From Spaceflight Insider: “James Webb Space Telescope may be delayed again”


Spaceflight Insider

August 5th, 2017
Joe Latrell

NASA/ESA/CSA Webb Telescope annotated

The much delayed and over budget next-generation James Webb Space Telescope (JWST) has suffered another setback prior to its journey to the launch pad: the October 2018 launch may be in conflict with Europe’s BepiColombo mission to Mercury. Both spacecraft are to be flown on Ariane 5 boosters, but the spaceport at Kourou, French Guiana, cannot support two flights in the same month. BepiColombo has priority due to the tight launch window to reach Mercury. This will result in the JWST having its launch date pushed back to 2019 at the earliest.

The James Webb Space Telescope

The JWST is a space-based infrared telescope. To operate properly, it needs to maintain a temperature of 37 kelvins (–236 °C / –393 °F). In order to achieve this when in space, the telescope relies on a large tennis court sized sunshield to protect it from external heat and light sources, such as the Sun as well as the Earth and Moon.

Light gathered from the segmented 6.5-meter (21-foot) diameter mirror is directed to the four science instruments: Fine Guidance Sensor / Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS), Mid-InfraRed Instrument (MIRI), Near InfraRed Camera (NIRCam), and Near InfraRed Spectrograph (NIRSpec). Due to the requirement of the MIRI to operate at an even lower temperature than the other science instruments, it will utilize a cryocooler to decrease its temperature to less than 7 kelvins (–266 °C / –447 °F).

While smaller than telescopes here on Earth, the JWST is the most powerful space telescope ever constructed and is the science successor to the Hubble telescope.

NASA/ESA Hubble Telescope

Originally projected to cost $1.6 billion, the telescope’s price tag has ballooned to over $8.8 billion. Several factors, from delays in choosing a launch vehicle to management issues, contributed to the soaring costs. Additionally, the vehicle proved harder to construct than originally envisioned. For example, during vibration testing, the spacecraft experienced several anomalies that required NASA engineers to stop the test. After analysis and modifications, the tests resumed and the JWST was given a clean bill of health.

Despite the technical issues and threats of cancellation, the project continued and the cost estimates grew. A launch delay into 2019 will only add to that dollar figure.

The BepiColombo mission

ESA/JAXA BepiColombo

ESA/JAXA Elements of the BepiColombo Mercury Composite Spacecraft. From left to right: Mercury Transfer Module (MTM), Mercury Planetary Orbiter (MPO), Magnetospheric Orbiter Sunshield and Interface Structure (MOSIF), and Mercury Magnetospheric Orbiter (MMO).

BepiColombo is a mission to explore the planet Mercury that is being conducted by the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). The mission is actually two spacecraft: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). The objective is a comprehensive study of Mercury, including the planet’s surface, magnetic field, and interior structure.

The MPO is a solar-powered spacecraft carrying 11 scientific instruments. These instruments include laser altimeters, spectrometers, magnetometers, as well as several cameras. It has a mass of 1,150 kilograms (2,540 pounds) and is capable of producing 1,000 watts of power for onboard instruments.

The MMO has a mass of 285 kilograms (628 pounds) and carries five scientific payloads. Built mostly by Japan, this spacecraft will study plasma particles including high-energy ions and electrons emanating from the planet. A third spacecraft, the Mercury Surface Element (MSE), a small lander craft, was removed due to budgetary issues.

The two Mercury spacecraft are scheduled to arrive at the planet in 2025 after performing numerous flybys: one at Earth, two at Venus, and six at Mercury. The craft must launch sometime between October 5, 2018, and November 28, 2018, to reach the planet as scheduled.

Both missions as slated to fly on the Ariane 5 booster. The 52-meter (171-foot) vehicle is capable of lifting over 10,500 kilograms (23,100 pounds) to Geosynchronous Transfer Orbit (GTO).

JWST chills in Chamber A

Currently, the JWST is undergoing low-temperature checks at NASA Johnson Space Center’s Chamber A. The temperature of the chamber is steadily being reduced to approximately 20 kelvins (–253 °C / –424 °F) – the same temperature that the JWST will be when operating in space. These tests will validate that the JWST instruments can operate properly at the extremely low temperatures.

Unlike Hubble, the JWST will be positioned at the Earth-Sun Lagrange point (L2) which is 1,500,000 kilometers (930,000 miles) from Earth. That location is currently beyond NASA’s manned space capabilities; therefore, precluding the JWST from being serviced on orbit.

LaGrange Points map. NASA

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