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#26 2018-07-29 19:25:32

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Key Debates

Very much a chicken and egg situation I think, GW.  Because Space X are sending a big BFR to Mars, they need to put in place propellant production - they can't just drop 1000 tonnes of propellant to the surface! So that will certainly dominate what is done on Mission One if Space X succeed in taking their project forward...but on the other hand the fact that they can deliver so much tonnage to the surface from the get-go means they have a lot of flexibility about what they might attempt on Mission One - a whole range of scientific experiments, some initial hydroponic agriculture, some rover exploration, use of rocket hoppers etc. 

GW Johnson wrote:

To answer Spacenut in post 22:  it depends upon what resources you think you need while you are there.  Could be ice,  could be a lot more.

To answer RobertDyck in #23 and Spacenut in #24:  What I pointed out was that your mission architecture and vehicle designs are utterly driven by what you intend to accomplish while you are there.  This is further constrained by the expense and difficulty of even making just one trip. 

What that really means is that "what you intend to do while there" REALLY IS a fundamental debate item!  It's probably the prerequisite for all the others!

GW


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

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#27 2018-07-29 20:17:09

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Key Debates

Louis,

You have to hand wave a lot of fundamental problems with the BFR / BFS to believe that this idea will work without extensive testing and development, and likely modification to deal with reality.  Apart from supersonic retro-propulsion and reuse of rocket boosters, there's been very little of that to date.  Is it possible that all of that will work without any snags?  Sure.  From all past space exploration and aerospace technology development endeavors, how likely is that to happen?  Name off a significant multi-disciplinary technology development program where everything went according to plan.

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#28 2018-07-29 20:22:39

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,701

Re: Key Debates

Lious your post for BFR really is the post 1 indicated 1, 5, 7, 10, 11 for hopes and dreams but we agree on that we should be going to mars.

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#29 2018-07-30 19:11:17

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,701

Re: Key Debates

I do believe that scale of size is an issue as we are still no closer to being able to land 1 person and returning versus  any number in between that of a cool 100 that a projected BFR would be plausible to do.

Solve the equations for 1 or 2 crewmen and lets go to mars to continue to push us outward to other places and not just mars.

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#30 2018-10-08 21:23:27

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,701

Re: Key Debates

How quickly the popes of mars have not returned to the topic as Void had describe the thoughts with in it....

We know that it takes for 1 BFR loaded with up to 150 tonnes of good 6 more to get it on its way to mars. Thay it will take for a mars cycle 2 years 7 weeks before another can be launched if they can not load up another in orbit with in a 30 day window of BFR launches. With yet another BFR for a crew to go and be the first to land after 6 more launches. Giving a total of BFR to get 3 going to mars of 21 launches in that 30 days.
Now once on mars we will need to not only get all the gear out of the 2 BFR's to the ground before doing any science. Initial setup of Solar power fields are a must since its packed so high off the ground. Starting the insitu refueling plant is next to setup and get running as well as the oxygen generation system as well. These are all very time consuming items.

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#31 2018-10-09 06:14:53

kbd512
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Registered: 2015-01-02
Posts: 1,977

Re: Key Debates

SpaceNut,

You're pointing out some of the obvious operational issues that will arise with the "as-is" BFS concept.  Nobody has answered any of these questions because nobody has any clue about how to go about doing it and that's pretty obvious now.  We have ideas about what might work, but we also have basic physics which overrides all fanciful notions we may have of what might work.  One can be as "optimistic" as the day is long, yet simple physics will continue to beat them mercilessly about the head until the pain is so great that the problem mandates a realistic solution.  The engineers at SpaceX have zero experience landing a telephone pole on anything besides a concrete or steel pad and it shows.  When I see a booster land on sand dune somewhere, I'll become a "true believer".  Until I see that kind of booster landing, I've already seen enough military aircraft crash land in places where the terrain was not suitable for landing to believe that that problem has been solved.

Physics doesn't care if you think a 150 foot tall ship with a pair of M1 tanks as the payload can be successfully landed in a vertical attitude on rough terrain using narrow track landing gear.  It doesn't matter if your name is Elon Musk or Joe Blow, the problems GW and others have pointed out aren't going away.  They require engineering solutions because they're real problems that wishful thinking won't overcome, at all or ever.  The BFS is too tall and the landing gear too narrow to reliably land on rough terrain and that's a cold hard engineering fact.

If you can't reliably land BFS anywhere but a concrete or steel pad, worrying about how quickly you can unpack the cargo is a pointless exercise when the goal is to land on a planet that clearly lacks anything resembling a prepared landing pad.

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#32 2018-10-09 07:12:34

tahanson43206
Member
Registered: 2018-04-27
Posts: 20

Re: Key Debates

For kbd512 in #31:

Your observations in this message reminded me (for some reason) of the physics of ice, and specifically of an artificial ice rink.

There may not be enough water available on Mars to make a landing platform, but if there is, water ice has demonstrated strength sufficient to hold large structures against the force of gravity, or to demolish large structures, for that matter. 

Due to sublimation, such a landing platform would have a limited lifetime, but that might not be a problem if the first payload is a load of concrete and the equipment to mix and set it.

(th)

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#33 2018-10-09 07:35:52

Belter
Member
Registered: 2018-09-13
Posts: 144

Re: Key Debates

There needs to be a 1-way BFR-DS [for drop ship].    Which means the forward section is a lander, the current engine section merely a second detachable stage.  The second stage gets the lander to Mars, burns its remaining fuel to slow down, then detaches.  The second stage would attempt an aerobrake orbit, but it disposable.  The lander would drop directly to Mars surface and would be able to detach its engines or even have them lift off and crash land.    The lower itself to the ground to off load cargo or be used as a habitat.    If a BFS started to fall over, the "holy shit" moment for the crew would be horrifying.    The thing is going to be not just narrow, but top-heavy.    So, unless Musk can also demonstrate robots that can convert regolith into concrete platforms on the surface, or at the very least scout accidentally ideal landing spots that are rigid and roughly flat.........

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#34 2018-10-09 07:57:13

kbd512
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Registered: 2015-01-02
Posts: 1,977

Re: Key Debates

tahanson43206,

I'm not saying there's no places on Mars where a BFS could potentially land.  There are thousands of places that are reasonably flat that can also support the weight of the ship without shifting under load.  There's just one critical problem with that methodology.  You have to know exactly which sites are suitable and then you have to land on the exact spots where ground conditions permit.  That can only be accomplished with ground-testing and precision landing capabilities.  There's sub-orbital velocity precision using a fully operational GPS constellation to assist in that task and then there's hitting a moving target tens of millions of miles away at interplanetary transfer velocity precision without the use of GPS.  That latter is completely unlike the former in more ways than one.  And yes, there are other ways to lick the problem, most notably radio beacons to mark the landing area...  That we still don't have on Mars.  Fixable?  Sure.  With a few billion dollars, I'm sure JPL can get a rover to the candidate landing area with the required equipment.

The US Air Force accomplishes that critical testing task with a special ground compaction test set.  It's little more than a probe and grey box with electronics that gives a "go" / "no-go" indication based upon the expected landing weight of the aircraft in question.  If they want to land something like a C-130 on something other than a runway, for example, then they send a guy or gal out with the test set and repeatedly shove it into the ground at the selected landing area to prove, rather than guess at, what the load carrying capacity of the soil actually is.  The same thing needs to be done on Mars, but we lack the scout transport capability to get that forward air controller to his or her candidate test site.

Furthermore, we (meaning all of humanity, in general, and NASA, specifically, since their Mars landing capabilities are the most accurate demonstrated to date) can't accurately land (hundreds of meters, versus several kilometers) a spacecraft coming in at interplanetary transfer velocity due to the variability of the atmosphere and lack of sufficiently precise guidance.  Obviously a completely propulsive landing will help a bit with landing precision since more control is afforded over where the exact landing is made, but is that something you're going to bet billions of dollars on and the lives of a half dozen or more irreplaceable astronauts (unless someone out there really is naive enough to believe that a bunch of amateurs are going to make the initial landings and play "house" on Mars)?

Oversimplifying the problem doesn't change the nature of the problem or make it go away.  No amount of cheap talk will fix it, either.  NASA isn't serious about sending humans to Mars unless they rectify those very real problems and probably dozens of other problems I've never thought about.  Then again, neither is anyone else.  PowerPoint presentations and CGI aren't an acceptable substitute for solid engineering.

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#35 2018-10-09 09:35:08

tahanson43206
Member
Registered: 2018-04-27
Posts: 20

Re: Key Debates

For kbd512 #34 .... the next opportunity for "guys and gals" to pound some stakes is coming up:
Begin Quotation:
From Google:
NASA Launch Schedule | Rocket Launches
https://www.nasa.gov/launchschedule
Date: November 26, 2018. Mission: InSight Landing on Mars. Description: The Entry, Descent and Landing phase is the final plunge of the Mars InSight Lander ...
End Quotation.
(th)

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#36 2018-10-09 10:12:15

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Key Debates

tahanson43206,

Some of us are eagerly awaiting the landing associated with that mission, but what it's going to tell us, we hope, is what the overall geology of the planet is like.  To identify and certify a specific landing area for BFS, it needs to be free of any significant obstructions and hard enough to support many tens of tons of lander weight.  We need a different hardware set to do that.  Even so, InSight should tell us a lot about where the best water deposits are and what kind of tectonic activity we're up against, if any.  My basic thought process, as it relates to Mars exploration, is that more is better.  However, we need to start setting a series of incremental missions that set the stage for a human landing.

I'd like to see:

1. a high-power and high-resolution millimetric wave radar, laser, and IR imager equipped replacement for MRO, sufficient to function as a weather satellite
2. ISPP demonstrator
3. GPS constellation with laser and radio communications capabilities
4. robotic scout lander demonstrator
5. interplanetary transport vehicle demonstrator (Earth to lunar orbit and back, over a realistic mission timeframe)
6. initial crewed scouting missions
7. initial Mars colonist landings at a previously identified location suitable for sustainment of human life

That sequence of missions and hardware build-up in preparation for crewed missions seems like a logical progression of capability demonstration to significantly reduce risks associated with crewed missions so far from home.  Everyone else seems to want to charge into the unknown, ignoring all the fundamental problems that will inevitably be encountered along the way.  I don't think that's a recipe for success, but opinions on the matter clearly vary.  I think it's a bad case of "get-there-itis" because we've been goofing off for so long.

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#37 2018-10-09 10:28:09

Belter
Member
Registered: 2018-09-13
Posts: 144

Re: Key Debates

Last I checked, Space X is creating 1 kg of methane per day with its test equipment.  3 orders of magnitude from where it needs to be.

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#38 2018-10-09 10:33:05

spacetechsforum
Member
Registered: 2018-08-18
Posts: 32

Re: Key Debates

Belter, I had the same idea for one-way cargo transportation to Mars and I did some calculations and simple model.

Here are the calculations for reference:
http://spacetechs.ovh/myfiles/Calculati … 9_2018.ods

During this work I realised that there is a lot better way to deliver cargo to Mars surface (I did not update the calculations yet). It goes like this:
1. There is a lander with cargo in LEO.
2. You attach big tank with engines and control unit.
3. You do the burn into Hoffman.
4. When you reach the Mars you are on direct reentry trajectory (some small correction may be needed but that is not a problem) .
5. You detach the lander - the cargo stays on reentry trajectory and lands.
6. Meanwhile the tank-engine section do a small burn that lifts the periphrasis above the atmosphere - now you are on hyperbolic trajectory (ref. Mars).
7. You fly by the Mars - you are on elliptical Sun orbit that crosses Mars and Earth orbits  - another burn is needed to adjust timing to hit Earth atmosphere and try aerobrake.

I think that this is the best setup for dead cargo delivery to Mars - no matter the engine type.

The biggest advantage of this approach is that there is a very few critical failure points to lose cargo. You can do a full maintenance and check in orbit - then you do a single (or staged) burn into Hoffman (first potential failure), detach the cargo (can this fail? - not likely i think) and finally reentry (second possible failure point). If this succeeds (and i cannot image a solution that does not have those failure points) the cargo is in place, so even if the very hard maneuver of aerobrake fails you loose only the empty ship and the colony is still successfully resupplied.

Sorry tahanson, the ice platform idea seems naive. Wont it melt from engine work? How would you protect it?

Seriously i cannot image any way to evaluate landing options. I was doing lately the calculations linked above and I do not know the subject very well. Are yours opinions based on any data? Do we have any ground parameters? Cross-section maybe? - (this is actually quite important) Also - keep in mind that if we are talking concrete and dynamic load - reinforcement with steel bars is also needed.

Last edited by spacetechsforum (2018-10-09 10:34:44)

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#39 2018-10-09 12:33:25

tahanson43206
Member
Registered: 2018-04-27
Posts: 20

Re: Key Debates

For spacetechsforum #38

Thanks for the evaluation << grin >>

In the winter, when lakes and rivers freeze over, heavy freight shipments are enabled for delivery to Northern Canada.  There is a television series broadcast on the Weather Channel (in the US) showing the travails of drivers who undertake the journey.  The risks of driving across frozen bodies of water are emphasized for dramatic effect.  Never-the-less, it is apparent that ice only a few inches (half a meter) thick can support massive loads.

I remembered that there was an interest in building an aircraft landing zone out of ice in World War II, and fortunately Mr. Google fetched the specifics:
https://www.tms.org/pubs/journals/JOM/9 … -9902.html

While the "aircraft carrier" was never built, the research yielded a material which was (and still is) as strong as concrete.

I think your question about ablation of the surface of an ice platform under rocket thrust during landing is interesting and worth testing, if the idea of using water to create a solid landing platform catches on.  My impression (from ordinary experience with ice) is that the exhaust of a rocket would heat the water directly under the nozzle, with almost no effect whatsoever beyond the immediate area.  Testing this concept on Earth is possible.  An advantage of using water to create a temporary landing platform is that most of the water can be recovered and reused for other purposes, such as a permanent concrete pad.

While I agree that steel reinforcement is highly desirable for a permanent concrete landing pad, it seems (to me at least) to be an enhancement that can be added when steel mills are up and running on Mars.

Thanks again for noting the suggestion.

(th)

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#40 2018-10-09 12:48:35

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Key Debates

Surely putting stuff into LEO is not dependent on the Mars launch window of 30 days: don't you just have to ensure the Mars-bound BFRs are ready to go within the 30 days launch window. So I think the 21 launches could take place over a longer period - maybe 3 months.  1 or 2 launches per week sounds doable then.

The initial power requirement will be relatively low before propellant production starts.  Automated mobile PV units with integral chemical batteries could provide that power before the major solar power fields are set up.



SpaceNut wrote:

How quickly the popes of mars have not returned to the topic as Void had describe the thoughts with in it....

We know that it takes for 1 BFR loaded with up to 150 tonnes of good 6 more to get it on its way to mars. Thay it will take for a mars cycle 2 years 7 weeks before another can be launched if they can not load up another in orbit with in a 30 day window of BFR launches. With yet another BFR for a crew to go and be the first to land after 6 more launches. Giving a total of BFR to get 3 going to mars of 21 launches in that 30 days.
Now once on mars we will need to not only get all the gear out of the 2 BFR's to the ground before doing any science. Initial setup of Solar power fields are a must since its packed so high off the ground. Starting the insitu refueling plant is next to setup and get running as well as the oxygen generation system as well. These are all very time consuming items.


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

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#41 2018-10-09 12:59:27

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Key Debates

Oldfart and GW have been crunching the data. I think the three fin lander has got a cautious thumbs up from one or both of them. The fin span is surprisingly wide.

Anyway, the reality can easily be tested on rocky/sandy/whatever ground on Earth. It's not as though they will head off to Mars without first testing the craft. It depends what you mean by "rough terrain". The experts who have been looking at potential landing site have identified stable areas with less than 5% gradient.

Let's at least give the Space X engineers some credit - I am sure they can see the problems.


kbd512 wrote:

SpaceNut,

You're pointing out some of the obvious operational issues that will arise with the "as-is" BFS concept.  Nobody has answered any of these questions because nobody has any clue about how to go about doing it and that's pretty obvious now.  We have ideas about what might work, but we also have basic physics which overrides all fanciful notions we may have of what might work.  One can be as "optimistic" as the day is long, yet simple physics will continue to beat them mercilessly about the head until the pain is so great that the problem mandates a realistic solution.  The engineers at SpaceX have zero experience landing a telephone pole on anything besides a concrete or steel pad and it shows.  When I see a booster land on sand dune somewhere, I'll become a "true believer".  Until I see that kind of booster landing, I've already seen enough military aircraft crash land in places where the terrain was not suitable for landing to believe that that problem has been solved.

Physics doesn't care if you think a 150 foot tall ship with a pair of M1 tanks as the payload can be successfully landed in a vertical attitude on rough terrain using narrow track landing gear.  It doesn't matter if your name is Elon Musk or Joe Blow, the problems GW and others have pointed out aren't going away.  They require engineering solutions because they're real problems that wishful thinking won't overcome, at all or ever.  The BFS is too tall and the landing gear too narrow to reliably land on rough terrain and that's a cold hard engineering fact.

If you can't reliably land BFS anywhere but a concrete or steel pad, worrying about how quickly you can unpack the cargo is a pointless exercise when the goal is to land on a planet that clearly lacks anything resembling a prepared landing pad.


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

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#42 2018-10-09 13:02:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Key Debates

Not sure I've read about this test. Do you have a link? 

There are of course two approaches: 1. Scale up and 2. Take 1000 small processors with you.  Scaling up normally delivers economies of scale but of course taking lots of small machines is less risky.

Belter wrote:

Last I checked, Space X is creating 1 kg of methane per day with its test equipment.  3 orders of magnitude from where it needs to be.


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

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#43 2018-10-09 13:05:34

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Key Debates

Ain't gonna happen so why waste time on it?

Belter wrote:

There needs to be a 1-way BFR-DS [for drop ship].    Which means the forward section is a lander, the current engine section merely a second detachable stage.  The second stage gets the lander to Mars, burns its remaining fuel to slow down, then detaches.  The second stage would attempt an aerobrake orbit, but it disposable.  The lander would drop directly to Mars surface and would be able to detach its engines or even have them lift off and crash land.    The lower itself to the ground to off load cargo or be used as a habitat.    If a BFS started to fall over, the "holy shit" moment for the crew would be horrifying.    The thing is going to be not just narrow, but top-heavy.    So, unless Musk can also demonstrate robots that can convert regolith into concrete platforms on the surface, or at the very least scout accidentally ideal landing spots that are rigid and roughly flat.........


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

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#44 2018-10-09 13:16:31

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Key Debates

Louis,

You can put up all the hardware ahead of time and any real mission should start that way, but cryogenic propellants boil off without active cooling and serious insulation.  The insulation that works best in a substantial atmosphere doesn't work best in a vacuum, either.  Furthermore, LEO is a shooting gallery.  It's not the best place to park your payloads.  We've cluttered up the environment in LEO to the point where active cleaning and substantial MMOD is required.

Regarding the ground power for the Mars mission, we've already gone over why it is that you keep batteries and solar panels separated from each other.  There's a reason ISS was built the way it was and it's not just because the engineers were bored.  Fire is not a major problem on the truss structure, but it's still a real design consideration.  If they weren't concerned about the Lithium-ions melting they would not have expended so much effort isolating them from everything else.  An explosion is highly unlikely without substantial O2 or H2O present or egregiously poor design (Boeing Dreamliner), but one good electrical short is all it takes to turn a battery into jelly in less time than it took to deploy it.  The Dreamliner and ISS use the exact same battery pack from the exact same manufacturer.  One was built with proper isolation and venting, whereas the other was not.

The pouch format are all about practicality when it comes to packaging for thermal management, even if energy density is less than the smaller cells used by Tesla.  I'm sure the 18650 and 21700 cells could be incorporated into a functional pack, but the technology used has traditionally been the pouch since it's much more difficult to engineer a lightweight thermal management system for thousands of smaller cells, despite the power density improvements offered by using numerous smaller cells.  There must be some reason for that, too.

Battery and solar tech will keep marching forward, but right now we don't have the breakthrough cell chemistry required to keep battery pack mass to something sane and mobile.  This particular problem has proven to be far more intractable than anyone would've imagined about ten years ago, certainly 20 years ago.  I remain, dare I say it, optimistic that we'll have something better by the time we're ready to set sail.  As always, time will tell.

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#45 2018-10-09 13:20:49

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Key Debates

Landing an aeroplane on a planet on a non-prepared runway is way more problematic than landing a rocket.  There is really no point in comparing the two. In terms of stability, landing a rocket is more akin to landing a heavy helicopter.  NASA managed to land 7 rockets on rough ground on the moon 50 years or so ago with no major issues.  Landing a tall rocket is obviously more challenging, but Space X have access to a wealth of technology not available to NASA back in the 60s.

Given it is a propulsive landing, there's not much point in referencing "interplanetary transfer velocity". 

We know cruise missiles can "read" topography to reach targets with high level of accuracy. I think a combination of laser landing techniques, topographical recognition and (in the case of the human landers) radio beacons will get the BFS where it's supposed to be.

It is important to recognise that Mission One has a two stage structure - the human landers won't even leave for Mars unless the cargo landers have successfully landed. Even if no cargo is unloaded from the cargo BFSs, they can undertake detailed reconnaisance.  I think it quite possible they could eject mini rovers (a bit like those JAXA ones on the asteroid) to further investigate the surface. The cargo BFSs would have radio beacons incorporated.


kbd512 wrote:

tahanson43206,

I'm not saying there's no places on Mars where a BFS could potentially land.  There are thousands of places that are reasonably flat that can also support the weight of the ship without shifting under load.  There's just one critical problem with that methodology.  You have to know exactly which sites are suitable and then you have to land on the exact spots where ground conditions permit.  That can only be accomplished with ground-testing and precision landing capabilities.  There's sub-orbital velocity precision using a fully operational GPS constellation to assist in that task and then there's hitting a moving target tens of millions of miles away at interplanetary transfer velocity precision without the use of GPS.  That latter is completely unlike the former in more ways than one.  And yes, there are other ways to lick the problem, most notably radio beacons to mark the landing area...  That we still don't have on Mars.  Fixable?  Sure.  With a few billion dollars, I'm sure JPL can get a rover to the candidate landing area with the required equipment.

The US Air Force accomplishes that critical testing task with a special ground compaction test set.  It's little more than a probe and grey box with electronics that gives a "go" / "no-go" indication based upon the expected landing weight of the aircraft in question.  If they want to land something like a C-130 on something other than a runway, for example, then they send a guy or gal out with the test set and repeatedly shove it into the ground at the selected landing area to prove, rather than guess at, what the load carrying capacity of the soil actually is.  The same thing needs to be done on Mars, but we lack the scout transport capability to get that forward air controller to his or her candidate test site.

Furthermore, we (meaning all of humanity, in general, and NASA, specifically, since their Mars landing capabilities are the most accurate demonstrated to date) can't accurately land (hundreds of meters, versus several kilometers) a spacecraft coming in at interplanetary transfer velocity due to the variability of the atmosphere and lack of sufficiently precise guidance.  Obviously a completely propulsive landing will help a bit with landing precision since more control is afforded over where the exact landing is made, but is that something you're going to bet billions of dollars on and the lives of a half dozen or more irreplaceable astronauts (unless someone out there really is naive enough to believe that a bunch of amateurs are going to make the initial landings and play "house" on Mars)?

Oversimplifying the problem doesn't change the nature of the problem or make it go away.  No amount of cheap talk will fix it, either.  NASA isn't serious about sending humans to Mars unless they rectify those very real problems and probably dozens of other problems I've never thought about.  Then again, neither is anyone else.  PowerPoint presentations and CGI aren't an acceptable substitute for solid engineering.


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

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#46 2018-10-09 13:29:02

Belter
Member
Registered: 2018-09-13
Posts: 144

Re: Key Debates

louis wrote:

Ain't gonna happen so why waste time on it?

It's going to happen, even if Space-X isn't the one to do it.   Someone else will build a system dedicated to the actual task and will get all the funding for shipping habitats and supplies for an actual base, and Space-X will not.  Not with the ships they have designed.   They simply aren't a good design for delivering what a Mars base needs.

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#47 2018-10-09 13:36:46

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Key Debates

Louis,

I haven't reviewed the latest geometry, but I know that GW knows how to calculate what acceptable CG's and moments of inertia should be to create a stable landing gear track.  If that issue has been acceptably addressed, then I withdraw my critique of that feature of the previous design.  There was just no way the previous design would ever be stable enough for a rough field landing without some sort of articulating landing gear or a highly experimental anchoring system and that was my only point.

Irrespective of where they want to land BFS, I don't think the fueled mass of the vehicle will permit a landing on much of a gradient.  That said, I'm more concerned with ensuring that everyone gets there alive.  Reusing the BFS is a secondary consideration, as in good (everyone walks away) vs great (you get to reuse the BFS) landing.  Maybe some sort of crew-deployed stabilization mechanism could permit subsequent fueling and takeoff of BFS from a substantial grade, but it'd be an iffy proposition at best.

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#48 2018-10-09 13:48:26

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,817

Re: Key Debates

"you keep batteries and solar panels separated from each other" - not sure what your point is exactly but I don't think anyone would be putting them in the same packaging. Batteries have been used in space for over 50 years.  I am sure that engineers are aware of the safety issues.  Cost will not be an issue. Whatever it costs to make sure battery units don't self-combust (or, if they do, any fire is extinguished) will be done.

I was only really seeing the chemical batteries being a major component of the power system in those early first days. It would be useful to have a mobile unit that has a very large PV panel fan that can open up - covering maybe 200 sq. metres - and with a battery pack that could provide night/low light (NLL)hours .  The human pioneers could then decamp from their BFS into fairly large pressurised rovers. It will be useful to have units that can provide power to those and any robot rovers in operation at that point.

Otherwise, it makes more sense to use the methane and oxygen you are using to make your fuel/propellant to also power a methane generator to provide power during NLL hours.

I presume that there are other geocentric orbits that the BFR could use where the risk of impacts is much less?


kbd512 wrote:

Louis,

You can put up all the hardware ahead of time and any real mission should start that way, but cryogenic propellants boil off without active cooling and serious insulation.  The insulation that works best in a substantial atmosphere doesn't work best in a vacuum, either.  Furthermore, LEO is a shooting gallery.  It's not the best place to park your payloads.  We've cluttered up the environment in LEO to the point where active cleaning and substantial MMOD is required.

Regarding the ground power for the Mars mission, we've already gone over why it is that you keep batteries and solar panels separated from each other.  There's a reason ISS was built the way it was and it's not just because the engineers were bored.  Fire is not a major problem on the truss structure, but it's still a real design consideration.  If they weren't concerned about the Lithium-ions melting they would not have expended so much effort isolating them from everything else.  An explosion is highly unlikely without substantial O2 or H2O present or egregiously poor design (Boeing Dreamliner), but one good electrical short is all it takes to turn a battery into jelly in less time than it took to deploy it.  The Dreamliner and ISS use the exact same battery pack from the exact same manufacturer.  One was built with proper isolation and venting, whereas the other was not.

The pouch format are all about practicality when it comes to packaging for thermal management, even if energy density is less than the smaller cells used by Tesla.  I'm sure the 18650 and 21700 cells could be incorporated into a functional pack, but the technology used has traditionally been the pouch since it's much more difficult to engineer a lightweight thermal management system for thousands of smaller cells, despite the power density improvements offered by using numerous smaller cells.  There must be some reason for that, too.

Battery and solar tech will keep marching forward, but right now we don't have the breakthrough cell chemistry required to keep battery pack mass to something sane and mobile.  This particular problem has proven to be far more intractable than anyone would've imagined about ten years ago, certainly 20 years ago.  I remain, dare I say it, optimistic that we'll have something better by the time we're ready to set sail.  As always, time will tell.


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

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#49 2018-10-09 13:56:31

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Key Debates

louis wrote:

Landing an aeroplane on a planet on a non-prepared runway is way more problematic than landing a rocket.  There is really no point in comparing the two. In terms of stability, landing a rocket is more akin to landing a heavy helicopter.  NASA managed to land 7 rockets on rough ground on the moon 50 years or so ago with no major issues.  Landing a tall rocket is obviously more challenging, but Space X have access to a wealth of technology not available to NASA back in the 60s.

Landing gear stability is landing gear stability, even when you're landing a helicopter or a rocket.  Our version of a heavy lift helicopter is a fraction of the weight of this vehicle, even on Mars.  We're talking about vertically landing a Space Shuttle on Mars.  That's the mass analogue for BFS.  We're just ignoring the numbers associated with impact loading from the vertical descent phase of flight and the fact that the vehicle will be many times heavier when fully fueled.

NASA had very wide landing gear tracks for the LM's and there's a reason for that.  GW pointed it out numerous times.

louis wrote:

Given it is a propulsive landing, there's not much point in referencing "interplanetary transfer velocity".

Extreme speed coupled with dramatically variable atmospheric effects doesn't assist with the task of achieving a pinpoint landing.

louis wrote:

We know cruise missiles can "read" topography to reach targets with high level of accuracy. I think a combination of laser landing techniques, topographical recognition and (in the case of the human landers) radio beacons will get the BFS where it's supposed to be.

Cruise missiles fly at subsonic speeds, not hypersonic speeds, with the aid of GPS and a very accurate map (far more accurate than anything that exists for Mars).  A radio beacon would be of far greater assistance for intercepting the target than a map we don't have.  That'd be one of the reasons I advocated for a more sophisticated MRO replacement.  If we were so confident in our ability to precisely maneuver to a point in space at orbital speeds and beyond, we wouldn't launch to ISS using an orbit just under the station and then raise the orbit to intercept ISS.  I doubt that point will be taken, since we've exchanged information about this before.

louis wrote:

It is important to recognise that Mission One has a two stage structure - the human landers won't even leave for Mars unless the cargo landers have successfully landed. Even if no cargo is unloaded from the cargo BFSs, they can undertake detailed reconnaisance.  I think it quite possible they could eject mini rovers (a bit like those JAXA ones on the asteroid) to further investigate the surface. The cargo BFSs would have radio beacons incorporated.

Agreed.

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#50 2018-10-09 14:16:00

kbd512
Member
Registered: 2015-01-02
Posts: 1,977

Re: Key Debates

louis wrote:

"you keep batteries and solar panels separated from each other" - not sure what your point is exactly but I don't think anyone would be putting them in the same packaging. Batteries have been used in space for over 50 years.  I am sure that engineers are aware of the safety issues.  Cost will not be an issue. Whatever it costs to make sure battery units don't self-combust (or, if they do, any fire is extinguished) will be done.

I'm just pointing out the details...  The devil, really.  But we're not going to simply take a Tesla battery pack out of an electric car and start using it as is on Mars.  The "thermal events" associated with those packs, as GM would call them, are also completely unacceptable on Mars.  I'm not at all concerned about cost.  If we just wanted to do something cheap, we wouldn't even be entertaining this idea.

louis wrote:

I was only really seeing the chemical batteries being a major component of the power system in those early first days. It would be useful to have a mobile unit that has a very large PV panel fan that can open up - covering maybe 200 sq. metres - and with a battery pack that could provide night/low light (NLL)hours .  The human pioneers could then decamp from their BFS into fairly large pressurised rovers. It will be useful to have units that can provide power to those and any robot rovers in operation at that point.

Understood.  Makes sense from a general utility perspective.  Pitch the idea.  I think it has merit.

louis wrote:

Otherwise, it makes more sense to use the methane and oxygen you are using to make your fuel/propellant to also power a methane generator to provide power during NLL hours.

You have to make it before you get to use it, but then it makes sense to siphon off some of the product to "keep the lights on" at night.

louis wrote:

I presume that there are other geocentric orbits that the BFR could use where the risk of impacts is much less?

Yes...  At the cost of additional propellant consumption.  I was just commenting on the fact that I wouldn't leave a delicate payload in LEO for months on end if I was going to rely upon it for at least the next several years.  There's too great a possibility of something getting perforated by all the junk floating around up there.  The ISS can be abandoned in hours, if required.  A Mars-bound ship?  Not so much.

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