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#51 2017-12-27 01:50:41

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

One of the truisims we always used in my field: "make the mistakes on a small scale--the successes on a large scale." This is something Elon has yet to learn, w/r the BFR project. All I'm saying here is that I believe it's a mistake to put all one's eggs in too big of a basket. I'm hopeful SpaceX is wildly successful, but also think it's a mistake to abandon the Red Dragon without a single flight and landing.

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#52 2017-12-27 05:35:14

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

I may be wrong but my understanding is the propellant production starts robotically soon after the cargo craft land. Therefore you will know through various sensors if that is working, before humans launch for Mars (ie you can abort if the propellant production isn't working properly).


SpaceNut wrote:

Loius you have missed the point that its not just the cargo its the massive weight of the entire rocket that lands as its not only untested on a mars surface but we can not even take off once we have landed the beast until we have refueling capability on mars. Any crew will be landing in a simular rocket with it being outfitted for the crew. Space X BFR if tried here on an unprepared landing as a test of whether it will or will not work without knowing if it will, then how can we do so on mars.....

Last edited by louis (2017-12-27 05:36:35)


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

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#53 2017-12-27 11:21:07

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

louis wrote:

I may be wrong but my understanding is the propellant production starts robotically soon after the cargo craft land. Therefore you will know through various sensors if that is working, before humans launch for Mars (ie you can abort if the propellant production isn't working properly.

To this point, we haven't seen whether or not a Moxie unit will work on the scale needed. We haven't seen a robotic Sabatier reactor. We don't have a power supply figured out yet. We don't even have any plans for a refueling system in the works. All of these issues could be sorted out by a Red Dragon mission, but they have been cancelled. At least NASA has begun work on  Kilopower nuclear reactor. That could possibly fly on a Red Dragon if it were significantly uprated.

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#54 2017-12-27 16:13:09

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

I would agree these are major jigsaw pieces that haven't been cut before.

Musk seems confident solar can supply the power and I am with him on that.

With 300 tonnes to the surface there is plenty of scope for redundancy.

Oldfart1939 wrote:
louis wrote:

I may be wrong but my understanding is the propellant production starts robotically soon after the cargo craft land. Therefore you will know through various sensors if that is working, before humans launch for Mars (ie you can abort if the propellant production isn't working properly.

To this point, we haven't seen whether or not a Moxie unit will work on the scale needed. We haven't seen a robotic Sabatier reactor. We don't have a power supply figured out yet. We don't even have any plans for a refueling system in the works. All of these issues could be sorted out by a Red Dragon mission, but they have been cancelled. At least NASA has begun work on  Kilopower nuclear reactor. That could possibly fly on a Red Dragon if it were significantly uprated.


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

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#55 2017-12-27 17:01:33

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

"Musk seems confident solar can supply the power..."

That's just not good enough. Blind faith and wishful thinking cannot replace experimentation and hard data.

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#56 2017-12-27 20:41:55

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

I've been looking but can't find what is the total power requirement to produce on Mars  about 1200 tonnes  (is this right?) of propellant to get the return BFR off Mars and into Earthbound trajectory.  Do you have a figure? If you do that would be very helpful! smile

Oldfart1939 wrote:

"Musk seems confident solar can supply the power..."

That's just not good enough. Blind faith and wishful thinking cannot replace experimentation and hard data.


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

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#57 2017-12-28 01:53:01

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,124

Re: Falcon Heavy Assembly Underway

Louis,

GW did a cursory analysis on an ideal energy expenditure scenario to determine the amount of electrical power required to produce the LOX and run the Sabatier reactor.  The figure was well into the tens of megawatts to produce the quantity of propellant required in 2 years, but that was for the first incarnation of BFS, and it didn't account for energy lost in the process or energy required for cryogenic propellant storage.  We're talking about a LOT of electrical power.

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#58 2017-12-28 04:46:48

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

I agree. Which is why I was wondering how Musk proposes to deliver it with solar alone, given that is his stated intention. I was thinking probably a minimum of 15 MWes constant. That seems beyond the reach of a 300 tonne cargo delivery system, whether it's solar or nuclear.

I think we can agree Musk is not stupid, so what's his game?  Are we missing some key factor here? Is there some sort of cyrogenic energy trick he can pull off?  I don't know.   But as things stand, I can't really see how it all adds up.


kbd512 wrote:

Louis,

GW did a cursory analysis on an ideal energy expenditure scenario to determine the amount of electrical power required to produce the LOX and run the Sabatier reactor.  The figure was well into the tens of megawatts to produce the quantity of propellant required in 2 years, but that was for the first incarnation of BFS, and it didn't account for energy lost in the process or energy required for cryogenic propellant storage.  We're talking about a LOT of electrical power.


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

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#59 2017-12-28 11:03:09

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

Louis-
The power requirement is FAR beyond that available by the first solar arrays which can be robotically deployed. I think NASA has reached the same conclusion and has begun working on a space-rated nuclear system. That is also the conclusion reached by Robert Zubrin in "Entering Space." One of the interim ideas floated at one of the Mars conferences was bringing a high-density fuel supply, (UDMH), and only manufacturing the LOX on Mars through the Moxie units and cryogenic systems. If we only need to manufacture LOX, the energy requirement abates somewhat--but still exceeds the power available through solar.

It's one thing to be in love with a particular system (solar, in your case), but the numbers just don't lie. What we'll wind up with is something of an eclectic package of power utilizing BOTH solar and nuclear.

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#60 2017-12-28 11:11:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

My point is that a 15MWe constant is also far beyond the reach of a nuclear solution forming part of the 300 tonne cargo load. 

I think Musk have something up his sleeve...


Oldfart1939 wrote:

Louis-
The power requirement is FAR beyond that available by the first solar arrays which can be robotically deployed. I think NASA has reached the same conclusion and has begun working on a space-rated nuclear system. That is also the conclusion reached by Robert Zubrin in "Entering Space." One of the interim ideas floated at one of the Mars conferences was bringing a high-density fuel supply, (UDMH), and only manufacturing the LOX on Mars through the Moxie units and cryogenic systems. If we only need to manufacture LOX, the energy requirement abates somewhat--but still exceeds the power available through solar.

It's one thing to be in love with a particular system (solar, in your case), but the numbers just don't lie. What we'll wind up with is something of an eclectic package of power utilizing BOTH solar and nuclear.


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

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#61 2017-12-28 11:26:58

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,124

Re: Falcon Heavy Assembly Underway

Louis,

To produce 15MWe in something that's even remotely portable, you'd need a fission reactor that uses traveling wave direct energy conversion of fission fragments into electricity.  NASA continues to do work on such a device, but wants to combine the conversion concept with a pie-in-the-sky aneutronic fusion reactor that doesn't exist.  Right now we have fission reactors.  DoE knows how conventional heat exchange fission reactors work, but this is definitely new for them, even if the basic concept is many decades old.

Using thin film Am242m or dusty U235, it is possible to obtain efficiencies in the 60% to 75% range.  This has been modeled or demonstrated (60% efficiency actually demonstrated) using a series of physics experiments with a proton source.  Basically, they fired an ion engine into their TWDEC device to test its efficiency.  They think they can improve that to 75% by tweaking some things.  Needless to say, such a device would drastically reduce the mass of the radiator panels required for waste heat rejection.

Combine a TWDEC equipped fission reactor with that new Tungsten impregnated stainless steel foam for combined high-Z (gamma) / low-Z (neutron) shielding (apparently it performs substantially better and weighs far less than the old solution of using alternating W or DU with LiH), and then maybe you have something that could provide the kind of power required.

The good news is that core design of such a reactor limits the amount of other heavy materials required, like fissile material, fuel cladding (not used at all), and even the reflector material changes to something lighter than BeO (special type of carbon composite).  It would basically have a very small number of moving parts (could be limited to just the control rods or drum and could be a single servo-operated assembly) and does not use a heat exchange fluid to do work.  The reaction can be self-moderating.  If the temperature goes up to much, then it kills fission, but that's entirely dependent on design.  Accidental criticality is a greater risk with this design than SAFE-400 or KiloPower.  The entire assembly is far less radioactive at launch than any RTG, provided it doesn't go critical.

Musk is as much a salesman as an engineer.  He wants to sell an idea to his investors.  It's an idea that has merit, but he hasn't worked out all the technical details.  He owns a rocket company.  SpaceX is not NASA.  They're not going to pull this off on their own without considerable government resources being devoted to his project.  I see SpaceX as a rallying point for those interested in moving the ball down the field.  NASA still needs to apply their "secret sauce" (literally speaking, since lots of this stuff is classified) of public/private partnership for life support, radiation protection, space suits, computation (if someone so much as misses a decimal place somewhere, you're going to have a very bad day), and human health factors.  Someone also needs to light a fire under NASA's artificial gravity program.  I'm kinda surprised that the astronaut office hasn't read management the riot act.

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#62 2017-12-28 11:27:28

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

You mean some sort of repeal of the Laws of Thermodynamics?

What Musk may come to realize is his BFR to Mars may not work immediately w/o some sort of preliminary smaller scale undertakings. It's sometimes called a "reality check." The old Russians when discussing military plans stated "the plan looks smooth on the maps, but they forgot about the ravines."

If Musk has any tricks up his sleeves, maybe it would include an interstage in Mars orbit to power the BFR from there back to Earth with a refueling system? I can conceive of making a jump from mars surface into Mars orbit with only LOX manufacture on the surface by ISRU, but until there is more infrastructure developed, the energy spreadsheet is out of whack.

Last edited by Oldfart1939 (2017-12-28 11:28:01)

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#63 2017-12-28 17:57:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway


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

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#64 2017-12-28 18:09:16

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

I think that's a bit demeaning and dismissive towards Musk...a man who has revolutionised space transport and  EV transport -  and may in the next few years revolutionise or retire air transport either with Hyperloop or Earth link BFR.

Would he really stand up on a stage in public and make a claim about propellant production that can so easily be shown to be false if taken entirely at face value?

I'm inclined to think not. 

One possibility I'm thinking he may have been working on is solar reflectors. They could be ultralightweight. If you could increase solar input into the panels x100 via solar reflectors, that might make enough of a difference.



kbd512 wrote:

Louis,

To produce 15MWe in something that's even remotely portable, you'd need a fission reactor that uses traveling wave direct energy conversion of fission fragments into electricity.  NASA continues to do work on such a device, but wants to combine the conversion concept with a pie-in-the-sky aneutronic fusion reactor that doesn't exist.  Right now we have fission reactors.  DoE knows how conventional heat exchange fission reactors work, but this is definitely new for them, even if the basic concept is many decades old.

Using thin film Am242m or dusty U235, it is possible to obtain efficiencies in the 60% to 75% range.  This has been modeled or demonstrated (60% efficiency actually demonstrated) using a series of physics experiments with a proton source.  Basically, they fired an ion engine into their TWDEC device to test its efficiency.  They think they can improve that to 75% by tweaking some things.  Needless to say, such a device would drastically reduce the mass of the radiator panels required for waste heat rejection.

Combine a TWDEC equipped fission reactor with that new Tungsten impregnated stainless steel foam for combined high-Z (gamma) / low-Z (neutron) shielding (apparently it performs substantially better and weighs far less than the old solution of using alternating W or DU with LiH), and then maybe you have something that could provide the kind of power required.

The good news is that core design of such a reactor limits the amount of other heavy materials required, like fissile material, fuel cladding (not used at all), and even the reflector material changes to something lighter than BeO (special type of carbon composite).  It would basically have a very small number of moving parts (could be limited to just the control rods or drum and could be a single servo-operated assembly) and does not use a heat exchange fluid to do work.  The reaction can be self-moderating.  If the temperature goes up to much, then it kills fission, but that's entirely dependent on design.  Accidental criticality is a greater risk with this design than SAFE-400 or KiloPower.  The entire assembly is far less radioactive at launch than any RTG, provided it doesn't go critical.

Musk is as much a salesman as an engineer.  He wants to sell an idea to his investors.  It's an idea that has merit, but he hasn't worked out all the technical details.  He owns a rocket company.  SpaceX is not NASA.  They're not going to pull this off on their own without considerable government resources being devoted to his project.  I see SpaceX as a rallying point for those interested in moving the ball down the field.  NASA still needs to apply their "secret sauce" (literally speaking, since lots of this stuff is classified) of public/private partnership for life support, radiation protection, space suits, computation (if someone so much as misses a decimal place somewhere, you're going to have a very bad day), and human health factors.  Someone also needs to light a fire under NASA's artificial gravity program.  I'm kinda surprised that the astronaut office hasn't read management the riot act.


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

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#65 2017-12-28 18:45:28

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

Louis-

I mean no disrespect or to make demeaning comments, but I'm well versed in chemistry, physics, and have a substantial engineering background to boot. Maybe Musk is totally sincere--which I believe he is--but is also capable of self-delusion with his dreams. I'll simply reiterate what I've said all along: he may be taking too big a step all at once. His plans will hopefully come to fruition, but not until he shows some serious infrastructure planning on Mars.

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#66 2017-12-28 19:47:31

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

I just don't believe he isn't doing the infrastructure planning.  I think he is as capable of self-delusion as any human being but I think he shows that most in his discussion of human colonisation or rather his inability to grapple with the very real social challenges.

I may be completely wrong, but I just can't believe he hasn't thought through how to power the propellant plant since it is such an obvious and early question that would arise.  It may be he is running with ultra lightweight solar...that might make it doable. But that is clearly not an existing technology that has been tested in Mars type conditions. It would be something he had to develop.  Given his Tesla involvement, that is something he may think can be cracked in the next few years. That's not so much delusional as perhaps crazily optimistic.

It's all v. odd because of course if you can land 300 tonnes you have the solution in your hands...land a kind of tiny Apollo ascent craft that is then used to take humans up to LMO - I am guessing it could be less than 20 tonnes for two people. In LMO they meet the return BFR.  For a crew of six, perhaps you need to land 3, so maybe 60 tonnes but that is still fine with an overall budget of 300 tonnes.


Oldfart1939 wrote:

Louis-

I mean no disrespect or to make demeaning comments, but I'm well versed in chemistry, physics, and have a substantial engineering background to boot. Maybe Musk is totally sincere--which I believe he is--but is also capable of self-delusion with his dreams. I'll simply reiterate what I've said all along: he may be taking too big a step all at once. His plans will hopefully come to fruition, but not until he shows some serious infrastructure planning on Mars.


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

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#67 2017-12-28 21:54:00

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,757
Website

Re: Falcon Heavy Assembly Underway

I see two fundamental but unresolved problems with Mr. Musk's published Mars plans. 

(1) Not enough power will be available to manufacture the return propellant load for one BFS vehicle in less than several-to-many years,  maybe even a decade or so.  This requirement is something like 1000-1200 tons of propellants,  ~80% of which is LOX,  the rest LCH4.  This is true whether you use solar power,  or nuclear power,  or both.  2 years is just out-of-the-question,  even with multiple SAFE-400 plants (each 100 KW electric if running 100% 24/7,  which abuse is a recipe for early failure).  You need something like 5-10 MW just to electrolyze the water in 2 years,  unless you really can do a lot better than the 6% efficiency typical of school lab equipment.  A LOT better.

(2) I consider it irrational and extremely foolhardy to land a tall,  skinny object on unprepared ground.  I know Spacex is landing tall, skinny Falcon-9 first stages,  BUT:  those landing pads or barge decks are utterly smooth and flat.  Mars is simply neither,  not even on the planitias where Viking 1 and 2 set down. 

I have no solution to offer for problem (1).  But,  one could possibly send a 2-3 ton bulldozer rover to Mars with a Falcon-Heavy,  if one could figure out how to incorporate it into a Red Dragon in place of the capsule pressure shell (the proposed normal Red Dragon is around a 5-6 ton item,  I think,  not including payload aboard,  which was ~ 2 tons,  and propellant,  which was ~1.2 tons). 

Such a dozer could likely scrape a landing field flat enough for a BFS,  as a robotically-controlled item,  unless it encountered outcrops.  (Which are all over Mars,  by the way.)  One would also need to test soil bearing load capability,  to make sure the landing pads on the BFS have enough area not to sink into the sand.  If all that is successful,  then all you have to do is actually hit the target with the BFS! 

How big a landing field do you really need?  Touchdown accuracy determines that.  Just how will that accuracy be achieved?  That is not known yet.  Another serious problem,  but maybe not as fundamental as the two I listed.

That is why I see a real need for some Red Dragon pathfinders,  which actually was Musk's originally-presented plan.  Not to mention somehow looking for buried-water-as-ice on site to electrolyze. 

As for scaling-up to enormous rocket sizes,  I see Falcon-Heavy as the necessary intermediate step.  Its payload is about 3 times that of Falcon-9.  Depending upon what you believe about BFR/BFS,  that payload is ~ 3 times Falcon-Heavy.  Or,  look at first stage thrust levels. Same story.  Looks about right to me. 

GW

Last edited by GW Johnson (2017-12-28 22:03:55)


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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#68 2017-12-28 23:02:22

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

GW has, in his above post, neatly summarized what I've been saying in "polite English" in my posts #36, #45, #53, #59, and #62 above. The architecture of the vehicle is inherently unstable on rough terrain, as GW clearly states. The MAJOR problem regarding Earth return is having enough of both water and electric power to accomplish return fuel production. Maybe the SpaceX engineers will build more of an outrigger size set of landing legs, and maybe there will be a Megapower nuke reactor in the cargo only missions? These problems have not yet even been identified and not yet addressed in Elon's talks.

If we are talking about manned flights, we have to over engineer EVERYTHING,  since FAILURE IS NOT AN OPTION!

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#69 2017-12-29 05:50:50

elderflower
Member
Registered: 2016-06-19
Posts: 1,149

Re: Falcon Heavy Assembly Underway

Failure has always been an option in exploration. You have only to look at European exploration history over the past 1000 years to appreciate that. Of course we must minimise foreseeable risks but there are still unknown unknowns....
Everybody dies in the end, some are prepared to risk doing so a bit early. Their choice of risky activities doesn't mean we have to ban hang gliding or deep diving or racing automobiles, yachts or horses. Or manned exploration.

Last edited by elderflower (2017-12-29 07:33:33)

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#70 2017-12-29 18:15:14

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,757
Website

Re: Falcon Heavy Assembly Underway

There's voluntary risk-taking,  and involuntary risk-taking.  Astronauts typically volunteer to take risks,  yes,  but it is unethical for those building spacecraft not to mitigate all known risks to the max extent possible.  Failure to do it right in the beginning essentially forces the astronauts to take involuntary risks that could have been mitigated,  but were not.  THAT is what I object to.

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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#71 2017-12-29 19:15:02

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

GW, I think (1) is the real issue.

Regarding (2) it's not such a gamble...I would give three reasons:

(a) Scale. The BFR is huge.  So as long as you are landing in a small boulder field, you are unlikely to have a disastrous landing. Of course if it was a tiny BFR in the same boulder field, you might well come unstuck.

(b) Water is never "utterly smooth and flat"...there is a lot of gyro going on there! So Space X have already proven an incredible ability to land tall thin rocket ships on dodgy surfaces.

(c) On previous missions we have "taken a punt" with admittedly smaller craft in similar landing sites (with little or no robotic guidance) and more often that not come up trumps.  One must assume the BFR cargo ships will have some sort of robotic guidance to avoid the worst landing areas as the ship closes in - a Neil Armstrong on board as it were.  I am not aware of any Mars Mission that has failed because of the nature of the terrain on landing.

(d) If the boulder field is composed of a sufficiently small average sized boulder, I think we don't need boulder removal for a cargo mission but we can have full boulder removal for the human mission that follows up.

And of course, if it is a failure, it's only a Cargo ship failure. No humans were injured in the making of this mission...

So back to (1)...

Well I was coming up with a ball park figure of 15 MW for this level of propellant production...It's well beyond a nuclear or solar solution with a 300 tonne cargo delivery...so what gives?  You appear as puzzled as I am! Not for the first time, Musk keeps us guessing.





GW Johnson wrote:

I see two fundamental but unresolved problems with Mr. Musk's published Mars plans. 

(1) Not enough power will be available to manufacture the return propellant load for one BFS vehicle in less than several-to-many years,  maybe even a decade or so.  This requirement is something like 1000-1200 tons of propellants,  ~80% of which is LOX,  the rest LCH4.  This is true whether you use solar power,  or nuclear power,  or both.  2 years is just out-of-the-question,  even with multiple SAFE-400 plants (each 100 KW electric if running 100% 24/7,  which abuse is a recipe for early failure).  You need something like 5-10 MW just to electrolyze the water in 2 years,  unless you really can do a lot better than the 6% efficiency typical of school lab equipment.  A LOT better.

(2) I consider it irrational and extremely foolhardy to land a tall,  skinny object on unprepared ground.  I know Spacex is landing tall, skinny Falcon-9 first stages,  BUT:  those landing pads or barge decks are utterly smooth and flat.  Mars is simply neither,  not even on the planitias where Viking 1 and 2 set down. 

I have no solution to offer for problem (1).  But,  one could possibly send a 2-3 ton bulldozer rover to Mars with a Falcon-Heavy,  if one could figure out how to incorporate it into a Red Dragon in place of the capsule pressure shell (the proposed normal Red Dragon is around a 5-6 ton item,  I think,  not including payload aboard,  which was ~ 2 tons,  and propellant,  which was ~1.2 tons). 

Such a dozer could likely scrape a landing field flat enough for a BFS,  as a robotically-controlled item,  unless it encountered outcrops.  (Which are all over Mars,  by the way.)  One would also need to test soil bearing load capability,  to make sure the landing pads on the BFS have enough area not to sink into the sand.  If all that is successful,  then all you have to do is actually hit the target with the BFS! 

How big a landing field do you really need?  Touchdown accuracy determines that.  Just how will that accuracy be achieved?  That is not known yet.  Another serious problem,  but maybe not as fundamental as the two I listed.

That is why I see a real need for some Red Dragon pathfinders,  which actually was Musk's originally-presented plan.  Not to mention somehow looking for buried-water-as-ice on site to electrolyze. 

As for scaling-up to enormous rocket sizes,  I see Falcon-Heavy as the necessary intermediate step.  Its payload is about 3 times that of Falcon-9.  Depending upon what you believe about BFR/BFS,  that payload is ~ 3 times Falcon-Heavy.  Or,  look at first stage thrust levels. Same story.  Looks about right to me. 

GW


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

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#72 2017-12-29 20:06:54

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

Landing accuracy can be controlled by landing some transponders ahead of time. Build what in the aviation industry is the WAAS system: Wide Area Augmentation System, using fixed transponders to assist the Earth GPS constellation. We need to populate Mars with a GPS system before any serious manned/unmanned missions. Then add a set of transponders by unmanned flights which are semi controlled by the GPS constellation.

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#73 2017-12-29 20:23:27

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,368

Re: Falcon Heavy Assembly Underway

Yes - I've always argued for the Transponder approach.

Do we not already effectively have a Mars GPS already (taking all the satellites together)?  Or perhaps I am wrong.

Oldfart1939 wrote:

Landing accuracy can be controlled by landing some transponders ahead of time. Build what in the aviation industry is the WAAS system: Wide Area Augmentation System, using fixed transponders to assist the Earth GPS constellation. We need to populate Mars with a GPS system before any serious manned/unmanned missions. Then add a set of transponders by unmanned flights which are semi controlled by the GPS constellation.


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

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#74 2017-12-29 21:25:31

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,798

Re: Falcon Heavy Assembly Underway

Getting back on track with the Falcon Heavy; here's the link to spacefilghtinsider story on Falcon Heavy raised to vertical on LC-39a.

http://www.spaceflightinsider.com/organ … ce-center/

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#75 2017-12-29 21:31:24

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,862
Website

Re: Falcon Heavy Assembly Underway

There is a Mars relay antenna on Odyssey, MRO, Mars Express, and MAVEN. It can relay data from a lander or rover, and can be used to measure range (distance) from orbiter to lander/rover. With 3 satellites, or 3 measurements from the same satellite over enough time that rotation of the planet moves the lander/rover to a new location, you can calculate exact position by intersecting spheres. It's not nearly as precise as GPS, but is something.

I believe it computes range by calculating time for a signal from rover to orbiter. Multiply by speed of light gives you distance. Using the precise topography map of Mars produced by the laser altimeter, intersection will give you a ring. Then calculate angle to the orbiter based on signal Doppler shift, together with known speed and position of the orbiter. That will give you two possible positions for the lander/rover, one to the left of the orbiter, the other to the right. A second measurement with the orbiter has moved could tell you which one, or just assume the lander/rover is in the same hemisphere of Mars where it landed.

I've been told some of the extreme technology in GPS satellites that give them extreme precision. Mars orbiters don't have that.

Mars Reconnaissance Orbiter: Electra

Electra is a telecommunications package that acts as a communications relay and navigation aid for Mars spacecraft.

Toward the end of the primary science phase, other Mars missions launched in 2007 and beyond will begin to arrive. Mars Reconnaissance Orbiter will use its Electra UHF radio to support any navigation, command, and data-return needs these missions may have. If the arriving spacecraft has an Electra communications payload, it can receive these signals and use them to determine its distance and speed in relation to Mars. This communication allows much more precise navigation.

After incoming landers or rovers have arrived safely on Mars, Electra can provide precise Doppler data which, when combined with Mars Reconnaissance Orbiter's position information, can accurately determine the location of the lander or rover on the surface of Mars.

Electra can also provide UHF coverage to Mars landers and rovers on the surface that may not have sufficient radio power to communicate directly with Earth by themselves, using its nadir-pointed (pointed straight down at the surface) antenna.

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