Atlantis Online
September 21, 2019, 10:17:03 am
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Update About Cuba Underwater Megalithic Research
http://www.timstouse.com/EarthHistory/Atlantis/bimini.htm
 
  Home Help Arcade Gallery Links Staff List Calendar Login Register  

Cassini–Huygens Probe

Pages: [1] 2   Go Down
  Print  
Author Topic: Cassini–Huygens Probe  (Read 195 times)
Abraxas
Superhero Member
******
Posts: 3194



« on: June 21, 2007, 01:44:28 am »

Overview

Huygens was designed to enter and brake in Titan's atmosphere and parachute a fully instrumented robotic laboratory down to the surface. When the mission was planned, it was not yet certain whether the landing site would be a mountain range, a flat plain, an ocean, or something else, and it was hoped that analysis of data from Cassini would help to answer these questions.


Based on pictures taken by Cassini at 1,200 km away from Titan, the landing site appeared to be, for want of a better word, shoreline. Assuming the landing site could be non-solid, the Huygens probe was designed to survive the impact and splash-down with Titan's liquid surface for several minutes and send back data on the conditions there. If that occurred it was expected to be the first time a human-made probe would land in an extraterrestrial (i.e. non-Earth) ocean. The spacecraft had no more than three hours of battery life, most of which was planned to be taken up by the descent. Engineers only expected to get at best 30 minutes of data from the surface.

The Huygens probe system consists of the 318 kg probe itself, which descended to Titan, and the probe support equipment (PSE), which remained attached to the orbiting spacecraft. Huygens' heat shield was 2.7 m in diameter; after ejecting the shield, the probe was 1.3 m in diameter. The PSE included the electronics necessary to track the probe, to recover the data gathered during its descent, and to process and deliver the data to the orbiter, from which it will be transmitted or "downlinked" to the ground.

The probe remained dormant throughout the 6.7-year interplanetary cruise, except for bi-annual health checks. These checkouts followed preprogrammed descent scenario sequences as closely as possible, and the results were relayed to Earth for examination by system and payload experts.

Prior to the probe's separation from the orbiter on December 25, 2004, a final health check was performed. The "coast" timer was loaded with the precise time necessary to turn on the probe systems (15 minutes before its encounter with Titan's atmosphere), then the probe detached from the orbiter and coasted in free space to Titan in 22 days with no systems active except for its wake-up timer.

The main mission phase was a parachute descent through Titan's atmosphere. The batteries and all other resources were sized for a Huygens mission duration of 153 minutes, corresponding to a maximum descent time of 2.5 hours plus at least 3 additional minutes (and possibly a half hour or more) on Titan's surface. The probe's radio link was activated early in the descent phase, and the orbiter "listened" to the probe for the next 3 hours, including the descent phase, and the first thirty minutes after touchdown. Not long after the end of this three-hour communication window, Cassini's high-gain antenna (HGA) was turned away from Titan and toward Earth.

Very large radio telescopes on Earth were also listening to Huygens's 10-watt transmission using the technique of very long baseline interferometry and aperture synthesis mode. At 11:25 CET on January 14, the Robert C. Byrd Green Bank Telescope (GBT) in West Virginia detected the carrier signal from the Huygens probe. The GBT continued to detect the carrier signal well after Cassini stopped listening to the incoming data stream. In addition to the GBT, eight of the ten telescopes of the continent-wide VLBA in North America, located at Pie Town and Los Alamos, NM; Fort Davis, TX; North Liberty, IA; Kitt Peak, AZ; Brewster, WA; Owens Valley, CA; and Mauna Kea, HI, also listened for the Huygens signal.

The signal strength received at Earth from Huygens was comparable to that from the Galileo probe (the Jupiter atmospheric descent probe) as received by the VLA, and was therefore too weak to detect in real time because of the signal modulation by the (then) unknown telemetry. Instead, wide-band recordings of the probe signal were made throughout the three-hour descent. After the probe telemetry was finished being relayed from Cassini to Earth, the recorded signal was processed against a telemetry template, enabling signal integration over several seconds for determining the probe frequency. It was expected that through analysis of the Doppler shifting of Huygens' signal as it descended through the atmosphere of Titan, wind speed and direction could be determined with some degree of accuracy. Through interferometry, it was also expected that the radio telescopes would allow determination of Huygens's landing site on Titan with exquisite precision, measuring its position to within 1 km at a distance from Earth of about 1200 million kilometres). This represents an angular resolution of approximately 170 microarcseconds. A similar technique was used to determine the landing site of the Mars exploration rovers by listening to their telemetry alone.


Report Spam   Logged


Pages: [1] 2   Go Up
  Print  
 
Jump to:  

Powered by EzPortal
Bookmark this site! | Upgrade This Forum
SMF For Free - Create your own Forum
Powered by SMF | SMF © 2016, Simple Machines
Privacy Policy