June 23, 2014 Ann Jenkins

How Hubble Observations Are Scheduled

This is the third in a three-part series.

After observing time is awarded, the Institute creates a long-range plan. This plan ensures that the diverse collection of observations are scheduled as efficiently as possible. This task is complicated because the telescope cannot be pointed too close to bright objects like the Sun, the Moon, and the sunlit side of Earth. Adding to the difficulty, most astronomical targets can only be seen during certain months of the year; some instruments cannot operate in the high space-radiation areas of Hubble ’s orbit; and the instruments regularly need to be calibrated. These diverse constraints on observations make telescope scheduling a complex optimization problem that Institute staff are continually solving, revising, and improving.”

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 selection is done automatically by the Institute’s computers, which choose two stars per pointing from a catalog of almost a billion stars. These guide stars will be precisely positioned within the telescope’s fine guidance sensors, ensuring that the target region and orientation of the sky is observed by the desired instrument.”]

A weekly, short-term schedule is created from the long-range plan. This schedule is translated into detailed instructions for both the telescope and its instruments to perform the observations and calibrations for the week. From this information, daily command loads are then sent from the Institute to NASA’s Goddard Space Flight Center to be uplinked to Hubble.

Hubble’s Flight Operations Team resides in the Space Telescope Operations Control Center at NASA’s Goddard Space Flight Center in Greenbelt, Md. In addition to monitoring the health and safety of the telescope, they also send command loads to the spacecraft, monitor their execution, and arrange for transmission of science and engineering data to the ground.

The journey from proposal through selection and scheduling culminates in the email informing astronomers that their data is ready to be accessed. Usually, the process takes more than a year from idea to data—sometimes even longer. Of course, that’s when the real work begins—the analysis of the data and the hard work of uncovering another breakthrough Hubble discovery!

June 16, 2014 Ann Jenkins

How Hubble Observations Are Planned

This is the second in a three-part series.

Researchers awarded telescope time based on the scientific merit of their Phase I proposal must submit a Phase II proposal that specifies the many details necessary for implementing and scheduling of the observations. These details include such items as precise target locations and the wavelengths of any filters required.

Once an observation has occurred, the data becomes part of the Hubble archive, where astronomers can access it over the Internet. Most data is marked as proprietary within the Institute computer systems for 12 months. This protocol allows observers time to analyze the data and publish their results. At the end of this proprietary-data-rights period, the data is made available to the rest of the astronomical community. (Most of the very large programs, such as Frontier Fields, have given up proprietary time as part of their proposal.)

This is a view of the many computers that are part of the Barbara A. Mikulski Archive for Space Telescopes (MAST), located at the Space Telescope Science Institute (STScI) in Baltimore, Md. The archive is named in honor of the United States Senator from Maryland for her career-long achievements and becoming the longest-serving woman in U.S. Congressional history. MAST is NASA’s repository for all of its optical and ultraviolet-light observations, some of which date to the early 1970s. The archive holds data from 16 NASA telescopes, including current missions such as the Hubble Space Telescope and Kepler. Senator Mikulski is in the center, STScI Director Matt Mountain at her right, and STScI Deputy Director Kathryn Flanagan at her left. The plaque to image right is a photo of Supernova Milkuski, an exploding star that the Hubble Space Telescope spotted on Jan. 25, 2012. It was named in honor of the Senator by Nobel Laureate Adam Riess and the supernova search team with which he is currently working. The supernova, which lies 7.4 billion light-years away, is the titanic detonation of a star more than eight times as massive as our Sun.

Along with their Phase II proposal, observers can also apply for a financial grant to help them process and analyze the observations. These grant requests are reviewed by an independent financial review committee, which then makes recommendations to the Institute director for funding. Grant funds are also available for researchers who submit Phase I proposals to analyze non-proprietary Hubble data already archived. The financial committee evaluates these requests as well.

Up to 10 percent of Hubble ’s time is reserved as director’s discretionary time and is allocated by the Institute director. Astronomers can apply to use these orbits any time during the course of the year. Discretionary time is typically awarded for the study of unpredictable phenomena such as new supernovae or the appearance of a new comet. Historically, directors have allocated large percentages of this time to special programs that are too big to be approved for any one astronomy team. For example, the observations of the Frontier Fields use director’s discretionary time.

In my last post, I talked about how observations are proposed. In my next post, I will talk about how observations are scheduled.

April 11, 2014 Ann Jenkins

Hubble Observations: From the Ground to Your Computer

This post is the second in a two-part series.

In my last post, “Hubble Observations: From the Sky to the Ground,” I wrote about the route Hubble images take as they are digitally transferred from space to the ground.

This is the story of what happens after that data makes the 30-mile trip over land-lines from NASA’s Goddard Space Flight Center in Greenbelt, Md., to the Space Telescope Science Institute in Baltimore, Md., and ultimately to your computer as iconic Hubble pictures.

Hubble generates approximately 855 gigabytes of new science data each month. That’s the equivalent of an 8,550-yard-long shelf of books. Astronomers, in turn, typically download six terabytes of data monthly from this growing archive. That would be the equivalent of the printed paper from 300,000 trees. By the beginning of April 2014, Hubble data had been used to publish more than 12,000 peer-reviewed scientific papers.

The raw Frontier Fields data are available to the public immediately from a repository called the Barbara A. Mikulski Archive for Space Telescopes, or MAST. However, these data are not the beautiful, color Hubble images we have come to know and love. Raw images from the telescope are black and white, and include distortions introduced by the instruments, as well other unwanted artifacts from Earthshine, occasional Earth-orbiting satellite trails, bad pixels, and random hits by small, charged particles called cosmic rays.

Cosmic ray signatures are removed by combining two exposures in a way that removes everything not in both images. Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, the HFF Team, and Ann Feild (STScI).

It takes a team of about a dozen instrument analysts to “clean” these images by removing the distortions and artifacts. The refined images are posted once a week on MAST. These are the combination of multiple exposures taken in seven different filters, which allow light at specific wavelengths to enter the instruments.

Hubble’s instruments have many filters. The Frontier Fields observations use four in infrared from the Wide Field Camera 3 (WFC3), and three in visible light from the Advanced Camera for Surveys (ACS). The final, deep, combined color image for each Frontier Field will have a total of 560 exposures, divided evenly between the main cluster and its parallel field.

To produce a color picture, exposures from the seven filters are assigned the three primary colors of blue, green, and red based on their wavelengths. Images from the shortest, bluest wavelengths are assigned to blue, while images from the longest, reddest wavelengths are assigned to red, and intermediate wavelengths are assigned to green. These primary color images are then composited to produce the full-color picture so familiar to Hubble followers.

The top row shows the combined exposures through each of the seven filters as single images. To produce the color pictures, exposures from several selected filters from Hubble’s WFC3 and ACS were combined into one of three primary colors based on their wavelengths. The primary color images were then composited to produce the full-color image. Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, the HFF Team, and Ann Feild (STScI).

See a large collection of color Hubble images.

Amateur astronomers may want to see the raw Frontier Fields images.

There is a Facebook page for amateur astronomical image processors to exchange information, tips and techniques, and share their work.

April 1, 2014 Ann Jenkins

Hubble Observations: From the Sky to the Ground

This post is part one in a two-part series.

How does what Hubble sees become what you see? The first part involves moving science data from the sky to the ground—a complicated matter.

When Hubble views an astronomical target, the digital information from that observation is stored onboard the telescope’s solid-state data recorders. The telescope records all of its science data to prevent any possible loss of unique information. Hubble’s flight operations team at Goddard Space Flight Center, in Greenbelt, Maryland manages the content of these recorders.

Four antennae aboard Hubble send and receive information between the telescope and the ground. To communicate with the flight operations team, Hubble uses a group of NASA satellites called the Tracking and Data Relay Satellite System (TDRSS). Located in various positions across the sky, the TDRSS satellites provide nearly continuous communications coverage with Hubble.

Hubble’s operators periodically transmit the data from Hubble through TDRSS to TDRSS’s ground terminal at White Sands, New Mexico. From there, the data are sent via landline to Goddard to ensure their completeness and accuracy.

Goddard then transfers the data over landlines to the Space Telescope Science Institute in Baltimore, Maryland for processing, calibration, and archiving. There, they are translated into scientific information, such as wavelength and brightness, and ultimately into the iconic images that have become the hallmark of Hubble.

We’ll discuss how those images are made in a future post.