The James Webb Space Telescope Mission

Ed Weiler signed the Formulation Authorization Document in 1999, defining NGST as a NASA priority, but a mid-infrared instrument was a goal rather than a requirement. The 2000 Decadal Survey ranked NGST #1 in large space missions. The ranking was predicated on the inclusion of a mid-infrared instrument, which established it as a requirement for the mission. NASA chose an Interim Science Working Group (ISWG) to write the specifications for the instruments and advise about the telescope. NASA and ESA formed a joint Mid-Infrared Steering Committee, which developed a concept for a mid-infrared instrument (MIRI) doing both imaging and spectroscopy. The agencies negotiated a partnership in which ESA would provide the optical bench and NASA would provide the detectors and cooling system.

In 2001, while preparing the statement of work for the solicitation of the main industrial contract, Goddard descoped the telescope from 50m² to 25m² in collecting area, or 8m to 6.5m diameter. The descope was to address a mismatch between the budget and the scope in the solicitation. In mid-2002, NASA chose TRW to build the observatory, reserving the ISIM to be built by Goddard. NASA renamed NGST for James E. Webb, who was the second administrator of NASA, from 1961 to 1968. Webb was responsible for getting astronauts to the Moon in 8 years, and for expanding NASA’s science program, which built space telescopes, sent probes to Venus and Mars, and started missions to the outer planets.

In 2002, NASA selected a proposal led by Marcia Rieke of the University of Arizona to build the NIRCam. In the same proposal call, NASA selected several members of the flight Science Working Group (SWG; see Table 1), including 6 interdisciplinary scientists and the US members of the MIRI science team. NASA signed MOUs with ESA and CSA detailing the international partnership. ESA would provide the launch vehicle, the NIRSpec and the optical bench for MIRI. CSA would provide the FGS, and install a tunable-filter imager (TFI) on the other side of the FGS optical bench. The development of a cryogenic etalon meeting the requirements for the TFI would prove to be challenging and ultimately was not successful. The SWG also includes NASA Project Scientists and representatives of the partner agencies.

Phil Sabelhaus was selected as the Project Manager as the project entered its detailed design phase. In late 2003, the part of TRW selected to build JWST was acquired by Northrop Grumman. Northrop, in consultation with Goddard and the optics Product Integrity Team, selected beryllium for the mirror material. The competing glass sandwich technology had failed to meet its figure stability requirements. In addition, the Spitzer Space Telescope (building on other IR space missions) had demonstrated that construction of a high-precision beryllium mirror was possible. In 2003, the fabrication of the flight mirrors began by Northrop through a sub-contract to Ball Aerospace.

Beginning the mirrors was a key step and reflected the expectation that they could be a critical path pacing item. The Spitzer Space Telescope was launched 2003 August 25. Spitzer rapidly demonstrated the power of mid-IR space missions [140, e.g.,], and confirmed the wisdom of including the MIRI in JWST. On 2004 March 3, construction officially began for the JWST. In 2005, in order to conserve mass, a helium pulse tube cryocooler to be built by Northrop Grumman was chosen to replace the planned solid hydrogen cooler for the MIRI. published a special issue of the journal Space Science Reviews, detailing the JWST science objectives and design. In 2005 Mike Griffin replaced Sean O’Keefe as NASA Administrator, and in 2007, Griffin approved the contribution of the European Ariane 5 rocket for JWST. The final servicing mission for HST was conducted in 2009, freeing the large cleanroom at Goddard for the integration of the JWST instruments into the ISIM, the integration of the Optical Telescope Element (OTE), and the assembly of the ISIM and the OTE.

II.4 2010s

In 2010, CSA realized that they would not be able to deliver the tunable filter imager on schedule, removed the etalon, and redesigned the camera as the NIRISS. The near-infrared detectors were found to be degrading, and it became clear that they would have to be replaced. The spacecraft and sunshield were also behind schedule.

Budget troubles mounted, and Senator Mikulski asked for an independent review and a realistic budget estimate that would not grow every year. Congress was very skeptical of the planned 2014 launch date and the budget. The HgCdTe detectors were found to be degrading in storage, and a new version was ordered. NASA responded to the growing concerns around schedule and cost, by setting up a Test Assessment Team for advice on the testing path forward. In response to Senator Mikulski’s request for a full review of what was going wrong, the NASA Administrator set up the Independent Comprehensive Review Panel (ICRP). The ICRP report was hard hitting and direct, confirming the basic soundness of the mission and concurring with the recommendations of Project management that additional budget and schedule were needed. The formal recommendations were all accepted by the Administrator. The ICRP emphasized the scientific value of JWST, but outlined the budgetary issues that had plagued the Project and recommended that a thorough Joint Cost and Schedule assessment be done quickly. Project Manager Phil Sabelhaus was replaced by Bill Ochs. In 2011, that budget assessment was finished, and indicated that it would take a total budget of $8B to complete JWST with a launch in 2018, 4 years later than planned.

Frustration with JWST led to a proposed zero budget by the House Appropriation Sub-Committee on 2011 July 7. A grassroots public effort was undertaken to support Senator Mikulski’s efforts to restore the budget. The public support was remarkable. The effort paid off and agreement was reached to restore JWST. JWST’s budget of $8.0B to launch was approved by Congress late in 2011, but with strong language capping the cost. In 2012, the MIRI and NIRISS/FGS instruments arrived at GSFC. A Derecho storm cut off all three electrical power lines to GSFC in the middle of a cryo-vacuum test, but there was no damage to the JWST hardware. In 2013 the NIRCam and NIRSpec arrived at GSFC, and the four instruments were assembled into the ISIM by 2014. Altogether three cryo-vac tests were done on the instrument module, and it was assembled to the telescope and given vibration and acoustic tests at GSFC. Challenges during the three cryo-vac tests included a major snowstorm, a lightning strike on the building and a fire in the clean room prompting evacuation of the personnel. No people or flight hardware were harmed in these events, which took place between 2014 and 2016.

The eighteen primary mirror segments, the secondary mirror, the tertiary mirror, and the fine-steering mirror are all made of beryllium with a gold optical coating. Of the 18 primary mirror segments, there are 6 each of 3 optical prescriptions, to enable the six-fold symmetry of the primary mirror. Three spare mirrors, one of each optical prescription, were also prepared. In order to meet the 25nm root-mean-squared surface figure requirement for each mirror segment, the mirrors were initially polished to a surface accuracy of about 100nm, using an iterative process. The segments’ surface figures were then measured at the cyrogenic operating temperature in the X-Ray and Cryogenic Facility (XRCF) at NASA’s Marshall Space Flight Center. Using those cryogenic measurements, the segments were polished again so that they would meet the surface figure at their operating temperature. The secondary, tertiary and FSM were treated in a similar manner. The mirrors were then coated, underwent environmental testing, and acceptance testing at the operating temperatures was conducted again in the XRCF. The individual mirrors were complete by early 2012.

With the mirrors complete, the hexapod actuators were assembled onto each mirror. Assembly of the primary mirror segments onto the backplane took place at Goddard during late 2015 and early 2016. The integration of the ISIM onto the back of the primary mirror was complete by 2016 May 24, at which time, the assembled Optical Telescope element and ISIM became known as OTIS. Vibration and acoustic testing took place over the following year.

On 2017 May 7 the OTIS was flown to NASA’s Johnson Space Center on a C5C aircraft, and spent 6 months there, including a 100-day full scale cryo-vac test (see Figure 2), right through Hurricane Harvey and 1.3m of rain. On 2018 February 2 the OTIS arrived at Northrop Grumman in Redondo Beach for integration with the warm spacecraft and sunshield, which themselves were undergoing their element-level acoustic and vibration tests [88, this issue]. In 2017, delays in the spacecraft (e.g., propulsion system welding problems) and the sunshield development at Northrop began to indicate that a 2018 launch was not likely. By early 2018 it was clear that added time and money was needed, and another Independent Review Team was set up. They emphasized “mission success” but noted that a launch delay was inevitable for the integration and testing (I&T) that remained. In 2018 May, loose screws and washers were found after a vibration test of the sunshield, making it clear that a significant delay was necessary to get JWST back on track. Rework of the sunshield followed. A new launch date in 2020 was selected as likely.

During this decade the Mission Operations Center was being set up at STScI, and a major software development effort was being undertaken by STScI with GSFC management for mission operations, science support and science operations. The JWST Science Advisory Committee (JSTAC) was chartered to help STScI and NASA develop science policies and approaches with the explicit goal of “maximizing the scientific return” from JWST. The JSTAC met for 8 years in parallel to the SWG. Both advisory committees were eventually succeeded by the JWST Users Committee (JSTUC).