Space Telescope Science Institute
The Space Telescope Science Institute is the science operations center for the Hubble Space Telescope, science operations and mission operations center for the James Webb Space Telescope, and science operations center for the Nancy Grace Roman Space Telescope. STScI was established in 1981 as a community-based science center that is operated for NASA by the Association of Universities for Research in Astronomy. STScI's offices are located on the Johns Hopkins University Homewood Campus and in the Rotunda building in Baltimore, Maryland.
In addition to performing continuing science operations of HST and preparing for scientific exploration with JWST and Roman, STScI manages and operates the Mikulski Archive for Space Telescopes, which holds data from numerous active and legacy missions, including HST, JWST, Kepler, TESS, Gaia, and Pan-STARRS.
Most of the funding for STScI activities comes from contracts with NASA's Goddard Space Flight Center but there are smaller activities funded by NASA's Ames Research Center, NASA's Jet Propulsion Laboratory, and the European Space Agency.
The staff at STScI consists of scientists, spacecraft engineers, software engineers, data management personnel, education and public outreach experts, and administrative and business support personnel. There are approximately 200 Ph.D. scientists working at STScI, 15 of whom are ESA staff who are on assignment to the HST and JWST project. The total STScI staff consists of about 850 people as of 2021.
STScI operates its missions on behalf of NASA, the worldwide astronomy community, and to the benefit of the public. The science operations activities directly serve the astronomy community, primarily in the form of and observations and grants, but also include distributing data from other NASA and ground-based missions via MAST. The ground system development activities create and maintain the software systems that are needed to provide these services to the astronomy community. STScI's public outreach activities provide a wide range of resources for media, informal education venues such as planetariums and science museums, and the general public. STScI also serves as a source of guidance to NASA on a range of optical and UV space astrophysics issues.
The STScI staff interacts and communicates with the professional astronomy community through a number of channels, including participation at the bi-annual meetings of the American Astronomical Society, publication of regular STScI newsletters and the STScI website, hosting user committees and science working groups, and holding several scientific and technical symposia and workshops each year. These activities enable STScI to disseminate information to the telescope user community as well as enabling the STScI staff to maximize the scientific productivity of the facilities they operate by responding to the needs of the community and of NASA.
STScI activities
Telescope science proposal selection
The STScI conducts all activities required to select, schedule, and implement the science programs of the Hubble Space Telescope. The first step in this process is to support the annual community-led selection of the scientific programs that will be performed with HST. This begins with publishing of the annual Call for Proposals, which specifies the currently supported science instrument capabilities, proposal requirements and the submission deadline. Anyone is eligible to submit a proposal. All proposals are critically peer-reviewed by the Time Allocation Committee. The TAC consists of about 100 members of the U.S. and international astronomical community, selected to represent a broad range of research expertise needed to evaluate the proposals. Each proposal cycle typically involves reviewing 700 to 1100 proposals. Only 15 - 20% of these proposals will eventually be selected for implementation. The TAC reviews several categories of observing time, as well as proposals for archival, theoretical, and combined research projects between HST and other space-based or ground-based observatories. STScI provides all technical and logistical support for these activities. The annual cycle of proposal calls was occasionally altered in duration in years when a HST servicing mission was scheduled.Proposers fortunate enough to be awarded telescope time, referred to as General Observers, must then provide detailed requirements needed to schedule and implement their observing programs. This information is provided to STScI on what is called a Phase II proposal. The Phase II proposal specifies instrument operation modes, exposure times, telescope orientations, and so on. The STScI staff provide the web-based software called that allow GOs to estimate how much observing time any of the onboard detectors will need to accumulate the amount of light required to accomplish their scientific objectives. In addition, the STScI staff carries out all the steps necessary to implement each specific program, as well as plan the entire ensemble of programs for the year. For HST, this includes finding guide stars, checking on bright object constraints, implementing specific scheduling requirements, and working with observers to understand and factor in specific or any non-standard requirements they may have.
Observation scheduling
Once the Phase II information is gathered, a long-range observing plan is developed that covers the entire year, finding appropriate times to schedule individual observations, and at the same time ensuring effective and efficient use of the telescope through the year. Detailed observing schedules are created each week, including, in the case of HST operations, scheduling the data communication paths via the Tracking and Data Relay Satellite System and generating the binary command loads for uplink to the spacecraft. Adjustments can be made to both long-range and weekly plans in response to Targets of Opportunity. The STScI uses the Min-conflicts algorithm to schedule observation time on the telescope. The STScI is currently developing similar processes for JWST, although the operational details will be very different due to its different instrumentation and spacecraft constraints, and its location at the Sun-Earth L2 Lagrange point rather than the low Earth orbit used by HST.Flight operations
Flight Operations consists of the direct support and monitoring of HST functions in real-time. Real-time daily flight operations for HST include about 4 command load uplinks, about 10 data downlinks, and near continuous health and safety monitoring of the observatory. Real-time operations are staffed around the clock. Flight operations activities for HST are done at NASA's GSFC in Greenbelt, Maryland.Science data processing
Science data from HST arrive at the STScI a few hours after being downlinked from TDRSS and subsequently passing through a data capture facility at NASA's Goddard Space Flight Center. Once at STScI, the data are processed by a series of computer algorithms that convert its format into an internationally accepted standard, correct for missing data, and perform final calibration of the data by removing instrumental artifacts. The calibration steps are different for each HST instrument, but as a general rule they include cosmic ray removal, correction for instrument/detector non-uniformities, flux calibration, and application of world coordinate system information. The calibrations applied are the best available at the time the data passes through the pipeline. The STScI is working with instrument developers to define similar processes for Kepler and JWST data.Science data archiving and distribution
All HST science data are permanently archived after passing through the calibration pipeline. NASA policy mandates a one-year proprietary period on all data, which means that only the initial proposal team can access the data for the first year after it has been obtained. Subsequent to that year, the data become available to anyone who wishes to access it. Data sets retrieved from the archive are automatically re-calibrated to ensure that the most up-to-date calibration factors and software are applied. The STScI serves as the archive center for all of NASA's optical/UV space missions. In addition to archiving and storing HST science data, STScI holds data from 13 other missions including the International Ultraviolet Explorer, the Extreme Ultraviolet Explorer, the Far Ultraviolet Spectroscopic Explorer, and the Galaxy Evolution Explorer. Kepler and JWST science data will be archived and retrieved in similar fashions. The internet serves as the primary user interface to the data archives at STScI. The archive currently holds over 30 terabytes of data. Each day about 11 gigabytes of new data are ingested and about 85 gigabytes of data are distributed to users. The Hubble Legacy Archive, currently in development, will act as a more integrated and user-friendly archive. It will provide raw Hubble data as well as higher-level science products.Science instrument calibration and characterization
STScI is responsible for in-flight calibration of the science instruments on HST and JWST. For HST, a calibration plan for the observatory is developed each year. This plan is designed to support the selected GO observation programs for that cycle, as well as to provide a basic calibration that spans the lifetime of each instrument. The calibration program includes measurements that are made relative to on-board calibration sources or to assess internal detector noise levels as well as observations of astronomical standard stars and fields, needed to determine absolute flux conversions and astrometric transformations. The external calibrations on HST typically total 5-10% of the GO observing program, with more time required when an instrument is still relatively new. HST has had a total of 12 science instruments to date, 6 of which are currently active. Two new instruments were installed during the May 2009 HST servicing mission STS-125. Electronic failures in STIS and in the ACS Wide-Field Channel were also repaired on-orbit in May 2009, bringing these instruments back to active status. All 12 HST instruments plus the 4 planned for JWST are summarized in the table below. HST instruments can detect light with wavelengths from the ultraviolet through the near infrared. JWST instruments will operate from the red-end of optical wavelengths to the mid-infrared. Instruments listed as decommissioned are no longer on board.| Instrument name | Instrument function | Instrument Status | Telescope |
| High Speed Photometer | Rapid Timescale Photometry | Decommissioned in 1993 | HST |
| Wide Field and Planetary Camera | UV/Optical Imaging | Decommissioned in 1993 | HST |
| Faint Object Spectrograph | UV/Optical Spectroscopy | Decommissioned in 1997 | HST |
| Goddard High Resolution Spectrograph | UV/Optical Spectroscopy | Decommissioned in 1997 | HST |
| Faint Object Camera | UV/Optical Imaging | Decommissioned in 2002 | HST |
| Wide Field and Planetary Camera 2 | UV/Optical Imaging | Decommissioned in 2009 | HST |
| Fine Guidance Sensor | Precision Astrometry | Active | HST |
| Space Telescope Imaging Spectrograph | UV/Optical Spectroscopy | Active | HST |
| Near Infrared Camera and Multi-Object Spectrometer | NIR Imaging and grism Spectroscopy | Active | HST |
| Advanced Camera for Surveys | UV/Optical Imaging and grism Spectroscopy | SBC and WFC Active; HRC Inactive | HST |
| Cosmic Origins Spectrograph | UV Spectroscopy | Active | HST |
| Wide Field Camera 3 | UV/Optical/Near-IR Imaging and grism Spectroscopy | Active | HST |
| Near Infrared Camera | Optical/Near-IR Imaging | Active-Undergoing Calibration | JWST |
| Near Infrared Spectrograph | Near-IR Spectroscopy | Active-Undergoing Calibration | JWST |
| MIRI | Mid-IR Imaging & Spectroscopy | Active-Undergoing Calibration | JWST |
| Tunable Filter Imager | Near to Mid-IR Medium-band Imaging | Active-Undergoing Calibration | JWST |
STScI staff develops the calibration proposals, shepherd them through the scheduling process, and analyze the data they produce. These programs provide updated calibration and reference files to be used in the data processing pipeline. The calibration files are also archived so users can retrieve them if they need to manually recalibrate their data. All calibration activity and results are documented, usually in the form of Instrument Science Reports posted to the public website, and occasionally in the form of published papers. Results are also incorporated into the Data Handbooks and Instrument Handbooks.
In addition to calibration of the instruments, STScI staff characterizes and documents the performance of the instrument, so users can better understand how to interpret their data. These are generally effects that are not automatically corrected for in the pipeline. They include global effects, such as charge transfer efficiency in the charge-coupled devices, as well as effects specific to modes and filters, such as filter "ghosts". Awareness of these effects can come from STScI staff as they analyze calibration programs, or from observers who find oddities in their data and provide feedback to STScI.
The STScI staff also performs the characterization and calibration of the telescope itself. In the case of HST, this has evolved to primarily be a matter of monitoring and adjusting focus, and monitoring and measuring point spread functions.. In the case of JWST, the STScI will be responsible for using the wavefront sensor system developed by JPL and Northrop Grumman Space Technology to monitor and adjust the segmented telescope.