Flexible Levitation on a Track (FLOAT)

Ethan Schaler
NASA Jet Propulsion Laboratory

We want to build the first lunar railway system, which will provide reliable, autonomous, and efficient payload transport on the Moon. A durable, long-life robotic transport system will be critical to the daily operations of a sustainable lunar base in the 2030’s, as envisioned in NASA’s Moon to Mars plan and mission concepts like the Robotic Lunar Surface Operations 2 (RLSO2), to:

— Transport regolith mined for ISRU consumables (H2O, LOX, LH2) or construction

— Transport payloads around the lunar base and to / from landing zones or other outposts

We propose developing FLOAT — Flexible Levitation on a Track — to meet these transportation needs.

The FLOAT system employs unpowered magnetic robots that levitate over a 3-layer flexible film track: a graphite layer enables robots to passively float over tracks using diamagnetic levitation, a flex-circuit layer generates electromagnetic thrust to controllably propel

robots along tracks, and an optional thin-film solar panel layer generates power for the base when in sunlight. FLOAT robots have no moving parts and levitate over the track to minimize lunar dust abrasion / wear, unlike lunar robots with wheels, legs, or tracks.

FLOAT tracks unroll directly onto the lunar regolith to avoid major on-site construction — unlike conventional roads, railways, or cableways. Individual FLOAT robots will be able to transport payloads of varying shape / size (>30 kg/m^2) at useful speeds (>0.5m/s), and a large-scale FLOAT system will be capable of moving up to 100,000s kg of regolith / payload multiple kilometers per day. FLOAT will operate autonomously in the dusty, inhospitable lunar environment with minimal site preparation, and its network of tracks can be rolled-up / reconfigured over time to match evolving lunar base mission requirements.

In Phase 2, we will continue to retire risks related to the manufacture, deployment, control, and long-term operation of meter-scale robots / km-scale tracks that support human exploration (HEO) activities on the Moon, by accomplishing the following key tasks:

— Design, manufacture, and test a series of sub-scale robot / track prototypes, culminating with a demonstration in a lunar-analog testbed (that includes testing various site preparation and track deployment strategies)

— Investigate impacts of environmental effects (e.g. temperature, radiation, charging, lunar regolith simulant contamination, etc.) on system performance and longevity

— Investigate / define a technology roadmap to address technology gaps and mature manufacturing capability for critical hardware (e.g. large-area magnetic arrays with mm-scale magnetic domains, and large-area flex-circuit boards)

— Continue refining simulations of FLOAT system designs with increased fidelity, to provide improved performance estimates under the RLSO2 mission concept We will also leverage these sub-scale prototypes to explore opportunities for follow-on technology demonstrations on sub-orbital flights (via Flight Opportunities / TechFlights) or lunar technology demos (via LSII / CLPS landers)

2024 Phase I Selection

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Loura Hall

Radioisotope Thermoradiative Cell Power Generator

Stephen Polly
Rochester Institute of Technology

In this project we will continue our Phase I efforts to develop and demonstrate the feasibility of a revolutionary power source for missions to the outer planets utilizing a new paradigm in thermal power conversion, the thermoradiative cell (TRC). Operating like a solar cell in reverse, the TRC converts heat from a radioisotope source into infrared light which is sent off into the cold universe. In this process, electricity is generated. In our Phase I study, we showed 8 W of electrical power is possible from the 62.5 W Pu-238 pellet from a general purpose heat source using a 0.28 eV bandgap TRC operating at 600 K. The necessary array includes 1,125 cm² of TRC emitters, or just over 50% of the surface area of a 6U cubesat. With a mass (heat source + TRC) of 622 g, a mass specific power of 12.7 W/kg is possible, over a 4.5x improvement from heritage multi-mission radioisotope thermoelectric generator (MMRTG) was shown. Building on our results from Phase I, we believe there is much more potential to unlock here.

Using low-bandgap III-V materials such as InAsSb in nanostructured arrays to limit potential loss mechanisms, a 25x improvement in mass specific power and a four order of magnitude decrease in volume from a MMRTG is an early estimate, with higher performance possible depending on operating conditions. TRC technology will allow a proliferation of small versatile spacecraft with power requirements not met by photovoltaic arrays or bulky, inefficient MMRTG systems. This will directly enable small-sat missions to the outer planets as well as operations in permanent shadow such as polar lunar craters.

This study will investigate the thermodynamics and feasibility of the development of a radioisotope enabled thermoradiative power source focusing on system size, weight, power (SWaP) while continuing to integrate the effects of potential power and efficiency loss mechanisms developed in Phase I. Experimentally, materials and TRC devices will be grown including InAsSb-based type-II superlattices by metalorganic vapor phase epitaxy (MOVPE) to target low-bandgap materials with suppressed Auger recombination. Metal-semiconductor contacts capable of surviving the required elevated temperatures will be investigated. TRC devices will be tested for performance at elevated temperature facing a cold ambient under vacuum in a modified cryostat testing apparatus developed in Phase I.

We will analyze a radioisotope thermoradiative converter to power a cubesat mission operating at Uranus. This will include an engineering design study of our reference mission with the Compass engineering team at NASA Glenn Research Center with expertise on the impact of new technologies on spacecraft design in the context of an overall mission, incorporating all engineering disciplines and combining them at a system level. Finally, we will develop a technological roadmap for the necessary components of the TRC to power a future mission.

2024 Phase I Selection

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Loura Hall

The Great Observatory for Long Wavelengths (GO-LoW)

Mary Knapp
MIT

Humankind has never before seen the low frequency radio sky. It is hidden from ground-based telescopes by the Earth’s ionosphere and challenging to access from space with traditional missions because the long wavelengths involved (meter- to kilometer-scale)

require infeasibly massive telescopes to see clearly. Electromagnetic radiation at these low frequencies carries crucial information about exoplanetary and stellar magnetic fields (a key ingredient to habitability), the interstellar/intergalactic medium, and the earliest

stars and galaxies.

The Great Observatory for Long Wavelengths (GO-LoW) proposes an interferometric array of thousands of identical SmallSats at an Earth-Sun Lagrange point (e.g. L5) to measure the magnetic fields of terrestrial exoplanets via detections of their radio emissions at

frequencies between 100 kHz and 15 MHz. Each spacecraft will carry an innovative Vector Sensor Antenna, which will enable the first survey of exoplanetary magnetic fields within 5 parsecs.

In a departure from the traditional approach of a single large and expensive spacecraft (i.e. HST, Chandra, JWST) with many single points of failure, we propose an interferometric Great Observatory comprised of thousands of small, cheap, and easily-replaceable

nodes. Interferometry, a technique that combines signals from many spatially separated receivers to form a large ‘virtual’ telescope, is ideally suited to long wavelength astronomy. The individual antenna/receiver systems are simple, no large structures are required, and the very large spacing between nodes provides high spatial resolution.

In our Phase I study, we found that a hybrid constellation architecture was most efficient. Small and simple “listener” nodes (LNs) collect raw radio data using a deployable vector sensor antenna. A small number of larger, more capable “communication and computation” nodes (CCNs) collect data from LNs via a local radio network, perform beamforming processing to reduce the data volume, and then transmit the data to Earth via free space optics (lasercomm). Cross correlation of the beamformed data is performed on Earth, where computational resources are not tightly constrained. The CCNs are also responsible for constellation management, including timing distribution and ranging. The Phase I study also showed that the LN-CCN architecture optimizes packing efficiency, allowing a small number of super-heavy lift launch vehicles (e.g. Starship) to deploy the entire constellation to L4.

The Phase I study showed that the key innovation for GO-LoW is the “system of systems.” The technology needed for each individual piece of the observatory (e.g. lasercomm, CubeSats, ranging, timing, data transfer, data processing, orbit propagation) is not a big leap from current state of the art, but the coordination of all these physical elements, data products, and communications systems is novel and challenging, especially at scale.

In the proposed study, we will (1) develop a real-time, multi-agent simulation of the GO-LoW constellation that demonstrates the autonomous operations architecture required to achieve a

large (up to 100k) constellation outside of Earth’s orbit, (2) continue to refine the science case and requirements by simulating science output from the constellation and assessing major error sources informed by the real-time simulation, (3) develop appropriate orbital modeling to assess propulsion requirements for stationkeeping at a stable Lagrange point, and (4) further refine the technology roadmap required to make GO-LoW feasible in the next 10-20 years. GO-LoW represents a disruptive new paradigm for space missions. It achieves reliability through massive redundancy rather than extensive testing. It can evolve and grow with new technology rather than being bound to a fixed point in hardware/software development. Finally, it promises to open a new spectral window on the universe where unforeseen discoveries surely await.

2024 Phase I Selection

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Pulsed Plasma Rocket (PPR): Shielded, Fast Transits for Humans to Mars

Brianna Clements
Howe Industries

The future of a space-faring civilization will depend on the ability to move both cargo and humans efficiently and rapidly. Due to the extremely large distances that are involved in space travel, the spacecraft must reach high velocities for reasonable mission transit times. Thus, a propulsion system that produces a high thrust with a high specific impulse is essential. However, no such technologies are currently available.

Howe Industries is currently developing a propulsion system that may generate up to 100,000 N of thrust with a specific impulse (Isp) of 5,000 seconds. The Pulsed Plasma Rocket (PPR) is originally derived from the Pulsed Fission Fusion concept, but is smaller, simpler, and more affordable. The exceptional performance of the PPR, combining high Isp and high thrust, holds the potential to revolutionize space exploration. The system’s high efficiency allows for manned missions to Mars to be completed within a mere two months. Alternatively, the PPR enables the transport of much heavier spacecraft that are equipped with shielding against Galactic Cosmic Rays, thereby reducing crew exposure to negligible levels. The system can also be used for other far range missions, such as those to the Asteroid Belt or even to the 550 AU location, where the Sun’s gravitational lens focuses can be considered. The PPR enables a whole new era in space exploration.

The NIAC Phase I study focused on a large, heavily shielded ship to transport humans and cargo to Mars for the development of a Martian base. The main topics included: assessing the neutronics of the system, designing the spacecraft, power system, and necessary subsystems, analyzing the magnetic nozzle capabilities, and determining trajectories and benefits of the PPR. Phase II will build upon these assessments and further the PPR concept.

In Phase II, we plan to:

1. Optimize the engine design for reduced mass and higher Isp
2. Perform proof-of-concept experiments of major components
3. Complete a ship design for shielded human missions to Mars

2024 Phase I Selection

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Fluidic Telescope (FLUTE): Enabling the Next Generation of Large Space Observatories

Edward Balaban
NASA ARC

The future of space-based UV/optical/IR astronomy requires ever larger telescopes. The highest priority astrophysics targets, including Earth-like exoplanets, first generation stars, and early galaxies, are all extremely faint, which presents an ongoing challenge for current missions and is the opportunity space for next generation telescopes: larger telescopes are the primary way to address this issue.

With mission costs depending strongly on aperture diameter, scaling current space telescope technologies to aperture sizes beyond 10 m does not appear economically viable. Without a breakthrough in scalable technologies for large telescopes, future advances in

astrophysics may slow down or even completely stall. Thus, there is a need for cost-effective solutions to scale space telescopes to larger sizes.

The FLUTE project aims to overcome the limitations of current approaches by paving a path towards space observatories with largeaperture, unsegmented liquid primary mirrors, suitable for a variety of astronomical applications. Such mirrors would be created in

space via a novel approach based on fluidic shaping in microgravity, which has already been successfully demonstrated in a laboratory neutral buoyancy environment, in parabolic microgravity flights, and aboard the International Space Station (ISS). Theoretically

scale-invariant, this technique has produced optical components with superb, sub-nanometer (RMS) surface quality. In order to make the concept feasible to implement in the next 15-20 years with near-term technologies and realistic cost, we limit the diameter of the primary mirror to 50 meters.

In the Phase I study, we: (1) explored choices of mirror liquids, deciding to focus on ionic liquids, (2) conducted an extensive study of ionic liquids with suitable properties, (3) worked on techniques for ionic liquid reflectivity enhancement, (4) analyzed several alternative architectures for the main mirror frame, (5) conducted modeling of the effects of slewing maneuvers and temperature variations on the mirror surface, (6) developed a detailed mission concept for a 50-m fluidic mirror observatory, and (7) created a set of initial concepts for a subscale small spacecraft demonstration in low Earth orbit.

In Phase II, we will continue maturing the key elements of our mission concept. First, we will continue our analysis of suitable mirror frame architectures and modeling of their dynamic properties. Second, we will take next steps in our machine learning-based modeling and experimental work to develop reflectivity enhancement techniques for ionic liquids. Third, we will further advance the work of modeling liquid mirror dynamics. In particular, we will focus on modeling the effects from other types of external disturbances (spacecraft control accelerations, tidal forces, and micrometeorite impacts), as well as analyzing and modeling the impact of the thermal Marangoni effect on nanoparticle-infused ionic liquids. Fourth, we will create a model of the optical chain from the liquid mirror surface to the science instruments. Fifth, we will further develop the mission concept for a larger-scale, 50-m aperture observatory, focusing on its highest-risk elements. Finally, we will mature the concept for a small spacecraft technology demonstration mission in low Earth orbit, incorporating the knowledge gained in other parts of this work.

2024 Phase I Selection

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Loura Hall