This article provides an overview of completed and planned testing campaigns for the Wide Field Instrument (WFI) and its sub-components. Descriptions of the test set-ups are given for a user to understand the scope of the testing. Key findings at each testing phase are provided for context.

Overview 

To ensure Roman's mission success, all spacecraft components are thoroughly tested and characterized on the ground. Roman's Wide Field Instrument (WFI) was tested in several phases. These phases include the component-level testing (Component Testing), Subsystem Testing, completed WFI Thermal Vacuum (TVAC) testing, and testing of WFI installed in the payload (SCIPA TVAC). These testing campaigns provide our best understanding of the characteristics of WFI before flight operations. A quick overview of the testing campaigns can be found in the Ground Testing Campaigns Summary Table. This overview will provide a concise summary of the testing and findings with additional technical information on the testing campaigns provided in the sub-sections in this article. In addition to the WFI detectors, this article will cover information about filters and other sub-systems that are relevant to describing the ground testing campaigns and their outcomes. More information about the detectors can be found in the WFI Detectors article, and more information about the WFI filters can be found in the WFI Optical Elements article.

Component Testing was largely undertaken at the Detector Characterization Laboratory (DCL) at Goddard Space Flight Center or at BAE Systems (formerly Ball Aerospace). This testing isolated individual components of the WFI and provided in-depth characterization of its actual properties against mission requirements for acceptance by the project. Of note, a set of twenty-eight individual H4RG-10 detectors for WFI were first analyzed, tested, and characterized at the DCL without the flight electronics. These initial tests provided detailed characterization of detector properties such as dark current, quantum efficiency, and persistence and led to the initial selection of eighteen flight detectors and six spares. Other components, such as the optical elements, were also studied in detail. Component Level testing with non-selected H4RG-10 detectors continues at the DCL on an as-needed basis.

Subsystem Testing combines components. Of note, the Focal Plane System (FPS) TVAC (FPS) was also conducted at the DCL. The first round of this integration and testing (FPS1) placed the initial flight complement of eighteen detectors into the Mosaic Plate Array (MPA). During FPS1, several detectors were identified as having anomalously high dark current, known as the Dark Current Anomaly; this change was due to exposure to high temperatures (Mosby et al. 2024). Three detectors were swapped out with spares for a second round of FPS integration (FPS2). In FPS2, the detectors were assembled in the MPA with the final flight electronics (ACADIA). The FPS passed its subsystem level requirements. 

The full WFI was assembled and tested for the first time at BAE Systems, and this required the integration of the focal plane system, sRCS, and the optical wheel assembly. WFI TVAC refers to testing of the full WFI and using the Stimulus of Ray Cones (SORC), an external light source. The first round of WFI TVAC (WFI TVAC1) ran from September 2023 to November 2023 in BAE's Titan chamber. The tests during TVAC included aliveness tests (e.g., "Is component X on/off and working?") and functional science-motivated tests to understand detector performance. During this testing campaign approximately 200 TB of data were collected. Testing was planned to occur at three different stable temperature levels, known as plateaus, and these are COLD_QUAL, NOM_OPS, and HOT_QUAL. Due to time constraints, some tests that were less sensitive to temperature changes took place during the transitions between these plateaus. WFI TVAC1 was very successful and the instrument was, overall, found to operate consistently with expectations from previous tests and models.

The second iteration of WFI TVAC (WFI TVAC2) ran from the end of March 2024 to the end of May 2024. WFI TVAC2 was the last opportunity to test certain aspects of WFI on the ground. The overall testing procedures were similar to WFI TVAC1. The instrument was tested in the Titan chamber and three thermal plateaus were considered: COLD_QUAL, NOM_OPS, and HOT_QUAL. For TVAC2 the temperature set points for each plateau were slightly different than those of TVAC1. Specifically, the temperature differences between COLD_QUAL and NOM_OPS and between NOM_OPS and HOT_QUAL were smaller than those in TVAC1. During TVAC2 both aliveness and functional tests took place, and features detected in TVAC1 were further tested. WFI met requirements or has shown progress toward requirements. 

The next testing campaign will be the Spacecraft and Integrated Payload Assembly (SCIPA TVAC) and will constitute the last time to test WFI and the Roman observatory before launch. This testing is planned to take place in 2025 at Goddard Space Flight Center in the Space Environment Simulator (SES).

Ground Testing Campaigns Summary Table

Testing Campaign	Objectives of Campaign	Location of Testing	Timing	Findings	Data Availability
Component Testing	Acceptance testing and characterization of individual components of WFI	Goddard Space Flight Center, Detector Characterization Laboratory.	On-going.	Characterized detectors and other subcomponents. Selected eighteen best performing detectors for flight and six spares.	TBD
Triplet Tests	Characterize detectors with flight-light hardware	Goddard Space Flight Center, Detector Characterization Laboratory.	June 2021 - February 2022,  May 2022	Characterized detectors with flight-like hardware.	Available at MAST as a High-Level Science Product (HLSP)
Focal Plane System (FPS) TVAC	Functional and aliveness tests of focal plane system. First characterizations.	Goddard Space Flight Center, Detector Characterization Laboratory.	December 2022 - April 2023	After Semi-Flight FPS, a set of detectors were identified with high-dark signal. These were swapped out for Flight FPS.	Will be available in RITA in 2025.
Wide Field Instrument (WFI) TVAC1	Functional and aliveness tests of the full Wide Field Instrument (element wheel assembly, mosaic plate array, relative calibration system, etc.). Using the SORC for some tests.	BAE systems, Titan chamber.	September - November 2023	Overall trending consistent with FPS findings. Some light leaks identified. SORC required  enhancements to verify some requirements.	Will be available in RITA in 2025.
Wide Field Instrument (WFI) TVAC2	Functional and aliveness tests of the full Wide Field Instrument (element wheel assembly, mosaic plate array, relative calibration system, ++). Using the SORC for some tests.	BAE systems, Titan chamber.	March - May 2024	Light leaks corrected from TVAC1. SORC performance improved. Trending consistent with FPS and TVAC1 findings. WFI requirements verified.	Will be available in RITA in 2025.
SCIPA TVAC	Functional and aliveness tests of full Spacecraft and payload.	Goddard Space Flight Center, Space Environment Simulator (SES).	To occur in 2025		TBD

Descriptions of Ground Testing Campaigns  

Component Testing

Component testing focused on evaluating components of the WFI. Major campaigns focused on the sensor chip assembly (SCA) units (detectors, hereafter), optical elements, LEDs, and diodes. While this article focuses on the overall detector performance, some performance characterizations cannot be fully decoupled so non-detector testing is mentioned. These datasets are limited in scope, but they often provide the best characterizations of some detector phenomenon because only limited time could be spent on each test. Component tests also set the baseline performance of each component before integration with other components. The majority of these tests occurred at the Detector Characterization Laboratory (DCL) in Goddard Space Flight Center without the flight electronics. A thorough description of the H4RG-10 detectors is given in Mosby et al. (2020).

SCA Acceptance tests

After initial testing at Teledyne, a set of twenty-eight H4RG-10 detectors went through a standard set of tests to characterize their performance known as the Acceptance Tests. The tests determined whether these detectors were suitable for further consideration as flight parts. These tests were conducted in a large dewar at the DCL that accommodated four detectors for each test round. The tests conducted included: the characterization of correlated-double-sampled (CDS) noise, dark current, disconnected pixels, e-gain correction, flat field, linearity, persistence, and quantum efficiency (QE). All Acceptance Tests were conducted using Leach controllers. After testing, eighteen detectors were chosen to populated the focal plane with six detectors identified as spares. 

Optical Element Acceptance tests

The optical elements (the filters, prism, and grism) also underwent extensive acceptance testing after fabrication. Many of these tests occurred at BAE Systems (formerly Ball Aerospace). A description of the filter testing campaign and modelling is given in Cromey et al. (2023). Descriptions of the testing for the grism is given in Gong et al. (2020) and Dominguez et al. (2021). A full description of slitless spectroscopy performance through the grism and prism testing is given in Bray et al. (2024). Descriptions of the diffusers on the back of the optical elements are given in Cromey et al. (2023). All elements passed acceptance and environmental testing as of September 2022 (J. Schlieder 2022, presentation).

Other Component Testing

Other component testing includes testing the LEDs and Diodes used in other parts of WFI.

Engineering Testing

Additional tests were undertaken at the DCL to study specific detector performance characteristics. Such tests have occurred using flight-selected detectors and will continue to occur as needed with flight-spares to understand detector behavior. Some notable tests include the following:

• Count Rate Non-Linearity (CRNL) Tests: All detectors that passed acceptance underwent count-rate non-linearity (CRNL) testing, which were carried out at the DCL. This testing campaign was conducted using a small dewar under very dark conditions with two light sources: one working at 880 nanometers and the second one at 1550 nanometers with two photodiodes to measure the light output. The primary test consisted of a sequence of dark and illuminated exposures, with illumination levels ranging between 0.2 and 2000 DN per second and exposure times chosen to reach one of three levels of total counts (2000, 6000, and 20000 DN). These tests were obtained with Leach controllers in lieu of the flight-controllers (ACADIA). 
• Defocus Tests: Defocus data were obtained at the Precision Projection Lab at JPL. This test used a non-flight detector with a Leach controller. The detector was illuminated with pinhole masks with different spacings. The mask was placed in the nominal focus and in two defocus positions. Darks and flats were also obtained. The test setup had significant background light. The main goal of this test was to determine whether in-focus and out-of-focus images would generate the same total photometric response in the detector if a sufficiently large aperture is used to collect the signal. 
• Combinatorial Flux Addition (CFA) Tests: Combinatorial flux addition tests were performed at DCL using non-flight detectors and engineering-grade ACADIA controllers. This dataset consists of a sequence of exposures illuminated by two LEDs with variable settings. The main goal of this test was to determine to what extent the signal is additive, i.e., when known light levels are obtained from each LED, whether the signal recorded when they are both on is the sum of signals obtained when only one of them is on. Deviations from additivity can be interpreted as non-linearity in the detectors.

Subsystem Testing 

Triplet tests 

Seven sets of triplet tests were conducted from June 2021 to February 2022 for all 28 flight-accepted H4RG-10 detectors. They were run in the same large dewar as the Acceptance tests, four detectors at a time, with engineering-grade ACADIA controllers and flight-like harnesses. These tests were aimed at characterizing the detector properties with flight-like hardware, in order to identify the best parts for the focal plane. In addition, they provided baseline information on the detectors in preparation for the full FPS tests, and enabled fine-tuning of the ACADIA controller parameters for each detector. The data were stored as FITS cubes. The tests included inter-pixel capacitance (IPC), crosstalk, gain, linearity, total noise, and photometric stability. Guide windows were used during the testing campaign, but only at a limited number of pre-set locations. An additional triplet test was conducted in May 2022 to experiment with single-ended mode readout, which enables the Improved Roman Reference Correction (IRRC). However this test suffered from significant interference from 60 Hz noise, making hard to quantify the improvements due to the IRRC.

Focal Plane System Testing

The Focal Plane System (FPS) is comprised of the eighteen flight detectors mounted on a mosaic plate, eighteen ACADIA application integrated circuits (ASIC), a focal plane electronics box to provide overall control, and associated harnesses, mechanical, and thermal hardware. There were two sets of testing for the populated focal plane with flight-like hardware: the first is known as the Semi-Flight FPS TVAC and the second is the Flight FPS TVAC. Two rounds of tests were performed to test for changes in the focal plane after environmental testing (including vibration, thermal, electric interference, among others). An important feature of the two FPS tests is that the data were obtained in single-ended readout mode instead of correlated double samples and this impacts the readout noise. Data from both FPS testing campaigns will be stored in the Roman Integration and Testing Archive as Level-1 equivalent files with all test-related metadata stored for future use.

Semi-Flight FPS TVAC

The Semi-flight FPS testing (FPS1) was carried out in December 2022 using the first set of detectors selected for flight, flight ACADIA controllers (Loose et al. 2018), and flight-like focal plane electronics (FPE). This test showed a significant degradation of dark current performance for three of the detectors known as the Dark Current Anomaly (Mosby et al. 2024). Semi-Flight FPS testing consisted of several segments with changes in environmental conditions between each segment. The tests included dark and illuminated exposures, as well as electronic tests such as crosstalk and IPC, based on single-pixel resets.

Dark Current Anomaly 

During the Semi-flight FPS testing an increase in the total dark current was noted in comparison to the component-level testing for several detectors. For three detectors this change in performance made them unacceptable for flight as a sufficient number of pixels exceeded the operability requirement of 0.5 electrons per second. An Anomaly Review Board (ARB) was established by the Roman Project and, in collaboration with Teledyne, a testing campaign was initiated to understand the cause and also to select replacements amongst the spare detectors. A full description of the anomaly, tests to identify the cause, models of the degradation, and demonstrations of improved performance can be found in Mosby et al. (2024). The paragraph that follows provides a high-level summary. 

The ARB determined that there was a correlation between pixels with degraded dark current and the locations of void defects, which are crystal imperfections that occur during the detector layer growth. The ARB testing campaigns demonstrated that exposure to elevated temperatures can "activate" impurities in the defects to migrate, which explains much of the degraded performance seen in the Semi-Flight FPS tests. The ARB recommended (1) to reduce the operational temperature of the focal plane as much as practical and (2) limit exposing the focal plane to temperatures above 23 C. The three detectors with an increase in dark current (SCA22066 at WFI01, SCA22077 at WFI12, and SCA22073 at WFI04) were replaced with suitable spares (SCA22081 at WFI01, SCA20829 at WFI12, and SCA21115 at WFI04). Tests in the Flight FPS TVAC demonstrated functionality at 85 K, 88 K, and 90 K and later tests in WFI TVAC1 demonstrated WFI system-wide functionality as low as approximately 89 K.

Flight FPS TVAC

The Flight FPS test was carried out in April 2023 using the final set of flight detectors and flight focal plane electronics (FPE). Flight FPS testing consisted of several segments with changes in environmental conditions between each segment. The tests included dark and illuminated exposures, as well as electronic tests such as crosstalk and IPC, based on single-pixel resets. Changes were made in the readout procedures prior to the Flight FPS test to minimize additional noise and artifacts in the readout electronics. As of May 2023, the full flight FPS cleared all functional and performance testing (A. Choi May 2023, presentation).

Wide Field Instrument (WFI) TVAC Testing 

The subsystems of WFI were assembled at BAE Systems in late 2022 and early 2023. These subsystems include the focal plane system, the optical wheel assembly, the simplified Relative Calibration System, the Alignment Compensation Mechanism (ACM), and all associated electronics and control systems. Once assembled, the next phase of testing is known as the WFI Thermal Vacuum Testing or WFI TVAC. Like FPS testing, WFI TVAC is separated into three stages: data collection in a flight-like environment (TVAC1), a series of vibration and environmental tests, and data collects in a flight-like environment (TVAC2). For full testing of the WFI instrument, the Stimulus of Ray Cones (SORC) was developed to send different types of light sources through the full instrument. This combined system was placed in the Titan Chamber at BAE Systems and the Figure Showing Components of the TVAC Setup demonstrates the full configuration of the equipment. Only minor changes occurred to this setup between TVAC1 and TVAC2. Within each TVAC campaign were several phases with different temperatures and the Table of WFI TVAC Testing Phases provides a summary with separate figures of the temperature profile provided for each TVAC campaign.

All data collected during the WFI TVAC has been homogenized and curated in the Roman Integration and Test Archive (RITA) in MAST at the Science Operations Center as Level-1 equivalent files with all test-related metadata stored for future use. Additional descriptions of the testing are provided for WFI TVAC because of the high utility of the data and the importance of these data in establishing a pre-flight performance. This additional information may help users to understand the limitations of calibration information derived from data acquired in ground testing as well as other caveats related to pre-flight resources for the user. 

Stimulus of Ray Cones (SORC) 

First WFI Thermal Vacuum Integration and Testing (TVAC1)

The first time the WFI was fully assembled happened during the TVAC1 campaign, which took place between September and November of 2023 and included 60 days of testing. This testing campaign was conducted at BAE systems in Boulder, Colorado and was directed by the WFI team and BAE. The goals of TVAC1 were to test the functionality of all instrument systems, establish a pre-environmental (vibration, acoustics) instrument baseline with a focus on optical performance, and perform risk reduction activities for further characterization in TVAC2. TVAC1 used heritage tools from JWST including the Test Planning Tool (TPT) and the Optical Test Procedure (OTP) (A. Choi Dec 2023, presentation). During this testing campaign the testing and analysis team focused on the verification of WFI requirements. Overall, the performance and trending obtained from TVAC1 were consistent with expectations and models from FPS testing.

TVAC1 Test Setup and Planning

During TVAC1 approximately 200 TB of data were collected from 270 individual data collection periods (with the longest taking over 9 hours). These tests included: aliveness tests, which focus on checking whether the instruments are working and responding to commands, and functional tests, where the functionality of the instrument is verified and validated. The archive of the data produced in this testing campaign is maintained by the SOC in RITA. 

The testing campaign included several phases, which correspond to different operating temperatures of the instrument. Periods where the conditions were stable are known as "plateaus" and when conditions were changing are called "transitions." The overall temperature profile is shown in the Figure of TVAC1's Thermal Profile and it includes test categorization. Most requirements verification tests occurred at plateaus, whereas some risk reduction tests or tests that did not depend on full thermal stability occurred in transitions. To aid users who may need to use integration and test data, we provide descriptions of when image data were taken in the Table of WFI TVAC Testing Phases.

Findings from TVAC1

The major findings from TVAC1 were presented to the Roman Community Forum (A. Choi Dec 2023, presentation) and are summarized here, as follows. 

1. "The Focal Plane System (FPS) performance and reliability were remarkable." Multiple WFI-level requirements for the mission were met and the overall performance baseline was established successfully.
2. "In-band stray light performance was excellent". Multiple WFI-level requirements for the mission were met or the risk reduction data that was collected demonstrated that the system is capable of meeting requirements in later testing campaigns. Some thermal light leaks were identified, investigated, and strategies developed for remediation.
3. "sRCS flat field smoothness appeared excellent." The data collected in TVAC1 demonstrated that the system is capable of meeting requirements that will be fully tested in later testing campaigns. The overall performance baseline was established successfully, with full characterization planned in TVAC2. 
4. "Confocality between elements across the field was excellent." The full suite of optical elements were able to focus in the same plane, with the exception of the prism that showed signs of being slightly out of tolerance. The requirements for the prism are overall more forgiving, but further analysis would be required.
5. "Focus-corrected wavefront error performance was excellent." The SORC was able to produce suitable light sources to provide feedback on instrument performance. Using the SORC for wavefront sensing exceeded expectations. The overall performance requirements were met, with margin, for all elements.
6. "Executed a very successful campaign of risk reduction tests." Specially designed risk-reduction data collects provided enough data to demonstrate that the system is capable of meeting requirements when the full tests were executed. The data collected in these tests also proved critical for refining and optimizing the final characterization plans for TVAC2. 

Several changes were made to WFI after the conclusion of TVAC1 (A. Choi et al. 2024, presentation), as follows:

• Baffles were physically added to the filters, grism, and prism to mitigate thermal stray light paths that were identified from analysis of data taken in TVAC1.
• The SORC was upgraded to mitigate stray light, improve the precision of positioning mechanisms, and expand the light source capabilities, all of which was necessary to test instrument requirements.
• The operating temperatures of the detectors were reduced to 89.5 K. This change was made after incorporating thermal-performance data obtained in TVAC1 into the instrument thermal model and confirmation that sufficient margin was available to operate the instrument at this temperature. The motivation of the change is described in the Dark Current Anomaly section in this article or Mosby et al. (2024).

Table of WFI TVAC Testing Phases 

WFI TVAC Phase Name	Description	Was Image Data Collected?	TVAC1?	TVAC2?	Notes
HOT_SURVIVAL	This plateau corresponds approximately to the hottest temperature that the instrument will be exposed to.	No image data are taken during this phase.
COLD_SURVIAL	This plateau corresponds approximately to the coldest temperature that the instrument will be exposed to.	No image data are taken during this phase.
TO_COLD_QUAL	Transition between COLD_SURVIVAL and COLD_QUAL.	Tests with image data are conducted during this phase.
COLD_QUAL	This plateau corresponds to a temperature slightly colder than the nominal operations temperature for the mosaic plate assembly (MPA).	Tests with image data are conducted during this phase.			The temperature is different between TVAC1 and TVAC2.
TO_NOM_OPS	Transition between COLD_QUAL and NOM_OPS.	Tests with image data are conducted during this phase.
NOM_OPS	This plateau corresponds approximately to the nominal operating temperature for the mosaic plate assembly (MPA).	Tests with image data are conducted during this phase.			Data collected during this plateau was used to generate reference products for data processing.  The temperature is different between TVAC1 and TVAC2.
DECON_OPS	This plateau corresponds approximately to the temperature during the decontamination procedure. Decontamination is a part testing in thermal vaccum environments that is used to minimize impacts of the outgassing from flight equipment. This is particularly important when other materials in the equipment are sensitive to molecular contamination.	No image data are taken during this phase.
TO_HOT_QUAL	Transition between DECON_OPS and HOT_QUAL.	Tests with image data are conducted during this phase.
HOT_QUAL	This plateau corresponds to a temperature slightly higher than nominal operations temperature for the mosaic plate assembly (MPA).	Tests with image data are conducted during this phase.			The temperature is different between TVAC1 and TVAC2.

Second WFI Thermal Vacuum Integration and Testing (TVAC2) 

TVAC2 took place between March and May of 2024 at the Titan Chamber in BAE systems in Boulder, Colorado. The testing was conducted by the WFI team and personnel from BAE, with an in-person participation by members of the SOC. This testing campaign built on the TVAC1 experience, and constituted the last chance to test WFI with an external light source (the SORC). Tests run in TVAC1 as risk reduction were run in full and many tests were completed as the "run for the record" for the requirements verification at the WFI level. The goals of TVAC2 were to (1) verify that the WFI meets requirements, (2) collect data to produce calibration reference files, (3) establish cryo performance for science calibration and characterization, and (4) perform risk reduction tests to prepare for in-flight operations.

TVAC2 Test Setup and Planning

During TVAC2 there were an additional 461 data collects, constituting ~270 TB of data. The overall thermal profile for TVAC2 was similar to TVAC1 and can be viewed in the Figure of TVAC2's Thermal Profile. However, the operating temperatures at the COLD_QUAL, NOM_OPS, and HOT_QUAL plateaus were different than those for TVAC1, and the temperature differences between those stages were smaller. Furthermore, the DECON_OPS plateau was removed. Generally, when image data was taken is the same as the description for TVAC1. The Table of WFI TVAC Testing Phases provides a summary of the phases.

Before TVAC2, changes to the WFI  and testing hardware were made based on the conclusions of TVAC1 (A. Choi et al. 2024, presentation). For completeness, these changes were: (1) the addition of baffles on the optical elements to mitigate thermal stray light paths, (2) updates to the SORC to enable more light source capabilities and mitigate stray light, and (3) a change to the operating temperature of the detectors to 89.5 K (also see the Dark Current Anomaly section in this article or Mosby et al. 2024). Based on analysis of TVAC1 datasets, some of the testing procedures were revised before the final test run to determine if requirements were met. For example, the WFI_SCIENCE_MONITOR test exposures were revised to be illuminated with higher flux levels which will aid the characterization of the sensors and bright-source tests were added to understand performance when observing extremely bright stars (A. Choi et al. 2024, presentation).

Findings from TVAC2

Major findings from TVAC1 were presented to the Roman Community Forum (A. Choi et al. 2024, presentation and J. Schlieder 2024, presentation) and are reproduced here, as follows:

1. The thermal background requirement is met with margin at all thermal phases. Stray thermal background identified in TVAC1 was reduced with the addition of baffles.
2. The baffle mitigation for grism and prism was highly successful. Stray thermal background was reduced with the addition of baffles.
3. The dark current, total noise, and CDS noise meet requirements. These were mostly unchanged since TVAC1. More specifically, the background at NOM_OPS is less than 0.045 electrons per pixel per second and the total noise is less than 7.5 electrons. Consistent with expectations based on recommendations from the Roman Detector Anomaly Review Board, the dark current operability fraction showed excellent stability at the revised operating temperature. As expected, detectors that started with less operability appear to change more.
4. The bandpass edges comply with requirements for all filters. Filter bandpass edges were measured as were pupil transmission for the grism and prism. The filter model describes the bandpass edges with an accuracy of +\- 0.05%, and the edge-gradient has been measured across the field.
5. The dispersion and bandpass edges were measured for the grism and prism. 
6. The simplified Relative Calibration System (sRCS) has been extensively characterized and will enable on-orbit calibrations. The sRCS flatfielded the full array over five orders of magnitude in flux for six wavelength bands. The sRCS dynamic range of the LEDs was found to be greater than required. The sRCS was shown to be produce data sufficient for characterizing the count-rate non-linearity (CRNL) in three modes: the lamp-on, lamp-off mode for six bands (LOLO), using combinatorial flux addition (CFA) in five of six bands, and an additional method using photodiodes in the sRCS.

Spacecraft + Integrated Payload Assembly Thermal Vacuum Integration and Testing (SCIPA TVAC) 

The final planned testing campaign that will provide performance data for the WFI is the Spacecraft + Integrated Payload Assembly TVAC (SCIPA TVAC) that will take place in 2025 at the Space Environment Simulator (SES) at Goddard Space Flight Center. SCIPA TVAC is the most complex and the most operations-like testing that will be performed for Roman. The scope and time planned for specific WFI characterization will be more limited than in prior campaigns because no external illumination is feasible. Nonetheless, this will be the final end-to-end performance testing of the instrument and will be the final time that the WFI will be at operating temperatures until orbit. There are plans to collect additional trending data to check the WFI performance as well as end-to-end ground system testing. Additional information on SCIPA TVAC is given in Perkins et al. (2024).

For additional questions not answered in this article, please contact the Roman Help Desk at STScI.

References

Articles and Reports:

• "The ACADIA ASIC: detector control and digitization for the Wide-Field Infrared Survey Telescope (WFIRST)", Loose et al. 2018
• "Characterization of Nancy Grace Roman Space Telescope Slitless Spectrometer (grism)", Gong et al. 2020
• "Properties and characteristics of the WFIRST H4RG-10 detectors", Mosby et al. 2020
• "Evolution of the Roman Space Telescope Flight Grism Component", Dominguez et al. 2021
• "Spectral Characterization of the RST Prism Assembly Bandpass Filters", Patel et al. 2022
• "The Roman Space Telescope optical system: status, test, and verification", Bolcar et al. 2023
• "Reflective engineered diffusers on the Roman Space Telescope Wide Field Instrument", Cromey et al. 2023
• "Science filter performance summary on the Roman Space Telescope Wide Field Instrument", Cromey et al. 2023
• "Spectral Characterization of the Grism and Prism Slitless Spectrometers for the Nancy Grace Roman Space Telescope", Bray et al. 2024
• "Resolving the dark current anomaly in the Nancy Grace Roman Space Telescope focal plane", Mosby et al. 2024
• "The Roman Space Telescope observatory build, test, and verification status", Perkins et al. 2024
• "Survey science with the Nancy Grace Roman Space Telescope Wide Field Instrument", Schlieder et al. 2024

Instrument Update Presentations:

• "Wide Field Instrument Status" presentation at the Roman Community Forum on September 12, 2022 by J. Schlieder
• "Wide Field Instrument Status" presentation at the Roman Community Forum on May 24, 2023 by A. Choi
• "Wide Field Instrument Update" presentation at the Roman Community Forum on December 13, 2023 by A. Choi
• "Wide Field Instrument Updates" presentation at the Roman Community Forum on June 26, 2024 by A. Choi, J. Schlieder, and E. Switzer
• "WFI Pre-Ship Review and Delivery Update" presentation at the Roman Community Forum on August 28, 2024 by J. Schlieder, A. Choi, and E. Switzer