The International X-ray Observatory (IXO) - Selected 4th in the NASA decadel survey and subsequently dropped

Prior to its termination, IXO was hosen 4th in the NASA decadal study.  IXO was to be the next observatory class space satellite for X-ray detection across the 0.1 keV to 40 keV energy range.  IXO's aim was to address the following questions in high energy astrophysics:

  1. Black hole formation and evolution
  2. he equation-of-state for neutron stars
  3. Galaxy velocity structure, mass and metallicity distribution
  4. The nature of the cosmic web of baryons (WHIM)
  5. ow feedback mechanisms in the Universe work

As part of the phase zero study a collaboration was formed between the CEI, the Universities of Iowa and Colorado, Northrup Grumman and e2v technologies to investigate the possibility of providing a high resolution soft X-ray spectrometer, based on off-plane gratings, for the IXO mission.  The instrument would have been able to resolve separate absorption lines generated in the Warm-Hot Intergalactic Medium (WHIM) and help identify the location of the missing baryonic content of the Universe.

The CEI was investigating the type, number and orientation of detectors that would be best used for this instrument and the goal was to use EM-CCDs in the camera final array.

image courtesy of ESA

image courtesy of ESA

The Advanced Telescope for High ENergy Astrophysics (ATHENA) - now ATHENA+ and scheduled for launch in 2028

After IXO was terminated by NASA, ESA re-scaled the L-class issions to allow a scaled down version of IXO to be proposed - ATHENA - that only had European involvement.

This scaled down observatory concept did not include a grating spectrometer; however, the European parts of the IXO off-plane grating spectrometer team were involved in the planning of this mission.  ATHENA's core science objectives were in the fields of:

  1. Black hole and accretion Physics
  2. Cosmic feedback
  3. Large-scale structure of the Universe

The L-class mission was chosen to be JUCIE leading to the end of the ATHENA concept study.

image courtesy of ESA

image courtesy of ESA

The Warm-Hot Intergalactic Medium Explorer (WHIMEx) - Not selected

WHIMEx was a scaled down version of the instrument designed as the off-plane X-ray grating spectrometer on IXO.  

The concept was to fly a small area X-ray optic on an explorer class mission.  Off-plane gratings mounted directly behind this optic would disperse incident X-rays over a CCD based camera array at the focus of the optic.  WHIMEx would have the ability to meet many of the science goals of IXO but in a more affordable explorer mission with the CEI working on the detector development as planned for IXO.  WHIMEx planned to address the following scientific questions:

  1. What happens close to a black hole?
  2. When and how did super-massive black holes grow?
  3. How does large-scale structure evolve?
  4. hat is the link between super-massive blac hole formation and the evolution of large-scale structure (i.e. cosmic feedback)?
  5. How does matter behave at very high density?

WHIMEx was not chosen as a NASA explorer class mission

image courtesy of Randall McEntaffer

image courtesy of Randall McEntaffer

The Off-plane Grating Rocket Experiment (OGRE) - Scheduled for launch in 2018

Sounding rockets are used as a high risk platform for the testing of new technologies in a space environment in order to increase their Technology Readiness Level (TRL) to make them less risky to use on future space missions.  They are seen as a means of technology development.

Randall McEntaffer from the University of Iowa is planning to aunch a sounding rocket (OGRE) in 2017 that will be used to test his grating technology alongside an EM-CCD camera system designed and constructed by the CEI.  If successful, this sounding rocket programme will pave the way for future explorer mission proposals.

mage courtesy of Randall McEntaffer

mage courtesy of Randall McEntaffer

ASTRO-H (Hitomi) - Launched in 2016

ASTRO-H (due for launch in 2015) is the next major space mission to be launched by the Japanese Space Exploration Agency (JAXA) and the 6th dedicated X-ray satellite they have built.  The mission’s goal is to aid our understanding of the structure and evolution of the Universe through the use of the following observational capabilities:

  1. One of the first imaging and spectroscopic observations with a hard X-ray telescope
  2. The first spectroscopic observations with an extremely high resolution micro-calorimeter
  3. The most sensitive wide-band observation over an energy range of 0.3 keV to 600 keV

To achieve its scientific goals, ASTRO-H has a payload made up of 6 different instruments:


  1. The Hard X-ray Telescope (HXT)
  2. The Soft X-ray Telescope (SXT)
  3. The Hard X-ray Imager (HXI)
  4. The Soft X-ray Spectrometer (SXS)
  5. The Soft Gamma Ray Detector (SGD)


Image courtesy of JAXA

Image courtesy of JAXA

The Off-plane Grating Rocket for Extended Source Spectroscopy (OGRESS) - launched in May 2015

An article published in the University of Iowa magazine - Iowa Now

The Off-plane Grating Rocket for Extended Source Spectroscopy (OGRESS) sounding rocket payload, based at the University of Iowa, is designed to perform moderate resolution (R~10- 40) spectroscopy of diffuse celestial X-ray sources between 0.3 – 1.2 keV. A wire grid focuser constrains light from diffuse sources into a converging beam that feeds an array of diffraction gratings in the extreme off-plane mount. The spectrum is focused onto Gaseous Electron Multiplier (GEM) detectors. OGRESS will obtain accurate physical diagnostics of the Cygnus Loop supernova remnant and will increase the technical readiness level of GEMs. OGRESS is the fourth-generation of similar payloads from the partnership between the University of Iowa and the University of Colorado, with higher throughput, and improved noise characteristics over its predecessors.

ARCUS - not selected in the 2015 mid-Ex announcement of opportunity

Arcus is a proposed X-ray grating spectrometer mission to be deployed on the International Space Station. The baseline design uses sub-apertured X-ray silicon pore optics feeding into off-plane gratings to achieve both high spectral resolution with a large effective area. The instrument would achieved a resolution of 2800 and and effective area of ~800 sq. cm over the 8-52Å (0.25-1.5 keV) bandpass.  ARCUS would allow the following science to be observed:

  • How mater cycles in and out of galaxies
  • How black holes grow and affect their surroundings
  • How stellar systems & environments form and evolve
MAGE COURTESY OF the arcus team - pi randall smith

MAGE COURTESY OF the arcus team - pi randall smith