Is the James Webb Space Telescope all alone out there?

In December, an Ariane 5 rocket finally launched the James Webb Space Telescope (JWST). It is currently on its way to the Sun-Earth Lagrange point L₂. And scheduled to arrive there on 24 January. But wait a minute, what is a Lagrange point? And are there more active spacecrafts at Lagrange points? Or is it all alone out there?

What are Lagrange points?

Let’s start with the Lagrange points. At these points, the gravitational forces of two large bodies (e.g., the Sun and the Earth) and the centrifugal force balance each other. This makes them very interesting for positioning satellites, as very little orbit corrections are necessary to keep them in place. Which in turn means you need less propellant and therefore can have a longer mission duration.

There are five such points for each combination of two orbital bodies. Leonhard Euler discovered the points named L₁ to L₃. Later, Joseph-Louis Lagrange discovered the points named L₄ and L₅. And he also published an “Essay on the three-body problem” in 1772.

If this is a very short summary, I recommend watching “What Makes Lagrange Points Special Locations In Space” by Scott Manley.

With JWST on its way to the Sun-Earth L₂ point, do we currently have more active spacecrafts at the Sun-Earth Lagrange points? And what about the Earth-Moon Lagrange points? The short answer, yes we do. Let’s start with the spacecrafts at the Earth-Moon L₂ point I briefly mentioned in my previous post.

Earth-Moon Lagrange point L₂

The Earth-Moon L₂ point is, seen from Earth, located behind the Moon. It is located about 448,900 km from Earth’s center. So, what can we find out there?

Queqiao

Queqiao (‘magpie bridge’) is basically a relay satellite for China’s Chang’e 4 lander and rover. It launched on 20 May 2018 on a Long March-4C and is in a Halo orbit of the Earth-Moon L₂ point. It was placed in this orbit because from there it always has a direct line of sight with Earth and the far side of the Moon. Enabling the satellite to relay communication signals from the Chang’e 4 lander and rover on the far side of the Moon to ground stations on Earth.
Because the Moon always faces the Earth with the same side, the far side always faces away from Earth, called tidal locking. So, if you want to communicate with a lander or rover there, you have to use a relay satellite. Which is what China did with Queqiao and Chang’e 4. Take a look at my last post for more details about the Chang’e 4 mission.

But Queqiao has more to offer. It also features the Netherlands-China Low Frequency Explorer (NCLE). This is a prototype of a radio telescope to record weak radio signals from a period just following the Big Bang. It is not possible to record these signals on or near Earth because its atmosphere blocks those signals.

Sun-Earth Lagrange point L₁

Now, let’s move on to the Sun-Earth Lagrange points. We’ll start with L₁. The location of the Sun-Earth L₁ point is on a line between the Sun and Earth – at about 1.5 million kilometers from Earth. From there, you can permanently see the sunlit side of Earth. And now over to the spacecrafts.

SOHO – Solar and Heliospheric Observatory

SOHO is a spacecraft dedicated to studying the Sun – from the inside out, up to the solar wind. It launched on 2 December 1995. And moved to the Sun-Earth L₁ point for an unobstructed view of the Sun. SOHO is a collaborative mission between NASA and ESA. It features 12 scientific instruments. With the goal to study structure and dynamics of the solar interior, the Heliosphere as well as the solar wind. In addition, it studies the interaction of solar energetic particles with the Earth.

ACE – Advanced Composition Explorer

Like the SOHO spacecraft, ACE is a spacecraft mainly studying the sun. Or more specifically, to investigate the energetic particles ejected from the Sun. Also called the solar wind. But its instruments also collect and analyze particles of interplanetary, interstellar and galactic origins.

It launched on 25 August 1997 on a Delta II out of Cape Canaveral. It is run by NASA. And can theoretically continue its mission until about 2024. With the main limiting factor being the fuel aboard the spacecraft.

As of 2015, ACE primarily provides space weather reports. Therefore, it delivers near-real-time coverage of solar wind parameters and measures the intensities of energetic solar particles. Scientists use the data to provide warnings of geomagnetic storms that can disrupt communications on Earth, threaten spacecrafts in orbit and harm astronauts in space.

With DSCOVR it already has a successor, also still being operational. Let’s look at DSCOVR.

DSCOVR – Deep Space Climate Observatory

This one has an interesting story, before finally reaching orbit and 100 days later the Sun-Earth L₁ point. Originally proposed under the name Triana to observe Earth as a planet in 1998. It was scheduled to launch on the Space Shuttle in 2002. In 2001, the new Administration ordered NASA to limit the number of Space Shuttle launches. Dropping the spacecraft of the launch manifest. This led to the suspension of all work on the already built spacecraft. Therefore, it got the new name Deep Space Climate Observatory and was put into storage.

In 2008, the Committee on Space Environmental Sensor Mitigation Options (CSESMO) decided the spacecraft could be put to good use. Therefore, technicians removed it from storage, powered it on and ran some test to determine its status. As the spacecraft was in nearly perfect condition, NASA provided funding to refurbish and recalibrate the two Earth science instruments in 2009. In 2011, NOAA, NASA, and the USAF agreed on plans to fully refurbish and launch DSCOVR. It finally launched aboard a Falcon 9 v1.1 on 11 February 2015. If you want to, you can rewatch the webcast of its launch.

While maintaining its original instrument complement, the primary mission of DSCOVR changed. It is now tasked to monitor space weather. And hence becoming a successor to ACE. Its primary objective is to measure the solar wind and the interplanetary magnetic field, then transfer this data to forecasters on Earth in real-time. This gives forecasters warnings about solar storms 15 to 60 minutes before they reach Earth.

The secondary objective is earth observation. This is done by the Earth Polychromatic Imaging Camera (EPIC). Which has a constant view of the sunlit side of Earth and takes a new picture every two hours. The pictures are publicly available on their website. Epic also captures images of solar eclipses and of the Moon as it passes between the spacecraft and the Earth. Where latter show a unique view, the far side of the Moon. At least for us on Earth.

WIND

We have another mission to study the solar wind, the WIND spacecraft. It launched on 1 November 1994 and therefore is the oldest active spacecraft at L₁. The objective is to study sources, acceleration mechanisms and propagation processes of energetic particles and the solar wind.

In the past, WIND has changed orbits quite a bit. Before arriving at the L₁ point, the spacecraft operate in a unique figure-eight-shaped elliptical orbit around Earth at about 28,000 × 1.6 million kilometers. There it used its instruments to observe the Earth´ magnetosphere. It arrived at L₁ in November 1996. Only two years later, it changed orbit again to finally return to L₁ and remain there in 2004. Although the mission is already running for 27 years, it is expected the fuel last for another 60 years, which allows WIND to add its data to our understanding of the solar wind.

Sun-Earth Lagrange point L₂

As with the Earth-Moon L₂ point, the Sun-Earth L₂ is behind the Earth. At least seen from the Sun. It is about 1.5 million kilometers from Earth, if you extend the line between the Sun and Earth further out. This is the destination JWST is headed for. And to answer the question from the title, no it is not alone out there.

Gaia – Global Astrometric Interferometer for Astrophysics

For once, there is Gaia, which is mother Earth in Greek mythology. It launched onboard a Soyuz-ST-B / Fregat-MT from Centre Spatial Guyanais (CSG) on 19 December 2013. Its mission is to create a three-dimensional map of our Galaxy. It therefore measures the positions and velocity of approximately one billion stars. As well as determine their brightness, temperature, composition, and motion through space.

It also helps to create a catalog of more than one billion stars in our galaxy. This allows astronomers to make precise measurements of the movement of a star across the heavens. And thereby enabling them to determine its distance and motion through space. Allowing us to trace the history of the Milky Way.

Spektr-RG/SRG

The Spektr-RG/SRG launched onboard a Proton rocket on 13 July 2019 from the Baikonur Cosmodrome. Its mission is to perform the first all-sky survey using an X-ray imaging telescope. This might lead to the discovery of several hundred thousand obscured supermassive black holes.

In addition, it is tasked with observing selected regions of sky with high sensitivity to detect clusters of galaxies. And in turn make pointed observations of selected sources. Helping to improve our understanding of Dark Matter and Dark Energy.

JWST – James Webb Space Telescope

As the James Webb Space Telescope is almost at the Sun-Earth L₂ point, I already included it in this list. After decades of development and testing, it finally launched on 25 December 2021 onboard an Ariane 5. It is an optical observatory optimized for observations in the infrared wavelengths of light. Therefore, it is more of an addition than a successor to the Hubble Space Telescope. And as Hubble is still operational, they might be used to observe the same targets.

If you want to know more about JWST, browse through the links below or make a general search for JWST, as there has been a lot of great coverage lately.

Sun-Earth Lagrange point L₄ & L₅

The location of the Sun-Earth L₄ & L₅ points is ahead (L₄) of and behind (L₅) of Earth on its orbit around the Sun. For a more specific description of its location, watch the video mentioned above or take a look at this Wikipedia article. And what can we find there? Two spacecrafts of one mission.

STEREO – Solar-Terrestrial Relations Observatory

If you thought, we’d have enough spacecrafts watching the sun, there are two more at the Sun-Earth L₄ & L₅ points. They are part of the STEREO mission, which stands for Solar TErrestrial RElations Observatory. One spacecraft (STEREO A) is ahead of Earth in its orbit. The other spacecraft (STEREO B) is following behind in Earth orbit.

They both launched on a Delta II on 26 October 2006 from Cape Canaveral. By now, they have far exceeded their mission duration of a two-year mission. They are the first spacecrafts to enable stereoscopic measurements of the sun and coronal mass ejection (CME). With the goal of the mission being to understand more about the latter. Like tracking and calculating the direction of CMEs. As well as understanding their origin and consequences interacting with the Earth.

Together with data from the other spacecrafts observing the sun, they enable us to make space weather forecasts. Like for example Dr. Tamitha Skov regualarly does on her YouTube-Channel.

Final thoughts

Let’s look back at what we found. First, the James Webb Space Telescope is not alone out there. Second, the spacecrafts use Lagrange points, which mostly fit their specific mission. At Sun-Earth L₁ (and L₄, L₅) we have spacecrafts dedicated to sun observation. On the other side, at Sun-Earth L₂, we have spacecrafts dedicated to observations of outer space. And finally, at the Earth-Moon L2 point, we have a relay satellite needed for missions on the far side of the Moon.

But why do we need all those satellites watching the sun? What is the space weather? And how does it affect me? Well, that would be a post of its own. To give you a quick overview. Space Weather happens when a solar storm hits Earth. The impact can lead to disruption of communication (using radio frequencies), satellite services (like GPS or Starlink) or problems with power supply on Earth. So understanding Space Weather, and being able to predict it, becomes more important as we rely more and more on modern technology. For more details on Space Weather, start by visiting https://www.spaceweatherwoman.com.

Thank you for reading!