A wide variety of experiments can be conducted on the Space Station that involve the physics of small particles of planetary significance. Processes of interest include nucleation and condensation of particles from a gas, aggregation of small particles into larger ones, and low velocity collisions of particles. All of these processes could be investigated with a general purpose facility on the Space Station. The microgravity environment would be necessary to perform many experiments, as they generally require that particles be suspended for periods substantially longer than are practical at 1 g. Only experiments relevant to planetary processes will be discussed in detail here, but it is important to stress that a particle facility will be useful to a wide variety of scientific disciplines, and can be used to address many scientific problems

Corso, G. J.

Griffiths, L.

Mackinnon, I.

Marshall, J.

Nuth, J. A., III

Squyres, S.

Werner, B.

Wolfe, J.

English

NASA Technical Reports Server

4.0 PARTICLE FORMATION AND INTERACTION
Steven Squyres (Chairman), NASA Ames Research Center; George J. Corso,
Northwestern University; Lynn Griffiths, MATSCO; Ian Macklnnon, University of
New Mexico; John Marshall, NASA Ames Research Center; Joseph A. Nuth III, NASA
Headquarters; Brad Werner, California Institute of Technology; John Wolfe, San
Jose State University
4.1 Introduction
A wide variety of experiments can be conducted on the Space Station that
involve the physics of small particles (_m to cm in size) of planetary
significance. Processes of interest include nucleation and condensation of
particles from a gas, aggregation of small particles into larger ones, and low
velocity collisions of particles. All of these processes could be
investigated with a general-purpose facility on the Space Station for study of
the physics of small particles. The mlcrogravlty environment of the Space
Station would be necessary to perform many experiments, as they generally
require that particles be suspended for periods substantially longer than are
practical at I g. Only experiments relevant to planetary processes will be
discussed in detail here, but it is important to stress that a particle
research facility will be useful to a wide variety of scientific disciplines,
and can be used to address many scientific problems. We will also discuss
briefly some experiments that would not utilize such a facility. More
detailed descriptions of some specific experiments are presented in the
workshop abstracts.
4.2 Background and Scientific Rationale
Some of the most fundamental processes involved in the origin and
evolution of the Solar System concern the condensation of solid matter from a
gas, the aggregation of small particles to form larger particles, and the
colllsional interaction of particles over a range of sizes. Understanding
particle condensation is critical to understanding the earliest stages of
solar system formation. Classical nucleation theory is inadequate to predict
the condensation of clrcumsolar grains from the early solar nebula.
Experiments have been performed in terrestrial laboratories to duplicate the
nucleation and condensation of planetary particles from the solar nebula, but
such experiments suffer from convective instabilities induced in the gas from
which the condensation takes place. In a microgravlty environment, it will be
possible to conduct condensation experiments with more quantitative accuracy,
and to extend experiments to much more refractory materials. Experiments
extended to low temperature condensation will also be able to investigate
formation of icy grains that went into accretion of the outer planets, their
satellites, and comets.
Once grains formed by condensation in the early solar nebula, they
underwent aggregation into planeteslmals. This process is poorly understood,
particularly in the scenario where significant amounts of gas are still
present. Particle aggregation is also an important part of any process that
injects large amounts of commlnuted material into a planetary atmosphere.
Three such processes are dust storms, explosive volcanic eruptions, and large
impact events. For example, it has been hypothesized that a large impact
could have caused substantial atmospheric dust loading on Earth and subsequent
4-I
https://ntrs.nasa.gov/search.jsp?R=19860017667 2020-03-20T14:27:24+00:00Z
faunal extinctions. Such hypotheses are dependent on the efficacy of dust
aggregation and the rate at which particle aggregates settle from the
atmosphere. Aggregation rates also play a crucial role in calculations of
"nuclear winter" scenarios, and control the lifetime of some volcanic plumes
and large dust storms. Some laboratory experiments suggest that aggregation,
at least under some conditions, is surprisingly effective, but all aggregation
experiments are severely restricted in duration by rapid settling in a I g
gravitational field. The microgravity environment on the Space Station will
allow the process of particle aggregation to be studied in great detail under
a wide range of conditions. Specific parameters that need investigation
include aggregation rates, the size distribution of aggregates, the dependence
of aggregation efficacy on material properties, etc.
Immediately after the first stages of particle aggregation in the solar
nebula, planetesimal formation probably involved collision of particles at
relative velocities of a few m sec -I or less. The detailed dynamics of such
collisions are poorly understood, including particularly the nature of the
conditions necessary for particles to adhere together after a collision.
Factors that affect collision dynamics probably include particle composition,
relative sizes, spin, and ambient gas pressure. The effects of all these
factors are poorly known. Low velocity particle collisions also take place in
planetary ring systems. Collisions result in an effective viscosity for the
rings, and development of diffuslonal instabilities that are manifested as
intricate small-scale structures. In this case the important parameter to
understand is the coefficient of restitution, which describes the inelasticity
of collisions. Attempts have been made to study low velocity particle
collisions by suspending particles from pendula, but such experiments suffer
severely from the restriction of particle motions to two dimensions. Full
three-dimensional interactions, including interaction of more than two
particles, can be conducted in a mlcrogravlty environment.
4.3 Hardware Concept
The high cost of experimentation on the Space Station provides a strong
motivation to develop orbital laboratory facilities that will be capable of
addressing as wide a range of problems as possible, rather than highly
specialized facilities applicable to only one narrow problem. In principle,
all of the investigations outlined above could be conducted in a chamber in
which particle formation and interaction could be induced and observed. One
possible concept for such a facility will be described below. A critical task
to be carried out in the near term is determination of which investigations
can be conducted in a general particle research facility, and which require
more specialized facilities. The general objective will be to design a
facility that is as flexible as possible, admitting as many hlgh-priority
investigations as is feasible without compromising the science. The design
discussed here is very preliminary, and will be subjected to substantial
review, refinement, and revision.
The basic facility is envisioned as residing in a glove box in one of the
Space Station laboratory modules. It is felt that the glove box approach is
necessary to ensure against contamination of the module interior with
particles. The glove box must be at least the size of a double rack ( 38
inches wide) in order to accommodate the necessary equipment. It should be as
voluminous as possible, and include internal power outlets and attachment to a
4-2
thermal control system. The experimental chamber itself would be mounted
inside the glove box. It should also be as voluminous as possible while
allowing space for external attachments within the confines of the glove box;
for a double rack glove box, an experiment chamber 24 inches on a side might
be appropriate. All faces should be readily accessible to an experimenter
outside the glove box, and the positioning of the chamber within the glove box
should be adjustable. The chamber should be pressure tight, and at least one
face should be completely removable. Each face should be equipped with a
general-purpose port to which investigators may attach equipment. Some
standard pieces of equipment should be provided as part of the facility.
These might include illumination sources, still ormotion picture cameras,
laser nephelometers, or photometers. In the case where an investigator could
not build a piece of equipment that would be compatible with a general-purpose
port, the investigator could provide an entire removable face of the chamber
to which his or her equipment would be attached. In the extreme case where
the chamber itself is unsuitable for an investigator, it should be possible
for the investigator to remove the chamber and insert a specialized one that
meets his or her requirements.
The amount of crew interaction that will be required by these experiments
will of course vary from one experiment to the next. In general, however, it
is expected that most will require the close attention of at least one
individual, either the investigator or a trained crew member. A particle
research facility shares the need to effectively handle significant quantities
of small particles with a number of other possible Space Station experiments,
including impact experiments and a wind tunnel. This common need suggests
that a standardized procedure for transporting and handling particles should
be established. Equipment developed for particle transportation, handling,
and storage should be as general as possible.
Several of the partlcle-related experiments described in the abstracts
could not be accomplished in a facility within the Space Station, but could be
conducted outside the Station. These include experiments to collect
mlcrometeorltes, and experiments to study the orbit properties of colliding,
co-orbitlng bodies. Facilities for the conduct of these experiments might be
constructed outside the Space Station, or could perhaps be accommodated on
free-flying spacecraft.
4.4 Recommendations
A particle research facility should be developed for the Space Station
and maintained as a national facility for research involving the physics and
chemistry of small particles in microgravity.
A multi-dlsciplinary workshop will be conducted to define clearly the
scientific rationale for the particle research facility, establish the desired
capabilities of the facility, and establish a strawman design. This workshop
will be conducted at Ames Research Center on August 22-24, 1985. A major
focus of the workshop will he to establish the degree to which widely
differing investigations can share the same facility, and how many specialized
chambers are actually necessary.
The results of this workshop should be incorporated in a report that is
provided to the appropriate individuals at Johnson Space Center, Goddard Space
4-3
Flight Center, and, especially, in the Office of Space Science and
Applications at NASA Headquarters. The report should define the need for the
facility and its configuration as fully as possible. The report should be
completed as soon as possible, and well before the Space Station Interface
Requirements Review in January, 1986.
An effort should be made to obtain funding for the facility at a level
sufficient for completion at the time the Space Station reaches its Initial
Operating Capability (IOC). Potential funding sources include the
Astrophysics, Planetary Science, and Life Sciences programs in the Office of
Space Science and Applications, as well as the Space Station Office itself.
The Space Station should be constructed in a manner that allows the
development of large particle collection and interaction experiments outside
the main Station structure.
4-4


Particle formation and interaction

Particle formation and interaction

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server