Note: I am posting my old blog entries from elsewhere on the internet. This entry was originally posted on 1/28/09
I haven’t blogged about my work for a while, and I’d like to do so. I recently sat down with my husband and tried to explain what I do for a living now. It took about an hour, and a page of little diagrams and notes. Here I’ll attempt to do the same with words…this is very long, and therefore behind a cut. I hope it is comprehensible!
For 80% of my time, according to my timecard anyway, I work on Cassini. (The rest is continuing my Mars research.) Within that work, I essentially have two jobs, one of which has two phases – so I ultimately have three hats: I’m a science planning engineer, I’m a co-lead for the planning team concerned with flybys of icy satellites, and I’m the assistant investigation scientist for one of the instruments.
Taking the last one first – Cassini is organized differently than Phoenix, in part because it is a much larger, more complex mission. Each of the twelve instruments onboard has its own science team, made up of scientists doing research on many different aspects of the Saturnian system – Saturn’s atmosphere, the rings, the magnetic and small particles environment, and the major moons. Any one scientist doesn’t study everything; the teams bring together geologists, astrophysicists, atmospheric scientists, ring dynamicists, and more. Each instrument team is headed up by a Principal Investigator, who is responsible to the Project Science office for that instrument from development through operations and publications of the resulting research. However, the instrument teams (including the PIs) are scattered around the world, so it is helpful to have someone physically at JPL to be a liason, to attend meetings and answer questions and generally keep the communication lines open. That person is the Investigation Scientist (also called the Instrument Scientist on some some missions). I am assisting the IS on the UVIS (ultraviolet imaging spectrograph) instrument, so that when she eventually moves on to the next outer planets mission I will be ready to step into her shoes.
As a science planning engineer, I am concerned with getting from having Cassini’s trajectory information from the navigation team to uploading a sequence of commands telling the spacecraft where to point the instruments and telling the instruments when to take data. Each planned orbit around Saturn is broken into chunks, or segments, and each segment is assigned to a planning theme group. These theme groups are divided by topic – Saturn, Rings, Magnetosphere, Titan, and Icy Satellites. The groups are made up of reps from each instrument team, plus a few science planning engineers to help out and a couple scientists to serve as Co-Chairs. So, if a chunk of time has a flyby of Titan, that segment goes to the Titan group; if there’s great viewing geometry of the rings, it goes to the Rings group. Of course, sometimes you have a flyby of Enceladus at the same time as good rings geometries, and then the groups have to duke it out over who needs the time more.
Once the segments are assigned, the groups go in and assign time to individual instruments. The instruments are all fixed on the spacecraft (the scan platform that would allow them to move independently was scratched during spacecraft design for budgetary reasons) and each point in a slightly different direction. They take turns controlling the orientation of the spacecraft to optimize their observations, although other instruments can be on at the same time. So now the instrument teams fight over time within the groups, sometimes down to seconds. As a member of the icy satellites planning group, I help to herd the segment through this process, and make sure that we’re fitting within data volume and power constraints. A delivered segment contains primary instrument and pointing directions for each moment within the segment, and represents an agreement between the instrument teams.
Many segments are then put together to make a sequence. A sequence represents 10 weeks of activities on the spacecraft, and takes about 25 weeks to get through this final process. We go from a series of agreements to the full line-by-line commands that gets uplinked to the spacecraft. Science planning engineers serve as the ringleaders to get the instruments through this process. We manage many of the spacecraft resources – time, data volume, data rate, power, and pointing – within the constraints set by the spacecraft office, who are the engineers concerned with the health and safety of Cassini (they worry about trajectory maneuvers, thruster and reaction wheel behavior, and things like that). We also work out how we downlink all the data (negotiating for time on the DSN stations). As changes are made, our job is to fight to minimize the impact on the science plan, and to try to spread the pain out equally among all the instrument teams.
Once a sequence is onboard, there’s other things we do, but I haven’t gotten that far yet with the sequence I’m training on.
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