Starship concrete Mars landing pad

SpaceNut · 2021-11-16 20:45:45

Even if we land on an unprepared surface safe we will not have a stand for it to launch from mars as earth does and that means for the few seconds of thrust build up we will be blowing rocks about causing possible damage to the ship and engines of the starship that is being launched.

GW Johnson · 2021-11-17 16:33:08

We can talk about exposed rock deposits to use as landing fields, and maybe there's buried glaciers nearby, and maybe there's not. As I have often contended, ground truth still even today proves quite different from remote sensing results. Remote sensing is certainly wrong enough, often enough, not to risk lives upon.

As to the supposed rock units we might use for a landing platform, you have to consider exactly what the vast bulk of Mars really is, and how it got that way. The bedrock units are heavily cratered, and there's gobs of loose rubble from fines to building-sized blocks, scattered all over. Covering this in some places is aeolian deposits: dust and fine sand that that thin atmosphere can blow around. None of this stuff sticks together, it is too thoroughly dessicated after billions of years exposure to pressure too low for liquid water (or exposed ice) to be stable. "Loose fine sand" is going to be more common by far than any sort of imaginable duricrust.

This dust and sand is in aeolian motion all over Mars. We've seen the moving dunes in photos from orbit. One year your flat rock outcrop may be exposed, a year or two later, it may be under a sand dune. Look at what happens in the Sahara to get an idea how variable such exposures can be. It could conceivably change radically during the months of the voyage to Mars. And there's not one thing that can be done about that!

My point is that looking at some photo of what appears to be a flat rock outcrop and saying we will land there is a fool's errand quite likely to kill a crew. Simple as that. It's a fools errand exactly because of the sand and dust constantly moving about Mars.

Given that situation, which is quite distinct from the moon, it would behoove mission planners to simply resolve to cope with landing on a meter or more of soft fine sand covering up any rocks you thought might be at your landing site. Such regolith, whether it has cobbles dispersed in it or not, has a safe bearing pressure of 0.1 to 0.2 MPa, as best we can guess, because what it most closely resembles is the "soft fine sand" blowing around the Sahara.

None of the science missions has so far seen fit to run any soil bearing strength tests, on Mars or even on the moon. But we have been successful landing probes on both places, and manned landers on the moon, that more-or-less correspond to landing pad sizes and vehicle weights that produce pressures well under 0.1 MPa.

Static weight factored-up by 2 for the dynamics of not being dead still as you touch down, and by another 2 for an uneven-touchdown among your legs, is what you use for this calculation. You need no factors on the weight for a takeoff. But if refilled, that weight will be higher.

Spacex's Starship will probably mass around 230-250 metric tons at touchdown on Mars. That's a static weight of about 857 to 932 MN at 0.38 gee on Mars. Using the larger number, factored 2 for dynamics, and 2 for uneven touchdown, the transient force to support is 3.728 MN. At 0.1 MPa allowable bearing pressure (so as not to sink into the sand), that's 37.3 sq.m of landing pad area required, summed for all the landing legs!

It's even worse if you want to come home. The fully-refilled Starship with minimal cargo masses pretty close to 1370 metric tons, for a static weight on Mars of about 5.1 MN. It needs no factoring for takeoff. At the same 0.1 MPa, you need 51 sq.m of landing pad, or you risk uneven settlement and sinking-in as you refill.

Now that's just the facts of life. The numbers do not lie. Nor do the surface observations from the landers and rovers. If you were to find a suitable outcrop, the safe bearing load might by 10 times higher, or possibly more, if not too badly fractured. That gets you down to 5.1 sq.m of pads instead of 51. sq.m. Much better.

But you DO NOT know the rock is really that strong (no tests have EVER been run!!!), or that it won't be covered by a meter or more of sand and dust when you get there (windblown dunes may march slow, but they march rather inexorably)! THAT is my point!

It is possible that the aeolian deposits on Mars are stronger than the soft fine sand of a Saharan sand dune. I don't deny that. But, NO ONE KNOWS THAT!! The tests have NEVER been done! Plus, you can't assume that an outcrop exposed this year will not be covered next year.

You simply MUST be prepared to land on sand.

GW

Last edited by GW Johnson (2021-11-17 16:35:18)

tahanson43206 · 2021-11-18 08:19:04

It is time to bring this topic back into view ...

Recent posts by kbd512 and Calliban in the Ballistic Delivery topic appear to be showing the way toward delivery of supplies needed to make a concrete pad of whatever dimensions are required for safe landing and take-off of Starships.

The work is NOT going to be done by SpaceX, any more than the landing/launch pads on Earth are built by SpaceX. The work will be done by contractors who specialize in making concrete pads for customers. The implication that I take from the posts by kbd512 and Calliban is that a cannon ball sized object with a suitable ablative covering can slow down while travelling through the atmosphere of Mars, and then slow down gently when impacting a suitable sand dune of soft Martian dirt.

Extrapolating, because we have NO proof one way or the other (that I know about) I would expect that concrete mix could be packed inside a metal shell, in the proportions needed to make rebar out of the metal, and concrete mix out of the Martian rock rubble that can be made on site.

Water is the remaining component that would be needed, and a ground truth expedition would reveal locations where water is present and from which it can be extracted with feasible equipment to be soft landed from Earth.

(th)

SpaceNut · 2021-11-18 14:30:41

Direct delivery of cement mix already made sealed in the ballistics just waiting to be exposed to the heat of entry and then to have the shell break on contact makes the cement self disperse over the surface. Have a bag of water to burst on entry and then spin on entry would mix the concrete cement mixture. Sending several with in a give area would make the pad for a trial run.

SpaceNut · 2021-12-04 20:49:16

Elon Musk's SpaceX Building Starship Launch Pad for Mars, Moon Trips
SpaceX CEO Elon Musk tweets Saturday that the company has started construction on an orbital launch pad at the Kennedy Space Center in Florida for missions to the Moon and Mars.

SpaceX's ultimate goal is to launch an un-crewed mission to Mars in 2024 and a crewed mission to the planet in 2026. NASA confirmed that SpaceX is “within the rights of their lease agreement to make launch infrastructure improvements within the boundaries of the pad,” according to a CNBC report on Friday. The agency said that it is not providing funds for the Starship launchpad.

Seems that launching in Texas may not happen so a launch from Florida is a win...

SpaceNut · 2021-12-09 18:42:02

Calliban wrote:

From the discussions that have taken place elsewhere on this board, it will be challenging to even land a Starship on Mars without a preconstructed landing pad. We simply don't know enough about the load bearing capabilities of the regolith to be able to commit to a manned landing.
Maybe the first task will be to land a robot that can construct such a landing pad? Could it be controlled by a crew in orbit? Louis' idea of a stone stacking robot may turn out to be a good idea. Maybe even a number of robots - some to gather the rocks, some to transport them to the site, others to stack them and perhaps apply compacted soil between layers.
Teleoperation of these machines would be far more rapid and practicable, if they were controlled by a crew in Mars orbit, effectively in real time. It isn't an ideal situation having to wait in Mars orbit whilst we use machines to build a landing pad. But it appears to be the only solution to this problem. Could we build such a pad in 30 days? Is that possible?

That is exactly why we were putting together a Scouting Mars for Landing Sites mission sales pitch to have that knowledge.

Calliban · 2022-01-05 07:03:56

I remember some time back, someone (I believe Tom) referenced fibre reinforced ice as a structural material. Apparently, it was investigated as part of an initiative for building floating airstrips in WW2.

I was thinking about this material last night and it occurred to me that it is a good option for the first landing pad to be built on Mars. After the first mission, we will probably use layers of stone and compacted clay to build up landing pads. But the first Starship landing on Mars poses a chicken or egg problem. We need a landing pad with sufficient load bearing capability before the first starship can land.

Which brings me back to the fibre reinforced ice material. The Martian lower atmosphere contains small amounts of water vapour and much larger quantities can be released by heating soil. To build a landing pad without any human presence, we could ship to Mars an inflatable airbed, containing a 3 dimensional web of carbon fibres. This can be inflated into a flat pancake shape, by filling it with CO2 to a pressure of a few tens of mbar. To produce a landing pad, we then fill the airbed with water and let it freeze. The carbon fibres would gives the ice plenty of shear strength, so I am thinking we need a circular slab of ice, maybe 15m wide and 0.5m thick. That is about 88m3 of water ice, which requires 79m3 of water to fill.

Once frozen, the entire mat would be covered in Martian regolith to a depth of several inches, to keep the ice at the average diurnal temperature at that location. This ensures that the ice does not soften at peak day time temperatures. Allowing it to cool to -60°C or lower, will increase its strength. The layer of regolith also protects the ice from the heat of engine exhaust during landing.

There are several variations of this idea that could be used to produce a landing pad. We could fill the air bed with compressed liquid CO2 and let it freeze in much the same way. According to this reference, dry ice can have compressive strength of 20-30MPa.
https://agupubs.onlinelibrary.wiley.com … 19JE006217

This concept has the advantage that it is much easier to source CO2 on Mars than water. The Martian atmosphere contains about 14 grams of CO2 per cubic metre, but only about 2mg of water vapour. So to build a landing pad with water we would need to process 40 billion cubic metres of Martian air, vs only 6 million for dry ice. We could chill the interior of the air bed to beneath the CO2 freezing point and then flood it with liquid CO2, allowing it to freeze.

There are downsides to using dry ice. The first is that CO2 can only be liquid at pressure greater than 5.1 bar. So our airbed needs to be rated to at least that pressure. The second is that the structural integrity of the landing pad would rely upon active cooling. The advantages are than all we really need to produce liquid CO2 of Mars is a compression plant. Once the dry ice slab is formed and covered in regolith, a small heat pump can be used to cool it, dumping heat into the Martian night.

If the entire package can be crafted to weigh no more than a few hundred kg, then we might be able to deliver it to Mars without need for an expensive sky crane landing system. Just a parachute and a solid propellant rocket to reduce landing speed.

Last edited by Calliban (2022-01-05 07:59:56)

SpaceNut · 2022-01-05 19:16:06

If the bag we are using does not have a back side cushion to prevent sharp rocks of penetrating once mass is applied we are going to not be able to keep it stable from subliming away whether its water or co2 inside that we have frozen. For the top side we will also need a reflective coating to keep the day time sun from melting the frozen bags contents. I am assuming that the bag is with multiple pockets to allow for it be to be thick which seal-able layers.

Power will be a tough one as some will want solar while others know we need to have nuclear since the compressor will need to run for quite a period of time to fill the cavities such that we can get it to phase change from gas to liquid so that we can freeze it. Likewise going with one large compressing unit is asking for it to fail to fill.

SpaceNut · 2023-05-21 19:43:44

bump after seeing what happened to a concrete pad maybe the thermite would be better to make the soil into cast metal.

Calliban · 2023-05-24 01:51:37

This is interesting.
https://www.nextbigfuture.com/2023/05/i … ore-182993

Maybe the first landing pad can be a rolled out steel sheet on a bed of compacted regolith. Liquid CO2 could be pumped into the steel pad providing cooling as it changes phase and bleeds through holes on the surface of the sheet. Maybe gaps in the chain link surface could also serve as coolant bleed sites.

Last edited by Calliban (2023-05-24 01:52:37)

SpaceNut · 2024-08-24 16:54:00

Yes, this is from the moon topic of Void's but I believe it lessens the burden of suppling or creating materials for a mars landing pad for starship once created. As you can see a falcon can land on a minimal concrete landing pad even if you do not change the ships current Falcon 9.

The blue ring is the landing pad which means less materials are needed to make it. Of course, that does not change the need to go with a smaller ship design for constructing the first return to mars site for man.

Last edited by SpaceNut (2024-08-24 16:56:40)

tahanson43206 · 2024-08-24 17:11:39

For SpaceNut re #36

The proposal that Void created is for the Moon.

It is not as attractive for Mars, because of the presence of an atmosphere.

I know you don't have time to read every post by every member, so you may have missed GW Johnson's detailed analysis.

As a result of that analysis, GW has revised Void's idea for Mars. The alternative idea is to mount "toes" on the side of the rocket that look a lot like the landing legs for the Falcon 9. I'm pretty sure GW posted images showing what that would look like.

The landing "toes" would contain cargo, which would eliminate the need to unload cargo from the top of a rocket. They would also serve as actual braces for the rocket, so that it can remain vertical even if it lands on an inclined surface or if the surface is uneven.

If you can find time, you might find GW's posts interesting.

(th)

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#26 2021-11-16 20:45:45

Re: Starship concrete Mars landing pad

#27 2021-11-17 16:33:08

Re: Starship concrete Mars landing pad

#28 2021-11-18 08:19:04

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#29 2021-11-18 14:30:41

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#30 2021-12-04 20:49:16

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#31 2021-12-09 18:42:02

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#32 2022-01-05 07:03:56

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#33 2022-01-05 19:16:06

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#34 2023-05-21 19:43:44

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#35 2023-05-24 01:51:37

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#36 2024-08-24 16:54:00

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