Messenger to enter mercury orbit

Mar 09, 2011
Messenger to enter Mercury orbit
Artist's impression of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft as it leaves Earth. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

On March 17, the 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.

Antennas from each of the three Deep Space Network (DSN) ground stations have begun a round-the-clock vigil, allowing engineers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., to monitor MESSENGER on its final approach to Mercury.

At 10:40 a.m. on Tuesday, the spacecraft began executing the last cruise command sequence of the mission. This command load will execute until next Monday, when the command sequence containing the orbit-insertion burn will start.

“This is a milestone event for our small, but highly experienced, operations team, marking the end of six and one half years of successfully shepherding the spacecraft through six planetary flybys, five major propulsive maneuvers, and sixteen trajectory-correction maneuvers, all while simultaneously preparing for orbit injection and primary mission operations,” says MESSENGER Systems Engineer Eric Finnegan. “Whatever the future holds, this team of highly dedicated engineers has done a phenomenal job methodically generating, testing, and verifying commands to the spacecraft, getting MESSENGER where it is today.”

Messenger to enter Mercury orbit
Mercury is the planet nearest the Sun and its mass is just 5-1/2 percent that of Earth. The planet Mercury was first photographed in detail on March 29, 1974, by the U.S. probe Mariner 10. Credit: NASA

The mission operations team now turns its attention to the final preparations for the insertion burn next week and establishing nominal operations for the primary mission. As with the last three approaches to Mercury, the navigation team and the guidance and control team have been successfully using the solar radiation of the Sun to carefully adjust the trajectory of the spacecraft toward the optimum point in space and time to start the orbit-insertion maneuver.

As of the most recent navigation report on February 22, the spacecraft was less than 5 kilometers and less than three seconds from the target arrival point.

“These figures place the spacecraft well within the target corridor for successful orbit insertion,” Finnegan says. “Over the next week, additional body and solar-array attitude alternations will further refine this approach and nudge the spacecraft closer to the optimum target location. This approach will require the spacecraft to spend extended amounts of time at attitudes that do not support transmission of telemetry from the spacecraft, so monitoring of the spacecraft over the next week will be conducted with both telemetry and carrier signals.”

The in-flight preparations for this historic injection maneuver began on February 8, when several heaters on the spacecraft were configured to condition the bi-propellant used during the maneuver.

“Similar to pre-heating the diesel engine of a truck or car prior to starting in cold weather to allow ignition and prevent damage to the engine, the MESSENGER team turns on and off different heaters on the spacecraft so that the pressures for each of the two propellant species (hydrazine and nitrogen tetroxide) are at the optimum ratio for safe and efficient maneuver execution,” Finnegan explains.

Last Wednesday, the engineering and operations teams convened the last detailed review of the injection command sequence. After three iterations of this command sequence, countless Monte-Carlo simulations by the guidance and control team, numerous propulsion modeling simulations, and more than 30 hardware simulations covering all manner of nominal and anomalous operating configurations, the sequence and the associated fault protection configuration have been given the green light to start final preparations for upload to the spacecraft this week.

"The cruise phase of the MESSENGER mission has reached the end game,” adds MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "Orbit insertion is the last hurdle to a new game level, operation of the first spacecraft in orbit about the solar system’s innermost planet. The MESSENGER team is ready and eager for orbital operations to begin."

Studying could yield important information about how rocky, terrestrial planets form and evolve. Such information can help astronomers determine how and where potentially habitable planets are most likely to form beyond the solar system.

Explore further: NASA completes successful battery of tests on composite cryotank

add to favorites email to friend print save as pdf

Related Stories

Messenger spacecraft on way to Mercury

Aug 03, 2005

NASA's Messenger spacecraft swung by Earth for a Tuesday gravity assist that propelled it deeper into space on its long journey toward Mercury.

Mercury Messenger Probe Flips Sunshade Towards The Sun

Jun 23, 2006

The Messenger spacecraft performed its final "flip" maneuver for the mission on June 21. Responding to commands sent from the Messenger Mission Operations Center at The Johns Hopkins University Applied Physics ...

Messenger Sets Course For Earth Flyby

Jun 29, 2005

A short maneuver on June 23 kept Messenger on track for its Aug. 2 flyby of Earth – the major gravity assist that starts the next leg of the spacecraft's journey toward Mercury.

MESSENGER On Its Way

Aug 04, 2004

The MESSENGER spacecraft lifted off on-time aboard a Boeing Delta II rocket from pad 17-B at Cape Canaveral Air Force Station, Fla., at 2:15:56.537 a.m. EDT. MESSENGER has successfully begun its mission to u ...

NASA rescheduled MESSENGER start to Mercury to August 3

Aug 02, 2004

Today's launch of the MESSENGER spacecraft has been canceled due to weather constraints. The launch team will try again tomorrow, August 3, at 2:15:56 a.m. MESSENGER is a scientific investigation of the planet ...

MESSENGER Spacecraft Flies by Mercury

Sep 30, 2009

Shortly before 5:55 p.m. EDT, MESSENGER skimmed 228 kilometers (141 miles) above the surface of Mercury in its third and final flyby of the planet.

Recommended for you

Local model better describes lunar gravity

4 hours ago

Two satellites orbiting the Moon as a part of NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission have been mapping its inner structure by measuring subtle shifts in the pull of gravity on the ...

User comments : 0