If you need to generate an orbit for your proposal you will need an ephemeris file. This file should be used in conjunction with the parameter in gtorbsim set to
EphemName = FERMI_TLE_09033.78481577.tle
EphemFunc = tlederive
If you feel you need a more current TLE they can be obtained from NORAD using the link Space & Earth Science and search for FGRST (Fermi Gamma Ray Space Telescope) or for GLAST.
In addition to the TLE file to define the orbit you will need to input the Fermi definition of the SAA (South Atlantic Anomoly) so that the tool will correctly account for the presence of the SAA. You can download the file here
The observation simulator needs three input files. An xml file defining the input model. This is a flux-style definition file which can be created or edited with the modeleditor. Here is an example file that can be used as an template. When you use the latest diffuse emission model, gll_iem_v02.fit, in a likelihood analysis you will want to use the corresponding model for the isotropic diffuse emission, which includes the residual cosmic-ray background. To simulate the isotropic model you will need to download the following files isotropic_iem_v02.txt and isotropic_allsky.fits. The isotropic spectrum is valid only for the P6_V3_DIFFUSE response functions and only for data sets with front + back events combined.
You will need a file that contains the names of the sources you wish to simulate. This allows you to evaluate the effects of any of the sources in your xml file without rewriting your input xml.
In addition you need to specifiy the orbital motion and orientation of the spacecraft via a pointing history file. You can use one generated from the output of gtorbsim or use a pregenerated file The example pointing file covers the time period from MET = 255571200 to 260323200 (2009-02-06 00:00:00.000 UTC to 2009-04-02 00:00:00.000 UTC.
Using the likelihood tool to fit extracted data also requires an xml file but the file format is not the same as for the observation simulator. gtlike uses a src model format for its xml file and an example can be found here. The current model for the isotropic emission used in the Likelihood xml model file is isotropic_iem_v02.txt and is available here. Models for the isotropic emission for the events that convert in the front and back of the detector are also available. The Galactic diffuse model can be downloaded here. All of the background models along with a description of the models are available here.
The current model for the isotropic emission used in the Likelihood xml model file for use with the dataclean class is isotropic_iem_p6v3dataclean_v02.txt and is available here. Note that this file is appropriate for front + back events only.
The pulsar data for the pulsar tools can be downloaded here.
The pointing history for the Fermi spacecraft can be downloaded here. This file covers from 2239557417.5 to 266144559.2 in Mission Elapsed Time (MET) or from 2008-08-04 15:43:34.507 UTC to 2009-06-08 09:02:39.2 UTC.