Once Endeavour is ready to undock, Lopez-Alegria will send a command to release the docking mechanism. At initial separation of the spacecraft, springs in the docking mechanism will push the shuttle away from the station. Endeavours steering jets will be shut off to avoid any inadvertent firings during this initial separation.
Once Endeavour is about two feet from the station, with the docking devices clear of one another, Lockhart will turn the steering jets back on and fire them to very slowly move away. From the aft flight deck, Lockhart will manually control Endeavour within a tight corridor as she separates from the ISS, essentially the reverse of the task performed by Wetherbee just before Endeavour docked.
Endeavour will continue away to a distance of about 450 feet, where Lockhart will begin a close fly around of the station, much like the one he did on STS-111 in June, circling the complex about one and a quarter times. Lockhart will pass a point directly above the station, then behind, then underneath, then in front and then reach a point directly above the station for a second time. At that point, passing above the orbiting laboratory, Lockhart will fire Endeavours jets for final separation from the station. The fly around should take about an hour and 20 minutes after undocking.
(UPDATE: due to the amount of propellant used for the station orbit raising maneuver during the mission, Endeavour will only make a quarter-lap fly around before making the separation burn.)
Endeavour commander Jim Wetherbee discusses the MEPSI experiment:
Primarily, we will deploy the satellite; investigators on the ground will track the satellite and remotely sense how it is operating up in space. It doesn't have a very long life. This is an experiment in pico satellites -- it refers to, you have regular satellites and then microsatellites, which are smaller, about the size of a breadbox; pico satellites are about the size of a softball. We have two of them that are connected by a 50-foot-long tether, and we will eject it from the payload bay, send it on its way, and it orbits around the Earth several times before its orbit decays and it falls through the atmosphere and burns up. But during its lifetime the ground trackers will monitor its life and see how it's operating. The goal for pico satellites in the future is to have them operating and be able to be attached to a regular satellite, and then if there are problems with the satellite this little pico satellite can remotely fly around the vehicle, take camera views, and you can also envision someday in the distant future maybe a smaller satellite being able to autonomously repair a satellite or remotely repair a satellite and so it's a pretty exciting time. As the technology with computers and things down here on the Earth gets smaller and smaller, satellites are getting smaller, too. And so we will test this ability, see how the satellite operates under the harsh environments of radiation and being up in outer space.
Endeavour pilot Paul Lockhart discusses the MEPSI experiment:
Well, this is an attempt with the Air Force Research Laboratory, to try and develop the capabilities of pico satellites, or micro-satellites, to perform basically an inspection task in space. So, what the Air Force Research Lab is looking to do is develop the capability to have little micro-satellites that can be flown attached to larger satellites or, I suspect, can be brought up on other types of vehicles later and can be deployed to actually come out and around a critical piece of equipment -- i.e., a satellite or something else that's in orbit that is of concern-and actually have these pico satellites or micro-satellites fly out and then perform an inspection task; in other words, take sensor data and determine the health or the status of that critical item, whether it be a satellite or whatever. So for us, we're going to actually show that this little system of two pico satellites, or micro-satellites, can be deployed properly and that they will function together as one. They're tied together with a cord, and so they're interested in the capabilities of the thing being deployed properly, that the physics of it being in orbit doesn't cause the two micro-satellites to behave improperly, and then just to show in a gradual increase of capability, that these little micro-satellites can be functioning properly. So, on our flight I basically get to deploy one of these, and then we're just going to film them as they move on up, and then they're going to be transmitting the data back down to the ground.
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