Author Topic: MCT Speculation and Discussion Thread 4  (Read 610598 times)

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1560 on: 02/02/2016 03:43 AM »
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

Depends on your assumptions for "closed loop".

3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?

Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).
As you can see in the joined graph (Ames research center trajectory browser), most synods offer 120 to 180 day missions to Mars.  So if you do the math, you will find 52 tonnes of consumables for 180 days with 5 kg/person.  As mentionned by others, you will only be having 100 passengers when there is a base in place, so the rest of the trip time is not applicable.
To reduce to 25 tonnes you need to go to dehydrated foods, and do some fierce water and atmospheric recycling.  But that equipement will be essential on Mars, so it should be part of a colony package.
...one of the reason I dislike that tool is that it isn't really made for looking for short transits, and the numbers you get can be very misleading (including how it optimizes things) unless you're really careful. Just keep in mind that it's not telling you the limits of what can be done. In actuality, 100 day transits are available except for maybe 20% of synods, and even then opportunities are available for less than 120 days.
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1561 on: 02/02/2016 07:03 AM »
Some people are getting way off base on consumables, here.  We already have nearly total water and air closure and dehydrated food of around a kg a day is already the norm.

We are on the verge of getting that to the point where the metabolic byproducts of the food will be able to make up the losses of air and water at which point these will become de-facto fully closed when packaged food is being consumed, and on Mars we can certainly obtain them from the environment at greater then the loss rate if we expect to be making return Propellants in volume.

Most of the remaining consumables are packaging materials, clothing, toiletries, and spare parts.  The way to drive them down is things like developing space-laundry, more efficient bulk food packaging rather then individual MRE like meals, and more reliable systems using a common pool of highly interchangeable spare-parts.

The consumable masses can certainly come down but it will be done with techniques that will be from the efficiency of scale associated with a large crew size where a true 'galley' and 'laundry' area can exist.  You won't see much per-capita consumable mass reductions until the crew sizes get up into the mid 20's.
« Last Edit: 02/02/2016 10:54 PM by Impaler »

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1562 on: 02/02/2016 02:18 PM »
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

Depends on your assumptions for "closed loop".

3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?

Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).
My guess is the breakdown of the 5 kg is :
0,7 kg of oxygen, turned into CO2
3 kg of water
1,3 kg of food,
So there would be no allocation for recycling at all?

The oxygen can be recycled from CO2 using the sabatier process and some hydrogen, either stock of from the water coming from the food combustion.  As long as the unit weighs less that ,7*100*180 = 14 tonnes, including solar cells to run it, then we're ahead on that.

The water should be easy, the ISS already does that.  We need to treat 300 kg per day, plus whatever is used for sanitation and cleaning.  We can allow for some of it to get dirty, since even dirty water will be a good Martian import.  Again 5x100x180 = 52 tonnes, and we should be able to have a good cleaning system for much less mass than that.

The food will become compost.  It'll be recycled on the colony.
Why are you guys guessing and assuming and conjecturing when you could just be reading the NASA technical report on the subject I conveniently linked and picking apart individual numbers therein?

One snippet from the report states that water needs are filled mostly by food water content based on presentday space-food menus:
Quote
Although overall water recovery rates are less than 100% for the assumed ECLSS system, there is a net surplus of water produced. This surplus occurs because additional water is added to the system in the form of water in the food that the crew consumes. Although the food is “dehydrated” it still contains approximately 28% water. The result is that, under the assumptions made for the study, no additional water needs to be added to satisfy water or oxygen generation requirements. Further closure of the ECLSS system will not reduce total logistics requirements.

Quote
Water reclamation from H2O contained within food promotes water-rich operating conditions for the partially closed ECLSS. As such, only 30 days of contingency water and oxygen were required to be delivered with the habitat, resulting in 362kg and 99kg of water and oxygen required
respectively

On the other hand, long-run hygiene and laundry needs in excess of this report are something I've heard speculation about.

From their future possibilities section, it sounds like going from 3kg per person*day to 2kg per person*day is probably doable with compromises on food palatability, much better container design, better loop closure, lighter weight waste management, and a few other things, but more is pushing it.
« Last Edit: 02/02/2016 02:45 PM by Burninate »

Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #1563 on: 02/02/2016 02:49 PM »
>
On the other hand, long-run hygiene and laundry needs in excess of this report are something I've heard speculation about.

 A supercritical CO2 washer unit requires no water, which also eliminates the dryer and any humidity or airborn lint issues..
« Last Edit: 02/02/2016 02:55 PM by docmordrid »
DM

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1564 on: 02/02/2016 03:08 PM »
I drink Spylent quite often. Less than 500grams per day are needed for complete nutrition, and you should be able to get that safely less than 400 grams by replacing some of the carbs with more fats. Some people live solely off of Soylent.

It then just becomes a question of how good your water recycling system is, and there's no limit there except at some point improving it further isn't worth it from a mass standpoint.

There's no fundamental reason you can't get the consumables mass per person down below 1kg/day.
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Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1565 on: 02/02/2016 03:23 PM »
One snippet from the report states that water needs are filled mostly by food water content based on presentday space-food menus:


"Water needs filled mostly by food water" and "presentday space-food menus". Two invalid assumptions if I ever saw any. Certainly for the 100 passenger transfer and probably for early flights too.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1566 on: 02/02/2016 03:53 PM »
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

Depends on your assumptions for "closed loop".

3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?

Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).
A) Where do you get 5kg/day?
B) Wait, what?  10 cargo missions per crew mission... of MCT?  1000 tons of cargo landed on the surface per 100 tons of manned mission?

And how many propellant missions per crew mission is that?  If you limited it to 6km/s each = 5:1 mass ratio @ 380s (probably not reasonable, given 3.2 C3, 0.5 minimum to MTO, more for single-synod reuse, and largely propulsive SSRP EDL), 40 prop launches to feed 10 cargo launches to feed 1 manned launch with its own 4 prop launches = 0.55 launches per person.

That would mean that a $500k ticket for 100 people per MCT needs to cost not $50M/launch, but ~$1M/launch.

Chain the math together.  Is this credible?
« Last Edit: 02/02/2016 04:05 PM by Burninate »

Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #1567 on: 02/02/2016 04:25 PM »
One must have bulk food for proper intestinal function.  Fiber.  It can be filled with dry grains such as oatmeal, whole wheat, wild rice, and such.  But frozen vegetables also.  A space freezer can be an air lock opened to space for some foods. 

I think before 100 people can go to Mars, smaller 4-12 people will go to set up ISRU equipment, solar systems, find water, etc.  Then cargo ships will bring supplies for storage, habitation units, more solar power systems, etc.  After a base is established, then 100 people can come.  Then they can receive more cargo and set up more habitation units, greenhouse units, etc.  Like someone said 10-1 cargo vs people.  A few I think will come with the cargo to get everything set up for the first group of colonists.  Then they will return while these colonists set up everything for the next group and so on.  I see people only staying a few years at first, then return to earth. 

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1568 on: 02/02/2016 04:28 PM »
Soylent includes fiber.

Remember, this is for 3 months, not for surface living.
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1569 on: 02/02/2016 11:49 PM »
Soylent includes fiber.

Remember, this is for 3 months, not for surface living.

Trying to save consumable mass by reducing the palatability of food ranks up their with pure oxygen atmospheres in the 'gram wise, kilo foolish' category of space speculation.

Food has been consistently rated the most important morale boosting thing Astronauts get, this is why NASA has spent so much effort in improving it's quality and done away with tubes of goo.  The mass is WELL worth it.  And it is not even a significant mass savings either, an astronaut on average consumes 1 kg per day of actual dry foodstuffs (an astronauts calorie consumption ranges from 2000 to 3000 calories a day a 50% increase over your calorie estimate).   The dry powder your proposing is going to be between 500g - 750g per day according to the products nutritional information.  Thus squares with the earlier reference that astronauts freeze-dried food still contains 28% water.  So the savings would only amount to that water difference because the powdered food product is completely desiccated.

So the savings are just 500g - 250g per day in the raw foodstuff itself at the cost of what would likely be a horrendous loss in morale.  While their would certainly be some potential for savings in packaging mass with a powdered product it would all come from using bigger pouches and containers, if it were packaged as individual servings it would be no improvement over the current food system of individual serving pouches.  Some packaging system that combines a full meal for several dozen people would be needed to get any real savings in packaging, but even this would have potential to negatively impact morale as individuals would lose the ability to choose what and when they eat individually.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1570 on: 02/02/2016 11:55 PM »
People can pay more for more food, then. Problem solved. But for those willing to skimp, save $10,000-100,000 and go with Soylent on the way there, that option should be available to them.
« Last Edit: 02/02/2016 11:57 PM by Robotbeat »
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Offline JamesG123

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Re: MCT Speculation and Discussion Thread 4
« Reply #1571 on: 02/03/2016 02:29 AM »
People can pay more for more food, then. Problem solved. But for those willing to skimp, save $10,000-100,000 and go with Soylent on the way there, that option should be available to them.

And they'll be barking mad and stealing other people's food and toothbrushes by the time they get to Mars.

Besides, you would need to carry a lot of extra people if you are going to use Soylent as a food supply.  ;)

Offline llanitedave

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Re: MCT Speculation and Discussion Thread 4
« Reply #1572 on: 02/03/2016 02:35 AM »
Soylent tends to increase flatulence, from what I've read.  We really don't want unpleasant conditions for all during the trip.
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Offline JamesG123

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Re: MCT Speculation and Discussion Thread 4
« Reply #1573 on: 02/03/2016 02:40 AM »
Soylent tends to increase flatulence, from what I've read.  We really don't want unpleasant conditions for all during the trip.

They can just open a window.  ;D

Offline launchwatcher

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Re: MCT Speculation and Discussion Thread 4
« Reply #1574 on: 02/03/2016 02:58 AM »
Soylent tends to increase flatulence, from what I've read.  We really don't want unpleasant conditions for all during the trip.

They can just open a window.  ;D
They wouldn't let another methane source go to waste, would they?



Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1575 on: 02/03/2016 03:03 AM »
"Why would anyone want to live on Mars?? I wouldn't want to! This is a fool's errand and should be stopped!"
"Why would anyone want to just drink Soylent?? I wouldn't want to! This is a fool's errand and should be stopped!"



You all are going to make me into a Ron-Paul-loving libertarian!

(I can see QuantumG and jongoff smiling right now.)
« Last Edit: 02/03/2016 03:03 AM by Robotbeat »
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Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #1576 on: 02/03/2016 04:13 AM »
I agree that going to a super restricted diet wouldn't be good. But consumables mass could still be quite low without that extreme.

A) Where do you get 5kg/day?

Basic human life support requirements per day are about 5kg - less than 1kg oxygen, less than 1kg dry food, and over 3kg water (including water in food).

This assumes either doing something other than normal bathing, or 100% recycling of cleaning water.
Quote
B) Wait, what?  10 cargo missions per crew mission... of MCT?

I believe Musk tweeted that.

Quote
And how many propellant missions per crew mission is that?

I don't know... depends on the size of MCT and the architecture.

Quote
If you limited it to 6km/s each = 5:1 mass ratio @ 380s (probably not reasonable, given 3.2 C3, 0.5 minimum to MTO, more for single-synod reuse, and largely propulsive SSRP EDL), 40 prop launches to feed 10 cargo launches

That assumes that the MCT arrives in LEO empty.

If BFR is really too large for any existing pad, I would expect MCT to either go to a higher energy orbit than LEO or arrive with significant propellant.

But cost per launch will nonetheless have to be incredibly low by current standards.

Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #1577 on: 02/03/2016 04:15 AM »
"Why would anyone want to live on Mars?? I wouldn't want to! This is a fool's errand and should be stopped!"
"Why would anyone want to just drink Soylent?? I wouldn't want to! This is a fool's errand and should be stopped!"

Rare people will willingly do all kinds of bizarre things, but if Musk wants a colony of millions (who can all spend $500k - ruling out lots of the people who might want to go) the conditions have to be not *that* bad.

EDIT: For something like Mars Direct, austere conditions make sense, since you can be extremely selective if you're only sending 4 people.
« Last Edit: 02/03/2016 04:16 AM by Vultur »

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1578 on: 02/03/2016 04:45 AM »
If you're going to Mars for years, drinking a protein shake on the way is going to be the very least of your psychological worries, I PROMISE you. Ridiculous.
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Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #1579 on: 02/03/2016 05:04 AM »
If you're going to Mars for years, drinking a protein shake on the way is going to be the very least of your psychological worries, I PROMISE you. Ridiculous.

Isn't that practically how some popular diets work these days? :)

And I agree with others... Flatulence is a great resource for ISRO production of propellant.  ;)
« Last Edit: 02/03/2016 05:04 AM by Lars-J »

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