October 2, 2015

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

With the aim of studying the microwave background radiation (traces of the intense heat in the Universe approximately 380,000 years after the Big Bang), the PILOT astrophysics gondola flew on Sunday, September 20, 2015 at 21pm local time from Timmins, Canada. Under a 800,000 m3 balloon, the PILOT experiment collected scientific data for about 24 hours.

24 hours of flight ...

Launched on Sunday evening around 21 pm, the end of the PILOT flight was controlled from the Timmins base after 24 hours of data collection. Both the scientific gondola and the envelope landed in forest approximately 300 km northeast of the launch base. The successful flight is a rich reward for the efforts of PILOT’s project scientists and operational teams.

The full mission of the PILOT instrument is split across three flights, each of them dedicated to observing different directions in the Galaxy. By 2018, two other flights (from Australia and Sweden) will have completed the data collection that has successfully begun during PILOT’s first flight.



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

Features of the balloon

  • Volume of the main envelope: 800 000 m3
  • Volume of the auxiliary balloon: 1200 m3
  • Mass of the PILOT gondola: 1058 kg
  • Load weight under the envelope hook: 1749 kg

The PILOT Mission

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.

PILOT arrives on the launch pad. Credits: CNES.

For more details about this phenomenon, read the article « Planck révèle l’écran de poussière polarisée devant le fond diffus cosmologique(*) » (Planck reveals polarized dust screen before the cosmic microwave background ).

(*) Scientific articles use two terms to describe the concept of radiation left over from the Big Bang: microwave background radiation, and the cosmic microwave background.



Image of the cosmic microwave background by the Planck instrument. Credits: ESA and Planck collaboration.

The instrument, the heart of the measurement

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
The combination of bolometers, the observing frequency and the signal measurement method makes PILOT the most sensitive experiment of its kind.

The PILOT instrument in 2D and 3D. Credits: IRAP.


The gondola: to carry the instrument

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.

Developed in parallel with the PILOT gondola, a diurnal star sensor, ESTADIUS can identify the position of the gondola with respect to a star catalog, at night but also during the day. The accuracy of ESTADIUS’s position measurements is approximately 1 arcsec (1/3600 degrees).

The aluminium lattice of the PILOT gondola. Credits: CNES.


The PILOT partners: from design to development

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

PILOT team in the integration hall of Timmins. Credits: CNES/E. Grimault.

Prime Investigator PILOT: Jean-Philippe Bernard (IRAP).
CNES Project manager: Muriel Saccoccio (CNES).
CNES Gondola Project manager: Nicolas Bray (CNES).
Responsible for the PILOT program (astronomy): Olivier La Marle (CNES).

Clickable slideshow (Credits: CNES/E. Grimault).