OUTLINE. OVERVIEW MAIN MISSION OBJECTIVES INSTRUMENTS LAT GBM AGILE-EGRET-GLAST COMPARISION. OVERVIEW.
MASS :The GLAST observatory weighs ~4,303 kg
LAT mass : ~2,789 kg
GBM mass :~99.2 kg
DIMENSION of the spacecraft : 2.8 m(high) X 2.5 m in diameter when stowed
POWER CONSUMPTION :~1,500 watts average over an orbit(solar panels supply up to 3,122 watts in sunlight)
DATA DOWNLINK : 40 Mbit/s, multiple contacts per day
LAUNCH SITE : Cape Canaveral Air Station,Flo.
EXPENDABLE LAUNCH VEHICLE : DeltaII Heavy launch vehicle ,with 9 solid rocket boosters.
LAUNCH DATE : early 2008
Fig1 : Instruments of GLAST
Fig1: The subsystems of LAT.4x4 modular array.
With its very large FOV,the LAT sees about 20% of the sky at any given moment. It was assembled at SLAC.
Consists of a four-by-four array of tower modules. Each tower module consists of interleaved silicon-strip detectors and lead converter sheets.
SSD are able to more precisely track the electron or positron produced from the initial gamma-ray than previous type of detectors.
SSDs have the ability to determine to location of an object in the sky to within 0.5 to 0.5 arcmin.
The pair conversion signature is also used to help reject the much larger background of charged cosmic rays.
Fig3 : The LAT has 16 towers of particle detectors
When a particle interacts in the silicon ,its position on the plane can therefore be determined in two dimensions.
The third dimension of the track is determined by analyzing signals from adjacent planes, as the particle travels down through the telescope towards the calorimeter.
Fig4 : A cross-section of the TRACKER.
1 After background rejection2 Single photon, 68% containment, on-axis3 1-σ, on-axis4 1-σ radius, flux 10-7 cm-2 s-1 (>100 MeV), high|b|5> 100 MeV, at high |b|, for exposure of one-year all sky survey, photon spectral index -2
The calorimeter design for GLAST produces flashes of light that are used to determine how much energy is in each γ-ray.
CsI(Tl) bars, arranged in a segmented manner, give both longitudinal and transverse information about the energy deposition pattern.
Cesium-iodide blocks are arranged in two perpendicular directions, to provide additional positional information about the shower.
Fig5 : CsI bars..
The data acquisition system (DAQ) is the brain behind GLAST, as it makes the initial distinction between false signals and real gamma ray signals, and decides which of the signals should be relayed to the ground.
The DAQ consists of specialized electronics and 32-bit radiation-hard processors that record and analyze the information generated by the silicon-strip detectors and the calorimeter.
The ACD is LAT’S first-level defense against the charged vosmic ray background that outnumbers the γ-rays by 3-5 orders of magnitude.
The ACD covers the top and 4 sides of the LAT tracking detector,requiring a total active area of ~8.3 m2 .
It uses the plastic scintillator tiles with wavelength shifting fiber readout.
Fig6 : ACD in final phase of integration. The bottom tile rows are not installed yet.
Fig7: GLAST Burst Monitor Principal Investigator Charles Meegan,an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville,tests the GBM.
--the generation and dissemination of near real-time burst locations accurate enough to initiate counterpart searches by ground or space-based observers.
5. production and publication of a catalog of GRBs detected by the GBM including those uncovered in the search for untriggered events. This catalog will contain parameters such as burst fluence, peak flux, and duration.
6. the availability of archived data for investigations into non-GRB phenomena such as solar flares, galactic black-hole candidates, and soft gamma-ray repeaters (SGR), which may be strong and variable above background radiation levels in the hard X-ray regime.
Fig8 : (UP)NaI detector-shipped from Jena Optronik August 2002.
(DOWN)Engineering Quality model BGO Detector on test bench at NSSTC June 2005
Fig9 : NaI and BGO detectors in thermal vacuum chamber at MPE ,April 2005.
SWIFT can rapidly and precisely determine the location the GRBs and observe their afterglows at X-ray,ultraviolet and optical wavelengths.
3. Sonoma State University