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#176 2019-05-21 16:59:09

From: New Hampshire
Registered: 2004-07-22
Posts: 16,139

Re: Lunar economics etc

Sorry to hear that GW, I hope all will be well..

I tried as well to point the image issue but had not covered anything for radar as thats not going to be able to tell much as I do not believe we can get that sort of depth measurements and then look even deeper with each pass of the probe over head so as to create a void detection let alone tell if its solid or soft....


#177 2019-05-21 21:17:01

Registered: 2015-01-02
Posts: 2,957

Re: Lunar economics etc


I hope you're feeling better now.


#178 2019-05-22 04:31:19

From: UK
Registered: 2008-03-24
Posts: 4,896

Re: Lunar economics etc

Hi GW,

Sorry to hear you've been in hospital. Hope you are feeling much better.

Regarding knowledge of the surface, my understanding is that by various other methods (in addition to photography), including radar and spectrometers, NASA and ESA have been (through their orbiting satellites) acquiring pretty detailed knowledge of the surface.  For instance, I think they can ascertain if a rock platform is many metres thick or not. 

It's true that no one can be 100% sure until a landing takes place but the beauty of Space X's mission architecture is you send cargo craft first before humans arrive in the area.

Obviously I don't have specific technical knowledge... I am just going on what I have read about landing site selection in particular via this very helpful link: … entations/

I was surprised at just how detailed the knowledge of potential landing sites is. I presume they are looking for a granite-style rock platform that isn't going to sink at all under the weight of a 1000 ton fuelled rocket.

So I think the takeaway points are:

- There are rock platforms that could serve as landing areas.

- We can be assured they aren't going to crumble on impact.

- We can be assured what the gradient is and so select a less than 5% gradient site in line with NASA requirements.

- We can send cargo craft first to Mars and thereby test the actual landing site conditions to a very high degree of confidence.

My view is that the propellant production and a possible need for rocket refurbishment (the latter rarely gets addressed) is far more challenging than the landing or take-off on Mars.

I get the impression that the lunar surface is more challenging for landing and take off than for Mars.  So not sure how that plays out.

GW Johnson wrote:

In one of the other threads,  Louis was talking about 6 cm resolution capability,  which I presume is photography from one of the orbiting probes at Mars.  He was trying to make a case that this "proves" there are safe places to land a Spacex Starship,  with its current landing pad design sizing. 

That's a very impressive photographic resolution,  but photography is of the surface,  and says absolutely nothing about what's beneath.  Given the current state of humanity's technologies,  the ONLY way to find out what's beneath the Martian surface is real ground truth.  You have to go there and dig or drill.

His other point was based on some kind of definitional argument.  Something about landforms being classified as "exposed rock platforms".  Trouble with that is,  anything definitional is just a best guess based on surface appearances.  Ground truth trumps all.  Best to be prepared to land in soft sand,  which a lot of Mars seems to be.  Then you can land anywhere,  and not be restricted by local soil types.

For the Spacex Starship design,  touchdown is less of a problem than re-launch after refilling.  The refilled weight,  even on Mars,  is about 6 times the touchdown weight.  You don't want it sinking into the dirt (and tipping over),  while you refill it with propellants.

I've got those numbers posted over at "exrocketman" some time ago,  along with a listing of various Earthly soil strengths I got out of an older edition Marks' Mechanical Engineer's Handbook.  Doesn't matter that it's an old reference.  Those numbers haven't changed in over a century.


Last edited by louis (2019-05-22 06:25:05)

Let's Go to Mars...Google on: Fast Track to Mars


#179 2019-05-22 10:07:04

GW Johnson
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,643

Re: Lunar economics etc

I forgot about ground-penetrating radar.  The resolution is far poorer,  because resolution is inherently related to wavelength,  but it ought to be capable of distinguishing a "thin" layer of rock from a "thick" layer of rock.  May not be able to tell busted boulders laying together from solid rock,  though.  Quite a difference in strength there,  at the larger weight-to-be-supported scale. I'm no electromagnetics expert,  so I dunno,  myself.  Just what I read.

Hospital stay was for something resembling a mini-stroke,  but imaging showed no damage,  so it's not classified as such.  I got classified in the grab bag bin:  they don't know what it was,  how it worked,  or what causes it.  It seems to be rare,  though,  and the recurrence rate is low,  too.  There's just 2 hours missing from my life,  and I'm told I was awake and talking,  and absorbing no new info,  that whole 2-hour time. Been normal ever since I came out of that 2-hour gap. 

Got home from the hospital Monday evening,  and Tuesday went back to ER with something I never had before.  I got stung by a wasp,  and had the potentially-fatal reaction to it.  Still recovering from that today,  but I'm gonna be OK.  Must carry the Benadryl-etc "kit" from now on,  though.


Last edited by GW Johnson (2019-05-22 10:09:54)

GW Johnson
McGregor,  Texas

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


#180 2019-05-22 11:23:00

Registered: 2011-12-29
Posts: 3,011

Re: Lunar economics etc

GW, very happy for your recovery.  Also I will express thanks for the work you do to keep us honest about what can and cannot work.

Earth and Moon from a "synestia": … heory.html
Moon from magma ocean splash: … gma-ocean/
Earth's water from outer solar system: … earth.html
Notion of how water forms on the Moon.  First, solar wind embeds Hydrogen, then impactors impart enough energy, to cook up water from the Hydrogen, and Oxides in the regolith:

I think the information may be interesting to the members.  It also suggests that going to the Moon to get more "Ground Facts" is justified even for space haters, as if we know more about the Moon, we may well then understand our home planet better, and that is a thing of value.

The last link suggests that the Moon may have a relatively constant flow of water formation, in most or all of the regolith.  First Hydroxyl being formed and bonded to minerals as I understand it, and then actual water being formed and going into the Lunar atmosphere.  Then some of that water, we now think gets captured to some of the polar shadowed craters.

So, up to a point, it may be a renewed resource for our utilization.  We don't yet know how much we can take to conserve it for our long term needs.

So going to the Moon is quite justified in my opinion.

I will otherwise leave you and the other members alone on this topic.


Oh, I lied.  I also wonder about solar wind impacting the atmospheres of Venus and Mars, and perhaps creating water.  We typically assume that the water of Venus and Mars was all put there early on, and that the loss of Hydrogen, left a heavy Hydrogen concentration.  But I am not completely sure about that.  There may be a water cycle where Sun Hydrogen>Atmosphere>Hydrogen off to space.  That also being able to concentrate heavy Hydrogen.

But not proven, not even properly examined yet.

Now I promise, I am done.

Last edited by Void (2019-05-22 11:34:36)

I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.


#181 2019-06-04 21:55:04

From: New Hampshire
Registered: 2004-07-22
Posts: 16,139

Re: Lunar economics etc

We should probably know the answers to these Five ethical questions for how we choose to use the Moon



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