The Hubble Space Telescopersquo;s journey to becoming one of the most iconic and productive astronomical instruments of our time included a significant setback that required an intervention to correct a flaw that eluded multiple quality control checks. This mirrors the complexity and human involvement in space technology projects and the rigorous scrutiny involved in ensuring perfect optical performance.
Polishing the Masterpiece: The Hubble Mirror
The Hubble Space Telescope was designed to capture images and data with incredible precision. The key to this precision was its primary mirror, which had to be polished to a very specific and exacting standard. Prior to installation, the mirror was meticulously polished to an excruciating level of accuracy, with its shape meticulously controlled to a fraction of a wavelength of light. However, a critical flaw was introduced during this process, leading to a phenomenon known as spherical aberration.
The spherical aberration, or more specifically, the slight polishing of the edges of the mirror to be too flat, rendered the telescope unable to focus light perfectly. This flaw seemed minusculethe mirrorrsquo;s shape was off by less than 1/50th the thickness of a human hair. Yet, this tiny imperfection had significant consequences, degrading the quality of the Hubblersquo;s images and the performance of all its instruments. The primary mirror was designed specifically to address this aberration, focusing light correctly on the Faint Object Camera (FOC), Faint Object Spectrograph (FOS), and the Goddard High Resolution Spectrograph (GHRS).
Quality Control and Human Error
The creation of the Hubblersquo;s primary mirror was a complex and precise process carried out by PerkinElmer. The company employed a reflective null corrector (RNC) to control the curvature of the mirror surface through laser interferometry. This technique allowed for unparalleled accuracy, ensuring the mirror was polished to a fraction of a wavelength of light.
However, a series of errors occurred during the setup of the RNC, leading to the mirror being polished to the wrong shape. Initially, the protective end cap on the RNCrsquo;s reference surface reflected a laser beam, causing a misalignment. Despite this, the technicians proceeded to adjust the RNC to compensate for what they believed to be a correct reading. Given the projectrsquo;s budget constraints and the impending deadline, there was insufficient time or resources to properly investigate this anomaly, leading the mirror to be polished to an incorrect shape.
Following months of polishing, the mirror was subjected to final tests using the same RNC setup, which appeared to indicate satisfactory results. However, a secondary test using a simpler null corrector revealed serious spherical aberration. NASA and PerkinElmer dismissed this result, overlookingly the simpler null correctorrsquo;s certifications.
The Crucial Realization
It was only after the Hubble was launched into space that NASA realized they had a problem. The first images received from the telescope were blurred and distorted, starkly revealing the mirrorsrsquo; imperfection. The full extent of the issue became apparent, and a corrective optics were hastily developed and installed in the form of a contact lens. This corrective lens, specifically designed to correct the spherical aberration, was successfully installed, restoring the Hubblersquo;s ability to perform at its expected level of precision.
The story of the Hubblersquo;s primary mirror and subsequent correction serves as a poignant reminder of the critical importance of meticulous quality control, the inevitability of human error, and the resilience of space technology in the face of unforeseen challenges.
Keywords: Hubble Space Telescope, Spherical Aberration, PerkinElmer