Module 1: Living and Working Underwater

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Background: 

Living and working underwater poses unique engineering challenges, similar to visiting outer space.  Indeed, there is enough similarity between missions to the International Space Station and living in an underwater habitat, that NASA astronauts train at Aquarius.  This module will examine Aquarius as an underwater outpost, and provide an overview of the habitat from the inside out.  Life support systems, communications, living space, “physiological housekeeping”, and food preparation will be examined during an interior tour, followed by a swimming tour of the outside of the habitat, the quadrapod upon which it sits, the gazebo and high pressure air storage used as an emergency shelter if the habitat became uninhabitable, the umbilical to the Life Support Buoy, and the diving equipment used by the aquanauts.  This classroom will also discuss the scientific benefits and physiological challenges of saturation (habitat) diving, including the need for a 17 hour decompression at the end of any Aquarius mission.

 

What students will see during the show:

Dr. Mark Patterson, a marine scientist from VIMS, and veteran habitat user, will welcome everyone to Aquarius, and address a group of graduate students at his home institution over an Internet video connection.  He will then give a quick overview of the remaining 5 classroom module to be broadcast live Monday evening, Tuesday (2 classrooms), and Wednesday (2 classrooms).  Students from VIMS will ask Mark some questions and then he will turn the interior tour of the habitat over to Mr. Jim Buckley, Habitat Operations Manager.  Jim will provide a walking tour of the interior engineering systems of the habitat, and when he arrives at the wet porch, the entrance to the ocean, he will introduce Capt. Phil Renaud (USN, ret.), the Executive Director of the Living Oceans Foundation, and Dr. Annelise Hagan, Chief Scientist of the Foundation, both first-time aquanauts.  They will take students on a diving tour of the exterior of the habitat and its engineering systems, with Dr. Hagan giving a short introductory description of the biological and geological setting of the Aquarius habitat.

 

At the end of the module, students will be able to:

1. Describe the Aquarius habitat, list the number of rooms in the habitat and explain what each room is used for.

2. List the number of aquanauts that can live in the habitat, recall where they sleep, what they eat, and describe how they cook their food.

3. Discuss how the habitat is provisioned with fresh water, electricity, air, food, linens and towels and mail.

4. Explain how the aquanauts would cope with life threatening emergencies like fire, decompression sickness, and hurricanes.

5. Describe the special SCUBA gear that is used by the aquanauts and how they get more air for their tanks when they run out.

6. Contrast aquanaut SCUBA diving vs. diving from a boat at the surface in terms of: how many hours a day can be spent SCUBA diving and the depths at which the two types can dive.

7. Describe how the habitat is connected to the outside world via the internet, radio, and cell phone.

8. Explain why scientists like using Aquarius for studying the coral reef and performing in situ experiments.

9. Explain what needs to happen at the end of the mission so that the aquanauts can safely return to the surface.

10. Calculate several different parameters associated with the physiology, physics, and chemistry of living and working in and around the Aquarius habitat.

 

Reading:

First person accounts of living and working in Aquarius:

  Ten Days under the Sea; October 1996; Scientific American Magazine; by Peter J. Edmunds; 8 Pages.  Available at your local library or click here for online purchase at.

 Deep Science: Sleeping with the Fishes; September 2003; National Geographic Magazine; by Gregory Stone. Available by clicking here.

A nice reference book about living and working underwater in habitats:

 Miller, J.W. and Koblick, I.G. 1995. Living and Working in the Sea. 2nd Ed., Five Corners Publications, Ltd., ISBN 1-886699-01-1.

 

Web resources:

Virtual tour of the inside of Aquarius:

 http://www.uncw.edu/aquarius/virtual_tour/ipix.html

Detailed article from the Marine Technology Society Journal on Aquarius, with high resolution images:

 http://www.uncw.edu/aquarius/about/MTS_journal.htm

User manual for scientists wanting to use the habitat:

  http://www.uncw.edu/aquarius/about/usermanual.htm#ums4

Nice article about underwater habitats from the 1960’s onward:

 http://en.wikipedia.org/wiki/Underwater_habitat

 

Quantitative exercises:

1. Physiology:

Significant space inside Aquarius is devoted to storing food for a mission (Fig, 1).    At sea level in temperate climates, the National Research Council estimates it takes about 2000 calories of energy to keep an average woman from losing weight, and 2500 calories for an average man.  The thermal loading of the aquanauts is severe.  They are outside the habitat for 6-8 hours per day, and even when wearing wet suits, they still come back to the habitat chilled.  Inside, even though the air temperature may be in the 70’s, they are losing radiant energy to the walls of the habitat which are heat sinks to the surrounding ocean.  Living underwater in the tropics is the physiological equivalent of camping out in the Arctic or Antarctic.   Many people lose weight during a saturation mission in Aquarius, despite consuming lots of high calorie foodstuffs.  During a 16 day saturation mission in February 2000, Dr. Patterson ate normally, yet lost 20 lbs of weight by mission end.
 
 a) Assuming Dr. Patterson got leaner, and that 1 lb of fat = 3500 calories, what was his daily caloric deficit?  (Or how many calories should he have eaten per day when in Aquarius in order to maintain his body weight?)

 b) Imagine a fast-growing mold attacked the food stores in the habitat one night rendering them inedible next morning, and an unexpected storm prevents the shore crew from visiting the habitat for the next two days to resupply the aquanauts.  The only item not affected by the mold are 2 unopened 1 pint jars of peanut butter.  Each ½ cup of peanut butter holds 760 calories.  Assuming the maintenance metabolism computed in (a), will the aquanauts have enough food, in the form of peanut butter, to tide them over 2 days?  If not, how much weight will each one lose on average, assuming they have Dr. Patterson’s metabolism?

 c) Now imagine Dr. Patterson’s evil twin, who also is saturating on this mission, was the only one to discover the untainted peanut butter.  Being evil, he hoards it in his bunk and surreptitiously eats it over the two days, without sharing it with the starving others.  Does he lose weight, maintain his weight, or gain weight?

 

<<< Figure 1.  Dr. Patterson's Evil Twin, burning through the calories.  

  

2. Physics:

Special provisions are necessary inside Aquarius to prevent the build-up of the byproduct of animal respiration, carbon dioxide (CO₂).  Soda lime pellets (manufactured by W.R. Grace Co. under the tradename, Sodasorb) are installed at strategic locations in the habitat to react with the carbon dioxide produced by the aquanauts (Fig. 2).  Buildup of carbon dioxide in the atmosphere of the habitat can result in a condition known as hypercapnia in the aquanauts. This can lead to headaches, respiratory distress, nausea, and other potentially dangerous physiological derangements.  At rest, at sea level, human beings produce 4 ml of carbon dioxide per minute per kg body mass.  Because the habitat is underwater, with a moon pool open to the ocean at a depth of 15 m, the pressure inside is about 2.5X sea level pressure.  This means each 1 ml of carbon dioxide produced by an aquanaut breathing at the surface, will only occupy 1/(2.5) = 0.4 ml when breathed out by an aquanaut, in the habitat.  Another way to look at it, is that gases in the habitat are 2.5 times denser than they are at the surface.

 a) Assuming Aquarius is occupied by 6 aquanauts in the evening from 6 PM till 6 AM the next morning, and that their average biomass each is 75 kg, how much carbon dioxide, in ml, will accumulate in the habitat if there was no Sodasorb?

 b) Assume the habitat is a cylinder 3 m in diameter and 15 m long.  Compute the volume, in ml, of air in the habitat (neglect the volume occupied by the 6 aquanauts).  (Remember that 1 cm3 = 1 ml).  Using the result in (a), what percent of the atmosphere in the habitat is now carbon dioxide, assuming no flushing of the habitat atmosphere by the compressors on the Life Support Buoy?

 c) Some people start feeling the effects of hypercapnia, excess buildup of carbon dioxide inside the body, when the percentage of carbon dioxide exceeds 0.3 %.  Are the aquanauts in trouble?

 d) Repeat your computations, but now assuming that because of the excitement of being underwater, the thermal stress of living underwater, and staying up late talking and writing reports, that each aquanaut’s metabolism is double that of resting metabolism.  How are they faring now?

 

<<< Figure 2. Jim Buckley, Habitat Operations Manager, Aquarius, changes out Sodasorb during a mission.

  

3. Chemistry

The following is taken from the Sodasorb Manual, W.R. Grace Co,, p. 29 ff, available by clicking here. 

“Chemical Process of Sodasorb CO₂ Absorption"
 
Sodasorb absorbent is a proprietary mixture of calcium hydroxide, sodium hydroxide and water.  Hydroxides are used in acid gas absorption because they are efficient, stable, and can be easily handled. They are derived from alkalies and alkaline earth metals and are the most efficient absorbers of carbon dioxide available.

The absorption of carbon dioxide (CO₂), or of any acid gas, by Sodasorb absorbent is a chemical process, not a physical one. The reaction is quite different from absorption by activated carbon, for example, which involves physical entrapment of gases.

In Sodasorb absorption, the CO₂ first reacts with water to form carbonic acid, subsequently reacting with the hydroxide to form soluble salts of sodium carbonate. The soluble salts then react with the calcium hydroxide to form insoluble calcium carbonate. By-products include both heat and water.

Neutralization of CO₂ by Sodasorb may be expressed by the following equations:
(i) CO₂ + H₂O <---->  H₂CO₃
(ii) 2H₂CO₃ + 2NaOH <---->  Na₂CO₃ + 4H₂O + Heat
(iii) 2Ca(OH)₂ + Na₂CO₃ <----> 2CaCO₃ + 2NaOH + Heat
 
In (reaction i) the CO₂ dissolves at a rate governed by a number of physical chemical factors. The rate is not proportional to the partial pressure of the CO₂ which is in contact with the film of moisture coating the Sodasorb pellets, but is greater because some of the CO₂ combines chemically with the water to form carbonic acid. The rate is directly proportional to the rate of removal of H₂CO₃ from solution by reaction with active hydroxide (reaction ii). Thus, the rapidity of removal of combined CO₂ is directly related to the availability of active hydroxide. Since the reaction between H+ and OH- is instantaneous, forming water, reaction (ii) is extremely rapid and active hydroxides are quickly exhausted. Hence, equation (iii) must supply additional active hydroxide to keep the absorption of CO₂ progressing. The last reaction is, therefore, rate limiting.”

The Sodasorb manual states later that 13,500 calories of heat are released for each 22.4 L of CO₂ absorbed at sea level.  (Remember that in the habitat, the pressure is 2.5x that of sea level, which means an equivalent amount of carbon dioxide only occupies 22.4/2.5 = 9.0 L in the habitat.)

 a) How much heat, in calories, is generated by the Sodasorb during the 12 hours the aquanauts are inside?  Assume the conditions given above in 2 (a) for “resting metabolism” by the aquanauts.

 b) Energy/time is called power.  The power generated by a resting aquanaut is about 100 W = 100 Joules/sec.  How much heat power does the Sodasorb generate at night and how does it compare to the metabolic power of the aquanauts?  Will they need to crank up the air conditioning?  (Assume that 1 Joule = 0.24 calories)

 c) Repeat your calculations for the conditions given in 2 (d).  For purposes of cooling the habitat, in terms of “body count”, having Sodasorb on board is equivalent to how many extra aquanauts heat-wise?