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

Dennis C. Reuter^1^, S. Alan Stern^2^, John Scherrer^3^, Donald E.
Jennings^1^, James Baer^4^, John Hanley^3^, Lisa Hardaway^4^, Allen
Lunsford^1^, Stuart McMuldroch^5^, Jeffrey Moore^6^, Cathy Olkin^7^,
Robert Parizek^4^, Harold Reitsma^4^, Derek Sabatke^4^, John Spencer^7^,
John Stone^3^, Henry Throop^7^, Jeffrey Van Cleve^4^, Gerald E.
Weigle^3^ and Leslie A.Young^7^

^1^NASA/GSFC, Code 693, Greenbelt, MD 20771

^2^Space Sciences and Engineering Division, Southwest Research Institute
(SwRI), 1050 Walnut St., Suite 400, Boulder CO, 80302

^3^SwRI, 6220 Culebra Rd., San Antonio TX, 78228

^4^Ball Aerospace and Technology Corporation (BATC), 1600 Commerce St,
Boulder, CO 80301

^5^SSG Precision Optronics, 65 Jonspin Rd., Wilmington MA, 01887

^6^NASA/Ames Research Center, MS 245-3, Moffett Field, CA 94035-1000

^7^Dept. of Space Studies, Southwest Research Institute (SwRI), 1050
Walnut St., Suite 400, Boulder CO, 80302

######### ABSTRACT

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 IR 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.

###### 1. INTRODUCTION

New Horizons, a flyby mission to the Pluto/Charon system and the Kuiper
Belt, is the first in NASA's New Frontiers line of moderate-scale
planetary missions and is the first mission to explore Pluto and its
moons Charon, Nix and Hydra. Launched on January 19, 2006, it is
scheduled for a closest approach of about 10,000 km on July 14, 2015.
The scientific rationale for New Horizons and the overall mission
planning are described in detail in several papers in this issue (Stern,
Young *et al* and Fountain *et al*.). The New Horizons mission is led by
Principal Investigator Alan Stern of the Southwest Research Institute of
Boulder, CO and is managed by SwRI and the Johns Hopkins Applied Physics
Laboratory in Laurel, MD. A core remote-sensing instrument on New
Horizons is Ralph, a visible/NIR camera and infrared spectral mapper.
The instrument's primary purpose is to measure surface characteristics,
including geological processes, geomorphology, photometric properties,
and surface composition. In addition, surface temperature will be
inferred from the shapes and positions of well-established, thermally
diagnostic reflectance spectral features in H~2~O, CH~4~, and N~2~ ices.
Ralph will also be used to measure haze optical depths (if present) and
to search for rings and small satellites. This paper describes Ralph and
specifies its characteristics (See also Reuter *et al*., 2005).

The Ralph instrument is mounted to the exterior of the New Horizons
spacecraft (Fountain *et al*., this issue). Ralph consists of a single
telescope that feeds two sets of focal planes: 1) the Multi-spectral
Visible Imaging Camera (MVIC), a visible, near-IR imager and 2) the
Linear Etalon Imaging Spectral Array (LEISA), a short-wavelength, IR,
spectral imager. The telescope uses an unobscurred, off-axis,
three-mirror anastigmat design. The entire telescope assembly, including
the three diamond turned mirrors, is constructed from grain aligned
6061-T6 aluminum. The optical mounts, housing and baffles are diamond
turned from a single Al block. This combination of an all Al structure
and optics is lightweight, athermal and thermally conductive. It ensures
that the optical performance of the system is minimally sensitive to
temperature and that thermal gradients are minimized. The highly baffled
75 mm aperture, VIS/IR telescope provides ample sensitivity at
Pluto/Charon, while minimizing size and mass. The f/8.7 system's
approximately 658 mm Effective Focal Length offers a good compromise
between photometric throughput and alignment stability. Stray light
control is improved by using a field baffle at an intermediate focus
between the secondary and tertiary mirrors, and by using a Lyot stop at
the exit pupil after the tertiary mirror. A dichroic beamsplitter
transmits IR wavelengths longer than 1.1 μm to LEISA and reflects
shorter wavelengths to MVIC.

MVIC is composed of 7 independent CCD arrays on a single substrate. It
uses two of its large format (5024x32 pixel) CCD arrays, operated in
time delay integration (TDI) mode, to provide panchromatic (400 to 975
nm) images. Four additional 5024x32 CCDs, combined with the appropriate
filters and also operated in TDI mode, provide the capability of mapping
in blue (400-550 nm), red (540-700 nm), near IR (780 -- 975 nm) and
narrow band methane (860 -- 910 nm) channels. TDI operates by
synchronizing the parallel transfer rate of each of the CCDs thirty-two
5024 pixel wide rows to the relative motion of the image across the
detector's surface. In this way, very large format images are obtained
as the spacecraft scans the FOV rapidly across the surface. The presence
of 32 rows effectively increases the integration time by that same
factor, allowing high signal-to-noise measurements. The FOV of a single
MVIC pixel is 20x20 μradian^2^. The panchromatic (pan) channels of MVIC
will be used to produce hemispheric maps of Pluto and Charon at a double
sampled spatial resolution of 1 km^2^ or better. The static FOV of each
of the TDI arrays is 5.7°x0.037°. In addition to the TDI arrays, MVIC
has a 5024x128 element, frame transfer panchromatic array operated in
staring mode, with an FOV of 5.7°x0.15°. The primary purpose of the
framing array is to provide data for optical navigation (OpNav) of the
spacecraft.

LEISA is a wedged filter infra-red spectral imager that creates spectral
maps in the compositionally important 1.25-2.5 micron short wave
infrared (SWIR) spectral region. It images a scene through a wedged
filter (linear variable filter, Rosenberg *et al*., 1994) placed about
100 μm above a 256x256 pixel Mercury Cadmium Telluride (HgCdTe) detector
array (a PICNIC array). An image is formed on both the wedged filter and
the array simultaneously (there is less than 5% spectral broadening by
the f/8.7 beam). LEISA forms a spectral map by scanning the FOV across
the surface in a push broom fashion, similar to that of the MVIC TDI
channels. The frame rate is synchronized to the rate of the scan, so
that a frame is read out each time the image moves by the single pixel
IFOV. The LVF is fabricated such that the wavelength varies along one
dimension, the scan direction. The difference between a LEISA scan and a
TDI scan is that in LEISA the row-to-row image motion builds up a
spectrum while in TDI the motion increases the signal over a single
spectral interval. The filter is made in two segments. The first covers
from 1.25 to 2.5 microns at an average spectral resolving power
(λ/∆λ) of 240. This section of LEISA will be used to obtain composition
maps. The second segment covers 2.1 to 2.25 microns with an average
spectral resolving power of 560. It will be used to obtain both
compositional information and surface temperature maps by measuring the
spectral shape of solid N~2~.

The MVIC and LEISA components of Ralph were originally developed in 1993
for what was then called the "Pluto Fast Flyby" mission using grants
from NASA's "Advanced Technology Insertion" (ATI) project. At the time,
they were combined with a UV mapping spectrometer (also developed under
the ATI grant) into a fully integrated remote-sensing package called
HIPPS (Highly Integrated Pluto Payload System, Stern *et al*, 1995). For
the New Horizons mission, HIPPS evolved into the Pluto Exploration
Remote Sensing Instrument (PERSI), in which the UV spectrometer, now
named Alice, was decoupled from the MVIC and LEISA components. This
allowed the UV and Vis/IR optics to be separately optimized and reduced
the chances of contamination of the sensitive UV optics. Versions of
Alice are flying on the Rosetta comet orbiter mission and have been
chosen for the Lunar Reconnaissance Orbiter (see Stern *et al*., in this
issue and references therein). Instruments based on the ATI LEISA
concept have flown on the Lewis mission (Reuter *et al*., 1996) and the
EO-1 mission (Reuter *et al*., 2001, Unger *et al*, 2003). The Lewis
spacecraft prematurely re-entered the atmosphere before any instrument
aboard could take data, but the version of LEISA aboard EO-1 provided
numerous images. Now that the UV Alice spectrometer is a separate entity
from the MVIC/LEISA sub-assembly, the latter is named Ralph in honor of
Ralph and Alice Kramden of "Honeymooner's" fame. New Horizons is the
first mission on which the Ralph instrument has flown.

Ralph is a joint effort of the Southwest Research Institute (SwRI, San
Antonio, TX and Boulder, CO which is the home institution of Alan Stern,
the Ralph Principal Investigator), Ball Aerospace and Technologies Corp.
(BATC, Boulder, CO) and NASA's Goddard Space Flight Center (GSFC,
Greenbelt, MD).

###### 

###### 2. RALPH SCIENCE OVERVIEW

The scientific rationale for the New Horizons mission to the Pluto
system (and beyond into the deeper Kuiper Belt) is given in detail in
another paper in this volume (Young *et al*.) and will not be repeated
at length here. In brief, the Kuiper Belt is an extended disk containing
numerous primordial bodies whose planetary evolution was arrested early
in Solar System formation. In essence, Kuiper Belt Objects (KBOs) are
the "fossils" of planetary evolution and the Kuiper Belt is the prime
"archeological site" in the Solar System. Pluto is among the largest
known KBOs and is a full-fledged dwarf planet. Because Charon is
approximately half of Pluto's size, the center of mass of the
Pluto-Charon system lies between the two objects, making it a true
binary system. The first exploration of the Pluto-Charon system and the
Kuiper Belt is both scientifically and publicly exciting. It will
provide invaluable insights into the origin of the outer solar system
and the ancient outer solar nebula. It will explore the origin and
evolution of planet--satellite systems and the comparative geology,
geochemistry, tidal evolution, atmospheres, and volatile transport
mechanics of icy worlds.

The Ralph instrument will play a leading role in this exploration. It
directly addresses two of the three Group 1, or primary, mission
requirements (see Stern, this volume): 1) to characterize the global
geology and morphology of Pluto and Charon and 2) to map the surface
composition of Pluto and Charon. It also contributes to the third Group
1 requirement of searching for atmospheric haze. High spatial resolution
(≤1 km/line pair) panchromatic maps generated by the MVIC component of
Ralph will be used to address the first Group 1 requirement. These maps
will be obtained for the hemisphere visible at closest approach, and
will address many of the outstanding questions about these bodies. What
is their cratering history? What types of structures are found on their
surfaces? What is the spatial variability and scale size of surface
features? What is the effect of seasonal volatile transport on the
"smoothness" of surface features? Answers to these questions will
revolutionize our understanding of the formation and evolution of the
Pluto/Charon system.

The second Group 1 goal will be addressed both by MVIC and by LEISA.
LEISA will obtain hemispheric maps in the 1.25 to 2.5 μm spectral region
with an average resolving power (λ/∆λ) of 240 and a spatial resolution
of less than 10 km. Similarly, MVIC will provide hemispheric surface
color maps and maps of surface methane (CH~4~) at even higher spatial
resolutions. Pluto's surface is known to contain the species CH~4~,
N~2~, and CO, while Charon's is primarily H~2~O but is also likely to
contain ammonium hydrates. LEISA's hemispheric maps will allow us to
address questions pertaining to composition. What is the surface
distribution of the main species? Are there areas of pure frost and
mixed areas? What is the effect of seasonal transport? Are there more
complex species in selected regions of the surface? Is there a
connection between geology and composition? Answers to these questions
will significantly advance our understanding of the chemical and
physical processes that occur on icy objects and of the processes that
occurred in the cold outer regions of our solar system during its
formation. Figure 1 shows simulated spectra for Pluto and Charon. As is
evident from this figure, there is a wealth of information to be gleaned
from this spectral region even from globally averaged spectra. LEISA's
spectral maps will permit the correlation of composition with both
geology and atmospheric transport of volatiles. They will also enable
the study of Pluto's crustal composition where craters or other windows
into the interior so permit.

.

In addition to the primary, Group 1 objectives, Ralph will address
numerous Group 2 and Group 3 measurement goals. These include: obtaining
stereo images of Pluto and Charon (MVIC), mapping the terminators
(MVIC), obtaining high resolution maps in selected regions (MVIC and
LEISA), refining the bulk parameters and orbits of the Pluto system and
searching for rings and additional satellites (MVIC). LEISA will use its
high resolution (\<λ/∆λ\> = 560) 2.1 to 2.25 μm segment to obtain
surface temperature maps of Pluto employing a technique that relates
temperature to the spectral shape of the N~2~ transition near 2.15 μm.
This technique is particularly sensitive for temperatures near 35 K, the
temperature at which N~2~ undergoes a transition from α phase to β phase
(Grundy *et al*., 1993). Thirty five K is close to the predicted surface
temperature of Pluto at the time of the flyby in 2015. For Pluto,
additional temperature information will be obtained from the band shape
of the CH~4~ features measured using the lower resolution LEISA filter.
For Charon which does not have a prominent N~2~ band, reasonably
accurate temperature maps can be deduced from the shape of the water
bands observed with the lower resolution LEISA filter. These secondary
and tertiary objectives, while not mission critical like the Group 1
goals, will add substantially to our understanding of Pluto and Charon.
MVIC panchromatic and color maps and LEISA spectral maps will also be
obtained of Nix and Hydra, two recently discovered satellites in the
Pluto system.

Table 1 summarizes the science objectives that determined the Ralph
design, the measurement strategies that address these objectives and the
derived instrument performance requirements. Except for the spectral
resolution and coverage of the high-resolution segment of LEISA, the
performance requirements were determined by the need to address the
Group 1 goals. The high-resolution LEISA segment was added specifically
to address the Group 2 goal of mapping Pluto's surface temperature, but
it will prove useful in the surface composition mapping as well. The
MVIC framing camera will be used to perform optical navigation. This
gives rise to the additional requirement that it be capable of measuring
a 10^th^ magnitude star with a signal-to-noise ratio of 7 in a 0.25
second exposure.![](media/image1.jpeg){width="3.986111111111111in"
height="5.44375in"}

###### 

###### 3. OPTO-MECHANICAL DESIGN

Figure 2 shows a model of Ralph and a picture of the assembled
instrument before addition of the final MLI. The major elements are
labeled in the model. The mass of the instrument is 10.5 Kg and the
maximum peak power load is 7.1 Watts. The low power and mass are
especially important for the New Horizons mission where both of these
resources are at a premium. As shown in Fig. 2, Ralph has two
assemblies, the telescope detector assembly (TDA) and the electronics
assembly. The TDA consists of the telescope optical elements, the
baffling, the MVIC and LEISA focal planes, the two-stage passive
radiator that cools the focal planes and the flat fielding Solar
Illumination Assembly (SIA). The aperture of the TDA was closed by a
one-time use door with a partially transmitting window (about 20%
throughput). The door protected the optics from contamination prior to
and during launch and protected the focal planes from accidental solar
exposure during the early flight stage. The door was opened when the
spacecraft was 2.3 AU from the sun and can not be closed. The TDA is
mounted to the spacecraft by thermally isolating titanium flexures. The
in-flight temperature of the TDA is about 220 K, The temperature of the
electronics box, which is mounted directly to the spacecraft, is about
290 K. The low temperature of the TDA reduces the conductive and
radiative thermal load on the focal planes. It also limits the
background signal at the long wavelength end of LEISA. The inner stage
of the externally mounted passive radiator cools the LEISA detector to
\< 130 K. The outer annulus maintains the MVIC CCDs at temperatures
below 175 K and lowers the temperature of an f/2.4 cold shield for LEISA
to below 190 K. The 75 mm aperture, 657.5 mm focal length, f/8.7
telescope provides good image quality over the 5.7°x1.0° field of view
spanned by the MVIC and LEISA arrays. The instrument parameters for
Ralph are summarized in Table 2. Figure 3 shows a model of the TDA
interior with a raytrace diagram.

**Table 1: Science Objectives and Derived Instrument Requirements**

+---------+------------+------------+-------+-----------+------------+
| **      | **M        | **Derived  |       |           |            |
| Science | easurement | Instrument |       |           |            |
| Obje    | Strategy** | Requ       |       |           |            |
| ctive** |            | irements** |       |           |            |
|         |            |            |       |           |            |
|         |            | **Spectral |       |           |            |
|         |            | coverage   |       |           |            |
|         |            | Resolution |       |           |            |
|         |            | Image      |       |           |            |
|         |            | Quality    |       |           |            |
|         |            | Signal-    |       |           |            |
|         |            | to-noise** |       |           |            |
+---------+------------+------------+-------+-----------+------------+
| Global  | Pa         | 400 -- 975 | N/A   | MTF ≥0.15 | 50 (33 AU, |
| geology | nchromatic | nm         |       | @ 20      | 0.35 I/F)  |
| and     | images:    |            |       | cycles/mi |            |
| mor     | spatial    |            |       | lliradian |            |
| phology | resolution |            |       |           |            |
| of      | of 1       |            |       |           |            |
| Pluto   | km/line    |            |       |           |            |
| /Charon | pair       |            |       |           |            |
+---------+------------+------------+-------+-----------+------------+
| Map the | Color      | 400 -- 550 | N/A   | No        | 50 (33 AU, |
| surface | images:    | nm (blue)  |       | a         | 0.35 I/F)  |
| comp    | spatial    |            |       | dditional |            |
| osition | resolution | 540 -- 700 |       | req       | 50 (33 AU, |
| of      | \<10       | nm (red)   |       | uirement. | 0.35 I/F)  |
| Pluto   | km/line    |            |       |           |            |
| /Charon | pair       | 780 -- 975 |       |           | 50 (33 AU, |
|         |            | nm (NIR)   |       |           | 0.35 I/F)  |
|         |            |            |       |           |            |
|         |            | 860 -- 910 |       |           | 15 (33 AU, |
|         |            | nm (CH~4~) |       |           | 0.35 I/F)  |
+---------+------------+------------+-------+-----------+------------+
| Map the | SWIR       | 1.25 --    | λ/∆λ  | No        | 32 (1.25   |
| surface | spectral   | 2.5 μm     | ≥ 250 | a         | μm; Pluto) |
| comp    | images:    |            |       | dditional |            |
| osition | spatial    |            |       | req       | 27 (2.00   |
| of      | resolution |            |       | uirement. | μm; Pluto) |
| Pluto   | \<10 km    |            |       |           |            |
| /Charon |            |            |       |           | 18 (2.15   |
|         |            |            |       |           | μm; Pluto) |
+---------+------------+------------+-------+-----------+------------+
| Map     | High       | 2.10 --    | λ/∆λ  | No        | No         |
| Pluto's | spectral   | 2.25 μm    | ≥ 550 | a         | additional |
| surface | resolution |            |       | dditional | re         |
| temp    | images in  |            |       | req       | quirement. |
| erature | the 2.15   |            |       | uirement. |            |
|         | μm N~2~    |            |       |           |            |
|         | band       |            |       |           |            |
+---------+------------+------------+-------+-----------+------------+

**3.1 The MVIC Focal
Plane**![](media/image2.wmf){width="6.686805555555556in"
height="2.907638888888889in"}

The MVIC focal plane assembly consists of a customized CCD array
provided by E2V Corp. of Chelmsford, England. It is mounted to a heat
sink plate and placed directly behind a "butcher block" filter assembly.
The array has six identical 5024x32 pixel (5000x32 pixel photoactive
area) TDI CCDs and one 5024x264 pixel (5000x128 pixel photoactive area)
frame transfer CCD on a single substrate. Figure 4 shows a schematic of
the array indicating the positions of the CCDs and a picture of the
actual flight array. The long dimension of 5000 elements was chosen
because to obtain a 1 km/line pair image across Pluto's 2300 km diameter
in a single scan requires at least 4600 pixels. The remaining 400 pixels
allow for pointing inaccuracies and drift during the scan. All MVIC
pixels are 13x13μm^2^.

The frame transfer array consists of two regions; the 5024x128 pixel
image gathering area, and a 5024x136 pixel image storage area. The extra
eight rows in the image storage area contain injection charge that
reduces charge traps. For both the TDI and framing arrays, the extra 24
dark pixels (12 on each side of the 5000 pixel active region) are used
as reference pixels and for injected charge. A front-side illuminated
CCD is used to optimize the imaging qualities of the array. The filter,
which was provided by Barr Associates, is mounted about 700 microns
above the surface of the array. It has five segments, four with the
passbands described in Table 2 placed directly over the four CCDs
forming the color segment of MVIC. The remaining two TDI CCDs and the
frame transfer array are overlain by a clear filter so that the focus
position is the same for all seven arrays. In TDI mode, the spacecraft
is rotated to scan the image of each segment of the surface across the
focal plane in a pushbroom fashion. The entire surface may be imaged in
this way. The nominal rotation rates are about 1600 μrad/sec for the pan
band and about 1000 μrad/sec for the color bands. These correspond to
integration times of about 0.4 and 0.6 seconds respectively. The
clocking of each 5024 element pixel row is synchronized with the
spacecraft motion using attitude control knowledge obtained from the
spacecraft so that the effective integration time is 32 times the row
transfer period. In this way, the signal-to-noise ratio of the
observations is increased while the time required to obtain a full image
is reduced. TDI mode takes advantage of the ability of the spacecraft to
scan smoothly in attitude and does not need the multiple pointing
operations that a mosaic of framing images would require. In flight, the
CCD clocking rate errors in the TDI (along scan) direction have been
shown to cause less than ¼ of a pixel of excess image "smear" for
integration times of 0.7 seconds or less.

![](media/image3.jpeg){width="6.584027777777778in"
height="2.4305555555555554in"}

**3.2 The LEISA Focal Plane**

The LEISA IR spectral imager also works in pushbroom mode, except in
this case, the image motion is used to scan a surface element over all
spectral channels. The wedged filter effectively makes each column of
the array responsive to only a narrow band of wavelengths, so that,
conceptually, the filter may be considered as consisting of 256 adjacent
narrow band filters. As with MVIC, the image is scanned over the LEISA
focal plane by rotating the spacecraft. The nominal rotation rate is
about 120 μrad/sec for a frame rate of 2 Hz. Here again, the frame rate
is synchronized to the spacecraft-measured rotation rate, so that the
image moves one column per
frame.![](media/image4.pct){width="4.084027777777778in"
height="2.186111111111111in"}![](media/image5.pct){width="3.917361111111111in"
height="2.725in"}

The LEISA detector is a 1.2 to 2.5 μm HgCdTe PICNIC array, supplied by
Rockwell Scientific Corporation of Camarillo CA. The array is a 256x256
pixel array and each pixel is 40x40μm^2^ in area. However, several
modifications were made to the standard PICNIC array. The HgCdTe was
grown on a CdTe substrate using Molecular Beam Epitaxy (MBE) to provide
good lattice matching and low dark currents. The detector was bump
bonded to a standard PICNIC multiplexer and the resulting hybrid was
mounted to molybdenum pad. This process reduces mechanical stress
induced during cooling to operational temperature. It is estimated that
the assembly can safely undergo at least 1000 thermal cycles. The
electrical interface to the array is provided by two ribbon cables and a
multilayer fan-out board that were fabricated into a single element. The
LEISA array is back illuminated, but the substrate has been thinned from
800 μm to 200 μm so that the active area of the array is significantly
closer to the surface than is usual. This puts both the filter and the
array within the depth of focus. The filter, supplied by JDSU Uniphase/
Optical Coating Laboratories Inc. of Santa Rosa CA, was made in two
segments. The first, covering from 1.25 to 2.5 μm at a constant
resolving power (constant ∆λ/λ) of about 240, provides information
primarily for surface composition mapping. The second, covering from 2.1
to 2.25 μm at a constant resolving power of about 560, uses temperature
dependent changes in the spectral structure of solid N~2~ near the α to
β phase transition at 35 K to provide surface temperature maps. In both
segments, a constant resolving power is achieved by making the
transmitted wavelength depend logarithmically on position. The two
segments were bonded together to form a single filter element. This
filter was, in turn, bonded into a holder and mounted such that the
filter surface is about 100 μm above the surface of the array. The
refractive index of the array is approximately 2.7 so that the total
optical path between the filter and photo-active area of the array is
less than 200 μm. In this distance, the f/8.7 beam spreads about 0.5
pixel, so when the focus position is optimized between the array and
filter surface, the convolved image smear is about 0.04 pixel. A picture
of the array and the complete focal plane assembly is shown in Figure 5.

**3.3 The Solar Illumination Assembly (SIA)**

The SIA is a second input port whose FOV is along the spacecraft antenna
pointing direction at 90 degrees with respect to the main aperture. It
is designed to provide diffuse solar illumination to both the MVIC and
LEISA focal planes. In practice, it illuminates all of the LEISA array
and about 3000 pixels of the each MVIC array with a reproducible pattern
that can be used for determining the stability of the pixel-to-pixel
response (flat-fielding) during the mission. The SIA consists of a small
fused silica lens (4 mm aperture, 10 mm focal length) that images the
sun onto the input end of a 125 μm core fiber. The output end of the
fiber illuminates a pair of lenses, which are directly under the Lyot
stop (the exit pupil) and about 10 cm from both focal planes. To obtain
an SIA measurement, the spacecraft is oriented so that the SIA lens
images the sun onto the fiber. At Pluto, the diameter of the image of
the Sun on the fiber would be about 50 μm. This is significantly larger
than the diffraction limited image size because of chromatic aberration
in the single element lens. Nevertheless, the solar image underfills the
fiber, so the intensity level is relatively insensitive to pointing
errors. The fiber is about 10 cm long and is contained in a stainless
steel tube. It is more than 50% transmitting over the full spectral band
from 0.4 to 2.5 μm. There is a second fiber in the SIA with an
attenuation factor of about 40 that can be used for flat fielding nearer
the Sun (e.g. at
Jupiter).![](media/image6.jpeg){width="6.584722222222222in"
height="3.686111111111111in"}

A second possible use of the SIA is as a solar limb viewing port. In
this mode, an atmospheric spectrum can be measured as a function of
tangent height as a planet's atmosphere occludes the Sun. Vertical
spectral profiles would be obtained using this capability. To increase
sensitivity in sparse atmospheres, such as Pluto's, the spectra from all
rows may be summed into a single spectrum. The SIA is co-aligned with
the Alice solar occultation (SOC) port (Stern *et al*., this volume).

**4.0 ELECTRONICS**

The Ralph control electronics consist of three boards; detector
electronics (DE), command and data handling (C&DH) and a low voltage
power supply (LVPS). These are contained within an electronics box (EB)
mounted directly to the spacecraft, below the TDA (see Fig. 2), and
operate essentially at the spacecraft surface temperature, which is near
ambient. The DE board provides biases and clocks to both focal planes,
amplifies the signals from the arrays and performs the A/D conversion of
the imaging data. The science data are converted with 12 bits per pixel.
The C&DH board interprets the commands, does the A/D conversion of the
low speed engineering data and provides both the high speed imaging data
interface and the low speed housekeeping data interface. The LVPS
converts the 30V spacecraft power to the various voltages required by
Ralph.

In a long duration mission such as New Horizons, reliability of the
electronics is of paramount importance, particularly for a core
instrument that addresses all three Group 1 objectives. To ensure that
Ralph is robust, almost all of the electronics are redundant. As
illustrated in Figure 6, Ralph can operate on two separate sides (side A
or B) which have very few components in common. The only common elements
are: 1) the relays that choose whether side A or side B is to be
powered, 2) The arrays themselves and 3) the interface to the
spacecraft. However, the spacecraft interface has two identical circuits
and is inherently redundant. For MVIC, the potential single point
failure mode of the array is mitigated by dividing the six TDI arrays
into two groupings, each containing two color CCDs and one panchromatic
CCD. The first grouping is composed of a pan band and the red and CH~4~
channels. The second grouping is composed of the other pan band and the
blue and NIR channels. If either group should fail, the other would
still be able to meet the science requirement of observations in 2 color
bands and 1 panchromatic band. LEISA has 4 outputs corresponding to the
four 128x128 quadrants of the array. If any one quadrant should fail,
all science can still be completed. The same is true for the four out of
six possible two-quadrant failures that still have active pixels at all
wavelengths. ![](media/image7.pct){width="4.986805555555556in"
height="3.6083333333333334in"}

MVIC always produces image data in correlated double sample (CDS) mode
in which the reset level is subtracted from the integrated level. LEISA
can send either CDS data, which is its standard operating mode, or "raw"
data that contains both the reset levels and the integrated levels. The
"raw" mode produces twice the data volume of the CDS mode and is used to
set the LEISA A/D converter offset level for each quadrant of the array.
The same offset is used in both CDS and "raw" modes. The selectable
offset compensates for voltage drifts in the analog signal train over
the life of the mission, maintaining dynamic range without sacrificing
signal resolution (increasing quantization noise). For both focal planes
the measured spacecraft rotation rate is fed back to the instrument to
optimize the TDI or frame rate. That is, after a scan has been initiated
the spacecraft determines the actual rotation rate and sends that
information to Ralph, which uses it to calculate a TDI or frame rate
such that the image moves a single row during a clock period. This
reduces smear in the along-track direction.

For both MVIC and LEISA, the dominant noise source at low light levels
is the system electronics noise, including array read noise. For MVIC
this is about 30 e- (\~ 200 μV) and for LEISA it is about 50 e- (\~ 100
μV). The overall average gain for MVIC is about 58.6 e-/DN (Digital
Number, or least significant bit), while for LEISA it is approximately
11 e-/DN.

**5.0 PRE-LAUNCH INSTRUMENT CHARACTERIZATION**

An extensive pre-launch program of performance verification measurements
was carried out for Ralph at both the component level and the full
instrument level. The component level characterization included
measurements of the wavelength dependent quantum efficiency for the MVIC
and LEISA array/filter assemblies and measurements of the wavelength
dependence of the other optical elements (i.e. reflectance of the
mirrors, transmission of the filters and throughput of the
beamsplitter). Full instrument level testing was carried out under
spaceflight-like conditions in a thermal vacuum chamber at BATC. The
primary performance characteristics verified in these tests were
relative system throughput (relative radiometric sensitivity) and image
quality. The directional characteristics of the SIA were also measured.

**5.1 Component Level Measurements**

*LEISA Spectral Lineshape*: The instrument line shape was determined for
the LEISA filter/array focal plane assembly over the entire 1.25 to 2.5
μm band by using a combination of multi-order grating and narrow band
filter measurements. In this way a pixel-by-pixel table of the central
wavelength, resolving power and out-of-band transmission was generated.
Figure 7a shows an example of the readout along a single LEISA row when
the focal plane assembly was illuminated using the output of a grating
monochromator. The first five peaks correspond to orders 6 through 10 of
the grating. The intensity decrease is primarily caused by the spectral
shape of the source and by the decreasing efficiency of the grating at
higher order. The line at 2.2 μm occurs in both segments of the filter.
Figure 7b shows the intensity measured at a single pixel as the grating
is scanned in small wavelength increments (0.33 nm). This instrument
lineshape is representative of all pixels and is approximately gaussian.
At this wavelength (2165 nm), the full width at half maximum (FWHM) is
8.3 nm, giving a resolving power of 260. Figure 8 shows the average
resolving power for both filter segments of LEISA generated using the
measurement technique described above. As may be seen from this figure,
the average resolving power for the lower resolution segment is 240,
with variations of 10 to 15 percent lower and higher. This is slightly
below the requirement of 250. The resolution determines the reliability
with which pure materials may be differentiated from mixtures and the
accuracy of temperatures determined from line shapes. The slight
decrease in accuracy in the lower resolution regions will not have
significant scientific impact. Temperatures will be determined most
accurately using the high-resolution segment. As required, the resolving
power of the higher-resolution segment is greater than 550 in the region
of the 2.15-μm N~2~ band.
![](media/image8.png){width="6.501388888888889in"
height="2.5006944444444446in"}![](media/image9.pct){width="4.2875in"
height="2.9243055555555557in"}![](media/image10.pct){width="4.588888888888889in"
height="3.1395833333333334in"}

*MVIC spectral response:* The spectral resolution of the MVIC channels
is much lower than for LEISA and the CCD response varies relatively
slowly, so a coarser measurement of the wavelength dependence of the
filter/CCD assembly is acceptable. Figure 9 shows the measured
sensitivity of the combined array/filter focal plane assembly. These
measurements were obtained at 50 nm intervals using a broad spectral
source filtered with 50 nm wide spectral filters as an input. In order
to account for observational sources with greater spectral variation,
the spectral responses of the filters were determined at higher spectral
resolution and finer point spacing. Figure 10 shows the spectral
response curves for the MVIC color filters. In addition to allowing for
the retrieval of more accurate spectral models, these data will be used
to calculate the sensitivity of MVIC to the source spectral distribution
(e.g. a solar reflectance spectrum vs. the blackbody spectrum of a
volcano on Io). ![](media/image11.pct){width="4.485416666666667in"
height="3.438888888888889in"}

**5.2 Full Instrument Level Measurements**

*Absolute Radiometry*: A spectrally calibrated integrating sphere
filling about a 1° field of view was used as the radiometric source.
Radiometric response over the full MVIC image plane was measured by
rotating the sphere illumination using a cryomirror assembly in the
chamber. This technique was used to determine accurate relative
radiometry (flatfields). The MVIC absolute radiometry was determined
with an accuracy of approximately ±30%. The accuracy of the LEISA
absolute radiometry was lower because water contamination in the
integrating sphere caused significant absorption at some wavelengths.
Radiometric calibration is being performed in-flight and the combined
results of the pre-flight and in-flight calibration are shown in the
next section.

*Image Quality*: The image quality, defined in terms of system MTF
(Modulation Tranfer Function), was determined using a collimated point
source to simulate a distant object. Collimation was verified
interferometrically, as were corrections for pressure and thermally
induced optical power in the chamber window. By defocussing the point
source in a controlled fashion, this system could also be used to
determine the best focus position for the focal planes. At the best
focus position, a point source produced a spot in the focal plane whose
FWHM was 1.2 ±0.1 pixel. After the tests were completed, it was found
that there was some optical power in the cryomirror that was not
accounted for in determining the focus. However it was determined that
for the Ralph system with its 650-mm focal length, the focus error
caused by the cryomirror curvature was negligible. The pre-flight image
quality measurements were used to determine an expected budget for the
full system MTF that is shown in the next section.

*SIA Pointing*: The pointing direction and spatial distribution of focal
plane illumination for the SIA were also determined in the instrument
level tests. When illuminated by a source simulating the angular size of
the sun at Pluto, the SIA produced a stable pattern in both the MVIC and
LEISA focal planes that was insensitive to the exact source position
over a range of 0.5° in each dimension.

**6.0 COMBINED PRE-LAUNCH AND IN-FLIGHT INSTRUMENT CALIBRATION RESULTS**

Calibration of Ralph is being carried out in flight. To date, standard
stars and Jupiter observations are being used to determine image
quality, to measure over-all system radiometric sensitivity and, for
LEISA, to verify the spectral calibration. Additionally, dense
star-fields are being used to determine overall optical distortion. A
Jupiter gravity assist will occur in 2007 with closest approach on
February 28. It will provide additional opportunities for measuring the
flat field response, and will permit radiometric and spectral
calibration. Afterwards, every year during the flight, there will be a
50-day checkout period during which calibration will be checked.
Extensive calibration will also be carried out during the 6-month period
prior to and after the planned Pluto encounter on 14 July, 2015. Because
the initial in-flight calibration analyses are not complete, the
following results should be considered to be preliminary estimates.

So far in flight, the MVIC and LEISA system random noises have remained
at their pre-launch values: ≤ 1 count (≤60 e-) for all the MVIC CCDs and
4.5 counts (50 e-) for LEISA. In addition to the random noise, the MVIC
CCDs have some periodic noise (as much as 2 counts) that may be removed
by post-processing. This noise was present before launch. The MVIC dark
current is completely negligible; it is not measurable for the
integration times allowed by the Ralph electronics. The LEISA dark
current is \~40 counts/second (\~440 e-/sec), and does not contribute
significantly to the noise even for the longest allowed integration time
(4 sec.). So far, the Ralph decontamination heaters have been left on
except for 24-hour periods around data collection events in order to
minimize the condensation of contaminants produced by spacecraft
outgassing and thruster operation. This means that, as of this writing,
the LEISA focal plane has not reached its quiescent operating
temperature when acquiring data. A cool-down period of greater than 24
hours is common in low temperature, passively cooled systems. When the
heaters are left off for longer periods, it is expected that the focal
plane temperature will drop a few more degrees. The dark current will
decrease by about a factor of two for every five degrees drop in the
focal plane temperature.

**6.1 Image Quality and MTF**

The point spread function of MVIC's panchromatic TDI channels determined
in-flight is well represented by a 2-D gaussian function. Fittings of
the point source intensity distribution to this PSF for about 30
relatively bright stars has yielded FWHMs of 1.48±0.13 pixels in the
in-track direction and 1.40±0.1 pixels in the cross-track direction.
These observations are all for integration times of 0.5 seconds or less,
for which the contribution of the uncorrected spacecraft motion is less
than half a pixel. Taking the Fourier transform of the fitted PSF yields
the expression:

> MTF(d) = e^-(dπ0.01977FWHM/(2(ln2)1/2))2^ (1)

for the value of the MTF at spatial frequency, d (cycles/milliradian).
Using this expression, MTF(20) = 0.30±0.07 (in-track) and MTF(20) =
0.34±0.06 (cross-track). Both the in-track and cross-track MTF(20)
values surpass the requirement that they must be greater than 0.15 (see
Table 1). These results are summarized in Figure 11, which shows the
pre-launch MTF curves, determined solely by the optical characteristics,
and the pre-flight model of the full system. In this figure the top area
in each panel ("measured spots") represents the measured contribution of
the instrumental characteristics to the MTF. Off array integration is a
term that accounts for the effect of insufficient masking of the bulk
silicon from the light. The other factors are based on predicted
spacecraft behavior at the 3σ level. The temporal aperture and the TDI
error have to do with uncompensated spacecraft motion. The point labeled
"requirement" is the 15% minimum overall MTF at 20 cycles/milliraian
(0.4 cycles/pixel) that satisfies the science requirements. The measured
in-flight image characteristics clearly exceed requirements and agree
remarkably well with the predicted behavior based on the pre-flight
instrument level measurements.

The MVIC color channels and the LEISA spectral channels have no
additional requirements on image quality beyond the requirement that
they be in focus to within 0.5 pixel. This is because the required
spatial resolutions for the observations using the MVIC color and LEISA
channels are significantly lower than for the MVIC panchromatic channel.
The MVIC color channels are at the same focal distance as the
panchromatic channel by virtue of being on the same substrate. The LEISA
focal plane was focused separately. Table 3 summarizes the preliminary
results of the analysis of the PSF for all the Ralph channels. The
effect of diffraction is apparent in the FWHM measurements for the MVIC
color channels. The LEISA results are based on a single stellar
observation that only covered from 1.25 to 1.8 μm. Diffraction effects
are not apparent in these LEISA measurements because the LEISA pixels
are three times larger than the MVIC pixels.
![](media/image12.wmf){width="4.188194444444444in"
height="4.045833333333333in"}

**6.2 Optical Distortion**

The MVIC focal plane covers 5.7° in the cross track direction, which
means that it is expected that there will be optical distortion of on
the order of a few pixels at the ends of the FOV. In addition, the
three-mirror anastigmat design is known to be anamorphic. That is, the
spatial scale in the cross track direction is slightly different from
that in the along track direction. These effects both make the apparent
position of objects different from their true position. In order to
account for this effect, both to maintain spatial fidelity in the
science data and to allow accurate observations for optical navigation,
a distortion correction must be found that maps the apparent position to
the true position. The distortion effect is illustrated in Figure 12 for
a set of observations of a dense star field using MVIC's panchromatic
framing camera. This plot shows the difference between the true position
of a star and the position obtained assuming that each pixel is 19.77 μm
square. The stellar positions are typically known to better than 5 μrad.
As may be seen from this figure, there is about a three-pixel distortion
at the ends of the focal plane. Note that the column distortion is
sinusoidal about the center of the FOV, while the row distortion is the
same sign on opposite sides of the array. The anamorphism is the
principle driver for the row distortion. These results are preliminary
and are being refined further, but they indicate the effects are easily
modeled. ![](media/image13.jpeg){width="4.883333333333334in"
height="3.0840277777777776in"}

**6.3 Radiometric Calibration**

The absolute radiometric calibration of the MVIC and LEISA components of
Ralph is primarily being carried out in-flight, using point sources
(standard stars) and Jupiter. The flatfields determined during the
pre-launch testing are used to interpolate the stellar and Jupiter
results over the entire focal planes. This work is still progressing.
The results below are preliminary, and are expected to be accurate to
about 10%. Figure 13 shows an example of the stellar source calibration
measurements for the MVIC framing array. This figure shows a plot of the
integrated signal at the focal plane *vs* the visual magnitude of a
star, for a number of A-, B- and K-type stars. A fit was done using data
for B9-type stars that is linear to a very high degree of accuracy (it
accounts for 99.5% of the standard deviation of the data). The other A-
and B- type stars are well described by this fit as well. The colder,
K-type star is a bit of an outlier, but no correction has been made for
color temperatures of the stars. These data indicate that, for the
framing array, a 14^th^ magnitude B9 star will produce an integrated
signal of one count per second. Given the MVIC frame noise
characteristics (\~ 0.6 counts of noise at low illumination levels), a
tenth magnitude star will produce a measurement with a signal-to-noise
ratio of 14 in 0.25 seconds if it is focused onto a single pixel. If the
same signal is spread out over 4 adjacent pixels it produces an average
SNR of 8, which still meets the OpNav requirement.
![](media/image14.wmf){width="4.186111111111111in"
height="3.2729166666666667in"}

Table 4 shows the sensitivities and the predicted signal-to-noise ratios
for the MVIC channels and for the LEISA wavelengths at which the LEISA
SNR performance requirements were defined. The predictions are made for
the conditions specified in Table 1 which are representative of the flux
levels expected at Pluto. The table also lists the noise performance
requirements set forth in the Announcement of Opportunity (AO) for the
mission. As can be seen from this table, all MVIC channels easily meet
their sensitivity requirements. Similarly, LEISA meets the AO
radiometric performance specifications, but with significantly smaller
margin, particularly at shorter wavelengths. The decreased performance
in this spectral region is caused by a known drop in quantum efficiency
of the array at wavelengths shorter than 1.6 μm, and by lower
transmittance of the filter at shorter wavelengths. However, solar flux
increases at the shorter wavelengths so the decreased efficiency is
compensated for by the larger flux. Figure 14 shows the LEISA
radiometric sensitivity as a function of wavelength. Figure 15 shows the
predicted signal-to-noise ratio of LEISA observations (average of two
scans, 0.5 second /pixel integration time) of Pluto and Charon for the
nominal albedos plotted in Figure 1. At the Pluto flux levels the noise
is dominated by the system noise (read noise), so that the
signal-to-noise ratio grows nearly linearly with increased integration
time.

**6.4 Anomalous Solar Light Leak**

In-flight testing of Ralph has shown the presence of an anomalous
background signal in the LEISA imager that appears to be caused by the
transmission of a very small fraction of the ambient solar flux into the
area behind the focal plane. These photons pass between the filter and
the array and give rise to a "solar light leak" signal that, in the
worst case, is less than 1 part in 10^7^ of the ambient solar flux. The
background may be eliminated by using structures on the spacecraft to
shield Ralph from the sun. This behavior, and the R~sun~^2^ dependence
of the magnitude of the background signal are both evidence of the sun
as the source of this anomaly. Ralph can not always be shielded. When
Ralph is not shielded, the magnitude of the effect is a slowly varying
function of the position of the sun relative to Ralph and it may be
removed to a high degree of accuracy. This means that the primary result
of the light leak is to increase the system noise because of photon
counting statistics. At Pluto's heliocentric distance, and for the
integration times that are possible with LEISA, the excess background
introduced by the effect is at least a factor of two less than the
read-noise equivalent input flux. Therefore, after the background is
removed, there will be little or no measurable effect of this excess
flux on the LEISA observational results. As of yet, the root
manufacturing cause of the light leak has not been determined. It is
possible that light is more of less uniformly penetrating the
multi-layer insulation (MLI) thermal shield that encloses the
instrument, and propagating along LEISA's interface cables to the focal
plane. However, definitive answers, if they can be determined, await
further laboratory and in-flight measurements. Nevertheless, for
practical purposes, the phenomenology is well understood. MVIC shows no
evidence of this effect.
![](media/image17.png){width="6.585416666666666in"
height="2.532638888888889in"}

7.0 IN-FLIGHT INSTRUMENT OPERATION

Ralph data collection operations fall into one of four categories: 1)
panchromatic MVIC TDI, 2) color MVIC TDI, 3) LEISA and 4) panchromatic
MVIC framing. Ralph may operate in only one of these categories at any
time meaning, for example, that LEISA data may not be taken
simultaneously with MVIC data. The panchromatic MVIC TDI category covers
operation in either of the panchromatic TDI CCD arrays, but only one pan
array can be operated at any time. All four color TDI CCDs operate
simultaneously. As a result, a color MVIC scan is slightly longer than
the equivalent Pan TDI scan, because the target must be scanned over all
4 color CCDs. The category is chosen by command and implemented by a set
of relays.

For the MVIC TDI and LEISA data categories operation may be either in
calculated rate mode or forced rate mode. In calculated rate mode, the
array read-out rate is set using the measured rotation rate about the
scan axis (the Z-axis) as determined by the spacecraft's star trackers
and gyroscopes. This scan rate is provided to Ralph at the beginning of
a scan by the spacecraft's guidance and control (G&C) system. The array
readout rate is set such that the scan moves a spot on the image a
single row between reads. In calculated rate mode, the MVIC TDI arrays
may scan only in one direction, but LEISA may scan in either direction.
In forced rate mode, the array readout rate is set by a command and is
not coupled to the G&C scan rate. For all categories, data collection is
initiated with a start command and continues until a stop command is
received. MVIC framing data is always obtained in forced rate mode.

There are two types of scans. The normal scan type is used when the
target is sufficiently distant that the effective scan rate of the
boresight caused by the relative motion of the target and the spacecraft
remains constant during the scan. For a normal scan, once the rotation
rate has stabilized, the along track thrusters are disabled and the
spacecraft is allowed to rotate at a constant rate. In calculated rate
mode the rotation rate, measured to a 3σ accuracy of ±7μrad/sec is
passed to Ralph and the calculated frame rate is matched to the
boresight motion. A normal type scan using calculated rate mode is the
most common form of either MVIC TDI or LEISA operation. Typically, in a
normal LEISA scan, the cross track thrusters are enabled so that the
target does not drift off the focal plane in the direction perpendicular
to the scan during the data collection event. For a given target, the
MVIC scans are usually almost an order of magnitude faster than the
LEISA scans, so the cross track thrusters are typically disabled in MVIC
TDI scans. Correct operation of the normal scan type has been verified
in flight for both MVIC and LEISA using stellar sources.

When the target is sufficiently close that the effective rotation rate
induced by the relative motion of the target and the spacecraft changes
during the scan, the scan becomes more complex. In this case, the
rotation rate of the spacecraft is changed during the scan by thruster
firings. This type of scan, called a pseudo CB3 scan, is implemented by
making the boresight track an artificial object whose ephemeris is
defined in such a fashion to keep the combined boresight rotation rate
constant. The frame rate is set by the commanded scan rate, and not by
the changing spacecraft rotation rate as measured by the G&C system. The
scan is controlled to within ±34μrad/sec. Pseudo CB3 scans are only used
when the target is close to the spacecraft, such as the near closest
approach LEISA and MVIC Pluto scans. For this type of operation, both
the in track and cross track thrusters are enabled during LEISA scans,
while only the in track thrusters are enabled during MVIC scans. Correct
operation of the pseudo CB3 scan type has been verified in flight for
both MVIC and LEISA using an asteroid near encounter (Olkin *et al*,
2007).

**8.0 CONCLUSION**

This paper describes the design, operation and performance of Ralph, a
highly capable remote sensing imager/IR spectral imager flying on the
New Horizons mission to the Pluto/Charon system and the Kuiper belt
beyond. Ralph consists of a telescope feeding two focal planes, the
visible/NIR MVIC imager and the LEISA IR spectral imager. MVIC will
provide very sensitive, high fidelity, full hemispheric panchromatic
maps of Pluto and Charon at a spatial resolution of 1 km/linepair and
VIS/NIR color maps at a spatial resolution of better than 4km/linepair.
LEISA will provide full hemispheric, SWIR, spectral maps with spatial
resolutions of 7 km/pixel or better. These will be used to accurately
characterize the surface composition. At closest approach, MVIC will
obtain images with spatial resolutions on the order of a few hundred
meters in selected areas, while LEISA will measure spectra at the 1-2 km
spatial scale. Ralph has been extensively tested at the component and
full instrument level and its in-flight operation has verified that it
meets all its performance requirements with margin. Ralph will provide a
wealth of information on the geology, composition, morphology and
thermal characteristics of the Pluto/Charon system. The data it produces
during its flyby will revolutionize our understanding of Pluto and its
neighbors and will shed new light on the evolution of our solar system
and the nature of the objects in the Pluto system.

Eight years prior to arriving at Pluto, Ralph will observe Jupiter for a
period of about 4 months during its close approach for a gravity assist,
starting in January of 2007. The closest approach of \~33 R~J~ will
occur on 28 February, 2007. During this period, numerous Ralph
observations of Jupiter and its moons are planned to provide encounter
practice and to obtain calibration measurements on the last fully
resolved object prior to the Pluto encounter 8 years hence. The LEISA
observation obtained at this time will be some of the highest
spectral/spatial data ever obtained of Jupiter in the SWIR spectral
range. Thus New Horizons will provide exciting new science, even before
its rendezvous with Pluto.

ACknowledgements

The authors would like to thank the entire Ralph support teams at BATC
and SwRI and the LEISA support team at GSFC for their untiring efforts
in making Ralph a reality. The support of JDSU/Uniphase, E2V, Barr
Associates and Rockwell Scientific Corporation is also gratefully
acknowledged.

**9.0 REFERENCES**

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Olkin, C. B., D. C. Reuter, A. Lunsford, R. P. Binzel, S. A. Stern, "The
New Horizons Distant Flyby of Asteroid 2002 JF56.", in preparation

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Rosenberg, K. P., K. D. Hendrix, D. E. Jennings, D. C. Reuter, M. D.
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Stern, S. A., D. C. Slater, W. Gibson, H. J. Reitsema, Alan Delamere, D.
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Ungar, S. G., J. S. Pearlman, J. A. Mendenhall, D. Reuter, "Overview of
the Earth Observing One (EO-1) mission", *IEEE Transactions on
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