ARISS Contact at Hawthorne Brook School

Photo courtesy KB1ESR
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November 29 2005 was the culmination of two months of preparation for an ARISS contact between the International Space Station and Hawthorne Brook Middle School in Townsend.

Two month’s earlier we had been contacted to provide radio communications for the event by Steven Best VE9SRB who was involved in the original application and Marilyn Richardson (the teacher). The club that had signed up on the original application in April of 2002 was not able to support the event. After some brief discussions and a club meeting we decided to support the event. The kids after all have been waiting three and one half years for this to happen.

From that point on it was a scramble to assemble the required two satellite stations for the contact. Not having been involved in the original application we had a lot to learn.

We made site visits to the school to check out the classroom, the possible antenna locations like the roof, adjacent athletic field, and a basketball court near the classroom. Knowing something of the terrain there were concerns. But anticipated ISS passes were expected to have Acquisition of Signal (AOS) in the southwest and Loss of Signal (LOS) in the southeast. These were the optimum places due to a high ridge that runs east-west on the north side of the school. It is very important to verify the horizon limits which means reviewing either maps or software to do terrain profiles. Since a satellite spends a significant portion of the total pass time near the horizon avoiding obstacles such as heavy tree cover or hill is critical to maximizing the total pass time.

We also had a lot to learn about the NASA requirements for the equipment used. A review of the original application and several other sources revealed exactly what NASA expected. This included for the primary station; a radio, power amplifier, large cross polarized antenna, rotator system, emergency power, and some audio amplifier, and lots of cables.

After looking at what radios might be acceptable it was decided to use a satellite type radio. Bob W1XP had a Yaesu FT-847 which would fit the bill. To make operation and programming easier it was decided to use two of the same radios. After sending out an all-club email we located three more of the same rig. When we started assembling the second station Hank Lane KB1JLA supplied the second rig. Once we received the primary and secondary frequency matrix with the Doppler shift frequencies we programmed the primary station radio. Since we had two of the same radio and they had cloning capability loading the two frequency sets with the seven frequency steps to account for Doppler shift was easy.

To improve the radio performance NASA recommends a power amplifier with a receive preamp. We used two different model Mirage (now MFJ) 160 watt amplifiers both with preamps. One needed 50 watts of input for 160 watts out and the other took 10 watts in for 160 out. A Bird wattmeter was placed at the output of each system to monitor power output. One problem here is the requirement to run on emergency power. We chose to run on a deep cycle 12 volt battery for the primary station and equipment. With that power source we were unable to get 50 watts out of the radio. This resulted in slightly better than 100 watts out of each amplifier which we decided was acceptable. The secondary station ran from an Astron 35 amp power supply. The two Ft-847’s and the power amplifiers were wired directly to their battery or power supply. All of the other equipment was wired to use Anderson Powerpole connectors and connected to either a Powerpole distribution box or directly to a heavy pigtail connected directly to the station power source.

The available antennas needed to be repaired, some elements replaced, matching cables built, and the antennas tuned and checked out. The antennas we had to work with were a KLM 2M-22C a 22 element antenna and a KLM 2M-14C a 14 element antenna both circularly polarized The 22 element antenna was the primary and the 14 element the secondary antenna. That work was completed by mid October.

Coax is critical with the weak signals you are trying to receive at the start and end of a satellite pass. RG-8 types are the absolute minimum. Never use RG-58 coax as the losses are too great. Better cable is better and cable such as LMR-400 which we used is preferred. One tradeoff, besides price, is the LMR-400 is not very flexible and should be rolled and unrolled carefully. Rolled in coils with a four foot diameter is reasonable.

Software was obtained to track the satellites and International Space Station. The software we used was NOVA which costs approximately $60. Some practice was required to understand the program, learn to update the KEPS, and synchronize time. You need to set up the software with the location you will be operating from and the satellites you want to track.

For testing purposes a key was used to make contacts on satellites where that was an appropriate mode. On the ISS packet is the alternate mode. When the astronauts are not using the FM radio to make contacts it is connected to a packet system. Contacts are made by monitoring transmissions of other stations through the packet repeater. They are made without directly connecting.

A rotator system was available but untested. Cabling had to be made to test the system. For the event rotator and RF cables needed to be extended to 250 feet. Rotator cables for such long runs needs to be at least #18 gauge. Often this cable comes in 100 foot lengths. This creates a problem of too many connectors for reliable service. For the most part the cables should be the minimum number of pieces with the fewest connectors possible. For accurate aiming, computer control of the azimuth and elevation of the primary antenna was needed. A computer interface and software was obtained. The interface is by EA4TX and the software is ARSWIN. The software for the rotator interface takes data from the NOVA satellite tracking program to point the antennas in the correct direction. Calibration of the system to synchronize the position and feedback from the controller was required. One important consideration is the rotator stops. The normal configuration is to have the azimuth stop set at north and most controllers are configured to show this on their display. If the satellite is to pass to the north of your location the rotator will run into the stop. At this point it will have to rotate fully around to pick up tracking. This may result in a loss of signal for 30 seconds or more which is unacceptable. Once the pass is known the rotator should be calibrated with the stop in the proper position (north or south) so that you have continuous tracking for the pass you have. For the controller and software we used there is a setting for north or south centered rotation.

The primary station was completed more than three weeks before the contact. We still only knew the week and not the day of the contact. But we started testing equipment by making packet QSO’s through the ISS packet system on nearly a daily basis as passes were available. Ultimately more than fifteen packet QSO’s were made through the ISS with a variety of continental US stations. We also made several contacts using other satellites to test systems.

Over the course of the two month’s the prospective date had narrowed from a list of weeks in a November and December to the last week in November. With a week to go we received news the contact would be November 29 th at about 1:24 PM. The good news was we now had the date and time. The bad news was the pass was now going to come up in the northwest where we knew there was a significant hill and set in the southeast. Ralph KD1SM set to work again computing the horizon elevation angles where we expected AOS and LOS. To our dismay we found that with the new LOS bearing a new hill in the southeast would now be a problem. With this information we estimated the total length of the contact. This is less than the flat land horizon to horizon calculation the program gives. After a few adjustments to the calculations we estimated that the 9 minute 44 second pass would be more like 9 minutes. This information was passed on to Marilyn so she could plan the students question and answer time.

The week before the contact Bob and Stan practiced with the students. Using the actual radio and microphone setup they transmitted to a local handheld and recorder. After all the students asked their questions which now included the word “over” the tape was played back so they could see how they sounded and if they needed to speak louder. That process was repeated several times.

Another problem was audio distribution and a desire to record the event. Bob had built two audio preamps so conventional powered computer speakers could be driven by the fixed audio output of the rigs. This made the speaker audio level independent of the rig volume control that might need be adjusted by the operator if he were wearing headphones. The original requirement was only to have audio in the classroom which would only have the 20 students asking questions and some visitors. A simple PA system using computer speakers satisfied this requirement. Providing audio from both the uplink and downlink in a way that doesn’t cause feedback is more of a challenge. Not to mention the basic problem of RF getting into the system. Larry KB1ESR put together a mixing and distribution system that he thought would satisfy the requirements. A second amplified output from the preamps would have been better to feed the audio distribution system.

The week before the scheduled event both stations, all the antennas and all the peripheral equipment were assembled. On the weekend we scheduled a training session to go over last minute details and have everyone assigned a role. Gary K1YTS, Joel W1JMM, Bob W1XP, Stan KD1LE, and Larry KB1ESR made the meeting. As a plus there was an actual pass of the ISS so we could track in auto and manual, compare received signals on both stations, and try to make a few packet QSO’s. As the ISS approached antennas were positioned. When the ISS came over the horizon at AOS we expected to hear packet bursts. Much to our surprise and pleasure we heard voices. We quickly switched from the packet uplink frequency to the voice frequency which was already programmed into the radios. Bill McArthur, the astronaut we would talk to in the school contact, was making contacts as he came up the east coast. One of those contacts was to the Naval Academy. During that QSO he wished them good luck at the upcoming Army Navy football game but said he would be rooting for Army. .As he worked stations Stan KD1LE called and after a few tries was acknowledged. On closing Stan mentioned we would be the calling station for next Tuesdays school contact which he acknowledged. A number of additional stations made QSO’s and as the ISS neared the horizon Joel W1JMM made several calls which were answered. We weren’t sure he repeated the callsign correctly but we hope so.

After the practice contacts on Sunday the equipment was taken down including the cables, accessories, microphones, etc. It was packaged and labeled as station one or station two so that all of the parts would end up in the right place at the school.

The Monday afternoon before the contact the two stations and the main antenna system were set up. Participating were Joel W1JMM, Stan KD1LE, Bob W1XP, Larry KB1ESR, and Gary K1YTS. We planned on four or more people to set up and an equal number or more on the next day for the final setup and contact.

Tuesday morning we arrived around 10:00 AM and continued set up and testing. The crew was composed of Larry KB1ESR, Bob W1XP, Dick KB1MBR, Stan KD1LE, Gary K1YTS, Les N1SV, and Joel W1JMM.

Cables were re-run to the primary antenna and rotator as we did not leave them across the driveway overnight. The secondary antennas were set up and cables run. An hour and one-half before our pass everything was set up. Since there was a pass around noon Bob started sending CQ on the packet frequency the space station uses. During the pass a message came back from the ISS “are you the station for the school QSO today?” Bob replied “roger we’re just checking out the system”. The reply came back from the ISS “good luck.”

After that exchange everything was set and we only had to wait. Now there was time to pose for pictures as Marilyn and her crew of 20 students below.

After the contact was over Larry replayed the audio for the students. The video made by the school was played in the school library.

The school provided a pizza lunch after the event. After everyone had calmed down we started packing up. It took a while to pack all the equipment and take down the antennas but considering it took two days to set up the two hours to take down was not bad. For additional information on getting involved in the ARISS program refer to these resources; http://www.arrl.org/ARISS/ and http://www.amsat.org/amsat-new/ariss/.