CHAPTER 14 DAY IN THE LIFE: VITAL VISITING VEHICLES—KEEPING THE REMOTE OUTPOST CREWED AND OPERATING 240 computer simulator, which includes hand controllers to replicate the grappling with the robotics system in preparation for the real operation. The crew members will also review their monitor procedures, criteria to take action, and the actions. The crew and the flight controller teams will conduct a conference led by the flight director about 1 to 2 days prior to the arrival of the vehicle to make sure everyone is ready for the operation. Are we there yet? As noted in Chapter 7, the ISS orbits the Earth at an altitude of about 410 km (255 miles) above the surface. About a dozen vehicles from various countries and organizations visit the ISS every year. When describing the physics that govern their rendezvous with the ISS, two principles should be considered— principles that are too complicated to go into here. First, Newton’s Law of Gravity says that gravity pulls on objects in lower orbits with more strength than it pulls on objects in higher orbits. Second, Kepler’s Laws of Planetary Motion say, in part, that objects traveling in lower orbits go around the Earth faster than objects in higher orbits. In planning orbital rendezvous, both principles need to be considered simultaneously. In short, the process is similar to the case of a police officer who is sitting at the side of the road, looking for speeders. The officer cannot leave his or her observation spot (i.e. “launch”) until the speeding car passes. Once this happens, the officer has to catch up—first accelerating to higher speeds to close the gap and then gradually slowing to match the speed of the car he or she is pursuing. If the officer doesn’t slow down and match the speed of the other car, he or she risks hitting it and causing damage. If the officer lets the car get too far ahead before pursuing, he or she may not have enough fuel to catch the speeder. If a cylinder on the car is misfiring or if the weather is bad, the officer will have to make additional driving adjustments. In the case of the ISS, the visiting spacecraft will launch when the ISS flies overhead. The vehicles are uncrewed and rendezvous with the ISS autonomously with guidance from the control center. During the mission, the Visiting Vehicle Officer monitors the maneuvers or burns of the spacecraft as it climbs to the orbit of the ISS, and then matches the speed for a capture by the robotic arm or gentle docking. The trajectory is updated as things change during rendezvous, which can happen if a thruster does not quite burn as expected or if atmospheric drag is different than expected due to variations in the sun— among a multitude of other reasons. Small burns may be added to the mission to compensate for these issues. To complicate matters, the rendezvous has to be timed precisely so that the sun does not blind cameras or crew members. This process can take as few as 6 to 8 hours but typically takes about 2 to 3 days. When the vehicle is in close proximity of the ISS, even a few meters a way, it is technically in a different orbit and therefore will move slightly differently than will the ISS. At this point, it is a little like keeping a balloon off the floor, Gravity will try to pull the balloon back to the Earth, but small upward taps with the hand will keep it in the air. Newton told us that the Earth will try to pull the visiting vehicle down faster than the ISS however, thrusters are used to tweak the motion to keep it in close proximity. The visiting vehicle officers watch this dance very closely to ensure a successful rendezvous while the flight director ensures the ISS is ready for the new spacecraft. Cargo Delivery and Loading As the flight control teams prepare the mission, the cargo teams finalize the list of cargo to fly on the visiting vehicle. The supplies on the ISS, including spare or replacement parts, are meticulously tracked and resupply schedules are set and reset on a continual basis. Time is also allocated for carefully packing the cargo on the spacecraft. Not only does it have to be meticulously packed to withstand the forces of the launch, but the mass has to be precisely balanced to ensure the vehicle flies correctly. Last-minute issues on board the ISS that require unplanned resupplies or new hardware are balanced against the mission schedule to determine what can be accommodated. Consumables such as food, water, and oxygen have to be very carefully managed. Not only are enough supplies needed,