Christopher E. Carr, Sc.D.

| Research Scientist

Studying the origin(s), evolution, and adaptability of biological systems through the prism of computation and engineering analysis

Russian CO2 removal equipment onboard ISS

Extravehicular Activity Test at Meteor Crater

Research

The Search for Extraterrestrial Genomes (SETG):
An In-situ Detector for Life on Mars Ancestrally Related to Life on Earth

The SETG Project will test the hypothesis that life on Mars, if it exists, shares a common ancestor with life on Earth. There is increasing evidence that viable microbes could have been transferred between the two planets, based in part on calculations of meteorite trajectories and magnetization studies supporting only mild heating of meteorite cores. Based on the shared-ancestry hypothesis, this instrument will look for DNA and RNA through in-situ analysis of Martian soil (or ice) samples.

By applying recent advances in microfluidics, embedded systems, and biological automation, our team is developing an instrument that can isolate, amplify, detect, and classify any extant DNA or RNA-based organism. We are applying core engineering skills to build the required control systems, implement microfluidic systems, integrate hardware and software, and ultimately to space-qualify our system for cruise to and operation on Mars.

Accordingly, the project provides superb opportunities for undergraduate and graduate students to participate in an aerospace project from conception to operation, while contributing to and advancing the state of the art in a number of traditional engineering disciplines. This project has open positions.

Metabolism, Insulin Signalling, and Aging

In partnership with Dr. Andrew Samuelson and Prof. Gary Ruvkun at MGH, I have built a pipeline for automated demographic analysis of survival and mortality data to enable high-throughput longevity/aging assays in the worm C elegans, including classification of different genes (via RNAi based inactivation). This work has already contributed to understanding how insulin signaling, a key regulator of lifespan, and its associated genetic network, contribute to aging.

Astronauts and Carbon Dioxide

Humans produce carbon dioxide (CO2) as a natural bioproduct of metabolism, eliminating CO2 through the lungs. In the enclosed volume of space vehicles, high CO2 becomes a health hazard and must be removed, an energy intensive endeavor. As part of a clinical rotation during my doctoral program, I carried out a study with (then NASA Flight Surgeon, now astronaut) Dr. Thomas Marshburn to understand why astronauts were experiencing symptoms consistent with elevated CO2 exposure. While the study remains unpublished (due to presence of private medical data), it has been cited by the NASA chief toxicologist and used in negotiations with the Russian Space Agency to determine the allowable exposure limits for CO2 onboard the space station. Modeling of the human ventilatory control system to determine whether space-related physiological changes sensitize astronauts to CO2 remains an interesting future project: see openings for more information.

Human Energetics, Space Suits, and Extravehicular Activity (EVA)

I began my work in this area as a graduate student by assisting in two studies related to space suit mobility: the first used a humanoid robot to make direct measurements of space suit joint torques, and demonstrated that suit torques can be explained largely from gas thermodynamics, e.g., pressure and volume changes. The latter study evaluated mobility during a series of realistic tasks, and provided me with first-hand experience in a space suit.

Early in my graduate career I had the opportunity to execute a project with an MIT Media Lab-Boeing-Hamilton Sundstrand team to explore whether we could deliver information to astronauts using an in-suit wearable computer. We demonstrated that this was feasible, and carried out space suit tests that revealed efficiency improvements through the use of a system that utilized an in-suit microdisplay (Carr et al. 2002; Hodgson et al. 2003).

Based on this information management work, I developed a series of mission planning and analysis tools to improve planetary extravehicular activity, and demonstrated how these tools could have been used to overcome some of the obstacles encountered during the Apollo lunar missions (S.M. Thesis; Carr et al., 2003). Another graduate student, Jessica Marquez (now at NASA Ames), built on this work for her Ph.D. and the work continues as a current NASA-funded humans-in-the-loop mission-planning tool.

Knowing that astronaut EVA was limited in part due to metabolic loads, I performed an extensive review of the literature (going back to obscure 1960s studies), and in part through non-dimensional analysis, developed a model that succinctly captured the key determinants of metabolic cost during human movement (Carr et al. 2007a). I also demonstrated that running was more efficient (per unit distance) than walking in a space suit (Carr et al. 2005; Carr et al. 2007b). I then set about testing this model in humans.

Due to lack of access to a space suit by this point, I evaluated how to simulate one or build one myself. I learned of an exoskeleton under development in Hugh Herr’s lab (MIT) and determined that I might be able to use it to simulate a space suit. I built an adapted version of this lower-body exoskeleton and demonstrated that it very accurately simulated the knee torques of the current NASA space suit (Carr et al. 2008). Exoskeleton in hand, I carried out experiments to study metabolic expenditures as a function of gait, gravity, and under “suited” or unsuited conditions.

No statistical deviation from the model was found, and indeed the results suggested that energy recovery (through pendular motion in walking, and spring-like energy storage in running) may play a key role in gait switching (Ph.D. dissertation; manuscript in preparation). I advised graduate student Andrew Rader in carrying out a follow-up study to investigate loping, a long-discussed funny gait adopted by astronauts on the lunar surface, and we demonstrated that this gait is energetically favorable (Rader et al. 2007).