Design of a Control Allocation Solution for the Winged Reusable Launch Vehicle ReFEx

This paper presents a control allocation solution for the technology demonstrator mission ReFEx, which focuses on a vertical takeoff and horizontal landing strategy with autonomous navigation, online guidance, and controlled flight throughout the mission. The trajectory for the demonstration flight is aimed as one for a winged launch vehicle first stage: maintaining stability and control of the vehicle while reaching a predefined target. During the atmospheric phase the vehicle is stabilized by using an active aerodynamic control system which transforms inputs from the guidance and navigation systems into control commands for the individual actuators. In that sense, the control allocation subsystem translates commanded moments into commanded aerodynamic surface deflections. Due to the effect of modeling uncertainties, navigation errors, and underactuated regions, this subsystem needs to be robustified. The algorithm proposed in this paper addresses this challenge via a combination of the deflections required to trim the vehicle together with delta-deflections that aim at converging iteratively to the commanded moments. The combination of these two contributions is able to respond fast to state changes, compensate for modeling uncertainties and navigation errors, and provide a safe mode for the underactuated regions. The performance of the system is studied using a high-fidelity simulator

Highly sensitive force measurements in an optically generated, harmonic hydrodynamic trap.

The use of optical tweezers to measure forces acting upon microscopic particles has revolutionised fields from material science to cell biology. However, despite optical control capabilities, this technology is highly constrained by the material properties of the probe, and its use may be limited due to concerns about the effect on biological processes. Here we present a novel, optically controlled trapping method based on light-induced hydrodynamic flows. Specifically, we leverage optical control capabilities to convert a translationally invariant topological defect of a flow field into an attractor for colloids in an effectively one-dimensional harmonic, yet freely rotatable system. Circumventing the need to stabilise particle dynamics along an unstable axis, this novel trap closely resembles the isotropic dynamics of optical tweezers. Using magnetic beads, we explicitly show the existence of a linear force-extension relationship that can be used to detect femtoNewton-range forces with sensitivity close to the thermal limit. Our force measurements remove the need for laser-particle contact, while also lifting material constraints, which renders them a particularly interesting tool for the life sciences and engineering

Feedback-based positioning and diffusion suppression of particles via optical control of thermoviscous flows.

The ability to control the position of micron-size particles with high precision using tools such as optical tweezers has led to major advances in fields such as biology, physics and material science. In this paper, we present a novel optical strategy to confine particles in solution with high spatial control using feedback-controlled thermoviscous flows. We show that this technique allows micron-size particles to be positioned and confined with subdiffraction precision (24 nm), effectively suppressing their diffusion. Due to its physical characteristics, our approach might be particular attractive where laser exposure is of concern or materials are inherently incompatible with optical tweezing since it does not rely on contrast in the refractive index

Optical plasticity of mammalian cells.

Transparency is widespread in nature, ranging from transparent insect wings to ocular tissues that enable you to read this text, and transparent marine vertebrates. And yet, cells and tissue models in biology are usually strongly light scattering and optically opaque, precluding deep optical microscopy. Here we describe the directed evolution of cultured mammalian cells toward increased transparency. We find that mutations greatly diversify the optical phenotype of Chinese Hamster Ovary cells, a cultured mammalian cell line. Furthermore, only three rounds of high-throughput optical selection and competitive growth are required to yield fit cells with greatly improved transparency. Based on 15 monoclonal cell lines derived from this directed evolution experiment, we find that the evolved transparency frequently goes along with a reduction of nuclear granularity and physiological shifts in gene expression profiles. In the future this optical plasticity of mammalian cells may facilitate genetic clearance of living tissues for in vivo microscopy

Mechanisms and microenvironment investigation of cellularized high density gradient collagen matrices via densification

Biological tissues and biomaterials are often defined by unique spatial gradients in physical properties that impart specialized function over hierarchical scales. The structure of these materials forms continuous transitional gradients and discrete local microenvironments between adjacent (or within) tissues, and across matrix-cell boundaries, which is difficult to replicate with common scaffold systems. Here, the matrix densification of collagen leading to gradients in density, mechanical properties, and fibril morphology is studied. High-density regions form via a fluid pore pressure and flow-driven mechanism, with increased relative fibril density (10x), mechanical properties (20x, to 94.40 +/- 18.74 kPa), and maximum fibril thickness (1.9x, to >1 mu m) compared to low-density regions, while maintaining porosity and fluid/mass transport to support viability of encapsulated cells. Similar to the organization of the articular cartilage zonal structure, it is found that high-density collagen regions induce cell and nuclear alignment of primary chondrocytes. Chondrocyte gene expression is maintained in collagen matrices, and no phenotypic changes are observed as a result of densification. Collagen densification provides a tunable platform for the creation of gradient systems to study complex cell-matrix interactions. These methods are easily generalized to compression and boundary condition modalities useful to mimic a broad range of tissues

ReFEx: Reusability Flight Experiment - Architecture and Algorithmic Design of the GNC Subsystem

The German Aerospace Center (DLR) "Reusability Flight Experiment" (ReFEx) aims to demonstrate the Guidance, Navigation, and Control (GNC) capabilities for an aerodynamically controlled Reusable Launch Vehicle (RLV) stage. The GNC subsystem is responsible for maintaining stability and steering the vehicle to achieve a target state, specifically transitioning from the supersonic to subsonic flight regime. This objective is accomplished through: 1) planning and updating a feasible trajectory from separation up to the target state (Guidance); 2) estimation of the vehicle’s current state by leveraging sensor measurements (Navigation); and 3) tracking the guidance’s attitude commands while maintaining vehicle’s stability using the actuators (Control). This paper provides a comprehensive overview of the algorithms employed within these modules, their integration into the GNC architecture, and an evaluation of their performance. The results demonstrate that the GNC algorithms meet the requirements, while acknowledging the need for further improvements in the accuracy of the navigation solution. By showcasing the GNC capabilities of the ReFEx project, this research contributes to advancing the field of aerodynamic control for RLV stages

FLUCS - Focused Light-Induced Cytoplasmic Streaming : Optically controlled microflows for biology and the life sciences.

FLUCS is a new photomanipulation technique that allows scientists to optically generate and precisely control microscopic flows within cells, embryos and other viscous fluids. The development of the module is the result of a collaboration between engineers and scientists from Rapp OptoElectronic, the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) in Dresden, Germany, and Olympus Europe. The integration of the Rapp FLUCS module into the Olympus IXplore SpinSR spinning disk confocal microscope system allows to generate microflows in the specimen and to image the resulting dynamic biological processes at high spatial and temporal resolution. The system is now available as a finalized and tested product to a broad scientific community worldwide. https://analyticalscience.wiley.com/do/10.1002/was.0004000255; https://analyticalscience.wiley.com/do/10.1002/was.00070072/full/blaetterkatalog_sim0222.pd

The Reusability Flight Experiment – ReFEx: From Design to Flight – Hardware

The hypersonic flight experiment ReFEx has been under development at the German Aerospace Center (DLR) for a number of years and passed CDR in September of 2021. It will be launched on a VSB-30 sounding rocket in 2023 from Koonibba Test Range (KTR) in Southern Australia. The sounding rocket will inject ReFEx into a trajectory typical of aerodynamically controlled RLV-booster stages, where it will test several key technologies required for future reusable aerodynamically controlled first stages. A key feature of ReFEx is its sole reliance on aerodynamic means for the return leg of the flight, including a heading change of more than 30°, providing valuable flight data at the other end of the spectrum for RLVs (Reusable Launch Vehicle) from current propulsive return concepts [1]. With its length of 2.7 m, a wingspan of 1.1 m, a mass of approx. 400 kg, ReFEx features a densely packed fuselage, containing systems critical for flight as well as sophisticated sensors for flight analysis. With the passage of CDR, the project is progressing into the flight hardware production and verification phase [1]. The paper summarizes the latest status of ReFEx and shows how key challenges such as trajectory optimization, aerodynamic control with control reversals of the aero surfaces, thermal loading, folding wind systems as well as operational issues such as flight safety and campaign planning where tackled to be able to freeze the design and reach CDR status