Monday, August 6, 2012

Artifacts of a Major Event

Somehow I managed to weasel my way out of needing to be physically at work last night for the big Entry, Descent, and Landing (EDL) event of the Curiosity rover on Mars.  I was able to stay home and watch the proceedings with my wife and children, who stayed up WAY past their bedtime to see the festivities.

I don't think any of them truly comprehended just how critical a successful landing was to my career, and so while I was literally twitchy with anticipation and hanging on every word from the NASA feeds, they were nonchalant and overly chatty.  They were so noisy that much of the time I couldn't actually hear what was being said.  I finally had to snap at them towards the end to get them to be quiet.  Seriously, didn't they know that their Daddy REALLY needed to hear Every. Single. Word being said by the commentators and his co-workers?  Because, really, every word was of historic significance and were never to be heard again ... okay, I felt a little bad for snapping at them, but I was seriously stressed out.

In any case, the landing went exceptionally well.  The artifacts we've seen come out attest to that over the past little while, some of which I'll share below.  During EDL itself, the orbiter did experience a plasma blackout.  The recorded UHF spectrum from both of the orbiters we had overhead that were recording the events in an open-loop manner clearly showed the Doppler effects as the spacecraft decelerated from 13,000 mph to 0 mph in just 7 minutes.  I'd include one of the graphics here, but I don't think it's publicly releasable, yet.

During descent, the Mars Reconnaissance Orbiter (MRO), which I worked on for many years, took a picture of the rover as it was hanging from its parachute.  We first did this 4 years ago, when the Phoenix spacecraft had its own EDL.  We had a 50/50 chance of getting that picture, and it was a stunner; and we had a 40/60 chance of getting this one, and it's even more stunning, but in a different way.  For Phoenix, the picture was remarkable for the giant crater visible in the background.  For Curiosity, it's remarkable for the detail that can be seen in the image.

This first picture is the larger image and sets the context:

This next picture shows a zoomed in and slightly more processed view, which clearly illustrates the parachute with its "ring" around the perimeter and the hole in the middle.  Stunning.

We had maneuvered all 3 orbiters, namely NASA's MRO and Odyssey, and ESA's Mars Express; so that all three of them would be geometrically visible to MSL during its descent.  The hope was to record the signal being transmitted from the rover as it made its way to the surface.  We did manage to get all the vehicles in position, with MRO at +9 seconds from its intended overflight time (it was early), Odyssey at -25 seconds, and Mars Express at +41.5.  Considering these are orbital geometries, and we didn't expend a lot of fuel to get any one of them into position, that was pretty darn good.

Odyssey recorded the signal coming out of the rover and demodulated the signal to extract data at 8 kbps.  This was transferred directly to Earth during the EDL event and provided the primary means of information regarding the health and safety of the rover.  It was this signal that told us that the rover was passing through its various configuration changes on the way to the ground, and that it was safely on the ground.  Further, it was this signal that transferred from the rover on the surface the very first images received from the rover, which showed unambiguously that the rover was on Mars.

This first picture was from one of the rear HazCams ("hazard camera") which is used when driving around.  The project decided, somewhat late, to add the taking and transmission of this picture (with a thumbnail) as something to be done right after landing, in the event that Odyssey could transmit the picture.  Here, you can see the pebble-strewn surface behind a dirty lens.  This was the first picture from Mars returned by Curiosity.

 The dirty lens was expected, and so this is actually a picture taken through a faceplate that was later removed.

This next picture came from a front HazCam, and interestingly it shows the shadow of the rover in the afternoon sun.  Despite the dirty lens, it has an oddly beautiful quality to it.

This picture, though, reminded me of something I'd seen before ... hmm, what was that? Oh, yeah! When a Decepticon killed Beagle 2, that's it ...

But back to the first image.  Soon the cover plate, which was expected to get dirty in the mess of landing, was "blown" (explosive bolts are awesome) and the next image came back clear.  Yep, that looks like a barren wasteland.  It must be Mars.  Despite how boring this is to Martian neophytes, this image actually suggests a lot of juicy potential for scientific exploration and discovery. 

This next image was annotated to show some of the hardware in the image.

All the while this was coming down, the people in the control room were going nuts with excitement.  This following picture shows a fellow I know pointing ecstatically.  Ah, happy nerds ...

Come the morning, I showed up at work for an early 7 am meeting.  Everything was going normally.  The recorded signals from MRO and Mars Express had been processed, with beautiful spectrum diagrams clearly showing the recorded signal and the plasma blackout that occurred just after entry, and a remarkable swing in the Doppler as the spacecraft decelerated maniacally.

Later, images were returned from the descent imager, which have not yet been released, yet; which clearly show the heat shield falling away after the parachute was deployed and a long series of images which show the landing all the way to the ground.  I'm confident the images will be assembled into a movie quite shortly.  It is truly something to behold.

So, today's been quite exciting.  I haven't been able to get much done in all the excitement, but I suppose nerds get to enjoy the fruits of their labor every once in a while.  It's been a good day, and the mission hasn't even really started, yet ...

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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