STRATO SCIENCE 2015 : PILOT lifts a veil of dust ...

PILOT main envelope. Credits: CNES  E. GRIMAULT 2015.

Progress in cosmology (the study of the structure, origin and evolution of the Universe) results from the combined effort of multiple teams of astrophysicists around the world, each of them striving to answer some of humanity’s most fundamental questions: How did the Universe begin? What were the first moments of the Universe like?

Since the Universe is expanding, observing events in the young Universe requires observations over very long distances. But as the target distance increases, so does the number of "pollutants" that contaminate the signal from the young Universe.

The goal of PILOT (Polarized Instrument for the Long wavelength Observation of the Tenuous interstellar medium) is to measure the polarized emission (and intensity) of dust grains in the interstellar medium (a mixture of gas and dust that fills the space between stars) of our Galaxy. This is essential to cosmology because such measurements are needed to subtract the contribution of dust grains ("pollutants") to the total emission, and hence to "clean" the signal from the young Universe.

The PILOT instrument is a telescope made of:

• a main mirror (1 meter diameter) that collects the observation signal (radiation) from the astronomical target. The baffle keeps out stray radiation from other sources

• a photometer, the heart of the instrument, which includes:
• a signal detection area that collects the radiation focussed by the mirror. The detector package consists of 2048 bolometers, small units that are very sensitive to radiation and work at very low temperatures (0.3 Kelvin or -272.85 ° C). The energy received by the bolometer causes its temperature to rise, which changes its resistance. This resistance, transformed into an electrical potential, yields the measurement of the signal
• a cryostat, responsible for maintaining the bolometers at the correct temperature

• electronic units for instrument management

To prepare PILOT for a balloon flight, the PILOT instrument was installed in a dedicated gondola, designed and constructed by CNES. The gondola fulfils both the robustness constraints of the flight (particularly for the landing), and the need to build a structure as light as possible (since mass is the number one enemy of ballooning).

The two parallel walls of the gondola are a lattice of aluminum bars and balls, with an open central passage that accommodates the instrument.

Essential for the PILOT mission, the gondola keeps track of its position in space and the direction where it is pointing with extremely high precision. It is what we call a “pointed gondola”.  New research and technical developments by the CNES on the gondola’s pointing performance have achieved the accuracy needed by PILOT.

PILOT is an international project, with several European research and engineering teams contributing to the design and the realization of the PILOT experiment.
On the French side, participating teams are based at CNRS laboratories, institutions and public agencies (CEA and CNES). Other main project partners include teams based at Italian and Welsh universities, but there is broad European involvement, including ESA:

• CNES has provided project management, system coordination and development of the pointed gondola, including the Estadius stellar sensor
• IRAP (French Acronym: Institut de Recherche en Astrophysique et Planétologie) has defined the scientific objectives of the PILOT mission and provided project management of the scientific instrument. The treatment of data collected during the flight will also be coordinated by IRAP
• IAS (French Acronym: Institut d'Astrophysique Spatiale d'Orsay) has provided project management of the photometer
• CEA (French Acronym: Commissariat à l'Energie Atomique ) has provided the detector package for the instrument (the bolometers)
• Cardiff University provided optical components
• The University of Rome has developed the cryostat