# Presentation: 246640

## 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

- Capella “simulation” 1 as and 10000 sq cm

-   Calculated Image of M87  @ 0.1 as

- X-ray variability of ~1000 seconds suggests
-      that the hard emission is coming from a
-                      few Rs

## Slide 5

## A Simple X-ray Interferometer

- Flats

- Beams Cross

- Detector

- s

- L

- d

- Fringe Spacing:

-  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

## Grazing Incidence is an Advantage for X-ray Interferometry

- 1/sin for  2 degrees
- Loosens the baseline tolerances by 2 orders  of magnitude.
- -->  1-10 nm baseline tolerance.

## Laboratory Demonstration

- W. Cash *et al,*
- Nature 407
- 14 September 2000

- Experiment by CU and
- MSFC.
- 10 Angstroms
-       (1.25 keV)
- ~ 1mm Baseline
- ~100 mas
- “/20”  flat mirrors
- ~100 m optics/detector
-               distance
- X-ray CCD Detector

## Fringes at 1.25keV

- Profile Across Illuminated Region

- W. Cash *et al*
- Nature 407
- 14 September 2000

## Basic MAXIM Design

- 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.

- Fringes Form Here

- Baseline

## Original MAXIM Implementations

- MAXIM Pathfinder

- Full MAXIM- the black hole imager

- “Easy” Formation Flying (mm control)
- Optics in 1 s/c act like a thin lens

- Nanometer formation flying
- Primaries must point to milliarcseconds

- ~1-2 m Baseline

- ~500-1000 m Baseline

- ~10 m

- ~500 km

- ~10 km

- ~5000 km

## Pathfinder

- MAXIM

- Optic Spacecraft

- Detector Spacecraft

-  100as Resolution
-  Laser alignment system provides metrology between satellites.
-  Much more complicated for Full MAXIM mission

-  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

***Pathfinder***

- L=50-500 km!

## Original Full Maxim Design

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-   200 M baseline
-  Optics divided between multiple spacecraft.
-   0.1 as Angular Resolution
-  “Extreme” Formation Flying
-   Detector flown 1000s of km from optics to make fringes comparable to detector pixel sizes

## Improved MAXIM Implementation

- ~20,000 km

- Group and package Primary and Secondary Mirrors as “Periscope” Pairs

- “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.

- ~500-1000 m Baseline

**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.

## Periscopes to be placed on paraboloidal surface to achievephase closure, or we can individually adjust phase for each periscope.

- 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

- To Detector

- LOS

- X

- Roll

- Z

- Y

- Pitch

- Yaw

- Primary

- Secondary

## The “New” MAXIM Pathfinder

- 2 mission phases
- phase 1:  100 as 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 as Science
- Optics s/c separates into 7 s/c  to extend angular resolution to a few as
- 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 as and 0.1 as imaging.

## Launch Configuration

- Delta IV Heavy
- 5m X 19.1m fairing

**Delta IV**
**5m X 14.3m fairing**

- P/L Sta. 0.00

- Sta. 1550

- C.G. Sta. 2500

- Sta. 4300

- Sta. 7600

- Propulsion/Hub SpaceCraft

- Hub SpaceCraft/Detector SpaceCraft

- Propulsion/Hub SpaceCraft

**Delta IV**
**5m X 14.3m fairing**

## Mission Sequence

- Launch

- Transfer Stage

- Science Phase #1
- Low Resolution (100 as)

- 200 km

- Science Phase #2
- High Resolution
- (100 nas)

- 1 km

- 20,000 km

## Slide 23

## Slide 24

## Technical Components:  Mirror Modules

- Grazing Incidence Mirrors
- Grazing Incidence loosens our surface quality and figure requirements by 1/sin
- Flatness > 
- “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 > 

## 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 m- using “periscope” configuration (metrology to better than 1 m).
- 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 m
- Large CCD arrays possible with fast readout of small regions.
- Pixel size determines the focal length of the interferometer  F~s/res
- 10 m 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

## dX

- d

**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.

- 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).

- o

- 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).

## 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 m. 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 ~ /D
- If you get N photons, you can centroid a position to /D / N1/2
- Nearby stars have as and mas structure
- Stars “move” so you need VERY accurate Gimbals
- Parallax  (stars @500 pc can move up to 40 as in a day)
- Aberration of Light  (as big as 40 as 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 as.
- 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

- 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)

**MAXIM Pathfinder Overview**

- Optic Spacecraft

- Detector
- Spacecraft

- L=50-500 km!

**http://maxim.gsfc.nasa.gov**

## 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 as/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 ~N)
- 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, ~ micron, ~>5 year life
- High Precision/Low Drift Gyroscopes Options
-  GP-B superconducting gyroscope (0.3 as/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 as/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 (m 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