Time-resolved Emission Spectroscopy of Impact Plasma

AbstractOne phenomenon observed at hypervelocity impacts (HVI) is the generation of plasma with a very short lifetime of a few microseconds. Due to this short lifetime, characteristic plasma parameters such as the electron density and the electron temperature of the expanding plasma were not investigated thoroughly in the past. This paper will present a method to measure these parameters with a time-resolution of 500 ns for the full period of impact plasma expansion and discuss results gained in impact experiments.At the Fraunhofer EMI, impact experiments on solar panels were performed using a two-stage light-gas gun to accelerate aluminum spheres with a diameter of a few millimeters up to a speed of 8 km/s. A measurement system consisting of a spectrograph and a streak camera was applied for time-resolved spectroscopy of the impact plasma.To derive plasma properties, the recorded streak image was evaluated using different methods for different expansion states of the plasma cloud. The spectra show strong self-absorption lines in the first microseconds of expansion. In the present work, these features are explained by the electron density and temperature gradient in the plasma. For the determination of electron temperature and density, a one-dimensional radiative transfer model was adapted to the measured spectra. After 2 μs of expansion, the plasma is optically thin and emission lines can be observed. For this expansion state, the electron temperature was determined by the ratio of line to continuum radiation, whereas the electron density was determined through the line broadening due to the Stark effect.Using these methods, it was found that the electron temperature decreases in the first 3 μs of propagation from 45,000 K to 2,000 K in the experiments performed. The electron density decreases from 1019 cm-3 to 1017 cm-3

Reliable, Fast, and Flexible: A Thermal Modeling Approach for Small Satellites

The ongoing revolution of space access by means of cost-effective and highly performant small satellites, in particular CubeSats, drives the development of a vast host of new and increasingly complex applications. However, the use of small satellites for ambitious missions brings its own challenges with thermal breakdown as one of the key contributors to component failure. We have therefore developed a lightweight approach specifically tailored to the thermal modeling of small satellites to localize and mitigate the associated thermal risks while maintaining the flexibility and low resource footprint necessary to be applicable in the framework of small satellite mission design. At the core of the methodology, we implemented an experimental database of physical parameters as well as highly parallelized numerical analysis methods. In particular, we introduce an efficient way to determine view factors for insolation and internal radiative energy transport based on a hemicube radiosity algorithm. The results agree within 1 K with commercially available modeling software and allow us to perform highly reliable temperature predictions while conserving the flexible and cost-efficient spirit of small satellite missions

Small and Large Satellites: Joint Operations in Earth Observation

While projects for the exploration of space remain ambitious and financially as well as technologically demanding projects, their benefit in understanding our planet is unrivaled [1]. On top of enabling technologies that keep drastically altering the way we communicate, navigate, or build our cities, they currently present the only means of assessing key environmental variables on a global scale [2]–[5]. Today, we witness the New Space era with promises of ever easier, faster, and cheaper space access as a major driving force for the future development to four space capabilities, specifically in Earth Observation (EO), but also in communication (COM) and navigation (NAV) applications. Since from an economic point of view, only now it became possible to achieve resolution and coverage matching the needs of many applications outside the scientific community by means of small satellite constellations[6]–[9]

Additive Manufactured Structures for the 12U Nanosatellite ERNST

One of the emerging technologies in recent years is additive manufacturing. It promises unprecedented design freedom in both modeling and rapid manufacturing. We are reaping the benefits of additive manufacturing for our 12U nanosatellite ERNST by printing the optical bench that supports the spacecraft payloads. We design the structures by using a finite-element numerical approach for optimizing the topology with respect to 1) available design space, 2) payload interfaces, 3) mechanical launch loads, and 4) thermal loads generated by the cryocooler of the MWIR main payload. We cope with the latter by integrating a pyramidal structured radiator surface in the optical bench as a functional element. Making use of the selective laser melting technique, we manufactured the first version of the optical bench for the engineering model of the ERNST spacecraft from AlSi10Mg alloy. Vibrational testing proved the suitability of our multidisciplinary design approach and the production quality. We are currently implementing the next version of the ERNST optical bench including spacecraft design changes and using Scalmalloy®, a material developed for additive manufacturing that provides high tensile strength and low thermal expansion. This marks a next step on the way to the application of additive manufactured components in space

ERNST: Demonstrating Advanced Infrared Detection from a 12U CubeSat

The ERNST mission will demonstrate complex infrared detection capabilities using a 12U CubeSat platform. ERNST’s main payload is an advanced cryogenically-cooled infrared imager that implicates demanding requirements in terms of power demand, heat dissipation, and vibration response for a nanosatellite. The optical bench that integrates optics, a filter-wheel for switching between spectral bands, and the detector-cooler system has been additively designed and manufactured, giving it a bionic appearance and combined with a highly efficient radiator. An onboard radiation monitor and a COTS camera complete the mission payloads. The ERNST 12U platform is based on high-performance CubeSat subsystems for avionics, UHF, and X-band communication, attitude control, and power management. The commercial components are made compatible through a backplane solution. In-house developments include a fast DPU and an autonomous de-orbit dragsail. The platform provides 30 Watt (OAP) and \u3e6U payload volume. After comprehensive environmental and functional testing of the Engineering Model, the Flight Model is currently being integrated. Starting operations in February 2023, ERNST will verify early warning concepts and technology

In-Situ-Detektion von Partikeleinschlägen auf Satelliten mittels Antennen

Der Hypervelocity-Impakt von Partikeln der Orbitumgebung erzeugt eine transiente Plasmawolke auf Raumfahrtsystemen, die zur In-Situ-Detektion von Impaktereignissen genutzt werden kann. In numerischen Simulationen mit einem eigens entwickelten Modell wurde ein einfaches Detektionskonzept untersucht, das auf der Wechselwirkung des Impaktplasmas mit Antennen beruht. Es konnte gezeigt werden, dass ein Array von wenigen, zentimetergroßen Antennen auf der Außenseite eines Raumfahrzeugs ausreichend ist, um die Bedingungen des Impakts aus den induzierten Spannungssignalen abzuleiten

Using antennae for in-situ measurements of micrometeoroid and space debris impact

The hypervelocity impact of micrometeoroids and space debris produce a transient plasma cloud when colliding with spacecraft surfaces. We studied the feasibility of using the interactions between the fast expanding impact plasma clouds with spacecraft antennae for in-situ impact detection. We used a numerical model for computing the formation and evolution of the plasma cloud as well as the signals generated at the antenna sensors. The generation of secondary electrons at the antennae due to fast ions in the plasma cloud proofed to be an effective mechanism to correlate sensor signals to impactor characteristics. We demonstrated that a simple array of seven centimeter-sized antennae is sufficient to trace back impactor size and impact velocity

Integrating a large nanosatellite from CubeSat components - challenges and solutions

Since the first release of the CubeSat standard a diverse market for CubeSat components has developed. Recent years have also seen a trend towards larger CubeSats. Consequently, all components necessary for systems in the range of small microsatellites are now available on the CubeSat market. This also includes more advanced subsystems like ADCS with three-axis stabilization and high data rate transmitters. When combining systems from different manufacturers, several compatibility issues arise. While all subsystems share the PC/104 format, missing standardization of pin assignment as well as low flexibility of the components make integration harder than necessary. Fraunhofer EMI currently designs and builds the 12U nanosatellite ERNST (Experimental Spacecraft based on Nanosatellite Technology). The satellite contains an advanced mid-wavelength-infrared imaging payload. Most requirements of this payload exceed the capabilities of 1-3U CubeSats. Instead of realizing the mission with a commercially available microsatellite bus, we pursue the concept of building a 12U nanosatellite from components designed for smaller CubeSats. For ERNST, the subsystem compatibility issues are solved using a PC/104 backplane. The components are grouped into multiple stacks that are connected through this backplane, which then translates between the different pin assignments