LOLS has been active in different space technologies since 1986:

  • Optical Navigation of satellites
  • Optical Metrology for satellite formation flying
  • Instrument processors and instrument simulators
  • Remote sensing
  • Micro-satellites
  • Space system and instrumentation innovative concepts

Navigation

Optical navigation in autonomous navigation

In the early 90’s, within the development of the PoSAT-1 microsatellite project (launched in 1993), FCUL was in charge of its star mapper at both the engineering and flight models, and developed the operational concept of the mapper and the software to estimate attitude from star fields, using the PPM catalogue. In addition, FCUL was also in charge of the AODCS sensors and actuators, namely magnetometers, the Earth and sun sensors, and performed extensive experimentation on PoSAT-1 GPS, together with the University of Porto. Some effort was dedicated to the development of the SIMSAT simulator to understand in detail PoSAT-2 attitude dynamics and navigation and to test control strategies. Later, SIMSAT was extended within EUCLID projects to include other actuators (thrusters, electrical propulsion and spin wheels) in the context of automatic orbit change.

The background of FCUL in optical instrumentation and digital image processing was used in the ESA context immediately after Portugal became a member in November 2000. FCUL has been, since then, involved in modelling and development activities for autonomous navigation, planetary landing and localization, and spacecraft rendezvous, for both passive and active (LIDAR) sensors.

FCUL is active in simulation of optical instruments and image processing (AutoNav,  AEROFAST, PlaNav, VBrNav, PROBA 3), feature detection for navigation (NPAL), and lidar or optical processing for hazard mapping (LiGNC, VBrNav, HASE and LAPS).

Planetary landing in Mercury and Mars is being designed using optical images and LIDAR range data in order to update navigational data and assess hazard mapping for landing. Autonomous navigation concepts were developed by image processing of star fields (to estimate attitude) and of planets or faint asteroids (up to magnitude 13) to estimate line-of-sight to their centre of mass or to locate the limb accurately.

The same family of models was implemented on Beagle2 ground segment to locate the spacecraft accurately after landing, using the movement of Mars moons (Phobos and Deimos) against a fixed star background.

Rendezvous and docking technologies are being designed in the context of the Mars Return Vehicle mission, by deriving navigational data from patterns of light sources on the ascending vehicle and controlling the orbit of the chaser spacecraft. These technologies are under consideration for the PROBA 3 mission.

FCUL models were implemented on the ground control centre for Beagle2 and will be tested in real flight conditions in the frame of SMART-1 and probably also in Rosetta.

In optical navigation, FCUL has been cooperating with EADS Astrium (Fr), Deimos Engenharia (P), Lusospace (P), Solscientia (P), VisionBox (P), University of Dundee (UK) and GMV (Sp).

Metrology

Instrument and constellations internal optical metrology

FCUL background on coherent optics is used to analyse and design metrology systems for multiple aperture telescopes (MAT), either in the free-flyers context or on mechanically-linked configurations.

To discover new planets on very far solar systems or to observe the Earth from GEO orbit requiring very large angular resolution, the aperture must be overwhelmingly large and cannot be monolithic.

Consequently, a multiple aperture telescope approach must be implemented. Nevertheless, to coherently phase independent telescopes – and thus generate a large synthetic aperture, the set of telescopes (sub-apertures) must observe simultaneously the object while maintaining constant (within a small fraction of the wavelength) the relative phase of the various wavefronts. Co-phasing thus requires stringent optical metrology and suitable control.

Optical interferometry was used by FCUL in the context of ESA / HPOM (High Precision Optical Metrology) and EUCLID/RTP 9.9 / HROSS (High Resolution Optical Satellite Sensor).

HPOM is a demonstration activity within the ESA Darwin Technology Package; FCUL cooperates with ASTRIUM (Fr, Ge), TPD/TNO (Nl), SIOS (Ge) and EADS-CASA (Sp), and developed an absolute metrology interferometer breadboard to measure distances based on frequency sweeping (150 GHz) tunable lasers.

HROSS focused on the definition of an interferometric instrument optimized for the high-resolution optical surveillance from Geostationary Earth Orbit, by means of the synthetic aperture technique, and on the definition and development of its enabling technologies, namely the complex optical metrology system. FCUL cooperated with ISR/IST (Po), CSL (Be) and ALENIA (It), and designed, tested and integrated into the instrument prototype, the internal absolute metrology and the image restoration algorithms to compensate from synthetic aperture artefacts, within the spatial bandwidth of the instrument.

The internal metrology sensor, based on frequency sweep interferometry, was incorporated in a multiple aperture telescope metrology demonstrator, composed of a white light interferometer (simulating the telescope), relative metrology (Michelson heterodyne interferometer) and absolute metrology. Disturbances were injected to simulate, in a controlled way, the structural mechanical disturbances in a space environment. Co-phasing was achieved easilyThe FSI technology demonstrated in HPOM and HROSS was further developed under the FP-MET (Fabry-Perot Metrology, 2007-2010) activity, which is developing the EQM system that will undergo vacuum tests in 2009 and is a candidate to fly in the PROBA 3 mission in 2012, to measure the longitudinal distance between two spacecrafts separated by 25-150 m, implementing a solar coronograph. Previous prototypes were adapted to IR wavelengths, reference fibres were introduced and the opto-mechanics was completely redesigned

ESA also addressed the potential of mode-locked femtosecond lasers for constellations metrology. In cooperation with TNO (NL), FCUL assessed system accuracies as a function of all subsystem and system parameters, with special emphasis on the Darwin and XEUS missions (FEMTO activity, 2007-2008). In order to pave the way for the future use of mode-locked semiconductor lasers in such systems, FCUL  performed a complete evaluation and experimental testing of such devices, in cooperation with Reflekron (FI) and EADS Astrium (Ge), in an ESA-ITI activity (2008-2010).

Earth Observation

EO instruments and instrument processors

LOLS team was very active in remote sensing in the 90's, driven by the NATO-SFS-SATCART funding and the SATCART consortium (INETI, EID, Geometral). Landsat and SPOT, mixed image - GIS processing, texture and modelling were experimented and tested in SATCART, in parallel with the generation of thematical cartography and training of military photointerpreters in satellite IMINT - the PAIESAT program.

Image modelling has been an intensive topic for LOLS. To analyse performances of new optical instrument concepts for military Earth Observation, FCUL built the SATSIM simulator for very high resolution images (visible and near-infrared) to be captured from space, taking into account the complete physical chain: illumination source, atmospheric propagation, material properties, optics and sensor and detector electronics. 3D objects were modelled and were rendered by ray-tracing techniques. SATSIM was later upgraded to include turbulence effects, for low altitude satellites or UAV, to assess methodologies for image restoration of man-made objects of military interest.

In the late 90's and 00's, LOLS capitalized on its background in optics, especially in radiometry and atmospheric optics, to support the industrial implementation of the ground segment of IASI (for METOP), MIRAS (for SMOS) and to perform X SAR interferometry applied to tectonics.

IASI (2002) – The Infrared Atmospheric Sounding Interferometer is one the EUMETSAT / METOP payloads, to be launched in 2005. IASI is a multi-purpose sounding instrument for global measurement of temperature, water vapour, trace gases, surface temperature, surface emissivity and cloud characteristics. It has 8461 channels in the infrared (3.62 – 15.5 mm). LOLS – contracted by Skysoft, and in cooperation with Critical Software and Edisoft – implemented the data processing chain in Matlab to validate the industrial implementation of Level 2 PPF (Product Processing Facility), including interfaces, the geometric co-registering of the other METOP payloads (AMSU, AVHRR, MHS, ATOVS and the retrieval of geophysical data.

MIRAS (2003) – The L-band Microwave Imaging Radiometer using Aperture Synthesis interferometer is one payload of SMOS (Soil Moisture and Ocean Salinity) mission. MIRAS measures radiometric brightness temperature at large incidences for different polarisations, to observe and monitor soil moisture over land and ocean salinity over oceans, two crucial variables of the Earth climate system. SMOS Level 1 Processor is being developed in Portugal. FCUL - under contract from Deimos Engenharia and in cooperation with Critical Software - addressed the issue of adaptive striping (in order to ensure that data can be recovered on a constant grid of locations over the Earth, to cope with FOV shape and irregular distributions of footprints within the FOV) and worked on the testing of the industrial processor and in error propagation in the processing pipeline.

In the NorseWind (2008-2012) activity, led by OBS (UK), the general goal was the creation of offshore wind atlas for the Baltic, Irish and North Seas and improve the accuracy of short-term forecasting  -  critical for the integration of wind power into the grid. FCUL tasks are related to the processing of data from the network of wind speed sensors, ground-based remote sensing technologies, (SoDAR - Sound Detecting And Ranging & LiDAR – Light Detecting And Ranging) and meteorological masts (offshore or near shore) combined with the horizontal resolution offered by SAR (Synthetic Aperture Radar) and scatterometer techniques.

Ground Segment

Microsatellites, operational system concepts, OGSE

In the field of space systems, FCUL was the leader of an industrial consortium that built the PoSAT-1microsatellite in 1992-1993, with the strategic goal of preparing entrepreneurial resources to cope with the challenges to be provided by ESA after Portugal membership. This project was based on a transfer of technology agreement with the University of Surrey (UK). In addition to the overall project preparation, control and management, FCUL was in charge of the technical direction, interfaces with the Universities and development of the engineering model of PoSAT-1. Specific activities of FCUL were:

  • Space segment: The following technical activities were executed directly by FCUL: star mapper, attitude sensors and actuators, thermal modelling, mission analysis, GPS data experiments.

​Satellite operations

FCUL addressed new concepts for portable ground stations for microsatellites, decentralised satellite control, autonomous orbit transfers and attitude dynamics equilibrium:

  • Ground segment: FCUL developed a portable ground station to profit the communication facilities onboard of the satellite: fixed, mobile and portable satellite ground stations for half duplex communications of voice and data, with either omnidirectional or tracking high gain antennas Specific hardware and software modules were developed, using GPS capabilities, to allow the use of the terminals in mobile operational scenarios. These systems were actually used by Portuguese Armed Forces in United Nations humanitarian missions in Mozambique and Kosovo.
     
  • Decentralised satellite control - The problem of satellite control and information dissemination during conflicts is critical. FCUL evaluated scenarios enabling the final user to request images to observation satellites using LEO constellations (with cross-links) to provide global communications between the user and the imaging satellite, forwarding requests and transferring data to the user. Such generalized satellite constellations (which may also include meteorological satellites) are highly dynamic have interesting topologies, and enables a minimum intervention from centralized control systems. A model to study the end-to-end delay performance of such satellite communication system was developed, together with Alenia, based on an "IRIDIUM-like" system, modelled as a non homogeneous, seamed, with two intra-plane and two inter-plane inter-satellite links and a non-uniform traffic distribution. The corresponding handover and routing strategies were chosen, connections between communication satellites and an observation satellite were proposed using geometrical criteria (namely, coverage of observation satellites by the inter-satellite antennas of the IRIDIUM system).
     
  • Autonomous orbit transfers - FCUL implemented autonomous orbit transfers based on the analytical Edelbaum model, from the theory of optimal control. Analytical models can be easily implemented on-board in the context of missions with navigation autonomy. The SIMEP simulator was developed to assess accuracies. In general terms, the Edelbaum model can be used for transfers between circular orbits, with constant acceleration and no perturbations and it is a matter of research to evaluate how it copes with non-ideal cases.
     
  • Attitude dynamics equilibrium - There is a growing interest in small cheap satellites operating in low Earth orbit. The methods using environmental torques to maintain the satellite orientation are most appropriated for such satellites. FCUL has been assessing aerodynamic torques for passive satellite stabilization. The concepts of stability, related to satellite attitude control, deal with stability of equilibrium. Stability domains for all possible equilibrium orientations were determined and analysed for pure passive aerodynamic stabilized satellites, using nonlinear and linear methods.

Optical Ground Systems Equipment

FCUL cooperated with Lusospace in the development and calibration of an optical head to test Gaia focal plane (a large mosaic of large format 106 CCD) in thermal vacuum. FCUL focused on radiometric issues to ensure that the light beams generated by the optical head generated the right radiance in the focal plane.

See all LOLS projects in Space and Astrophysics, their inter-relations and funding organizations.