PDA

View Full Version : ISEE-3 post-Earth orbital numbers

algomeysa
2014-Aug-17, 11:01 PM
So now that ISEE-3 is a good 1.5 million kilometers from Earth, it should be out of Earth's sphere of influence, and the Hill sphere. It seems like its orbit should be a lot easier to describe, more like a comet or asteroid.

Is there anywhere I can get orbital numbers for it? To plug in items into my old Starry Night program, I need:
mean distance (a) in AU, eccentricity(e), inclination(i), Ascending Node, arg of pericenter (w), mean anomaly(L), epoch.

grapes
2014-Aug-18, 03:08 AM
When it's not firing its engines!

Have you looked over this webpage?
http://spacecollege.org/isee3/

CJSF
2014-Aug-18, 11:19 AM
I thought they were unable to pressurize the tanks, so no engine firings possible? Did I mis-read or misunderstand that?

CJSF

algomeysa
2014-Aug-18, 12:28 PM
So I got some numbers from the JPL email bot and tried to convert them into Starry Night.

Epoch=2456889.309027778
mean distance A = 1.1035163 AU
eccentricity EC= .08464981542641729
inclination inclination 1.220562970160595
ascending node OM= 317.0442659836478
arg of pericenter W = 337.6312052704203
mean anomaly MA= 27.26392211514002
Nearcircular, Ecliptic 2000

There's something I'm not doing right though, because it's already showing over 1 AU from Earth.

Here's the original JPL email bot numbers.
Can anyone spot what I'm doing wrong?

\$\$SOE
2456889.309027778 = A.D. 2014-Aug-19 19:25:00.0000 (CT)
EC= 8.464981542641729E-02 QR= 1.511093845670798E+08 IN= 1.220562970160595E+00
OM= 3.170442659836478E+02 W = 3.376312052704203E+02 Tp= 2456857.242466830648
N = 9.840614172186752E-06 MA= 2.726392211514002E+01 TA= 3.216060670214677E+01
A = 1.650836883126585E+08 AD= 1.790579920582373E+08 PR= 3.658308248864125E+07
\$\$EOE
************************************************** *****************************
Coordinate system description:

Ecliptic and Mean Equinox of Reference Epoch

Reference epoch: J2000.0
xy-plane: plane of the Earth's orbit at the reference epoch
x-axis : out along ascending node of instantaneous plane of the Earth's
orbit and the Earth's mean equator at the reference epoch
z-axis : perpendicular to the xy-plane in the directional (+ or -) sense
of Earth's north pole at the reference epoch.

Symbol meaning

JDCT Epoch Julian Date, Coordinate Time
EC Eccentricity, e
QR Periapsis distance, q (km)
IN Inclination w.r.t xy-plane, i (degrees)
OM Longitude of Ascending Node, OMEGA, (degrees)
W Argument of Perifocus, w (degrees)
Tp Time of periapsis (Julian day number)
N Mean motion, n (degrees/sec)
MA Mean anomaly, M (degrees)
TA True anomaly, nu (degrees)
A Semi-major axis, a (km)
PR Sidereal orbit period (sec)

Ross 54
2014-Aug-18, 03:37 PM
It appears that A=1.1035...AU refers to the mean distance from the Sun, of the spacecraft's orbit, not to its present distance from Earth. The ISEE 3 has an orbit around the Sun quite similar to that of Earth.

algomeysa
2014-Aug-19, 03:02 PM
Ok, I see what I was doing wrong; my old version of Starry Night isn't set up for a spacecraft in solar orbit, so it defaulted to Earth orbit, which is why I was always 1 AU from Earth.

When I entered those numbers again as if it was an asteroid in near-circular orbit, they come out right-ish;

.012 AU or 1 795 174.45 kilometers from Earth

Which is pretty much what that simulation is showing on their website:
1,794,478 kilometers http://spacecraftforall.com/live

Though it doesn't hold up over time; supposedly the next closer encounter between ISEE-3 and Earth is "17 years from now", so 2031, and my simulation doesn't show that...