A description of the Pluto-bound New Horizons spacecraft.pdf

8/14/2019 A description of the Pluto-bound New Horizons spacecraft.pdf

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Acta Astronautica 57 (2005) 135144www.elsevier.com/locate/actaastro

A description of the Pluto-bound New Horizons spacecraftDavid Y. Kusnierkiewicz a ,, Chris B. Hersman a , Yanping Guo a, Sanae Kubota a ,

Joyce McDevitt baThe Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA

bFutron Corporation, Bethesda, MD, USA

Available online 10 May 2005

Abstract

Pluto is the only planet in our solar system that has not yet been visited by a spacecraft from Earth. Beyond the orbit of Plutolies the Kuiper-Belt: home to many primordial objects from the earliest days of the formation of the solar system, preservedin a cosmic deep freeze. The Johns Hopkins University/Applied Physics Laboratory (JHU/APL) is planning the missionfor the Principal Investigator, Dr. S. Alan Stern of Southwest Research Institute. The planned design of the New Horizonsspacecraft, along with a discussion of the design drivers, is presented. The design lifetime of the spacecraft would be 15.25years. Measures taken to ensure the reliable operation of the spacecraft over the life of the planned mission are discussed. 2005 Published by Elsevier Ltd.

1. Introduction

Pluto remains the only planet in our solar systemthat has never been visited by a spacecraft. The NewHorizons (NH) mission would nally remedy this de-ciency in our exploration of the outer planets bysending a spacecraft to rendezvous with Pluto, andits moon, Charon, as early as July 2015 after launch-ing from Cape Canaveral Air Force Station in Jan-uary 2006, using a Jupiter gravity assist trajectory.

Corresponding author. Tel.: +1 2402285092; fax:+1240228 3237.

E-mail addresses: [email protected] (D.Y.Kusnierkiewicz), [email protected] (C.B. Hersman),[email protected] (Y. Guo), [email protected](S. Kubota), [email protected] (J. McDevitt).

0094-5765/$- see front matter 2005 Published by Elsevier Ltd.doi:10.1016/j.actaastro.2005.03.030

While New Horizons is planned as a yby missionof Pluto, and not an orbiter, an intensive sciencecampaign would begin approximately 5 months be-fore closest approach and end 2 months after. Thespacecraft would carry seven instruments to fulllits scientic objectives. These instruments are pro-vided by six institutions, and are supported by aworld-class science team. After the PlutoCharonencounter, in an extended mission phase, the space-craft would proceed to rendezvous with at leastone, and as many as three Kuiper Belt Objects. TheJohns Hopkins University/Applied Physics Labora-tory (JHU/APL) is planning the New Horizons mis-sion for the Principal Investigator (PI), Dr. S. AlanStern of the Southwest Research Institute (SwRI), andthe National Aeronautics and Space Administration(NASA).
http://www.elsevier.com/locate/actaastromailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://www.elsevier.com/locate/actaastro


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136 D.Y. Kusnierkiewicz et al. / Acta Astronautica 57 (2005) 135 144

2. PlutoCharon background

The PlutoCharon system is unique in the solar sys-

tem. Pluto is neither a terrestrial world like the innerplanets, nor is it a gas giant like the other outer planets.It is instead an ice dwarf, common to the deep outersolar system, and similar in many ways to the objectsfound in the Kuiper Belt. These worlds are primordialremnants from the earliest days of the formation of thesolar system, which have been preserved in their pris-tine states in a cosmic deep freeze. By studying thesebodies, we will advance our understanding of the fun-damentals involved in the formation and evolution of the solar system.

Pluto and Charon are also the only example in oursolar system of a true binary system; these two bodiesorbit about the center of mass between them.Addition-ally, the atmosphere of Pluto is a transitional case be-tween classical planetary and cometary atmospheres,and may also exhibit the phenomenon of hydrody-namic exchange, much as mass is exchanged betweenbinary star systems. The New Horizons mission is inthe best tradition of scientic exploration: a journeyinto the unknown [1].

3. New Horizons science

New Horizons would be the rst spacecraft to pro-vide reconnaissance of PlutoCharon and a KuiperBelt Object (KBO). Scientic questions regardingthe surfaces, atmospheres, interiors, and space envi-ronments of Pluto and Charon would be investigatedusing imaging, visible and infrared spectral mapping,ultraviolet spectroscopy, radio science, and in situplasma sensors. The science objectives for the missionhave been prioritized into measurement groups as

follows:

3.1. Group 1 objectives

Characterize the global geology and morphologyof Pluto and Charon.

Map surface composition of Pluto and Charon. Characterize the neutral atmosphere of Pluto and

its escape rate.


Characterize the time variability of Plutos sur-

face and atmosphere. Image Pluto and Charon in stereo. Map the terminators of Pluto and Charon with

high resolution. Map the composition of selected areas of Pluto

and Charon at high resolution. Characterize Plutos ionosphere and solar wind

interaction. Search for neutral species including H, H 2 , HCN,

and C x Hy , and other hydrocarbons and nitrilesin Plutos upper atmosphere, and obtain isotopicdiscrimination where possible.

Search for an atmosphere around Charon. Determine bolometric Bond albedos for Pluto

and Charon. Map the surface temperatures of Pluto and

Charon.


Characterize the energetic particle environmentof Pluto and Charon.

Rene bulk parameters (radii, masses, densities)and orbits of Pluto and Charon. Search for magnetic elds of Pluto and Charon. Search for additional satellites and rings.

The New Horizons mission plans to address all of these measurement objectives, with the exception of one Group 3 objective: the search for magnetic eldsof Pluto and Charon. It is not expected that such mag-netic elds exist. A magnetometer was not included inthe New Horizons payload suite, thereby eliminatingthe requirement for a magnetically clean spacecraft.The presence of a magnetic eld, should one exist, canbe deduced from other instruments. As designed, theNew Horizons payload suite consists of the followingseven instruments:

Alice: Ultraviolet mapping spectrometer (pro-vided by SwRI).

Ralph: Visible imager and infrared mappingspectrometer (provided by NASAs GoddardSpace Flight Center and Ball Aerospace Corpo-ration).


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D.Y. Kusnierkiewicz et al. / Acta Astronautica 57 (2005) 135 144 137

LORRI: Panochromatic long-range imager (pro-vided by JHU/APL).

PEPSSI: Energetic particle spectrometer (pro-

vided by JHU/APL). SWAP: Solar wind analyzer (provided by SwRI). REX: Radio science experiment (provided by

Stanford University). SDC: Student-built dust counter (provided by the

Laboratory for Atmospheric and Space Physics).

4. Mission design and trajectory

The New Horizons spacecraft would be launched di-rectly into an interplanetary trajectory (see Fig. 1 ) fromCape Canaveral Air Force Station, Florida, in January2006 on a Lockheed Martin Atlas V 551 launch vehi-cle. A Boeing-supplied third stage is also required toachieve the launch energy C 3 of 164 km 2/ s2 .

The spacecraft would then embark on an approx-imately 10-year journey that will bring it to Plutoand Charon, at the earliest, in July 2015 after a ybyof Jupiter in March 2007.The arrival date at Pluto isdependent on the launch date, as shown in Fig. 2 .A Jupiter gravity assist, which enables earlier arrivaldates at Pluto, is available only during the rst 23 daysof the 2006 launch window. A 14-day backup launchopportunity is available in February 2007. The trajec-tory design for this back-up opportunity does not usea Jupiter gravity assist [2,3] .

The NH operational lifetime requirement is 15.25years, beginning after launch and extending through

Pluto Encounter

July 2015July 2016

July 2017Jupiter Gravity Assist FlybyFeb - Mar 2007

Jupiter

Saturn

LaunchJan 11 - Feb 2, 2006

Planetary positionat Pluto encounterin July 2015

Uranus

Neptune

Onward to Kuiper Belt Object(s)

Fig. 1. New Horizons trajectory.

the retrieval of all PlutoCharon science data. TheKBO encounters are not required to achieve full mis-sion success but are part of an extended mission to

be approved after launch. Therefore, the spacecraftdesign must not preclude operations for up to 18.35years.

Science plans call for the rst KBO rendezvous tooccur by the time the spacecraft reaches a distance of 40 Astronomical Units (AU); the mission would endby the time the spacecraft reaches 50AU.

The distance from Pluto to the Earth during the en-counter is approximately 33 AU. The round-trip lighttime is about 9 h. At a downlink data rate of 600 bps,the encounter data would be transmitted to Earthover a 9-month period using NASAs Deep SpaceNetwork.

5. Spacecraft design drivers

Driver Impact

Long Mission Life

(15.25 years re-quired/18.35 year goal)

Cross-strapped redun-

dant avionics architec-ture; beacon-hiberna-tion mode with coldsparing of redundantcomponents; physicsof failure analysis tovalidate processes andmaterials

Minimize mechanisms,scanning mechanisms,etc. for enhanced relia-bility

Thruster-only con-trol, agile spacecraft,minimum impulse-bitthrusters for ne vehi-cle control

Limited power availablefrom baselined Radio-isotope ThermoelectricGenerator power source

Duty cycling of sci-ence instruments re-quired during encounterto ensure adequate pow-er margins are main-tained
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P l u t o a r r

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Launch date (2006)

17 d

4 d

6 d

4 d

2d

2dLaunch Period: Jan 11 -Feb 14, 2006 (35 days)

JGAJGAPluto-directPluto-direct

Fig. 2. New Horizons 2006 launch window.

Large spacecraft-to-Earth distance at Plutoencounter and longround-trip light traveltime

Low downlink datarates (600 bps) for sci-ence data playback;robust spacecraft au-tonomy design

High launch energy re-quirement

Limits spacecraftlaunch mass to 465 kg(2006 launch opportu-nity)

NASA desire to mini-mize burden on heavilysubscribed DSN

Use of beacon-hiberna-tion mode for cruise be-tween Jupiter and Pluto

The long mission lifetime requirement of 15.25 yearsis within the experience of long-life commercial com-munications satellites. Single-point failures are mini-mized. For example, as seen in the spacecraft block diagram ( Fig. 3 , found at the end of the paper), a hy-brid coupler is designed to cross-strap the Radio Fre-quency (RF) Communications system. This couplerdoes represent a single point failure for the RF sub-system; however, it is a highly reliable passive devicethat has been used in previous deep space missions.

For New Horizons, as with many other JHU/APL-designed spacecraft, deployable mechanisms andscanning platforms are to be kept to a minimum.

Several instruments would have protective covers thatare deployed shortly after launch. One instrumentwould have an internal shutter to operate at the Plutoencounter. The Thermal control system would em-ploy louvers. The spacecraft would have no scanningplatforms or deployment mechanisms. The spacecraft

would operate in a spin-stabilized mode (for launch,early operations, and cruise phases) and in a three-axis mode (for encounter phases). As planned, thespacecraft is required to be agile in the three-axismode in order to provide the proper pointing for thescience instruments. The propulsion system woulduse Cassini-heritage minimum impulse-bit thrustersfor ne attitude control. There are no reaction wheelson board the spacecraft as designed.

Fig. 3 also shows that the spacecraft avionics arecongured in a highly redundant cross-strapped ar-chitecture. The scientic payload design incorporatesphysical redundancy in some elements of the corepayload, and functional redundancy among the instru-ments.

Limited spacecraft power from the baselined Ra-dioisotope Thermoelectric Generator (RTG) wouldrequire that the science instruments be duty cy-cled throughout the encounter to maintain adequatepower margins. The sensitivity of the RTG to powertransients requires strict control of component turn-on transients; a large (33 mF) capacitor bank helps


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Fig. 3. New Horizons spacecraft block diagram.

source these transients, and fast-reacting solid-statecircuit breakers provide further protection againstRTG overloads. The spacecraft must also be able to

autonomously recover from any power faults on thespacecraft bus. The spacecraft power system wouldnot employ a battery.


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PEPSSI

LORRI

RALPH

ALICE

StarTrackersSWAP

HGAMGA

LGA

+X

+Y

+Z

Fig. 4. New Horizons spacecraft.

For the planned mission, the high launch energy re-quired from the launch vehicle and third stage lim-its available spacecraft mass to 465 kg for the 2006launch opportunity. The even higher C3 requirementof 166 .2 km 2/ s2 for the 2007 launch opportunity lim-its spacecraft mass further to only 445kg. This 20kgreduction would be achieved by a reduction in theamount of fuel carried by the spacecraft propulsionsystem.

The long cruise period between Jupiter and Plutowould make use of a beacon-hibernation mode wherethe spacecraft is spin-stabilized with most of theavionics turned off to conserve operating life. Accord-ing to mission plans, the axis of the high gain antennais pointed towards the Earth (see Fig. 4 ). Spacecraftautonomy monitors the health of the spacecraft andbroadcasts a tone, rather than downlinking teleme-try once per week. A green tone is broadcast if the spacecraft autonomy system has not detectedany anomalies. A total of seven red tones may bebroadcast if anomalies are detected, alerting groundcontrollers to take remedial action. This minimizes

the burden on the DSN for spacecraft communicationsduring the cruise period. New Horizons would bethe rst mission to make operational use of a beaconmode; Deep Space One, a NASA JPL mission im-plemented this feature as a technology demonstration[4,5].

6. Spacecraft overview

The New Horizons spacecraft (provided byJHU/APL) is a robust design featuring a heritage-

Fig. 5. Spacecraft primary structure.

based, highly redundant, fault-tolerant architectureallowing for a 31 kg science payload package, whichrequires 21W of electrical power. The primary struc-ture is composed of an aluminum central cylinderthat supports surrounding honeycomb panels ( Fig.5). Power is baselined to be provided by an RTG of the same design as the Cassini RTGs, though withslightly different fuel characteristics. The communi-cations system uses two low-gain antennas (LGA)for early communications and emergency uplinks to5AU, a medium-gain antenna (MGA) for uplink ca-pability to 50AU, and a high-gain antenna (HGA) tosupport 600 bps downlink at 36AU. Thermal controlis accomplished through use of electrical dissipation,RTG waste heat, and a Thermos bottle design.The NH hydrazine monopropellant propulsion sys-tem is integrated into the spacecraft structure to makeeconomical use of mass. The guidance and controlfunctions are accomplished with various sensors andthruster actuators. Command and data handling is

performed with two redundant Integrated ElectronicsModules (IEMs) on a Mil-Std 1553 bus. The IEMsare embedded with many autonomy rules that enablethem to handle anomalies without a ground contact.

The NH spacecraft is designed with a high degree of redundancy and cross strapping to deal with all cred-ible single-point faults and some double-point faults.Some double-point faults (such as providing multipleclocks in hardware and command loss timers in bothsoftware and hardware) are addressed due to the longduration of this planned mission. All nonessential
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subsystems are powered off during the long cruisephase between Jupiter and Pluto/Charon,Pluto/Charonand the rst KBO, and between subsequent KBOs,

in order to increase reliability for the overallmission. Redundant units of essential compo-nents (command receivers, Power Distribution Unit(PDU) command decoders, Ultra-Stable Oscilla-tors (USOs), Command & Data Handling (C&DH)processors, and PDU 1553s) can be switched off,but are automatically switched on in the eventof a fault in the redundant unit or when space-craft power is applied. At least one side of a re-dundant pair of essential components is alwayson.

As currently planned, the instruments are located onthe spacecraft panels opposite the RTG, limiting radia-tion and thermal effects.Additionally, a thermal shieldwould prevent excess RTG waste heat from affect-ing the spacecraft thermal balance. The instrumentsare xed-mounted, so coverage of PlutoCharon isobtained by spacecraft maneuvers. Thus, deployablemechanisms are minimized, increasing overall missionreliability.

7. Structure

The spacecraft structure is designed to support thescience instrument sensors, spacecraft subsystems,and electronic packages; maintain proper dimensionalrelationships, instrument alignments and clear eldsof view (FOVs); and efciently distribute loads asso-ciated with transportation, lifting, handling, launch,and ight operations.

The primary structure is composed of an aluminum7075-T73 central cylinder that supports the surround-

ing honeycomb panels to complete the NH structureas shown in Fig. 5 . The primary structure measuresapproximately 0 .68 m 2.11 m 2.74 m. The centralcylinder serves as the payload adapter tting (PAF),supports the RTG/SC interface, and houses the propel-lant tank. The panels surrounding the central cylinderhave a core of aluminum honeycomb with aluminumface sheets.

In addition to the launch vehicle and instrument sup-port stated above, the spacecraft structure also housesall the other subsystems of the spacecraft and provides

the following:

Suitable guidance and control sensor placements,with clear FOVs.

Accessibility and exibility for integration andtest.

Spin stabilization with correct inertia properties. High-gain antenna mounting support. Thruster mounting and operation support. Transportation and handling survival/stability. Launch survival/stability.

8. Power subsystem

The power subsystem is designed to provide thespacecraft with sufcient power throughout the mis-sion. It provides 30V (nominal) power to the space-craft essential and nonessential loads. The spacecraftbaselined power subsystem consists of the RTG, aninternally redundant PDU with power transient man-agement capabilities, a fault-tolerant, majority-votedShunt Regulator Unit (SRU), and a bank of powerbus capacitors. (The baseline design does not includebatteries.)

To protect the power bus, the RTG and power bus aredesigned to be double insulated, all power-switchingcards are fuse protected, and all individual switchedloads have a circuit breaker function. The PDU hasfully redundant power-switching and distribution elec-tronics. The spacecraft SRU would be tied directly tothe RTG, maintaining it at a regulated 2931V.

The RTG baselined for use on the NH mission isa General Purpose Heat Source RTG supplied by theDepartment of Energy (DOE) with support from Lock-heed Martin. Because RTG-based power systems donot typically employ batteries, careful attention is paid

to specifying maximum limits for transients due tothe switching of loads, operational load transients, andfault conditions. The power bus response to these tran-sients would be controlled by the combination of abus capacitor bank, current limiters and electronic cir-cuit breakers. Power consumed by the NH spacecraftwould be managed so as not to exceed the steady-state output of the RTG, which will decrease overtime. In vacuum, at the beginning of the mission, theRTG would supply approximately 253 (TBD) W at30VDC. It is expected that in July 2015, the earliest


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Pluto encounter date, the RTG will supply approxi-mately 202 (TBD) W at 30 VDC.

9. Thermal control subsystem

The electrical power limitations and the naturalthermal leakage through the multi-layer insulationblankets and instrument/component apertures drivethe New Horizons thermal design. The thermal designuses a Thermos bottle approach, which balancesthe internal dissipation with the naturally occurringleaks. As designed, the spacecraft body is almostcompletely surrounded with thermal blankets. Thedesign calls for utilization of some of the waste heatprovided by the baselined RTG power source. Ther-mal louvers are included to provide additional thermalbalance, if the spacecraft temperatures are too high.Power not dissipated inside the spacecraft bus wouldbe dissipated on two external shunt plates. Each plateshares the total shunt current, and they are sized toreject the RTG maximum power while looking atthe sun at 1AU. As planned, the propulsion systemcomponents are thermally tied to the spacecraft busand are kept warm through thermal contact with thestructure. Heat leaks from the thruster modules andother penetrations through the thermal blankets areaccounted for in the thermal design. Heat pipes arenot used in the thermal control subsystem design.

10. RF communications subsystem

The RF communications subsystem is designed toprovide the required science data return, a reliablecommand/telemetry link, precise radiometric track-ing, and to be supported by four antennas. The radio

science experiment (REX) would be integrated intothe RF subsystem. The NASA Deep Space Network would transmit signals to the NH spacecraft for theradio science to achieve the required signal-to-noiseratio. The on-board RF receiver would be a new, low-power digital design, and an enabling technology forthis mission.

The antennas are shown schematically in the block diagram of Fig. 3 and are depicted graphically in Fig.4 (with the exception of the aft LGA, which is onthe opposite side of the spacecraft). Switching be-

tween the four antennas is accomplished through anRF switching assembly controlled from the spacecraftCommand and Data Handling (C&DH) subsystem.

The entire communications system is redundant ex-cept for the antennas and the hybrid coupler in thedownlink path. All antennas have Right Hand Circu-lar (RHC) and Left Hand Circular (LHC) polarizationfeeds. To accommodate spin-stabilized attitude con-trol, all antenna boresights are aligned with the spinaxis (+ Y ) of the spacecraft.

Together the forward and aft LGAs (broad beam, 40 3-dB beamwidth) provide spherical coverage.These LGAs are used during the early operations phaseand any pre-Jupiter encounter emergency mode. TheMGA (0.3 m dish, 5 3-dB beamwidth) is focus-fedand can be used for commanding at 7.8 bps out to50AU using a pointing accuracy of 4 . The HGA(2.1 m dish, 0.5 3-dB beam width) is a dual re-ector and is used in nominal mode for uplink anddownlink. Uplink and downlink are accomplished bytwo sets of X-band (7/8 GHz) transceivers, two Ultra-Stable Oscillators (USOs), and two Traveling WaveTube Ampliers (TWTAs). The USOs and TWTAs arecross-strapped to the IEMs.

11. Propulsion subsystem

The New Horizons propulsion system would impartlarge velocity burns and ne attitude control as thespacecraft makes its way to PlutoCharon. The 80 kghydrazine fuel load provides 397 m/s delta-V for the2006 launch mass of 465kg. The use of a Jupiter grav-ity assist, along with the fact that NH would not enterorbit around Pluto, reduces the amount of propellantrequired for the mission.

As planned, the NH propulsion system is mounted

directly to the structure. The system includes fourmonopropellant 4.4 N V thrusters and 12 smallermonopropellant 0.8N thrusters positioned aroundthe spacecraft. The individual thrusters are mountedon the spacecraft in eight locations: four groupings(called Rocket Engine Modules) and four independentthrusters. The hydrazine would be stored in a titaniumtank separated from the gaseous nitrogen pressurantby a girth-mounted diaphragm.

The propulsion system, which includes functionalredundancy, would provide small minimum-impulse


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bit performance to achieve accurate three-axis attitudecontrol for science imaging operations. The systemwould also support both three-axis and spinning V

maneuvers. Nitrogen would provide the pressure toensure ow from the tank to the various thrusters.Flow control and thruster ring are handled with

in-line latch valves and thruster valves, respectively.The layout (shown in Fig. 3 ) is designed to improvesystem fault tolerance.

12. Guidance and Control subsystem

The Guidance and Control (G&C) subsystem is de-

signed to determine and control the spacecrafts atti-tude. This system is responsible for de-spinning andde-tumbling the spacecraft following third-stage sep-aration. It must provide for three-axis and spinningoperational modes, and provide accurate and stablepointing for instrument observations and communica-tions. The G&C subsystem also executes trajectorycorrection maneuvers, which impart translational V for trajectory control.

G&Cs sensor and actuator suite consists of two startrackers from Galileo Avionica; two Honeywell In-

ertial Measurement Units containing three gyros andthree accelerometers each; two Adcole-developed sunsensors (Fine Sun Sensor and Sun Pulse Sensor); andthe 16 propulsion system thrusters. There are no reac-tion wheels in the design; all spacecraft control is per-formed via thrusters. G&C would interface with thepropulsion system thrusters through the PDU. G&Csoftware resides redundantly in the two G&C (Mon-goose V) Processors located in the IEMs.

The NH G&C software is designed to support threeseparate ight modes: passive spin, active spin, andthree-axis. While in the spinning modes, the spacecraftwould nominally spin at 5 rpm about the + Y axis. Inthree-axis mode, the spacecraft would be commandedto track a celestial body at a parameterized rate or holdan inertial attitude.

13. Command and Data Handling subsystem

The functions provided by the C&DH subsystem arecommand management, telemetry management, time

distribution, power/thermal management, and auton-omy rule evaluation and execution.

On NH, resources within the IEMs would imple-

ment the C&DH functions. Of the nine cards in eachIEM, the C&DH functions would be spread across vecards:

C&DH Processor Card. Solid State Recorder (SSR) Card. Instrument Interface Card. Critical Command Decoder (CCD), on the Up-

link Card. Downlink Formatter on the Downlink Card.

In addition to the cards in the IEM, the external Re-mote Input/Output (RIO) units would provide temper-ature and voltage measurements for monitoring thehealth and safety of the spacecraft.

Communication between cards within the C&DHsection of the IEM would be over a Peripheral Com-ponent Interconnect (PCI) backplane. RIOs are de-signed to connect to the IEMs on an I 2C bus. AMIL-STD-1553 serial bus interface would be usedbetween the IEMs to allow for redundancy and cross-strapping.

During normal operations, the C&DH section of oneIEM would be fully powered and designated as prime.The prime C&DH processor would be the 1553 buscontroller and is responsible for all spacecraft func-tions. The plan is to power the C&DH section of thesecond IEM, but in standby mode, during most oper-ations.

During beacon-hibernation, however, the secondC&DH section is planned to be powered off to in-crease the system reliability. If a failure in the primeIEM occurs, the second IEM is fully powered anddesignated as the new prime. As designed, full redun-

dancy is provided for C&DH including data storage,RF communications, and G&C processing.The C&DH processor distributes all non-critical

commands to the addressed subsystem, collectsand processes instrument data, sequences downlink telemetry, and performs advanced autonomy algo-rithms for operations. The C&DH processor evaluatesthe performance of the spacecraft by monitoringthe data ow and content of the 1553 data bus. Alow-power, 8-Gbyte SSR card, using ReedSolomonerror-correcting code, stores data between ground


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contacts. The instrument interface card provides RS-422 interfaces to six instruments, and high-speedLVDS interfaces for images and radio science data.

14. Conclusion

The New Horizons mission would complete ourpreliminary reconnaissance of the planets in our so-lar system by exploring Pluto, the farthest planet fromthe sun, and its moon, Charon. The New Horizonsspacecraft and instrument suite is designed to fulllthe missions scientic objectives by employing a ro-bust architecture with considerable redundancy to en-

sure mission success at Pluto and beyond. Spacecraftand instrument development are on track for a January2006 launch opportunity.

Acknowledgements

The authors gratefully acknowledge the contribu-tions and accomplishments of the entire New Horizonsteam of scientists and engineers whose unagging

efforts resulted in the realization of the vision. Specialmention must be made of Dr. S. Alan Stern, whosededication to a New Horizons mission has been the

embodiment of persistence and perseverance.

References

[1] S.A. Stern, Journey to the farthest planet, Scientic AmericanMay 2002, pp. 5663.

[2] Y. Guo, R.W. Farquhar, New Horizons Pluto-Kuiper Beltmission: Design and simulation of the PlutoCharon encounter,IAC Paper, IAC-02-Q.2.07, 53rd International AstronauticalCongress, The World Space Congress-2002, October 1019,2002, Houston, Texas.

[3] Y. Guo, R.W. Farquhar, New Horizons mission design forthe PlutoKuiper Belt mission, AIAA/AAS Paper, AIAA-2002-4722, AIAA/AAS Astrodynamics Specialist Conference,August 58, 2002, Monterey, California.

[4] E.J. Wyatt, et al., Beacon Monitor operations on the DeepSpace One mission, Fifth International Symposium on SpaceMissions Operations and Ground Data Systems, Tokyo, Japan,1997.

[5] R. Sherwood, et al., Lessons learned during implementation andearly operations of the DS1 Beacon Monitor experiment, ThirdInternational Symposium on Reducing the Cost of GroundSystems and Spacecraft Operations, Tainan, Taiwan, 1999.

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A description of the Pluto-bound New Horizons spacecraft.pdf