Author Topic: MCT Speculation and Discussion Thread 4  (Read 626168 times)

Offline Lampyridae

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Re: MCT Speculation and Discussion Thread 4
« Reply #1700 on: 02/18/2016 05:56 AM »
The bunks will almost certainly be vertical. Say 1.5m in from the wall, 1.5m of wall circumference, and then you can do an inner ring of bunks with similar dimensions. With such an arrangement you can easily fit 30 people in a 12m diameter floor, half that for your 8.3m radius tank. Also, the central corridor and doors are wasted space. Doors need space to open and if they open into a corridor can smack an unsuspecting passenger or snag some cargo being pushed along. All you need is a standard door-sized hole to make a corridor.
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Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1701 on: 02/18/2016 06:29 AM »
The bunks will almost certainly be vertical. Say 1.5m in from the wall, 1.5m of wall circumference, and then you can do an inner ring of bunks with similar dimensions. With such an arrangement you can easily fit 30 people in a 12m diameter floor, half that for your 8.3m radius tank.
That might have worked on Shuttle but how were you going to handle launch?
Quote
Also, the central corridor and doors are wasted space. Doors need space to open and if they open into a corridor can smack an unsuspecting passenger or snag some cargo being pushed along. All you need is a standard door-sized hole to make a corridor.
Perhaps but a single depressurization event anywhere in this connected space now threatens everyone.

Yes it's probably the number of headaches caused by people being hit by closing compartment doors will be higher than the number of blow outs on any given flight but the consequences if one did happen are much more severe.
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Offline Lampyridae

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Re: MCT Speculation and Discussion Thread 4
« Reply #1702 on: 02/18/2016 06:49 AM »
The bunks will almost certainly be vertical. Say 1.5m in from the wall, 1.5m of wall circumference, and then you can do an inner ring of bunks with similar dimensions. With such an arrangement you can easily fit 30 people in a 12m diameter floor, half that for your 8.3m radius tank.
That might have worked on Shuttle but how were you going to handle launch?

It did work on shuttle too. The spare seats are folded and stowed.



Launch/landing is the least of the worries for layout. We're not going to be pulling 20g like Tintin on the way to the moon - maybe 3 or 4.

Quote
Quote
Also, the central corridor and doors are wasted space. Doors need space to open and if they open into a corridor can smack an unsuspecting passenger or snag some cargo being pushed along. All you need is a standard door-sized hole to make a corridor.
Perhaps but a single depressurization event anywhere in this connected space now threatens everyone.

Yes it's probably the number of headaches caused by people being hit by closing compartment doors will be higher than the number of blow outs on any given flight but the consequences if one did happen are much more severe.

Sorry, I was not clear - a door in the floor and ceiling, which can close. In kaoru's design, a blowout could depressurise the corridor and leave everybody trapped (assuming they shut all ~50 doors). Also, it has the problem of opening a pressure-sealed door to get to your cabin, when a simple zip-up soundproofed flap works just as well.

You just need one door in the floor, one in the ceiling. And if you seal off every floor (fire is a lot more likely on a spaceship than a blowout), you have the tricky problem of what to do about reaching survivors in a trapped compartment. Airlocks on every floor? Suits? Docking ports? These will need to be trade spaced for the best solution.
« Last Edit: 02/18/2016 06:53 AM by Lampyridae »
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Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1703 on: 02/18/2016 06:50 AM »
BTW

100 people weigh somewhere around 9-10 tonnes. Open loop LSS is 50 tonnes of consumables (hopefully 1/2 that or less with SoA ECLSS closing most of the loops)

But whats the power  & thermal situation?

I mean what are current figures of merit for PV arrays and radiators? In 2008 80-100W/Kg for a rigid array was SoA.  The same report gave thin film systems around 2000W/Kg It lists ISS as roughly 1W/Kg, a staggeringly low number IMHO.

http://www.spacefuture.com/archiveearly_commercial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml

But what about radiators.

On Earth a human being has been simulated by a 400W incandescent lamp. So figure 40Kw for humans alone?  It's also likely to be low temperature heat, so radiation efficiency is likely to be low.

Does anyone have some actual numbers? IIRC ISS is about 40W/m^2 but that sounds like garbage.
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Offline Lampyridae

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Re: MCT Speculation and Discussion Thread 4
« Reply #1704 on: 02/18/2016 07:04 AM »
BTW

100 people weigh somewhere around 9-10 tonnes. Open loop LSS is 50 tonnes of consumables (hopefully 1/2 that or less with SoA ECLSS closing most of the loops)

But whats the power  & thermal situation?

I mean what are current figures of merit for PV arrays and radiators? In 2008 80-100W/Kg for a rigid array was SoA.  The same report gave thin film systems around 2000W/Kg It lists ISS as roughly 1W/Kg, a staggeringly low number IMHO.

http://www.spacefuture.com/archiveearly_commercial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml

But what about radiators.

On Earth a human being has been simulated by a 400W incandescent lamp. So figure 40Kw for humans alone?  It's also likely to be low temperature heat, so radiation efficiency is likely to be low.

Does anyone have some actual numbers? IIRC ISS is about 40W/m^2 but that sounds like garbage.

400W? No, more like 100W. 400W is like a champion cyclist going full tilt. 40W/m^2 sounds about right on average for low-temperature ammonia radiator panels. Google is your friend. Each radiator panel can dump a maximum of about 200W/m^2.
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Online hkultala

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Re: MCT Speculation and Discussion Thread 4
« Reply #1705 on: 02/18/2016 08:15 AM »

400W? No, more like 100W. 400W is like a champion cyclist going full tilt. 40W/m^2 sounds about right on average for low-temperature ammonia radiator panels. Google is your friend. Each radiator panel can dump a maximum of about 200W/m^2.

You are confusing mechanical power created vs heat energy generated. Humans have only about 30-40% energy efficiency when converting food to mechanical work, the rest is going to heat.

Top cyclist full power is about 1 kW, sustainable aerobic power about 400W. (I can do 700W on sprint and 300W sustained and I'm not a top cyclist.) Multiply that by 3 to get the total energy consumed(and heat generated assumed the work goes to heat) and that champion cyclist created 3 kW of heat on full spring, or 1.2 kW sustained.

But the 100 watts is still quite close to the idle consumption of humans,
women might be able to produce just 100 watts, men are typically bigger and heavier and produce something like 120-130 watts.
« Last Edit: 02/18/2016 08:20 AM by hkultala »

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1706 on: 02/18/2016 12:27 PM »
2000kcal diet works out to 100Watts average. Conversion efficiencies irrelevant, it all becomes heat. :P
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Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #1707 on: 02/18/2016 02:38 PM »
After reading the NASA reports/specs for "orbital" modules and reading the posts here, there seems to be a disjoint.  The MCT has to ascend and land which means passengers will need a seat.  Moreover, the MCT will be on Earth and Mars (in the vertical position) therefore orientation is predetermined.  This means that the vertical height will be fixed, most likely 7 feet.  The area (not volume) for a crew/sleep station should the size of a bed and storage.  The bed would articulate into a seat and workstation (aka cubicle).  Think of like a first class seat on a long haul aircraft.  Bed at (simulated) night and cubicle by day.  Not that different from my life if you minus my commute.  :)

Kaoru

The seat will need to oriented properly for takeoff and landing, but in microgravity during flight it can be moved to the wall. That will allow the personal space to be more vertical than horizontal. There will need to be enough room for a computer and storage of some personal items along the walls. 1.5m by 1m by 2.25m high totaling 3.375m^3 should be plenty of volume for personal space.

Sleeping and working in shifts can easily result in a crewperson spending 50% of their time in their personal space. With that in mind, 15m^3 per person would be about the same as 27m^3 per person if there was only one shift. That's a comfortable volume for a few months in microgravity. Going from 15m^3 down to 12m^3 would still be reasonable.

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1708 on: 02/18/2016 08:00 PM »
The bunks will almost certainly be vertical. Say 1.5m in from the wall, 1.5m of wall circumference, and then you can do an inner ring of bunks with similar dimensions. With such an arrangement you can easily fit 30 people in a 12m diameter floor, half that for your 8.3m radius tank. Also, the central corridor and doors are wasted space. Doors need space to open and if they open into a corridor can smack an unsuspecting passenger or snag some cargo being pushed along. All you need is a standard door-sized hole to make a corridor.
Obviously, I thought about making the bunks vertical (a la NASA) but that mode is only good for orbit/space.  What about when landed on Mars.  You can't move 100 people plus cargo when no or a limited hab is in place.  You'll need a place and do a migration over time; that means normally oriented beds.

As for doors, notice how they open.  I oriented the doors so that they are inline.  Why?  My intent was to model a top to bottom grab rail for traversing the core *on orbit* without being in the way of the doors.  The grab rails are door guards.  Also, the grab rails will do double duty as rails for a elevator/lift when *on surface*.

The doors can be auto-closing in case of depressurization.  As for case of the central core or any passenger station being depressurized, the NASA standard of wearing a pressure suit (like SpaceX's one) on ascent/EDL ops is given.  The suit will be stored under the seats when not in use.  If a emergency depressurized occurs, doors automatically close and occupants would don their suits.  Software can control the locking/unlocking of the doors via simple rules.

Kaoru

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1709 on: 02/18/2016 08:11 PM »
The seat will need to oriented properly for takeoff and landing, but in microgravity during flight it can be moved to the wall. That will allow the personal space to be more vertical than horizontal. There will need to be enough room for a computer and storage of some personal items along the walls. 1.5m by 1m by 2.25m high totaling 3.375m^3 should be plenty of volume for personal space.

Sleeping and working in shifts can easily result in a crewperson spending 50% of their time in their personal space. With that in mind, 15m^3 per person would be about the same as 27m^3 per person if there was only one shift. That's a comfortable volume for a few months in microgravity. Going from 15m^3 down to 12m^3 would still be reasonable.
You still need a bed in the horizontal position if one of the modes is to use the module as a temporary hab on Mars.  It is *great* idea to allow the seat/bed to be reconfigured for more space while on orbit.  With an articulating frame you can have a normal (horizontal) seat, horizontal bed (for Mars surface; temporary), and a vertical bed for on orbit.  I'll see if I can work that into my module.

Kaoru

Offline RocketmanUS

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Re: MCT Speculation and Discussion Thread 4
« Reply #1710 on: 02/18/2016 08:18 PM »
The seat will need to oriented properly for takeoff and landing, but in microgravity during flight it can be moved to the wall. That will allow the personal space to be more vertical than horizontal. There will need to be enough room for a computer and storage of some personal items along the walls. 1.5m by 1m by 2.25m high totaling 3.375m^3 should be plenty of volume for personal space.

Sleeping and working in shifts can easily result in a crewperson spending 50% of their time in their personal space. With that in mind, 15m^3 per person would be about the same as 27m^3 per person if there was only one shift. That's a comfortable volume for a few months in microgravity. Going from 15m^3 down to 12m^3 would still be reasonable.
You still need a bed in the horizontal position if one of the modes is to use the module as a temporary hab on Mars.  It is *great* idea to allow the seat/bed to be reconfigured for more space while on orbit.  With an articulating frame you can have a normal (horizontal) seat, horizontal bed (for Mars surface; temporary), and a vertical bed for on orbit.  I'll see if I can work that into my module.

Kaoru
Inflatable mattress would work on Mars if needed for sleeping. Low mass, small volume when not inflated.

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1711 on: 02/18/2016 09:11 PM »
From the comments given on my model, I got some ideas on how to improve space and access.  The idea RonM gave me got me thinking on how to have the seat/bed articulate horizontal to vertical.  For a display/workstation, I always planned to make it part of the seat/bed with an overhead console that contains air vent/fan (on orbit will always be on; got to move air around), lighting, connections (for pressure suit), and communications.  The pressure suit can be store in the overhead console/bin.  Think like an airplane.  However, this seat/bed with overhead console/storage would be fully integrated together.  This means that it will be functional as a horizontal bed, seat, or vertical bed.  Using this fold-away notion other equipment can now fold into this space for use.

One possible uses for this space is for exercise.  For example, an exercise treadmill will be necessary for everyone to stave off the effects of weightlessness.  However, having equipment as such per passenger station or in a common area has pros and cons.  I would like hear people opinions on how the space could be utilized (without costing a lot of mass) vis--vis common areas like food prep, eating, hygiene, exercise, etc.

Update:  I forgot to mention my idea for the doors.  Originally I oriented the doors so that I could do a grab rail/lift rail that extends from the top to the bottom.  However, I like the idea of having a large central core but having the 8 doors latching onto the 4 rails shrinks the core space.  I got a brilliant idea from the Model X, make the doors double hinged (aka a folding door) and automatic (with sensors).  This effectively doubles the core space and doubles the elevator/lift area.

Kaoru
« Last Edit: 02/18/2016 09:22 PM by kaoru »

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #1712 on: 02/18/2016 09:55 PM »
That's an order of magnitude greater duration than the MCT's 3 month trip. Also, everything seems quite hand-wavy as to why /exactly/ that much space is needed.


90 day transit is insanely expensive in propellant, and while it might be possible to do it from LEO at huge cost in propellant.  But the longest leg of the journey is what you need to plan around and that is likely to be the Earth return leg.

Do your remember the discussion we had back on page 39 & 40 when we found that just 100 days Earth return launches from Mars surface would require 8.8 km/s DeltaV and significant aero-braking or propulsive capture at Earth.


Transit times of 120-180 days for Earth return are the range that's actually achievable.
I think this is no problem since you will land on Earth and you could easy recover from long voyage. What is important is trip to Mars, when arrived you have to be ready to work hard make colony alive.

Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #1713 on: 02/18/2016 10:46 PM »
From the comments given on my model, I got some ideas on how to improve space and access.  The idea RonM gave me got me thinking on how to have the seat/bed articulate horizontal to vertical.  For a display/workstation, I always planned to make it part of the seat/bed with an overhead console that contains air vent/fan (on orbit will always be on; got to move air around), lighting, connections (for pressure suit), and communications.  The pressure suit can be store in the overhead console/bin.  Think like an airplane.  However, this seat/bed with overhead console/storage would be fully integrated together.  This means that it will be functional as a horizontal bed, seat, or vertical bed.  Using this fold-away notion other equipment can now fold into this space for use.

One possible uses for this space is for exercise.  For example, an exercise treadmill will be necessary for everyone to stave off the effects of weightlessness.  However, having equipment as such per passenger station or in a common area has pros and cons.  I would like hear people opinions on how the space could be utilized (without costing a lot of mass) vis--vis common areas like food prep, eating, hygiene, exercise, etc.

Update:  I forgot to mention my idea for the doors.  Originally I oriented the doors so that I could do a grab rail/lift rail that extends from the top to the bottom.  However, I like the idea of having a large central core but having the 8 doors latching onto the 4 rails shrinks the core space.  I got a brilliant idea from the Model X, make the doors double hinged (aka a folding door) and automatic (with sensors).  This effectively doubles the core space and doubles the elevator/lift area.

Kaoru

I think as much as possible should be in common areas.

Having three shifts as Robotbeat suggested would get the maximum use out of the space. If a crewperson had to exercise for about one hour a day and if treadmills were available 24 hours a day, then the ship would only need five or six treadmills (some spare capacity for when one needs repair). A mess room for meals would only need to handle about fifteen people at a time. It could be larger if they wanted to avoid a strict schedule. There would just have to be a schedule for using these areas. Generic common areas would be larger for people to social, have meetings, etc.

Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1714 on: 02/19/2016 01:33 PM »
2000kcal diet works out to 100Watts average. Conversion efficiencies irrelevant, it all becomes heat. :P

OK so a baseline radiator needs to dump 10Kw from LEO out to Mars. I don't have a good number for specific power. 40W/m^2 from ISS gives 250 m^2 but what's that in mass? A quarter tonne? 25 tonnes? More?

I know over the years there have various proposals for tricky high efficiency space radiators using molten metals etc but AFAIK none of these have flown. Any updates on that would be greatly appreciated.

IMHO it's going to be liquids in a loop or vapors cooling back to liquids for the foreseeable future. I think tricks could be played with the surface properties to "tune" the IR emission frequency to most probable temperature, but I'm not sure how much that buys you in efficiency terms.

« Last Edit: 02/19/2016 01:39 PM by john smith 19 »
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1715 on: 02/19/2016 09:42 PM »
For a radiator, the figure of merit you want is mass per unit area. State of the art experimental radiators can do 1.5-2kg/m^2. I think older heritage designs are more like 6kg/m^2.

Power per unit area is determined by the Stefan-Boltzmann law:

Power/area = 5.67*10^-8 W/(m^2*K^4)*T^4
(Use absolute temperature, i.e. Kelvin)
So to reject 10kW using state of the art radiator at 300 Kelvin (10 degrees below body temp) is about 32 kilograms.

More realistically, 273Kelvin rejection temp (0Celsius) and 100kW of heat and a more conservative (but still aggressive) 2kg/m^2 requires 635kg.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1716 on: 02/19/2016 10:25 PM »
But note that the body of the spacecraft itself emits heat, though it's insulated for reentry. Which is a good argument for putting the crew quarters inside a cargo bay with doors that can open to space like Shuttle.
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Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1717 on: 02/20/2016 07:04 AM »
For a radiator, the figure of merit you want is mass per unit area. State of the art experimental radiators can do 1.5-2kg/m^2. I think older heritage designs are more like 6kg/m^2.
That's what I was looking for. Indicates propellant and HSF consumables are still the big mass items.
Quote
More realistically, 273Kelvin rejection temp (0Celsius) and 100kW of heat and a more conservative (but still aggressive) 2kg/m^2 requires 635kg.
I think the Shuttle payload bay door radiators worked around 60-80c
But note that the body of the spacecraft itself emits heat, though it's insulated for reentry.
True. I wanted to start with the human thermal load as we know the design is expected to support 100 people.

Above that will be heat from all the hardware in the system and solar radiation, close to 1300 W/m^2 above the  atmosphere at LEO.

That said I will note 2 things.

Heat can be treated as a resource. IIRC Shuttle hydraulic fluid circulated continuously on orbit to keep the actuators (out in the wings and tail) warm. I'm thinking better thermal control on mechanical stuff like aerial bearings perhaps.

Another option would be to use human power. 

Instead of packages of motors/gearboxes/sensors/power/data cabling just have someone pull on a lanyard at the right moment.  :)

I know. Very low tech. Very steam punk. But light weight, mechanically simple (theres a really neat way to transmit rotary motion through a solid metal wall which completely air tight) and with fault reporting just needs an intercom channel.
Quote
Which is a good argument for putting the crew quarters inside a cargo bay with doors that can open to space like Shuttle.
Maybe, but that would add substantial complexity and significant power requirements.

Worst case failure mode. Doors can't close. What do you do about Mars entry? Can you still do it?  Can you carry enough supplies for a free return back to Earth?
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1718 on: 02/20/2016 03:09 PM »
You'll have failure modes like that no matter what because you need doors to open for the radiators and solar arrays. There are ways to deal with such failure modes. And actually, back shell temperatures are quite modest.
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Offline JamesH

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Re: MCT Speculation and Discussion Thread 4
« Reply #1719 on: 02/21/2016 06:50 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?

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