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#1 2017-08-20 08:49:19

Oldfart1939
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Registered: 2016-11-26
Posts: 1,718

Crewman size and mass affects mission to mars

Edit: SpaceNut:
I broke this out as it seems to get to the heart of a mission to mars is not just about a crew count but also of its mass per person and mission duration on the surface, as that means more fuel used to get to mars as well as to return home from Mars.

Oldfart1939 wrote:

My apologies to Rob, but it was late last night when I was writing and I was intending my reply to be aimed at Ian. The average weight per colonist that I use in calculating food requirements is the same as what the FAA uses for an "average passenger," or 170 pounds. That's a more realistic estimate than 140 pounds.

GW Johnson wrote:

FAA should be using closer to 200 lb than 170 lb for the "average passenger".  You run a weight-and-balance calculation with realistic weights,  and the results can be dramatic.  I suspect there have been some serious gross weight violations. 
GW

IanM wrote:

The problem with using the average weight of Americans is the fact that 70% of American adults are overweight or obese (https://www.cdc.gov/nchs/fastats/obesity-overweight.htm), and I worry that the same might happen to Martians if they adopt the same eating habits. (I myself am guilty of this; I'm 5'10", and in the summer of 2015 weighed a whopping 205 lb. I have since dropped to 180, but am still a bit pudgy.) 170 lb is around the upper limit of a healthy weight range of someone who is 5'10". In all fairness, Martians would probably be a bit taller due to lower gravity. According to space.com this would be an increase of up to 3% in microgravity, so someone who would be 5'10" on Earth would be up to 6' in a low-gravity situation (not necessarily Mars, which does have a sizeable gravity). In that case the maximum healthy weight would be 180 lb.

Oldfart1939 wrote:

We should be dealing with reality, not the ideal configuration of an individual. I too, am a 205 pound guy--not totally pudgy and a still fairly muscular at my 5' 10" height. When I was doing my calculations for a 550 day stay on the surface of Mars stay for early missions and a 7 man ("Person") crew, this resulted in a pretty heavy food supply. This calculated to a 7,000 kg food supply in a prepositioned location.

SpaceNut wrote:

At 5'4" and 140lbs I would probably not qualify as an astronaut due to hieght but then again I fit where most people can not to work on things.

RobertDyck wrote:

Astronaut Requirements
5'4" and 140lbs would qualify.

louis wrote:

You sound like the ideal dimensions to me! That's fighter pilot outline. But obviously age is another consideration. smile

SpaceNut wrote:

At 5'4" and 140lbs I would probably not qualify as an astronaut due to hieght but then again I fit where most people can not to work on things.


I'm certain that individuals of smaller stature and weighing less will have a distinct place in the earlier flights to and from the Red Planet. Considering the cost per kilogram of the payload, it would only make sense to prefer smaller and leaner crew. Not only that, but smaller crew also means less food and water necessary based on the 2% per Earth day food requirement.

Doing a quick calculation based on a crew of 4 200 pound astronauts, we get a food requirement of ~ 6900 kg for the total 950 day mission (200 days going, 550 on the surface, and 200 days returning). On the other hand we could send 5 astronauts averaging 150 pounds which results in a weight of food required of ~ 6500 kg for the same mission profile. Then, there would also be a reduction in weight of the astronauts themselves, and water required.

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#2 2017-08-20 09:46:16

RobertDyck
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Re: Crewman size and mass affects mission to mars

Mars Direct was based on 180 days transit to Mars, 500 days on the surface, 180 days back. I've argued to trim the surface stay a bit, down to 425 days. That would require a little more propellant to launch before optimal launch window, and a little more propellant for return. Same transit time both ways. This ensures one mission every time the planets align, and ensures the first crew arrives back home before the second crew departs. That has a couple advantages: (1) only one mission in space at a time, simplify mission control. (2) second crew has assurance they can get back alive, because the first crew did. (2) first crew can pass on lessons learned to second crew. Yes, there is radio, but when they're in transit between planets the signal delay means they can't talk in real time. They can only send recorded messages. That hinders conversation. It's much better if they can meet face-to-face, and actually talk.

That shorter time reduces food a bit. And improved air and water recycling means we can increase the proportion that is dehydrated, like Space Shuttle food. You still wouldn't send all dehydrated and dry food, but more than a mission would have using 1989/1990 vintage life support. That's when Mars Direct was developed. I don't know exactly what food would be like, but it should reduce food.

But again, this discussion thread is supposed to be about producing food on Mars for an early permanent settlement. Possibly the first permanent Mars base. It isn't about a science mission where you can bring food.

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#3 2017-08-20 11:11:56

SpaceNut
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Posts: 16,144

Re: Crewman size and mass affects mission to mars

As I opened in the edit of the first post this is a game changer for mass to mars being launched from earth and needing to be landed on mars surface.

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#4 2017-08-20 11:34:56

IanM
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Posts: 276

Re: Crewman size and mass affects mission to mars

Weight is something that can generally be controlled, in that if you have the same diet and exercise as someone of your height who is 150 lb (or any given weight) you will generally eventually gain/lose weight to become 150 lb yourself. That's why I "assumed" a healthy weight for Martians in calculating and controlling portions, so that there wouldn't be an obesity epidemic on Mars like there is in America.

What can't be controlled, however, is height. I assumed that the average Martian man would be 5'10 and the average woman 5'5, which are the respective median heights for white Americans (and I myself am a 5'10 male). However, more height in general means more mass, so for the sake of economics shorter people will probably be dominant in an early permanent settlement. Also, lower gravity means that people will be slightly taller, and according to Space.com, in microgravity this can be up to 3%, or around 2 inches for most human heights, which would further increase the amount of food needed for a colony.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#5 2017-08-20 14:34:43

elderflower
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Re: Crewman size and mass affects mission to mars

IanM wrote:

Weight is something that can generally be controlled, in that if you have the same diet and exercise as someone of your height who is 150 lb (or any given weight) you will generally eventually gain/lose weight to become 150 lb yourself. That's why I "assumed" a healthy weight for Martians in calculating and controlling portions, so that there wouldn't be an obesity epidemic on Mars like there is in America.

Ian, you have assumed that all humans have the same metabolism. They don't. They can have different weights for the same calorie intake and work output.

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#6 2017-08-20 17:14:38

IanM
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Re: Crewman size and mass affects mission to mars

elderflower wrote:

Ian, you have assumed that all humans have the same metabolism. They don't. They can have different weights for the same calorie intake and work output.

That is true, and that does reflect certain things as different heights, ages, and body fat percentages. But Calories in-Calories out is still the general rule of weight gain/loss, despite what exactly a "calorie" is being somewhat complicated. (http://physiqonomics.com/calories/)


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#7 2017-08-20 17:53:56

SpaceNut
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Re: Crewman size and mass affects mission to mars

So I take it that the ISS needs an experiment for work output for caloric intake for crew mass size as I got a feeling that a small man will put out the same amount of work at lessor caloric intake.

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#8 2017-08-20 18:34:28

IanM
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Posts: 276

Re: Crewman size and mass affects mission to mars

So I take it that the ISS needs an experiment for work output for caloric intake for crew mass size as I got a feeling that a small man will put out the same amount of work at lessor caloric intake.

I share your suspicion. The Total Daily Energy Expenditure (TDEE) is the number of calories a person expends every day. It depends on a lot of things, including height and weight, and you should eat that amount in food if you want to keep your body weight. So a smaller person will have a lower TDEE, and thus will eat less.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#9 2017-08-20 18:54:53

SpaceNut
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Posts: 16,144

Re: Crewman size and mass affects mission to mars

Also having seen the past ISS resupply failures prove out that rationing might be needed as well. It could be a point that should be considered when reducing the amount of food for any size crew count and mass make up such that there is a buffer of needed calories should some of the crew need more food.

So back to the other topic then I would suggest that if you want more that you must grow it on your time....

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#10 2017-08-20 20:01:28

Oldfart1939
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Registered: 2016-11-26
Posts: 1,718

Re: Crewman size and mass affects mission to mars

This discussion highlights the wisdom of prepositioned food supply well in excess of anticipated needs. Nobody wants to emulate Mark Watney. I've argued that there should be a 110% surplus above projected mission needs, just in case there's a supply failure due to a launch window accident. This is not a case for being pennywise and pound foolish; saving the pennies and skimping on the pounds (sent). If we're going there with a plan to stay, then everything sent will ultimately be used.

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#11 2017-11-15 14:20:25

pamelamartin
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Registered: 2017-11-15
Posts: 1

Re: Crewman size and mass affects mission to mars

I can agree with you but I think that in our world we could find couple of people who will prefer to emulate Mark Watney


I think that humanity will conquer outer space like we can see it in different futuristic movies and games. Because there are a lot of ways to win in such technological race

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#12 2017-11-15 15:49:36

Oldfart1939
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Re: Crewman size and mass affects mission to mars

They may WANT to emulate Mark Watney--until they've missed 3 meals.

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#13 2017-11-15 17:06:48

louis
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From: UK
Registered: 2008-03-24
Posts: 4,900

Re: Crewman size and mass affects mission to mars

My feeling on this subject is that "all has changed" now that Space X is set to begin constructing the BFR in 2018. 

My understanding is that Space X plan to land 300 tonnes of cargo two years prior to landing a craft with humans on board (and presumably a good deal of additional supplies as well).

With that sort of landing capacity a lot of assumptions about crew numbers and so on go out of the window. Suffice to say,  that a crew of 6 (my original suggestion in a 2x3 mission configuration) would present no problems at all.  Individual crew weight and height could probably be close to average for young people.

I think there is a good argument for not going beyond a mission crew of 10 people for Mission One.  Mission One needs to be focussed on some key life support and propellant production targets - so we need to keep the numbers down to retain that focus and minimise risk creation.


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

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#14 2017-11-15 20:08:11

SpaceNut
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Posts: 16,144

Re: Crewman size and mass affects mission to mars

Since bowing out of the red dragon landing with retro-propulsion I am waiting and watching for better information to run numbers with,,,,
Saying 150 tons of payload without the sytem to do it is just more paper....

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#15 2017-11-16 17:52:20

IanM
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From: Chicago
Registered: 2015-12-14
Posts: 276

Re: Crewman size and mass affects mission to mars

Starting with the following assumptions:
-10 160 lb (73 kg) men for a crew
-2% of body mass for food per day/sol (the difference is irrelevant)
This results in each crew member needing 1.46 kg of food per sol. I imagine the first agriculture could be set up in 10 sols, and the growing season of many crops are 90 days, so I'd imagine the crew would need around 100 sols to rely on pre-landed food. This results in 146 kg of food needed in total for each crew member, or 1,460 kg of food for the whole crew. Assuming that the capacity of the cargo lander is indeed 300 tonnes, or 300,000 kg, rounding the food up to 1,500 kg means that only 0.5% of the cargo lander need be non-perishable food. That being said, my calculations don't take into account the food needed by the crew en route to Mars, although that would be on the rocket with them, and not in the cargo lander.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#16 2017-11-16 18:27:59

louis
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From: UK
Registered: 2008-03-24
Posts: 4,900

Re: Crewman size and mass affects mission to mars

I use 1.5 kg per person per day for food requirement.  It could be less if you used dried food and efficient water recycling. 

I personally don't think any risks will be taken over food on Mission One. Maybe there will be provision for growing salad vegetables but not a lot more.  Also, I think they will build in the risk of a propellant production failure so for a ten person crew we might be looking at
1850 x 10 x 1.5 kgs =  27.75 tonnes (including 200 days x 2 for transits both ways).  Still easily manageable within the Space X cargo capacity.  It could be reduced marginally I think by including a proportion of dried food or a higher proportion of highly calorific food by weight (e.g. olive oil).



IanM wrote:

Starting with the following assumptions:
-10 160 lb (73 kg) men for a crew
-2% of body mass for food per day/sol (the difference is irrelevant)
This results in each crew member needing 1.46 kg of food per sol. I imagine the first agriculture could be set up in 10 sols, and the growing season of many crops are 90 days, so I'd imagine the crew would need around 100 sols to rely on pre-landed food. This results in 146 kg of food needed in total for each crew member, or 1,460 kg of food for the whole crew. Assuming that the capacity of the cargo lander is indeed 300 tonnes, or 300,000 kg, rounding the food up to 1,500 kg means that only 0.5% of the cargo lander need be non-perishable food. That being said, my calculations don't take into account the food needed by the crew en route to Mars, although that would be on the rocket with them, and not in the cargo lander.


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

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#17 2018-01-27 18:27:52

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,144

Re: Crewman size and mass affects mission to mars

This topic leads me back to wanting to design a small pioneering mission of using what we have to build and preload the needed means on mars as well as to us ION drive to place what is the return ships fuel at a minimum in mars orbit. This is to get samples and plant the seeds for longer missions.

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#18 2019-09-11 19:04:20

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,144

Re: Crewman size and mass affects mission to mars

Seems food has been some what settled on but not water or oxygen when considering recycling might not be as good as we would like to be so as to reduce the mass such that BFR's are not required.

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