TESS Commissioning Plan
TESS-EXP-MKI-XXXX-NNNN, 37-15020, Rev 01
Table of Contents
1 Introduction .................................................................................................................. 2
1.1
1.2
1.3
Purpose & Scope ................................................................................................................ 2
Document Organization.................................................................................................. 2
Reference Documents ..................................................................................................... 2
2 Mission Overview ........................................................................................................ 2
3 Commissioning Overview ......................................................................................... 3
3.1
3.2
Goals of Commissioning.................................................................................................. 4
Basic Commissioning Timeline .................................................................................... 4
4 Commissioning Tasks ................................................................................................ 5
4.1
4.2
4.3
4.4
4.5
4.6
Instrument Checkout ....................................................................................................... 5
Instrument Thermal Performance ............................................................................. 5
Camera Orientation.......................................................................................................... 6
Fine Pointing....................................................................................................................... 6
Calibration Data ................................................................................................................ 7
Operational Parameters ................................................................................................. 7
5 Commissioning-in-a-Life .......................................................................................... 8
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
Days 1-5: Orbit 1 ............................................................................................................... 8
Day 5: Perigee 1 ................................................................................................................ 8
Days 5-14: Orbit 2 ............................................................................................................ 8
Day 14: Perigee 2 ............................................................................................................. 8
Days 14-24: Orbit 3.......................................................................................................... 9
Day 24: Perigee 3 ............................................................................................................. 9
Days 24-42: Orbit 4.......................................................................................................... 9
Day 42: Perigee 4 .......................................................................................................... 10
Days 42-56: Orbit 5....................................................................................................... 10
Day 56: Perigee 5 ........................................................................................................ 10
Days 56-70: Orbit 6 .................................................................................................... 10
6 List of Open Items and/or TBD/TBRs ............................................................... 10
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Introduction
The commissioning of the TESS spacecraft and instruments occurs during the sixty (60)
days following launch. In this period, the spacecraft and instrument are checked out, and
key instrument calibration parameters are measured in the flight environment.
1.1 Purpose & Scope
This document describes the goals, methods, and timing of instrument commissioning.
1.2 Document Organization
A mission overview is presented in Section 2 to provide context for the commissioning
activities. An overview of the basic goals of the commissioning period, including a timeline
for commissioning operations, is given in Section 3. Subsequent sections describe the
commissioning tasks in more detail. A set of detailed Commissioning Test Procedures is
included as an Appendix: this appendix may split off into a stand-alone document.
1.3 Reference Documents
This following list of reference documents is relevant to the discussion of the TESS POC
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2
Mission Requirements Document
SOC requirements
POC requirements
SPOC requirements
POC-SPOC ICD
Operations ICD
Mission Overview
The Transiting Exoplanet Survey Satellite is designed to detect the presence of exoplanets
by monitoring the brightnesses of hundreds of thousands of stars distributed over the
celestial sphere. The brightness of each star is measured every two minutes for periods
ranging from 27 days to one year: the resulting data are reduced and calibrated to form
light curves, and the light curves are examined for evidence of periodic decreases in
brightness, the signature of a transiting planet.
The TESS instrument consists of four wide-field (24° square) CCD cameras. The four
cameras are arranged in a 4x1 array and oriented along a line of ecliptic longitude, with one
camera near the ecliptic and the pole-most camera centered on an ecliptic pole. The primary
data collected during these observations is a set of pixel subarrays (“postage stamps”)
centered on the locations of up to 15,000 target stars. The postage stamps have an effective
exposure time of two minutes. In addition to postage stamps, full-frame images (FFIs) with
an effective exposure time of 30 minutes are accumulated on board.
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Figure 1: Sky coverage of TESS observations over a two-year mission.
TESS observations of the target stars are quantized in units of the orbital period, which is
nominally 13.7 days. Each “observation sector” – – a north-south oriented strip of the sky
measuring 24°x96° – – is monitored for two orbits, or ~27 days. Once observations of one
sector are complete, the instrument FOV is shifted ~27° eastward, and a new observation
sector is observed for 27 days. One ecliptic hemisphere is covered during the first year of
the mission, the other during the second. For thermal stability, the observation sectors are
oriented in the antisolar direction. Figure Figure 1 shows the resulting sky coverage,
including regions of overlap between contiguous sectors.
Data are collected over the period of an orbit and downlinked at perigee. The data are
compressed and CCSDS-encoded and fed to a 100 Mbps transmitter for downlink to one of
three DSN stations. The compressed data set is retrieved from DSN, then decoded and
uncompressed. A complete set of data taken during an observation sector is accumulated
over two orbits. The resulting data are sent to the Science Processing Operations Center
(SPOC), where they are calibrated, reduced, and analyzed for the presence of transiting
planets.
3
Commissioning Overview
TESS commissioning occurs during the 60 days after launch. In this period, the flight
instruments will be activated and checked for nominal performance. Subsequently,
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instrument performance features critical to flight operations and proper data reduction will
be measured.
3.1 Goals of Commissioning
The goals of the commissioning period are
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Instrument checkout
Evaluation of instrument thermal performance on orbit
Calibration of intra-camera pointing in the flight environment
Tuning of parameters used in ACS fine-pointing mode
Collection of calibration data required for data reduction
Collection of data used in operations planning
Each of these goals is discussed in detail, below.
3.2 Basic Commissioning Timeline
The sixty days following launch are allocated to observatory commissioning. During these
60 days, TESS will be put into its final orbit through a series of timed burns. The orbital
radius as a function of time is shown in Figure 2.
Because instrument data can only be downlinked at perigee, the commissioning period is
broken up into four TBR periods during which calibration data can be collected or
procedures practiced. Because the commands for the first science orbit will be uplinked at
the final perigee, no data downlinked at that perigee (and collected in the previous orbit)
shall be critical to the flight operations during the first science orbit.
A detailed Commissioning timeline is described in Section Error! Reference source not
found..
Figure 2: Orbital radius as a function of time (Figure is old and needs updating)
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Commissioning Tasks
The following sections describe the commissioning tasks in more detail. Many of the tasks
are performed by collecting FFIs on orbit and analyzing them on the ground. Because one
FFI can be used in multiple measurements, procedures involving FFIs do not have to be
performed sequentially.
4.1 Instrument Checkout
Instrument checkout consists of the running of a series of short-form and long-form tests,
then comparing the results with values measured on the ground. Once all short- and longform tests have been completed and passed, the instrument is ready for calibration. Failed
short- or long-form tests will require special diagnostic operations.
Short-form tests require ~15 minutes in ground testing, and long-form tests ~1 hour. TBD
is how such tests can be run during LAHO passes.
4.1.1 Short-Form Tests
The short-form tests include TBR
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SF-1:
SF-2:
SF-3:
SF-4:
Power on and voltage checks
HK checks
Instrument clocking and voltage checks
FFI generation
A subset of these tests must be performed while the spacecraft is in contact with the
ground, i.e. in real time.
4.1.2 Long-Form Tests
The long-form tests include TBD
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LF-1:
LF-2:
4.1.3 Diagnostic Procedures
In case of errors in the basic checkout, certain diagnostic procedures can be run:
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DP-1:
DP-2:
4.2 Instrument Thermal Performance
Thermal stability is important to photometric stability on TESS. While ground postprocessing can remove a large fraction of the systematic error due to temperature
variations, a thermally-stable spacecraft will lead to an overall lower systematic error
contribution.
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The thermal performance procedures are intended to help characterize the thermal balance
of the spacecraft and cameras. High-fidelity simulations of thermal performance will allow
initial values of thermal control parameters to be estimated; the on-orbit thermal balance
testing will confirm these values and suggest possible changes to them.
Preliminary analyses of the spacecraft thermal model indicate that the initial cool-down of
the spacecraft will require ~3 days, and the recovery from a thermal transient ~2 days.
4.2.1 Thermal Performance Procedures
The thermal performance measurement procedures are TBD.
4.3 Camera Orientation
A precise understanding of the relative orientations of the four cameras and their
orientation with respect to the spacecraft coordinate system is critical for
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Fine pointing stability
Target definition
Ground processing of flight data
These values are estimated before launch, based on the mechanical design of the
instrument, but an on-orbit measurement is required to achieve the required measurement
accuracy.
4.3.1 Camera Orientation Measurements
The absolute camera orientation and the relative orientation of the cameras are measured
using a set of FFIs taken on orbit. The FFIs will be taken over multiple points in the orbit to
improve the precision of the measurement and to measure predicted temporal variations
(due to thermal effects and DVA). As the FFIs will be taken over the entire orbit, they will
reflect the variations in the thermal environment of the observatory.
The analysis of the FFIs is performed using the Focal Plane Geometry (FPG) tool. FPG can
measure the absolute pointing of each camera, using a detailed knowledge of the camera
distortions, and can account for effect such as DVA.
4.4 Fine Pointing
The precision of ACS fine pointing is dependent on the precision of measurement of the
absolute (TBR relative) orientation of each camera in the spacecraft coordinate system. The
quaternions relating the camera frames of reference are collected using the procedures
described in Section 4.3. The correlation of these reference frames with the spacecraft
coordinate system is calculated by comparing each camera’s attitude with the attitude
measured by the spacecraft star trackers. Because the precision of the star trackers is less
than required for fine pointing, a cycle of “tuning” the ACS is required.
4.4.1 Fine Pointing Calibration Procedures
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A nominal set of quaternions relating each camera’s orientation to the spacecraft frame of
reference is uploaded to the SC (and DHU?). The spacecraft and instrument are commanded
so that they enter fine pointing mode. In fine-pointing mode, quaternions are generated by
the DHU and sent to the MAU. These inputs and the calculated quaternions are stored and
sent to the ground for analysis.
Ground analysis compares predicted performance to actual performance. The differences
between the two are used to adjust TBD quaternions in TBD fashion.
4.5 Calibration Data
Pixel Response Function (PRF) and Focal Plane Geometry (FPG) are the two calibration
terms required by the SPOC for ground data processing that cannot be calculated in their
final form before launch. FPG is the mapping of CCD pixels to spacecraft coordinates, which
is impacted by any motion (“settling”) of the cameras with respect to the common
boresight. PRF is the effective response of the camera to an incident point source of light
and is affected by camera temperature.
Calibration of FPG and PRF is an iterative process. The input to the process is a series of
subarrays centered on bright, isolated stars, the locations of which were estimated using.
The subarray’s pixels are calibrated, and the centroid of each star is calculated using PRF.
The mapping of centroids to celestial coordinates (FPG) is calculated using the FPG tool,
which accounts for the impact of various levels of distortion. Once the FPG is calculated, the
PRF is recalculated, using the new FPG. This process continues to iterate until the proper
level of residuals is achieved.
4.5.1 Calibration Data Collection
Data for PRF and FPG calibration can be extracted from two-minute FFIs. To map the PRF
over the full pixel, FFI data are collected over ~1.1 pixels in 0.1 pixel (2.1”; TBR) steps, with
~10 TBR images per pointing.
4.6 Operational Parameters
The efficacy of the lens hoods should be calibrated on orbit. Lens hood scattering efficiency
is measured by measuring the variation in the measured background in all four cameras as
a function of angular distance (and TBD azimuth) of the camera boresight from either the
Earth or the moon.
4.6.1 Lens Hood Calibration Procedures
Lens hood calibration requires the collection of two-minute stacked images in a variety of
spacecraft orientations. The spacecraft should be oriented such that the angle of each
camera to the Earth and/or moon varies from 0° to 60° in steps of 5°. Additional
observations may be required to map the azimuthal dependence of the scattered light: this
is TBD.
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Commissioning-in-a-Life
Below is a preliminary timeline of commissioning operations based on the strawman orbitraising schedule described above. Because data are downlinked and commands are
uplinked only at perigee, the schedule is based on the perigee schedule.
The nominal schedule has science operations beginning in Orbit 6, following Perigee 5. If
there is slip in the commissioning schedule, the first science orbit will slip to Orbit 7, after
Perigee 6. Orbit 5 might be able to be used as contingency in case a contact is missed;
however, the baseline plan is to use Orbit 6 as contingency.
Commands uplinked at Perigee N are intended for Orbit N+1. As contingency for a missed
contact at Perigee N+1, the identical command set is uplinked for Orbit N+2.
The possibility of mid-orbit uplinks is TBD. If available, they may be used to uplink tables
used in ACS fine-pointing mode. These possibilities are noted, below.
Because there is insufficient time to use the data collected in Orbit 5 to plan Orbit 6, the data
collected in Orbit 4 will be used in the first science orbit.
5.1 Days 1-5: Orbit 1
No instrument operations are planned for Orbit 1.
5.2 Day 5: Perigee 1
Short-form (and long-form TBD) instrument checkout is done during the Perigee 1 contact.
Initial table loads (list TBR) and commands for Orbit 2 are uploaded.
5.3 Days 5-14: Orbit 2
During Orbit 2, FFIs are collected for initial determination of the intra-camera orientation
(aka FPG). These FFIs are likely to be two-second integrations to reduce the impact of
spacecraft motion in coarse-pointing mode.
TBD: initial attempts at fine pointing using ground-calibrated FPG.
Temperature measurements are made throughout the orbit to determine the thermal
balance of the instrument/spacecraft.
5.4 Day 14: Perigee 2
TBD Additional short- and long-form procedures are performed in real time during Perigee
2. Identical command sets for Orbits 3 and 4 are uplinked.
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5.5 Days 14-24: Orbit 3
During Orbit 3, the results of Orbit 2’s observations are analyzed. Because no FPG data are
available until the analyses are complete, initial instrument operations are devoted to those
that do not require fine pointing. A series of FFIs will be taken at various boresight
pointings to determine the scattered light suppression performance of the lens hoods.
If mid-orbit uplinks are possible, then the results of Orbit 2’s FPG analyses may be uploaded
for initial ACS fine-pointing tests.
5.6 Day 24: Perigee 3
Identical command sets for Orbits 4 and 5 are uplinked.
5.7 Days 24-42: Orbit 4
The spacecraft will be commanded into fine-pointing mode using FPG calculated from Orbit
Day after
Launch
1
1-5
5
Event
Launch
Orbit 1
Perigee 1
5-14
Orbit 2
14
14-24
Perigee 2
Orbit 3
24
24-42
Perigee 3
Orbit 4
42
42-56
Perigee 4
Orbit 5
56
Perigee 5
56-70
Orbit 6
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Commissioning Activities
None
TBD S/C events
Short-form instrument checkout
Analysis
Activities
None
None
None
FFIs for initial FPG calibration
Thermal balance measurements
Possible first ACS fine-pointing
checks
TBD
Initial ACS fine pointing checks and
FPG calibration
FFIs for lens hood calibration
Review of shortform results
ACS fine-pointing checks
Initial FFIs for PRF
Initial science operations
Analysis of ACS
performance
Final ACS fine-pointing checks
FFIs for final PRF/FPG checks
Contingency
Upload of commands for Orbits
6&7
None
None
Analysis of FFIs
for ACS matrices
Comments
Possible uplink of
new ACS tables
mid-orbit when
FFI analysis
complete
Possible uplink of
new ACS tables
mid-orbit based
on ACS, FFI
analyses.
PRF/FPG
calculated here
will be used in
planning first
science orbit
First Science
Orbit
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2, and PRF calibration observations will be performed. If mid-orbit uplinks are possible,
FPG information collected in Orbit 3 will be used to correct ACS and FPG tables mid-way
through Orbit 4, and the PRF data collection will be repeated. The FPG/PRF data collected
here will those used in planning the operations in the first science orbit.
Initial tests of science operations will be performed.
5.8 Day 42: Perigee 4
Identical command sets for Orbits 5 and 6 are uplinked.
5.9 Days 42-56: Orbit 5
Because the science calibration data were collected in Orbit 4, Orbit 5 is used to tweak finepointing parameters and take yet another data set for PRF/FPG measurements. Multiple
command set uplinks might be useful for ACS tweaking (TBR).
During Orbit 5, the POC is operating in full science mode.
5.10 Day 56: Perigee 5
The orbit following perigee 5 is the first science orbit. The operational commands for the
first two science orbits (orbits 6 and 7) are uplinked during Perigee 5.
5.11 Days 56-70: Orbit 6
Orbit 6 is the first science orbit.
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List of Open Items and/or TBD/TBRs
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Need discussion with Orbital on their ACS fine-pointing procedures
Clarification of HASO S-band contact frequency and duration
Discussion of instrument products in S-band
Do all instrument S-band products need to be readable by MAESTRO?
Better understanding of thermal state as a function of time during commissioning
List of short- and long-form tests
Procedure for running short- and long-form tests during commissioning,
particularly those requiring prompt response via Ka-band, requires discussion
Range of angles for lens hood tests
Details of duration, step size for PRF tests
Method of measuring observatory “thermal state” (Section 4.2.1)
Correct version of Figure 2.
Exact day numbers in Commissioning in a Life might be off by a day or so
Perigee #1-2 are at low altitude and therefore are a high-radiation environment;
TBD whether it is prudent to run tests there
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