Environmental Engineering Reference
In-Depth Information
L5
L3
L1
L2
Earth
Sun
L4
Fig. 3.2.
Lagrange points (not to scale)
planet formation, etc. In the past, spacecraft were launched mounting rela-
tively smaller science instruments that were pointed at their science targets
by pointing the entire spacecraft (e.g., HST). Some science instruments were
equipped with swivels that allowed the science instrument to be pointed inde-
pendently and, in the case of survey SIs, the swivel could be rotated continu-
ously to map out a swath of the sky (e.g., RXTE and Swift). On a few missions,
the survey function was carried out without a swivel by continuously spinning
and precessing the entire spacecraft (e.g., WMAP). But for interferometry
missions, whose performance capabilities are driven by the length of their
baseline, in effect a small spacecraft bus supports a very large science instru-
ment (on the order of many tens of meters long). And for some interferometry
missions currently on the drawing boards, to achieve even larger baselines, the
science instrument is a composite object that is an amalgam of the individ-
ual light collecting capabilities of many individual detector spacecraft whose
data are consolidated within a hub spacecraft. For these missions, preproposal
planning usually concentrates on developing a feasible design for the science
instrument, paying less attention to the spacecraft bus whose design needs
are often assumed to be satisfiable by an existing Rapid Spacecraft Develop-
ment Oce (RSDO) spacecraft design. This is a major paradigm change from
GSFC's earlier approach of paying equal or greater attention to the spacecraft
bus design during the early planning phases.
The most interesting developments in flight autonomy may be those fea-
tures required to support formation flying and spacecraft constellations. Such
missions will demand a much heightened degree of spacecraft self-awareness
and self-direction, as well as an awareness of the “outside world.” Until now,
a spacecraft has needed to be knowledgeable regarding outside “entities” to
the extent that it needed to use them. For example, to use a TDRS space-
craft to communicate with the ground, a spacecraft had to know both its
own ephemeris and that of the TDRS spacecraft. But for a constellation of
