Most of human experience in spaceflight has been in Low Earth Orbit (LEO) - in fact, only about 0.5% of total human spaceflight time has occurred beyond LEO, during the Apollo lunar missions. Now, with six decades of LEO experience behind us, planning for long-duration missions beyond LEO is a priority. The idea of setting a permanent human base on Mars and Moon is considered achievable within our lifetime, but, in order to make this dream come true, there are several technological issues that must be considered. The most important issue is to create the adequate protection against space radiation that is the main risk to astronaut health. Shielding can be a difficult task because of the high energy of the primary charged particles and the secondary particles produced as a fission product of the primary radiation sources with the soil or the spacecraft or the spacesuits. One of the chief technical barriers to feasible distant-destination missions by humans is space radiation.
New materials, to facilitate and improve extra-vehicular activities (EVAs), will be an essential component to be able to work and live in these airless environments safely. These new materials can provide special protection to particularly vulnerable organs in humans and engineering systems for critical operability.
This project will address how to design, manufacture and incorporate new materials (in particular, based on graphene and polyethylene polymer) with synergistic capabilities (radiation protection, mechanical strength, thermal and electrical conductivities), that will lead to the design of improved EVA suits (with focus on radiation resistance and mobility). In particular, the team will focus on the development of novel composite polymer materials containing graphene oxide. The polymer composites are expected to yield highly flexible, lightweight polymers that have high thermal and electrical conductivities while maintaining high mechanical strengths.
Human radiation risks and mitigation approaches for long-duration deep-space missions are only partially understood, and are the subject of a variety of ongoing and long-term ESA and NASA studies. Although radiation shielding is surely required for humans in deep space, equally essential is new materials for spacesuits, habitats, and vehicles with experimentally tested responses to radiation, thermal and mechanical stress, dust, and mechanical fatigue.
Radiation protection standards for missions to LEO were revised and approved by NASA in 2014 under guidance of the National Council on Radiation Protection and Measurements (NCRP). These standards have been applied to International Space Station (ISS) missions, which typically have been up to six months, with a recent one-year extended stay by two crewmembers (NCRP, 2014). Current spacesuit designs have single function layers, including pressure garments, air bladder, restraint layer, thermal cooling, insulation and a micrometeoroid protective layer. Radiation/meteoroid mitigation relies on Tungsten loaded silicone (75% by wt) with an areal density of 0.85 g/cm2. These layers reduce the astronauts dexterity. Moreover, radiation protection is limited to short term exposure within a protective environment (the Earth's magnetic field), and therefore is not adequate for human exploration missions beyond near Earth orbit (NASA Space Technology Roadmaps and Priorities from 2012; ESA Roadmap and Priorities from 2017).
Design drivers of novel spacesuits for human exploration should therefore include multifunctional, lightweight materials with optimal mobility/flexibility, robust radiation protection, and high durability, along with appropriate thermal and electrical conductivities. This latter functionality is being advocated by the investigators, analogously to the skin conductivity requirements of spacecraft immersed in space plasmas. All these operative requirements are the results we expected to achieve in this project. In fact, we propose a novel flexible nanocomposite materials, with an estimated areal density of 0.02 g/cm2 (extremely lightweight), which act as radiation protection and in the same time have appropriate thermal and electrical conductivities. We will exploit the multifunctional properties of the graphene with radiation shielding properties of both graphene and polyethylene to form a flexible lightweight protection.
Instead of developing a new suit design (impractical) we intend to approach the application of novel, flexible materials in terms of suitability for specific areas of a suit based on the NASA PXS and Z2 technology demonstrator suit designs, as well as the currently-used EMU (current spacesuits). This approach allows us to obtain potential results in relatively short time.
Experimental Approach for Advancing the State of Knowledge:
We propose 3 routes to the formation of these graphene nanocomposites, as we seek to optimize the interaction of the polymeric host with the graphene and PE fiber fillers through covalent bond formation for high mechanical integrity, while simultaneously providing a low graphene percolation transition for high electrical and thermal conductivity.
Reactive Aromatic Polymers With GO. Beginning with GO, we will use the multitude of oxidized sites formed at the graphene edges and PE fiber surfaces as points for chemical reactivity with a compatabilizing aromatic polymer precursor. Covalent bond formation between these components will provide high mechanical integrity.
Ion Functionalized Polymer With KMG. Base treatment of GO yields the highly ionic potassium modified graphene (KMG), which will be used with the ionic aromatic polymer precursor as a means of refining and controlling the extent of graphene phase separation. This will provide conducting percolation pathways at low contents of the conducting phase.
In Situ Polymerization with GO and KMG. As we consider the possible preparation of nanocomposite materials in space where we would like to have the highest degree of flexibility in property control, we will explore formation of the aromatic polymer precursor via in situ polymerization in the presence of GO and the modified reinforcing PE fibers. In this manner, mechanical flexibility can be balanced with the electrical, thermal and radiation-stopping properties for varied use.