STUDY SUMMARY - IPMU

SUMMARY REPORT
WIDE FIELD FIBER-FED OPTICAL
MULTI-OBJECT SPECTROMETER (WFMOS)
ID
1
2
3
4
5
6
7
Table 7.4-1: Summary of Risk Assessment and Management
Item
Custom detectors don't meet
performance requirement
schedule risk on the spectrograph
gratings
The square wave drive approach
does not adequately drive the
positioner motors.
Positioner resolution too high or
velocity versus position and/or step
size too erratic.
Telescope environment not as
expected and affects instrument
performance
Positioner contractor unable to
perform
Spectrograph Aspherics difficult to
manufacture
2 4
3 2
2 3
2 2
2 2
1 2
1 2
Likelihood
Consequence
Mitigation
Change to a 6k×4k format from Hamamatsu with
15µm pixels
Start testing w/ one grating or early low-spec grating.
Consider Kaiser Optics as a second supplier
Work w/ NST to modify motor design. Return to the
sine wave drive and switching network - size growth
could exceed envelope
Enhanced positioner learning algortihm, Design
modifications after EM characterization
Early (design phase) test and/or characterization of
telescope environment and interfaces
JPL support to New Scale w/ engineering, facilities,
other resources.
consider multiple vendors, manage aggressively, block
off out of spec areas
Table 7.4-1 presents the current risks. The probability of occurrence is indicated by the likelihood
rating. A short description of the risk and the mitigation plan is provided below.
1. The square wave drive approach does not adequately drive the positioner motors. Proper
packaging design and techniques are necessary to make the 2.5-volt signals from the
FPGA compatible with the 120-volt square wave out of the drivers. Testing will be
performed to ensure noise and crosstalk issues are addressed. An electronics design that
utilizes sine wave drive signals, increases isolation, and increases packaging volume of
the electronics. If the noise and crosstalk cannot be minimized, the existing motor
electronics design from NST may be repackaged as a third option.
2. Positioner Resolution too high or velocity vs. position and/or step size erratic. The
current time allocation for repositioning fibers to a new target within 5 µm is 80 s. The
completed positioner bench test indicates reposition can actually be done in 40 sec;
however, the unknown of the consistency among positioners as well as any unpredicted
errors when integrating the full system prevents retiring this risk completely. The current
risk assessment represents growth in timeline. Modest design modifications and/or
enhanced positioner software algorithms will be employed if needed after early testing
with the positioner module EM.
3. Custom detectors do not meet performance requirement. The baseline design has custom
detectors from LBL with custom coatings from JPL. The CCD and coating designs are
not risky since they will be assembled from proven components and processes, however,
this is dependent on a single resource at LBL. An alternate supplier (Hamamatsu) has
been identified in case LBL withdraws for any reason. The penalty will be higher cost
and lower sensitivity in the blue and extreme red.
4. Telescope environment not as expected and affects instrument performance. Additional
information on the thermal and dynamic environment of the telescope may reveal the
stability of the coupled system of the telescope and instrument does not meet
performance requirements. Mitigation is early acquisition of additional data on the
80