WASHINGTON — NASA will provide an updated launch date for the James Webb Space Telescope early next year, even as some warn that the mission might face further delays.

At a Dec. 6 hearing of the House Science Committee’s space subcommittee, Thomas Zurbuchen, NASA associate administrator for science, said the revised launch date would come after an independent review of the status of the spacecraft.

“At this moment in time, with the information that I have, I believe it’s achievable,” he said of the current launch window of March to June 2019, which NASA announced in September after delaying the launch from October 2018. However, he said an independent review “is exactly what we should be doing, and frankly I have directed the team to do just that in January.”

That review won’t start until January, he said, because of ongoing tests of unfolding the sunshade of the space telescope. Previous tests, he said, took much longer than anticipated, playing a key factor in the decision to delay the launch. An updated launch date, he said, would likely come in “January or February.”

Such an independent review was proposed earlier in the hearing by another witness, retired aerospace executive Thomas Young. “In my opinion, the launch date and required funding cannot be determined until a new plan is thoroughly developed and verified by independent review,” he said.

Young warned that attempting to minimize schedule delays or additional cost to JWST could add risk to the mission. “JWST is at a point in its development where the only criterion that is important is mission success,” he said. “At this stage in the project, a few extra days or weeks or even months of schedule delay, or the expenditure of some additional dollars, is a small price to pay to ensure success of a mission as important as JWST.”

Zurbuchen didn’t identify any additional issues that might lead to more delays for JWST. However, Cristina Chaplain of the Government Accountability Office cautioned that the risk for such delays remained given the assembly and testing phase the spacecraft is in.

“More delays are possible given the risks associated with the work ahead and the level of schedule reserves that are now below what is usually recommended,” she said.

The hearing also addressed issues with the Wide-Field Infrared Survey Telescope (WFIRST), the next flagship-class astrophysics mission after JWST. In October, Zurbuchen directed the project to examine changes to the spacecraft, still in an early design phase, after an independent review found the mission was “not executable” without design changes or additional funding. Zurbuchen said at the hearing he expected to get a redesigned concept for the mission in February.

Young, in his testimony, said he was not concerned about WFIRST because NASA is addressing the cost concerns while the mission is still in an early phase. “NASA is to be congratulated for taking an important step” in the form of the independent review, he said.

“I want to emphasize that there is no cause for panic,” he said. “What is transpiring is a perfectly healthy process to assure that the scope, cost and risk are appropriately defined prior to proceeding past milestone B,” a reference to Key Decision Point B, which NASA has postponed while the WFIRST redesign takes place.

In his opening statement, subcommittee chairman Rep. Brian Babin (R-Texas) said that NASA’s decision to use a donated telescope assembly from the National Reconnaissance Office may not have provided the cost savings once promised for WFIRST, and hinted that decision should be revisited.

“Several years ago, this committee suggested NASA study WFIRST to determine if the assets from NRO would be appropriate for this mission, and whether it would cost more to repurpose existing hardware than to build the observatory from the ground up,” he said. “Now we face additional questions about the scope of the mission.”

Zurbuchen also faced questions about another, smaller space telescope mission, the Transiting Exoplanet Survey Satellite (TESS), which is scheduled for launch by March 2018. He said a focus shift detected in the spacecraft’s camera during low-temperature testing, announced earlier this year, should not prevent the spacecraft from achieving its science goals.

Rep. Mo Brooks (R-Ala.) quizzed Zurbuchen about the status of TESS’ launch vehicle, the SpaceX Falcon 9. The Block 4 version of the rocket that will be used to launch TESS has yet to be certified by NASA for the mission, and Brooks asked if there were concerns that the rocket will not be certified in time.

“At this moment in time I don’t have any such concerns,” Zurbuchen said, anticipating the certification process would be completed by early 2018.