Project Nautilus

Nautilus: A Revolutionary Space Telescope

Nautilus is a revolutionary space telescope concept that builds on a novel technology – engineered material diffractive-transmissive optical elements – to overcome the greatest limitations of space telescopes: non-scalable primary mirrors. By providing large but ultra-light telescope apertures, the Nautilus technology will enable the launch of a large fleet of identical telescopes. With a light-collecting power equivalent to a 50m diameter mirror Nautilus will be capable of surveying thousands of earth-sized habitable zone planets for atmospheric signatures of life.

The Search for Life in the Galaxy

Over the past two billion years life has profoundly changed the atmosphere of our planet: the abundance of the free molecular oxygen and ozone – both highly reactive gases – along with water vapor and methane represent a yet unique atmospheric composition. The combined presence of these gases, atmospheric biosignatures, in our planet’s atmosphere is a tracer of life that could be detected remotely, even over galactic distances. But identifying the spectral fingerprints of these atmospheric components in the light reflected by or transmitted through the atmospheres of earth-like planets requires very large telescopes. Even though NASA’s Kepler mission has discovered over 4,000 planets, no existing or planned space telescope has large enough diameter to search for life in their atmospheres.

Finding and correctly interpreting observations of extraterrestrial life is going to be very difficult and a large sample of planetary atmospheres with high-quality that can be compared is likely to be essential for robust results.

Our Nautilus team embarked on a challenge to build a telescope capable of studying a thousand earth-like planets. Our study shows that a telescope with a light-gathering power equivalent to a 50m telescope is required to reach this goal.

Collecting Starlight

Since the 1970s the complexity and, approximately, the speed of integrated electric circuits have increased by over 5 million fold, transforming most aspects of our life. However, the size of astronomical telescopes has changed much more modestly: the 2.4m Hubble Space Telescope’s primary mirror (designed in the mid seventies and launched in 1990) was only superseded  by the Herschel Space Observatory’s 3.6m mirror in 2009, almost three decades later. The next major step will be the launch of the James Webb Space Telescope, with its 6.5m segmented aperture in 2019.

The evolution from HST to JWST represents a 7-fold increase in light collecting power over about five decades, demonstrating how extremely difficult it is to scale the astronomical mirrors larger. In fact, most of the increases in mirror size are due to increased computational processing speeds: segmented mirrors can be aligned and controlled with a high enough cadence and precision to allow them to form a single optical surface (Keck, JWST), while in other large telescopes the surface of large, but thin monolithic mirrors is correct by computer-driven actuators.

Over the past decades astrophysics has been limited by our ability to collect starlight with our telescopes: any technology that enables breaking away from the difficult-to-scale-in-size primary mirrors is set to transform astronomy. Large-scale ultralight-weight optical elements offer such an alternative to primary mirrors.

The Impact of the Nautilus Technology

The goal of our Nautilus team is to change the paradigm of how space telescopes are designed, built, and launched. It will not only transform NASA’s astrophysics missions, but will greatly expand commercial and government satellite technology capabilities.

Why Nautilus?

We named our telescope Nautilus after the revolutionary fictional submarine of Jules Verne (itself named after the first truly operational submarine). Since the publication of the Twenty Thousand Leagues under the Sea in 1870 the Nautilus name has been synonymous with visionary nautical and aeronautical projects, from the ship of Fernando Villaamil that circumnavigated the globe through the Nautilus submarine that served on Arctic expedition in 1931  and the USS Nautilus, the first nuclear submarine, to the Exploration Vessel Nautilus.

Like these projects, our Nautilus Space Telescope builds on a revolutionary new technology to achieve the ambitious goal of exploring the depths of the Universe and other Earth-like planets in the Galaxy.

Science Goals

One of the most fundamental and oldest questions of science is Are we alone? Modern astrophysical methods allow us to analyze the chemical composition of atmospheres of planets orbiting other stars – all we need is a large enough telescope to collect the light filtering through the atmospheres.

The science goal of the Nautilus Array is to carry out a comprehensive search for atmospheric biosignatures in about 1,000 transiting earth-sized exoplanets  to measure the occurrence rate of life flourishing on other worlds.

We will study the atmospheric composition of about one thousand earth-size habitable zone exoplanets to assess the diversity of their atmospheres. This large sample will allow a detailed statistical study of earth-sized exoplanets and the identification of Earth twins.

Even though over 4,000 exoplanets are known today, no telescope is yet capable of reliably detecting atmospheric biosignatures in any of them. The James Webb Space Telescope, which will be launched in 2019, may be able to inspect the atmospheres of a couple of earth-sized planets around the smallest stars in the direct vicinity of the Sun. No existing or currently approved telescope is capable of carrying out a systematic search for life or completing a statistical study of the diversity of earth-like planets.

The Nautilus Array will allow the comparison of atmospheric compositions of each planet to the range of atmospheric compositions consistent with abiotic processes. We will identify atmospheres whose composition is not in line with abiotic processes and necessitates the existence of life.

The Nautilus technology will allow orders-of-magnitude increase in sensitivity in exoplanet transit spectroscopy due to the very large collecting area.

EnMat Technology

The transformative technology behind Nautilus are the ultralight, very large-aperture engineered material multi-order diffractive lenses (MOD-EnMat) developed at The University of Arizona’s College of Optical Sciences.

Traditional lenses use refraction – the change of light’s direction as it enters a  medium with different refractive index – to focus light onto the focal plane, thereby creating images. However, large lenses are exceedingly difficult to manufacture.

The MOD-EnMat lenses (multi-order diffractive engineered material lenses) are very light-weight diffractive-transmissive alternatives to the heavy reflective elements (mirrors) used in state-of-the-art ground- and space-based telescopes. Technology similar to MOD-EnMat lenses is used in some commercial optics, including high-quality Canon EF photo-lenses. The optimized multi-order design of these lenses provides essentially achromatic, diffraction-limited performance.

Other Large Diffractive Lens-based Telescope Concepts

Large space telescopes  utilizing conceptually similar, but distinct technologies have been in development by multiple groups: a team led by Rod Hyde at Lawrence Livermore National Laboratory, developed the Eyeglass concept, a 20m diameter space telescope also utilizing transmissive diffractive optics. In 2002 a 5m prototype was built at LLNL with funding from DARPA. The Eyeglass concept is using a very large number of flat glass panels that deployed in an origami fashion.

From 2010 DARPA has been pursuing MOIRE (Membrane Optic Imager Real-Time Exploitation), which also uses transmissive diffractive optics, but replaces the thin glass tiles with flexible optical membranes, in which the diffraction pattern is produced in a lithographic process. The MOIRE project demonstrated in 2013  a partial 5m diameter ground-based telescope, a milestone toward the eventual goal of a 20m diameter earth-observing space telescope. (DARPA MOIRE concept video , S&TR article on Eyeglass and MOIRE)

Our Nautilus project also uses diffractive transmissive optics, but with and advanced, high-order harmonics surface optimized for astrophysical observations.

The MOD-EnMat lenses designed by the Nautilus optical design and fabrication team  can be replicated rapidly and at low cost. The Nautilus Array is made possible by the lightweight, replicated MOD-EnMat lenses that allow light-weight telescope structure, overall greatly reduced launch costs, combined with cost-effective fabrication of large quantities of the lenses.

 

Prototypes at University of Arizona

The Nautilus team has been developing diffractive-transmissive optics and studying the design, fabrication, and testing of large-scale MOD-EML since 2015. Our team has designed and fabricated multiple generations of MOD-EML lenses. We have also successfully replicated lenses. As of November 2017 laboratory and on-sky tests using a Celestron refracting telescope in which the original refractive lens has been replaced with a small-scale MOD-EML element.


A prototype MOD-EML lens mounted in an adaptor plate for on-sky and laboratory tests with a Celestron astronomical refractor. The MOD-EML replaced the original achromat in the telescope.

 

Nautilus Array

The Nautilus Array will consist of approximate one hundred identical unit  telescopes. The unit telescopes are all light-weight with a single, non-cooled instrument, a visual/near-infrared spectrograph, located at the geometric center of the spherical spacecraft.

Every single Nautilus unit telescope has four times more collecting area than the Hubble Space Telescope.
Nautilus units in launch configuration and after deployment

Launch and deployment: The unit telescopes are launched in a compact format and deployed in orbit. Fundamentally, each unit telescope consists of three components: the lightweight MOD-EnMat lens, the instrument package, and an inflatable spherical mylar balloon. With the balloon deflated the unit telescopes are approximately 1m x 5m cylinders; in orbit the inflation of the balloon deploys the sunshield and moves the instrument packages into the focal plane. Depending on the launch vehicle more than a dozen Nautilus units can be launched simultaneously.

The Nautilus array’s combined light-collecting area equals that of a 50m space telescope: over four hundred times more powerful than the Hubble Space Telescope!

Operations: The Nautilus Unit operates in two modes: the survey mode, in which it will carry out the most comprehensive exoplanet transit search to date; and the atmospheric analysis mode, in which it will perform the most detailed studies of atmospheric composition and climate diversity in earth-like exoplanets.

Survey mode: The unit telescopes carry out a sensitive exoplanet transit search by independently monitoring up to one hundred target fields, each with a light-collecting power four times greater than that of the Hubble Space Telescope and about twenty five times greater than the Kepler mission. The unit telescopes will be able to detect the transits of earth-sized planets around sun-like stars over galactic scales (up to about 10 kpc or about 33,000 light years).

Atmospheric Analysis Mode: During known transit events all unit telescopes will target the same star. Each telescope will be able to individually measure minute changes in the starlight as it filters through the planet’s atmosphere. Several key components of planetary atmospheres have prominent signatures in transmitted light – by measuring the depths of the exoplanet transits at different wavelengths we can explore what gases are present in the atmosphere.  The data from the individual Nautilus telescopes can combined (digitally co-added), creating a light gathering power and data quality equivalent to those of a 50m space telescope.

The Nautilus array is optimized to detect atmospheric components that emerge from biological processes or can test the habitability of the targeted planets: for example, with its wavelength coverage of 0.5-1.6 microns the Nautilus array will be capable of detecting molecular oxygen (O2), ozone (O3), and water (H2O).

Team

The core of the Nautilus team is based at The University of Arizona’s College of Optical Sciences and Departments of Astronomy and Planetary Sciences. Additional expertise is provided by team members at Northrop-Grumman and NASA Goddard Space Flight Center.  Our team combines experts in astrophysics and observational astronomy, planetary sciences, innovative optical design, optical fabrication, and optical surface metrology, and spacecraft design and engineering, human spaceflight and space servicing, among many other areas.

 

Prof. Daniel Apai
Nautilus Array Principal Investigator
University of Arizona Associate Professor for Astronomy and Planetary Sciences

Daniel Apai is an expert on extrasolar planet studies and leads major atmospheric characterization programs on the Spitzer and Hubble Space Telescopes. He is also principal investigator of the NASA Nexus for Exoplanet System Science program Earths in Other Solar Systems, a large, multi-disciplinary project aimed at understanding the formation of earth-sized habitable zone planets.

Prof. Thomas Milster
Lead, Optical Design
University of Arizona Professor for Optical Sciences

Tom D. Milster is a Professor in the College of Optical Sciences and Electrical and Computer Engineering at the University of Arizona.  Since 1989, his research interests include physical optics of high-performance optical systems and diffractive optics, with applications in microscopy, optical data storage, lithography and astronomy.

Prof. Rongguang Liang
Lead, MOD-EnMat Fabrication
University of Arizona Professor for Optical Sciences 

Rongguang Liang is a Professor at College of Optical Sciences, University of Arizona.  His current research focuses on optical design, fabrication, testing, and optical imaging technologies. His group designed three cameras in NASA’s OSIRIS-REx mission.  Dr. Liang is a SPIE fellow and an Associate Editor of Optica.

Prof. Dae Wook Kim
Lead, Optical Surface Metrology, Large Optics Fabrication and Testing
University of Arizona Assistant Professor for Optical Sciences

Dae Wook Kim has been working in the optical engineering field for more than 10 years, focusing on very large astronomical optics such as 25m diameter Giant Magellan Telescope primary mirror and 4.2m Advanced Technology Solar Telescope primary mirror. His main research area has been the precision optical fabrication field. He is also working on various optical metrology topics such as interferometric testing using computer generated holograms, direct curvature measurement and dynamic deflectometry systems.  He is an Associate Editor for Optics Express journal.

Dr. Jonathan Arenberg
Lead, Spacecraft Architecture and Performance Assessment
Chief Engineer, Northrop Grumman Advanced Systems

Jonathan Arenberg is Chief Engineer for Space Science Missions at Northrop Grumman Aerospace Systems in Redondo Beach CA, and  has worked on the Chandra X-ray Observatory, James Webb Space Telescope and the starshade. His research interests development of future missions of traditional and novel technologies.

Dr. John Grunsfeld
In-orbit Assembly, Launch, and Serviceability
Astrophysicist, NASA Goddard Space Flight Center
Former NASA Associate Administrator for Science
Astronaut, Mission Specialist and EVA Astronaut to Hubble Space Telescope Servicing Missions

Chuck Fellows, MSc, E. E. 
Project Manager
University of Arizona

Lee Johnson
Optical design and testing
Optical Sciences Graduate Student, University of Arizona

Alex Bixel, BSc
Science Requirements
Astronomy Graduate Student, University of Arizona
NASA Earth and Space Science Fellow