The LOng-Range Reconnaissance Imager (LORRI) is the high resolution
imaging instrument for the *New Horizons* mission to Pluto, its giant
satellite Charon, its small moons Nix and Hydra, and the Kuiper Belt,
which is the vast region of icy bodies extending roughly from Neptune's
orbit out to 50 astronomical units (AU). *New Horizons* launched on
January 19, 2006 as the inaugural mission in NASA's New Frontiers
program. LORRI is a narrow angle (field of view=0.29°), high resolution
(4.95 μrad pixels), Ritchey-Chrétien telescope with a 20.8 cm diameter
primary mirror, a focal length of 263 cm, and a three lens
field-flattening assembly. A 1024 × 1024 pixel (optically active
region), thinned, backside-illuminated charge-coupled device (CCD)
detector is used in the focal plane unit and is operated in frame
transfer mode. LORRI provides panchromatic imaging over a bandpass that
extends approximately from 350 nm to 850 nm. LORRI operates in an
extreme thermal environment, situated inside the warm spacecraft with a
large, open aperture viewing cold space. LORRI has a silicon carbide
optical system, designed to maintain focus over the operating
temperature range without a focus adjustment mechanism. Moreover, the
spacecraft is thruster-stabilized without reaction wheels, placing
stringent limits on the available exposure time and the optical
throughput needed to satisfy the measurement requirements.

# 1. Introduction

The *New Horizons* mission launched on January 19, 2006 on its way to
perform the first reconnaissance of the Pluto-Charon system and the
Kuiper Belt. First, however, New Horizons made a Jupiter swingby with
closest approach on Feb 28, 2007. Extensive observations of the Jovian
atmosphere, rings, and satellites were acquired. Pluto closest approach
will occur on July 14, 2015. The prioritized measurement objectives of
the New Horizons mission, and the contributions from LOng-Range
Reconnaissance Imager (LORRI) observations, are summarized in Table 1.

Pluto is an icy dwarf planet with a significant atmosphere consisting
mainly of nitrogen, CO and methane. High resolution images from LORRI
will yield important information on Pluto's geology and surface
morphology, collisional history, and atmosphere-surface interactions.
Will Pluto have a young surface, with evidence of endogenic activity
like plumes or cryovolcanism? Will there be evidence for tectonism in
the form of faulting or ridge and groove formations? Will there be
layered terrains? Will there be evidence for atmospheric hazes or for
surface winds forming dunes (dunes on Pluto may be mostly grains of
nitrogen ice)? Pluto is known to have an active surface, with changes in
surface colors and reflectances observed by Earth-based telescopic
monitoring. LORRI's high resolution images will reveal features as small
as 100 m on Pluto (260 m on Charon).

Charon is Pluto's giant satellite: at about half the size of Pluto, it
is larger than any other planetary satellite relative to its primary.
Unlike Pluto, Charon has no detectable atmosphere, and it probably has
an old surface that may preserve a cratering record from collisional
evolution within the Kuiper Belt. LORRI data will play a critical role
in determining the crater size distribution and morphologies on Charon.
Equally important, LORRI images will provide precise measurements of the
shapes and sizes of both bodies. In addition, LORRI will obtain high
resolution images of the newly discovered moons Nix and Hydra (Weaver et
al. 2005), comparable in terms of resolution elements across the
illuminated disk to the Galileo images of Gaspra.

After the Pluto-Charon encounter, *New Horizons* will make the first
visit to one or more Kuiper Belt objects. Owing to the likely small size
of these targets, LORRI's high resolution is especially important to
capture as much surface detail as possible. Will these Kuiper Belt
objects look like the asteroid Eros, or will there be bizarre surface
features like the flat-floored, steep-walled depressions (craters?)
found on the nucleus of comet 81P/Wild 2?

The *New Horizons* mission has a long focal length, narrow angle imager
for several reasons. Pluto is a dwarf planet, and *New Horizons* flies
by quickly, so the encounter science observations occur within one Earth
day -- but with LORRI, *New Horizons* will be able to image the Pluto
system at higher resolution than any Earth-based telescope can (even the
Hubble Space Telescope, or its successor in 2015) for 90 days prior to
encounter. These images will provide an extended time base of
observations, for studies of the shapes, rotations, and mutual orbits of
both Pluto and Charon, and for characterizing surface changes.

Moreover, Pluto and Charon both rotate at the same rate as for their
6.38 day mutual orbit, always keeping the same faces towards each other.
Hence, during the near encounter, which lasts less than an Earth day,
only one hemisphere of each body, that which faces *New Horizons*, can
be studied at the highest resolution. The opposite faces of both Pluto
and Charon are last seen some 3 days earlier, when the spacecraft is
still \~4 million km away. Despite this distance, LORRI will obtain
images with 40 km resolution. These will be the best images of the
portions of Pluto and Charon which are not visible during the near
encounter period.

Finally, we have not yet discovered the Kuiper Belt object(s) to which
*New Horizons* will be targeted after the Pluto-Charon encounter, and
extensive Earth-based observing campaigns are searching for potential
targets. However, even after discovery, the heliocentric orbits of the
targets cannot be measured with sufficient accuracy from Earth to enable
the *New Horizons* spacecraft to fly to them, unless the targets are
also observed directly from the spacecraft. The direction in which the
target is seen from the spacecraft is then used to steer the spacecraft
to the target by optical navigation. LORRI is expected to play a key
role, by making the first and highest resolution detections of the
Kuiper Belt target object from *New Horizons*, more than 40 days before
closest approach.

The *New Horizons* instrument payload includes three imaging
investigations: LORRI, the focus of this manuscript; Alice, a
ultraviolet imaging spectrometer; and Ralph, a visible imager and
infrared imaging spectrometer. These optical instruments are all
approximately co-aligned to view a common boresight direction, and the
spacecraft will maneuver as required to provide pointing during the
various planetary encounters. The Ralph instrument includes a
multispectral imaging channel (MVIC), which is a four-color, medium
angle imager with a field-of-view (FOV) 5.7° wide, scanned by time-delay
integration. LORRI provides complementary imaging data, as a
panchromatic, narrow angle (field-of-view 0.29°) framing camera.

Table 1. Pluto and Charon Prioritized Measurement Objectives

+-----+------------------------------+---------------------------------+
| Gr  | Goal                         | LORRI Contribution              |
| oup |                              |                                 |
+-----+------------------------------+---------------------------------+
| 1.1 | Characterize the global      | > Hemispheric panchromatic maps |
|     | geology and morphology of    | > of Pluto and Charon at best   |
|     | Pluto and Charon             | > resolution exceeding 0.5      |
|     |                              | > km/pixel                      |
+-----+------------------------------+---------------------------------+
| 1.2 | Map surface composition of   |                                 |
|     | Pluto and Charon             |                                 |
+-----+------------------------------+---------------------------------+
| 1.3 | Characterize the neutral     | > Search for atmospheric haze   |
|     | atmosphere of Pluto and its  | > at a vertical resolution \<5  |
|     | escape rate.                 | > km                            |
+-----+------------------------------+---------------------------------+
| 2.1 | Characterize the time        | > Long time base of             |
|     | variability of Pluto\'s      | > observations, extending over  |
|     | surface and atmosphere       | > 10 to 12 Pluto rotations;     |
|     |                              | > panchromatic maps of the      |
|     |                              | > far-side hemisphere           |
+-----+------------------------------+---------------------------------+
| 2.2 | Image Pluto and Charon in    | > Panchromatic stereo images of |
|     | stereo                       | > Pluto and Charon              |
+-----+------------------------------+---------------------------------+
| 2.3 | Map the terminators of Pluto | > High resolution panchromatic  |
|     | and Charon with high         | > maps of the terminator region |
|     | resolution                   |                                 |
+-----+------------------------------+---------------------------------+
| 2.4 | Map the surface composition  |                                 |
|     | of selected areas of Pluto   |                                 |
|     | and Charon with high         |                                 |
|     | resolution                   |                                 |
+-----+------------------------------+---------------------------------+
| 2.5 | Characterize Pluto\'s        |                                 |
|     | ionosphere and solar wind    |                                 |
|     | interaction                  |                                 |
+-----+------------------------------+---------------------------------+
| 2.6 | Search for neutral species   |                                 |
|     | including H, H~2~, HCN, and  |                                 |
|     | C~x~H~y~, and other          |                                 |
|     | hydrocarbons and nitriles in |                                 |
|     | Pluto\'s upper atmosphere,   |                                 |
|     | and obtain isotopic          |                                 |
|     | discrimination where         |                                 |
|     | possible                     |                                 |
+-----+------------------------------+---------------------------------+
| 2.7 | Search for an atmosphere     |                                 |
|     | around Charon                |                                 |
+-----+------------------------------+---------------------------------+
| 2.8 | Determine bolometric Bond    | > Panchromatic, wide phase      |
|     | albedos for Pluto and Charon | > angle coverage of Pluto and   |
|     |                              | > Charon                        |
+-----+------------------------------+---------------------------------+
| 2.9 | Map the surface temperatures |                                 |
|     | of Pluto and Charon.         |                                 |
+-----+------------------------------+---------------------------------+
| 3.1 | Characterize the energetic   |                                 |
|     | particle environment of      |                                 |
|     | Pluto and Charon             |                                 |
+-----+------------------------------+---------------------------------+
| 3.2 | Refine bulk parameters       | > Orbital parameters, bulk      |
|     | (radii, masses, densities)   | > parameters of Pluto and       |
|     | and orbits of Pluto and      | > Charon                        |
|     | Charon                       |                                 |
+-----+------------------------------+---------------------------------+
| 3.3 | Search for magnetic fields   |                                 |
|     | of Pluto and Charon          |                                 |
+-----+------------------------------+---------------------------------+
| 3.4 | Search for additional        | > Search for satellites and     |
|     | satellites and rings.        | > rings; refine orbits, sizes,  |
|     |                              | > shapes of Nix and Hydra       |
+-----+------------------------------+---------------------------------+

# 2. LORRI Requirements

LORRI is a long focal length imager (see Figure 1) designed for high
resolution and responsivity at visible wavelengths. LORRI will perform
its primary measurements while *New Horizons* approaches Pluto and its
satellite Charon in July, 2015, obtaining images from a closest approach
distance of 11100 kilometers to Pluto, at a fly-by speed of 13.77
kilometers per second. New Horizons performed a Jupiter flyby, with
closest approach on Feb. 28, 2007. During the Jupiter system flyby,
LORRI imaged the atmosphere of Jupiter, its ring system, and several of
its satellites. Finally, after the Pluto and Charon encounter, the *New
Horizons* spacecraft will be targeted to encounter a Kuiper Belt object
(KBO), at which LORRI will again obtain high resolution images.

LORRI is required to obtain high resolution, monochromatic images under
low light conditions. Other instruments on *New Horizons* have
multispectral and hyperspectral capabilities. At Pluto encounter, 33 AU
from the Sun, the illumination level is \~1/1000 that at Earth, but
Pluto is an unusually bright object with a visible albedo of \~0.55. At
the Kuiper Belt object, likely to be encountered outside 40 AU from the
Sun, the illumination will be still lower, and the object will be
darker, with an albedo of typically \~0.1.

The main objectives of LORRI are: (1) obtaining high resolution images
of Pluto and Charon during the approach phase, including the hemisphere
that will not be observed during closest approach, (2) taking images at
closest approach with instantaneous field of view (IFOV) of
approximately 50 meters per detector element and (3) obtaining optical
navigation images required to support trajectory corrections. LORRI\'s
reflective telescope is a Ritchey-Chrétien design, with a
field-flattening lens group near the focal plane. The digital image is
captured by a frame transfer CCD detector. The FOV is 0.29° x 0.29°; the
1024 x 1024 square detector elements have a pixel resolution (or IFOV)
of 4.94 μrad. A summary of the characteristics of the LORRI instrument
appears in Table 2

Table 2. Summary of LORRI Characteristics

+-----------------------------------------------------------------------+
| Visible Panchromatic Imager                                           |
|                                                                       |
| Telescope Aperture 208 mm                                             |
|                                                                       |
| Focal Length 2630 mm                                                  |
|                                                                       |
| Passband 0.35 -- 0.85 μm                                              |
|                                                                       |
| Field-of-view 0.29^o^ × 0.29^o^                                       |
|                                                                       |
| Instantaneous field-of-view 4.95 μrad                                 |
|                                                                       |
| Back-thinned, frame transfer CCD                                      |
|                                                                       |
| Nominal exposure times 50-200 ms                                      |
|                                                                       |
| On-chip 4×4 pixel binning available                                   |
|                                                                       |
| Autoexposure                                                          |
+-----------------------------------------------------------------------+

![](media/image1.jpeg){width="3.4493055555555556in"
height="2.3in"}![](media/image2.jpeg){width="3.057638888888889in"
height="2.2993055555555557in"}

Figure 1 (left) LORRI telescope assembly, showing SiC mirrors and
metering structure; (right) LORRI composite baffle and flexure mount on
test stand

The LORRI instrument is mounted inside the *New Horizons* spacecraft,
the interior of which is designed to remain near room temperature. As
the telescope views cold space, and the CCD is designed to operate below
--70° C, the thermal implementation of the system was a challenge. In
order to maintain optical performance, a material with high thermal
conductivity and low coefficient of thermal expansion (CTE) was
required. As a result, the LORRI optical telescope assembly (OTA) has
both primary and secondary mirrors and a metering structure fabricated
from silicon-impregnated silicon carbide (see Figure 1).

![](media/image3.png){width="5.5680555555555555in"
height="4.772916666666666in"}

Figure 2. LORRI mounted within New Horizons spacecraft, with outer
panels of spacecraft removed. LORRI is wrapped in thermal blanketing,
cover door closed.

During the approach to Pluto, which occurs under high sun conditions
(small phase angle or Sun-Pluto-spacecraft angle), LORRI is required to
image the surface of Pluto at signal-to-noise ratio (SNR) \> 100 in
single frames. The encounter geometry is such that near closest approach
to Pluto, where the highest resolution images would be obtained, LORRI
views regions near the terminator under low sun conditions and still
less illumination; here LORRI has the goal of imaging at SNR \> 20 in
single frames. Likewise, at the Kuiper Belt object LORRI has an SNR goal
\> 20.

The resolution requirement near Pluto closest approach is for LORRI to
resolve 100 meters per line pair at a distance of 10,000 km from the
surface. An IFOV required to be \<5 μrad (Table 3) was derived, with a
modulation transfer function (MTF) goal of 0.05 for spatial modulation
at 1 cycle per 10 μrad. LORRI is designed to meet imaging requirements
not only at nominal operating temperature (as low as approximately
-100°C for the telescope), but also at room temperature.

For optical navigation, LORRI is required to be able to image a star of
visual magnitude V=11.5 at SNR\>7 in a single 100 ms exposure, with full
width at half maximum (FWHM) \>1 pixel. It is not desirable for too
great a fraction of the energy from a point source to be imaged onto a
single pixel, because stellar images become too undersampled. LORRI has
a 4×4 pixel binning mode, for which its limiting magnitude requirement
is V\>17 in a single exposure of 9.9 s. This 4×4 pixel-binning mode will
be used to search for the target KBO and to perform optical navigation
on approach. A special spacecraft guidance mode is available for the KBO
search in which the spacecraft will hold the target within the 4×4 pixel
pointing tolerance for 10 second exposures. At 40 AU from the Sun, LORRI
is predicted to be able to detect a 50 km diameter object, of albedo
0.04 and at phase angle 25°, from a distance of 0.35 AU, more than 40
days before the object would be encountered. This is ample time for
targeting of the spacecraft.

Table 3. LORRI Measurement Requirements at Pluto

  ------------------- ---------------------------------------------------
  Resolution          Resolve 100 m per line pair at 10,000 km

  Derived requirement Map full illuminated disk of Pluto at better than 1
                      km per pixel resolution with a 3×3 mosaic

  Derived requirement IFOV \<5 μrad with FOV 0.29°; image frame pixel
                      format 1024×1024

  Signal-to-Noise     Achieve SNR \>100, single pixel, single exposure at
  Ratio               Pluto during approach, for albedo 0.55 at low phase
                      angle

  Derived requirement Achieve SNR \>20 (goal), single pixel, single
                      exposure at Pluto, at 110° phase angle near
                      terminator

  Optical Navigation  Achieve SNR \>7 for star of visual magnitude 11.5
                      with a single exposure of 100 ms

  Derived requirement Achieve stellar limiting magnitude \>17 for 9.9
                      second exposure in 4x4 binned mode for KBO search
                      at SNR \>7
  ------------------- ---------------------------------------------------

Observations of the Pluto system begin at least 90 days prior to the
July, 2015 encounter, with both Pluto and Charon already resolved (see
Table 4). Initial observations are planned to refine the orbits of
Pluto, Charon and the two newly discovered moons Nix and Hydra. Pluto
and Charon can be imaged in single frames or in 2×1 mosaics through at
least ten full orbits (orbit period 6.38 days) ending about 14 days
before Pluto closest approach (c/a), to refine orbital ephemeredes and
especially the eccentricity. In the last week prior to c/a, searches for
librations of Pluto and Charon are performed, where Pluto subtends 123
pixels one half rotation before c/a. Nix and Hydra are expected to be
detectable in 4×4 binned images about 90 days before c/a, and in
unbinned single frames within the last 14 days.

The last full frame image of Pluto is acquired about 10 hours before
c/a, and two 3x3 global mosaics of the full illuminated disk are
acquired during the near encounter. The full illuminated disk
observations will be useful to construct global base maps, to determine
the global shape of Pluto, and to search for oblateness and tidal
bulges. Additional images near c/a are obtained at successively higher
resolutions but covering smaller portions of the illuminated disk. The
Pluto near encounter image dataset will be used to study surface
morphology, geologic processes, and atmosphere-surface interactions.
Likewise, the full illuminated disk of Charon will be imaged with 3x3
LORRI mosaics at resolution of better than 0.5 km per pixel, meeting the
Group I panchromatic imaging requirement for Charon (the corresponding
0.5 km per pixel imaging requirement for Pluto will be met by MVIC).

Table 4. LORRI Planned Observations of the Pluto System

  -----------------------------------------------------------------------
  Approach imaging starts c/a-90 days, Pluto and Charon already resolved,
  Nix and Hydra detectable (refine orbits)

  Through at least ten full orbits ending c/a-14 days, both Pluto and
  Charon can be acquired in single frame or 2x1 mosaic together with
  background stars

  At c/a-14 days, Pluto subtends 28 pixels

  By c/a-7 days Pluto subtends 57 pixels, both Pluto and Charon can be
  acquired with 3x1 image strip

  At c/a-3.2 days, Pluto subtends 123 pixels, imaging far side of Pluto
  (unseen side during c/a)

  At c/a-10 hours, last full frame image of Pluto, 2.5 km/pixel at nadir

  Near encounter Pluto observations -- 3x3 mosaics of full disc better
  than 1 km/px; image strips at progressively finer resolutions to 110
  m/px; terminator imaging sequence with 50 m/px resolution (goal)

  Near encounter Charon observations -- full frame illuminated disk
  images; 3x3 mosaics of full disc better than 0.5 km/px; terminator
  observation 130 m/px

  Near encounter observations of Nix and Hydra, better than 200 m/px
  resolution (goal)
  -----------------------------------------------------------------------

The LORRI data sets acquired during the Jupiter encounter in January
through March of 2007 are summarized in Table 5. Images of the Jovian
atmosphere and its clouds and storms include full disk rotation
sequences, acquired up to two months before Jupiter c/a on February 28,
as well as high resolution 2×2 mosaics of specific features acquired
near c/a. Imaging sequences ware executed for each of the Galilean
satellites, including observations of the night sides of Io, Europa, and
Ganymede acquired while the respective satellites ware in eclipse (i.e.,
in Jupiter's shadow). The Jupiter ring systemewas imaged atsboth low and
high solar phase angles, as well as during the ring plane crossing.
Images to study the shapes and photometric properties of Elara and
Himalia, two of Jupiter's irregular satellites,dwere obtained.

Table 5. LORRI Observations of the Jovian System

  -----------------------------------------------------------------------
  Global imaging of Jupiter atmosphere, full rotation sequences, during
  approach

  Near encounter imaging of Jovian cloud and storm dynamics near c/a,
  best resolution 12 km/pixel

  Global imaging of Io, illuminated portion, best resolution 12 km/pixel

  Io plume inventory (plumes higher than 60 km)

  Io nightside imaging from eclipse; Io hot spots and auroral emissions

  Global imaging of Europa; map broad, regional-scale arctuate troughs,
  best resolution 15 km/pixel

  Map Europa nightside auroral emissions in eclipse

  Map Ganymede nightside auroral emissions in eclipse

  Global imaging of Callisto, best resolution 23 km/pixel

  Jovian ring plane crossing; map vertical structure of ring systems

  Map longitudinal structure of Jovian rings

  Resolved images and phase curves of irregular satellites Himalia and
  Elara
  -----------------------------------------------------------------------

# 3. LORRI Instrument Description

## 3.1 LORRI Overview

The LORRI instrument was designed and fabricated by a combined effort of
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) and
SSG Precision Optronics Incorporated (SSG), of Wilmington,
Massachusetts, USA. LORRI has four subassemblies in close proximity
connected by electrical harnesses. These are the OTA, the aperture cover
door, the associated support electronics (ASE), and the focal plane unit
(FPU). Except for the door, all are mounted inside the spacecraft on its
central deck; the door is mounted to an external spacecraft panel. LORRI
is electronically shuttered, with no moving parts aside from the cover
door. The ASE implements all electrical interfaces between LORRI and the
spacecraft except for the door control, several spacecraft thermistors,
and two decontamination heaters. Figure 3 is a block diagram of the
instrument. Conard et al. (2005) give a detailed description of LORRI
design, manufacture and test.

![](media/image4.wmf){width="6.490277777777778in"
height="4.705555555555556in"}

Figure 3. LORRI block diagram , showing subassemblies: optics (OTA) and
aperture door; focal plane unit (FPU); and associated support
electronics (ASE) with three slices, which are the low voltage power
supply, the event processing unit, and the imager input/output board.

A summary of LORRI instrument specifications is given in Table 6. The
LORRI boresight is required to be aligned within 0.1° of the boresight
of the Ralph imager (MVIC). For a combined summary of the fields-of-view
for the three imaging instruments on New Horizons, see the payload
overview companion paper (Weaver et al. 2007)

The OTA, aside from the focal plane unit and thermal blanketing, was
designed and built by SSG Precision Optronics, Inc. The primary and
secondary reflecting optical elements are constructed of SiC. The
telescope is a 2630 mm focal length, f/12.6 Ritchey---Chretien design.
Three field-flattening fused silica lenses, located in front of the
focal plane unit, are the only refractive elements in the system.

Table 6. LORRI Instrument Specifications

  -----------------------------------------------------------------------
  Optical telescope assembly mass 5.6 kg

  Total mass 8.6 kg

  Electrical Power 5 W

  Heater Power 10 W

  Focal plane calibration lamps (two)

  Data interfaces Low Voltage Differential Signaling (LVDS) and RS-422
  (both dual redundant)

  ADC 12 bit

  Image format 0: 1024×1028 (including 4 dark columns)

  Image format 1: 256×257 (4x4 binned, including one dark column)

  Embedded image header (first 408 bits of image data per frame, either
  format)

  32-bin image histogram provided for every image
  -----------------------------------------------------------------------

The SiC metering structure of the telescope holds the mirrors and field
flattening lens cell. It is a monolithic structure consisting of a
primary mirror (M1) bulkhead, short cylindrical section, and three-blade
spider with secondary mirror (M2) mounting. The field flattener assembly
mounts to the M1 mounting plate and protrudes through the M1 mirror. The
metering structure is mounted to the graphite composite baffle using
three titanium, vibration-isolating feet. The baffle assembly is mounted
to the spacecraft using six glass-epoxy legs, which provide thermal
isolation. The entire OTA is covered with multi-layer insulation (vented
away from the OTA), except for the entrance aperture.

LORRI is protected from contamination and solar illumination using a
one-time-open door mechanism. The door is mounted to the exterior of the
spacecraft, and the LORRI baffle tube extends into the door to form a
contamination seal. The door is aluminum, with thermal blankets for
temperature control prior to deployment. The mechanism uses redundant
springs and redundant paraffin actuators for deployment. A port allowing
for installation of a witness mirror or small window is also part of the
door. The door was opened successfully in flight on August 29, 2006.

The ASE provides the data and control interfaces to the spacecraft and
to the focal plane unit. It consists of three 10 cm by 10 cm printed
circuit cards electrically interfaced to one another via stackable
connectors. They are in a magnesium housing, mounted directly to the
spacecraft deck, a short distance from the OTA.

The LORRI FPU has a back-illuminated, thinned, high quantum efficiency
CCD (an E2V Technologies Model 47-20). The FPU consists of a magnesium
box mounted to the spacecraft deck, housing a 15 cm by 10 cm circuit
card that controls the frame transfer CCD and provides interfaces to the
imager board of the ASE. This circuit card is connected by a flex
circuit to a small electronics board mounted at the focal plane. The
small focal plane board holds the CCD itself and is mounted on thermal
stand-offs, allowing the CCD and the small board to operate at ≤ -70° C
while the magnesium box operates near room temperature. The CCD is in a
window-less mount to avoid scatter and multiple reflections, with a
black, anodized aluminum plate installed over the CCD storage readout
area.

### 3.1.1 Design requirements and trades

The stringent optical, thermal and structural requirements for the LORRI
OTA presented many design challenges. The primary design driver for
LORRI instrument was the resolution requirement as described in section
2.2. The resolution is limited by a number of factors, including the
stability of the spacecraft while an image is being exposed. The
pointing stability of the spacecraft is characterized as a typical drift
rate of 25 μrad per second. The minimum exposure time is limited by the
frame transfer time of the CCD. In order to remove completely the image
smear which occurs during transfer, the exposure time should preferably
exceed the frame transfer time (approximately 13 milliseconds), although
acceptable image quality has been achieved in flight at exposures as
short as 1 millisecond. LORRI was designed for an exposure time range
between 50 and 200 milliseconds, with 100 milliseconds the nominal
design value. Over this exposure range, the spacecraft orientation would
drift \~2 to \~7 μrad.

After the range of exposure times was determined, IFOV had to be traded.
A smaller IFOV yielded higher resolution, though it would ultimately be
limited by spacecraft stability. Diffraction limited system resolution
when the entrance pupil became appreciably smaller than 200 mm diameter.
Strict mass limitations combined with cost limitations prevented
increasing the aperture much beyond 200 mm diameter. An aperture of 208
mm was selected.

With reasonable assumptions about the type of telescope and detector and
their associated efficiencies, and with the range of nominal exposure
times, a nominal IFOV of 5 μrad was chosen, which defined an effective
focal length of 2630 mm. The FOV of the final design was 0.29° square.

The aperture requirement drove the telescope to reflecting optics. Mass
and cost limitations, combined with the FOV and imaging requirements,
drove the design to a Ritchey-Chrétien design. Refractive elements were
used as field flattening lenses, as the Ritchey-Chrétien focal plane
curvature over the flat CCD would have limited imaging performance
without them. The field flattening lenses allowed LORRI to meet the
requirement of \<0.1% distortion at all points over the full field of
view. There was no requirement for color imaging. An optical ray trace
layout for LORRI is shown in Figure 4.

![](media/image5.png){width="4.8125in" height="2.8875in"}

Figure 4. Optical Ray Trace Layout, showing primary and secondary mirror
surfaces, plus fused silica lenses.

During the New Horizons mission, LORRI is exposed to the following
radiation environments: a total dose of ionizing radiation 15 krad and a
neutron fluence (worst case) of 1.4 × 10^10^ n/cm^2^. The neutron
fluence is from the radioisotope thermal generator over the course of
the mission. In the OTA, the refractive optics, antireflective coatings,
and reflective coatings were required to be tolerant to the specified
radiation environments. The LORRI CCD is operated below -70°C to
mitigate degradation of charge transfer efficiency from exposure to the
neutron fluence.

### 3.1.2 Optical design

The LORRI OTA is a Ritchey-Chrétien design, with high system throughput
required because of the short allowed exposure time and low light level
at Pluto. The complete LORRI OTA design was evaluated with a
computer-aided design model including stray light analysis. Specular
reflections and bidirectional reflectance distribution functions of the
Aeroglaze Z-306 black paint, primary and secondary mirrors, field group
optics and focal plane were included in the model. The primary and
secondary baffle tubes were sized to minimize obscuration and suppress
direct paths to the FPA's active area. The telescope magnification and
obscuration were balanced, affecting the optical sensitivity and MTF,
respectively. Out-of-field stray light was evaluated by generating point
source transmittance curves with angular scans across the boresight in
two orthogonal directions (-70° to +70° for each scan) to search for any
obscured paths with unacceptable amplitude.

The OTA design required multiple baffle vanes, fabricated from graphite
composite material, surrounding the metering structure to suppress stray
light. In addition, an inner baffle is used extending from the hole in
the primary mirror. This inner baffle has both inner and outer vanes
plus threading in its interior. All baffle design features were
optimized through TracePro ray tracing analysis. This analysis shows
that out-of-field stray light is adequately suppressed and that ghosting
is acceptable. The derived OTA system root-mean-squared (rms) wavefront
error requirement based on the MTF requirement was \<0.10 waves @ 632.8
nm, over an operating environmental temperature range of -125°C to 40°C
and after g-release. The system throughput requirement drove a surface
roughness requirement on all optics to a goal of \<20 Ǻ rms.

### 3.1.3 Thermal requirements and design

The extreme thermal environment posed a design challenge. LORRI is
mounted within the interior of a spacecraft with deck temperature in the
range 0 to +40ºC temperature, while it has an open, 208 mm aperture
radiating into cold space. The challenge was to minimize defocus due to
gradients developed in the OTA metering structure. The derived
requirement was to limit the heat loss from the spacecraft to the OTA to
less than 12 W, requiring conductive isolation at the interface and near
zero radiative coupling to the spacecraft. The gradients in the OTA
metering structure were limited to 2.5° C axial and 1.0° C lateral, and
0.5 W heater power was available for mirror gradient control without any
in-flight focus adjustment mechanism.

The thermal requirements were met by an athermal, single material
solution, which is self-compensating under soak conditions. SSG's SiC
55A formulation was chosen due to its inherent high conductivity, which
acts to minimize gradients, and its low coefficient of thermal
expansion, which minimizes the thermal strain impact of such gradients.
Invar 36, a good match to SiC 55A over the temperature range of
interest, was chosen for the metallic inserts that allow bolting
together of the OTA assembly. All invar inserts, as well as the
secondary mirror foot, were epoxy bonded to the SiC. In addition, the
OTA is mounted inside of the telescope baffle tube, made of highly
conductive K13C graphite composite. The baffle tube provides a
relatively uniform cold sink along the length of the telescope which
helps to reduce longitudinal thermal gradients.

Additional thermal control features on the LORRI telescope help to
reduce system gradients. The telescope is mounted to the spacecraft via
G-10 isolators which isolate the OTA conductively from the spacecraft
deck. Covering the appropriate OTA and spacecraft surfaces with
multi-layer insulation minimizes radiative coupling between the OTA and
the spacecraft deck. The LORRI multi-layer insulation, which represents
15% of the instrument mass, consists of 23 separate pieces.

Areas where material mismatches occur are flexured or otherwise
configured to minimize induced strain and resulting optical degradation.
The secondary mirror is mounted to a flexured Invar 36 mount plate,
which in turn mounts to the end of the SiC metering structure. The
secondary and primary mirror magnesium baffles are flexure mounted to
the OTA structure (SiC) and the lens cell (Invar 36), respectively. The
system aperture stop is made of aluminum 6061-T6 and is flexure-mounted
to the middle ring of the OTA structure. The CCD mount plate is attached
to the OTA structure by titanium flexures which have the dual purpose of
mitigating thermal strain and thermally isolating the CCD from the
structure. The G-10 mounts have titanium post flexures on either end.
Additionally, the OTA itself is mounted to the K13C baffle tube via
titanium isolators, which act to mitigate thermal strain and vibrations
and to provide conductive isolation.

The baseline mission requires decontamination of the CCD at temperatures
\>-18°C before door opening, with decontamination heaters.
Decontamination can be achieved at lower temperatures, but long time
periods may be necessary to desorb water.

An additional thermal requirement is that the CCD must be maintained at
a temperature of \< -70 °C while acquiring science data. This
requirement is met by mounting the CCD to a bracket which is mounted to
the OTA via conductively isolating titanium flexures; the CCD bracket is
in turn attached to a gold-coated beryllium S200F conduction bar that is
bolted to a gold-coated beryllium S200F thermal radiator whose outside
surface is painted white with Aeroglaze A276. Since the radiator is
mounted to a separate spacecraft panel from the OTA itself, there must
be some compliance to allow motion between the two, provided by a highly
conductive 1100 series aluminum alloy S-link.

The LORRI in-flight temperatures were predicted via the creation of a
finite difference thermal model that included all conductive and
radiative heat transfer. A thermal balance test of the instrument was
performed that validated the thermal model in five separate test cases.
The results of thermal balance testing predict that the 0.5 Watt
gradient control heater will not be required in flight. Flight data
shows a gradient of 1.5 °C, well within the 2.5 °C requirement for
gradient.

### 3.1.4 Telescope mechanical requirements and design

The structural requirements of the OTA were geared towards achieving
minimum mass, while maintaining performance over operational
temperatures and allowing for the stiffest design that will survive the
launch environment. The requirements were a maximum mass of 5.64 kg, a
minimum resonant frequency of 60 Hz, and survival under launch-induced
vibration and stresses.

The inherently high stiffness-to-weight ratio of SiC, (\~4.5 times that
of aluminum) allowed the fabrication of a low-mass structure with a
light-weighted primary mirror of open back, hub-mounted design to
minimize weight. The main baffle tube was fabricated from graphite
composite (K13C2U, M55J, and T300), another very high
stiffness-to-weight material (\~2.5 to 4 times that of aluminum). The
smaller internal baffles were fabricated from a light-weight magnesium
alloy (ZK60A).

Vibration isolation was required to survive the launch environment.
Titanium isolators were incorporated to mount the structure to the main
baffle tube at three points approximately at its center of gravity
location. Another important structural design consideration was to
minimize any potential for mount-induced distortion of the optics.
Intimately connected to this design consideration is the requirement for
the OTA to mount to a surface with only moderate mounting coplanarity,
namely, a spacecraft aluminum honeycomb panel. To avoid degradation of
optical quality, a 3-point mount was adopted, with the bases of each of
the three mount locations on the OTA outfitted with a ball joint that
can be loosened and re-tightened if necessary.

At the interface between the main baffle tube and the OTA inner
assembly, the vibration isolators also act to mitigate any mount-induced
strains. The flexurized mount plate at the secondary mirror serves the
dual purpose of controlling thermally induced distortions, as well as
mount-induced distortions; the CCD flexure mounts also serve this dual
purpose.

Due to its mass, the primary mirror was not flexure-mounted, as the low
resultant frequency and dynamic responses would have increased the risk
to the OTA under vibration. Instead the primary mirror is hub-mounted,
with a post and a foot bolted via three invar inserts to a mount plate.
The mount plate is in turn bolted to the structure. Because the lens
cell is made of Invar and mounts to the structure, close to the primary
mirror, the mount plate helps to separate any induced thermal strain in
the structure from being transferred to the primary mirror.

### 3.1.5 Instrument integration, focus and alignment

When the OTA was assembled at SSG, a convex spherical reflector was
centered at the focus using interferometry. Metrology, combined with
knowledge of the shim size used to connect the reflector to the carrier
plate, determined the location of the focus relative to the interface
location on the carrier plate. SSG also provided a reference mirror on
the back of the secondary mirror mount, such that the telescope
line-of-sight was parallel to the reference mirror's normal. Two optical
reference flats at right angles to the line-of-sight were mounted to the
LORRI metering structure for use in alignment monitoring after mounting
to the spacecraft.

The depth of focus for LORRI at the detector, with mechanical tolerances
on the CCD, allowed initial shim sizes to be selected for system
focusing at the SSG-provided focus location. A 300 mm aperture, f/5
off-axis parabolic collimator was used to project a point-like image
into LORRI. This image was produced by a laser unequal path
interferometer (LUPI) at the collimator focus. A series of exposures
were made at nine points in the LORRI field by moving within the field
using a fold mirror. At each location, the spot was centered on a
detector element by viewing the live image from the CCD through ground
support electronics, and balancing the wings of the image symmetrically
about the center detector element. This was repeated for seven focus
adjustments of the collimator, with slight measured changes from nominal
to allow for deterministic shimming of LORRI. Data from these exposures
were examined to find the best LORRI focus versus the collimator
adjustment. New shims were then installed to move the plane of the CCD
onto the plane of best focus.

Once at nominal focus, the CCD was centered on the optical axis by use
of a theodolite viewing both the reference mirror on the back of the
secondary mount and the primary mirror. The theodolite was
autocollimated on the reference mirror, and the azimuth and elevation
recorded. The theodolite then viewed the four corners of the CCD off the
primary mirror, and these azimuth and elevation values were recorded and
averaged. The CCD location was shifted in the plane of best focus such
that the average of the four CCD corners was within tolerance of the
normal to the reference mirror.

After the best focus was found in ambient conditions, LORRI was
installed in the NASA Goddard Space Flight Center's Diffraction Grating
Evaluation Facility for a focus check at flight-like thermal and vacuum
conditions. This was done by viewing a collimated beam, which projected
a small point-like image into LORRI, and stepping the spot over the
field by tilting LORRI on a gimbal platform.

Prior to delivery to the spacecraft, LORRI's line-of-sight was measured
relative to the optical reference flat mounted to the back of the
secondary mirror support. Additionally, the roll angle was measured by
viewing the CCD corners, and referencing to the orthogonal alignment
mirrors. These data, combined with measurements performed referencing
the flats to the spacecraft coordinate system, showed that LORRI's
line-of-sight was within mission requirements. Tracking of the LORRI
alignment references through the spacecraft environmental test program
did not show any significant movement relative to the spacecraft
coordinate system.

### 3.1.7 Contamination control

The LORRI telescope assembly remained under a nitrogen purge during all
phases of integration and test until launch, except for limited times
when images were taken or when put under vacuum. The internal
cleanliness requirements for the LORRI OTA per the LORRI performance
specification are a beginning-of-life specification of 250 A/2 and an
end-of-life specification of 300 A per MIL STD 1246C. The resulting
predicted reduction in optical efficiency (Conard et al. 2005) is \< 4%.

## 3.2 Electronics

As shown in Figure 3, LORRI electronics consist of the ASE and FPU. The
ASE contains three printed circuit cards. These are the low voltage
power supply (LVPS), the event processor unit (EPU), and the imager
input/output (IM I/O). The ASE is the primary interface between the
spacecraft and the FPU, which mounts and controls the CCD. Additional
information can be found in Conard et al. (2005).

### 3.2.1 Focal plane unit

The LORRI FPU is required to read out a complete image in 1 second, with
the charge level in each pixel represented by a 12 bit binary word. A
highly sensitive CCD with antiblooming was required, leading to the
choice of the E2V Technologies CCD47-20. This is a 1024×1024 pixel frame
transfer CCD with 13 micron square pixels. This device is
back-illuminated for high quantum efficiency and has a frame transfer
time of 13 milliseconds. The FPU noise is required to be \<40 electrons
per pixel, well above the CCD read noise which is calculated to be about
10 electrons at the readout time of about 0.7 microsecond per pixel. In
general, exposures of 50 to 200 milliseconds are typical for LORRI,
although the maximum exposure time is 29.9 seconds. The FPU design
includes switchable 4×4 pixel on-chip binning. The FPU also includes two
small incandescent bulbs that can illuminate the CCD through multiply
scattered light, so that testing can be performed even when imaging is
not possible through the optics (e.g., when the cover door is closed).

All CCDs have a number of clocks that must be driven to specific levels
for satisfactory operation. The E2V CCD uses three phase clocks for
image zone, memory zone and line transfer. These clocks are highly
capacitive, particularly for the image and memory areas of the chip, and
they have capacitive coupling between different phases. LORRI uses
Micrel MIC4427 drivers which are designed to drive high capacitance
loads at the required voltage levels from logic level inputs. They are
switching, not linear, devices so that low and high voltage levels are
obtained by suitable choice of supply voltages, and transition rates
must be adjusted at the output. This is done with series resistance
which adds to the internal switch resistance of the drivers, forming a
simple time constant with the capacitance of the CCD phase. The CCD
requires 29 volts bias for the output field effect transistor. A charge
pump with pre- and post-regulation was used to generate this voltage.

The LORRI FPU uses an Analog Devices AD9807 integrated circuit that
performs correlated double sampling, signal amplification, and analog to
digital conversion to 12 bits at maximum rates of 6 MHz, comfortably
above the pixel readout rates which are close to 1.5 MHz. The AD9807 is
susceptible to latch-up from ionizing radiation in space, and the LORRI
FPU incorporates latch-up protection circuitry. The CCD output is low
enough for the AD9807 amplifier to contribute significant noise, so a
low noise, wide band operational amplifier is added between the CCD and
the correlated double sampler, and the AD9807 is run at low gain.

### 3.2.2 Associated support electronics

The LORRI EPU controls the instrument via interfaces to the LVPS and IM
I/O boards. The EPU communicates to the spacecraft using an RS-422 link,
which receives commands and transmits engineering data. The EPU uses a
RTX2010RH processor and runs FORTH code.

The main function of the IM I/O board is to receive serial image data
from the FPU and transmit that data to either of two Integrated
Electronics Modules (IEMs) in the required format. There are dual,
redundant IEMs on the *New Horizons* spacecraft, which provide command,
data handling, and telemetry functions. One IEM is active and one is a
back-up; LORRI provides both interfaces (LVDS and RS-422) to both IEMs.
Secondary functions of the LORRI IM I/O board include the ability to:
store and transmit the image header, receive commands from the RTX
processor, calculate a 32-bin histogram, generate test patterns without
an FPU present, command the FPU mode and exposure times based on input
from the RTX.

The Imager I/O board contains two field programmable gate array (FPGA)
designs. The first is called the imager-interface FPGA, and the second
is called the RTX-bus FPGA. The main function of the imager-interface
FPGA is to read images from the FPU and send them to the IEM. As an
added feature, the IM I/O board can generate test pattern images across
the IEM interface without an FPU present. The first pattern consists of
a horizontal ramp and the second pattern consists of a vertical ramp.
The imager interface FPGA can also receive data from the RTX. These data
are sent across the ASE backplane and through the RTX-bus FPGA. The data
are used to set the FPU mode and exposure time, to set the active IEM
low voltage differential signaling port and to write the 408 bit header.
The FPU mode data is transmitted to the FPU across the pixel data signal
at the beginning of each second. The header data replaces the first 34
pixels when data is sent to the IEM, to provide redundancy in
associating instrument engineering data with each image. The instrument
engineering data are transmitted by the spacecraft within a separate
data stream from the science data, and the engineering data must be
associated with individual images in ground processing. For LORRI, the
critical header information is also encoded into the images themselves,
at the cost of 34 pixels in the first row of each image.

The RTX-bus FPGA also calculates a 32-bin histogram of the FPU image
data currently being transmitted. This histogram is then made available
to the RTX for future exposure time calculations. The RTX FPGA also
collects the FPU status and temperature data, making it available to the
RTX.

The LVPS provides 2.5 V, 6 V, and 15 V power as required by the other
boards within the ASE and by the FPU. The input voltage from the
spacecraft is 30±1 V. The LVPS also provides for current, voltage, and
temperature monitoring via an I^2^C serial interface to the EPU board.
The LVPS board provides switching to control power on/off to the FPU and
the telescope trim heaters.

### 3.2.3 Flight software {#flight-software .Style-Heading-3-+-(Complex)-14-pt-First-line:--0.5\"-Before:--6-pt...}

The LORRI RTX-2010 processor shares a common design with that of the
PEPSSI instrument on *New Horizons* (see accompanying paper). This
common design extends into the software. The common flight software
provides packet telemetry and command handling services. Besides
handling LORRI-specific packets, the common software automatically
generates a variety of standard packets, including housekeeping/status,
command echo, memory dump, and alarm packets. Similarly, besides
handling LORRI-specific commands, the common software also handles
standard commands for memory loads and memory dump requests. The command
handling software also provides storage and execution of command
sequences. The common software has timekeeping, voltage and current
monitoring, and memory management services and a standard boot program.

The LORRI-specific flight software controls heaters, collects voltages,
currents, and temperatures from the LVPS board, and manages the FPU. In
the FPU, the software controls the exposure time, either by manual
command or automatically based on the hardware-provided image histogram,
generates an image header, and enables routing of the image to the
spacecraft. The software also controls the FPU's test patterns and
calibration lamps. Whenever the software has nothing to do, it reduces
the processor's clock rate to save power.

## 3.3 Laboratory Test and Calibration

The LORRI instrument was subjected to an environmental qualification
program. Performance and environmental testing was performed at both the
subassembly and instrument levels. Typically, performance tests or
calibrations were done before and after environmental testing.

### 3.3.1 Subassembly Test and Calibration {#subassembly-test-and-calibration .Style-Heading-3-+-(Complex)-14-pt-First-line:--0.5\"-Before:--6-pt...}

The OTA was tested by SSG. Wavefront testing was performed using a LUPI
operated in double-pass mode. Wavefronts were measured before and after
vibration test and during thermal vacuum test. No change was detected
due to the vibration test. Some change was noted at cold temperature
during thermal vacuum testing, but it was determined that the level of
change was acceptable within the LORRI performance requirements. As a
secondary verification of performance, modulation transfer function
testing was also performed by projecting small features into the OTA,
and recording highly magnified images on a non-flight detector. This
testing was performed only in ambient conditions and showed excellent
correlation to wavefront data.

The FPU and CCD were also subjected at JHU/APL to testing at the
subassembly level. They were calibrated at predicted operating
temperatures and then subjected to environmental testing. The
calibration of the FPU and CCD was not repeated after the environmental
series due to time limitations.

### 3.3.2 Instrument Level Calibration  {#instrument-level-calibration .Style-Heading-3-+-(Complex)-14-pt-First-line:--0.5\"-Before:--6-pt...}

Results of the LORRI instrument-level laboratory calibrations are
discussed in detail by Morgan et al. (2005). The instrument-level
optical calibrations under ambient conditions were performed at JHU/APL.
Due to schedule conflicts with another instrument development program at
JHU/APL, LORRI instrument-level optical calibrations in thermal vacuum
were performed at the NASA Goddard Space Flight Center, in the
Diffraction Grating Evaluation Facility (DGEF).

The objective of radiometric calibration is to determine the conversion
from the observed signal in instrumental units to the scene radiance in
physical units. For LORRI, the radiometric calibration equation relates
the digital output *S* expressed as DN (12-bit 'data numbers') to the
scene radiance (or surface brightness) *I*

![](media/image6.wmf){width="5.711805555555555in"
height="0.45555555555555555in"} (1)

where subscripts *x; y* denote dependence on detector position (i.e.,
line and pixel numbers), *λ* on wavelength, *T* on temperature, *t* on
exposure time, *φ* on optical power at other points within the FOV, and
Φ on total optical power within the telescope. The quantities and their
units are: *I* the scene radiance in W m^-2^ sr^-1^ nm^-1^; *S* the
observed signal in DN; *Bias* the electronic offset of the CCD signal in
DN; *Dark* the detector dark current in DN; *Smear* the signal in DN
acquired by a pixel as it is shifted through the scene during frame
transfer; *Stray* the signal in DN due to stray light; *FF* the
(dimensionless) flat field response which normalizes responses of
individual pixels using a uniform diffuse source; *R* the absolute
responsivity in \[DN s^-1^pixel^-1^\]/\[Wm^-2^sr^-1^nm^-1^\]; and *t*
the exposure time in seconds.

Of the terms in the radiometric calibration equation, bias and smear
were characterized over the relevant parameters; dark is insignificant
at operational temperatures; stray light was tested at discrete off-axis
source angles; flat field response was measured, but there were
difficulties obtaining the desired 0.5% accuracy at all pixels from
ground-based data, and in-flight measurements are planned to replace or
correct the current flat field; and absolute response was measured with
sufficient accuracy for LORRI science goals. In addition to radiometric
calibration, instrument characteristics such as detector read noise, the
imaging point spread function (PSF), effective focal length and
field-of-view were determined during calibration. The PSF was measured
at several locations across the FOV, and the field-of-view and read
noise were determined.

### 3.3.3. Calibration setup {#calibration-setup .Style-Heading-3-+-(Complex)-14-pt-First-line:--0.5\"-Before:--6-pt...}

To confirm stability of LORRI's focus and response, key measurements
were conducted at the nominal operating temperature as well as
temperatures at the upper and lower ends of the operational range. The
telescope assembly temperature ranged from -97°C to -60°C during
calibration, while the CCD temperature ranged from -96°C to -78°C. At
these low temperatures it was necessary to operate LORRI in vacuum to
avoid condensation. The calibration was conducted at the NASA/GSFC DGEF
which operates as a large vacuum chamber for optical calibrations.
Calibrations at DGEF were conducted in July, 2004 prior to
instrument-level environmental (vibration and thermal vacuum) testing of
LORRI, and again in September, 2004 after environmental testing, to
establish stability of the calibration.

Figure 5 is a block diagram of the DGEF calibration setup for LORRI. A
light source outside the vacuum chamber was fiber optically coupled into
the chamber, feeding an integrating sphere. The integrating sphere
backlit a rotating target wheel that contained various apertures such as
pinholes and resolution targets. The target wheel was at the focal plane
of a 38 cm diameter collimator, the output of which illuminated LORRI,
which was mounted on a two-axis gimbal approximately two meters from the
collimator aperture. Between LORRI and the collimator, a 30.5 cm
diameter off-axis paraboloid (OAP) reflector could be rotated into the
beam to focus a pinhole image onto a calibrated photodiode, providing a
measurement of the integrating sphere port radiance for radiometric
calibration.

A 150 Watt, high pressure, ozone-free xenon arc lamp was used for the
LORRI calibration in order to provide a high radiance, solar-like
spectrum. Since there are significant spectral variations in response
over the LORRI bandpass, it is important to approximate the expected
spectral radiance distribution in order to infer broadband radiometric
response from calibration measurements with reasonable accuracy. Pluto,
Charon, Jupiter, and Jovian satellites have spectra ranging from
generally neutral to moderately red relative to a solar spectrum.

![](media/image7.png){width="6.499305555555556in"
height="4.663194444444445in"}

Figure 5. Calibration Facility at the NASA Goddard Space Flight Center

The arc lamp output was collimated using a fused silica condenser and
transmitted through two six-position filter wheels, one with bandpass
(BP) filters and the other with neutral density (ND) filters. The output
then passed through an airmass zero (AM0) filter and was refocused into
a fiber optic providing input to an integrating sphere inside the vacuum
chamber. The AM0 filter attenuates the near-infrared portion of the
spectrum to make the overall spectral energy distribution more
solar-like. The BP filters were centered at 400 nm, 500 nm, 600 nm, 700
nm, and 850 nm. Bandpasses at full width half maximum (FWHM) for the
filters were 65 nm for the 400 nm filter, 119 nm for the 850 nm filter,
and approximately 90 nm for the others.

The radiance at the integrating sphere output port, spectrally
integrated over the LORRI bandpass, was 46 μW cm^-2^ sr^-1^. Figure 6
shows the source spectrum. Although the lines appear to dominate the
spectrum in Figure 6, they contribute a modest fraction of the total
energy in the spectrum because their widths are relatively narrow. The
calibration source spectrum is compared to the spectra of Pluto and
Jupiter, as well as LORRI's calculated spectral response in Figure 6
(Morgan et al. 2005).

The target wheel (Figure 5) contained image masks, including pinholes
ranging in size from 5 μm to 1000 μm, an NBS 1963A resolution target,
and an open position. The target wheel was located at the focal plane of
a Cassegrain collimator with a 38 cm aperture, 460 cm focal length, and
0.5° unvignetted field of view. The collimator aperture was large enough
to overfill the LORRI aperture without vignetting over the LORRI FOV and
gimbal motion range, with tolerance for easy co-alignment. The two-axis
gimbal was stepper motor-driven with a Unidex controller at 63 steps per
arcsecond to scan LORRI across targets. A LORRI pixel subtends roughly
one arcsecond. The reference photodiode was a Hamamatsu S1336-8BQ, whose
responsivity was calibrated by the vendor at 10 nm intervals from 200 to
400 nm, and at 20 nm intervals from 400 to 1180 nm.

![](media/image8.png){width="6.488194444444445in"
height="2.495138888888889in"}

Figure 6. (left) Arc lamp calibration source spectrum and (right)
Spectra of Pluto, Jupiter normalized to unity at 607.6 nm and LORRI
response normalized to unity at maximum (Morgan et al. 2005)

For thermal control during calibration, a shroud cooled by liquid
nitrogen was constructed surrounding the telescope. A small annular
shroud encircling the telescope inside the cold shroud was heated to
control the telescope temperature to the desired set point. The thermal
conductivity of the telescope structure was sufficient to guarantee a
uniform temperature distribution despite the uneven heating. The shrouds
were fixed, with LORRI gimbaled inside them. LORRI viewed the collimator
through a ten inch aperture in the main cold shroud, which kept the
shroud edge well out of the LORRI FOV over the maximum gimbal motion
range used. LORRI calibration temperatures are listed in Table 7.

Table 7. LORRI calibration temperatures

  ------------------------- ---------------- ------------- ---------------
                            Nominal          Cold          Hot

  CCD                       -80°C            -93°C         -75°C

  FPU Board                 26°C             10°C          35°C

  Primary mirror            -72.5°C          -98.9°C       -62.1°C

  Secondary mirror          -73.3°C          -99.3°C       -63.5°C
  ------------------------- ---------------- ------------- ---------------

### 3.3.4. Laboratory calibration results {#laboratory-calibration-results .Style-Heading-3-+-(Complex)-14-pt-First-line:--0.5\"-Before:--6-pt...}

Results of pre-flight calibrations are summarized here, and preliminary
analyses of in-flight calibrations from instrument commissioning are
summarized in the next section. Pre-flight and in-flight calibrations
are fully consistent, considering limitations of ground test equipment.

The detector read noise was estimated from zero exposure time exposures
taken in the DGEF at nominal temperature with no illumination. One
hundred of these dark images were acquired, and the standard deviation
of the signal of each pixel was evaluated. The distribution of the
standard deviations is plotted in Figure 7. The most probable standard
deviation is 1.2 DN, which is adopted as a read noise estimate.

![](media/image9.png){width="3.482638888888889in"
height="2.245138888888889in"}

Figure 7. Read noise distribution, from 100 dark images measured
pre-flight. The estimated read noise is 1.2 DN.

The detector bias (signal at zero illumination due to electronic offset)
depends on the focal plane electronics board temperature. From subsystem
level tests, the bias in unbinned 1×1 mode is

*Bias* \[DN\] = 509.941 (±0.151) + 1.073 (±0.005) × *T* (2)

in units of DN as a function of board temperature *T* in °C. The
observed in-flight board temperature range is +34 (±0.7)°C. The bias
ranges from 546 to 547 DN over that range. The bias in 4×4 binned mode
is 2 DN higher. Detector dark current is negligible over the flight CCD
temperature range, for exposure times up to at least one second. Planned
exposure times are on the order of 100 ms. Also from subsystem level
testing, the FPU gain is 22 (+0,-0.5) electron/DN for CCD temperatures
of -50°C and -70°C and for board temperatures of 0°C and 40°C. This was
determined from analyses of photon counting noise in flat field
exposures using constant illumination with a green light emitting diode.
A gain estimate of 22±0.4 electron/DN was also obtained with analyses of
noise in flat field exposures versus net signal with eight different
exposure times. The linearity of the FPU was found to be within ±1% over
DN values from 900 to 3900, where the saturation level is 4095.

During calibration at the DGEF, point source imaging performance was
evaluated by observing a 3×3 grid of 5 μm pinholes. The grid target was
arranged with 4 pinholes near the corners of the FOV, 4 along the edges,
and one near FOV center. LORRI was gimbaled through a 6×6 subpixel grid
of positions spanning approximately 1.5 pixels, acquiring 10 images at
each step. A fitting process was applied to the images to estimate the
sub-pixel irradiance distribution. Results indicated a PSF with FWHM on
the order of 2 pixels, with no discernible dependence on position within
the FOV. No significant variation of the FWHM with temperature was
observed, verifying focus stability from ambient temperature to -100°C.
These tests were adversely affected by diffraction by the collimator
secondary obscuration, which was larger than the LORRI secondary.

More accurate PSF measurements were obtained in bench tests at ambient
temperature at APL. A source was projected through a Laser Unequal
Pathlength Interferometer (LUPI) and then an off-axis parabola
collimator with an unobstructed aperture to generate a collimated beam
that completely filled LORRI\'s aperture. For LORRI tests, the beam was
reflected from an optical flat mounted with tip/tilt controls, which
allowed focus and PSF measurements at five positions in the LORRI FOV
(near the corners and near the center). Image analysis indicated a PSF
with FWHM of 1.5 pixels with little variation across the FOV, when fit
with a two dimensional Gaussian function. With the spot near pixel
center, ensquared energy in a pixel exceeded 0.3 at all four corners and
the center of the CCD.

![](media/image10.wmf){width="6.496527777777778in"
height="6.488194444444445in"}

Figure 8. Provisional flat-field measured at APL: logarithmic stretch
from 0.95 (black) to 1.05 (white). Dust particles form 'donuts' and dark
spots. There is 4% vignetting in the corners, but in the upper left
corner and in the center of the field, there is excess brightness from
image ghosting which is not removed in preliminary processing.

Although LORRI flat field images were obtained during the
post-environmental calibration at the DGEF, the CCD was subsequently
cleaned by blowing ionized nitrogen across it. New flat field
measurements conducted at APL with a quartz halogen lamp (see Figure 8)
showed that the number of pixels affected by particle shadowing was
reduced to 62 from over 150. These new flat field measurements were
conducted in air at room temperature. There is vignetting of
approximately 4% in the corners, consistent with expectations based on
the design of the baffles and field stop. Low amplitude, dark
"doughnut\" rings (up to 1% amplitude) are seen from particles probably
on the field-flattening lenses, and dark spots (typical 20% signal loss
in single pixels) are seen from particles on the CCD. Comparison with
in-flight images of Jupiter and with calibration lamp images shows that
the particles have not moved since pre-launch calibration, and no new
particles have been introduced since launch.

A central region of approximately 200 pixel radius is brightened by a
maximum of 1.5% by ghost images that result from multiple reflections
between surfaces in the field flattening lens group. There is also
excess diffuse brightness from image ghosting in the upper left corner
of Figure 8 such that the known vignetting is masked, and arc-like ghost
features have been removed for preliminary processing. The ghosts are
dominated by out-of-field illumination at the red extreme of the LORRI
passband, depending on the radiance distribution over field angles just
outside the FOV up to approximately 0.37° off-axis. The ghosts are
strongly dependent on source spectrum and will be characterized
extensively with Jupiter observations. Also seen in Figure 8 is fringing
of 0.5% amplitude from constructive and destructive interference in the
CCD.

The DGEF flat fields showed no significant temperature dependence. The
maximum differences between the flat field at nominal temperature and
those at the hot and cold extremes were on the order of 1%, with fewer
than 250 pixels exceeding 0.5% variation in either case.
Bandpass-filtered flat fields showed somewhat more variation with
temperature, but for most of the filters the variations are not
statistically significant. Only 10 images were used for the filtered
flats, compared to 100 for the panchromatic flats. There appeared to be
significant temperature dependence in the 850 nm flat, possibly due to
interference in the CCD with the emission lines in the xenon arc lamp
spectrum. These strong lines do not occur in natural targets, and the
panchromatic flat fields are practically independent of temperature for
flight conditions.

However, laboratory flat field calibrations apply only imperfectly to
the flight system, because of limitations such as use of non-solar
source spectra. The provisional flat field of Figure 8 will be replaced
with in-flight flat field observations, using Jupiter as an extended
source during the Jupiter flyby, either to use directly or to be
combined with the laboratory flat field data. Additional in-flight flat
field data are planned using solar stray light.

The absolute radiometric response of LORRI was also determined at the
DGEF. When system responsivity varies significantly over the spectral
bandpass, as is the case for LORRI, the measured signal depends on the
scene spectrum, which will depend on the target. As can be seen in Table
3, LORRI has requirements for relative, not absolute, radiometry.
However, the source spectra that LORRI will view in flight will be
measured by other instruments on New Horizons (namely Ralph, see
companion papers). With the aid of independent spectral observations,
LORRI can provide useful radiometric data.

LORRI\'s absolute responsivity as a function of wavelength was
determined (Morgan et al. 2005) using panchromatic absolute measurements
together with a calculated relative response curve. First, the LORRI
responsivity spectrum was calculated from geometrical throughput of the
optical design and from spectral characteristics of optical components
and the CCD. It was assumed that an unknown constant factor would scale
this response spectrum to the correct absolute level. The calculated
spectral responsivity accounted for the measured mirror reflectance
curves and lens transmissions, and it used E2V\'s typical quantum
efficiency curve for the model 47-20 CCD which was not individually
measured for the flight CCD.

Second, the absolute LORRI response was estimated by scaling the
calculated spectral responsivity to match the DGEF flat field
observations. The flat field source spectrum was corrected to an
absolute scale using reference photodiode measurements taken immediately
before each set of flat field images. The 1 mm pinhole was imaged onto
the calibrated photodiode with the OAP mirror to obtain the spectral
radiance of the integrating sphere port (see Figure 6). Correction was
made for signal reduction from the partial blockage of LORRI\'s aperture
by the collimator secondary, which is larger than LORRI\'s secondary.
The LORRI obscuration by spider and secondary is 11%. The LORRI signal
was taken from the median flat field signal, which was 15908 DN/s/pixel
viewing this diffuse source spectrum. From this signal, the absolute
LORRI response curve shown in Figure 9 was derived (correcting the
figure shown in Morgan et al. 2005)s The flat field source was also
observed through the BP filtere of §3.3.3veand a similar procedure was
used to obtain the responsivity within each bandpass, which was plotted
at the signal-weighted mean wavelength for each filter. The BP filter
data suggest that LORRI's response peaks at a shorter wavelength than
would be inferred from the calculated spectral responsivity. The
absolute response will be refined in future work using in-flight
calibration data.

![](media/image11.wmf){width="5.729861111111111in"
height="3.660416666666667in"}

Figure 9. Absolute monochromatic response in (DN/s/pixel)/(W/cm^2^/sr).
Asterisks indicate bandpass filter measurements, which agree well with
the absolute response curve at the three shorter wavelengths but lie
below the curve at longer wavelengths (Morgan et al. 2005).

Lastly, the response to realistic scene spectra was calculated
numerically by integrating the product of the assumed scene spectra and
the LORRI response spectrum derived from calibration. From the
calibrated response curve, LORRI\'s responsivity to specified scene
spectra can be calculated by integrating the product of the LORRI
absolute response curve and the normalized scene spectrum. For a source
with the average Pluto spectrum, the absolute response of LORRI is
estimated from the DGEF calibrations as

$R_{\lambda,T}\ \left( \text{607}\text{.}6\ \text{nm} \right) = 2\text{.}2 \times \text{10}^{\text{11}}\ \frac{\text{DN/s/pixel}}{\text{W/cm}^{2}\text{/sr/nm}}$
(3)

giving the conversion from spectral radiance at the LORRI pivot
wavelength (Horne, 2004), which is 607.6 nm, to signal expressed in
units of DN/pixel/s. The spectral radiance in the denominator is
understood to correspond to the pivot wavelength. The absolute response
depends on the shape of the adopted scene spectrum; for additional
details see Morgan et al. (2005) and discussion of in-flight
observations below.

### 3.3.5 In-Flight Calibration

###### LORRI has successfully completed its in-flight commissioning tests. LORRI's cover door opened on August 29, 2006, and successful observations have been acquired of the open star cluster Messier 7 and the prime mission target Pluto as well as the planets Uranus, Neptune, and Jupiter. Instrument commissioning tests through September, 2006 are summarized in Table 8. {#lorri-has-successfully-completed-its-in-flight-commissioning-tests.-lorris-cover-door-opened-on-august-29-2006-and-successful-observations-have-been-acquired-of-the-open-star-cluster-messier-7-and-the-prime-mission-target-pluto-as-well-as-the-planets-uranus-neptune-and-jupiter.-instrument-commissioning-tests-through-september-2006-are-summarized-in-table-8. .tabletitle}

Table 8. LORRI In-Flight Commissioning and Calibration Test Summary

  ----------------------------------------------------- -----------------
  **Dates and description**                             **Sequence name**

  24 Feb 2006: all currents, voltages, power, and       LORRI-005
  temperatures nominal                                  

  23-24 April and 2-3 May 2006: in-flight noise test    LORRI-025

  30 Jul 2006: Dark series bias images, cover door      LORRI-006
  closed                                                

  29 Aug 2006: Door opening verification images         LORRI-007
  (Messier 7)                                           

  31 Aug 2006: Radiometric/PSF images (Messier 7)       LORRI-010

  31 Aug 2006: MVIC co-alignment images                 LORRI-018

  10,19 Sep 2006: Uranus                                LORRI-029

  10,19 Sep 2006: Neptune                               LORRI-030

  04 Sep 2006: Jupiter exposure/auto exposure/scattered LORRI-027
  light tests                                           

  21, 24 Sep 2006: Pluto                                LORRI-023a
  ----------------------------------------------------- -----------------

The commissioning test sequences LORRI-005, LORRI-006 and LORRI-025,
with the door still closed, were used to verify the FPU noise and bias
characteristics in-flight versus the ground calibrations. Results of the
in-flight tests have been consistent with the ground calibrations of the
FPU. For instance, the difference of two consecutive zero-exposure time
images, obtained from LORRI-005 on February 24, 2006, yielded a read
noise estimate of 1.11 ± 0.12 DN, where DN \~ 22 e^-^. The cosmic ray
"hit rate" was also measured from LORRI-005, with the rate of hits (mean
± standard deviation) determined as 15.7 ± 13.3 per frame for nominal
exposures \<0.5 s, where a "hit" was defined to be a pixel with DN at
least 5 standard deviations above the mean.

The result of preliminary in-flight measured bias correction, from
analysis of 25 frames acquired during the LORRI-006 test performed on 30
July, 2006, is shown in Figure 10. A total of 100 frames were acquired
in that test and are under analysis. The preliminary analysis used 25 of
the available dark frames, all of which are exposures of zero seconds.
For each of these dark frames, the median DN is found of all the pixels
in the four dark columns (which are the masked columns at the right side
of the image), and the resulting scalar is subtracted from each pixel
value in the image zone to obtain a corrected dark frame. After removal
of outlier pixel values (more than 3 standard deviations from the mean
of the 25 values at the same row and column numbers), the 25 corrected
dark frames are then averaged to obtain the so-called *delta_bias* frame
which is shown in Figure 10. This frame shows the pixel-level variations
of the bias and demonstrates the excellent uniformity of the LORRI
flight CCD. The low-level vertical banding in Figure 10 is the result of
amplifier oscillation in the FPU; the maximum peak-to-trough amplitude
of this wave-like feature is \~0.8 DN.

The *delta_bias* frame is used in the LORRI pipeline data processing to
remove the FPU bias from a LORRI image as follows. First, the median of
the pixels in the four dark columns of the raw image is determined and
subtracted from each pixel in the image zone of the raw image. Then, the
*delta_bias* frame is subtracted to obtain the final bias-corrected
result. The statistics of *delta_bias* frame are: the mean value in DN
is -0.0049; the standard deviation is 0.26; the maximum value is 1.64;
the minimum value is -1.56. Since the pipeline processing uses the
absolute bias level estimated from the dark columns of every image, the
bias estimate from Equation (2) is not used, although the latter
provides an independent check.

![](media/image12.png){width="5.680555555555555in"
height="4.9847222222222225in"}

Figure 10. *Delta_bias* frame: in-flight measurement of FPU bias
correction, based on analysis of 25 frames acquired 30 July 2006. This
image is linearly stretched between -1 DN and +1 DN.

The next step in LORRI pipeline processing is to apply the flat field
correction. Acquisition of in-flight flat field observations is planned
during and after Jupiter encounter in 2007. The in-flight observations
to date have been reduced with flat fields determined in pre-flight
laboratory testing, see Morgan et al. (2005).

![](media/image13.png){width="6.4944444444444445in"
height="7.613194444444445in"}

Figure 11. Jupiter observed 9/4/2006. Panel a. Raw image MET 19683344 on
logarithmic scale, showing readout smear. Panel b. Same image after
calibration on same logarithmic scale, showing bias and smear removal.
Panel c. Average of indicated columns showing different readout smear on
either side of Jupiter. Panel d. Same as c. for calibrated image,
showing removal of readout smear. Panel e. Image of panel a. after
calibration, on linear scale. Panel f. Five LORRI images including that
of panel a., all with 6 ms exposures, after calibration and co-addition.
Io and Europa (both barely resolved) and their shadows are indicated.

Also required to complete the data reduction is removal of an effect
called readout smear. This arises from the operation of the frame
transfer CCD used in LORRI, where first the image zone is flushed, then
an exposure is taken, and finally the image is transferred into the
storage zone. Hence a pixel of the raw image is exposed to the scene
radiance from the corresponding geometrical element of the scene, but it
is also exposed to the radiances of all the scene elements in the same
image column during the image transfers. Thus the raw image is the
superposition of the scene radiance and the signal acquired during frame
transfers, which is called readout smear.

The readout smear is removed as follows. Let
$P_{i,j}^{\text{meas}}\  = \text{measured image array in DN}$where *i,
j* are the column and row indices, respectively. Let the exposure time
be written *T~exp~*, with the transfer times for the frame scrub
*T~f~*~1~ and the frame storage *T~f~*~2~ and with *N* the number of
rows (which is 1024 for 1×1 images). Let *T~f~*~avg~ be the average of
*T~f~*~1~ and *T~f~*~2~ to define the constant
$A = \frac{T_{\text{exp}}}{T_{\text{exp}} - \frac{T_{\text{favg}}}{N}}$.
Finally we define the *N*×*N* constant matrix
$$$\varepsilon_{k,j} = \left\{ \begin{matrix}
\frac{T_{f1}}{T_{\text{favg}}}\ \text{for k} < j \\
1\ \text{for k} = j \\
\frac{T_{f2}}{T_{\text{favg}}}\ \text{for k} > j
\end{matrix} \right.\ $\
with *k, j* = 1, ..., *N* , and we calculate the *N*×*N* matrix
$\lambda_{i,j}^{(1)} \ast T_{\text{exp}} = A\ \left\lbrack P_{i,j}^{\text{meas}} - \frac{A\ T_{\text{favg}}\sum_{k}^{}{P_{i,k}^{\text{meas}}\varepsilon_{k,j}}}{N\left( T_{\text{exp}} + A\ T_{\text{favg}} \right)} \right\rbrack$.

The desmeared image is then

$P_{i,j}^{\text{desmear}} = A\ \left\lbrack P_{i,j}^{\text{meas}} - \frac{A\ T_{\text{favg}}\left\lbrack \sum_{k}^{}{P_{i,k}^{\text{meas}}\varepsilon_{k,j}} + \frac{E_{i,j}}{A} \right\rbrack}{N\left( T_{\text{exp}} + A\ T_{\text{favg}} \right)} \right\rbrack$

with
$\frac{E_{i,j}}{A} = T_{\text{favg}}\left\lbrack \sum_{k}^{}{\lambda_{i,k}^{(1)}\ \varepsilon_{k,j}} - \frac{1}{N}\sum_{l}^{}{\sum_{k}^{}{\lambda_{i,k}^{(1)}\ \varepsilon_{k,l}\varepsilon_{l,j}}} \right\rbrack$.
In-flight tests have verified desmear by this technique using
observations of Jupiter obtained at exposure times as short as 1 ms. For
the image in Figure 11, *T~f~*~avg~ = 10.5 ms and *T~f~*~1~/ *T~f~*~avg~
= 1.044, while *T~f~*~2~/ *T~f~*~avg~ = 0.956.

In-flight photometric calibration was obtained using observations of the
open star cluster Messier 7 obtained from LORRI-007 on 29 Aug 2006. The
visual magnitude is given by

V = -2.5 log *S* + 18.94 + *CC*

with *S* in \[DN/second\]. We find the color correction *CC* = -0.06 for
OB stars, *CC* = 0 for FG stars, and *CC* = 0.4 for K stars.

The Messier 7 observations (see Figure 12) also confirm from stellar
images that the point source function of the LORRI system, including the
effects of spacecraft pointing jitter, is 1.8 pixels FWHM. Stars to at
least 12^th^ magnitude are detected. The plate scale, based on
comparisons of pixel separations of bright stars in the field versus
cataloged positions, is 4.955 μrad/pixel. Any geometric distortion in
this image is less than 0.5 pixel.

![](media/image14.png){width="5.965277777777778in"
height="5.970138888888889in"}

Figure 12. LORRI image of open cluster Messier 7 obtained in flight.
This image has been logarithmically stretched. North is up, east is to
the left.

# 4. Summary

The LORRI instrument was successfully developed, qualified, and
calibrated, and it was delivered to the New Horizons spacecraft on time
and within budget. It has operated successfully in flight, and its
performance is completely nominal. It will obtain the first high
resolution imaging observations in the Pluto system and at one or more
additional Kuiper Belt objects.

# Acknowledgments

We thank NASA and the New Horizons Project teams for support. We also
thank many more members of the LORRI team whose contributions have
helped to make LORRI a success.

# References

S. Conard, F. Azad, J. Boldt, A. Cheng, K. Cooper, E. Darlington, , M.
Grey, J. Hayes, P. Hogue,

K. Kosakowski, T. Magee, M. Morgan, E. Rossano, D. Sampath, C. Schlemm,
and H. Weaver, "Design

and fabrication of the New Horizons Long-Range Reconnaissance Imager,\"
in Astrobiology and Planetary

Missions, G. R. Gladstone, ed., Proc. SPIE 5906, 2005.

F. Morgan, S.J. Conard, H.A. Weaver, O. Barnouin-Jha, A.F. Cheng, H.W.
Taylor, K.A.

Cooper, R.H. Barkhouser, R. Boucarut, E.H. Darlington, M.P. Grey, I.
Kuznetsov, T.J.

Madison, M.A. Quijada, D.J. Sahnow, and J.M. Stock. Calibration of the
New Horizons Long-Range Reconnaissance Imager, in Astrobiology and
Planetary Missions, G. R. Gladstone, ed., Proc. SPIE 5906, 2005.

Cheng, A.F. and Young, L.A., Mission Seeks to Explore Pluto-Charon, EOS
Trans. AGU, 83, pp. 384, 389, 2002.

K. Horne, The ways of our errors: optimal data analysis for beginners
and experts, star-www.stand.

ac.uk/ kdh1/pub0/ada/woe/woe.ps, University of St. Andrews, 2004.

##