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Tag Cloud. Since Nov. This again will follow the same principles and development rules of Nanosat, together with the acquired know-how and lessons learned up to now. The target for the MicroSat development planning since the programme presentation in Oct. The wheels and coil torquers will be the nominal actuators.

We will like also to thank INTA top level management, for their big support and encouraging recommendations along the past years. Reference 1. Angulo, MR. Canchal, JM. Mi, P. Baker, Philip Davies, and Lee Boland Abstract This paper outlines the heritage and future plans of SSTL in enabling high performance cost effective Earth observation services through constellations of small spacecraft. The paper will discuss two new spacecraft for customers in Spain and Nigeria, and how these meet traditional needs for Earth Observation data at a low cost.

The range of payload options which SSTL can offer for a wide variety of Earth imaging applications covering high and medium resolution, wide area coverage, frequent revisits and near real-time tasking and data return in various wavebands, including visible light and microwave will be discussed.

Baker et al. The Beijing-1 microsatellite was added to the constellation after launch in October Satellites can cover hundreds to hundreds of thousands of square kilometres, depending on the resolution, against hundreds of square kilometres for aerial platforms.

In contrast, a typical small spacecraft such as NigeriaSat-2 can be built for an order of magnitude less, will offer a GSD as low as 2 m, and can offer daily repeat with as few as 2 spacecraft, both of which can be positioned using a single low cost launcher.

The plots above demonstrate the increasing capability of cameras and sensor arrays available for small satellite platforms, enabling attractive combinations of wide field of regard, rapid repeat and high resolution to be affordable. RapidEye aims to deliver Earth agricultural and insurance industry specific information products derived from multispectral wide area Earth Observation data.

RapidEye will serve 3 markets: 1. Agricultural Insurance: supporting the loss adjustment process by provision of regularly updated field maps.

Agricultural Producers: assisting precision farming by regularly providing information about crop conditions and yield predictions. International Institutions: assessing expected crop harvests and monitor usage of subsidies for disaster relief. Spain DMC is funded through anticipated data sales to a small set of countries, and will reach new levels of image throughput performance for the next generation DMC constellation.

To this end, subsystem design changes include i. Replacement of NiCd battery with higher capacity, greater Depth of Discharge, higher energy density and longer life Li-Ion battery.

Improving the imager resolution has been increased from 32 m to 22 m at nadir without reducing swath, by utilising a custom lens and the latest CCD linear array, while maintaining overall mass, envelope and power consumption.

Digitisation fidelity has also been improved from 8 to 10 bit. The operations strategy targets maximum imaging time in the sunlit part of the orbit. Operating modes with imaging and downlinking data during each orbit, and imaging orbits followed by downlinking orbits have been developed. A key customer requirement is to deliver complete coverage of Spain and Portugal within 5 days using a combination of operating modes.

This requires a significant increase in the number of scenes per day delivered to the customer, compared to the original Moving Towards Commercial Earth Observation Services 61 DMC spacecraft.

A balance is struck between covering the maximum area per orbit, which requires a subsequent orbit or orbits to downlink all the data, and reducing the area covered but allowing all operations to be conducted within an orbit. A future goal for SSTL missions is to allow stripmap imaging, where the imager can be run continuously in parallel to downlinking for the sunlit part of the orbit.

This would deliver up to 12M km2 of imagery per orbit, assuming the ground segment could handle this data throughput! NigeriaSat-2, weighing about kg at launch, will feature a high-capacity solid-state onboard recorder with a gigabyte memory and an X-band downlink capacity exceeding megabits per second.

In excess of accurately geolocated images with a 2. NigeriaSat-2, shown above will be built in 30 months and is scheduled for launch in mid along with a co-passenger NigeriaSat-X which will be an advanced training model for the Nigerian engineers who began their training with the NigeriaSat-1 DMC spacecraft launched in Moving Towards Commercial Earth Observation Services 63 4 Payloads for Small Satellites SSTL has carefully studied the Earth Observation market, and has made efforts to ensure that its platforms are applicable to a range of payloads operating in various wavebands outside the visible spectrum, and carrying out activities in addition to electro-optical imaging.

Missions studies have ranged from altimetry, geolocating electronic intelligence signals, spectrometry of a wide range of atmospheric species and greenhouse gases, and both active and passive microwave imaging. Mindful of the breadth of the market for Earth Observation and small satellites, SSTL spacecraft continue to be designed in an adaptable modular fashion which can support multiple payload options.

Two popular options are detailed below: SSTL developed the wide area medium resolution SLIM-6 camera, shown below, and in acquired the optical instrument capability of the UK firms Sira electrooptics, which developed the Beijing-1 microsatellite high resolution imager, also shown below: Fig.

Primary on Medium Res. Sub-1 m GSD performance using a microsatellite platform is being examined by SSTL in collaboration with a leading UK payload provider, allowing additional production capacity to meet the requirements of future constellations. Monitoring the rate of calving of the Greenland ice sheet, which would raise global sea level temperatures by 7 m, were it to melt entirely. CHRIS is currently the highest resolution capability spectrometer in orbit, and with a mass of only 14 kg and a power draw of 8 W is a highly attractive payload for a small spacecraft.

Example applications include mapping aerosol concentrations, water and land surface use, and chlorophyll concentrations. Leaf angle is indicator of crop ripeness 6 Supporting Mission Elements SSTL also offers a number of supporting capabilities to give a spacecraft mission appropriate utility: r r r r Ground stations, fixed or mobile. Launch contracts, operations and operational support contracts, as well as image data processing, sales and marketing.

Sale of a complete range of ITAR free spacecraft subsystems. Know-How transfer and Training, in the form of i Improving customer ability to specify and procure low cost space systems, ii Training technical organisations in the SSTL approach to space systems development and iii Training spacecraft operators.

These are now a mature technology and have demonstrated their potential as a product with complementary performances to more conventional mission solutions. With continued advances in technology, new areas in Earth observation are being explored and applications like high resolution-, hyper spectral- and small SAR radar missions become feasible with a PROBA scale platform and its derivatives.

As small satellite missions become more ambitious, so the space industry is adapting to the challenge of creating organisations which can deliver the advantages of small satellite technology while retaining compatibility with international data standards and operating practices. This paper will outline high-performance solutions for future Earth observation missions, highlighting the role that cutting-edge technologies have to delivering unique capability to meet customer needs.

Bermyn, C. Dorn 1 Small Missions Heritage 1. HRC instrument — 4 m pan images and has agility to execute demanding mapping and push-broom scanning scenarios e. CHRIS instrument — 18 m multispectral images. Although designed for a lifetime of only 2 years, PROBA 1 is now functioning in-orbit for more than 5 years and providing earth observation images through ESA to the science community on a daily basis. In the meantime, its successor PROBA 2 carrying sun observation instruments is under final integration at Verhaert Space and is planned for launch early Dorn 1.

It has since been producing high quality imagery to satisfy a range of user requests. The purpose of the programme is primarily to demonstrate the ability to build and operate a low cost optical satellite capable of generating high quality imagery. A flexible response to the customers needs is the hallmark of the QinetiQ-Verhaert approach.

Simplified programmatic structures, integrated teams, on-board automation and new technologies all have their part to play in reducing costs. The mission must be 72 J. Dorn viewed as a complete system and the component segments design to minimise through life costs by matching risk with customer expectation and technical solutions. To date, the application field stays limited to imagery with up to a few meters of ground resolution and a few spectral bands in the visible and near-infrared spectrum.

Clearly, this is driven by the resources and performances available on small platforms but thanks to the evolving technologies on payloads and platform side a lot of other applications come within our reach. Small missions will never be suited, and are not intended, to replace the full capability of large systems, but they will be a very interesting complement to it. Over the years, several concepts and ideas wore worked out to show the potential of our PROBA platform for emerging applications.

Indeed, we can talk about the Proba Spacecraft Family of which some key potential is highlighted hereafter. Several studies were carried out to demonstrate the feasibility of following missions based on a PROBA platform: 2. These offer the possibility of even smaller and more electrically efficient sub-systems. Multi — and hyper spectral instruments work typical at lower resolutions but generate huge amounts of data.

Here solutions can be worked out in several areas, starting with data capturing optimisation to reduce the capture of un-usable data , data compression and storage and high power downlink capacity. Studies are ongoing to fly optimised systems with shorter lifetime less redundancy on a small platform, and investigation continues in to low altitude missions. Before entering in a very ambitious science mission, critical technologies can be developed and demonstrated in orbit in a fast and cost-effective way.

In addition to the existing LEO applications of small spacecraft, new missions are being developed to utilise small satellites in other Earth orbits. These can be coupled with a range of propulsion systems for new mission solutions. Dorn 2. As small missions prime, we enter the so-called Mid-Tier segment, where challenging missions based on small satellite platforms will be developed. Small missions require smart and innovative solutions but at the same time they have to stay affordable and require realisation within reasonable timescales.

The QinetiQ-Verhaert teaming allows such mission to be undertaken in an appropriate and efficient way, with the right priority small mission are a key account for us. Furthermore, we combine the flexibility and cost efficient approach of smaller organisations with the quality standards, facilities and credibility of larger organisations. During the summer , 33 students from the International Space University ISU worked on a project aiming at making EO accessible to small countries and regions.

Although EO programs are costly to initiate, they are often feasible and beneficial for small countries and regions. However an information gap exists between EO providers and decision makers. As small satellites are amongst the cheapest systems to develop and launch, this will often be the preferred option of small countries and regions, and the selection tool is thus likely to bring benefits to the small satellite industry. The region of Catalonia, one of the three test cases studied in the project, is used as example to illustrate this statement.

Examples of such decision makers include resource managers, urban and regional planners; agricultural producers and disaster first responders. Examples of EO applications include facilitating public services and natural resource management. Earth Observation data can be especially useful for small countries and regions in assisting their future development.

However a gap often exists between the capabilities of EO systems to serve applications and the knowledge base of decision makers about EO capabilities, especially at the level of small countries and regions. EO programs are often technologically complex and costly to initiate and are therefore difficult to develop with the limited budget of a small country or region. However, in some cases, small countries and regions that A. Schoenmaker carefully investigate and develop EO programs can establish their own EO programs despite the cost and complexity issues.

Alternatively, cooperation between regions or small countries can allow regions to overcome resource constraints and lack of expertise to harness the potential of these powerful technologies. Small countries and regions establishing EO capacity, whether they are cooperating or not, must determine the most cost-effective way of implementing this capacity.

Several options exist for these actors to take full advantage of EO technology to answer their needs. Amongst them, buying existing data, obtaining data free of charge or commercially, or developing their own system, are the most realistic ones. Developing a space-based system for a small country or region with a limited budget almost automatically implies small satellites.

The prototype was developed using three test cases that have shown an interest in developing an EO program: Catalonia, Spain; Alsace, France; and the Island of Mauritius. Earth observations are a technologically complex and costly set of tools that can be instituted effectively for small countries and regions, if developed appropriately. Five major, non-exclusive options for developing EO capacity were identified: 1. Obtain EO data from existing aerial and satellite EO data providers; Establish aerial EO programs; Develop locally owned and operated satellite EO systems small satellites ; Create a data processing centre that converts data to information for decision makers; or 5.

Any or all of the above in cooperation with another small country or region. EO developers must assess the applications, needs, technical capabilities, and policy and legal implications of using the technology. Developing an Earth Observation project is a truly interdisciplinary work, and this is how this project was put together. The following figures show how the same EO process can be seen from different perspectives: technical and financial.

Indeed, the technical process is a very important aspect of an EO system, but a country or region envisaging building its own EO system should not overlook Small Satellites and Earth Observation Systems for Small Countries and Regions 79 Fig. An understanding of the financial considerations for EO programs is one of the most essential points.

A proposed value chain for EO systems, from the EO provider and to the end users who exploit the information is shown in Fig. The principal concepts applied to the value chain are the EO ventures analyzed, cost estimating methods and financing options.

When a small country or region develops EO programs, the national and international policies and legal framework for space should also be considered, in concert with the technological development path and program financing. Given this technological, financial and legal context for EO program development, small countries and regions are often best served by employing a cooperative model, e.

Using a cooperative model, small countries and regions can overcome obstacles and develop EO programs that meet the specific needs of the region. The SOL project encompasses all these different aspects of EO to find out the best options for small countries or regions, whose decision makers are the targets of this study.

Apart from providing an interdisciplinary background in Earth Observations the project also includes three test cases and the idea of a tool, which will be discussed next.

The local economy of Catalonia is highly 80 A. Schoenmaker dependent on tourism and industry. Agriculture, including viticulture and cereals, is also an important factor for the economy. Currently, private industry and academic research centers comprise the extent of EO capabilities in Catalonia; however, interest in expanding EO capability locally has grown recently.

This project has identified an opportunity for Catalonia to consider developing a regional EO system to stimulate local industry and to improve the use of EO for current and future applications. EO can be useful in Catalonia for viticulture, mapping, environmental monitoring, disaster management, and humanitarian aid. Catalonia is currently using EO data for some applications, but the region could further capitalize on EO technology and build capacity in EO system development.

Given the current capacity and the potential budget for EO systems, a small dedicated satellite is one viable option for Catalonia. Such a system could satisfy some of the technical EO needs e.

Different sectors where EO could be useful for Catalonia have been analyzed, starting with vineyards. The analysis of the density and vigor of the vine canopy is an essential tool to assess the yield and quality of the wine. To achieve such target, a minimum spatial resolution of at least 1. This requirement is driven by the conventional vineyard row spacing. Unfortunately this resolution does not provide sufficient resolution for the development of precise viticulture.

Therefore, another proposed option which should supplement the space-based solutions is based on airborne systems in combination with on-site ground observations. This sensor is an optical multispectral sensor, offering a typical spatial resolution below 1 m, depending on the flight altitude. Concerning environmental applications, there is a wide range of EO applications that could be tackled by means of different solutions space-, airborne- or groundbased , and within the set budget constraints.

Considering the general approach of this particular example, the possible solutions are very broad. One of the alternatives would be to buy data from the huge number of currently orbiting satellites and sensing systems scattered around the world. Another possibility would be to make use of airborne systems in combination with on-site ground observations.

A feasible space-based solution could be based on the use of a micro-satellite, with medium-to-high resolution sensors. An example of implementation would be the use of a suitable platform to be integrated in the DMC-2 constellation, with a CHRIS sensor achieving spatial resolutions of about 17 m.

With this proposed system operating in LEO orbits, a vast range of applications could be developed, as is the case of mapping and monitoring to assess the change of the territory over time, precision agriculture, urban planning in coastal areas to avoid denaturalization Small Satellites and Earth Observation Systems for Small Countries and Regions 81 of the seashore, forestry, water shed control, wetlands monitoring in the Ebro river delta, coastal erosion control, snow measurement in the Pyrenees, etc.

This new development is very encouraging for the small satellite industry in Spain, and is related to the third important application in Catalonia: Disaster management. In this case, the SOL report advised that the revisit time of the EO systems should be relatively short.

Revisiting times below one or two days would be desired for a proper management of river flooding, as well as for the identification of the current state of infrastructures under the effects of any natural disaster of short life time.

That is why any new satellite should be integrated into an already flying constellation, such as DMC. The same kind of micro-satellite could be used by Catalonia for mapping purposes.

After this analysis it is thus striking to see all the possible applications of the capabilities of a micro-satellite in this region, whilst staying in a limited budget. These proposed systems would however be best developed in cooperation with other regions or countries in order to facilitate technology transfer, to encourage political ties between regions, to improve EO system capabilities e. This is an aspect that is now being addressed by Deimos Imaging by entering into the DMC constellation.

Schoenmaker EO capacity building in Catalonia could result in valuable economic and social spin-offs for the region. High-tech EO systems can be beneficial for the local economy by stimulating economic growth, industry, commercial development, and fostering new ventures in EO. This would occur if Catalonia began developing its own satellites or if the region established other EO competencies. A data processing center, for example, could serve regional data processing needs, stimulate revenues for the region, and provide a mechanism for Catalonia to assist other regions in harnessing the potential benefits from EO.

A center of this type could be based on a public-private partnership PPP model. EO capacity building in Catalonia could also encourage scientific and technology competitiveness and promote scientific education. GEOSS is a project that attempts to centralize the existing EO databases in order to facilitate gap analysis in available data and enhance dissemination and sharing of existing EO data. However the scope of GEOSS is limited to sharing observational data and connecting information from separate sources.

The usefulness of the GEOSS centralized database will be limited to experienced users that have already identified the datasets that they need. Accessing GEOSS requires technical expertise in EO technology; potential users need a simple tool to help them target needed data and assess the cost. As a result, the need to map and centralize existing technologies, research centers, and added-value actors remains despite the more recent efforts. A tool such as SOLST could assist users to target the appropriate options of datasets for a particular application or interest.

This issue is pressing for small regions and countries with limited resources. The restricted financial capacity places emphasis on a tool that can facilitate a search for existing and future EO tools, giving preferential consideration to cooperation models with other participants in EO. The system architecture of the proposed tool is composed of databases, an electronic interface, and linkages between the databases and interface.

The databases consist of specific information about EO applications, data types and availability, and estimated system and data costs. These databases link together in such a way that multiple outputs can be selected, depending on the level of detail sought by the tool user.

The tool selects EO options with a set of criteria like budget, technical requirements, applications, and cooperation opportunities. The criteria are not ranked by order of importance. Small Satellites and Earth Observation Systems for Small Countries and Regions 83 The intentions of the user are divided into three main options: building a system; searching for datasets; searching for added-value services e.

A combination of these three options could be selected. A cooperation entry can lead to both an output tutorial on cooperative models and an access to posted inquiries. The four entries can be independently left blank if unknown by the user. If all are left blank, the user will be directed to a high level introduction to EO applications and its potential. A search and selection tool can help accomplish this. The beneficiaries of SOLST could include decision makers at different levels, technical EO users, and small countries and regions that are open to collaboration.

The primary objectives of SOLST are: r r r r r r To increase the awareness of the potential of EO through a high level introduction and application-based description; To bridge the gap between the potential users of EO systems; To provide an initial set of available EO options based on user selection criteria, and to give a preliminary overview of options prior to making a local or global decision; To guide small countries or regions through the decision-making process by facilitating the identification and definition of an EO system that meets their needs; To enhance collaboration options particularly for small countries or regions through the use of a Forum and a posted inquiries compartment; and To provide technical EO users an accessible database of EO systems.

SOLST incorporates three primary functions. Apart from the search selection tool, an information request option and a forum section should also be included, to answer the needs of the users that are not met in the tool itself. For example it will allow them to ask for a summary describing the legal aspects of remote sensing, or to interact with other users of the tool to enhance communication and help cooperation.

Schoenmaker Several implementation and maintenance options for the tool have been proposed and a prototype database has been constructed. However, this needs further and long-term development and testing to evolve in an operational tool. First, it would increase the awareness of decision makers about the capabilities of small satellite technology and therefore increase the demand.

For a region like Catalonia, which already has an interest in Earth Observation technology, the tool mainly confirms the option that a small satellite would best suit their needs.

It adds however that cooperation would be the best way to go about it, and gives an approximation of the total cost that would have to be invested in such a system.

This rapidly accessible information might quicken the process for local decision-makers. The EO documents available in the tool also give them information about already existing small satellite programs.

In this case the tool gives an easy access to information about the sought after technology. In other cases, the tool and the available EO introductory documents might be the first exposure a user has to EO and small satellite technology.

The tool would then fulfill its mission of increasing awareness amongst worldwide decision makers about EO, and in this case small satellites. Increasing awareness and giving easy access to information will surely help increase the demand for small satellites but also improve the technology, as a variety of payloads might be carried on small satellites. As mentioned earlier, cooperation is often the most reliable and realistic way for small countries and regions to gain access to EO data, and this seems to be favorable to small satellites as well.

Surrey Satellite Technology Limited SSTL is a good example of a cooperative venture that led to the development, building and launching of several identical small satellites. Second the tool will help in addressing the limitations of small satellites by emphasizing possible trade-offs. For small countries or regions, budget, technical capability and human resources are critical factors.

As mentioned before, a small satellite will not usually be feasible for them; cooperation with other entities will allow them to spread the costs and the risks and to take advantage of a range of sensors or resolutions even if they develop only one themselves. Third, some specific programs involving small satellite technology such as KnowHow Transfer programs and Rent-a-Sat options seem to prove to be very well adapted to the needs of small countries and regions, as they are solutions both to lack of capacity and lack of funds, two of the main issues for small countries and regions.

The utility of EO for such countries and regions, however, rests on the ability of an organizing body for the EO program to identify and select the most suitable option s for EO in the region. This selection must fall within the technical and budgetary constraints, which are case specific. Combining cooperation and small satellites is here often a winning solution.

To assist in identifying and selecting the best option for the small countries and regions, this project has identified one method and illustrated that method using the SOLST prototype. In the long term, it is proposed that this method and prototype be developed in conjunction with other initiatives that are attempting to facilitate this type of EO program decision.

Its optical aperture diameter is mm, the effective focal length is mm, and its full field-of-view is 5. To demonstrate its performance and versatility, hyper-spectral imaging using a linear spectral filter was chosen as the application of the prototype.

The spectral resolution will be less than 10 nm and the number of channels will be more than 40 in visible and near-infrared region. In this paper, the progress made so far on the prototype development and the future plan will be presented.

Recently, the technology development efforts within SI have been focused on advanced optical and opto-mechanical systems to meet the increasing demand from Y. Choi et al. Funded by the Ministry of Commerce, Industry, and Energy of Korea in , SI has initiated the development of the prototype model of an advanced high-performance optical system, the TIS system as part of the national space research and development program.

The TIS system is designed to be versatile with a wide field-of-view, no obscuration, and no refractive element. Therefore, it can be used for various missions such as super-swath imaging, hyper-spectral imaging, infrared imaging, and aerial imaging.

In addition, its compactness and light weight are ideal for small satellites. The development of two prototype models is planned together with a field test for each model.

The progress made so far on the 1st prototype development will be presented: optical design, analysis, and manufacturing; opto-mechanical design, analysis, and manufacturing; and demonstration of hyper-spectral imaging.

The optical design was simplified to use an on-axis spherical secondary mirror. The primary and tertiary mirrors are off-axis segmented aspheric mirrors. Its optical aperture is mm, its effective focal length is mm, and its full field-of-view is 5.

The key features of the TIS system are listed in Table 1. The spectral band range is from to nm and the spectral resolution is less than 10 nm for HS channels. The number of HS channels is more than The reference planes for the optical surfaces are implemented with invar inserts through the honeycomb panels.

The spectrometer of the TIS system is implemented with a linear variable filter LVF on a two-dimensional detector array instead of conventional dispersive elements such as prism and grating.

Using aspheric surfaces for an optical system usually gives high performance but, it will increase the manufacturing cost and needs a complex alignment process. To minimize the manufacturing cost and to make the alignment process simpler, the secondary mirror of the TIS system is an on-axis spherical mirror and the tertiary mirror has a small deviation from a spherical surface.

The design MTF at shorter wavelength is higher than that of nm. The tolerance analysis includes manufacturing, assembly, and alignment errors. The parameters used for the analysis includes the surface quality of mirrors. The analysis shows a wavefront error of 0.

The secondary mirror M2 was aligned in two steps: coarse alignment and precision alignment. The coarse alignment of M2 was performed with respect to M1 using CMMs coordinate measurement machines and alignment telescopes. CMMs were used to correct the M2 de-center and de-space and alignment telescopes to correct the M2 tilt.

It is believed that this was caused by the fact that the Zernike calculation perpendicular to the exit pupil was not correct because the image plane is slanted against the optical axis. For the precision alignment of M2, the sensitivity of M2 movement was measured. The optimum position and tilt was estimated based on the measured sensitivity. The first excitation was measured at Hz from the interface flexure of the main structure.

Others were measured at frequencies higher than Hz from translational and local motions of the structure and at frequencies higher than Hz for the motion of mirror assemblies. Figure 15 shows the mages acquired in the channel 22 nm , 30 nm , 47 nm , and 62 nm. The development of the 1st prototype model will be completed by the end of August, with the hyper-spectral imaging demonstration through a field test.

In parallel, the development of 2nd prototype model has been initiated. The 2nd model will have a bigger optical aperture of mm and thus, the complete system will become larger and will give higher performance compared with the 1st model. The 2nd model will give 5 m GSD for one panchromatic and 10 m GSD for four multi-spectral bands at the design orbit of km. The imaging swath width will be larger than 60 km at the design orbit. Recent studies on OMAD and TOMS data found quantitative agreement in the radiances and indicated the detection of the volcanic eruption plume of Nyamuragira volcano due to its sulphur dioxide content [2].

A new analysis of OMAD data using an improved version of the simplified algorithm to find ozone content has been developed and tested. Multiple days were analysed using composites of up to 15 days and ozone contents ranging from DU to DU. The potential of small satellites for atmospheric missions is discussed, including factors to consider when planning such missions. Mackin Surrey Satellite Technology Ltd.

Fernandez-Saldivar et al. Each channel uses a single fused silica anti-reflection coated lens with a focal length of The signals are sampled continuously tobit resolution, and the entire instrument draws only mW when in operation [1]. Once the factors are derived these are applied to all cloud conditions where we are aware of the errors in determining the ozone content below clouds due to their properties: height and thickness.

The expected errors after the retrieval should be within this error range. Reflectivity is then derived through vicarious calibration between reflectivity data from the TOMS nm channel and the OMAD nm channel, based on radiometric calibration from [5] once the data has been referenced to a common grid 0.

This is shown in Fig. Furthermore, the pixel sizes and time of overpass are different accounting for dissimilar cloud fractions covering the scene.

Finally aerosols would introduce another variation however those are ignored here. Reflectivity is not directly taken into account in the retrieval procedure but it allows a selection of low cloud cover from where the empirical factors are derived thus the discrepancies just described do not affect the algorithm directly.

Firstly, we obtain a slant column amount based on a J. Secondly the geometrical observing conditions are taken into account with the solar zenith angle, this is known as geometrical air mass factor and is then subtracted in its logarithmic form from the slant column. Finally the empirical factors convert this un-calibrated vertical column into a real vertical column content. The algorithm works as follows: The un-calibrated slant column amount is derived from the initial simplified algorithm based on the estimated radiance from two channels L and L Even though it seems a rather arbitrary designation, the purpose is to have multiple reduced datasets with similar ozone profile and content for each zone.

This consideration also excludes the latitudes closer to the poles since these areas have the most extreme conditions on solar angle, radiance values and ozone Comparison of Atmospheric Ozone Measurements content; polar regions would need a different analysis. The evaluated regions are illustrated in Fig. However, it is desired to have single linear parameters M and B that would apply to all days, these will be the final empirical parameters described in 4.

The temporal and regional dimensions were analysed considering the variations of these parameters represented in the contour maps shown in Fig. This is partly due to the fitting method resulting in certain coupling between M and B; nonetheless this is useful for deriving the other by having defined one of them once proper relationship between them is identified. In order to help the definition of regional parameters, the corresponding 1-sigma uncertainty estimates of each parameter the fit are included so that the best daily fits are weighted accordingly before obtaining their regional representatives for all those days.

A trend is observed throughout the days indicating the validity of the empirical parameters to represent each zone condition. The M-parameter trend is non-symmetrical with respect to the equator neither to the solar angle indicating the different ozone profiles for each region. The sigma-M also shows a trend that is somehow symmetrical with respect to the equatorial zones except in the southernmost regions where an ozone hole condition normally develops around this time of year.

Comparison of Atmospheric Ozone Measurements The uncertainties of the fit are explained by the different conditions over the regions where the overpass occurred on a specific day.

In order to get day-independent representative regional parameters, an average of the M-parameter is obtained with 10 out of 15 days when the uncertainty estimates are lowest; a representative value is then obtained and the B-parameter is derived from there through the coupling between them. Figure 7 below shows a linear relationship between these two parameters for all zones. The same analysis is carried out for all zones with consistent results.

The parameters used are the same as before but the number of data points included varies. Table 1 shows the results of the four different reflectance limits considered and the empirical factors used.

Errors are lowest near equatorial regions where the smallest solar angle occurs; as we get closer to the poles the GAMF increases and the errors increase accordingly. The errors between OMAD and TOMS are explained by changes in real cloud fraction due to difference timing of overpasses and also the determination of ground reflectance for different viewing conditions.

Comparison of Atmospheric Ozone Measurements The days and zones analysed here, even though they represent a relatively narrow window to observe the complex ozone dynamics, nevertheless provide an insight into the processing required to obtain valuable scientific data at low-cost and without the heavy computational burden required by recursive radiative transfer methods.

Because of the temporal variations of ozone, further analyses are required for other months and also polar regions need to be included in order to observe phenomena such as the known ozone hole development. This region is likely to need special treatment due to the extremely low solar elevation angles encountered. Underwood, C. Newchurch, M. Journal of Geophysical Research, Herman, J.

Fernandez-Saldivar, J. Low-cost microsatellite UV instrument suite for monitoring ozone and volcanic sulphur dioxide. MIBS is a spectrometer operating in the thermal infrared wavelength region, designed in the frame of the phase A study for the ESA EarthCARE mission, which uses an uncooled 2D microbolometer array detector instead of the more common MCT detectors, which allows for a significant reduction in size, and power consumption.

Although the detectivity of microbolometers is less then for MCT detectors, they offer specific advantages due to the wider wavelength response, which can be tailored to suit the application. This allows the design of an instrument that can image both the 3. In order to demonstrate feasibility of the concept a breadboard has been designed and built of which the first measurement results are presented here. Leijtens et al. The radiation is then dispersed by the prism and imaged on the detector via Germanium lenses L1 and L2.

For this purpose the mirror of the MIBS breadboard can be rotated by means of a small stepper motor. Given the close proximity of the parts CFM1, SFM1, slit and SFM2 and the desire to assemble the entire system on basis of manufacturing tolerances as much as possible a single mechanical assembly is created out of these parts. This so called slit assembly Fig.

The alignment of the optical parts is facilitated through the availability of wedged shims that allow to adjust the tilts of the components in an easy way and a number of dedicated alignment openings are provided in the housing in order to be able to measure the position of the optical components. Since the entire system up to the prism is reflective with a transmissive slit all of the measurements can be done using standard theodolites.

During the assembly and alignment of the system it was proven that the alignment filosophy worked well in the sense that although additional shimming possibilities where provided, they where not needed during the alignment and all parts are mounted using manufacturing tolerances and dedicated alignment shims only. The camera assembly consists of the mount for the prism and the camera lenses. It is a selfstanding assembly which is made of titanium in stead of the aluminium which is the base material for the rest of the instrument.

Untill now no further measurements have been made on this assembly with exception of the mounting position of the prism. The camera assembly has dedicated heaters and temperature sensors in order to enable accurate temperature stabilization. This stabilization is required in case absolute temperature measurements are to be made with the instrument. The need to stabilize the temperature is related to the absorbtion in the Germanium. Since the absorbtion in the Germanium is less for lower temperatures, and the change in absolute radiation in less for lower temperatures, there is a preference to operate the optical bench at as low as possible temperatures in order to have an as high as possible absolute radiometric accuracy.

Since the setup has only been used to do NETD measurements, the thermal control hardware has been mounted but has not yet been operated. The rotation of the prism in its holder is slightly above spec 1, 3 mrad instead of 1 mrad which will potentially influence the co-registration for the end of swath.

In case full performance is required in a later stage, this mis-alignment can be solved through a more elaborate alignment procedure, but for the moment it is deemed more important to know what the deviation from nominal is, then to be within the nominal tolerances as there are no real fixed requirements for the breadboard and recalculation with the actual values will allow the correlation of real life measurements with theoretical predictions.

As for the other optical tolerances everything else with exception of the nadir pointing repeatability has been proven to be well within spec. The repeatability of the steppermotor used to rotate the calibration mirror however has been proven to be within 0. The lower than required repeatability should be weighed against the need to design a new calibration unit anyway in case the instrument is to be operated in vacuum. As all blackbodies used are oversized, the reduced repeatability is not seen as a serious constraint for this stage of the project.

The final alignment of the detector behind the camera has not yet been performed because it was felt that a slight defocus would not have dramatic effects on the NETD to be measured. Therefore, in order to find the largest noise contributors and possible large deviations, we decided to do a set of preliminary NETD measurements.

The first images produced gave us the confirmation that the optical curvature correction seems to be working, Fig. The gain and offset uses a cold flat plate blackbody at room temperature and another hot plate blackbody at approximately 60 degrees.

Some bright pixels can be discerned as well as some dark pixels showing less then average signal levels but no signal is visible in the raw image.

Nevertheless the slit image at the detector can be clearly seen as well as the image of the two starting and endingpoints of the slit. The bright spots left and right in the image are caused by drilled holes at the beginning and end of the slit used for the spark erosion manufacturing process. In order to do some NETD measurements, one column was selected for further analysis. Mean difference of “hot” and “cold” frames at column 25 20 15 intensity [—] 10 5 0 —5 —10 —15 —20 —25 0 50 row position [pixel] Fig.

This is in line with expectations and can be explained when looking at the response of the microbolometer detector. The leading edge is determined by the long wavelength response which gradually improves with decreasing Germanium absorbtion. Longer wavelengths are to the left Shorter wavelengths will be transmitted by the high pass filter deposited on the detector window, and a combination of filter damping and decreased bolometer response cause the response to decrease fast with wavelength.

This prompted some investigations aimed at providing additional insight into the cause of the lower then expected NETD.

During these investigations a number of contributors have been identified. Although the investigations have not been exhaustive a good feeling has been developed regarding the optical throughput of the system. First of all the reflection of a spare mirror that was coated at the same time as the mirrors used in the breadboard was measured. The results of these measurements showed the reflection to be less than presumed during the NETD calculations. In first instance this may not seem to dramatic, but considering that the beam passes 7 surfaces, the total system transmission is 0.

Furthermore during the initial measurements it was found that the intensity variations of the entire image are quite significant. When tracking the average intensity of the image over time, it can be seen Fig. As compared to the signal found in Fig.

Mean intensity evolution mean intensity of frame [—] 0 20 40 60 80 frame [—] Fig. The large fluctuations however were not directly expected but may be related to some limit cycling in the thermal control hardware. For normal imaging applications this will not be a real problem, but this becomes a significant effect for the spectrometer application where the input signal is reduced Serious Microsats Need Serious Instruments, MIBS and the First Results due to the fact that the available signal is dispersed over a number of pixels.

It is not expected that this effect can be easily remedied for the breadboard, as it would involve interference with the thermal control hardware of the camera used. Deviation of first frame from average of consecutive frames row position [pixel] 50 50 column position [pixel] Fig.

This leads to a considerably improved image quality Fig. The performed exercises show that the measured NETD is above the expected NETD, but a number of contributors have been identified: r r r r Poor quality of the blackbody used Lower then expected reflection of mirrors High average image intensity variations EMC disturbance J.

Deviation of first frame from average highest modes removed row position [pixel] 50 50 column position [pixel] Fig. Furthermore a number of potentially relevant issues have not been specifically investigated yet. This will lead to an instrument that can be manufactured and aligned at a competitive price.

During this year TNO will continue with the characterization of the MIBS breadboard and further results can be expected in the course of this year. We also study the feasibility of controlling a constellation of such small satellites by means of air drag by extracting one or more flaps. It is found that it is indeed possible, but for best performance it is limited to altitudes around to km, depending on the time of launch with regard to the solar sunspot cycle.

Description of the geomagnetic M. Lyngby, Denmark e-mail: [email protected] J. Lyngby, Denmark P. Lyngby, Denmark S. Lyngby, Denmark N. Lyngby, Denmark L. Lyngby, Denmark R. Thomsen et al. Unfortunately it is still expensive to integrate and launch large satellites. Due to the lack of high-precision attitude data, only the magnetic field intensity will be used for this purpose.

The availability of GPS position measurements for just a fraction of the time e. Fortunately, along-track position errors result in much smaller magnetic field errors compared to vertical and across track position errors.

All of these current systems will influence the magnetic field as measured by a low Earth orbiting LEO satellite, and can therefore in principle be investigated by such. The current systems are highly dynamic, varying at a large range of time scales, partly due to the time variations of the solar wind and partly due to internal magnetospheric and ionospheric dynamics.

Measurements of the time variations of the total magnetic field intensity at low earth orbit can be used to investigate the magnetospheric currents and also the ionospheric currents. During geomagnetic storms the magnetospheric ringcurrent increase and act to decrease the magnetic field near the Earth.

This means that energetic particles trapped in the Earths radiation belts will be able to penetrate to lower altitudes, thereby endangering astronauts and spacecraft instruments. Feasibility of a Constellation of Miniature Satellites A detailed description of this magnetic field decrease, its spatial variation and relationship to the solar wind, is therefore of high priority.

The spatial variations can be investigated statistically by combining single satellite measurements with solar wind data, or instantaneously by using multipoint measurements from widely separated spacecraft. A LEO satellite will pass through the field-aligned currents FACS in the upper polar ionosphere, and can be used to investigate time-variations in their structure and intensity, provided that the satellite attitude is stable during the passage. During eclipse periods the attitude can be found using a magnetometer.

The last requirement is fulfilled by mounting the magnetometer on a deployable boom and by designing the entire spacecraft with respect to a magnetic cleanliness program.

The magnetometer will be mounted in a carbon-fiber cylinder on the top of a short boom. A number of boom design options will be discussed in the following section. Likewise it is possible to mount a passive GPS patch antenna at the end of the boom, but another location may be required in order to archive the best signal strength.

Correlation and position calculations can be done in the FPGA, possibly using a softcore microcontroller. The attitude does not need to be very well controlled, as long as the spacecraft is not spinning unreasonably fast.

Since we are performing measurements of the magnetic field, attitude control based on permanent magnets is not possible. On the other hand attitude control based on magnetorquers can be used but may only be operated at known intervals in order to correlate to the magnetometer data. In order to control the distance between the two satellites in the constellation, flaps on the sides of the satellites can be extracted to increase the area facing the flight direction and therefore increase the air drag on one of the satellites, thus reducing or increasing the inter-satellite distance.

It should be noted that if this system is to be used the orbit must be reasonably low; otherwise the air density is too small to generate a sufficient drag, we will look further into this issue in a later section. To minimize the power consumption, it may be desirable to only operate the GPS receiver part of the time. One scenario would be to operate the GPS receiver for one orbit per day. On board and later ground propagation of the GPS data can later be used to determine the position accurately.

For the small spacecraft proposed here a required boom length has been estimated to about 25 cm. The two deployable designs are shown mounted on a cubesat on the illustration below. Both designs will be stowed in the spacecraft during launch and will be deployed by releasing a locking mechanism.

Feasibility of a Constellation of Miniature Satellites Fig. A slightly conical design of the cylinder elements will ensure the rigidity and stability of the boom in the deployed position. They are fixed at the bottom of the well in the satellite, and mounted through hinges on the top mercedes-structure of the boom. The longerons are very flexible allowing the complete structure to be stowed in a very small space.

The spring-like properties of the longerons ensure that the boom will be unfolded to a fairly rigid structure, although the carbon fiber boom will be more rigid it also has a higher mass. However for vector measurements attitude information is required, which is not included in the data calculations.

The GPS has been estimated to generate less than 1 kB per 10 minutes, including protocol overhead. Depending on the orbit of the satellite the window for communication varies drastically. Simulations using STK based on a sun synchronous orbit and a minimum elevation angle of 10 degrees result in the following windows for a ground station at the same latitude as Copenhagen This can be mitigated by using additional ground stations, or by choosing a location at higher latitude.

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