Instrument Host Information
This description is based on several sources used with the                    
permission of the New Horizons project, SWRI and JHU/APL:                     
- Stern & Spencer, New Horizons: The First Reconnaissance Mission to          
  Bodies in the Kuiper Belt, 2004 [STERN&SPENCER2004A]                        
- The New Horizons web page originally at                                                                                  
    The New Horizons spacecraft observatory includes propulsion,              
    navigation, and communications systems, plus the payload. The             
    spacecraft is roughly 2.5 meters across and its mass is 465 kg            
    including propellant. Design features include 64 Gbits of redundant       
    solid-state data storage, a 290 m/s propulsion budget, and the            
    capability to transmit data from 32 AU at almost 1 kilobit/second.        
    The instrument payload [Stern & Cheng, 2002, STERN&CHENG2002]             
    comprises the two-sensor RALPH Vis-IR remote sensing package, the         
    ALICE UV imaging spectrograph, the REX radio/radiometry experiment,       
    the two-sensor PEPSSI/SWAP plasma suite, the LORRI long-focal-length      
    imager, and the SDC student-built dust counter.                           
    The New Horizons team selected instruments that not only directly         
    measure NASA-specified items of interest (NASA AO 01-OSS-01, 2001,        
    [NASAAO2001]), but also provide backup to other instruments on the        
    spacecraft should one fail during the mission.                            
    The payload comprises seven instruments:                                  
      The main objectives for the RALPH instrument are to obtain high         
      resolution color maps and surface composition maps of the surfaces      
      of Pluto and Charon. The instrument has two separate channels: the      
      Multispectral Visible Imaging Camera (MVIC) and the Linear Etalon       
      Imaging Spectral Array (LEISA). A single telescope with a 3-inch        
      (6-centimeter) aperture collects and focuses the light used in both     
      RALPH/MVIC operates at visible wavelengths and has 4 different          
      filters for producing color maps. One filter allows measurement of      
      the methane frost distribution over the surface (860-910nm), while      
      the others are more generic and cover blue (400-550nm), red             
      (540-700nm) and near-infrared colors (780-975nm), respectively. MVIC    
      also has two panchromatic filters that pass essentially all visible     
      light (400-975nm).  This will be useful for low-light level             
      observations requiring maximum sensitivity.  In all cases, the light    
      passes from the telescope through the filters and is focused onto a     
      charge coupled device (CCD).                                            
      RALPH/LEISA operates at infrared wavelengths (1.25-2.5 micron,          
      plus a separate section of higher resolving power covering 2.1 to       
      2.25 micron); its etalon (wedged filter with a narrow spectral          
      bandpass that varies linearly in one dimension) is bonded to the        
      illuminated side of the IR detector.  As a result, each row of          
      detector pixels receives only light of a particular wavelength.         
      Spectral maps are produced by sweeping the FOV of the instrument        
      across a scene, sequentially sampling each point in the scene at each   
      wavelength.  LEISA maps the distribution of frosts of methane (CH4),    
      molecular nitrogen (N2), carbon monoxide (CO), and water (H2O) over     
      the surface of Pluto and the water frost distribution over the          
      surface of Charon.  LEISA data may also reveal new constituents on      
      the surfaces that have never before been detected.                      
      Alice is an ultraviolet imaging spectrograph that probes the            
      atmospheric composition of Pluto.                                       
      The Alice wavelength range is from 520 - 1870 Angstroms. Alice          
      has two modes of operation: an airglow mode, which measures             
      emissions from atmospheric constituents, and an occultation mode,       
      which views either the Sun or a bright star through the atmosphere      
      producing absorption by the atmospheric constituents. The Alice         
      occultation mode occurs just after New Horizons passes behind Pluto     
      and looks back at the Sun through the Pluto atmosphere.                 
      REX is an acronym for Radio EXperiment. It is integrated into the       
      New Horizons radio telecommunications system.                           
      Using an occultation technique similar to that described above for      
      the Alice instrument, REX probes the Pluto atmosphere. After New        
      Horizons flies by Pluto, its 2.1 meter radio antenna points back at     
      Earth. On Earth, powerful radio transmitters in the NASA Deep Space     
      Network (DSN) point at New Horizons and send radio signals to the       
      spacecraft.  As the spacecraft passes behind Pluto, the atmosphere      
      bends the radio waves by an amount that depends on the average          
      molecular weight of the gas in the atmosphere, the atmospheric          
      temperature, and the closest approach distance of the raypath at        
      each instant of time. REX samples the received radio signal and         
      sends the data back to Earth for analysis                               
      REX also has a radiometry mode, which measures the weak radio           
      thermal emission from Pluto itself. When REX looks back at Pluto        
      following the flyby, radiometry data are taken to derive a value for    
      the Pluto nightside temperature.                                        
      The instrument that provides the highest spatial resolution on New      
      Horizons is LORRI - short for LOng Range Reconnaissance Imager -        
      which comprises a telescope with a 20.8cm aperture that focuses         
      visible light (350 - 850nm) onto a charge coupled device (CCD).         
      LORRI has a very simple design; there are no filters or moving          
      parts. Near the time of closest approach, LORRI takes images of         
      the Pluto surface at 100m resolution.                                   
      The Solar Wind Analyzer around Pluto (SWAP) instrument measures         
      charged particles from the solar wind near Pluto to determine           
      whether Pluto has a magnetosphere and how fast the atmosphere is        
      Another plasma-sensing instrument, the Pluto Energetic Particle         
      Spectrometer Science Investigation (PEPSSI), searches for neutral       
      atoms that escape the Pluto atmosphere and subsequently become          
      charged by their interaction with the solar wind.                       
      The Student Dust Counter, which was later re-named The Venetia          
      Burney Student Dust Counter (SDC), is an Education and Public           
      Outreach project.  SDC measures the dust density of the                 
      Interplanetary Dust Particles (IDP) by measuring the charge             
      generated in the SDC sensor from dust impact events.  From this may     
      be inferred the size and distribution of dust particles along the       
      entire New Horizons trajectory, including regions of interplanetary     
      space never before sampled.  Such dust particles are created by         
      comets shedding material and Kuiper Belt Objects (KBOs) colliding       
      with other KBOs.  The SDC is managed and was built primarily by         
      students at the University of Colorado in Boulder, with supervision     
      from professional space scientists and engineers.                       
      The SDC is located on the -Y side of the spacecraft near the -X edge    
      of that side, near the star trackers, so it will be near the            
      direction-of-flight side of the spacecraft during most cruise, spin     
      and hibernation activities.                                             
  Spacecraft reference frame (a.k.a. Coordinate system)                       
    During hibernation and other periods of inactivity, the spacecraft is     
    designed to spin about its +Y axis, which is also the nominal             
    boresight of the High Gain Antenna (HGA) and REX.  Imaging instruments    
    have nominal boresights pointing along the -X spacecraft axis.  The       
    RTG (see Power below) is a cylinder extending out along the +X            
    spacecraft axis to keep it away from the instruments.  The +Z axis        
    completes a right-handed three-dimensional Cartesian coordinate           
    system.  Note that each instrument has its own reference frame.           
    The following two sketches, extracted from the SPICE Frames kernel,       
    represent the spacecraft as viewed from the spacecraft +X and +Y          
    directions.  The instrument locations are approximate; refer to           
    [STERNETAL2008] and [FOUNTAINETAL2008] for more detail.                   
Spacecraft sketches                                                           
     +X view:                                                                 
                                   / | \                                      
                                  /  |  \                                     
                                 /   |   \                                    
                                /    |    \                                   
                               /     |     \                                  
           `-.                                   HGA(REX)   ,-'               
              `-.                                        ,-'                  
                 `-.                                  ,-'  __                 
                    `-.____________________________,-'    /  / PEPSSI         
         .-|                |               |                |______          
   Alice | |                |      RTG      |                |     ||         
         '-|                |     .-*-.     |                |_____|| SWAP    
           |                |    /     \    |                |     ||         
      |----|                |    \     /    |                |     ||         
      |    |                |     '-.-'     |                |                
Ralph |___ |                |               |                |                
      |    |________________|_______________|________________|                
                 [_________|_ _ _ _]    +X (out of page)                      
             SDC*         /__<------o_________\                               
                            +Zsc    |       adapter ring                      
  *  N.B. In the graphic above, SDC                                           
     is behind, i.e. in the -X direction                                      
     from, the adapter ring                                                   
     +Y view:                                                                 
             ||   SWAP                                                        
           _|__|______   __..---..__                                          
          | |  \     _`-'           ``-.   HGA(REX)                           
   PEPSSI | ----  _'     `-_            `-.                                   
          |     .'          `-_            `.                                 
        .-|   ,                `-_           `.                               
  LORRI : |  .                    `-_          `.                             
        : | /                        `-_         \                            
        '-|.                            `-_       . _______   _______         
          |'                .-*-.          `-_    ||+|+|+|+| |+|+|+|+|        
          |   SDC**        /     \            `|--`-------------------|       
          + - - +         !   o-----> +X       |  |                   |       
          |                \  |  /           _,|--.-------------------|       
 ASTR 1 \ |.    |           '-|-'         _,-     ||+|+|+|+| |+|+|+|+|        
        \\|'                  |        _,-        ' -------   -------         
  Star   \| '   |             V     _,-          /    RTG (Radioisotope       
Trackers  |  `               +Z  _,-            .          Thermoelectric     
         /+ - - +             _,-              -           Generator)         
        //|    `.          _,-               .'                               
 ASTR 2 / |       '.    _,-              _.-'                                 
          |__________',-__         __,,,''                                    
            |     |       '' --- ''                                           
            |     |                                                           
            `-----'  Alice and Ralph                                          
 **  N.B. In the graphic above, SDC                                           
     is behind, i.e. on the -Y side                                           
     of, the spacecraft                                                       
    The spacecraft has three antenna systems:  Low-, Medium- and High-Gain    
    Antennas (LGA, MGA, HGA).  The New Horizons mission operations team       
    communicates with the spacecraft through the Deep Space Network (DSN).    
    The DSN comprises facilities in the Mojave Desert in California; near     
    Madrid, Spain; and near Canberra, Australia.                              
    Electrical power for the New Horizons spacecraft and science              
    instruments is provided by a single radioisotope thermoelectric           
    generator, or RTG, supplied by the Department of Energy.  The New         
    Horizons trajectory takes it into the Kuiper Belt and more than six       
    billion kilometers from Earth, where light from the Sun is over           
    1,800 times fainter than at Earth.  An RTG is used on missions, such      
    as New Horizons, that can not use solar power yet require a proven,       
    reliable power supply that can produce up to several kilowatts of         
    power and operate under severe environmental conditions for many          
    Carrying out the New Horizons mission safely is a top priority at         
    NASA. As part of that focus, NASA informed the public about use by New    
    Horizons of an RTG by publishing a detailed Environmental Impact          
    Statement - or EIS - and several fact sheets. The Final EIS, which        
    includes public comments on the Draft EIS and the NASA responses to       
    those comments, was released in July 2005.                                
    The propulsion system (see [FOUNTAINETAL2008], section 3) includes        
    twelve 0.8N thrusters, four 4.4N thrusters, and the hydrazine             
    propellant tank and associated control valves. The titanium               
    propellant/pressurant tank feeds the thrusters through a system           
    filter, a flow control orifice, and a set of latch valves that prevent    
    flow of the fuel until commanded to the open position after launch.       
    Helium was selected as the tank pressurant instead of nitrogen to         
    allow the loading of an additional kilogram of hydrazine. Measurements    
    of tank pressure and temperatures at various points in the system         
    allow the mission operations team to monitor system performance and       
    the amount of fuel remaining in the tank.                                 
    The 16 rocket engine assemblies (REAs) are organized into 8 sets and      
    placed on the spacecraft as shown in Figure 5 of [FOUNTAINETAL2008].      
    Pairs of the 0.8N thrusters (each thruster from a different set) are      
    usually fired to produce torques and control rotation about one of the    
    three spacecraft axes. The one exception to the use of coupled thruster   
    firings to control spacecraft rates is that of controlling rates about    
    the spacecraft X axis during science observations, where uncoupled        
    thruster firings are required to meet the maximum spacecraft drift        
    rates allowed during this operation mode. Control rates for each of       
    the spacecraft axes are shown in [FOUNTAINETAL2008] Table 2.  One pair    
    of the 4.4N thrusters is aligned along the -Y spacecraft axis to          
    provide delta-V for large propulsive events such as trajectory            
    correction maneuvers (TCMs). The second pair of 4.4N thrusters is         
    aligned to produce thrust along the +Y axis. These thrusters are          
    rotated 45 degrees in the YZ plane to minimize the plume impingement      
    on the HGA dish. The net propulsive effect of these thrusters is          
    therefore reduced. They still provide the required redundancy and the     
    ability to generate thrust in both directions without a 180-degree        
    rotation of the spacecraft.                                               
    Each thruster requires a heater to warm its catalyst bed to a minimum     
    temperature prior to use. Each thruster catalyst bed has both a           
    primary and a secondary heater element, with each element drawing         
    approximately 2.2 W of power. Control of the catalyst bed heater          
    circuits is grouped functionally by pairs (to minimize the number of      
    switches required), so that a total of 16 switches control the heater     
    elements, allowing great flexibility to operate the spacecraft safely     
    while drawing the minimum required power.                                 
    The pulse duration and total on-time of each thruster are commanded       
    very precisely, providing accurate control of the total impulse           
    generated during a maneuver. The 0.8N thrusters can be turned on for      
    periods as short as 5 ms. The initial propellant load was allocated       
    between primary mission TCMs, attitude control (including science and     
    communication operations), and primary mission margin. At the end of      
    the primary mission, sufficient margin may allow for an extended          
    mission to one or more objects in the Kuiper Belt. The original margin    
    was augmented during the final mission preparations when the unused       
    dry mass margin was converted to additional propellant.                   
    Given the mass and moments of inertia at launch, the delta-V              
    propellant cost is approximately 4.9 m/s/kg. A change in spin rate of     
    5 rpm (i.e., the change from the nominal spin rate to zero rpm for        
    3-axis control mode) requires approximately 0.125 kg of hydrazine.        
    Propellant budget allocations                                             
                                        delta-V   Propellant                  
        Description                         m/s           kg                  
        -----------------------------   -------   ----------                  
        Primary mission TCM                 110         22.3                  
        Attitude control                    N/A         29.3                  
        Primary mission margin              132         25.2                  
         - original margin allocation      ( 91)       (17.5)                 
         - Additional margin obtained      ( 41)       (29.3)                 
           from unused spacecraft dry                                         
           mass allocation                                                    
        Total navigation delta-V            242                               
        Total propellant load                           76.8