Week of September 16, 1996
As you can see from the live image, the mechanical team has completed installation of the three lander petals. Each of these petals are mounted on a hinge that allows them to open and close by more than 110 degrees of travel. The petals are moved under software command via three actuators mounted along the "hinge line" of each of the three petals. One or more of these petals open up, after the airbags are retracted, about an hour and fifteen minutes after landing. They are the mechanism for automatically righting the tetrahedral-shaped lander so that no matter how the lander comes to rest inside the inflated airbag cocoon, the lander will always end up "top side up" and not the reverse!
Once the petals were installed, the "rock membrane" was placed on each of the petals (except for the rover petal which will be done next week). This is a layer of aluminum sheet metal placed on the outside of the petals (but under the airbags). The petals are about two inches thick, but for the most part are hollow. The inside of the petals have the lander's solar arrays attached on an aluminum substrate. This layer will provide protection from any tall sharp rocks that might be inclined to try to penetrate a side (or base) petal and damage the delicate solar arrays from below. When the lander rolls onto its base petal from a side petal during the righting phase, the 270 kg lander (only 223 lbs on Mars) can roll quite hard. The airbags will help some, but aluminum will really do the trick.
The three solid rockets used to stop the lander just before landing are now installed. Frist they had to be prepared with heaters and thermal blanketing before mounting to the inside of the backshell. The backshell, the heatshield and the cruise stage are not far from the lander, but are out of sight of the camera.
Progress on the cruise stage is also being made. We decided some time ago to separate the fuel tank heater circuits from the propellant line heaters so that we can maintain the option of turning off the tank heaters during battery charging while also not allowing the fuel in the propellant lines to freeze. Turning the tank heaters on for the few hours of battery charging allows us to gain a few extra precious watts when we need it most during "cruise". The necessary cabling changes on the cruise stage were done this past week and verified.
Next week: Airbag installation!