Rev.
01
ECO
37-232
Description
Author
Initial Release
Approved
R. Vanderspek
Date
3/26/2015
Massachusetts Institute of Technology
Kavli Institute for Astrophysics and Space
Research (MKI)
TESS Instrument Handbook
Dwg. No. 37-19501
Revision 01
February 1, 2015
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Table of Contents
1.1
1.2
1.3
Introduction ............................................................................................................................................... 5
Purpose and Scope ...............................................................................................................................................5
Intended Audience ...............................................................................................................................................5
Reference Documents .........................................................................................................................................5
Introduction to TESS ................................................................................................................................ 6
2.1
2.2
2.3
2.4
2.5
Mission Overview..................................................................................................................................................6
Observations...........................................................................................................................................................6
Commissioning ......................................................................................................................................................6
Flight System Elements .......................................................................................................................................6
Data Products .........................................................................................................................................................6
Pixels Data ......................................................................................................................................................................... 6
Full-Frame Images ......................................................................................................................................................... 6
Housekeeping Data ........................................................................................................................................................ 6
Instrument Description .......................................................................................................................... 6
3.1
3.2
3.3
Overview ..................................................................................................................................................................6
Instrument Properties ........................................................................................................................................6
Temperature Sensor Placement ......................................................................................................................6
CCD Temperature Sensors .......................................................................................................................................... 7
External Temperature Sensors ................................................................................................................................. 8
Internal Temperature Sensors .................................................................................................................................. 8
Optics and Images..................................................................................................................................... 8
4.1
4.2
4.3
4.4
4.5
4.6
4.7
5.1
5.2
5.3
Camera Design Summary ...................................................................................................................................8
Lens Design .............................................................................................................................................................8
Aberrations .............................................................................................................................................................8
Pixel Response Function ....................................................................................................................................8
Pointing Requirements and Performance ...................................................................................................8
Ghost Images and Scattered Light ...................................................................................................................8
Differential Velocity Aberration ......................................................................................................................8
Detector Properties ................................................................................................................................. 8
CCD Architecture ...................................................................................................................................................9
Imaging Array .................................................................................................................................................................. 9
Frame Store.....................................................................................................................................................................10
Serial Register ................................................................................................................................................................10
Charge Injection ............................................................................................................................................................10
CCD Readout ...................................................................................................................................................................10
Physical Characteristics................................................................................................................................... 12
CCD Mounting ................................................................................................................................................................12
Pixel Dimensions...........................................................................................................................................................12
CCD Performance Summary ........................................................................................................................... 12
Readout Noise ................................................................................................................................................................12
Charge-Transfer Inefficiency ...................................................................................................................................12
Dark Current ...................................................................................................................................................................12
Depletion Depth ............................................................................................................................................................12
Quantum Efficiency......................................................................................................................................................12
CCD Gain ...........................................................................................................................................................................13
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Nonlinearity ....................................................................................................................................................................13
Bias Level .........................................................................................................................................................................13
Full Well, Saturation, and Charge Bleeding........................................................................................................13
5.4 Pixel Numbering ................................................................................................................................................. 13
5.5 Signal Content ..................................................................................................................................................... 13
5.6 A/D Converter Differential Non-Linearity ................................................................................................ 13
5.7 Inter-Pixel Response Nonuniformity .......................................................................................................... 13
5.8 Intra-Pixel Response Nonuniformity .......................................................................................................... 13
5.9 Flat Fields.............................................................................................................................................................. 13
5.10 Bad Pixels ........................................................................................................................................................... 14
5.11 Cosmic Rays ....................................................................................................................................................... 14
6.1
6.2
7.1
7.2
7.3
Focal Plane Array ................................................................................................................................... 14
Focal Plane Array Overview ........................................................................................................................... 14
Physical Characteristics................................................................................................................................... 14
Gaps between CCDs .....................................................................................................................................................14
CCD Skew and Aplanarity..........................................................................................................................................14
Focal Plane Electronics ........................................................................................................................ 14
Description ........................................................................................................................................................... 14
Clocks and Sampling ......................................................................................................................................... 14
Other Issues ......................................................................................................................................................... 14
Detector Assembly ................................................................................................................................ 14
9.1
9.2
9.3
Electronic Image Artifacts and Mitigation .................................................................................... 15
10.1
10.2
Type 1 ..................................................................................................................................................................... 15
Type 2 ..................................................................................................................................................................... 15
Type 3 ..................................................................................................................................................................... 15
Instrument Calibration ..................................................................................................................... 15
Ground Measurements Relevant to Flight Calibration ...................................................................... 16
Flat Field ........................................................................................................................................................................16
On-orbit Calibration ....................................................................................................................................... 16
Focal Plane Geometry...............................................................................................................................................16
Pixel Response Function .........................................................................................................................................16
Observing with TESS .......................................................................................................................... 16
11.1
11.2
11.3
11.4
11.5
11.6
Flight Modes and States................................................................................................................................. 16
Table-Based Parameters .............................................................................................................................. 16
Requantization ............................................................................................................................................................16
Huffman Tables ...........................................................................................................................................................16
Commissioning Tables .............................................................................................................................................16
Guide Star Table .........................................................................................................................................................16
Target Table .................................................................................................................................................................16
Miscellaneous Tables................................................................................................................................................16
Default Operating Parameters ................................................................................................................... 16
Times and Time Stamps ................................................................................................................................ 16
Photometric Precision Estimation ............................................................................................................ 16
Mapping Targets to Pixel Coordinates..................................................................................................... 16
Acronyms and Abbreviations.......................................................................................................... 16
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References ............................................................................................................................................. 16
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Introduction
This document is meant to be a full description of the TESS instrument at a level of detail
relevant to a knowledgeable user of the instrument.
1.1 Purpose and Scope
The purpose of this document is to be a single reference for the nominal operation of the
TESS instrument. It is meant to be a handbook, not an encyclopedia: details of design or
operation are found in other documents, which are referenced here as needed.
1.2 Intended Audience
The intended audience of this document is composed of systems engineers, software
engineers, scientists, and operations staff of TESS.
1.3 Reference Documents
The following documents are referenced in and provide more detail for this Instrument
Handbook.
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Introduction to TESS
2.1 Mission Overview
2.2 Observations
2.3 Commissioning
2.4 Flight System Elements
2.5 Data Products
Pixels Data
2.5.1.1 Targets, Apertures, and Pixel Maps
2.5.1.2 Types of Target
2.5.1.3 Collateral Data
Full-Frame Images
Housekeeping Data
Instrument Description
3.1 Overview
3.2 Instrument Properties
3.3 Temperature Sensor Placement
Temperature sensors are mounted to the lens and detector housings to allow monitoring of
the thermal properites of the camera. See Figure T.
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CCD Temperature Sensors
A four-terminal temperature sensor (RTD) is provided on the chip. It consists of a long,
folded strip of the same metal (AlCu) as used for the first level of device metallization. The
device is used by forcing current through two pads and reading the voltage on two different
pads.
Preliminary data of resistance versus temperature from the CCID77 device are shown in
Figure 10. The resistance is linear over the temperature range of the measurement, and the
temperature dependence is 2.87 and 2.65 Ω/ ̊C for the two cases.
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External Temperature Sensors
Internal Temperature Sensors
Optics and Images
4.1 Camera Design Summary
4.2 Lens Design
4.3 Aberrations
4.4 Pixel Response Function
4.5 Pointing Requirements and Performance
4.6 Ghost Images and Scattered Light
4.7 Differential Velocity Aberration
Detector Properties
The detectors within the FPA are MIT/LL CCID-80 CCDs. The CCID-80 is backsideilluminated with a depletion depth of 100 µm for good red sensitivity. The following
sections describe the properties of the CCID-80.
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Figure 1: Layout of CCID-80
5.1 CCD Architecture
The architecture of the MIT/LL CCID-80 is shown in Figure X. The CCID-80 is a deepdepletion, frame-transfer CCD with a full frame store. Figure 1 depicts the overall
architecture of the device. The device has four outputs; each output is associated with an
array of 512(H)×2048(V) imaging pixels, for a total imaging area of 2048(H)×2048 (V)
imaging pixels. The die size is 31.920(W)×63.955(H) mm TBR for an area of 20.4 cm2.
Imaging Array
The imaging array for the CCID-80 is comprised of 2048(H)×2048(V) pixels, and the pixel
size is 15(H)×15(V) μm.. The active imaging array is surrounded by 10 extra rows and
columns each on the left, right, top, and bottom sides to buffer the active imaging array from
uneven fields due to the substrate bias. These extra rows allow for photolithography
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stitching as well as misalignment and vignetting effects of a metal light shield deposited on
the device. Some additional features, such as guard rings to enable deep-depletion
operation, are not shown.
The 10 buffer rows are real pixels, but some of them are masked. The 10 buffer rows above
and below the imaging are uncovered, but are not used because of the uneven fields.
The 10 buffer columns are not clocked into the serial register, but rather into a “charge
sink”, or scupper (not shown in Figure X). They can be ignored for the purposes of this
document.
Frame Store
The frame store for the CCID-80 is divided into two independent halves, labeled “AB” and
“CD”. Each section contains 1024(H)×2068(V) pixels, as shown in Figure X. The number of
rows in the frame store differs from that of the imaging array because there are two sets of
buffer rows, 10 above and 10 below the imaging area; 2048+10+10=2068. The number of
rows in the frame-store area in Figure 1 is 2064 because of the presence of four rows
between the frame-store region and the serial register.
Serial Register
The serial or output register allows charge to be directed to either of two output ports at the
ends of the register. Moreover, the clock buses are partitioned in a manner that allows the
left and right halves of the register to be clocked in opposite directions. Each register has
five clock connections, with independent phases 1 and 2 for the left and right halves and a
phase 3, which is common to both halves. The output ports are assigned as A, B, C, D from
left to right for a back-illuminated part.
There are 11 leading columns in all ports of the serial register that can be used as ``black’’ or
``bias’’ pixels.
Charge Injection
The charge injection register is shown in Figure X.
CCD Readout
In normal operation, the imaging area will be exposed to the sky for 2.0 seconds, after which
the chip is read out. The basic readout process shifts the imaging area rows into the framestore area, a process that takes ~40 msec, The rows are then sequentially read out through
ports A, B, C, and D. Ports A and C read out pixels first-pixel-first; ports B and D read out
pixels last-pixel first.
5.1.5.1 Number of Rows
The number of rows read from the imaging area into the frame-store area is 2078. This is
somewhat counterintuitive, because the imaging area consists of 2068 rows. By shifting
2078 rows, the top 10 rows are not real imaging rows, but they are exposed to light during
the row-shifting process. These “smear” rows are used in post-processing to account for the
fact that starlight is still falling on the pixels as they’re being read out. The result of the
shifting of 2078 rows from the imaging area into the frame-store area is the loss of the
bottom 10 buffer rows. These rows are partially masked and subject to fringe field effects,
and they were never intended for use in high-precision photometry.
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The shift of the frame-store area into the serial register for readout is more measured: one
row is shifted into the serial register, and then the serial register is read out. The readout of
the serial register raises the overall readout time of the frame store to the estimated 1.8 s.
The frame store rows are shifted 2078 times. As a result, the first 2068 rows are the
imaging area rows plus 10 smear columns; the last 10 rows are virtual rows that are
subjected to the frame-store readout time and can be used as a measure of the dark current
in the CCD.
5.1.5.2 Number of Columns
The CCD serial register naturally has 11 pixels between the first active pixel and the readout
amplifier; the first 11 pixels are therefore virtual pixels, sometimes referred to as
“horizontal underclocks”. These 11 pixels apply to each of the 4 readouts, A-D: thus,
clocking out the active pixels and the horizontal underclocks requires 512+11=523 serial
shifts.
Any pixel clocked after the first 523 will not correspond to an active pixel and is therefore
virtual. For TESS, there will be 11 such “horizontal overclocks”, for symmetry reasons.
Clocking a full row requires 11+512+11=534 serial shifts.
5.1.5.3 Full-Frame Images
The full-frame images created from a single CCD will account for the serial under- and
overclocks, vertical smear rows, and vertical virtual rows. GSE and post-processing
software will assemble the data clocked from the FPE such that the FFI is a correctlyoriented image. This means that the order of pixels from outputs B and D are reversed, and
the horizontal under- and overclocks are collected on the side of the image. The resulting
pixel map is shown in Figure 2.
Figure 2: The structure of a full-frame image. The imaging area pixels are arranged to represent the
physical layout, and the virtual columns are collected to each side of the imaging area. The 10 buffer
rows, smear rows, and virtual (overclock) rows are collected at the top of the image.
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5.2 Physical Characteristics
CCD Mounting
As shown in Figure 1, the CCID-80 is mounted to a die measuring 32.0 x 64.0 mm (TBR: the
text above and in the CCD descriptive document differs). As a result, the edge of the imaging
area is inset from the edge of the die by 640 µm parallel to the columns and 600 µm at the
top of the imaging area. These gaps contribute to the gap between CCDs in the focal plane
array, discussed in Section X.
The CCDs are bonded to the die using TBD glue/epoxy. The surface of the CCDs is parallel to
the die mounting surface to within TBD µm. The edges of the CCD are parallel to the edges of
the die to within TBD µm.
There is a maximum TBD µm of “bowing” or “potato-chipping” over the imaging area.
Pixel Dimensions
The pixels each measure 15 µm x 15 µm x 100 µm deep. The profile of a pixel resembles
more a chimney than a box, as shown in Figure X (Figure X will show a TESS chimney vs. a
Kepler box).
5.3 CCD Performance Summary
The following sections discuss the performance of the CCID-80s used on TESS. For now,
nominal values are given; later, either a range of values for the flight units or the exact
values for the flight units will be given.
Readout Noise
The readout noise of the CCID-80 is estimated to be closer to 10 e– than 20 e–.
Charge-Transfer Inefficiency
The CTE of the CCID-80 has not been measured. Because brighter stars are more sensitive
to loss of charge than fainter ones, the signal levels relevant to CTE on TESS are significantly
larger than those usually measured, i.e. Fe55 X-rays. There is currently no estimate of the
high-signal-level CTE for the CCID-80.
Dark Current
The dark current in the CCID-80 is estimated to be <1 e–/sec/pixel at a CCD temperature of 40°C, and thus <1 e–/cadence/pixel at flight temperatures. Details TBR.
Depletion Depth
The thickness of the silicon of the CCID-80 CCDs is 105 µm ± 10 µm (TBR). All CCDs will be
fully depleted.
Quantum Efficiency
The theoretical CCD QE vs wavelength for a 100 µm depletion depth and an operational
temperature of -75°C is shown in Figure Y. The QE at low wavelengths is dominated by the
performance of the AR coating, as all photons are absorbed within a few tens of microns of
the (backside) surface of the CCD. At longer wavelengths, photons penetrate deep into the
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silicon, and the probability of a photon passing through the silicon entirely becomes nonnegligible, leading to a drop in QE at the red end of the spectrum.
The probability of absorption of a photon is a function of the band-gap energy within
silicon, which varies with temperature as shown in Equation X. Figure Y shows that the
change in CCD temperature affects the shape of the QE curve at the red end of the spectrum.
As a result, the measured brightness of stars of different spectral types will vary differently
with temperature.
CCD Gain
The nominal gain of the CCID-80s will be ~7 e–/ADU.
Nonlinearity
The nonlinearity of the CCDs has not been measured.
Bias Level
The CCDs electronics will be tuned so that the bias level is near 100 TBR ADU.
Full Well, Saturation, and Charge Bleeding
The full well of the CCID-80 is estimated to be near 300,000 e–. The charge from a
moderately-saturated pixel will bleed into neighboring rows, but will not be lost. Charge
loss due to TBR effect begins near 10,000,000 TBR e–.
5.4 Pixel Numbering
5.5 Signal Content
Leftover from KIH. Not sure what it is.
5.6 A/D Converter Differential Non-Linearity
TBD
5.7 Inter-Pixel Response Nonuniformity
Not sure how this differs from flat fields.
5.8 Intra-Pixel Response Nonuniformity
This is sub-pixel non-uniformity. TBD.
5.9 Flat Fields
Flat fields are a measure of the local pixel-to-pixel nonuniformity in response (PRNU). The
PRNU of each CCD will be measured during camera I&T. (Method will be described briefly
here). PRNU maps (flat fields) are stored at the POC and used by the SPOC during data
processing.
Updates to flat field maps are not possible once TESS is on orbit.
Need to figure out what goes in here and what goes in 3.3.1.1.
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5.10 Bad Pixels
Bad pixels on the CCD are those that display either 1) no response, 2) anomalously low
response, 3) high dark current. Before launch, the number and location of bad pixels on all
CCDs will be cataloged (TBD give location in poc database). FFIs will be reviewed regularly
to detect the presence of new warm or dead pixels, and the table will be updated.
5.11 Cosmic Rays
Oh, where do we start. Big topic, will get to it soon.
Focal Plane Array
6.1 Focal Plane Array Overview
The TESS FPA consists of four CCDs abutted so as to create an imaging area of ~62 mm on a
side, as shown in Figure X. Each CCD is mounted to a SiC pedestal; the four pedestals are
mounted to a (what’s the word here?). The wtwh is mounted to XX, cold straps, titanium
supports, show pictures.
6.2 Physical Characteristics
The ideal FPA would consist of four CCDs abutted directly to one another to form a perfectly
flat array of 2048x2048 pixels. The TESS FPA deviates from the ideal; the following sections
describe the deviations and the means to minimize them.
Gaps between CCDs
Because the CCD is inset from the edge of the mounting die, there is a gap of ~1.5-2 mm
(100-130 pixels) between the imaging areas of the four CCDs. The gap is not the same for
each FPA, and thus will be bookkept separately.
CCD Skew and Aplanarity
Mounting method allows fine tuning of skew and aplanarity. Precision of aplanarity
mounting is 5 µm TBR. Precision of skew mounting is TBD. Skew and aplanarity measured
after assembly and included in PRF (maybe).
Focal Plane Electronics
7.1 Description
7.2 Clocks and Sampling
7.3 Other Issues
Detector Assembly
The FPE+FPA assembly, installed in its housing, is defined as the detector assembly (Figure
3). The CCDs in the FPA are identified as 1-4 based on how they are connected to the FPE.
Which CCD is which in the FPA is keyed from the location of the CCD with respect to the
vent pipe shown in Figure 3, and is described in the FPG_detail memo.
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Figure 3: TESS Detector Assembly, with CCDs numbered
Electronic Image Artifacts and Mitigation
9.1 Type 1
9.2 Type 2
9.3 Type 3
Instrument Calibration
Instrument properties relevant to data processing must be calibrated before science
operations and, to the extent possible, monitored for changes during flight. The list of
calibration products is given in Table X. A subset of instrument properties, indicated in the
table, can only be calibrated on the ground. Other properties can be estimated before
launch, but must be calibrated during on-orbit commissioning, to account for the effect of
the on-orbit instrument environment.
Instrument Property
Readout noise
Flat field
Focal Plane Geometry
Pixel Response Function
System Gain
System Linearity
CTI
Dark Current
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Number
Calibration Method
TBD
TBD
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10.1 Ground Measurements Relevant to Flight Calibration
Flat Field
Flat field calibration methods
10.2 On-orbit Calibration
Focal Plane Geometry
FPG estimation (ground) and flight calibration
Pixel Response Function
PRF estimation (ground) and flight calibration
Observing with TESS
11.1 Flight Modes and States
11.2 Table-Based Parameters
Requantization
Huffman Tables
Commissioning Tables
Guide Star Table
Target Table
Miscellaneous Tables
List the tables that are sent once or rarely. Will a bullet list be enough, or does it need a
table, or individual “Heading 4” entries? Ed will know.
11.3 Default Operating Parameters
11.4 Times and Time Stamps
11.5 Photometric Precision Estimation
11.6 Mapping Targets to Pixel Coordinates
Acronyms and Abbreviations
References
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