Introduction - Autonomous and Autonomic Systems - page 6

Fig. 1.2. STEREO mission spacecraft (image credit: NASA)
The STEREO instrument and spacecraft will operate autonomously for
most of the mission due to the necessity of the two spacecraft maintaining
exact distances from each other to obtain the needed stereographic data. The
spacecraft use a beacon mode where events of interest are identified. Broad-
casts are then made to the ground for notification and any needed support.
The beacon mode automatically sends an alert to earth when data values ex-
ceed a threshold level. Each of the STEREO spacecraft is able to determine
its position, orientation, and orbit, and react and act autonomously to main-
tain proper position. Autonomous operation means significant savings over
manual operation.
1.1.3 Magnetospheric Multiscale
The Magnetospheric Multiscale (MMS) mission, scheduled to launch in 2014,
will use a four-spacecraft cluster that will study magnetic reconnection,
charged particle acceleration, and turbulence in regions of the earth's magne-
tosphere (Fig. 1.3 ) . The four spacecraft will be positioned in a hexahedral or
quad tetrahedral configuration with separations of 10 km up to a few 10 s of
thousands of kilometers [ 51 ]. This arrangement will allow three-dimensional
(3D) structures to be described in both the magnetosphere and solar wind.
Distances between the Cluster spacecraft will be adjusted during the mis-
sion to study different regions and plasma structures. Simultaneous measure-
ments from the different spacecraft will be combined to produce a 3D picture
of plasma structures. The spacecraft will use interspacecraft ranging and com-
munication and autonomous operations to maintain the correct configuration
and the proper distances between spacecraft.