PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 2007-07-27 NOTE = " E-mail and other messages concerning MGS Radio Science on or about 1997/302." END_OBJECT = TEXT END From trish@rodan.jpl.nasa.gov Wed Oct 29 09:43:56 1997 Received: from rodan.Jpl.Nasa.Gov (rodan.jpl.nasa.gov [128.149.43.24]) by magellan.Stanford.EDU (8.8.5/8.8.3) with ESMTP id JAA23759 for ; Wed, 29 Oct 1997 09:43:52 -0800 (PST) Received: from 128.149.43.27 (trish-mac.jpl.nasa.gov [128.149.43.27]) by rodan.Jpl.Nasa.Gov (8.8.5/8.6.6) with SMTP id JAA26961; Wed, 29 Oct 1997 09:42:56 -0800 (PST) Message-Id: <199710291742.JAA26961@rodan.Jpl.Nasa.Gov> Date: 29 Oct 97 09:45:25 -0800 From: Trish Priest Subject: FWD: Back to Aerobraking To: John Armstrong , Sami Asmar , Georges Balmino , Jennifer Caetta , Mick Connally , Paula Eshe , David Hinson , Frank Lemoine , Richard Simpson , Bill Sjogren , Joe Twicken , Richard Woo X-Mailer: QuickMail Pro 1.0.2d1 X-Priority: 3 Reply-To: Trish Priest Content-Type: text/plain; charset="iso-8859-1" Content-Length: 4996 Status: RO ------------------------------------- Date: 10/28/97 6:28 PM From: Glenn Cunningham To the MSOP / MGS project team: With an excellent presentation yesterday of the analysis of the in-flight performance of the -Y solar panel, and additional information from structural analysis of the solar panel's yoke and some ground testing, I believe we have a good enough understanding of our situation to return to aerobraking at a somewhat reduced pressure level on the solar panel. I have decided that we will return to aerobraking on Friday, Nov. 7 (the first anniversary of the MGS launch) with a step down into the atmosphere at apoapsis number 36. This will cause the first drag pass on November 8th. We will move the spacecraft's orbit down to an average dynamic pressure level on the solar panels of 0.2 N/m^2. This is about one third of the pressure level that we were to have experienced during the main phase of aerobraking that we had just gotten into when we pulled out after periapsis 18. The analysis and tests just concluded indicate that a secondary failure occurred when the -Y solar panel deployed undamped after launch as a result of the damper arm breaking off. At that time and throughout cruise, we only observed the result of the damper arm lodging in the panel's hinge point that preventing it from opening all the way. It wasn't until we saw the effects of the pressure of the Martian atmosphere on the panel that the secondary failure, that we recognized that something else was wrong. The additional failure acts like an another flexure point or hinge, that allowed the panel to deflect more than we would have expected during high pressure drag passes. Although we don't know for sure, it is possible that the panel moved to its fully open position and latch during periapsis passes 11 and 12. Now we can go ahead with the mission because we understand why it flexes as it does, and we plan to learn how much it can flex before something catastrophic happens. The hypothesized failure is a crack or deformation on the bottom (opposite side from the solar cells) of the yoke near the metal fitting that connects the yoke to the actuator. The yoke is the triangular shaped structure that connects the solar panel to the to the gimbal actuators. It is made of an aluminum honeycomb with graphite epoxy face sheets (looks a lot like corrugated cardboard material). The face sheet is probably cracked or deformed in an area that was never designed to take the stress that the undamped deployment subjected it to and has become unbonded from the aluminum honeycomb beneath it. This allows it to flex slightly, and thus the panel which is connected to it flexes also when the atmospheric pressure is against it. I believe that this is a safe level for the spacecraft because we experienced three drag passes at this level before we stopped, the panel returns to original position after each pass (the deformation is still elastic), the natural frequency of the panel doesn't change substantially, and its stiffness doesn't change. We will carefully monitor the flexure as we continue aerobraking, and stop again if it exceeds some preset metrics. Even though we are restarting aerobraking, we still don't know exactly what orbit we will finally get to. It is clear that aerobraking is required to maximized the mission return. We really want to achieve global coverage and we really want to be in position over the southern polar area to support radio relay from the New Millennium microprobes and the MSP'98 lander in late 1999. The mission design folks will work with the Project Science Group to establish the target orbit, and then will develop a "playbook" that tells us how to get to that target orbit given the many options we have to get there (easy aerobraking and a long time, heavy aerobraking and a short time, and a mix of aerobraking and the use of the remain propulsion fuel). This is really inside information for today. A formal press release on Thursday will tell the world that we are going back into aerobraking. Then, after we've been back in the atmosphere for a couple of days, we'll have a press conference on Monday, Nov. 10. At that time, the science investigators will also talk about their results from exceptionally good data they have been able to take during the previous aerobraking period and during the hiatus. The development of the new mission may take a couple of months. In addition, we'll have to verify that the spacecraft, which was very carefully optimized for the 2 pm circular mapping orbit, can handle the new orbit. We are probably looking at a longer aerobraking period, and an extension of the mapping mission past January 2000. Things are looking very good so far. There are a few parameters that need to be verified before I give the final go ahead to resume and we'll review them on Nov. 5th. 'Stay tuned, and we'll keep you up to date on the mission design as it progress. --------------------------------------------------------------------- -------------------------------------------------------------------------- From trish@rodan.jpl.nasa.gov Wed Oct 29 14:36:34 1997 Received: from rodan.Jpl.Nasa.Gov (rodan.jpl.nasa.gov [128.149.43.24]) by magellan.Stanford.EDU (8.8.5/8.8.3) with ESMTP id OAA25305 for ; Wed, 29 Oct 1997 14:36:29 -0800 (PST) Received: from 128.149.43.27 (trish-mac.jpl.nasa.gov [128.149.43.27]) by rodan.Jpl.Nasa.Gov (8.8.5/8.6.6) with SMTP id OAA01423; Wed, 29 Oct 1997 14:36:28 -0800 (PST) Message-Id: <199710292236.OAA01423@rodan.Jpl.Nasa.Gov> Date: 29 Oct 97 14:38:57 -0800 From: Trish Priest Subject: Radio Science Reliable Data To: Young Lee CC: Tom Boreham , John McKinney , Richard Simpson , Peter C Theisinger X-Mailer: QuickMail Pro 1.0.2d1 X-Priority: 3 Reply-To: Trish Priest Content-Type: text/plain; charset="iso-8859-1" Content-Length: 1480 Status: R Hello, Young, We have been using the fully-automated Reliable Data system to collect data from four MGS periapsis passes. In almost all cases, no records were missing from the data. In one case, their was a buffer problem just outside the Radio Science equipment at the station, and some data were lost. We have seen this problem before, and it does not involve the reliable data system. On one occasion, the data made it to the TDS from the Radio Science equipment at the station in just over an hour with no missing records. It worked perfectly! On the other occasions, we did not see data on the TDS in a reasonable amount of time, so we re-initiated the FTP from the CDR to "Tom's Machine." (We are able to do this through a Web page, which also allows us to see which data are on the CDR.) As of yesterday afternoon, we have received all the data which we were expecting for the four periapsis passes. On the occassions when the data did not appear on the TDS, it was not clear where the problem actually occurred. We may not have needed to repeat the FTP. It could have been a TDS problem. To summarize, the system is now functioning and fully-automated. There may still be a few bugs, but the data are coming through with no missing records. We will be collecting data for the next six periapsis passes, so we will continue testing the delivery system for another week and a half. Please let me know if you have any questions. -Trish