Hubble Science Operations – NASA Science

Selecting Observation Proposals

The first step in the science process is generating scientific proposals to use Hubble. This annual “Call for Proposals” goes to astronomers worldwide who have approximately two months to submit an initial phase-one proposal that presents a scientific case for using Hubble. These initial proposals outline an observing program that requests observing time in Hubble orbits and describes the scientific objectives and the Hubble instrument(s) the observing program requires.

The Institute organizes a stringent scientific peer-review process. Panels of scientists from around the world who specialize in different disciplines of astronomy (stars, galaxies, exoplanets, etc.) assemble to rank each proposal and recommend how to allocate Hubble’s limited observing time. The panels only consider proposals that require Hubble’s unique combination of sensitivity, resolution, instrumentation, and wavelength range for their success. The proposal must illustrate that Hubble is the best instrument to gather the data researchers seek, as opposed to a ground-based or other space-based observatory. A Time Allocation Committee (TAC) that comprises chairpersons of those original panels assembles the results and recommends Hubble’s observing program for the coming year. The final decision rests with the Institute’s director.

Over the years, more than 40 countries have submitted winning proposals for observing time on Hubble. By virtue of the European Space Agency’s (ESA) contributions to develop Hubble and their continuing support of its operation, astronomers from ESA countries are guaranteed 15 percent of Hubble’s observing time. ESA provides approximately 13 staff members co-located with other Institute employees in Baltimore to support the science operation functions.

Individual astronomers and astronomy teams submit many more proposals than Hubble can possibly accommodate. In a typical year, researchers request five to six times more than Hubble’s available observing time.

Planning the Observations

Astronomers receive telescope time based on the scientific merit of their phase-one proposal. Researchers then must submit a phase-two proposal that specifies the many details necessary to implement and schedule the observations.

These details include items like precise target locations and the wavelengths of any filters required to achieve the scientific goal. After the telescope completes an observation, researchers can have proprietary access to the data for six months. This protocol allows scientists time to analyze the data and publish their results. At the end of this proprietary-data-rights period, the data are made publicly available via the Barbara A. Mikulski Archive for Space Telescopes (MAST).

Along with their phase-two proposal, United States investigators can also apply for a financial research award to help them process and analyze their observations. Research awards are also available to scientists who submit phase-one proposals to analyze non-proprietary Hubble data already archived.

Up to 10 percent of Hubble’s time is discretionary time allocated by the Institute’s director. Astronomers can apply to use these orbits any time during the year. Discretionary time is typically awarded to study unpredictable phenomena such as an unexpected collision within the solar system or the appearance of a new comet. Historically, directors allocate large percentages of this time to special programs that may be too large for any one astronomy team, are high risk, or are the result of a community-wide initiative. For example, the Hubble Deep Field and Hubble Ultra Deep Field observations both used director’s discretionary time.

Scheduling the Telescope’s Observations

The Institute creates a long-range schedule that orders the diverse collection of observations as efficiently as possible. This task is complicated because the telescope must avoid looking at regions of the sky that are too close to bright objects like the sunlit side of Earth, the Sun, and the Moon. Adding to the difficulty, each astronomical target is only visible during certain months of the year; some instruments cannot operate in the high space-radiation areas of Hubble’s orbit; and instruments regularly need calibration. Preparing for an observation also involves selecting guide stars to stabilize the telescope’s pointing and center the target in the instrument’s field of view.

The scheduling team also creates a weekly, short-term schedule from the long-range plan, translating it into detailed instructions for both the telescope and its instruments to perform the observations and calibrations for the week. This information is sent to Hubble Mission Operations on the campus of NASA’s Goddard Space Flight Center. Mission Operations reviews the command loads and sends them to Hubble via a constellation of NASA communications satellites in geosynchronous orbit.

Data Analysis and Storage

The next step in the sequence is processing and storing the data Hubble collects in an archive. Observers and visiting astronomers can easily retrieve and examine stored data using tools provided in the archive.

To calibrate the science data, the Institute uses telescope and instrument engineering data (such as instrument detector temperatures) and observations of “standard” astronomical sources whose physical properties are well known. The Institute also calibrates data to remove the instruments’ properties, such as a variation in a detector’s sensitivity across its surface. The Institute processes science data within 24 hours of receipt. When the Institute receives science data, it automatically reformats the information and verifies its quality. In addition, Hubble Mission Operations archives all of the engineering telemetry reported by Hubble’s sensors and uses it to discover and track changes in the performance of Hubble’s systems.