Date: November 23rd, 2012
Title: MESSENGER’s End Game
Podcaster: Bob Hirshon
Organization: American Association for the Advancement of Science (AAAS)
Description: The MESSENGER Mission to Mercury is now in its second year of orbit around the planet. At a recent meeting, the MESSENGER science team discussed the future of the spacecraft, including some thrilling possibilities for low altitude imaging and data gathering, but also the possibility that new budget constraints may make these plans moot. In this podcast, Bob Hirshon speaks with MESSENGER Mission Design Lead Engineer about the different scenarios.
Bio: Bob Hirshon is Program Director for Technology and Learning at the American Association for the Advancement of Science (AAAS) and host of the daily radio show and podcast Science Update. Now in its 25th year, Science Update is heard on over 300 commercial stations nationwide. Hirshon also heads up Kinetic City, including the Peabody Award winning children’s radio drama, McGraw-Hill book series and Codie Award winning website and education program. He oversees the Science NetLinks project for K-12 science teachers, part of the Verizon Foundation Thinkfinity partnership. Hirshon is a Computerworld/ Smithsonian Hero for a New Millennium laureate.
Today’s Sponsor: This episode of 365 Days of Astronomy is sponsored by The Education and Outreach team for the MESSENGER mission to planet Mercury. Follow the mission as the spacecraft helps to unlock the secrets of the inner solar system at www.messenger-education.org
Additional sponsorship for this episode of 365 days of astronomy was provided by Clear Skies Observing Guides, a Modern Day Celestial Handbook. www.clearskies.eu..Clear skies observing guides, or CSOG, is a new concept in visual amateur astronomy. The observing guides contain thousands of objects to observe through amateur telescopes, with matching tours for GOTO telescopes and matching AstroPlanner plan-files. CSOG allows you to target deep-sky objects and carbon stars you never observed before, night after night. Wishing astronomers around the world: Clear skies..! ”
Welcome to the 365 Days of Astronomy podcast! I’m Bob Hirshon, host of the AAAS radio show and podcast Science Update. I’m just back from the 28th meeting of the MESSENGER Mission to Mercury science team. This one was in Santa Monica, California. In case there are still some people out there who don’t know, the MESSENGER spacecraft has been in orbit around the planet Mercury for about 20 months now. It’s the first spacecraft ever to orbit Mercury—ever as in EVER– and it’s returned stunning high res images of the surface. And it’s helping scientists answer lots of questions about the nearby yet mysterious little planet and how it formed.
The primary mission of MESSENGER involved one year of orbital observations, but thanks to extraordinary design and mission planning, it’s well into its second year in orbit. Jim McAdams is MESSENGER Mission Design Lead Engineer. He says that in addition to lengthening the mission, they were able to tighten the orbit to allow more observations.
An opportunity presented itself where I thought, well, we have enough propellant to lower the orbit period from 12 hours to 8 hours. For the southern hemisphere, you’re about a third closer, and you can get better resolution coverage or image maps of the surface of Mercury.
The new plan was reviewed and adopted in April.
And so the spacecraft has been in an 8-hour orbit since then.
What other challenges are there to orbiting like that? Are there any?
There are thermal considerations in that given you have less time, a third less time to dissipate heat. So that analysis had to be done. And it appears to be not to be much of a problem. But as we move in time, the closest point of the orbit rotates up over the pole and onto the other side of the planet, which then causes new challenges with the thermal design and operation of the spacecraft. You have to point the spacecraft in special directions at different points of the orbit so it doesn’t overheat as the reflected sunlight and radiation off the surface of Mercury hits that unprotected part not protected by the sunshade.
The new orbit has been a boon to the science team, but now decisions on MESSENGER will get trickier: as the second year in orbit winds down in March, McAdams says the orbit will begin to decay.
And that results in an ultimate impact on the surface of Mercury. And if we do nothing, and make no changes to the orbit, that would occur in August of 2014.
On the other hand, they could use the remaining propellant to alter the orbit again, and try to optimize the data gathering potential of the spacecraft.
So at this recent science team meeting in Santa Monica, we were looking at and reviewing options that we have for extending the mission or if funding was cut short, bringing the spacecraft down in its orbit for an early impact. So we have different options that we’ve been discussing, and looking at the science benefits for different extensions of the mission.
The discussion of bringing the spacecraft down early was made necessary not because of engineering constraints, but due to problems here on earth: negotiations concerning the federal budget, budget deficits and the so-called fiscal cliff. Many NASA missions have been asked to make plans with the assumption that anticipated funds may not be forthcoming. As a result, the MESSENGER team may have to deliberately crash the spacecraft, even though it still has propellant and the cameras and other equipment are still functioning perfectly.
The earliest scenario that we’ve looked at would be bringing the spacecraft orbit down in mid-December of 2013 for an impact either very late in the year or into January of 2014. That’s an earliest scenario. It could be extended into March of 2015 if we use all the propellant on the spacecraft to extend the life of the mission.
And then you’d have more time to collect more data…
Right, a tremendous amount of science goals have been defined at this meeting, where they’ve been able to say we can do so much more with a mission that goes to March of 2015 versus one that ends early in, say, January of 2014.
In fact, the added time will bring the opportunity for some incredibly low-orbit observations over fairly long time frames.
If we use all the propellant very carefully, we can have up to three very low altitude seasons—now seasons might last from maybe a week to up to four or close to five weeks. And for those seasons where we have a near constant altitude, or only small changes, where we are having the spacecraft low altitude, like ten, eight, a few kilometers over the surface, where it is quite stable. If you get too low, of course, down to the one to two kilometer range, you have the potential of hitting something, where you have a mountain sticking up, or a crater rim. And so the digital elevation map that has been developed will be very important to track the very end days of the mission.
But excitement over taking full advantage of this scenario—essentially flying the spacecraft over the surface for an extended period at an altitude lower than that of a commuter plane—was tempered by the expectation that the odds of its happening are slim.
Still, it’s hard to be too disappointed in a mission that has met or exceeded virtually all its original objectives. You can learn more about MESSENGER at messenger.jhuapl.edu, and find educational materials at messenger-education.org. And stay tuned to future podcasts to find what’s been decided about the fate of the spacecraft. Thanks for listening. For the 365 Days of Astronomy Podcast, I’m Bob Hirshon.
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365 Days of Astronomy
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