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

Stress responses in alfalfa (Medicago sativa L.) XIX. Transcriptional activation of oxidative pentose phosphate pathway genes at the onset of the isoflavonoid phytoalexin response

Article on stress responses in alfalfa (Medicago sativa L.) XIX and transcriptional activation of oxidative pentose phosphate pathway genes at the onset of the isoflavonoid phytoalexin response

Blunted angiogenesis and hypertrophy are associated with increased fatigue resistance and unchanged aerobic capacity in old overloaded mouse muscle.

We hypothesize that the attenuated hypertrophic response in old mouse muscle is (1) partly due to a reduced capillarization and angiogenesis, which is (2) accompanied by a reduced oxidative capacity and fatigue resistance in old control and overloaded muscles, that (3) can be rescued by the antioxidant resveratrol. To investigate this, the hypertrophic response, capillarization, oxidative capacity, and fatigue resistance of m. plantaris were compared in 9- and 25-month-old non-treated and 25-month-old resveratrol-treated mice. Overload increased the local capillary-to-fiber ratio less in old (15 %) than in adult (59 %) muscle (P < 0.05). Although muscles of old mice had a higher succinate dehydrogenase (SDH) activity (P < 0.05) and a slower fiber type profile (P < 0.05), the isometric fatigue resistance was similar in 9- and 25-month-old mice. In both age groups, the fatigue resistance was increased to the same extent after overload (P < 0.01), without a significant change in SDH activity, but an increased capillary density (P < 0.05). Attenuated angiogenesis during overload may contribute to the attenuated hypertrophic response in old age. Neither was rescued by resveratrol supplementation. Changes in fatigue resistance with overload and aging were dissociated from changes in SDH activity, but paralleled those in capillarization. This suggests that capillarization plays a more important role in fatigue resistance than oxidative capacity

High-Temperature, Nonreacting Flowfields Generated By A Hypersonic Chemical-Laser Nozzle

A shock-tube facility was modified to include a single endwall-mounted chemical-laser nozzle, a windowed test section and a 15-m3 dump tank. Single-frame schlieren images of the flowfield with and without secondary injection were obtained. The resulting images showed shock-structure details that were useful in the understanding and optimization of chemical-laser nozzles