Understanding the Differences Between the Hubble Telescope and KH-11 Spy Satellites

One persistent myth is that the Hubble Telescope was based on the KH-11 Kennan spy satellite technology. While both orbital instruments share a similar overall size due to the constraints of being transported in the space shuttle's cargo bay, their primary functions, design, and uses are fundamentally different. Let's explore these differences in depth.

Origins and Design Principles

The Hubble Telescope and KH-11 spy satellites were designed for distinct purposes, reflecting different scientific and operational requirements. The Hubble Telescope, launched in 1990, is an astronomical observatory that focuses on observing distant objects in space, including the most distant galaxies and the formation of the universe. In contrast, the KH-11 series of spy satellites, designed in the 1970s by the National Reconnaissance Office, were primarily built for earth observation and military reconnaissance. Both share the characteristic of having large mirrors, as this was the only design that could fit within the space shuttle's cargo bay, but beyond that, their design philosophies diverge significantly.

Optical Design and Functionality

In terms of optical design, the key difference lies in their respective targets. The Hubble Telescope is focused on celestial objects, often located at distances far beyond the atmosphere, effectively looking at infinity from an optical perspective. This means that even though the Hubble orbits the Earth, the objects it observes are so far away that they appear to be at an infinite distance. This is similar to how a DSLR camera sets its focus to infinity for distant objects.

The Hubble, therefore, does not need to compensate for atmospheric distortions or other elements that would affect focus or image quality when looking at distant objects. For instance, the focus adjustment ring on a DSLR lens is effective for focusing on objects within a finite range, such as a few feet away. However, once the range extends beyond a few feet, the lens is set to infinity, and no further adjustment is necessary. This is not a significant concern for the Hubble Telescope as it observes objects that are infinitely far away.

Focus Differences and Technological Adaptations

Despite their differences, both the Hubble and KH-11 satellites share the principle that their mirrors can be adjusted to focus on any distance, including infinity. This is because the design of both telescopes and lenses is based on the same principles: the adjustment of the focal plane (the camera sensor in the case of telescopes) determines the focus. For the Hubble, this would involve moving the camera sensor slightly closer or farther from the mirror.

The Hubble Telescope does not benefit from the same technological adaptations as the KH-11 satellites. The KH-11 series are designed to observe the Earth's surface and may require specialized techniques for atmospheric compensation and focusing. Conversely, the Hubble is engineered for the vastness of space, where atmospheric distortion is negligible, and distance does not affect focus in the same way.

Upcoming Automated Systems and Re-Purposed Technology

While the Hubble is a bespoke design for astronomical observation, upcoming projects like WFIRST (Wide Field Infrared Survey Telescope) are re-purposed from existing spy satellite technology. However, WFIRST is expected to require significant modifications and nearly a billion dollars of re-work to align with the new mission requirements. This underscores the distinct engineering challenges and tailored designs for each type of optical system.

The WFIRST project is indicative of how technology can be repurposed but still necessitates a great deal of customization. The inherent differences between looking down to the Earth's surface and up to the stars highlight the unique challenges and adaptations required in each scenario.

While both the Hubble and KH-11 satellites have large mirrors and serve as observatories in their own right, their core functions, design principles, and operational requirements differ significantly. The Hubble is renowned for its unparalleled astronomical observations, while the KH-11 series is a testament to the advancements in surveillance and reconnaissance technology.