NASA’s WFIRST space telescope may be on the Trump Administration’s chopping block, but it just cleared a critical milestone review to move forward into construction. Congress has saved the telescope — the follow-on to the Hubble Space Telescope and the James Webb Space Telescope (JWST) — from cancellation twice already. It is expected to do so again for FY2021 despite the Administration’s proposal yet again to terminate it.

The Wide-Field Infrared Survey Telescope (WFIRST) was the top priority for a flagship space mission in the last astrophysics Decadal Survey issued by the National Academies of Sciences, Engineering, and Medicine. NASA and Congress rely on Decadal Surveys from the Academies to set science priorities for NASA and other agencies, like the National Science Foundation that conducts ground-based astronomy.

The Trump Administration asserts in its FY2021 budget request for NASA that it supports Decadal Survey priorities, but then proposes terminating three of them — WFIRST and two recommended in the 2007 Earth Science and Applications from Space Decadal Survey (PACE and CLARREO-Pathfinder).

WFIRST will study the universe in the infrared portion of the spectrum to advance research into dark energy and dark matter and discover new planets around other stars (exoplanets). Its field of view will be 100 greater than Hubble’s.

Development of WFIRST was delayed for several years because the money NASA planned to spend on it was needed to cover substantial cost overruns on JWST. There is no disagreement that JWST-like overruns must be avoided this time. Exasperated by continuing cost growth, Congress finally set a cost cap of $8 billion for development of JWST, but it breached that cap in 2018 and Congress had to raise it to $8.8 billion (not including launch or operations).

Congress has already set a cost cap of $3.2 billion for WFIRST, but supports the program. It provided sufficient funds in FY2020, $510.7 million, to keep it on schedule for launch in 2025. The request was zero.

Today’s announcement uses the $3.2 billion figure for the cost of WFIRST, but excludes the cost of what it calls a “ride-along” technology demonstration instrument — a coronagraph.

WFIRST’s design has changed considerably from what the Decadal Survey recommended. Adding a coronagraph was one of the most significant. Coronagraphs are disks within a telescope that essentially create an eclipse, blocking the light from the center of a star so that the area around it can be studied in more detail to determine if, for example, there are planets in the vicinity.

Two subsequent reports from the Academies warned of the technological complexities involved that could raise costs and stretch schedules, but NASA has persevered despite indications that costs were rising early-on that led to a requirement that the program be descoped. It decided to make the coronagraph a “technology demonstration” instead of part of the science package so that if it does not work it will not impact the anticipated science return of the mission.

Acknowledging the cost concerns, however, NASA today separated the coronagraph from the $3.2 billion estimate. Adding it and operations after launch takes the total to $3.934 billion.

NASA’s announcement today is that WFIRST passed the Key Decision Point-C (KDP-C) milestone “giving the mission the official green light to begin hardware development and testing.” Then it dutifully added: “The FY2021 budget request proposes to terminate funding for the WFIRST mission and focus on the completion of the James Webb Space Telescope, now planned for launch in March 2021. The Administration is not ready to proceed with another multi-billion-dollar telescope until Webb has been successfully launched and deployed.”

Based on past support, Congress is expected to restore funding for WFIRST to keep it on schedule, but time will tell if it agrees to exclude the coronagraph from the $3.2 billion cost cap.

Princeton astrophysicist David Spergel, co-chair of the WFIRST science team, tweeted a reminder that getting the program restored by Congress is a critical step.

While WFIRST Is on schedule and on budget for a Fall 2025 launch, we need to again ask Congress to restore the mission to the Federal Budget. Please ask your representatives to #SaveWFIRST by signing Representative Beyer’s Dear Colleague letter. https://t.co/CVGFHqef0A — David Spergel (@DavidSpergel) March 2, 2020

Like Hubble and JWST, development of WFIRST is managed by NASA’s Goddard Space Flight Center in Greenbelt, MD and it will be operated by the Space Telescope Science Institute in Baltimore. The coronagraph will be provided by the Jet Propulsion Laboratory in Pasadena, CA, and an Infrared Processing and Analysis Center will be located there.