A Birthday Card for Chandra

This is a slightly abridged version of a note that was recently sent around to the Chandra team by Harvey Tananbaum (Director of the Chandra X-ray Center) and Roger Brissenden (CXC Manager and Deputy Director of the Harvard-Smithsonian Center for Astrophysics) to congratulate everyone on Chandra’s 12th birthday. With the end of the Space Shuttle program just last week, it was a fitting reminder just that a short dozen years ago, Columbia blasted off carrying Chandra safely into orbit.

Dear Chandra Family,

On July 23, we passed Chandra's 12th birthday so we would like to take note of this special event.

Chandra continues to be an amazing observatory in terms of the science discoveries and in terms of the smooth operations. With regard to the latter, most of you are aware of the first Chandra "safe mode" in over 11 years, which occurred about 2 weeks ago. It took a few anxious days with long hours for the operations team members to figure out that a combination of unusual factors had caused the on-board computer to over-estimate the rate of momentum change. The calculated value exceeded the acceptable limits and tripped the safe mode -- even though the reaction wheels and gyroscopes indicated no real problems on-board. After the cause was understood and it was established that there were no hardware failures, it then took a couple of days to extract Chandra from safe mode and restart the science program. The team did a fantastic job in handling this "event"!

On the science side, we remain enthusiastic about all of the discoveries over the past few years as well as the prospects for the coming years. With the evolution of the orbit -- lower perigee and more time above the radiation belts -- plus the quiet Sun and the efficient scheduling by the team, the Chandra viewing efficiency (fraction of time doing science) has been around 75% for the past year compared to 65-67% in the early years of the mission. While the efficiency will decrease some as the orbit continues to evolve, we are using the additional time currently available to institute a category of X-ray Visionary Programs using 1 to 6 million seconds each. This year's Peer Review recommended four such projects that might otherwise not have been practical from a time perspective.

Perhaps this note is beginning to sound more like a newsletter than a birthday card. The main thought is to congratulate one and all for contributions -- past, present, and future -- making Chandra a fantastic success.

Our thanks and best to all,
Harvey and Roger