Rainer Sandau

Trends and Visions for Small Satellite Missions

Small satellite missions can be achieved by using different approaches and methods. One possible approach takes full advantage of ongoing technology development efforts leading to miniaturization of engineering components, development of micro-technologies for sensors and instruments, and others which allow the design of dedicated, well-focused Earth observation missions. Application Specific Integrated Micro-instruments (ASIM) are enabled by Micro-Electro-Mechanical Systems (MEMS) using microelectronics for data processing, signal conditioning, power conditioning, and communications. These micro- and nano-technologies have led to the concepts of nano- and pico-satellites, constructed by stacking wafer-scale ASIMs together with solar cells and antennas on the exterior surface. Space sensor webs are one outcrop of this technology. Further milestones in the cost-effective Earth observation mission developments are the availability and improvement of small launchers, the development of small ground station networks connected with rapid and cost-effective data distribution methods, and cost-effective management and quality assurance procedures. The paper is based on the outcomes of the study “Cost.Effective Earth Observation Missons” by an international team of experts in the framework of the International Academy of Astronautics cite ch03:bib01. It deals with general trends in the field of small satellite missions for Earth observation as well as trends specific for the segments of a misson: space segment, launch segment, ground segment. Visions are given for their further developments in the direction of improvement of cost-effectiveness of Earth observation missions.

Guest Editorial Focused Section on Aerospace Mechatronics

The 11 papers in this Focused Section contain theoretical and practical or experimental results documenting recent advances in aerospace mechatronics and, in particular, new ideas and approaches in the related fields.

Reasons for satellite mission miniaturisation and its consequences

Abstract There are at least two reasons for satellite missions miniaturisation: • - Transition from Earth exploration to Earth watch with concentration on specific phenomena to be observed with optimised sensor systems, • - Development of advanced technologies in many fields of engineering sciences. The miniaturisation is supported by high-end off-the-shelf technologies and instruments for quick and low-cost realisation as well as by the extensive use of advanced technologies leading to increased mission performance but also to higher costs. The paper gives examples for mission design, space segment design, and instrument design, respectively. All the experiences and examples shown in this paper are mainly based on activities of the DLR - Institute of Space Sensor Technology.

An integrated sensor and camera control center for a small planet or comet lander

Abstract In-situ measurements on the surface of planets, comets or asteroids are very interesting from the scientific point of view (see Mars-96 mission or the ESA Rosetta mission). But it is very difficult to realize a reliable lander under hard cost constraints. One problem consists in the control of the operations of a complex of instruments. A conventional way to do this is the connection of different instruments via standard bus. The proposed system design is characterized by the separation of the instrument electronics in sensor specific front-end electronics close to the sensor and a more general electronic part. The strong limited resources of the lander and the limited instruments require a reliable system architecture by a minimum of hardware. For this reason a centralized system architecture is selected with a redundant processor structure. This combines the advantages of a high reliable central processor and the non-sensitivity of the system on interface failures. The paper describes few imaging experiments on a cometary lander as an case study and appropriate architectures for a centralized command and data handling system. One chapter describes the system implementation, especially the use of the advanced microelectronics packaging technologies for a high-density micro-electronics. The electronic circuitries can be arranged together with the necessary instrument interfaces on a single multi-chip module.

Future Trend, Potential, Risks

During the last decades, the concept of distributed space systems has significantly progressed in terms of space applications, including Earth remote sensing. This chapter is devoted to a critical analysis of the achieved improvements and of the areas of major key issues in order to analyze potential and risks of distributed space systems. A discussion of future activities needed to prepare more advanced distributed space missions is also provided. In particular, payloads and applications are first discussed. Then, guidance, navigation, and control as well as other technological challenges, including modularity and architecture, follow.

The Role of Small Satellite Missions in Global Change Studies

There is an increasing need for Earth Observation (EO) missions to meet the information requirements in connection with Global Change Studies. Small and cost-effective missions are powerful tools to flexibly react on information requirements with space borne solutions. Small satellite missions can be conducted relatively quickly and inexpensively and provide increased opportunity for access to space. The spacecraft bus and instruments can be based either on optimised off-the-shelf systems, with little or no requirements for new technology, or on new high-technology systems. Thus a new class of advanced small satellites, including autonomously operating “intelligent” satellites may be created, opening new fields of application for scientific purposes as well as operational, public and commercial services. Further milestones in the small satellite Earth observation mission developments are the availability and improvement of small launchers, the development of small ground station networks connected with rapid and cost-effective data distribution methods, and cost-effective management and quality assurance procedures. Advantages of small satellite missions, complementing the large complex missions are: more frequent mission opportunities and therefore faster return of science and application data; larger variety of missions and therefore also greater diversification of potential users; more rapid expansion of the technical and/or scientific knowledge base; and greater involvement of local and small industry. The paper deals with general trends in the field of small satellite missions for Earth observation. Special attention is given to the potential of spatial, spectral, and temporal resolution of small satellite based systems. Examples show that constellations give the unique for small satellites possibility to provide good daily coverage of the globe or/and allow to observe dynamic phenomena.

New airborne digital camera with multispectral and stereo capability

Joint development work by DLR and LH Systems has produced a new camera concept called Airborne Digital Sensor which is using forward-, nadir- and backward-looking linear arrays on the focal plane. The camera system provides panchromatic and stereo information using three CCD lines and up to five more lines for multispectral imagery including two NIR channels. Each CCD array for panchromatic measurements has 24000 elements, resulting in a field of view of 64 degrees (across track FOV) by using a focal length of 62.5 mm. The sensitivity covers a dynamic range of 12 bit with a recording interval time of 1.2 ms per line. The performance of the camera allows a 3D and multispectral image with a ground sample distance of 25 cm for an area of 300 square miles within a flight time shorter than one hour.

Advanced Detectors and Instruments for Small Satellites

Abstract This paper presents some approaches to the development of advanced detectors and to miniaturized instrument design which are pursued in the Institute of Space Sensor Technology of DLR (the German Aerospace Research Establishment). The instrument design approach is demonstrated for a low-weight (3 kg) dual camera system with narrow-angle in-track stereo and wide-angle multispectral features. Each camera has its own signal processor and 0,5 G Bit mass memory. The activities for advanced detector development are concentrated on two different kinds of detectors and instrumentations: infrared detector arrays and instruments at wavelengths out to about 240 μm, and superheterodyne receivers in the submillimeter and far-infrared spectral ranges.

Aspects of the determination of ocean wave parameters by means of an optoelectronic satellite sensor

Abstract In this paper, the task and mode of operation of an optoelectronic spaceborne sensor system with CCD lines and a digital 2-D Fourier transform device for the determination of such parameters of ocean waves, like wavelength and propagation direction, are outlined. Starting from both required and estimated parameters of the sensor system, the signal-to-noise ratio of spatial frequencies of wave representation is calculated outside the glitter range. Presupposed for the simulation was a sinusoidal wave pattern with different propagation directions in relation to the sensor viewing angle and the sun elevation angle. It turns out that the optimization of the sounding direction plays an important role for the determination of wave parameters at given sun angles. Furthermore, for the interesting range of wave parameters it is sufficient to analyse an area of about 5 × 5 km. Therefore it is possible to work under partial cloudy conditions too. Obtaining good estimates for the height of ocean waves seems to be difficult with that type of sensor. As a result from comparing some types of transforms, their implementation requirements into a real-time on-board processor, and their data compression estimates, the “bottlenecks” of a very sophisticated optoelectronic sensor system are characterized.