MESSENGER Enters Orbit Around Mercury

krswan writes "From the NASA press release: 'At 9:10 p.m. EDT, engineers in the MESSENGER Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., received the anticipated radiometric signals confirming nominal burn shutdown and successful insertion of the MESSENGER probe into orbit around the planet Mercury.' If you don't know much about this little spacecraft, check out its website. Designed with a completely passive cooling system, it will stay at 600C on the sun side, but room temperature behind the sunshade. During its 6-year journey it used solar panels as sails, relying on the solar wind instead of thrusters to adjust its trajectory. Over the next year it will build a high-res map of Mercury, and maybe determine if there is really ice hiding within polar craters (PDF)."

Comments

Untrue

[MyLongNickName]

". During its 6-year journey it used solar panels as sails, relying on the solar wind instead of thrusters to adjust its trajectory"

I do not think this is true;

"These views of MESSENGER show the orientation at the start of trajectory correction maneuver 43 (TCM-43). Because TCM-43 will use the large bi-propellant thruster to place the spacecraft into orbit about Mercury, TCM-43 is also called Mercury orbit insertion (MOI). "

"MESSENGER’s dual-mode propulsion system includes a 660-newton (150-pound) bipropellant thruster for large maneuvers and 16 hydrazine-propellant thrusters for smaller trajectory adjustments and attitude control. The Large Velocity Adjust (LVA) thruster requires a combination of hydrazine fuel and an oxidizer, nitrogen tetroxide. Fuel and oxidizer are stored in custom-designed, lightweight titanium tanks integrated into the spacecraft’s composite frame. Helium pressurizes the system and pushes the fuel and oxidizer through to the engines."

And I know I read about this mission using chemical propulsion several times during the mission to make course adjustment.

Re:Untrue

[Digicrat]

Inaccurately worded, but true none-the-less.

The solar wind isn't used in place of traditional thrusters, but as a complement to them, allowing the spacecraft to save precious fuel.

Google yields a good explanation of this from an old article at http://www.spacedaily.com/reports/MESSENGER_Sails_On_Sun_Fire_For_Second_Flyby_Of_Mercury_999.html discussing the cancellation of several TCMs due to the successful usage of solar sailing.

Re:Untrue

[MyLongNickName]

I think I see the source of the confusing

The author of this submission did a wikipedia search and found two things:

1) Wikipedia reports that this mission will MEASURE solar wind.
2) Wikipedia's solar wind article states "Both the Mariner 10 mission, which flew by the planets Mercury and Venus, and the MESSENGER mission to Mercury demonstrated the use of solar pressure as a method of attitude control in order to conserve attitude-control propellant."

The article submitter then took that grain of usage and made it the sole method of propulsion. Bad article submitter.

Re:Untrue

[camperdave]

Just because it had chemical thrusters, doesn't mean that it didn't use solar panels as sails and the solar wind to adjust its trajectory at some point during its 6-year journey. The sentence "During its 6-year journey it used solar panels as sails, relying on the solar wind instead of thrusters to adjust its trajectory" only says that it happened, not that it was the sole method used. (Granted, the sentence is somewhat ambiguous.)

Re:Not solar sails or thrusters but gravity assist

[Anonymous Coward]

It's worse than that - you're not at the lip of a crater, but pinned to the wall of a large centrifuge. Now try rolling the ball into the tiny crater.