1) Make the first ever measurements of high energy cosmic rays from suborbital space using a fluorescence detector.
2) Measure UV backgrounds looking down on the ocean and land
3) Search for faint UV signatures in the atmosphere from other phenomena. (Discover Potential!)
4) Establish methods and techniques for a future high energy astroparticle space observatory
Flying the EUSO_SPB instrument on an ultra-long duration balloon flight from Wanaka NZ will provide the exposure that is required to achieve the mission objectives.
Extreme Energy Cosmic Rays
Extreme Energy Cosmic Rays (EECR) are the highest energy sub-atomic particles known to exist in the universe. EECRs result from extreme conditions in the extra galactic universe. The source(s) of these particles is unknown.
When an EECR strikes the earth's atmosphere it interacts in the atmosphere and creates a shower of secondary lower energy particles. The electrons in this extensive airshower excite nitrogen molecules in the atmosphere. The nitrogen mocules then radiate fluorescence light. Much of the light is emitted at UV wavelengths. The amount of light radiated is nearly proportional to the energy of the original cosmic ray. So in this sense the earth's atmosphere is used as a calorimeter. A cosmic ray air shower travels at almost the speed of light. The optical signature can be imagined as a UV light bulb moving at the speed of light. Before the cosmic ray particle interacts the bulb is off. After the cosmic ray interacts and the number of particles in the extensive air shower build up the bulb brightens Then the bulb dims as the particles in the air shower are absorbed. Higher energy air showers often reach ground level before they are fully absorbed. A second component of light, called Cherenkov light, is also produced in the form of a beam along the direction of the original cosmic ray.
The instrument was built by members of the JEM-EUSO international collaboration. It will fly suspended from the super pressure balloon and look down on the atmosphere from suborbital space to record the faint traces of UV light produced by cosmic ray extensive air showers. At its heart is a sensitive Photon Detection Module (PDM) that is mounted at the focus of a custom optics system of UV transmitting fresnel lenses. The lenses are 1x1 m in size. An array of 36 64 channel multichannel photomultiplier tubes form the PDM array. The signals of the PDM are digitized with a 2.5 microsecond time exposure. The data acquisition system records "video clips" containing 128 of these images. The field of view of the detector is 11x11 degrees. The recorded “videos clips” will show the trajectories of EASs as they develop in the atmosphere. To improve the contrast of the faint air showers above the night background, each subsection of the PDM is covered by a UV transmission filter. The instrument will operate at night when the moon is down.
Following the successful aircraft underflight of 2014 Canada campaign, an aircraft with a laser and calibrated UV LEDs is planned for the 2017 Wanaka campaign. These light sources will produce tracks and flashes to calibrate the instrument while it is at float altitude and operating. The expected height of the airplane will be about 10,000 ft. The goal is to fly the aircraft under the balloon for 1 hour with the light sources operating.