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NEAR/Eros vs. Spirit/Mars landing



 
 
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Old January 8th 04, 10:59 AM
Richard Clark
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Default 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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