As NASA evolves its vision for space exploration and Earth science, greater demands are placed on advanced communications and sensing systems to allow for higher data-rate communications from the Moon, Mars, and beyond, as well as for more precise Earth and planetary remote sensing activities. Taking into consideration the cost of launching hardware into space (about $20K per kg), as well as the fairings’ volume limitations, there is need for novel antenna technology concepts to circumvent these limitations, without jeopardizing the desired capabilities. To address this scenario, NASA is investigating the development of large aperture, inflatable/deployable antenna (IDA) technologies as a viable option to fulfill the aforementioned requirements. Attainment of these requirements demands overcoming a series of critical challenges as discussed below.
What Are the Challenges of IDA Technology?
A series of challenges confronts the development of IDA technologies: low cost, the ability to operate efficiently at high frequencies (i.e., Ka-band and above), low aereal density (< 2Kg/m2), large deployed area to stowage volume ratio (>10:1), and reliable deployment mechanisms. In addition, regardless of the type of aperture (i.e., parabolic or flat), the antenna may require surface correction approaches, either at the aperture itself (e.g., actuators) or at the feed (e.g., phased array feeds). As the antenna aperture increases, the beam width narrows, thereby exacerbating pointing issues. Consequently, effective antenna pointing schemes become more critical to mitigate antenna pointing losses.
What is NASA Doing?
Currently, NASA is involved in an effort to evaluate different types of large aperture IDA technologies such as mesh antennas, inflatable membrane antennas, shape memory polymer composite antennas, and hybrid inflatable antennas. Each of these antenna types has their merits and limitations. For example, while the mesh antenna is considered a mature technology at low and intermediate frequencies (e.g., 12-meter aperture L-band Thuraya; Ku-band TDRSS), there may still be issues to be resolved at Ka-band frequencies and above (e.g., surface accuracy, faceting induced sidelobes, etc.). Likewise, membrane antennas and shape memory polymer antennas required rigidization approaches (particularly for the former to eliminate the requirement of make-up gas) and surface-quality optimization.
The hybrid approach, which combines a solid reflector at the center (a highly desirable risk mitigation feature) with an external deployable reflector, appears very promising. However, it is still in the material optimization and selection stage. Large deployable reflect array antennas have been demonstrated in the laboratory, and testing with a phased array antenna feed to account for surface limitations has been identified as the next logical step.
What Applications Does NASA Envision?
Large aperture IDA has applications for high data-rate communication relays from Mars and beyond, as well as large aperture antennas for radiometry and global climate prediction and other Earth science missions (e.g. hurricane intensity monitoring).