Concerns grow for X-ray astronomy satellite ASTRO-H

Japan’s ASTRO-H X-ray astronomy satellite is in trouble, just weeks after launch. Following a loss of nominal communication, observers have noted the spacecraft is tumbling, while tracking information has cataloged pieces of debris in the area of the satellite. The spacecraft is a high-energy astronomy mission led by the Japan Aerospace Exploration Agency (JAXA).

ASTRO-H Failure:

Japan launched the ASTRO-H X-ray mission via its H-IIA rocket on February 17, launching from the country’s Tanegashima launch site.

2016-03-28-182506As of later that month, the satellite appeared to be performing as advertised, with JAXA confirming the completion of a checkout sequence that included turning on the cooling system, test operations of the Soft X-ray Spectrometer (SXS), and extending the Extensible Optical Bench (EOB).

This confirmed the Critical Operation Phase (COP) was completed.

JAXA was then to perform the initial functional verification tasks of the onboard instruments for a period lasting about one and half months, before conducting calibration observations for another six weeks. The spacecraft would then be ready to begin full operational observations.

However, over the weekend, JAXA noted that the spacecraft had failed to communicate as originally scheduled on Saturday. As such, controllers were unable to check the health of the satellite.

“While the cause of communication failure is under investigation, JAXA received a short signal from the satellite, and is working for recovery,” noted a statement from the agency.

“Under these circumstances, JAXA set up emergency headquarters for recovery and investigation. The headquarters held its first meeting (Saturday) and has been working for recovery and the investigation of the cause.”

Space tracking information then noted the orbit of object 41337 (the spacecraft’s tracking number) had dropped from 564.6×580.5 to 561.0×580.1 km just before the failed communication pass.

2016-02-17-015932Joint Space Operations Center (JSpOC) – which detects, tracks, and identifies all artificial objects in Earth orbit – then noted several objects, potentially pointing to the observation of debris. However, the debris can’t be identified and could simply be liberated insulation near the spacecraft.

However, amateur trackers also cited they observed “tumbling”, as the satellite made its passes.

The latest note from JSpOC on Monday spoke of a breakup being confirmed.

“Analysis shows ASTRO-H breakup occurred 26 March at 01:42 UTC. JSpOC confirmed breakup at 08:20 UTC.”

However, “breakup” could be a reference to the observation of debris and JAXA is yet to provide a statement to confirm if the mission is lost. At present, no specific root cause of the issues has yet been noted.

If the satellite (also named Hitomi) is still alive – as is potentially the case due to what JAXA described as a “short signal” after the initial loss of main communications, something that is indicative of a tumbling spacecraft – there may still be a chance to put a plan in work that could recover the satellite.

The spacecraft’s status is likely to be updated later this week.

Spacecraft Information:

JAXA’s mission is in partnership with NASA – along with the European Space Agency (ESA), Canadian Space Agency (CSA), Netherlands Institute for Space Research and universities in Japan, Europe and North America.

Carrying a suite of instruments dedicated to observing X-rays, ASTRO-H – if successfully recovered – is expected to operate in low Earth orbit for three years.

2016-02-17-021105The 2,700-kilogram (6,000 lb) satellite is equipped with four telescopes and six detectors, which would allow it to study both “hard” and “soft” X-rays and gamma rays.

An X-ray is electromagnetic radiation with an energy of between 0.1 and 100 kiloelectronvolts (keV); between ultraviolet radiation and gamma rays in the electromagnetic spectrum.

Astrophysicists term the most energetic X-rays as hard X-rays, typically ones with energies above 10 keV, while less energetic X-rays are termed “soft”. Gamma rays are more energetic still than hard x-rays.

Once in orbit, a pair of three-panel solar arrays were tasked with providing a minimum of 3.5 kilowatts of power for the satellite’s systems and instruments.

The apertures of ASTRO-H’s telescopes are located on the forward surface of the satellite, known as the Fixed Optical Bench (FOB), focussing incident X-rays onto the instruments. The FOB had successfully deployed during initial checkouts.

2016-02-17-020933The four telescopes include two Soft X-ray Telescopes; SXT-I and SXT-S. SXT-I focusses X-rays onto the Soft X-ray Imager (SXI), while SXT-S collects incident rays for the Soft X-ray Spectrometer (SXS).

The remaining telescopes are a pair of Hard X-ray Telescopes (HXT), which focus hard X-rays onto imagers mounted to a six-meter (19-foot) boom at the rear of the spacecraft.

With its boom – the Extensible Optical Bench (EOB) – fully deployed, ASTRO-H would grow to 14 meters (46 feet) long. This would enable a focal length of 12 meters (39 feet) for the hard X-ray imaging system.

The twin Hard X-ray Imagers (HXI) collect X-rays with cadmium telluride detectors to produce images of the distribution of incident photons at energies of between five and eighty kiloelectronvolts within a nine-by-nine arcminute field of view.

The soft X-ray detectors – which wouldn’t require such a long focal length – are located within the body of the satellite – attached to the rear panel, or aft bulkhead.

2016-02-17-021013The Soft X-ray Imager, or SXI, pair up with the SXT-I telescope to provide an imaging system that has a focal length of 5.6 meters and capable of imaging incident rays with energies between 0.4 and 12 keV. It has a field of view of 38 by 38 arcminutes.

The Soft X-ray Spectrometer, or SXS, is a NASA instrument that consists of a high-resolution X-ray microcalorimeter which measures the energies of incident photons and produce spectra showing the intensity of individual energies in the observed radiation. The spectrometer is able to observe photons with energies of between 0.3 and 12 keV, with a resolution of fewer than 7 electronvolts.

The instrument is equipped with filters which could be put into place to allow particularly intense X-ray sources to be observed while the satellite also carried its own X-ray source to allow the spectrometer to be calibrated.

2016-03-28-184326To achieve accurate results, the SXS will have to be cooled using a multi-stage liquid helium system to a temperature of 0.05 Kelvin (-273.10 degrees Celsius, -459.58 Fahrenheit).

ASTRO-H also carries two Soft Gamma-ray Detectors (SGD), which use Compton telescopes to observe gamma rays through Compton scattering caused when the photons interact with semiconductor plates in the detector.

Mounted on either side of the spacecraft, these sensors will be able to detect gamma ray sources emitting radiation with energies of between 60 and 600 keV.

The latest statement from JAXA on Monday simply noted that the cause of the communication failure remains unknown and that further information will be provided when they have new data to provide.

(Images via JAXA and NASA).

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