4-Attachment D - Payload Paper.pdf

Pachowicz 1 40th Annual Small Satellite Conference

SSC26-II-03

The Landolt Mission Payload: An Artificial Star for Precision Astronomy

Peter Pachowicz, Peter Plavchan, Gabrielle Belle, Jay Deorukhkar, Phillip Cunio

Mason Space Center, George Mason University

4400 University Dr., Fairfax, VA 22032, USA ppach@gmu.edu

Eliad Peretz, John Mather, Peter Kurczynski

NASA Goddard Space Flight Center

Greenbelt, MD 20771, USA

Angelle Tanner

Mississippi State University, USA

Susana Deustua, Brian Alberding, Joseph Rice

National Institute of Standards and Technology, USA

Thomas Michaud-Baeyens, Jean-Thomomas Landry, Marc-Andre Boucher

OMP Inc., Quebec, QC, G1K 4L2, Canada

David Ciardi, Mike Lund

California Institute of Technology, USA

Justin Albert

University of Victoria, Canada

Greg Alderling

Lawrence Berkeley National Laboratory, USA

Brian Stalder

Rubin Observatory, Chile

Daniel Stevens

University of Minnesota, USA

Jamie Tayar

University of Florida, USA

Daniel Kuesters

University of California, Berkeley, USA

Tabetha Boyajian

Louisiana State University, USA

ABSTRACT

The Landolt Mission represents a significant advancement in space-based instrumentation, serving as NASA’s first hybrid space mission. Central to the mission is a smallsat deployed in Geostationary Orbit (GEO), carrying the SI

Traceable Absolute Radiometer [STAR] comprised of two Laser Instruments (LI) and an Element Wheel technology demonstrator. The LI utilizes six specialized Laser Trays to project SI-calibrated light beams at various wavelengths into ground telescopes. By creating a stable, SI-traceable calibration source, the Landolt mission aims to provide an unprecedented level of precision in astronomical observations. These advancements are expected to facilitate

ATTACHMENT D - PAYLOAD PAPER

mailto:ppach@gmu.edu

Pachowicz 2 40th Annual Small Satellite Conference transformative discoveries in exoplanet host stars, supernova cosmology, interferometry, and dark matter research.

Beyond the scientific objectives, the mission addresses critical engineering challenges involved in deploying high-precision optics in the GEO environment and integrating complex optics. Furthermore, the $20M NASA Pioneers

Program project emphasizes a collaborative framework between government, industry, and academia, providing essential hands-on training for the next generation of aerospace engineers and scientists. This paper focuses on the design and engineering of the Landolt Payload and its three instruments.

1. INTRODUCTION

Modern astronomical observations still depend mainly on Earth-based telescopes with sophisticated instrumentation. The scientific quality of the collected data depends not only on the telescope's size and sensitivity but also on the accuracy with which the received light can be calibrated. The absence of accurate and precise absolute flux calibration, with flux being the amount of energy that a telescope receives from a given star, can impose significant constraints on our ability to make impactful new discoveries about multiple astronomical objects, including the Universe itself.

While historically observations have utilized sets of specially selected “standard stars”, these objects are imperfect calibration sources because their brightness must be measured at multiple wavelengths and their complex atmospheres modeled to detangle the star from

Earth’s atmosphere and the properties of the telescope detectors and optics. Even more daunting, each telescope and instrument suite must be calibrated separately as they include a unique combination of detectors and internal optics.

Historically, astronomical flux calibration relied on the bright star Vega and white dwarfs, which carry uncertainties of 1–5%. White dwarfs are ideal calibration sources since they have a simple, mostly hydrogen, atmospheric spectra and exhibit low levels of stellar activity. Modern observatories employ SI-traceable standards to push flux calibration uncertainties below

1%. A standard star is considered SI-traceable when there is an established connection between measurements made in a lab with NIST (National

Institute of Standards and Technology) instrumentation to the observations of that star. Such calibration methods include comparing telescope instruments with optical radiometers so that the flux is not a relative measure from star to star (NIST Stars project). To date, this type of careful lab-to-telescope calibration has only been completed for Vega and about three dozen faint white dwarfs. Another state-of-the-art flux calibration is based on a grid of 200-300 hot, well-known stars that are calibrated to a 1% accuracy. They are cross-checked with the CALSPEC system used by space telescopes

(The Gaia Spectrophotometric Standard Stars SPSS). As space missions such as JWST, Roman, and Euclid probe ever-fainter sources, and ground-based surveys including Rubin, DES, and Argus build deep, all-sky maps of unprecedented depth, we must expand and strengthen a network of SI-traceable standard stars so these facilities can deliver accurate, high-precision science.

For the study of extrasolar planets, better stellar calibration can improve the characterization of host stars and, therefore, the properties of orbiting planets. In supernova cosmology, more accurate luminosity measurements improve distance estimates and reduce uncertainties in studies of cosmic expansion. For stellar astronomy, better constraints on the physical properties of a star can inform its formation and evolutionary processes. Interferometry and high-resolution imaging also benefit from precise knowledge of instrument response and source brightness. In each case, improved calibration strengthens the connection between the observed signal and the physical interpretation.

One way to improve and expand the standard star absolute flux network is to provide a calibration source above the Earth’s atmosphere. A space-based artificial star would offer a stable, well-characterized source of light that can be observed by ground-based (and possibly some space-based!) telescopes under realistic observing conditions (Figure 1). Unlike a laboratory calibration source, an artificial star in a stable orbit would be observed through the same telescope system and atmospheric path used for scientific observations. This makes it especially valuable for evaluating the full observing system, including the atmosphere, telescope, optics, filters, and detector response. The Landolt

Mission is designed to address this calibration need. By placing a calibrated optical source in geostationary orbit, the mission aims to provide ground-based observatories with a known reference to support improved astronomical measurements. The mission has the potential to benefit not only a single observatory or science team but also the broader astronomical community. If successful, it will provide an important step toward more precise and reliable measurements across many areas of astronomy and astrophysics.

Landolt will produce catalogs of stars with reduced uncertainties in temperature and luminosity that can be compared with stellar models (Tayar et al. 2022).

We decided to name the mission after Arlo Landolt, Arlo

U. Landolt - Wikipedia, because his work was extremely influential in observational astronomy.

https://en.wikipedia.org/wiki/Arlo_U._Landolt https://en.wikipedia.org/wiki/Arlo_U._Landolt

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Figure 1: Landolt artificial star in the sky for ground assets calibration

2. LANDOLT MISSION

The Landolt Mission is a space-based calibration mission designed to function as an artificial star for ground-based optical astronomy. The mission uses a smallsat launched into a geostationary orbit and equipped with a system of six calibrated wavelengths spanning the near-infrared and the blue region of the electromagnetic spectrum. Its primary purpose is to project well-characterized light toward large-aperture ground telescopes so that these telescopes can calibrate their observations against a source of known luminosity.

Thus, the spacecraft becomes a reference object in the sky whose emitted light is known with high precision.

The mission's central payload (STAR) is the Laser

Instrument, which includes multiple Laser Trays. These trays emit light at selected wavelengths relevant to astronomical observations, as described in the introduction. The selected wavelengths allow the mission to support calibration across important optical and NIR bands and observing modes. Rather than producing a broad, calibrated, continuous spectrum, the mission uses discrete, well-controlled wavelengths from a fiber-optic laser. These wavelengths will be carefully characterized before launch and monitored during flight.

The wavelength selection is an important part of the mission design because it directly connects the spacecraft payload to the needs of ground-based astronomical instruments.

The choice of geostationary orbit also plays a significant role. In a geostationary orbit (GEO), a spacecraft appears directly above the sky from the perspective of the ground observer. This provides longer and more predictable observation opportunities than those from a rapidly moving spacecraft in low Earth orbit. This also makes it easier for Earth-based observatories to plan repeated calibration observations. GEO also allows the mission to support multiple observatories, depending on spacecraft visibility, telescope location, and observing constraints.

The orbit, therefore, supports the artificial star concept by providing relatively stable observing geometry.

The Landolt Mission is also significant because it represents a hybrid mission structure that combines scientific goals, technology development, engineering implementation, and educational participation as required by the NASA Pioneers Program. The mission is intended not only to produce calibration data for astronomy but also to demonstrate the integration of complex optical payloads on a small satellite platform, such as a smallsat. This is especially important because the mission must achieve high-precision optical performance within the size, mass, power, and budget constraints.

Mission operations will require coordination between the spacecraft, the communications network, mission control, the data system, and participating observatories

(Figure 2). After launch and deployment, the spacecraft will undergo commissioning, including checkout of the bus, payload systems, laser instruments, and supporting electronics. Once operational, the spacecraft operators will coordinate laser observations with ground-based telescopes. Data from these observations will then be processed, stored, and made available for calibration and scientific use. Ground assets such as Mason Mission

Control, communications, databases, cloud-based storage, and partner observatories will therefore play a critical role in the overall mission concept. The estimated launch date is October 2029.

Figure 2: Landolt concept of operations

The NASA Landolt Mission is both a scientific and an engineering demonstration. Scientifically, it aims to improve the calibration foundation of Earth-based astronomy. Technically, it demonstrates how a compact spacecraft can support precision optical calibration from

GEO. The mission, therefore, bridges small-satellite engineering and high-precision astrophysical measurements.

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3. SPACECRAFT ARCHITECTURE

The Landolt mission team selected the smallsat standard to host the payload. The decision was guided by the payload's large volume and mass, and the SatBus critical subsystems required to perform the mission in a GEO (or near-GEO) orbit at an altitude of ~35,786 km. The total mass limit of the spacecraft has been set to 36 kg, with the payload mass ~12 kg

The power budget during science operations has been limited to 40W, with proper sizing of solar panels and battery capacity. The thermal system includes active thermoelectric cooler (TEC) controls and passive radiators to mitigate the GEO extremes and eclipse transitions. The communication system has been set to operate on the S-band, with encrypted uplink/downlink and a data rate above 1 kps. Pointing accuracy

(knowledge) has been defined as better than 400 arcsec to maintain the laser beam alignment with the observatory over a prolonged period (up to 1 hour). The expected total ionizing dose (TID) for the one-year mission has been determined by simulations to be ~40 krad. This requires the system to have heavier shielding and be built with space-rated electronics, rather than

COST components. The propulsion system (with ΔV

~200 m/s) will bring the spacecraft from a transfer orbit to the target GEO orbit and will dispose the spacecraft to the graveyard (at an altitude ~500 km above the GEO orbit) at the end of the mission. Due to the mission class, the SatBus needs to be classified at TRL9 with a proven flight heritage at GEO.

Figure 3: Spacecraft architecture

The spacecraft architecture is shown in Figure 3. The

SatBus provides power and a serial communication link to three payload instruments. The first two instruments are redundant Laser Instruments (LI-A and LI-B). Each

LI is equipped with six lasers and photodiodes for measuring emitted laser flux. The Laser Instrument plays a central role in the calibration of ground optical telescopes. The decision to make them redundant was driven by a need to minimize risk to the mission, the harshness of the GEO environment, and the need to maintain very tight performance parameters over the mission span. Each LI carries sensitive electronics and optical components that can be affected by launch and the space environment. When one of the LI subsystems fails or loses its performance parameters, the redundant system can be used in observations. The third payload instrument is an Element Wheel (EW) classified as a technical demonstration system (at a “do not harm” risk level). It will provide additional methods for measuring the emitted laser flux across all selected wavelengths.

Figure 4 shows the complete payload assembly. The EW is mounted on the front-end of the payload assembly with a heat shield covering the rotating Element Wheel.

Two laser beacons from redundant Laser Instruments exit through the opening in the wheel and the shield.

Behind the EW there are two LIs with a stack of laser subsystems and the main processor.

Figure 4: Payload assembly, with and without the heat shield

4. LASER INSTRUMENT

4.1 Laser Instrument architecture

The Laser Instrument (LI) comprises six single-mode fiber-fed laser channels (three visible and three near-infrared), each calibrated to the SI standard by NIST, before launch. These beams serve as an artificial star, providing characterized photon flux to ground observatories such as Palomar, Rubin, UH 2.2m, and

GMU. The stack of six channels is commanded by a separate On-Board-Computer (OBC).

The LI architecture is shown in Figure 5 and Figure 6.

Six LaserTrays are stacked together with the OBCTRay, forming the LI box. The OBCTray is powered by the

SatBus and converts and distributes power to the

LaserTrays. OBCTray is also communicating with the

SatBus via the LVDS/UART serial link. The operations of the tray stack are integrated by a network of microcontrollers (MCU) where the OBCTray MCU is the main controller of the network and the stack. The

OBCTray MCU switches on/off individual LaserTrays, sends commands, and receives telemetry data from

LaserTrays. It briefly analyzes the data for nominal/fail conditions (assigning Green, Yellow, or Red flags) and

Pachowicz 5 40th Annual Small Satellite Conference forwards the telemetry packets to the SatBus database.

Up to two LaserTrays can be powered simultaneously, providing a laser beacon of two wavelengths. The

OBCTray can also reprogram individual MCUs on the network. This in-flight reprogramming will provide an opportunity to update the LaserTray flight software with new functionality, if requested by the science team.

Figure 5: Laser Instrument architecture

Figure 6: Laser Instrument assembly

4.2 Laser Tray system

The LaserTray includes a power system, the laser module in a Butterfly package, the frequency doubler module, circuitry to control laser current, a system for thermal stabilization of both laser and frequency doubler using integrated TECs, and electronics to control individual components and collect telemetry data. The main processor is a Texas Instruments MSP430FR5969-

SP radiation-hardened MCU. The choice of the processor was guided by the extensive flight heritage of this MCU, and the fact that our students use this MCU in their coursework. The engineering model of the Laser

Tray PCB is shown in Figure 7. All active components and connectors are space-rated, with passive components of military or automotive grade.

Figure 7: Landolt LaserTray PCB

Figure 8: Landolt LaserTray with fiber cassette

The single-mode fiber connected to the laser module and frequency doubler (Figure 8) is split into two fibers with power divided into 99%/1% sections. The 99% fiber is routed to the outside of the LI box and provides the main laser beacon pointed towards a ground observatory. The

1% fiber remains inside the LI box and is connected to a monitoring photodiode. A separate small PCB hosts a photodiode and signal conditioning circuitry. It is mounted vertically to the LaserTray. This approach allows us to monitor the laser light intensity and detect potential anomalies. In addition, the instrument will

Pachowicz 6 40th Annual Small Satellite Conference monitor light intensity at the laser diode, inside the laser’s Butterfly package.

4.3 Laser Instrument architecture

The OBCTray commands the payload and relays telemetry for all LaserTrays. It is powered by the SatBus and linked to the SatBus by a bidirectional command/data interface implemented as an

LVDS/UART/DMA stack. The OBCTray MCU (TI

MSP430FR5969-SP) executes a script uploaded to the spacecraft. It turns on and commands target trays to conduct scientific observations. Telemetry data received from LaserTrays is screened for anomalies and relayed to the SatBus for storage and downlink.

The OBCTray power system converts power from unregulated 12VDC to regulated 5VDC. The tray assembly includes the following three systems: Gamma radiation sensor, Particle radiation sensor, and

Photodiode signal converter. The decision behind having a gamma radiation sensor on board the LI was driven by the need to monitor the radiation environment affecting optical components and fiber. This data can provide an opportunity to recalibrate laser light intensity (to be performed by NIST). To significantly decrease the radiation level, the LI box has thick aluminum walls

(>8mm) and multiple internal 2.5mm plates mounted at the bottom of each LaserTray. Additional external aluminum plates are mounted on the spacecraft surfaces.

The role of a particle sensor is to detect particle flux density of the space environment. A high-energy particle hitting a photodiode can generate a short-duration electric pulse influencing measured photon flux. In addition to implemented filters on the photodiode signal, knowledge of the space environment affecting measured parameters provides an opportunity to associate the science data with a confidence level.

The third sensory system on board the OBCTray converts signals from six Hamamatsu photodiodes mounted on the Element Wheel. These photodiodes measure laser flux reflected by EW mirrors. This is another added sensory system capable of measuring the light intensity exiting the 99% fiber. Hence, each Laser

Instrument can measure light intensity at three points of the optical path: inside the laser module, at the 1% fiber, and at the 99% fiber.

5. ELEMENT WHEEL

5.1 Element Wheel assembly

The Landolt element wheel system (Figure 9) has multiple roles. It is the front facing instrument providing openings for laser output towards observatories (primary role), photodiodes for calibration, solar mirrors of different curvature (used as a second source of calibration) as well as the opto-thermal shield used to reduce emitted light and reflect light away from the lasers to ensure that less than 1% of the light received at the observatory comes from reflected or emitted sources.

To perform these multiple functions, the wheel rotates on its axis with transmitted motion from two stepper motors (one for redundancy) on a range of 355°. Cables for the electronic elements mounted on the wheel are routed through the central hole in the middle (diameter:

30mm) and are connected to the laser module and element wheel OBCs. A hard stop and limit switches are used to prevent damaging the cables due to over-rotation.

The element wheel assembly also serves a structural role as the two laser modules are mounted on the back of the element wheel structural frame. Another frame is mounted on the back of the laser modules to complete the substructure of the payload, attached to the Satbus frame. The structural elements are made of aluminum

6061-T651. Some parts are bead-blasted and anodized for a matte, low-reflectivity finish to reduce light noise perceived at the observatory.

Precautions are taken to isolate the optical parts from potential outgassing coming from PCBs and other elements, as well as particulates from gear operation, with labyrinths and separate chambers for electronics and optics.

Figure 9: Element Wheel assembly showing the internal parts and subassemblies

The Element Wheel rotor assembly consists of the rotating element wheel itself, which houses the actuated solar mirrors, photodiode PCBs, a reference mirror

(never exposed to space and used to compare and characterize degradation of the solar mirrors), the absolute encoder used for wheel positioning, as well as the opening for the laser module outputs.

The solar mirrors are curved mirrors of three different curving radii to simulate three apparent star magnitudes

Pachowicz 7 40th Annual Small Satellite Conference by reflecting sunlight towards the observatory. They are actuated with stepper motors to flip them inside the spacecraft for protection when not in use and for internal scanning for degradation monitoring (compared with a reference mirror, never exposed to space). To use the solar mirrors, the wheel rotates until the solar mirror is facing the opening of the opto-thermal shield and the mirror is flipped to face outer space and reflect sunlight towards the observatory. The solar mirrors are locked in their 0 position with a samarium cobalt magnet. A clear aperture with a coning angle of 45° allows flexibility in the angle of reflection. The wheel rotor assembly is mounted on the element wheel structural frame, which consists of a static aluminum frame on which the adjustable laser output plate is mounted.

The laser output plate consists of two Diamond SA space-qualified fiber connectors (one for each laser module) mounted on a rigid aluminum frame. The six fiber lasers of the laser module are combined into a single custom-made ferrule, polished after assembly for optimal co-pointing between fibers. The plate itself is adjustable in tip-tilt to precisely align the laser module outputs with the spacecraft axis. The adjustment mechanism is a custom assembly allowing precise adjustment by turning one of the threaded sleeves (12° turn = 1.4 arcmin) until the desired angle is reached. The sleeves are then locked in place with locknuts, transforming the adjustment mechanism into a hard mount.

The element wheel assembly is closed by the wheel chamber subassembly on which the adjustable stepper motors, limit switches, absolute encoder stator, wheel drive electronics and opto-thermal shield are mounted. A copper thermal strap connects the shield to a radiator to cool the shield and reduce the infrared noise caused by radiated heat.

5.2 Element Wheel structural and thermal analysis

The mechanical design is supported by rigorous thermal and structural modeling/analysis. Different cases were considered based on the mission Concept of Operations to ensure the payload and its components can survive and operate optimally during the mission. The GEO environment is thermally challenging due to temperature extremes ranging from -194°C to +126°C. The results from the thermal analysis formed the following design choices:

• Insulate opto-thermal shield from the spacecraft environment and link to radiators using a copper thermal strap to reduce infrared noise.

• Insulate laser module from spacecraft to prevent the spacecraft thermal environment to affect temperature sensitive lasers. Kapton heaters are placed on the modules to provide active heating when observing in eclipse during equinoxes.

• Place a Kapton heater on the wheel to actively warm up solar mirrors before exposing them to sunlight to avoid breaking mirrors due to thermal shock.

• Insulate fiber guide from laser tray housing to prevent rejected laser heat from creating temperature gradients in routed fibers. The fiber guide is made of aluminum and provides a uniform temperature to the fibers, since it was shown during testing at NIST that thermal gradients in the fiber affect the output wavelength.

• Insulate photodiode and laser tray PCBs from laser tray housing to prevent rejected laser heat from overheating electronics and affecting photodiode readings.

The results from the structural analysis are used to validate the payload’s capacity to withstand launch stresses and identify areas in need of structural reinforcement.

Figure 10: Landolt payload thermal analysis (left), and EW modal analysis (right)

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6. SUMMARY

The Landolt Mission is a $20M NASA Pioneers Program project launched in late 2029 to deploy an artificial standard star into Geostationary Orbit (GEO). Operating as NASA's first hybrid space mission, it addresses a fundamental problem in ground-based astronomy:

absolute flux calibration uncertainties currently sit at 1–

5%. By projecting an SI-calibrated laser source at six distinct visible and near-infrared wavelengths directly into major ground telescopes, Landolt establishes a stable, laboratory-to-sky calibration baseline that pushes absolute flux uncertainty below 1%. This unprecedented precision will optimize instrument evaluation and catalyze breakthroughs across exoplanet host star characterization, dark matter research, and supernova cosmology. The SmallSat platform will operate its central payload, the SI Traceable Absolute Radiometer

(STAR), for a 10-month science window before using its onboard propulsion system to maneuver into a graveyard disposal orbit.

Structurally, the payload integrates two fully redundant

Laser Instruments with an Element Wheel technology demonstrator. To survive GEO’s extreme temperature swings and radiation environment, the architecture incorporates thick 8mm aluminum shielding, active thermoelectric coolers, and an active internal network of radiation-hardened microcontrollers. Precision photon flux is constantly cross-checked using a triple-point monitoring system that samples light intensity inside the laser package, at an internal 1% fiber split, and at the final 99% output path via photodiodes on the Element

Wheel. The front-facing Element Wheel executes multiple roles, using space-grade stepper motors, absolute encoders, and custom anti-backlash gears to align laser paths, deploy protective opto-thermal shielding, and actuate curved solar mirrors that reflect sunlight to safely simulate varying star magnitudes.

ACKNOWLEDGEMENTS

This work is supported by the NASA Astrophysics

PIONEERS program NASA grant# 80NSSC24M0086, the Mason Space Center funded by the Congressionally directed community project, NASA grant #

80NSSC24K1002, the CANDLE APRA NASA project, and the ORCAS mission concept study.

We thank the Landolt mission team of Co-Is, Collaborators and Mission Contributors not listed above, including Steven Robeson, Orbital Velocities LLC, Pulsar Space Systems LLC, Odyssey Space LLC, and the following students: Ashley C Knox, Chapin Turkel, Aidan Tomhave, Rebekah Gerhardt, Kasey Davidson, Aurelia Klunder, Elizabeth Lillehei, Kareem

Elsharkawy, Fatemah Bahzad, Harshini Vedula, Tanush

Bhardwaj, Sydney Treglown, Dakota Jett, Nhi Nguyen, Owen Alfaro, Sasha Oxley, Nasiir Davis-Barkley, Apoorva Jayanthi, Tommy Thomas, Alexandra Boicu, Alan Zhu, Kevin Collins, Leo Raskin, Leslie Morales, Kayla Carmical, Andrew Lewis, Dawn Pierce, Aiden

Kriel, Nadin Said, Jeff James, and Rebekah Brown.

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