Occaisionally, the ham operators on board would squeeze in a few minutes of hamming in between tasks during their work day. On some missions, the pre and post sleep times never occured when the Shuttle was visible over the United States, leading to the development of the telebridge system. With the telebridge system, students could still talk to the crew during the pre and post sleep periods by using a ham station located where the shuttle would be visible during those times.
As SAREX moved into Phase II, NASA flight planners began to consider school contacts as secondary mission objectives and started scheduling contacts as part of the normal workday timeline. These contacts remained secondary objectives, meaning that if the crew time was needed to accomplish a primary payload objective, the SAREX contact event would be cancelled and rescheduled. However, even after the contact with a school has been officially scheduled in the mission timeline, and a date and time established, this will often change, and sometimes signficantly with little notice.
It is not unusual for a contact to be moved forward in the timeline, that is, moved from a later date to an earlier one, sometimes as late as only 24-hours before the new scheduled contact time. Launch delays, unexpected events once the mission begins, considerations of the primary payload, and other factors can all combine to affect your scheduled contact time. It is therefore important to have an understanding of the NASA flight planning process, as well as launch delays and their reasons.
Every minute spent on-orbit is a precious resource, and many of the experiments have complex operating procedures, the mission "timeline" of events is planned far in advance of the launch. By using Mission Elapsed Time (MET) for timeline, changes resulting from the exact time of launch are kept to a minimum. Mission Elapsed Time is the time from liftoff. MET 00/00:00 (0 Days, 0 Hours, 0 Minutes) is the moment that the Solid Rocket Boosters ignite and the shuttle lifts off.
There are three categories of mission events:
Pre-mission planning is done based on a launch at the very beginning of the launch window. If launch actually occurs sometime later in the launch window, the timeline may need to be adjusted. A team of engineers in the Payload Operations Control Center update the timeline in 12-hour segments, which are then "uplinked" to the crew onboard.
Surprisingly, the Tracking Data Relay Satellites (TDRSs) are "earth-fixed" because they revolve around the earth once a day; i.e., they are geostationary. Since each TDRS satellite is earth-fixed, the Shuttle's antenna will be in line-of-sight for communication at the same time after launch, independent of any launch delays.
As an illustration: your house and your mailbox are both earth-fixed. If you walk out to get the mail, and you always walk about the same speed, it will take the same length of time to arrive, no matter what time you leave the house. SAREX contacts are earth-fixed events. They take place with respect to a fixed point on earth - your QTH (location)!
They often are dependent on other conditions, though. For example, you cannot schedule the Pilot to take pictures on the mid-deck before you schedule taking the camera out of its stowage locker and attaching the proper lens.
Because of the earth's rotation once every 24 hours and its yearly trek around the sun, the positions of the sun, moon, and stars overhead continuously change. Any event during a mission that is affected by those positions is "ephemeris dependent" and must be replanned if the Shuttle doesn't launch at the beginning of the launch window.
For example, the sun's position in the sky changes 360 degrees (the number of degrees in a circle) in 24 hours, or 15 degrees each hour. If we launch one hour into the window, the sun will have "moved" 15 degrees. The Shuttle circles the earth in 90 minutes, or 4 degrees every minute. So, if the goal of an on-board experiment is to observe sunrises, launching an hour late means each sunrise will occur almost 4 minutes earlier. Since each sunrise on-orbit lasts less than a minute, it's easy to see that we have to replan the observation or it will be missed.
As soon as the exact launch time is determined, computer programs are run that produce a new ephemeris for all important objects. A microgravity mission, conducted inside the Spacelab laboratory module, may not be concerned about the position of celestial objects. But, an astronomy mission pointing telescopes at stars with arc-second accuracy has to have the best, up-to-date ephemeris data possible. If the primary payload is scheduled on an Epheneris-Dependent Timeline, SAREX contact times could be very significantly altered, and in a way not predictable beforehand, should the launch get delayed from the target date/time for any reason.
After SAREX has been manifested on a Shuttle flight, selection of the schools is done. The proposals submitted to the ARRL and AMSAT are evaluated and from five to twenty groups are selected, depending on the duration of the flight and the workload of the astronauts. The selection process begins with a preliminary pool of international school groups, other stations of interest selected by crew requests, unique experiments which require crew and ground interaction (such as the onboard ATV reception capability still under development), and the school group proposals. The crew ultimately determines the number of contacts they wish to support during the flight.
The shuttle ground tracks are then plotted, and the rise and set times for each station is computed. The best orbits for each ground station are identified, and any constraints placed on the times by the groups are factored in (such as "only on a school day between 9 AM and 3 PM local time) and become known as "orbits of opportunity". These are the orbits that will best accommodate the groups. Each orbit that the Shuttle will make during its mission is assigned a number, starting with 0. Orbit 0 (also called "rev" which is short for "revolution") begins with lift-off and goes until the orbiter crosses the equator going from south to north. For more information on how the orbits are numbered, see the section on Orbital Mechanics. Other criteria that are used to select these orbits of opportunity are a minimum elevation constraint which specifies that the shuttle rise at least 30 degrees above the horizon for a ground station location for a period of at least two minutes, and the times when everyone would be awake, including the ham onboard the Shuttle. The list of orbits of opportunity (identified by the orbit number) are then taken to the Shuttle Flight Planning Team at the Johnson Space Center, in Houston, TX, for review and incorporation into the formal shuttle flight plan. Numerous factors are again considered, including the primary activities for the licensed crew member, orientation of the orbiter with respect to the earth, and other onboard mission factors. The reason that the Shuttle is flying the mission is to support the "primary payload". This may be to deploy or retrieve a satellite, perform experiments in the cargo bay, make astronomical observations, or repair a satellite. The primary payload takes precedence over SAREX activities, as SAREX is designated as a "secondary payload".
Following scheduling with the Flight Planning Team, the list of orbits of opportunity is pared down so that each site has a designated primary pass. A single backup pass for all school groups is usually also identified in case of trouble with one of the schools on a primary pass. The primary pass is your "Main Event". The time of the primary pass is the time you will attempt contact with the Shuttle.
Your pass times will attempt to accommodate your schedule constraints as much as possible, and time of day will be considered. However, the day of the contact itself will not be, nor will season of the year. In other words, if your contact is scheduled for a weekend or a holiday, or during school vacation time, then your group must work with that. The contact schedule is set by NASA and requests from groups to change will not be honored. Shuttle launches are often dictated by natural events and rarely take holidays and other man-made schedules into consideration! If you cannot use the scheduled pass, then it will be given to another group. Passes have occurred on Easter Sunday, during Christmas and spring breaks, in the evenings and early mornings, as well as over summer vacations. As a rule, even if the schedule is inconvenient, you will find that many will come to the event anyway, simply because of the rare and unique opportunity it presents.
Once the primary pass has been identified for your group, you are assigned to a specific orbit over your location. The exact date and time that this orbit will occur depends on numerous factors, the most important of which is the actual time of the launch. Once the solid rocket boosters (SRBs) have fired, the Shuttle is committed to launch, and this fixes the date and time that your pass will occur to within a few minutes.
Infrequently, the attitude of the Orbiter can be adjusted to reduce the offpointing angle of the antenna. However, this is rare and requires that there be no conflicts with the primary payloads, and is entirely dependent on the crew and Orbiter flight controllers. Realistically, the only way to minimize the offpointing angle and increase the length of time that it is possible for your group to sustain reliable two- way communications with the Orbiter is to move the onboard SAREX antenna to a window with a more favorable view of your location. However, relocating the antenna cannot always completely compensate for the Orbiter's attitude. Using current orbiter attitude data direct from the Shuttle’s navigational systems, the mission controllers watching over SAREX operations monitor the visibility of the onboard SAREX antenna. The SAREX Flight Controllers continually monitor the Orbiter’s attitude during flight and using sophisticated software, will request the crew to move the antenna to different windows. The purpose of this is to achieve the greatest possible duration that the antenna pointing will be favorable for your location and thus maximize the length of time which you will be able to maintain contact. Again, due to numerous other considerations, including the requirements of the primary payloads on board, there may be times when it is simply not possible to have favorable antenna pointing on board for the entire pass.
Therefore, while the shuttle may typically be visible at your location for eight or more minutes, the SAREX antenna may not be pointing favorably at you for up to over half of the pass. This would shorten the time that you can use to 3 1/2 to 4 minutes. Since you may only be able to use 3 1/2 or 4 minutes of the pass, you need to plan accordingly.
The launch window is a term that specifies the interval of time between the earliest time during a given day and the latest time during the same 24-hour period that the shuttle can launch and achieve its planned orbit. When the latest launch time has passed, the launch window is said to have closed. The next opportunity for launch as well as the length of time that the window is open is dependent on a number of factors including the position of the earth with respect to other orbiting or planetary bodies. However, for most missions, the window is "open" for about three hours or so and once closed, reopens again about 24 hours after the prior opening. NASA always schedules lift-off for the moment the window "opens", or the first time they can launch. That gives them the most flexibility and the most time to decide if they can launch that day or not.
Numerous factors go into determining the launch window. If they are deploying a satellite, they will schedule the release for a time, in daylight, with optimal sun angles at a point in their orbit where the kick motors of the satellite being deployed can reach the intended orbit of the satellite. If it is a free flyer they are deploying, designed to fly free of the shuttle during the mission, and then be retrieved later in the mission, the primary concern is usually just the lighting conditions in orbit. Other factors always play in here, such as daylight conditions at the launch abort sites over in Spain, the Canary islands, Gambia, etc. Lighting conditions at the Cape are important in case they need to abort and return to the launch site. And lighting conditions out at Edwards AFB are also considered in case they need to abort to that site. They can also do an AOA or "Abort Once Around" where they jettison the external tank and either land back at KSC after one rev, or come in at Edwards AFB after nearly one full rev. And then they must consider the lighting conditions at the primary and backup landing sites (KSC and Edwards) at the end of a nominal (planned length mission). That is why you see a lot of launches shortly after sunrise at the Cape.
They also don't want to keep the crew suited up, sitting on the pad, waiting on their backs for more than a few hours. Once crew ingress begins (boarding), this starts another clock running, called the "on-the-back time". It is both physically and psychologically exhausting to keep the crew in this status. NASA doctors limit this to about 3 or so hours. After that the crew's ability to perform, especially during the critical phase of ascent (launch into orbit) begins to degrade.
Many other things will work to determine the exact launch time. Perhaps the biggest unpredictable event is the weather at the launch site (Kennedy Space Center - KSC). The winds and cloud conditions must be within a narrow margin to allow for a landing back at the launch site if needed. Also, upper altitude winds must be right to minimize stress of the vehicle as it makes it ascent through them. Weather "outlooks" which are provided by the Range Weather Operations Facility at Cape Canaveral begin at Launch minus 5 days. These include weather trends, and their possible effects on launch day.
The basic weather parameters on the pad at liftoff must be:
After tanking begins, the countdown shall not be continued nor the Shuttle launched if the temperature is lower than the prescribed minimum value for longer than 30 minutes unless sun, wind and relative humidity conditions permit recovery.
The minimum temperature limit in degrees F. is specified by the table below and is a function of the five minute average of temperature, wind and humidity. The table becomes applicable when the observed temperature reaches 48 degrees. In no case may the Space Shuttle be launched if the temperature is 35 degrees or colder.
Wind Speed Relative Humidity (kts) 0-64% 65-74% 75-79% 80-89% 90-100% 0 - 1 48 47 46 45 44 2 47 46 45 44 43 3 41 41 41 40 39 4 39 39 39 39 38 5 - 7 38 38 38 38 38 8 - 14 37 37 37 37 37 >14 36 36 36 36 36
The above table can be used to determine when conditions are again acceptable for launch if parameters have been out of limits for thirty minutes or less. If longer than thirty minutes, a mathematical recovery formula of the environmental conditions is used to determine if a return to acceptable parameters has been achieved. Launch conditions have been reached if the formula reaches a positive value.
For launch, when the wind direction at the launch pad is between 300 degrees and 060 degrees, the highest wind allowable is 34 knots. When the wind direction is between 150 degrees and 200 degrees, the highest wind allowable is 20 knots. The peak allowable wind speeds are on a descending scale between the directions of 060 degrees and 150 degrees, and an ascending scale between 200 degrees and 300 degrees.
The upper atmosphere wind profile must conform to either one of two wind loading programs developed by the Johnson Space Center. This profile is determined by a series of Jimsphere wind balloon releases from Cape Canaveral Air Station. A final recommendation is made by the JSC Launch Systems Evaluation Advisory Team (LSEAT) to the KSC launch director at Launch minus 30 minutes. The Space Shuttle will not be launched within 30 minutes of the time a determination has been made that the upper wind profile will adversely affect the performance of the launch vehicle.
A downrange weather advisory shall be issued by the Shuttle Weather Officer to the Mission Management Team for their consideration if the wind in the solid rocket booster recovery area is forecast to exceed 26 knots during retrieval operations.
The above rule need not apply if the following two conditions are observed to exist:
1. There are no clouds within 10 nautical miles of the flight path except those which are transparent. Also excepted are clouds with tops below the 41 degrees F. temperature level that have not have been previously associated with a thunderstorm, or associated with convective clouds having tops above the 14 degrees F. temperature level during the last three hours.
2. A known source of electric fields such as ground fog or smoke that is occuring near the field mill which has been previously determined and documented to be benign is clearly causing the elevated readings.
KSC Seasonal Altitudes of Temperature Levels in thousands of feet
January July
Temp Low Avg High Temp Low Avg High
-4 F 21 Kft 24 Kft 26 Kft -4 F 23 Kft 27 Kft 29 Kft
14 13 18 21 14 18 21 23
23 9 15 18 23 16 18 20
32 sfc 12 16 32 13 15 18
41 sfc 9 14 41 10 12 15
The landing criteria for the Trans-Oceanic Abort Sites (TAL), and the Abort Once Around (AOA) sites of Edwards Air Force Base, and White Sands Space Harbor are:
The scheduled time for your contact first provided to you by your Technical Coordinator is often based on preliminary flight plans developed by NASA. Infrequently, the flight planners at JSC will revise the mission timeline for various reasons and change the assignment of SAREX orbits. This often changes the entire assignment of contact times for most or all of the school groups. Flight plan changes can cause your schedule contact to occur earlier or later in the mission than originally planned, and these changes can be several hours to several days. Flight plan changes can also occur during the mission and your pass may be suddenly moved to a different orbit. All of this emphasizes the need to keep your plans as flexible as possible. If, for any reason, your scheduled contact time changes, you will be notified by your Technical Mentor as soon as possible.
To you and your team, all of this means that your contact time can "slip", or be later than originally planned. In fact, it is almost a certainty that from the time you are first notified of your selection, the launch date will slip at least once. You must allow for this, but you must also be ready in case it does not slip. Do not adjust your planning schedules until after you have been notified by your AMSAT Technical Mentor that your launch date has changed. At T-0 (lift-off), the times will be locked in fairly closely, but could be subject to some changes due to orbital adjustments and possible timeline revisions. The closer we get to your contact time, the more accurate the estimates get. Its a constant refinement process. By the time we reach 24 hours before your contact, the time will be fairly certain and usually known to within seconds.