LCROSS Flight Team Breakdown

Posted on by .

OK, so my last post contrasted flying LCROSS from flying an airplane, in touchy-feely terms, but now it’s time for some detail.  This post provides describes the makeup and specific responsibilities of the Flight Team.


The Flight Team is officially known as the LCROSS Mission Operations System, or MOS.  The MOS is divided into “subsystems” or specialty areas that work on different aspects of the mission.  Space missions are really complicated, no matter how simple the spacecraft is.  Perhaps it’ll be easiest for me to describe all of the MOS subsystems as a way of relating all the things the Flight Team needs to think about and do.  Here they are:


Mission & Maneuver Design Subsystem (MMDS): Spacecraft fly on orbits (or “trajectories”) around massive bodies like the Earth and moon.  The MMDS plans how to get from the orbit LCROSS is left in after launch to an orbit that will impact the moon at a very specific point at a specific time.  LCROSS can change its orbit either by firing thrusters (Trajectory Correction Maneuvers, TCM’s), or by using the moon for a gravitational assist.  The MMDS plans a series of “maneuvers” to use as little propellant as possible, and yet to satisfy the requirements of impact (accuracy, impact angle, velocity, sun exposure, Earth visibility, etc).  Our MMDS team is headed by NASA Ames, but also has team members from Goddard Spaceflight Center (GSFC) in Greenbelt, MD.


Navigation Subsystem (Nav):  The Navigation team determines where LCROSS is at any time, and predicts where it will go under the influence of gravitational forces, solar pressure, and thruster firings.  TCM’s are designed to target specific trajectories, but firing thrusters is never perfectly accurate, so we’re never precisely on the orbit we intended to follow.  Even if we were, external forces like solar radiation pressure would push us off of it over time.  To keep track of where the spacecraft actually is, the Deep Space Network (see CLASS below) tracks the distance and relative speed between ground antennas and the spacecraft, over time.  This information can be used to determine the orbit we’re following.  Our Nav team works out of the Jet Propulsion Laboratory (JPL) in Pasadena, CA.


Communications Link Analysis & Scheduling Subsystem (CLASS): LCROSS communicates using radio frequency (RF) signals, between antennas on the spacecraft and large dish antennas on Earth.  As it turns out, we can’t communicate with LCROSS any old time.  The Deep Space Network (DSN), operated by NASA, provides three major antenna sites around the globe (Goldstone, CA, Madrid, Spain, and Canberra, Australia) to provide communications access to spacecraft.  LCROSS shares the DSN with lot of other space missions, so we have to negotiate our contact times out of a very busy schedule.  CLASS has to consider when LCROSS will be geometrically visible (or “in-view”, above the local horizon) from each of the ground sites, considering its orbit and the rotation of the Earth.  For in-view periods, CLASS determines whether there is sufficient “link margin” to enable the spacecraft to communicate to Earth, and vice-versa.  This is based on distance, spacecraft orientation, and the physical characteristics of the transmitting and receiving antennas and electronics.  CLASS has members from NASA Ames, as well as schedulers from JPL.


Activity Planning & Sequencing Subsystem (APSS):  To perform a complicated set of operations, individual commands have to be composed into coherent command sequences.  For each communications opportunity, the APSS creates an “activity plan” that includes the list of activities to be performed on the spacecraft (e.g. reorient the spacecraft, perform a TCM, dump data from virtual recorders, etc), the timing and order of the activities, and parameters they need to be fully specified.  APSS then compiles a combination of ground-based commands and onboard command sequences to perform the activities.  Our APSS team is based exclusively at NASA Ames.


Engineering Analysis & Support Subsystem (EASS): If you’re going to fly a spacecraft, you better have a team that knows how it operates, inside and out.  For LCROSS, that’s the EASS.  EASS monitors spacecraft telemetry to determine whether it is healthy and operating as expected, and requests activities to be performed to maintain health (e.g. adjust power subsystem settings, calibrate the onboard clock).  They need to be able to detect subtle hints that might suggest a problem on the spacecraft, and need to know how to fix a variety of problems using available commands.  EASS also performs quality assurance for APSS, to make sure the command sequences follow spacecraft “flight rules” to keep the spacecraft safe.  Our EASS team includes both LCROSS lead systems engineers from NASA Ames, as well as a deep team of systems and subsystems engineers (many of whom designed the hardware and software) from Northrop Grumman, the company that built most of LCROSS.


Simulation & Testbeds Subsystem (Sim): A key tool for the Flight Team is the LCROSS spacecraft simulator.  It’s a close copy of the LCROSS avionics (flight computer) and flight software, combined with a dynamic simulator that replicates the flight dynamics of the spacecraft (orbital mechanics, attitude dynamics) as well as many of the other spacecraft subsystems (power and thermal control, propulsion, communications, etc).  In many respects, the simulator behaves just like LCROSS, so we use it to test command sequences from APSS before using them in real life.  The Simulator Engineer runs the simulator and works with EASS and APSS to provide feedback on command products.  Sim is run out of NASA Ames.


Payload & Science: The Payload Engineers are to our science instruments what EASS is to the rest of the spacecraft.  They have a deep knowledge of the science payload, having developed and integrated those systems at NASA Ames during the spacecraft development phase.  The science team is headed by the LCROSS Principal Investigator.  During science activities like instrument calibrations and the sampling sequence after Centaur impact, the science team performs real-time analysis of data coming from the instruments to detect possible faulty instrument conditions.  In that unlikely event, the Science team can request instrument or Data Handling Unit power-cycles to attempt to correct the problems.  The Science Team also coordinates the ground-based observation effort, conducted from several major observatories, in real-time based upon the observed location of the Centaur impact.  And of course the Science Team carries the ultimate responsibility for science data interpretation – to determine whether LCROSS actually found water.


Data Acquisition & Commanding Subsystem (DACS): The DACS is the heart of commanding and telemetry operations from the ground.  It includes the people that send commands to the spacecraft (“Flight Controllers”), the Flight Directors, and Data Management Engineers who help collect telemetry for plotting and analysis by EASS.  The Ground Data System includes DACS hardware and software that decodes telemetry received from the spacecraft and displays it on virtual instrument displays, and encodes commands to be sent to the spacecraft via the Deep Space Network.  Our DACS team resides at NASA Ames.


Data Management & Archival Subsystem (DMAS): The DMAS preserves the data generated by the mission, to make sure we don’t lose any of it.  The DMAS performs backups of all operational computers used by the Flight Team, and stores it locally and off-site to ensure we can suffer a major system fault and still carry on.  The DMAS is also run out of NASA Ames.


Management: The MOS is headed up by the Mission Operations Manager (MOM), who ultimately ensures that the rest of Flight Team is always working in the best interests of mission objectives (defined formally in project requirements) and spacecraft safety.  The MOM stays largely hands-off for nominal operations, but steps in to help the Flight Directors if the team encounters anomalous conditions and departs significantly from the planned operations path.  He also acts as the liaison between the Flight Team and project management and mission stakeholders at the program level (Lunar Precursor Robotic Program – LPRP, run under the NASA Exploration Systems Mission Directorate or ESMD), and at NASA Headquarters. 

Flying LCROSS vs. Flying a Plane

Posted on by .

First, my apologies for not writing since my last post a week ago – things have been really busy as we prepare for our First Week Rehearsal this coming week (more on that in future posts).  So, I’m posting two entries in a row to catch up.  There’s so much to write about – I’ll get started!


LCROSS will be “flown” out of NASA Ames Research Center (Ames or ARC for short), at Moffett Field, CA, about 40 minutes South of San Francisco, and 20 minutes North of San Jose.  Ames is perhaps best known for its impressive collection of wind tunnels for aerodynamics research, its supercomputing facilities, information technology and artificial intelligence research, thermal protection systems, human factors, and astrobiology.  Though Ames has operated spacecraft and space-based experiments in the past, including Lunar Prospector and Space Shuttle life sciences payloads, it is now strengthening its mission operations base with missions like Kepler, for which Ames operates the Science Operations Center, and LCROSS, whose spacecraft and science operations are focused at Ames.  The LCROSS Flight Team will “fly” LCROSS starting just 3 hours or so after launch, all the way through lunar impact in October. 


What is it like to “fly” a spacecraft?  Is it anything like flying an airplane?  For LCROSS, truthfully, no.  A single pilot can fly a plane.  A spacecraft typically takes a team of people – there’s just too much to think about for one person.  How do we control LCROSS?  Our control center has no joystick, no rudder pedals, no throttle, and, except on special occasions when the science cameras are active, not even a good view of space!  Instead of instrument gauges and windows to look out of, our team has to rely on “telemetry”, time-tagged information on every aspect of the spacecraft (temperatures, currents, orientation, propellant tank pressures, valve states, etc).  Instead of a stick, rudder, throttle, buttons and knobs, the flight team has to send “commands” to LCROSS – strings of data that tell the spacecraft to do something.  The spacecraft offers an interface of a hundred or so possible commands, with parameters and syntax, just like the user interface to a software application.  Individual commands usually perform simple tasks, for example “open a thruster valve”.  Sequences of commands can perform quite complex activities.  Think of LCROSS as a teleoperated robot, with the Flight Team providing the intelligence it needs to perform its mission.


Another important aspect of flying a spacecraft that sets it apart from piloting an aircraft is reaction time.  Controlling a spacecraft is much slower-paced than flying a plane.  Even at lunar distance, commands take a few seconds or more to reach the spacecraft from our control center, even at light speed.  Even though the spacecraft is moving much faster than an airplane, the distances are much more vast, and so we generally don’t need to rush.  Rushing is risky – things can go wrong quickly if we’re not careful, and our team might miss something important.  We’re not typically in much of a hurry anyway, so slow and safe is a good place to be.


And yet, flying LCROSS is a lot faster-paced and interactive than flying a spacecraft orbiting Mars or another body at similar distance.  Operators of spacecraft orbiting Mars and beyond must wait for tens of minutes or even hours to get any feedback from commands they send.  The only practical way to operate those spacecraft is to upload fully pre-planned command sequences or plans, and then to examine telemetry hours later to determine what actually happened.  With LCROSS, given its relative proximity to Earth, our Flight Team gets feedback from commands seconds after they execute, meaning we can adjust our actions in near real-time based on their success or failure.  So in this sense, operating LCROSS is more like real flying than for other missions.


Before pilots fly a plane, they file a flight plan that documents the basic details of the journey.  Space mission operations takes that idea to the extreme.  We’ve been planning LCROSS’s flight plan for years now, down to the last detail.  We don’t leave anything to chance if we can help it.  Before we launch, we’ll have a pretty good idea what we’ll be doing for most days of our 120 day mission.  The more our team prepares now, the better off we’ll be if something goes wrong. 


In the next post, I’ll describe the Flight Team in detail.  Stay tuned…


Meanwhile, LCROSS and LRO sit in the payload fairing, on a flatbed truck at Astrotech, waiting for a window in the weather to be driven to the VIF and integrated with the Centaur at Kennedy Space Center.  Check out this link for live views, as well as the countdown clock for the LCROSS First Week Rehearsal simulated launch:



Our last view of LCROSS

Posted on by .

This past week, LCROSS and LRO were finally mated together, LCROSS on the bottom, and LRO on top, as I described on my 5/13 post.  On Friday, both spacecraft were encapsulated inside the Atlas V payload fairing, the sleek nosecone of the launch vehicle.  Now that they are inside, they will remain in this cocoon until they are released into space after launch.  Seeing this in photos brought a strange sense of finality to the whole development.  Years of effort, and now the team is done designing, done building, and nearly done testing.  It really comes down to the launch team and the operations team now.  Launch is one month away!

Here’s a photo of LCROSS and LRO, united at last after years of independent development in different facilities – LRO at Goddard Spaceflight Center, Greenbelt, MD, and LCROSS at Northrop Grumman in Lanham, MD and Redondo Beach, CA. 

Photo courtesy of NASA Kennedy Space Center

LRO is the silver-colored spacecraft, LCROSS the gold-colored spacecraft.  Having never seen LRO, members of our flight team were stricken by how different the two spacecraft look.  Both are covered in Multi-Layer Insulation (MLI for short) that protects the spacecraft from the harsh thermal environment of space.  But the kinds of materials each spacecraft uses in their MLI are tailored to their respective missions – their orbits, how long they expect to dwell in the shadow of the moon, which sides of the spacecraft will face the sun, the sensitivity of some spacecraft elements to heat and cold, and the amount of heat specific electronics units produce.

So what’s the big deal about mating the two spacecraft together?  You might think that connecting two spacecraft together would simply mean bolting them, but in reality, the interfaces between LCROSS and LRO, and between LCROSS and the Centaur, are pretty intricate.

Most importantly, the mechanical interface between each vehicle has to be entirely reliable during launch so as not to damage either spacecraft or to amplify vibrations that might endanger the stability of the launch vehicle.  For LCROSS, since we carry the Centaur with us for most of our mission, this connection persists for months beyond liftoff, all the way to 10 hours before lunar impact. 

However, each spacecraft must also be able to reliably separate from the rest of the stack.  This is a tricky operation.  On command, the mechanism holding the spacecraft must transform from an ultra-solid connection, to one that releases and pushes the two pieces from each other using strong springs.  The release must avoid snags, and must provide a good push off – just the right amount of speed, as little rotation as possible, and without re-contact!

Aside from the mechanical aspects, there are a number of electrical connections bridging the interfaces.  On the pad, the Centaur acts as a conduit for telemetry data from both spacecraft on the launch pad so that both the LRO and LCROSS teams can monitor spacecraft health immediately prior to launch.  Just after the stack leaves Earth orbit, the Centaur also sends the signal to activate the separation mechanism between LRO and LCROSS.  That means data cabling has to somehow get from LRO to the Centaur, with LCROSS in between.  LRO’s data lines cross the LRO-LCROSS boundary, run down the side of LCROSS, and across the LCROSS-Centaur boundary.  In the meantime, LCROSS launches powered off.  Some time after LRO separates, the Centaur also sends signals commanding LCROSS to wake up, and other signals to notify LCROSS it is time to take control of the Centaur.  All of these electrical connections cross the separation planes between the vehicles.  The connectors must reliably transmit data after the rough ride to orbit, but then disconnect when they’re supposed to at separation.

Here’s a parting shot of LCROSS.  If all goes well, we’ll not see it again.  During the mission, we can only imagine how it appears on its way to the moon.  In October, that spacecraft will have its final, brief hurrah in just 4 minutes of data transfer back to Earth, observing the Centaur impact.  At the end of that 4 minutes, it too will impact, and will become part of the moon.

Photo courtesy of NASA Kennedy Space Center


Posted on by .

A couple of readers brought an error to my attention regarding the type of engines used on the Atlas V.  The engines are RD-180’s, not RL-10’s as I had originally posted.  Thank you for pointing out the error!  I’ve corrected the original post.

For those interested in a little more detail on the Atlas V 400 series:

I’m really happy to see people are paying close attention.  Please keep the comments coming!  I’m getting the hang of running the blog software, and I believe now that the blog comments should be viewable publically.


What is a Flight Director?

Posted on by .

So I described in my post from 5/8/2009 that I am the Flight Team Lead and one of the Flight Directors.  What does that mean?  Let me take a shot.


As Flight Team Lead, I’m the guy in charge of defining the “concept of operations” for LCROSS: how the LCROSS spacecraft is operated during flight, from launch through impact on the moon.  I’m also responsible for preparing the mission operations team for the mission.  I write flight procedures and flight rules (rules that protect against overstepping the capability of the spacecraft and other systems during flight), and help to plan all kinds of exercises and tests that simulate actual flight scenarios so that when we launch, the team will be totally ready.


My other role as one of two Flight Directors takes effect each time our team holds a team-wide mission test or rehearsal, and will pick up for real on launch day.  The Flight Directors are the tactical leaders of the flight team during the mission.  We’ll direct our team in planning for different events and commanding the spacecraft to do various things to accomplish its mission.  If things go wrong, we are the ones who will organize the team to correct problems, or even to try and save the mission, if need be. 


Perhaps the most famous of all Flight Directors is Gene Kranz, of Apollo program fame.  His leadership of the Mission Control Center in Houston was instrumental to the success of Mercury, Gemini and Apollo, most famously in the triumphant safe return of the Apollo 13 astronauts following the equipment failure aboard their Command and Service Module.  Apollo was far grander a mission that LCROSS, but the concept of Flight Director was conceived in those early days of spaceflight, and continues now.


Perhaps most importantly, Flight Directors have to keep the “big picture” view of the mission – we need to keep in mind how everything works together, and what constraints apply at various times to keep the spacecraft safe.  If something malfunctions, we need to know how it might affect mission success, and know what to work on first to keep things running as smoothly as possible.  Think of us as conductors in an orchestra.  There are a lot of good “musicians” on our team, by analogy some playing horns, strings, woodwinds or percussion.  The Flight Director, as a conductor, has to make sure the team is “playing” together, at the right tempo, to create the “music” that gets LCROSS to impact the moon at the right spot.


I couldn’t possibly do the jobs of Flight Team Lead or Flight Director all by myself.  I work as part of a much bigger team – others developed and tested the spacecraft, conceived of the science and designed the instruments that will look for water, and managed the project budget, schedule and risk.  The Mission Operations team has the honor of flying the spacecraft that so many people have worked on.  Each team member has put in enormous numbers of hours to plan for every aspect of the flight to make it a success.   Working with them on such a fun project makes this one of the best jobs I can imagine.  I hope to introduce you to some of those other people in upcoming installments.


News from Recent Mission Operations Events:


DSN Mission Events Readiness Review (5/5): The folks at Deep Space Network did a very professional job, as always, in planning and presenting their plan of support for both LCROSS and LRO.


Launch Countdown Rehearsal (5/6):  A portion of our team spent the better part of last Wednesday rehearsing our pre-launch and early post-launch procedures, following the countdown timing as it will be for launch.  This is more complicated that it might sound.  Prior to launch, we have to determine whether all the systems – LCROSS, LRO, the launch vehicle, the ground antennas, and the people are all ready for launch.  Each system representative has to give their “GO” or “NO-GO” status, just like in the movies.  We communicated over our “voice loops”, with people and Kennedy Space Center (our launch site) relaying simulated data to us before and after the simulated liftoff.  We carried on for five hours after the launch time, past when our spacecraft would be on its way to the moon. 


Even though this was all make-believe, the simulation was realistic enough to send chills down our spines.  It was very easy to imagine how we’ll feel on the big day!


Upcoming Mission Operations Events:


First Week Rehearsal (5/27 through 6/1): Our team will rehearse the entire first week of operations, beginning with launch.  We’ve been rehearsing various mission phases for the past year, but none of these tests have been more than 2-3 days long.  For this test, just as during the mission, we’ll be operating around the clock, with all the events occurring at precisely the same times of day as they will in flight.  This is a test of nearly everything we’ve developed, and of our team’s ability to endure a week of long, possibly stressful days.


Posted on by .

Welcome everyone to the first installment of the LCROSS Flight Blog!  LCROSS stands for Lunar Crater and Observation and Sensing Satellite.  It is one of two spacecraft launching to the moon in June of 2009, as part of a coordinated effort to explore the moon in unprecedented detail, in preparation for human missions in the not-so-distant future.  If you’re not familiar with the mission concept, I’d suggest you start with our project website:


What you may not know is that LCROSS does not fly all by itself.  During our mission, a team, called the Mission Operations Team (or Flight Team for short), will remotely operate the spacecraft from NASA Ames Research Center in the Bay Area in California, as well as from other operations facilities around the country and around the world.  

My name is Paul Tompkins, and I’m the Flight Team Leader and one of the Flight Directors for the LCROSS mission.  In this blog, I’ll do my best to describe what it’s like to be a part of this team.  I’ll be posting as often as possible as the LCROSS launch date approaches, and during the mission to provide play-by-play updates of the mission.  Above all, I hope I can convey the excitement all of us on the team are all feeling, and to get you excited about the moon!

So, what does the Flight Team do?  Well, most spacecraft can’t do a whole lot without human input.  LCROSS is a simple robotic spacecraft – there’s no one on board, it can’t do too much thinking on its own, and so we control it from the ground.  After launch, the Flight Team gets to “take the keys” to “fly” the spacecraft to complete its mission. 

The specifics aren’t quite so romantic, but are still pretty interesting (hopefully you’ll agree!).   The Flight Team has a “mission plan” that describes what activities need to happen at different times in the mission, so that we can accurately target our impact location on the moon, and be ready to observe the impact to find water.  In broad terms, the main activities are:

  1.  “Trajectory Correction Maneuvers” or TCM’s for short.  Basically making changes to the orbit to precisely target the impact site.
  2. Science Payload Calibrations: The set of instruments LCROSS has onboard to detect water, along with a special computer that is dedicated to instrument control, is collectively known as the “Payload”.  All high-precision instruments need to be calibrated so that a scientist knows how a particular measurement relates to known, physical quantities.  By the time of impact, our instruments need to be well calibrated.
  3. Other Supporting Engineering Activities: There are a lot of other things we command the spacecraft to do to support the other activities.  Things like changing the orientation of the spacecraft to point instruments or antennas in a specific direction, calibrating our onboard clock, changing the rate at which we return data to Earth, etc. 

The Flight Team gets information from the spacecraft, called telemetry, that tells us whether the spacecraft is healthy or not – things like temperatures at different locations, the pressure in the propellant tank, the battery voltage, electrical currents flowing to each unit in the system. 

According to the mission plan and based on what we read in telemetry, we design specific sequences of commands to perform the activities listed earlier.  Then we actually sit in a control room and send the commands to the spacecraft, and monitor how it behaves.  If it does what we expect, then everything is OK.  If it malfunctions, then our team can detect that and make corrections, and keep the spacecraft safe.    Think of the movie “Apollo 13”.  Except MUCH smaller scale, with no astronauts onboard the spacecraft, no pocket protectors, cigars or jazzy vests.  Our team is pretty small, and doesn’t have quite the responsibility of a team overseeing human spaceflight operations.  Still, lots of responsibility!

Well, that’s it for today.  Thanks for reading, and I’ll post again soon!

Page 3 of 3123