WASHINGTON — Despite spending nearly $200 million on spacesuit development over the last eight years, NASA runs the risk of not having a next-generation spacesuit ready for testing on the International Space Station before the station is retired, the agency’s auditors warned.

In an April 26 report, NASA’s Office of Inspector General (OIG) also warned that NASA’s declining current inventory of spacesuits, developed in the 1970s, pose a risk to continued operations of the ISS, particularly if its life is extended to the late 2020s.

Those current spacesuits, formally known as Extravehicular Mobility Units (EMUs), are used for spacewalks outside the ISS. A key element of the suit is its Primary Life Support System (PLSS), the backpack-like structure that houses equipment to regulate levels of oxygen and carbon dioxide within the suit and control its temperature.

NASA built 18 PLSS units, but only 11 remain available for use today. Of those 11, four are considered flight-ready today and are on the ISS, with the other seven in various stages of disassembly or testing on the ground.

The OIG report warned that further losses of PLSS units, either from launch failures or because of irreparable damage, could jeopardize NASA’s ability to perform spacewalks outside the station, which in turn could affect station maintenance. The agency said that the current supply of spacesuits should be sufficient to support station operations, but auditors were not convinced.

“NASA will be challenged to continue to support the EVA needs of the ISS with the current fleet of EMUs through 2024 — a challenge that will escalate significantly if Station operations are extended to 2028,” the report concluded.

NASA has ruled out building additional PLSS units, citing a cost as high as $250 million per unit given their old technology. Instead, NASA has worked on new spacesuit designs, including those that could support future missions beyond Earth orbit. Those efforts, though, have suffered a series of problems, according to the OIG report.

Auditors were particularly critical of the Constellation Space Suit System program, which started with a 2009 contract to Oceaneering International to develop a spacesuit as part of the Constellation exploration program. NASA kept that contract active until January 2016 despite the cancellation of the overall Constellation program in 2010, spending a total of $135.6 million on it, including $80.8 million after NASA cancelled Constellation.

The report criticized NASA for extending the program, with a new focus on developing spacesuit technologies, in part because it duplicated work on another NASA effort, the Advanced Space Suit Project. Technologies being developed by that project were often more advanced than those being developed simultaneously by the Constellation suit program, auditors found, even though NASA spent nearly three times as much on the Constellation contract.

The Advanced Space Suit Project, though, has had issues of its own, including a lack of defined destinations for NASA exploration missions that affect spacesuit design as well as “competing funding priorities” that meant that the project was funded for only half of the 2016 fiscal year.

That project is now working on a spacesuit design known as an Exploration EMU, or xEMU, that will start with a prototype called xEMU Lite to be tested on the ISS. Current schedules call for that suit to be delivered to the station in 2023 for testing. “This schedule leaves only one year for testing before the Station’s planned 2024 retirement,” the report stated, but added that “extending ISS operations beyond 2024 would alleviate this schedule pressure.”

A third program, the Orion Crew Survival Suit, is a pressure suit designed for use in the Orion spacecraft and is based on the Advanced Crew Escape System suits used during the shuttle program. That program, too, is facing schedule pressures, with a delivery of the suits currently planned just five months before the current launch date for the first crewed Orion mission in August 2021. That date, though, may be delayed, based on a recent separate OIG review of NASA’s exploration programs.

NASA has spent nearly $200 million on those three next-generation spacesuit programs. “Despite this investment, the Agency remains years away from having a flight-ready spacesuit capable of replacing the EMU or suitable for EVA use on future exploration missions,” the report concluded.

Auditors made several recommendations to NASA, including creating a formal plan for developing a next-generation spacesuit, performing a trade study comparing maintaining the current EMU spacesuits versus developing a new one, and apply lessons learned from existing spacesuit efforts to new designs. NASA accepted all three recommendations, and plans to have a spacesuit development plan completed by the end of September.