In late 2015/early 2016, a major cryo-vacuum test was carried out for the Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST). This test comprised the final cryo-certification and calibration test of the ISIM, after its ambient environmental test program (vibration, acoustics, EMI/EMC), and before its delivery for integration with the rest of the JWST observatory. Over the 108-day period of the round-the-clock test program, the full complement of ISIM flight instruments, structure, harness radiator, and electronics were put through a comprehensive program of thermal, optical, electrical, and operational tests. The test verified the health and excellent performance of the instruments and ISIM systems, proving the ISIM element’s readiness for integration with the telescope. We report here on the context, goals, setup, execution, and key results for this critical JWST milestone.
The James Webb Space Telescope (JWST) Project has an extended integration and test (I&T) phase due to long
procurement and development times of various components as well as recent launch delays. The JWST Ground
Segment and Operations group has developed a roadmap of the various ground and flight elements and their use in the
various JWST I&T test programs. The JWST Project's building block approach to the eventual operational systems,
while not new, is complex and challenging; a large-scale mission like JWST involves international partners, many
vendors across the United States, and competing needs for the same systems. One of the challenges is resource
balancing so simulators and flight products for various elements congeal into integrated systems used for I&T and flight
This building block approach to an incremental buildup provides for early problem identification with simulators and
exercises the flight operations systems, products, and interfaces during the JWST I&T test programs. The JWST Project
has completed some early I&T with the simulators, engineering models and some components of the operational ground
system. The JWST Project is testing the various flight units as they are delivered and will continue to do so for the
entire flight and operational system. The JWST Project has already and will continue to reap the value of the building
block approach on the road to launch and flight operations.
The James Webb Space Telescope (JWST) is the first NASA mission at the second Lagrange point (L2) to identify the
need for data rates higher than 10 megabits per second (Mbps). The JWST will produce approximately 235 gigabits (Gb)
of science data every day. In order to get this data downlinked to the Deep Space Network (DSN) at a sufficiently
adequate date rate, a Ka-band 26 gigahertz (GHz) frequency (as opposed to an X-band frequency) will be utilized. To
support the JSWT's utilizations of Ka-band, the DSN is upgrading its infrastructure. The range of frequencies in the Kaband
is becoming the new standard for high data rate science missions at L2. Given the Ka-band frequency range, the
issues of alternative antenna deployment, off-nominal scenarios, NASA implementation of the Ka-band at 26 GHz, and
navigation requirements will be discussed in this paper. The JWST is also using the Consultative Committee for Space
Data Systems (CCSDS) standard process for reliable file transfer using CCSDS File Delivery Protocol (CFDP). For the
JWST mission, the use of the CFDP protocol enables level zero processing at the DSN site. This paper will address
NASA implementation of ground stations in support of Ka-band 26 GHz and lessons learned from implementing a file
based protocol (CFDP).
The James Webb Space Telescope (JWST) is part of a new generation of spacecraft acquiring large data volumes from
remote regions in space. To support a mission such as the JWST, it is imperative that lessons learned from the
development of previous missions such as the Hubble Space Telescope and the Earth Observing System mission set be
applied throughout the development and operational lifecycles. One example of a key lesson that should be applied is
that core components, such as the command and telemetry system and the project database, should be developed early,
used throughout development and testing, and evolved into the operational system. The purpose of applying lessons
learned is to reap benefits in programmatic or technical parameters such as risk reduction, end product quality, cost
efficiency, and schedule optimization. In the cited example, the early development and use of the operational command
and telemetry system as well as the establishment of the intended operational database will allow these components to be
used by the developers of various spacecraft components such that development, testing, and operations will all use the
same core components. This will reduce risk through the elimination of transitions between development and
operational components and improve end product quality by extending the verification of those components through
continual use. This paper will discuss key lessons learned that have been or are being applied to the JWST Ground
Segment integration and test program.
Proc. SPIE. 5496, Advanced Software, Control, and Communication Systems for Astronomy
KEYWORDS: Databases, Interfaces, Control systems, Space telescopes, Software development, Chemical elements, Space operations, System integration, Commercial off the shelf technology, James Webb Space Telescope
Ideas, requirements, and concepts developed during the very early phases of the mission design often conflict with the reality of a situation once the prime contractors are awarded. This happened for the James Webb Space Telescope (JWST) as well. The high level requirement of a common real-time ground system for both the Integration and Test (I&T), as well as the Operation phase of the mission is meant to reduce the cost and time needed later in the mission development for recertification of databases, command and control systems, scripts, display pages, etc. In the case of JWST, the early Phase A flight software development needed a real-time ground system and database prior to the spacecraft prime contractor being selected. To compound the situation, the very low level requirements for the real-time ground system were not well defined. These two situations caused the initial real-time ground system to be switched out for a system that was previously used by the flight software development team. To meet the high-level requirement, a third ground system was selected based on the prime spacecraft contractor needs and JWST Project decisions. The JWST ground system team has responded to each of these changes successfully. The lessons learned from each transition have not only made each transition smoother, but have also resolved issues earlier in the mission development than what would normally occur.
Selections and tradeoffs during mission concept development and ground system architecture definition determine the cost-effectiveness of the spacecraft operations. The Next Generation Space Telescope (NGST) makes this difficult due to its unique mission requirements. Experience has shown a greater savings can be achieved at the ground station and it's interfaces with the spacecraft. Since a majority of the bandwidth is used for science data, this is one of the major areas to explore.
This paper will address problems and experiences with the various approaches to accommodate the ground station interfaces with the spacecraft. As a team we have explored several approaches:
- Antenna size, frequency, and transmit power on the spacecraft is a big driver in determining the ground station cost,
- Data guarantee verses data loss risk,
- Down-linking all data verses putting more logic for science processing on board. This includes discussions on guaranteed data delivery protocols and downlink change only data,
- Evaluation of recording the data at the ground station for a reduced rate playback later, and
- Transmitters at different frequencies for simultaneous downlinks.
Many of these topics and how they are applied, change over the course of time as projects implement their requirements. To achieve the goal of 'low cost', innovated approaches have to be taken into consideration.