Ariane 5 to loft two satellites in important lead-up to James Webb launch

Close to one year after its last flight, the Ariane 5 ECA is about to… The post Ariane 5 to loft two satellites in important lead-up to James Webb launch appeared first on NASASpaceFlight.com.

Ariane 5 to loft two satellites in important lead-up to James Webb launch

Close to one year after its last flight, the Ariane 5 ECA is about to return to service with its first launch of 2021 scheduled to lift off at 21:00 UTC on Friday, July 30. The sixth overall mission for Arianespace this year follows a rework of the payload fairing due to vibration issues that could have endangered payloads.

On board the mission, named VA254, are two communications satellites bound for geostationary transfer orbit. This flight is the first of two that will precede the launch of the James Webb Space Telescope as early as this November.

The JWST program found that residual air in the telescope’s sunshield could cause an over-stress condition at the time of fairing separation, so the payload fairing was redesigned for a smoother de-pressurization process with new passive vents and sealant to trap air inside the fairing’s honeycomb material, in order to help ensure mission success for this most important payload. RUAG of Switzerland delivered these fairings for flights starting in early 2020.

However, during the Ariane flights in February and August 2020, the separation process with these redesigned fairings induced unacceptable vibrations into the payload stack. While these vibrations did not result in any sort of mission failure, Arianespace stopped flights of the Ariane 5 to investigate the issue.

The investigation also affected certain United Launch Alliance Atlas V flights that use similar fairings.

Ariane 5 launches the VA253 mission in August 2020, the final flight before a stand-down to investigate and resolve a payload fairing vibration issue – via ESA

Although no damage was done to the payloads on board the two flights where these vibrations were observed, they could have damaged the JWST and other future payloads, so a further redesign of the fairing was needed. The reworked fairings were delivered by RUAG to Arianespace and must now prove themselves on two flights before the James Webb Space Telescope can proceed on its long-awaited launch.

Ariane 5 VA254 UPDATES

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  • Flight VA254 will launch two satellites into geostationary transfer orbit from Arianespace’s launch facility in Kourou, French Guiana. The Ariane 5 is scheduled to launch at 21:00 UTC on Friday, July 30 with the Star One D2 and Eutelsat Quantum communications satellites.

    The Star One D2 satellite, massing 6190 kilograms and based on the Maxar 1300 bus, is intended to support telecommunications in South America, Central America, and the Atlantic, and was built for Brazilian operator Embratel by Maxar Technologies at its factory in Palo Alto, California. This satellite, which will occupy the 70 degrees West longitude slot in geostationary orbit, features Ku, Ka, C, and X-band transponders, which enables it to support communications using different wavelengths for multiple purposes.

    For example, the X-band transponder will support government communications traffic over the Atlantic Ocean, while the other bands will be used to offer broadband services in South and Central America, though not with the speeds that low Earth orbit constellations like Starlink would offer due to the distance signals travel between Earth’s surface and geostationary orbit at 35,786 kilometers altitude. Underserved populations would be the primary users of this service.

    The Star One D2 satellite undergoing testing at Maxar prior to shipping for launch – via Maxar

    The Eutelsat Quantum satellite has a launch mass of 3461 kilograms and is built by Airbus Defence and Space based on the SSTL GMP-T bus. It is the first European commercial-sector communications satellite with programmable frequencies and power usage so that customers can shape the coverage to their specific needs. The satellite features an electronically steerable Ku-band antenna with eight independent, configurable beams to enable this capability.

    Eutelsat Quantum will use a slot at 48 degrees East longitude to cover the Middle East and North Africa, with possibilities to cover a region from West Africa to further east in Asia. The spacecraft is equipped with the ability to support encrypted traffic, as its services are being offered to government users in the Middle East.

    The Ariane 5 was rolled out to the launch pad on Thursday, July 29, and is fueled with liquid hydrogen and liquid oxygen starting just under five hours before the launch. The Vulcain 2 engine on the core stage will ignite at T-0 and build up its thrust.

    At T+7 seconds, the solid rocket boosters will ignite and the vehicle will leap off the pad with its satellite passengers. The SRB’s will be jettisoned around T+2:20, and the all-important fairing separation will occur around T+3:10.

    The core stage’s Vulcain 2 engine will shut down around the T+9 minute mark, and the ESC-D upper stage will separate and fire shortly afterward to place the stage and the satellites in a 250 by 35,726 kilometer geostationary transfer orbit inclined three degrees to the Equator.

    After the ESC-D stage does its work, the Star One D2 satellite will separate first, from the top of the SYLDA structure (a “fairing within a fairing”) that contains the Eutelsat Quantum satellite.

    The SYLDA structure will separate after Star One is away, exposing Eutelsat Quantum for its deployment. The Eutelsat Quantum satellite’s deployment at the T+36:24 mark will end the VA254 mission, and both satellites will continue coasting on their own to geostationary altitude.

    Once at the apogee of 35,726 kilometers, they will use their own propulsion systems to circularize the orbit and change their orbital inclinations to zero degrees to occupy their operational slots, where they are expected to stay in service for the next fifteen years.

    The launch vehicle’s performance, particularly the performance of its reworked payload fairing, will be closely scrutinized by NASA as well as ESA and RUAG in the run-up to flight VA255 no earlier than September with the SES-17 and Syracuse-4A satellites, to be followed by the VA256 flight of the James Webb Space Telescope, which promises to make significant discoveries in astronomy.

    (Lead photo via ESA)

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    Chinese Long March 2D carries Tianhui survey satellite into orbit

    A Chinese Long March 2D rocket lifted off from the Jiuquan Satellite Launch Center in… The post Chinese Long March 2D carries Tianhui survey satellite into orbit appeared first on NASASpaceFlight.com.

    Chinese Long March 2D carries Tianhui survey satellite into orbit

    A Chinese Long March 2D rocket lifted off from the Jiuquan Satellite Launch Center in Inner Mongolia at 04:01 UTC today, July 29, carrying Tianhui 1-04, the fourth in China’s series of Tianhui 1 Earth observation satellites, into Low Earth Orbit.

    The launch marked the 25th orbital launch attempt from China this year and the sixth in the month of July.

    The Long March 2D‘s four YF-21C engines ignited shortly before liftoff, providing the launch vehicle with 2,962 kN of thrust, allowing the carrier rocket to loft the approximately 1,000 kg satellite into a 97.3 degree inclined Sun-Synchronous Orbit, around 490 to 500 kilometers above the surface of the Earth.

    The liftoff marks the 381st launch of a Long March series rocket, and the 54th mission using a Long March 2D, which has seen an illustrious career having seen regular service since 1992 and only one partial failure in 2009.

    Long March 2D carrying Tianhui1-04. seconds prior to liftoff – via China Daily

    The Tianhui 1 series of satellites, which first began launching in 2010 with the launch of Tianhui 1-01, are a set of topographical mapping satellites built by Aerospace Dongfanghong Satellite Company, a subsidiary of the Chinese Academy of Space Technology (CAST).

    Tianhui-1-04 Updates
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  • CAST is itself a subordinate of the China Aerospace Science and Technology Corporation (CASC), which operates China’s Long March family of rockets. The Long March launchers are also known by Chang Zheng in China.

    Literally translating to “Sky Drawing,” the Tianhui series of spacecraft are built for remote sensing and Earth observation roles on behalf of the Chinese government. The program began development in 2005, and began operation five years later with the launch of Tianhui 1-01.

    Tianhui 1-02 and 1-03, the second and third spacecraft in the series, were launched in 2012 and 2015 respectively. The three previous Tianhui spacecraft, like 1-04, were also launched aboard Long March 2D vehicles.

    Each spacecraft is built off of the CSAT2000 spacecraft bus and is equipped with a number of electro-optical sensors to facilitate it’s mission.

    Like it’s three predecessors, Tianhui 1-04 is equipped with three separate Earth observation cameras: a three-line array panchromatic camera with a spatial resolution of five meters, a panchromatic CCD camera with a spatial resolution of two meters, and a multi-spectral imager with a spatial resolution of 10 meters.

    The CSAT2000 based VRSS-2 spacecraft prior to launch in 2017 – via CAST

    The spacecraft is also fitted with three star-sensors in order to keep the spacecraft stable for long periods of time while it observes Earth’s surface.

    The CAST2000 bus is specifically made for remote sensing satellites, featuring an S-band Telemetry Tracking and Control (TT&C) sub-system and X-band data transmission sub-system communications systems, as well as its three aforementioned star sensors which provide three-axis stabilization in order to keep the spacecraft stable when conducting observations.

    The bus has seen large amounts of usage outside of the Tianhui 1 series of satellites, providing the base spacecraft for several other Earth observation programs, including the Indian Space Research Organization’s OceanSat 1A and 1B spacecraft, Venezuela’s VRSS-1 and VRSS-2 remote sensing missions, and China’s Huanjing 1A and 1B disaster and environmental monitoring spacecraft.

    Thursday’s mission lifted off from the SLS-2 pad at the Jiuquan Satellite Launch Center, one of China’s inland launch sites. Missions from Jiuquan, the Xichang Satellite Launch Center, and the Taiyuan Satellite Launch Center all result in rockets overflying populated areas on the way to orbit. This contrasts with the safety norm upheld by the majority of space faring nations, where launches are either conducted over bodies of water or uninhabited desert.

    The Long March 2D is also one of China’s launch vehicles which is fueled by toxic, hypergolic propellants. Both of the rocket’s stages are fueled by Unsymmetrical dimethylhydrazine (UDMH) with Dinitrogen tetroxide oxidizer. This can cause issues when combined with overflight of populated areas, as discarded stages containing carcinogenic fumes can land near civilians.

    The Chinese space program has been slow to transition to their new coastal launch site at the Wenchang Spacecraft Launch Site and their newer launch vehicles fueled by liquid hydrogen or kerosene with liquid oxygen. Experimental attempts to control downrange landing locations of both booster stages and fairings have been made, but no such attempt was incorporated into the launch of Tianhui 1-04.

    (Lead photo via China Daily)

    The post Chinese Long March 2D carries Tianhui survey satellite into orbit appeared first on NASASpaceFlight.com.

    Source : NASA More   

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