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Formation RF Sensors
Task Objective
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Terrestrial Planet Finder |
To develop and demonstrate a RF-based integrated 4p-coverage range
and bearing sensor that would enable multiple spacecraft to perform
lost in space recovery, coarse formation flying, and collision avoidance.
Task Description
NASA is currently investigating several missions that
would require high-precision formation flying with instruments distributed
among several spacecraft. One of these missions is the formation
flying interferometer (FFI) version of the Terrestrial Planet Finder
(TPF) mission. The FFI is envisioned to consist of up to seven spacecraft
(as many as six “collector” with IR telescopes, and a “combiner”)
flying in precise formation within ±1 cm of pre-determined
trajectories for synchronized observations. The spacecraft-to-spacecraft
separations are variable between 20 m and 100m during observations
to support various interferometer configurations in the planet-finding
mode. The challenges involved with TPF autonomous operations, ranging
from formation acquisition and formation maneuvering, to high precision
formation flying during science observations are unprecedented for
deep space missions.
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Prototype Ka band AFF sensor hardware |
To meet these challenges, the development of a suite of sensors is
required to enable formation acquisition, stabilization, and precise
control to stay within the operating range of the optical system. For
this purpose, the formation sensor task area will develop and demonstrate
the key technology of the acquisition sensor. Key performance targets
for the acquisition sensor are an instantaneous 4p-steradian field
of view and simultaneous range and bearing-angle measurements for multiple
spacecraft with accuracy better than 50 cm and 1 degree, respectively.
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JPL Mesa Ka band AFF sensor testbed |
Main technical challenges to meet these requirements are:
1. Robustness to spacecraft accommodation and the interference of
indirect signal bounced off from the spacecraft structure.
2. Simultaneous multiple spacecraft operation in a distributed environment.
3. Auto-calibration without requiring complex spacecraft rotation
maneuver.
4. Collision avoidance in case of temporary single spacecraft failure.
5. Hardware accommodation on the spacecraft.
To mitigate these challenges, a new signal structure will be
developed to enable 1) an order of magnitude reduction of range
error compared
to what was demonstrated on the StarLight AFF sensor, 2) fine
bearing angle measurement without the need for spacecraft rotation
calibration
maneuver, 3) simultaneous operation for more than two spacecraft,
4) integrated radar capability for collision avoidance for multiple
spacecraft, and 5) integrated formation sensor with inter-spacecraft
communication. The acquisition sensor will operate at S-band.
The existing baseband processor as well as software will be
modified
to allow prototype system demonstration.
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Stellar Imager
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