Any change from the routine operations described in the preceding sections will entail notification to mission elements at short notice. Mission element contact details are given in §10.6. Each mission element should ensure that their contact information remains current and notify the VSOG of any changes.
The most likely contingency will be a change in the satellite observing schedule, which could arise if there is a time-critical Target of Opportunity observation, a correction to the existing schedule, etc. For simplicity, notification of the mission elements by the VSOG will be made via an e-mail distribution list - dit@vsop.isas.ac.jp - which contains multiple direct points of contact for the VSOG, tracking stations, orbit determination centers, correlators, and GRT arrays. GRTs will be notified individually or collectively as necessary to inform them of the location and name of new schedule files, or of the cancellation of observations as appropriate.
Non-VSOG mission elements will also use the ``dit'' list to notify the VSOG (and all other mission elements) of unexpected events that may impact operations elsewhere, e.g., if a tracking station discovers that the spacecraft is in an unexpected configuration. Such notification by non-VSOG mission elements should be considered ``information-only'' communications that do NOT imply specific unscheduled action by other non-VSOG mission elements. When and if possible (see next paragraph), the VSOG will respond with clarification of future expectations, recommendations, or directives.
In the special case of unexpected spacecraft problems (e.g., unexplained loss of downlink signal at a tracking station), rapid notification of appropriate spacecraft operations personnel in the VSOG is possible via a pager system that is activated by email sent to vsopsos@vsop.isas.ac.jp. To alert other mission elements to the possibility of forthcoming recommendations from the VSOG, any email sent to this address will be forwarded to the ``dit'' distribution. However, it will usually be necessary to wait for a Kagoshima Space Center operations tracking pass to better determine the satellite's status (see the VSOP WWW site /astro/halca/vsop/ops/Operations.html for the KSC schedule). For this reason, observations should continue at all mission elements until the VSOG determines the utility of continuing and, if necessary, explicitly cancels observations.
In general, two-way communications on timescales shorter than 24 hours is most desirable between the VSOG and the tracking stations for clarification of real-time spacecraft status and information. However, the many complexities of scheduling space VLBI observations imply that meaningful changes to the observing schedule on this timescale or shorter are extremely difficult and failure-prone, except perhaps for explicit cancellations, and are therefore very unlikely. Thus, receipt and acknowledgement of such communications will be undertaken on a locally-determined best-efforts basis, especially at mission elements not directly involved spacecraft operations. Any mission element with special requirements in this regard should make them clear to the entire mission.
Since the pager system is monitored principally by spacecraft operations personnel, communications via vsopsos@vsop.isas.ac.jp which concern non-spacecraft emergencies are discouraged (especially Monday-Saturday in Japan) unless a response is absolutely required within a few hours. Use of dit@vsop.isas.ac.jp as described below should be sufficient in most if not all such cases, with a reply from a VSOG representative usually available within 24 hours.
Since the ``dit'' list is also used for routine communication among the mission elements, information that is, as determined by the originator, especially time-critical in nature should be so indicated with ``** VSOP SOS **'' in the Subject line of the message. In the body of the message, the sender should indicate their name, the date, and the mission element they represent, and concisely describe the nature of the contingency. If acknowledgement from other mission elements is required or desired this should be explicitly requested. To avoid confusion, ``** VSOP SOS **'' messages (and all replies to them) should be carefully considered before sent. Only explicit directives from the VSOG should be considered authoritative instructions to alter operations (except for local determinations of safety, etc.).