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DATA TRANSFER LINK 2: 3D VISUALISATION CLIENT AT CUSTOMER PREMISES
H. Guijt(1)
, K. Debeule(2)
(1) TERMA, Schuttersveld 9, 2316XG Leiden, The Netherlands, tel: +31 71 524 0835, fax: +31 71 514 3277, email:
(2)
ESA/ESTEC, Keplerlaan 1, 2201AZ Noordwijk, The Netherlands, tel: +31 71 565 5345, fax: +31 71 565 3911,
email:
1 ABSTRACT
During environmental tests of a spacecraft in a vacuum
chamber a large amount of measurement data is
continuously generated and made available for real-time
monitoring and analysis, or further elaboration. In the
frame of DTL1 (Data Transfer Link 1) a data
communication capability between ESTEC Test Centre
and customers’ premises was created such that test data
were made available in near real-time to test engineers
located remotely.
The objective of DTL2 (Data Transfer Link 2) is to
enhance the visibility of test data by means of Virtual
Reality techniques. For instance, search and position
identification of a specific sensor on board of the test
specimen (usually out of several hundreds of sensors)
can be quickly done. Evolution of the measured
physical quantity (e.g. temperature) can be visualized or
processed for further analysis.
At customers’ premises an interface website allows
downloading of several files to enable the installation of
a 3D presentation client for the test actually in progress.
As far as the ESTEC Test Centre is concerned, all the
measurement data collected in STAMP (System for
Thermal Analysis, Measurement and Power supply
control), including test specimen position and chamber
properties, can be rapidly transmitted and visualized at
different remote locations.
Starting from the system performance requirements
specified for DTL 2, this paper will present the main
features of DTL 2 and the current status of operability.
Figure 1: the virtual reality presentation
2 THE NEED FOR REMOTE MONITORING
The goal of remote monitoring is to reduce the cost and
increase the flexibility of thermal tests. It achieves these
goals by allowing thermal experts to work from the
comfort of their own office, i.e. by removing the need
for them to travel to the Test Centre to witness the test
in person. Instead the test data is brought directly to
their desktop, where it can be observed in real time, and
processed using any of the usual in-house tools, even
while the test is still running.
Moreover, since there are no restrictions on the remote
monitoring client, it is possible to observe the test from
any location that has an internet connection (and for
places that don’t have an internet connection, the remote
client can work in offline mode with any data it has
received previously).
3 SECURITY ASPECTS
In order to be able to work, remote monitoring requires
a connection between the data handling system and the
outside world. This raises two security concerns:
1. Since the data handling system plays a critical
role in the thermal testing process, it is vital
that it cannot be compromised by an outside
attack.
2. Data transmitted by the remote monitoring
system may not be intercepted or altered by
unauthorized 3rd
parties.
DTL2 employs a range of techniques to address these
concerns. Figure 2 shows the main components of the
security system:
Figure 2: security setup
The “master server” (on the left) is responsible for
conducting the test within the Test Centre. To protect it
from outside intrusions, firewall 1 is configured to only
allow connections to be created from inside the Test
Centre. Thus it is possible for the master server to
initiate communication with the teletest server, but
connections in the opposite direction are always rejected
by the firewall. In this way, even if the teletest server is
compromised somehow, the master server is protected
from outside interference.
The “teletest server” (in the centre) is responsible for
the remote monitoring system. It contains a copy of the
test configuration and data, allowing these to be
displayed on the remote clients. The teletest server itself
is protected by a second firewall, “firewall 2”. This
firewall is configured to only allow incoming
connections for the remote monitoring system.
Moreover, such incoming connections are required to
present a trusted certificate (which are created by the
Test Centre on a per-customer basis). If the remote
client cannot present a trusted certificate, or if the
presented certificate is not a valid certificate that was
signed by the Test Centre, the connection attempt is
rejected.
If the trusted certificate of an incoming connection is
found to be valid, the remote client must then present a
username and password. These determine which subset
of the data on the teletest server the remote client is
allowed to see; access to thermal tests, spacecraft
models, and specific sensors is all determined on a per-
user basis.
Finally, all traffic between the teletest server and the
remote client is encrypted using strong encryption,
making it impossible to intercept or alter the data that is
being exchanged.
4 DATA VISUALISATION USING VIRTUAL
REALITY TECHNIQUES
The remote monitoring client uses virtual reality
techniques to increase the visibility and overview of the
test. It does this by displaying a 3D model of the
spacecraft and test facility, and projecting known
information (such as sensor values, spinbox rotation
angles, solar state, etc.) onto the model. The user can
then navigate around the model in real time.
Figure 3 shows a spacecraft mounted inside the Large
Space Simulator at ESTEC. The coloured dots indicate
the locations of sensors; the scale on the right correlates
the colours of the dots to the actual temperature of each
sensor.
Although it is possible to obtain exact numeric values
for each sensor simply by hovering the mouse over it,
the strength of the virtual reality presentation lies in the
overview it offers over the total state of the test:
Figure 3: virtual reality presentation
� The orientation of the spacecraft within the test
facility is immediately visible.
� The overall thermal state can be observed at a
glance.
� The “find mode” highlights sensors with a
specific name or number (shown in the
previous image as an arrow).
� New operators will find it easy to get up to
speed on the positioning of the sensors by
examining the 3D model.
� The 3D model makes it easy to understand
which part of the spacecraft is visible to the
solar beam and which is not.
� The 3D model is a useful entry point to more
detailed presentations (such as graphs or
tabular displays). Any node of the spacecraft
model may be selected for visualisation in
another style of presentation; for example, to
display all sensors on a specific instrument as a
graph, just select the instrument in the 3D
display and choose “show as graph” from its
context menu.
4.1 Model reuse
The virtual reality presentation relies on having a 3D
model of the spacecraft (3D models of the facility are
available at ESTEC). Since creating 3D models is
expensive, DTL2 makes it possible to reuse existing
mechanical or thermal models of the spacecraft. These
models are converted using an off-the-shelf tool that can
convert models in a variety of formats (including
CATIA, STEP, Pro*E, and many others).
One potential problem, especially with mechanical
models, is that they may be extremely detailed and
therefore contain a very large number of polygons.
While modern VR workstations have no problem
displaying extremely complex models (one of the
models we tried has ~20 million polygons and displayed
fine), older machines may have trouble handling very
large models. In order to maintain an acceptable
rendering speed, the remote monitoring client has the
ability to reduce the number of displayed polygons in
real-time. Thus visualisation on slower machines is also
supported, with minimal loss of rendering fidelity.
4.2 Sensor placement
In addition to the model itself, the locations of the
sensors must also be entered into the remote monitoring
client. Sensor locations are entered using a simple point
and click mechanism: to place a sensor, select it from
the list of sensors and click in the 3D window on the
location of the model where the sensor is located. Using
this method, sensors can be accurately placed on any
part of the model. Sensors need to be placed only once;
after the sensor definitions have been entered into the
configuration database, all users of the test can use
them. To avoid accidental movement of sensors, sensors
can only be placed by specifically authorized users.
Typically this authorisation is revoked after the sensors
have been placed, and before the test starts.
After the sensors have been placed, it is possible to
create 2D line drawings of the model from any
viewpoint. These line drawings clearly indicate the
locations of the sensors on the spacecraft (and on the
facility, if so desired). See Figure 4 for an example:
Figure 4: 2D drawing showing sensor locations
The figure shows the Large Space Simulator (with one
part cut out to allow a view of the spacecraft), and all
sensors that are visible from this viewpoint.
4.3 Visualisation modes
The main visualisation mode of the virtual reality
presentation is to display temperatures as coloured dots.
However, it is also possible to display the equilibrium
state of each sensor. The equilibrium state is defined as
the absolute value of the difference between the average
value of the sensors over a recent period, compared to
the average value of the sensor over a period in the past,
and provides a measure of the thermal stability of the
system.
Moreover, in either mode it is possible to display the
sensors on a neutral grey background, or to colour each
part by the average of the values of the sensors located
on that part. Figure 5 shows how this works for the
equilibrium values:
� Grey parts do not have any sensors located on
them, and thus remain grey.
� Green, strongly visible parts have a high
equilibrium value (i.e. a high degree of thermal
instability).
� Green, almost transparent parts have a low
equilibrium value (i.e. are thermally stable).
Thus the virtual reality presentation shows at a glance
which parts are thermally stable and which are still
fluctuating.
Figure 5: equilibrium display
It is also possible to combine both modes, using
transparency to indicate the equilibrium value and
colour to indicate the temperature.
It is not necessary to display the entire model all the
time: parts of the model may be selectively made
transparent or invisible with the click of a button.
Multiple, different models may be kept in memory,
although only one is displayed at any given time.
With the correct hardware, the virtual environment can
be displayed as a stereo image, giving a much greater
sense of depth than what is available on a 2D display.
5 CONNECTION WITH OTHER
PRESENTATION STYLES
Apart from the new virtual reality presentation, the
remote monitoring client also offers all the usual
presentations available within STAMP. Among others,
these include:
� Graphs: STAMP has powerful, highly versatile
graph presentations that can display any
number of curves over any length of time
(memory permitting), with multiple vertical
scales, choice of linear / logarithmic modes,
powerful scaling options, markers, plotted
against time or against other sensors.
� Tabular: these presentations show the values of
many sensors, either over time or at a single
timestamp.
� Alarm: generates alarms if sensors exceed their
warning limits, alarm limits, or delta limits, or
if their predicted value exceeds their alarm
limits.
� Connector: transmits data on a socket to
another application. This offers a simple way
to connect the remote presentation client to
other tools at remote sites.
� Excel: creates .CSV files ready for loading into
Excel (or other tools).
� Equilibrium: determines the equilibrium values
of a group of sensors.
� Prediction comparison graph: allows predicted
values from the thermal analysis software to be
compared in real time to actual measured
values obtained from the test.
� Waterfall graph: shows the evolution of a
group of sensors over time.
All STAMP presentations support both real-time and
archived data mode where possible.
Figure 6: other presentations in the remote client
6 USER FRIENDLINESS
Although user-friendliness was already a design goal for
STAMP, for the remote presentation client it is
especially important since it is intended to be used by
remote users who do not have easy access to Test
Centre operators for asking questions.
Several measures were taken to accommodate these
users:
� The user interface of the remote presentation
client was overhauled to a significant degree to
produce the maximum possible degree of
clarity. This includes such changes as
removing jargon, adding unobtrusive help
messages, and changing screen layouts to be
identical between different presentation styles.
� An easy to use installer was created that
installs the remote presentation client with just
a few mouse clicks.
� Online, context-sensitive help was added to all
presentations.
Together these measures go a long way towards making
the remote presentation client accessible to novice users.
7 APPLICABILITY TO OTHER (ESTEC)
TEST FACILITIES
The only thing that is facility-specific about the virtual
reality presentation or the remote monitoring client are
the models of the test facility. However, like the
spacecraft models, these can be loaded into the system
on an as-needed basis. Thus, to support different test
facilities (such as the new Phoenix chamber at ESTEC),
all that is needed is a test facility model.
8 INITIAL EXPERIENCES
The virtual reality presentation was used for the first
time during the Herschel test campaign at ESTEC in
January / February 2007. Although it was still in
prototype form at this stage the users were enthusiastic
about the possibilities of the new system.
The remote monitoring feature was used for the first
time during the SMOS test campaign at ESTEC in April
2007 (this was also the second use for the virtual reality
presentation). Data was presented remotely in Madrid
during the course of the test, receiving a similar
enthusiastic response.
No problems were encountered during either test,
although a few very good suggestions for further
evolution of the system were received.
In both cases, we were able to reuse existing models (an
engineering model for Herschel and both an engineering
model and a thermal model for SMOS). Placing the
sensors was performed onsite at ESTEC, and took about
one hour for Herschel (placing 60 sensors – note that
most of this time was spent locating them in the
Herschel documentation!) and about two and a half
hours for SMOS (placing 460 sensors).
9 CONCLUSIONS
9.1 Remote monitoring
Remote monitoring is an effective way to decrease the
cost and increase the flexibility of thermal testing. It
allows the customer to bring in extra experts on
demand, without incurring the cost of flying them in or
keeping them onsite at the Test Centre all the time.
Similarly, it offers a middle road between having
operators onsite at all times and unsupervised testing:
operators can check the progression of the test remotely,
only coming in if a problem is spotted during test
execution.
9.2 Virtual reality presentation
Virtual reality is a great way to offer a good overview of
the total state of the spacecraft and chamber. It is not a
replacement for graphs and tables (nor is it intended as
such), but it augments those presentation styles with
extra information that can be understood very quickly.
Moreover, since it offers those other presentation styles
through a “drilldown” interface, it acts as an effective
stepping stone towards obtaining a detailed
understanding of the current state of the test.
10 ACKNOWLEDGEMENT
The authors of this paper would like to thank Astrium
(Herschel) and CASA (SMOS) for allowing the use of
their spacecraft models, and for investing the time
needed to actually use the virtual reality presentation.
Furthermore, we would like to thank J. van der Meulen
(ETS) for his invaluable help for setting up the
machines and software for both test campaigns.
The virtual reality presentation is based on an earlier
development called “VRAIV”, which was developed in
the frame of an ESA contract. VRAIV is a virtual reality
simulation tool geared towards simulating AIV
processes. It is described in one of the other papers
submitted for this conference.
Terma is currently in the process of commercializing
STAMP for other customers. For more information,
please contact H. Guijt ( ).