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#1 2020-01-10 18:06:22

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Keep It Simple, Stupid - and that's what the Starship does

The KISS Principle - Keep It Simply, Stupid - is definitely one to keep in mind.

Having read Apollo Mission - The Inside Story  one of the main take-home points is that multi modular missions, of the Apollo type, build in a  lot of potential error-risk points: module separation, multiple modules in play, descent and ascent modules etc. To a certain extent, as Apollo 13 showed, the USA were lucky. There were plenty of human errors, but none so critical as to cause mission failure or death. It was good fortune.

These sort of multi-modular missions seem to find favour with a lot of people here but I prefer Musk's KISS approach in having just one big rocket that goes straight from LEO to the Mars surface and then returns in one piece to Earth.

Of course with Space X's Mission architecture there are two points of complexity (a) initiall refuelling in LEO and (b) the refuelling process on Mars.  As for the first, well that is very low risk. The human pioneers will be in LEO and so, if something goes wrong, they can be rescued.  The second refuelling challenge is the one that adds complexity. But at least with refuelling on Mars, it is an extended process, probably spread out over as much as 500 sols. If something goes wrong, there's time to put it right.

There is the risk of a devastating explosion on Mars with a large rocket being refuelled but that must be far less of a risk in the oxygen-starved, near vacuum, atmosphere of Mars than on Earth.

With modular systems of the Apollo type you normally have a series of narrow windows within which to execute tasks, during which you either abort or "go". But of course if you make the wrong decision you either cause the whole mission to fail or, worse, potentially sign your own death warrant. These windows can be very short - down to tens of seconds.

So, for me it's preferable to "Keep It Simple" with a single stage rocket to the surface of Mars and back again.


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

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#2 2020-01-10 21:00:41

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,455
Website

Re: Keep It Simple, Stupid - and that's what the Starship does

Louis:

Simpler is more reliable,  yes.  But I disagree with your supposition that a rocket explosion on Mars might pose less of a risk because of the thin air. 

The thin carbon dioxide atmosphere of Mars has little to do with the explosion of a rocket. It's the same hazard there as here,  if not worse in some very significant ways. 

The rocket contains both fuel and oxidizer,  and in the proportion for essentially max energy release.  All that is required to create the explosion is to breach both the fuel tank and the oxidizer tank,  and provide some sparks or other fire (ionized species) for ignition,  if the propellants are not hypergolic. 

The thin atmosphere of Mars merely affects the distribution of shrapnel.  All the little bits follow essentially the same just-about parabolic but-high-supersonic trajectories as the big bits,  unlike here on Earth,  so the shrapnel problem is far worse than on Earth.  The blast wave is weaker than on Earth,  due to the low density.  In vacuum,  there is almost no blast wave at all.

There is a classic piece of movie footage from a failed V-2 launch about late 1943 or early 1944.  The rocket rose off the pad,  then fell back,  and fell over,  and exploded quite violently. 

Upon the V-2 smacking the ground and splitting the propellant tanks,  you can see a puddle of alcohol fuel spread from the forward fuel tank for a split second,  before the liquid oxygen from the aft tank reached it,  with the fire around the nozzle the ignition source.   Then,  kaboom! 

This had zero to do with 20.9% oxygen in the air. Or its pressure,  for that matter. It had everything to do with liquid oxygen reaching liquid fuel in the presence of an ignition source.  There are always vapors when liquids get free,  and it is the vapor reaction that starts the explosion.

Not so sure about liquid rocket explosions,  but solid rocket explosions usually produce shrapnel that leaves the scene of the crime at about 8000 ft/sec (independent of any atmospheric conditions,  or even the presence of an atmosphere at all). 

That's why the fragment impact test is spec'd at 8000 ft/sec. The liquids might be a different number,  but it would be in roughly the same ballpark. 

GW

Last edited by GW Johnson (2020-01-10 21:03:17)


GW Johnson
McGregor,  Texas

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

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#3 2020-01-10 21:57:28

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 28,832

Re: Keep It Simple, Stupid - and that's what the Starship does

The brute force solution of multiple landings of starship to do what can not be done in the first 100 mT is not a solution its what nasa had trouble with in Battlestar galatica mission designs. Each needing multiple lanchers to refill the ship is also an issue for going to mars. It just does not work for one let alone the sheer number of them to make the 5 go to mars. Then you have the power to refueling needs to be able to come home, the quantity of fuel to even get 1 ship home. Its not simple.

Information of past missions failure and success to mars.

A Novel Entry, Descent and Landing Architecture for Mars

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#4 2020-01-11 12:36:14

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Keep It Simple, Stupid - and that's what the Starship does

Many rocket explosions do seem to be caused by leakage into the external air - my thought was that that sort of risk would not be present on Mars.  I do understand that internal leakage or pressure events remain a real threat.

GW Johnson wrote:

Louis:

Simpler is more reliable,  yes.  But I disagree with your supposition that a rocket explosion on Mars might pose less of a risk because of the thin air. 

The thin carbon dioxide atmosphere of Mars has little to do with the explosion of a rocket. It's the same hazard there as here,  if not worse in some very significant ways. 

The rocket contains both fuel and oxidizer,  and in the proportion for essentially max energy release.  All that is required to create the explosion is to breach both the fuel tank and the oxidizer tank,  and provide some sparks or other fire (ionized species) for ignition,  if the propellants are not hypergolic. 

The thin atmosphere of Mars merely affects the distribution of shrapnel.  All the little bits follow essentially the same just-about parabolic but-high-supersonic trajectories as the big bits,  unlike here on Earth,  so the shrapnel problem is far worse than on Earth.  The blast wave is weaker than on Earth,  due to the low density.  In vacuum,  there is almost no blast wave at all.

There is a classic piece of movie footage from a failed V-2 launch about late 1943 or early 1944.  The rocket rose off the pad,  then fell back,  and fell over,  and exploded quite violently. 

Upon the V-2 smacking the ground and splitting the propellant tanks,  you can see a puddle of alcohol fuel spread from the forward fuel tank for a split second,  before the liquid oxygen from the aft tank reached it,  with the fire around the nozzle the ignition source.   Then,  kaboom! 

This had zero to do with 20.9% oxygen in the air. Or its pressure,  for that matter. It had everything to do with liquid oxygen reaching liquid fuel in the presence of an ignition source.  There are always vapors when liquids get free,  and it is the vapor reaction that starts the explosion.

Not so sure about liquid rocket explosions,  but solid rocket explosions usually produce shrapnel that leaves the scene of the crime at about 8000 ft/sec (independent of any atmospheric conditions,  or even the presence of an atmosphere at all). 

That's why the fragment impact test is spec'd at 8000 ft/sec. The liquids might be a different number,  but it would be in roughly the same ballpark. 

GW


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

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#5 2020-01-11 12:48:13

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Keep It Simple, Stupid - and that's what the Starship does

Well obviously not "simple" but certainly "simpler" I would say. Every time you have a module separation you require hundreds of things to go right. You need to train your crew how to handle the complex procedures.

Methane and oxygen manufacture will be challenging but certainly well within capabilities. It will be a long process, allowing for errors to be corrected. As for the actual refuelling of the craft, I don't know how complex that will be. Clearly safety will be a top priority.



SpaceNut wrote:

The brute force solution of multiple landings of starship to do what can not be done in the first 100 mT is not a solution its what nasa had trouble with in Battlestar galatica mission designs. Each needing multiple lanchers to refill the ship is also an issue for going to mars. It just does not work for one let alone the sheer number of them to make the 5 go to mars. Then you have the power to refueling needs to be able to come home, the quantity of fuel to even get 1 ship home. Its not simple.

Information of past missions failure and success to mars.

A Novel Entry, Descent and Landing Architecture for Mars


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

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#6 2021-04-03 11:15:26

tahanson43206
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Registered: 2018-04-27
Posts: 17,047

Re: Keep It Simple, Stupid - and that's what the Starship does

For Louis .... your topic is not about stupidity, but it ** does ** address those who respond to "stupid"

According to the article at the link below, the number of folks who you might be addressing appears to be astonishingly large ...

https://getpocket.com/explore/item/the- … ket-newtab

“Such change in the composition of the non-stupid population inevitably strengthens the destructive power of the [stupid] fraction and makes decline a certainty,” Cipolla concludes. “And the country goes to Hell.”

Corinne Purtill writes about culture, behavioral science, and management. Based at various times in Washington, D.C., Phnom Penh, New York, and London, she has written about everything from terrorism to the search for the Loch Ness Monster. She has a BA in English from Stanford University and reports now from southern California.

The professor whose work is quoted in the article at the link above is deceased, but his work lives on.

(th)

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#7 2021-04-03 11:32:38

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 28,832

Re: Keep It Simple, Stupid - and that's what the Starship does

While large mass to orbit is a simple solution its not so simple once its there as the complexity continues to increase with each required transport of fuels and other goods to make it work. Its that continued layer of complexity which does not make it simple.

One launch to destination is simple of which starships is a design for earth surface to orbit. Its multiple flavors of what remains in orbit makes them a version that is simple from there to the new destination but the complete package is made from those variations that make it no longer simple.

The version for the moon and for mars are also different as the requirements are different for how to land plus how to return and each destination has other layers of requirements that the delivered to earth orbit versions are needed in order to make each work with the unique destination requirements.

The on orbit versions for each destination also make the not so simple complexity of starship even greater.

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#8 2021-04-03 14:59:57

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,455
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Re: Keep It Simple, Stupid - and that's what the Starship does

Things are often not as "simple" as perceived.  That includes Spacex's "Starship".  It makes a pretty good design proposal for a transport to low Earth orbit.  That operation falls within its unrefueled capabilities.  But to get those capabilities,  you have to engineer both entry heat protection and terminal touchdown capabilities into what is otherwise just an upper stage pushing payload into orbit.  And you have to do it in a design capable of flying multiple times with minimal refurbishment between flights,  lest you lose all those advantages

Designs that can do all of that are NOT "simple".  Period!  Which is EXACTLY why all four prototypes so far flown have been lost to crashes,  post-landing fires-and-explosions,  or mid-air explosions. 

To go beyond low Earth orbit requires on-orbit refueling. With cryogenics,  not the storables the Russians have pioneered for ISS.  And which NASA (or anyone else) has NEVER YET done!   The number of refueling tanker flights is not trivial!  My numbers range from 4-5 tanker flights for a Mars mission flown at less-than-max propellant loadout and payload,  to ~8 tankers for a lunar landing flight,  at rather low delivered payload. 

To land such a craft on the moon or on Mars requires a rough-field capability that Spacex has yet to address,  at all!  So far,  their landing leg system designs,  whether Starship or Falcon core,  have ONLY landed on level,  smooth reinforced concrete pads,  or level-and-smooth hard steel decks! 

The moon and Mars require landings on what is essentially a soft sand dune,  and which is neither smooth nor level.   Even abort landings from orbit-only operations here on Earth have the same requirement.  Perhaps even soft mud landings!  I'm sorry,  but all those things are distinct possibilities!  Which makes them actually highly probable,  sooner or later.

Spacex's designs avoid the staging designs required of the Apollo LEM,  but at the cost of a far higher delivered Isp.  In turn,  that requires the most complicated rocket engine design ever attempted.  Anywhere in the world.  Period!  End of issue!  By definition,  not simple!

Docking two things together is not the most challenging thing to do anymore.  Apollo proved that,  although the initial feasibility was demonstrated earlier on Gemini.  It is still possible to screw that up,  as Boeing recently demonstrated with its CST design alternative to Dragon,  for manned missions to orbit.

Appearances are still quite deceiving,  Louis. 

GW


GW Johnson
McGregor,  Texas

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

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#9 2021-04-03 17:53:22

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Keep It Simple, Stupid - and that's what the Starship does

I think the recent Starship failures rather prove my point about the dangers of leaks into an oxygen rich atmosphere on Earth, compared with on Mars.

I think the rough field landing is the least of Space X's worries really. Likewise docking - I can't really see that being a problem when your car can park itself. Orbital refuelling will require some new tech but I think hasn't been done to date because it hasn't been needed.

The real issue seems to be the need to master regular safe landings. As far as I can tell Space X seem pretty good at getting the rockets up to 10Km and doing the necessary flip-over. It's after that the problems start. Is it because shutting off of or switching on an engine in an enclosed testing facility is a totally different proposition to shutting off and starting engines when you are plumetting towards Earth with all that turbulence and blow back?


GW Johnson wrote:

Things are often not as "simple" as perceived.  That includes Spacex's "Starship".  It makes a pretty good design proposal for a transport to low Earth orbit.  That operation falls within its unrefueled capabilities.  But to get those capabilities,  you have to engineer both entry heat protection and terminal touchdown capabilities into what is otherwise just an upper stage pushing payload into orbit.  And you have to do it in a design capable of flying multiple times with minimal refurbishment between flights,  lest you lose all those advantages

Designs that can do all of that are NOT "simple".  Period!  Which is EXACTLY why all four prototypes so far flown have been lost to crashes,  post-landing fires-and-explosions,  or mid-air explosions. 

To go beyond low Earth orbit requires on-orbit refueling. With cryogenics,  not the storables the Russians have pioneered for ISS.  And which NASA (or anyone else) has NEVER YET done!   The number of refueling tanker flights is not trivial!  My numbers range from 4-5 tanker flights for a Mars mission flown at less-than-max propellant loadout and payload,  to ~8 tankers for a lunar landing flight,  at rather low delivered payload. 

To land such a craft on the moon or on Mars requires a rough-field capability that Spacex has yet to address,  at all!  So far,  their landing leg system designs,  whether Starship or Falcon core,  have ONLY landed on level,  smooth reinforced concrete pads,  or level-and-smooth hard steel decks! 

The moon and Mars require landings on what is essentially a soft sand dune,  and which is neither smooth nor level.   Even abort landings from orbit-only operations here on Earth have the same requirement.  Perhaps even soft mud landings!  I'm sorry,  but all those things are distinct possibilities!  Which makes them actually highly probable,  sooner or later.

Spacex's designs avoid the staging designs required of the Apollo LEM,  but at the cost of a far higher delivered Isp.  In turn,  that requires the most complicated rocket engine design ever attempted.  Anywhere in the world.  Period!  End of issue!  By definition,  not simple!

Docking two things together is not the most challenging thing to do anymore.  Apollo proved that,  although the initial feasibility was demonstrated earlier on Gemini.  It is still possible to screw that up,  as Boeing recently demonstrated with its CST design alternative to Dragon,  for manned missions to orbit.

Appearances are still quite deceiving,  Louis. 

GW


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

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#10 2021-04-04 10:42:49

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,455
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Re: Keep It Simple, Stupid - and that's what the Starship does

If you get plumbing leaks of fuel,  you will eventually also get plumbing leaks of oxygen. So far,  the methane is far more prone to leaks than the oxygen,  but eventually you will have both.  And that's a recipe for a blowtorch followed quickly by an explosion,  even in the vacuum of space. 

So really,  it's not so much about air or not.  It's about leaks.  They must be stopped.  Could be plumbing lines,  control valves and similar components,  might even be cracks in welds or panels on the tanks.  Lots of possible sources,  and they all have to stopped. 

Why stopped?  Because Starship first and foremost,  is a transport from the surface of the Earth to low Earth orbit.  It HAS to operate in Earth's oxygenated atmosphere.  PERIOD.

And don't discount the rough field landing issue,  which Spacex has not addressed yet,  choosing instead to put it off and ignore it.  We'll likely see one of these miss the pad,  and come down in the mud or the shallows immediately adjacent,  in one of these flight tests. 

If they succeed in going operational with this thing (most certainly not yet a sure bet),  eventually one will have to make an emergency landing off-site.  On a sand beach.  In a plowed field.  In a swamp.  In the desert canyonlands.  In a scrub forest.  In the mountains. 

Somewhere not hard,  not flat,  not smooth.  It WILL happen! 

And nothing is as expensive as a dead crew.  Especially one dead because of a bad management decision.  Ask NASA,  they know. 3 times now.

GW

Last edited by GW Johnson (2021-04-04 10:51:37)


GW Johnson
McGregor,  Texas

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

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#11 2021-04-04 18:57:03

kbd512
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Registered: 2015-01-02
Posts: 7,416

Re: Keep It Simple, Stupid - and that's what the Starship does

louis wrote:

I think the recent Starship failures rather prove my point about the dangers of leaks into an oxygen rich atmosphere on Earth, compared with on Mars.

I think Starship's oxidizer tank is quite a bit richer in Oxygen than Earth's atmosphere.

louis wrote:

I think the rough field landing is the least of Space X's worries really. Likewise docking - I can't really see that being a problem when your car can park itself. Orbital refuelling will require some new tech but I think hasn't been done to date because it hasn't been needed.

I think soft-docking two multi-hundred ton spacecraft, in order to transfer fuel between them in a microgravity environment, may be a tad more complicated than your making it out to be.  When a car parks itself, it's moving in two dimensions and the other cars near it are typically stationary.  No such similar situation exists in LEO where these precision maneuvers are performed.

louis wrote:

The real issue seems to be the need to master regular safe landings. As far as I can tell Space X seem pretty good at getting the rockets up to 10Km and doing the necessary flip-over. It's after that the problems start. Is it because shutting off of or switching on an engine in an enclosed testing facility is a totally different proposition to shutting off and starting engines when you are plumetting towards Earth with all that turbulence and blow back?

SpaceX could literally put Starship's landing pads on a trio of dimes every single time, but if it's leaking fuel like a SR-71 afterwards, then chances are better than average that someone could have a really bad day.

In general, starting / stopping a rocket engine while gliding back to Earth like a brick is a very different proposition than starting / stopping one on the ground while the vehicle is stationary.  However, all of that becomes less of an issue when the vehicle in question isn't leaking fuel like a sieve.

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#12 2021-04-05 09:58:12

Oldfart1939
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Registered: 2016-11-26
Posts: 2,379

Re: Keep It Simple, Stupid - and that's what the Starship does

I disagree, re: rough field landings. That needs to be dealt with in a most expeditious manner before proceeding too much further. One issue I see is adequate ground clearance for the engines and the exhaust to escape without damaging the engines, as they discovered in the static fire testing and chunks of the landing pad being sent airborne. It's a simple Sophomore Statics problem about stability and having an adequate footprint defined by the leg contact points with the surface. Until they get real and address the landing leg design, they aren't going to either the Moon or Mars, landing and returning.

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#13 2021-04-05 14:31:24

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Keep It Simple, Stupid - and that's what the Starship does

I've suggested before this might be a mass problem.

The eventual Starship two stage vehicle will be lifted by something like 34 Raptor engines So I am guessing this 3 engine Starship is not designed to have a full rock-field landing leg system as that (with the battery activator) would add too much mass.

I am sure they are fully aware of the need to integrate a successful landing leg system.

Oldfart1939 wrote:

I disagree, re: rough field landings. That needs to be dealt with in a most expeditious manner before proceeding too much further. One issue I see is adequate ground clearance for the engines and the exhaust to escape without damaging the engines, as they discovered in the static fire testing and chunks of the landing pad being sent airborne. It's a simple Sophomore Statics problem about stability and having an adequate footprint defined by the leg contact points with the surface. Until they get real and address the landing leg design, they aren't going to either the Moon or Mars, landing and returning.


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

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#14 2021-04-05 15:38:54

kbd512
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Re: Keep It Simple, Stupid - and that's what the Starship does

Oldfart1939,

I don't think you can get enough ground clearance for engines that powerful, at least not a practical vehicle design.  In all probability, the engines, some portion of the lower tank structure, and landing gear, all need to be reinforced to handle accidental impacts from debris dislodged by the engines, to assure reliability in a rough field environment.

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#15 2021-04-05 16:36:44

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,379

Re: Keep It Simple, Stupid - and that's what the Starship does

kbd512-
That's why I believe that the lunar lander design would (and should) be considered for Mars as well as the moon.
The puller versus pusher designs have a long history, beginning with the early Robert Goddard rockets, and also with the Hermann Oberth and Werner von Braun designs in the 1930's. They were called "Repulsors."

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#16 2021-04-06 12:38:47

GW Johnson
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From: McGregor, Texas USA
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Posts: 5,455
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Re: Keep It Simple, Stupid - and that's what the Starship does

Actually,  given plume impact/spreading,  the thrown rock hazard to the landing spacecraft is low,  except for the landing legs themselves.  The risk to anything else adjacent is very,  very high. 

The debris more-or-less follows a fanned-out "apron" of high velocity gases oriented not horizontally 360-degrees around,  but angled upward a few degrees.  The debris pieces won't be moving at full gas speed,  but at a fair fraction of it,  which is quite high.  It will arc out there a very long ways.  Measured in kilometers,  not tens of meters.

That does assume the skirt is high enough off the surface to let the gas fan out like that.  If there is no gap under the skirt,  all bets are off.  Stupid is as stupid does.

GW

Last edited by GW Johnson (2021-04-06 12:40:00)


GW Johnson
McGregor,  Texas

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

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#17 2021-04-06 15:07:34

kbd512
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Registered: 2015-01-02
Posts: 7,416

Re: Keep It Simple, Stupid - and that's what the Starship does

That means the base needs to be located many kilometers away from the landing area to avoid being pelted with bits of rock, so motorized vehicles are a hard requirement, unless someone here thinks a handful of people are going to hand-cart 100 tons of supplies back to their base.  The habitats would be protected by regolith and bricks, but astronauts in the field, windows, external cameras or scientific instruments, vehicles in the open, communications antennas, solar panels, radiator panels, and electrical cables (although I suppose these would be buried), would all be very vulnerable to damage.  Beyond that, each landed Starship needs to give all others a very wide berth so they don't get pelted with rocks, unless someone here wants to determine how thin-walled pressure vessels react to dents.  I'd wager a minimum of 10km between ships and bases is prudent.  People who come to view the launches at KSC are kept 4 to 5 miles from the pad, for example.

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#18 2021-04-06 17:55:13

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 28,832

Re: Keep It Simple, Stupid - and that's what the Starship does

Land it near and elevator tunnel exit entrance and dumb waiter it to where it needs to go from the concrete pad....

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#19 2021-04-06 18:16:55

louis
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From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Keep It Simple, Stupid - and that's what the Starship does

Let's not get carried away. They won't be landing on literal rock fields. They will be landing on rock platform with a scattering of rocks and boulders. The big boulders will be identifiable from satellite photos and will probably be the basis used for an accurate pin pointing landing.

Remember Space X will be landing cargo ships 2 years in advance of humans landing. Assuming the cargo ships land OK, the human landing site can be surveyed. I suspect as well as having cameras on board the Starships there will very likely be robots sent out from the cargo ships to do up close reccy. It's even possible they might take to Mars a landing pad in the form of maybe square metre pads weighing perhaps 50 kgs per sq metre. The pads would comprise some very resistant, non flammable material but with some give on the underside to help flatten the overall landing area. Robots could assemble the sq metre pads into a 12 x 12 metre landing pad and lay out laser guidance instruments around the landing pad, as well as radio transponders. Total mass of the landing pad would be 7.2 tons.

Alternatively the robot(s) might simply move all rock and boulders out of the way of the landing point on a rock plaform.

GW Johnson wrote:

Actually,  given plume impact/spreading,  the thrown rock hazard to the landing spacecraft is low,  except for the landing legs themselves.  The risk to anything else adjacent is very,  very high. 

The debris more-or-less follows a fanned-out "apron" of high velocity gases oriented not horizontally 360-degrees around,  but angled upward a few degrees.  The debris pieces won't be moving at full gas speed,  but at a fair fraction of it,  which is quite high.  It will arc out there a very long ways.  Measured in kilometers,  not tens of meters.

That does assume the skirt is high enough off the surface to let the gas fan out like that.  If there is no gap under the skirt,  all bets are off.  Stupid is as stupid does.

GW


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

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#20 2021-04-06 19:52:37

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 28,832

Re: Keep It Simple, Stupid - and that's what the Starship does

You do realize the rocks that move are the size of a fist and smaller that it would not move a rock that is larger than a softball very far at all.

Reality is this is Mars

BB1fm2dV.img?h=598&w=799&m=6&q=60&o=f&l=f


Not far from this is the other mars which is rugged

BB1fn2Pg.img?h=474&w=634&m=6&q=60&o=f&l=f

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#21 2021-04-07 21:01:18

GW Johnson
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From: McGregor, Texas USA
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Posts: 5,455
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Re: Keep It Simple, Stupid - and that's what the Starship does

The Apollo LM had its descent engine bell lip about 1-2 exit diameters off the surface.  That worked just fine.  You can see the particles being blown in the fan of expanding exhaust gases,  in the landing films.  You can also see the 1-inch landing pad penetration into lunar regolith.  At VERY LOW applied bearing pressures!

It's not like nobody has ever faced this problem before.  Every probe that has landed on Mars has faced the same problem,  except the two airbag bounce landers.  There's no fundamental problem with an engine bell close to the surface,  other than debris impact to the landing legs.  That and regolith accumulations on top of the landing pads (something Armstrong noticed on the moon).

What you see in the photos from Mars is not quite like the moon,  but it is still close in many ways.  What you see is loose regolith.  That is,  a mix of loose sands and loose rocks of various sizes.  There is much particulate matter,  and some rather significant chunks of rock,  to be blow around by the expanding fan-shaped plume. 

There is also,  in most locations,  large boulders to get in the way.  Just like what Armstrong had to avoid when he landed on the moon. 

And almost NONE of the Mars photos show flat,  solid rock!  Which is EXACTLY why I said (more than once) that 98+% of the Martian surface is loose,  soft sand mixed with loose gravel and cobbles,  usually nowhere near "flat" or "level",  and certainly NOTHING AT ALL like a concrete landing pad or steel deck.  It has a very low allowable bearing strength,  and it offers 5+ degree slopes very frequently.

That last is something Spacex has so far refused to address with its landing leg designs,  not Starship,  and not Falcon. The only surfaces they have ever landed ANYTHING on,  are level reinforced concrete pads,  and steel decks on ships.  When the sea is not too rough.

GW


GW Johnson
McGregor,  Texas

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

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