Now Chandra has a glitch

The Chandra X-Ray Observatory has developed a glitch and gone into safe mode. The 19 year old spacecraft is well past it's design life but continues to produce incredible science so hopefully it'll be back to full serviceability very soon.

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It seems that NASA had to deal with not so great news in the last couple of days with Hubble problems then Expedition 57 not making it to the International Space Station, and now the space telescope Chandra X-ray observatory, which has also developed a glitch. The telescope went into safe mode at 1355 GMT on 10 October.

These informations need to be taken in context of just how amazing and robust the failsafe devices that keep astronauts alive and space telescopes in space way above and beyond their expiration date.

Chandra was launched on STS-93 on 23 July 1999 and has exceeded its 5 year design life by 14 years. The current extended mission is far beyond what it was initially supposed to do so it’s little surprise that bits of it are starting to wear out. It seems the main problem that spacecraft tend to have is they either run out of power or their gyroscopes go on the blink. That happened with Kepler, and it has happened with Hubble in the past and again just last week and this could also be the problem with Chandra.

The issue, as reported from the status page, appears to be with one of the gyroscopes that experienced a glitch which lasted three seconds. This glitch caused a “momentum violation” which tripped the spacecraft into entering a safe mode.  There were no other problems with the instruments or sensors on board. The plan is to run the gyroscopes in a mixed mode by using one gyroscope from each of the inertial reference units (IRU). Each of these IRUs contain two 2-axis gyroscopes which are important parts of the Observatory’s Pointing Control and Aspect Determination System (PCADS). It’s heartening that there appears to be enough redundant systems available to keep Chandra running.

Chandra is a big spacecraft weighing just under 6000kg and about 15m long and jammed pack with CCDs for imaging and spectrometers for understanding the nature of the light it is capturing. It has on board a High Resolution Camera, an Advanced CCD Imaging Spectrometer and two high resolution spectrometers. All of these are powered by Chandra’s large solar panels that feed a bank of batteries. NASA extended the mission of Chandra in 2001 for 10 years when it was only two into its planned lifespan. Now it is well past even that ten year extension. The Chandra X-ray observatory, as the name suggests, is designed to look at the universe in x-rays. X-rays are not so easy to see on Earth because our atmosphere is quite good at absorbing them so to get the best view you need to go into space. Chandra orbits on a 139,000 km orbit so well beyond any interference that the Earth can create. Unfortunately it is also beyond any repair mission so hopefully Chandra will come right in the very near future.

Part of the one of the high resolution spectrometers being assembled (Credit: NASA/Havard)

X-rays are very important in astronomy as they can tell astronomers a lot about what is going on in the subject they are looking at. Visible light is great for many things but to understand what is happening within the atoms of the subject then more than just visible light needs to be examined.

X-rays are high energy photons that indicate activities that are occurring involving high temperatures and loads of energy. They are useful in exploring star formation as accretion disks around protostars can have very hot patches where the material is being added to the embryonic star and also the processes going on around black holes where enormous gravitational forces are squashing particles around the event horizon. X-rays can be created numerous different ways but generally from electrons that have been excited that are falling back to a lower energy state and emit a high energy x-ray photon. The electrons can get excited either through high speed collisions, such as in a very hot gas, or through the absorption of an x-ray photon.


Another special case of x-rays that is exciting for astronomers is that in some circumstances where there is a very powerful magnetic field electrons can whizz around the magnetic field lines at nearly the speed of light. When that happens some of the electrons produce very high energy photons called Synchrotron Radiation. These emissions can tell us a lot about what is happening around these high energy areas in space, such as around quasars and the jets coming out of black holes, they also help us understand what is happening in supernovae. So the work that Chandra does is very important in unlocking the secrets of the universe.

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