Everybody planning to submit an XMM observing proposal as Principal Investigator (PI) must register as a user of XRPS. Upon entry into XRPS from the XRPS entry page at the URL http://www.xmmsoc.ops.esa.int/, each user can choose between two options:
Obviously, upon first entry there is nothing yet to load. Therefore, one
selects the ``New proposal'' option. The software then assumes that the
user wants to register as Principal Investigator (PI) of an XMM proposal.
Upon first entry, please leave the User ID field empty; you will
be assigned a User ID automatically.
Please choose a password (it is typed in clear text on the screen and
no validation check is performed). Only alphanumeric keys should
be used, because punctuation keys, such as e.g. 
or !, can lead to
XRPS performance problems! Then make an entry in each field
marked with an asterisk. Asterisks mark the mandatory input fields.
Additional information requested in the other, voluntary input fields
is welcome, because it can help the SOC (e.g., getting in touch with
an observer quickly if necessary).
Once this is done, press the ``commit'' button at the bottom of the page to send your input to an intermediate memory (more details on this will follow in § 4.4). If all entries are supplied as requested, XRPS will return a success message (text displayed in blue), telling the user which User ID has been assigned. Users should immediately make careful note of their ID and password.
Some users might want to use more than one User ID (e.g., when preparing a proposal not only for themselves, but also somebody else). In such a case, it is NOT possible to enter XRPS, from one browser window, under a user ID other than the one entered first. In order to enter under a new user ID, the browser session must be exited and a new one started. This is a safety procedure, because XRPS works with cookies to identify the user accessing it via a browser. Once all applications of the session are closed down, the cookie is removed. A new session can then be started with a new cookie, which is then the identifier of the current user ID.