Research Center, flew on a Midstar-1, a US Naval Academy satel-lite, and demonstrated the capability to detect trace amounts of nitrogen dioxide. A compact trace gas sensor (“electronic nose”) consisting of a nanoparticle impregnated polymer primary sensor and a carbon nanotube-based auxiliary sensor successfully flew on the International Space Station in 2008. Carbon nanotube-based composites were used in an engine cover and struts for the Juno probe for the mitigation of electrostatic charging.In order to better plan its investments in nanotechnology R&D, NASA has recently drafted a 20+ year roadmap for the develop-ment and insertion of nanotechnology in future space missions. The Nanotechnology Space Technology Roadmap,2 one of 14 tech-nology roadmaps developed under the auspices of the NASA Chief Technologist, identified opportunities for nanotechnology in four main areas: engineered materials and structures; propulsion and propellants; energy generation, storage, and distribution; and electronics, sensors and devices. Fourteen key capabilities enabled by nanotechnology developments were identified along with five grand challenges, high payoff nanotechnology research thrusts for future NASA investment.This chapter will discuss the Nanotechnology Roadmap and provide a glimpse into future opportunities for research and de-velopment activities in nanotechnology for aerospace applications. A particular emphasis of the chapter will be on a discussion of the

grand challenges identified in the roadmap and on the developments necessary to meet these challenges. 12.2 Discussion

12.2.1 Grand Challenge: 50% Lighter CompositesVehicle weight is a major concern for most NASA missions. Reductions in vehicle weight enable increased payload capacity that can be utilized to carry more instrumentation, supplies, and/or power systems. For aeronautics, vehicle weight reduction leads to reduced fuel consumption and emissions. The current trend within the aerospace community is to maximize the use of lightweight composites in both aircraft and spacecraft. Composite utilization in the Boeing 787 is 50% compared to 7% in the Boeing 777. NASA is actively pursuing technologies to enable wider use of composites in launch vehicle dry structures and cryogenic propellant tanks. Replacement of conventional carbon fiber reinforced polymer composites with materials that are 50% lighter would lead to as much as a 30% overall reduction in the dry mass (vehicle without propellant) of aircraft and spacecraft. While reducing the density of composites by 50% seems to be an impossible goal, recent results in nanotechnology R&D suggest that it is achievable.In conventional composites, it is desirable to have a fully

densified matrix since voids can act as mechanical defects resulting in premature failure and can also act as sites for environmental degradation of the composite. However, by introducing nanoscale pores or voids into a matrix in a controlled manner, it may be possible to make matrixes that can sustain the same types of mechanical loads and with the same durability as conventional fully dense polymer matrixes. Researchers at the NASA Glenn Research Center have been working on structural polymer aerogels for use in multifunctional insulation.3 These nanoporous polymers have densities on the order of 0.2 g/cm3, roughly 1/5 that of a fully dense polymer. At this density level, replacement of a conventional polymer matrix with one of these aerogels would reduce the density of a composite by about 25%. While the mechanical properties of these materials are quite impressive compared to conventional polymer foams (tensile strengths as high as 8 MPa and compressive moduli up to 100 MPa) they are not sufficient for use as a composite

matrix. Further improvements in mechanical properties could be achieved by adding nanoscale fillers (carbon nanotubes, nanoclays or graphene) to strengthen nanopore walls in these materials.