This page will be used as a collection point for common questions submitted to the EOSOC mailing list, or to the EOSOC Administrator. If you have a question that is not answered here, please send it to the EOSOC mailing list shown on the resources page – you probably aren’t the only one with that question!

Q: What are the requirements of the EOSOC program?

A: The EOSOC task requirements are listed below:

  • Active Payloads (4) – Observe four different objects that are active, i.e. operational, payloads. Examples include the Hubble Space Telescope, GPS satellites, etc.
  • Rocket Bodies (4) – Observe four different objects that are discarded rocket bodies. These are often annotated with “r/b” in the name in the elset file.
  • Manned Spacecraft (2) – Observe two different manned spacecraft. For example, the International Space Station and a manned Soyuz spacecraft.
  • Iridium Flares (4) – Observe four Iridium flares, one during daylight or civil twilight hours. Note: when producing a observation log for the daylight/twilight flare, no background stars or constellation are required.
  • Multinational Spacecraft (4) – Observe four objects that belong to four different countries, other than the USA. Examples include objects belonging to Russia, India, China, Brazil, France, etc.
  • Multipass (2) – Observe two different objects, recording observations of each satellite on two different passes in the same night. Note: this task will result in four different observations. For example, two passes for rocket body one, and two passes for payload two.
  • Formation (2) – Observe two pairs of objects flying in formation. For example, a resupply vehicle and the International Space Station just prior to docking (or just after undocking). Each pair of satellites should be visible at the same time. The satellites observed must be deliberately flying in formation, and not a coincidental alignment. Each formation recorded is considered one observation, and the satellite pair should be recorded on the same log sheet. Both satellites should be visible at the same time.
  • Aged Elsets (2) – Observe two different objects with current and aged element sets. The current elset observations should be made with elsets less than one week old, and the aged elset observations should be made with elsets more than three weeks old. Note: this task will result in four different observations.


Q: What, exactly, is a “pass”?

A: A pass refers to when a satellite rises above the horizon, crosses some portion of the sky, and then sets. Low Earth orbits (like the Hubble Space Telescope) generally orbit the Earth about 15 times per day, resulting in potential passes about every 90 minutes. For the purposes of the Earth Orbiting Satellite Observers Club, a given pass of any satellite can only be used to satisfy one observing task. For example, if the International Space Station (ISS) makes a pass overhead, you can use that pass to satisfy one of the manned spacecraft tasks. If you wish to use ISS for another task (perhaps a formation task), you must wait for another pass.

Q: Can I reuse the same object on two different tasks?

A: Yes, provided two conditions are met: 1) you must not use the same pass for two different tasks, and 2) the task description doesn’t explicitly state that different objects must be used. For example, using the International Space Station (ISS) to satisfy a manned spacecraft task, and then on a separate pass, to satisfy a formation task is permitted. However, using the ISS to satisfy a manned mission in February, and then again to satisfy a manned mission in November is not allowed (the manned tasks are required to use two different objects).

Q: Is a “dead” satellite considered an “active payload”?

A: No. An active payload is defined as an object that continues to serve its primary mission. If, for example, the Hubble Space Telescope were to die in orbit, it would no longer be usable as an active payload task. Similarly, spent rocket bodies are not considered active payloads (they no longer serve their primary mission). There are a few special cases to this rule – some objects are simply passive objects that are used for space surveillance or gravitational geopotential references. These often consist of an inert, shiny object, with no active on-board components. These would qualify as active payloads.


Q: Can I use observations of satellites that I recorded in the past?

A: Yes, provided you have the information specified on the EOSOC Observation Logs (observer position, elset date, etc.), and that an “official” elset archive can be located that can be used to verify the observation.


Q: Can I use an Iridium flare to make the Aged Elset task easier?

A: Yes, but… The aged elset task requires you to observe an object using a current elset (elset less than one week old), and then observe the same object with an aged elset (elset more than three weeks old). The goal is to demonstrate how a satellite’s orbit (or the errors associated with propagating a satellite’s position into the future) can change over time. Observing an Iridium flare can potentially reduce uncertainty of a satellite’s position when using the aged elsets, and you are welcome to use Iridium flares for this purpose. Keep in mind, however, that if a satellite’s orbit changes over time, you ability to know the position of the satellite will also change. This could result in a flare not being visible from your observing position, even when the flare was predicted to occur using old elsets.


Q: Can I use geosynchronous satellites to satisfy observing tasks?

A: Yes, however you need to realize these satellites can only be viewed through a moderate size telescope as they average about 12th magnitude. The  difference is in how to plot the position of a geosync satellite on the observation forms. You can certainly observe the satellite over an extended period of time to generate a “pass” with respect to the stars (actually, the stars would be streaks and the satellite would be stationary). To save your sanity, however, I suggest that you simply plot the satellite as a point with respect to the background sky, and identify it accordingly on the chart.

Q: Can I use two geosynchronous satellites to satisfy the formation flight tasks?

A: No. The intent of the formation flight tasks is to location and track two (or more) objects that are deliberately flying in close proximity to each other. In the case of geosync satellites, the fact that any two are near each other is coincidental, as they do no rely on being near each other to complete their respective missions. Similarly, two satellites that happen to pass near each other (in different orbits) do not qualify for the formation tasks. The likely candidates for formation flight are ISS and space vehicles arriving just before docking (or just after separating), or payload/booster pairs just after staging.


Q: Can I use “classified” satellites to satisfy EOSOC tasks?

A: No. There are two obstacles to using “classified” satellites to satisfy EOSOC tasks: 1) A reliable (and legal) source of elsets for observation verification is not available, and 2) many people that are interested in satellite tracking can’t use this type of information without adversely affecting their careers. Nuf said!

Q: Will there be an advanced EOSOC award program?

A: Unlikely.  The relatively low level of interest in the current (basic) EOSOC award program, during the first 10 years (2001-2011) does not justify a follow-on program at this time. An advance version would probably include tasks such as observing geosynchronous satellites, GPS satellites, Molniya satellites, initial orbit determination (with provided tools), and photograph/CCD imaging. We will continue to monitor overall interest.