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Centrifuge module
The centrifuge module planned for the ISS, but later cancelled. For decades NASA and other agencies have not capitalized on reduced gravity research despite its importace for human Mars exploration. (credit: NASA)

Reduced gravity: the 400-kilogram gorilla in the room


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As bizarre as it seems in retrospect, NASA officials have managed to ignore one of the biggest challenges in human space exploration in decades. In 1975, as part of the required work for a post-graduate course in bioengineering, I did a literature survey on human adaptation to artificial gravity and to rotating environments. Most of the work had been done in Russia. In 1976 and 1977, my research paper was expanded to discuss the effects of rotation on people living in O’Neill space colonies. Gerard K. O'Neill and I wrote and published a paper on that work in 1977.

However, research related to hypo-gravity (hypo-G, less than Earth gravity) has been sporadic around the world and very nearly non-existent in the United States.

A few years ago, I was somewhat eager to look into what progress had been made on “artificial gravity” in the intervening 38 years. The results astounded and appalled me. Little progress had been made and some of the research facilities had been shut down. Very little meaningful additional work had been done on the use of artificial gravity or the effects of rotating environments!

Considerable work has been done on microgravity’s negative effects on different systems of the human body. Astronauts and cosmonauts largely recover from these effects after a few weeks or months back in surface gravity with the exception of vision problems. Some have required glasses to correct their vision anomalies.

However, research related to hypo-gravity (hypo-G, less than Earth gravity) has been sporadic around the world and very nearly non-existent in the United States. The following quote is from the report of the 2014 International Workshop on Research and Operational Considerations for Artificial Gravity Countermeasures (NASA/TM-2014-217394) held at NASA Ames Research Center on February 19–20, 2014. The following is excerpted from the introduction to the final report (emphasis added):

In the executive summary of the “Proceedings & Recommendations” of the AG [Artificial Gravity] Workshop 15 years ago in 1999 in League City, Texas, we stated that “More than 30 years of sporadic activity in AG research has not elucidated the fundamental operating parameters for an AG countermeasure. For this reason, we do not advise NASA to discontinue support of countermeasures under development. Instead, we recommend that NASA appropriate the resources—primarily deploying and funding a peer-review research program—necessary to initiate AG parametric studies on the ground and in flight. Such rudimentary studies would serve as a basis for exploring an AG countermeasure and must precede prescriptions for the application of AG during long-duration space flight.” Finally, we concluded “our final recommendation is that NASA establishes a standing AG working group. The group would meet annually for the purpose of continuing and advancing our progress.

The only difference from then to today is that 15 more years have elapsed. The above statements are as valid today as they were back then, except the opening statement could be “More than 45 years of sporadic activity in AG research has not …” Because NASA’s vision for space exploration includes some nine design reference missions to send humans into deep space for long-duration (years) periods, the selection of the final health protecting countermeasure suites should include considerations for AG. The unique feature of AG is that it protects not just one but all of the physiological systems against low gravitational loads (hypo-G). For the time being, protective countermeasures are being developed to target specific physiological systems, which may be protective for one system, but with less or no protection for other systems. In addition, gender differences and individual differences exist in the response to various countermeasure interventions, which further complicates development of efficient countermeasure suites. AG has none of these drawbacks, because all humans have throughout evolution adapted to the same 1-G level.

“One possible reason why NASA has not seriously implemented AG as a health-protecting countermeasure during spaceflight is that the development of AG in space faring vehicles is perceived as being too expensive and complicated, from an engineering standpoint. Multiple studies, however, have shown that this argument may not be valid. Also, in the intervening years of research, NASA has gained insight into the efficiencies of our currently used countermeasures—in particular from utilization and research on the previous Mir space station and now on the ISS—so that a trade-off of these against implementing AG can be implemented on a more mature basis. This was the reason for reconvening this AG Workshop at Ames Research Center on February 19-20, 2014.”

This makes for quite a strong opening for the report and the details in the document back it up. Conclusions and recommendations follow (emphasis added):

“The main conclusion from the Workshop is that AG during long-duration space missions are feasible from an engineering perspective, and that three types of scenarios should be considered: 1) centrifugation inside a space vehicle; 2) spinning part of a vehicle; or 3) spinning the whole vehicle. Research should be initiated as soon as possible to establish the life science AG requirements such as G-levels, durations, and centrifuge size, and in regard to whole-vehicle spinning the minimum G-level (threshold). In addition, the extent to which current countermeasures need to be combined with AG must be determined.

“Countermeasures” is the term applied to attempts to prevent a variety of these degradation issues. The word is plural; one thing most in the space medicine community seem to agree on is that there is no single countermeasure that solves every problem, with the possible exception of artificial gravity. The paper “Another Go-Around: Revisiting the Case for Space-Based Centrifuges,” published in Gravitational and Space Biology in 2011, noted that past studies “have long identified artificial gravity (AG) facilities as a top priority for the gravitational biology and aeromedical communities. Given the apparent preponderance of expert opinion, one might ask why so little work has been done on artificial gravity in the past 40 years.

Given the apparent preponderance of expert opinion, one might ask why so little work has been done on artificial gravity in the past 40 years.

There are multiple answers, but the primary reason has been funding priorities. Officially, the answer has been that the environment most suitable for doing interesting science in space is microgravity, so AG was not considered a requirement for the International Space Station (ISS). Providing a working environment of microgravity plus an off-time and sleeping area of artificial gravity would have seriously impacted the cost and schedule of the ISS.

However, one of the objectives of the ISS became evaluation of countermeasures for human body microgravity degradation, and that continues to this day. A small centrifuge has been added to support some very limited experiments with insects and rodents, but serious AG research does not appear to be on the horizon, based on NASA’s budget breakdown.

Speaking of budgets and technology programs, you might ask why there are so few Mars expedition technology initiatives in the current and planned budgets. Good question, given all of the “we’re going to Mars” hype.

Technology programs generally find their way onto planning charts when the advocate can link his or her project to one or more currently funded programs, some nifty new buzzwords, and/or popular future initiatives. Promoting support from members of Congress whose districts and states will benefit from the funding of that technology effort is strictly forbidden, but it is always a plus.

However, getting a technology effort listed on a long-range planning chart holds no sway unless it shows up as an ongoing program or new start within a current or near-term budget planning cycle. Then the fighting and dickering has only just begun. Every technology development or demonstration effort that does not have an established and funded program office fighting for it is automatically at a disadvantage.

A trip to Mars, even one way, requires a tremendous effort in requirements definition, component and subsystem design, scheduling, integration, system level testing, and thousands of other activities.

This approach to selection and execution of technology programs leads to continuity and integration issues, especially for an initiative that is supported by vagaries. An excellent example is the lip service being given to a human mission to Mars in the mid-2030s. If President Kennedy had committed the United States and NASA to landing on the Moon and returning safely sometime in the mid-1970s, Apollo 11 would never have happened.

Lip service is not a substitute for realistic commitments, especially in the arena of supporting technology development and demonstration. A trip to Mars, even one way, requires a tremendous effort in requirements definition, component and subsystem design, scheduling, integration, system level testing, and thousands of other activities. Those are the kinds of things that program offices make sure are done in an integrated fashion. Otherwise, all you usually get is a mish-mash of people’s pet projects. An adequately funded program office for exploring and settling Mars, one that can support work in artificial gravity that may be critical to the health of the crews that journey there, does not exist in the United States, or anywhere else.


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