ATIC-2 (Advanced Thin Ionization Calorimeter)

Responsable institution:  Louisiana State University, University of Maryland, Marshall Space Flight Center, Purple Mountain Observatory (China), Moscow State University (Russia) and Max-Planck Institute for Solar System Research (Germany)
Principal Investigator:  Dr. John Wefel - Dr. Gregory Guzik

Cosmic rays are the only sample of matter from distant regions of the galaxy, and possibly elsewhere in the Universe, that can be directly observed by space experiments in the Solar System. This high energy matter consists of atomic nuclei that travel at speeds very close to the speed of light and includes electrons, the natural elements from Hydrogen and Helium to Iron and beyond as well as anti-matter in the form of positrons and anti-protons.

ATIC experiment was designed to measure the energy spectrum of individual cosmic ray elements in order to study the validity of the model that predicts that cosmic rays gain their very high energy as the result of supernova explosion shock waves traveling through interstellar gas. Several goals on regard this objective are for example to obtain energy spectra for individual elements of a broad energy range with a single instrument; to discover 'breaks' or 'bends' in the spectra, to measure the energy dependence of the H/He ratio as well determine the spectral differences between elements and obtain the composition of the cosmic ray matter.

To achieve its scientific objectives, the ATIC experiment must be capable of measuring the incident cosmic ray charge and energy over an energy range of 50 GeV to >100 TeV. A schematic of the instrument, can be seen at left (Click to enlarge).

The instrument is based on the technique of ionization calorimetry, the most practical method of energy determination for cosmic ray nuclei from H to Fe over the target energy range. The fully active ATIC calorimeter is composed of 10 layers of Bismuth Germanate (BGO) scintillating crystals and is located on the bottom of the instrument. Above the calorimeter is the target section consisting of three plastic scintillator strip hodoscopes to define the instrument aperture and provide redundant charge and trajectory measurements, as well as layers of inert carbon (between hodoscopes) to provide a volume for the incident particles to interact.

On the top of the detector stack is the highly segmented silicon matrix detector that provides an accurate measure of the incident particle charge even in the presence of shower particles backscattered from the calorimeter. Surrounding the detector stack, electronics bays hold the flight computers, readout electronics, power system boards and other instrument electronics. Finally, on each of the four corners three struts transfer the loads of the experiment through the pressure vessel ring to an external structure that attaches to the balloon.

The total weight of ATIC is about 1,500 kg (3,300 lbs), the total power consumed is less than 350 Watts (including power conversion efficiency), and the payload is designed to be quickly field stripped under Antarctic conditions.

Details of the balloon and launch operations

Launch site:Williams Field, McMurdo Station, Antarctica  
  Launch team: National Scientific Balloon Facility (NSBF)
Balloon: Open balloon (zero pressure) Raven 29X - 1.000.000 m3 - SF3-29.47-.8/.8/.8-NAR
Serial number: W29.47-2X-50
Flight identification number: 515N
Campaign: - 
Payload weight: 3845 lbs
Gondola weight: -
Overall weight: 4927 lbs

The balloon was launched by dynamic method December 29th, 2002 at 4:59 UTC and reached float altitude 8:10 UTC on the same day, strating an anti-clockwise path around the Antarctic Plateau.

After 19 days and 21 hours of flight the payload was cut down from the balloon at 2:01 utc of January 18th 2003 at 74º 40' S - 160º 19' E while flying at 124.700 ft. Impact of the payload was at 2:36 utc at 74º 38' S 160º 25' E.

The payload tipped over on landing onto its stern, where the antenna boom was mounted and was dragged about 60 ft before the parachute was cut.

The chase plane and recovery crew landed near the payload but spent only about 10 min on the ground to disconnect the battery and the solar panels, close the gas bottles and get the disks from MSFC cut out since they were very easy to get to in that position. Were necessary another 3 trips to recover the rest of the ATIC payload.

This was the first scientific flight of the instrument, after a first test launch -which also yieled scientific results in 2000/2001-.

Nominal data collection began on 30 Dec. 2002 at 5:40 UT and continued until 18 Jan. 2003 at 1:32 UT. During this period all data was recorded on board.

The ATIC dataset obtained in this first scientific flight consumed 65 Gbytes of the 70 Gbytes available in the flight disk and contains 16.9 million cosmic ray triggers, 1.6 million calibration records, 0.18 million housekeeping records plus rate and command records.

Internal pressure (~8 psi) of the vessel decreased slightly (~0.7 psi) for 1st 10 days and then held constant. In regard the internal temperature it was between 12 and 22 ºC

External references and bibliographical sources