XACT Sounding Rocket Alignment System

In Brief

Currently, NASA's Goddard Space Flight Center is developing a sounding rocket program for the X-Ray Advanced Concepts Testbed Project. Its goal is to provide inexpensive, low resolution x-ray telescopy using sounding rockets. X-ray telescopy requires very precise alignment of the x-ray detectors and collectors, and this project aims to develop a proof of concept for an optical, laser-based alignment system.

The XACT Rocket

Sounding Rocket
XACT Sounding Rocket
Image courtesy Goddard SFC.
In comparison to shuttle, satellite, and other full orbital launches, sounding rockets serve as a comparatively low cost platform for testing equipment at the edge of space, as well as performing experiments or taking readings that only require short times in space, such as small and quick telescopy experiments. Reaching their target height in less than a minute, they remain at altitude for a few minutes before returning to earth. The XACT rocket is based around the prSounding Rocketeviously used Black Brant VC sounding rocket. More sounding rocket information can be found in the Background section.

The Payload

XACT Payload
Image courtesy Goddard SFC.
The key to the XACT payload is maintaining alignment between its critical x-ray collector/concentrator and star tracker and its x-ray detectors on the opposite end of the payload. Originally aligned, vibration and heat from the rapid launch can generate both displacement between the two ends of the sensor package and tip/tilt angles between the two. These deformations in turn cause imaging errors, since the source of the x-rays cannot be definitively determined based off the misaligned star tracker. As such, it is key to track these changes, so they can be reversed in image processing post-flight or actively corrected for in-flight.

The Alignment System

The alignment system this project seeks to develop utilizes reflected lasers and position sensitive photodiodes (PSD) to track the displacements over time. Using the X and Y displacement sensing ability of the PSD, the four different displacements (x/y linear, x/y tilt) can be solved for. For more information see the Physical Set-Up and Processing pages.