New Mars Forums

Official discussion forum of The Mars Society and MarsNews.com

You are not logged in.

Announcement

Announcement: We've recently made changes to our user database and have removed inactive and spam users. If you can not login, please re-register.

#251 2019-06-01 11:38:04

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,768
Website

Re: Official MSL / Curiosity Rover Thread | Aug 5, 2012 10:31 p.m. PT

Metal matrix composites have the potential to be as strong and as energy-absorbing as straight wrought metals.  Dispersing aluminum oxide particles in cast aluminum is not the way to achieve that,  although a strength improvement over wrought aluminum is likely.  I doubt the elongation will be there with particle reinforcement instead of fiber reinforcement.  Woven fabric reinforcement is the approach that works best.  That would be aluminosilicate fire curtain fabric wetted with molten aluminum,  but I know of no products on the market like that to choose from.

Assuming particle-reinforced aluminum products cost no more than 316 stainless per what Kbd512 said just above,  then you are trading impact resistance for weight between the two.  The aluminum composite may be stronger than wrought aluminum,  but I very seriously doubt it has more impact resistance than a 300-series stainless.  Those stretch a really long way before they fail.  The integral under the stress-strain curve is huge,  especially in the annealed state,  which is EXACTLY what you want for impact resistance.

Since impact damage accumulates over time,  time is the deciding variable.  If you require only a short mission,  you can save a handful of pounds,  and use the aluminum composite tires.  They will hold up a little better than the wrought aluminum tires,  and be no heavier. 

But if you want a long mission,  you add the few pounds and use the stainless.  Then you get years out of your rover over any terrain, instead of just months even with route restrictions to avoid sharp rocks.

You get EXACTLY what you design for,  as well as what you pay for.  It would appear that nobody with any authority asked the "how long" question designing Curiosity.

That's a fundamental part of engineering design.  There's just more to it than just the bottom line of the weight statement,  or the $bottom $line of the item price tag. Inherent with constrained optimization. 

I used to see more folks in authority allowing for that,  but not so much anymore. Sad.

GW

Last edited by GW Johnson (2019-06-01 11:40:50)


GW Johnson
McGregor,  Texas

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

Offline

#252 2019-06-01 13:05:50

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Official MSL / Curiosity Rover Thread | Aug 5, 2012 10:31 p.m. PT

I do not think longevity was ever a question as when we look to spirit and opportunity these were for a 90 day mission that lasted way longer as they stayed functional. Most likely that was how curiousity was designed as well with thoughts that it might survive longer but not planning for it with design....
What I am not seeing is the lessons learned entering in with the next ones that are built for rover use.

Offline

#253 2019-06-02 11:15:26

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,768
Website

Re: Official MSL / Curiosity Rover Thread | Aug 5, 2012 10:31 p.m. PT

Spirit and Opportunity were designed with solar electric as power source,  with an expected lifetime of months to maybe a year or so.  They were also rather small, lowering the impact loads on wheels of any practical design. 

Curiosity is nuclear-powered,  with an expected lifetime of several years.  It is very much larger and heavier,  which greatly increases the impact loads on any conceivable wheel design.  Like the small rovers,  it also has 6 wheels. 

They got a lot of things right with Curiosity's design,  but they obviously screwed up the aluminum wheel design.  On the face of it,  I suspect that was just a design question they forgot to ask themselves.  And it would be someone outside their spacecraft design realm that would have the "right" answer. 

Having developed a piece of farm equipment that is a drag tool used on rocky land,  I know by hard knocks' experience that when you drag steel through rocks,  the rocks eventually win.  You make it big and heavy,  and the "eventually" part gets long enough to be practical.  Aluminum is right out.  So is titanium.  Neither has anything near the "engineering toughness" of a steel,  especially 300-series Austenitic stainless. Especially in the cold of Mars.

I doubt there is anyone at all at JPL with that kind of hard-knocks experience dealing with moving through and over rocks.  I was an aerospace engineer for 20 years in the industry,  and I didn't get that knowledge from anything I ever did in that career!  I got it on my home farmstead in rural Texas,  doing pasture improvement.  That's not aerospace,  it's agriculture.  But it is engineering.

Point is,  sometimes your best solutions to problems come from unlikely places you would never have imagined.  That's just life.

GW

Last edited by GW Johnson (2019-06-02 11:18:46)


GW Johnson
McGregor,  Texas

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

Offline

#254 2019-06-02 11:37:47

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

Re: Official MSL / Curiosity Rover Thread | Aug 5, 2012 10:31 p.m. PT

That is a very good thought.

I have some speculation on such probes, and Starship.  I will try to color inside the lines of reality though and hope to not "Put you out".

I have read some chatter, that the two actual Starships that are being built are intended to do sub-orbital testing, and then if possible an orbital launch.  It gets fuzzier after that.  They may not even try to bring them back.  This could explain why they look like sheets of metal pasted together with welding.  If they do not bring them back, then I wonder if they have any utility in orbit after that.  But that gets far off the track of what I want to actually talk about.  If they do that though then they can save solving the heat shield problem for later editions of the Starship.

If they do what is said in the previous paragraph, I guess it means that they don't mind expending the effort, as it will give them important test information, to base subsequent editions of the device on.  So test information may be worth the expenditure.

So, I have thought of several missions to Mars that might supply test information that may be of similar value, and may even justify sacrificing a Starship for.

Spirit, Opportunity, and Curiosity may be devices that can be replicated with some upgrades such as the wheels you have spoken of.  But for the most part, you would not have to re-invent the wheel.

So, I would suggest that a multitude of such probes could be conveyed to Mars by various methods also using a Starship.  The reason to do this would be to get "Ground Truth" from many locations on Mars.  This could be preferable to having humans scout out the planet from a Mars base.  I think humans at the Mars base will have their hands full just trying to make the base work.  The Starship in this case may not have a heat shield since it may be discarded into a solar orbit.

So, here are a few ideas for it:

1) Fully expendable Starship.  Starship does not ever land anywhere.  But it carries a bunch of these probes to Mars and releases them.  They each have to make their way through the atmosphere to the ground.  In this case, it may be possible to try to sterilize the probes.

2) Landing ship.  It would release the probes prior to landing, and they would be on their own, but it would land itself.  Perhaps with little or no cargo.  It's use on the surface after that might be extra living space at the base to be built.  It may not make sense to try to sterilize the probes, since the landing Starship would not be sterilized anyway.

*In #2, I can see the costs going down quite a lot.

3) A starship deploy of probes to Mars, and a return to Earth.  Heat shield desired.  Here it is not clear to me if enough propellants can be available.  It would have to get the probes offloaded to go to Mars.  Perhaps those probes would have some ion thrusters such as Starlink devices do, to trim their paths to what is wanted.  The Starship may after disposing of the probes, use a gravity swing around Mars, but would also likely need sufficient propellants to further put it's path to Earth.

As I have said, the purpose of these notions would be to allow people on Earth to explore Mars further, possibly locating resources, but for sure better defining what Mars is like.  Knowing more about Mars will make any effort to settle people on Mars would enhance the possibility of success in the effort.

And I guess to pull this off with so many probes, it would be necessary to upgrade communication abilities Earth<>Mars.

Done

Last edited by Void (2019-06-02 12:00:04)


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

Offline

#255 2019-08-05 21:45:14

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Official MSL / Curiosity Rover Thread | Aug 5, 2012 10:31 p.m. PT

This would explain the images in some parts of mars
An ancient Mars crater likely spawned a devastating mega-tsunami

Offline

#256 2019-08-06 19:01:46

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Official MSL / Curiosity Rover Thread | Aug 5, 2012 10:31 p.m. PT

Happy Birthday its been seven years.... time for a selfy
capture-26.jpg

Offline

#257 2019-08-11 21:12:56

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Official MSL / Curiosity Rover Thread | Aug 5, 2012 10:31 p.m. PT

Investigating past as well as present life will come in the viewing of mars clay... Investigating

Offline

#258 2019-10-07 21:17:03

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,892

Re: Official MSL / Curiosity Rover Thread | Aug 5, 2012 10:31 p.m. PT

Offline

Board footer

Powered by FluxBB