight container. It is lined
> with high temperature superconductor that is kept superconducting.
> This forms a resonant uhf/microwave cavity with infinite Q.
> While in orbit a microwave generator pumps microwave energy into
> the chamber until the fields are just below vacuum breakdown.
> Impact this on the Moon. The chamber and the RF fields will be
> squashed and the energy dumped in one flash !
I had thought this sort of thing might be possible, but never got far
enough in EE courses to even get good concepts formed. Thanks for
confirming it's a possibility! Can anyone go into more details on this
sort of device?
> Personally I think the most sensible way to go is to start at
> a collapsed lava tube and trace it from the surface until
> you are suitably far from the collapsed part. For this a gravity
> survey is probably the best way to go. A small robot rover could
> zig-zag across the line of the tube making gravity anomily measurements
> This would be slow but reliable and I am looking into the sensitivity
> required.
>
While I remain skeptical about gravity( at least one member of the local
team still has hopes for it) the on-site cart or "rover" is certainly one
option even for GPR, since this is how much GPR is done on Earth. I just
don't think we'll get a budget for doing that anytime forseeable from
here. The payback in info about the next investment possibility per
dollar spent doesn't seem great enough for each lander mission. It seems
you'd need several to get a good survey of potential lavatube fields over
those areas of interest to people with further money to spend. It also
requires much time for each possible ite surveyed. It just requires a BIG
spender.
>
> --
> Dave Stephenson
> Geological Survey of Canada * BEWARE!
> Ottawa, Ontario, Canada *
> Internet: step...@ngis.geod.emr.ca *Bill Gates is lurking you!
Thanks again Dave!
Thomas L. Billings
Stephenson) wrote:
> Thomas L. Billings (it...@teleport.com) wrote:
SNIPPED all the build up to the "flashbulb concept"
> : Then I was reminded of homopolar generators.
If we could do, just once and very fast, the
> : same thing with the linear motion of a compressible impacting "Thumper"
> : that homopolar generators do again and again with rotary motion, then we
> : might just have a good source of EMR for a lunar EMR "flashbulb".
>
> : Of course, the current pulse has to be converted into a properly modulated
> : radar pulse and then directed down into the lunar crust, and all in 1/2350
> : seconds if the "Thumper"'s linear compressive motion is about a meter
> : long. Then the Thumper is splattered. That conversion part I'm not
> : enough of a radar engineer to work out yet. Still, I've been told in
> : passing by those who are experienced in that field that the idea sounds
> : "not-impossible". So we may have the elements of a useful search system
> : for underground lunar phenomena, including lunar lavatubes most
> : prominently.
>
> A couple of brainstorm ideas for you emr flashbulbs. One. The
> thumper is stablised so that one end hits first. It carries a
> magnet that is driven back through a coil of wire by the impact.
> This a homopolar generator that makes a big current, that is then
> squashed as the tail of the thumper hits the surface. Problem
> the current will take time to build up, and the impact will probably
> be over before the emr pulse can be created.
This has generally been the concept I've tossed around, basically two
concentric cylinders, one of which strikes the ground first and is driven
down the axis of the other. The largest losses and delays of current
build-up I can remember from my old circuits courses would be from
inductance. The most I can think of is to balance this off with is a BIG
capacitance supplied by the types of lightweight capacitors developed at
Sandia for very fast circuits, like bomb triggers.
> Two. The thumper is a hollow light weight container. It is lined
> with high temperature superconductor that is kept superconducting.
> This forms a resonant uhf/microwave cavity with infinite Q.
> While in orbit a microwave generator pumps microwave energy into
> the chamber until the fields are just below vacuum breakdown.
> Impact this on the Moon. The chamber and the RF fields will be
> squashed and the energy dumped in one flash !
I had thought this sort of thing might be possible, but never got far
enough in EE courses to even get good concepts formed. Thanks for
confirming it's a possibility! Can anyone go into more details on this
sort of device?
> Personally I think the most sensible way to go is to start at
> a collapsed lava tube and trace it from the surface until
> you are suitably far from the collapsed part. For this a gravity
> survey is probably the best way to go. A small robot rover could
> zig-zag across the line of the tube making gravity anomily measurements
> This would be slow but reliable and I am looking into the sensitivity
> required.
>
While I remain skeptical about gravity( at least one member of the local
team still has hopes for it) the on-site cart or "rover" is certainly one
option even for GPR, since this is how much GPR is done on Earth. I just
don't think we'll get a budget for doing that anytime forseeable from
here. The payback in info about the next investment possibility per
dollar spent doesn't seem great enough for each lander mission. It seems
you'd need several to get a good survey of potential lavatube fields over
those areas of interest to people with further money to spend. It also
requires much time for each possible ite surveyed. It just requires a BIG
spender.
>
> --
> Dave Stephenson
> Geological Survey of Canada * BEWARE!
> Ottawa, Ontario, Canada *
> Internet: step...@ngis.geod.emr.ca *Bill Gates is lurking you!
Thanks again Dave!
Frank Crary
Dave Stephenson <step...@ngis.geod.emr.ca> wrote:
>Personally I think the most sensible way to go is to start at
>a collapsed lava tube and trace it from the surface until
Agreed.
>...For this a gravity survey is probably the best way to go.
I don't think so. Collapsed tubes can be identified from
orbital images (with sufficient resolution, e.g. Clementine)
and might be traced for a sufficient distance from their
surface manifestations (if they are less than a tube
diameter or so deep.) If not, then the tube could be
traced by sending a rover up it from the collapse
point.
>...A small robot rover could
>zig-zag across the line of the tube making gravity anomily measurements
>This would be slow but reliable and I am looking into the sensitivity
>required.
I think it would be impractically slow. You are talking about
a surface survey, which is very different from the orbital
work we've discussed before. The rover would have to stop
to take a measurement, since traveling over the surface
produces vibrations which prevent gravity measurements.
The resolution, both horizontal and in depth, of the survey
would depend on the distance between stops. So we're talking
about stopping every hundred meters or so. That's as slow
as using seismic techniques to map out the area. If you're
looking for a completely uncollapsed tube, in would be
easier than seismic work, but for a partially collapsed
tube, I think you could do much better from remote sensing.
Frank Crary
CU Boulder
doyle@problem_with_inews_gateway_file
> In article <DLsoJ...@emr1.emr.ca>,
> Dave Stephenson <step...@ngis.geod.emr.ca> wrote:
> >a collapsed lava tube and trace it from the surface until
> Agreed.
> >...For this a gravity survey is probably the best way to go.
> I don't think so. Collapsed tubes can be identified from
> orbital images (with sufficient resolution, e.g. Clementine)
> and might be traced for a sufficient distance from their
> surface manifestations (if they are less than a tube
> diameter or so deep.) If not, then the tube could be
> traced by sending a rover up it from the collapse
> point.
A rover inside a lava tube would be difficult to communicate with.
> >...A small robot rover could
> >zig-zag across the line of the tube making gravity anomily measurements
> >This would be slow but reliable and I am looking into the sensitivity
> >required.
> I think it would be impractically slow. You are talking about
> a surface survey, which is very different from the orbital
> work we've discussed before. The rover would have to stop
> to take a measurement, since traveling over the surface
> produces vibrations which prevent gravity measurements.
> The resolution, both horizontal and in depth, of the survey
> would depend on the distance between stops. So we're talking
> about stopping every hundred meters or so. That's as slow
> as using seismic techniques to map out the area. If you're
> looking for a completely uncollapsed tube, in would be
> easier than seismic work, but for a partially collapsed
> tube, I think you could do much better from remote sensing.
I think a combination of techiques is the best way to search
for a lunar base site in a lava tube. Remote sensing to find
likely candiate sites and surface survey to the best site.
A radar and gravity survey from orbit and surface rovers
doing seismic and in tube surveys
will probably be the best way to go.
Allen Thomson
[snip]
>I think it would be impractically slow. You are talking about
>a surface survey, which is very different from the orbital
>work we've discussed before. The rover would have to stop
>to take a measurement, since traveling over the surface
>produces vibrations which prevent gravity measurements.
>The resolution, both horizontal and in depth, of the survey
>would depend on the distance between stops. So we're talking
>about stopping every hundred meters or so. That's as slow
>as using seismic techniques to map out the area. If you're
>looking for a completely uncollapsed tube, in would be
>easier than seismic work, but for a partially collapsed
>tube, I think you could do much better from remote sensing.
While I'm quite skeptical about the lunar base/lava tube business,
the idea of a fine-grained lunar gravity survey does have some appeal.
Gravimeters aren't big (I carried one around the Arizona desert one
summer), power requirements and data rates are low -- all in all,
it should be something a microrover could do nicely. Land several
on the lunar near side, set up a very modest ground station, and
let the data accumulate over the years. Far-side mapping would
require a store-and forward microsat in lunar polar orbit, but that
should be pretty cheap too.
Thomas L. Billings
fcr...@rintintin.Colorado.EDU (Frank Crary) wrote:
> In article <itsd1-25019...@ip-pdx20-60.teleport.com>,
> Thomas L. Billings <it...@teleport.com> wrote:
> Even so, I have a question about the JBIS paper. You estimate
> the signal to noise ratio for a VLBA radar survey, but the
> equation you use doesn't seem to account for attenuation
> as the radar pulse goes through the regolith. The only
> possible place I can see is in radar cross section,
> which you give as 50m x 50m x 1E-3. You don't mention where
> the 1E-3 comes from, so it might be attenuation from
> the regolith.
Indeed, in later study and contacts I came to regard this estimate as
being too optimistic. Don Campbell, from Cornel,l was one of the many
kind people who helped me and, among other things, he suggested this value
for the paper's presentation. It is quite possible that he would have
meant that 1E-3 value only as a representative one for computational
example, and I may have missed that point. By now I regard this lack,
(completely on my own part) as the greatest weakness of the paper. It is
part of why I'm so interested in high power EMR at the lunar surface these
days. With a big enough hammer...
> >So, what would happen if we delivered, to the area near a suspected
> >lavatube, a powerful EMR source of appropiate frequency, to make the
> >object of desire more "cooperative". Good news! It could have close
> >range penetrating power! It's equivalent equation to the radar equation
> >should have only a 2nd power on the range coefficient, thus giving a much
> >better s/n ratio! Bad News! It would cost like sin to set such a power
> >source down on the lunar surface by soft landing! I remembered the
> >"Thumpers"...
> >Then I was reminded of homopolar generators. These are neat storage
> >devices for energy that turn K.E., from gyroscopes on steroids, into
> >monster electric currents. If we could do, just once and very fast, the
> >same thing with the linear motion of a compressible impacting "Thumper"
> >that homopolar generators do again and again with rotary motion, then we
> >might just have a good source of EMR for a lunar EMR "flashbulb". At 2350
> >meters/sec. that's a lot of ergs available for conversion into a really
> >massive radar pulse!
It's quite possible less than one part
This would be very nice at that level of simplicity. Even with the lower
vaporization point of Cesium though, I would think the losses would leave
little energy actually in the EMR pulse. This would be even more the case
if the impactor merely accellerated to impact under lunar gravity, to
2.35km/sec. I had assumed that propulsion for greater terminal velocity
would cost more than the fanciest electronics.
Thus, I had hoped for efficient microwave power conversion and processing
of an electrical current pulse that would put more energy into a coherent
narrow bandwidth pulse. That's why I suggested the homopolar
generator-like device. Perhaps, however, a broader bandwidth will have
some desriable characteristics for analysis?
>
> This is totally irrelevant, but one question that occurred to
> me reading your JBIS paper: Why do you think lava tube is
> a single word?
>
> Frank Crary
> CU Boulder
Actually, this comes from a simple preference on the part of the Chair of
Oregon L-5's Research Team, Bryce Walden. One day, Bryce noticed with
annoyance the designation "pseudo-karst" for these wonderful formations we
had been tromping through. " There's nothing 'pseudo' about them!" , says
he. "We'll show 'em a proper name for a proper type of cave, a lavatube,
all in one word". Soon all of the team used it that way. And so it came
to be, best beloved...
Regards,