Re: (meteorobs) [ASTRO] A humming bird approach to comet probes

----- Original Message -----
From: "Lew Gramer" <dedalus@latrade.com>
To: "Meteor Observing Mailing List" <meteorobs@jovian.com>
Sent: Thursday, April 20, 2000 5:18 PM
Subject: (meteorobs) [ASTRO] A humming bird approach to comet probes

> From: Larry Klaes <lklaes@BBN.COM>
> Date: Thu, 20 Apr 2000 09:14:06 -0400
> Subject: [ASTRO] A humming bird approach to comet probes
> A hovering hummingbird dips in and out of a deep flower with its long
> extracting nectar in a fleeting visit. Now the touch-and-go techniques of
> this small bird have inspired a NASA mission to check out comets. A space
> probe will be equipped with dangling tethers and will use "bump sampling"
> strategies to dig deep into the very core of a comet. The space agency
> its Hummingbird will capture deep-frozen material left over from the big
> bang. "What I think is the most interesting question to answer is the
> relationships of comets to material that ended up on the early Earth and
> took part in the origin of life," says Glenn Carle of the Ames Research
> Center in Moffett Field, California.
> http://www.newscientist.com/nl/0422/touch.html

Hello. I'm new to this list. My name is Paul Johnson. I'm a retired
physicist in Dallas, Texas. I was intrigued by this message relayed by Lew,
so I read the original article published in New Scientist, and there are a
couple of things about the idea that I don't understand.

The NASA team leader, Mr. Carle, says his probe would orbit the comet for up
to a year sampling the comet's atmosphere, by which I assume he means its
coma. The article doesn't say what the probe's orbital radius is, but it can
be pretty high and still be inside the coma. I assume it's high enough so
that the probe's orbital speed is sufficiently slow to permit imaging of the
nuclear surface. For a nuclear mass of 10exp15 kg, an orbital period of
50-100 minutes shouldn't be difficult. That would permit short exposure

The article says the probe would then "advance slowly toward the comet's
nucleus, stopping frequently for safety checks." The only way the probe
could "approach" the nucleus would be to spiral in, which would cause its
orbital speed to increase dramatically. By "stop frequently," I assume he
means to keep the orbital radius constant for a while. Then it says, "the
probe would not land; only two dangling tethers would touch the nuclear
surface." If the probe is orbiting just meters above the nucleus, its speed
relative to the surface would be so great I don't see how the tethers could
make any reasonable contact. And since the coma's density increases with
nearness to the surface, the probe's temperature will obviously increase
dramatically as it approaches.

I must be missing something here. Can someone explain to me how this thing
will work?


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