John Scherrer

Ralph: A Visible/Infrared Imager for the New Horizons Pluto/Kuiper Belt Mission

The New Horizons instrument named Ralph is a visible/near infrared multi-spectral imager and a short wavelength infrared spectral imager. It is one of the core instruments on New Horizons, NASA’s first mission to the Pluto/Charon system and the Kuiper Belt. Ralph combines panchromatic and color imaging capabilities with SWIR imaging spectroscopy. Its primary purpose is to map the surface geology and composition of these objects, but it will also be used for atmospheric studies and to map the surface temperature. It is a compact, low-mass (10.5 kg) power efficient (7.1 W peak), and robust instrument with good sensitivity and excellent imaging characteristics. Other than a door opened once in flight, it has no moving parts. These characteristics and its high degree of redundancy make Ralph ideally suited to this long-duration flyby reconnaissance mission.

The CYGNSS nanosatellite constellation hurricane mission

The Cyclone Global Navigation Satellite System (CYGNSS) is a spaceborne mission concept focused on tropical cyclone (TC) inner core process studies. CYGNSS attempts to resolve the principle deficiencies with current TC intensity forecasts, which lies in inadequate observations and modeling of the inner core. CYGNSS consists of 8 GPS bistatic radar receivers deployed on separate nanosatellites. The primary science driver is rapid sampling of ocean surface winds in the inner core of tropical cyclones.

Alice : The rosetta Ultraviolet Imaging Spectrograph

We describe the design, performance and scientific objectives of the NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will be the first UV spectrograph to study a comet at close range. It is designed to obtain spatially-resolved spectra of Rosetta mission targets in the 700–2050 Å spectral band with a spectral resolution between 8 Å and 12 Å for extended sources that fill its ∼0.05^ × 6.0^ field-of-view. ALICE employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a toroidal concave holographic reflection grating. The microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr and CsI) and employs a two-dimensional delay-line readout array. The instrument is controlled by an internal microprocessor. During the prime Rosetta mission, ALICE will characterize comet 67P/Churyumov-Gerasimenkos coma, its nucleus, and nucleus/coma coupling; during cruise to the comet, ALICE will make observations of the missions two asteroid flyby targets and of Mars, its moons, and of Earths moon. ALICE has already successfully completed the in-flight commissioning phase and is operating well in flight. It has been characterized in flight with stellar flux calibrations, observations of the Moon during the first Earth fly-by, and observations of comet C/2002 T7 (LINEAR) in 2004 and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing campaign.

Ultraviolet Discoveries at Asteroid (21) Lutetia by the Rosetta Alice Ultraviolet Spectrograph

The NASA Alice ultraviolet (UV) imaging spectrograph on board the ESA Rosetta comet orbiter successfully conducted a series of flyby observations of the large asteroid (21) Lutetia in the days surrounding Rosettas closest approach on 2010 July 10. Observations included a search for emission lines from gas, and spectral observations of the Lutetias surface reflectance. No emissions from gas around Lutetia were observed. Regarding the surface reflectance, we found that Lutetia has a distinctly different albedo and slope than both the asteroid (2867) Steins and Earths moon, the two most analogous objects studied in the far ultraviolet (FUV). Further, Lutetias ~10% geometric albedo near 1800 A is significantly lower than its 16%-19% albedo near 5500 A. Moreover, the FUV albedo shows a precipitous drop (to ~4%) between 1800 A and 1600 A, representing the strongest spectral absorption feature observed in Lutetias spectrum at any observed wavelength. Our surface reflectance fits are not unique but are consistent with a surface dominated by an EH5 chondrite, combined with multiple other possible surface constituents, including anorthite, water frost, and SO2 frost or a similar mid-UV absorber. The water frost identification is consistent with some data sets but inconsistent with others. The anorthite (feldspar) identification suggests that Lutetia is a differentiated body.

The NASA EV-2 Cyclone Global Navigation Satellite System (CYGNSS) mission

The NASA EV-2 Cyclone Global Navigation Satellite System (CYGNSS) is a spaceborne mission focused on tropical cyclone (TC) inner core process studies. CYGNSS attempts to resolve the principle deficiencies with current TC intensity forecasts, which lies in inadequate observations and modeling of the inner core. The inadequacy in observations results from two causes: 1) Much of the inner core ocean surface is obscured from conventional remote sensing instruments by intense precipitation in the eye wall and inner rain bands. 2) The rapidly evolving (genesis and intensification) stages of the TC life cycle are poorly sampled in time by conventional polar-orbiting, wide-swath surface wind imagers. CYGNSS is specifically designed to address these two limitations by combining the all-weather performance of GNSS bistatic ocean surface scatterometry with the sampling properties of a constellation of satellites.

ALICE~AN ULTRAVIOLET IMAGING SPECTROMETER FOR THE ROSETTA ORBITER

We describe the design concept and scientific objectives of ALICE: a lightweight (2.2 kg), low-power (2.9 W), and low-cost UV imaging spectrometer for the ESA Rosetta Orbiter. Ultraviolet spectroscopy is a powerful tool for studying astrophysical objects, and has been applied with great success to the study of comets. ALICE is designed to obtain far-UV (FUV) spectra of the Rosetta comet nucleus and coma in the 700–2050 A bandpass; it will achieve spectral resolutions between 9.8 and 12.5 A across the bandpass for extended sources that fill its 0.1 × 6.0 deg.2 field-of-view. It employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a concave holographic reflection grating. The imaging microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr and Csl) and a 2-D wedge-and-strip readout array. ALICE will deepen the Rosetta Orbiter remote sensing investigation through its ability to detect and measure (1) noble gases; (2) atomic abundances in the coma; (3) major ion abundances in the tail; and (4) production rates, variability, and structure of H2O and CO/CO2 molecules that generate cometary activity. In addition, ALICE will allow an investigation of the FUV properties of the nucleus and its solid grains, and can provide unique information during asteroid flybys and at en-route planetary encounters, most notably, Mars.

The interstellar boundary explorer (IBEX): Update at the end of phase B

The Interstellar Boundary Explorer (IBEX) mission will make the first global observations of the heliosphere’s interaction with the interstellar medium. IBEX achieves these breakthrough observations by traveling outside of the Earth’s magnetosphere in a highly elliptical orbit and taking global Energetic Neutral Atoms (ENA) images over energies from ∼10 eV to 6 keV. IBEX’s high‐apogee (∼50 RE) orbit enables heliospheric ENA measurements by providing viewing from far above the Earth’s relatively bright magnetospheric ENA emissions. This high energy orbit is achieved from a Pegasus XL launch vehicle by adding the propulsion from an IBEX‐supplied solid rocket motor and the spacecraft’s hydrazine propulsion system. IBEX carries two very large‐aperture, single‐pixel ENA cameras that view perpendicular to the spacecraft’s Sun‐pointed spin axis. Each six months, the continuous spinning of the spacecraft and periodic re‐pointing to maintain the sun‐pointing spin axis naturally lead to global, all‐sky images. Over the course of our NASA Phase B program, the IBEX team optimized the designs of all subsystems. In this paper we summarize several significant advances in both IBEX sensors, our expected signal to noise (and background), and our groundbreaking approach to achieve a very high‐altitude orbit from a Pegasus launch vehicle for the first time. IBEX is in full scale development and on track for launch in June of 2008.The Interstellar Boundary Explorer (IBEX) mission will make the first global observations of the heliosphere’s interaction with the interstellar medium. IBEX achieves these breakthrough observations by traveling outside of the Earth’s magnetosphere in a highly elliptical orbit and taking global Energetic Neutral Atoms (ENA) images over energies from ∼10 eV to 6 keV. IBEX’s high‐apogee (∼50 RE) orbit enables heliospheric ENA measurements by providing viewing from far above the Earth’s relatively bright magnetospheric ENA emissions. This high energy orbit is achieved from a Pegasus XL launch vehicle by adding the propulsion from an IBEX‐supplied solid rocket motor and the spacecraft’s hydrazine propulsion system. IBEX carries two very large‐aperture, single‐pixel ENA cameras that view perpendicular to the spacecraft’s Sun‐pointed spin axis. Each six months, the continuous spinning of the spacecraft and periodic re‐pointing to maintain the sun‐pointing spin axis naturally lead to global, all‐sky images. Over...

The IMAGE Observatory

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission will be the first of the new Medium-class Explorer (MIDEX) missions to fly. IMAGE will utilize a combination of ultraviolet and neutral atom imaging instruments plus an RF sounder to map and image the temporal and spatial features of the magnetosphere. The eight science sensors are mounted to a single deckplate. The deckplate is enveloped in an eight-sided spacecraft bus, 225 cm across the flats, developed by Lockheed Martin Missiles and Space Corporation. Constructed of laminated aluminum honeycomb panels, covered extensively by Gallium Arsenide solar cells, the spacecraft structure is designed to withstand the launch loads of a Delta 7326-9.5 ELV. Attitude control is via a single magnetic torque rod and passive nutation damper with aspect information provided by a star camera, sun sensor, and three-axis magnetometer. A single S-band transponder provides telemetry and command functionality. Interfaces between the self-contained payload and the spacecraft are limited to MIL-STD-1553 and power. This paper lists the requirements that drove the design of the IMAGE Observatory and the implementation that met the requirements.

The U.S. Rosetta project: NASA's contribution to the International Rosetta Mission

The International Rosetta Mission was successfully launched on March 2, 2004. NASAs contribution to this mission consists of the following three hardware experiments: Alice (an ultraviolet spectrometer), the ion and electron sensor (IES - a plasma instrument), and the microwave instrument for the Rosetta orbiter (MIRO), as well as other components. Collectively these elements are known as the U.S. Rosetta project. In this paper, we present an overview of the U.S. Rosetta project. We present and summarize the successful launch and early operations phases of the U.S. Rosetta project. Finally, an unplanned science target appeared in the form of Comet C/2002 T7 (LINEAR). Comet Linear was successfully observed by the U.S. Rosetta project on two occasions, April 30 and May 17, 2004, by both Alice and MIRO.

Radiometric and calibration performance results of the Rosetta UV imaging spectrometer ALICE

We describe the design, scientific objectives, and radiometric performance and calibration results of the Rosetta/ALICE instrument. ALICE is a lightweight (3.0 kg), low-power (4 W), low-cost imaging spectrometer optimized for cometary ultraviolet spectroscopy. Funded by NASA (with hardware contributions from CNES, France), ALICE will fly in 2003 on the ESA Rosetta Orbiter to characterize the cometary nucleus, coma, and nucleus/coma coupling of the Rosetta mission prime target comet 46P/Wirtanen. ALICE will also make observations of two asteroid flyby targets and of the Moon and Mars during the cruise portions of the Rosetta mission. It will obtain spatially-resolved, far-UV spectra of Wirtanens nucleus and coma in the 700-2050A passband with a spectral resolution of 8-12A for extended sources that fill the entrance slits 0.05 degree(s) x 6 degree(s) field-of-view. An improved derivative of the Rosetta/ALICE is also the UV spectrometer aboard the PERSI remote sensing suite proposed for the Pluto Kuiper Belt mission. ALICE uses modern technology to achieve its low mass and low power design specifications. It employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a concave (toroidal) holographic reflection grating. The imaging microchannel plate (MCP) detector utilizes dual solar-blind opaque photocathodes of KBr and CsI deposited on a cylindrically-curved (7.5-cm radius) MCP Z-stack, and a matching 2-D cylindrically-curved double delay-line readout array with a 1024 x 32 pixel array format. Three data taking modes exist: (i) histogram image mode for 2-D images, (ii) pixel list mode with periodic time fiducials for temporal studies, and (iii) count rate mode for broadband photometric studies. Optical and radiometric sensitivity performance results based on integrated system level tests of the ALICE flight model are presented and discussed.