SAREX Field Operations Guide

SAREX Technical Overview and Requirements

SAREX contacts are presently carried out on the two-meter (2-M) amateur radio band. The frequency of this band is from 144 MHz to 148 MHz. This is in the same range of frequencies used by police, fire, and commercial aviation (passenger jets, etc.), known as the VHF public service band. Since the contact will take place on a VHF frequency (near 145 MHz), it will have all the characteristics of a VHF radio conversation, the most important of which is that the two stations involved must be able to see each other. This means that they must be "in line of sight". For SAREX contacts, it specifically means that the Shuttle must be above the horizon, and in the sky for your location. SAREX contacts are impossible when the Shuttle is below the horizon, or above the horizon, but obscured by trees, mountains, buildings, or the body of the Shuttle orbiter itself.

Determining When Radio Communications Are Possible

The times that the Shuttle or MIR will be above the horizon in your area can be computed on personal computers (PCs) using tracking software available from AMSAT. These times are dependent on a number of things, including the latitude, longitude, and elevation above sea level of your location. Once in orbit, the Shuttle circles the Earth about once every 90 minutes, moving over 17,500 MPH. How high the Shuttle gets in your sky as it moves over your location depends on how close it will pass to you. If it is too far away, it will never get above your horizon. The closer it passes by you, the higher in your sky it will appear. If it passes directly overhead, it will appear straight up in the sky. The point where the Shuttle first comes up over your horizon, the path it takes across your sky, and the point where it disappears below your horizon depends on a number of factors explained in the section of this guide on orbital mechanics and tracking the shuttle.

You will hear the term "pass" used frequently to refer to your scheduled contact opportunity. When the Shuttle, or any satellite, moves across an observer’s sky, it “passes” overhead. The pass lasts from the time the Shuttle rises to the time it sets, and takes anywhere from a couple of seconds for passes that stay low to the horizon, to 10 minutes or so for a pass which the shuttle moves directly overhead of your location. Your school will be scheduled to use the entire duration of the pass; however, for reasons explained in Section 5.2, Contact Time and Duration, you may only be able to use the first or last half of your pass. Scheduled SAREX contacts are arranged by NASA flight planners to provide the best possible chances for a linkup to work.

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. This visibility is critical in determining exactly how long your group will be able to maintain contact with the Shuttle. During the preflight planning phases, the the attitude, or orientation of the Shuttle with respect to the Earth, is factored in to selecting the time when your group will be assigned to contact the Shuttle. However, the Orbiter’s attitude is subject to change without notice and this may affect the quality of your contact considerably. 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 lenght 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 and not try to do too many things with your contact.

Amateur Radio Station Requirements for SAREX Contacts

This section outlines the minimum requirements for amateur radio stations employed in the support of a SAREX contact. Emphasis is placed on reliability and redundancy to establish and maintain a high-quality communications link for the duration of the pass.

Direct Contacts - Station Requirements

For direct contacts, the entire responsibility of the establishing and maintaining the radio link is on your group. This essentially requires a solid, 2-meter side of an OSCAR station as follows:

You will need to install your antennas with as unobstructed view of the horizon as possible. Horizon obscuration can interfere with the duration of reliable communications with the crew. You are establishing contact with a low earth orbiting satellite with both the uplink and the downlink taking place using Frequency Modulation (FM, F3 emmissions) in the VHF 2-meter Amateur Radio Band. Specifically, the frequencies are in the 2-meter Amateur Radio Space Subband (144.0 to 146.0 Mhz). The speed, frequencies, and narrow band FM modes involved mean that doppler shift effects will be present only during the first and last 60 seconds of the pass. Depending on the selectivity of your reciever, the apparent frequency at your location may be near the outer edge of its bandpass. They should still be readable; but tuning by 5 Khz to compensate might improve reception.

Telebridge Contacts - Station Requirements

Telebridge contacts require considerably less technical work on your part, because the link between the Shuttle and the ground is handled by one of several pre-qualified ham radio operators, part of the AMSAT/ARRL SAREX Team located strategically around the world. The telebridge method is used when it is not possible or desirable to use a direct contact for a given school. This can be for many reasons; however, the principal ones are:

In a telebridge contact, the radio link is handled by the telebridge station and your group is connected by a telephone line. Typically, only one telebridge station is scheduled for your pass and if there are problems with your contact, a backup pass may scheduled. However, occasionally, it is possible to arrange the telebridge stations so that there is a primary station and a backup station located further along the Shuttle’s path over the earth. When the shuttle sets for the primary station, it rises in the backup station's sky a short time later, providing for up to another 10 minutes of time to talk to the crew The backup station can make the attempt only a few minutes later, avoiding rescheduling your event and re-assembling your students and parents several days later. However, it is infrequent that this is possible, so you should expect your primary and backup passes to be separately scheduled several days apart.

The primary mission of SAREX is a positive educational experience for the students involved. Emphasis is placed on establishing a reliable contact path and maximizing the chances of success. Direct contacts maximize the Amateur Radio content and are used to the maximum extent possible. However, the goal of showcasing amateur radio practice is secondary to the educational goals. When the telebridge conact method is employed, amateur radio practice is showcased using different means than building and operating a space communications station. In a telebridge contact, hams can use their expertise and ingenuity to develop a simulated link and engineer the audio distibution system for the event. Hams can participate in technical demonstrations to students as requested by the teachers as part of the educational program surrounding a scheduled SAREX contact. A telebridge contact offers opportunity to coach the children in science and technology through an enhanced educational program through time that would otherwise be consumed with the details of establishing a direct contact station. And most importantly, hams can display the integrity, dependibility and reliability to community support and service, long traditional to amateur radio operators world-wide.

Contact Schedule Considerations

You will be provided with an approximate date and time for your primary pass about two months prior to the launch. A backup pass may or may not be assigned to your school before launch. Some Shuttle missions do not allow for backup passes due to the tight schedules that the astronauts must work, and many will have only a few backup passes with several school groups identified for that pass if it is needed. The backup pass is typically several days later and your planning should take this into account. All passes are scheduled by the Flight Planning Team at NASA, from constraints provided by AMSAT/ARRL and are typically assigned on a secondary basis. That means, they are scheduled last and therefore, are often not likely to be at the exact times you requested. Although exceptions can occur, contacts are typically scheduled between 6 AM and 10 PM local time. The day of the week and holidays; however, are not considered. For example, a pass was conducted on STS-55 at 10:15 PM Easter Sunday, 1993. If you are unable or unwilling to use the timeslot allocated, you will be deleted from the mission and another school selected who is able to utilize the time. If you are deleted from a flight, you must reapply to the SAREX program and go through the usual selection process before you will be rescheduled on another flight. In short, it could take another two years or more before you get another chance.

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