Juno development, launch, and cruise, Including Earth flyby imaging Oct 9 2013 |
Juno development, launch, and cruise, Including Earth flyby imaging Oct 9 2013 |
Apr 3 2006, 09:57 PM
Post
#1
|
|
Member Group: Members Posts: 172 Joined: 17-March 06 Member No.: 709 |
I thought that it was time to start a new thread devoted to the JUNO Jupiter
Orbiter mission. This New Frontiers Mission #2 seems to be a "stealth" project with little information available on the Web. In fact, the official NASA JUNO web site is quite pitiful. It contains the minimal amount of information on what seems to be an intriguing mission, in terms of both science and engineering. Does the UMSF community have information on this mission that has not been widely seen before? Another Phil |
|
|
Mar 14 2007, 09:35 AM
Post
#2
|
|
Senior Member Group: Members Posts: 1870 Joined: 20-February 05 Member No.: 174 |
Early deep space missions (not including REALLY early pre-Mariner stuff, which I think tended to use lower frequencies) used S-band. X-band and Ka-band let you focus your spacecraft transmitted power (say 20 watts RF) onto smaller and smaller targets surrounding the Earth. The beam-spots are essentially diffraction limited and cover a vastly larger area than the Earth. You just try to have pointing accurate enough that Earth is in the near-center of the beam-spot. The result of higher frequencies is more bits of data per transmitted watt per hour.
Drawbacks include more precise antenna pointing required at the spacecraft and opacity of heavy precipitation on Earth to the shorter wavelengths. With 2 or 3 frequencies, you can play valuable games increasing precision in ranging and doppler measurements. Space is NOT empty, it contains ionized plasma, as does Earth's ionosphere, and planetary ionospheres crossed during radio occultations. Earth also has an atmosphere, containing various vertical temperature and humdity profiles. All these have effects on the radio transmission. With one frequency, you just model them as best as you can. With more frequencies, you can start to separate out plasma effects and atmosphere effects and maybe variable column water vapor abundance effects -- directly from the data. Plasma/ionospheres have more effect at long wavelengths... look at HF (strong) VHF (usually weak) and UHF (minimal) ionosphere bounce of radio transmissions on Earth. Gasses have different frequency dependent effects. Mariner 5 carried a radio RECEIVER for a dual frequency occultation experiment at Venus. Stanford university transmitted a dual frequency carrier wave at the spacecraft which measured the signal strength (and maybe doppler shift, I can't remember) of each signal as it went behind the planet. JPL, meantime, did a Spacecraft-to-Earth S-band occultation like Mariner 4 did at Mars. It turned out the low frequency occultation data (C band? L band?) was so strongly refracted that below certain altitudes, refracted raypaths crossed and there were "caustiics"... mirages... in the signal and it could not be uniquely interpreted. Similar experiments have not flown since on deep space missions. It would still be useful for things like Io ionosphere and trace atmosphere occultations. |
|
|
Lo-Fi Version | Time is now: 27th September 2024 - 03:46 AM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |