SAR-DiskSat for Mega-Constellation

We have developed and demonstrated in 2021 small SAR satellites of 1-m ground resolution with novel deployable slot array antennas. This paper newly proposes a novel concept of quasi-two-dimensional SAR satellites, SAR-DiskSats with this deployable passive slot array antenna. The deployable slot array antennas can be compactly folded in the quasi-two-dimensional satellite body. Also, it is possible to install flexible solar cell sheets on the back side of the antenna because the antennas do not dissipate heat. This quasi-two-dimensional satellite configuration is suitable to for stacking in a rocket faring for mega-constellation launching. Another advantage of the SAR-DiskSat is the possibility of VELEO (very low Earth orbit) operation. A thin edge cross-section makes aero drag small and there is an advantage of short range in terms of signal-to-noise ratio. This advantage of RF power makes it easier to improve its ground resolution. We are developing a new corporate feed slot array antenna with very wide-band (1.2-GHz bandwidth in X band) for 0.25-m ground resolution. The final goal of this SAR-DiskSat would be a mega- constellation of 0.25-m ground resolution in VLEO

The DiskSat: A Two-Dimensional Containerized Satellite

A key factor in the remarkable expansion of the CubeSat class of spacecraft over the past two decades is launch containerization. The container protects the launch vehicle and primary payload from issues that might arise from the CubeSat (which is essential for rideshare), and the standardized and highly-simplified launch interface reduces integration cost for the launch provider and development cost for the CubeSat builder. The downside of containerization is that the size of the contained satellites is rigidly limited. While there are available designs for larger dispensers and CubeSats, very few CubeSats larger than 6U have flown, and none have been larger than 16U. Future space missions will benefit from more power and RF aperture, beyond what can be provided by conventional CubeSats, even with complex deployables. We propose here the DiskSat, a containerized, large-aperture, quasi-two-dimensional satellite bus architecture. A representative DiskSat structure is a composite flat panel, one meter in diameter and 2.5 cm thick, to which components are affixed in a flat pattern within the panel. The volume of the representative DiskSat is almost 20 liters, comparable to a hypothetical 20U CubeSat, while the structural mass can be less than 2.5 kg. The surface area of a single disk face is substantially larger than the total surface area of any conventional CubeSat, supporting over 200 W of peak solar power without the complexity of deployables, thereby improving mission assurance and reducing vehicle cost. Alternatively, a single fixed deployable panel can ensure that the vehicle has over 100 W orbit-average power while maintaining nadir pointing in any beta angle. For launch, multiple DiskSats are stacked in a fully-enclosed container/dispenser using a simple mechanical interface, and are released individually once in orbit. Stacking of 20 or more DiskSats is possible in small launch vehicles, making it ideal for building large constellations of small satellites in multiple discrete orbital planes. The 1-m-diameter DiskSat was developed with the Rocket Lab Electron in mind; the concept can be extended to larger diameters (1.2 m for the Virgin LauncherOne, for example), or to other flat shapes (square for an ESPA port, for example), and to greater thicknesses if the mission requires it. The DiskSat concept was developed as a cost-effective solution for a LEO constellation that required significant power and RF aperture. Since then we have explored the utility of the bus architecture for a broad range of missions including Earth observation and space science, among others. One particularly useful feature of the DiskSat is the high power-to-mass ratio, enabling high-delta-v electric propulsion missions, including deep-space applications. Another feature is the ability to fly in a low-drag orientation which, in combination with electric propulsion for drag makeup, enables flight at very low altitudes in LEO. This paper will detail the design of the DiskSat and its dispenser, will explore the range of missions enabled by the DiskSat, and will describe current development activities in support of a DiskSat demonstration flight

CubeSat Laser Communication Crosslink Pointing Demonstration

An opportunity arose to demonstrate optical crosslink pointing between two CubeSats in LEO using spacecraft not specifically designed for that purpose. The AeroCube-7 spacecraft, designed for optical downlinks as part of the Optical Communication and Sensor Demonstration mission, was tasked to point its communications laser at the ISARA spacecraft to demonstrate the capability of one CubeSat to track another in LEO. The ISARA spacecraft, which does not carry a data receiver, but does carry a short-wave infrared camera (SWIR) as part of the CUMULOS payload, was tasked to track the AeroCube-7 spacecraft and use the SWIR camera to record the OCSD laser. The SWIR images were downloaded over an RF channel and used to evaluate the pointing and tracking of both spacecraft. Two successful tests of crosslink pointing were completed between AeroCube-7 and ISARA, providing a demonstration in principle of the capability, and laying the groundwork for more refined experiments that will use this technique for on-orbit measurements of beam profiling. Further tests between AeroCube-11 and ISARA are also in preparation to demonstrate crosslink pointing in a more-challenging orbital configuration

Shape-Memory Alloy Actuators for Small Satellites

A frequently‐used hold‐and‐release mechanism for spacecraft deployables is the “meltwire” or “burnwire”. Here an electrically resistive heating element melts through a fusible restraint to free some sliding, pivoting, or flexing element such as a hinged solar array, an instrument boom, or an antenna. The heating element is often a length of nichrome wire, but discrete electrical resistors, both surfacemount and through‐hole have also been used. Meltwire release mechanisms present a unique challenge for testing in that they cannot be reused; once melted, the fusible restraint must be replaced. Since this is often a laborious and time‐consuming task, the testing regime is often limited, particularly for small, low‐budget spacecraft. In addition, since the fusible restraint must be replaced after each use, the component that ultimately flies will be one that has not, itself, been tested. We have found that simple mechanisms actuated by Shape Memory Alloy (SMA) devices are an effective alternative to meltwires for small spacecraft applications. In contrast to meltwires, these mechanisms are easily resettable, enabling a low‐cost but robust test campaign to ensure operational reliability. In each case the heart of the device is a length of nitinol wire, nitinol being a nickel titanium alloy that can be configured to contract 3 to 4% on heating. Heating is accomplished by passing an electrical current through the wire. The resulting contraction exerts a force that can be used to move a structure attached to the wire, so implementation of SMA‐actuated release mechanisms revolves around design of mechanisms that can be operated through a simple pull force. When the nitinol returns to its original temperature, it can be stretched mechanically to its original dimension with essentially no degradation of its properties (provided it has not been overheated), allowing the mechanism to be reset and ready for the next actuation. Many of the features of SMA wire actuators are particularly suited (but not limited to) to the kinds of one‐time‐use mechanisms found on satellites. They are light, simple, and easily tested and reset. They present no magnetic signature when not energized. They can also be built into more complex devices that have multiple discrete positions and can even be used to produce or control a motor. In addition, they are clean; they can often be designed without greases or other lubricants that could pose a contamination risk, and they produce no debris when actuated. While there are many reasons to consider SMA wire actuators, prudence demands an understanding of their limitations, particularly with respect to actuation speed, electrical efficiency, longevity, and force limitations. Another key consideration is that the performance of SMA actuators can be severely degraded by overheating. As such, the thermal design must take into account operations in both air and vacuum, and particular care must be taken to ensure that vacuum test procedures do not result in unacceptable thermal stresses. SMA actuators have flown and operated successfully on six spacecraft in the AeroCube series, and these actuators are designed into a number of upcoming missions. This paper will review design, assembly, and testing techniques and present several case studies from recent AeroCube flights

Multimaterial tandem electrospinning for spatially modulated neural guidance

The goal of this work is the creation of an in vitro platform to investigate the combined effects of patterned topographical and bioactive cues towards achieving the spatially controlled growth of peripheral sensory neurons

A One‐Step Biofunctionalization Strategy of Electrospun Scaffolds Enables Spatially Selective Presentation of Biological Cues

To recapitulate the heterogeneous complexity of tissues in the human body with synthetic mimics of the extracellular matrix (ECM), it is important to develop methods that can easily allow the selective functionalization of defined spatial domains. Here, a facile method is introduced to functionalize microfibrillar meshes with different reactive groups able to bind biological moieties in a one‐step reaction. The resulting scaffolds prove to selectively support a differential neurite growth after being seeded with dorsal root ganglia. Considering the general principles behind the method developed, this is a promising strategy to realize enhanced biomimicry of native ECM for different regenerative medicine applications

A one-step biofunctionalization strategy of electrospun scaffolds enables spatially selective presentation of biological cues

To recapitulate the heterogeneous complexity of tissues in our body with synthetic mimics of the extracellular matrix (ECM), it is important to develop methods that can easily allow the selective functionalization of defined spatial domains. Here, we introduce a facile method to functionalize microfibrillar meshes with different reactive groups able to bind biological moieties in a one-step reaction. The resulting scaffolds proved to selectively support a differential neurite growth after being seeded with dorsal root ganglia. Considering the general principles behind the method developed, this is a promising strategy to realize enhanced biomimicry of native ECM for different regenerative medicine applications

DiskSat: Demonstration Mission for a Two-Dimensional Satellite Architecture

The DiskSat is a quasi-two-dimensional satellite bus architecture designed for applications requiring high power, large apertures, and/or high maneuverability in a low-mass containerized satellite. A representative DiskSat structure is a composite flat panel, one meter in diameter and 2.5 cm thick. The volume is almost 20 liters, equivalent to a hypothetical 20U CubeSat, while the structural mass is less than 3 kg. The surface area is large enough to host over 200 W of solar cells without deployable solar panels. For launch, multiple DiskSats are stacked in a fully enclosed container/deployer using a simple mechanical interface and are released individually in orbit. The Aerospace Corporation, with the support of the NASA Space Technology Mission Directorate (STMD), is preparing a flight of four DiskSats for launch in 2024 to demonstrate the feasibility of both the dispenser and the DiskSat bus. In addition, the flight is expected to demonstrate several features of the DiskSat including the unprecedented high power-to-mass ratio, the maneuverability of the bus using low-thrust electric propulsion, and the ability to fly continuously in a low-drag orientation, enabling operations in very low Earth orbits (VLEO). The DiskSats will be launched in and deployed from a dispenser that provides a containerized rideshare environment; the dispenser fully encloses the DiskSats during launch and then opens to dispense the satellites one at a time once in orbit. The dispenser is modular in design and expandable from the capacity of four DiskSats for this flight to as many as 20 DiskSats for future flights. NASA STMD seeks disruptive and innovative technologies that could help lead to the next-generation systems for future science and exploration missions. DiskSat is a potentially disruptive technology that may lead to, and enable, new mission architectures using ever-more capable small spacecraft. Data generated from this flight will inform the drafting of a DiskSat standard intended to encourage easy and frequent access to space, in the same manner as the CubeSat standard. DiskSat is expected to become a standard format for rideshare-compatible, high-power, maneuverable, low-mass satellites for Earth-orbit, cis-lunar, and deep space applications

Solid-material-based Coupling Efficiency Analyzed with Time-of-Flight Secondary Ion Mass Spectrometry

The coupling behavior of a microparticle embedded amino acid active-ester into a Poly(ethylene glycol)methacrylate-film, synthesized onto a silicon wafer by a grafting from approach, is characterized using dynamic time-of-flight secondary ion mass spectrometry (ToF-SIMS) to analyze the 3d distribution of the amino acids in the polymer film. Besides standard solid phase peptide synthesis, employing solubilized amino acids in a solvent, we used solid polymer microparticles, incorporating the amino acids. These microparticles were especially designed for a new technique to produce high-density combinatorial peptide microarrays: upon heating, the particles become viscous, which releases the embedded amino acids to diffuse and couple to the surface. In the scope of the development of this new particle-based application, ToF-SIMS is used to analyze a complex chemically modified polymer surface layer. Due to depth profile measurements, it is possible to investigate the particle-based coupling reaction not only on the surface, but also into the depth of the PEGMA film