| Observer | Name of the observer.
Changing this affects:- The
position of the
observer (e.g., which spacecraft?).
- The set
of SPICE kernels used to initialize GV. Different
trajectory
files assume different planetary ephemerides, and GV handles this
carefully.
- The
list of available FOVs (e.g., no need to have NH FOVs if observer is
Cassini).
- The values set after hitting
'Reset Inputs to Default Values' button.
- The list
of plotted bodies (e.g., no need to plot small Saturnian satellites
from New Horizons).
- The list of available target
bodies (although all bodies are available using the 'Other Bodies'
target option).
- The boresight rotation direction.
The
list
of observers includes:
- New Horizons.
Includes numerous candidates
trajectories for Pluto encounter planning. Examples include:
- New Horizons, Reference Metakernel -- Recommended for tour planning
- New Horizons, Nominal
-- Nominal trajectory
- New Horizons, Predict
-- Predict trajectory
- New Horizons, Encounter 20
-- C/A date of 20-Jul-2015
- New Horizons, Encounter 5000
-- C/A distance of 5000 km
- Messenger.
Includes two strawman square FOVs (M1, M2).
- Rosetta.
Includes Alice, OSIRIS, VIRTIS, and MIRO FOVs.
- Cassini.
Includes UVIS and ISS FOVs.
- Earth. Choosing this lets GV operate like an Earth-based
planetarium
program, useful for planning coordinated observations. Observer is
assumed to be at the Earth's center (although additional
terrestrial observers could be easily incorporated). E1 and E2 are simple rectangular FOVs.
- Sun. Useful for
planning atmospheric occulations. S1, S2, and S3 are simple circular FOVs.
- Pluto. Useful for planning occultations. P1 and P2 are simple circular FOVs.
- Juno. Available to team members. Includes UVS, JIRAM, and JunoCAM FOVs.
- LRO. Available to team members. Includes LAMP FOV.
|
| Start Time | Time
of the observation. Appropriate
light-time corrections are made; positions calculated are apparent
positions, at the specified time, from the observer's location.
Format is flexible;
any standard SPICE time format is acceptable. Examples include:
- January
20 2006
- 2006-31-Jan 01:00:34.12
- JD
2454156.45
- 2006-180T18:28:12
- MET 51623454.1
| UTC; time assumed to be 00:00:00
UTC
Julian date
Day-of-year
MET (Mission Elapsed Time); New Horizons only |
Close-approach
times can be automatically looked up by entering 'CA':
| Computes C/A time to body named in Target field
Computes C/A time to Hydra |
A real-time
computation can be done by leaving the field blank:
| Use current, real-time UTC |
|
| End Time | [Optional] GV can plot the motion of
solar system objects as seen from the moving observer. If
this
value
is set, then the positions of the bodies are plotted at evenly spaced
intervals between the start time and end time. If the start time is
before the end time, then the table and plot are generated in reverse
order. |
| Interval | [Optional]
If set, then defines a number of discrete timesteps to use when
plotting motion of solar system objects, and generating data tables.
The input allows for several different formats, such as:
| Three equally-spaced steps, between Start Time to End Time.
Plot at 3-day intervals, from Start Time to End Time.
The number of intervals is determined automatically.
Plot at 25.5-second intervals.
|
The maximum number of intervals is a hard-coded limit based on computation time:
- 500, if planets or satellites are being rendered;
- 10,000, otherwise.
The
higher limit is useful for making data tables; GV can usually generate
tables of this size in < 1 minute. To use the higher
limit, uncheck the boxes to Draw planets and
satellites. Rendering bodies takes far longer than computing their
position for a table, so use short intervals with caution!
GV's default is to make only one plot (i.e., '1 Timesteps'). |
| Movie | If
set, create an animation based on the given input parameters. The movie
will be created with the specified start time, end time, and number of
timesteps.
The results will be returned in GV's "Movie Panel'',
not the main GV screen. This panel creates a preview of the movie,
including first frame, last frame, # of frames, duration, and the frame
rate. The frame rate is user-settable. The movie is generated after
being previewed in the "Movie Panel.'' Once generated it can be
downloaded in a variety of formats: Animated GIF, AVI, tarball, or raw
frames in an HTML page.
**
Movie Mode has less error-checking than the single
frame-by-frame mode of GV. If errors are generated during the movie
creation (e.g., for a time range not covered by the kernel), the error
message will likely not be reported back to you, and GV may appear to
have hung. Check your inputs before making long movies! For an
alternate way to make movies (more work but more flexible), check out batch mode. |
| Center Position | Position
at which the central FOV is pointed. This can be a
specified position, or a body name. The position may be
specified
in terms of J2000 celestial coordinates (RA/Dec), or in terns of
ecliptic coordinates (Lon/Lat). Either one of these may be
entered in units of
- Degrees
('45.00')
- (H/D)MS ('4 12 34.4', or '4:12:34.4').
(Hours/Degrees) Minutes Seconds
- Radians
('2.12239')
The reference frame may be
specified as:
- J2000: Celestial coordinates
(i.e., Earth's rotation axis is oriented with Dec=0 deg)
- ECLIPJ2000:
Ecliptic coordinates (i.e., Earth's orbital plane is oriented with
Dec=0 deg)
If
a body name ('Sun', 'Pluto', 'Io', etc.) is specified for the center
position, then its proper
coordinates are automatically filled in for its RA/Dec or Lat/Lon.
If the target is specified as SPICE Lookup,
then the actual spacecraft orientation (RA, Dec, Rotation*) at the
specified time is automatically filled in, based on the available SPICE
C-Kernels. This lookup functionality works only for the New Horizons
and Rosetta missions.
(*) Rotation angle is computed and applied properly, but not displayed.
If the target is specified as Other Body,
then the body named in the field next to the selection menu is used.
This allows for use of target bodies not explicitly listed in the
pull-down selection menu. The named target can be any valid NAIF name or code, such as:
- 'Phobos'
(equivalent to '401')
- '537' (equivalent to Jovian
moon 'Kale')
- '0' (equivalent to 'Solar System
Barycenter')
- 'Pluto Barycenter' (equivalent to '9')
- 'Pluto'
(equivalent to '999')
- 'Galileo Orbiter' (equivalent
to '-77')
Even
though all NAIF IDs are recognized, kernel files for all bodies may not
be available. Please inquire regarding kernel files to add. |
| FOV Position | Position of the selected FOV in the sky. By default, the FOV is centered on the target. Options are:
- Degrees from Target: e.g., 4 deg in RA and dec from the target
- Radii from Target: Distance in body radii; e.g., 3 RJup from Jupiter.
- RA/Dec degrees: Absolute position, in degrees.
- RA/Dec (H/D)MS: Absolute position, in hours/degrees/minutes/seconds.
- Degrees along Limb:
Positions the FOV center on the limb of the target body. The two angles
entered are not interpreted as RA & Dec, but are used as:
- RA: Counterclockwise degrees around the limb. The zero-point is arbitrary.
- Dec: Degrees inside (-) or outside (+) limb; 0 = limb itself.
- Degrees Roll from Nadir.
In this mode, the FOV begins pointed 'downward' at the target center. A
slew is then performed, according to the angles specified. The two
angles entered are not interpreted as RA & Dec, but are used as:
- RA: Side-to-side slew ('Roll'), in degrees. Referenced relative to spacecraft velocity; i.e., orbit normal.
- Dec: Front-to-back slew ('Pitch'), in degrees. Referenced to orbit normal.
- Only a Roll or a Pitch may be performed; they may not be combined.
|
| FOV Footprints | This allows for plotting of mosaics and scans, such as:
- "Cover
Pluto with a 4x4 LEISA mosaic, spaced at 0.5 deg intervals, in a
lawnmower-type scan pattern, with a slew every 75 seconds."
To
turn on the option, select 'Enable Menu', and then replot. The
following options are then shown. A 'Footprint' refers to a
single placement of the FOV; a mosaic is made up of many different
footprints.
- # of Footprints: The size of the mosaic, for instance, a 1x10 mosaic (10 frames, linear) or a 4x4 mosaic (16 frames, square).
- Footprint Spacing: The center-to-center spacing between footprints. If this spacing is less than the FOV width, the footprints will overlap.
- Fooprint Path: If
'Draw' is selected, the path between the footprints will be drawn, to
show the order in which the scan is to be performed. Three scan
patterns are possible: Lawnmower, Zamboni, and Typewriter.
- Footprint Ref. Frame:
The default mode is Inertial, in which case footprints are placed on
the sky instantaneously with no correction for target motion or
rotation. If Target mode is selected, then body motion and rotation is
considered (e.g., for performing a mosaic at closest-approach to a
body). Target mode requires use of a Footprint Interval.
- Footprint Interval: Optional. The delay (in seconds) between subsequent footprints.
Keep in mind that GV doesn't model spacecraft inertia, pointing
stability, etc. The Footprints mode is primarily for sketching out
mosaic patterns, not performing sequencing.
|
Center FOV
|
Name
of the FOV to point. Options include
all
remote sensing instruments, plus the spacecraft boresight.
CtrPlot on: Allows the
final plot to be centered on the target (e.g., Pluto), or the FOV
(e.g., LORRI). If the values in the FOV Position filed are zero, then
the the Target and FOV positions are both centered. |
| Plot Radius | Angular
size of the plot.
Can be set to:
- Degrees: Selected
value is the plot radius, in degrees. The width is an arclength, not a
positional difference --
e.g., near the poles, a 5 degree radius plot covers a far greater
region of the sky than near the equator.
- Target Radii:
Plot size is based on size of the target. For instance, with
Target=Jupiter, set Plot Radius=1 to make Jupiter exactly fill the plot
window in the width direction. If multiple timesteps are plotted (e.g.,
many timesteps of Jupiter, all of which can have different sizes), then
the plot radius is based on the size at the central time, midway
between the start and end times.
|
| Plot
FOVs | FOV
footprint plots for each of the instruments can be individually
selected. If
plotted, a red cross is marked at the center of each FOV.
Additionally, a red cross within a circle is plotted for the
spacecraft boresight.
If S/C Axes
is selected, then the projected positions of the spacecraft's six
principle axes are marked and labeled (+X, +Y, +Z, -X, -Y, -Z).
For NH PEPSSI, sector 0 is indicated with a heavy outline.
The
list of FOVs
depends on the Observer. In most cases the FOV positions are read directly from the relevant SPICE files.
|
| Roll Angle | Rotation
angle in clockwise degrees, around the instrument's boresight
axis. For New Horizons, the rotation angle zero-point can
be specifed based on either:
- NCP (North Celestial Pole)
: For angle 0 degrees, the spacecraft is rolled about the boresight
until the scan axis (-Z) reaches its minimum separation to the NCP.
- Orbit Normal:
For angle 0 degrees, the spacecraft is rolled about the boresight
until the scan axis (-Z) reaches its minimum separation to the orbit
normal vector. The orbit normal
is defined as the vector product of (observer to target body center) X
(velocity of observer). Using
Orbit Normal mode requires using a named target, not an RA/Dec
position. For MVIC scans of Pluto near C/A, this orientation (for 0 deg) keeps the HGA roughly
Earth-pointed, and allows for far-to-near or dark-to-sunlit scans.
In the terminology used by New Horizons MOps, these two options specify the 'external reference vectors.'
|
| Objects | GV
can plot HD stars, Tycho-2 stars, and solar system objects.
Each object can be plotted, or plotted with a label attached.- Planets: GV calculates positions for the 9 planets. Latitude/longitude
grids are drawn, and the lit and unlit portions are
indicated. Bodies
are assumed to be spherical, with their size taken from
their equatorial radius. Plotting Jupiter also plots its main ring. The Sun is always plottted.
- Satellites: GV calculates positions for selected satellites of Jupiter, Saturn,
Uranus, Neptune, and Pluto. If selected, orbits of satellites
will also be plotted, with 360 points per orbit. Orbital
plotting assumes satellites have
zero eccentricity and inclination, and should be used with caution. For
precise calculations, plot the positions using the Timesteps option.
- Stars: GV plots stars
from the HD and Tycho-2 star catalogs.
- Searching
for stars is slow,
especially for HD and for plots wider than a few
degrees. For wide plots, turn off star plotting unless
necessary.
Each object has a series of possible options:
- Draw:
Draw the body. Stars are plotted as points of varying size; the
magnitude scale automatically adjusts. Planets/satellites are rendered
using the surface style chosen below. Bodies are assumed to be spherical with equatorial radius; for higher precision, use limbs mode.
- Label:
Label the body. For stars the ID, magnitude, and type (if available)
are listed. If multiple magnitudes are available, the brightest one is
used.
- Orbits: Plot the orbits of all satellites drawn.
- Barycenters: Plot the
center-of-mass of the system. This option is only enabled if GV has one
or more barycenters in its list of targets (e.g., Pluto Barycenter for
NH-GV).
Objects are plotted
in the following order:
- Stars
- Planets
and Satellites, in order of decreasing distance
- Barycenters
- FOVs
Tip:
There
are three ways to identify objects in a plot:
- Click
the Label box to print labels next to each object.
- Create
a table (see below), which lists all objects and their parameters.
- Move the mouse over the objects,
and a label will appear identifying it.
|
| Stellar
Catalog | There
are three options for the star catalog:
- Tycho-2:
(c. 2000) 2.5M stars with two-color
magnitudes (B and V) but no spectral
types, complete to roughly V=11.5, although with some data to V=16.
Positions are accurate to ~ 0.05 arcsec, and are adjusted for proper
motion. Compared to HD,
Tycho-2
has better positions, is more complete, and is much faster to search.
- HD: (c.
1924) 272,150 stars with
two-color magnitudes (photographic and photovisual) and spectral
types, complete to V=8.5 or so. Positions are poor (~1
arcsec) and no proper motion is available. Missing magnitudes
are indicated by -999,
which is never a
valid data value.
- USNO-B1.0:
(c. 2004). 1.04B stars with five-color magnitudes
(B1/R1/B2/R2/I), compete to V=21. Positions are accurate to
0.2
arcsec. Photometry is 'marginal' (0.3 mags).
Searching is
very slow because of the catalog's size. Don't use USNO-B1.0 unless you
must! If you do, use it only on small fields, and/or with
a sensible magnitude limit.
Support for the 2MASS
catalog can be incorporated with minimal
effort; if desired, please ask. |
| Stellar Mag Lim or Range | Takes
either one value, or two.
One value: Plot only
stars which are brighter than this limit.
Two
values: Plot only stars which are within this magnitude range.
Some
stars in standard catalogs (e.g., HD) have no listed stellar
magnitudes. GV plots these depending on the input to the Stellar Mag
Limit field. These stars are always plotted if one value is supplied to
GV; they are never plotted if two values are supplied to GV. |
| Stellar
Type Filter | [Optional]
A list of stellar types to plot. List is a series of single
characters which are matched against the stellar type. For instance,
'OB' plots only stars which have 'O' or 'B' in their
spectral type field. Ignored for catalogs with no spectral types.
Available filters are O, B, A, F, G, K, M, GK, KM, GKM, OB, OBA, OBAF.
|
| Surface
Style | Change
the way that planets are displayed. Options are:
- Wireframe:
Shows a grid, with longitude markers and N/S pole indicators.
The
lit/unlit portion is indicated with a change in color. For Earth,
continents and DSN station locations are shown. Wireframe
uses the most accurate projections, and is recommended for all times
when the observer is near the body (e.g., in-orbit missions, or close
approaches at < several radii). Other projections can be inaccurate
for close distances.
- Albedo:
Project an albedo map onto the surface. Lit/unlit portion is
indicated by a brightness change and a visible terminator. The
wireframe grid is
superimposed. Available for Mars, Earth, Moon, Jupiter, and Pluto only.
- Composition: Show a
composition map. Wiregrame grid and terminator are
superimposed. Available for Pluto only.
- Elevation: Shows a digital elevation model (DEM). Available for Moon only.
- I/F: Show a map of
I/F for V-band or B-band. Based on model of Buie. Available
for Pluto only.
- I/F
Contour: Same as I/F, but add a contour map. Available for
Pluto only.
- Aurora:
Plot the north and south auroral ovals (blue). Also plot the
auroral ovals for Io (red), as well as Io's footprint (black).
Available for Jupiter only. Data supplied by Randy Gladstone.
- Wireframe, No Fill: Same
as Wireframe mode, but draws only the limb and terminator (no grid
lines, and the body's not filled in). Because the body is 'see-thru',
this can be useful for planning occultation observations.
|
Projection
| Sets the method of mapping sky coordinates onto the display.
- Rectangular:
RA and Dec (or ecliptic Lat and Lon) are mapped linearly to X and Y.
This is simple and works well for observations which are not close to
the zenith. At high values of Dec, distances and shapes become
distorted, because of the smaller area covered by a degree of
coordinate. GV properly plots their distorted shapes. For New
Horizons, this projection system usually works fine, because all of its
targets are near the equatorial plane. An advantage of rectangular
projection is that it is easy to measure coordinates directly off of a
plot.
- Spherical:
Shapes and and angular distances are not distorted. but lines of
constant RA and Dec become curved. For observations near the
pole, this mode is recommended. Spacecraft orbital missions, especially
polar orbiters, should use this mode. Requires Units = Degrees, and
Surface Style = Wireframe.
- Spherical with Grid: Same as above, but also draws a grid of RA and Dec lines.
|
| Show
Data Tables | Output
HTML-formatted tables listing
the position of each visible object.
- FOVs
: Lists all FOVs, and the spacecraft boresight. For each,
lists:
- FOV name, or S/C principle axis
name
- FOV boresight position,
RA/Dec, in degrees
- FOV boresight
position, RA/Dec, in (H/D)MS
- Solar elongation angle
(i.e., angle between boresight, and center of Sun)
- Spatial
resolution of target (km/pixel), if Target
is set to a named body. Assumes square pixels with fixed
angular resolution.
- Quaternions : Display a table listing the pointing quaternions for each
footprint location. Quaternions are 4-element unit vectors, and are
printed in both 'SPICE order' and 'STK order.' A third format,
'Engineering order,' is not printed. Quaternions specify rotations, and
there is a 1-to-1 correlation between SPICE's internal 3x3 rotation
matrices, and the 4-element quaternions. Rotations are from [0,0] to
the specified instrument pointing (e.g., from RA=0, Dec=0 in J2000
coords.) See NAIF M2Q documentation for information on element ordering.
- Stars
: For each star in the frame, lists:
- Catalog
ID
- Position, RA/Dec, in degrees.
Positions are corrected for proper motion, for TYC2 and
USNO-B1.0 catalogs.
- Position, RA/Dec, in (H/D)MS
- Magnitudes,
in each filter available
- HD: Photographic
and Photovisual
- TYC2: B_T, V_T
- USNOB-1.0:
U, B, V, R, I
- Stellar type, if known (HD
catalog only)
- Solar
System :
Lists all objects, whether visible or not. For each one, lists the
following quantities:
- Name
- Position,
RA/Dec, in degrees. All positions indicate apparent position
at given UTC, with light-time correction.
- Position, RA/Dec, in
H/DMS
- Position,
Ecliptic Lon/Lat, in degrees
- Distance
(center-to-center), in AU
- Distance
(center-to-center), in km
- Angular diameter, in
microradians
- Phase
angle [Sun -
Target_Center - Observer], in degrees
- Solar
elongation angle [Sun - Observer - Target_Center], in
degrees
- Sub-Solar
Lon/Lat, on body, in
degrees
- Sub-observer
Lon/Lat,
on body, in degrees
- Sub-satellite Lon/Lat,
on primary, in
degrees. For satellites only.
- Pole
angle, in degrees. Angle between (projection of
body's rotation
axis onto sky) and (vector from observer to North celestial pole).
19-Jun-07:
There has been an error in the Pole Angle computation identified,
causing <1 deg errors in pole position for Europa and a
small number of other satellites. Not yet fixed.
- UTC date/time of
observation
- Julian date/time of observation
- Plutocentric Solar Heliographic
: Lists the observer's position and velocity in the Plutocentric Solar
Heliographic coordinate system (PSH). This is a coordinate frame
useful for plasma instruments. It is defined such that:
- +X_PSH points from Pluto center, to the Sun center;
- +Y_PSH is in the H x X_PSH direction, where H is the solar spin axis (pointing north);
- +Z_PSH completes the right-handed system.
Lon/Lat on all bodies is
planetographic. Lon/Lat
are defined in the standard fixed-body reference frames (IAU2000),
which is System III for Jupiter/Saturn/Uranus/Neptune. Caution:
Some bodies (such as Nix, Hydra, and some asteroids) indicate lon/lat
positions even though their pole positions may not be accurately
determined. Nix and Hydra are assumed to have rotation vectors parallel
with Pluto's, and be in synchronous rotation. This may or may not be
right! For these bodies, the lon/lat values on the body are printed in red to indicate that they are provisional and to be used with caution. If
the Close bodies only
option is checked, then solar system bodies are tabulated only for the
closest planet, plus its satellites, plus the Earth and Sun.
Invalid
values (e.g., missing stellar
magnitudes, or sub-solar longitudes for small satellites with no
defined longitude system) are indicated as -999. -999 is never
a
valid data value.
|
| Downtrack
Error | [Optional]
If set, this specifies the uncertainty in the observer's
position, in seconds along its track. The uncertainty is
plotted
by outlining each
body with an ellipse which shows its position at each end of the
uncertainty. Blue '+' signs indicate the body centers at each end. Value is the halfwidth; i.e., error ellipse
corresponds to t-dt .. t+dt.
For New Horizons Pluto
encounter planning, the recommended 1σ
value to use is 50 seconds halfwidth, as per Leslie Young. |
Groundtrack t/2
|
[Optional] If specified, the
spacecraft groundtrack on the target body is plotted. For instance,
'500' plots the sub-spacecraft groundtrack position 500 second before
and after the current time, for 1000 seconds total.
Currently available only for LRO, but can be enabled for other missions if requested.
|
Ref Frame
|
Specifies
whether the plot should be generated in J2000 celestial coordinates
(RA/Dec), or ecliptic coordinates (Lon/Lat). The coordinates
of
the plot need not be the same as the coordinates of the center
position, although they may be. If they are not (for
instance,
celestial RA/Dec specified for the center position, and the plot
generated in ecliptic Lon/Lat), then the proper conversions applied
between the two coordinate systems. |
| Plot Size
[pixels] | Change the width of the returned plot. Default is 700 pixels. Height = width + 70. |
| Plot
Title | [Optional]
A title for the plot. Printed on the top line, preceding the
UTC range. |
| Flip RA? | By
default, RA is plotted such that values decrease along the X
axis. If checked, RA values will be inverted such that they increase along the X
axis. |
| White sky? | Default is black sky with white stars (better
for web). If checked, plot is made with black stars on a white sky
(better for printing). Note that this is not reverse video: albedo maps are the same in both. |
| List
kernel info? | If
checked, prints a list of the
kernel files passed to SPICE to generate the ephemeris. As per the
SPICE kernels.txt convention, if a body is listed in multiple files for
the
same time range, then the last one listed is used. |
