Since I promised everyone a more regular input to this blog, I guess I should try to live up to that promise. I’m afraid I took some time off over the holidays after such a busy year.
The Kepler spacecraft uses four distinct attitudes for its observations. We’ll monitor the same part of the sky all the time, but as the spacecraft orbits the sun, the geometry of it all requires that we periodically roll the vehicle a quarter of a revolution (90 degrees) to keep sunlight falling on our solar panels, and the radiator that keeps the detectors cool pointed to deep space. The focal plane has been built with four-fold symmetry and the mission has been designed such that we roll the spacecraft exactly 90 degrees, about every 91 days. That’s four times an “orbital year”, and we conveniently term them our Spring, Summer, Fall and Winter attitudes. The spacecraft orbits the Sun in 372 earth days. We launched into the Spring attitude, and since then we’ve been rolling the vehicle per plan. Just before the holidays, we rolled to the Winter attitude, so now the vehicle has “seen it all”! We’ve now successfully operated in all four of the attitudes that we will use of the entire duration of the mission over and over again.
Each roll has been a bit of an adventure, as we are rolling to an attitude we’ve never been at before. While taking science data, we guide the spacecraft with fine guidance sensors located in the four corners of the focal plane, so we use the same guide stars, season after season. The star trackers mounted on the outside of the spacecraft that provide our coarse pointing during non-science activities (like downloading data to the ground) are pointed more or less off to the side and see different stars in different seasons. This means we do have to be a bit careful with each roll. Last month, one of the new star tracker guide stars proved to be tracking poorly and we had to switch stars to get stable enough to transfer over to the fine guidance sensors.
And although we’ve already been at the Spring attitude, we have changed the way we track stars with the fine guidance sensors and we’ll have to be a bit careful to get it right. But at least the star trackers will recognize their view. A year after launch, come March, the trackers will once more see the same stars they saw when we first started taking science data.
Charlie Sobeck, Kepler Chief Engineer
Update: find the main page of this blog at https://blogs.nasa.gov/cm/blog/kepler. Subscribe to the blog’s rss feed by clicking on the orange icon on the top right.
Sorry we’ve been gone so long, hopefully we’ll reward your wait with some interesting reading.
I know there are a lot of people out there interested in the Kepler Mission and how things are going. We’ve asked team members to submit content, to give you some glimpses into what they’re doing, with very little filtering. So you should soon be seeing postings from a variety of personalities with different interests and writing styles. Just what they will be writing about I can’t quite imagine, but we did give the team some guidance, so here’s what you might expect:
- Everyone has agreed to be civil and follow normal etiquette, but there will be no political correctness police,
- This will not be the forum for the release of mission results, so we will refrain from discussing the raw findings that come from Kepler, though there may be some stories later, after official announcements have been made, about how we did it and how it felt,
- We will be sensitive to our supervisors and will not be announcing late breaking news about mission anomalies before they have a chance to learn about them through channels, but once they have been reported we may well try to give you an inside look at how our understanding evolved,
- Since we want to let the team members write what they want with little filtering, you may find contradictions in the entries, and we do not guarantee the accuracy of all the numbers put out, but maybe that will be a feature, an opportunity for the public to ask us for clarification!
The Kepler team is quite busy, but we want to share our excitement in this mission, so we’ll try to keep this blog more lively from now on, with at least one entry each week.
Visit us online! It’ll be fun!
Posted by Charlie Sobeck, Kepler Chief Engineer
If you haven’t heard about the Kepler mission yet, you should. The mission is set to launch in a little over two weeks so the excitement is building. Kepler is a mission that will search for Earth size planets orbiting other stars in our galaxy. For thousands of years, humans have looked up to the sky and wondered if we are alone. It is a question that nearly every human has pondered at one time or another.
Soon we may have an answer to that question.
The Kepler mission is designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size planets in or near the habitable zone and determine the fraction of the hundreds of billions of stars in our galaxy that might have such planets.
Stay tuned to find out more about how the Kepler mission will do this.
The Kepler spacecraft precisely measures the light variations from thousands of distant stars, looking for a moment where the light will change. This light change could signify a planet.
Kepler has a telescope that will focus on the stars that are as large as our Sun. These are the stars that we think may have planets orbiting them. If these stars do have a planet orbiting them then there should be a time where the planet is blocking our solar system’s view of the star. This is known as a transit.
Three or more transits of a given star all with a consistent period, brightness change and duration provide a rigorous method of detection and confirmation. Orbital period can be determined from the time between transits. Orbital size can be determined from the mass of the star and the length of time between transits, and temperature from the planet’s orbit.
The results from this data can be used to calculate the fraction of stars that have planets, as well as the different planetary sizes and orbits for many different types of stars. These results are especially exciting because they will tell us how often planets occur in the habitable zone of other stars.