Monday, August 6, 2012

Until Today, Curiosity Was Just An Academic Exercise

I'm sitting here contemplating how to write about the events of the past day.  It's been pretty big news, and almost none of what's been happening is the result of my own efforts.  Well, that's not entirely true, but I'll get there.  With Curiosity - a.k.a. the Mars Science Laboratory - now securely landed in Gale Crater on Mars, I can now proceed with the rest of my life.

Too dramatic?  Sorry, but let me explain.  My job at work is to coordinate when and how spacecraft that are orbiting the planet Mars transfer data to and from spacecraft on the surface of Mars from and back to Earth.  We use UHF radios to communicate between the various spacecraft, and my job is to help all the good people who independently operate each spacecraft to figure out the details.  To that end, part of my work is in the day-to-day effort to schedule these "relay" sessions between the rovers and orbiters; and the other part of my work is to help the high-level managers for each of these spacecraft to agree on what is allowed to be done.

Sound a little esoteric?  Let me explain some more.  Say, for example, that you have an orbiter that goes around Mars once every two hours.  This is the case for the two NASA orbiters at Mars which both orbit in a north/south direction - a polar orbit - in a manner where when the orbiter passes over the Martian equator, the surface is at a relatively fixed angle to the sun.  This is called a sun-synchronous orbit and has the benefit of allowing the orbiters to image the surface of Mars with consistent sun exposure (i.e. the observed shadows aren't greatly variable).  The scientists love this.

Operators of landers on the surface of Mars also love this because, from the lander's perspective, the orbiter is always visible at roughly the same time every day.  For example, if an orbiter is at a "3 pm orbit", then the orbiter will be coming overhead every day at roughly 3 pm (and 3 am ...).  This makes planning easier because the rover operators then would always know roughly when they can have the rover transmit data to an orbiter.  However, we typically don't get just 1 "pass" at 3 pm - we usually get 2 because, again from the lander's perspective, the orbiter will come from the north (or south) and pass on the east side of the rover and then one orbit later it will pass on the west side as Mars rotates beneath the orbiter.

Sounds great, right?  Well, from a relay planning perspective it is.  Unfortunately, none of the orbiters are built in such a way that they can support both relay activities AND continue with other science activities simultaneously without impact.  This means that every time an orbiter has a relay session with a lander, there is some interruption to or other impact on ongoing science data acquisition.  The scientists hate this.

Therein lies the quandary for the second part of my work.  I have to get orbiter projects to agree to provide relay support to landed projects when it is not in their interests to do so.  As all the projects are independently funded and operated, this can be problematic.  In the case of Curiosity - an exceptionally capable vehicle that can generate far more bits of data than we can possibly return to Earth given the relay spacecraft we have at Mars - this meant we held extensive negotiations with the orbiter projects before they came to agreement on how many of those relay passes that are geometrically viable that the orbiters would support.  As Curiosity is the new kid on the block and all the other projects are in "extended mission" we did have a little weight to throw around, but that didn't mean the orbiters agreed to their needs easily or quietly.

In the end, I and others managed to get these agreements between the projects in order.  The lander is content and the orbiters begrudgingly agreed to the outlined plans.  Once these plans were in place, we had to go through all the exercises to test and verify the inter-project interfaces (both Earth-based networks and the radio-to-radio interfaces that were to be in place once Curiosity landed on Mars) and the operational test and training plans.  This effort has consumed my professional life for the past few years, but all of it - every bit - was purely academic until Curiosity made it to the ground.  Now it is real.  *phew*

So, my job is to help all the landers and all the orbiters at Mars to work together.  Before Curiosity made it safely to the ground, there was only one rover there, Opportunity - an aging rover which has been trundling epically around on Mars since early 2004.  There are 3 orbiters at Mars right now, 2 NASA vehicles and one from the European Space Agency.  The collection of all of these spacecraft at Mars consists what we call the "Mars Relay Network".  Now this network consists of 5 projects, and I have work to do ...

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