[X] My Assistant

[elakdawalla]

I am building some web pages about MRO (we're hosting the team website for Mars Climate Sounder) and am looking for a tool that I can use to draw some pictures of the shapes of orbits and ground tracks. I know that there are fancy tools out there, like SOAP, but I am hoping that there are some tools out there that are a little easier to use that I can use to generate some simple diagrams. For instance, I'd like to create one diagram on a flat map projection (simple, mercator, whatever) that shows the 17-day ground track repeat for MRO, and one with Mars as a sphere showing the position of the near-polar orbit, maybe one comparing the orbits of MRO, MGS, and Odyssey, even maybe generate a bunch of diagrams to make an animation showing how as MRO goes around Mars its orbit is sun-synchronous. I know I could do all of this with SOAP but I was never able to use SOAP without a lot of hand-holding from a very patient person at JPL. I would appreciate any advice or help on simpler tools to visualize orbits at Mars!

--Emily

[elakdawalla]

Thanks for the comments and suggestions. Looks like I may have to try pounding my forehead against SOAP to get what I want.

--Emily

[mcaplinger]

Looks like I may have to try pounding my forehead against SOAP to get what I want.

I looked around but it looks like Aerospace Corp has continued to make it difficult to get SOAP, and I don't have a copy here, or I would try to help you out.

For the groundtrack walk, I could crank something with our targeting software.

I installed Celestia and it's not too bad, but for the fact that it only processes Keplerian orbital elements, which for spacecraft will stay accurate for a few days at best. And translating Mars orbits to the right coordinate system will be a somewhat painful bit of tedium (if you recognize the phrase "IAU vector and equinox of epoch", you know what I mean).

Here's an example of what Celestia shows for MGS and Odyssey. It's pretty, but the positions (based on some config files I found on the net) are fiction. And Celestia appears to save JPEGs flipped left-for-right. Oh well, so close!

[helvick]

Here's an example of what Celestia shows for MGS and Odyssey. It's pretty, but the positions (based on some config files I found on the net) are fiction. And Celestia appears to save JPEGs flipped left-for-right. Oh well, so close!

Celestia shouldn't be that far off on the instantaneous locations of the spacecraft\solar bodies provided you are using accurate spacecraft xyz files but the orbital tracks have been an issue IIRC. There was a problem at one time with the texture maps for Mars where the default Mars surface texture was 180deg out of line with reality - that was in a fairly early version so it shouldn't be a problem with anything recent. I've never seen the inverted jpeg problem before - spooky.

[mcaplinger]

Celestia shouldn't be that far off on the instantaneous locations of the spacecraft\solar bodies provided you are using accurate spacecraft xyz files...

No, wait a minute, you're right. I was assuming that the only way to put the orbit into Celestia was to supply orbital elements. I now see that there's an option to use "SampledOrbits" which are just the XYZ locations at some time spacing. Assuming that Celestia wouldn't choke with, say, a few months' worth of 5-minute or 1-minute spacing, one could write a program to extract that from the SPICE files. Then there's just the wrinkle of figuring out the coodinate system.

[helvick]

No, wait a minute, you're right. I was assuming that the only way to put the orbit into Celestia was to supply orbital elements. I now see that there's an option to use "SampledOrbits" which are just the XYZ locations at some time spacing. Assuming that Celestia wouldn't choke with, say, a few months' worth of 5-minute or 1-minute spacing, one could write a program to extract that from the SPICE files. Then there's just the wrinkle of figuring out the coodinate system.

Sorry I wasn't clear about that - the Celestia forum guys have some tools for this.
This Celestia forum thread delves into the topic

[jmknapp]

Emily -- glad you can use the map.

Helvick -- do the Celestia xyz files use J2000 coordinates?

[helvick]

Emily -- glad you can use the map.

Helvick -- do the Celestia xyz files use J2000 coordinates?

Yes - The data (with some reformatting) is the same as that produced by http://ssd.jpl.nasa.gov/horizons.cgi although on the only occassion that I used it I used the email option as per the following:

Here's a sample template for an e'mail message to request xyz coordinates
from Horizons for use with Celestia. You will have to edit the returned
message into the format that Celestia uses.

The message must be mailed to the address "horizons@ssd.jpl.nasa.gov"
The subject must be "JOB" ( do not include the quotes in either )

The body of the message should consist of the following text which
is between the lines of =====. Don't include those lines.
The lines starting with "!$$" are required, however.
Replace the fields ending in "here" with appropriate values.
Don't touch any of the other lines until you've read and understood
Horizons' documentation.
==========================================================
!$$SOF (ssd) JPL/Horizons Execution Control VARLIST
EMAIL_ADDR = 'your address here' ! 'you@there.com'
COMMAND = 'object name or id# here' ! e.g. 'TRITON'
OBJ_DATA = 'NO'
MAKE_EPHEM = 'YES'
TABLE_TYPE = 'VECTORS'
CENTER = '@10'
REF_PLANE = 'ECLIPTIC'
SITE_COORD = '0,0,0'
START_TIME = 'starting date here' ! e.g. '1989-Aug-23 09:00'
STOP_TIME = 'ending date here' ! e.g. '1989-Aug-27 09:00'
STEP_SIZE = 'sample period here' ! e.g. '10m' or '2d'
REF_SYSTEM = 'J2000'
OUT_UNITS = 'KM-D'
VECT_TABLE = '1'
VECT_CORR = 'NONE'
TIME_DIGITS = 'MIN'
CSV_FORMAT = 'NO'
VEC_LABELS = 'NO'
ELM_LABELS = 'NO'
R_T_S_ONLY = 'NO'
CA_TABLE_TYPE= 'EXTENDED'
CALIM_SB= '0.1'
CALIM_PL= '.1, .1, .1, .1, 1.0, 1.0, 1.0, 1.0, .1, .003'
!$$EOF++++++++++++++++++++++++++++++++++++++++++++++++++++++
==========================================================

[mcaplinger]

[font=Courier New]Yes - The data (with some reformatting) is the same as that produced by http://ssd.jpl.nasa.gov/horizons.cgi although on the only occassion that I used it I used the email option as per the following...

Note that Horizons is outputting everything in heliocentric XYZ. If you did that for a Mars-orbiting spacecraft, then if Celestia's idea of where Mars is would have to match JPL's exactly, or the orbit would come "unstuck" from the planet. I'm pretty sure that the XYZ coordinates that Celestia uses should be Mars-centered. I'll have to get the source to see if it's oriented in J2000, but I seriously doubt that it is.

[mcaplinger]

I'm pretty sure that the XYZ coordinates that Celestia uses should be Mars-centered. I'll have to get the source to see if it's oriented in J2000, but I seriously doubt that it is.

I found the following about Celestia's SampledOrbits:

"The origin is the center of the parent object, whether it's a star or a planet. If the parent is a planet, the +z axis is the planet's north pole and the xy plane is the planet's equatorial plane at the reference epoch J2000. The x axis points at the ascending node of the equatorial plane on the ecliptic."

I believe this is the same inertial frame as the NAIF Toolkit's MARSIAU frame (not to be confused with the rotating IAU_MARS frame, alas.)

edit: for those of you still reading this obscure discussion, I think I was wrong: the Celestia frame is what we usually call Mars Mean Equator and Equinox of J2000, which is different from MARSIAU. Back to the drawing board.