The Emergency Science Hologram (ESH) was a development from the Emergency Medical Hologram (EMH) and the extension Emergency Command and Conn Hologram (ECCH) concepts. It was part of the Emergency Holographic Complement of fleet carrier classes and the heavy battleship classes of Starfleet.
The ESH was developed simultaneously with the ECCH in 2380, after tests have shown that the Science department of a Starfleet facility or starship could benefit from an emergency holographic program as much as a Starfleet sickbay or infirmary did with an EMH.
Essentially, the ESH was a 'backup science officer', intended to assume responsibility for investigating any new scientific phenomenon and advising the command staff on questions of science, such as spatial phenomenon, new life forms, and unknown energy forces in the event that the current science crew would be incapacitated for some reason. The ESH possessed over 5 million science subroutines from the science databases of all the leading Science Officers in Starfleet, and could incorporate them into its plans as it performs its tasks.
There were three (3) ESH in the Emergency Holographic Complement of the fleet carrier classes and the heavy battleship classes of Starfleet and of Vanguard Command. In all other starships, there is only one (1) ESH in the Emergency Holographic Complement.