OrbitalHub

Credits: NASA/JPL

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a high-energy X-ray space telescope that will expand our understanding of the origins and the development of stars and galaxies.

NuSTAR was proposed to NASA in May 2003. In 2006, while NuSTAR was undergoing an extended feasibility study, NASA cancelled the program due to budgetary constraints. However, in September 2007, the program was restarted.

In 2007, Orbital Sciences Corporation was selected by NASA to design, manufacture, and test the NuSTAR telescope.

The spacecraft is based on a proven design, used by Orbital for other NASA Small Explorer missions: SORGE, GALEX, AIM, and OCO. NuSTAR will have a launch mass of 360 kg, and will be powered by articulated solar arrays providing 600 W.

The spacecraft incorporates a ten-meter long extendable mast. The mast allows the telescope to fit into a small launch vehicle.

The technology used to build the telescope is not new. A team of researchers, led by Dr. Fiona Harrison, professor of physics and astronomy at Caltech, has been improving the NuSTAR technology for the last ten years. A previous high energy X-ray telescope (High Energy Focusing Telescope or HEFT) was developed as part of a high altitude balloon payload.

The currently operational X-ray telescopes, Chandra and XMM-Newton, observe the sky in the low energy X-ray spectrum (X-ray energies less than 10 keV). NuSTAR will make observations in a higher range, up to 79 keV. As much of the energy emitted by a black hole is absorbed by the surrounding gas and dust, observations in the high-energy X-ray spectrum can reveal in greater detail what is happening closer to the event horizon.

Credit: NASA/CXC/CfA/R.Kraft et al./MPIfR/ESO/APEX/A.Weiss et al./ESO/WFI

The NuSTAR telescope will have a sensitivity two orders of magnitude greater than any other instrument used to detect black holes. NuSTAR will help scientists understand how black holes are distributed throughout the universe, and what powers the most active galaxies.

The NuSTAR instrument consists of two co-aligned hard X-ray telescopes. The ten-meter mast mentioned above separates the mirrors and the imaging detectors. The detectors are Cadmium Zinc Telluride (CdZnTe) detectors and do not require cryogenic operation.

On February 9, 2009, NASA awarded Orbital the launch services contract for the NuSTAR mission. The telescope will be launched in 2011 aboard a Pegasus XL launch vehicle. Pegasus XL will be carried beneath a L-1011 aircraft and released over the Pacific Ocean. The air-launch system is very cost-effective, providing flexibility during operation and requiring minimal ground support.

NuSTAR will be deployed into a 525×525 km low Earth orbit (LEO) with a twenty-seven degree inclination.

For more details about the science of NuSTAR, you can visit the mission’s home page at Caltech. Orbital has also posted a NuSTAR fact sheet on their web site.

Credits: NASA

Kepler is the first NASA mission capable of finding terrestrial exo-planets. Of particular interest are the planets orbiting in the so-called habitable zone, where conditions are met so that liquid water can exist on the surface of the planet.

The observations made so far have brought clear evidence that planets orbiting around other stars are a common thing, rather than the exception to the rule. Due to the limitations of present technology, only gas giants, hot-super Earths in short period orbits, and ice giants have been discovered.

The Kepler mission, part of NASA’s Discovery Program, is designed to survey a portion of our region of the Milky Way. Kepler will survey a large number of stars, and explore the structure and diversity of many planetary systems.

The scientific objectives of the mission are very ambitious: determine the fraction of terrestrial planets in or near the habitable zone, determine the distribution of sizes and the orbits of exo-planets in the surveyed planetary systems, determine reflectivity, size, and density of short-period giant planets, estimate how many planets are in multiple-star systems, and determine the characteristics of the stars that have planets orbiting around them. Scientists hope to discover additional members of the planetary systems surveyed using other indirect techniques.

Credits: NASA/Ball Aerospace

The duration of the mission must be selected to allow the detection and confirm the periodic nature of the planet transits in or near the habitable zone. Due to the characteristics of orbits of such planets, a lifetime of three and a half years (as currently envisioned) would allow a four-transit detection of most orbits up to one year in length and a three-transit detection of orbits of length up to 1.75 years.

The mission lifetime will be extendible to at least six years. The extension will permit the detection of planets smaller than Earth with two-year orbits.

Kepler will be inserted in an Earth-trailing heliocentric orbit, then the spacecraft will slowly drift away from Earth. The selected orbit offers a very stable pointing attitude, and it avoids the high radiation dosage associated with an Earth orbit. However, Kepler will be exposed occasionally to solar flares.

The communication protocol with the spacecraft includes establishing contact twice a week for commanding, health, and status, and science data downlink contact once a month.

Credits: Jon Lomberg

There are two requirements that dictated the selection of the target field. The first requirement is the ability to monitor continuously the stars surveyed because transits last only a fraction of a day. This can be achieved by having the field of view out of the ecliptic plane, so the Sun will not interfere with the observations at any time during the year. The second requirement is to have the largest possible number of stars in the field of view.

To meet both requirements, a region in the Cygnus and Lyra constellations of our galaxy has been selected as the field of view.

Kepler will use the transit method for detecting exo-planets. The sensitivity of the photometer will allow the discovery of terrestrial exo-planets (planets comparable in size and composition to Earth that are orbiting other stars).

The transit occurs when a planet passes in front of its star as viewed by an observer. Depending on the size of the planet, the change in the brightness of the star has different amplitudes. Transits of terrestrial planets cause a change in the star’s brightness of about 1/10,000, and they last from two to sixteen hours.

Credits: NASA

Changes in star brightness that are produced by a planet transit must be periodic, and all transits produced by the same planet must cause the same variation of brightness and last the same amount of time.

Of course, the case when two or more planets are in transit at the same time must be considered, and this can make the detection method a little bit more complicated.

The method allows for the calculation of the orbit, the mass, and the characteristic temperature of the exo-planet. Once we know the characteristic temperature of an exo-planet, the question of whether or not the planet is habitable (by our standards) can be answered.

The Kepler instrument is a special telescope called photometer or light meter. The telescope has a very large field of view for an astronomical telescope, 105 square degrees. The primary mirror of the telescope is 0.95 m in diameter. The telescope needs a large field of view because it has to continuously monitor the brightness of more than 100,000 stars for the duration of the mission.

Credits: Ball Aerospace

The photometer is composed of one instrument, which is an array of charge-coupled devices (CCD), 42 in total. Each CCD is 50mm x 25mm and has 2200 x 1024 pixels. Data from the individual pixels that make up each star are recorded continuously and simultaneously.

The primary mirror of the photometer was coated with enhanced silver, which allows more light to reach the telescope’s detectors.

The spacecraft provides power, attitude control, and telemetry for the photometer. The mission requirements contributed to the simple design of the spacecraft. The only moving parts are the reaction wheels used to control the attitude of the spacecraft.

The launcher selected for the mission is Delta II. Delta II is a versatile launcher, and can be configured in two or three-stage vehicles in order to accommodate a variety of requirements.

Ball Aerospace is the prime contractor for the Kepler mission, building the photometer and the spacecraft, as well as managing the system integration and testing of the spacecraft. The Jet Propulsion Laboratory is managing mission development, while NASA Ames Research Center is responsible for ground system development, mission operations, and science data analysis.

Once the first observation results are downloaded from Kepler and made available to scientists, we will be able to place our solar system within the context of planetary systems in our galaxy.

The launch of Kepler is planned for March 5, 2009. For more information about the Kepler mission, you can visit the Kepler mission web page.

Credits: NASA

The James Webb Space Telescope (JWST) is the successor of the Hubble Space Telescope (HST). While Hubble looks at the sky in the visible and ultraviolet light, JWST will operate in the infrared.

JWST is a joint mission of NASA, ESA, and the Canadian Space Agency.

The project started in 1996 and was initially known as the Next Generation Space Telescope (NGST). In 2002, the project was renamed the James Webb Space Telescope in honor of NASA administrator James E. Webb, who led the agency from February 1961 to October 1968.

The JWST will use a large deployable sunshade to keep the temperature of the telescope to about 35K. Operating at this temperature gives the telescope exceptional performance in near-infrared and mid-infrared wavebands. The JWST observatory will have a five to ten year lifetime and it will not be serviceable by astronauts.

JWST will be able to see the first galaxies that formed in the early Universe, and how the young stars formed planetary systems.

Credits: NASA

The JWST observatory includes the Integrated Science Instrument Module (ISIM), the Optical Telescope Element (OTE), and the Spacecraft Element containing a spacecraft bus (which offers the support functions for the observatory) and the sunshield.

I will say a few words about each one of them.

The Optical Telescope Element (OTE) collects the light coming from space. Thanks to a 6.5 meter primary mirror, JWST will be able to see the galaxies from the beginning of the Universe. The OTE is also composed of the Fine Steering Mirror (FSM), the secondary mirror support structure (SMSS), and the primary mirror backplane assembly (PMBA). Other subsystems of the OTE are the tertiary mirror and the fine steering mirror. The PMBA contains the Integrated Instrument Module (IIM).

Because the primary mirror is too large to fit inside any available payload fairing, it had to be made out of eighteen hexagonal segments. Some of the elements will be folded before the launch and unfolded during the commissioning phase at the L2 point. NASA made available some neat animations showing how the observatory will be folded in order to fit into the launcher payload, and how the sun shields and the primary mirror will unfold before the observatory becomes operational.

Credits: NASA

The sunshield will keep the scientific payload of the observatory away from any light from the Sun, the Earth, or the Moon. Because JWST will observe primarily the infrared light from very distant objects, the temperature of the scientific payload must be maintained at very low values (under 50K). This requirement is so important that even a part of the observatory (the spacecraft bus) had to be placed on the warm side of the sunshield.

The sunshield not only protects the scientific instruments from the heat of the Sun, the Earth, the Moon, and the warm spacecraft bus electronics, but it also provides a stable thermal environment. This is necessary in order to maintain the alignment of the eighteen hexagonal components of the mirror while the observatory changes its orientation relative to the Sun.

The primary mirror is the essential component of a telescope. The design of the primary mirror was driven by a number of important requirements: the size, the mass, and the temperature at which the mirror will operate.

Credits: NASA

In order to be able to see galaxies from thirteen billion light-years away, scientists determined that the mirror must have a diameter of at least 6.5 meters.

The weight of the primary mirror has only one tenth of the mass of Hubble’s mirror per unit area. Considering the size of the mirror, this made the task of launching the telescope into space achievable.

Due to the fact that the telescope will observe the light in the infrared spectrum, the temperature of the mirror has to be as low as –220 degrees Celsius. If operating at the same temperature as the ground telescopes do, the infrared glow of the mirror would interfere with the light received from distant galaxies. Basically, these distant galaxies would disappear in the noise generated by the telescope.

The engineering challenge that scientists faced was to build a lightweight mirror that would preserve its optical and geometric properties when cooled to –220 degrees Celsius. Using beryllium was the solution. Beryllium is lightweight (it is widely used in the aerospace industry) and it is very good at holding its shape across a range of temperatures.

As we mentioned above, the PMBA contains the Integrated Instrument Module (IIM), which is the scientific payload onboard the observatory. The scientific payload includes the following scientific instruments: the Mid-Infrared Instrument (MIRI), the Near-Infrared Spectrograph (NIRSpec), the Near-Infrared Camera (NIRCam), and the Fine Guidance Sensor (FGS).

The MIRI is an imager/spectrograph that covers the wavelength range from 5 to 27 micrometers. The nominal operating temperature for the MIRI is 7K. The NIRSpec covers two wavelength ranges: from 1 to 5 micrometers (medium-resolution spectroscopy) and from 0.6 to 5 micrometers (lower-resolution spectroscopy). The NIRCam was provided by the University of Arizona. NIRCam covers the spectrum from 0.6 to 5 micrometers. The FGS is a broadband guide camera that is used for guide star acquisition and fine pointing.

Credits: ESA

The spacecraft bus is composed of every subsystem of the observatory minus the sunshield and the scientific payload, and it provides the necessary support functions for the operations of the observatory. The spacecraft bus contains the Electrical Power Subsystem (EPS), the Attitude Control Subsystem (ACS), the Communication Subsystem (CS), the Command and Data Handling Subsystem (C&DHS), the Propulsion Subsystem (PS), and the Thermal Control Subsystem (TCS).

One interesting thing I would like to mention here is that the C&DH subsystem is using a solid-state recorder as memory/data storage for the observatory. I cannot envision a hard disk drive taking all of the vibrations during the launch and running for ten years without any flaws, so the choice of using radiation hardened solid-state memory units on long-term space mission spacecrafts seems to be the optimal choice.

The launch vehicle chosen for this mission is the European Ariane 5. The Ariane 5, carrying the James Webb Space Telescope, will liftoff from Guiana sometime in 2013. The space telescope will operate from the L2 point of the Sun-Earth system.

All three agencies that are part of the project, ESA, NASA, and CSA, have web pages dedicated to the JWST observatory.

Credits: ESA/AOES Medialab

In a previous post, we presented the Planck spacecraft. We would like to dedicate this post to Planck’s big brother, Herschel. Why b(r)other? Because Planck and Herschel will be launched into space by the same Ariane 5 launcher and they will share the fairing section during the launch phase of the mission. Why big? Well, because Herschel is a larger spacecraft than Planck… actually Herschel is the largest space telescope ever built.

Just to have an idea about the size of the infrared telescope onboard the Herschel spacecraft, the primary mirror has a diameter of 3.5 m and a mass of only 350 kg. In comparison, the mirror of the Hubble space telescope has a diameter of 2.4 m and a mass of 1.5 tons. Obviously, a great deal of effort has been put into minimizing the mass of the telescope, an advance made possible by present-day technology.

The infrared telescope will become operational four months after its launch and will have a nominal mission lifetime of three years. The objectives that ESA set for the Herschel Space Observatory are ambitious: the study of the galaxies in the early universe, the investigation of the creation of stars, the observation of the chemical composition of the atmosphere and surfaces of comets, planets and satellites, as well as examining the molecular chemistry of the universe.

Like Planck, Herschel will observe the sky from the second Lagrangean Point (L2) of the Sun-Earth system. The instruments onboard Herschel will collect long-wavelength infrared radiation. Herschel will be the only space observatory to cover the spectral range from the far infrared to sub-millimeter, which is the reason why the initial name of the space observatory was Far Infrared and Sub-millimeter Telescope (FIRST).

Credits: ESA

The Herschel spacecraft will have 3.3 tons at launch, with a length of 7.5 m and a cross section of 4×4 m. The spacecraft comprises of two modules: the service module and the payload module. While the service module contains the systems for power conditioning, attitude control, data handling and communications, and the warm parts of the scientific instruments, the payload module contains the telescope, the optical bench, the cold parts of the scientific instruments and the cooling system. A sunshield protects the telescope and the cryostat from solar radiation. The sunshield also carries solar cells for power generation.

In order to make accurate observations of the infrared spectrum, parts of the scientific instruments onboard have to be cooled to temperatures close to absolute zero. Two thousand liters of liquid helium will be used for primary cooling during the mission. In addition, each detector onboard is equipped with additional cooling systems.

Credits: ESA/Guarniero

Herschel will not be the first infrared telescope launched into space. There are three predecessors that we would like to mention here: IRAS, the US-Dutch-British satellite launched in 1983, ISO – launched by ESA in 1995, and the NASA’s Spitzer Space Telescope – launched in 2003. However, these three infrared space telescopes were operated on Earth orbits. As we mentioned, Herschel will operate in the L2 point, away from any interference that would affect the scientific instruments onboard. Operating in the L2 point will also help with regard to thermal stability because the spacecraft will not move in and out of eclipse regions.

The launch date is set for early 2009. The journey to the final operational position will take around four months. The European Space Operations Control Center (ESOC) in Darmstadt will coordinate the mission.

Credits: CNES / D. Ducros

Stellar seismology is a relatively new field of study. Since 1995, the ESA/NASA mission SOHO (SOlar Heliospheric Observatory) has pioneered the study of stellar seismology through observations of our own star, the Sun. Despite its name, stellar seismology is the study of stellar pressure waves and not stellar seismic activity (There is no such thing as seismic activity inside a star).

The COROT mission uses a similar approach to study other stars. Three stars similar to the Sun – known as HD499933, HD181420, and HD181906 – have been probed and starquakes have been detected.

Credits: CNES

Starquakes, or oscillations of distant stars, can be detected through variation in the light emitted by the star as sound waves hit the star’s surface.

This method reveals the internal structure of the star, and the patterns that the energy follows when transported from the core to the surface. These observations also allow astronomers to calculate the star’s mass, age, and chemical composition.

The COROT satellite, carrying a 27 cm diameter telescope, was launched in December 2006 by a Soyuz rocket from the Baikonur Cosmodrome. COROT is a 360 kg satellite and operates on a polar orbit at an altitude of 896 km. COROT is a mission lead by the French Space Agency (CNES); ESA, Austria, Belgium, Germany, Spain, and Brazil also contributed to the mission. The main objectives of the mission are to search for exoplanets and to study stellar interiors.

Credits: CNES

The telescope onboard COROT cannot see exoplanets directly. The method employed by COROT to discover exoplanets is to measure variations in the luminosity of stars. Planets cause such variations as they pass in front of their parent stars. These celestial alignments are called planetary transits. Obviously, the smaller the planet, the higher the telescope’s sensitivity must be in order to detect it.

Ground telescopes have detected more than 200 exoplanets to date (all of them gas giants). COROT continues the search for new worlds outside of our solar system from above the Earth’s atmosphere. Without the distorting effects of the atmosphere, COROT is able to find planets that are made out of rock and are smaller than the gas giants. COROT marks the first step in understanding other solar systems, how planets are formed, and how life can develop on these planets.

From February 2 to February 5, 2009, the first COROT International Symposium will be held in Paris, France.

Credits: ESA

After operating flawlessly in orbit for almost nine years, the XMM-Newton X-ray observatory lost contact with the ESA’s ground stations.

In the case of a space mission, losing contact with a spacecraft can mean anything from a technical problem onboard to a collision with space debris or even a meteorite.

The contact was lost when the satellite switched from one ground station to another. The satellite must perform such operations in orbit in order to maintain radio contact with the ground control center of the mission. The ESA’s ground station in Villafranca, Spain, reported that it was not able to re-establish radio contact with the satellite.

Several astronomic observatories have managed to take images of the satellite in orbit. By now it is clear to the ground investigators that the satellite is intact and it is maintaining a constant altitude on the expected orbit. By using a more powerful ground antenna (the 35m diameter antenna at New Norcia in Australia), a weak radio transmission was received from XMM-Newton, proving that the satellite is still alive. Engineers hope to re-establish nominal radio contact with the satellite.

Credits: NASA/ESA/R. Massey (Caltech)

ESA launched the X-ray Multi-Mirror Mission (XMM-Newton) on December 10th, 1999. The mission has an operational lifetime of ten years. XMM-Newton has a large collecting area due to its three X-ray telescopes. In addition, the high altitude orbit offers the ability to make long uninterrupted exposures.

X-rays are absorbed by the Earth’s atmosphere, so only a space telescope like XMM-Newton can detect and study celestial X-ray sources.

Data collected by the XMM-Newton was used to compile a three-dimensional large-scale map of the dark matter for the first time. The dark matter is an invisible form of matter that accounts for most of the mass of the Universe.

ESA has an entire website dedicated to the XMM-Newton mission. For more details about XMM-Newton you can visit the XMM-Newton Science Operations Center (XMM-Newton SOC) page.