There has been a recent Update to the NASA Keplar Mission Manager. What the Kepler Mission is, and why the Update is important, has ramifications to our knowledge of exactly how many planets exist in our galaxy which might potentially be capable of supporting life. 274 such new planet candidates were discovered, according to the most current available information from NASA.
The main purpose of the Kepler Mission, NASA Discovery Mission #10, is specifically designed to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets.
This mission’s results will allow us to place our solar system within the continuum of planetary systems in the Galaxy.
What is the Keplar Mission Update?
The most recent Keplar Mission Manager Update has to do with NASA findings about a crucial component of the Keplar spacecraft designed to discover exoplanets: Reaction Wheel 4 (RW4). Reaction wheels, which are small electric motors mounted on the spacecraft that control the three axes of motion: up/down, forward/back and left/right. High-precision pointing of the Kepler spacecraft is controlled by these reaction wheels.
Getting this particular wheel, RW4, to function smoothly and accurately is one of the keys to detecting exoplanets.
That’s why Thursday’s successful tests, when NASA scientists got the wheel to spin in two different directions in response to commands, were important to possibly the overall Keplar Mission.
One drawback, though, was that, though the Reaction Wheels RW4 and RW2 spun bi-directionally, friction levels remained “higher than would be considered good for an operational wheel,” according to NASA’s website.
If the friction level remains constant over time, such a condition can be “correctable in the spacecraft’s attitude control system.” However, “a variable friction level will likely render the wheels unusable.”
With both reaction wheels moving, what’s the next step?
Getting both the RW4 and RW2 to function and move bi-directionally was a major step that needed to succeed before NASA’s Keplar Mission can progress any further.
Now that both wheels are working in conjunction with each other, the next step will be “a system-level performance test to see if the wheels can adequately control spacecraft pointing.”
Though friction levels on RW4, the wheel that failed in May, are higher than NSAS would prefer, no additional testing is planned at this time.
The pointing test involves determining the performance of the wheel as part of the spacecraft system. There will be three stages to the pointing test, according to NASA.
The first stage of the pointing test will determine if the spacecraft can sustain coarse-point mode using RW1, 2 and 3. Coarse-point mode, as the name suggests, is a rough, or coarse, mode.
It is regularly used during normal operations, but has insufficient pointing accuracy to deliver the high-precision photometry necessary for exoplanet detection.
Star trackers during coarse-point mode measure the pointing accuracy of the spacecraft. Pointing, when using wheels to control the spacecraft, is typically controlled to within an arcsecond. A fault is declared if the pointing error exceeds a quarter of a degree.
How accurate is this?
This degree of pointing accuracy would be equivalent to keeping an imaginary Kepler telescope pointed at a theater-size movie screen in New York City’s Central Park from San Francisco.
The power, pointing and telemetry for the photometer is provided by the spacecraft. There are no other moving or deployable parts on the spacecraft other than the four reaction wheels used to maintain the precision pointing and an ejectable cover.
Testing in the second stage will be to point the high-gain antenna to Earth and downlink the data currently stored aboard — that is, if RW2 can sustain coarse-point in stage 1, the second stage of the test
For the RW2 to accomplish this requires that the pointing be controlled more tightly than simply avoiding safe mode, yet does not require the very fine control needed to return to science data collection.
If the RW2 can achieve and maintain fine-point, the operating mode for collecting science data, it will pass the final stage of the test. During fine-point the fine-guidance sensors measure the spacecraft pointing.
When using wheels to control the spacecraft, pointing is controlled to within a few milliarcseconds.
Using our imaginary Kepler telescope example, this degree of pointing accuracy would be equivalent to pointing at a soccer ball in New York City’s Central Park from San Francisco.
When will the pointing performance testing begin?
The pointing performance testing will begin on Thursday, August 8, 2013 and will continue into the following week if all goes well. A determination of whether Kepler can return to exoplanet data collection is expected a couple weeks after these pointing tests are complete.
Scientists continue to analyze the existing data as engineers explore recovery of the spacecraft.
Earlier this week the team delivered their findings for 1,236 new Kepler Objects of Interest (KOIs) to the NASA Exoplanet Archive. The new KOIs were found by searching the observational data from Quarters 1 to Quarter 12. Of the 1,236 new KOIs, 274 were determined to be planet candidates, while many others were determined to be false positives.
The current count of Kepler planet candidates is now 3,548. Some of these new planet candidates are small and some reside in the habitable zone of their stars. Much work remains to be done to verify these results, but according to the latest NASA Keplar Mission Manager Update, 274 additional new planet candidates have been discovered.
Written by: Douglas Cobb