IEEE Aerospace and Electronic Systems Magazine - July 2020 - 27

Credit: Jet Propulsion Laboratory

Deep Space exploration community efficiently and
without interruptions.

SPACECRAFT TRACKING AND NAVIGATION
Spacecraft tracking in deep space has been mostly based on
radio signals, where radiometric data types of Doppler,
range, and delta Differential One-Way Ranging (DOR) are
collected and provided as inputs to the navigation algorithm.
This method uses the powerful DSN antennas for the collection of radiometric data. Although this approach has served
the deep space community well for decades, for certain
applications like rendezvous with comets and asteroids, formation flying and entry/descent/landing (EDL), autonomous
optical navigation usually provides better performance,
examples of which can be found in [1]-[3]. By using only
radiometric data types, it is very difficult to rendezvous with
a small body when its orbit and shape are not precisely
known. However, such a rendezvous can be accomplished
via the use of onboard sensors and cameras combined with
onboard autonomous navigation algorithms.
Optical navigation can provide for autonomy, meaning
spacecraft navigation with little or no ground interaction.
This approach would use images of landmarks on solar system bodies, images of natural or artificial satellites, images
of asteroids in interplanetary space, and images of stars for
inertial reference. Because of a mission's accuracy requirements, the utility of optical navigation is mission dependent;
certain missions can conduct optical navigations throughout
the whole mission duration, whereas others may need RF
navigation. Equipping a mission with both RF and optical
JULY 2020

instrumentation is likely to yield the best result for complex
navigation endeavors. This is also true for missions demanding high levels of robustness, e.g., manned missions.
As mentioned above, an important feature of navigating optically is that it can perform autonomously with little need to contact earth because the observables can be
collected without the use of the DSN. Taking advantage
of this feature would reduce the DSN antenna time and
provide for navigation in places where contact with earth
may not be possible or desirable. Moreover, it transfers
the burden of navigating the mission from the ground
crew to the onboard computer, hence, reducing labor.
Independence from the ground permits quick maneuvers
that would not be possible with traditional navigation
schemes, which are limited in response time by the roundtrip delay between the spacecraft and ground.
NASA has a successful history of integrating sensors
and flight software to accomplish complex onboard navigation functions, e.g., EDL, formation flying, science
operations, etc. Examples of prior demonstrations of
autonomous optical navigation of deep space missions are
DS-1, Deep Impact, and Stardust missions [1]-[3].
In the above-mentioned cases, flight software was developed for each mission separately with the effort being
repeated without taking much advantage of the previous
work. Redeveloping the navigation software and tools for
each mission is cost and schedule inefficient, so future work
could benefit by coordinating standard navigation software
and tools. A concept known as Deep Space Positioning System (DPS), where all navigation functions are provided
autonomously by the DPS instrument, can remedy the

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IEEE Aerospace and Electronic Systems Magazine - July 2020

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