It is an exciting time for astronomers and cosmologists. From the James Webb Space Telescope (JWST), astronomers have enjoyed the most vivid and detailed images of the Universe ever taken. WebbPowerful infrared imagers, spectrometers, and coronagraphs will enable even more in the near future, including everything from studies of the early Universe to direct imaging studies of exoplanets. In addition, several next-generation telescopes will be operational in the coming years with 30-meter (~98.5 ft) primary mirrors, adaptive optics, spectrometers, and coronagraphs.
Even with these impressive instruments, astronomers and cosmologists look forward to an era when even more sophisticated and powerful telescopes become available. For example, Zachary Cordero
of the Massachusetts Institute of Technology (MIT) recently proposed a telescope with a 100 meter (328 ft) main mirror which would be built autonomously in space and be bent into shape using electrostatic actuators. His proposal was one of several concepts selected this year by the NASA Innovative Advanced Concepts (NIAC) for the development of Phase I.
Corder is the Boeing Professor of Professional Development in Aeronautics and Astronautics at MIT and a member of the Aerospace Structures and Materials Laboratory (AMSL) and Small Satellite Center. His research integrates his expertise in process science, mechanics, and design to develop new materials and structures for emerging aerospace applications. His proposal is the result of a collaboration with Professor Jeffrey Lang (from the MIT Electronics and Microsystems Technology Labs) and a team of three students with the AMSL, including Ph.D. student Harsh Girishbhai Bhundiya.
His proposed telescope addresses a key problem with space telescopes and other large payloads being packaged for launch and then deployed into orbit. In short, size and surface accuracy tradeoffs limit the diameter of deployable space telescopes to tens of meters. Consider the recent release James Webb Space Telescope (JWST), the largest and most powerful telescope ever sent into space. To fit into its payload fairing (on an Ariane 5 rocket), the telescope was designed so that it could fold into a more compact shape.
This included its primary mirror, its secondary mirror, and its sunshade, which were deployed once the space telescope was in orbit. Meanwhile, the primary mirror – the most complex and powerful ever deployed – measures 6.5 meters (21 feet) in diameter. Its successor, the Large UV/Optical/IR Surveyor (LUVOIR), will have a similar folding assembly and a primary mirror that will measure from 8 to 15 meters (26.5 to 49 feet) in diameter, depending on the design selected (LUVOIR-A or -B). As Bhundiya explained to Universe Today via email:
“Today, most spacecraft antennas are deployed in orbit (for example, Northrop Grumman’s Astromesh antenna) and have been optimized for high performance and gain. However, they have limitations: 1) They are passive deployable systems. That is, once you deploy them, you can’t adaptively change the shape of the antenna. 2) They get harder to kill as their size increases. 3) They exhibit a tradeoff between diameter and precision. That is, its precision decreases as its size increases, which is a challenge to achieve astronomy and sensing applications that require large diameters and high precision (for example, JWST).”
While many in-space construction methods have been proposed to overcome these limitations, detailed analyzes of their performance for building precision structures (such as large-diameter reflectors) are lacking. For the sake of his proposal, Cordero and his colleagues conducted a quantitative, system-level comparison of materials and processes for manufacturing in space. Ultimately, they determined that this limitation could be overcome using advanced materials and a novel manufacturing method in space called bend-forming.
This technique, invented by AMSL researchers and described in a recent article co-authored with Bhundiya and Cordero, is based on a combination of computer numerical control (CNC) High-performance hierarchical material and deformation processing. As Harsh explained:
“Bend-Forming is a process for manufacturing 3D wire structures from metal wire raw material. It works by bending a single strand of wire at specific nodes and to specific angles, and adding joints to the nodes to make a rigid structure. So, to make a given structure, it turns it into bending instructions that can be implemented in a machine like a CNC wire bender to make it from a single strand of raw material. The key application of Bend-Forming is manufacturing the support structure for a large orbiting antenna. The process is well suited for this application because it is low power, can make structures with high compaction rates, and has essentially no size limit.”
Unlike other in-space manufacturing and assembly approaches, bend-forming is low-powered and enabled only by the extremely low-temperature environment of space. In addition, this technique enables intelligent structures that take advantage of multifunctional materials to achieve new combinations of size, mass, stiffness, and precision. In addition, the resulting intelligent structures take advantage of multifunctional materials to achieve unprecedented combinations of size, mass, stiffness, and precision, breaking design paradigms that constrain conventional or tension-aligned spatial structures.
In addition to their native precision, large curve shaped structures can use their electrostatic actuators to contour a reflective surface with sub-millimeter precision. This, Harsh said, will increase the accuracy of his orbit-manufactured antenna:
“The active control method is called electrostatic actuation and uses forces generated by electrostatic attraction to precisely shape a metal mesh into a curved shape that acts as a reflector for the antenna. We do this by applying a voltage between the mesh and a ‘command surface’ consisting of the Bend-Formed support structure and the deployable electrodes. By adjusting this voltage, we can precisely shape the reflector surface and achieve a high-gain satellite dish.”
Harsh and his colleagues deduce that this technique will enable a deployable mirror greater than 100 meters (328 ft) in diameter that could achieve a surface accuracy of 100 m/m and a specific area of more than 10 m.2/kg. This capability would surpass existing microwave radiometry technology and could lead to significant improvements in storm forecasting and a better understanding of atmospheric processes such as the hydrological cycle. This would have significant implications for Earth observation and exoplanet studies.
The team recently demonstrated a 1 meter (3.3 ft) prototype of an electrostatically actuated reflector with a Bend-Formed support structure at the 2023 American Institute of Aeronautics and Astronautics (AIAA). scitech conference, which ran from January 23 to 27 in National Harbor, Maryland. With this NIAC Phase I grant, the team plans to mature the technology with the ultimate goal of creating a microwave radiometry reflector.
Looking ahead, the team plans to investigate how bend-forming in geostationary orbit (GEO) can be used to create a microwave radiometry reflector with a 15 km (9.3 mi) field of view, a terrain resolution of 35 km (21.75 mi) and a proposed frequency range of 50 to 56 GHz: the super high and extremely high frequency (SHF/EHF) range. This will allow the telescope to retrieve temperature profiles of exoplanet atmospheres, a key feature that allows astrobiologists to measure habitability.
“Our goal with NIAC now is to work to implement our bend-forming and electrostatic actuation technology in space,” Harsh said. “We plan to manufacture 100m diameter antennas in geostationary orbit with a bent support structure and electrostatically actuated reflective surfaces. These antennas will enable a new generation of spacecraft with greater sensing, communication, and power capabilities.”
Other reading: POT
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