How much will your weight matter when going to Mars, SpaceX style?

Posted on October 3, 2016

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I think space is awesome. I think going to Mars is awesome. I think it’s important to do. I’m not going to make an argument why, but you can see one here.

A problem for human spaceflight is countering the negative impacts of moving in an environment where gravity is less than Earth’s. This is the predominant impetus for some space posts I’ll have, as there is a ton here which can be applied to everyday people on Earth, and vice versa.

Sometimes I’ll hit on current treatments; sometimes I’ll hit on ways I think things could potentially be improved. Maybe this can be my small way to help the Mars movement.

Finally, I want to stress, even if you’re not interested in space, this can be valuable to learn about. This post has application to appreciating the financial implications your weight can have. 

SpaceX recently announced their Mars architecture.

The name of the game is reducing cost as much as possible. To use Musk’s slides, they’re trying to go from this,

mars-cost-who-can-afford-to-go-venn-diagram

To this,

mars-cost-who-can-afford-to-go-venn-diagram-2

The cost of space travel is dictated by the cargo’s mass more than any other mode of transport. The point of SpaceX’s mission is to transport people. This involves various groups working together-

aircraft-design-interdisciplinary-various-groups

Credit: DelftX: AE1110x Introduction to Aeronautical Engineering

People, and what they need, are mass. The heavier you are, the more you need to bring, the more it will cost to take the trip. Let’s see if we can influence the “Who Can Afford To Go” portion of the Venn diagram by being part of the weight group.

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It costs $140,000 per ton on the Mars Colonial Transporter. A ton is 907.2 kg or 2000 lbs.

  • $140,000 / 2000 lbs = $70 per lb

phenomenal decrease in the cost of space travel. However, from the individual perspective, think about how much it costs you to check a bag at the airport. $25 for up to 50lbs?

  • $25 / 50 lbs = $0.5 / lb

It’s still 140 times more expensive than flying on American Airlines. You’re going to want to minimize your cargo, like how much mass is on your body.

There are now more obese people in the world than underweight people. 40% of women and 37% of men are currently obese. Nearly every other woman you see is obese! That’s a gigantic portion of the population. Again, the bigger the “Who Can Afford To Go,” the better. How much more money will say, an obese person, have to spend?

Looking at the average height of an American at 5’6″, an obese, but not morbidly (BMI: 35), person will have a weight of 217 lbs. If we wave a magic wand and get this person to a BMI of 22, skinny but still healthy, they’ll be at 141 lbs.  That’s a 76 pound savings.

A lesser weight person needs less food. Calories are energy, energy is proportional to mass => calories have mass.

Using this basal metabolic rate (how many calories one burns each day just being alive) calculator, again average height of 5’6″, perhaps an average age of 49 years -we’ll lean towards older as they have more money to pay for something like this (younger people need more calories so they’ll be more expensive too)- then multiplying this number by 1.725 for a high activity level -it sounds like Musk wants to make things cruise like. If you’ve never been on a cruise, many actually move around a good deal, even exercising (plus they’ll want to be doing it, whether for health or to combat boredom)- then comparing obese to a BMI of 22:

  • 5’6″, 49 years old, 217 lbs = 1679 kcal
    • * 1.725 = 2900 kcal
  • 5’6″, 49 years old, 141 lbs = 1349 kcal
    • * 1.725 = 2327 kcal
  • 2900 – 2327 = 573 calories more expensive per day, when obese.

A wild guess: it’s two years until food can be reliably grown on Mars. (It could easily be much longer, inflating these numbers.) That means SpaceX has to transport two years of food for you until then.

  • 573 kcal * 365 days * 2 years = 418,290 calories more when obese

Assuming a person eats evenly amongst carbs, protein, and fat:

  • 418,290 / 3 = 139,430 kcal per macronutrient

Macros contain:

  • 4 calories per gram carbohydrate
  • 4 calories per gram protein
  • 9 calories per gram fat

Knowing 453 grams = 1 pound,

  • 1812 calories per pound of carbohydrate
    • 453 * 4 = 1812
  • 1812 calories per pound of protein
  • 4077 calories per pound of fat

Pounds for each macro,

  • 139,430 / 1812 = 77 lbs of carbs
  • 139,430 / 1812 = 77 lbs of protein
  • 139,430 / 4077 = 34.2 lbs of fat

NASA stores food in things like,

The good people at Grass City tell me a baggie weighs 1.5 grams and holds 100 calories.

  • 418,290 extra kcal / 100 calories per bag = 4,183 extra bags * 1.5 grams per bag = 6,275 grams = 14 lbs

A space suit is a necessity on Mars. The suits currently used on the International Space System are 300lbs. SpaceX is working on their own suits. One would imagine someone will have improved on this within the next decade or so, but we’ll use 300 pounds.

Using this calculator (admittedly not sure how accurate it is) the volume of a 141 lb person is 63,323.29 cm^3.

I’m not sure if NASA has a range their suits are made for, or if each suit is specifically tailored to the person. However, a lighter looking female astronaut said the suit is 300 lbs. Let’s say then,

  • 300 lbs / 63,323.29 cm^3 = 0.005 lbs per cm^3

The volume of a 217 lb person is 97,455 cm^3. That’s 34,131.71 extra cm^3.

  • 0.005 lbs per cm^3 * 34,131.71 extra cm^3 = 171 extra lbs

How many back up suits do we need? Say one, so two suits total = 342 lbs.

  • 76 lbs less bodyweight
  • 77 lbs less carbs
  • 77 lbs less protein
  • 34.2 lbs less fat
  • 14 lbs less baggies
    • For every year food is not produced in situ, there would have to be 38.5 + 38. 5 + 17.1 + 7 = 101.1 more food related pounds
  • 342 lbs less space suit
    • = 620.2 lbs more total
    • 620.2 lbs * $70 per pound = $43,414
    • $43,414 / purported $200,000 ticket price = 22% difference in ticket price
    • ($70 * 101.1 lbs = $7,077 more for each extra year we need to bring food items.)

Few ways to look at this-

A bump to four years for us to reliably / sustainably produce food on Mars and we’re at $58,000.

Some freak out over only a 10% discount, while for others it’s irrelevant. However, 43 grand isn’t irrelevant to many. If we’re looking at this like the average family buying a house,

mars-cost-who-can-afford-to-go-venn-diagram-2-median-house

it’s no doubt relevant.

For the average person, the less money they make, the more obese they are. Therefore, this is most relevant for the obese population. (Again, which more than a third of the population is made of.) Rather than focus on saving $243,000, they can instead focus on $200,000.

The median net worth in America as of 2013 was $81,000. The difference between needing to save upwards of $162,000 or $119,00 more may not seem a lot when only looking at those numbers, but relative to $81,000, $43,414 more sure is.

The median yearly wage is $43,000. A 10% savings per year is $4,300.

  • $243,414 / $4,300 = 56.6 years
  • $200,000 / $4,300 = 46.5 yeas

That’s too long. Doubling our savings rate would bring things to 28 and 23 years. A 22 year old could be ready to go by their 40s. Reasonable. By not being obese you could then make the trip five years sooner.

Actually, an obese person may very well spend more money on calories each year, on Earth. Add in healthcare savings, the fact food takes up room and space will be a luxury when traveling through it, other little things like obese clothing in general will weigh more, not having to transport medications for things like diabetes or hypertension; saving for 20 years -sparing everyone the math- and you could get there at least another year sooner.

Six plus years sooner; save upwards of $50,000? Seems worthwhile!

Being at a healthy weight helps you physically and mentally, partially because of how it can help you financially. It never hurts to have more incentive to be at a healthy weight, and transportation is one of the more obvious, everyday examples of this. Whether it be walking, being ok with a compact car rather than needing a SUV to fit into, being more comfortable on a plane ( / not having to buy two seats / decreasing everyone’s ticket price), or being a Martian!

Edit: Accidentally used median wage for only males. Changed wage to reflect both genders.

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