From: jtk@s1.gov (Jordin Kare)
Subject: The BB Gun experiment (was Re: Asteroid explorer)
Organization: LLNL
Distribution: usa
Date: Mon, 14 Sep 1992 21:44:04 GMT

In article <pgf.716428199@srl02.cacs.usl.edu> pgf@srl02.cacs.usl.edu (Phil G. Fraering) writes:
>steinly@topaz.ucsc.edu (Steinn Sigurdsson) writes:
>
>>As per the AO you get $17million (1992) for hardware, R&D,
>>staff etc, same again for launch; mission ops and data analysis
>>are extra. So, put together a CCD camera, a (IR?) spectrometer,
>>a low(medium?) gain antenna, redundant tape recorders, the best CPU
>>and memory that's flight qualified (is the intel chip qualified yet?)

Clementine (SDIO sensor test mission which will do a 2-month lunar mapping
mission followed by an asteroid flyby) will fly a MIPS R-3000-type processor
and 1.6 gigabit solid state memory.

>I've been thinking, though... what we really want from these
>asteroids is structural data. How could we get that?
>
>[Following idea Patent Pending Phil's Crazy Ideas Inc. ...] ;-)
>
>As Marvin Minsky pointed out a short while ago, small fuel tanks
>and large fuel tanks have the same mass to fuel mass ratio. So
>for an ion-drive powered probe you could with little mass overhead
>have lots of small tanks instead of one large tank for your
>fuel. Suppose for example you use six tanks.
Plumbing tends to make multiple small tanks less desirable, but the
differences are small.
>
>Every once in a while in the mission you need to "stage" and
>drop an empty fuel tank. Well, instead you use it: you keep
>it around until you're about to do a flyby of an asteroid.
>A small dogleg/jettision manuever, and you've slammed a fuel tank
>into the asteroid, giving your seismometer network lots of data.
>
>Oh, you don't have a seismometer network on the asteroid? 
>Hmmm... what about using a laser rangefinder of some sort,
>to observe the "ringing" in the rock? Would this only be 
>feasible for low probe flyby speeds?

Clementine is flying a state-of-the-art laser rangefinder, with
200 mJ laser pulses at up to 8 Hz for a limited number of pulses, or
1 Hz indefinitely.  It has a 500 km range and 10 m resolution, 
(limited by electronics; could do 3-5 m with some engineering changes).
Not useful for observing seismic vibrations.  Unfortunately, interior
composition will probably require rendezvous for the foreseeable future.

What you _can_ do is use impacts to measure the composition of the
top few cm of surface, reaching below surface dust layers.  I proposed
an  experiment for Clementine, the Impact Plume SPectroscopy experiment,
which would have done this.  It was also called the BB gun experiment,
because it involved launching few-gram, BB sized projectiles from a
spring-powered launcher.  The BB impacts would occur just before
Clementine passed the asteroid, and the impact flares would be observed
spectroscopically.  It's not flying for several reasons, but it would
have been a fun experiment to do.

	Jordin Kare

	[Disclaimer:  any statements made here are my personal opinions
and do not represent the positions of LLNL, the University of California,
or the U.S. Department of Energy]

>
>(which would cause problems: you would like the fuel tank to
>slam in at high speed...)
>
>Well?
>
>--
>Phil Fraering pgf@srl0x.cacs.usl.edu where the x is a number from 1-5.
>Phone: 318/365-5418 SnailMail: 2408 Blue Haven Dr., New Iberia, La. 70560
>
>           --> Support UN military force against Doug Mohney <--


-- 

	Jordin Kare	jtk@s1.gov	510-426-0363