International Cometary Explorer

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Operator NASA, ESA
Mission type ISEE-3: Earth/Moon L1 orbiter
ICE: 21P/G-Z & Halley fly-by
Launch date August 12, 1978
Launch vehicle Delta 2914
Satellite of Sun
COSPAR ID 1978-079A
Mass 390 kg (860 lb)
Orbital elements
Eccentricity 0.05
Inclination 0.1°
Apoapsis 1.03 AU
Periapsis 0.93 AU
Orbital period 355 d

The International Cometary Explorer (ICE) spacecraft (designed and launched as the International Sun/Earth Explorer 3 (ISEE-3) satellite), was launched August 12, 1978, into a heliocentric orbit. It was one of the three spacecraft, along with a mother/daughter pair (ISEE-1 and ISEE-2), of the ISEE (International Sun-Earth Explorer) international cooperative program between NASA and ESRO/ESA to study the interaction between the Earth's magnetic field and the solar wind.

ISEE-3 was the first spacecraft to be placed in a halo orbit at one of Earth-Sun Lagrangian points (L1). Renamed ICE, it became the first spacecraft to visit a comet, passing through the tail of Comet Giacobini-Zinner within about 7,800 km (4,800 mi) of the nucleus.[1]

NASA suspended routine contact with ISEE-3 in 1997, and made brief status checks in 1999 and 2008.[2][3]

On May 29, 2014, two-way communication with the spacecraft was reestablished by the ISEE-3 Reboot Project, an unofficial group[4] with support from the Skycorp company.[5][6][7] On July 2, 2014, they successfully fired the thrusters for the first time since 1987. However, later firings of the thrusters failed. The cause currently under investigation, was originally believed to be a lack of nitrogen pressurant in the fuel tanks: this has now been proven not to be the case.[8] The team is continuing to work the thruster issue before the craft reaches a point where the remaining fuel will not be sufficient to meaningfully alter its course. According to the project team, an alternative plan in the use of the spacecraft is to "collect scientific data and send it back to Earth."[9]

Original mission: International Sun/Earth Explorer 3 (ISEE-3)[edit]

ICE mission

ISEE-3 carries no cameras; instead, its instruments measure energetic particles, waves, plasmas, and fields.

ISEE-3 originally operated in a halo orbit about the L1 Sun-Earth Lagrangian point, 235 Earth radii above the surface (about 1.5 million km, or 924,000 miles). It was the first artificial object placed at a so-called "libration point", proving that such a suspension between gravitational fields was possible. It rotates at 19.76 rpm about an axis perpendicular to the ecliptic, to keep it oriented for its experiments, to generate solar power and to communicate with Earth.

The purposes of the mission were:

  • to investigate solar-terrestrial relationships at the outermost boundaries of the Earth's magnetosphere;
  • to examine in detail the structure of the solar wind near the Earth and the shock wave that forms the interface between the solar wind and Earth's magnetosphere;
  • to investigate motions of and mechanisms operating in the plasma sheets; and,
  • to continue the investigation of cosmic rays and solar flare emissions in the interplanetary region near 1 AU.

Second mission: International Cometary Explorer[edit]

On June 10, 1982, after completing its original mission, ISEE-3 was renamed the International Cometary Explorer (ICE) and given a new mission: to study the interaction between the solar wind and a cometary atmosphere. On September 1 of that year, a thruster burn was used to knock it loose from its halo orbit, and the craft then used the instability of the Earth/Moon and Earth/Sun Lagrange points to make a series of lunar orbits over the next 15 months. Its last and closest pass over the Moon, on December 22, 1983, was a mere 119.4 km (74 mi) above the Moon's surface. By the beginning of 1984, ICE was in heliocentric orbit.

Giacobini-Zinner encounter[edit]

Its new orbit put it ahead of the Earth on a trajectory to intercept Comet Giacobini-Zinner. On September 11, 1985, the craft passed through the comet's plasma tail.

Halley encounter[edit]

Top-down view of the orbit of ISEE-3 (ICE) relative to the inner solar system in and after 2009.

ICE transited between the Sun and Comet Halley in late March 1986, when other spacecraft were near the comet on their early-March comet rendezvous missions. (This "Halley Armada" included Giotto, Vega 1 and 2, Suisei and Sakigake.) ICE flew through the tail; its minimum distance to the comet nucleus was 28 million km[10] (for comparison, the Earth's minimum distance to Comet Halley in 1910 was 20.8 million km[11]).

Heliospheric mission[edit]

An update to the ICE mission was approved by NASA in 1991. It defines a heliospheric mission for ICE consisting of investigations of coronal mass ejections in coordination with ground-based observations, continued cosmic ray studies, and the Ulysses probe. By May 1995, ICE was being operated under a low duty cycle, with some data-analysis support from the Ulysses project.

End of mission[edit]

On May 5, 1997, NASA ended the ICE mission, leaving only a carrier signal operating. The ISEE-3/ICE downlink bit rate was nominally 2048 bits per second during the early part of the mission, and 1024 bit/s during the Giacobini-Zinner comet encounter. The bit rate then successively dropped to 512 bit/s (on December 9, 1985), 256 bit/s (on January 5, 1987), 128 bit/s (on January 24, 1989) and finally to 64 bit/s (on December 27, 1991). Though still in space, NASA donated the craft to the Smithsonian Museum.[12]

By January 1990, ICE was in a 355-day heliocentric orbit with an aphelion of 1.03 AU, a perihelion of 0.93 AU and an inclination of 0.1 degree.

Further contact[edit]

In 1999, NASA made brief contact with ICE to verify its carrier signal.

On September 18, 2008, NASA, with the help of KinetX, located ICE using the Deep Space Network after discovering that it had not been powered off after the 1999 contact. A status check revealed that all but one of its 13 experiments were still functioning, and it still had enough propellant for 150 m/s (490 ft/s) of Δv.

It was determined to be possible to reactivate the spacecraft in 2014,[13] when it again made a close approach to Earth. NASA scientists may attempt to reuse the probe to observe more comets in 2017 or 2018.[14]

Reboot effort[edit]

International Sun Earth Explorers Orbits

Sometime after NASA's interest in the ICE waned, others realized that the spacecraft might be steered to pass close to another comet. A team of engineers, programmers, and scientists began to study the feasibility and challenges involved.[7]

In April 2014, its members formally announced their intentions to "recapture" the spacecraft for use, calling the effort the ISEE-3 Reboot Project. A team webpage said, "We intend to contact the ISEE-3 (International Sun-Earth Explorer) spacecraft, command it to fire its engine and enter an orbit near Earth, and then resume its original mission...If we are successful we intend to facilitate the sharing and interpretation of all of the new data ISEE-3 sends back via crowd sourcing."[15]

On May 15, 2014, the project reached its crowdfunding goal of US$125,000, which will cover the costs of writing the software to communicate with the probe, searching through the NASA archives for the information needed to control the spacecraft, and buying time on the dish antennas.[16] The project then set a "stretch goal" of $150,000, which it also met with a final total of $159,502 raised.[17]

The project members are working on deadline: if they get the spacecraft to change its orbit by late May or early June 2014, or in early July by using more fuel, it can use the Moon's gravity to get back into a useful halo orbit. If not, the spacecraft will, for all practical purposes, be lost.[18][19][20]

Earlier in 2014, officials with the Goddard Space Flight Center said the Deep Space Network equipment necessary to transmit signals to the spacecraft had been decommissioned in 1999, and was too expensive to replace.[21] However, project members obtained the needed hardware (power amplifier, modulator/demodulator[22]), and installed it on the 305-meter Arecibo dish antenna on May 19, 2014.[22][23] Following successfully gaining control of the spacecraft, the capture team plans to transition the primary ground station to the 21-meter dish located at Kentucky's Morehead State University Space Science Center.[22] The 20-meter dish antenna in Bochum Observatory, Germany, would be a support station.[22]

Although NASA is not funding the project, it made advisors available and gave approval to try to establish contact. On May 21, 2014, NASA announced that it had signed a Non-Reimbursable Space Act Agreement with the ISEE-3 Reboot Project. "This is the first time NASA has worked such an agreement for use of a spacecraft the agency is no longer using or ever planned to use again," officials said.[24]

On May 29, 2014, the reboot team commanded the probe to switch into Engineering Mode to begin to broadcast telemetry.[25][26]

On June 26, 2014, project members using the Goldstone Deep Space Communications Complex DSS-24 antenna achieved synchronous communication and obtained the four ranging points needed to refine the spacecraft's orbital parameters.[27] The project team received approval from NASA to continue operations through at least July 16, and plan to attempt the orbital maneuver in early July.[19][28]

On July 2, 2014, the reboot project successfully fired the thrusters for the first time since 1987. They spun up the spacecraft to its nominal roll rate, in preparation for the upcoming trajectory correction maneuver in mid-July.[29][30]

On July 8, 2014, a longer sequence of thrusters firings failed, the cause currently under investigation, was originally believed to be a lack of nitrogen pressurant in the fuel tanks: this has now been proven not to be the case.[8] The team continues to work the issue, and according to the project team an alternative plan for the spacecraft is being considered. There is also a possibility that ISEE-3 is now on course to crash into the moon in August 2014, providing some scientific data.[9]

Spacecraft design[edit]

The ISEE-3, (later ICE), undergoing testing and evaluation.

The ICE spacecraft is a barrel-like cylindrical shape covered by solar panels. Four long antennas protrude equidistant around the circumference of the spacecraft, spanning 91 metres (299 ft).[31] It has a mass of 390 kg (860 lb) and can generate a nominal power of 173 watts.


ICE carries 13 scientific instruments to measure plasmas, energetic particles, waves, and fields. As of May 2014, all but one are thought to be functional. It does not carry a camera or imaging system. Its detectors measure high energy particles such as X and gamma rays, solar wind, plasma and cosmic particles. A data handling system gathers the scientific and engineering data from all systems in the spacecraft and formats them into a serial stream for transmission. The transmitter output power is five watts.

Scientific payload and experiments[32][edit]

  • Solar wind plasma detector, failed after February 26, 1980
  • Vector Helium Magnetometer
  • Low-Energy Cosmic Rays, designed to measure solar, interplanetary, and magnetospheric energetic ions
  • Medium Energy Cosmic Rays, 1-500 MeV/n, Z = 1-28; Electrons: 2-10 MeV
  • High-Energy Cosmic Rays, H to Ni, 20-500 MeV/n
  • Cosmic-Ray Energy Spectrum charged-particle telescope
  • Plasma Waves Spectrum Analyzer
  • Energetic Particle Anisotropy Spectrometer (EPAS), designed to study low-energy solar proton acceleration and propagation processes in interplanetary space
  • Interplanetary and Solar Electrons 2 keV to > 1 MeV
  • Radio Mapping of Solar Wind Disturbances (Type III bursts) in 3-D; 30 kHz - 2 MHz, to map the trajectories of type III solar bursts
  • Solar Wind Ion Composition, a hemispherical electrostatic energy analyzer
  • Cosmic Ray Isotope Spectrometer, designed to study the isotopic constitution of solar matter and galactic cosmic-ray sources
  • X- and Gamma-Ray Bursts, to provide continuous coverage of solar-flare X rays and transient cosmic gamma-ray bursts
  • Gamma-Ray Bursts, designed to recognize and record the time history of gamma-ray bursts, and to provide high-resolution spectra of gamma-ray burst photons



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  2. ^ Robertson, Adi (May 23, 2014). "Spaceship come home: can citizen scientists rescue an abandoned space probe?". The Verge. Retrieved June 26, 2014. 
  3. ^ McKinnon, Mika (April 15, 2014). "Can This 1970s Spacecraft Explore Again?". Retrieved June 26, 2014. 
  4. ^ "We do NOT like...". June 25, 2014. Retrieved June 25, 2014. 
  5. ^ Geuss, Megan (May 29, 2014). "ISEE-3 spacecraft makes first Earth contact in 16 years". Ars Technica. Retrieved May 31, 2014. 
  6. ^ Matheson, Dan (May 2014). "Citizen-scientists look to reboot 35-year-old spacecraft". CTV News. Retrieved May 31, 2014. 
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  8. ^ a b McKinnon, Mika (July 10, 2014). "Distributed Rocket Science is a Thing Now - ISEE-3 Status Report (July 10, 2014)". ISEE-3 Reboot Project. Retrieved July 12, 2014. 
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  10. ^ Murdin, Paul, ed. (November 2000). "International Cometary Explorer (ICE)". Encyclopedia of Astronomy and Astrophysics. IOP Science. Bibcode:2000eaa..bookE4650.. doi:10.1888/0333750888/4650. 
  11. ^ Reddy, Francis. How bright will it be?. "Comets". Archived from the original on June 7, 2010. 
  12. ^ Thomson, Iain (April 24, 2014). "Privateers race to capture forgotten NASA space probe using crowdsourced cash". The Register. Retrieved May 20, 2014. 
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  14. ^ Lakdawalla, Emily (October 3, 2008). "It's Alive!". The Planetary Society. 
  15. ^ Cowing, Keith (April 14, 2014). "ISEE-3 Reboot Project (IRP)". Space College. 
  16. ^ Cowing, Keith (May 15, 2014). "ISEE-3 Reboot Project Passes Funding Goal". Space College. 
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  32. ^ "ISEE 3: Experiment Search Results". NASA. 

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