posted
Remember the Genesis Probe, NASA's attempt to capture particles from solar wind? It will finally be reaching Earth on Sept. 8th. They've got helicopter stunt pilots that are going to try to catch its sample pod as it hurtles toward Earth. What I wonder is this: why didn't they just equip the thing with a parachute, design it so that it would float, and have it splash down in the pacific or something? Why the elaborate and tricky helicopter catch? Anybody know? Steve, you maybe?
Posts: 16059 | Registered: Aug 2000
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quote:But if the capsule were to descend all the way to the ground, some of its precious cargo would be destroyed. Hence, the mid-air retrieval by helicopter.
I took this to mean more that the impact of hitting the surface (with or without parachute - because I think it has one) they felt would do more damage than it is worth, and the capture in the air will save more data...
posted
There are parachutes involved, Noemon. A better explanation can be found here:
quote:Nearly 19 miles above the ground, the SRC begins to decelerate when the lid of the re-entry capsule ejects and releases the first parachute. This small drogue chute helps to break the speed and stabilize the 500-pound capsule. Moments later, when the SRC is just 1½ miles above ground, a larger rectangular-shaped parafoil—much like a hang glider—allows the capsule to gently spiral downward at an approximate speed of 10 miles per hour.
Meanwhile, two chase helicopters (one lead and one backup) outfitted with specially designed retrieval equipment, move in for the mid-air capture. The lead helicopter flies into the parafoil's glide path, hooks and collapses the chute, and gently lowers the SRC into a sealed container; all in an effort to safely transport the capsule to contamination-controlled laboratory tents, without disturbing the solar samples inside
posted
Cool, thanks Farmgirl! I can understand why they wouldn't want it to strike land, even at 10 MPH, but why not a water splashdown? If the capsule were designed in such a way that it were conical, or perhaps a cylinder with a tapered, pointed end, and were weighted properly so that the tip would point downward, couldn't it be made to hit the water with a relatively low impact?
Now, given, at 10 mph it shouldn't be *too* tricky to catch the thing with the helicopters, but why not the water landing? I know that when struck with sufficient force, water can be as yielding as concrete, but wouldn't the relatively slow 10 mph speed, coupled with the pointed tip entering the water first, prevent this from being a problem? I wonder how much force this capsule is designed to cushion its contents from?
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posted
Well, I think it is a contamination issue, as well, not just an impact issue. Splashing in water, or hitting ground, might contaminate the samples.
That is why they have having the helicopters lower it INTO a sealed container...
posted
Is anyone else maybe thinking this particular project should have waited for a moon base or the international space station? I mean, what if the Solar wind is inhabited by aliens that posess our bodies by means of a creepy black slime that crawls into our eyes and makes us eerily seductive?
:looks at post count:
Well, it was worth it.
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If it's that subject to contamination, though, wouldn't its entering the atmosphere itself risk its integrety? I guess not, but it seems odd. Why couldn't it have been designed to seal itself well enough to keep out sea water? I had assumed that they were afraid that the casing would crack in the event of a landfall, which was why I was suggesting a splashdown.
Hm. This mission got off the launch pad long before the latest shuttle disaster. Why didn't they just have the probe enter into orbit around earth, and then send a shuttle up, have it match the thing's course and velocity, and either use their big robot arm or send out an astronaut to do a space walk and retrieve the thing? Cost, I suppose. Much cheaper to hire a couple of helicopters & crew than to fly a shuttle mission, I'm sure.
posted
"why didn't they just...design it so that it would float, and have it splash down in the pacific or something?"
Possibly because it would sink after hitting water. A floation device has mass/"weight". The more mass an object has, the more expensive it is to get into orbit, to escape velocity, to the chosen solar orbit, and return. Similarly, strengthening an object to withstand the greater force of a land impact would increase its mass.
Like most pure science engineered by a university and sponsored by NASA, the Genesis project was done on a shoestring budget -- with the choice of more money being spent on scientific instruments vs more money being spent on the boosters -- and naturally, the university chose to maximize instrumentation.
Nor is this even vaguely a new retrieval method.
The US's first-generation spy satellites of the 60s used film cameras because of, amongst many other things: The extreme weight of video cameras and short-range video-transmitter; the "portable" shoulder-mounted television camera which caught the slaying of LeeHarveyOswald by JackRuby weighed close to 40kilograms/90pounds (I may be thinkng of a later generation of portable videocams that were cheap enough to be used by local TV stations: the figure that first came to mind was 70kilograms/150pounds). The extreme weight of the associated communications equipment; the local video-receiver and satellite uplink-transmitter for that camera was housed in a moving van. Extremely low pixel resolution compared to photographic film; 35milimetre film had multiple tens of times more pixels than the video cameras of the era. Extremely low light range; film had multiple hundreds of times the dark-to-light gradations of video between the minimum and the maximum brightness it could capture. Extremely low light sensitivity; film could pick up light at levels multiple thousands of times lower than video.
That being the case, the US chose to use film cameras for its surveillance satellites. In order to get the film down for processing&evaluation, the satellites ejected cannisters containing the exposed film in a deorbit trajectory. The cannisters in turn deployed parachutes to slow their descent when re-entry temperature and speed became sufficiently lowered by atmospheric braking.
After the parachuting cannisters' fall-rate and height became low enough, USAF TalkingBirds (mostly C130 cargo planes modified for communications and surveillance missions) plucked the falling cannisters out of the air by use of a nose-mounted forked probe snaring the parachute lines. Later, when computers made deorbit trajectory predictions more reliable -- ie could project a smaller recovery area -- slower helicopters came into occasional use (depending on retrieval target and distance to the recovery zone) because the higher speeds of the cargo planes were no longer necessary to guarantee intercept.
I think that the most intelligence-sensitive spy satellites still used film and mid-air cannister retrieval up until the sixth generation of spy satellites was deployed during the ClintonAdministration.
So we aren't talking about hauling in the Genesis samples by using inexperience pilots trying out a new recovery method.
posted
What you say about the added weight makes sense, aspectre, and it was interesting reading the rest of that informaton. Thanks!
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