It's Helios, but not as you know it... (xyz & model)

[JackHiggins]

Hey all

Following up on TERRIER's great Helios model, I have a new model- of a completely different craft! This Helios was 2 seperate probes launched in 1974 & 1976, which went to within 0.3 AU of the Sun (The closest we've ever been, I think...?) It was a joint American and German project. (Well, West Germany as it was then...)

The xyz is from HelioWeb again, so it's not the best but it's still pretty good...

Download from the Spacecraft page on my site http://homepage.eircom.net/~jackcelestia/ but check out some screenshots first...




And here is Helios 2 on it's closest approach to the sun- 0.287AU!

That had a normal 45 deg FOV...

Both Helios probes had a spin rate of 1RPS (once per second), so if it's too fast for you, you can slow it down in the ssc file.

Helios 2 also made a relatively close approach to Mercury, in March 1979 (5.8 million km) but i'm almost certain didn't carry any cameras...
Enjoy!

[ElPelado]

so what did they do? what was their mission?

[JackHiggins]

According to the NSSDC:

This spacecraft was one of a pair of deep space probes developed by the Federal Republic of Germany (FRG) in a cooperative program with NASA. Experiments were provided by scientists from both FRG and the U.S. NASA supplied the Titan/Centaur launch vehicle. The spacecraft was equipped with two booms and a 32-m electric dipole. The payload consisted of a fluxgate magnetometer; electric and magnetic wave experiments, which covered various bands in the frequency range 6 Hz to 3 MHz; charged-particle experiments, which covered various energy ranges starting with solar wind thermal energies and extending to 1 GeV; a zodiacal-light experiment; and a micrometeoroid experiment. The purpose of the mission was to make pioneering measurements of the interplanetary medium from the vicinity of the earth's orbit to 0.3 AU. The spin axis was normal to the ecliptic, and the nominal spin rate was 1 rps. The outer spacecraft surface was dielectric, effectively (because of the sheath potential) raising the low-energy threshold for the solar wind plasma experiment to as high as 100 eV. Also, sheath-related coupling caused by the spacecraft antennae produced interference with the wave experiments. The spacecraft was capable of being operated at bit rates from 4096 to 8 bps, variable by factors of 2. While the spacecraft was moving to perihelion, it was generally operated from 64 to 256 bps; and near 0.3 AU, it was operated at the highest bit rate. Because of a deployment failure of one axis of the 32-m, tip-to-tip, dipole antenna, one axis was shorted, causing the antenna to function as a monopole. The major effect of this anomaly was to increase the effective instrument thresholds, and to introduce additional uncertainties in the effective antenna length. Instrument descriptions written by the experimenters were published (some in German, some in English) in Raumfahrtforschung, v. 19, n. 5, 1975.

And the experiments it carried out were:

Fluxgate Magnetometer for Field Fluctuations
Fluxgate Magnetometer for Average Fields
Search Coil Magnetometer
Fine Frequency, Coarse Time Resolution Spectrum Analysis
26.5-KHz to 3-MHz Radio Wave
Cosmic-Ray Particles
Galactic and Solar Cosmic Rays
Plasma Detectors
Energetic Electron and Proton Detector
Zodiacal Light Photometer
Micrometeoroid Detector and Analyzer
Celestial Mechanics
Solar Wind Plasma Wave

[ElPelado]

ok
1) what is "perihelion"? i heard about it but don't know what it is.
2) what exactly is the "zodiacal light"?

[JackHiggins]

perihelion is the point in an object's orbit where it's closest to the thing it's orbiting, but it's only noticable in objects with pretty eccentric orbits (Pluto, Chandra, comet Halley etc) For halley it'd be the place where the tail is biggest.

zodiacal light is just sunlight reflected by tiny dust particles orbiting in our Solar System. Many of these particles were ejected by comets. Zodiacal light is easiest to see in September and October just before sunrise from a very dark location.

That's from http://antwrp.gsfc.nasa.gov/apod/ap970826.html

(I didn't know that until now!)

[selden]

ElPelado,

English uses many Greek and Roman words in scientific terminology.
Peri = near
Helios = sun
It's the point in the oribit which is closest to the sun.

Zodiacal Light = a very, very faint glow in space seen when looking at the night sky directly away from the sun. It's sunlight reflected from the interplanetary dust.

Does this help?

[ElPelado]

Yes it helped, thanks Jack and Selden.

For halley it'd be the place where the tail is biggest.

Does this also hapen in Celestia? Does the tail change or remain the same all the time?

[JackHiggins]

I recently discovered that the Helios 1 & 2 trajectories were a bit innaccurate... Turns out they were offset 30 degrees from where they should have been! I've converted some more accurate (.asc format) trajectories from the NSSDC ftp site, and you can get the new xyz's from the spacecraft page on http://homepage.eircom.net/~jackcelestia/ (number 30)

The new trajectories are a bit shorter than the originals, but I think it's worth it for the accuracy improvements...