MESSENGER Webcast: MESSENGER Mission Overview
James Leary's Presentation

Tiffany Nail: Hello everyone, I'm Tiffany Nail, thanks for being with us for coverage of NASA's mission to Mercury live on NASA Direct! This exciting mission will explore the unknown regions of Mercury, the closest planet to the Sun.

Today, we'll talk with the Mission Systems Engineer, get a live launch day weather report and get a unique look at the launch vehicle with NASA's launch manager for MESSENGER. Plus, we'll answer some NASA Direct! viewer questions live. We have a lot to get to!

The last time a NASA spacecraft voyaged to Mercury it was the Mariner Mission in the 1970s. Since then, scientists have spent years preparing for MESSENGER, eager to pick up where Mariner left off.

Our first guest is someone who knows the design and development of MESSENGER intimately: Mission Systems Engineer James Leary. In a few minutes, James will answer some of your questions live. But first, he gives us a closer look at the MESSENGER spacecraft.

Hello, I'm James Leary. I'm the mission systems engineer for MESSENGER. MESSENGER is the first mission to orbit Mercury. I'll be discussing the mission design and spacecraft system. MESSENGER is an acronym. It stands for the MErcury Surface Space ENvironment, Geochemistry and Ranging mission.

This is the first mission to Mercury since the 70s when Mariner 10 went. The MESSENGER mission design is a complex journey through our Solar System. The mission will take about 7-1/2 years. The mission launches in August 2004, one year later flies by Earth, and then has two Venus flybys in 2006 and June 2007. Three Mercury flybys are then performed where key science data is taken in January 2008, October 2008 and September 2009. All of these gravity assists allow us to set up for an orbit insertion in March 2011.

The MESSENGER mission is a compilation of scientists' and engineers' efforts from the past 30 years since Mariner 10 arrived at Mercury in the mid-70s. The Johns Hopkins Applied Physics Laboratory has been actively working the mission for the past four years. Some engineers have been working on this mission for seven years of their lives.

The spacecraft integration and test and development period started in February 2003 and completed in July 2004 when integration with the launch vehicle proceeded. The MESSENGER spacecraft is about a four foot cube. It weighs nearly a ton, around 1,100 kilograms and is about the size of a small car. The MESSENGER spacecraft had to be very light to allow us to carry almost 60 percent of the mass as fuel. In order to do this, the spacecraft structure was built out of a composite material, similar to the material you'll see in a golf club. Lightweight fuel tanks were also designed specifically for this mission to allow us to carry a large amount of fuel without incurring a very large mass penalty.

The miniaturized set of instruments also helped to save mass and provided the key science data we need for this mission. These miniaturized instruments allowed the mission to be very mass-efficient, providing for the 60 percent of fuel that we need in order to get into Mercury orbit. The key challenges for MESSENGER revolve around the extreme environment it's going to see in orbit.

The sun shade, that ceramic cloth material stretched over a titanium frame, eliminates all the solar input to the spacecraft and allows the spacecraft to run at nearly room temperature. Some parts of the spacecraft, however, aren't behind the sun shade. The solar panels, for example, had to be about two-thirds mirrors to reflect the Sun's input and allow us to still have power. Also, the orbit is designed to keep us near the hot planet only for a short period of time while we take science data, and then spend roughly 11 hours cooling down before we come back to the planet.