Where does IBEX orbit?

IBEX’s first few oval orbits
IBEX’s first few oval orbits (left) and new predicted orbits over the next decade (right).  Image Credits: Applied Defense Solutions

IBEX orbits Earth. In June 2011, IBEX concluded a maneuver that placed it into a new orbital configuration, represented by the image to the left. The farthest point of IBEX’s orbit is still around 200,000 miles (320,000 kilometers) from Earth. The closest point of IBEX’s orbit is now about 30,000 miles (48,000 kilometers) from Earth, above the harsh environment of Earth’s radiation belts. IBEX completes one of these orbital "lobes" in 9.1 days, and completes three orbits every 27.3 days, which is the same amount of time for the Moon to orbit Earth once. The benefit of this new orbit is that the spacecraft’s orbit is incredibly stable and is not affected by the Moon’s gravitational pull, as it was to a large extent prior to the maneuver.

The images above show renderings of the IBEX spacecraft’s orbit, just after launch in 2008 (left) and after IBEX’s orbital maneuver in June 2011 (right). Each of these orbit plots shows IBEX’s orbit with respect to the Moon’s orbit, which is the white circle surrounding the green petal–shaped lobes. Earth is in the middle of each image. The white line connecting Earth and the Moon serves to give you a better visual sense of the Moon's location in the image. In each image, the Moon's location is "fixed," meaning that the Moon’s location is held in one place (even though in reality, the Moon revolves around the Earth), which gives us a chance to plot IBEX’s position with respect to the Moon. In the left–side image, you can see that IBEX’s orbital path sometimes carried it closer to the Moon’s location and sometimes it was farther away. Because of this, the Moon’s gravitational pull on IBEX would cause the spacecraft’s position to change by different amounts, which introduced a lot of uncertainty into future orbital predictions. After IBEX’s orbit maneuver, its orbital path is a lot more stable, as shown by orbital paths that do not vary much. In fact, IBEX’s orbit is so stable, we are confident that it will not need a major maneuver for several decades.

IBEX completes an orbital lobe in 9.1 days, and it completes one entire three–lobed orbit every 27.3 days. This is the first time this particular orbit has been used by a NASA spacecraft. Periodically during each orbit, the spacecraft uses antennae that are attached to the outside of the spacecraft to send radio signals to receivers on Earth. Due to the rotation of the Earth each day and IBEX’s movement through space, the IBEX team needs a global network of receivers so that, no matter how the satellite and Earth are lined up, there is a receiver available to accept the signal. IBEX is never far from Earth, so it takes a second or less for signals to travel between IBEX and Earth. 

IBEX communications are slow, but they do not need to be on par with DSL connections on Earth. Communication from the satellite to the ground is 320,000 bits of information per second, and from the ground to the satellite is only 2,000 bits per second. Compare this to a typical home cable modem connection, where the download speed is often 6 million bits per second, and the upload speed is about 500,000 bits per second! IBEX does not need a high–speed connection, though, since it does not need to transmit a vast amount of information to Earth, just information on the particles it collects. Once on Earth, the signal is sent to the IBEX Mission Control Center in Dulles, Virginia.

Systems on the ground to support the IBEX mission consist of the Mission Control Center (MCC) at Northrop Grumman Dulles, VA facility, Swedish Space Corporation (SSC) ground stations and the IBEX Science Operations Center (ISOC) located at the University of New Hampshire in Durham, NH. The ISOC is responsible for evaluating mission data, monitoring payload performance, and delivering IBEX data products. It plans the operations and generates the detailed science and engineering schedule. The ISOC processes all mission science and science instrument calibration data, distributes science data to the IBEX team, makes data continuously available to the public through a web interface to an database, and prepares and releases the IBEX science archive to the National Space Science Data Center (NSSDC) .