As Above, So Below: The Sea/Space Analogue

What follows is an article I wrote for the Mars Society while taking part in MDRS, a Mars base simulation exercise in the Utah desert. It concerns the historical use of undersea habitats for astronaut training and was well received upon original publication.

As above, so below: The sea/space analog

It was by fortunate happenstance that my mission on analog Mars coincided with James Cameron’s history making dive to the Challenger Deep. Mr. Cameron is, for reference, a member both of the Mars Society and the Atlantica Expeditions. On the 25th, Cameron sailed down 7 miles to the hadal depths in a vessel not so dissimiliar to the capsules which first put men in orbit.

Within the Deep Sea Challenger, a 2.5 inch thick steel sphere withstood the tremendous pressure differential and the pilot’s respiratory needs were provided for by a chemical rebreather that is in principle identical to the life support systems which kept the Apollo astronauts supplied with fresh oxygen and removed their exhaled CO2. These are the commonalities familiar to everyone, which spring to their minds immediately when sea/space similarities are brought up.

However, the parallels run considerably deeper than it initially seems; For instance, many aren’t aware that just as astronauts suffer loss of bone density in microgravity, so do deep saturation divers although for them it is a product of breathing exotic gas mixtures under high pressure.

The surface is also effectively as unreachable as Earth would be for astronauts on the Moon, because even at 60 feet their tissues saturate with nitrogen such that to simply swim to the surface would mean certain death. No matter how close it looks, it cannot safely be reached except by 17 hours of decompression.

In each following section, I’ll explore commonalities between the technology and methodology of sea/space exploration towards a list of proposals for the Mars Society as to how they might benefit from either a low cost undersea space analog program or related concepts that may apply to MDRS operations.


A hypothetical base on Mars as simulated by MDRS is, when broken down to it’s constituent parts, a pressure vessel accessible by airlocks powered by a nuclear reactor, and which extracts oxygen by chemical refinement process from Martian regolith. This same configuration exists in analog today, in the form of a nuclear submarine.

The modern SSGN is accessible by diver lockout, the undersea equivalent of an airlock. The compact naval reactor onboard provides the raw power needed for undersea in-situ resource utilization, specifically the extraction of oxygen directly out of seawater, as well as desalination (by way of reverse osmosis) and of course heat, light, dehumidification and the other basics of maintaining a comfortable shirtsleeves environment.

Additionally just as Robert Zubrin hopes to produce fuel from elements in the Martian atmosphere and soil, hydrogen is a byproduct of the process used aboard submarines to make oxygen, and a small number of new submarines now use hydrogen fuel cells. They could of course not make a surplus of fuel or even replace what they use for very obvious reasons but it does permit them to reclaim some of the energy lost in the oxygen extraction process and put it back towards propulsion and electricity generation.

As yet no nuclear powered undersea lab exists which can extract oxygen as needed from the surrounding seawater, but the Aquarius Undersea Lab in the Florida Keys[1] makes another illuminating point of comparison; Like the MDRS hab it is used as a space analog (albeit by NASA) because the helmet and rebreather setups used by NEEMO program[2] divers are so similar in principle to space suits, because divers can be weighted against their own buoyancy to whatever precise degree is needed to simulate the gravity on any body in the solar system (or LEO) and because there is no easy return from saturation; once the tissues are filled with nitrogen any attempt to escape by swimming to the surface would certainly be fatal. Only 17 hours of decompression inside Aquarius itself can outgas the tissues sufficiently that a safe ascent is possible.

Like any potential base on the Moon or Mars, Aquarius includes a double door airlock permitting the living section to be depressurized to a surface normal 14.7psi or 1atm if desired; either gradually as part of decompression, or potentially Aquarius could be operated as a 1atm base like Hydrolab before it, keeping the occupants constantly at 1atm and admitting divers through the airlock in a process familiar to any astronaut who has ever completed a spacewalk.


During historical man in the sea missions such as those aboard the La Chalupa, in situ resource utilization came in simpler forms; Fish at that depth would swarm the habitat’s moon pool as it was illuminated from within and a few overly eager specimens would jump through the water/air interface and wind up flopping around on the floor of the wet room. A crewman nearby would pick it up, pop it in the microwave for a three second kill, gut it, clean it and serve it for dinner. Experiments in circulating seawater through a shallow pan with a large surface area also proved that the gas exchange between the water and the habitat atmosphere was swift enough, with circulation, to meet the respiratory needs of one crew member at a resting heartrate.

Similar experiments involving a thin microporous silicone membrane were carried out in the Soviet Union, employing a positive pressure ‘inflatable’ subsea habitat named Selena-1. The microporous membrane permitted passive admission of oxygen from the surrounding seawater and the removal of CO2, striking a balance that produced without any electricity or traditional life support equipment an internal atmosphere breathable by a single occupant indefinitely, provided that occupant took care to prevent the growth of a biofilm on the membrane exterior.

Perhaps the most valuable sea/space analog program that was carried out before the modern era was the simulated orbit of the Grumman Piccard “Ben Franklin” PX-15 simulated space station along a 1,444 mile stretch of the Gulf Stream. Although equipped with electric thrusters, the vessel drifted for the entirety of it’s journey, using those thrusters only for course adjustment just as the ISS does. Onboard, habitable space equivalent to the Aquarius Reef Base undersea habitat provided beds, a bathroom and kitchen facilities for six men. The journey lasted 30 days and provided behavioral and operational data on what it would entail to run a single-launch, six man space station similar to what eventually became Skylab. An internal schematic of the Ben Franklin can be found here[3].

The future

However, the life support technology which holds the most promise for both sea and space settlement is bioregenerative and algae based. Spirulina algae is very nearly nutritionally complete although not possible to eat as an entire diet on account of kidney stones and related health issues. It can however safely replace a great deal of your daily nutritional requirements when eaten alongside traditional dehydrated foods, significantly reducing the storage space needed for food and providing a constant source of fresh plant protein.

Aside from being eaten it is also an astonishingly efficient carbon sink and oxygen producer, such that a biocoil needed to support six crew members could be integrated into the structure of a cylindrical habitat so that once landed, it would absorb sunlight, circulate air from the habitat through the full length of the coil and function as an organic life support system. The uses do not end there; An algae based grey water system can very efficiently recycle solid and liquid waste such that clean water is returned and the alage is nourished. If the recycling is incomplete the water can also be passed through a modest hydroponic farm, nourishing the plants (which would provide an additional source of fresh food) and comprising what is basically an aquaponic farm, but with humans eating the algae and nourishing it with their waste as opposed to fish.

Propulsion is another area of commonality, which comes as a surprise to most. Ion engines are extremely similar in principle to the magnetohydrodynamic drives used experimentally in submarines. Both are essentially electromagnetic linear accelerators, but one uses water as a working fluid rather than ambient ions. Rockets are also employed beneath the sea, in vessels and torpedos which ‘supercavitate’; that is, they redirect some of the exhaust out of pores in the nosecone to forcibly create a bubble of gas around the vehicle, so that it bypasses the greater friction of water, which is nearly 800 times denser than air. The Russian Shkval fits this description, as do rounds in some undersea weapons, and most recently Darpa’s “Undersea Express” which purports a top speed of 115mph (although the actual top speed is likely to exceed that considerably, as the top speed of SSGNs is reported to be 40mph when crew members candidly admit that it’s a deliberately lowballed figure. The true top speed of any military vehicle or weapons delivery platform is always classified).

The mind

Of the 70 undersea labs that have existed worldwide between 1962 and 1980, all but a few made the study of human social interaction and psychological health in confined spaces a major component of their research agenda. Perhaps the most famous was Tektite, an unusually large station built by General Electric and deployed in the Virgin Islands first in 1969 and then again in 1970. The name refers to a type of meteor fragment that lands in the ocean, an appropriate name for a program intended to use a relatively confined underwater living space to study crew dynamics over a two month period in preparation for extended space missions.

Accordingly, crew mixtures were varied and often chosen primarily to satisfy scientific curiosity about the long duration viability of different kinds of pairings, including the historic first all woman undersea team dismissively labelled the “aqua belles” by the media of the day. Questionnaires plying into each crew member’s feelings about various exercises, meals and events as well as what they thought of their comrades were compulsory although in some cases morale broke down to the extent that these questionnaires were ignored entirely and two crews even became overtly hostile to topside support.

Later interpretation of their behaviors led the psychologists involved to conclude that they felt that they lived in what was essentially a different world, that the stresses and dangers they faced on a day to day basis were so alien to ordinary surface experience that they felt topside support could not understand their situation and was not in a position to issue them orders or advice. Topside support, in their view, lacked the direct experience with how day to day life underwater worked and therefore couldn’t come to informed conclusions as to what changes if any were needed.

Reportedly the pace of life slowed, they became intimately well adapted to their environment and began to think of themselves as legitimate inhabitants of the sea. It felt as if they belonged there, a closely knit social bond formed and everyone from the surface whether issuing orders or bringing supplies became an unwelcome outsider in their eyes. This could be compared, speculatively, to the tendency for colonies to rebel against their founding nations and seek sovreignty. The increased complexity and stress of life underwater or on Mars with a pseudo-familial group in confined quarters may well accelerate this process, and magnify the effect.

The body

The health effects of exposure to cosmic rays are, by now, relatively well known. Less well known is the full extent to which deep saturation affects humans. The deepest saturation ‘dive’ took place on land in a hyperbaric chamber as part of an experiment conducted by Comex in 1992. A diver was gradually acclimated to the air pressure equivalent of exposure to ocean water at 2,300 feet.[4] Just as cosmic ray exposure primarily affects the CNS, so too does exposure to high pressure. Apollo era astronauts suffer from cataracts as a result of their radiation exposure on the way to the moon as well as other sensory defects, impaired motor control, and even marked behavioral changes as non-trivial amounts of brain cells are destroyed by ionizing radiation.

The undersea equivalent is Nitrogen Narcosis, or “rapture of the deep” and the wide variety of different symptoms that manifest themselves with increasing depth. The shallow water symptoms are actually extremely pleasant; At 50 feet, considered to be the maximum safe depth for breathing a normal air mixture for long periods (115 feet being the short term limit for scuba diving) the effects are similar to intoxication. This is why the shallow water effects of NN are often called “The Martini Effect”. Aquarius aquanauts experience this for their entire stay and report a greater sense of wellbeing, deeper and more restful sleep, a propensity to laugh at even unfunny jokes and a diminished capacity for aggression. This explains in part why undersea living is so attractive and addictive to those who have experienced it and why some might wish to do so fulltime. The health effects, such as a tripled rate of healing and more restful sleep are attributable mainly to the higher oxygen content in the compressed air, the rest owe to the effects of higher air pressure on the permeability of neurons, but more on that later.

The symptoms of water pressure at 33–100 feet include mild impairment of performance of unpracticed tasks, mildly impaired reasoning and mild euphoria.

Symptoms at 100–165 feet include delayed response to visual and auditory stimuli, diminished reasoning and memory capacity (to a greater extent than motor functions), calculation errors and wrong choices, obsessive fixation on a single and sometimes arbitrary idea, over-confidence and an increased sense of well-being, laughter and a tendency to talk much more than usual.

Symptoms at 165–230 feet include sleepiness, impaired judgment, confusion, hallucinations, severe delay in response to signals/instructions, dizziness, uncontrollable laughter/hysteria, and occasionally terror.

Symptoms at 230–300 feet include poor concentration and mental confusion, stupefaction with further decreased dexterity and judgment, greater loss of memory and increased excitability.

Symptoms at 300 feet and beyond include severe hallucinations, increased intensity of vision and hearing, sense of impending blackout, euphoria, dizziness, manic or depressive states, a sense of levitation, disorganization of the sense of time, changes in facial appearance, and in some cases unconsciousness or death. All of this assumes a normal atmospheric mixture, hence the use of alternative breathing gases like hydrox, heliox, nitrox and trimix for different depth ranges, requiring very deep dives to transition from one breathing gas to the next on descent and ascent.

Alternative atmospheric mixtures were also tried in Skylab (such as a 5psi 100% oxygen atmosphere) but lacking the frightening symptoms of saturation diving that are alleviated with alternative breathing gases for the most part but which return in force at depths in excess of 1,000 feet. It is not yet known what effects await deep saturation divers below the 2,300 foot limit, except to say that at very high pressures the firing threshold of neurons is diminished, possibly to a level that would make any sort of higher brain function impossible. The fmri image of that diver’s brain would make for a spectacular lightshow, and it is difficult to imagine the powerful madness he would be experiencing. It is because of this that ocean exploration is sometimes said to be more difficult in certain ways that space exploration, and also why the future focus of deep diving corporations has been the development of rigid 1atm diving exoskeletons like the Newt Suit, and upcoming Exosuit, the deep sea equivalents of space suits worn on ISS EVAs.


The squat white drum sitting on the San Rafel Swell in which I have lived these past two weeks is probably difficult to envision as an undersea station if only for it’s surroundings. But this desert was once an ocean bed as the geology of the surrounding region will attest to, and as I trudged across the dusty plain in my simsuit I couldn’t help but compare it to experiences with helmet diving. The simsuit helmet, I remarked, would make an excellent diving helmet with the sole additions of lead ballast around the neck and a great deal of silicone to seal those seams where air might escape. With that in mind I saw myself and my crewmates trekking not across an arid desert but a soft, white sand seafloor with matching streams of bubbles trailing from our helmets. Long dead prehistoric sea creatures now regularly extracted from these cliffs by paleontological expeditions swimming around us, very much alive and intrigued by their air breathing alien visitors.

The similarities from a research standpoint is by comparison very clear, and easy to see even for those not versed in the history of ‘man in the sea’ programs. Although it’s is a smaller part of the focus (at least for this mission) psychological studies at MDRS represent some of the most valuable science it’s capable of carrying out, similar studies having taken place aboard multi million dollar seafloor facilities, and possibly the science most usefully applicable to an actual Mars mission. Ample data exists for the social dyanmics of relatively homogeneous single gender crews but Tektite was unique in studying unorthodox crew mixtures and produced higher value data as a result.

Future crews occupying MDRS should devote more mission time to sociological studies, ideally with outside observers rather than a specific member of the crew assigned to that role. Simply havin a replica habitat in a geologically similar environment and sending crews through the motions of what day to day life would consist of for a ‘Marsonaut’ does much to make the idea of manned colonization of Mars more ‘real’ and less abstract/specultive for skeptical senators and congressmen, However, due to non-trivial limitations in terms of how closely the MDRS experience can mirror an actual Mars mission due to equipment costs the best use of the facility at present is for a longer term program in the same vein as Tektite.

To improve the accuracy of the environmental simulation itself and facilitate experiments in Mars equivalent gravity and with genuine functioning life support equipment, a true sea/space analog habitat is required. Recognizing that commissioning the construction of one is well outside of the scope of the MDRS budget, I suggest based on personal knowledge of the few habitats remaining in operation today (and the smaller subset available for scientists to rent time on) that the MDRS administration investigate the Florida Keys Undersea Park, and the Marinelab and Jules habitats contained in it’s inland emerald lagoon. Marinelab is a fully equipped, albeit modestly sized undersea laboratory with a transparent spherical cupola/observatory and a deployable ROV called the “Video Ray”

From this platform, exercises in piloting UAVs for exterior hab checks and simulations of extended duration missions in a pressurized rover (owing to the small size of the habitat and it’s panoramic acrylic bubble section) could be carried out with a degree of accuracy and resulting in insights impossible to gain from an analog habitat on land. While Marinelab stands in for the pressurized rover, the nearby (and considerably more spacious) Jules habitat would serve as the analog Mars base, with two bedrooms both equipped with bunks (Housing four comfortably) a shared livingroom/kitchen/entertainment area and a moon pool/staging room between them. EVAs could be carried out from the Jules as they are from MDRS, substituting a five minute wait in the staging room for the wait in the airlock, and with precise ballasting each aquanaut could weigh exactly what they do on Mars.

This, coupled with the genuine necessity of their life support systems would greatly increase the authenticity of the program and by extension the applicability of it’s findings. As the Jules owner normally covers it’s operational costs by making it available to tourists as a hotel, it also has a history of brief rental by teams of scientists and there is a special rate available for that purpose. THe going rate for tourists is $300-$400 a night depending on the “package”, the rate for scientific crews is dependent on their relationship with the owner and with ocean exploration but in all cases less than what tourists pay. At a depth of 25 feet (with a hatch depth of 21 feet) the internal pressure is 1.6atm, the limit below which saturation does not occur and no decompression is required to return to the surface. This makes it safer in some respects than even the existing MDRS program and (even at the tourist rate) potentially cheaper to run, provided missions are annual or monthly rather than continuous. To be clear I suggest this not as an alternative to MDRS but as an alternative to building additional analog mars stations, as it is my understanding that two more are planned.

In the absence of such a program, or more optimistically in anticipation of it, there are exercises that could be incorporated into any crew’s MDRS agenda and affordable additions to current equipment that would more closely reflect equipment available to astronauts on Mars.

The first and most obvious example is vehicular; All vehicles from submersibles to diver propulsion units underwater are battery electric. Internal combustion engines will not work underwater unless you carry a liquid oxygen supply with you (a solution that is only practical for torpedos, but not widely used anymore).

Likewise, on Mars there would be no internal combustion engine vehicles but rather battery electric rovers similar to the ones used by Apollo astronauts on the Moon. While theirs was powered by a single-use primary cell, obviously any similar vehicle purchased by or built for the Mars Society would employ low cost off the shelf lead acid batteries for propulsion.

At present there are several options available to those looking for an affordable electric alternative to an ATV. Actual electric ATVs exist but their lithium batteries make them cost prohibitive. The kind of vehicle I am describing is more akin to a ruggedized offroad golf cart of the type manufactured by Polaris industries[5] and sold for use by hunters who want a silent way to move friends and gear through the forest such that they do not alert wildlife.

Additional batteries could be added in parallel to increase the range with no alteration needed to the vehicle’s charger or onboard electronics, and a rooftop solar cell would provide a means of remotely charging a rover if it is stranded due to depleted batteries.

The second is some means of shared life support; During extended scuba diving expeditions, “pony bottles” are carried along as a provision of emergency air for diving buddies who may experience malfunctions with their equipment. More cautious divers carry a second, smaller redundant air supply about the diameter of a soda can and the length of your foot called a “spare air”.

Triple redundancy has been a dogma for aerospace engineering and marine engineering since the dawn of both disciplines. In the MDRS simsuits this capability would be simple to add; A plug located below the power switch and specially marked would permit two suits to share battery power or for one suit’s fans to run directly off the other’s batteries in the event that they are not just low on power but suffering some genuine disconnection between their suit’s power supply and circulation fans.

Multiple suits could be daisy chained in this manner and it would make possible valuable exercises for the development of methods to rescue crew members who are low on oxygen or suffering a life support systems malfunction. The addition of low cost usb charged GPS trackers of the sort used today by wary parents to monitor the driving habits of their teenagers[6] would permit the capcom to see on an overhead map of the region exactly where each crew member is in realtime.

The addition of a sealed tupperware container mounted within the simsuit backpack would make possible the use of Camelbak resevoirs[7] inside of them (which have been found to be superior in terms of resisting leaks compared with the Platypus models provided) with no danger of spillage damaging the backpack’s electronics. Lastly, as reported the radio systems require upgrading.

You might consider integrating it into the simsuit so that a large antenna mounted to the backpack could provide superior reception/transmission. All of these additional electronics could be charged simultaneously when the suit is plugged in by mounting an interior power strip into which the radio, gps tracker, and battery charger would be plugged. Most of these systems have some undersea equivalent for safety reasons and so would genuine Mars spec space suits, and as these capabilities are now relatively affordable to add there is little reason not to.

A pricier but potentially also worthwhile addition would be both heating and cooling vests from Venture Heat[9] and DSKool[10] respectively. One uses lithium batteries in the pockets to power resistive heating pads sewn into the vest itself while the other is veined with coolant carrying tubes and passes that coolant through a hip or back mounted refridgeration unit, also battery powered.

This would decrease discomfort and fatigue on very hot or cold days and mirror both the environmental control systems inside of actual space suits and the thermally controlled suits worn by deep saturation divers. There also exist full sets of heated clothing which run on a 12 volt power source, so they could source electricity directly from the simsuit battery for increased accuracy and at a lower price (as these outfits are designed for motorcyclists, they do not cme with a battery but rather plug into the 12v socket on their bike).

Lastly it is my understanding that the Greenhab systems can no longer be used for greywater processing. If the intention is to convert it into a grow space, consider strongly an aquaponics kit. It is nothing more than a hydroponic grow op, which can be built largely with aquarium pumps and PVC pipe, with the addition of a fish tank in which algae grows. The algae nourishes the fish, the fish droppings nourish the algae and also the plants as the tank water is circulated through the hydroponics setup.

Fairly straightforward guides are available on the internet for largely automating such a setup and amateur DIY enthusiasts have setups which take readings from various sensors including water Ph, soil Ph, temperature and so on to be remotely reported via an internet connected laptop.

A new, more glorious dawn awaits

Going forward, even as Aquarius and the Mars Desert Research Station continue generating data that will prepare man to set foot on the red planet and beyond, there awaits a mission which perfectly embodies the sea/space analog concept and which takes it from preparatory exercise into reality.

Jupiter’s icy moon Europa conceals beneath it’s frozen shell a global ocean between thirty and sixty miles deep. The holy grail for the ocean explorer and a formidable challenge for the space explorer. It will require a spacecraft for delivery to the surface and a subsea craft to explore Europa’s frigid abyss upon arrival.

It’s thought to be extremely likely that, due to gravitational flexing forces exerted on Europa by Jupiter as it orbits, there should be deep sea hydrothermal vents on Europa’s ocean floor. It’s geologically active on account of the heat generated by those forces, and everywhere we find hydrothermal vents on Earth we find extremophiles.

It is not yet known whether life could have evolved in those conditions or whether it can only evolve in gentler waters and then gradually adapt to the searing heat and toxic chemicals of the vents, but the warm, wet conditions surrounding Europa’s hydrothermal vents present the most promising target for our search for life next to Mars.

Technologies specific both to space and the sea will combine to send an AUV (autonomous underwater vehicle) like NASA’s Depth-X[11] to Europa, where it would descend to the ocean bed and map it in 3D. Depth-X completed such a mapping via sonar and lasers at the Zacaton sinkhole in New Mexico.

Descending along the shaft wall, Depth-X mapped in three dimensions every contour and crevice down to a depth of 1,016 feet where it took a bacterial sample before heading for the surface. All of this took place without human input, as it would need to on Europa due to the impossibility of communicating with the AUV while it’s under the ice.

Although JIMO (Jupited Icy Moons Orbiter) was cancelled, new proposals for AUV missions in Europa’s profoundly deep global sea have emerged and it is only a matter of time before a vessel combining every lesson learned in space and the deep sea sails the vacuum to Europa where it may definitively answer the question “are we alone in the universe”.

And if Dr. Zubrin sees his grand ambitions realized, there will come a day when Mars has a sea of its own. The lessons we learned exploring, industrializing, farming, mining and settling our own ocean will carry over such that ocean dwellers on Earth may one day have aqueous Martian cousins.

As I see it, that day cannot arrive soon enough. But until then we must prepare, not only in desert analog sims like MDRS but in the radiant blue mirror image of space which encircles this planet. If Mars is to be our future, the ocean must be our present.



I post text here, often accompanied by images and sometimes video. People then clap or don't depending on whether they enjoy what I posted.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store