Chandra XRay Observatory CXC Update on ACIS Operations

Chandra X-Ray Observatory CXC Update on ACIS Operations I. New Patch for ACIS Flight SW II. Control of the ACIS FP temperature Paul Plucinsky 1 EPI Cal 2010

Chandra X-Ray Observatory CXC Update to the ACIS Flight SW • ACIS flight SW has been updated three times during the mission in 2000, 2004, & 2008 • We are preparing the fourth patch for uplink in Spring 2010 • This new patch contains two new items: 1) 2) Fixes a bug in a subarray mode – the list of bad pixels and columns onboard is misinterpreted if the subarray starts in a row other than row 1 Prevents Back End Processor (BEP) from crashing when one of the Front End Processors (FEPs) is powered down - there have been several occurrences when radiation levels have been high, that ACIS was commanded by the stored command load to start the first science observation of the orbit, it started collecting the bias data, but then received a high radiation shutdown signal from the satellite, but ACIS waits for the bias maps to be collected before stopping the science run, but before the bias maps are collected a command is sent which powers down the FEPs, this caused the BEP to crash in the past Paul Plucinsky 2 EPI Cal 2010

Chandra X-Ray Observatory CXC Control of the ACIS FP Temperature • Desired temperature -119. 7 C, FI/BI CCDs go out of gain spec at -119. 2 C/-118. 2 C • Mean T of science observations • ACIS DH heater turned off in April 2008 • SIM FA 6 heater turned off in August 2009 Paul Plucinsky 3 EPI Cal 2010

Chandra X-Ray Observatory CXC Controlling the ACIS FP Temperature • Camera Body used to be held at -60 C, it now floats between -65 and -70 C FP is contained in the “Camera Body” DH heater is on the “Camera Body” Paul Plucinsky 4 EPI Cal 2010

Chandra X-Ray Observatory CXC Exploded View of ACIS HW Paul Plucinsky 5 EPI Cal 2010

Chandra X-Ray Observatory CXC Restrictions on Spacecraft Attitude • unfortunately there are no other heaters we can turn off which would help to keep the FP cold • must now consider imposing restrictions on the satellite’s orientation during observations (which is already done for several other systems on Chandra) Paul Plucinsky 6 EPI Cal 2010

Chandra X-Ray Observatory CXC Impact of Current Restrictions on Spacecraft Pitch Angle • restrictions imposed in 2005 significantly increased the amount of time spent at tail-Sun attitudes, pitch>115 • unfortunately this is a hot attitude for the ACIS FP temperature Paul Plucinsky 7 EPI Cal 2010

Chandra X-Ray Observatory CXC Chandra in the Shuttle Bay Before Launch • thermal properties of the back surfaces of SIM are changing with time Paul Plucinsky 8 EPI Cal 2010

Chandra X-Ray Observatory CXC Chandra in the Shuttle Bay Before Launch • heating on the back surface of the SIM, heats the ACIS Camera Body • heating of the shade for the radiator, heats the radiator Paul Plucinsky 9 EPI Cal 2010

Chandra X-Ray Observatory CXC Earth in the ACIS Radiator FOV • Earth in the ACIS radiator FOV has a significant impact on the FP temperature • The complex shape of the shade has been approximated by a simpler shape, we are working on a more realistic model • we recently included reflections off of the interior surfaces of the shades Paul Plucinsky 10 EPI Cal 2010

Chandra X-Ray Observatory CXC ACIS FP Temperature vs. Earth Solid Angle Without Reflections Adams -Wolk (SAO) Paul Plucinsky 11 EPI Cal 2010

Chandra X-Ray Observatory CXC ACIS FP Temperature vs. Earth Solid Angle With Reflections Adams -Wolk (SAO) Paul Plucinsky 12 EPI Cal 2010

Chandra X-Ray Observatory CXC Future Strategies to Keep the ACIS FP Cold There are two reasons the ACIS FP temperature gets warm now: 1) Earth in the ACIS radiator FOV 2) Sun on the back surfaces of the SIM and the radiator shade Our only option now is to impose restrictions on the spacecraft attitude, but that will be difficult because: Paul Plucinsky 13 EPI Cal 2010

Chandra X-Ray Observatory CXC Backup Material Paul Plucinsky 14 EPI Cal 2010

Chandra X-Ray Observatory CXC Chandra’s Changing Orbit and Implications for the FP Temperature • Chandra’s orbit is changing such that in 2012 the inclination will be at its highest value in the mission and the perigee will be at it lowest • the solid angle of the Earth in the ACIS radiator FOV will also reach missions highs in 2012 • other mission constraints such as momentum management and thermal issues frequently conflict with keeping the ACIS FP cold during perigee passages Davis (Chandra FOT) Paul Plucinsky 15 EPI Cal 2010

Chandra X-Ray Observatory The FP Temperature during Recent Perigee Passages CXC Adams-Wolk (SAO) science perigee cal science Example of a good perigee passage Paul Plucinsky 16 EPI Cal 2010

Chandra X-Ray Observatory CXC The FP Temperature during Recent Perigee Passages Adams-Wolk (SAO) science perigee cal science Example of a bad perigee passage Paul Plucinsky 17 EPI Cal 2010