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Maxing Out Kepler

What happens to a spacecraft at the end of its mission depends on where it’s located. We sent Galileo into Jupiter on September 21, 2003 not so much to gather data but because the spacecraft had not been sterilized before launch. A crash into one of the Galilean moons could potentially have compromised our future searches for life there, but a plunge into Jupiter’s atmosphere eliminated the problem.

Cassini met a similar fate at Saturn, and in both cases, the need to keep a fuel reserve available for that final maneuver was paramount. Now we face a different kind of problem with Kepler, a doughty spacecraft that has more than lived up to its promise despite numerous setbacks, but one that is getting perilously low on fuel. With no nearby world to compromise, Kepler’s challenge is to keep enough fuel in reserve to maximize its scientific potential before its thrusters fail, thus making it impossible for the spacecraft to be aimed at Earth for data transfer.

In an Earth-trailing orbit 151 million kilometers from Earth, Kepler’s fuel tank is expected to run dry within a few months, according to this news release from NASA Ames. The balancing act for its final observing run will be to reserve as much fuel as needed to aim the spacecraft, while gathering as much data as possible before the final maneuver takes place. Timing this will involve keeping a close eye on the fuel tank’s pressure and the performance of the Kepler thrusters, looking for signs that the end is near.

Image: K2 at work, in this image from NASA Ames.

Meanwhile, as we await the April launch of the Transiting Exoplanet Survey Satellite (TESS), we can reflect on Kepler’s longevity. The failure of its second reaction wheel ended the primary mission in 2013, but as we’ve discussed here on many occasions, the use of photon momentum to maintain its pointing meant that the craft could be reborn as K2, an extended mission that shifted its field of view to different portions of the sky on a roughly three-month basis.

As the mission team had assumed that Kepler was capable of about 10 of these observing campaigns, the fact that the mission is now on its 17th is another Kepler surprise. The current campaign, entered this month, will presumably be its last, but if we’ve learned anything about this spacecraft, it’s that we shouldn’t count it out. Let’s see how long the fuel will last.


Comments on this entry are closed.

  • Mike March 15, 2018, 15:38

    The Kepler mission, both versions, have played a major part in demonstrating both the ubiquity of planets and the astonishing variety of planetary arrangements. It’s been a great success despite the setbacks.

    I wish the original mission could have continued a few more years to help bore down deeper into extracting Earth-sized transits in HZ orbits around the noisy G and K dwarfs.

    However the recovery of the spacecraft to allow it to continue the productive K2 mission observations is a great tribute to the ingenuity of the Kepler and NASA teams.

    I am certain that Kepler’s findings will form the basis for explorations centuries from now. There can’t be a bigger tribute to the Kepler team then that.

    • Spaceman March 15, 2018, 17:15

      Well said, Mike. I especially like your last paragraph about how future interstellar wayfarers, if there are any, many centuries from now may make use of this amazing catalog to guide their explorations.

  • Spaceman March 15, 2018, 17:11

    Kepler data enabled a huge leap to occur in our understanding of exoplanets. This is particularly true in the case of exoplanet statistics such that now we know that planets exist around a majority of main sequence stars. Speaking of statistics, the final planet occurrence rates from the entire mission data set are still in preparation, right?

  • J. Jason Wentworth March 15, 2018, 17:30

    If a Kepler flight spare was built (or if a high-fidelity thermal testing model was built–these models can often be upgraded to become flight hardware, as was an option if Mariner 10 had failed [the Mariner 10 duplicate in the National Air and Space Museum is its flight-upgraded thermal model]), it could be launched as Kepler 2, to continue the Kepler–and later–the K2 observations.

  • Robin Datta March 15, 2018, 18:13

    Before Kepler, the very existence of exoplanets, now recognised as a major feature of stellar systems, were a matter of speculation. While there is still much room for speculation pending the aquisition of more data, much missing detail has been filled in to the picture of the universe. Short of the discovery of intelligence elsewhere in the universe, the existence and prevalence of exoplanets is perhaps the most important discovery in the understanding the universe.

  • Brett Bellmore March 15, 2018, 18:46

    Aside from propulsion, how is the craft doing? Would it be feasible to send a robotic probe to latch onto it with a new propulsion system, and continue using it?

    • Robert Feyerharm March 15, 2018, 21:39

      And install a new reaction wheel too!

    • Robin Datta March 15, 2018, 22:13

      Robotic probe with propulsion systems? And a few gyroscopes would be de rigueur!

    • J. Jason Wentworth March 16, 2018, 5:55

      Paul would know that better than I, but the technology to give Kepler new propulsion and attitude control capability is, in principle, available. A “life-extending satellite,” that could latch onto an old but otherwise (except for propulsion and attitude control) operational geosynchronous communications or meteorological satellite and provide its propulsive and control needs, is under development. Such a spacecraft could also, with suitable modifications, be sent out to Kepler to “jump-[re]start” it.

      • Holger March 16, 2018, 13:23

        I don’t imagine such a mission would be at all feasible (at a reasonable cost). Kepler is not in an Earth orbit, but in a solar orbit at currently 1 AU (and increasing) from the Earth. In terms of propulsion, it would be much cheaper to launch a new Kepler spacecraft than to reach the old one. Unless we wait a few decades, when Kepler will be a full orbit behind Earth and thus quite close to us again.

        • J. Jason Wentworth March 17, 2018, 0:12

          As a technology demonstration of such “grappling/service-providing” spacecraft (like the demonstration Space Shuttle retrievals–and on-orbit repair–of geosynchronous communications satellites that were stranded in low Earth orbits), a Kepler “rejuvenation” mission could occur, despite its uneconomic (at *present*; it may not also be so) cost. None of the Shuttle satellite rescue missions “penciled out” economically, because NASA–which wanted to demonstrate the Space Shuttle’s claimed abilities (partly to justify its greater-than-expected development and per-flight costs)–bore the costs of the missions.

          • J. Jason Wentworth March 17, 2018, 0:14

            Argh! I meant to write “(at *present*; it may not ^always^ be so).”

        • Michael C. Fidler March 17, 2018, 11:20

          Actually, it would be easier to reach Kepler then to reach the moon, it would just take longer. The spacecraft main problem, besides the gyros and gas, is that it needs new and improved CCD’s. Ten years has seen a lot of improvement in CCD technology and would require a major repair. The point is that the BFR and New Glen will be cheap and used more often, so cost could be kept low. If this type of repair could be done in LEO then all that is needed is to bring it back from deep space.
          It would make good use of space station!

  • Robert Feyerharm March 15, 2018, 21:42

    Top on my wish list for Kepler’s last days would be to target Proxima Centauri and attempt to confirm the planet transits from earlier observations.

  • Coolstar March 21, 2018, 0:23

    The idea that Cassini and Galileo were crashed into Saturn and Jupiter respectively to keep from the possible contamination of the moons is largely just a red herring/publicity meme. The more dominant reason is that NASA got tired of spending the few million dollars a year to keep the satellites running and to pay the engineers and scientists working on the projects. Essentially saving only a tiny fraction of the billion dollar plus budget of each satellite. Each could have saved enough fuel to put them into safe parking orbits and to continue doing science for years with a very, very small chance of a collision with a possible life bearing moon. NASA uses this tactic or similar ones repeatedly to save pennies on the dollar (see IUE) and it is, essentially, a lie.

    • ljk March 27, 2018, 12:49

      I was told something similar about the Viking 1 Mars lander, which was given a supposedly errant command to turn its main antenna away from Earth in 1982, thus ending communications. The nuclear-powered robotic explorer was predicted to keep transmitting data and images to Earth until at least 1994. An exhibit at the National Air and Space Museum in Washington, D.C., was even set up to show visitors the latest views of the Red Planet from Utopia Planitia for years.

      Operating Viking 1 would not have been very expensive at all to operate, but this was the early 1980s where the Reagan Administration seriously considered shutting down the Voyager probes to save money, thus no missions to Uranus or Neptune.

      No new American deep space probes were launched in that time as well, but the Soviet Union, Japan, and the European Space Agency (ESA) filled in that gap when it came to Venus and Comet Halley. That the USA did not send anything to Halley in 1986 is both embarrassing and mind-boggling now.

      Mars was in the middle of a two-decade gap between successful missions. Viking 1 could have added welcome data to that period of Martian weather et al between 1982 and perhaps even to the arrival of Mars Pathfinder in 1997.

  • Michael C. Fidler March 24, 2018, 22:04

    Interesting problem with TESS and it’s 21 arcsecond per pixel resolution in crowded fields. A solution and could this be used on other optical telescopes wide field surveys for transiting exoplanets?


    “The Transiting Exoplanet Survey Satellite (TESS) will observe ∼150 million stars brighter than Tmag ≈ 16, with photometric precision from 60 ppm to 3 percent, enabling an array of exoplanet and stellar astrophysics investigations.While light curves will be provided for ∼400,000 targets observed at 2-min cadence, observations of most stars will only be provided as full-frame images (FFIs) at 30 min cadence. The TESS image scale of ∼ 21”/pix is highly susceptible to crowding, blending, and source confusion, and the highly spatially variable point spread function (PSF) will challenge traditional techniques, such as aperture and Gaussian-kernel PSF photometry. We use official “Endto-End 6” TESS simulated FFIs to demonstrate a difference image analysis pipeline, using a δ-function kernel,that
    achieves the mission specification noise floor of 60 ppm hr−1/2. We show that the pipeline performance does not depend on position across the field, and only ∼2% of stars appear to exhibit residual systematics at the level of ∼5 ppt. We also demonstrate recoverability of planet transits, eclipsing binaries, and other variables. We provide the pipeline as an open-source tool at https://github.com/ryanoelkers/DIA in both IDL and PYTHON. We intend to extract light curves for all point sources in the TESS FFIs as soon as they become publicly available, and will provide the light curves through the Filtergraph data visualization service. An example data portal based on the simulated FFIs is available for inspection at https://filtergraph.com/tess_ffi.”


  • ljk March 27, 2018, 12:51

    Kepler is even returning data on a supernova, and a rare one at that:


  • ljk April 9, 2018, 12:31

    Perhaps we will have an astronomical satellite named after Maria Cunitz next…


  • ljk April 17, 2018, 10:30

    Let us look at the incredible accomplishments of the astronomical satellite that paved the way for TESS:


    To quote:

    And some of Kepler’s discoveries defied imagination.

    The mysterious “mini Neptunes” aren’t the only weird planets discovered in Kepler data. Scientists have found evidence of water worlds, hot Jupiters, lava worlds, and even circumbinary exoplanets, which, like the fictional planet Tatooine in “Star Wars,” orbit two stars.

    “The diversity of planets is breathtaking,” Professor Kaltenegger says. “If we had just found planets like those in our solar system, it would’ve been nice, but kind of boring.”

    Another astonishing exoplanet was spotted orbiting a white dwarf, the smoldering embers of an extremely old star near death. A closer look at the system revealed that the planet was being pulled apart and drawn into the dying star, illustrating one end of planetary evolution.

    This discovery has the potential to expand where and how astrobiologists search for signs of life, too. “This told us that these have been around for a long time, and we shouldn’t think of things just in space, we should think about them in time, also,” says Elisa Quintana, an astrophysicist at NASA’s Goddard Space Flight Center who served as a Kepler mission scientist for a decade before joining the TESS mission as a support scientist.

    “Maybe every system has a little slice of time where there’s life,” she adds.

    Kepler has provided considerable data for astronomers to start to piece together models of planetary evolution. But, “like most great science missions,” Professor Seager says, “it created more questions than it answered.”

    Kepler laid the groundwork for TESS and other future missions, and it wasn’t easy. “Kepler basically plowed down everything in its way” to lead the way, Kaltenegger says. When the principal investigator, William Borucki, first proposed it in 1992, the Kepler mission was seen as too uncertain and risky. It took him five tries to finally get it approved in 2000.

  • ljk May 24, 2018, 11:06

    JPL News | May 23, 2018

    Kepler Begins 18th Observing Campaign with a Focus On Star Clusters


    Specifically Messiers 44 and 67.

    Check out this cute and informative cartoon from the news item:


  • ljk September 6, 2018, 12:09

    The rocket model that delivered Kepler into space is retiring…

    Delta II: End of an era

    Later this month the venerable Delta II rocket will lift off for the final time, carrying a NASA satellite. James Michael Knauf recalls the history, and the accomplishments, of that launch vehicle over nearly three decades.

    Tuesday, September 4, 2018