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#1 2018-09-30 18:03:15

louis
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From: UK
Registered: 2008-03-24
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Looking at the Mars Colony's development, based on Space X & BFR

We are now getting closer and closer to a real Mars colonisation project whether humans land in 2024, 2026 or 2028. The likelihood is they will do so as part of a Space X project using BFRs...

So what does that suggest for Mars colony development?

1.  Space X have hinted that landed BFRs could be used as habitat. I am a little sceptical about that.  A craft designed for  a zero G environment is in my view going to be pretty useless as habitat on Mars. But it could certainly serve as a warehouse for supplies and also as emergency habitat in the event of some catastrophe with the main ground level habitat. So, yes a skyline of landed BFRs will definitely be part of the scene. The BFRs could presumably also deploy their solar "wings" to provide additional PV power.

2. The BFR (or BFS if you prefer) is a huge rocket. This is not an Apollo style craft! So landing and launches will create disruptive effects over several hundred metres' radius. Once landed the BFRs can't be moved prior to launch.  So that means other BFR landings have to be well away from already landed craft.  The BFR landing area will have to cover a very large area - perhaps as much as 30-40 sq kms as more and more BFRs are landed. So, one feature of the Mars colony will be what we might term a very large Spaceport area, covering the sort of area a large international airport might spread over. The Mars Spaceport will  likely need a terminal building where people can stop off after exiting the BFRs. Here they will receive v thorough medical checks before they are transported to their main habitats.

3.  The Space X colonisation project is based on propellant manufacture on Mars and cannot proceed without it.  So from the outset, there must be a propellant production facility on Mars.  Given the nature of the product this will need to be located some distance from the BFRs and the main habitat but close enough that refuelling does not become problematic.

4.  Fire and explosion are deadly enough on Earth, but on Mars - because there is "nowhere to run to" (it being a near vacuum) - fire and explosion would prove even more deadly, leading to 100% fatalities in all likelihood.  Therefore it will be necessary to ensure industrial, warehousing and agricultural facilities (which will be a type of indoor farming) are located well away from the main habitats and also spread out one from the other.  I would guess that you would want at least 0.5 km between facilities. Also, you want to have back-up -  so there won't just be one industrial or agricultural facilitiy. 

5.  From the above we are getting the idea that this colony is going to be very spread out, over maybe hundreds of sq. kms within the first 10 years or so. It will have a v. low population density of perhaps no more than 10 people per sq. km. but it will cover as large an area as some million-person cities on Earth.

6. The colony is going to grow so quickly that it will soon resemble a small town. It will definitely need a name - more than just a "base name". I favour Sagan City but there will be lots of candidates for naming. 

7.  Space X appear to have abandoned their earlier vision of hundreds of thousands of homesteaders setting up on Mars.  It seems they see Mars developing first as a research base. This is indeed most likely.  I predict there will be huge interest from universities, private firms,  space agencies and other institutions in sending their people to Mars. This is the basic business model for a Space X colony. The people who go there will need to buy their tickets from Space X and once they are there their habitat and life support will be provided by Space X  - at a cost.  So we need to think in terms of life support plants generating air, pure water and energy for various habitats.

8.  Space X are dedicated to the idea of Mars colonisation and so I expect them to be strongly committed to ISRU on Mars.  That in turn implies lots of mining activity at various locations at some distance from the main colony. In turn that implies cleared roadways, the beginnings of a Mars transport network that will have 1000 kms of roadway.  In terms of agricultural production, though, the ability of Space X to import so much food will I think somewhat slow down development of ISRU agriculture. I think the importance of maintaining the morale of Mars's pioneers will be paramount. So, yes to supplemental fresh foods - the full range of salad foods for instance - but probably no to any major push to provide staple foods like wheat, rice, maize and so on. Certainly livestock farming or even fish farming is unlikely to be developed in the first few decades.

9.  A colony with a big land area spread will require a good transport system.  Electric powered pressurised "golf buggy" type vehicles that can simply from one air lock in a hab to another air lock in another hab are likely to be the solution on Mars. Travelling at maybe 15 Kms per hour, the longest journey from one peripheral area of the colony to another might be in the region of 30 minutes.  Of course journeys to mining areas may take longer and will likely require more robust rovers.

10.  The above really describes the first era of colonisation. As the colony grows in population, it will tend to resemble more and more Earth-based cities.

Last edited by louis (2018-09-30 18:12:18)


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#2 2018-10-01 06:46:47

elderflower
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Re: Looking at the Mars Colony's development, based on Space X & BFR

In case of fire, venting the enclosure will pretty much resolve most fires. People will need to carry emergency oxygen and have access to shelters or suits and exit points and be able to run when the alarm is given so that they can escape the venting section.

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#3 2018-10-01 08:17:42

louis
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Re: Looking at the Mars Colony's development, based on Space X & BFR

That may well be part of fire safety plans. But I don't really believe the fantasy Space X pics where everything is cheek by jowl connected by surface tunnels.  If you did have fire or explosion in one facility it could quickly spread to all other facilities given all the oxygen connections in the habs...you would again be left with "nowhere to run to".  I feel pretty confident that when Space X people get down to designing the layout of the colony, they will quickly come to see the risks and opt for a more spacious layout.  People will be connected by pressurised electric golf buggies which can travel from one air lock to another (so no need for EVA suits). Most journeys would be a matter of just a few minutes max. It would be more than a shame if Space X put all that effort to getting to Mars and starting colony, and then just let it burn down due to a failure to segregate facilities. For me it's a no brainer - safety first... but I will be interested in what others think. There isn't really any downside to segregating your facilities that I can see.

elderflower wrote:

In case of fire, venting the enclosure will pretty much resolve most fires. People will need to carry emergency oxygen and have access to shelters or suits and exit points and be able to run when the alarm is given so that they can escape the venting section.


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#4 2018-10-01 08:54:16

Terraformer
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Re: Looking at the Mars Colony's development, based on Space X & BFR

Segregation can be achieved by airlocks. Each compartment will have it's own redundant life support system - if there's a problem in one area, it can be sealed off. I don't expect there to be a situation where an explosion in the Aluminium plant results in the air supply being poisoned, because all the oxygen is coming from there...


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#5 2018-10-01 10:20:24

louis
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Re: Looking at the Mars Colony's development, based on Space X & BFR

Well I would think that approach would only work if you segregated life support systems for each hab since wires, conduits, pipes and plumbing could spread fire. And there is the risk of explosion damaging neighbouring habs.

Terraformer wrote:

Segregation can be achieved by airlocks. Each compartment will have it's own redundant life support system - if there's a problem in one area, it can be sealed off. I don't expect there to be a situation where an explosion in the Aluminium plant results in the air supply being poisoned, because all the oxygen is coming from there...


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#6 2018-10-01 17:01:42

SpaceNut
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Re: Looking at the Mars Colony's development, based on Space X & BFR

Any connecting tunnel would have sealing doors on both ends of them for making a fire explosion break and with any connecting wires, plumbing to be external to the internal pressure vessel or what is called the people tank (think Submarine). Tunnels are lined with air sensing detection to send early warning for the crews in the area. Midway down the tunnels that are very long should have escape chambers that have there own external supplied life support for any member that must use them when the ends get sealed.

This issue can also occur on the many months of travel to and from earth to mars and back and this means mass that will be taken from payload to serve in the same manner to isolate, give safe havens and means to survive while in them until repairs are completed.

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#7 2018-10-02 00:16:23

louis
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Re: Looking at the Mars Colony's development, based on Space X & BFR

Another aspect of a Space X led colony will of course be that there will be very extensive PV array fields around or interwoven with the settlement. The absence of aggressive weather on Mars means the look of such arrays may be different from on Earth. We might see PV film suspended on guy ropes or wires, rather than the heavily structured arrays we are used to seeing on Earth.


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#8 2018-10-02 07:01:49

Belter
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Re: Looking at the Mars Colony's development, based on Space X & BFR

1.  I don't see the issue with the gravity/0gravity thing.    Pretty sure they're going to be designed for a vertical gravity layout and in space, it is what it is because it just doesn't matter what the layout is in 0G.     

2.  Not so sure these are going to have to land that far from each other.   The only effects are going to be a shitton of dust being kicked up, but that's going to be standard issue on Mars anyway, anytime a dust storm hits.   Sound?  No nearly so brutal in a low atmosphere environment.   Heat?   Also hard to transfer in such extreme cold with no pressure.  The only real thing they really need to worry about is landing them so close that one toppling could fall into another.    I bet Musk's goal for landing the unmanned permanent models is going to be to put them as close as they can and I'm sure they've already run the calculations on what kind of pressure/heat/sound waves they'd create and what the closest safest distance is.   

3.  I think propellant manufacture is a goal, but I'm not so sure we're anywhere near that state.  I think the reality is that BFRs aren't leaving the surface before 2050, even if they get there in 2024.    I think Musk is going to have to leave some BFRs in orbit, or he will try to leave enough fuel in, say, in the first 6-10 BFRs to allow one to be fueled with the remainder for takeoff.   And i suspect they are going to have to switch to a version of this where they are landing at least half a dozen unmanned supply ships before the first manned BFR sets down.   I think it would be reckless to do otherwise.   One idea might be to have robots unload one ship, fuel it back up and do a test launch and make sure they can get one back into orbit.   Then leave it there as a space station/spare parts/backup

Last edited by Belter (2018-10-02 07:08:27)

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#9 2018-10-02 13:30:17

louis
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Re: Looking at the Mars Colony's development, based on Space X & BFR

1.  I think there are issues. Systems designed for zero G have pumps and so on but they are not operating in gravity conditions. You might be able to have a vertical arrangement, but that's not necessarily the best arrangement for space.  Just take floors...you will have to adapt those. If you are designing them for gravity conditions you will probably be making them far heavier than they need be...it will be wasteful mass.  I am sure there are lots of issues like that. Will vaccuum toilets work well on Mars? I don't know.

2.  So you've got people living in these BFRs but you're not concerned about rocks flying through the air and damaging them...or even worse, a full scale explosive catastrophe?

3.  There is no way humans are going to Mars with Space X unless they can be assured a working propellant production facility will be awaiting them. Propellant production isn't that difficult, in any case - it's not exactly rocket science you might say. You probably don't need more than 100 tonnes or so devoted to a propellant production plant and associate mass.





Belter wrote:

1.  I don't see the issue with the gravity/0gravity thing.    Pretty sure they're going to be designed for a vertical gravity layout and in space, it is what it is because it just doesn't matter what the layout is in 0G.     

2.  Not so sure these are going to have to land that far from each other.   The only effects are going to be a shitton of dust being kicked up, but that's going to be standard issue on Mars anyway, anytime a dust storm hits.   Sound?  No nearly so brutal in a low atmosphere environment.   Heat?   Also hard to transfer in such extreme cold with no pressure.  The only real thing they really need to worry about is landing them so close that one toppling could fall into another.    I bet Musk's goal for landing the unmanned permanent models is going to be to put them as close as they can and I'm sure they've already run the calculations on what kind of pressure/heat/sound waves they'd create and what the closest safest distance is.   

3.  I think propellant manufacture is a goal, but I'm not so sure we're anywhere near that state.  I think the reality is that BFRs aren't leaving the surface before 2050, even if they get there in 2024.    I think Musk is going to have to leave some BFRs in orbit, or he will try to leave enough fuel in, say, in the first 6-10 BFRs to allow one to be fueled with the remainder for takeoff.   And i suspect they are going to have to switch to a version of this where they are landing at least half a dozen unmanned supply ships before the first manned BFR sets down.   I think it would be reckless to do otherwise.   One idea might be to have robots unload one ship, fuel it back up and do a test launch and make sure they can get one back into orbit.   Then leave it there as a space station/spare parts/backup


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#10 2018-10-02 14:48:16

spacetechsforum
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Posts: 32

Re: Looking at the Mars Colony's development, based on Space X & BFR

Louis, the BFR is designed for take-off from earth (so it must be parked on earth vertically) so we can safely assume that all internal components will also work well in lower gravity (when parked on Mars vertically). Also i think the layout will be designed for vertical use (floor, walls, stairs) since in space the orientation does not matter.
For rocks... Well, the structure must withstand it either way - you need to fly the ship back.
Also, I personally think the people will fly to Mars when there will be a fully tanked, parked, well pictured from space and ready to go back BFR. All task needed will be completed by automatic machinery beforehand.

Last edited by spacetechsforum (2018-10-02 14:55:35)

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#11 2018-10-02 14:52:32

Belter
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Re: Looking at the Mars Colony's development, based on Space X & BFR

No, you'd land the BFRs all before anyone gets there.       Flying rocks could be a problem, I suppose though I doubt they'd do much more than make dents.   The ships already have to be resistant to meteorites.    Though it could be interesting to drop retaining fences for the landing sites to prevent rocks from flying round.   Or have the BFRs drop some sort of protective barrier to shield them.   Another option would be to try to send robots to prep the landing sites and ensure that they are solid enough for landing.  If one foot lands on a pocket of dust, it would be pretty ugly.     

To the contrary, I don't think anyone is going to go to Mars if the only way off the rock is a functioning propellant plant that has all the necessary supplies.    This could be a good use for the SFR.   Send several of those for launch vehicles and leave a BFR or two in orbit, while landing 2-10 BFR-Cargos.

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#12 2018-10-02 16:33:39

Oldfart1939
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Registered: 2016-11-26
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Re: Looking at the Mars Colony's development, based on Space X & BFR

louis wrote:

We are now getting closer and closer to a real Mars colonisation project whether humans land in 2024, 2026 or 2028. The likelihood is they will do so as part of a Space X project using BFRs...

Louis-
This past weekend whist on a mini vacation in Yosemite National Park, I visited with an old friend who is a Principal Investigator at the Nuclear Ignition Laboratory at Lawrence Livermore National Laboratory. After getting an update on progress towards a sustained fusion reaction, the topic turned to going to Mars. My friend Ed simply stated that he didn't believe NASA would be responsible for getting humans to Mars, and he believed SpaceX would accomplish it far sooner than NASA could ever accomplish the task.

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#13 2018-10-02 16:59:34

GW Johnson
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Re: Looking at the Mars Colony's development, based on Space X & BFR

BFS cannot stop in Mars orbit as it is currently designed.  The mass ratio is not there to provide the 1.6-1.8 km/s delta-vee to decelerate from a Hohmann transfer orbit into low Mars orbit.  The variation is due to Mars's elliptical orbit about the sun. 

BFS has the mass ratio to provide the 3.9 km/s delta-vee to depart low Earth orbit onto the Hohmann transfer orbit,  with at most 1 km/s delta vee left.  It needs 0.7 utter-min to 1 more-realistic km/s delta-vee to land,  with all the rest of the deceleration from hypersonic aerobraking on a direct entry trajectory. 

The propellant "margin" above that total 4.9 km/s delta-vee capability is measured in single-digit percentages.  So no,  it cannot stop in low Mars orbit,  not without a major redesign that is essentially a new design with 5.7+ km/s delta-vee capability.

And,  even with reduced payload returning from Mars,  there is no margin at all to launch into the return Hohmann trajectory (5.3-5.4 km/s),  and direct-entry aerobrake to that final propulsive landing on Earth.  It takes the full 1100 ton propellant load to do this.  It arrives at Earth with only ~0.7 km/s worth of delta-vee for the landing.  To capture into Earth orbit is another 3.9 km/s burn,  so,  no,  it cannot do that either!  The only way it can do this baseline return is with a reduced payload of 30-something tons.

Sorry to bust some pet ideas,  but the BFR/BFS design has some very definite and stringent limits.  And it does NOT have the delta-vee capability to fly a faster trajectory to and from Mars,  either.  Hohmann min energy-only. 

You don't want to land these things very close to anything else at all.  If it topples over (and it easily could!!!),  it WILL explode.  That throws major chunks of debris distances measured in km on Mars.  Showing these things within half a km to a km apart,  or that close to a base,  is UTTER NONSENSE!!!

GW

Last edited by GW Johnson (2018-10-02 17:05:23)


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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#14 2018-10-02 17:36:16

louis
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Re: Looking at the Mars Colony's development, based on Space X & BFR

That's not part of the Space X plan, and this is about how the Space X project will affect Mars colony development.

SpaceNut wrote:

The ships use verticle for landing and gravity of the planets but in space we will be creating artificial gravity to keep the crew healthy and that could be tumbling end over end or rotating in some designs...which would also change what we are calling floors and ceilings....

Of course there is also the impact on plumbing through out the ship under those same conditions of use.

Happy to hear that you got to see old freinds Oldfart1939....It isinteresting that they whom do work for Nasa and others would see Nasa as not getting to mars.


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#15 2018-10-02 17:37:52

louis
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Re: Looking at the Mars Colony's development, based on Space X & BFR

Good to hear Oldfart!  But whether it's 2024 or some later, possibly much later, date remains to be seen.

Oldfart1939 wrote:
louis wrote:

We are now getting closer and closer to a real Mars colonisation project whether humans land in 2024, 2026 or 2028. The likelihood is they will do so as part of a Space X project using BFRs...

Louis-
This past weekend whist on a mini vacation in Yosemite National Park, I visited with an old friend who is a Principal Investigator at the Nuclear Ignition Laboratory at Lawrence Livermore National Laboratory. After getting an update on progress towards a sustained fusion reaction, the topic turned to going to Mars. My friend Ed simply stated that he didn't believe NASA would be responsible for getting humans to Mars, and he believed SpaceX would accomplish it far sooner than NASA could ever accomplish the task.


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#16 2018-10-02 19:34:13

SpaceNut
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Re: Looking at the Mars Colony's development, based on Space X & BFR

louis wrote:

1.  Space X have hinted that landed BFRs could be used as habitat. I am a little sceptical about that.  A craft designed for  a zero G environment is in my view going to be pretty useless as habitat on Mars.

Belter wrote:

1.  I don't see the issue with the gravity/0gravity thing.    Pretty sure they're going to be designed for a vertical gravity layout and in space, it is what it is because it just doesn't matter what the layout is in 0G.

louis wrote:

1.  I think there are issues. Systems designed for zero G have pumps and so on but they are not operating in gravity conditions. You might be able to have a vertical arrangement, but that's not necessarily the best arrangement for space.  Just take floors...you will have to adapt those. If you are designing them for gravity conditions you will probably be making them far heavier than they need be...it will be wasteful mass.  I am sure there are lots of issues like that. Will vaccuum toilets work well on Mars? I don't know.

What this means is with not AG then you must design BFR with 2 plumbing systems in order to have what you need when you need it...That cuts into useable payload once more....0G systems use on mars would be dangerous...

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#17 2018-10-03 01:35:06

louis
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Re: Looking at the Mars Colony's development, based on Space X & BFR

Yes, I'm no engineer as you know, but I do know there's a difference between systems designed for 0G and a gravity environment.

SpaceNut wrote:

What this means is with not AG then you must design BFR with 2 plumbing systems in order to have what you need when you need it...That cuts into useable payload once more....0G systems use on mars would be dangerous...


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#18 2018-10-03 04:33:48

spacetechsforum
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Re: Looking at the Mars Colony's development, based on Space X & BFR

SpaceNut, why would you need two systems? I did not find any valid reason that is preventing the use of system working without gravity in 1G.
Reverse is more problematic. There is a problem of settling fluids on the bottom of the tanks in space, but solving that with small accelerations allows use of normal gravitational devices.

GW Johnson, I think you are wrong on that. You do not need to do a stop burn at Mars. BFR is designed with very good TPS and it can in theory perform aerocapture (the difference from reentry with landing seems to be only the reentry angle). There is around 1.6km/s of dv between crash and bouncing off into the void and the last visualisations show the BFR will be capable of some steering in atmosphere, but still doing this you will probably end up with not very precise long elliptical orbit. The problem is that the rocket will be stuck there since there are no means to refuel the craft.

Also I doubt there exist possibility to land BFR on the exact spot. Mass is big and the atmosphere density on Mars may be too diverse to calculate proper reentry parameters to stop at right moment. Even if this is manageable I think just for safety the landing sites will be far apart (Like wing failure may direct rocket straight at colony).

Last edited by spacetechsforum (2018-10-03 04:34:42)

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#19 2018-10-03 05:40:28

Belter
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Re: Looking at the Mars Colony's development, based on Space X & BFR

GW Johnson wrote:

BFS cannot stop in Mars orbit as it is currently designed.  The mass ratio is not there to provide the 1.6-1.8 km/s delta-vee to decelerate from a Hohmann transfer orbit into low Mars orbit.  The variation is due to Mars's elliptical orbit about the sun. 

BFS has the mass ratio to provide the 3.9 km/s delta-vee to depart low Earth orbit onto the Hohmann transfer orbit,  with at most 1 km/s delta vee left.  It needs 0.7 utter-min to 1 more-realistic km/s delta-vee to land,  with all the rest of the deceleration from hypersonic aerobraking on a direct entry trajectory. 

The propellant "margin" above that total 4.9 km/s delta-vee capability is measured in single-digit percentages.  So no,  it cannot stop in low Mars orbit,  not without a major redesign that is essentially a new design with 5.7+ km/s delta-vee capability.

And,  even with reduced payload returning from Mars,  there is no margin at all to launch into the return Hohmann trajectory (5.3-5.4 km/s),  and direct-entry aerobrake to that final propulsive landing on Earth.  It takes the full 1100 ton propellant load to do this.  It arrives at Earth with only ~0.7 km/s worth of delta-vee for the landing.  To capture into Earth orbit is another 3.9 km/s burn,  so,  no,  it cannot do that either!  The only way it can do this baseline return is with a reduced payload of 30-something tons.

Sorry to bust some pet ideas,  but the BFR/BFS design has some very definite and stringent limits.  And it does NOT have the delta-vee capability to fly a faster trajectory to and from Mars,  either.  Hohmann min energy-only. 

You don't want to land these things very close to anything else at all.  If it topples over (and it easily could!!!),  it WILL explode.  That throws major chunks of debris distances measured in km on Mars.  Showing these things within half a km to a km apart,  or that close to a base,  is UTTER NONSENSE!!!

GW

First, not sure why it can aerobrake to 0 mph, but not aerobrake to 10,000 mph.

Second, that's why you only do this with the cargo ships.  After all, there *is no base*.  And there won't be for a long, long time.   The first ships that arrive will be "the base" for years, if not decades.

Third, at some point, robots are going to be sent to clear landing areas, perhaps even construct a platform.  If we're worried about rockets tipping over, we shouldn't be sending huge manned landers like the BFR and should be doing something more along the lines of the SFR.

I think it's a serious issue if they can't land these things within about 100m or so of each other.   You can't call ships spread over km "a base".  There would be minimum contact between the crews since it would be a full suit affair just to go back and forth.    The other issue with these ships is that the manned part is 30m up with no elevator.  So.....they need to deal with lowering vehicles and such to the ground, but with no way to dock them.   So just to go visit another ship is going to be an all day affair.     At some point, either these things are designed to be cannibalized, or they need to be adaptable enough to convert the rocket chamber into living quarters and close enough that tunnels can be built between them.   Otherwise, the BFRs serve little purpose as cargo ships OR as habitats.   

By time they land, they should have less than 5-10% of their fuel capacity on board.   So while an explosion would be catastrophic for the ship, I don't think that would necessarily inflict any kind of deal breaking damage to the others.   The actual safe [enough] distances is are up for debate but minor damages could be repaired.  And I think the first ship could use laser targeting to guide the next ships in to an accurate position, since we don't have GPS on Mars.   

When the manned ships land, they won't have to worry that much.  They can land around the periphery and pray there isn't a failure because they'd be screwed.  But at a distance that would still allow them to take off, though I still think the BFR is the wrong ship for that.   It seems to me that a staged ship that left the booster in orbit would make more sense.   Like the Falcon first stages, let them separate, use aero braking or sling shot techniques to slow them into eventual low Mars orbit for future possible uses.  Let just the tip of the ship land, which would make it far more stable and less prone to falling over from a bad landing.   I guess the "beauty" of the design is in the fact that it only needs one group of engines.    I think Musk is saying "permanent Mars base", but he's running it more like Apollo.  Go, hang out, leave.   Because I don't see much going on that leads me to believe an actual base is going to happen out of these launches.

Last edited by Belter (2018-10-03 07:20:41)

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#20 2018-10-03 05:44:45

Belter
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Re: Looking at the Mars Colony's development, based on Space X & BFR

louis wrote:

Yes, I'm no engineer as you know, but I do know there's a difference between systems designed for 0G and a gravity environment.

I don't see this is some sort of insurmountable issue.  Especially with plumbing.   Just design it for both situations.  That leaves little else.   People are clever.   These aren't remotely the big challenges.

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#21 2018-10-03 07:04:42

louis
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From: UK
Registered: 2008-03-24
Posts: 4,591

Re: Looking at the Mars Colony's development, based on Space X & BFR

Why put all that extra mass in if it's not necessary.

Belter wrote:
louis wrote:

Yes, I'm no engineer as you know, but I do know there's a difference between systems designed for 0G and a gravity environment.

I don't see this is some sort of insurmountable issue.  Especially with plumbing.   Just design it for both situations.  That leaves little else.   People are clever.   These aren't remotely the big challenges.


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#22 2018-10-03 07:21:08

Belter
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Registered: 2018-09-13
Posts: 184

Re: Looking at the Mars Colony's development, based on Space X & BFR

Because it's necessary, and it won't be that much mass.

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#23 2018-10-03 09:36:36

GW Johnson
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Re: Looking at the Mars Colony's development, based on Space X & BFR

To answer Spacetechsforum in post 18 and Belter in post 19:  if you direct-enter from the transfer orbit,  your velocity at entry interface is about 5.3 km/s (just above Mars escape) from a min-energy Hohmann transfer orbit,  up to 6-7 km/s from a faster trajectory.  A one-pass entry aerobrakes that to just about local Mach 3 (when the hypersonics are over for a blunt object),  which is about 0.7 km/s.  It's NOT zero speed,  it's still quite high. 

On Mars,  this occurs for a big object at very low altitudes,  under 5 km,  so that you are scant seconds from impact. 

To land,  you must "kill" that remaining speed with an engine burn,  and you have to do it at the 3-4 gee deceleration class.  That's all the time you have.    It would be just about the same,  whether a high-speed direct entry,  or just landing from low Mars orbit. 

There is not time for a parachute to have any effect,  and the dense object that is the vehicle is too big for a chute,  anyway.  Spacex's Mars landing simulation presented in 2017 showed a pull-up that decelerated the vehicle,  almost into a tail-slide maneuver,  at which point the engine burn begins for the landing. 

I'm skeptical about pulling-up in air that thin;  I think they will need thrust from the engine to make up deficient lift,  so the landing burn delta-vee is closer to 1 km/s than it is 0.7 km/s. 

What Musk showed in 2018 with the "skydiver" descent is an Earth landing,  not a Mars landing.  Don't be fooled by that. 

I only bring up braking into orbit,  because others on these forums keep grasping at that straw.  If you decelerate into Mars orbit at 3.5 km/s from a 5.3 km/s near-Mars velocity,  that's a 1.8 km/s engine burn delta-vee,  period.  No way to avoid that.  You are doing that after spending 8-9 months in transit exposed to zero-gee.  Bodies are weakened by this,  but experience coming home from ISS after 6 months says entry gees under 4 are no health hazard in that weakened state.  You must contend with braking gees,  and eventually with 3-4 gees on landing.

Did you notice that crews staying a year are NOT routine at ISS?  Ever think there might be a reason for that?  There is,  and they don't like to talk about it.  The crew's bodies are further weakened,  and the 4 gee return is a lot more of a health risk.  Upon reaching Mars,  we will have crews exposed to zero-gee for 8-9 months in transit.  Worse than a 6-month ISS crew,  but not as bad as a 1-year ISS crew. 

The alternative to direct entry is aerobraking capture into an elliptical orbit that grazes into the atmosphere at its perigee.  Beside the fact that Mars atmospheric density erratically varies by a factor of 2,  unlike Earth,  making predictions uncertain,  this means repeated deceleration gee exposures at some level,  and multiple months added to the flight as the orbit apogee slowly reduces from the repeated aerobraking decelerations.  You'll be weaker from close-to-a-year exposed to zero gee,  before you have to endure that 3-4 gee landing. 

Add to that the fact that repeated aerobrake passes are inevitably repeated burns on a heat shield that is a finite-life ablative (it's PICA-X ablative).  With its worst burn-up threat at the end of its life when you enter at Earth upon return home.  At harsher conditions than at Mars.  I show about 11 km/s at entry interface from a min energy Hohmann transfer.  It can be up to about 17 km/s for faster trajectories. 

The risks of using repeat aerobrake capture into orbit with a manned BFS just look like unnecessary things to be avoided.  Besides,  in orbit,  there is no way to refuel it,  because the propellant plant has to be on the surface where the ice and the CO2 are.  You have to land anyway,  to refuel.  Why not just land direct and be done with it?  One entry heating exposure,  shorter human zero-gee exposure.  I'm pretty sure that is how Spacex views it,  too. 

As for the explosion of a nearly empty ship upon toppling,  yes,  the yield is lower.  That's fewer pieces of shrapnel.  But the explosion pressure and velocities are unchanged.  Only the amount,  not the type,  of chemistry changed.  So the shrapnel velocity and range are unchanged.  No,  it's not significantly safer to explode nearly-empty tanks.  I worked with explosives and fuels.  I know. They need to land these things ~2 km apart and away from anything else of any value at all. 

And a revetment around the landing pad doesn't change that.  The shrapnel that flies the furthest is that which leaves on a 45-degree trajectory above horizontal.  There is no practical revetment for that. 

I do agree that hard-paved landing pads would be far better for the BFS.  Even with fins as landing legs.  It's the rough-field effects that are going to cause one of these to topple over and blow up.  Height / leg span ratio is still about 3 for BFS.  It was under 1 for every other successful rough-field lander,  anywhere,  any-when. 

We're talking foot-thick (still undeveloped) equivalents to reinforced concrete,  to get the bearing strength to support the thing,  and the thermal heat-sink capacity to survive the jet blast. There's still a thermally-induced spalling danger,  so repairs will have to be made constantly. 

That spalled concrete stuff is also flung shrapnel,  by the way.  Just like loose rocks on a rough-field site being shrapnel.  Even if the ship lands successfully. 

GW

Last edited by GW Johnson (2018-10-03 10:19:03)


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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#24 2018-10-03 13:48:59

louis
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From: UK
Registered: 2008-03-24
Posts: 4,591

Re: Looking at the Mars Colony's development, based on Space X & BFR

It's only necessary if you think it's a good idea having humans perched 20 metres up on rockets - probably with residual fuel and propellant on board.  Will there be an airlock to the outside [I mean one at ground level connected to the rocket by some sort of tunnel]?  If so, that's a whole new bit of engineering you have to put in place. If not, they have to do an EVA (takes hours to get into a conventional EVA suit, and even an MCP won't be quick - probably 30 mins or so).

Either Space X haven't thought this through (quite possible, but a bit surprising) or they are throwing out chaff to confuse their competitors (possible, but less likely I feel).

Belter wrote:

Because it's necessary, and it won't be that much mass.

Last edited by louis (2018-10-03 14:24:46)


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#25 2018-10-03 14:11:39

Belter
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Registered: 2018-09-13
Posts: 184

Re: Looking at the Mars Colony's development, based on Space X & BFR

To be clear, I'm only really talking about orbital aero braking for a few unmanned ships to be dropped in orbit.    Ideally, these would be linked to landers that would would be better designed for an aerobraked landing.  Wider, shorter, more stable.    Better designed for being recycled into habitats or torn down for building materials.  More similar to the lunar lander, but larger.   The crew would leave the orbital vehicle to make the aerobraked landing, then be able to return, dock and then use the now orbiting ship to depart for Earth as needed.   Like the LM, the descent platform would become the launch pad for the ascent module, but would also be engineered to converted to living quarters and/or drop critical supplies.  It would be even better if the legs could be retracted to allow it to sit directly on the ground.   The Ascent module would be used to ferry back to the orbital ship for return trips until manufacturing and fueling became reality.    I'm imagining something that looks like a hamburger with legs.   The Ascent module could have its own engine/fuel tank, or could simply detach from a ring shaped descent module, more like a mushroom detaching from a donut.

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