MESSENGER Begins Historic Orbit Around Mercury


MESSENGER MOI

NASA’s MESSENGER spacecraft successfully achieved orbit around Mercury at approximately 9 p.m. EDT Thursday. This marks the first time a spacecraft has accomplished this engineering and scientific milestone at our solar system’s innermost planet.

For the next several weeks, APL engineers will be focused on ensuring the spacecraft’s systems are all working well in Mercury’s harsh thermal environment. Starting on March 23, the instruments will be turned on and checked out, and on April 4 the mission’s primary science phase will begin.

Getting into Mercury orbit…

On March 18, 2011 UTC (March 17, 2011 EDT), after almost five years in development and more than six and a half years in cruise toward its destination, NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft will execute a 15-minute maneuver that will place it into orbit about Mercury, making it the first craft ever to do so, and initiating a one-year science campaign to understand the innermost planet. The Mercury Orbit Insertion maneuver and subsequent orbital activities are described in the next few pages.

Just over 33 hours before the main Mercury orbit insertion event, two antennas from the Deep Space Network — one main antenna and one backup — will begin to track the MESSENGER spacecraft continuously. Nearly thirty-one hours later, at 6:30 p.m. EDT on March 17, 2011, the number of antennas tracking MESSENGER will increase to five — four of these are arrayed together in order to enhance the signal coming from the spacecraft, and a fifth will be used for backup.

About two and a half hours later, at 8:00 p.m. EDT, the solar arrays, telecommunications, attitude control, and autonomy systems will all be configured for the main thruster firing (known as a “burn”), and the spacecraft will be turned into the correct orientation for MESSENGER’s Mercury orbit insertion maneuver.

In order to slow the spacecraft down sufficiently so that it can be captured into orbit around Mercury, the main thruster will begin firing at 8:45 p.m. and will continue for 15 minutes until 9:00 p.m. About 31% of the spacecraft’s original allotment of propellant is required for Mercury orbit insertion, and MESSENGER’s thrusters must slow the spacecraft by just over 0.86 kilometers (0.53 miles) per second. As the spacecraft approaches Mercury, the largest thruster must fire close to the forward velocity direction of the spacecraft. After the thruster has finished firing, the spacecraft will be turned toward Earth and reconfigured for normal post-maneuver operations. Data will be collected by Deep Space Network antennas and transferred to the Mission Operations Center at APL to be analyzed. It is expected that by 10:00 p.m. EDT the Mission Operations Team will be able to confirm that MESSENGER has been successfully captured into orbit around Mercury.

Approximately one and a half hours after the maneuver is complete, the DSN coverage will be stepped back to two stations. At 2:47 a.m. EDT on March 18, the spacecraft will begin its first full orbit around Mercury (as measured from the highest point in the orbit). About 10 hours later, the Deep Space Network coverage will be further reduced to continuous coverage with only one station.

The MESSENGER spacecraft will continue to orbit Mercury once every twelve hours for the duration of its primary mission. The first two weeks from orbit insertion will be focused on ensuring that the spacecraft systems are all working well in the harsh thermal environment of orbit; this interval is known as the orbital commissioning phase. Starting on March 23 the instruments will be turned on and checked out, and on April 4 the science phase of the mission will begin and the first orbital science data from Mercury will be returned.

* Ground Receipt Time adjusted for one-way light time, which gradually decreases through reporting period.
— Events without specific execution times are initiated by direct commands from the ground.

This table summarizes the spacecraft events surrounding Mercury orbit insertion. Note that the times given in the first column are ground receipt times, which are approximately 9 minutes after a maneuver is executed on the spacecraft.

Three views of MESSENGER’s insertion into orbit about Mercury are shown above; they include a view from the direction of Earth, a view from the direction of the Sun, and a view from over Mercury’s north pole looking down toward the planet. Time is given in Coordinated Universal Time (UTC). The 15-minute orbital insertion maneuver is shown in light blue in the figures and places the spacecraft into the primary science orbit, which is shown in dark blue. The bright areas near the poles indicate portions of the surface not imaged by either Mariner 10 or MESSENGER during their respective flybys.

…and staying there

After MESSENGER arrives in its primary science orbit, small forces, such as solar gravity — the gravitational attraction of the Sun — slowly change the spacecraft’s orbit. Although these small forces have little effect on MESSENGER’s 12-hour orbit period, they can increase the spacecraft’s minimum altitude, orbit inclination, and latitude of the surface point below MESSENGER’s minimum altitude. Left uncorrected, the increase in the spacecraft’s minimum altitude would prevent satisfactory completion of several science goals.

To keep the spacecraft’s minimum altitude below 500 kilometers (310 miles), propulsive maneuvers must occur at least once every Mercury year — one complete revolution around the Sun, or 88 Earth days. The first, third, and fifth maneuvers after Mercury orbit insertion will occur at the farthest orbital distance from Mercury, where a minimum amount of propellant will be used to slow the spacecraft just enough to lower the minimum altitude to 200 kilometers (124 miles). The act of lowering the spacecraft’s altitude in this way has an unavoidable side effect of also lowering orbit period by about 15 minutes.

The second and fourth maneuvers after orbit insertion will increase the orbit period back to about 12 hours by speeding up the spacecraft around the time when it is closest to Mercury. Because the sunshade must protect the main part of the spacecraft from direct sunlight during propulsive maneuvers, the timing of these maneuvers is limited to a few days when Mercury is either near the same point in its orbit as it was during Mercury orbit insertion, or near the point where Mercury is on the opposite side of the Sun from that for orbit insertion.

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22 thoughts on “MESSENGER Begins Historic Orbit Around Mercury

  1. Very nice to see we’re still doing real science. It’s a heck of an accomplishment to get a spacecraft orbiting Mercury at speed it’s moving.

  2. Sorry there is a serious typo in this article. You said ‘NASA’ but I’m pretty sure they don’t do space stuff any more! :-)

  3. OT but something interesting at COLA. It seems they have expanded anomaly to +/-2C which now means the temperature anomaly maps appear mostly white (no anomaly) It makes much more sense than the massive reds and blues they had before. In fact it shown how insignificanttemp changes are LOL

    http://wxmaps.org/pix/clim.html

  4. From an earlier orbit of Mercury by Messenger this article describing some of what they saw happening with Mercury’s magnetic field.

    “””Magnetic Tornadoes Could Liberate Mercury’s Tenuous Atmosphere
    06.02.09

    http://www.nasa.gov/mission_pages/messenger/multimedia/magnetic_tornadoes.html

    ..During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury’s magnetic field can be extremely leaky indeed. The spacecraft encountered magnetic “tornadoes” – twisted bundles of magnetic fields connecting the planetary magnetic field to interplanetary space – that were up to 500 miles wide or a third of the radius of the planet.

    “These ‘tornadoes’ form when magnetic fields carried by the solar wind connect to Mercury’s magnetic field,” said Slavin. “As the solar wind blows past Mercury’s field, these joined magnetic fields are carried with it and twist up into vortex-like structures. These twisted magnetic flux tubes, technically known as flux transfer events, form open windows in the planet’s magnetic shield through which the solar wind may enter and directly impact Mercury’s surface.” ..
    ..The process of linking interplanetary and planetary magnetic fields, called magnetic reconnection, is common throughout the cosmos. It occurs in Earth’s magnetic field, where it generates magnetic tornadoes as well. However, the MESSENGER observations show the reconnection rate is ten times higher at Mercury.

    “Mercury’s proximity to the sun only accounts for about a third of the reconnection rate we see,” said Slavin. “It will be exciting to see what’s special about Mercury to explain the rest. We’ll get more clues from MESSENGER’s third flyby on September 29, 2009, and when we get into orbit in March 2011.” ..

    Now why would this be? “Mercury’s proximity to the sun only accounts for about a third of the reconnection rate we see,” said Slavin.
    Happy Friday..

  5. Nice to put a mark in the win column for NASA’s space program. Very big congratulations to the team team that designed and engineered this project!

    George V.

  6. Sorry to harp on about the COLA thing again. However by having expanded the temperature anomaly to show no color beyond +-2C it is very very apparent that there is pretty intense cooling (blue) occuring globally (looks like -6C plus in Asia check it out fun

    http://wxmaps.org/pix/clim.html

  7. OT – CERN Cloud experiment
    Does anyone know whether this event here:

    http://pacificclimate.org/event/2011/cloud-experiment-cern

    is likely to announce anything new on Wednesday March 23, 2011 ?

    Jasper Kirkby, Head of the CLOUD experiment, CERN, Geneva, presents “The CLOUD Experiment at CERN” as part of the seminar series “Global Warming: A Science Perspective” hosted by Simon Fraser University’s Faculty of Science.

    This seminar will be streamed live on the web at http://www.irmacs.sfu.ca/about/live-video.

    Abstract: Understanding the causes of climate change is one of the most important challenges facing science today. The Intergovernmental Panel on Climate Change attributes more than 90% of the observed warming during the last century to anthropogenic causes, especially the increase in atmospheric carbon dioxide from fossil fuels. However, during the last ten thousand years since the end of the last ice age, and prior to industrialisation, the climate has frequently changed on 100-year time scales by amounts comparable to the current warming. At present there is no established mechanism to explain these natural climate changes, but associations are frequently found with solar variability, which is recorded in archives that measure past variations of cosmic ray intensity. This raises the intriguing question of whether cosmic rays may directly affect the climate. This talk presents an overview of the palaeoclimatic evidence for solar/cosmic ray forcing of the climate, and the initial results from the CLOUD experiment at CERN which is investigating and quantifying the physical mechanisms that may link cosmic rays with aerosols, clouds and climate.

  8. Carla
    I think direct observation of solar magnetic field from a close proximity may be one of major benefits of this mission. I just hope the probe is lucky, and does not get hit by a major CME, otherwise at that distance from the sun, the exposed parts of its transmission equipment could be instantly disabled.

  9. thanks Anthony – it’s dumpin’ outside, and this will keep us busy for an hour or so. After that, I got a bag of chocolate chips and a bag of those peppermint hard candies – you smash the peppermints with a hammer (peel the wrappers off first and put them in a zip-lock bag), melt the chips, spread the melted chocolate on a sheet, sprinkle on the candy bits, and put it in the fridge. Within 30 minutes you got “peppermint bark.”

    White chocolate is nice too.

    Have a good one!

  10. Great timing for this, as I saw Mercury only half an hour ago. From England it’s hard to see it on more than a few days a year, what with the elongation only being 18 degrees in the spring, and the weather. Further south you’ll have a better chance for a few more days yet. (I also saw it 4 days ago when it was on the Sun-side of Jupiter.)

    Rich.

  11. I hope the science isn’t too settled to have put a surface temp recorder in the bundle. Seems like a good place to check out the effect of solar cycles on temp variation.

  12. Some interesting temperature series from the NH.

    Greenland:

    Extending Greenland temperature records into the late eighteenth century
    B. M. Vinther,1 K. K. Andersen,1 P. D. Jones,2 K. R. Briffa,2 and J. Cappelen3
    Received 24 October 2005; revised 11 January 2006; accepted 28 February 2006; published 6 June 2006.
    “the warmest year in the extended Greenland temperature
    record is 1941, while the 1930s and 1940s are the
    warmest decades.”

    Greenland (and Danmark)

    http://www.dmi.dk/dmi/index/klima/klimaet_indtil_nu/temperaturen_i_groenland.htm

    Norway

    http://eklima.met.no/metno/trend/TAMA_G0_0_1000_NO.jpg (!)

    http://met.no/?module=Articles;action=Article.publicShow;ID=881

    http://met.no/?module=Articles;action=Article.publicShow;ID=882

    Sweden

    http://www.smhi.se/klimatdata/meteorologi/temperatur/1.2430 (sinificant warming since 1990?)

    Finland

    http://en.ilmatieteenlaitos.fi/normal-period-1971-2000 (significant warming since 1990?)

    Iceland

    http://en.vedur.is/climatology/clim/nr/1213 (1930-1940)

    England (CET)

    http://hadobs.metoffice.com/hadcet/ (significant warming since 1989?)

    http://hadobs.metoffice.com/hadcet/ssn_HadCET_mean.txt (look at wintertemperature since 1989)

    Netherlands

    http://www.knmi.nl/klimatologie/lijsten/jaar_xtr.html (year ranking significant warming since 1990?)

    http://www.knmi.nl/klimatologie/lijsten/jaar_xtr.html (winter ranking all winters colder than 1990)

    Spain

    http://www.aemet.es/documentos/es/elclima/datos_climat/resumenes_climat/anuales/res_anual_clim_2010.pdf

    (significant warming since 1990?)

    France
    http://www.onerc.org/category/classification-indicateurs/atmosphere-et-climat (signifgicant warming since 1990?)

    Canada

    http://www.ec.gc.ca/dccha-ahccd/default.asp?lang=en&n=1EEECD01-1 (some work to be done)

    Alaska

    http://climate.gi.alaska.edu/Climate/Location/TimeSeries/index.html

    Look for Ostrov Dikson

    via Climate Explorer http://climexp.knmi.nl/start.cgi?someone@somewhere

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