SPACECRAFT ACCIDENTS: EXAMINING THE PAST, IMPROVING THE FUTURE Hubble Recovery with STS Bryan Palaszewski working with the Digital Learning Network NASA.

SPACECRAFT ACCIDENTS: EXAMINING THE PAST, IMPROVING

THE FUTURE

Hubble Recovery with STS

Bryan Palaszewski working with the

Digital Learning NetworkNASA Glenn Research Center

Hubble Space Telescope Recovery (1/3)

• Launch: April 24, 1990, aboard the STS-31• Successful Deployment: April 25, 1990, with

planned duration of up to 20 years• Mission: Observe the universe with large optical

telescope– Explore the solar system. – Measure the age and size of the universe. – Search for our cosmic roots. – Chart the evolution of the universe. – Unlock the mysteries of galaxies, stars, planets,

and life itself.

Hubble Space Telescope Recovery (2/3)

• While testing the telescope, it was unable to focus correctly.

• With further testing, it was found that the primary mirror had been manufactured (or ground) incorrectly.

• A new instrument with corrective optics (lenses) was needed to improve the telescope’s performance.

Hubble Space Telescope Recovery (3/3)

• Recovery Flight: Launched on December 2, 1993, aboard STs-61.

• Mission: Capture, repair, and redeploy (release) the Hubble Telescope.

• Astronauts used many tools, as well as specialized new instruments, to correct the effects of the spherical aberration (distortion).

• The COSTAR system provided the correction.

COSTAR

• Corrective Optics Space Telescope Axial Replacement (COSTAR).

• Added as part of another instrument and inserted into the Hubble’s light path.

Corrective Optics Space Telescope Axial Replacement (COSTAR)

STS-61 Crew   

• Richard O. Covey, Commander • Kenneth D. Bowersox, Pilot• F. Story Musgrave, Payload Commander• Kathryn C. Thornton, Mission Specialist • Claude Nicollier, Mission Specialist • Jeffrey A. Hoffman, Mission Specialist • Thomas D. Akers, Mission Specialist

Hubble Servicing Missions after 1990 Deployment

• STS-61, December 2-13, 1993, aboard Endeavor.

• STS-82, February 11-21, 1997, aboard Discovery.

• STS-103, December 19-27, 1999, aboard Discovery.

• STS-109, March 1-12, 2002, aboard Columbia.

Eagle Nebula EGGs

Hubble Investigation

• The error that caused the on-orbit spherical aberration (distortion) in the primary mirror was traced to the assembly process of the Reflective Null Corrector, one of the three Null Correctors developed as special test equipment (STE) to measure and test the primary mirror.

• The investigation covered the events and the overall Product Assurance environment during the manufacturing phase of the primary mirror and Null Correctors (from 1978 through 1981).

Hubble Investigation: Cross-Checking Data (1/2)

• An optical-based verification/ certification test plan for programs of similar size to the Hubble Space Telescope typically include error budget-driven optical acceptance criteria.

• The criteria are used to cross-check interferogram data from Null Corrector tests within the tolerances imposed by the error budgets.

Hubble Investigation: Cross-Checking Data (2/2)

• Without cross-checking the data, the optical engineers missed a series of key indicators (warning flags) that should have evolved from comparisons of interferograms such as:– Phase I Refractive Null Corrector data

compared to initial Phase II Reflective Null Corrector data.

– Phase II Reflective Null Corrector data compared to Refractive Null Corrector vertex radius test results.

– Data from the Inverse Null Corrector combined with the Reflective Null Corrector compared to Reflective Null Corrector data only.

Hubble Investigation Findings• The on-site representatives (at Lockheed) for the

NASA and Quality Assurance organizations were not specifically trained in optics, which would have enabled them to provide an informed and independent evaluation of the assembly and manufacturing operations.

• The HST Program lacked: – an independent second means of final testing

each critical component. – a complete end-to-end test of the optical

system. • Either of these independent tests would have

surfaced the spherical aberration.

Hubble Investigation Findings

• NASA focused its resources on systems integration and guidance control systems, which were considered to be more susceptible to anomalies that could adversely impact on-orbit HST operation.

• Conversely, the design/manufacture of large mirrors for space applications was considered to be within the scope of existing state-of-the-art optical technology.

Hubble Investigation Findings

• For large-scale, complex programs (such as the Hubble Space Telescope), if system specification compliance and validation requirements are focused at the component level only, rather than looking at the components as part of the overall system, the formal validation of the system may be flawed.

Orbital Debris Damage

• Hubble also experiences damage from orbital debris, primarily natural micrometeoroids.

• Pieces returned to Earth (solar arrays, thermal blankets) exhibit small macroscopic and microscopic holes.