MIRAX: make an image from shadows

MIRAX, the Monitor e Imageador de Raios X, was conceived to investigate the changing high-energy sky, including the region toward the Galactic center. The mission team’s early papers describe a wide-field X-ray monitoring concept. INPE’s October 2026 catalog says the project is undergoing reconsideration and resizing. Historical instrument configurations and forecast launch dates should therefore be read as stages in a design history, not as a description of an observatory already operating in orbit.

High-energy photons can reveal hot gas and energetic processes around compact objects. A detector records interactions, however, rather than automatically producing a recognizable photograph of a star field. To identify where the photons came from, an instrument needs a way to encode direction and a model that connects its measurements to the sky. Different energy ranges and science goals lead to different instrument designs.

A coded-mask instrument places a pattern of open and blocking elements above a detector plane. Incoming radiation casts a pattern whose position depends on direction. Analysis compares the recorded pattern with the response expected for possible sources. The detector image and the reconstructed sky map are different products. A bright patch in raw detector counts is not automatically a bright object at the same location in the sky.

Imagine a simplified teaching model with a patterned screen and a row of light-sensitive cells. Moving a distant lamp sideways shifts the screen’s shadow. Two lamps contribute overlapping patterns, making interpretation more difficult. This visible-light analogy illustrates encoding, not the material properties or exact performance of a hard-X-ray telescope. Real analysis must also account for background, detector sensitivity and uncertainty rather than merely matching one attractive pattern.

Decode the observation

The protoMIRAX experiment developed a balloon-borne coded-aperture telescope and associated pointing, data-handling and ground systems. Its value lies in developing and checking parts of the measurement chain. A balloon environment differs from orbit, so a prototype cannot by itself qualify every spacecraft function. The science objective, detector response, environmental background and operating conditions must remain connected when interpreting a test.

The accompanying photograph shows the separate European INTEGRAL observatory during ground preparation, with its solar arrays extended. It is a comparison with real high-energy observatory hardware, not a picture of MIRAX or protoMIRAX. Use it to consider the support systems around a scientific payload: power, structure, communication and pointing. The Brazilian design history then shows how an instrument concept and its supporting systems can evolve before an orbital mission is realized.