Environmental Engineering Reference
In-Depth Information
partially offsetting the need for many direct-to-spacecraft communications
paths from ground antennas.
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Some constellation missions may require that the spacecraft communi-
cate with one another for science or formation purposes. One spacecraft
may need to broadcast information to many other spacecraft in its vicin-
ity. Alternatively, one spacecraft may need to communicate with another
spacecraft in the constellation, for example, to cue it so that the second
spacecraft can record an event that the first could not. But these spacecraft
may be located in orbital planes where they are rarely if ever in direct line
of sight of each other. Multihop networked inter-satellite communications
may be necessary to synchronize operations of the entire constellation, or
just a subset of it.
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Trend analysis is an important element for any spacecraft mission. It helps
the mission operations staff determine whether a failure may be imminent
so that switchover to backup or redundant subsystems can be performed,
or if necessary, to have the spacecraft enter safemode until the problem
can be identified and a corrective course of action implemented. Greater
automation in ground data processing will be required to support this.
Perhaps data mining techniques that are presently implemented for ter-
restrial databases and e-commerce applications may provide solutions for
consideration and adaptation to this new problem.
9.3 Advantages of Constellations
A wide variety of missions could be best implemented with constellations of
satellites working together to meet a single objective. Reasons cited for using
constellations include lower mission costs, the need for coordinated science,
special coverage or survey requirements, and the need for quick-reaction tac-
tical placement of multiple satellites. The following discusses these in more
detail.
9.3.1 Cost Savings
The cost of producing spacecraft for a constellation and getting them to or-
bit may actually be lower than traditional “one of a kind” satellites that
use a dedicated launch vehicle. With a traditional satellite, system reliabil-
ity requirements force a high level of component protections and redundancy,
which leads to higher overall weight and launch costs. Due to their size and/or
weight, a dedicated launch is often required for these missions. With a con-
stellation, system reliability can be met by having spare satellites. The use of
per-satellite redundancy can be significantly reduced. In some cases, it may
be practical to use lower-rated components at a much lower cost combined
with an on-orbit sparing plan. Additional savings could be obtained through
the use of assembly-line production techniques and coordinated test plans,
