This page contains a description of our CDF and how to set it up when new sessions are planned. Since the infrastructure is not currently permanent, make sure to follow and complete the checklists for material and equipment provided at the end of this page.
Adapted from the design of ESA/ESTEC's CDF and built with the support of ESA's Systems and Concurrent Engineering Section, eSpace CDF has a much smaller configuration, as shown in the figure below, and focuses on the core subsystems of a space mission. The current setup has been tailored to be used for ESA's concurrent engineering challenge. The layout can be altered and adapted based on the requirements of a given study. Subsystem stations can be added or removed depending on the customers' needs and the mission/system requirements. The final room layout shall be prepared by the study coordinator and/or the systems engineer/facilitator before the start of a new CEsession.
While concurrent engineering benefits for the colocation of multiple teams with varying expertise under the same roof, some of the subsystems or stations can be connected remotely. Compared to the distribution of stations in the ESA/ESTEC facility (see here), our current layout does not include a station for the customer, who in the case of the concurrent engineering challenge were connected via WebEx displayed on the main screen.
For remote teams, WebEx, Zoom, Skype or any other video conferencing platform can be used, ideally combined with an online messaging platform like WebEx Teams or Slack.
The large screen (TV) and the white board at the front are extremely important and shall allow participants to interact and discuss in small groups or in front of everyone when needed. They can support brainstorming and ideation, which are really useful processes at the beginning of a session.
The tables are placed this way so everyone can see each other. This facilitates communication. It is also better if the videoconferencing infrastructure is a the front, so all subsystems can interact with other teams or experts joining remotely.
The subsytems are spread so teams that have to interact extensively together are close to one another. Like propulsion and trajectory analysis, or power and thermal subsytems. But, of course, nothing shall prevent participants to move and talk to others across the facility if needed.
The systems engineer(s) and session facilitators can also have desks to work on their computers but they shall be around the center of the room to constantly stay in contact and coordinate the participants. They have a role of support in every tasks: design, budgets, requirements, but also in communication and coordination of the process.
The customers shall also have a central position in the layout as they are the ones who can clarify requirements or validate design choices during the process. They shall be in contact with the systems engineers which have the task to translate their needs into technical requirements for each subsystem.
As mentioned, the CDF infrastructure is not permanent at eSpace. The room currently used is regularly kept in its meeting room configuration. Although most of the material and equipment needed to turn the room into its CDF configuration is already present in the room, some things may need to be rented or transfered from other rooms prior to the start of a new study.
Follow this guideline to prepare the CDF for a new study. Make sure to also check the Start Here page for information on tasks required in preparation for a new study.
Invite participants and external experts
Using email templates
Find suitable dates to conduct the sessions with everyone available.
Request a loan to 'Poseidon' for as many laptops and headsets as needed.
For this, go to support.epfl.ch.
Log in with your EPFL credentials.
Then click on 'Request' > 'Information Systems' > 'Computer hardware & software' > 'POSEIDON Request loan equipment' or 'Poseidon Request for events'.
Complete the form and submit. Make sure to add any additional details in the 'Comments/specific requests' section (e.g., additional days required for the loan).
Make sure to do this a few weeks ahead of the study. Don't forget to request equipment to be collected at least a day prior to the study so that the room can be set up and the equipment tested before the first session starts.
Collect equipment, set up stations, and test.
Make sure all the videoconferencing equipment works as intended. For how to set up each workstation, following this action list:
Connect the computers to the EPFL wifi with staff credentials (external participants would not have access to it).
Confirm that all the stations (or additional CDF computers) have access to the required software.
Under the "Model" tab, select the finite states of the current iteration
Create possible finite state lists (eg. list of mission phases or list of system(s)' modes.) by clicking on the "+" sign
Define lists' names
Click on "+" sign to add new finite states (eg. phases or modes).
Create actual finite states
Under the "Model" tab, select the finite states of the current iteration
Create actual finite state lists (eg. list of associated mission phases and system(s)' modes.) by clicking on the "+" sign
Select 2 or more possible finite states lists that will be associated (eg. phases --> modes), click "ok"
In the "Actual Finite State List" folder, modifiy Actual Finite States to change the state kind (from "mandatory" to "forbidden") for those that are not allowed.
Define the top element in COMET (right click on the element), this will be the top level product / mission / system made up of all the other element definitions in the model.
Inform experts about the topic of the study and their role.
Make sure participants are aware of their roles.
Inform them with a rough planning of the sessions (see workflow).
Provide them with an introduction, in some cases, the prepared data pack.
Set up the room into its CDF configuration
Additional desks and chairs can be brought in temporarily from either PPH325 or PPH327.
Extra power strips can be found in (?).
General logistics (always depending on the number of participants).
Organize an adjacent room for breaks
Changing air and socializing with other participants is beneficial for the efficiency of the session.
(Optional) order food and drinks for the coffen break.
Make sure there is a place/restaurant with enough seats to host everyone if the session lasts the whole day.
On the figure, the "test mission" element is the top element.
Subscribe to Parameters owned by other Domains of Expertise on the COMET software by right-clicking on a parameter and clicking on "Subscribe to this Parameter". In the product tree, parameters have a sphere symbol next to them: an orange sphere means no one is subscribed, a blue sphere means someone is subscribed, and a white one means you (your domain) are subscribed.
Parameter Subscriptions appear in the Parameters worksheet upon “Pull Owned” or "rebuild"
Assign a first value (best guess, initial research) in the "manual" switch
For mass of subsystem, SEs can allocate a first value based on the mass budget and percentage division in the latest Space Mission Analysis and Design (SMAD) book.
For any parameter, use heritage from previous or ongoing similar missions if it can be justified
The subscriber owns the Parameter Subscription, and can (temporarily) change its value – e.g. as a starting point
Communicate with other subsystems to announce new parameters you've created, and ask for the ones you need from others.
Systems engineers should supervise this process, and encourage experts to subscribe to parameters that impact them, to increase the number of interconnections between subsystems
On the parameters sheet, the "actual value" column stores the latest value that has been pushed by a domain expert (one can change from "computed", "manual", and "reference" using the switch input).
The cells in the "actual value" colum already have a symbolic cell name, to be used to compute owner's values in other sheets.
Compute values for your own subsystem's parameters (using the Excel worksheet or any other engineering software)
Link your results to the Parameters worksheet in the "Computed" fields. "Manual" fields will not remember the formula! Also by creating a stable link with a symbolic cell name form another sheet.
!! The parameter sheet is created upon "rebuild" (see below). It is used by the COMET add-in to get and send data from and to the COMET server. No computation shall be made inside this sheet !! Link the parameter with symbolic cell names to make computation in other sheets !
For every parameters that have a "computed" value, toggle the switch to "computed" so the model knows this is the most up-to-date value.
In the final stages of a study all Parameter Subscriptions should be set to “Computed” in order to use the value provided by the owner Domain
Synchronise COMET server and Excel Workbook
“Rebuild” will synchronise the COMET Excel plugin panels with the COMET server and create the Parameters and Option sheets
“Synchronize” is used to pull the data from COMET server into the Excel Workbook
“Submit” is used to push the parameter values from the Excel Workbook to the COMET server. Make sure the correct option is selected in the "switch" column
The “Publications” are under the control of the Design Authority Participant. They publish the latest values to all Parameter Subscriptions after checking for consistency. The Design Authority can select to publish any subset of Parameters
The loop "Submit" → "Publication" → "Synchronise" ("Push" → "Publish" → "Pull") is called the three switch mechanism, and ensures a correct sharing of the information. These steps need to be coordinated by the systems engineers.
On COMET, pushed values that have not yet been published are shown in blue.
Systems engineers publish all parameters after validation (just not their own). The new values and parameters now appear in the product tree.
SEs pull values on their worksheet to compute the budget(s) and later push and publish the new values for total mass and others.
Then everyone can pull again to start a new iteration.
COMET has advanced modelling features, do learn and apply them all, have a look at the user manual. Here below are two features much used within eSpace's CDF:
The concept of redundancy allows to increase safety of the system. In case an element fails, the whole mission is not aborted. Redundancy is particularly used in space mission and can have a large impact on the mass budeget or power needs of a system, thus it is important to account for it since the beginning. To define the redundancy concept of an element:
Drag and drop the "redundancy concept" parameter type into the element
Define values for the 4 parameters grouped in the "redundancy concept" : scheme, type, k, n
Scheme is either hot (all units are on all the time) or cold (only k units are on, the other n - k units are off if not needed)
Type is either internal (units are all in single package / box) or external (units are explicitly modelled in design)
k, the number of units needed for nominal operation
n, the total number of units in the system
State dependency (used to model system's modes, mission's phases, and other states, see also point 4 - Set up COMET)
Under Model > Finite states, SEs create lists of possible finite state (eg. for mission's phases and systems' modes)
Define list of actual finite states
Select 2 or more possible lists
Change state kind to “forbidden” if the combinaison is not allowed (eg. phase: early operation with mode passivated)
Define parameter state-dependant value by "editing" it, and selecting the actual finite states list that you've created
It's important to notify to the other experts that you value is now state-dependant so they can subscribe to the one(s) they need (either the worse case or the one in a specific state)
Stop the iteration process
After a given number of iteration loops, or once the system's solution has converged to a point where the change in mass is smaller than the remaining margins (at system level), or when the customer decides, it is time to close the study.
For the final iteration, the idea is to freeze the design of the subsystems one after the other, in this proposed order: 1) trajectory and propulsion 2) CDHS 3) structure and configuration 4) AOCS 5) power and thermal 6) SE budgets
In between each freeze, the subsystem to be frozen has to pull, update their values, and push the new ones. So the SEs can publish (at which point the parameters are considered frozen). This logic is needed to make sure the subsystems are using the most up-to-date values in the final computation.