The Athena spacecraft will have three key elements:
- an X-ray telescope with a focal length of 12 m and an effective area of ~1.4 m² at 1 keV
- two instruments:
- an X-ray Integral Field Unit (X-IFU) for high-spectral resolution imaging
- a Wide Field Imager (WFI) for high count rate, moderate resolution spectroscopy over a large field of view
The telescope will use silicon pore optics (SPO), which will provide a unique combination of a large collecting area and good angular resolution across a large field of view while meeting a stringent mass budget. SPO offers an areal density roughly six times better than the electroformed nickel optics used for XMM-Newton.
|Silicon pore optics mirror stack.
Credit: cosine Research
Each pore in the SPO acts as a very small section of a Wolter I telescope. Two reflections from the inner surfaces of the pore bring the X-rays to a common focus. The pores have a cross-section of only a few mm², and around 1.5 million pores will be used to provide the required collecting area. Arrays of pores are manufactured in modules using commercially available silicon wafers. The wafers are diced into rectangles, typically 60 mm wide and with varying heights, and a thin wedge of material is deposited onto both sides of the wafer, so that when they are stacked the reflecting surfaces are arranged in a radial pattern that provides a common in-plane focus. This technology has now been under development by ESA for over a decade.
The Mirror Assembly Module (MAM) will support the X-ray optics and the associated structure, and will include a straylight baffle, a thermal baffle and an expandable Sun protection baffle to maximise the field of regard. During ground operation and launch, the X-ray mirror will be covered by a door, which can also be used for Sun protection after deployment. To maintain the performance of the optics and simplify calibration, a thermal control system will be required for the mirror. Magnetic diverters will be implemented to deflect soft protons and electrons thereby reducing the particle background.
A fixed structure will connect the MAM to the Focal Plane Module (FPM), which will be part of the Service Module (SVM). The two instruments will be mounted on a moving platform that will position one or the other in the focal plane of the telescope.