CEDAR Distinguished Lecture
Choose your own adventure
Larry J. Paxton
larry.paxton@jhuapl.edu
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25 June 2026
Your nomination letter highlighted your seminal and sustained contributions to CEDAR science through pioneering ultraviolet remote sensing of the ionosphere–thermosphere system, transformative space-based instrumentation, and the development of observational datasets and models that have fundamentally advanced our understanding of thermospheric composition, auroral energy input, and equatorial plasma structures.
It also emphasized your exceptional leadership and service to the community, your role in enabling major scientific advances through experimental innovation, and your long-standing commitment to mentoring and workforce development
Red Pill or Blue Pill?
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25 June 2026
You take the blue pill ... the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill ... you stay in Wonderland, and I show you how deep the rabbit hole goes.
Morpheus The Matrix
DISCLAIMER:
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25 June 2026
Most importantly: be genuine, be true to yourself, believe in your intrinsic worth
Spaceflight Instrumentation and YOU
Some thoughts on my own career, life as a human, and the realities of the world
Larry J. Paxton
GOAL: Provide some insights into instrumentation
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25 June 2026
https://en.wikipedia.org/wiki/Who_Moved_My_Cheese%3F
What do you want to do in your career?
Change is hard...but you have the basic tools to make that change
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25 June 2026
Why work on instruments?
The ITM questions haven’t changed for decades
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25 June 2026
CHALLENGE : Change from a ‘scarcity mindset’ to an ‘abundance mindset’
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25 June 2026
| Scarcity Mindset | Abundance Mindset |
Core Belief | Life is a zero-sum game | Life is abundant in its possibilities |
Central Question | What is missing, lost, or unavailable? | What is available, possible, and might be created? |
Others | Fear, envy, suspicion, and the belief that to succeed others must fail. | Recognize that you are valuable as are others, collaboration succeeds, success comes in many forms and timescales |
Time Horizon | Short-term survival and energy spent on restricting opportunities for others and gaining access to restricted opportunities | Long-term growth, learning, and investment in others by creating opportunities. |
CHALLENGE : Change from a ‘scarcity mindset’ to an ‘abundance mindset’
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25 June 2026
| Scarcity Mindset | Abundance Mindset |
Core Belief | Life is a zero-sum game | Life is abundant in its possibilities |
Central Question | What is missing, lost, or unavailable? | What is available, possible, and might be created? |
Others | Fear, envy, suspicion, and the belief that to succeed others must fail. | Recognize that you are valuable as are others, collaboration succeeds, success comes in many forms and timescales |
Time Horizon | Short-term survival and energy spent on restricting opportunities for others and gaining access to restricted opportunities | Long-term growth, learning, and investment in others by creating opportunities. |
We think small because we live small
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25 June 2026
We think small because we live small
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25 June 2026
Firefly would enable science by viewing the Sun from all vantage points
Polar, equatorial – leading and trailing edge and farside
What could we learn from a ‘4π’ view of the Earth?
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25 June 2026
Robert F. Kennedy (1925-1968) recast a phrase from G.B. Shaw during his 1968 presidential campaign
"Some men see things as they are and say why. I dream of things that never were and say, why not."
https://en.wikipedia.org/wiki/Robert_F._Kennedy
We do what we can do – but we need to change
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25 June 2026
https://quoteinvestigator.com/
�
1989, Classic Tales of Mulla Nasreddin, Retold by Houman Farzad, Translated from Persian by Diane L. Wilcox, Looking for the Missing Ring, Quote Page v,Mazda Publishers, Costa Mesa, California -- might be over 800 years old.
You do what you can with what you have
Larry Paxton
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Larry Paxton
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Transformative Abundance Mindset and Practicing Gratitude
The person that has lost their keys has many options:
Rideshares.
Asking for help.
Finding another source of illumination
Wait for a new dawn.
How many can you think of? Apply that to your life.
Always start with the ‘Why?’
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25 June 2026
We Heard the How
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25 June 2026
Let’s develop new instruments!
BUT – we need a ‘Why?’ this is just the ‘What’
The realm of ITM science
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25 June 2026
CHALLENGE: What do we focus on and how do we address it?
What tools can we use to observe these processes?
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25 June 2026
CHALLENGE: What do we focus on and how do we address it?
What tools can we use to observe these processes?
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25 June 2026
CHALLENGE: What do we focus on and how do we address it?
The upper atmosphere
The upper atmosphere
Region characterized by FUV Emissions
Region characterized by FUV Emissions
This is the Very Low Earth Orbit (VLEO) environment and it is the new frontier for satellite operations
Below 300km where orbital lifetimes without propulsion are less than 1 year
Point At Which the Vertical Optical Depth Equals 1 Defines How Far Down Into the Atmosphere You Can See
O2 SR Continuum
O2 SR Bands
O3
FUV
FUV
FUV Spectrum of the Earth
The processes that give rise to the emissions constrain the energy, momentum and continuity equations
Quantum mechanics indicates the ‘selection rules’ that explain spectral transitions as ‘allowed’ or ‘forbidden’
ALLOWED (resonant scattering)
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25 June 2026
Quantum mechanics indicates the ‘selection rules’ that explain spectral transitions as ‘allowed’ or ‘forbidden’
FORBIDDEN (photoelectron impact excitation)
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25 June 2026
Molecular Spectra Arise From Transitions Between Electronic States
LBH
“blue” line
From Meier, 1991
Atomic Transitions Adequately Understood
The OI 135.6 2p4 3P – 3s 5S is spin forbidden and produces a doublet. – [OI] 1356
The OI 130.4 2p4 3P – 3s 3S transition is allowed and produces a triplet. – OI 1304
Note the green line
And the red line
(also measured by SSUSI)
From Meier, 1991
How does FUV remote sensing work?
See e.g. Meier, 1991; Paxton and Anderson, 1992
The General Form of the Radiative Transfer Equation Includes Multiple Scattering
Formal solution of the RT equation
Solving the integral form of the emission rate
where
for photoelectrons
for solar resonant scattering
See e.g. Meier, 1991; Paxton and Anderson, 1992
Photoelectron Flux Calculations Show the Dependence on the Neutral Atmosphere
contribution from direct photoionization
photoelectron production in the range to due to cascading from higher energy photoelectrons undergoing inelastic collisions
mean pitch angle
Elastic scattering cross section
probability
Inelastic cross section
From Banks and Kockarts
Signatures map to I/T processes in the Thermosphere
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25 June 2026
| HI (121.6 nm) | OI (130.4 nm) | OI (135.6 nm) | N2 (LBHs) | Nitric Oxide | N2 (LBHl) |
AURORAL ZONE (Disk) | Energetic proton precipitation & boundary Energy and Flux | Auroral Boundary and amount of column O2 present1
| Region of electron and (possibly) proton precipitation O outflow O Doppler shift | Used with LBHl to form Eo and the ionization rate and conductance information Hemispheric power Radar clutter S/C charging | NO production | Measure of the effective precipitating flux, used with LBHl to form Eo and the ionization rate and conductance information |
AURORAL ZONE (Limb) | H profile | O outflow | O outflow |
|
|
|
DAYSIDE LIMB | H profiles and escape rate1 | Amount of O2 absorption1 | O altitude profile | Amount of O2 as seen in absorption Temperature | NO profile | N2 profile Temperature |
DAYSIDE DISK | Column H | Amount of O2 absorption1 | Used with LBHs to form O/N2 | O/N2 ratio Solar EUV | NO column density | Solar EUV |
NIGHTSIDE LIMB | H profile and escape rate | Ion/ENA precipitation | EDP HmF2 NmF2 Tplasma | Ion/ENA precipitation characteristic energy |
| Ion/ENA precipitation characteristic energy |
NIGHTSIDE DISK | Geocorna and Ion/ENA precipitation | Ion/ENA precipitation | TEC Ion/ENA precipitation | Ion/ENA precipitation |
| Ion/ENA precipitation |
Inversions vs Assimilation
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25 June 2026
Forward Modeling
Inverse Problem
Measurement
Measurement System
Radiative Transfer
Signal Mechanism
Physical Quantity
NOTE: FUV Remote Sensing Contributes to the Solution – it is NOT the Solution
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25 June 2026
CHALLENGE: What do we focus on and how do we address it?
Choose your own adventure!
Ask me what we could work on together.
I have a ‘hammer’ – everything looks like a ‘nail’ to me.
Escape the tyranny of the TRL�Let’s build new instruments
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25 June 2026
Mission/Instrument Design is Purpose Driven
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Simplified Flowdown Used for Tradespace Analysis
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25 June 2026
Simplified Flowdown Used for Tradespace Analysis
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25 June 2026
A useful solution considers altitude, orbit, measurement requirements, s/c accomodation, budget, schedule, design (imager, spectrograph) .... etc.
FUV Hyperspectral Imagers Can Provide Operational Support or Science
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25 June 2026
We are going back to the moon
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25 June 2026
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“We choose to go to the moon. We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.
President John F. Kennedy
Rice University
12 September 1963
John W. Young on the Moon during Apollo 16 mission Charles M. Duke Jr. took this picture. The LM Orion is on the right. April 21, 1972
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“We choose to go to the moon. We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.
President John F. Kennedy
Rice University
12 September 1963
Astronaut John W. Young, commander of the Apollo 16 lunar landing mission, participates in lunar surface extravehicular activity (EVA) training in the Flight Crew Training Building at the Kennedy Space Center (KSC). Young adjusts a training model of a Far Ultraviolet Camera/Spectroscope, an instrument which will be placed on the
Moon during the Apollo 16 EVA. Image # S72-19739
panchromatic FUV electronographic imager
George
What do you see?
Larry Paxton
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DAY
NIGHT
The Earth in the FUV: The Subject of this Talk
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Star
Aurora
Star viewed in occultation
Geocoronal hydrogen
Limb profile
Dayglow
Nightglow
Aurora
Nightglow on the limb
Equatorial Arcs
First FUV image of the Earth- taken from the Moon by the Apollo 16 crew
Carruthers and Page, 1972
The Moon would be a useful vantage point
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First FUV image of the Earth- taken from the Moon by the Apollo 16 crew
Carruthers and Page, 1972
SSUSI and GUVI: Astonishing data record
GUVI
SSUSI
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6/25/26
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I have a flight SSUSI instrument sitting in a dry box. It could be flown
SSUSI-Lite DPU
Also successfully flown High Altitude Balloon test of APL Gamma Ray Neutron Spectrometer
DMSP F20 SSUSI SIS
The MODULAR DESIGN of the Scanning Imaging Spectrograph (SIS) readily enables component-level and end-to-end testing and evaluation.
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6/25/26
Scan Mirror
Cover, Side
SIS Cover (shown without pin puller)
Detector�(not shown)
Grating (located inside housing)
Telescope Housing
Scan Motor/Gear Box and Adapter
Slit Mech�(internal)
SIS Main Housing
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Scan Mirror Shaft and Counterweight
Scanning Imaging Spectrograph – Cross Track Scanner
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GUVI and SSUSI see about 1.5 hours on each side of the s/c from LEO
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O/N2 is a signature of the bottomside ionosphere
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6/25/26
O/N2 reference is point where N2 column = 1017 cm2
or about 135km-165km depending on solar zenith angle, exospheric temperature, etc.
November 2003 Storm
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VLEO – VERY LOW EARTH ORBIT�The new frontier that sustains the outward journey
https://mashable.com/video/spacex-satellites-burn-up-atmosphere-space-storm
Interesting problem: what causes perturbations in the bottomside?
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25 June 2026
bottomside ionosphere
APL is a coin-operated machine – I’m always looking for new opportunities
Why should you care about O/N2?
figure from Justin Yonker
O+
For medium high solar activity (F10.7=170), Figure 5.1 follows the chain of events beginning with the deposition of solar energy, through the ion-neutral chemical cascade, eventually resulting in the production and loss of NO (Yonker 2013). As the thermospheric species with the second highest ionization energy, N+ is very reactive and lies near the top of this chain.
Most of the NO GUVI emission comes from the NO density peak near 106 km (Barth and Bailey 2004). At these altitudes, N+ is lost rapidly (chemical lifetime <1 sec) and primarily to O2.
There are three product channels
N+ + O2 → NO + O+ R1 (50%)
→ NO+ + O R2 (40%)
→ N(2D) + O2+ R3 (10%)
with 50% of the reaction leading to N(2D) (the main NO production source
O/N2 is a proxy for changes in TEC and hmF2
Signal responds instantly to rapid changes in the bottomside
Another simple idea: Where is hmF2?
This indicates that ingesting O/N2 is a messenger for changes in hmF2 – important in an assimilative model
Global access provided by small LEO sensor
If there are small depletions in n(z) at the bottomside (nmF2 stays constant) then
changes in intensity are directly related to changes in TEC
dTEC driven by changes in O/N2 will be below the F2 peak
January 2021 Sudden Stratospheric Warming Event�
The polar vortex began showing signs of disturbance in late December 2020, and by around January 5–6, 2021, a full vortex displacement had occurred — the vortex was shoved off the pole toward Eurasia rather than splitting cleanly in two.
Stratospheric temperatures over the Arctic rose sharply while zonal winds at 10 hPa reversed to easterlies, meeting the formal definition of a major SSW.
It was one of the stronger events of the prior decade in terms of how rapidly and thoroughly the vortex was disrupted.
Movie to follow provided by Sebastijan Mrak
night
day
day
Night : we use ‘1356’ the atomic oxygen 135.6nm emission feature arising from O+ recombination
Day : we use the ‘O/N2 ratio’ (the ratio of the O 135.6 nm emission to the N2 LBH band emission)
(lots of details here for the experts in the room to savor)
teminator
A single GUVI orbit
We usually have 4 SSUSI/GUVIs collecting data
BLUE indicates NIGHT
RED indicates DAY
Nightside O 135.6nm observations seem to be broadly consistent with a wavelength of 500km and an amplitude of ±0.2 TECU
Detailed analysis will be performed.
We can map small (and large) scale changes in dTEC
Chemical lifetime in the bottomside is 10s to 100s of seconds
1R ~ 1 TECU
Chemical lifetime in the bottomside is 10s to 100s of seconds
COST has been a barrier
https://www.nasa.gov/ocfo/nasa-instrument-cost-model-nicm/
Our community could do a ITM QB50
https://cordis.europa.eu/project/id/284427
https://www.eoportal.org/satellite-missions/iss-nanoracks-qb50#eop-quick-facts-section
https://www.nasa.gov/mission/station/research-explorer/investigation/?#id=7479
A Lesson on the Journey to the Abundance Mindset
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25 June 2026
https://www.youtube.com/watch?v=X09_sw_vc6w
https://www.theguardian.com/stage/2005/sep/29/comedy.religion
Emo Phillips
A Lesson Along the Journey to the Abundance Mindset
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25 June 2026
https://www.youtube.com/watch?v=X09_sw_vc6w
https://www.theguardian.com/stage/2005/sep/29/comedy.religion
Emo Phillips
A Lesson Along the Journey to the Abundance Mindset
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25 June 2026
https://www.youtube.com/watch?v=X09_sw_vc6w
https://www.theguardian.com/stage/2005/sep/29/comedy.religion
Emo Phillips
What do heroes look like?�Everyone that made DYNAMIC happen is a hero
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25 June 2026
Practice the abundance mindset!
What do heroes look like?
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25 June 2026
This is our call to action – we need to support GDC-Trailblazer and DAPHNE
Whether we see an immediate return or not
There may be others that will seize upon any remarks that experts in our community make as reasons not to prioritize funding of DYNAMIC or GDC-Trailblazer in the PBR
Dao and Stoicism (many others) tell us to accept what we cannot change – peace lies within
Let’s try to live in an ‘abundance mindset’
Let’s shape the future - together
A sincere thank you to you all
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25 June 2026