Abstract:
The space data association (SDA), an association of global satellite operators working
to ensure a controlled, reliable, and efficient space environment, has run a survey
among its members to gather data on their Conjunction Assessment concept of
operations. These include collision avoidance Go/No-Go metrics, collision avoidance
targets, and operational constraints. This paper assesses the various positional
accuracy requirements of space situational awareness (SSA) data associated with
each of these diverse "Go/No-Go" metrics as employed in the conjunction mitigation
processes used for space traffic coordination and spaced traffic management.
These metrics include miss distance at the time of closest approach (TCA), componentized
miss distance (e.g., TCA radial separation to preclude collision even
when in-track or cross-track separations or uncertainties are unknown), and maximum
collision probability and estimated actual probability. A common practice is to
approximate a spacecraft’s hardbody with an encapsulating sphere. This one-shapefits-
all approach eliminates the need to determine orientation, but results in an overestimated
object volume and an overinflated probability unless both satellites are
actually spheres. The dependence of collision probability on orientation and configuration/
shape of the satellites at TCA is examined in contrast to the use of an encapsulating
spheres to produce more representative probabilities. To overcome the lack
of knowledge of the enveloping box’s orientation a spectrum of collision probability
values corresponding to a range of box orientations, from which the interrelationship
between attitudinal knowledge and position accuracy required for a given collision
probability threshold can be determined. It was found that such an approach can
typically reduce probability by a factor of 3 or more. The interrelationships between
SSA positional accuracy, the operator-selected Go/No-Go metric and its threshold,
timeliness, and resulting maneuver frequency is also explored. For example, the
necessity to perform a collision avoidance maneuver adhere to a squared relationship
on the adopted miss-distance threshold. The miss distance threshold adopted
by the operator should, if done properly, be a function of the estimated accuracy of
the primary and secondary objects as a function of time. This paper concludes by comparing the accuracy requirements derived for each metric above with estimates
of positional accuracy observed in actual SSA data fusion experiments conducted
this past year. In many situations, the accuracy of legacy and commercial SSA systems
is insufficient to support the adopted Go/No-Go metric without using comprehensive
data fusion techniques. Recommendations for operators are provided.
Keywords:
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Alfano, S., Oltrogge, D.L., and Arona, L., “Operators’ Requirements for SSA Services,” Jour Astro Sci, 27 Oct 2022, https://doi.org/10.1007/s40295-022-00346-8
