Polar-Orbiting, Passive,
Atmospheric Calibration Spheres
(POPACS)
Presented by
R. Gilbert Moore
Director, Project POPACS
Monument, CO
AIAA RM Second ATS at UCCS
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Statement of the Problem
• Upper atmospheric drag causes the orbits
of Low Earth Orbiting (LEO) spacecraft to
decay, over time
• Re-boosts from on-board propulsion
systems are required to maintain orbits of
high-value assets and maneuvering burns
are sometimes required to avoid collisions
with orbital debris
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International Space Station Orbit Decay
Due to Atmospheric Drag, Showing Reboosts from Zarya Module
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Complications from Solar Storms
• Solar flares and Coronal Mass Ejections
temporarily heat up and increase the density of
Earth’s upper atmosphere at satellite altitudes by
as much as three orders of magnitude
• These events cause increased drag on Low
Earth Orbiting (LEO) spacecraft and debris
• The ability to predict collisions between
spacecraft and orbital debris is complicated by
these random density increases
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Sunspot, Flare and Prominences
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Solar Cycle 24
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Coronal Mass Ejection (CME)
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CME Effect on Earth’s Magnetic
Field and Upper Atmosphere
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POPACS Mission Objectives
• Measure variations in atmospheric density
resulting from solar storms during the
descending phase of Solar Cycle 24 and all of
Solar Cycle 25
• Use the density data to help improve orbital
collision avoidance accuracy
• Involve university students in all facets of a
solar-terrestrial physics research project
AIAA RM Second ATS at UCCS
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Methodology
Launch small, hollow Aluminum spheres,
ballasted to differing masses, into near-polar
elliptical orbits
Track the spheres with Space Command radars
and network of university student “Go To”
telescopes
Compute the spheres’ orbits
Calculate atmospheric density from the amount
that the spheres’ apogees shrink as a result of
atmospheric drag at each perigee pass
AIAA RM Second ATS at UCCS
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Methodology (cont.)
• Measure northern and southern auroral region
atmospheric densities before, during and after
arrival of solar coronal mass ejections (CMEs)
• Observe the way that high-latitude density
increases migrate to the equator
• Use density variation data to improve short-term
predictability of satellite and debris orbits during
future solar storms
• Help improve accuracy of orbital collision
avoidance forecasts and our basic
understanding of solar-terrestrial relationships
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Program Status
• Three 10 cm diameter Aluminum spheres with
masses of 1, 1.5 and 2 kilograms were deployed
into orbit on 9/29/2013 from SpaceX’s Falcon
9v1.1 ELV launched from Vandenberg AFB
• The orbit is inclined 80 degrees to the equator,
with a period of 100.3 minutes, a perigee altitude
of 318 km and an apogee altitude of 1488 km.
• Predicted sphere orbit lifetimes are 10, 12.5 and
15 years, with the lightest sphere de-orbiting and
being consumed by aerodynamic heating first
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POPACS Spheres and Spacers
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Falcon 9v1.1 @ Vandenberg
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Falcon 9v1.1 Launch – 9/29/2013
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CSD Deployment of Spheres and
Spacers
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SSN Tracking of POPACS Spheres
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Tracking
• The Joint Space Operations Center (JSpOC) is currently
radar tracking the spheres with its Space Surveillance
Network sensors and publishing the spheres’ Two-Line
Element sets (TLEs)
• Analytical Graphics, Inc. and Utah State University are
coordinating a U.S. network of university student “Go To”
telescopes and professional telescopes to track and
capture images of the spheres.
• The students will calculate the spheres’ orbital elements
using their sphere images, star charts and pattern
recognition software and then calculate atmospheric
densities at the orbits’ perigee locations
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“Go To” Telescope with GPS
Receiver, Computer and Recorder
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Example Sequence from Go To
Tracking of Satellites
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Data Analysis
• Our student teams will monitor solar storms
during the remainder of Solar Cycle 24 and all of
Solar Cycle 25 and correlate their atmospheric
density data with the intensity of those storms
• Their data will be combined with radar-derived
data to help improve the accuracy of Air Force
and Naval Research Laboratory atmospheric
density models and collision avoidance
forecasts
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Contact Information
• Additional universities in the U.S. and
around the world are welcome to
participate in the tracking and analysis
phases of the POPACS project
• Contacts:
• For tracking, t.s.kelso@centerforspace.net
• For analysis, jjsojka@usu.edu
• For general info., gilmoore12@aol.com
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Thanks to our team members
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