MAXIM Pathfinder Keith Gendreau, Webster Cash, Ann Shipley, and Nick White
MAXIM Pathfinder • Science Goals • Provide Scientific Context for MAXIM • Study stellar coronae, AGN jets, accretion disks, and more • Technical Role and Issues • Provides for 2 intermediate technical stepping stones toward full MAXIM • Current Baseline Design • More robust and scalable toward a full MAXIM mission • Tallest Technical Poles • Line-of-Sight alignment of multiple spacecraft • Pointing of individual spacecraft • Formation Flying
Visiting a Blackhole with an X-ray Interferometer • Current best estimates for the size of the event horizon of a blackhole: a few microarcseconds • Variability and spectral data describe an x-ray bright region near the event horizon. • Baselines at 1-10Å are a factor of of 1000 shorter than at 1000-10000Å • The MAXIM mission will have resolution of 0.1 as. • For Scientific and Technical context, we are exploring MAXIM Pathfinder mission concepts. http://maxim.gsfc.nasa.gov
Visiting a Black Hole with an X-ray Interferometer • AGN • Stellar Coronae X-ray variability of ~1000 seconds suggests that the hard emission is coming from a few Rs Calculated Image of M87 @ 0.1 mas Capella “simulation” 1 mas and 10000 sq cm
A Simple X-ray Interferometer L d Beams Cross Flats Detector • Grazing Incidence softens tolerances by ~2 orders of magnitude. Optics that are diffraction limited for normal incidence UV is diffraction limited for grazing incidence X-rays. • Use “simple” optics to keep diffraction limit. • Demonstrated in lab at ~10 Angstroms (1.25 keV). W. Cash et al, Nature 407 14 September 2000 s Fringe Spacing:
Grazing Incidence is an Advantage for X-ray Interferometry 1/sinq for 2 degrees Loosens the baseline tolerances by 2 orders of magnitude. --> 1-10 nm baseline tolerance.
Laboratory Demonstration Experiment by CU and MSFC. l =10 Angstroms (1.25 keV) ~ 1mm Baseline ~100 mas “l/20” flat mirrors ~100 m optics/detector distance X-ray CCD Detector W. Cash et al, Nature 407 14 September 2000
Fringes at 1.25keV W. Cash et al Nature 407 14 September 2000 Profile Across Illuminated Region
Basic MAXIM Design Baseline Fringes Form Here • Each Channel Consists of 2 flats • Primary mirrors determine baseline • Secondary mirrors combine channels at detector. To implement this basic design, you choose how to group the mirrors.
Original MAXIM Implementations MAXIM Pathfinder • “Easy” Formation Flying (mm control) • Optics in 1 s/c act like a thin lens ~1-2 m Baseline ~10 m ~500 km Full MAXIM- the black hole imager • Nanometer formation flying • Primaries must point to milliarcseconds ~500-1000 m Baseline ~5000 km ~10 km
MAXIM Pathfinder • 1-2 m Baseline • Optics in one spacecraft. • Detectors in separate spacecraft. • Formation Flying at 50-500km separation in order to make fringes well matched to detector pixels L=50-500 km! Detector Spacecraft • 100as Resolution • Laser alignment system provides metrology between satellites. • Much more complicated for Full MAXIM mission Optic Spacecraft
2 0 0 M C O L L E C T O R S P A C E C R A F T ( 3 2 P L A C E S E V E N L Y S P A C E D ) C O N V E R G E R S P A C E C R A F T D E T E C T O R S P A C E C R A F T Original Full Maxim Design C O N S T E L L A T I O N B O R E S I G H T H u b S p a c e c r a f t 1 0 K M • 200 M baseline • Optics divided between multiple spacecraft. • 0.1 mas Angular Resolution • “Extreme” Formation Flying • Detector flown 1000s of km from optics to make fringes comparable to detector pixel sizes 5 0 0 0 D E L A Y L I N E K M S P A C E C R A F T
Improved MAXIM Implementation Group and package Primary and Secondary Mirrors as “Periscope” Pairs ~20,000 km ~500-1000 m Baseline • “Easy” Formation Flying (microns) • All s/c act like thin lenses- Higher Robustness • Possibility to introduce phase control within one space craft- an x-ray delay line- More Flexibility • Offers more optimal UV-Plane coverage- Less dependence on Detector Energy Resolution • Each Module, self contained- Lower Risk. A scalable MAXIM concept.
“Periscope” Implementation to Hold MAXIM Mirrors • In original implementations for MAXIM, the primary mirrors are held in separate spacecrafts from those for the secondary mirrors. • Requires ~milliarcsecond pointing and ~ nm formation flying control for satellites • Limits our coverage of the UV plane • The new “Periscope” concept groups the primary mirrors with their secondary mirrors to form periscopes. • Essentially the same basic design, but this grouping behaves as a thin lens. • Requires milliarcsecond pointing but only ~10 micron formation flying control for space craft. More robust than original implementation. • Allows for optimal sampling of UV plane • Lower risk, since each periscope module is fully contained. • Lower Costs as the individual periscope modules can be “mass” produced • Direct scalability from pathfinder to full MAXIM using the same technology.
A thin lens bends light in-phase to a point. A thin lens can be simulated with a series of periscopes bending light toa point in-phase. Periscopes to be placed on paraboloidal surface to achievephase closure, or we can individually adjust phase for each periscope.
Rotating a thin lens does not change the position of the focus. Nor will the periscope approximation.
Periscope Module Optics Layout LOS Primary Secondary Y Pitch Yaw Z Roll X LOS To Detector
The “New” MAXIM Pathfinder • 2 mission phases • phase 1: 100 mas Science • Very similar to original MP concept, but some looser tolerances • 2 formation flying s/c • Studies Stars, AGN, Black hole Jets and Accretion Disks • phase 2: 1 mas Science • Optics s/c separates into 7 s/c to extend angular resolution to a few mas • Tougher Formation Flying tolerances (10 microns) • Tougher Line-Of-Sight Requirements • Get a Glimpse of a Black Hole Event Horizon! • Test and develop concepts for the full MAXIM mission • Design to accomplish all mode 1 science with capability to explore mode 2 science • Gyroscope Solution instead of SIM for telescope alignment • Grass roots and Parametric Costs Analysis ~$ 550M
Principle Differences Between the Original Pathfinder and the New MAXIM Pathfinder • 2 Phases • Relative Astrometry with High Precision Gyros instead of absolute Astrometry with SIM • CCD Detectors instead of Calorimeters • New Pathfinder provides intermediate scientific and technical steps between 100 mas and 0.1 mas imaging.
Launch Configuration Delta IV 5m X 14.3m fairing Delta IV Heavy 5m X 19.1m fairing Propulsion/Hub SpaceCraft Sta. 7600 Delta IV 5m X 14.3m fairing Sta. 4300 Hub SpaceCraft/Detector SpaceCraft C.G. Sta. 2500 Sta. 1550 Propulsion/Hub SpaceCraft P/L Sta. 0.00
Mission Sequence 1 km Science Phase #2 High Resolution (100 nas) Science Phase #1 Low Resolution (100 mas) Launch 200 km 20,000 km Transfer Stage
Technical Components: Mirror Modules • Grazing Incidence Mirrors • Grazing Incidence loosens our surface quality and figure requirements by 1/sinq • Flatness > l/100 • “Simple” shapes like spheres and flats can be made perfect enough • At grazing angles, mirrors that are diffraction limited at UV are also diffraction limited at X-ray wavelengths • Long and Skinny • Bundled in Pairs to act as “Thin Lens” • Thermal/mechanical Stability appropriate to > l/100.
Technical Components: Arrays of Optics • Baselines of > 100 m required for angular resolution. • Formation flying a must for distance >~20 m. • Miniaturization of ALL satellite subsystems to ease access to space. • S/C Control to 10 mm- using “periscope” configuration (metrology to better than 1 mm). • A system spanning from metrology to propulsion • Individual optic modules are thin lenses with HUGE fields of view
Technical Components: The detector • In Silicon, the minimum X-ray event size is ~1 mm • Large CCD arrays possible with fast readout of small regions. • Pixel size determines the focal length of the interferometer F~s/qres • 10 mm pixels -> Focal lengths of 100s to 1000s of km. • Formation Flying Necessary • Huge Depth of focus loosens longitudinal control (meters) • Large array sizes loosen lateral control (inches). • High angular resolution requirement to resolve a black hole: The Line-Of-Sight Requirement.
Technical Components: Line-of-Sight • We must know where this telescope points to 10s-100s of nanoarcseconds • Required for ALL microarcsecond imagers • The individual components need an ACS system good to only arcseconds (they are thin lenses) • We only ask for relative stability of the LOS- not absolute astrometry • This is the largest technical hurdle for MAXIM- particularly as the formation flying tolerance has been increased to microns
Using a “Super Startracker” to align two spacecraft to a target. In the simplest concept, a Super Star Tracker Sees both Reference stars and a beacon on the other space craft. It should be able to track relative drift between the reference and the beacon to 30 microarcseconds- in the case of MAXIM Pathfinder. For a number of reasons (proper motion, aberration of light, faintness of stars,…) an inertial reference may be more appropriate than guiding on stars. The inertial reference has to be stable at a fraction of the angular resolution for hours to a day. This would require an extremely stable gyroscope (eg GP-B, superfluid gyroscopes, atomic interferometer gyroscopes). o dX The basic procedure here, is to align three points (the detector, the optics, and the target) so they form a straight line with “kinks” less than the angular resolution. The detector and the optics behave as thin lenses- and we are basically insensitive to their rotations. We are sensitive to a displacement from the Line-of-Sight (eg dX). d
Options to Determine Line-Of-Sight • All options require beacons and beacon trackers to know where one s/c is relative to another. • OPTION 1: Track on guide stars • Use a good wavelength (radio, optical, x-ray) • Use a good telescope or an interferometer • OPTION 2: Use an inertial reference • Use a VERY good gyroscope or accelerometer • GP-B
Summary of Key Technical Challenges • The mirrors and their associated thermal control are not a tremendous leap away. • “Periscope” implementation loosens formation flying tolerance from nm to mm. This makes formation flying our second most challenging requirement. • Determination of the line-of-sight alignment of multiple spacecraft with our target is the most serious challenge- and MAXIM is not alone with this.
Using Stars as a Stable Reference • A diffraction limited telescope will have a PSF ~ l/D • If you get N photons, you can centroid a position to l/D / N1/2 • Nearby stars have mas and mas structure • Stars “move” so you need VERY accurate Gimbals • Parallax (stars @500 pc can move up to 40 mas in a day) • Aberration of Light (as big as 40 mas in a minute) • Stellar orbits, wobble due to planets • Other effects…
An Optical Star Tracker • A “reasonable” size telescope (<1m diam.) @ optical wavelengths will require 1012 photons to centroid to 0.1 mas. • Practical limits on centroiding (1/1000) will need large F numbers • Lack of bright stars requires complicated gimbals to find guide stars • HST would barely squeak by with 15th mag stars
MAXIM Pathfinder Overview http://maxim.gsfc.nasa.gov • Objectives • Demonstrate X-ray interferometry in space as pathfinder to full up MAXIM • Image with 100 micro-arc second resolution using a 1-2 m baseline • 1000 times improvement on Chandra • Coronae of nearby stars • Jets from black holes • Accretion disks • Two spacecraft flying in formation: • Telescope spacecraft with all the optics • 300 micro arc sec pointing control • 30 micro arc sec knowledge • “Detector spacecraft” positioned 50-500 km 10 m and laterally aligned 2 mm from Telescope spacecraft to make fringes well matched to detector pixels • Detector and optics fit within medium class launch vehicle (e.g., Delta IV H) Detector Spacecraft L=50-500 km! Optic Spacecraft
Key Technologies for MAXIM • “Super Star Tracker” • High efficiency, reliability lasers (eg LISA ~10% efficiency, > 5year life, ~ micron wavelength, ~1 watt output power) • High precision, low drift gyroscopes (better than 1 mas/day drift eg. GP-B, superfluid gyroscopes, atomic interferometer gyroscopes ) • Thermal Mechanically Stable Telescopes (eg Quartz telescope on GP-B, ~0.1-1nm stability over ~m long structures) • Low power, light weight, ~0.1 arcsecond class star trackers (eg. N. Clark @ Langley: 2 watts, 200 gram) • formation flying sensor and initial target acquisition • Wide dynamic range propulsion (5 orders of magnitude of thrust down to ~mN) • PPTs, FEEPS, MEMS microthrusters • Light weight, flat (~2 nm figure) oblong optics.
Technologies Potentially Useful in Aligning MAXIM (“Super Startracker”) • Thermal/Mechanically stable telescopes with high speed readouts to monitor the position of formation flying s/c. • High Reliability, Efficiency Lasers (eg. LISA) • ~10% efficiency, l~ micron, ~>5 year life • High Precision/Low Drift Gyroscopes Options • GP-B superconducting gyroscope (0.3 mas/day) • “Superfluid” quantum gyroscope (R. Packard Group at Berkeley, K. Schwab at UMD- now at ~100 mas/hour with potential to go to nanoarcseconds/day) • Atomic interferometer gyroscope (now at 10s of mas/sec with potential to go to ~10 nanoarcseconds/day)
An Alternate MAXIM Approach: Normal incidence, multilayer coated, aspheric mirrors • Optics demonstrated today with 1-2 Angstrom figure • Multilayer Coatings yield narrow bandpass images in the 19-34 Angstrom range • Could be useful as elements of the prime interferometer or for alignment • Offers focusing and magnification to design • May require tighter individual element alignments and stiffer structures.
Overview • Developed new implementation of MAXIM design which offers: • Much looser formation flying tolerances (mm instead of nm) • Better coverage of the UV plane • Easier scalability • Completed a GSFC “Instrument Synthesis Analysis Lab” (ISAL) study of a “superstar tracker” to address alignment of microarcsecond class instruments • Completed a GSFC “Integrated Mission Design Center” (IMDC) study of a new MAXIM Pathfinder