Problems with lasers have caused a 17-month delay in the launch of a satellite that will measure changes in polar ice-sheet mass and elevation, according to a Government Accountability Office (GAO) assessment.
Two lasers designed for use aboard the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) failed during ground testing due to cracked crystal, the report stated. The lasers have been repaired and will be used for the $1 billion mission. Only one laser is needed for mission success; the other one is a backup in case of the failure of the primary laser.
The spacecraft is a follow-on to the earlier ICESat mission, which was launched in January 2003.
“The measurements will provide researchers a better understanding of the mechanisms that drive polar ice changes and their effect on global sea level,” the assessment found. “ICESat-2’s upgraded laser instrument will allow the satellite to make more frequent measurements and provide better elevation estimates over certain types of terrain than ICESat.”
ICESat-2 is scheduled to launch on Sept. 12 aboard a Delta II rocket from Vandenberg Air Force Base in California. The flight will be the final one for the Delta II booster, which entered service in 1989. The launch vehicle has flown 155 times, with 153 successes, one failure and one partial failure.
The GAO’s assessment of the ICESat-2 project is below.
NASA: Assessments of Major Projects
Government Accountability Office
May 1, 2018
Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2)
The Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) is a follow-on mission to ICESat that will measure changes in polar ice-sheet mass and elevation. The measurements will provide researchers a better understanding of the mechanisms that drive polar ice changes and their effect on global sea level. ICESat-2’s upgraded laser instrument will allow the satellite to make more frequent measurements and provide better elevation estimates over certain types of terrain than ICESat.
NASA Lead Center: Goddard Space Flight Center
International Partner: None
Launch Location: Vandenberg Air Force Base, CA
Launch Vehicle: Delta II
Mission Duration: 3 years
Requirement Derived from: 2007 Earth Science Decadal Survey
Budget Portfolio: Science, Earth Science
The project will miss its rebaselined committed launch date but does not expect the cost to exceed the rebaseline because it has sufficient cost reserves to cover the delay. The project will miss its committed launch readiness date of June 2018 due to issues with its sole instrument—the Advanced Topographic Laser Altimeter System (ATLAS). In July 2016, the ICESat-2 project encountered problems with
the flight lasers developed for ATLAS that caused NASA to delay the launch date to October 2018, which is 17 months beyond the original baseline and 4 months beyond the rebaselined date set in 2014.
The project held its system integration review and began system-level integration and test in August 2017. The two repaired lasers that will fly on the ATLAS instrument were shipped back to Goddard Space Flight Center, completed flight acceptance testing, and are integrated onto the instrument. The project entered the system assembly and testing phase in October 2017.
Cost and Schedule Status
The project will miss its rebaselined committed launch date but does not expect the cost to exceed the rebaseline because it has sufficient cost reserves to cover the delay. The ICESat-2 project is proceeding to integration and test after problems with lasers within the primary instrument—the Advanced Topographic Laser Altimeter System (ATLAS)—caused NASA to delay the launch readiness date from June 2018 to October 2018. This represents a 17-month delay beyond the original baseline and a 4-month delay beyond the rebaselined date set in 2014.
However, the project is working to an earlier, September 2018 launch readiness date. The project completed a cost and schedule replan in October 2017, which required a large portion of remaining headquarters-held cost reserves, but did not take the project over its baseline commitment of $1,063.5 million.
The project is holding cost and schedule reserves at the level required by NASA center policy, but the project will need to realign funding planned for system integration and testing to address a shortfall in cost reserves for the operations phase. The project held its system integration review in August 2017 and received approval to enter the system assembly and testing phase in October 2017.
Technology and Design
Over numerous years, the ICESat-2 project has addressed issues with its flight lasers, and continues to mitigate the risk that they might fail again in the future. During ATLAS environmental testing in 2016, the project determined two of its three lasers needed repairs due to cracked crystal. The remaining laser did not require rework and continued to operate—completing over 2,300 hours of runtime.
Subsequently, the project found that components on a test model—similar to the laser that did not need repairs—cracked while in storage. Project officials were unable to identify a single root cause of the cracking but determined this was an indication that the unrepaired laser could fail. ICESat-2 only needs one laser for mission success, but will carry a second for redundancy.
In July 2017, following the completion of a trade study to determine which two of its three flight lasers should fly on ATLAS, NASA decided to use the two lasers that were repaired for flight. Officials said this decision was due to uncertainty in the reliability of the unrepaired laser and that the repaired lasers fully address the factors that contributed to the fractures.
Since being repaired, together these lasers have completed a total of over 1,200 hours of runtime and have performed to requirements. Flying the two repaired lasers does not affect the project’s plans to launch in September 2018. However, the project is carrying multiple risks to account for the potential that the repaired lasers could still fail at various points in time. For example, the project is carrying two risks that weigh the effect of the lasers failing on the ground during integration and test or failing while on orbit. If a laser fails during integration and test, it would take 5 weeks to replace it with a spare.
Integration and Test
The ICESat-2 project is proceeding through integration and test now that the ATLAS flight lasers are integrated onto the instrument and undergoing performance testing. The project held its system integration review and began system-level integration and test in August 2017.
The two repaired lasers that will fly on the ATLAS instrument were shipped back to Goddard Space Flight Center and completed flight acceptance testing. On one of the repaired lasers, which was fully integrated onto the optical bench, the project observed an unusual pattern in its optical components during initial performance testing, and ATLAS officials have convened a review board to investigate the cause of this issue. The other repaired laser, which performed as expected during acceptance testing, began integration in September 2017 and is now undergoing performance testing.
Project Office Comments
In commenting on a draft of this assessment, ICESat-2 officials stated that during initial ATLAS testing, flight laser two exhibited an anomalous laser behavior. Project officials stated the laser was transported back to the contractor for cleaning and testing, which revealed comparable results to previous tests. The laser was returned to NASA and is performing normally. Project officials also provided technical comments, which were incorporated as appropriate.