Archeops flights

The first Archeops test flight took place on July, 18$^\mathrm{th}$ 1999 from the Italian balloon launching facility in Trapani (Sicily) to the South of Spain where the gondola landed on the next day. This test flight gave us 4 hours of good quality night-time data with the 6 bolometers that were mounted in the focal plane. This flight helped us in improving the instrument in order to reduce systematic effects.

The first scientific flight took place in January, 29 $^{\mathrm{th}}$ 2001 from the SSC³ base of Esrange (used by CNES⁴) in Kiruna in the North of Sweden. The focal plane contained 23 bolometers (one of them was blind in order to monitor systematic effects) with the following repartition: 8 bolometers at 143 GHz, 6 at 217 GHz, 6 at 353 GHz (sensitive to polarization using orthomode transducers) and 2 at 545 GHz. The interest in covering various frequencies is that we can monitor this way systematic effects and astrophysical foregrounds. During the flight, the temperature of the focal plane remained well below 100 mK (minimum of 89 mK) showing a perfect behavior of our cryostat. Unfortunately, due to unusually high stratospheric winds, we used a rather small balloon (150 000 m$^3$ instead of 400 000 m$^3$) and the maximum altitude of the gondola was 31.5 km inducing a higher background and atmospheric contamination. Also due to these winds, the gondola arrived too fast to our Eastern limit (Ural mountains) and therefore we had to stop the flight after 7.5 hours at ceiling. This reduced considerably the amount of data taken during the flight and especially the highly redundant scans that start after 7 hours of flight. The quality of the data was however excellent and allows us to perform a CMB anisotropy analysis, especially on the low $\ell$ edge of the first acoustic peak.