VEX Science Planning Options

[cndwrld]

Hello-

I wasn't sure how most people would like to see stuff posted. Or if this would interest many people. But in the interests of putting out more information, I created this topic as a place to put information on Venus Express science planning.

If you have any ideas about this, let me know.

Cheers-

Don Merritt

[cndwrld]

Venus Express Status, 25 March - 31 March

At the end of the last CEB pass in the reporting period (DOY 090, 18:00z) Venus Express was orbiting Venus at 183 million km from the Earth. The one-way signal travel time was 610 sec.

Mechanical and electrical systems continue to work without problems. We've got plenty of fuel, more than enough to take us through the recently approved Extended Mission until mid-2009. Batteries are fine.

The testing of operations during quadrature is on-going; the next quadrature phase will start in May 2007.

On 28/03/07, a proficiency test with the DSN Madrid 70-meter antenna (DSS-63) was held. This was in preparation for the five days of operations that will be used to take movies of the south pole region using the VIRTIS imaging spectrometer. VIRTIS movie passes are scheduled for the second week of April.

MTP014 (06 May - 03 June 2007) science pointing and command files have been accepted by the flight control team and flight dynamics team at ESOC, Darmstadt, Germany. MTP015 (04 June - 30 June) pointing files have been accepted; waiting to hear about the instrument command file processing.

MTP016 science planning has begun, with the spacecraft pointing files being worked on this week. This will include use of a recently approved pointing profile called 'pendulum pointing'. With our current thermal constraints, we have to follow pre-approved illumination profiles for each face of the spacecraft, each with a defined cooling period afterwards. If the spacecraft illumination from a desired pointing is not covered by a profile, the pointing is not allowed. If it is allowed, mandatory periods must be afterwards in a cooling attitude. These rules effectively forbid VEX from pointing to nadir when the Sun was directly behind the spacecraft; the +Z face has the instrument apertures, so pointing to nadir in such a situation exposed the -Z face for much longer periods than was allowed. The manufacturer, Astrium, has approved a profile that will allow us to look for about 24 minutes with reasonably high -Z exposure angles, then turn to a cooling attitude for similar periods. We will be able to get images now with the Sun at high angles while we are in the ascending arc of our orbit.

As with any device, whether spacecraft or new car, time is slowly taking its toll on VEX. The occasionaly spurious alarm or anomalous piece of telemetry; occasional minor malfunctions for no clear reason. Cosmic ray events that have to be separated from possible real problems. At this point, nothing unexpected, and enough so that checking it all out keeps the teams busy. In general, the thing is performing like a champ.

The last few months of science operations have included refinement of data modeling. In the fall of 2006, our technical support people put together a very nice system to allow the science operations engineers to see how much science data was returned by each instrument, and compare that with what was predicted. Given the margins that engineers put into everything when doing something for the first time, and the science teams not having lots of time to work on their models due to the rush to get ready for launch and operations, the predicted amounts were probably 25% higher than the actual received data. The good news is that it was too high, not too low, which would have caused us to lose data. But we were, in effect, "losing data" by not taking data for which we had capacity. The science engineers have worked with the instrument teams over the past six months, and the data predictions are becoming much better. This process will continue over the coming months. We are now beginning to review MTP011 results; MTP012 finished this week, and we have begun looking at the first week's results. We'll continue to refine the models to squeeze out every bit we can, to maximize the possible science return.

Cheers-

Don