An Overview of Active Space Telescopes (as of December 6th, 2024)
The Hubble Space Telescope in pre-deployment next to the Space Shuttle Discover (Courtesy of NASA)
“As when by night the glass of Galileo, less assured, observes imagined lands and regions in the moon”
***Originally written on April 11th, 2023, this post is inherently a snapshot in time. But time permitting, I will try to keep the list updated on as much as I can, thank you!***
In 2022, scientists and researchers around the world were completely put in awe by the images that were captured by the newly-deployed James Webb Space Telescope—“JWST” for short. While the JWST was frequently maligned for many delays and cost overruns during its development and kept everyone on the edge of their seats during its deployment, this anointed successor to the Hubble Space Telescope now appears to be a resounding success. In its first year of operation, the JWST has already produced some of the finest pictures of the universe that we have ever seen.
But the infrared-detecting JWST is not the only space telescope currently in operation. In Outer Space, there are several active telescopes monitoring signals from other segments of the electromagnetic spectrum as well. Working together, these space telescopes can give astronomers, scientists, and researchers a more complete picture of the cosmos that surrounds us.
Because of these telescopes’ importance to our understanding of the universe, this post is dedicated to providing an overview of these unsung heroes in Outer Space. I will start by providing a list of currently-active space telescopes along with key facts about each. Then, I will describe the different types of frequencies these telescopes are designed to detect. Finally, I will conclude with a brief primer as well as a link to the site containing, in my opinion, the most comprehensive information on each of these telescopes for your further exploration.
Before starting, it is worth noting that this overview keys in on space telescopes for the electromagnetic spectrum. Thus, I did not include any satellites that are focused solely on particle detection. But for the sake of completeness, I did touch upon gravitational wave detection in the frequencies overview section.
Currently-Active Space Telescopes
As of the date indicated above, the list below contains all of the currently-active space telescopes—by alphabetic order—that I found through my own research. Most of the links in the table will take you to the section of this post covering that telescope or frequency spectrum in question. The location links will take you to the relevant section in my previous post on common orbits and prominent locations around Earth.
NOTE: As these space telescopes move past their end-of-life/conclude their missions, I will gray them out in the chart and add in a footnote below about their end of life date.
[1] Mission concluded as of January 18, 2024 | Re-entry date of February 14, 2024
Different Frequencies of Detection
Before providing a brief primer on each of these space telescopes, I will first provide a quick overview of the different frequencies that these telescopes tend to focus on (no pun intended).
Gamma Rays
With waves of 0.1 angstrom or smaller, gamma rays are at the highest energy end of the electromagnetic spectrum. Because Earth’s atmosphere blocks most of the gamma rays that originate in Outer Space, space telescopes are essential to the detection of these signals. Specialized instruments are also needed for this collection process because gamma rays would, otherwise, just slip right through the lens of a standard optical telescope. In Outer Space, gamma rays are primarily generated by high energy objects and events such as neutron stars, pulsars, areas around black holes, and supernova explosions. By observing these gamma ray signatures, scientists and astronomers can determine the composition of their source.
X-Rays
After gamma rays come X-rays. With a wavelength of 10 picometers to 10 nanometers, X-rays are longer than Gamma rays and have frequencies in the range of 30 petahertz to 30 exahertz. X-ray space telescopes are important because most X-rays from Outer Space sources are absorbed by Earth’s atmosphere, so ground-based telescopes won’t be able to detect these signals. X-ray telescopes are equipped with mirrors that have very low angles of reflection because these signatures would typically pass through a standard reflection mirror. But with a low reflection angle, telescopes that are specialized for X-ray operations can bounce these waves into a collector via a technique known as grazing incidence. Outer Space objects that can produce X-ray radiation include galaxy clusters, stars, binary stars, neutron stars, and black holes.
Ultraviolet Waves
Following X-rays in the electromagnetic spectrum are ultraviolet waves, which have lengths of 10 to 320 nanometers. Ultraviolet (“UV”) waves are generally absorbed by Earth’s atmosphere as well, making space telescopes essential to fully capturing these Outer Space signals. Typically, UV waves are emitted by stars during their high-energy phases—which usually occur either around their birth or their death. Observations of these ultraviolet signals enable scientists and astronomers to study the energy composition of these stars as they progress through their most consequential phases of life.
Visible Light Waves
Visible light telescopes are the ones that we are most familiar with. Covering wavelengths of approximately 380 to 750 nanometers, visible light waves from Outer Space have been studied since time immemorial as all you need is your eyes and a clear night sky. However, this stargazing technique has improved through the centuries especially after the invention of the telescope. While the German-Dutch spectacle maker Hans Lippershey is largely credited with the invention of optical telescopes, Galileo Galilei made significant contributions to this invention by making a version that can magnify images by 30x. Known more commonly as a spyglass, the Galilean telescope proved to the world that these magnifiers are extremely useful for nighttime observations of the sky. Because Earth’s atmosphere can distort the quality of the resulting telescopic image, visible light space telescopes represented another giant step forward for astronomy. With these telescopes in operations, pictures of higher quality can be produced and more visible light wavelengths can be captured.
Infrared and Submillimeter Waves
After we get past the visible light section, the electromagnetic spectrum enters into the realm of infrared waves—which cover a span of 0.75 to 300 micrometers—and submillimeter waves—which are generally a few hundred micrometers to a millimeter long. These types of signals are emitted by objects that are slightly cooler in temperature. Additionally, while visible light can be scattered by cosmic dust, infrared and submillimeter radiation can pass through these regions of the universe relatively unchanged. Thus, scientists can get more information about the emitting object by analyzing their wave signatures. The compiled infrared images that result are generally more detailed and vibrant as well (such as this one of the Horsehead Nebula).
Microwave
After infrared and submillimeter waves come microwaves, which have frequencies of 3x10¹¹ hertz to 3x10¹³ hertz and a wavelength of 25 micrometer to 1 millimeter. Microwave telescopes serve an important role in helping scientists to study and understand the Cosmic Microwave Background (“CMB”). Discovered by chance in 1965, CMB describes all of the background microwave radiation that fills the void of Outer Space. While these waves initially existed as gamma rays during the Big Bang, they have since cooled to the microwave range. Thus, studying microwave signals allow scientists to piece together the history of the universe by gleaning additional information about how it was first formed. Because Earth’s atmosphere blocks out some microwaves, space telescopes that are capable of collecting microwaves enable researchers to complete their understanding of Outer Space.
Radio Waves
Next to microwaves, radio waves—with wavelengths greater than 1 millimeter—round out the electromagnetic spectrum. While radio waves are not blocked by Earth’s atmosphere, having space telescopes that can detect radio waves is important for a technique called “interferometry.” Through interferometry, two space telescopes can work together to create an image that a single telescope could only produce if the latter’s size is the same as the distance between the two telescopes working together. Thus, scientists can chain together space telescopes to compile images that would have otherwise taken an Earth-sized telescope to capture. With these telescopes, astronomers have studied signals from a diverse cast of objects in Outer Space including stars, galaxies, and black holes.
Gravitational Waves
Apart from telescopes observing the electromagnetic spectrum, there are also space telescopes designed to detect gravitational waves. First predicted by Einstein in his theory of general relativity, gravitational waves are fast moving (i.e., at lightspeed) ripples in the space-time continuum. These waves are generally produced by collision among objects of excessive mass such as black holes or neutron stars. Studying these waves enable scientists to obtain more information about the celestial origins of these waves as well as characteristics of gravity itself. While there are currently no active space telescopes in operation to detect gravitational waves, the European Space Agency is taking the lead in crafting one such detector-system for launch in the 2030s. Named Laser Interferometer Space Antenna (or LISA for short), this system will compose of three spacecrafts beaming lasers back and forth among each other to detect these fast-moving waves.
A Brief Overview of Currently-Active Telescopes
Now that I have explained the common frequencies and waves that these space telescopes are designed to detect, below are some key facts, by alphabetic order, on each of the currently-active space telescopes. For each space telescope, I also provided a link to, what I found to be, the best source of online knowledge to help the further curious to explore.
AGILE: Astrorivelatore Gamma a Immagini Leggero
Best source for comprehensive information: Space Science Data Center’s AGILE Page
The Astrorivelatore Gamma a Immagini Leggero, AGILE, is a gamma-ray space observatory ran by the Italian Space Agency. Launched on April 23, 2007, AGILE has already surpassed its original two- to four-year mission life by quite a bit! With a total mass of about 300 to 330 kilogram, AGILE operates in Low Earth Orbit at around 550 km above mean sea level. With an inclination of 0 to 6 degrees, it orbits Earth pretty much directly above the latter’s equator. AGILE is also one of the first new generation of space telescopes that has both a gamma-ray and a hard X-ray detector, enabling AGILE to simultaneously combine data from both segments of the spectrum.
AstroSat
Best source for comprehensive information: Indian Space Research Organization’s AstroSat Page
As the first fully-fledged multi-wavelength space telescope developed by India, AstroSat was launched on September 28, 2015 from the Satish Dhawan Space Center. This space telescope was placed in a six-degree inclined low Earth orbit with an altitude of 650 km above mean sea level. In its first year of operation, AstroSat made more than 5,400 orbits around Earth and collected 343 sets of data about 141 different cosmic areas of interest. Exceeding its planned mission life of five years, AstroSat is still going strong today.
Bright Target Explorer Constellation (BRITE)
Best source for comprehensive information: eoPortal’s BRITE site for Austria, Canada, and Poland
A series of six nanosatellites, the Bright Target Explorer Constellation—or BRITE—is a joint optical space telescope project operated by Austria, Canada, and Poland. A truly international effort, between February 25, 2013 to August 19, 2014, it took four launches via the space agencies of China, India, and Russia to fully deploy the BRITE constellation into low Earth orbit. However, only five became operational with one (BRITE-Montreal) failing to deploy. These nanosatellites currently occupy a sun-synchronous orbit at an inclination of approximately 98 degrees with an altitude of about 600 km to 900 km. Having surpassed its expected mission life of two years, the BRITE constellation is still working on its primary objective today: collecting photometry (light intensity) data on hundreds of bright stars in the universe.
Chandra X-Ray Observatory
Best source for comprehensive information: NASA’s Chandra X-ray Observatory Page
The Chandra is NASA’s flagship X-ray space telescope and is a member of NASA’s Great Observatories in Outer Space. Launched and inserted into high Earth orbit by Space Shuttle Columbia on July 23, 1999, the Chandra follows a highly elliptical orbit that can take the satellite anywhere from an altitude of 9,650 km to 140,000 km (or 1/3 of the way to the Moon) above mean sea level. During this 64-hour orbit, Chandra can take observations for 55 continuous hours. Named after the Nobel Prize laureate, Dr. Subrahmanyan Chandrasekhar, this space telescope played an instrumental part in the discovery of the massive super blackhole at the center of our galaxy.
CHaracterizing ExOPlanet Satellite (CHEOPS)
Best source for comprehensive information: University of Bern’s CHEOPS Site
CHEOPS, an acronym for CHaracterizing ExOPlanet Satellite, is the first space telescope devoted to studying transits through ultrahigh precision photometry. This light intensity measurement process is done on star systems that are known to have exoplanets. Launched on December 18, 2019, CHEOPS has already achieved its original 3.5-year mission goal after starting operations on April 4, 2020. Sitting in a Sun-Synchronous Low Earth Orbit at an altitude of 700 km, CHEOPS contains a single telescope that is based on a Ritchey-Chretien design. With this telescope, CHEOPS is able to study the structure of and gather mass-radius data for exoplanets that have radii one to six times that of Earth.
Dark Matter Particle Explorer (DAMPE) / WuKong (悟空)
Best source for comprehensive information: Spaceflight 101’s DAMPE/Wukong Page
Launched on December 17, 2015, Dark Matter Particle Explorer (DAMPE) or WuKong (悟空)—nicknamed after the protagonist, Monkey King, from the famous Chinese fable “Journey to the West”—is a space telescope ran by the Chinese Academy of Science and the Chinese National Space Administration. One of the goals of this satellite is to observe high-energy gamma rays emitted from Outer Space. DAMPE/WuKong can also gather information on the direction, energy, and electric charge of extremely high-energy photons and electrons caused by interactions with dark matter candidate particles. Thus, DAMPE/WuKong can capture evidence—via those photons and electrons—that would suggest dark matter’s existence. DAMPE/WuKong currently resides in a sun-synchronous low Earth orbit at an altitude of 500 km. It has an inclination of 97.4 degrees with an orbital period of 90 minutes.
Einstein Probe
Best source for comprehensive information: CNS’s Einstein Probe Page
On January 9th, 2024, the Einstein Probe was launched onboard a Long March-2C rocket from China's Xichang Satellite Launch Center. Anticipated to have a 3-year mission life (that might go up to five years), the Einstein Probe is designed to study the universe and search for cosmic variable objects and transients that produce X-ray outbursts. To do this, Einstein is equipped with two X-ray telescopes: (1) a wide-field X-ray (WXT) that has lobster-eye Micro-Pore Optics technology that allows for a wide field-of-view and (2) a Wolter-I Follow-up X-ray Telescope (FXT) that has a large effective area but a narrow field-of-view. The Einstein Probe will be located in a circular low Earth orbit at about 600 km above mean sea level with an inclination of about 29 degrees.
Euclid
Best source for comprehensive information: ESA’s Euclid Space Telescope Page
Named after the famed Greek mathematician, the Euclid space telescope was launched on July 1, 2023 onboard a SpaceX Falcon 9 from Cape Canaveral. An ESA-led mission with contributions from NASA, the Euclid space telescope is designed to study dark matter and dark energy. Residing in the Sun-Earth Lagrange Point 2, Euclid has both a visible-wavelength camera and a near-infrared camera/spectrometer. With a planned mission life of six years, Euclid is anticipated to take images that will eventually cover one-third of the extragalactic sky.
Fermi Gamma-ray Space Telescope
Best source for comprehensive information: NASA’s Fermi Gamma-ray Space Telescope Page
Formerly known as Gamma-ray Large Area Space Telescope (GLAST), the Fermi Gamma-ray Space Telescope was launched on June 11, 2008 and is now named after Professor Enrico Fermi (who is associated with the Fermi Paradox). Residing in Low Earth Orbit at around 560 km above mean sea level, the Fermi can circle the Earth in just 90 minutes. With a Large Area Telescope and a Gamma-ray Burst Monitor, Fermi is able to detect both X-rays and gamma rays. With these two instruments, Fermi became the world’s first telescope to detect a gamma-ray pulsar outside of our own Milky Way galaxy. Still operational, Fermi has exceeded its original plan mission life of five to ten years.
Gaia
Best source for comprehensive information: eoPortal’s GAIA Site
Gaia is a space telescope operated by the European Space Agency (“ESA”) that was launched on December 19, 2013. Using its two identical telescopes, Gaia’s primary goal is to create a 3D mapping and category of over 1000 million stars in the Milky Way galaxy. This would represent roughly 1% of all of the stars that exist in our home galaxy. Instead of residing near Earth, Gaia is located in Lagrangian Point 2 (L2), a location that only requires a unidirectional heat shield to block the Sun’s radiation. Far surpassing its expected mission life of five years, with the James Webb Space Telescope now operating in the same area, Gaia is currently scheduled to end its service on December 31, 2023.
Hard X-ray Modulation Telescope (Insight-HXMT)
Best source for comprehensive information: Spaceflight 101’s HXMT Page
Better known as Insight-HXMT, Hard X-ray Modulation Telescope is China’s first space-based X-ray telescope. Launched onboard a Long March 4B rocket on June 15, 2017, Insight-HXMT has three x-ray telescopes: a low-energy one covering the range of 1keV to 15keV, a medium-energy one covering the range of 5keV to 30keV, and a high-energy one covering the range of 20keV to 250keV. Insight-HXMT will operate in low Earth orbit at an altitude of 550 km above mean sea level with a 43-degree inclination. Insight-HXMT’s primary mission is to help scientists to get a better understanding of the cosmic X-ray background.
Hisaki / Spectroscopic Planet Observatory for Recognition of Interaction of Atmosphere (SPRINT-A)
Best source for comprehensive information: JAXA’s SPRINT-A Site
Hisaki Spectroscopic Planetary Observatory Satellite, or HISAKI/SPRINT-A, is the world’s first space telescope that is equipped with a far-ultraviolet spectrometer. Its primary mission is to observe other planets in our solar system to understand why those planets lost their atmosphere whereas Earth kept its. Specifically, SPRINT-A is studying the effect of strong solar winds on a planet’s atmosphere and whether such winds is able to sweep away the atmosphere that could have sustained life on those planets. SPRINT-A was launched from Uchinoura Space Center on September 14, 2013 and sits in an elliptical low Earth orbit with an inclination of 31 degrees.
Hubble Space Telescope
Best source for comprehensive information: The Hubble Site
One of the most well-known space telescopes, the Hubble Space Telescope (named after the famed astronomer Edwin Powell Hubble) has fundamentally challenged our understanding of the universe. Launched on April 24, 1990 by the Space Shuttle Discovery, the Hubble Telescope has already made over 1.5 million observations and transmits about 150 gigabits of raw data every week. Residing in low Earth orbit that has an inclination of 28.5 degrees, the Hubble, traveling at 27,000 kilometers per hour, can complete an orbit around the Earth in 95 minutes. While originally anticipated to have a 15-year mission life, the Hubble just celebrated its 30th anniversary and is expected to remain in operation until at least the late 2020s. This is quite the accomplishment for a space telescope that essentially had to have a contact lens inserted in December 1993 because the Hubble, as launched, had a flaw in its primary mirror that was significantly enough to distort its vision.
Imaging X-ray Polarimetry Explorer (IXPE)
Best source for comprehensive information: eoPortal’s IXPE Page
The Imaging X-ray Polarimetry Explorer (IXPE) allows scientists to gather more information about the polarization (directional vibrations) of high-energy X-ray radiation coming from black holes, neutron stars, and pulsars. Launched on December 9, 2021 onboard a Falcon 9 rocket, IXPE currently occupies the circular equatorial low Earth orbit at an altitude of about 600 km above mean sea level. With three x-ray telescopes, IXPE has already captured unique data on several extreme cosmic objects. Costing about $188 million, IXPE is expected to have a 2-year mission life.
Interface Region Imaging Spectrograph (IRIS)
Best source for comprehensive information: NASA’s IRIS Site
Launched on June 27, 2013, the Interface Region Imaging Spectrograph (IRIS) was delivered to Earth orbit via a Pegasus XL rocket. Expected to have a 2-year mission life, IRIS is still going strong today and orbits around Earth in a sun-synchronous orbit with an orbital period of 97 minutes. With an inclination of about 98 degrees, IRIS would pass by Earth’s two poles and resides at an altitude that is about 620 km to 670 km above mean sea level. In this orbit, IRIS has the capability to conduct eight months of continuous observations each year. The UV-detecting IRIS’s main objective is to study the Sun and further our knowledge of the interface region between the sun’s photosphere and corona.
International Gamma Ray Astrophysical Laboratory (INTEGRAL)
Best source for comprehensive information: eoPortal’s INTEGRAL Site
Operated by the European Space Agency (“ESA”), the International Gamma Ray Astrophysical Laboratory—INTEGRAL—was launched on October 17, 2002 onboard a Russian Proton rocket. Located in High Earth Orbit, the INTEGRAL space telescope is mainly designed to detect gamma-rays but is also able to sense X-rays as well as visible light waves. Even though INTEGRAL was only expected to operate for about two years, it is still going strong 20 years later. The INTEGRAL mission is now estimated to end around February 2029 when the telescope will reenter Earth as part of its natural orbit decay; in order to achieve this end, scientists have already started a series of four thrust burns that will use up half of the estimated 96 kilogram of fuel remaining.
James Webb Space Telescope
Best source for comprehensive information: The James Webb Space Telescope Site
The launch of the James Webb Space Telescope (JWST) was probably one of the most anticipated space events of this decade. Named after James Webb, NASA’s second administrator who was known for leading the Apollo Program, the JWST is widely seen as the successor to the well-regarded Hubble space telescope. But unlike the Hubble, which detects ultraviolet signals, the James Webb is designed to capture near- and mid-infrared signatures with wavelengths of 600 nm to 28,500 nm. After blasting off onboard an Ariane 5 rocket from Guiana Space Centre on Christmas Day 2021, the JWST arrived at Sun-Earth Lagrange point (L2) about a month after launch. Residing in this location will enable this space telescope to observe the galaxy without worrying about heat interference coming from the Earth and the Moon. JWST is expected to have a minimum mission life of five years but has an operational goal of ten years.
Lunar-Based Ultraviolet Telescope (LUT)
Best source for comprehensive information: Spaceflight101’s Chang’e 3 (嫦娥三号) Site
Launched as a part of Chang’e 3—China’s third lunar landing mission—the Lunar-Based Ultraviolet Telescope (“LUT”) is an ultraviolet-detecting Ritchey-Chretien telescope located on China’s first Moon lander. Situated on the lunar surface, LUT is not affected by atmospheric distortions that would plague UV observations of Outer Space taken from Earth. In addition, the LUT has an advantage over other space telescopes as it can rely on the Moon for stability and orbital movement. With the “night sky” moving 27 times slower on the Moon than on Earth, LUT can have long-durational uninterrupted observations of a target of interest. Launched on December 1, 2013, LUT’s lander had an expected mission life of one-year and is focused on studying the stellar atmosphere of variable stars, binaries, novae, quasars, and blazars.
Near Earth Object Surveillance Satellite (NEOSSat)
Best source for comprehensive information: eoPortal’s NEOSSat Site
Launched on February 25, 2013, Near Earth Object Surveillance Satellite (“NEOSSat”) is the first space telescope dedicated to observations of near-Earth asteroids and comets as well as human-made objects orbiting around Earth. NEOSSat operates in a sun-synchronous low Earth orbit with an altitude of about 786 km and an inclination of 98.55 degrees. For visible light observations, the NEOSSat contains a f/6 Rumak-Maksutov Cassegrain telescope that has an aperture of 15 cm. Although NEOSSat had some early challenges, it has far surpassed its original planned 2-year mission life.
Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE)
Best source for comprehensive information: UCLA’s WISE/NEOWISE Site
The Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) was first known just as WISE when it was launched from Vandenberg Air Force Base on December 14, 2009. The original WISE mission was to perform a sky survey using its infrared detectors. To achieve this objective, WISE contains a telescope with a 40-cm (16-inch) diameter aperture that can scan broad range of the universe at infrared wavelengths of 3.4 microns, 4.6 microns, 12 microns, and 22 microns. WISE then could output images with spatial resolutions that are about six arcseconds—distinguishing characteristics that are 1/600th of a degree apart—in the 3.4-micron, 4.6-micron, and 12-micron bands and 12 arcseconds—distinguishing characteristics that are 1/300th of a degree apart—at the 22-micron band. WISE’s original mission lasted for ten months and the satellite was decommissioned in February 2011 after achieving its primary objective. However, in September 2013, WISE was reactivated as NEOWISE with a new mission of searching and characterizing near-Earth objects (NEOs) as well as potentially hazardous objects (PHOs)—a subcategory of NEOs that have trajectories that could impact Earth. It currently sits in Low Earth Orbit at about 500 km above mean sea level.
Neil Gehrels Swift Observatory / Swift Gamma Ray Burst Explorer
Best comprehensive source for information: NASA’s Neil Gehrels Swift Observatory Site
The Swift Gamma Ray Burst Explorer is operated by NASA and is primarily dedicated to the study of gamma-ray bursts. Renamed the Neil Gehrels Swift Observatory in January 2018 in honor of its former principle investigator who passed away in 2017, this observatory can detect up to 100 gamma ray bursts a year. Alongside gamma rays, the Gehrels Observatory is also able to detect X-rays, ultraviolet waves, and optical waves as well. Swift was launched into Low Earth Orbit on November 20, 2004 onboard a Delta 2 rocket. Weighing about 1,470 kilograms, the Neil Gehrels Swift Observatory originally had a mission life of two years but is still in operation today.
Neutron Star Interior Composition Explorer (NICER)
Best source for comprehensive information: NASA’s NICER Page
Launched by SpaceX onboard its Falcon 9 rocket on June 3, 2017, the Neutron Star Interior Composition Explorer (“NICER”) is a space telescope that resides on the International Space Station. As its name suggests, NICER is devoted to the study of neutron stars. NICER conducts these studies through its timing instrument that can gather X-rays over a 30 arcmin² region of the sky. Its original mission life was planned to be 24 months (18 months for its primary mission and 6 additional months as a part of the Guest Observer program).
Nuclear Spectroscopic Telescope Array (NuSTAR)
Best source for comprehensive information: CalTech’s NuSTAR Page
Launched on June 13, 2012 via a Pegasus XL rocket, the Nuclear Spectroscopic Telescope Array (“NuSTAR”) was the first space telescope capable of focusing light in the high energy X-ray segment of the electromagnetic spectrum. Long past its original two-year mission life, NuSTAR currently orbits around the equatorial parts of the Earth via a six-degree inclination low Earth orbit that is about 600 km above mean sea level. NuSTAR stays near Earth’s equator because it would allow this space telescope to avoid the South Atlantic Anomaly (“SAA”), a region centered around the southern Atlantic Ocean where Earth’s inner Van Allen belt could create interference/background noise that is similar to the cosmic X-ray emissions that NuSTAR is designed to collect.
Odin Satellite
Best source for comprehensive information: eoPortal’s Odin Site
Designed by the Swedish Space Corporation, Odin was launched from Svobodny Cosmodrome on February 20, 2001 onboard a Russian Start-1 vehicle. Using its submillimeter wave radiometer and its optical spectrograph and infrared imaging system, Odin can conduct atmospheric studies of Earth as well as gather information about different astronomical objects of interest. With these systems, this space telescope is capable of detecting infrared wavelengths of 0.5 to 0.6 mm and microwave wavelength of 2.5 mm. Odin currently occupies a sun-synchronous orbit at an altitude of 570 km with an inclination of 97.77 degrees. As of February 2022, Odin has made over 114,000 orbits around the Earth and its operational life has far exceeded its original two-year mission life.
Project for On-Board Autonomy-3 (PROBA-3)
Best source for comprehensive information: ESA’s Proba-3 FAQ Page
On December 5, 2024, the European Space Agency (ESA) launched the PRoject for On-Board Autonomy-3 (Proba-3) space telescope onboard a Indian PSLV rocket. This pioneering mission comprises two satellites designed to fly in precise formation, creating artificial solar eclipses to facilitate detailed studies of the Sun's corona. The satellites will operate in a highly ellipitical orbit with a perigee of about 570 km and an apogee of about 600 km with an inclination of 59 degrees. The satellites will maintain a separation of approximately 150 meters, with one satellite blocking the Sun's direct light, allowing the other—using its Association of Spacecraft for Polarimetric and imaging Investigation of the Corona of the Sun (ASPIICS) coronagraph—to observe the faint corona without interference by capturing UV and visible light spectrum images. Each artificial eclipse will last around six hours (much longer than a natural eclipse which only lasts for a few minutes), enabling scientists to analyze Sun’s inner corona and the origin of solar weather. The mission is expected to last for two years after which the satellites are expected to slowly decay and burn up in Earth’s atmosphere.
Space Variable Objects Monitor (SVOM)
Best source for comprehensive information: eoPortal’s SVOM Page
The Space Variable Objects Monitor (SVOM) space telescope is primarily a joint project between the French Space Agency and the China National Space Administration. Launched on June 22, 2024 from the Xichang Satellite Launch Center aboard a Long March 2C rocket, the SVOM is designed to observe and study the explosion of massive stars or merging of compact stars by analyzing the resulting gamma-ray bursts (“GRB”). Aside from its gamma ray monitoring and imaging equipment, this space telescope also has a microchannel soft X-ray instrument as well as a visible telescope. These telescopes will enable SVOM to detect and analyze high-energy phenomena across multiple wavelengths, ranging from gamma rays to visible light. Expected to have a mission life of at least 3 years, SVOM will operate in a circular low Earth orbit at an altitude of approximately 625 km with an inclination of 30 degrees.
Spectrum + Röntgen + Gamma (Spektr-RG)
Best source for comprehensive information: eoPortal’s Spektr-RG/SRG Page
A joint-project primarily ran between the Russian Space Research Institute and the Max-Planck-Institute for Extraterrestrial Physics, Spectrum + Röntgen + Gamma (better known as Spektr-RG) was launched on July 13, 2019 from Baikonur Cosmodrome, Kazakhstan. While Spektr-RG initially resided in low Earth orbit at an altitude of about 580 kilometers above mean sea level, it now resides at L2 (Lagrangian Point 2), which is a point in Outer Space that sits on a straight line with the Earth and the Sun but is 1.5 million km past the Earth from the Sun. While it has a 7.5-year mission life, because of the current troubled relationship between Europe and Russia, Spektr-RG has been in safe mode since March 2, 2022.
Transiting Exoplanet Survey Satellite (TESS)
Best source for comprehensive information: MIT’s TESS Site
On April 18, 2018, the Transiting Exoplanet Survey Satellite (“TESS”) was launched into the P/2 orbit via SpaceX’s Falcon 9. Objects, such as TESS, in the P/2 orbit would experience gravitational forces from the Earth and the Moon that would cancel each other out, enabling long durational missions. The P/2 orbit is named for having an orbital period half that of the Moon. In this orbit, TESS has a primary objective of discovering exoplanets of surrounding stars. To accomplish this goal, TESS has four cameras that are equipped with custom f/1.4 lenses. While the mission was only expected to last for two years, TESS is still continuing its mission today and has so far discovered 282 confirmed exoplanets.
XMM-Newton
Best source for comprehensive information: eoPortal’s XMM-Newton Observatory Site
Launched on December 10, 1999 onboard an Ariane rocket, the X-ray Multi-Mirror Mission-Newton (“XMM-Newton”) has three different high-throughput X-ray telescopes and one optical monitor. XMM-Newton’s mission is to help scientists to get a better understanding of the very hot objects that existed when our universe was very young. With a 48-hour orbit, the XMM-Newton travels in a highly eccentric 40-degree inclined high Earth orbit that can take it to about 114,000 km above mean sea level at its apogee and 7,000 km above mean sea level at its perigee. Originally anticipated to last for a ten-year mission, XMM-Newton is still in operation today, making its original cost of 689 million euros money well-spent.
XPoSat
Best source for comprehensive information: ISRO’s XPoSat Site
The X-ray Polarimeter Satellite (“XPoSat”) is the Indian space agency’s first ever satellite that is dedicated to the study and collection of x-ray emissions in Outer Space. Launched on New Year’s Day, 2024 onboard the Polar Satellite Launch Vehicle, XPoSat is expected to be able to measure X-ray polarization from many different sources. To conduct such studies, the XPoSat is made up of two primary payloads: (1) a Polarimeter Instrument in X-rays (POLIX) that can study polarization of X-ray sources in the 8-30 keV energy range and (2) X-ray Spectroscopy and Timing (XSPECT) that can provide information about X-rays in the 0.8-15 keV energy band. Expected to have a mission life of 5 years, the XPoSat will be sitting in a circular low Earth orbit at an altitude of about 650 km.
XRISM
Best source for comprehensive information: JAXA’s XRISM Site
The X-ray Imaging and Spectroscopy Mission (“XRISM”) was launched onboard a H-IIA rocket from the Tanegashima Space Center on September 7, 2023. A collaborative endeavor between NASA and JAXA, XRISM inherits the mantle from its predecessor, ASTRO-H, and is primed to explore the cosmos through the lens of its X-ray spectrometer. Positioned in a low Earth orbit, the XRISM will sit at approximately 550 kilometers above the planet's surface with an inclination of 31 degrees and an orbital period spanning 96 minutes. While initially slated for a three-year odyssey, history suggests that, much like its predecessors in the realm of X-ray space telescopes, XRISM may well extend its operational prowess far beyond this designated timeline.
