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NEAR/Eros vs. Spirit/Mars landing
NEAR/Eros vs. Spirit/Mars landing
Was sci.physics: Mars has so much atmosphere Instead of the parachute and bouncing bal... In article , (Archimedes Plutonium) writes: I am looking for an alternative to the parachute and bouncing balls method. Usually there are alternative methods. [snip] A landing of a probe onto an asteroid could not be done with parachute. The landing of the NEAR probe on asteroid 433 Eros was accomplished with 5 de-orbit burns. (Keep in mind that NEAR was not designed to land - that was an after thought At the point of touchdown, the still active 5th burn sent it back up about 100 meters or so, and the weak gravity brought it back down with minimal damage. "A person who weighs 150 pounds on Earth would weigh from 0.56 to 1.3 ounces on Eros - about as much as one or two bags of airline peanuts." It is believed to have landed "about 7 meters to the left" of the final descent frame. http://nssdc.gsfc.nasa.gov/imgcat/ht...157417198.html After landing, the craft's gamma-ray spectrometer was used to gather "data on the elemental composition on and just below the asteroid's surface." After about two weeks of receiving data from the slow low-gain antenna through the Deep Space Network, they sent a final "goodbye" message. The "Spirit" rover landing system worked pretty much as planned. It came to a stop about 6 miles from the "ideal" target point, but all agree the "sweet spot" where it ended up couldn't be better. Spirit Overview Faqtoid excerpts: "The system for getting each rover safely through Mars' atmosphere and onto the surface relies on an aeroshell, a parachute and airbags. The aeroshell has two parts: a heat shield that faces forward and a backshell. Both are based on designs used successfully by NASA's Viking Mars landers in 1976 and Mars Pathfinder in 1997. "The parachute is attached to the backshell and opens to about 15 meters (49 feet) in diameter. "The backshell carries a deceleration meter used to determine the right moment for deploying the parachute. Solid-fuel rockets mounted on the underside of the shell reduce vertical velocity and any excessive horizontal velocity just before landing. "The airbags, based on Pathfinder's design, cushion the impact of the lander on the surface. Each of the four faces of the folded-up lander is equipped with an envelope of six airbags stitched together. Explosive gas generators rapidly inflate the airbags to a pressure of about 6900 Pascal (one pound per square inch). Each airbag has double bladders to support impact pressure and, to protect the bladders from sharp rocks, six layers of a special cloth woven from polymer fiber that is five times stronger than steel. The fiber material, Vectran, is used in the strings of archery bows and tennis racquets. "0434 GMT (11:34 p.m. EST) "No longer needed, the heat shield has been jettisoned, exposing the lander inside the descent module. "The heat shield has protected us but now we don't need it," Manning says "We have to undress ourselves. So the lander is now free to rappel down a 20-meter bridle. Once we are in this configuration, this is a great configuration to be in for the lander to both see the surface with a camera and to use a radar to detect its altitude. "When we get to the right altitude, the airbags are inflated. Now we are ready to fire the retrorockets to bring the system to a dead stop from about 180 mph to zero about 12 meters above the ground. "At this point we bounce and bounce and bounce. Just like Pathfinder, we will bounce maybe as much as a kilometer or more from where we let go of the bridle." "0436 GMT (11:36 p.m. EST) "Mission Control has received indications from the spacecraft that it is bouncing on the surface inside its airbags. "With Spirit on the surface, it will use motors to retract the airbags. This operation could take an hour to complete. The lander then will open up like a flower, lowering its petals to reveal the rover tucked inside. Since Spirit has landed with its base petal down -- the best case scenario -- the opening will take less time. [end excerpts] http://spaceflightnow.com/mars/mera/statustextonly.html (And the rest, as they say, is history. Clear Skies, Astro-Peeps! --Richard The Mote around the Beam? http://members.aol.com/RichClark7/read/mote.htm Getting the Right Interpretation http://members.aol.com/AVBibleTAB/av/interpre.htm |
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