João Pereira do Carmo

Imaging LIDARs for Space Applications

The European Space Agency (ESA)[1] foresees several robotic missions aimed for the preparation of the future Human Exploration of Mars. To accomplish the mission objectives Imaging LIDARs are one of the identified technologies that shall provide essential information to the spacecraft Guidance, Navigation and Control (GN&C) system. ESA awarded two technology development contracts to two industrial teams for the development and demonstration of novel technologies for Imaging LIDAR sensors. Both teams designed and are manufacturing an Imaging LIDAR breadboard targeting one specific application. The objective of using novel technologies is to reduce substantially the mass and power consumption of Imaging LIDAR sensors. The Imaging LIDAR sensors shall have a mass <10kg, power consumption <60Watt, measure distances up to 5000m, with a field of view (FOV) of 20x20 degrees, range resolutions down to 2 cm, and a frame rate higher than 1 Hz.

Real time processing enables fast 3D imaging at single photon level

3D LIDAR imaging is a key enabling technology for automatic navigation of future spacecraft, including landing, rendezvous and docking and rover navigation. Landing is typically the most demanding task because of the range of operation, speed of movement, field of view (FOV) and the spatial resolution required. When these parameters are combined with limited mass and power budget, required for interplanetary operations, the technological challenge becomes significant and innovative solutions must be found. Single Photon Avalanche Photodiodes (SPADs) can reduce the laser power by orders of magnitude, array detector format can speed up the data acquisition while some limited scanning may extend the FOV without pressure on the mechanics. In the same time, SPADs have long dead times that complicate their use for rangefinding. Optimization and balance between the instrument subsystems are required. We discuss how the implementation of real-time control as an integral part of the LIDAR allows the use of SPAD array detectors in conditions of high dynamics. The result is a projected performance of more than 1 million 3D pixels/s at a distance of several kilometers within a small mass/power package. The work is related to ESA technology development for future planetary landing missions.

Test results of the infrared single-mode fiber for the DARWIN mission

Nulling interferometry is the baseline technique for the DARWIN planet finding mission of the European Space Agency. Using this technique it will be possible to cancel, by destructive interference, the light from the bright star and look directly at its surrounding planets and eventually discover life on them. To achieve this goal wavefront errors need to be reduced to a very high degree in order to achieve the required nulling quality. Such a high wavefront quality can only be achieved with adequate wavefront filtering measures. Single mode fibers in general have excellent mode filtering capabilities, but they were not recently available for the broad infrared wavelength region of Darwin (4-20 um). Within an ESA technology development project, TNO has designed and tested an infrared single mode fiber based on chalcogenide glasses that has been manufactured by the University of Rennes. Several tests are carried out to characterize the materials used and the IR single mode fiber. Far field intensity distribution measurement at 10.6 um reveals the single mode operation of the manufactured fiber. Influence of coating, length, light coupling and bending of the fiber are also investigated.

Signal-to-noise ratio of pseudo-random noise continuous wave backscatter lidar with analog detection

Backscatter lidars are useful tools for range determination in various applications, particularly if they provide compact and robust set-ups with suitable light sources, efficient sensors and adequate signal processing. A promising perspective to achieve such requirements is offered by the Pseudo-Random Noise continuous wave (PRN cw) lidar technique, employing cw laser diodes as transmitter. Here the Signal-to-Noise ratio (SNR) of such lidar will be investigated in detail for the following cases: power (amplitude) modulation of the transmitted laser beam and analogue detection by an avalanche photodiode, surface detection. The SNR is calculated numerically, allowing selection of the factors limiting the lidar detection under various environmental conditions. A set of various measurements, obtained with a PRN cw lidar, employing a diode laser in the near IR spectral range and an avalanche photodiode will be presented. The results from the analytical and numerical study are compared with the experimental results. Various applications for the PRN cw lidar will be examined and critical factors influencing its detection performances discussed. Finally an outlook is provided for possible applications of such a lidar in specific atmospheric and surface measurements.

Imaging LIDAR technology developments at the European Space Agency

The European Space Agency (ESA) foresees several robotic missions to the Moon and to Mars ultimately aimed for the preparation of future Human exploration activities. To accomplish the robotic mission objectives Imaging LIDARs (LIght Detection And Ranging) are one of the identified key technologies that shall provide essential range and image information to the spacecraft Guidance, Navigation and Control (GN&C) system during spacecrafts critical and automatic operations. Two technology development contracts have been established for the development and demonstration of Imaging LIDAR technologies. The two applications considered were: to support spacecraft descent and landing manoeuvres; and to assist the rendezvous and docking operations between two spacecrafts. Two elegant breadboards have been designed and manufactured. The goal of these activities was to implement novel technologies in order to reduce substantially the mass and power consumption of Imaging LIDAR sensors. The Imaging LIDAR sensors foreseen for these two applications have a mass <10kg, power consumption <60Watt, measure distances up to 5000m, with a field of view up to 20x20 degrees, range resolutions down to 2 cm, and a frame rate higher than 1 Hz.The European Space Agency (ESA) foresees several robotic missions to the Moon and to Mars ultimately aimed for the preparation of future Human exploration activities. To accomplish the robotic mission objectives Imaging LIDARs (LIght Detection And Ranging) are one of the identified key technologies that shall provide essential range and image information to the spacecraft Guidance, Navigation and Control (GN&C) system during spacecrafts critical and automatic operations. Two technology development contracts have been established for the development and demonstration of Imaging LIDAR technologies. The two applications considered were: to support spacecraft descent and landing manoeuvres; and to assist the rendezvous and docking operations between two spacecrafts. Two elegant breadboards have been designed and manufactured. The goal of these activities was to implement novel technologies in order to reduce substantially the mass and power consumption of Imaging LIDAR sensors. The Imaging LIDAR sensors foreseen for these two applications have a mass <10kg, power consumption <60Watt, measure distances up to 5000m, with a field of view up to 20x20 degrees, range resolutions down to 2 cm, and a frame rate higher than 1 Hz.

Echo digitizing imaging lidar for rendezvous and docking

We present first experimental results with an imaging LIDAR developed for rendezvous and docking of a spacecraft and a passive sample canister in the Martian orbit. The LIDAR covers a field of view of 20 by 20 degrees at a range of 5,000 m down to 1 m to cooperative targets. The frame rate is 1 Hz. In close range, the canisters position is calculated from the measurement results of the individual cooperative targets attached to its surface in known configuration. The design of the LIDAR is aimed at low weight and power consumption employing a fiber laser and a small receiver aperture resulting in a small scanning mirror. The scanning concept is based on a Gimbal-mounted scan mirror avoiding scan gaps for optimally exploiting the lasers power and minimizing the scan time. Sensor concept and technologies can be also be adapted for future Planetary or Lunar Lander applications.

Development of large aperture telescope technology (LATT): test results on a demonstrator bread-board

The concept of a low areal density primary mirror, actively controlled by actuators, has been investigated through a demonstration prototype. A spherical mirror (400 mm diameter, 2.7 Kg mass) has been manufactured and tested in laboratory and on the optical bench, to verify performance, controllability and optical quality. In the present paper we will describe the prototype and the test results.

Technological developments for ultra-lightweight, large aperture, deployable mirror for space telescopes

The increasing interest on space telescopes for scientific applications leads to implement the manufacturing technology of the most critical element, i.e. the primary mirror: being more suitable a large aperture, it must be lightweight and deployable. The presented topic was originally addressed to a spaceborne DIAL (Differential Absorption LIDAR) mission operating at 935.5 nm for the measurement of water vapour profile in atmosphere, whose results were presented at ICSO 2006 and 2008. Aim of this paper is to present the latest developments on the main issues related to the fabrication of a breadboard, covering two project critical areas identified during the preliminary studies: the design and performances of the long-stroke actuators used to implement the mirror active control and the mirror survivability to launch via Electrostatic Locking (EL) between mirror and backplane. The described work is developed under the ESA/ESTEC contract No. 22321/09/NL/RA. The lightweight mirror is structured as a central sector surrounded by petals, all of them actively controlled to reach the specified shape after initial deployment and then maintained within specs for the entire mission duration. The presented study concerns: a) testing the Carbon Fiber Reinforced Plastic (CFRP) backplane manufacturing and EL techniques, with production of suitable specimens; b) actuator design optimisation; c) design of the deployment mechanism including a high precision latch; d) the fabrication of thin mirrors mock-ups to validate the fabrication procedure for the large shells. The current activity aims to the construction of an optical breadboard capable of demonstrating the achievement of all these coupled critical aspects: optical quality of the thin shell mirror surface, actuators performances and back-plane - EL subsystem functionality.

Last results of technological developments for ultra-lightweight, large aperture, deployable mirror for space telescopes

The aim of this work is to describe the latest results of new technological concepts for Large Aperture Telescopes Technology (LATT) using thin deployable lightweight active mirrors. This technology is developed under the European Space Agency (ESA) Technology Research Program and can be exploited in all the applications based on the use of primary mirrors of space telescopes with large aperture, segmented lightweight telescopes with wide Field of View (FOV) and low f/#, and LIDAR telescopes. The reference mission application is a potential future ESA mission, related to a space borne DIAL (Differential Absorption Lidar) instrument operating around 935.5 nm with the goal to measure water vapor profiles in atmosphere. An Optical BreadBoard (OBB) for LATT has been designed for investigating and testing two critical aspects of the technology: 1) control accuracy in the mirror surface shaping. 2) mirror survivability to launch. The aim is to evaluate the effective performances of the long stroke smart-actuators used for the mirror control and to demonstrate the effectiveness and the reliability of the electrostatic locking (EL) system to restraint the thin shell on the mirror backup structure during launch. The paper presents a comprehensive vision of the breadboard focusing on how the requirements have driven the design of the whole system and of the various subsystems. The manufacturing process of the thin shell is also presented.

From long range to high precision: pushing the limits of pulsed-time-of-flight measurement

We present experimental results on two breadboard systems developed within ESA contracts dealing with a long-range rendezvous and docking sensor on one hand and a high precision relative attitude control sensor on the other. A rendezvous and docking sensor to be used in a Mars sample return mission has been developed and recently tested over a range of 5 km. A high-speed 3-D laser scanner with range noise below 1 mm was realized and demonstrated. A critical assessment of the performance and potential for further developments of both systems is given.