Just 25 years ago, we had no evidence of the existence of worlds outside of our own solar system. At the time, there were just nine planets (including Pluto) known to us.
Now, just over two decades later, there are 3,509 confirmed exoplanets, as discovered and confirmed by the ground-based and space-based exoplanet hunting telescopes of planet Earth. There are still another 4,000+ exoplanet candidates, which have been observed by the Kepler Space Telescope and are still awaiting confirmation. Space isn’t the vacant lot that we thought it was, with scientists confirming that an exoplanet exists for approximately every star. Some of those exoplanets may hold conditions that are favorable to life, and a new European telescope is going to join in the search to assist other projects with identifying and characterizing exoplanets.
The new space telescope is the first fully Swiss-built spacecraft, as well as being the first Swiss-managed project for the European Space Agency (ESA).Dubbed CHEOPS (Characterising ExOPlanet Satellite),the telescope will continue to add to this ever-growing list of new worlds by using a similar transit method for detection as Kepler. The transit method uses a photometer on the telescope to measure the dimming in light from a host star, which is caused when an exoplanet transits in front of it.
The main differences between the Kepler mission and the CHEOPS mission, however, is that CHEOPS is focusing its efforts toward preselected star systems with known exoplanets in them, before monitoring a single star at a time. This is opposed to Kepler, which scans many thousands of stars simultaneously. There is an element of randomness to the Kepler project, in terms of which stars exactly are observed. CHEOPS is far more specific in its observation targets. If Kepler was a sledgehammer (observationally speaking), then CHEOPS is a scalpel.
Almatech states the CHEOPS as follows:
“CHEOPS will use its ultra-precise telescope to screen a list of 500 pre-established candidate stars to find Earth-like planets orbiting around them. During its 3.5-year mission, CHEOPS will be able to see details of about 100 times more accurately than the instruments on the ground, thus increasing the chances to identify new exoplanets likely to hold some forms of life.”
The decision to focus on known targets from previous surveys is said to make for a more efficient use of telescope time. Knowing where to look and when to make observations can be priceless information. In addition, CHEOPS will be able to view brighter stars than Kepler.
Being an ESA-funded project, the design and manufacture of CHEOPS was carried out in ESA member states, with the design and construction of the carbon fiber reinforced plastics (CFRP) structure being contracted to Almatech in Lausanne, Switzerland.
ENGINEERING.com spoke to Dr.Luc Blecha, CTO of Almatech, to gain some insight into how the company has been using finite element method (FEM) to aid with the development of CFRP components used within CHEOPS.
Tell us about your company.
Luc: We are a space and naval engineering company of 25 employees based in Lausanne, Switzerland. We were founded in 2009 by Myself, HervéCottard (GM) and 4 other space passionates, and we specialize in developing structures for use in extreme environments.
Have you worked on any other cool space projects?
Luc: Yes, we worked on Bepi-Columbo. We provided the MLI [multilayer insulation] for ExoMars, and now we are designing and manufacturing the structure for CHEOPS. They’re all very cool projects.
What components are you designing for CHEOPS?
Luc: We are responsible for all of the structure, including the CFRP tube, the titanium brackets and also the junction to the primary and secondary mirrors.
How much of the design, build and test process is carried out inhouse?
Luc: We design inhouse, then we send the manufacturing files and requirements to our partner Connova in Switzerland. They manufacture the CFRP parts, and they do the machining of the CFRP as well. Then we send the finished parts for environment testing over in Holland and France.
What was your preferred CAE software for this project?
Luc: We used Femap along with the MSC Nastran solver, and for the post processing we used MAYA HTT Structural Analysis toolkit. Out of our 25 employees, we have three Femap users.
What did you use Femap for specifically?
Luc: Femap was especially useful for thermal mechanical simulations of the main structural body. The focal distance needs to be tight. And the temperature changes in space can cause dimensional instability which is detrimental to the function of the telescope. Finding these issues early with the simulation can help us identify which parts are driving the thermally induced motion of the structure, and we could thus optimize the design of these parts. Generally, we used Femap for a lot of structural, thermal elastic, frequency response, static analysis and this kind of thing.
Can you give any examples of such issues?
Luc: Sure. There is a thermal mismatch between the core components of the CFRP, and this mismatch becomes an issue at around -40°C. As the structure warps, it causes high interlaminar stresses which can lead to weakness or failure. It’s nice to work with Femap because it showed good results for fiber level (at micron scale). It really is good for simulating failure criteria at low temps.
CFRP does have its limitations, and accurate FEM analysis helped us to find those limits and work within them.
Why use CFRP specifically?
Luc: In this case, we needed high stability over the range of temperatures experienced in space. The mirrors can’t be adjusted in flight, so it needs to be rigid and have very little deviation. Also, CFRP is very lightweight.
How heavy was the structure?
Luc: The flight model structure was 18kg. The whole spacecraft is 64kg. It’s a very small platform. The spacecraft bus itself is based on the SEOSAT platform, which is built by EADS CASA Espacio.
How long did the project take? And when is it ready to launch?
Luc: We made three models for the project, including the flight model. The whole project was completed in 1.5 years. The final integration of CHEOPS is done in Spain, and the final testing is done in Switzerland. It will then be shipped to Kourou in French Guyana, where it will be integrated to the Vega launcher, for launch in December 2017.
Thanks, Luc. Good luck to the CHEOPS team, then!
So, there you have it. Very soon we will have another eye in the sky, adding to the ever-growing list of known exoplanets. And not only will CHEOPS be able to detect them, but it will also characterize the structure of its targets, which will help us to understand the formation and evolution of planets.
According to the CHEOPS executive summary, the telescope will also be able to:
- Determine the mass-radius relation in a planetary mass range for which only a handful of data exist and to a precision never before achieved.
- Probe the atmosphere of known Hot Jupitersin order to study the physical mechanisms and efficiency of the energy transport from the day side to the night side of the planets.
- Provide unique targets for future ground- (e.g., E-ELT) and space-based (e.g., JWST, EChO) facilities with spectroscopic capabilities. With well-determined radii and masses, the CHEOPS planets will constitute the best target sample within the solar neighborhood for such future studies
- Offer up to 10 percent of open time to the community, whichwill be allocated through competitive scientific review.
- Identify planets with significant atmospheres as a function of their mass, distance to the star and stellar parameters. The presence (or absence) of large gaseous envelopes has a direct influence on fundamental issues such as runaway gas accretion in the core accretion scenario or the loss of primordial H-He atmospheres.
- Place constraints on possible planet migration paths followed during formation and evolution for planets where the clear presence of a massive gaseous envelope cannot be discerned.
CHEOPS is in the final integration phase now, and is scheduled to launch later this year. If you want to know more about the CHEOPS mission, you can read more about it over on the mission website.