Month: June 2008

Update 29 June 2008

Greetings from SLAC.  This week I am here at the LAT Instrument Science Operations Center with many others from the international LAT team, all working together around the clock to study the detailed engineering data and to prepare for science observations.

What has GLAST been doing lately?

Everything continues to go very well and the work is proceeding on schedule.

The LAT is an advanced particle detector with many adjustable parameters to tune, and for the past few days data have been taken with different values for many of those key parameters.  In addition, special data-taking periods are being devoted to characterizing the fluxes of background particles hitting the instrument.  The very detailed work is going smoothly.  The additional diagnostic data taking is keeping the onboard temporary data storage (solid state recorder, or SSR) and data transmission paths well exercised.  Over time, the data rate from the LAT will be reduced to the planned science operations level of about 1.2 megabits per second.

The GBM is continuing on-orbit calibrations and checkout as well.  A few days ago, the GBM rehearsed the burst-alert message chain.  (When an instrument on GLAST detects a gamma-ray burst, a special communications channel is immediately opened to the ground, and an alert is put onto the internet (here is what GLAST will report)  so that other observatories can repoint to study the burst.)

The observatory is powered electrically by solar panels that also charge an onboard battery.  The battery is important because during every 95-minute orbit GLAST spends some time in earth’s shadow (night time for GLAST).  Engineers in the Mission Operations Center at Goddard made adjustments this week on the rate at which the powerful solar arrays are allowed to charge the battery, based on operating experience.  These adjustments will help ensure a long life for the battery.

Looking forward

While work is proceeding to make sure the instruments are ready for science observations, we can’t help thinking about what we will soon be seeing for the first time in the months ahead!  Here are some thoughts from LAT team member Isabelle Grenier, from the Service d’Astrophysique, CEA Saclay

  Soon we will have a first look at the sky with the sharpest ‘gamma-ray glasses’ ever built! A sky that will at last appear as magnificent at the night sky we can admire with our naked eyes, filled with thousands of gamma-ray stars and barred by the bright shades of the Milky Way. But we will see a much more lively and tumultuous sky than the peaceful starry nights we are accustomed to. Intense flashes will last seconds to hours and many stars will blaze and fade away over days and months. A sky showing us how animated the Universe can be, how powerful too, with many objects capable of producing particles and light of incredible energy.
  Looking back at the successes of the previous telescopes that had discovered a handful of gamma-ray sources in the seventies, tens of them in the eighties, two hundred in the nineties, the team is preparing to detect thousands of them with GLAST. The task is complex because they appear on top of the bright emission from the clumpy nebulae of the Milky Way. It is equivalent to seeing small sail boats lost among big waves during a tempest: a small error on predicting the surface of the rough sea and we miss the tiny sails. We unfortunately don’t know so well our own galaxy and it impacts our ability to detect point sources.
  The team then needs to identify in other lights (radio to X rays) what black holes, neutron stars, supernova remnants, or binary stars are responsible for the gamma-ray sources. This is also a challenge because bright gamma-ray sources can be very faint in other lights and because the sky can be very crowded compared to the precision with which we can locate a source in the sky. It is often like looking for a needle in a haystack, even if the needle is as weird an object as a giant black hole! It took twenty years to identify the second brightest gamma-ray source, Geminga, with one of the nearest and faintest pulsars. Half of the currently known sources has remained unidentified for 17 years. We all hope that GLAST will solve those mysteries and replace them with many new surprises. For the moment, we look eagerly forward to the avalanche of new sources.

Coming up…

More details on instrument tuning and performance, checking the alignment of the LAT with the spacecraft, observatory maneuvers, and more reports from some of the international team members.  Please check back every few days for updates.

Update 25 June

Today was one of the best days yet for GLAST.  Overnight, the LAT high voltage was turned on, completing the instrument turn-on sequence more than a day early.  Around sunrise, the LAT started physics runs.  This was our first chance to use the LAT to detect high-energy particles from space — and everything just worked beautifully!  Data were shipped to the ISOC at SLAC (see previous posts) and processed quickly.  Just having the data chain work end-to-end without significant problems was a great accomplishment, and it was thanks to all the detailed rehearsals.  LAT scientists around the world then examined the data, and so far everything looks even better than we expected.  Initial estimates of backgrounds indicate they are at a very manageable level.  There are some minor details in the instrument diagnostic data (this tells us how the instrument itself is working) we don’t yet understand, but we will soon.  More about all this in future posts.  There are now many days of work ahead to tune, configure, and calibrate the instrument, and we are well on our way.

This evening, the GBM turned on its high voltage, and it is also now operational!  After about a week of testing and calibrations, the GBM should be ready to start looking for gamma-ray bursts.  More about this as well in posts over the next few days.  Everything looks good, and the GBM team is also very happy. 

Overnight, the observatory will transition from pointed mode (always looking in one direction) to sky survey mode: every two orbits (three hours) the LAT will sweep its field of view across the entire sky.  This is the primary science observing mode, so it is an important mode for tuning the instruments.

Here’s an interesting site to check if you’d like to know where your favorite satellite is at the moment.

We had a small celebration in the Mission Operations Center toward the end of the day.  We didn’t pause long, though, since there is much more work to do before we can start routine science operations.  However, none of us thought we’d be this far along so quickly.

24 June Evening Update

Another great day for GLAST.  The turn-on of LAT components went much faster than the nominal plan.  At this time, all the electronics in the LAT have been powered on (LAT has about one million channels of electronics, plus three onboard computers that are part of a sophisticated data gathering system — all of it running on <650 Watts or about half the power used by an ordinary hand-held hair dryer), and everything looks good so far.  We could not be happier!  The next step tonight will be to turn on the high voltage to the sensors in the anticoincidence detector (see below for links to information about the detectors), and tomorrow morning the LAT will start detecting individual particle events, at least 1-2 days ahead of schedule.  The fluxes of high-energy charged particles in space are surprisingly uncertain, and we expect it will take the next few weeks to tune the LAT to operate in its new environment.  The `rain’ of high-energy charged particles through the LAT (many thousands of particles per second) is much larger than the rate of celestial gamma rays (just a few per second), so the name of the game in gamma-ray astrophysics is background rejection — the detective work to identify the gamma rays.  The LAT design is very well suited to this task, of course.

Some of you have asked for pointers to more information about the detectors.  Thanks for the suggestion!  The Stanford University LAT page has a link to a brief description of the LAT subsystems, and there is also this description on the Mission site. Please also have a look at the introductory posting for this blog.  Even more detailed information can be found on the SLAC LAT Project Website.

Tomorrow we will start detecting individual particles passing through the LAT.  After several more days, we should be able to isolate a few individual gamma-ray candidate events.  Building up a first glimpse of the sky in gamma rays will take a few more weeks, while the instrument tuning takes place.  I’ll keep posting updates describing this process and the progress.  An overview of the science timeline is here (also linked to other entries in this blog and to the mission site.)

Tomorrow, the GBM will also turn on the high voltage to its sensors.  In other words, by the end of the day tomorrow both GLAST instruments should be operational.

As I was leaving the Mission Operations Center this evening, the lead engineer for the spacecraft commincations system asked me how I was feeling.  `Grateful and very lucky’, I said.  He replied we have a great team of very hardworking people, and that is why things have been going well.  He’s absolutely right — but I still feel very lucky, too.

We are happily ahead of schedule: nine of the sixteen LAT towers are now powered on, and things continue to look good.

Three of the 16 LAT towers are now powered on.  Everything looks good so far!  The power-up sequence will continue for most of the rest of today.  LAT team members are very excited about this, monitoring the progress in the Mission Operations Center, at the LAT Instrument Science Operations Center at SLAC, and around the world at their home institutions.  The GBM data processing unit continues to function as expected, and the first detector will be powered on later in the day.

I’ll post another update tonight.

What is GLAST doing now?

Very early this morning the LAT and GBM flight computers were powered on and booted successfully.  Later this morning, the process of turning on the LAT detectors will begin! 

Eric Grove (NRL), is the LAT Commissioner, and he wrote this from the Mission Operations Center today:
 
As I type this, LAT power-up is underway!  It’s an extremely exciting time.  After so many years of concept development, design, construction, integration, and testing, and thanks to the effort of so many people on hardware and software, it’s simply extraordinary to see the LAT beginning to come to life on orbit.

The spacecraft is operating well, and instrument telemetry is starting to appear.  In the next few days, the first instrument data will arrive at the LISOC at SLAC for processing, and we’ll all get to see how the LAT is operating in its new environment in orbit around the earth.

GLAST Education and Public Outreach efforts in Florida and Beyond

Professor Lynn Cominsky, from Sonoma State University in California, leads the GLAST Public Education and Outreach activities, and she shared the following:

After many months of designing, reviewing, printing and shipping, all of our hard work was enjoyed by over 600 guests at the Kennedy Space Center Visitor’s Complex, where each person who checked in received a bag of GLAST materials.  Aurore Simonnet was responsible for the beautiful design of all SSU’s products, and Aurore, Kamal Prasad and I personally stuffed over 400 bags at KSC.  It was fun, because we got to see the “inside view of Guest Ops!”

Eight of GLAST’s Educator Ambassadors (EAs) were able to travel to KSC for launch week, and enjoyed touring KSC as well as helping with our teachers’ workshops. Dave Thompson (GSFC) and I did a one-hour workshop for over 30 pre-service teachers on Friday June 6, at the KSC Education Center. It was recorded for future broadcast on NASA’s Education Channel. On Saturday June 7, SSU staff Kamal and Kevin John, and a few of our EAs helped me do a three-hour workshop for over 20 in-service teachers at KSC. It featured hands-on activities from the Active Galaxies Educator’s guide and pop-up book, as well as a “Make Your Own Pulsar” activity from our newly released Supernova Educator’s Guide. All GLAST classroom materials can be downloaded from here.

And last but not least, launch marked the occasion for unveiling a new look for the SSU group’s main web site.  Enjoy!

Coming up…

Further status reports on instrument activation.  Later tonight the GBM detectors will begin powering on.

GLAST Update for 23 June 2008

What is GLAST doing now?

After relatively simple, but important, software modifications were transmitted up to the spacecraft, some of the previously tested maneuvers were repeated to verify the software installation was successful.  The onboard use of the GPS orbit position information is now also spot-on. 

GLAST is ready for instrument turn-on, which will start early tomorrow morning!  First, power will be fed to the instruments, then their onboard computers will be booted up and configured.  GBM will start turning on first, followed by the LAT a few hours later.  Much of the next couple of days will be spent turning on and checking the many sensor subsystems on the LAT.  We’re very excited to start waking up the instruments after all these years of planning and testing.

Thoughts before waking up the instruments

On the eve of instrument turn-on, here are some thoughts of some of the members of the instrument teams.  First, from Dr. Chip Meegan, who is the GBM Principal Investigator at Marshall Space Flight Center:

The GBM team is eagerly anticipating the beginning of science operations on GLAST.  Our many years of hard work will soon be rewarded with the first real data from space.  Right now our only task is monitoring the temperatures of our detectors.  The good news is that these are very close to predictions.  Over the next week we will gradually power up GBM, verify that everything is working properly, and adjust the detector gains and other software parameters.

We have learned a lot about gamma-ray bursts (GRBs) in recent years.  We now know that that these events have incredible power, releasing as much energy in a few seconds as the sun will over its entire 10 billion year lifetime.  Although we have some idea of how this happens in general, the details remain mysterious.  Working together, the LAT and GBM will observe gamma radiation over an unprecedented range of photon energies, shedding new light on how GRBs work.  I am particularly interested in
what we will learn about a mystery that we got a glimpse of with the Compton Gamma Ray Observatory.  It appears that at least some bursts generate high energy photons (in the LAT range) after the lower energy photons (in the GBM range) have ceased.  This is difficult to understand theoretically, and GLAST will be able to study this in detail, perhaps telling us something important about how the photons are produced.

As Steve has often said, the most interesting things will be the new mysteries that GLAST discovers.  GRBs have surprised us many times over the years, and I don’t expect them to stop now.

The following is by Prof. Robert Johnson, from U.C. Santa Cruz.  The most complex part of the LAT by far is the Tracker (TKR) subsystem, and you can bet that Robert, as the TKR Subystem Manager, will be particularly interested in the progress of LAT turn on during the next few days.  Robert is also currently the co-coordinator of the LAT science group preparing to search for signals of dark matter and possible new physics.  I asked him what he most hopes will be learned with GLAST.

For me, the most exciting signal that GLAST could see would be gamma rays produced by dark matter.  Given the preponderance of gravitational evidence for dark matter, together with its complete lack so far of any other direct signature, its composition is one of the greatest mysteries in astrophysics.  It is amazing that despite our tremendous progress in physics and astrophysics we still do not know what makes up most of the matter in the universe.  Current theories bring ideas in fundamental physics together with the latest in cosmology and astrophysics to try to explain this mystery.  Since I began my career in experimental particle physics, it would be wonderful to use GLAST to make further connections between those fields and to begin to resolve the great dark matter enigma.

Coming up…

Progress turning on the instruments, plus more news from around the international GLAST team.  Please check back during the next couple of days.

GLAST Update 22 June 2008

What is GLAST doing now?

We’re almost two weeks into the mission now, and things continue to go well, thanks to coordinated efforts across the team.  Over the weekend, the spacecraft onboard attitude control software was further tested, with more challenging pointing sequences, autonomous repoints (once the instruments are activated and configured, they can request the spacecraft to change its orientation to keep a gamma-ray burst location detected onboard within the LAT field of view.  This is similar to what is done on the Swift satellite), and rehearsals for Targets of Opportunity (TOOs — quick-response repointing of the observatory via ground command — which we expect to do for GLAST only under extraordinary conditions, but we want to be ready!).  With such complex maneuvers, there have been a few interesting hiccups, all of which have been quickly understood and addressed.  Everything continues to function in a very stable manner, and it has been great fun watching the observatory move from baby steps to sophisticated, graceful motions.

Operating a spacecraft

Jack Leibee, one of my colleagues at Goddard, is the Mission Manager for GLAST (he is also the Systems Manager).  I asked him to write a few thoughts from his perspective about what it’s like to operate a satellite like GLAST:

Getting ready to operate a spacecraft, once it is in orbit, is a very demanding task.  For the last year and a half, we have been testing between the GLAST Operations Center and the spacecraft to verify that all commanding procedures are correct, as well as confirming that we have all the tools necessary (e.g. plotting and displaying observatory data) to monitor the performance of GLAST.  We conducted well over 300 hours of this type of testing, while GLAST was on the ground, executing around 400 command procedures.  We also conducted 10 simulations, where we had all the folks who are going to support the mission execute the activation command procedures with a GLAST simulator.  In some of the pre-launch tests, the Simulation Director inserted anomalies (e.g. a component fails) to test the operations team ability to respond: figure out what happened, why it happened, and how to recover back to normal operations.

During launch and ascent to orbit, we watched the spacecraft telemetry in the Mission Operations Center.  We also saw the spacecraft react to separation from the rocket by pointing to the Sun and deploying the solar arrays (needed to provided power to the spacecraft.)  Over the next 10 days we have been turning on spacecraft components and checking out the spacecraft (e.g. Slewing (moving) the spacecraft to look at different points in the sky) to verify it meets requirements.  This is all in preparation for the instrument turn on of the LAT and GBM in just a couple of days.

It has been an exciting and rewarding time for all of us as we see the results of everyone’s hard work and dedication.

Coming up…

In addition to regular status updates, you’ll be able to read about the GLAST Education and Public Outreach activities, as well as reports from other scientists working on GLAST from around the world about their hopes and expectations as the instruments are powered on and checked out.  Please check back regularly.

Update 19 June 2008

Observatory News 

Yesterday was another great day for GLAST.   After several days of successful maneuvering tests (see previous blog entry), it was time to activate the antenna that will very soon be used for science data transmission.  A gimbal points the antenna to one of several satellites in the Tracking and Data Relay Satellite System (TDRSS).  Engineers working in the Mission Operations Center had previously checked out the gimbal, solving a few minor glitches along the way.  The transmitter was activated yesterday, and the performance of the communication link was even better than expected!  After some initial tests, the link was used to dump data from the onboard solid state recorder (SSR), which temporarily stores the data pending transmission to the ground.  The data transmission contacts typically last about 15 minutes, and 5-10 contacts per day are planned during routine operations. 

The observatory is now smoothly executing the standard sky survey observing pattern while performing test data transmissions — which means GLAST is almost ready to start turning on its instruments next week, after just a few more preparatory steps.  Then the work to calibrate and tune the instruments for the on-orbit environment can begin, a process that will take many weeks of hard — but rewarding — work.  Stay tuned!

News from Italy

The following is from Prof. Ronaldo Bellazzini, who is the INFN Italian team coordinator:

There has been great interest in Italy in these weeks for the GLAST launch. GLAST has been on the national or local media media almost every day!  Our sponsor agencies (INFN, ASI, and INAF) are programming a further set of events related to the forthcoming milestones (LAT activitation, first light results, first skymap…).  Please visit this link for information on the launch-related public outreach activities in Italy.

The launch was the culmination of many years of hard work by many people coming from different scientific and technical cultures.  In Italy, as elsewhere, GLAST has been the result of a strong partnership between the particle physics and high-energy astrophysics communities.  We have united our efforts to share important science goals and technical expertise.  All members of the INFN team (from the Trieste, Udine, Padova, Pisa, Perugia, Roma2 and Bari INFN sections) are anxious for LAT activation and for first-light results from the instrument we have proudly contributed to building and testing.

We are sure that GLAST is starting its journey toward extraordinary discoveries that will help change our understanding of the Universe.

News from the LAT Instrument Science Operations Center (ISOC)

The following is from Dr. Eduardo do Couto e Silva, a Deputy Manager of the ISOC at SLAC and a LAT Team member:

We are just a few days away from turning on the LAT!  The team will be ready and waiting for the data, working in close coordination with our colleagues at the Mission Operations Center at Goddard Space Flight Center.  We are organizing about 100 of our collaborators around the world, who will be involved in LAT operations and who will take shifts at the Stanford Linear Accelerator Center (SLAC) in California, so that the LAT and its data can be monitored continuously.   Data will flow through the ISOC, for processing, and made available to the rest of the LAT team.  The LAT Collaboration distributed worldwide will work with those at SLAC to inspect the quality of the data and to ensure we have a calibrated telescope whose performance is optmized for the best scientific return.  This is a huge effort, and we are ready for the challenges ahead.  We can’t wait to see the gamma-ray sky through GLAST “eyes” and to share with the world what we find in the months and years ahead.

Coming up…

In future posts, we will have contributions from other GLAST team members from around the world.  Please check back every few days for status updates and more news from GLAST.