AMSAT-OSCAR 7

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 developed 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 various antennas with the transmitters and receivers. In addition, support was provided for the mechanical design as well as the integration of the satellite.

 

21 years in hibernation

The AO-07 satellite was successfully launched in November 1974 into a circular polar orbit of about 1,450 km altitude. 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. Due to the command decoder on board the satellite, contributed by the Australian AMSAT Group, 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 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. The AMSAT electronics are thus still fully functional 30 years after 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 full presentation can be downloaded here: AMSAT-OSCAR-7, A Still Operational, Small-Satellite History Lesson

 

Summary (automatically translated)

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 this satellite’s launch on November 15, 1974? and that, as you will see (and hear) in this post, the AMSAT-OSCAR-7 (AO-7) satellite 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 want to 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.

 

AMSAT-OSCAR-7: 50 years in a sun-synchronous orbit – and counting – confirmation of the long-term perturbation of the solar gravitational gradient

by Jan A. King, W3GEY and Karl Meinzer, DJ4ZC presented at the 38th Annual Small Satellite Conference in Logan, UT, USA The full paper can be downloaded here: AMSAT-OSCAR-7: 50 Years in a Sun-Synchronous Orbit – And Still Counting – Confirmation of the Long-Term Solar Gravity-Gradient Perturbation

 

Summary (automatically translated)

The first Delta launcher to launch multiple secondary payloads was Δ-104. The second piggyback payload on this mission was an amateur radio satellite, AMSAT-OSCAR-7 (AO-7). The launch took place on November 15, 1974 to an SSO 1460 km away. This satellite was, as the name suggests, the seventh in an ongoing series of satellites used in the amateur radio service. The amazing story associated with this small satellite’s mission is covered elsewhere in this report. Although the details of this satellite’s lifespan are exciting, we did not expect the tricks of this “old bird” to affect our study of its orbit. In particular, we wanted to find out when the satellite would be 100% in the sun as it moved forward in time. To this end, we examined the history of the orbit. The result surprised us. This paper describes our observations. We used the information now available on Space-Track.com to examine the first 50 years of this spacecraft’s orbital history. This website “publishes” the now famous TLEs (two-line items) going back to 1958, when NORAD (now CSpOC) began keeping a catalog of all space objects. To find out if the satellite was moving slowly forward in its sun-synchronous orbit as expected, we needed to track the sun’s angle (φ) over time. To simplify the procedure for tracking the mean solar time of the orbit, we describe a method for sampling the RAAN value of the AO-7 orbit at the vernal equinox of each year. Our search for drift in our SSO led to the unexpected finding that both the RAAN(Ω) and inclination(i) elements exhibit a sinusoidal variation with a period of about 29 years. We further found that this is caused by a torque of the solar gravity gradient perturbing the solar-synchronous LEO orbits. We present here in Appendix 2 the full analysis, which confirms that the solar gravity gradient torque acting on the orbital plane is the cause of the observed oscillation. The differential equation we derived is essentially the same as the classical pendulum equation, which can be linearized to a simple harmonic oscillator. While we initially thought we had discovered a new form of orbital perturbation, we have now come across an earlier discovery of this phenomenon described in a NASA X-document by Ken Duck. Ironically, in this discovery, K. Duck, a NASA/GSFC employee, used the ITOS serial orbit to demonstrate his version of the solution to this differential equation. This is the same orbit into which AO-7 was launched.

So we can’t claim to have discovered this perturbation of the solar gravity gradient and the coupling of this effect with the Earth’s J2 perturbation, but we can demonstrate from 50 years of NORAD data that K. Duck’s discovery is valid over almost two cycles of the perturbation. And we have verified this using not only the data from the still-functioning AO-7 probe, but also the TLEs from the NOAA-4 probe, the primary Δ-104 passenger (now defunct); this probe also experienced the same solar gravity gradient perturbation.

 

HELAPS

One of the two linear transponders on board AMSAT OSCAR-7 used the HELAPS modulation method developed by Dr. Karl Meinzer DJ4ZC for the first time. 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 Dr. Karl Meinzer DJ4ZC and the late Werner Haas, ex-DJ5KQ. Both were founding members of AMSAT-Deutschland e.V. (AMSAT-DL) see: HELAPS – AMSAT-Germany

 

LINKS

 

 

 

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