Arianespace’s lightweight Vega rocket launched on its penultimate flight Sunday, carrying the THEOS-2 Earth-observation satellite for Thailand, Taiwan’s Triton (FORMOSAT-7R) weather satellite, and ten small satellites. Lifoff from the Centre Spatial Guyanais in Kourou, French Guiana came after a scrub 48 hours previously.
The launch was only Arianespace’s third mission of 2023. Following the retirement of the Ariane 5, which made its last two flights in April and July, and with Soyuz operations from Kourou having been suspended after Russia’s invasion of Ukraine, Vega and its replacement Vega-C are currently the only operational vehicles in Arianespace’s fleet. This will be the first launch of the original version of Vega since November 2021, with this mission designated VV23.
Vega is being replaced with the upgraded Vega-C rocket, which increases payload capacity and sports a new first-stage P120C solid rocket motor that has been developed for the next-generation Ariane 6 vehicle, introducing commonality which will help to bring down costs. Vega-C first flew in August 2022, however, its second and most recent launch in December failed to reach orbit. The VV23 mission is the first for the Vega family since that failure.
There are twelve satellites aboard Vega for the VV23 mission. The primary payloads are THEOS-2 and Triton, while the other spacecraft aboard – termed “auxiliary payloads” by Arianespace – are CubeSats of various configurations.
THEOS-2 is an Earth-observation satellite to be operated by Thailand’s government-run Geo-Informatics and Space Technology Development Agency (GISTDA) as part of the Thai Earth Observation System (THEOS). The 417-kilogram satellite was constructed by Airbus Defence and Space, based on the AstroBus-S platform, and is expected to operate for at least ten years. It carries an imaging payload with a resolution of up to 0.5 meters.
A companion to THEOS-2, named THEOS-2 SmallSAT, has been constructed by Surrey Satellite Technology Ltd (SSTL) and is expected to be launched at a future date to join THEOS-2 in orbit. The THEOS-2 SmallSAT spacecraft is smaller than THEOS-2 and will carry a lower-resolution imaging payload to complement the higher-resolution sensor aboard THEOS-2.
THEOS-2 is a replacement for the original THEOS satellite, now known as THEOS-1, which was launched aboard a Dnepr rocket in October 2008. THEOS-1 was designed to operate for at least five years; it remains in service and continues to return valuable data fifteen years after its launch.
Triton, also known as FORMOSAT-7R, is a lightweight experimental weather satellite from the Taiwan Space Agency (TASA — formerly the National Space Organization or NSPO). The first weather satellite to be built in Taiwan, this 241-kilogram satellite is intended to gather data that will help to forecast typhoons. Triton will study how signals from navigation satellites – including the US Global Positioning System (GPS) and the Japanese Quazi-Zenith Satellite System (QZSS) – are reflected by the ocean surface to measure wind speeds in the lower atmosphere throughout a five-year mission.
The ten auxiliary payloads aboard Vega are all built to the CubeSat standard, which defines common form factors for small satellite missions based around a design unit of a cube (U), measuring 10 centimeters along each axis. Individual CubeSats may be built within the size of a single unit (or a fraction of a unit), or to occupy multiple units. These units define the CubeSat’s external dimensions but do not subdivide the spacecraft itself.
The largest CubeSat on the mission is the 12-unit (12U) Proba-V Companion CubeSat (PVCC), which measures three units along its long axis, and two units on its other two axes. This is a European Space Agency (ESA) mission that will serve the dual roles of a technology demonstrator and an Earth science research satellite. Its imaging payload comprises a single telescope with short-wave infrared (SWIR) and visible and near-infrared (VNIR) sensors. This was originally built as a ground spare for three identical instruments making up the Vegetation (VGT) payload aboard the Proba-V mission that was launched aboard Vega’s VV02 mission in May 2013.
The PVCC mission will serve to validate the technology readiness level of the satellite platform, which was developed by Belgium’s Aerospacelab, while also contributing to worldwide studies of crop and vegetation monitoring and land use. PVCC will add to the data that Proba-V is already collecting by enabling observations from different angles and at different times of the day. The companion satellite will also operate in a lower orbit than Proba-V, allowing it to produce higher-resolution images.
A three-unit CubeSat, ESTCube-2, which is being launched for the University of Tartu, will also contribute to vegetation research. It carries a pair of cameras operating at different wavelengths to map the normalized difference vegetation index (NDVI), a measure used to study the health and density of vegetation. This is one of four investigations that ESTCube-2 will carry out, with its main objective being to test an E-sail – a new technology that aims to use an electrically charged tether to adjust the satellite’s orbit. ESTCube-2 also serves as a prototype for a spacecraft platform that may be used for future deep space missions and will be used to study the corrosion of materials in the space environment.
PRETTY – Passive Reflectometry and Dosimetry – is a joint project between ESA and a consortium including the Technical University of Graz, Seibersdorf Laboratories, and Beyond Gravity. It is a 3U CubeSat, equipped with a pair of forward-facing antennae to pick up signals from navigation satellites close to the horizon.
One antenna will receive signals directly from the satellite, while the other will receive the same signals after they have been reflected by the Earth. By comparing the two signals, the satellite will be able to measure the height of ice or seawater to an accuracy of 50 centimeters, in a similar way to how Triton will use reflectometry to study ocean winds.
Advanced Nanosatellite Systems of Earth Observation Research (ANSER) is a constellation of three 3U CubeSats that will be operated by Spain’s national aerospace agency, Instituto Nacional de Técnica Aeroespacial (INTA). The ANSER Leader satellite will be responsible for communications with the ground, while the ANSER Follower 1 and 2 CubeSats will rely on the Leader to relay communications via inter-satellite links. The three satellites will fly in formation, about ten kilometers apart, using deployable wings and flaps to maintain their formation through lift and drag in the extremely thin atmosphere at their orbital altitude.
Each ANSER satellite carries part of the constellation’s imaging payload, named CINCLUS. The Leader is equipped with a panchromatic camera to allow observation conditions – such as cloud cover – to be checked, while the Follower satellites each carry a pair of hyperspectral VNIR spectrometers. INTA plans to use the ANSER constellation to monitor water quality and pollution within lakes and reservoirs on the Iberian peninsula.
Nanosat 3U pur la Surveillance du Spectre, or N3SS, will be operated by the French space agency, CNES. As its name suggests, it is a three-unit CubeSat and will be used to demonstrate whether a satellite can detect and identify sources of radio-frequency jamming.
A pair of CubeSat Carrier (CSC) satellites are being carried for Dutch-based ISISpace. The CSC-1 and CSC-2 satellites are six-unit CubeSats that host technology demonstration and space environment research payloads provided by ISISpace’s customers. MACSAT, another 6U CubeSat that will be operated by Luxembourg’s OQ Technology, will test satellite-based 5G connectivity for Internet of Things (IoT) devices.
The launch will took place from the Ensemble de Lancement Vega (ELV) launch pad at Arianespace’s spaceport – the Centre Spatial Guyanais or Guiana Space Centre – in Kourou, French Guiana. This was formerly Ensemble de Lancement Ariane 1 (ELA-1), the pad used by Ariane 1, 2, and 3 vehicles between 1979 and 1989. It was built on the site of an even earlier launch pad, CECLES, which was used for the only flight of the Europa II rocket in November 1971. ELV is today shared by Vega and Vega-C and is used for all launches made by both rockets.
Vega is a four-stage launch vehicle, consisting of three solid-propellant stages with a liquid-fuelled upper stage, the Attitude Vernier Upper Module (AVUM). AVUM provides precise final orbit insertion for the satellites via a restartable RD-843 engine. It first flew in February 2012 and has launched twenty times to date – with eighteen of its previous missions having been successful. Two additional missions have been flown by Vega-C: one of which was successful, while the other failed.
Rockets launched from ELV are assembled in place on the launch pad, with the aid of a mobile service tower. The Vega for the VV23 mission had already been stacked by the end of July, with the exception of the payload fairing and satellites which were integrated away from the launch pad and then installed on the rocket towards the end of the launch campaign.
It will take Vega about one-and-three-quarter hours from liftoff to complete the deployment of its payloads on this mission. At the zero mark in the countdown, the first stage P80 motor will ignite and propel the rocket away from its launch pad. Climbing quickly, Vega will reach a speed of Mach 1 about half a minute after liftoff and pass through Max-Q, the point at which it experiences peak aerodynamic forces, shortly after the fifty-second mark in the flight. The first stage will power the ascent for one minute and 55 seconds before it burns out and separates.
After first stage separation, the Zefiro-23 second stage takes over, making a one-minute, 44-second burn before also separating. About twelve seconds later the Zefiro-9 third stage will ignite for its burn, lasting approximately two minutes and 42 seconds. Once the third stage burns out, the mission will enter a brief coast phase as the vehicle climbs towards the apogee – or highest point – of its trajectory. The payload fairing, which protects the satellites during their ascent through the atmosphere, will separate from the rocket shortly after third-stage ignition.
Third stage separation will occur partway through the coast phase, six and a half minutes into the flight. The coast will end one minute and 35 seconds later with the start of the first of five planned fourth-stage burns required to complete the mission. This burn will place AVUM and the satellites into an initial parking orbit, with a second burn scheduled to begin at 51 minutes, 47 seconds mission elapsed time to circularise the orbit. With this complete, THEOS-2 and Triton will separate simultaneously at the 54-minute, 22-second mark in the flight.
For deployment of the primary payloads, Vega is targeting a Sun-synchronous orbit at an altitude of 600 by 617 kilometers, with an inclination of 97.9 degrees to the equator. Once these have separated, AVUM will make two further burns to lower its orbit before deploying the CubeSats.
The first of these burns will commence 35 seconds after the one-hour mark, with the second beginning 42 minutes and 14 seconds later on the opposite side of the planet. Each burn will last only a few seconds, and the CubeSats will begin to be deployed a little over a minute after the end of the fourth burn.
Once all payloads have been safely deployed, a fifth and final burn will commence one hour, 50 minutes, and 23 seconds after liftoff. This will deorbit AVUM, with its re-entry expected over the Indian Ocean between 03:45 and 05:01 UTC.
Once the launch is complete, only one more launch will remain for Vega: the VV24 mission. This is slated to carry ESA’s Biomass Earth science satellite, with launch expected no earlier than next April. Arianespace is also working towards the maiden flight of Ariane 6 towards the middle of 2024, while Vega-C’s return to flight is targeting the final quarter of next year.
Vega-C’s failure during last December’s VV22 mission was found to have been caused by unexpected erosion of a carbon-carbon throat insert in the nozzle on the second-stage engine. Vega-C uses a Zefiro-40 motor, larger than Vega’s Zefiro-23, and the investigation into the VV22 failure cleared Arianespace to resume Vega missions while modifications were made to correct the fault with Vega-C.
A new insert was designed, however, a test firing on June 28 to qualify the new component was unsuccessful with reduced performance and damage to the nozzle noted.
On Monday, the European Space Agency announced the results of an investigation into the failed test firing, identifying that the combination of the size and shape of the new insert and its different material properties to the one it had replaced had resulted in damage to other parts of the nozzle – ultimately causing it to fail. The investigation identified recommendations to improve the design of the nozzle and called for two additional test firings before flight operations are allowed to resume.
(Lead image: Vega on the launch pad ahead of a previous mission. Credit: Arianespace)