Space The Flight Design Process

When a mission or a Earth orbiting satellite launches, a lot of work have gone behind the scene!

The calculation of the orbit -or orbits- of a craft is a critical part of a space mission. Flight dynamicist engineers, which work in a field called 'Flight Design,' can compute what orbit(s) is needed, with what launch windows and maneuvers to achieve it, and determine the maximum weight of the craft, for a specified launcher, the fuel requirement or the tracking ground stations needed. Launch window is the term used to designate the overall length, which can vary from one second to several hours, when a launch is possible. Preferred launch time is the ideal time of departure. Determination of both is the work, in the USA, of lead flight design engineer at NASA's Launch Services Program (LSP), based at Kennedy Space Center in Florida as it also provides for a start trajectory. Once a rocket is selected for a given mission, the work of hammering out the best launch window and trajectory occurs. Launch windows are intended to absorb small delays while still offering plenty of chances to lift off on a given day. Launching at a time other than the preferred time however can reduce the rocket's performance and potentially limiting the payload mass for cause of fuel use with the more propellant available whatever launch time, the longer maneuvers or adjustments can be made. A initial trajectory depends upon where the craft is bound to, like a Earth-observing mission to reach low-Earth orbit, or a planetary mission to be set on a trajectory so to accurately aim to the Moon, or a moving planet at a long distance it is supposed to reach. A trajectory definition mostly rely upon how far away the target is and how fast it is moving. Of course, weather or technical problems can interfere with operations as a launch team also must comply with space debris collision avoidance, also called COLA. The U.S. Air Force's 45th Space Wing controls the Eastern Range surrounding Cape Canaveral Air Force Station in Florida as the 30th Space Wing, for example, operates the Western Range, including Vandenberg Air Force Base. Both range determine whether any orbiting spacecraft or debris could strike the vehicle during its climb to space, and cut out portions of the launch window that are too risky. During the trajectory design process, the team assumes certain propellant temperatures, but if the temperatures are slightly different on launch day, that will affect the propellant and trajectory. Such a work of determining a launch window and trajectory is tricky further as Earth motion about itself and around the Sun is making the launch pad a moving platform, or with a launcher moving at between 4.3 to 4.9 miles per second (7 to 8 km/s), half a second can result into a big difference. On launch day, the lead flight design engineer and other members of the flight design team are involved in the countdown and continue to fine-tune the trajectory analysis based on real-time data collected from weather balloons for example

A ground tracking station dish at NASA's Kennedy Space Center. picture NASA

Trajectory folks starting about a year before a launch and not winding up until weeks afterward. A team is analyzing the programming that goes into a rocket's flight control computer to make sure the launch will follow its intended course, or trajectory. That means more than simply telling the rocket to start at the launch site and then stop when it reaches orbit. The programming lays out how much thrust the engines will use at different points throughout the climb to space, when the rocket will need to point its nose toward the horizon instead of straight up and when to fire the bolts that separate stages and discard the payload fairing that protects a spacecraft during the early portion of launch. Aligning the launch profile for a spacecraft going into Earth orbit is tricky, but arranging the ascent for a mission to the Moon or one of the planets of the solar system adds more levels of difficulty since the rotation of the Earth has to be matched so that the spacecraft’s trajectory will result in a rendezvous with the distant world. The targets change at least on a daily basis, sometimes on a minute-by-minute basis. During launch, a rocket follows its predicted course and transmits a nearly constant stream of information as the information the rocket sends is generally known as telemetry as it tells how the vehicle is doing, if healthy and the conditions aboard, and generally, whether the launching vehicle is performing and following its trajectory like expected. The numbers sent back from the rocket tell a big picture story of power, speed and altitude, but also include a host of other data. They are often simple yes or no signals to indicate whether bolts fired as planned and can also relay data such as vibration and temperature aboard the launcher. Such data are tracked by ground tracking stations around the world. Strategically placed antennas all over the world are to be chosen as soon as one year before launch. The antennas chosen range from the powerful arrays permanently in place at and around the launch site such as those at Cape Canaveral Air Force Station in Florida, to facilities at bases in the Caribbean Sea, South Atlantic, Africa and Australia. There are more options all over the word including at bases in Hawaii, California, New Mexico, Europe and even Antarctica. For areas in between, NASA can call on mobile antennas mounted in airplanes or on ships and even portable arrays that can be erected by a few people who take them to a mountain or coastline in the flight path and then broken down to a couple suitcase-sized carriers when the launch is complete. The trajectory team has to make sure that as long as one of the engines on the launcher is firing, the rocket is being tracked and relaying data back to the team. Also, antennas have to be in position to pick up the point when the spacecraft separates from the booster and begins its mission. Which antennas get called up can change until the day of launch. NASA's orbiting Tracking and Data Relay Satellite System, called TDRSS -a system of relay satellites in orbit- is also available for some launches to receive telemetry from rockets including United Launch Alliance's Atlas V, Delta II and Delta IV. Other rockets currently rely on ground tracking stations

As far as weather forecast is concerned, NASA meteorologists who are part of Air Force's 45th Weather Squadron, the unit that handles forecasting for rockets launched at the Eastern Range on the Atlantic Coast of the United States, compare forecasting a lot on the launch day. The weather team monitors conditions from the ground level to a few thousand feet in the air, a region the rocket will fly through in a minute or two at most. Weather conditions dictate many of the activities around the launch site, not only the launches themselves. For instance, high winds can prevent crews from hoisting a spacecraft onto the top of a rocket. Thunderstorms can stop all activities on the launch pad. Weather forecasters keep score on how many predictions they get right at the effect of improving. The meteorologists work from a set of rules that everyone must agree are 'go' before a launch is allowed. Each rule covers a specific condition as weather officers do not just make subjective judgments. A lot of technological help comes into to show everything from clouds, rain and humidity levels to wind high above the surface, from weather balloons to Doppler radar and sophisticated computer models. There is one weather criteria the forecasters don't determine: upper-level winds. Instead, the data from the weather balloons and other instruments is sent to launch vehicle engineers who have specific computer models at hand that quickly simulate the launch of a specific rocket through specific conditions. Sometimes, though, forecasters want their own perspective, making their way to the roof of the Morrell Operations Center at Cape Canaveral Air Force Station and seeing most of the sprawling base and the sky and a rule called the 'good sense rule' can be invoked even if all the other rules are not in violation. A weather forecaster can -rarely however- invoke the rule to delay a launch. As far as details about weather balloons are concerned, those help to know how winds are behaving throughout the atmosphere as 'wind shear,' or the wind's change from point to point in altitude, is especially important at high altitudes for the rocket's trajectory. As the launch nears, balloons are released every twenty minutes to make sure conditions are right. Low-res balloons, or synoptic balloons, generally, are released all over the world for weather forecasting, often twice a day and they expand as they travel up through the atmosphere as pressure changes with altitude. High-res balloons are made of plastic and have spikes on the side to increase their stability. To prevent them from expanding as they rise, they have a release valve. They also have shorter strings to make them more stable. Once the balloons filled up with helium, the team fastens a radiosonde (a weather-sensing instrument) and a parachute to help break the radiosonde’s fall when the balloon inevitably bursts. The sonde's transponder sends information back on a certain frequency into a antenna then a computer system. Weather data are also of importance in case of a termination of the flight so the rocket's pieces to land at appropriate places

When a launch went awry after the payload fairing did not separate, for example, failure analysts begin extensive testing to prevent another problem in the future. NASA's Kennedy Space Center in Florida is home to a failure analysis lab system whose ancestral roots extend back to the 1960’s when failures were not uncommon during early days of rocket development, with stakes far greater when a launch failure could ground a fleet for years. Analyses cover a wide range of failures. Failures still may occur during a launch due to that engineers cannot test absolutely every component of a craft and launcher