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.

Key Mission Requirements:• Large Area, ~50 m2 at 1 keV• Fine angular resolution, 0."1

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

Gen-X enabled by Ares V

Adjust figure via strain parallel to reflecting surface.

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.

Ring Images (Chandra at MSFC cal facility)

Profile across ring diagnosis axial quality

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.

Spacing of the figure detector to resolve 40 shells into 100 bins

Tilt of P to H by 1µ displaces ring by ~200 µ

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!

Legendre Perturbations, 10,000/n Å

Legendre Perturbations, 10,000/n Å

Legendre Perturbations, 10,000/n Å

Legendre Perturbations, 10,000/n Å

Poorer quality figure spreads the ring further

19" rms10" rms

4.8" rms 2.2" rms

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?

Conclusions (so far)

• Ring Profile, Position and Spread are extremely sensitive to figure quality

• On-orbit Measurements are feasible• Actuator design is critical for

–Sufficient correction amplitude–Avoiding transfer of low spatial

frequency figure errors to higher frequencies