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conics_c

 Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input Detailed_Output Parameters Exceptions Files Particulars Examples Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

```   conics_c ( Determine state from conic elements )

void conics_c ( ConstSpiceDouble  elts[8],
SpiceDouble       et,
SpiceDouble       state[6] )

```

#### Abstract

```   Determine the state (position, velocity) of an orbiting body
from a set of elliptic, hyperbolic, or parabolic orbital
elements.
```

```   None.
```

#### Keywords

```   CONIC
EPHEMERIS

```

#### Brief_I/O

```   VARIABLE  I/O  DESCRIPTION
--------  ---  --------------------------------------------------
elts       I   Conic elements.
et         I   Input time.
state      O   State of orbiting body at et.
```

#### Detailed_Input

```   elts        are conic osculating elements describing the orbit of a
body around a primary. The elements are, in order:

RP      Perifocal distance.
ECC     Eccentricity.
INC     Inclination.
LNODE   Longitude of the ascending node.
ARGP    Argument of periapse.
M0      Mean anomaly at epoch.
T0      Epoch.
MU      Gravitational parameter.

The epoch T0 is given in ephemeris seconds past J2000.
T0 is the instant at which the state of the body is
specified by the elements.

The same elements are used to describe all three types
(elliptic, hyperbolic, and parabolic) of conic orbit.

et          is the time at which the state of the orbiting body
is to be determined, in ephemeris seconds J2000.
```

#### Detailed_Output

```   state       is the state (position and velocity) of the body at
time `et'. Components are x, y, z, dx/dt, dy/dt, dz/dt.
```

#### Parameters

```   None.
```

#### Exceptions

```   1)  If the eccentricity supplied is less than 0, the error
SPICE(BADECCENTRICITY) is signaled by a routine in the call tree of
this routine.

2)  If a non-positive periapse distance is supplied, the error
SPICE(BADPERIAPSEVALUE) is signaled by a routine in the call tree of
this routine.

3)  If a non-positive value for the attracting mass is supplied, the
error SPICE(BADGM) is signaled by a routine in the call tree of this
routine.

4)  If `elts' is such that the resulting orbit at periapsis has
either its position or velocity equal to zero, or the square
of the resulting specific angular momentum's magnitude is
zero, an error is signaled by a routine in the call tree of
this routine. This is an indication of invalid `elts' elements.

5)  If `et' is such that the offset in time from periapsis, at which
the state is to be determined, is so large that there is a
danger of floating point overflow during computation, an error
is signaled by a routine in the call tree of this routine.
```

#### Files

```   None.
```

#### Particulars

```   None.
```

#### Examples

```   Let `vinit' contain the initial state of a spacecraft relative to the
center of a planet at epoch `et', and let `gm' be the gravitation
parameter of the planet. The call

oscelt_c ( vinit, et, gm, elts );

produces a set of osculating elements describing the nominal
orbit that the spacecraft would follow in the absence of all
other bodies in the solar system and non-gravitational forces
on the spacecraft.

Now let `state' contain the state of the same spacecraft at some
other, later epoch. The difference between this state and the
state predicted by the nominal orbit at the same epoch can be
computed as follows.

conics_c ( elts,    later, nominal );
vsubg_c  ( nominal, state, 6, diff );

printf( "Perturbation in x, dx/dt = %f %f", diff[0], diff[3] );
printf( "                y, dy/dt = %f %f", diff[1], diff[4] );
printf( "                z, dz/dt = %f %f", diff[2], diff[5] );
```

#### Restrictions

```   None.
```

#### Literature_References

```   [1]  R. Bate, D. Mueller, and J. White, "Fundamentals of
Astrodynamics," Dover Publications Inc., 1971.
```

#### Author_and_Institution

```   N.J. Bachman        (JPL)
J. Diaz del Rio     (ODC Space)
E.D. Wright         (JPL)
```

#### Version

```   -CSPICE Version 1.1.2, 02-JUL-2021 (JDR)

#4 and updated entry #5 in -Exceptions section.

-CSPICE Version 1.1.1, 29-JUL-2003 (NJB)

-CSPICE Version 1.1.0, 24-JUL-2001 (NJB)

Changed protoype: input elts is now type (ConstSpiceDouble *).
Implemented interface macro for casting input array to const.

-CSPICE Version 1.0.1, 08-FEB-1998 (EDW)

```   state from conic elements
`Fri Dec 31 18:41:03 2021`