CRIA_Proposal - University of Colorado at Boulder

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Cosmic dust Reflectron
for Isotopic Analysis
(CRIA)
Proposal
Project Team:
Laura Brower
Loren Chang
Dongwon Lee
Marcin Pilinski
Mostafa Salehi
Weichao Tu
Drew Turner
Contact Information:
Loren Chang
[email protected]
Submitted To:
______________________________ Date: ___________
Dr. X. Li
______________________________ Date: ___________
Dr. S. Palo
______________________________ Date: ___________
Dr. Z. Sternovsky1. Executive Summary
The study of cosmic dust has become of increasing interest in the last decade.
1
NASA and the European Space Agency have put forth a multitude of spacecraft
to explore the inner and outer solar system, with a top-level goal of exploring the
origins of the solar system. The Cassini, Ulysses, and Stardust missions have all
contributed significantly to this goal by carrying instruments dedicated to the
study of cosmic dust flux and composition. However, a need still exists for a lowcost instrument with low mass and low power draw that can measure the
composition and flux of dust particles in the space environment. This instrument
should be easy to fabricate at relatively low-costs and be a suitable, low-impact
option for flights of opportunity.
The Cosmic dust Reflectron for Isotopic Analysis (CRIA), a time-of-flight (TOF)
mass spectrometer, is capable of providing in situ measurements of the mass
composition of spaceborne dust. The design concept of CRIA is inherited from
the laboratory prototype Large Area Mass Analyzer (LAMA)1. The large target
area and high mass resolution of LAMA makes it capable of measuring the mass
composition of low flux dust. LAMA expands upon the design of previous TOF
mass spectrometers by using a simple electrode geometry; this uniquely creates
a parabolic electric field to focus ions for detection. Other TOF mass
spectrometers in the past have utilized parabolic targets, which are costly to
manufacture and have a lower mass resolution; or have had target areas too
small to be effective outside of high flux regions.
The design of a low cost, high-resolution mass spectrometer for analyzing
spaceborne dust can be achieved by scaling down the LAMA instrument to a size
better suited for inclusion aboard missions of opportunity. The Technology
Readiness Level (TRL) of LAMA can be further improved from level 4 to level 5
with CRIA. The CRIA design will address the aforementioned goals in a one-year
time frame. Table 1 compares the specifications of LAMA and the proposed
CRIA design.
Parameter
Effective Target Area (m 2)
Mass Resolution (m/m)
Diameter (cm)
Power Consumption (W)
Instrument Mass (kg)
CRIA
>0.045
>100 (team goal of 200)
40
<10
<10
LAMA
0.2
200
64
>10
>10
Table 1: LAMA and estimated CRIA specifications.
2. Background
Cosmic dust particles are important mosaic pieces in the understanding of the
evolution of our solar system and galaxy. Spanning a range of sizes from a few
tenths of a millimeter to molecular lengths, cosmic dust permeates space, from
diffuse interstellar dust, to denser clouds, nebula, and planetary rings.
The cosmic dust present in the Solar System can be subdivided by origin into
2
interstellar dust, which originates from interstellar space, and interplanetary dust,
which is produced in the Solar System itself. The original sources of interstellar
dust are believed to be supernovae or older stars no longer on the main
sequence. These sources expel large amounts of gas and dust, including
oxygen, silicon, carbon, and other metals into the surrounding space. Expanding
and cooling over time, these clouds of gas and dust eventually contract, forming
the building blocks for new stars and planetary systems. In contrast to interstellar
dust particles which predate the Solar System, interplanetary dust is much
newer, and generated by mechanisms such as comets, asteroids, and collisions
between various Solar System bodies.
The elemental composition of cosmic dust is characteristic to the time and place
of its formation, and/or carries the signatures of the evolution of matter in various
environments. Analysis of cosmic dust yields information on both our own Solar
System, as well as on other stars elsewhere in our Galaxy.
The most direct method of studying cosmic dust is through sample return using
specialized aircraft or spacecraft, such as the dust collector on the Stardust
mission. Dust particles from the Wild 2 comet, as well as interstellar dust
particles were successfully captured using an aerogel target and returned to
Earth for analysis. However, this method requires very specialized mission
design and planning, while analysis of the returned samples requires
considerable time and labor. As such, instruments capable of performing in-situ
measurements of dust flux and composition are also desired, both for
convenience and for ease of inclusion aboard missions of opportunity.
In-situ dust analyzer instruments of various designs have been successfully
employed on several missions. The Student Dust Counter (SDC) flown aboard
the New Horizons spacecraft is an example of one such instrument. SDC utilizes
passive polyvinylidne fluoride (PVDF) sensors, capable of detecting dust impacts
as a change in capacitance. The resulting signal can then be used to infer the
mass and velocity of the incoming dust particle, as well as the overall dust flux.
However, the PVDF film cannot resolve smaller dust particles with masses less
than 10-12 g, or determine the elemental composition of dust particles.
The elemental composition of cosmic dust can be determined using a time-offlight mass spectrometer, which infers ion masses by accelerating them through
an electric field and examining the time required to travel a set path length to a
detector. An example of a TOF mass spectrometer is the Cosmic Dust Analyzer
(CDA), flown aboard the Galileo, Cassini, and Ulysses missions. In CDA,
incoming dust particles are ionized upon impact with a parabolic target, and then
electrically accelerated to a detector located at the focus. CDA provides analysis
of the elemental composition of dust particles and provides a large target area for
improved dust collection; however, the mass resolution of the instrument is rather
low. Additionally, the parabolic targets used in CDA are difficult to fabricate to a
high degree of precision.
3
The use of a parabolic target is avoided in the design of the Cometary and
Interstellar Dust Analyzer (CIDA), flown aboard the Stardust spacecraft. Rather
than using a parabolic target to focus ions, CIDA employs a reflectron in which
the ions are focused and accelerated to the detector using an electric field,
compensating for the spread in ion energies and allowing CIDA to achieve a
much higher mass resolution compared to CDA. However, CIDA has a much
smaller effective target area, only 1/20th that of CDA, limiting the number of
impacts detected by the instrument under low flux conditions.
Instrument
Focusing
Method
Mass Range
(g)
Mass
Resolution
Target Area
(m2)
Status
(m/m)
Parabolic
5 x 10-14 - 10-16
20 – 50
0.1
Target
CIDA
Reflectron
5 x 10-7 - 10-14
250
0.005
LAMA
Reflectron
10-10 – 10-16
200
0.2
-10
-16
CRIA
Reflectron
10 – 10
>100
0.045
Table 2: Comparison of past TOF dust analyzers. (* Projected)
CDA
TRL 9
TRL 9
TRL 4
TRL 5*
Previous instruments such as CDA, suffered degraded mass resolution in favor
of increased surface area, or vice-versa in the case of CIDA. Improved
technology, as manifested in the LAMA design, allows for a universal in-situ
instrument design that incorporates high performance and large surface area for
low flux environments and can be adapted to various missions at relatively low
cost. The LAMA concept thus serves as the basis for the CRIA instrument.
3. Science Goals
The instrument design should include the following capabilities:
 Adaptable to a wide range of flux environments
 Capable of analyzing the elemental composition and isotopic ratios of
individual dust grains
 Capable of determining the size distribution of dust particles
 Capable of interfacing with a Dust Trajectory Sensor (DTS) to determine
the source of the analyzed particles
4. Project Goals
Based upon the above considerations, the top level goals of the CRIA project are
as follows:
 To design an instrument capable of performing in-situ measurements of
the elementary and isotopic composition of space-borne dust particles.
 To detect dust particles and determine their mass composition and
4



isotopic ratios.
To design an instrument based on the LAMA concept that achieves the
following: reductions in size, mass, and power in order to be compatible
with possible missions of opportunity.
To achieve a Technology Readiness Level (TRL) of five or higher for the
instrument.
To investigate the limits of scalability of the instrument and determine the
upper and lower limits of sensitivity (size: between 50% and 125%) in
order to provide statistical data and options for a variety of possible
missions
5. Instrument Design Concept
The elemental composition of cosmic dust particles can be measured by the
ionization of the dust grain upon hypervelocity impact. The generated ions can
then be analyzed using the time-of-flight method. A nondestructive measurement
of the dust grain’s velocity and direction is possible using state of the art charge
sensitive amplifiers connected to charge pickup electrodes.
There has been a significant improvement in the basic design of mass analyzing
instruments. The electric field configuration of the LAMA instrument allows for a
higher mass resolution than previously flown mass spectrometers. Additionally,
the LAMA instrument has a large target area, allowing for more dust impacts.
The CRIA design will inherit the geometrical configuration of LAMA, allowing it to
retain the high mass resolution and relatively large target area.
The LAMA instrument is in the shape
of a cylinder and is comprised of an
impact target, an acceleration region,
an ion-focusing region, and an ion
detector (Figure 4.1). Incoming dust
particles are ionized upon impact with
the target and are accelerated by an
electric field between the target (held
at a positive potential) and an innergrounded grid. The accelerated ions
enter the focusing region where a
parabolic electric potential created by a
series of ring and annular electrodes
focuses them onto the ion detector.
The masses of the ions can then be
deduced from their time-of-flight.1
6. Mission Operations Concept
Figure 4.1: Diagram of the LAMA
instrument with dust impact simulated by CRIA will be designed with the goal of
laser. From Sternovsky et al, 2007.
5
inclusion aboard a future mission targeted at studying interstellar and
interplanetary dust. As no such mission has yet been announced, the design
parameters and environmental considerations will be based upon the now
defunct Cosmic DUNE (Cosmic DUst Observatory Near Earth) mission 2. The
Cosmic DUNE mission was proposed to study the near-Earth interplanetary and
interstellar dust environment for a two-year period. The spacecraft was based
upon the Mars Express platform, with an orbit located at the Sun-Earth L2 point;
this orbital design avoids debris belts at altitudes at and below geosynchronous
orbit. Relevant parameters of the Cosmic DUNE mission are listed in Table 3.
The operational environment at the Sun-Earth L2 point places several constraints
upon the design of CRIA. The primary source of thermal energy at the L2 point is
solar radiation, with fluxes of 1291-1421 W/m2. A spacecraft at the Sun-Earth L2
point will pass through all regions of the magnetotail as well as the free solar
wind. Here the plasma density is roughly 1-10 particles/cm3 with ion energies of
10 eV and electron energies of 50 eV. The plasma is comprised of 95%
hydrogen, and 5% helium, with a velocity of approximately 450 km/s. Predictions
of short-term variability in these conditions will require the use of space weather
models. The aforementioned plasma and thermal effects may result in differential
charging of the instrument, and possibly sustained arcing if electric potential
differences greater than 100 V result, though such effects at L2 will be less
severe than for spacecraft in geosynchronous or low Earth orbit.3
Dust charging is dominated by photoemission and the dust surface potential will
be around +5 V. However, the effects of the charged electrodes upon the
incoming dust particles will be minimal due to the small masses of the dust
particles.
As the main concentrations of orbital debris occur at or below geosynchronous
orbit, the debris flux at L2 is negligible. Micrometeoroids are a significant factor
with fluxes of approximately 10 m-2 year--1 for masses of 10-7 grams.3
Location
Total Available Payload Mass (kg)
Total Available Payload Power (W)
Stabilization
Instrument Command Uplink (per week)
Onboard Storage Capacity (Gbits)
Payload Data Rate (kbps)
Mission Duration
Earth-Sun L2 (~230 R)
63*
53*
3-axis stabilized
1-4
2
1
2 years, possible 1 year extension
Table 3: Overview of Cosmic DUNE mission parameters.
* Divided among 5 instruments.
7. Proposed Schedule
Major milestones for the CRIA project are listed in Table 4. Design reviews are
expected to be held in Spring 2007 with the goal of completing a paper design by
6
May 2007. The engineering model will be completed by December 2007.
Major Milestones
Kick-off
Draft Requirement Review
Conceptual Design Review
Preliminary Design Review
Critical Design Review
Date
1-17-2007
2-14-2007
2-23-2007
3-21-2007
5-4-2007
Table 4: Major milestones of CRIA project.
8. References
1. Z. Sternovsky, K. Amyx, G. Bano, M. Landgraf, M. Horanyi, S. Knappmiller, S.
Robertson, E. Grun, R. Srama, S. Auer, “Large area mass analyzer instrument
for the chemical analysis of interstellar dust particles”, Rev. Sci. Instr., 78, 1,
2007.
2. E. Grun et al, “Cosmic DUNE: An Observatory for the study of Interstellar and
Interplanetary Dust”, ESA Sci., 5, October 2001.
3. B.J. Anderson, R.E. Smith, “Natural Orbital Environment Guidelines for Use in
Aerospace Vehicle Development”, NASA Technical Memorandum 4527, June
1994.
Retrieved
on
February
11,
2007
from:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19940031668_1994031668.
pdf
9. Acronyms
CRIA:
LAMA:
TOF:
TRL:
Cosmic dust Reflectron for Isotopic Analysis
Large Area Mass Analyzer
Time-of-flight
Technological Readiness Level
7
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