Chandra
X-ray Observatory
Astrophysics
Division
Chandra
Guaranteed Time Observer
Policy
Wilton Sanders
Chandra Program Scientist
Chandra
X-ray Observatory
Astrophysics
Division
Statement of the Issue
•
The Report of the 2010 Senior Review of the Astrophysics Division
Operating Missions noted that the Chandra Guaranteed Time Observer
(GTO) program is still in effect more than a decade after launch, and
the committee questioned whether this is appropriate “when
considering the inevitable pressures on observing time and funding that
will persist in future years.”
•
The Astrophysics Division asked the Astrophysics Subcommittee for a
recommendation whether the Chandra GTO Program should continue
as it is presently implemented, continue in some modified form, or be
discontinued.
•
The Astrophysics Subcommittee recommended “that the current GTO
policy be retained, at least until the Chandra Users Group [sic] can be
asked to review this issue.”
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Chandra
X-ray Observatory
Astrophysics
Division
Astrophysics Subcommittee Report
“… In 1994, NASA HQ stated that the GTOs would receive 15% of the
observing time after the first 20 months of operations, for ‘the remainder of
the mission lifetime.’ The fraction of GTO time became 11.4% due to
changes in the GTO program roster. The GTO policy was reviewed in
2002 and it was concluded then that ‘Chandra is best served by the
current policy,’ on the basis of the overall strength of the Chandra science
program, maintenance of the instrument engineering competencies of the
instrument principal investigators (IPI), and fairness to the IPI community.
Eliminating the GTO program at the present time raises the risk of losing
the key engineering support provided by the IPI teams at a phase of the
Chandra mission when this support is most likely to become critical. In
addition, this elimination would achieve no net savings, as the GTO time
and funds would presumably be transferred to the General Observer (GO)
community. The APS therefore recommends that the current GTO policy
be retained, at least until the Chandra Users Group can be asked to
review this issue. If the Users Group concurs, then there is no need to
change the GTO policy. If the Users Group requests a change in the GTO
policy, then the APS should revisit this issue at that time.”
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Astrophysics
Division
GTO Time – Background Details
1. Originally, the Guaranteed Time Observers (GTOs) were assigned 100% of the
observing time during months 1 and 2 (after orbital checkout), 50% of the time
during months 3-20, and 20% of the time during months 21-30.
Chandra
X-ray Observatory
Source: Chandra AO (AO No. OSSA-3-83).
2. Prior to the launch of Chandra, to get more data to General Observers (GOs)
sooner, NASA HQ initiated a change to these numbers. Chandra IPI teams agreed
to receive less up-front GTO data in exchange for a longer guaranteed time:
GTOs, were granted, as a group, 100% of the data obtained during months 1 and
2 of operation, 30% during months 3-20, and 15% "the remainder of the mission
lifetime”.
Source: Advanced X-Ray Astrophysics Facility (AXAF) Level I Policy and Requirements
Document signed by the Associate Administrator Wesley T. Huntress (4/20/1994).
3. The percentage of time was reduced to 11.4 % as a consequence of the means by
which the Interdisciplinary Scientists (IDSs) received their time and subsequent to
the death of the Telescope Scientist, Leon Van Speybroeck.
Source: AXAF Observing Policy TA21 (96-048) signed by Alan Bunner and Martin C.
Weisskopf and decision made upon Leon's demise.
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Astrophysics
Division
HQ Review of Chandra GTO, 2002
Chandra
X-ray Observatory
Status (2002):
• 15% of observing time [now 11.5%] is allotted to GTOs for duration of mission.
• GTOs are guaranteed time and funding but not targets; they must compete with
GOs in the peer review for targets.
• GTO time is used for instrument sustaining engineering by IPI teams
• Instrument expertise resides in IPI teams not in the CXC
Fairness Issue:
• NASA agreed to this arrangement after requiring IPIs to give up the time they
were promised by the AXAF instrument AO.
• GTO programs were structured under the assumption of continuing GTO time.
Risk to Observatory:
• Without GTO time, IPI teams cannot continue sustaining engineering by pushing
instrument performance to the limits.
• Without GTO time, IPI teams cannot maintain core competency for solving
instrument problems through life of observatory.
• There is programmatic impact to changing the currently successful arrangement;
this impact includes increased risk and increased cost in exchange for some
increased GO time.
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Astrophysics
Division
HQ Review of Chandra GTO, 2002
Value to current observatory success
Chandra
X-ray Observatory
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Use of GTO time. Some GTO time is being used to push the instrument into
observing regimes that are scientifically risky but yield valuable data on
instrument performance, potentially extend range of instrument (e.g. grating
spectroscopy of extended sources). This time might not pass peer review. It is
not part of the minimum calibration program, yet is part of the GTO side of the
bargain and has benefited the Observatory
Use of GTO time. Some GTO time is used for additional calibration and
instrument insight. This includes trend analysis. This is not always included in
calibration time.
IPI teams support mission through continuing engineering and calibration.
Examples include timing problems with HRC and contamination problems with
ACIS. These functions are not totally provided by either the CXC or Project
Science. Arguably only the instrument specialists are best qualified to provide
these functions.
IPI teams are motivated to provide calibration, optimize science, push
instruments to limits. This requires a critical mass on the team; a single
scientists or two is not enough.
Guaranteed observing time (and the associated stable data analysis funding) is
required to attract and keep qualified scientists on the IPI teams. This is
necessary to maintain the required mix of people on the teams.
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Astrophysics
Division
HQ Review of Chandra GTO, 2002
Value to future observatory success
•
Chandra
X-ray Observatory
•
•
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Instrument problems are expected to increase in the extended mission. It is a
tactical error to weaken the ability to deal with these problems. The ability to
deal with these problems is not captured by the mix of skills developed at the
CXC and Project Science. The IPI teams are required.
As the observatory ages, critical skills will be needed to overcome problems.
Much corporate memory resides on IPI teams, especially in scientists since they
are longer-term employees than engineers because of the GTO rights. It will be
difficult if not impossible to bring new people in to solve problems during the
extended mission.
The Chandra GTO policies may be the best way to preserve observatory
capabilities for the long run. Alternative is to capture expertise in the science
center (e.g. HST, SOFIA) that de-facto is inefficient or to suffer through continual
observatory problems and decreased science return (e.g. ESA missions). This
efficiency allows Chandra to be operated at a lower cost.
There will be programmatic impact to such a change. The benefits to instrument
and observatory sustaining engineering, which are currently accomplished by
the IPI teams using their GTO time, will either need to be undertaken by the
CXC, undertaken during an increased calibration time allotment, or eliminated in
exchange for increased risk and decreasing capability.
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HQ Review of Chandra GTO, 2002
Chandra
X-ray Observatory
Astrophysics
Division
8
GTO Observing Time and Costs
• GTO observing time is 2.45 Ms for 3.5 teams (FY2011)
• $5M GTO funding for 3 US instrument PI (IPI) teams: $2.3M for
GTO science, $2.7M for engineering (2011)
• To date, IPI teams plus IDS have received $39M for GTO
Science, and $35M for instrument engineering support
• Table below gives GTO Observing Time for the four IPI teams,
the Telescope Scientist (TS), and Interdisciplinary Scientists
(IDS), & GTO Funding by fiscal year
Chandra
X-ray Observatory
Astrophysics
Division
9
Astrophysics
Division
Project’s Concern
• On some teams, only 1/2 FTE for key individuals is paid by
instrument engineering. The GTO funding is used to support the
other half. Core competencies may be at risk if funds cannot be
found to cover these people.
Chandra
X-ray Observatory
• If the GTO program goes away, some of the key scientists that
also provide engineering support may move on to other projects
and no longer be available to Chandra. The engineering support
is totally independent of the science effort.
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Astrophysics
Division
Comparison to other Great Observatories
Chandra
X-ray Observatory
• The US Chandra IPI teams have received through FY2010 (11
years) an average of $12.3M GTO funding support each.The US
Chandra IPI teams have received through FY2010 an average of
8.8 Ms of observing time each.
• The HST COS instrument PI receives over three years 553 HST
orbits of observing time, ~ 2 Ms, and ~ $10M in funding support.
The IPI receives targets before the GOs, and provides little or no
engineering support. STScI maintains engineering expertise.
• Spitzer IPI teams each received $11M GTO funding over 5.5
years, $40M total including SWG, and $11M total for engineering
support. Each IPI team received 1875 hours of observing time,
~6 Ms, and the SWG ~ 3 Ms.
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Astrophysics
Division
Chandra GTO Process
Chandra
X-ray Observatory
• GTOs can use any of the Chandra instruments for their GTO
time. GTOs are guaranteed to receive their observing time, but
cannot reserve targets in advance of the Call for Proposals.
• GTOs submit observing requests before the General Observers
(GO) proposal deadline.
• After the GO proposals are received, GO-GTO conflicts are
identified. GTOs are informed of the existence of a conflict, and
may either (i) replace a conflicted target with an non-conflicted
backup target, or (ii) write a proposal that is evaluated (“blind”) by
the peer review process in competition with the GO proposals.
• GTOs do not reserve targets to the exclusion of the GOs, rather,
the GOs get first choice.
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Astrophysics
Division
GTO Science Productivity
Chandra
X-ray Observatory
• At least 22.6% (944 of 4,182) of Chandra’s refereed papers
based on GTO data using 15% of the observing time over
duration of mission to date
• Important technical contributions to the program, e.g., ACIS CTI
corrector, ACIS pileup models, image reconstruction techniques,
catalog development (e.g., TGCat)
• Conceive observation types and instrument modes that optimize
or expand instrumental capabilities and validate feasibility of
“high risk” observations
• GTO science includes high value programs difficult to propose
to peer review such as monitoring of Sgr A*, M31 core, and
SNR 1987A, long grating observations of relatively faint AGN,
and large contiguous surveys (XBootes)
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Chandra
X-ray Observatory
Astrophysics
Division
Summary of Reasons to Continue GTO
• The current arrangement was signed-off pre-launch, and was
reviewed by NASA HQ three years after launch and found to be
still appropriate.
• The current Chandra GTO Program is scientifically highly
productive in terms of papers published, innovative data analysis,
and high-risk/high-reward projects undertaken.
• GTO targets are fairly competed.
• No money is saved by eliminating the GTO Program. The
instrument engineering support provided would still be required.
The observing time currently allocated to the GTOs would revert to
the GO time allocation, which would then require additional GO
funding.
• The GTO time and funding model is commensurate with that of
other Great Observatories.
• Potential unintended consequences include loss of core personnel.
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Astrophysics
Division
Summary Question
Chandra
X-ray Observatory
Is the 11.4% observing time allocation to the GTO teams the right
price to pay for optimizing the probability for sustaining
instruments in their most difficult phase (beyond 10 years)?
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Backup
Chandra
X-ray Observatory
Astrophysics
Division
16
Chandra GTO Time & Dollars
Chandra
X-ray Observatory
Astrophysics
Division
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Spitzer GTO Time
Chandra
X-ray Observatory
Astrophysics
Division
Each of the four GTO teams was awarded 5% of the observing time for the first 2.5
years of the mission (the level 1 requirement for mission length). The SWG time
was divided evenly between the 9 SWG members. After 2.5 years, the three
instrument teams (not the SWG) continued to receive 5% of the observing time
for the life of the cryogenic mission (5.5 years). There is no guaranteed time in
the warm mission.
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Chandra
X-ray Observatory
Astrophysics
Division
Spitzer GTO Engineering Support
In addition to their science data analysis funding, the three original Instrument
Teams, plus Ball Aerospace, were provided limited funding for engineering
support. Engineering support continues for the IRAC team during the warm
mission.
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