MAXIM Pathfinder IMDC Study

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MAXIM Pathfinder IMDC Study

• 13 May 2002

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Science Team

• Keith Gendreau Code 662 GSFC
• Webster Cash University of Colorado
• Ann Shipley University of Colorado

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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
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But, to resolve the event horizon of a black
hole, you need more
A Star like Capella is A few mas across..
But the event horizon for the black hole in M87
is only a few mas across.
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Full Maxim Design
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• 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

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The New MAXIM Pathfinder

• 2 mission modes
• mode 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
• mode 2 1 mas Science
• Adds N s/c to extend angular resolution to a
  few mas
• Tougher Formation Flying tolerances
• Tougher Line-Of-Sight Requirements
• Get a Glimpse of a Black Hole Event Horizon!
• Optimize Full MAXIM mission
• Design to accomplish all mode 1 science with
  capability to explore mode 2 science

N2
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Mode 1
5cm control /-15 mm Knowledge
200 km /- 5 m

• Detector S/C
• 320 kg (instbus est.)
• 400 watts (instbus est.)
• Pitch, Yaw, Roll control to 0.5 - 1 arcminutes
• Pitch, Yaw, Roll Knowledge to arcseconds
• Line-of-Sight Control to 5 cm

• Optics Hub S/C
• 600 kg (instbus est.)
• 200 watts (instbus est.)
• Pitch, Yaw, control to 1 arcsecond (TBR)
• Roll control to arcminutes
• Pitch, Yaw, Roll Knowledge to /- 1 arcsecond

• Target Science
• Stars
• Separate AGN Jets from Disks
• Neutron Stars
• SNR
• Other 100 mas science targets

• Formation Flying Challenges
• Range control to 10 meters, knowledge to cm
• LOS Control to inches (detector size)
• LOS to target knowledge to 30 mas (30 microns _at_
  200 km)
• 10 degree slews every 1-2 weeks. (100 targets
  in 2 years)

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Mode 2

• Optics Hub S/C
• Activate metrology system to freeflyer
  spacecrafts

5cm control /-15 mm Knowledge
20,000 km /- 5 m

• Detector S/C

100-500 m Control to 10 microns

• Target Science
• Event Horizons
• Separate AGN Jets from Disks
• Neutron Stars
• Other 1 mas science targets

2 arcsec

• FreeFlyer S/C
• 150 kg (instbus est.)
• 100 watts (instbus est.)
• Pitch, Yaw control to 1 arcsecond
• Pitch, Yaw Knowledge to arcseconds
• Roll Control to 1 arcsec.

• New Formation Flying Challenges
• LOS to target knowledge to 0.1 mas (15 microns
  _at_ 20,000 km)
• 10 degree slews every 1-2 months. (5 targets
  in 1 year)

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Mode 2

• Optics Hub S/C
• Activate metrology system to freeflyer
  spacecrafts

5cm control /-15 mm Knowledge
20,000 km /- 5 m

• Detector S/C

2 arcsec

• The array of optics spacecrafts
• These fly in a virtual plane that is normal to
  the Line-of-Sight to within 2 arcseconds
• How many can we fly without needing a second
  launch vehicle?

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Some Typical Numbers
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Optics Hub Spacecraft
71 Modules in a 4m Diameter (shrink as necessary)
Each Module has 2 30cm long optics 0.7
cm2/Module 5.4 kg/Module Total Module Mass 383
kg Total Effective Area 50 cm2
Thickness of assembly 1 m
Additional mass terms structure, Beacon, star
tracker, s/c bus. 180 kg??? Optics s/c
comes to about 600 kg now
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What would one of these modules look like?
msin(g)
msin(g)
m
m/3 msin(g)
3/2md
2(wgap)msin(g) By 2(wgap)msin(g)m/3actuator
encoder ASSUME wgap5 cm Encoderencoder5cm S
in(g)1/30 --(10cmm/30)x(15cmm/3m/30) --m30
cm- 13cmx26cm
m/6
Gapmsin(g)
Pitch Control
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Optics Hub Spacecraft
Total Mass 600 kg ACS Control Pitch, Yaw 1
arcsec Roll 1 arcminute ACS Knowledge
Pitch, Raw, Roll 1 arcsecond Payload Power
Requirements ( to be refined) Mirror
Heaters 2 watts/module- 160 Watts Beacons
Metrology 100 Watts
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Detector Spacecraft
Prime Instrument X-ray CCD 100 kg 50
Watts Wants to be in temperature range of -130
to -90 C Precision Line-Of-Sight Alignment
Instrument Super Star Tracker (ISAL) -120 kg
0.5m diam x 2 meter tall -250
watts -cryocoolers need ways to dump power at
room temp and 100 K Science Telemetry 5
kbits/s TOTAL Science Payload Mass 220 kg TOTAL
Science Payload Power 300 watts ACS
Requirements pitch,yaw,roll control to 1
arcminute (knowldege 1 arcsecond)
Line-Of-Sight control to 5 cm.
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CCD Camera
40cm
This side looks to optics hub s/c
40cm
1 m
50 kg
30cm
30cm
30cm
50 kg
To Radiator to unload heat from CCD. (900 cm2
area _at_-90 to -130)
30cm
Electronics Box for CCD
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Detector S/C
Line of Sight (LOS) Instrument Beacon Tracker
and Superconducting Gyroscope Insert. (0.5 m
diam x 2 m long) Will need radiators (Mike
Dipirro)
CCD Camera And Electronics. Maybe share a
radiator With the LOS instrument?
S/C bus
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FreeFlyer Spacecraft

• In Mode 2, we will use extra optical spacecraft
  to extend baselines to 100s of meters..
• 1m diam x 1 m long pill box
• 45 kg payload
• How many can we add before needing a new launch
  vehicle?
• 10 watts power (for heater and beacon system)
• ACS
• Pitch, Yaw, Roll control to arcseconds
• Translation control to 10 mm
• Integrated with BALL swarm sensor.

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FreeFlyer Spacecraft
8 Mirror Modules (5 cm2)
1m
This Side points toward Optics Hub S/C.
1m
How much can we exploit miniature component
technologies for nano and micro sats?
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What we want.

• This is a 2015 mission. Are we right?
• Cost estimate
• Refinement of mission profile (eg orbit analysis,
  )
• Identification of required Miracles and
  performance drivers
• Nice figures
• We will be back- but hopefully starting at a
  better position.

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Extensions

• My guestimate of the total masses suggest that
  all three s/c total to 1100 kg. I suspect that
  there is more capacity in the Delta III (maybe
  2500 kg?). If so, how many more free flyers can
  we put on?
• As with many of these distant missions, I wonder
  why we design a mission going 15 years from now
  to use present, off-the-shelf technology
• Eg. Solar concentrators.

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Backup Slides
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Designing a Mission 2
What angular resolution at what wavelength do you
want? qres, l
Tightest Formation Flying Tolerance between
optics s/c s. Lateral
What is the smallest X-ray pixel size(mm) you can
imagine? s
The Difference Here is That we will have fringes
10x bigger than the CCD pixel Size.
The baseline (2B) needs to be 2B l/ qres
The Focal Length (F) needs to be F 10 s/qres
Longitudal Formation Flying Tolerance between
optics s/c 80 (s/l)2 qresB
The FOV will be FOV 80 (s/l)2 qres
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Mirror Module Dimensions

• The Mirror modules are pairs of flat (better than
  l/100) mirrors.
• One mirror is fixed, the other has pitch (mas)
  and yaw (arcminute) control.
• The module also has the ability to adjust the
  spacing of the mirrors at the nm level to
  introduce angstrom pathlength control.
• Thermal control consistent to maintain optical
  figure (0.1 degrees).
• There is structure to hold the module together.

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Actuator Requirements
The pitch control should be to the some fraction
of the diffraction spot size. dql/(msin(g))30l
/m 6 mas for m100 cm, 62 mas for
m10cm 30 nm of control for any size
mirror The range of pitch control should be able
to accommodate the range of baselines over the
range of focal lengths. qmax B/F l/(20s)
1 arcsecond of range 5x10-6m of
linear range for a mirror of length m. where
sCCD pixel size
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In 1-D we have 3 unknowns ?d,???o, dx But
laser interferometers Only give us 2
measurements Dred, and Dgreen
Two Laser interferometers can make the two
spacecrafts virtually rigid- but we still need a
tie-in to the celestial sphere- we still need a
star tracker.
Interference pattern from optics space craft
laser interferometer? Dred
?o
dX
Interference Pattern from Detector Space craft
laser interferometer? Dgreen
?d
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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
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Sizing the Laser Beacon for LOS
Size of Footprint of laserp(l/LF)2 Fractional
coverage of tracker area pD2/4/
p(l/LF)2 (DL)2/(2Fl)2 Number of Photons/sec
into tracker (DL)2/(2Fl)2W12.5x1018photons/s
3x1014xL2xW photons/sec L in meters, W in output
laser power. LISA Laser power efficiency10 NOTE
The LASER DIVERGANCE MIGHT DRIVE THE PITCH AND
YAW CONTROL ON THE HUB to A FEW 1/10s of an arc
second!!!
1 Watt 6.25x1018 eV/s 620 nm 0.5 eV Laser _at_
620 nm 12.5x1018photons/sec Aperture of SST
Beacon Tracker D 125 mm Laser Beam Expander
Diameter L or so Distance from Laser To Tracker F 2x107
m MAX Required accuracy of LOSq10-7arcseconds Te
lescope is good to 1 arcsecond Required number
of Photons to get to accuracy N(1 arcsec/q)2
1014
OPTICS HUB
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Option 2 Gravity Probe-B-Like

• Telescope only centroids on beacon
• Gyro provides inertial reference frame
• Advantages
• Gyros exist!! 1/3 micro arc sec/day
• No need to find stars
• Just a beacon tracker telescope
• Cryo-cooler TRL 5 by 2005 (2-5M for
  cryo-cooler (flight model only), FM EM 3 to 7
  million, mass about 20kg
• Launches on Con-X 2010
• Gyro was to launch this year (Oct 2002)
• 10-100M for both cooler gyro
• Disadvantages
• Must know aberration Delta-V to 3cm/sec (Landis
  checks)
• GP-B expensive
• Cryogen or coolers/vibrations

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Option 2 Gravity Probe-B-Like (cont.)

• Deltas on GP-B
• Since 1/3 micro arc sec /day is not required,
  then we may be able to back off on this
  capability
• Cryo-coolers mean normal conductivity launching
• If negligible magnetic field _at_ L2, simplifies
  magnetic shielding design
• Requirements on magnets in s/c
• Neutralize cosmic-ray charging
• Respinning up gyro? (dynamic range)
• Cryo getters less important?
• Proof mass? Yes-maybe
• Squids will be better
• Venting vs. cooler mechanism
• Mass, power,size,cost,other reqts
  (mag,jitter,thermal)
• Need to integrate over 10 sec you get
  10E-13radians????
• ConX, NGST Cooler specs 150W BOL, 250W EOL, 10
  yr lifetime, 20-30kg include electronics, heat
  syncs 1_at_100K, 1_at_room temp, produces 7.5mWatts 6K
• Selection in March 2002
• Cryo cooler mating to Adiabatic Demagnetization
  Refrigerator (ADR) starts in 2005. Temperature 2
  K or less. Estimate 30 watts.

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Super Star Tracker Beacon System
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Thermal
Meeting a pointing requirement of 30 micro arc
sec requires extreme structural stability between
the attitude sensor and the instrument. Mounting
the attitude sensor and the instrument to the
same platform would help accomplish this in any
case, the interfaces must be extremely rigid to
prevent drift. In addition, temperatures must be
tightly controlled to maintain dimensional
stability, even with structural materials having
a very low coefficient of thermal expansion
(CTE).   Allowable temperature difference was
calculated as follows   1. Assume a perfectly
rigid structure. 2. Assume the best structural
material currently available (M55J composite,
with a CTE 10-7 per oC)   Since (sin 30 micro
arc sec) is 1.5 x 10-10, this represents the
distortion limit. The temperature change
producing this error is (1.5 x 10-10) / (10-7)
1.5mK   Developing a lower CTE structural
material should be a high research
priority!   Otherwise, temperature control must
be to about 0.1mK, which has been done only in
labs on very small sample volumes. Control to 1mK
has been achieved on space instruments, but again
in small volumes. This is another area requiring
a technology upgrade.
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Detectors
Note Mass is 4 kg for 2 detectors