Purpose of the flight and payload description

HELIX is the acronym for High Energy Light Isotope eXperiment a balloon-borne instrument designed to measure the chemical and isotopic abundances of light cosmic ray nuclei especially of Beryllium-10. Measurements by HELIX, from 0.2 GeV/n to beyond 3 GeV/n, will provide an essential set of data for the study of propagation processes of the cosmic rays. The instrument was built through a collaboration lead by the University of Chicago and eight more universities from the US, Canada, and Japan.

In the image at left we can see a basic scheme of the instrument (click for more details). It is composed by a Time of Flight system that triggers the measurement of incoming particles, and measure charge and velocity below 1 GeV/n; a Superconducting Magnet that bends the particle through the Drift Chamber Tracker that tracks the particle through the magnet to measure rigidity and finally a Ring Imaging Cherenkov that measures velocity above 1 GeV/n.

The time-of-flight and charge (TOF) system consists of three layers of 1cm-thick plastic scintillator paddles. One layer is located at the top of the spectrometer and another at the bottom, with a total separation of 2.3 m. A third layer (the bore paddle) is located just below the magnet, above the RICH radiator. The scintillators are read out with Silicon Photomultipliers (SiPMs) which are immune to magnetic field and can be operated with relatively low voltage.

The magnetic field for HELIX is generated by a 2-coil superconducting magnet designed originally for the HEAT instrument which made five successful balloon flights between 1995 and 2002. The magnet provides an approximately uniform field within a rectangular warm bore measuring 51 x 51 x 61 cm3. Two superconducting NbTi coils centered along the cryostat axis produce a 1 Tesla central field at a current of 91.7 Amperes. The coils are cooled to 4.2 K in a liquid-helium (LHe) bath and the cryostat employs a vapor-cooled radiation shield and super-insulation to isolate the inner helium vessel from the ambient surroundings. To provide a pressurized environment for the tracking system, the bore is sealed with a thin aluminum pressure cap. The total LHe capacity of the magnet is 260 L, which provides a hold time of 7 days, at a mass of 420 kg.

Since the cosmic ray is a charged particle, it gets deflected by the magnetic field. The amount of curvature in the path is related to the rigidity which is measured by the multiwire Drift Chamber Tracker (DCT). The DCT tracks particles by recording the ionization trail the cosmic ray creates in the gas-filled volume. There are 3 planes of "sense" wires that the cosmic ray-induced ionization drifts to and these wires measure the resultant voltage pulse. The DCT uses 10% Argon and 90% CO2 gas mixture kept at atmospheric pressure and constant temperature.

A Ring Imaging CHerenkov (RICH) detector utilize the velocity dependence of the emission angle of Cherenkov radiation, to accurately measure relativistic charged particle velocities. The main components of a RICH detector are a radiator assembly to produce the Cherenkov light and a detector plane to image the resulting ring. HELIX's RICH comprises a radiator plane and a detector plane separated by an expansion volume. The radiator plane is made up of 32 tiles of aerogel and four tiles of NaF. All tiles are 10 x 10 x 1 cm3. The detector plane is populated with 6 x 6 mm2 silicon photomultipliers (SiPMs) arranged in 8 x 8 arrays. There are 200 such arrays in a checkerboard pattern on a 100 x 100 cm2 surface located 50 cm below the radiator plane.

The data acquisition system of HELIX is based on a custom hierarchical architecture. Data from each subsystem is buffered by subsystem merger boards. Collected data in the subsystem merger board gets transferred to the master merger board. A mini-ITX science flight computer reads out the master merger, stores data to Solid State Discs, and manages all telemetry and housekeeping operations.

The HELIX solar power system uses an omni-directional photovoltaic (PV) array with 4 sides with an angle of inclination of about 22 degrees. Because of the high field of the magnet, the overall instrument at float is stray oriented to the local geomagnetic field. The omni-direction design was required to ensure that the payload will always have light incident on some panels. Each side of the solar array will have eight 31" x 27" Photo Voltaic panels, which provide enough power to run the instrumentation. Additional charging power will come from the non solar-facing panels that, due to the angle of incidence, will still receive enough light to generate an additional ~150 W.

Video footage of the pre-launch and launch operations

Details of the balloon flight

Balloon launched on: 5/28/2024 at 3:20 utc
Launch site: European Space Range, Kiruna, Sweden  
Balloon launched by: Columbia Scientific Balloon Facility (CSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon Aerostar - W39.57-2-113 - 39.570.000 cuft
Flight identification number: 738N
End of flight (L for landing time, W for last contact, otherwise termination time): 6/3/2024 at 11:47 utc (L)
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 6 d 8 h 27 m
Landing site: 120 miles NNE of Grise Fiord, Ellesmere Island, Canada

External references

Images of the mission

         

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