I am a graduate student in the Colorado Ultraviolet Spectroscopy Program (CUSP) at CU Boulder under Dr. Kevin France and Dr. Brian Fleming. We build sounding rocket payloads and cubesats and send them to space to make UV observations free of Earth's attenuating atmosphere. Each payload has both science and technical development goals. I currently work as a graduate student on SISTINE.
S.I.S.T.I.N.E.
Suborbital Imaging Spectrograph for Transition region Irradiance from Nearby Exoplanet host stars
The Instrument:
SISTINE is an f/14 Cassegrain telescope with a focal length of 7,000 mm, which feeds an f/32 spectrograph. The spectrograph has a designed resolving power of at least 10,000 across the 100 –160 nm bandpass with imaging performance between 0.7 – 2" .
The optical assembly includes a 0.5 m parabolic primary mirror and a 91 mm convex hyperbolic secondary mirror with a long slit (10" x 6'). The light is dispersed by a holographically ruled grating and imaged by two 110 x 40 mm micro-channel plate detectors. The entire assembly is housed in 22 in rocket skins.
This ray trace depicts the path FUV light travels (primary, secondary, through the slit, grating, fold, detector).
Optical assembly designed by Brian Fleming
Science:
Tech Dev:
Aluminum coated mirrors have a high theoretical reflectivity in the ultra violet (UV), but require additional protective coatings to avoid oxidation. Recent progress in the physical vapor deposition processes (PVD) of lithium fluoride (LiF + Al) coatings have made the greatest gains in advancing aluminum mirrors towards their theoretical limit. Though flown with success in past NASA missions (FUSE), aluminum optics are rarely used because the required protective LiF coatings are susceptible to hygroscopic degradation. See the plot below for quantitative measurements.
New physical vapor deposition processes (PVD) of LiF yield an enhanced LiF coating (eLiF), which has lower surface roughness and higher UV reflectance than traditional LiF. The primary mirror, secondary mirror, and fold mirror of SISTINE's optical assembly have been coated with eLiF. SISTINE is acting as a test bed for this new technology, and will be the first demonstration of their use in space. Furthermore, we are testing an additional coating deposited using atomic layer deposition (ALD). This is an ultrathin layer of aluminum trifluoride to help protect the optics from hygroscopic degradation. We will attempt to demonstrate the capability of these coatings, and that they can be maintained with reasonable laboratory practices - our next launch is in the summer of 2021.
The goal of SISTINE is to help characterize the ultra violet (UV) irradiance spectrum of exoplanet host stars. The extreme UV (EUV: 20 – 91 nm), far UV (FUV: 92 – 69), and near UV (NUV: 170 – 400 nm) comprise the UV irradiance spectrum of a star. These UV photons control atmospheric heating, stability, and the photochemical structure of the atmospheres. SISTINE will be observing in the FUV with a bandpass of ~100 – 160 nm.
A host star’s UV radiation drives the atmospheric chemistry of its orbiting planets, thus affecting their habitability (in regards to known biological life) and available bio-markers. The habitable zone (HZ) around a star is the area where liquid water can be maintained on the surface of a planet for some portion of its orbit. Stellar UV radiation can strip away atmospheres as well as disassociate water molecules present on terrestrial exoplanets. A complete understanding of the HZ requires a thorough characterization of the host stars UV output.
Additionally, when probing exoplanet atmospheres, astronomers have identified a number of atmospheric constituents to look for as possible signs of life - known as bio-markers. O2, O3, CH4, and CO2 are considered to be the most important bio-markers on Earth-like exoplanets. The photochemistry of these species is dependent on the intensity and type of UV output of the host star, which can disassociate (H2O, CO2, CH4) or drive the chemistry of (O2, O3) the different bio-markers.
The first launch of SISTINE was from White Sands Missile Range in the summer of 2019. This flight gathered useful data for calibrating the instrument and technology demonstration. Furthermore, the flight was preparatory for the payload's Australia campaign: a science focused launch in the summer of 2021. SISTINE will observe the nearest-to-Earth star system Alpha Centauri to characterize the UV output of exoplanet host stars.
ref: Kevin France et al. (2013), THE ULTRAVIOLET RADIATION ENVIRONMENT AROUND M DWARF EXOPLANET HOST STARS, ApJ 763 149
Figure ref: Brian Fleming et al. (2017), Advanced environmentally resistant lithium fluoride mirror coatings for the next generation of broadband space observatories, Applied Optics
Amanda Zangari, John Fazio (a U.S. ambassador to Argentina), and I successfully observe the occultation of Mu69 for New Horizons. NASA article
Occultations
An occultation occurs when one object passes through a line connecting two other objects. A solar eclipse is an occultation, with the moon occulting the sun from the point of view of the Earth.
Occultations are often the only method to probe small solar system objects other than a spacecraft flyby. I am part of a large collaboration of astronomers who operate ground based mobile telescopes to observe occultations in support of spacecraft missions. I have observed from the U.S., Argentina, and Senegal in support of the New Horizons and Lucy spacecrafts. For more information, see our publications listed in my CV.
Space Physics: The Io Plasma Torus
Io, the most volcanically active body in the solar system, fuels a plasma torus around Jupiter with dissociation products of SO2 at a rate of ~1,000 kg/s. We use a combination of in situ Voyager 1 data and Cassini Ultraviolet Imaging Spectrograph observations to constrain a diffusive equilibrium model of the Io plasma torus. The interaction of the Io plasma torus with Io launches Alfvén waves in both directions along magnetic field lines.
We use the recent Juno‐based JRM09 magnetic field model combined with our 3‐D model of the Io plasma torus to simulate the propagation of Alfvén waves from the moon to the ionosphere of Jupiter. We map the location of multiple reflections of iogenic Alfvén waves between the northern and southern hemispheres. The location of the first few bounces of the Alfvén wave pattern match the Io auroral footprints observed by the Hubble Space Telescope. Our 3D model of the torus is shown in the figure.
Results published: Hinton, P. C., Bagenal, F., & Bonfond, B. (2019). Alfvén wave propagation in the Io plasma
torus. Geophysical Research Letters, 46, 1242-1249.