Appendix A.

List of SPICE Kernels

All SPICE kernel types are contained in the list below.

SPK	"Ephemeris kernel, containing position and often velocity of as object relative to another object. May contain data for many objects. Might contain reconstruction (historical) data, or predictive data, or both types.
PCK	Planetary constants kernel, containing size, shape and orientation of solar system bodies. May contain additional physical or carographic data as well. Both text and binary forms exist. The binary form is available for just a few bodies and contains only orientation data. SPICE APIs made to read PCKs can read both types. Text PCKs are usually prepared using data endorsed by the International Astronomical Union.
IK	Instrument kernel, containing field-of-view size, shape and orientation for science instruments, and for any other spacecraft assembly for which field-of-view information given in the SPICE style could be useful (e.g. star tracker, high-gain antenna, heat radiator).
CK	Camera-matrix kernel, providing time-varying orientation (attitude) of a spacecraft bus or any attached struture that can be aritculated and for which oreintation data are available, such as a high-gain antenna, solar arrays, a rover's sampling arm, or an instrument's moveable scanning mirror. May contain rate data as well as position data, if available. Might contain reconstruction (historical) data, or predictive data, or both types.
EK	Events kernel, intended to logically encompas three kinds of information: science observation plans (ESP), science observation sequence specifications (ESQ) and scientist' notebook comments (ENB). The EK portion of SPICE was rarely used and should be considered depricated.
FK	Frames kernel, provides specifications for the many mission-specific reference frames defined for a mission. Typically included are the spacecraft bus, antennas and solar arrays, and instruments (often reffered to as "instrument mounting alignment"). Note that a variety of generic reference frames�ones not uniquely associated with a given mission�are also available to SPICE users: these specifications are hard-coded in SPICE Toolkit software. (Note that NAIF uses the term "reference frame" or simply "frame" where many people use the term "coordinate system." Within SPICE a "coordinate system" defines the method by which positions within a "reference frame" are measured: e.g. Cartesian coordinates, polar coordinates, etc.)
LSK	Leap seconds kernel, providing a tabulation of leap seconds declared by the International Earth Rotation Service (IERS) plus a few related terms, all needed for time conversions between Universal Time Coordinated (UTC, sometimes referred to as SCET) and Barycentric Dynamical Time (TDB), also reffered to within SPICE as Ephemeris Time (ET).
SCLK	Spacecraft clock kernel, a tabulation of spacecraft clock correlation parameters computed by others and used within SPICE, along with the LSK, for time conversions between spacecraft clock time (also called SCLK) and barycentric dynamical time (TDB).� (On rare occasions a time system other than barycentric dynamical time is used as one of the two time systems.)
DSK	Digital shape kernel, providing high-precision shape information for (usuall) solar system bodies. The DSK allows for two kinds of shape information: a tessellated plate model and a digital elevation model. Where appropriate source data exist for making a DSK, the DSK can substitute for the very simple tri-axial shape model data contained in a text-style PCK.� But note that unlike for a text PCK a DSK contains ONLY shape information: a text PCK must be used for the orientation of the object in question. The DSK design offers many features not usually found in other shape representations.

Appendix B.

Example of a SPICE Toolkit API Header

Below is an example of a Toolkit API "header." This is for the C language version of an API named SPKPOS, used to read an SPK (ephemeris) file and return the position of a "target" relative to an "observer."

-Procedure spkpos_c ( S/P Kernel, position )

-Abstract

�

�� Return the position of a target body relative to an observing

�� body, optionally corrected for light time (planetary aberration)

�� and stellar aberration.

�

-Disclaimer

�� THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE

�� CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S.

�� GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE

�� ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE

�� PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS"

�� TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY

�� WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A

�� PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC

�� SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE

�� SOFTWARE AND RELATED MATERIALS, HOWEVER USED.

�� IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA

�� BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT

�� LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND,

�� INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS,

�� REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE

�� REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY.

�� RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF

�� THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY

�� CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE

�� ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE.

-Required_Reading

�

�� SPK

�� NAIF_IDS

�� FRAMES

�� TIME

�

-Keywords

�

�� EPHEMERIS

�

�� #include "SpiceUsr.h"

�� #include "SpiceZfc.h"

�� #include "SpiceZmc.h"

��

�� void spkpos_c ( ConstSpiceChar�� * targ,

�� SpiceDouble�� et,

�� ConstSpiceChar�� * ref,

�� ConstSpiceChar�� * abcorr,

�� ConstSpiceChar�� * obs,

�� SpiceDouble�� ptarg[3],

�� SpiceDouble�� * lt�� )

-Brief_I/O

�

�� Variable� I/O� Description

�� --------� ---� --------------------------------------------------

�� targ�� I�� Target body name.

�� et�� I�� Observer epoch.

�� ref�� I�� Reference frame of output position vector.

�� abcorr�� I�� Aberration correction flag.

�� obs�� I�� Observing body name.

�� ptarg�� O�� Position of target.

�� lt�� O�� One way light time between observer and target.

�

-Detailed_Input

�

�� targ�� is the name of a target body.� Optionally, you may

�� supply the integer ID code for the object as

�� an integer string.� For example both "MOON" and

�� "301" are legitimate strings that indicate the�

�� moon is the target body.

�

�� The target and observer define a position vector

�� which points from the observer to the target.

�

�� et�� is the ephemeris time, expressed as seconds past

�� J2000 TDB, at which the position of the target body

�� relative to the observer is to be computed.� `et'

�� refers to time at the observer's location.

�

�� ref�� is the name of the reference frame relative to which

�� the output position vector should be expressed. This

�� may be any frame supported by the SPICE system,

�� including built-in frames (documented in the Frames

�� Required Reading) and frames defined by a loaded

�� frame kernel (FK).

�

�� When `ref' designates a non-inertial frame, the

�� orientation of the frame is evaluated at an epoch

�� dependent on the selected aberration correction. See

�� the description of the output position vector `ptarg'

�� for details.

�

�� abcorr�� indicates the aberration corrections to be applied to

�� the position of the target body to account for

�� one-way light time and stellar aberration.� See the

�� discussion in the Particulars section for

�� recommendations on how to choose aberration

�� corrections.

��

�� 'abcorr' may be any of the following:

�

�� "NONE"�� Apply no correction. Return the�

�� geometric position of the target body�

�� relative to the observer.��

�

�� The following values of 'abcorr' apply to the

�� "reception" case in which photons depart from the

�� target's location at the light-time corrected epoch

�� et-lt and *arrive* at the observer's location at `et':

�

�� "LT"�� Correct for one-way light time (also

�� called "planetary aberration") using a

�� Newtonian formulation. This correction

�� yields the position of the target at

�� the moment it emitted photons arriving

�� at the observer at `et'.

�

�� The light time correction uses an

�� iterative solution of the light time

�� equation (see Particulars for details).

�� The solution invoked by the "LT" option

�� uses one iteration.

�

�� "LT+S"�� Correct for one-way light time and

�� stellar aberration using a Newtonian

� ��formulation. This option modifies the

�� position obtained with the "LT" option

�� to account for the observer's velocity

�� relative to the solar system

�� barycenter. The result is the apparent

�� position of the target---the position

�� as seen by the observer.

�

�� "CN"�� Converged Newtonian light time

�� correction.� In solving the light time

�� equation, the "CN" correction iterates

�� until the solution converges (three

�� iterations on all supported platforms).

�

�� The "CN" correction typically does not

�� substantially improve accuracy because

�� the errors made by ignoring

�� relativistic effects may be larger than

�� the improvement afforded by obtaining

�� convergence of the light time solution.

�� The "CN" correction computation also

�� requires a significantly greater number

�� of CPU cycles than does the

�� one-iteration light time correction.

�

�� "CN+S"�� Converged Newtonian light time

�� and stellar aberration corrections.

�

�� The following values of 'abcorr' apply to the

�� "transmission" case in which photons *depart* from

�� the observer's location at `et' and arrive at the

�� target's location at the light-time corrected epoch

�� et+lt:

�

�� "XLT"�� "Transmission" case:� correct for

�� one-way light time using a Newtonian

�� formulation. This correction yields the

�� position of the target at the moment it

�� receives photons emitted from the

�� observer's location at `et'.

�

�� "XLT+S"� ��"Transmission" case:� correct for one-way

�� light time and stellar aberration using a

�� Newtonian formulation.� This option

�� modifies the position obtained with the

�� "XLT" option to account for the observer's

�� velocity relative to the solar system

�� barycenter. The computed target position

�� indicates the direction that photons

�� emitted from the observer's location must

�� be "aimed" to hit the target.

�� "XCN"�� "Transmission" case:� converged�

�� Newtonian light time correction.

�

�� "XCN+S"�� "Transmission" case:� converged�

�� Newtonian light time and stellar�

�� aberration corrections.

�

�� Neither special nor general relativistic effects are

�� accounted for in the aberration corrections applied

�� by this routine.

�

�� Case and blanks are not significant in the string

�� 'abcorr'.

�

�� obs�� is the name of an observing body.� Optionally, you may

�� supply the ID code of the object as an integer string.

�� For example, both "EARTH" and "399" are legitimate

�� strings to supply to indicate the observer is

�� Earth.

�

-Detailed_Output

�

�� ptarg�� is a Cartesian 3-vector representing the position of

�� the target body relative to the specified observer.

�� `ptarg' is corrected for the specified aberrations, and

�� is expressed with respect to the reference frame

�� specified by `ref'.� The three components of `ptarg'

�� represent the x-, y- and z-components of the target's

�� position.

�

�� Units are always km.

�� `ptarg' points from the observer's location at `et' to

�� the aberration-corrected location of the target.

�� Note that the sense of this position vector is

�� independent of the direction of radiation travel

�� implied by the aberration correction.

�

�� Non-inertial frames are treated as follows: letting

�� ltcent be the one-way light time between the observer

�� and the central body associated with the frame, the

�� orientation of the frame is evaluated at et-ltcent,

�� et+ltcent, or `et' depending on whether the requested

�� aberration correction is, respectively, for received

�� radiation, transmitted radiation, or is omitted. ltcent

�� is computed using the method indicated by 'abcorr'.

�

�� lt�� is the one-way light time between the observer and

�� target in seconds. If the target position is

�� corrected for aberrations, then `lt' is the one-way

�� light time between the observer and the light time

�� corrected target location.

�

-Parameters

�

�� None.

�

-Exceptions

�

�� 1) If name of target or observer cannot be translated to its

�� NAIF ID code, the error SPICE(IDCODENOTFOUND) is signaled.

�

�� 2) If the reference frame `ref' is not a recognized reference

�� frame the error SPICE(UNKNOWNFRAME) is signaled.

�

�� 3) If the loaded kernels provide insufficient data to�

�� compute the requested position vector, the deficiency will

�� be diagnosed by a routine in the call tree of this routine.

�

�� 4) If an error occurs while reading an SPK or other kernel file,

�� the error� will be diagnosed by a routine in the call tree�

�� of this routine.

�

-Files

�

�� This routine computes positions using SPK files that have been

�� loaded into the SPICE system, normally via the kernel loading

�� interface routine furnsh_c. See the routine furnsh_c and the SPK

�� and KERNEL Required Reading for further information on loading

�� (and unloading) kernels.

�

�� If the output position `ptarg' is to be expressed relative to a

�� non-inertial frame, or if any of the ephemeris data used to

�� compute `ptarg' are expressed relative to a non-inertial frame in

�� the SPK files providing those data, additional kernels may be

�� needed to enable the reference frame transformations required to

�� compute the position.� These additional kernels may be C-kernels, PCK

�� files or frame kernels.� Any such kernels must already be loaded

�� at the time this routine is called.

-Particulars

�

�� This routine is part of the user interface to the SPICE ephemeris

�� system.� It allows you to retrieve position information for any

�� ephemeris object relative to any other in a reference frame that

�� is convenient for further computations.

�

�� This routine is identical in function to the routine SPKEZP

�� except that it allows you to refer to ephemeris objects by name

�� (via a character string).

�

�� Aberration corrections

�� ======================

�

�� In space science or engineering applications one frequently

�� wishes to know where to point a remote sensing instrument, such

�� as an optical camera or radio antenna, in order to observe or

�� otherwise receive radiation from a target.� This pointing problem

�� is complicated by the finite speed of light:� one needs to point

�� to where the target appears to be as opposed to where it actually

�� is at the epoch of observation.� We use the adjectives

�� "geometric," "uncorrected," or "true" to refer to an actual

�� position or state of a target at a specified epoch.� When a

�� geometric position or state vector is modified to reflect how it

�� appears to an observer, we describe that vector by any of the

�� terms "apparent," "corrected," "aberration corrected," or "light

�� time and stellar aberration corrected." The SPICE Toolkit can

�� correct for two phenomena affecting the apparent location of an

�� object:� one-way light time (also called "planetary aberration") and

�� stellar aberration.

�� One-way light time

�� ------------------

�� Correcting for one-way light time is done by computing, given an

�� observer and observation epoch, where a target was when the observed

�� photons departed the target's location.� The vector from the

�� observer to this computed target location is called a "light time

�� corrected" vector.� The light time correction depends on the motion

�� of the target relative to the solar system barycenter, but it is

�� independent of the velocity of the observer relative to the solar

�� system barycenter. Relativistic effects such as light bending and

�� gravitational delay are not accounted for in the light time

�� correction performed by this routine.

�

�� Stellar aberration

�� ------------------

�� The velocity of the observer also affects the apparent location

�� of a target:� photons arriving at the observer are subject to a

�� "raindrop effect" whereby their velocity relative to the observer

�� is, using a Newtonian approximation, the photons' velocity

�� relative to the solar system barycenter minus the velocity of the

�� observer relative to the solar system barycenter.� This effect is

�� called "stellar aberration."� Stellar aberration is independent

�� of the velocity of the target.� The stellar aberration formula

�� used by this routine does not include (the much smaller)

�� relativistic effects.

�

�� Stellar aberration corrections are applied after light time

�� corrections:� the light time corrected target position vector is�

�� used as an input to the stellar aberration correction.

�

�� When light time and stellar aberration corrections are both

�� applied to a geometric position vector, the resulting position�

�� vector indicates where the target "appears to be" from the

�� observer's location.��

�

�� As opposed to computing the apparent position of a target, one

�� may wish to compute the pointing direction required for

�� transmission of photons to the target.� This also requires correction

�� of the geometric target position for the effects of light time

�� and stellar aberration, but in this case the corrections are

�� computed for radiation traveling *from* the observer to the target.

�� We will refer to this situation as the "transmission" case.

�� The "transmission" light time correction yields the target's

�� location as it will be when photons emitted from the observer's

�� location at `et' arrive at the target.� The transmission stellar

�� aberration correction is the inverse of the traditional stellar

�� aberration correction:� it indicates the direction in which

�� radiation should be emitted so that, using a Newtonian

�� approximation, the sum of the velocity of the radiation relative

�� to the observer and of the observer's velocity, relative to the�

�� solar system barycenter, yields a velocity vector that points in�

�� the direction of the light time corrected position of the target.

�

�� One may object to using the term "observer" in the transmission

�� case, in which radiation is emitted from the observer's location.

�� The terminology was retained for consistency with earlier

�� documentation.

�

�� Below, we indicate the aberration corrections to use for some

�� common applications:

�

�� 1) Find the apparent direction of a target.� This is

�� the most common case for a remote-sensing observation.

�

�� Use "LT+S":� apply both light time and stellar�

�� aberration corrections.

�

�� Note that using light time corrections alone ("LT") is

�� generally not a good way to obtain an approximation to an

�� apparent target vector:� since light time and stellar

�� aberration corrections often partially cancel each other,

�� it may be more accurate to use no correction at all than to

�� use light time alone.

�

�� 2) Find the corrected pointing direction to radiate a signal

�� to a target.� This computation is often applicable for

�� implementing communications sessions.

�

�� Use "XLT+S":� apply both light time and stellar�

�� aberration corrections for transmission.

�

�� 3) Compute the apparent position of a target body relative

�� to a star or other distant object.

�

�� Use "LT" or "LT+S" as needed to match the correction

�� applied to the position of the distant object.� For

�� example, if a star position is obtained from a catalog,

�� the position vector may not be corrected for stellar

�� aberration. �In this case, to find the angular

�� separation of the star and the limb of a planet, the

�� vector from the observer to the planet should be

�� corrected for light time but not stellar aberration.

�

�� 4) Obtain an uncorrected position vector derived directly from�

�� data in an SPK file.

�

�� Use "NONE".

�

�� 5) Use a geometric position vector as a low-accuracy estimate

�� of the apparent position for an application where execution�

�� speed is critical:

�

�� Use "NONE".

�

�� 6) While this routine cannot perform the relativistic

�� aberration corrections required to compute positions

�� with the highest possible accuracy, it can supply the

�� geometric positions required as inputs to these computations:

�

�� Use "NONE", then apply relativistic aberration

�� corrections (not available in the SPICE Toolkit).

�

�� Below, we discuss in more detail how the aberration corrections

�� applied by this routine are computed.��

�

�� Geometric case

�� ==============

�

�� spkpos_c begins by computing the geometric position T(et) of the

�� target body relative to the solar system barycenter (SSB).

�� Subtracting the geometric position of the observer O(et) gives

�� the geometric position of the target body relative to the

�� observer. The one-way light time, 'lt', is given by

�

�� | T(et) - O(et) |

�� lt = -------------------

�� c

�

�� The geometric relationship between the observer, target, and

�� solar system barycenter is as shown:

�

�� SSB ---> O(et)

�� |�� /

�� |�� /��

�� |�� /� T(et) - O(et)��

�� V� V��

�� T(et)

�

�� The returned position is

�

�� T(et) - O(et)

�

�� Reception case

�� ==============

�

�� When any of the options "LT", "CN", "LT+S", "CN+S" is selected

�� for `abcorr', spkpos_c computes the position of the target body at

�� epoch et-lt, where 'lt' is the one-way light time.� Let T(t) and

�� O(t) represent the positions of the target and observer

�� relative to the solar system barycenter at time t; then 'lt' is

�� the solution of the light-time equation

�

�� | T(et-lt) - O(et) |

�� lt = ------------------------�� (1)

�� c

�

�� The ratio�

�

�� | T(et) - O(et) |

�� ---------------------�� (2)

�� c

�

�� is used as a first approximation to 'lt'; inserting (2) into the

�� right hand side of the light-time equation (1) yields the

�� "one-iteration" estimate of the one-way light time ("LT").

�� Repeating the process until the estimates of 'lt' converge yields

�� the "converged Newtonian" light time estimate ("CN").

��

�� Subtracting the geometric position of the observer O(et) gives

�� the position of the target body relative to the observer:

�� T(et-lt) - O(et).

�

�� SSB ---> O(et)

�� | \�� |

�� |� \�� |

�� |�� \�� | T(et-lt) - O(et)

�� |�� \� |

�� V�� V V

�� T(et)� T(et-lt)

��

�� The light time corrected position vector is

�

�� T(et-lt) - O(et)

�

�� If correction for stellar aberration is requested, the target

�� position is rotated toward the solar system

�� barycenter-relative velocity vector of the observer.� The

�� rotation is computed as follows:

�

�� Let r be the light time corrected vector from the observer

�� to the object, and v be the velocity of the observer with

�� respect to the solar system barycenter. Let w be the angle

�� between them. The aberration angle phi is given by

�

�� sin(phi) = v sin(w) / c

�

�� Let h be the vector given by the cross product

�

�� h = r X v

�

�� Rotate r by phi radians about h to obtain the apparent

�� position of the object.

�

�� Transmission case

�� ==================

�

�� When any of the options "XLT", "XCN", "XLT+S", "XCN+S" is

�� selected, spkpos_c computes the position of the target body T at

�� epoch et+lt, where 'lt' is the one-way light time. 'lt' is the

�� solution of the light-time equation

�

�� | T(et+lt) - O(et) |

�� lt = ------------------------�� (3)

�� c

�

�� Subtracting the geometric position of the observer, O(et),

�� gives the position of the target body relative to the

�� observer: T(et-lt) - O(et).

�

�� SSB --> O(et)

�� / |�� *�

�� /� |� *� T(et+lt) - O(et)��

� ��/�� |*��

�� /�� *|��

�� V� V� V��

�� T(et+lt)� T(et)��

�

�� The position component of the light-time corrected position�

�� is the vector

�

�� T(et+lt) - O(et)

�

�� If correction for stellar aberration is requested, the target

�� position is rotated away from the solar system barycenter-

�� relative velocity vector of the observer. The rotation is

�� computed as in the reception case, but the sign of the

�� rotation angle is negated.�

�

�� Precision of light time corrections

�� ===================================

�

�� Corrections using one iteration of the light time solution

�� ----------------------------------------------------------

�

�� When the requested aberration correction is "LT", "LT+S",

�� "XLT", or "XLT+S", only one iteration is performed in the

�� algorithm used to compute 'lt'.

�

�� The relative error in this computation

�

�� | LT_ACTUAL - LT_COMPUTED |� /� LT_ACTUAL

�

�� is at most�

�

�� (V/C)**2

�� ----------

�� 1 - (V/C)

�

�� which is well approximated by (V/C)**2, where V is the

�� velocity of the target relative to an inertial frame and C is

�� the speed of light.

�

�� For nearly all objects in the solar system V is less than 60

�� km/sec.� The value of C is 300000 km/sec.� Thus the one

�� iteration solution for 'lt' has a potential relative error of

�� not more than 4*10**-8.� This is a potential light time error

�� of approximately 2*10**-5 seconds per astronomical unit of

�� distance separating the observer and target.� Given the bound

�� on V cited above:

�

�� As long as the observer and target are

�� separated by less than 50 astronomical units,

�� the error in the light time returned using

�� the one-iteration light time corrections

�� is less than 1 millisecond.

�

�� Converged corrections�

�� ---------------------

�

�� When the requested aberration correction is "CN", "CN+S",

�� "XCN", or "XCN+S", three iterations are performed in the

�� computation of 'lt'.� The relative error present in this

�� solution is at most

�

�� (V/C)**4

�� ----------

�� 1 - (V/C)

�

�� which is well approximated by (V/C)**4.� Mathematically the

�� precision of this computation is better than a nanosecond for

�� any pair of objects in the solar system.

�

�� However, to model the actual light time between target and

�� observer one must take into account effects due to general

�� relativity.� These may be as high as a few hundredths of a

�� millisecond for some objects.

�

�� When one considers the extra time required to compute the

�� converged Newtonian light time (the state of the target relative

�� to the solar system barycenter is looked up three times instead

�� of once) together with the real gain in accuracy, it seems

�� unlikely that you will want to request either the "CN" or "CN+S"

�� light time corrections.� However, these corrections can be useful

�� for testing situations where high precision (as opposed to

�� accuracy) is required.

�

�� Relativistic Corrections

�� =========================

�

�� This routine does not attempt to perform either general or

�� special relativistic corrections in computing the various

�� aberration corrections.� For many applications relativistic

�� corrections are not worth the expense of added computation

�� cycles.� If however, your application requires these additional

�� corrections we suggest you consult the astronomical almanac (page

�� B36) for a discussion of how to carry out these corrections.

�

-Examples

�

�� 1)� Load a planetary ephemeris SPK, then look up a series of

�� geometric positions of the moon relative to the earth,

�� referenced to the J2000 frame.

�

�� #include <stdio.h>

�� #include "SpiceUsr.h"

�� void main()

�� {

�� #define�� ABCORR�� "NONE"

�� #define�� FRAME�� "J2000"

�� /.

�� The name of the SPK file shown here is fictitious;

�� you must supply the name of an SPK file available

�� on your own computer system.

�� ./

�� #define�� SPK�� "planetary_spk.bsp"

�� /.

�� ET0 represents the date 2000 Jan 1 12:00:00 TDB.

�� ./

�� #define�� ET0�� 0.0

�� /.

�� Use a time step of 1 hour; look up 100 states.

�� ./

�� #define�� STEP�� 3600.0

� ��#define�� MAXITR�� 100

�� #define�� OBSERVER�� "earth"

�� #define�� TARGET�� "moon"

��

�� /.

�� Local variables

�� ./

�� SpiceInt�� i;

�� SpiceDouble�� et;

�� SpiceDouble�� lt;

�� SpiceDouble�� pos [3];

�� /.

�� Load the spk file.

�� ./

�� furnsh_c ( SPK );

�� /.

�� Step through a series of epochs, looking up a position vector

�� at each one.

�� ./

�� for ( i = 0;� i < MAXITR;� i++ )

�� {

�� et� =� ET0 + i*STEP;

�� spkpos_c ( TARGET,�� et,�� FRAME,� ABCORR,

�� OBSERVER,� pos,� &lt�� );

�� printf( "\net = %20.10f\n\n",�� et�� );

�� printf( "J2000 x-position (km):�� %20.10f\n", pos[0] );

�� printf( "J2000 y-position (km):�� %20.10f\n", pos[1] );

�� printf( "J2000 z-position (km):�� %20.10f\n", pos[2] );

�� }

�

-Restrictions

�� None.

-Literature_References

�

�� SPK Required Reading.

�

-Author_and_Institution

�

�� C.H. Acton�� (JPL)

�� B.V. Semenov�� (JPL)

�� N.J. Bachman�� (JPL)

�� W.L. Taber�� (JPL)

�

-Version

�� -CSPICE Version 2.0.4, 04-APR-2008 (NJB)

�� Corrected minor error in description of XLT+S aberration

�� correction.

�� -CSPICE Version 2.0.3, 17-APR-2005 (NJB)

�� Error was corrected in example program:� variable name `state'

�� was changed to `pos' in printf calls.

�� -CSPICE Version 2.0.2, 13-OCT-2003 (EDW)

�� Various minor header changes were made to improve clarity.

�� Added mention that 'lt' returns a value in seconds.

�

�� -CSPICE Version 2.0.1, 27-JUL-2003 (NJB) (CHA)

�� Various header corrections were made.

�� -CSPICE Version 2.0.0, 31-DEC-2001 (NJB)

�� Updated to handle aberration corrections for transmission

�� of radiation.� Formerly, only the reception case was

�� supported.� The header was revised and expanded to explain

�� the functionality of this routine in more detail.

�� -CSPICE Version 1.0.0, 29-MAY-1999 (NJB) (WLT)

-Index_Entries

�

�� using names get target position relative to an observer

�� position relative to observer corrected for aberrations

�� read ephemeris data

�� read trajectory data

�

Version	Date	Page Nos.	Reason
1.0	23 July 2013	All	Original
1.1	8 October 2013	Multiple	Corrected a few typos. Added in an appendix a list of kernels covered by this omnibus SIS.