Any hope humans have for an off-world future relies on several factors for survival. One of the most important? Water. Continuously shipping water across the galaxy to resupply astronauts requires extraordinary expense in transportation costs. The next planet humans inhabit will need to have access to a local supply. Scientists have labored to locate water on Mars—but finding it is only the first step. Now scientists and engineers need to tap into this supply which, given the harsh environmental conditions on Mars, isn’t as easy as it sounds.
The team investigated the use of a Rodriguez Well — a concept developed decades ago by the U.S. Army — as one of many approaches for extracting water from the massive ice deposits on Mars. A series of lab-scale Rodriguez Well tests were performed by Hoffman and Alida Andrews of Aerospace at the Johnson Space Center (JSC) Energy Systems Test Area facility. Using Mars-equivalent environmental factors such as atmospheric pressure and density, test results were used to replace terrestrial environmental factors with modeled Martian equivalents.
We spoke with Dr. Hoffman about water on Mars, how humans can access it and what happens next.
Is there water on Mars? If so, how much?
There is actually quite a bit and scientists are finding more deposits as the instrumentation they use in the search improves. For decades we’ve known that water ice exists at the poles on Mars — Earth-based telescopes could detect it using spectrometers. But early spacecraft flying by or orbiting the planet found a desert-like landscape at lower latitudes. For many years, it was assumed Mars had lost most of the water responsible for creating terrain features that appeared to be lakes, rivers, flood plains, and even shorelines for ocean-scale bodies of water. There has been an ongoing effort by scientists to understand what happened to all of this water. Orbiting spacecraft have carried more sophisticated instrumentation designed to answer this question.
Liquid water cannot exist on the surface of Mars under present environmental conditions. The atmospheric pressure at the surface is approximately 5–10 millibars — about 1% of sea level pressure on Earth. Mars atmospheric temperatures can range from -140 C to +30 C (-284 F to +86F). These conditions are near the triple point of water, but for the most part water exists only as ice or vapor at the surface of Mars unless some other special circumstances exist.
Scientists used two orbiting radars, named MARSIS and SHARAD, to look for liquid water aquifers below the surface where conditions would allow liquid water to exist. Following a global survey of Mars, no aquifers were found down to a depth of about 300 meters.
Using high resolution imagers and other remote sensing instruments also in orbit around Mars, scientists have begun to realize that there is a great deal of buried ice in the mid latitude — from roughly 35 degrees to 50 degrees — in both hemispheres. This ice is protected from surface conditions by a layer of sand, gravel, and dust. These deposits are occasionally revealed when small meteorites strike the surface and scatter very distinct white ice across the surface and these strikes are quite visible from orbit. Scientists have also spotted ice cliffs measuring 10s of meters in height in areas where some unknown event has exposed part of a buried ice deposit and the ice has slowly sublimated, revealing more and more of the deposit. A recent NASA-sponsored study called Subsurface Water Ice Mapping, or SWIM, has begun to correlate all of the independent data sets possibly indicating the presence of water to understand how much water is on Mars and where it is located.
To answer the original question, the estimates for the amount of water on Mars continues to evolve but it is safe to say that the total volume is many, many cubic kilometers.
How significant is mining this water to colonizing Mars?
Successful colonization is a long way off for many practical reasons. There is a great deal we still need to learn about Mars. But even early human missions of exploration and reconnaissance could benefit from access to significant quantities of water. There are technically feasible approaches to these early human missions in which everything needed for the mission is brought from Earth. Anything the crew can find and access on Mars means savings of many times its mass in rocket propellant and hardware that does not need to be transported.
Water is a very good example of this type of material. Water can be used for the obvious things like potable water and breathing gases for direct use by the crew, and even rocket propellant to launch the crew off the surface if electrolyzed into its constituent elements. If early exploration missions lead to a long-term presence then water will also be used in as many applications as it is known for here on Earth and its value will increase in proportion to the number of uses.
What is required to mine for water on Mars? What are some of the challenges?
Scientists have identified more and more significant deposits of ice on Mars. For purposes of this question, I would divide these deposits into two broad categories: those in which ice is mixed with significant quantities of dust or rocky material and those in which ice is essentially pure, i.e., greater than about 95% ice, the current limit of instruments to resolve the content of these deposits.
For ice mixed with dust or rocks, mining would require excavating the material and likely heating it to capture and condense the vapor. However, ice mixed with rocky material can be as hard as concrete and can be similarly difficult to excavate.
The pure ice deposits are typically covered by a layer of sand, gravel, and dust. Mining these deposits could be accomplished by stripping away this protective layer and excavating the ice. This approach would face similar difficulties as excavating the ice-mixed-with-rocks deposits.
Another method would be to drill through the overburden of sand, gravel, and dust and into the ice deposit where something called a Rodriguez Well could be established. This approach has been the focus of our applied research. It would face difficulties similar to drilling a water well here on Earth coupled with the unique aspects of establishing and maintaining a Rodriguez Well.
What is a Rodriguez Well? Why was it chosen for study?
The Rodriguez Well was developed by U.S. Army engineer Raul Rodriguez at Camp Century in Greenland during the early 1960s. A Rodriguez Well uses heat and a submersible pump to create a cavity filled with water deep under a glacier’s surface. The submersible pump is used to cycle heated water in the cavity, return cooler water to the surface, and siphon a portion of the flow for consumption before reheating the rest and sending it back down to the cavity. Diesel-electric generators in use at many of the field stations constructed on the Greenland ice sheet in the 1960s provided a “free” source of “waste” heat to make a Rodriguez Well and provide potable water. The Rodriguez Well was used operationally at several locations in Greenland, in addition to the well-known Camp Century.
The Rodriguez Well concept was tested at the National Science Foundation’s (NSF) Amundsen-Scott South Pole Station in the early 1970’s. When a major reconstruction of the South Pole Station was started in the mid 90’s the Rodriguez Well was chosen to provide potable water for the Station. South Pole Station still relies on a Rodriguez Well to this day. The Station is on its third well; the others were abandoned when the water pool reached a depth at which the pumps could no longer lift water to the surface.
I became aware of the Rodriguez Well concept while working with the U.S. Army’s Cold Regions Research and Engineering Laboratory (CRREL) on other NASA-related tasks. However, it was not until relatively recent discovery and confirmation of substantial bodies of ice in the Martian mid-latitudes that the feasibility of using a Rodriguez Well warranted a serious look at its application for human missions on Mars. The case for using the Rodriguez Well on Mars is compelling because of its relative simplicity and maturity, as well as the number of places and duration of use here on Earth. However, environmental conditions on Mars are different from here on Earth in several significant ways. Additional applied research is necessary to understand the changes in hardware or operations that may be required to make a significant commitment to using this technology on Mars.
How do you mimic the Mars environment?
It depends on what aspect of Mars you want to mimic. In our case we wanted to mimic the atmospheric composition, temperature, and pressures. We used a small bell jar facility available to us at the NASA Johnson Space Center. This bell jar can reach near vacuum pressures and cryogenic temperatures — both much more extreme than needed to mimic conditions on Mars. This bell jar has a testing volume measuring approximately two feet in diameter and two feet tall. We scaled our equipment to fit in this space, but this was sufficient for the initial testing. As we progress to more sophisticated tests, we will require larger volumes, but test chambers already exist at JSC and other NASA facilities to meet these needs.
What comes next in your work on this?
Our work so far has given us data we can use to customize computer simulation tools developed by CRREL for terrestrial use, allowing use for Mars applications. The data we have in hand are very basic — there are nuances that need to be explored with tests similar to those we have already completed.
Once we are more comfortable with how we think the Rodriguez Well will perform on Mars, we will confirm these findings by establishing and operating subscale versions of these wells in appropriately sized test chambers simulating Martian environmental conditions. These results will, in turn, be used to develop equipment and operations that can be demonstrated on Mars under actual conditions. At that point, we should know enough to determine whether this technology is effective and reliable enough to become part of the critical infrastructure supporting human crews on Mars.