CICERO is a constellation of 6U cubesats by GeoOptics. A few of them were launched today aboard a Rocket Lab Electron in today's “It’s Business Time” launch.

Each cubesat caries a phased array of GPS antennas and a CION (CICERO Instrument for GPS-RO) GPS receiver/processor with 16 GPS sub-channels (8 dual frequency satellites) optimized for radio occultation measurements of GPS signals, that can be used to map out 3D water concentration distribution in the Earth's upper atmosphere.

Question: In what ways was the configuration of this constellation of orbits designed to optimize for this observation? Was any attention to the structure of the GPS constellation's shape included?, Are the CICERO orbits just distributed evenly to sample uniformly in time an space? Have other factors been included?

CICERO GPS radio occultation satellite

CICERO GPS radio occultation measurement

CICERO GPS radio occultation constellation orbits

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1 Answer 1


Very little optimization is needed for a GNSS-RO constellation -- one of the nice properties of the technique. The figure below shows the daily coverage for a single CICERO spacecraft in a sun-sync orbit. Note that it is essentially random and uniformly distributed, which is ideal for global coverage. Another spacecraft in a similar or different high-inclination orbit (say, 72 deg) will show a similar coverage pattern, but with different effectively randomly placed soundings. Thus, each additional spacecraft can be placed into almost any low orbit (below 1,000 km) at relatively high inclination (say, >55 deg) and it will nicely complement what is already there, with rare nearly coincident soundings (which are great for validation). The distribution isn't truly random. High inclination orbits tend to converge near the poles and thus yield a higher concentration of soundings at high latitudes. This can be nicely compensated by an occasional lower inclination orbit, something like one out of every 5 or 6 at 30 deg or so. Nothing precise is required as almost any reasonably low inclination will densify around the equator. CICERO satellites observe occultations occurring as much as 60 deg left and right of their velocity vector and so cover a broad swath every orbit, which is why you do not see any pattern of swath tracks in the daily coverage. For the early launches, GeoOptics is content to take rides of opportunity where they occur, as they all provide effective global coverage. Later they will fine tune the coverage with some lower inclinations. Currently, two CICERO satellites are operating and a third will be launched later this month on a PSLV.

Daily coverage for the CICERO OP1-A spacecraft

  • 1
    $\begingroup$ Welcome to Space! Nice answer! $\endgroup$
    – DrSheldon
    Nov 12, 2018 at 17:40
  • $\begingroup$ Thanks for the great answer! Random distribution is good, it's certainly better than lumpy or swiss-cheese-like. I suppose an ordered pattern would require a carefully orchestrated and station-kept dance, but it would avoid the inevitable holes and clusters that any random or pseudo-random distribution will contain. I can see that that wouldn't be an option for this mission, I think this is wonderful, doing serious Earth observation and mapping of a difficult-to measure but important quantity with a modest constellation of 6U cubesats. Excellent! $\endgroup$
    – uhoh
    Nov 12, 2018 at 22:14
  • $\begingroup$ Can you add a link to and credit for the original source for the image? Thanks! $\endgroup$
    – uhoh
    Nov 12, 2018 at 22:14

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