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Satellite Missions Catalogue

AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment)

May 29, 2012



Magnetic field


Operational (nominal)



Quick facts


Mission typeEO
Mission statusOperational (nominal)
Launch date05 May 1997
Instrument typeMagnetic field
CEOS EO HandbookSee AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment) summary

AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment)

AMPERE is a U.S. Earth observing system (2010) providing near-realtime magnetic field measurements using commercial satellites as part of a new observation network to forecast weather in space. This is the first step in developing a system that enables 24-hour tracking of Earth's response to supersonic blasts of plasma ejected from the Sun at collection rates fast enough to one day enable forecasters to predict space weather effects. 1) 2)

The science objectives of the AMPERE program are to:

• Understand the global-scale coupled electrodynamic response of the ionosphere and magnetosphere to solar wind forcing

• Provide global continuous observations of Birkeland currents with sufficient re-sampling cadence to chart global-scale dynamics.

Background: The idea behind AMPERE, conceived by researchers at JHU/APL (Laurel, MD), was to use the measurement of the existing engineering magnetometers installed on every spacecraft of the commercial Iridium communications constellation. The nominal Iridium constellation consists of 66 spacecraft in LEO (Low Earth Orbit) in circular polar orbits at altitudes of ~780 km in six equally spaced orbital planes with at least 11 satellites in each plane. Such a dense global coverage of measurements would indeed be a great source of magnetic field information if it could be harvested in near realtime for on-ground processing - to obtain global maps of magnetic perturbations due to the FACs (Field Aligned Currents). 3)

The interaction of Earth's magnetic field and the solar wind produces an electric dynamo that couples energy from the solar wind and transports it to the polar regions of the upper atmosphere, delivering up to 1012 W to the atmosphere during geomagnetic storms. Aurorae are a result of an enormous global electrical circuit that carries current along the lines of magnetic force to the ionosphere. These FACs (Field Aligned Currents), or Birkeland currents, couple stresses in the magnetosphere to the ionosphere and drive polar ionospheric dynamics. Although an understanding of the basic configuration of these currents exists, there is little knowledge so far about their variability. In particular, during geomagnetic storms, aurorae and their current systems can expand toward the equator, as seen by ground observatories; a very limited knowledge of these most interesting and important events is available.

From a LEO perspective, the Birkeland current signatures are typically hundreds of nT so they are relatively easy to detect with commercial-grade attitude magnetometers. The average configuration of the Birkeland currents was first determined by magnetic field measurements of the TRIAD (Transit- Improved DISCOS) series spacecraft of the US Navy (launch of TRID-1 on Sept. 2, 1972) using data collected over a period of 16 months. This established that the large scale currents are composed of two primary systems, the equatorward Region 2 system and the Region 1 system immediately poleward of it. On the dusk side, Region 2 flows into the ionosphere and Region 1 flows out - while the converse holds in the morning.

The Birkeland currents are typically located at magnetic latitudes between 65º and 75º. During very quiet times the currents contract as far poleward as 75º and during geomagnetic storms can expand equatorward to 45º.

The Iridium constellation satellites carry engineering magnetometers as part of the ADCS (Attitude Determination and Control Subsystem) of each spacecraft. Data for scientific study were obtained from the Iridium system beginning in February 1999 on a non-interference basis; that is, the magnetometer data obtained for operational reasons, were made available to JHU/APL.

The evaluation of the engineering magnetometer data of the Iridium system provided a first opportunity to determine the large scale FACs. Despite the coarse time sampling, the conclusion was drawn that collecting data from the entire constellation will eventually provide enough statistics to build up a representation of the large scale magnetic perturbation pattern. The concentration of larger perturbations at high latitudes indicates that the signals signals are of physical origin.

These initial results imply that the magnetometer data of the Iridium constellation can be used to characterize the large scale FACs in both hemispheres on time scales of several hours or less. This will allow an improved ability to characterize the variation of the Birkeland currents with interplanetary conditions, particularly during magnetic storms for which very little dynamics information exists.

Figure 1: Schematic illustration of the AMPERE data collection scenario from the Iridium constellation (image credit: JHU/APL)
Figure 1: Schematic illustration of the AMPERE data collection scenario from the Iridium constellation (image credit: JHU/APL)

In the observation and processing scheme, currents are detected according to Ampere’s law by recording their magnetic signatures when the satellites pass through them. Eight years of the presently available, coarse time-sampled data have been used to prove that the Iridium magnetometers yield reliable measurements. As illustrated In Figure 2, magnetic perturbations are fit to spherical harmonics and the currents calculated by simply evaluating the curl of the magnetic field perturbation fit. The technique uses first principles and has no dependence on models. 4)

The standard capability is inadequate to observe the M-I (Magnetosphere-Ionosphere) system currents for all but a tiny fraction of cases during unusually stable conditions. To overcome this severe limitation, a solution has been developed to provide up to 100 x greater magnetic field data telemetry yielding 16 x more data in nine minutes than is now obtained in two hours.

New flight software is in place which buffers and transmits magnetometer data in a dedicated, real-time, telemetry stream. The data are transmitted around the clock (24 hours/7 days per week) and processed on the ground in real time, allowing unprecedented specification of the M-I system for basic research and space environment monitoring.

Figure 2: Schematic representation of the magnetic perturbation field (image credit: JHU/APL)
Figure 2: Schematic representation of the magnetic perturbation field (image credit: JHU/APL)

In May 2008, JHU/APL (Johns Hopkins University/Applied Physics Laboratory) received funding from NSF (National Science Foundation) to develop software for an experiment on the Iridium satellite constellation with the objective to demonstrate, for the first time, global and real-time space weather observations of near-Earth space. 5) 6) 7)

PPP (Public Private Partnership) arrangement: The AMPERE project uses a partnership between the commercial space industry, university researchers, and NSF (government) to enable fundamental new science that would otherwise be prohibitively expensive. ICI (Iridium Communications Inc.) of McLean, VA, owns the assets upon which the project depends. JHU/APL in Laurel Maryland heads up the project under NSF sponsorship (PI: Brian J. Anderson). The Boeing Company (Boeing) is contracted by JHU/APL to provide the data from the satellite constellation which Boeing operates for ICI. The University of Newcastle (UN), Australia, is partnered with JHU/APL to implement the Science Data Center.

Two elements are involved, the Space Segment & Ground Data System, and the Science Data Center:

1) The Space Segment & Ground Data System was implemented by Boeing and consists of flight and ground software to collect satellite magnetometer data and supplementary data, archive the data, and package it for delivery to the Science Data Center. Initial return of AMPERE-rate data occurred in December 2009.

2) The Science Data Center, developed by JHU/APL in partnership with UN, performs data processing and analysis to convert raw data into science data products. These products include maps of magnetic perturbations and Birkeland currents as well as other products derived in concert with datasets from radar and ground magnetometer networks.

Data products will be released for use during development as they are implemented to ensure rapid dissemination of AMPERE data to the community. Pro-active community engagement is underway to guarantee that the products are tailored to user interests.

Software Upgrade of the Iridium Constellation for AMPERE

A software upgrade had to be developed for the 3-axis magnetometers in each satellite to provide a 100-fold increase in the number of data measurements to be transmitted to the ground (in parallel to the nominal data provision of the ACS).

By early summer 2010, the Boeing operations team had uploaded the software changes to every Iridium satellite. During early testing, APL researchers gathered nearly 300,000 samples of space’s magnetic field per day. Over 40-hour-long test periods, the researchers ramped that up by 10-fold, collecting nearly 3 million data samples daily. Since then, APL has established a daily routine for collecting and processing the data into images of the Earth’s aurora region. 8)

The AMPERE magnetometer data is transferred from the satellites to Iridium’s SNOC (Satellite Network Operations Center) in Leesburg, VA, and is routed to APL’s Internet servers on a continuous basis.

First Demonstrations of Space Weather Observations

The new capability of near-realtime space weather provision was demonstrated for the first time in August 2010. The AMPERE team has shown that the program yields continuous, realtime measurements of the magnetic field over the entire Earth simultaneously with up to 100 times greater sampling density than previously possible. 9) 10) 11) 12)

Figure 3: Earth images of Feb. 14-15, 2010 when AMPERE measured electric currents during a small magnetic storm for 36 hours (image credit: NSF, JHU/APL, Boeing, Iridium) 13)
Figure 3: Earth images of Feb. 14-15, 2010 when AMPERE measured electric currents during a small magnetic storm for 36 hours (image credit: NSF, JHU/APL, Boeing, Iridium) 13)

Legend to Figure 3:

- The view of the left most image is from above the North Pole and slightly behind the Earth, with the Sun toward the top of the screen. Gray and blue colors represent weak currents while greens, yellows and reds show progressively stronger currents. This image shows the weaker currents at the start of the storm.

- The view of the center image is from above the North Pole and slightly behind the Earth, with the Sun toward the top of the screen. Gray and blue colors represent weak currents while greens, yellows and reds show progressively stronger currents. This image shows the currents getting stronger as the storm nears its peak, appearing in a pair of arcs that seem to form a circle around the North Pole.

- The view of the right most image is from above the North Pole and slightly behind the Earth, with the Sun toward the top of the screen. Gray and blue colors represent weak currents while greens, yellows and reds show progressively stronger currents. This image shows the strong currents at the peak of the storm, intensifying as they move from the pole toward North America and Asia.

This milestone of spaceborne magnetic field monitoring provided by AMPERE represents an important step on the way to accurate space weather forecasts on a global scale. Solar storms can disrupt satellite service and damage telecommunications networks, cause power grid blackouts and even endanger high-altitude aircraft.

Brief Summary on the Iridium Constellation

The commercial Iridium communications constellation was conceived, designed and developed by Motorola - a groundbreaking system that would provide wireless phone service (voice and data) anywhere in the world. The low-latency cross-linked constellation is capable of transmitting data instantly. Commercial operations of the mobile satellite communications constellation started in Nov. 1998. 14) 15)

Unfortunately, the high-profile Motorola venture crashed in a spectacular August 1999 bankruptcy after its satellite phone system failed to catch on with consumers. Only a handful of employees remained in 2000, when the new company, Iridium Satellites LLC, paid $25 million for the array of orbiting satellites that Motorola and other investors spent more than $5 billion to develop.

Originally, the system was envisioned to have 77 satellites in LEO (Low Earth Orbit) working as a digitally-switched communications network in space. The name of the system was inspired by the chemical element Iridium, which has the atomic number 77. The name was kept, even after the constellation was scaled back to nominally 66 satellites. Iridium was the frontrunner of a new class of systems, fueling considerable enthusiasm in the marketplace in the mid-1990s.

Business challenges: By the time Iridium was conceived in late 1980s to early 1990s, terrestrial cellular phone services were fragmented along national borders. Europe, for example, had many national standards that were incompatible with each other. A phone that could be used in France could not be used in Germany. This was inconvenient for frequent international travelers. Iridium saw an opportunity in developing a global phone that could be used anywhere on Earth. They perceived a high demand for this service, particularly among international business travelers and the military.
While the concept of Iridium was in its incubation stage, Europe started to work on the GSM (Global System for Mobiles) standard aimed at providing high quality and low cost international roaming cellular service. The GSM standard has been successful since its initial deployment in 1991. More than 200 GSM networks in 110 countries now provide service to 480 million users worldwide (January 2000). In a few years this number is expected to reach one billion users worldwide. By comparison, Iridium could provide relatively low quality communications at a higher cost. It is suspected that a large number of the projected customers for Iridium were seized by the GSM-type services. With the cost of terrestrial cellular telephones having fallen below $100 in some cases, astute international travelers would carry a set of 2-3 small cellular phones that would work in particular regions of the globe (USA, Europe, Japan, ...). These phones had become a low cost commodity. Newer cellular telephones in 2003 are tri-band which allow roaming in the U.S., Europe and Asia with the same handset (Ref. 14).

Technical challenges: Iridium was successful in deploying and operating an extremely complex engineering system. Motorola, as prime contractor, completed the project on time and on budget and within specifications. It met the project deadline and achieved the technical requirements, despite some start-up difficulties with dropped calls and voice quality during initial operations in 1998 and 1999. It was the first space project involving mass-manufacturing and mass-launching of large quantities of spacecraft in a short time period, i.e. 72 satellites were deployed on 15 launches from three countries in 12 months and 12 days. This was unprecedented and has not been repeated since then. Although a 2-15% failure rate for satellite deployment was normal, Motorola had a perfect record in initial satellite deployment. It took Lockheed Martin 28 days to manufacture a single spacecraft during peak production. Because ten satellites were assembled simultaneously at any moment, a satellite rolled off the production line every 4 and a half days. At that time the industry standard for satellite manufacturing was 12-18 months. Iridium also assembled and installed 12 gateways in 11 countries in 18 months.
Iridium pioneered the industry by being the first to implement many cutting-edge technologies in space. It was the world’s first global wireless digital (packetized) communication system. It overcame the time lag associated with GEO communication by staying in LEO. Iridium is also the first space system to utilize intersatellite links in LEO, thus avoiding unnecessary signal traffic through the atmosphere with the associated signal degradation. The onboard processing enables the system to have minimum reliance on the ground infrastructure – handing off calls from one satellite to another - which therefore improves its level of autonomy, especially over the oceans where permanent ground stations cannot be placed.


Recovery: In November 2000, a new company, Iridium Satellite LLC, purchased the operating assets of Iridium LLC, including the satellite constellation, the terrestrial network, Iridium real property and intellectual property owned by Iridium LLC. Iridium Satellite LLC has contracted with the Boeing Company to operate and maintain the satellite constellation. 16)


Iridium Satellite LLC managed to restructure is finances, to obtain bank loans, to restart operations of the constellation, and to provide communication services again. In 2000, the DoD (Department of Defense) signed a contract with Iridium Satellites LLC to provide military communications services using Iridium satellites. This customer support represented a crucial step in the recovery of the constellation. Eventually, Iridium Satellites was able to increase its business - and the prospects of profitability improved considerably over the years.

• On Feb. 12, 2001, 5 Iridium spare satellites were launched on a Boeing Delta-7920 vehicle to replenish the defunct satellites in the Iridium constellation. If nothing else, it reminded people in the industry that the Iridium system remained in operation and that its new owner, Iridium Satellite LLC, was doing well enough financially to be able to build and launch additional satellites.

• In October 2001, Iridium Satellite LLC announced that it has submitted a preliminary proposal to the FAA (Federal Aviation Administration) and other appropriate government organizations for a real-time cockpit voice and flight data monitoring capability utilizing its constellation of 66 low earth orbit satellites. The service, which would address national security concerns relating to aircraft safety and control, could be deployed quickly using commercial off-the-shelf components and the Iridium system. 17)

• Already in 2007, Iridium Satellite LLC, a wholly owned subsidiary of ICI (Iridium Communications Inc.), announced its plans to develop its Iridium NEXT constellation and start deployment in the timeframe 2015-2017. Iridium NEXT will be an IP-based, broadband network taking into consideration the latest satellite and wireless technologies available to support powerful new devices and services for commercial and government users. With the announced came the offer of hosted payloads for government and scientific organizations. 18) 19) 20)

The new Iridium NEXT constellation will consist of 66 cross-linked LEO satellites in six orbital planes intersecting over the North and South Poles. Iridium NEXT will have extensive built-in redundancy in the space and ground segment, with multiple backup spare satellites in orbit, and backup gateway and command and control facilities, ensuring a high degree of network survivability and resiliency. 21) 22)

• On Feb. 10, 2009, an inactive Russian military communications satellite (Cosmos 2251, 900 kg, launch June 16, 1993) collided with an active US communications satellite owned by the Iridium company (Iridium 33, 680 kg, launch Sept. 14, 1997). The incidence occurred at an altitude of ~780 km, a rather frequented orbit of many LEO spacecraft. The Iridium satellite, which was operational at the time of the collision, was destroyed, as was Cosmos-2251. The resulting debris field added to the already vast quantity of space junk in LEO. NASA reported that a large amount of debris was produced by the collision. 23) 24)

Although this event had minimal impact on Iridium's service, the company was taking immediate action to address the loss. Within 30 days, the company was able to move one of its in-orbit spare satellites into the network constellation to replace the lost satellite.

• In 2010, the Company's customers represent a broad spectrum of industry, including maritime, aeronautical, government/defense, public safety, utilities, oil/gas, mining, forestry, heavy equipment and transportation. 25)

The Iridium Communications Constellation is the world's largest and most sophisticated commercial satellite network providing global communications on the move – people, vehicles, aircraft, assets. Iridium is licensed for operations in over 133 countries and has over 200 distribution and solutions partners worldwide.


The original Iridium constellation of 66 satellites plus 6 spares was launched between May 5, 1997 and May 17, 1998 (a record launch service of spacecraft within a tineframe of one year and 12 days without any launch failures).

Orbit: Polar near-circular orbits, altitude of 780 km, inclination of 86.4º (prograde orbit), with 11 satellites plus a spare in each of the 6 orbital planes (the orbital planes are spaced 30º apart).

Figure 4: Illustration of an Iridium satellite in deployed on-orbit configuration (image credit: ICI)
Figure 4: Illustration of an Iridium satellite in deployed on-orbit configuration (image credit: ICI)

The Iridium minisatellites were manufactured by Motorola (Lockheed Martin designed and constructed the satellite bus). Each satellite has a mass of ~680 kg, 400 W of RF power, and dimensions of ~1.07 m side length x 4.3 m in length. The design life is 5 years.

Boeing's O&M (Operations and Maintenance) team is located at SNOC (Satellite Network Operations Center) in Leesburg, VA. All basic mission functions necessary to maintain network availability are provided at SNOC. 26)

Figure 5: Schematic view of the diistribution of satellites in the Iridium constellation (image credit: ICI)
Figure 5: Schematic view of the diistribution of satellites in the Iridium constellation (image credit: ICI)


1) “APL-Led Team Demonstrates Space Weather Observation System,” JHU/APL, August 18, 2010, URL:

2) B. J. Anderson, K. Rock, L. P. Dyrud, H. Korth, C. L. Waters, D. L. Green, R. J. Barnes, “AMPERE,” 2010 Fall AGU Meeting, Dec, 14, 2010, SM21C-01, URL:

3) Brian J. Anderson, Kazue Takahashi, Bruce A. Toth, “Sensing Global Birkeland currents with Iridium engineering magnetometer data,” Geophysical Research Letters, Vol. 27, No 24, December 15, 2000, pp. 4045-4048, URL:

4) AMPERE Fact Sheet, URL:

5) “APL-Led Team Wins NSF Grant to Develop New Observatory for Earth's Space Environment,” APL, July 21, 2008, URL:

6) “AMPERE Brings The 'Biggies' Together Predicting Space Weather Effects (Satellite),” Satnews Daily, August 18, 2010, URL:


8) “AMPERE A Real-Life Example of Iridium NEXT’s Hosted Payload Potential,” Feature Story of iridium everywhere, Volume V, Issue 3, November 2010, pp.4-6, URL:

9) “APL-led team demonstrates space weather observation system,” The JHU Gazette, Aug. 30 , 2010, URL:

10) Kit Eaton, “Real-Time Space Weather Forecasting Now Possible, Innovation Front Sweeping in From the Far North,” Fast Company, Aug. 18, 2010, URL:

11) “Iridium merges science with communications mission,” Spaceflight Now, Aug. 18, 2010, URL:

12) “The National Science Foundation, Johns Hopkins Applied Physics Lab, Boeing and Iridium Successfully Demonstrate Space Weather Observation (Multimedia Release) ,” Aug. 18, 2010, URL:


14) “Communications Satellite Constellations,” MIT Industry Systems Study, Unit 1: “Technical Success and Economic Failure,” Version 1.1, October 14, 2003, URL:


16) “Iridium satellite system purchased by new firm,” Spaceflight Now, Nov. 15, 2000, URL:

17) “Iridium Satellite Proposes Real-Time Cockpit Voice and Flight Data Monitoring to Federal Aviation Administration,” SpaceRef, Oct. 2, 2001, URL:

18) Matt Desch, “The View From Iridium Satellite,” SatMagazine, Dec. 2007, URL:

19) “Hosted Payloads: Iridium NEXT;” URL:

20) Don Thoma, Om Gupta, “Iridium NEXT GPS Radio Occultation Hosted Payload Opportunity,” GNSS Radio Occultation Workshop, Pasadena, CA, USA, April 7-9, 2009, URL:

21) “Iridium Reports Progress on 'Iridium NEXT' Hosted Payloads Initiative,” Nov. 19, 2009, URL:

22) Mike Guest, Chris Chaloner, “Long Term Measurement of the Earth's Radiation Budget using a constellation of Broadband Radiometers hosted on Iridium NEXT,” Proceedings of the 61st IAC (International Astronautical Congress), Prague, Czech Republic, Sept. 27-Oct. 1, 2010, IAC-10.B1.2.4

23) “Satellite collision threatens space assets,” Spacemart, Feb. 12, 2009, URL:

24) N. Atkinson, “Images, Video, Interactive Tools Provide Insight into Satellite Collision Universe Today,” Feb. 12, 2009, URL:

25) “Year in Rview .... Iridium,” SatMagazine, Dec. 2010, URL:

26) “Who's Watching Iridium's Network?”, Iridium Satellite LLC, 2006, URL:

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (