The Enduring Legacy of the Hubble Space Telescope: How It Has Lasted for Decades

For over three decades, the Hubble Space Telescope has provided astronomers and the general public with stunning images and invaluable scientific data. Despite facing challenges and a few operational hiccups, Hubble has managed to continue operating and delivering groundbreaking discoveries. So, what has made Hubble last so long?

Superb Design Engineering and Project Management

The longevity of Hubble can be attributed to remarkable design engineering and efficient project management by NASA. The telescope's development involved extensive collaboration between various stakeholders, including NASA's Goddard Space Flight Center, the Space Telescope Science Institute, and major contractors like the Lockheed Martin.

The telescope's construction included innovative materials and techniques that have stood the test of time. Key components such as titanium trunnion fittings and powdered metal castings were used to ensure cost, mass, reliability, and schedule. These innovative choices contributed significantly to Hubble's ability to function effectively in the harsh environment of space.

Correcting the Mirror Flaw: A Key Milestone

One of the most significant challenges Hubble faced was the mirror flaw in the curvature of the primary lens. This issue, discovered shortly after its launch, initially caused considerable alarm. However, the problem turned out to be correctable, and the Hubble Servicing Mission 1 in 1993 installed new optical devices to fix the mirror flaw. This critical intervention allowed the telescope to resume its mission and provided the basis for its ongoing success.

On-Orbit Servicing by Astronauts: A Game-Changer

The concept of on-orbit servicing by astronauts proved to be a vital component of Hubble's success. This capability, made possible by the design for servicing, allowed NASA to address hardware issues and extend the telescope's lifespan. Over the years, Hubble has undergone multiple servicing missions, each contributing to its continued operation. These missions included replacing faulty components, installing new instruments, and making critical upgrades.

Environmental Factors and Atmospheric Drag

While Hubble's design and engineering excellence contributed significantly to its longevity, environmental factors also played a role. The telescope's orbit around the Earth is relatively stable, and while it does suffer from some atmospheric drag, this does not impact its primary function. The orbit is set to be the maximum a Space Shuttle could safely reach, at 539 km above the Earth, and 28.5 degrees to the Equator.

Atmospheric drag causes a gradual decline in the orbit's altitude, but this effect becomes more pronounced over extended periods. As a result, the exact location in space becomes somewhat indeterminate beyond a few days due to atmospheric variations. This minor issue does not detract from Hubble's overall success.

Comparisons with Other Space Devices

The longevity of Hubble is a testament to the quality of space engineering. Devices operating in space are often over-engineered to avoid individual component failure, which can lead to the cessation of function. The Voyager probes from 1977, for instance, are still transmitting data back to Earth, albeit with the power source running down. Similarly, the Mars rovers Spirit and Opportunity continued to function well beyond their nominal mission requirements, highlighting the ingenuity and foresight in their design.

The Future of Hubble and James Webb Space Telescope

Unfortunately, NASA's decision to retire the Space Shuttle has impacted the future of Hubble. The Space Shuttle provided the capability to service and replenish the telescope, which will soon be necessary. With the James Webb Space Telescope (JWST) set to launch in March 2021 and be placed at a Lagrange point 930000 miles from Earth, Hubble will soon need to operate independently.

To ensure a controlled de-orbit and prevent littering of space debris, NASA is planning for a carefully orchestrated descent and re-entry into Earth's atmosphere. This process will allow Hubble to burn up mostly over the ocean, ensuring that the spacecraft does not pose a threat to human habitation.