Author Topic: MCT Speculation and Discussion Thread 4  (Read 569999 times)

Offline Hauerg

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Re: MCT Speculation and Discussion Thread 4
« Reply #1720 on: 02/21/2016 06:59 PM »
Usually when converting you have losses which express themselves as .... heat.
But SF might have "found" a better process.

Offline Jim

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Re: MCT Speculation and Discussion Thread 4
« Reply #1721 on: 02/21/2016 07:01 PM »
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity,

How was the electricity produced?  Conversion of energy produces heat.

Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1722 on: 02/21/2016 08:34 PM »
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?
No

The classic version of this is the Theremo Electric Modules used in RTGs to turn the decay heat from Plutonium directly into electricity. You're looking at about 8% efficiency.

So you need a smaller radiator, but you still need a pretty big one.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1723 on: 02/21/2016 09:17 PM »
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?
No

The classic version of this is the Theremo Electric Modules used in RTGs to turn the decay heat from Plutonium directly into electricity. You're looking at about 8% efficiency.

So you need a smaller radiator, but you still need a pretty big one.
Nope! You need a larger radiator because you're rejecting the heat at a lower temperature (all methods of extracting useful energy from heat require some sort of thermal gradient or thermodynamically equivalent).
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1724 on: 02/22/2016 06:02 AM »
Here's another quick grab of improvements to my passenger model.  The biggest change is the diameter which is now 10.1 meters, the same as the Saturn V first stage.  With this diameter, each deck holds 24 sleep stations and 24 seats (fold-away).  That means only 4 decks for 96 passengers.  The deck features an airlock door.  Being a work in progress, still got fill out the sleep stations and put in a fold-away ladder for up and down on surface access.

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Offline Lampyridae

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Re: MCT Speculation and Discussion Thread 4
« Reply #1725 on: 02/22/2016 07:15 AM »
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?

Nope because the electrical side gets hot and that needs its own set of radiators. Basically you make more waste heat than you throw overboard.

I read a paper ages ago which described a "laser radiator" which basically a very complex gasdynamic laser. Essentially it produced a beam of light with a blackbody radiation curve which carried the waste heat away (so not really a radiator which shoots heat away as a laser beam).
« Last Edit: 02/22/2016 08:22 AM by Lampyridae »
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Offline Lampyridae

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Re: MCT Speculation and Discussion Thread 4
« Reply #1726 on: 02/22/2016 07:44 AM »
Here's another quick grab of improvements to my passenger model.  The biggest change is the diameter which is now 10.1 meters, the same as the Saturn V first stage.  With this diameter, each deck holds 24 sleep stations and 24 seats (fold-away).  That means only 4 decks for 96 passengers.  The deck features an airlock door.  Being a work in progress, still got fill out the sleep stations and put in a fold-away ladder for up and down on surface access.

Kaoru

Unless you are designing for extended surface operations, you don't need the under-bed drawers, and you don't need the "dressing space" between the beds and the door. Designing for zero-g allows you to cheat by using a lot less space than normal. People don't stretch out in bed in zero gee - they float in foetal position, meaning your sleeping compartments are that much smaller. They can also go anywhere - wall, floor, ceiling. Lockers too can go anywhere. You don't need "floor" space where you can have a dual usage area - vertical corridors don't need landings, etc. Since your walls are all just partitions, you can just take them down and stow them for atmospheric entry and landing.



The 100-person MCT will only be operational much later in the 21st century. By then, Mars will have landing pads and domes / underground tunnels / modules/ whatever to handle an influx of colonists. Many of the initial colonists will earn their money by continually building colony habitats for the newcomers.

Now of course if you want to design for an artificial gravity environment during the trip, then that's going to change things and naval designs may be the better option (ie your current layout).
« Last Edit: 02/22/2016 08:00 AM by Lampyridae »
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Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1727 on: 02/22/2016 10:40 AM »
The 100-person MCT will only be operational much later in the 21st century.
And you know this how exactly? Musk seems quite clear on getting this up and running fairly soon.
Quote
By then, Mars will have landing pads and domes / underground tunnels / modules/ whatever to handle an influx of colonists. Many of the initial colonists will earn their money by continually building colony habitats for the newcomers.
Quite possibly.
Quote
Now of course if you want to design for an artificial gravity environment during the trip, then that's going to change things and naval designs may be the better option (ie your current layout).
It's a fair point that Musk does not not seem to have mentioned AG, although it would simplify some problems and effectively give everyone a workout without exercise machines.

But that would be a really bleeding edge design given our experience of in space AG systems to date IE one of the Geminis spinning on a tether with their booster.  :(
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Offline Lampyridae

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Re: MCT Speculation and Discussion Thread 4
« Reply #1728 on: 02/22/2016 02:18 PM »
The 100-person MCT will only be operational much later in the 21st century.
And you know this how exactly? Musk seems quite clear on getting this up and running fairly soon.
Quote

I have a soothsayer that says so. His name on these forums is Jim. :P

Some people would say AG would be less bleeding edge than landing a first stage rocket on a barge at sea. Or a reusable surface-to-surface Mars Colony Transport.
« Last Edit: 02/22/2016 02:18 PM by Lampyridae »
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1729 on: 02/22/2016 03:04 PM »
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.
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Online spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #1730 on: 02/22/2016 03:34 PM »
From one of the ISS videos, they show people sleeping in a bag attached to the wall.  This keeps them from floating around and touching something.  You don't need bunks in zero g.  I even saw one lady astronaut who designed a double bag for a husband/wife team for privacy.  Their work stations can double as their quarters like cubicles in large offices and they could have bags to sleep in and work quarters that also have doors for privacy.

If these living quarters could also be offloaded on Mars for habitats it would save a lot of money and trouble, even if you can only get 50 colonists at a time.   
« Last Edit: 02/22/2016 03:35 PM by spacenut »

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1731 on: 02/22/2016 04:24 PM »
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.

I agree. Short as in not much more than one year. We may need AG when we send people out to the asteroid belt or beyond.

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1732 on: 02/22/2016 05:20 PM »
Unless you are designing for extended surface operations, you don't need the under-bed drawers, and you don't need the "dressing space" between the beds and the door. Designing for zero-g allows you to cheat by using a lot less space than normal. People don't stretch out in bed in zero gee - they float in foetal position, meaning your sleeping compartments are that much smaller. They can also go anywhere - wall, floor, ceiling. Lockers too can go anywhere. You don't need "floor" space where you can have a dual usage area - vertical corridors don't need landings, etc. Since your walls are all just partitions, you can just take them down and stow them for atmospheric entry and landing.

The 100-person MCT will only be operational much later in the 21st century. By then, Mars will have landing pads and domes / underground tunnels / modules/ whatever to handle an influx of colonists. Many of the initial colonists will earn their money by continually building colony habitats for the newcomers.

Now of course if you want to design for an artificial gravity environment during the trip, then that's going to change things and naval designs may be the better option (ie your current layout).
I agree with you if the passenger module was going to be on orbit exclusively.  However, the modes that the passenger module will be employed is for both on orbit and on surface.  My take is that it will take lots of man power to build the first habitat on Mars.  This means the passenger module, as part of the Mars landing, will be the habitat for some time.  When on orbit, orientation or areas as you describe are meaningless.  However, on the surface it does matter so my layout inherently supports both on orbit and on surface modes.

Also, the use of walls and auto closing cabin doors (like a hotel room door) is for safety.  Ascent and EDL ops means that everyone will don their pressure suits (which are IVA only) and strapped in their fold-away seats.  The rest of the time, if a depressurization event occurs due to micro-meteoroid impact, etc. closed cabin doors prevent total loss of atmosphere.  In the event that the central core is loses pressure, the IVA suits and the deck doors (which can be made to close on pressure loss) can be used to get around and effect repairs.

Of course, my model is still a work-in-progress.  I had a lot done but now have to redo it for the new diameter.  Also, I'm adding interactive things like opening/closing doors.  I'm refining the model trying to be mass conscious.  My experience so far has shown me that building a BFR and BFS for 96-100 persons to Mars is doable, aka not outrageous to the extreme.

Kaoru

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1733 on: 02/22/2016 09:37 PM »
I don't believe we will see a large habitat that is intended for surface AND space usage.

Rather we will see SMALL (~10 person) habitats that are usable in both environments for early missions when their is no pre-existing base to move into.  And in this role I foresee a large wheeled habitat/rover filling the entire cargo bay and simply rolling out onto the surface as the ideal solution as it provides instant and maximum mobility for exploration.  The rover can act as the habitat for transit to mars, on mars and then back to Earth and the landing vehicles can all be of an identical nature with large empty cargo holds ideal for the heavy machinery and equipment that would dominate the early missions.  This also adds redundancy by allowing any of the landing vehicles to be the one used for return should one suffer a breakdown.

But that will be a VERY short-lived phase, maybe just 1-3 missions to do scouting, once real base building is done they will consist of  habitat structures permanently left on Mars with arriving persons immediately moving from the vehicle into these surface habitats. 

The vehicle will thus NOT need to be lived in under gravity.  At most the vehicle needs some kind of seating for experiencing g-forces on entry but that is it, it would otherwise be a habitat designed fully for zero-g living, much like the space shuttle.

Further I expect these later missions to use a larger space-only transit habitat as in Semi-Direct DRM mission plans, that will allow the landing vehicle to be designed around much much shorter duration usage, on the order of 3 days at most.  People can be packed in at around 1 m^3 each or less which will make it quit easy to understand how the same size vehicle can accommodate a 10 fold increase in head count, we must relax the time constraint proportionally. 

In something like coach air-plane densities the lander in this configuration is also an excellent high volume LEO taxi craft for rendezvous with the rest of the mission elements which will proceed to TMI (propellants habitats, cargo), thouse elements will have been built up over the 26 month period between departure windows and passengers must be brought to these elements only just before the TMI to minimize time in space and deleterious health effects of such so a high density taxi launched last is the most efficient solution.

Offline darkenfast

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Re: MCT Speculation and Discussion Thread 4
« Reply #1734 on: 02/23/2016 04:33 AM »
Here's another quick grab of improvements to my passenger model.  The biggest change is the diameter which is now 10.1 meters, the same as the Saturn V first stage.  With this diameter, each deck holds 24 sleep stations and 24 seats (fold-away).  That means only 4 decks for 96 passengers.  The deck features an airlock door.  Being a work in progress, still got fill out the sleep stations and put in a fold-away ladder for up and down on surface access.

Kaoru

Try stacking the bunks three-high, with pan lockers under the mattresses.  That will give you basically what enlisted personnel live in on U.S. Navy ships and better than some submarines.  You can put a surprising amount of stuff in one of those lockers.  Allow 100mm for the pan, 100mm for the mattress an .5 - .55 meters for the person.  Deck to overhead distance totals 2.1 - 2.25 meters.  For width and length, try .7m by 2 - 2.1m.

Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1735 on: 02/23/2016 06:45 AM »
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.
Most people would not consider 3-4 months a short trip.

However the practical work on AG is so limited it would absurd to bet your plans on it working.

If space exploration were done logically it's a technique that would have been tried decades ago and its benefits and problems already found. Yet in 2016 it still has had no full scale test.  :(
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Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1736 on: 02/23/2016 07:15 AM »
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.
Most people would not consider 3-4 months a short trip.

However the practical work on AG is so limited it would absurd to bet your plans on it working.

If space exploration were done logically it's a technique that would have been tried decades ago and its benefits and problems already found. Yet in 2016 it still has had no full scale test.  :(

Why do such a test? We do know for a fact that 1 year is not a problem. Advocates of AG should get over it.

Offline QuantumG

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Re: MCT Speculation and Discussion Thread 4
« Reply #1737 on: 02/23/2016 08:34 AM »
Yeah, I agree. Robotbeat convinced me of this years ago. Zero-g mitigation is now sufficient for exploration missions in the inner solar system. You could make the argument that it always has been.
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Offline Lampyridae

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Re: MCT Speculation and Discussion Thread 4
« Reply #1738 on: 02/23/2016 11:13 AM »
Zero-g certainly allows a much more compact ship than would otherwise be the case.
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Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1739 on: 02/23/2016 02:59 PM »
I agree that AG should not be in the critical path.  With that said...

Zero-g certainly allows a much more compact ship than would otherwise be the case.

Please convince me of this.  The counterpoint would be a bolo made of two MCTs connected by tether at the nose.  Spinup and spindown by synchronized use of RCS thrusters.

Assume MCT will not employ SEP, obviously.  Are booms to extend a small solar panel + radiator curtain roll so mass-expensive?
« Last Edit: 02/23/2016 03:00 PM by Burninate »

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