that AFSCN sites are ground-based and are only in
view for about 5 minutes (when in low Earth orbit, as
ASTRO and NextSat were), but TDRSS is satellite-based and is pretty much always in view. The challenge is that these resources are shared across many
missions, and each mission has to reserve time in
advance. But events can cause resources to become
available or to drop out, so it is often the case that we
need to be able to respond to these changes quickly.
A scenario (see figure 3) typically consisted of a
series of procedures, each of which was written by the
operations personnel in Microsoft Word table format.
Each procedure listed its steps and associated durations and represented the need for a contact and the
type of contact desired or required. Several procedures had other embedded procedures and some
spanned more than one day. As an example, the
unmated scenario required an initial setup procedure, then the unmated procedure would be kicked
off; the de-mate, hold, and re-mate would execute,
and then a postrendezvous and capture transfer procedure would be planned. See figure 4 for images of
the unmated scenario midexecution in the de-mated
configuration and in the final stages of berthing to
the mated state.
The schedule of each scenario was dependent on
what had been accomplished to date, as the goal of
each scenario was to become increasingly more
autonomous. The planning schedule was also
dependent on the state of the flight system, the
amount of preparation time needed before execu-
tion, and resources available on future dates. Calen-
dar planning was done by a combination of inputs
from flight directors, mission managers, project
management, and DARPA.
Procedures were delivered to the SRP and copied to
Excel. An ASPEN model-generation script was then
used to create ASPEN Modeling Language (AML) representations of the procedures. Once the AML model existed for a procedure, the ASPEN tool read the
AML description of the procedure and could be used
to add any number of different procedures in a plan
required to make up the scenario. See the data flow
diagram and the final daily plan in figure 5.
Roles of Mission Planning
Mission planning had two primary roles for Orbital
Express: ( 1) evaluate scenarios for feasibility early in
the design of the mission, and ( 2) provide responsive
communications and commanding planning and
scheduling during the mission. To serve both roles,
Figure 3. The Orbital Express Scenarios: Increasing Autonomy and Complexity.