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
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:
http://countdown.ksc.nasa.gov/elv/
Wow,I never knew all that information on what it takes to operate a spacecraft, thanks it is really interesting.