Jean Evrard

Performance of CLAIRE, the first balloon-borne γ-ray lens telescope

CLAIRE is a balloon-borne telescope dedicated to validating the concept of a crystal diffraction lens for nuclear astrophysics. For the first time, focusing γ-rays enters into the domain of the high energy astrophysics. This represents a breakthrough in γ-ray instrumentation, and will allow unprecedent sensitivities. CLAIREs first flights occurred on June 15 2000 and on June 14 2001. Here we present its performance during the two flights in terms of pointing accuracy, background noise and estimated efficiency of the lens.

Design and flight performance of a crystal diffraction telescope

We present the design and performance of the gamma-ray lens telescope CLAIRE, which flew on a stratospheric balloon on June 14, 2001. The objective of this project is to validate the concept of a Laue diffraction lens for nuclear astrophysics. Instruments of this type, benefiting from the dramatic improvement of the signal/noise ratio brought about by focusing, will combine unprecedented sensitivities with high angular resolution. CLAIREs lens consists of Ge-Si mosaic crystals, focusing gamma-ray photons from its 505 cm2 area onto a small solid state detector, with only 7.2 cm3 volume for background noise. The diffracted energy of 170 keV results in a focal length of 279 cm, yet the entire payload weighed under 500 kg. CLAIRE was launched by the French Space Agency (CNES) from its balloon base at Gap in the French Alps (Southeast of France) and was recovered near Bordeaux in the Southwest of France after roughly 5 hours at float altitude. After presenting the principle of a diffraction lens, the CLAIRE 2001 flight is analyzed in terms of pointing accuracy, background noise and diffraction efficiency of the lens.

CLAIRE – towards the first light for a gamma-ray lens

Abstract The CLAIRE collaboration is presently preparing the first astronomical observation of a gamma-ray lens. In June 2000, the instrument is to be flown on a stratospheric balloon by the French Space Agency CNES. CLAIRE features a Laue diffraction lens, a detector module with a 3×3 germanium array, and a balloon gondola stabilized to 15″ pointing accuracy. The instruments lens focuses gamma-ray photons from its 526 cm 2 area onto a small solid-state detector, with only 18 cm 3 equivalent volume for background noise. Hence, for the first time in gamma-ray astronomy, the statistics will be dominated by the signal. Besides its excellent sensitivity, the telescope has outstanding angular and spectral resolution. The primary objective for the first balloon flight of CLAIRE is to detect the Crab nebula and measure its extend at 170 keV with an angular resolution of about 1 arcmin. Scientific objectives for further flights include collapsed objects, SNRs, and broad class annihilators.

The French balloon program — Advancements in CNES balloon research and development

Abstract The French Space Agency (CNES) has been supporting scientific ballooning since its establishment in 1962. Balloon flights have being performing at high success rates from launch sites in France, Spain and Sweden. In parallel, the comprehensive Research and Development program (RD - gondola activities as platform for scientific payload of open stratospheric balloon: mainly with the improvements and operations of pointing systems gondola in collaboration with the Observatory of Geneva; • - the development of two new systems which improves the recovery conditions of gondolas after cut off; • - the development of a superpressure balloon as part of Strateole project.

Design and improvements of the Attitude Control System of the FIREBall balloon experiment

FIREBALL (the Faint Intergalactic Redshifted Emission Balloon, funded by CNES-NASA, PI C.Martin, Caltech) is a balloon-borne 1m telescope coupled to an ultraviolet Multi Object Spectrometer (MOS), designed to study the faint and diffuse emission of the circumgalactic medium. The third flight of the experiment is planned in summer 2017. The goal of this paper is to describe the accurate pointing system of the 5-metres high / 1500kg gondola - that has been designed to fulfill stringent pointing requirements: less than 1 arcsec in elevation and cross elevation, and about 1 arcmin in field rotation (around the line of sight axis), over long integration time (a few hours). The pointing system is based on a multi stage closed loop scheme (4 Degrees Of Freedom), relying on a 1DOF gondola azimuth controller, a 2DOF gimbal frame supporting a 1.2-meter plano siderostat, and a 1DOF field rotation control system. The attitude determination is based on the hybridization of two accurate sensors: a Fiber Optic Gyrometer measurement unit and a star sensor integrated inside the instrument. The manuscript presents the design of the ACS. We also focus on flight train stability issues - due to the pendulum and torsion modes -, on the geometric equations specific to a siderostat pointing system, and on the description of the tests facilities.

Challenges of the opto-mechanical conceptual design of a small far-IR balloon experiment

Astronomers require more and more precise instruments for their observations. Here we describe the challenges encountered in the optical and mechanical designs of the CIDRE (Campagne d’Identification du Deutérium par Réception hEtérodyne) project, which was to be flown on a high altitude balloon at 40 km. The project aimed to measure the transitions of the HD molecule at 2.675 THz band and some other THz lines in our galaxy. The astronomers asked to fly the biggest possible telescope in a standard balloon gondola, and required high pointing accuracy (7 arcsec). In January 2014, the technical project, including the optical and mechanical designs, was evaluated to be of excellent standard, but, for all that, the project was cancelled because of financial constraints. Nevertheless the phase A study allowed us to identify the optical and mechanical challenges of balloon projects and we were able to come up with a simple design, that fulfilled all the requirements. The 900 mm primary mirror and the rest of the optics were designed to be supported by a sandwich-panel composite structure with carbon epoxy skins and aluminum honeycomb core to improve the mechanical stiffness and the thermal behavior of the instrument without increasing its mass or its complexity. In this paper, we describe the optical design and the mechanical structure of the instrument. Finite element analysis is carried out to estimate the gravitational flexure and the thermal deformations, which can both harm the pointing accuracy and the performances of the instrument. These simulations show that the proposed design would fulfill the different requirements (pointing accuracy, landing survival as well as the dynamic behavior).

The French balloon program advancements in CNES balloon flight train & gondola developments

Abstract The French Space Agency (CNES) has been supporting scientific ballooning since its establishment in 1962. Flights of zero pressure balloon, whose volume could be as large as 800 000 m 3 (28 millions of cubic feet), have been performed at high success rates from launch sites in France, Spain and Sweden. The flight train, part of the aerostat hanging from the balloon hook (nadir end fitting of the balloon), is made of lines to bind its different components. In the CNES configuration, the flight train, whose mass could reach 1 000 Kg, comprises (starting from the balloon) : • -|the recovery system with the load parachutes and the cut off device; • -|the house keeping gondola (NSO) to control the aerostat flight : localisation, operational telemetry (TM) and telecommand (TC); • -|the scientific gondola, whose mass may vary from 30 Kg to 700 Kg, with its dedicated telemetry and telecommand system. Some scientific payloads, such as telescope or spectrometer, requires a pointing system to perform its measurements. From various development activities of balloon flight train and gondola by CNES, this paper presents an overview of three main areas : flight train recovery systems, aerostat TM /TC systems and gondola with pointing systems for scientific payload.