ICAPS Precursor Experiment IPE
INTRODUCTION
The different steps in the formation of planetary systems are still badly known; especially the
accretion of tiny dust particles to small pebbles and rocks is a badly understood phenomenon.
On earth, dust particle aggregation experiments are seriously hampered by sedimentation due
to gravity. This can be compensated for single sized particles, but it is impossible to
compensate this for collections of particles with different sizes, as will be the case for
growing particle aggregates. In order to get a better understanding of the early stages of planet
formation, these kinds of experiments should be performed in an environment where
sedimentation can be eliminated. The ideal place for this is the International Space Station
(ISS) that offers long periods of microgravity.
The only way to compare results of experiments run in the laboratory (either in space or on
earth) with astronomical observations is by looking at the effects that grains have on the
scattering of the light from the central star. However, since it is not yet known what kind of
aggregates will form, and because the light scattering calculations of ensembles of irregular
grains are not easy to solve, the study of light scattering measurements from grains formed by
accretion will significantly improve our knowledge not only in our own solar system, but also
around other planet forming systems.
The ICAPS Precursor Experiment (IPE) is based on a part of the microgravity experiment
proposal (Ref. AO-99-018), which a European expert team submitted to ESA in response to
the AO 98-99 on Microgravity Research and Applications in Physical Sciences and
Biotechnology.
The final presentation of Phase A/B of ICAPS-Sounding Rocket Experiment (ICAPS-SRE)
was given on 19 September 2003. Later the decision has been made by ESA to transfer this
experiment to the ISS (either in the Microgravity Science Glovebox (MSG), or as a free
standing experiment in the Russian module). The results of the above-mentioned study have
been used as guideline for the document at hand.
The complete IPE set-up shall be integrated into the Microgravity Science Glove Box (MSG)
on-board the International Space Station (ISS) or in the Russian Segment of the ISS. The
decision shall be taken within three months after the start of the project.
IPE shall be uploaded to the ISS in PROGRESS, ATV, MPLM or US Space Shuttle.
MISSION DEFINITION
Presently there are three types of experiments foreseen for IPE that are denoted as Type 1,
Type 2, and Type 3 experiments.
Type 1 experiments: CODAG-type experiments.
Type 1 experiments are foreseen to augment the knowledge on Brownian motion driven dust
agglomeration in molecular clouds and star-forming regions. From the CODAG missions it
became clear that Brownian agglomeration studies in dust clouds not only require high-
quality microgravity conditions but also the exclusion of other external accelerations. In
particular, the thermophoretic motion, which was responsible for the rather rapid loss of the
dust clouds in the CODAG experiments, must be reduced. Thus, an active temperature control
is required for an extension of previous experiments. There is a strong need to gain additional
information about
 Dust agglomeration with different particle materials, particle sizes, particle
morphologies as well as on non-monodisperse initial size distributions (e.g. bimodal
size distribution for inverse runaway growth simulations)
 Brownian motion and Brownian rotation of irregular particles (e.g. needles,
agglomerates).
It is estimated that the average runtime for experiments of Type 1 will be 10 minutes. This
does not take into account experiment preparation and data handling after the end of the
experiment. Therefore, these 10 minutes is the expected time between dust injection and the
last scientific measurement (image or LSU data).
The order of the main steps in experiment Type 1 is:
1. Select dust sample
2. Start cogwheel to bring the sample in the chamber
3. When there is (enough) dust stop the cogwheel
4. Observe the sample with the DHM/LDM,
5. Observe the sample with the overview camera’s
6. Observe the sample with the light scattering unit
7. End of the experiment and clean the chamber (if necessary).
Step 4, 5 and 6 might be operated simultaneously or separately.
Type 2 experiments: Paul-trap experiments.
Experiments on dust clouds suffer from diffusion- and thermophoresis-driven particle loss
even in the case of active temperature control for an estimated timescale of longer than 10
minutes. Thus, active capturing of dust clouds is required for long-duration agglomeration
experiments (in which, e.g., very large dust agglomerates are formed). Preliminary work has
shown that a 4-ring electrical quadrupole trap efficiently captures clouds of slightly charged
dust particles and prevents them from being lost to the walls of the experiment chamber. With
the use of a Paul trap scientifically important long-duration dust agglomeration experiments
can be performed with several additional advantageous properties:
 unlimited observation time
 non-Brownian motion velocity field
 further concentration of dust cloud reduces experimental timescales
 dust cloud is always concentrated towards the same point in space (but only if other
disturbing factors like thermophoresis can be minimized) so that a fixed observational
volume (for microscopes and LSU) can be used
 ideally one large agglomerate will form in the center of the Paul trap which can be
investigated by microscopy and LSU.
The runtime for Type 2 experiments is much harder to estimate because it denotes the time
between dust injection and the termination of the experiment. The latter might, in some cases,
be determined by the formation of single, large agglomerate in the center of the Paul trap with
some subsequent scientific measurements of its properties. For low concentration efficiencies
of the Paul trap (wanted or unwanted), the experiment duration is basically unlimited. Thus,
we give as a rough estimate 30 minutes runtime for Type 2 experiments. A better estimation
of the mean duration of Type 2 experiments will only be available when IPE is operational.
The order of the main steps in experiment Type 2 is:
1. Select dust sample
2. Start cogwheel to bring the sample in the chamber
3. Turn on the Paul trap
4. When there is (enough) dust stop the cogwheel
5. Observe the sample with the DHM/LDM,
6. Observe the sample with the overview camera’s
7. Observe the sample with the light scattering unit
8. Turn off the Paul-trap
9. End of the experiment and clean the chamber (if necessary).
Step 5, 6 and 7 might be operated simultaneously or separately and/or might require the
temporarily switching off of the Paul trap.
Type 3 experiments: Photophoretic experiments.
Manipulation of light-absorbing dust agglomerates is feasible and desirable. Photophoretic
drift velocity increases with increasing size of dust agglomerates so that with the use of four
collimated light sources (with a 1 cm diameter), large dust agglomerates can be arbitrarily
moved and manipulated within the embedding dust cloud. Note that much smaller dust
agglomerates, however, experience a much smaller photophoretic drift so that the embedding
dust cloud is not too much distorted. Thus, experiments can be realized with the following
objectives:
 Realistic simulation of preplanetary runaway growth
 Formation of growing single agglomerates and active positioning of these
agglomerates in the field of view of the microscope and LSU
Since dust coagulation in Type 3 experiments is expected to be faster than in Type 2
experiments due to forced run-away growth, we expect that the runtime of a single experiment
will be in the order of 10 minutes.
The order of the main steps in experiment Type 2 is:
1. Select dust sample
2. Start cogwheel to bring the sample in the chamber
3. Turn on the Paul trap
4. When there is (enough) dust stop the cogwheel
5. Observe the sample with the DHM/LDM,
6. Observe the sample with the overview camera’s
7. Observe the sample with the light scattering unit
8. Turn off the Paul-trap and select a target grain
9. Move the target grain with the optical manipulation device back and forwards
10. Repeat step 5, 6, 7 and 9
11. Stop the optical manipulation device
12. End of the experiment and clean the chamber (if necessary).
Step 5, 6 and 7 might be operated simultaneously or separately and/or might require the
temporarily switching off of the Paul trap. During step 10 it might be necessary to temporarily
switch of the optical manipulation device (e.g. for step 7) and it also might be necessary to
turn on the Paul-trap to confine the cloud again.
Estimation of the number of individual experiments to be performed
with IPE
A conservative estimate of the amount of dust required for a single dust-cloud injection is 0.1
g. The total amount of dust expected to be dispersed in a 1000 cm3 vacuum chamber with a
gas pressure of 100 Pa is ~1mg, assuming an efficiency of only 1% which, by experience, is a
lower limit to the efficiencies expected for IPE. Taken into account that a tray of dust samples
will contain about 50g, at least 500 dust-cloud experiments can be performed.
Estimation of the distribution of the dust-agglomeration experiments and the resources
required for their performance
The following table summarizes the estimated distribution of experimental parameters and
resources within the three types of dust-agglomeration experiments in IPE.
Experiment overview
Type 1
20
5
5
125
Type 3
5
5
1
25
Average runtime per experiment (minutes) 10
Total runtime for all experiments (minutes) 1000
30
3750
10
250
Amount of digital data recorded
per experiment (GB)
Total amount of digital data recorded
for all experiments (GB)
1
3
1
100
375
25
No. of materials
No. of individual experiments
No. of Paul trap parameters
Total no. of experiments
Type 1
20
5
100
These are the initial set of experiments that the scientists would like to perform. It is
envisioned that the results from this experiment will trigger new requests for experiments. In
conclusion, the estimated total runtime for the first 250 dust-agglomeration experiments will
be around 100 hours. Therefore the total runtime for the 500 dust agglomeration experiments
will be about 200 hours (Note that this only counts the real observing time, and not the
experiment preparation time).