nanoMIRAX: locate a burst with four detectors

nanoMIRAX is a small-satellite development associated with the LECX instrument, whose Portuguese name describes a locator of cosmic X-ray explosions. INPE’s October 2026 catalog separates an already developed engineering model from future flight-model integration, testing, launch and operation. The proposed spacecraft uses a two-unit CubeSat format. It is related to the MIRAX research effort, but it is not simply the larger mission reduced to an identical miniature.

A small spacecraft has limited volume, electrical power, data capacity and thermal resources. An effective design therefore begins with a question narrow enough for those limits. Detecting and approximately locating a sufficiently bright transient is a different task from producing a detailed, continuous map of every faint source. Mission success must be assessed against the chosen requirement, not against every capability of a much larger observatory.

The primary LECX instrument paper describes four detectors arranged in a square inside shielding. Radiation arriving away from the central direction can be partly shadowed by the walls, producing unequal illuminated areas. Relative detector responses can then constrain the arrival direction. This differs from reconstructing a sky image through a patterned coded mask — open definition. The shared interest in hard X-rays does not make the two measurement methods interchangeable.

For an original analogy, imagine four light meters at the bottom of a shallow box. A lamp directly above may illuminate them similarly; an oblique lamp can leave some meters partly shaded. Real detectors also differ in sensitivity and register background. Before attributing unequal readings to direction, the analysis must account for those effects. Equal readings alone likewise do not prove that every possible source configuration has been uniquely identified.

Locate the event in two coordinate systems

An instrument initially estimates direction relative to its own structure. To express that direction on a sky map, the analysis needs the spacecraft’s orientation at the event time. A good local estimate paired with an incorrect attitude — open definition record can point observers toward the wrong celestial region. Timing, detector calibration — open definition and attitude knowledge are therefore parts of the localization result rather than optional labels added afterward.

Suppose a fictional burst produces a usable directional estimate but the spacecraft attitude is uncertain. Report the resulting uncertainty region instead of an unjustifiably precise point. A follow-up observer needs to know where to search and how confident the estimate is. Larger counts can improve some statistical limits, but they do not automatically repair a wrong orientation record. nanoMIRAX illustrates how careful coordination of a compact instrument and a satellite platform can support a specific scientific purpose.