Week of October 8, 1996
A lot has been accomplished in the last two weeks. For those of you who have been watching the images from KSC regularly, you will have noticed that the airbags have been installed for nearly two weeks. The airbag and gas generator installation operation is quite complex, but the talented folks (Skip Wilson) from the airbag manufacturer (ILC Dover Inc. of Frederica, DE) and the JPL airbag cognizant engineer (Tom Rivellini) have done this so many times before on other test landers, that they make it look easy.
Once the bags were installed, a detailed "walk through" of the whole lander was performed early last week by some the best spacecraft mechanical engineers around. They looked for anything that might appear to be amiss. For example, they pointed out that the exposed edge of the solar panel honeycomb substrates really ought to be taped closed rather than provide the opportunity for manufacturing particulates to escape and potentially contaminate sensitive surfaces such as the camera optics. The edges were taped and bonded closed within two of hours of being mentioned by our very talented mechanical team.
One other item was reviewed and commented upon by the mechanical review team. We all noticed for the first time, that with the fully loaded mass of the lander and the airbags, the petal latches were no longer perfectly aligned when closed. This meant that when the six petal latch separation bolts are torqued down (they get released after landing released via pyrotechnic separation nuts) there may be some rebound in the structure that would "race" the separation nuts at the moment of release. The engineers were concerned that there was adequate time for the bolts to exit the holes before the structure moved to the point that the bolts could not clear the holes and hang up. Also we knew that the petal actuators and the mechanical petal stops used to prevent the lander petals from closing in on and making unwanted contact with the internal structures on the base petal, would also contribute some outward torque and angular acceleration at the moment of petal latch release.
So just to be on the safe side, with the help of Jim Baughman, the lander structural engineer and designer, we made the decision to slightly widen the separation bolt holes so that there will be plenty of time for the bolt to exit the hole before the structure moved to the point of impeding bolt motion (the bolts move out of the holes from the energy of the released tension in the bolt plus the bolt has a spring at the head of the bolt that moves it quite quickly out when the nut splits open).
This delayed the final petal closing a day or two and by last Saturday night we had the petals closed for the last time. Fortunately we still have plenty of time built into our schedule to get all of the work still to go completed before our first launch opportunity on Dec. 2.
This coming week, we will lift and weigh the lander and we will install it in to the backshell by raising it from below. Shortly thereafter we will install the heatshield for the last time. Later in the week we will take this "entry" assembly and place it upside down (heatshield up) onto a spin table in the high bay and we will balance the vehicle (much like an automobile tire) so that there is virtually no wobble when it spins at 2 rpm during Mars entry.