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Generation-X telescope: Measurement of On-Orbit
Adjustment DataDan Schwartz, R. J. Brissenden, M. Elvis, G.
Fabbiano, T. Gaetz, D. Jerius, M. Juda, P. B. Reid, S. J. Wolk, (Harvard-Smithsonian Center for
Astrophysics), S. L. O’Dell, J. K. Kolodziejczak (NASA/MSFC), W. W. Zhang (NASA/GSFC), for the
Gen-X Team5 December 2008
Generation-X Science Objectives
• Detection of first black holes at z~10-20
• Evolution of Black Holes, Galaxies, Elements, from formation to the present
• Behavior of matter in extreme environments of Density, Gravity, Magnetic fields, Kinetic Energy.
A Gen-X Mirror Configuration
• 204 shells, 0.2 – 0.4 mm thick glass • 16m outer diameter, (partially filled)• 8.3m completely filled, 3.5m inner
diameter• 60m focal length• 1m Shell length (each, P or S)• 5' radius FOV• 10mm shell clearance
Actuator Configuration Concept: continuous Piezo deposition, electrically divided
Correct < 0.025 /mm =40mm periodOversample: 20mm actuators axially, 50 per plate Circumference tolerance ~10x worse, 200 mm actuators, 5 axial strips per plate.• Oversample
measurements: 100 per axial strip.
Raytrace Study Objectives:
1. Detector requirements1. Placement
2. Resolution
2. Can we detect deviations from ideal figure?
3. Are the measurements practical?
Raytrace Study
• Shells 1, 2, 203, 204• Uniform incident rays, perfect reflection• Perfect Wolter I Geometry• Perfect kinematic mounting, alignment• Trace single axial strip• Perturb surface figure by low order
Legendre Polynomials• Introduce "toy" actuators
Measure ~50,000 axial positions (1cm2), ~1000 at once. 500s exposure to Sco X-1 at 2 104 s-1 gives 104 counts per azimuth per ring. Iterate 10
times at 50% duty cycle, factor 10 margin, 120day initial adjustment
Resolve 100 bins with detector resolution 10µ. Require 8.17m
forward of focus.
Ring profile for ∑Pn distortions proportional to 0.0001/n mm.Image size in focal plane is 0."21 rms and 0."11 half-power
Ring Profile can Detect Figure Errors!
Requirements on Figuring Detector
• X-ray range ~0.2 – 4 keV• Count 2x104 s-1 per field• Resolve events to 10µm• 2-4 units, 100mm x 100mm field each• Position ~1 to 10 m forward of focus
– accuracy ~1cm axial, 1mm radial• Radial positioning knowledge better than
10 µ
Issues to Investigate:• What is the required initial quality?
– Use optical Hartmann test?• Algorithm Concepts:
– Measure Derivatives– Simulated annealing– “forward-fit" a distorted raytrace model shell to the
ring profile measurement• Handling the P/H Degeneracy?
– Use =983.17mm?
– Fix Hyperboloid and adjust Paraboloid?