Breaking the Rocket Equation: How Refuellable Spacecraft Change the Dynamics of Space Transportation

One of the chief tenets of space transportation has been the immutability of the Tsiolkovsky rocket equation, placing great emphasis on the specific impulse of a thruster to determine the propellant mass. For applications where all propellant must be carried from the start, this drives most vehicle designs to the highest possible ISP. The compromise is the typical tradeoff between ISP and thrust magnitude. Thus, transfers which require either impulsive maneuvers or a tight timeline will favor low-ISP platforms. If adequate infrastructure is provided to allow for a refuellable spacecraft, a smaller and lighter vehicle can be used. This vehicle will have a payload mass fraction more in line with an equivalent system with many multiples higher specific impulse. As effective specific impulse increases to values approaching the highest performance electric propulsion systems, the time to destination remains of the same order of magnitude as an impulsive orbital maneuver. Further work must be done to optimize for the positioning and design of fuel depot infrastructure, especially bearing in mind both interactions with high radiation in the Van Allen belts, and ideal orbital planes to seed with these refuel depots

Reuseable Orbital Transfer Vehicles: Why it is the Future for LEO, Cislunar Space and Beyond

The emerging Low-Earth-Orbit commercial economy brings exciting opportunities for technological innovation in space at unprecedented speed. This vibrant new commercial space age is disrupting the status quo, driving down costs, and revolutionizing general accessibility and sustained presence in LEO. Today, however, there is a reluctance in the space industry to embrace reusable spacecraft because of the perception of increased mission risk for no additional return on investment. This hesitation appears similar to the industry’s initial caution in adopting reusable launch vehicles in the early 2000s. In this work we share our vision of the future: reusable orbital service vehicles (OSVs) will transform the space economy and grow the emerging on-orbit servicing sector. A reusable OSV serves as a satellite’s ‘connecting flight’ that provides multiple on-orbit destinations, analogous to the airline industry. Development of a reliable, reusable OSV will expand the utility of a single satellite, allowing for plane changes, escape trajectories, multi-orbit missions and more. OSVs further enable payload upgrades, satellite constellation maintenance, deorbiting at the end of operational life, and orbital debris removal. These added capabilities differentiate reusable OSVs from single orbit mission alternatives and increase the on-orbit economic opportunity. Once a network of OSVs has been established in LEO, rendezvous and transfers can be scheduled efficiently to minimize on-orbit wait times between connections. This poster emphasizes current trends in the industry and presents an OSV architecture and logistics model that enables expanded access to space. Safety and reliability aspects are considered, and a satellite constellation design reference mission discussed. Future work will leverage 6 decades of hard-won lessons and insights from the commercial airline industry with its hub and spoke carrier models to improve OSV reliability and cost effectiveness. Just like reusable launch vehicles drastically reduced launch costs, and well-placed hub airports transformed the costs and safety of commercial air travel, reusable OSVs and orbital infrastructure have the potential to increase space asset safety and return on investment. These vehicles have utility in LEO and cislunar space, as well as far reaching deep space missions to Mars and beyond. Ultimately, more affordable, sustained access to space will enable the next deep space telescope, space station, or other similarly bold and impactful endeavors to be built and deployed in orbit at a fraction of the cost of a terrestrially built equivalent

Glucose Sensing by Time-Resolved Fluorescence of Sol-Gel Immobilized Glucose Oxidase

A monolithic silica gel matrix with entrapped glucose oxidase (GOD) was constructed as a bioactive element in an optical biosensor for glucose determination. Intrinsic fluorescence of free and immobilised GOD was investigated in the visible range in presence of different glucose concentrations by time-resolved spectroscopy with time-correlated single-photon counting detector. A three-exponential model was used for analysing the fluorescence transients. Fractional intensities and mean lifetime were shown to be sensitive to the enzymatic reaction and were used for obtaining calibration curve for glucose concentration determination. The sensing system proposed achieved high resolution (up to 0.17 mM) glucose determination with a detection range from 0.4 mM to 5 mM

Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effect

The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas. Here, we used a unique dataset of 261 stands combining pure and two-species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests. We showed that by adding only one tree species to monocultures, the level (overyielding: +6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between-species asynchrony in mixtures in comparison to monocultures. Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature-based climate solution, which could contribute towards meeting EU climate target policies

Native fluorescence detection of flavin derivatives by microchip capillary electrophoresis with laser-induced fluorescence intensified charge-coupled device detection

To widen the scope of laser-induced fluorescence (LIF) for detection in microchip capillary electrophoresis (CE), a microchip CE LIF-ICCD (intensified charge-coupled device) system based on a tunable wavelength dye laser pumped by a pico-second pulse nitrogen laser for excitation and a spectrograph with ICCD for detection had developed to demonstrate the enhancement in detection sensitivity by the following three approaches: direct detection of native fluorescence, improvement of signal-to-noise ratio by pulse laser excitation and time delay detection, and selective spectral acquisition by multi-channel detection. Riboflavin, flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD) have been selected as they are dietetically important and microchip CE provides a promising onsite detection method. The results indicate a strong effect of wavelength on detection sensitivity and the need to tune wavelength for direct detection. Under optimized conditions (excitation 450nm, emission 520nm, gate delay time 45ns, 20mM phosphate buffer at pH 7.1), the following results were obtained under static condition: Working ranges (0.6-350μg/l, r>0.99), detection limits (0.15-1.0μg/l) and peak height repeatability (1.8-2.2% R.S.D.), all within the applicability range for body fluids or beverages such as human urine and cow milk. Baseline separation of three flavins was obtained under dynamic condition and the fluorescence spectra acquired assist the identification of alkaline-degraded products of riboflavin. Thus, the capability to check peak purity and identify unknown peaks has been demonstrated. © 2003 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex