On-Orbit Adjustment Calculation for the Generation-X X-ray mirror

Figure

D. A. Schwartz, R. J. Brissenden, M. Elvis, G. Fabbiano, 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 Team

SPIE Conference 7011Space Telescopes and Instrumentation II: Ultraviolet to

Gamma Ray 200824 June 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

High Resolution Imaging enables Gen-X science objectives

Wolter I Grazing Incidence X-ray reflection

A Gen-X Mirror Configuration

• 204 shells, 0.2mm thick • 16m outer diameter, (partially filled)• 8.3m completely filled, 3.5m inner

diameter• 60m focal length• 1m Shell length (each, P or H), 50mm gap• 5' radius FOV• 10mm shell clearance

Gen-X enabled by Ares V

Adjust figure via strain parallel to reflecting surface.

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

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 Diagnose Figure Errors!

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

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• 100mm x 100mm field• Position ~1 to 10 m forward of focus

– accuracy ~1cm axial, 1mm radial• Radial positioning knowledge better than

10 µ

Conclusions (so far)

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

• On-orbit Measurements are practical• Concept would "forward-fit" a distorted raytrace

model shell to the ring profile measurement• Actuator design is critical for

– Sufficient correction amplitude– Avoiding transfer of low spatial frequency

figure errors to higher frequencies