Technical data
Satellite abbreviation: AO- 07 Project name: Phase IIB Int. identifier: 1974-089B Catalog no.: 07530 Launch: November 15, 1974 Dimensions: Ø 43 cm x 36 cm Launch mass: 29 kg Orbital period: 115 min Orbital altitude: 1,450 km circular Inclination: 101.7 °
Payloads
- Linear transponder from 145 MHz to 29 MHz, beacon, 1.3 W PEP, omni/dipole antennas.
- AMSAT-DL linear transponder from 435 MHz to 145 MHz, beacon, 8 W PEP in HELAPS technology
- Omni antennas
- Beacons at 435 and 2304 MHz
The AMSAT-DL sets course for space
AMSAT-OSCAR 7 was created with international participation (USA, Canada, Germany and Australia). The electrotechnical parts of AMSAT Germany in this project are a transponder and an antenna coupler, which connects the different antennas with the transmitters and receivers. Support was also provided with the mechanical design and integration of the satellite.
21 years in hibernation
The AO-07 satellite was successfully launched into a circular, polar orbit at an altitude of around 1,450 km in November 1974. Compared to its predecessors, AMSAT-OSCAR 7 was equipped with an active battery charge controller that used the electrical power generated by the solar cells to charge the batteries in a controlled manner. However, this did not prevent a battery cell short circuit from causing the power supply to collapse in the summer of 1981. The fate of AMSAT-OSCAR 7 seemed to be over after more than six successful years in orbit. In the summer of 2002, a British radio amateur became aware of unusually strong Morse signals in the satellite range at 145 MHz. An analysis of the signals showed that this was the telemetry beacon of AO-07. It transmitted measured values such as temperatures and currents from the satellite. An analysis of the data by the designers showed that the short circuit in the battery must have opened after more than two decades. This allows the solar cells to power the satellite again as long as it is in sunlight. The command decoder on board the satellite contributed by the Australian AMSAT Group means that control from the ground is still possible to a limited extent.
With new technology
One of the two linear transponders on board AO-07 was the first to use the HELAPS modulation method developed by the founder of AMSAT-DL, Dr. Karl Meinzer. It serves to increase the efficiency by a parametric decomposition of the transmitted signal and the voltage-controlled modulation by a switching regulator. This so-called Mode B transponder, which opened up the satellite frequencies at 435 and 145 MHz to radio amateurs worldwide, was built by Karl Meinzer and the unfortunately deceased AMSAT-DL co-founder Werner Haas. In addition to the second transponder, one telemetry beacon each at 435 and 2304 MHz are on board. Unfortunately, the latter could never be put into operation due to changes in international frequency allocations. 
Due to the lack of battery buffering in the Earth’s shadow these days, AO-07 starts in an unpredictable mode when it enters the sunlight. However, temporarily both the so-called Mode A of the linear converter from 145 MHz to 29 MHz and the Mode B linear transponder can be used. Even the beacon signal at 435.1 MHz can sometimes be received. This means that the AMSAT electronics are still fully functional 30 years after the launch.
AMSAT-OSCAR-7, a small satellite still in operation – a lesson in history
by Jan A. King, W3GEY, Frank Wiesenmeyer, K9CIS and Scott Wiesenmeyer, K7WDO presented at the 38th Annual Small Satellite Conference in Logan, UT, USA The presentation can be downloaded here: AMSAT-OSCAR-7, A Still Operational, Small-Satellite History Lesson
Abstract
It is often reported that the oldest satellites still operating in space are the two JPL space probes, Voyager 1 and Voyager 2.
The Voyager probes were both launched in 1977 to utilize planetary alignment, which was called the “Grand Tour” at the time.
This was the outer planet alignment that allowed both Voyagers to visit multiple planets using gravity.
Both missions were nothing short of spectacular, and they continue to expand our imagination.
Their images have changed people’s view of our solar system.
But are they really the oldest, still-functioning spacecraft in space?
What if we include the spacecraft left behind in Earth orbit?
Is it even credible to claim that the oldest working satellite in space was not even developed or operated by NASA, the USAF, ESA or any other space agency?
What if it was said that this satellite was designed by radio amateurs and the final assembly took place in a basement laboratory not far from the Goddard Space Flight Center?
What if it was pointed out that 2024 marks the 50th anniversary of the launch of this satellite on November 15, 1974?
and that the AMSAT-OSCAR-7 (AO-7) satellite, as you will see (and hear) in this post, is still providing its services to hundreds of radio amateurs around the world, as it has for a very, very long time.
And would you believe that the oldest satellite operating around our planet is a 29 kg SmallSat?
This is all true, as far as we can tell, and this is the amazing story that made it possible and why this satellite is sometimes called the “Sleeping Beauty Satellite”.
We describe here the story of how the mission was conceived, how radio amateurs from four countries worked together to develop a very complex spacecraft with a quite creative payload.
We will explain the many successes of this communication satellite during its main mission and surprise you with the extended mission that continues to this day.
The technology used by AO-7 was advanced and in certain aspects ahead of the primary satellite it flew with (NOAA-4/ITOS-G).
We will tell this story and also summarize other forthcoming special features on the satellite’s orbit, power and communications systems, and radiation exposure.
If time permits, during the oral presentation of this paper, we will demonstrate the still-functioning, robust telemetry systems and communications transponders aboard AO-7.
This is possible because all of these systems can only be observed via audio transmission.
Much of the telemetry is provided by a very reliable 435 MHz beacon transmitter from Canada coupled to a novel circularly polarized antenna.
We would also like to invite all listeners to participate in the use of AO-7 and conduct their own experiments as AO-7 moves into the future.
AO-7 has already lived longer than many of its developers and operators. It is quite possible that it will outlive us all.
– It is still in its 1450 km SSO, waiting for the next generation of SmallSat engineers to learn from it.