Date: March 11, 2011
Title: MESSENGER Meets Mercury
Podcaster: Bob Hirshon
Organization: American Association for the Advancement of Science (AAAS) http://www.aaas.org
Description: After a trip of over six and a half years, the MESSENGER spacecraft finally goes into orbit around the planet Mercury on the morning of March 18, Universal Time, or the evening of March 17th Washington, DC time. Bob Hirshon spoke with Deputy Project Scientist Louise Prockter about the preparations for orbital insertion during these climactic final days.
Bio: Bob Hirshon is Senior Project Director at the American Association for the Advancement of Science (AAAS) and host of the daily radio show and podcast Science Update. Now in its 24th 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.
Transcript:
Hirshon:
Welcome to the 365 Days of Astronomy Podcast. I’m Bob Hirshon, host of the AAAS radio show and podcast Science Update. After travelling for over six and a half years, the MESSENGER spacecraft is finally about to go into orbit around the planet Mercury in just a few days. I spoke with MESSENGER Deputy Project Scientist Louise Prockter about these tense final days.
Prockter:
Most of the preparation is pretty much done: everything that can be tested has been tested, everything has been reviewed multiple times over the last year or so. And we’re now pretty much just waiting and putting the final touches on what will happen … orbit insertion.
Hirshon:
She says all eyes are now on the spacecraft as it nears Mercury.
Prockter:
Well, the engineers will be tracking the spacecraft very carefully and making sure that the spacecraft configuration occurs correctly. And this happens a couple of days before the actual event: On Tuesday, March 15th, we start configuring the propulsion system ready for the burn. The next day, on March the 16th, we start our critical deep space network coverage.
Hirshon:
The Deep Space Network is an international network consisting of three space antennas placed approximately 120 degrees apart. One is in California, another in Spain, and the third in Australia. Together, they can track spacecraft 24 hours a day as the earth rotates.
Prockter:
And then about four hours ahead of the encounter we begin to start tracking it in earnest, again with the deep space network and we start configuring the propulsion system for the burn, radio systems so we can track it, and we turn the spacecraft to the correct attitude. So on the east coast at about 8:54 pm in the evening—that’s the spacecraft’s time—the engine begins to fire. And it fires for about 15 minutes. And what that will do is hopefully we’ll be in the correct orbit that it’ll fire off and bend the trajectory enough that we get captured into orbit around Mercury.
Hirshon:
That will be followed by about a 45 minute wait before the team can fully confirm that the spacecraft is in orbit around the planet. Prockter says that even though Mercury and the Moon are about the same size, attaining orbit around Mercury is much more difficult because of the proximity of the sun.
Prockter:
The first issue is trying to get caught into Mercury’s gravity instead of just getting pulled in towards the sun. But also we are very close to the sun and it is extremely hot out there. The solar intensity at Mercury’s orbit is about eleven times on average what it is at the earth. And so we have to take several steps to try and resist that intense heat that we’re getting both from the sun and the reflected heat from the surface of Mercury itself.
Hirshon:
MESSENGER’s orbit will be highly elliptical, with the spacecraft skimming just 200 km from the surface at nearest approach, and then sailing out nearly 15,000 km before coming back for another approach. One reason for this is to protect the spacecraft from the intense heat reflecting off Mercury’s surface.
Prockter:
And by being in an elliptical orbit we only have that intense heat from the surface for short amounts of time. And then the spacecraft moves away from the planet, again about several thousand kilometers away, and then comes back in for another close pass. So that allows us to regulate the amount of heating that the spacecraft is experiencing.
Hirshon:
The elliptical orbit also requires a lot less energy to attain and maintain. Prockter explains that a circular orbit would have required the spacecraft to perform far more critical orbital maneuvers, and that would have required a lot more fuel—out of the question, since MESSENGER is an inexpensive Discovery class mission.
Once MESSENGER attains orbit, Prockter explains that it goes through a period of testing before it starts collecting data.
Prockter:
Although the orbit insertion takes place March the 17th East Coast time, we don’t begin the commissioning period for the instruments until a few days later. And in fact we spend the first few days checking out the spacecraft and making sure that it is behaving as we expect. Of course, again, the intense thermal environment – there may be things that we’re not expecting, but we should be good to go. So we’ll be checking everything out for the first few days. And then we turn on all the instruments except for the imager on Wednesday, March the 23rd. And we start checking those out. So they’re not taking science data yet, they’re just moving through a series of pre-recorded sequences to make sure they’re behaving as we expect.
Hirshon:
Prockter says that the imager is on a pivot that allows it to be stowed with its optics facing the spacecraft deck to keep them protected. It will stay that way until well after MESSENGER’s final orbital maneuver, based on a lesson learned over ten years ago with the NEAR spacecraft that visited the asteroid Eros. The NEAR imager was exposed during the spacecraft engine burns and little remnants of fuel from the burn ended up on the lens.
Prockter:
So by stowing the imager we protect the optics from any of that. And we don’t un-stow the imager for a couple of extra days. That finally gets turned on on March the 28th. And so at that point the whole payload is being checked out and is just taking commissioning data. Now the first science observations begin on Monday, April the 14th. That’s our first official science orbit. And at that point, we start taking proper science data with all of the instruments, sending it back to the ground. And we hope to start releasing images and things like that to the web on that day.
Hirshon:
Even though April is only a few weeks away, those events are on the back burner right now, as everyone focuses on Thursday night. Many members of the MESSENGER science team have been working on the project for over ten years. Rarely does a ten-year investment come down to a single evening’s events.
Prockter:
The next steps between now and then are mostly I think a lot of nail biting, to be honest. We’re obviously very excited but also a little nervous: going into orbit around a planet is never something you can take lightly. And I think we’ll all be glad when it’s over and we’re finally safely in orbit around Mercury.
Hirshon:
That’s all for now. Once MESSENGER is safely in orbit and operational, we’ll have a report on what it’s finding. Till then, for the 365 Days of Astronomy Podcast, I’m Bob Hirshon.
End of podcast:
365 Days of Astronomy
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