MAXIM Pathfinder

1
MAXIM Pathfinder

• Keith Gendreau, Webster Cash,
• Ann Shipley, and Nick White

2
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

3
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
4
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 _at_ 0.1 mas
Capella simulation 1 mas and 10000 sq cm
5
(No Transcript)
6
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
7
Grazing Incidence is an Advantage for X-ray
Interferometry
1/sinq for 2 degrees Loosens the baseline
tolerances by 2 orders of magnitude. --gt 1-10
nm baseline tolerance.
8
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
9
Fringes at 1.25keV
W. Cash et al Nature 407 14 September 2000
Profile Across Illuminated Region
10
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.
11
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
12
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

L50-500 km!
Detector Spacecraft

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

Optic Spacecraft
13
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
14
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.
15
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.

16
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.
17
Rotating a thin lens does not change the position
of the focus.
Nor will the periscope approximation.
18
Periscope Module Optics Layout
LOS
Primary
Secondary
Y
Pitch
Yaw
Z
Roll
X
LOS
To Detector
19
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
  

20
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.

21
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
22
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
23
(No Transcript)
24
(No Transcript)
25
Technical Components Mirror Modules

• Grazing Incidence Mirrors
• Grazing Incidence loosens our surface quality and
  figure requirements by 1/sinq
• Flatness gt 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 gt
  l/100.

26
Technical Components Arrays of Optics

• Baselines of gt 100 m required for angular
  resolution.
• Formation flying a must for distance gt20 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

27
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 Fs/qres
• 10 mm pixels -gt 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.

28
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

29
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
30
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

31
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.

32
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 _at_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

33
An Optical Star Tracker

• A reasonable size telescope (lt1m diam.) _at_
  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

34
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
L50-500 km!
Optic Spacecraft
35
Key Technologies for MAXIM

• Super Star Tracker
• High efficiency, reliability lasers (eg LISA 10
  efficiency, gt 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 _at_ 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.

36
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, gt5 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)

37
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.

38
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