Email sent to all Cycle 17 Hubble Space Telescope principal investigators (PIs):
Subject: SM4 Delay impact on Cycle 17 HST Program
Date: 10/15/2008 10:33 PM
As Cycle 17 PIs, you are no doubt as disappointed in the delay of Hubble Servicing Mission 4 (SM4) as we at STScI are. We were eagerly anticipating the installation of two new instruments, the repair of two old instruments, and the exciting discoveries these actions will enable. The purpose of this note is to inform you, as best we can in this fluid situation, of our expectations and plans for SM4 and Cycle 17.
On September 27, all the HST instruments, except for the FGS, were placed into safemode. The problem arose in a unit, the Control Unit/Science Data Formatter (CU/SDF), that is a part of the Science Instrument Command and Data Handling (SI C&DH) system. As its name implies, the SI C&DH is central to the operation of the instruments on Hubble. All commands to the instruments and all engineering and science data from the instruments must pass through the SI C&DH. The specific problem is limited to the handling of data by the Side-A CU/SDF, but it has the consequence that we cannot operate the instruments or obtain science data with this SI C&DH configuration. FGS data are not processed by this system and science operations have continued with the FGS. At this
time, the HST Project plans to switch to the redundant Side-B of the CU/SDF and related equipment around October 15, after which the ACS/SBC and WFPC2 will be recovered from safemode and begin observations. The NICMOS Cooling System will be restarted and NICMOS activated some time after that.
This leaves HST in a situation where another failure in the SI C&DH could permanently disable the scientific instruments. SM4 was delayed in order to provide time to remedy this situation. The SI C&DH design allows it to be replaced by astronauts during an EVA. A spare unit was built, but never fully qualified for flight. The Hubble Project will be completing qualification of that unit as rapidly as possible.
The obvious first question is, when will SM4 take place? It looks like the earliest possible time is February 2009. However, NASA is just beginning to go through the entire process of planning the Hubble work for testing the replacement SI C&DH, planning the astronaut training for the new task, and fitting the Hubble mission in with the other Shuttle flights planned this Spring. As a result, you should expect uncertainty in this date for several more months. The next obvious question is, will anything have to be dropped from the planned mission in order to include the replacement SI C&DH? The answer to
this question will depend on testing, training, and detailed EVA planning which will take several months to complete. We are hopeful that no changes will be required to the planned scientific enhancements to Hubble, but the servicing workload is already quite high.
We do plan to carry out the Cycle 17 observing program, as it is, after SM4 takes place. Accepted Cycle 17 programs that use the FGS, ACS/SBC, and NICMOS will not need to be held until after SM4; they will be executed as their scheduling allows. Our Program Coordinators and Contact Scientists will be getting in touch with the designated contacts for programs that look feasible prior to SM4. Following our standard practice, Cycle 17 funding for observational programs will be released after the first observations are taken. Funding for Cycle 17 archival and theory programs will be unaffected. We will soon solicit additional contingency observing programs, using the current instrumentation, in order to
keep HST scientifically productive until servicing does take place. These programs will not displace or delay the implementation of the accepted Cycle 17 observing program after SM4.
We will do our best to keep you and the rest of the astronomy community informed as NASA’s SM4 plans and our science operations plans evolve over the next several months. Two places to look for updated information will be: http://www.stsci.edu/hst/ and http://hubble.nasa.gov/index.php.