* Astronomy

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RE: MESSENGER

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Venus mission

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RE: MESSENGER

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MESSENGER Team Releases First Images From Venus 2 Flyby

The first images from MESSENGER's second flyby of Venus are in! The Mercury-bound probe flew within 338 kilometers (210 miles) of Venus on June 5, obtaining a gravity assist that shrank the radius of the probes orbit around the Sun, pulling it closer to Mercury. But the encounter also allowed the MESSENGER team to give its two cameras, known as the Mercury Dual Imaging System (MDIS), a thorough workout.

The MDIS consists of wide-angle and narrow-angle cameras that will map landforms, track variations in surface spectra, and gather topographic information at Mercury. It snapped a series of images as it approached Venus.

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MESSENGER Completes Second Flyby of Venus,
Makes Its Way toward First Flyby of Mercury in 33 Years
NASAs MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft swung by Venus for the second time early this evening for a gravity assist that shrank the radius of its orbit around the Sun, pulling it closer to Mercury. At nearly 15,000 miles per hour, this change in MESSENGERs velocity is the largest of the mission.
Mission operators at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., said MESSENGERs systems performed flawlessly as the spacecraft sped over the cloud tops of Venus at a relative velocity of more than 30,000 miles per hour, passing within 200 miles of the surface of the planet at 23:08 UTC (7:08 p.m. EDT).
For 20 minutes during this closest approach, MESSENGER was within the shadow of Venus, and in the absence of solar power the probe relied solely on its internal battery. By 1:32 UTC (9:32 p.m. EDT) the battery had fully recharged, and the spacecraft was operating as planned.

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At the time of closest approach, MESSENGER will be flying over Venus at an altitude of approximately 337 kilometres. Maximum vicinity will be reached at 01:08 CEST on 6 June, above the Venusian coordinates 12.25° South and 165° East.
At this time, Venus Express will be behind Venus, but it will look at the same regions observed by MESSENGER before and after the fly-by. This will allow the scientists to compare data of the same areas obtained by the two spacecraft within only a short difference in time from each other.

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NASA will host a media teleconference at 2 p.m. EDT on Monday, June 4, to preview the June 5 flyby of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft through the Venus system. The probe, the first space mission designed to orbit the planet closest to the Sun, will use Venus's gravity once again to guide it closer to Mercury's orbit.
During the flyby, the full suite of the spacecraft's instruments will be directed at Venus, providing several unique science opportunities that may offer insight never before revealed about the cloud-shrouded planet. The encounter also presents the opportunity to conduct collaborative and complimentary observations with the European Space Agency's Venus Express mission.

Briefing participants are:
-- Marilyn Lindstrom, MESSENGER program scientist, NASA Headquarters, Washington
-- Sean Solomon, MESSENGER principal investigator, Carnegie Institution of Washington
-- Eric Finnegan, MESSENGER mission systems engineer, Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
-- Hakan Svedhem, Venus Express project scientist, European Space Agency, Paris

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7 hours and 15 minutes to the spacecrafts Venus first Flyby on October 24, 2006.

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Today marks the second anniversary of MESSENGER's launch.

"It's still more than four and a half years to Mercury Orbit Insertion in March 2011, and there are many milestones between now and then. But it's worth pausing for a few moments today to appreciate how far we've come" - Dr. Sean C. Solomon, of the Carnegie Institution of Washington, who leads the mission as principal investigator.

And just how far has the spacecraft travelled since its August 3, 2004, launch from Cape Canaveral Air Force Station, Florida, US? Nearly 1.2 billion miles. MESSENGER's computers have executed 180,271 commands since liftoff, a time interval that includes seven major trajectory correction manoeuvres.

"It's been a busy two years. We've been by Earth and now we are headed for Venus, another major milestone in this mission" - Mark Holdridge, MESSENGER Mission Operations Manager, Johns Hopkins University Applied Physics Laboratory (APL) in Laurel.

MESSENGER team members have been running tests all summer to make sure the spacecraft will operate as intended during the Venus flyby - the first of two swings past the clouded planet scheduled for Oct. 24, 2006. There will be a 57-minute solar eclipse during that operation. So on Aug. 11, engineers will turn the spacecraft solar panels edge-on to the Sun and discharge the battery, much in the same manner that the power system will function during the Venus flyby, to verify that the system will respond Appropriately.
Two weeks later, on August 21, engineers will conduct a "star-poor" region test, pointing the spacecraft's star tracker in a region of the sky that might be utilised during the Venus operations.
A similar test was conducted on July 26, "and we got a positive result from that test; the preliminary results look good."

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MESSENGER Flips Sunshade Toward the Sun

The MESSENGER spacecraft performed its final “flip" manoeuvre for the mission on June 21. Responding to commands sent from the MESSENGER Mission Operations Centre at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., through NASA's Deep Space Network antenna station near Goldstone, California, the spacecraft rotated 180°, pointing its sunshade toward the Sun.
The 16-minute manoeuvre, designed to keep MESSENGER operating at safe temperatures as it moves closer to the Sun, wrapped up at 9:34 a.m. EDT, with successful reacquisition of signal from MESSENGER’s front-side antenna. The spacecraft was 196.5 million kilometres from Earth and 144.6 million kilometres from the Sun when the manoeuvre occurred.

MESSENGER had been flying with its back to the Sun since a March 8 “flop,” allowing it to maintain temperatures within safe operating ranges at Sun distances greater than 0.95 astronomical units (1 AU is Earth’s distance from the Sun). Mission plans call for the spacecraft to keep its sunshade facing the Sun for the remainder of its cruise and science orbital operations around Mercury.

"Initial indications look very good. Spacecraft temperatures are coming down as expected and all systems and instruments are nominal" - Mark Holdridge, MESSENGER Mission Operations Manager of APL.

The team will now turn its attention to preparing for the first Venus flyby on October 24.

"We have mission simulations and flight tests coming up to test particular operations that will have to occur during the Venus flyby. There will be a 57-minute solar eclipse during the October operation, so we will so be testing the flight systems in the flyby configuration to verify they will behave properly during the eclipse period" - Mark Holdridge.

On August 11, for instance, the team will conduct a flight test of the new autonomy that will power off components prior to the solar eclipse, allow the battery to discharge by approximately the same amount as during the real eclipse, and then power on components again once the battery is recharged, all in a more controlled setting with real-time visibility. This test will be combined with a battery reconditioning.

Later in August and through September, during the approach to Venus, MESSENGER’s navigation team will use the Mercury Dual Imaging System cameras onboard the spacecraft to take a series of optical navigation pictures. These images are not required for the Venus flyby but will be used by the MESSENGER navigation team for calibration and as practice for the optical navigation imaging to be utilized at Mercury.

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