How much does the ocean weigh?

Quick – how much does the ocean weigh?

Let’s say you’ve recently been spending a lot of time at home with a small child. You foolishly told them you can’t play right now because you’re busy doing important work calculating the weight of stuff. This has sparked their interest. And they won’t let go of that question.

Sigh. I don’t know how much the ocean weighs. I couldn’t even guess how many zeroes are in the number.

Or could I?

70% of the Earth’s surface is covered in ocean. I’ve watched enough nature shows to remember that’s about right. What would that surface area be? Let’s assume the Earth is a sphere (it’s not, but it’s close enough). What’s the formula for the surface area of a sphere? I don’t remember and my Weight Engineer’s Handbook is in the office. No matter – let’s assume Earth is a cube instead. I know how to find the surface area of a cube.

I know what you’re thinking – working from home with a hypothetical kid asking dumb questions all day has driven me bonkers. We can’t assume the Earth is a cube. But for this estimate we can. All I’m looking for is a number within a few orders of magnitude of reality. The difference between a sphere’s surface area and a cube’s (with the cube’s edge the same length as the sphere’s diameter) is negligible.

The surface area of a cube is six times the area of one side of height H, or 6xH². Since our cube’s height is the same as our sphere’s diameter, we need to know Earth’s diameter. Because “Apollo 13” is an awesome movie I know that a spacecraft in low Earth orbit moves about 17,500 miles per hour and takes 90 minutes to complete an orbit. That gives a circumference of 26,250 miles and a diameter of 8360 miles. Let’s call it 8,000 miles because I read somewhere that low Earth orbit is about 50 miles up, the Earth is rotating under the spacecraft and I’m kidding myself if I’m going to assume any precision in this calculation.

That gives us an ocean surface area on our Earth-cube of 70% x 6 x 8000² = 269 million square miles.

I don’t know the average depth of the ocean, but I know most of it’s deep. I’m guessing between one and ten miles because I heard “miles” and ocean depth mentioned together somewhere. Let’s say two miles deep. That gives us a total volume of 538 million cubic miles.

Every weight engineer knows the density of water – it’s 1 gram per milliliter. That’s fresh water – salty ocean water is denser, close enough. I remember it that way because I’m an expatriate Canadian and the metric system is a tenacious thing. No matter, I can convert. There are 454 grams in a pound (thanks, Canadian food packaging!), a milliliter is the same as a cubic centimeter and there are 2.54 centimeters in an inch. Put that all together and you get a water density of 0.036 lb/in³, or 9,181,017,236,653 pounds per cubic mile. Time for scientific notation: 9.2x10E12 pounds per cubic mile.

At a volume of 538 million cubic miles, our ocean weighs 4.9x10E21 pounds.

How did I do? According to the internet, “Earth’s ocean is made up of more than 20 seas and four oceans, weighing an estimated 1,450,000,000,000,000,000 short tons” – or 2.9x10E21 pounds.

There you go, kid. My estimate came within 2x the real value. That’s pretty good for starting out with no earthly idea!

This is called “Fermi approximation”, named after World War Two-era physicist Enrico Fermi, who was known for making good approximate calculations with little to no data. It’s a great way to get a quick rough guess before moving on to more precise methods.

My first boss when I was a brand new mass properties engineer used this method to devastating effect. He would send me off to spend days researching, interviewing designers and analysts, drawing sketches and running calculations to estimate the weight impact of a potential design change. When I returned, he would knock off an estimate in a few seconds that would invariably be within spitting distance of my hours of work. It was humbling, and I would ask him why he made me go to the effort. He’d say his method is quick, but now I have the data to back it up. He didn’t say it also made me a better mass properties engineer, by giving me a powerful tool to quickly understand the size of a thing, whether it’s a potential weight impact or the number of hours a task might take – or the answer to a childish question.

If you like hearing about the techniques, methods and experiences of other weight engineers, I encourage you to attend the 2020 SAWE Tech Fair, starting June 22. A wide range of technical presentations, industry seminars and training classes will be featured, all live and online, presented by your mass properties colleagues.

Welcome to the SAWE – Presentation

Have you ever wanted more information to take to your management to support your Weight Engineering endeavors? Would you like to learn more about our society as it stands today?

Well Thanks to Mr. Damian Yanez of Gulfstream Aerospace Corporation, your wishes are now at your fingertips.

Navigate to

https://www.sawe.org/system/files/Welcome_to_SAWE_Company.pdf

and learn more. Use it to further your career, make a case for training, conference attendance, developing technical content, and even securing your company as a SAWE Corporate Partner.

Call to the SAWE Membership – Academic Committee Needs your Help!

The Academic Committee is gathering all available materials regarding Classes, Presentations and Papers for Students (college-level) and Ideas for Student Projects and Events. The intent is to build a SAWE library of resources pertaining to introductory mass properties and introduction to the SAWE.  It is also the SAWE President’s desire to leverage existing work towards developing a Mass Properties training certification program for academic and newly assigned mass properties engineers.

Initially, these currently available materials will be able to be used by any SAWE member for a SAWE Chapter or local university outreach meeting, or for inspiring ideas for Chapter or local school events. Some of the very interesting and diverse materials we have so far include:

  • Introduction to the SAWE – Whidy Kiskunas
  • SAWE University Outreach Presentation – Casey Regan
  • Why Mass Properties Engineers Matter – Robert Zimmerman
  • The Value of Mass Properties Engineering  Roger Belt
  • Weight & Mass Properties Engineering for Aircraft Design – Whidy Kiskunas & Rod Van Dyk; Based on material originated by Casey Regan
  • The Secret Life of the Center of Gravity  Robert Zimmerman & Kristen Terry
  • Mass Properties Engineering as a Systems Engineering Discipline – Robert Zimmerman
  • Naval Architecture & Marine Engineering; Course NAME 581: Introduction to Ship Design – Andy Schuster

These resources will be available in the SAWE Group Office folder.  If you or your SAWE Chapter have any material you would like to contribute to our library, please contact me (V.P. of Academic Affairs) at Donna.Gerren@Colorado.EDU.  Let’s hope we can provide a wealth of information useful to our membership for SAWE meetings and outreach activities. Thank you very much for your contributions!

Donna Gerren

Technical Input on In Service Weight Control

I thought I would start a thread on a topic of conversation, In Service Weight Control, from recent SAWE events. After a platform is put into operation, configuration changes take place throughout operation.  This must be kept track of for safe and successful operation.

What related experiences can you share?

I’ll start.  I perform Integrated Mass Properties analysis on the International Space Station (ISS).   I gather inputs from the International partners on Visiting Vehicles coming and going.  I gather inputs from our International partners on modules.  I gather inputs from our Configuration team as changes are made, for example moving Orbital Replacement Units (ORUs) from their storage location on ISS to their new location to support continued operation.  I verify the inputs make sense and question everything that doesn’t.

When you put it all together, you have analysis of the ISS at any given point in time needed to operate the ISS as it orbits our Earth every 90 minutes.

Consider sharing your experiences here, at a local chapter meeting, in a presentation / paper, and/or at a conference.

I am hoping this will be a catalyst to increased technical discussion.

Thanks.

Clint.

New Chapter Arranged Training Policy

A new policy for Chapter Arranged Training as been produced.  This will be in the Operations Manual.  The purpose of this policy is to encourage local chapters to arrange and hold classes and to support the development of new classes. The Society encourages local SAWE chapters to utilize Training developed by the Society. Training is to be used as a resource to improve the local SAWE members’ technical abilities and also to be used to benefit the Chapter’s financial health. Since chapter arranged training can potentially incur a loss, or clash with International Conferences and On Site Training offerings, all chapter arranged training must be approved by the Vice President of Training in advance of a SAWE chapter marketing any class.  To read the full policy go to https://www.sawe.org/node/7636