After more than a dozen laps through the inner solar system, NASA's MESSENGER spacecraft will move into orbit around Mercury on Mar. 17, 2011. The durable spacecraft - carrying seven science instruments and fortified against the blistering environs near the sun - will be the first to orbit the innermost planet.



On Wednesday, Mar. 16, chat experts Jimmy Lee, NASA MESSENGER mission manager, and Mike Galuska, chief engineer of the Discovery, New Frontiers and Lunar Quest Program Office at NASA's Marshall Space Flight Center in Huntsville, Ala., answered your questions about MESSENGER'S orbital insertion.



More About MESSENGER



On Mar. 17 at 8:45 p.m. EDT, MESSENGER - having pointed its largest thruster very close to the direction of travel - will fire that thruster for nearly 14 minutes, with other thrusters firing for an additional minute, slowing the spacecraft by 862 meters per second (1,929 mph) and consuming 31 percent of the propellant that the spacecraft carried at launch. Less than 9.5 percent of the usable propellant at the start of the mission will remain after completing the orbit insertion maneuver, but the spacecraft will still have plenty of propellant for future orbit correction maneuvers.



The orbit insertion will place the spacecraft into a 12 hour orbit about Mercury with a 200 kilometer (124 mile) minimum altitude. At the time of orbit insertion, MESSENGER will be 46.14 million kilometers (28.67 million miles) from the sun and 155.06 million kilometers (96.35 million miles) from Earth.



MESSENGER has been on a six year mission to become the first spacecraft to orbit Mercury. The spacecraft followed a path through the inner solar system, including one flyby of Earth, two flybys of Venus, and three flybys of Mercury. This impressive journey is returning the first new spacecraft data from Mercury since the Mariner 10 mission over 30 years ago.



› More About Chat Experts Jimmy Lee and Mike Galuska



Chat Transcript



NASA: Hi everyone, Jimmy and Mike here. Welcome to the chat! We're ready to take your questions whenever you're ready...



clinton: Hi I'm from Australia, and we are currently doing a school project on Mercury... how do you deal with the increased heat from the sun whilst in Mercury orbit?



NASA: The sunshade keeps the instruments at room temperature, and you have a protective, multi-layer insulation around the spacecraft.



DavidM: Since 1999 NASA has required spacecraft to report their status during critical operations like MOI. What data is Messenger going to transmit during MOI through a low-gain antenna?



NASA: We'll have critical health and status data.



OlgaDobrovidova: Hi there! Olga Dobrovidova with RIA Novosti, Russia. could you tell us a bit more about the MESSENGER's polar ice search? what instruments will you use for that? could you compare this task to what was done for the Moon by LRO and LCROSS? Thanks!



NASA: Hi Olga. MESSENGER's neutron spectrometer will search for hydrogen in and polar deposits. The presence will suggest that the deposits are water-rich. On the moon, we had hints of ice from radar, and LCROSS fully confirmed ice and volatiles in lunar craters. On Mercury, the radar of the polar deposits is more extensive than on the moon.



Nick: When will you actually initiate the maneuver to change its trajectory and officially be in orbit?



NASA: Hi Nick. The burn starts at 8:54 p.m. EDT on Mar. 17 - the main engine will be ignited for about 15-minute burn to allow the spacecraft to begin its orbit around Mercury.



Bob: Good Morning all. I notice that the orbit for MESSENGER will be High elliptical. Is there enough fuel onboard to circularize it and if so will NASA consider alter it at a later date ?



NASA: Hi Bob. No plans to circulize the orbit, but there is enough fuel to accomplish the orbit insertion maneuver.



Lee_Roop: How long does it take a command sent from Earth to reach MESSENGER and data from MESSENGER to make it back here?



NASA: Between 4-12 minutes, depending on the distance from Earth.



DavidM: How will this "status data" tell you how the MOI burn is going?



NASA: It provides critical spacecraft parameters in the propulsion system.



Scicommer: What's the plan for the spacecraft's initial mission? How much time will be devoted to mapping, and what science projects are expected?



NASA: It's a one-year orbit that includes over four Mercury years. Mapping will continue at every pass - primary areas that haven't been mapped are the poles. The science includes a study of the surface composition and providing a global map, plus a study of the thin atmosphere and the magnetosphere.



Manu: There were three flybys with the instruments already collecting data. What new scientific results do you hope to get by orbiting Mercury?



NASA: A more detailed characterization of the surface, interior, atmosphere, and magnetosphere, plus enhanced color and stereo images, as well as specific targeting of sites of interest - many of which were discovered during the three fly-bys.



(Moderator Jason): We're working on answering all your questions right now. Have a question you'd like to ask, please ask it now by typing it in the box beneath the chat room and submit it by clicking the 'Ask' button on the right side.



AREweALONE: What is the maximum temperature that the Messenger can tolerate?



NASA: A lot depends on the specific location on the spacecraft. The sunshade the keeps electronic instruments at room temperature, and the multi-layer insulation helps keep the entire spacecraft cooler.



solareclipse1970: With regards to Messenger's elliptical orbit, will Messenger's instruments be able to detect water ice at Mercury's South Pole region?



NASA: We'll use the neutron spectrometer to try to measure and determine the presence of water ice on Mercury's south pole region.



Luna2: Why was the name Messenger chosen for this mission?



NASA: Mercury is the "messenger of the gods" in Roman mythology, hence MESSENGER.



Kevin: How long will MESSENGER stay in orbit? Is there a planned crash onto Mercury, or will we receive information until the power source runs out?



NASA: One-year orbit of the planet is planned in the baseline mission. After the mission is completed and the propellant is exhausted, the planet will ultimately draw the spacecraft into its surface.



a: What are the benefits of the mission to human-kind?



NASA: By gaining a detailed understanding of Mercury's characteristics and how it formed, it provides us with a better understanding of our solar system and Earth.



Nick: Is there any time of "live video" on the vehicle that will show the surface of the planet? OR do you just receive telemetry data and initial instrument results?



NASA: Once the science phase of the mission begins on April 4, daily images will be available on the NASA Web site (http://www.nasa.gov/mission_pages/messenger/main/index.html). More detailed educational and outreach information is available here: http://messenger.jhuapl.edu/. Johns Hopkins Applied Physics Lab is responsible for the MESSENGER mission operations, and the principle investigator for the mission -Sean Solomon - is at Carnegie Institute of Washington.



Manu: Just to get an impression: How many people are involved in the Messenger mission? How many engineers, scientists whatever are at the moment looking forward to this next phase in the project?



NASA: The APL MESSENGER Web site can give you more details about the team: http://messenger.jhuapl.edu/.



Moderator Jason: Have a question you've been waiting to ask? Go for it! Type it out in the box below the chat room and then click the 'Ask' button on the right side to submit it.



Scicommer: Given the proximity to the Sun, and the likelihood communications will be pretty episodic, how much data can Messenger record onboard? How often will it be dumping to the Deep Space Network?



NASA: Answering the second part of your question - once the science mission begins on April 4, eight of of every 24 hours will be dedicated to a downlink of data at 15 Mb/sec. (The spacecraft orbits the planet once every 12 hours.)



diane_Adrian S. (Canada): When Messenger gets to Mercury, what parts of the surface are you hoping to get photos of?



NASA: An extensive global characterization and mapping, in particular interest focused on the poles that weren't previously mapped on the fly-bys. In addition, there are numerous specific target locations that will be imaged during the one-year orbit of the planet.



clinton: How long will it be before accurate results are known? will it take the full year?



NASA: The first planetary data system (PDS) information will be available about six months (this is the first two months of orbit data collection) after orbit insertion. Scientists will build on the knowledge gained from the three Mercury fly-bys as they begin to study the more detailed data from Mercury.



diane_Colin (Canada): What kind of fuel is used in Messenger and how much is needed to complete the mission?



NASA: We've got one bi-propellant engine that's been used for all large trajectory adjustments, including orbit insertion, and it has hydrazine and nitrogen tetroxide. Also, there are 16 mono-propellant thrusters used for small attitude corrections and these use hydrazine.



OlgaDobrovidova: Just in the (hopefully) unlikely case of no orbit insertion on 17 March, when can MESSENGER 'try again'? and is it actually possible (do you have enough fuel for that)?



NASA: It depends on the results of the orbit insertion burn, but a near-term opportunity is unlikely, and it could be up to 5-6 years before another opportunity is feasible. Wish MESSENGER luck tomorrow!



Scicommer: What plans do you have for extended missions, if the fuel holds out?



NASA: Depending on the orbit achieved and the use of propellant, we may be in a position to pursue an extended MESSENGER mission.



solareclipse1970: If Messenger's main thruster burns for only 20% of the planned time to achieve MOI, what will happen to Messenger and how long would it take for Messenger to re-attempt MOI?



NASA: We don't have the details on that - the navigation team has done extensive analyses on contingencies.



George: What are the internal and external temperatures of the spacecraft at this time ?



NASA: We don't have that detail at hand, but the thermal team and mission operations teams are constantly monitoring the spacecraft.



BobKaplow: Why the multiple flybys of Mercury, instead of going into orbit earlier?



NASA: We needed the three fly-bys for gravity assist to slow down the spacecraft. We could never have put an engine on the spacecraft that would have had enough thrust to slow us down.



NASA: Fun fact, for the name question: the team built an acronym around it the MESSENGER name - MErcury Surface, Space ENvironment, GEochemistry and Ranging - to describe the science goals at Mercury.



Scicommer: How far out from Mercury's surface does the atmosphere extend, and will it have any effect on orbital operations? Will there be any attempts at physical sampling?



NASA: No attempts to sample the atmosphere (no grab samples).



OlgaDobrovidova: Certainly! Good luck to MESSENGER and many thanks for doing this! fingers crossed for tomorrow (not quite a question)



NASA: Thanks so much! The entire MESSENGER team is very excited about beginning orbital operations.



Moderator Jason: We've got time for a few more questions. Ask your question by typing it out in the box beneath the chat room and clicking the 'Ask' button on the right. Thanks.



NASA: BTW, these are great questions, everyone. Keep them coming, we're enjoying them!



diane: Adrian: What will happen to Messenger at the end of its mission. Will it return to earth?



NASA: No, a one-year orbit of the planet is planned in the baseline mission. After the mission is completed and the propellant is exhausted, the planet will ultimately draw the spacecraft into its surface.



George: Remind me again as to time when the OIB takes place?



NASA: On March 17 at 8:54 p.m. EDT and ending about 15 minutes later.



Scicommer: And with solar activity predicted to be rising toward maximum in 2013, are the instruments hardened enough to be able to withstand flares or mass ejections while in orbit?



NASA: The instruments and spacecraft avionics are radiation-hardened, but single event upsets are possible. The autonomy system is designed to accommodate these events.



OlgaDobrovidova: I know there's a plan to send another probe to Mercury - BepiColombo, I think? how can the MESSENGER mission results be useful? will you investigate the scene for it? since the spacecraft is boldly going where no one's gone before, you know :)



NASA: The MESSENGER and BepiColombo teams have been collaborating and the results will be shared with the BepiColombo team and provide them useful info in better planning their mission. The science for both missions complement each other.



George: Will there be any live coverage at that time and if so where ??



NASA: There will be a live public event at APL on Mar. 17 and a Webcast on the APL site. More detailed information is available at: http://messenger.jhuapl.edu/



raketenflugplatz: Is operational work of mission centre connected with Mercury's day (or night) or it'll work whole 24 hours? greetings from Warsaw we're crossing fingers for tomorrow!!!



NASA: Hello Warsaw, and thanks! The mission operations will monitor the spacecraft health 24-hours a day, but downlink is only provided eight of every 24 hours. The spacecraft orbits Mercury once every 12 hours.



solareclipse1970: Apart from the polar regions, do you have any favorite craters or other sites that you would like to see intensively studied by Messenger?



NASA: Yes! There are about 2,000 specific target sites that have been identified with a number of these discovered on the three fly-bys. One "big guy" - approximately 440 miles across - is called the Rembrandt Impact Basin. It was discovered on the second Mercury fly-by.



(Moderator Jason): Thanks for everyone who participated today. We'd like to give a big thanks to Jimmy Lee and Mike Galuska who took time out of their schedules to sit down with us today. Thanks! And thanks everyone for the great questions. Stay tuned on Thursday on http://www.nasa.gov/) for MESENGER's arrival at Mercury.



Editor's Note: These are two questions that were posed in the chat answered once the chat window was closed:



Guest 1: How fully will Messenger be able to characterize the magnetosphere's interaction with the Solar environment in a year's time?



NASA: The magnetometer will characterize Mercury's magnetic field in detail over four Mercury years - each Mercury year equals 88 Earth days - to determine its precise strength and how that strength varies with position and altitude. The effects of the sun on the magnetospheric dynamics will be measured by the magnetometer and by the energetic particle and plasma spectrometer. MESSENGER's highly capable instruments and broad orbital coverage will greatly advance our understanding of both the origin of Mercury's magnetic field and the nature of its interaction with the solar wind.



Guest 2: Are images being taken now upon approach to orbit, and being released?



NASA: Images were collected during the three previous Mercury fly-bys. Instruments will be turned off in preparation for orbital insertion burn, or OIB, on Mar. 17, and they'll be turned back on during the commissioning phase starting on Mar. 21. Actual science data collection begins on Apr. 4. Daily images will be available on the NASA MESSENGER mission Web site and APL Website starting on Apr. 4.