Future space telescopes could be 100 meters wide, built in space, then bent into a precise shape

This is an exciting time for astronomers and cosmologists. Since James Webb Space Telescope (JWST), astronomers were treated to 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 surveys of the early Universe to direct imaging studies of exoplanets. Additionally, several next-generation telescopes will become operational in the coming years with 30-meter (~98.5-foot) primary mirrors, adaptive optics, spectrometers, and coronagraphs.

Even with these impressive instruments, astronomers and cosmologists eagerly await an era when even more sophisticated and powerful telescopes become available. For example, Zachary Cordero
from the Massachusetts Institute of Technology (MIT) recently proposed a telescope with a 100-meter (328-foot) primary mirror that would be built autonomously in space and shaped by electrostatic actuators. His proposal was one of several concepts selected this year by the NASA Innovative Advanced Concepts (NIAC) program for Phase I development.

Corder is the Boeing Career Development Professor of Aeronautics and Astronautics at MIT and a member of the Aerospace Materials and Structures Laboratory (AMSL) and the 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 (of MIT’s Microsystems Technology and Electronics Laboratories) and a team of three AMSL students, including a PhD. student Harsh Girishbhai Bhundiya.

Their proposed telescope solves a key problem with space telescopes and other large payloads that are packaged for launch and then deployed into orbit. In short, trade-offs in size and surface accuracy limit the diameter of deployable space telescopes to tens of meters. Consider the recent launch James Webb Space Telescope (JWST), the largest and most powerful telescope ever sent into space. To fit into its payload fairing (on top of an Ariane 5 rocket), the telescope was designed so that it could be folded into a more compact shape.

This included its primary mirror, secondary mirror, and sunshade, all of which deployed once the space telescope was in orbit. Meanwhile, the primary mirror (the most complex and powerful ever deployed) is 6.5 meters (21 feet) in diameter. Its successor, the Large UV/Optical/IR Surveyor (LUVOIR), will have a similar collapsible assembly and a primary mirror measuring 8 to 15 meters (26.5 to 49 feet) in diameter – depending on the design chosen (LUVOIR-A or -B). As Bhundiya explained to Universe Today via email:

“Today, most spacecraft antennas are deployed in orbit (eg 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 cannot adaptively change the shape of the antenna. 2) They become difficult to kill as their size increases. 3) They present a compromise between diameter and precision. That is, their accuracy decreases as their size increases, which is a challenge to achieve astronomy and sensing applications that require both large diameters and high accuracy (e.g. JWST) .

While many in-space construction methods have been proposed to overcome these limitations, detailed analyzes of their performance for the construction of precision structures (like large-diameter reflectors) are lacking. For the sake of their proposal, Cordero and his colleagues performed a system-level quantitative comparison of materials and manufacturing processes in space. Ultimately, they determined that this limitation could be overcome using advanced materials and a new method of manufacturing in space called Bend-Forming.

This technique, invented by AMSL researchers and described in a recent paper co-authored by Bhundiya and Cordero, relies on a combination of computer numerical control (CNC) deformation processing and high-performance hierarchical materials. As Harsh explained:

“Bend-Forming is a process of making 3D wireframe structures out of metal wire. It works by bending a single strand of yarn at specific knots and with specific angles, and adding joints at the knots to create a rigid structure. So, to make a given structure, you convert it into bending instructions that can be implemented on a machine like a CNC wire bender to make it from a single strand of raw material. The key application of Bend-Forming is the fabrication of the support structure for a large orbiting antenna. The process is well suited for this application because it consumes little energy, can fabricate structures with high compaction rates, and has virtually no size limitations.

Unlike other in-space assembly and manufacturing approaches, Bend-Forming is low power and is only enabled by the very low temperature environment of space. Moreover, this technique enables intelligent structures that exploit multifunctional materials to achieve new combinations of size, mass, rigidity and precision. Additionally, the resulting smart structures leverage multifunctional materials to achieve unprecedented combinations of size, mass, stiffness, and precision, breaking design paradigms that limit conventional trusses or tension-aligned spatial structures.

In addition to their native accuracy, large curved structures can use their electrostatic actuators to bypass a reflector surface with sub-millimeter accuracy. This, Harsh said, will increase the accuracy of their in-orbit fabricated antenna:

“The method of active control is called electrostatic actuation and uses the forces generated by electrostatic attraction to precisely shape a wire mesh into a curved shape that acts as an antenna reflector. To do this, we apply a voltage between the mesh and a “control surface” which consists of the Bend-Formed support structure and deployable electrodes. By adjusting this tension, we can precisely shape the surface of the reflector and achieve a high-gain parabolic antenna.”

Harsh and his colleagues deduce that this technique will allow a deployable mirror measuring more than 100 meters (328 feet) 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 like the hydrological cycle. This would have important implications for Earth observation and exoplanet studies.

The team recently demonstrated a 1-meter (3.3-foot) prototype of an electrostatically actuated reflector with a curvature-like support structure at the American Institute of Aeronautics and Astronautics (AIAA) SciTech 2023 conference. , which took place from January 23 to 27 in National Port, Maryland. With this Phase I grant from NIAC, 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 can be used in geostationary orbit (GEO) to create a microwave radiometry reflector with a 15 km (9.3 mi) field of view, a ground 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 allowing astrobiologists to measure habitability.

“Our goal with NIAC now is to work on implementing our Bend-Forming and electrostatic actuation technology in space,” Harsh said. “We envision making 100m diameter antennas in geostationary orbit with a curvature-shaped support structure and electrostatically actuated reflector surfaces. These antennas will enable a new generation of spacecraft with increased detection, communication and power capabilities.

Further reading: NASA