ESA Solar Orbiter mission rides on ULA Atlas V to study the Sun

by Chris Gebhardt

A mission years in the planning and building took its next great leap Sunday evening as the European Space Agency’s Solar Orbiter blasts off on a 7-year mission to study the Sun. 

The probe launched atop a United Launch Alliance Atlas V 411 rocket from SLC-41 at the Cape Canaveral Air Force Station, Florida, at the start of a 2-hour launch window that opens at 23:03 EST Sunday evening (04:03 UTC Monday morning).

During the two-hour launch window, there were 25 single-second instantaneous opportunities — one every 5 minutes — in which Atlas V could launch owing to the ever-changing trajectories needed to insert Solar Orbiter into an interplanetary transfer heliocentric orbit to Venus.

The launch:

Launch of Solar Orbiter was scheduled to occur just 5 hours 24 minutes after Northrop Grumman launched their Antares 230+ rocket with the NG-13 Cygnus cargo resupply mission to the International Space Station. However, the Antares launch was scrubbed.

Ahead of the Cygnus standdown, the doubleheader launch campaign off the east coast of the United States marked a very rare occurrence of such an event and saw both the Mid-Atlantic Regional Spaceport and the 45th Eastern Range in Florida work together to ensure both missions could launch. 

For the Eastern Range in Florida, this included advancing some frequency and communication checks between Range assets and the Atlas V’s flight termination system.  Those Eastern Range systems and antennas were then powered off so they did not interfere with Antares’ ability to communicate with the Bermuda tracking station during its launch. 

All of the Eastern Range assets for flight termination of the Atlas V would have then been reactivated and reverified had Antares successfully launched.

Atlas V:

The launch vehicle tasked with sending Solar Orbiter on its way to Venus was the United Launch Alliance Atlas V rocket flying and its 411 configuration

This mission was the 82nd flight of the Atlas V and the sixth of its 411 configuration.

The Atlas V 411 is the most unique rocket configuration currently operational around the world — flying with a 4-meter payload fairing (4), a single solid rocket booster (1), and a single engine Centaur upper stage (1).

The single side-mounted solid rocket booster creates a tremendous amount of asymmetrical thrust that must be compensated for by the Thrust Vector Control systems on the Atlas V booster itself.

The ability for the Atlas V to fly with just a single solid rocket booster is only possible due to the gimbal range of the RD-180 main engine on the Atlas core booster.

Rockets fly by aiming the center of thrust through the center of mass of the vehicle — allowing them to fly a perfectly straight trajectory.

Atlas V rolls out to the pad for Solar Orbiter launch. (Credit: Nathan Barker for NSF/L2)

The RD-180 on the 411 configuration is progressively gimballed to counteract the asymmetrical thrust of the single solid rocket, allowing Atlas V to fly a straight trajectory.

For launch, the RD-180 engine was commanded to ignite at T-2.7 seconds.

At T0, the single solid rocket was lit and Atlas V lifted off.

After power-sliding off the pad and ascending through SLC-41’s lightning protection system towers and wires, the Atlas V performed a pitch and roll maneuver to align itself onto the proper azimuth – trajectory – for a flight to the east-southeast of Cape Canaveral.

The azimuth, in this case, will not be due east based on the position Centaur needs to obtain in Earth parking orbit before reigniting its engine to inject Solar Orbiter into a Venus-transfer heliocentric (Sun) orbit.

The mission:

Solar Orbiter is the 7th spacecraft built by the European Space Agency to study the Sun and how it affects Earth.

The mission follows in the footsteps of Ulysses, SOHO, and the four satellite Cluster missions with one notable difference: Solar Orbiter will be the first spacecraft to ever capture photographs and video of the Sun’s poles.

In its own right, Solar Orbiter is the first medium-class mission of the European Space Agency’s Cosmic Vision 2015-2025 Programme which seeks to answer questions about the development of the planets and the emergence of life, how the solar system works, the origins of the universe, and the fundamental physics at work in the universe. 

The Solar Orbiter in the clean room at Astrotech prior to encapsulation in the Atlas V payload fairing. (Credit: Mike Deep for NSF/L2)

Solar Orbiter, as the name implies, will seek to answer the second main objective of the Cosmic Vision Programme, examining how the Sun creates and controls the heliosphere.

The heliosphere is the vast bubble of charged particles blown through the solar system by the solar wind that extends outward to about 120 Astronomical Units from the Sun, with 1 Astronomical Unit being 149.59 million kilometers.

NASA’s Voyager 1 spacecraft crossed out of the heliosphere at a distance of 121 AU in August 2012, and Voyager 2 exited at a distance of 119 AU in November 2018.

While it took the Voyagers 35 and 41 years to escape the heliosphere, the region begins and is generated at the Sun, as is the solar wind. 

But large questions remain about exactly how the Sun creates and sustains the heliosphere and how the solar wind is formed and ejected from the Sun in all directions at a speed that is vastly and quickly accelerated within the solar corona.

In combination with NASA’s Parker Solar Probe, which was launched in 2018, the ESA Solar Orbiter will seek to gain new understanding and information about how the solar wind is generated, the heliospheric magnetic field generated by the Sun, solar energetic particles, transient interplanetary disturbances in the solar wind and heliosphere between Mercury, Venus, and Earth, and the Sun’s magnetic field.

While Parker Solar Probe seeks to answer similar questions by diving into the Sun’s corona, the region where the solar wind is formed and accelerated, the Solar Orbiter will seek to answer the same questions by observing from above and also examining the role the Sun’s poles play in the generation and sustainability of the heliosphere and solar wind.

To accomplish its mission, Solar Orbiter will use multiple gravity assist flybys of Venus and Earth to change its orbital inclination relative to the Sun’s equatorial plane so that it is inclined to the solar equator by 24 degrees by the end of its primary mission and up to 33 degrees by the end of its extended mission.

The spacecraft’s orbit will also be highly elliptical thanks to the gravity assist flybys of Venus and Earth, coming to within just 0.28 AU of the Sun at perihelion and swinging outward to 1.2 AU at aphelion. 

It will take the spacecraft two years to reach its operational orbit, which will then be followed by 5 years of a primary scientific mission. 

Solar Orbiter carries enough onboard propellant that its mission can be extended to at least 10 years total.

For its primary science mission, Solar Orbiter will have just 10 days of active science gathering operations each orbit — corresponding to each 0.28 AU perihelion pass of the Sun.

During these 10-day periods, doors on the front of the spacecraft’s heat shield will open, exposing some of Solar Orbiter’s instruments to the direct intensity heat and light of our parent star.

The instruments that will be directly exposed to the Sun during each perihelion dive are the Energetic Particle Detector, the Magnetometer, the Radio and Plasma Waves instrument, and the Solar Wind Plasma Analyser.

The Energetic Particle Detector from Spain, Germany, the United States, and the European Space Agency will measure the composition, timing, distribution, sources, acceleration mechanism, and transport processes of suprathermal and energetic particles.

The Magnetometer, provided by the United Kingdom, will provide high precision measurements of the heliospheric magnetic field and will facilitate detailed studies into:

  1. the way the Sun’s magnetic field links into space and evolves over the solar cycle,
  2. how particles are accelerated and propagate around the Solar System, including to the Earth, and 
  3. how the corona and solar wind are heated and accelerated.

Meanwhile, the Radio and Plasma Waves experiment from France, Sweden, the Czech Republic, and Austria will measure magnetic and electric fields using a number of sensors and antennas to determine the characteristics of electromagnetic and electrostatic waves in the solar wind.

It will be a constantly running experiment, performing both active measurements during perihelion and remote-sensing operations during all other periods of Solar Orbiter’s orbits.

Finally, the Solar Wind Plasma Analyser, provided by the United Kingdom, Italy, France, and the United States, is a suite of sensors that will measure the ion and electron bulk density, velocity, and temperature of the solar wind.

The instruments will help characterize the composition of the solar wind in the Carbon, Nitrogen, Oxygen group as well as Iron, Silicon, or Magnesium.

More impressively, for the first time ever, these instruments will be able to talk to each other in real-time, letting each other know if they find something interesting the others should immediately examine.

After each 10-day science perihelion pass of the Sun, Solar Orbiter’s remote-sensing instruments will continue constantly gathering information and measurements.

These instruments include:

  • Extreme Ultraviolet Imager
  • Coronagraph
  • Polarimetric and Helioseismic Imager
  • Heliospheric Imager
  • Spectral Imaging of the Coronal Environment
  • X-ray Spectrometer/Telescope

The Extreme Ultraviolet Imager is a collaboration between Belgium, the United Kingdom, France, Germany, and Switzerland and will provide image sequences of the solar atmospheric layers above the photosphere (the luminous envelope of a star from which its light and heat radiate).

This instrument will provide “an indispensable link between the solar surface and outer corona that ultimately shapes the characteristics of the interplanetary medium,” according to ESA.

It will also provide the first-ever Ultraviolet images of the Sun’s poles.

The Coronagraph, a partnership of Italy, Germany, and the Czech Republic, will simultaneously image the visible, ultraviolet, and extreme ultraviolet emission of the solar corona to determine, with unprecedented coverage and resolution, the structure and dynamics of the full solar corona — a region critical in linking solar atmospheric phenomena to their evolution in the inner heliosphere.

Additionally, the Polarimetric and Helioseismic Imager from Germany, Spain, and France will capture high-resolution, full-disc measurements of the photospheric vector magnetic field as well as line-of-sight velocity measurements to enable unprecedented investigations into the solar convection zone.

The solar convection zone is an area of the Sun that is unstable due to convection (like air currents on Earth that become unstable due to dynamic heating, creating updrafts of warm air and downdrafts of cooled air).

Solar convection is the en mass movement of plasma that forms a circular convection current where heated plasma shoots upward while cooled plasma falls back into the Sun.

The Atlas V 411 on Sunday morning at SLC-41. (Credit: Brady Kenniston for NSF/L2)

Meanwhile, the Heliospheric Imager from the United States will investigate and photograph the quasi-steady flow and transient disturbances in the solar wind over a wide field of view by observing visible sunlight scattered by solar wind electrons.

This instrument should allow heliophysicists to pinpoint Coronal Mass Ejections that could cripple our technology on the ground and in space.

Moreover, the Spectral Imaging of the Coronal Environment instrument from the United Kingdom, Germany, France, Switzerland, and the United States will seek to examine the plasma properties of the Sun’s on-disc corona to match real-time composition signatures of solar wind streams to their source regions on the Sun’s surface.

Finally, the X-ray Spectrometer/Telescope is provided by Switzerland, Poland, Germany, the Czech Republic, and France.  It will provide spectroscopy imaging of solar thermal and non-thermal x-ray emissions to provide details on timing, location, intensity, and spectra of accelerated electrons and high-temperature plasma associated with solar flares or micro-flares.

All of these instruments were designed to accomplish the missions primary scientific objectives:

  1. What drives the solar wind and where does the coronal magnetic field originate from?
  2. How do solar transients drive heliospheric variability?
  3. How do solar eruptions produce energetic particle radiation that fills the heliosphere?
  4. How does the solar dynamo work and drive connections between the Sun and the heliosphere?

In combination with the Parker Solar Probe, it is hoped that these two missions will provide us with enough insight into how the Sun creates the solar wind and the heliosphere and how Coronal Mass Ejections form and their underlying causes that we can accurately predict when and where these types of solar eruptions will occur.

Coronal Mass Ejections spew highly energetic particles and radiation outward from the Sun in huge blasts that could cripple or damage spacecraft electronics, Earth’s power grids and communications networks, and negatively and potentially seriously impact astronaut health on long-duration missions to the Moon and Mars.

Being able to accurately predict solar weather and Coronal Mass Ejections — like we predict weather here on Earth — could provide crucial time needed to safe ourselves, our astronauts, and our technology should a major solar eruption ever strike Earth.

And such an occurrence has happened at least once in recent history.

A major Coronal Mass Ejection storm struck Earth on 1-2 September 1859, crippling telegraph systems worldwide and producing visual auroras as far south as the Caribbean, south-central Mexico, Queensland, Cuba, and Hawaii and even Colombia near the equator.

Telegraph systems all over the planet failed and imparted electrical shocks to operators while lines and poles sparked.

A solar eruption of that same magnitude today would cause widespread electrical disruptions, blackouts, and damage to electrical grids and communications systems.

In fact, a storm of a very similar magnitude erupted from the Sun in 2012 and narrowly missed Earth by just 9 days.

With Solar Orbiter, we stand a chance of being able to protect ourselves in some ways — the very least of which would be preparations for impending blackouts and communications systems failures that could last weeks or months.

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