Space

Updates on Webb Telescope’s long journey to L2

Earlier NASA Webb Telescope tweet updates

On Twitter, NASA is providing near real-time updates when Webb successfully completes steps of its mission. You can follow along too at NASA Webb Telescope or watch our post here for updates.

EarthSky lunar calendars are back in stock! We’re guaranteed to sell out – get one while you can.

Why L2, and where is it?

Why is Webb going to a point so far away? This point in space – the second Lagrangian point – is where, in the Earth-sun system, gravitational forces and a body’s orbital motion balance each other. So a spacecraft can “hover” relatively easily at L2. It can stay near Earth, while both Earth and the spacecraft orbit the sun. In fact, the European Space Agency (ESA) has called L2 “a preeminent location for advanced space probes.” Other notable space observatories orbit or will orbit the sun at L2, including ESA’s redoubtable Gaia spacecraft, which has made so many fascinating discoveries about our Milky Way galaxy. And Gaia and Webb aren’t the only spacecraft at L2. Click here for a list of past, present and planned space probes at L2.

For Webb, another advantage of L2 is that it’s a step farther away from the heat of the sun and Earth. Satellites in Earth orbit – for example, Hubble or the space station – undergo temperature changes about every 90 minutes, depending on whether the satellite is in shadow or sun. At L2, Webb won’t undergo this same temperature-shifting effect, which has the potential to create distortions in the telescope’s ability to view the universe. Webb will observe primarily infrared light coming from faint and very distant objects. To be able to detect those faint signals, the telescope itself must be kept extremely cold: -370 F (about -220 C) or lower. That’s why Webb has a five-layer, tennis-court-sized sunshield, to protect the telescope from the heat of the sun and keep its instruments cold. Being at L2, farther from the sun than the Earth or moon, will help, too.

Illustration of Lagrangian points in sun-Earth system.
View larger. | A body’s distance from the sun – and the speed it maintains to keep that distance – are correlated. There are 5 points in the Earth-sun system where a spacecraft can move at such a speed that the craft stays put relative to the Earth and sun. These are the 5 Lagrange points, shown here. Webb is headed to L2. Image via NASA.

What happens next for Webb

See where Webb is now in this real-time graphic from NASA.

Timeline showing Webb launch and steps to get to L2.
View larger. | Here are some of the crucial steps that Webb must accomplish on its journey to L2. Image via AURA/ Twitter.

Webb’s unfolding, step by step

Webb successfully launched on an Ariane 5 rocket on December 25, 2021. It has since successfully deployed its solar array to stop draining battery power. It has also successfully completed two mid-course correction burns. Webb released its antenna, and everything continues to be in good working order. Its latest deployment was to lower the forward and aft pallet structures that will support the sunshield. Yet another success!

Next up, Webb will deploy its sunshield, raise its tower assembly and deploy the momentum flap. Day 10 might be the most nail-biting, as Webb hoists its secondary mirror into position. Heidi Hammel, a scientist on the mission, said:

For me, personally, that’s the scariest part of the whole deployment sequence, the secondary mirror … If we don’t have a secondary mirror, we don’t get any light from space into our cameras and spectrographs. There’s nothing.

The rest of the mirror will unfurl by the end of the second week. Then, on day 29, Webb will fire its thrusters to enter orbit. After those first 30 days, testing will begin. Because Webb’s primary mirror is three times larger than Hubble’s, it had to be made of 18 individual segments so it could be folded for launch. Those 18 segments will all need to be recalibrated (aligned), which will take about 10 days. A week of alignment followed by weeks of testing mean that the telescope won’t be ready for scientific operations for about six months.

What are the 30 days of terror?

The 30 days of terror are what we are experiencing now, as we nervously await news about the progress of the Webb. It was scary to see the $9.7 billion space telescope launch, but that was just the beginning. This telescope, under development for decades, has hundreds of moving parts that will need to unfold properly on its month-long trip to its final destination. With a giant mirror six times the light-collecting surface of Hubble’s mirror, Webb carries with it astronomers’ hopes and dreams. Its journey to L2 is almost 1 million miles (1.5 million km) behind Earth as viewed from the sun … or about four times the moon’s distance.

Webb vs. Hubble

The first images from Webb should be available by summer 2022. Because Webb is an infrared telescope, its focus will be spectroscopy. Hubble provided images in visible light. The advantage of infrared is that Webb will be able to look farther into the universe than ever before. NASA gave a great visualization of the power of Webb to look into the past during a Q&A session on Reddit:

Imagine all of time, from the beginning of the universe until now, is represented on a year-long calendar. If right now is December 31 at 11:55 pm, Webb will be able to see all the way back to January 6th.

NASA also explained why scientists want to see in the infrared and use spectroscopy. Spectroscopy allows astronomers to:

understand what is there, not just how it looks.

When a Reddit user asked if Webb was going to reproduce the famous Hubble Ultra Deep Field photo, NASA said:

Webb will observe the Ultra Deep Field in our first year of science operations. It’ll take Webb less than a day to see deeper than Hubble saw in two weeks of staring. Webb is going to go much deeper, finding tens of thousand of galaxies that are too red and too faint for Hubble to detect.

While we’ve all been wowed and moved for decades by what the Hubble Space Telescope has shown us of the universe, we expect to be further blown away by the images and revelations of Hubble’s successor, the James Webb Space Telescope.

But first, we have to get the telescope to L2, with its parts successfully unfurled.

Webb 30 days of terror: Illustration of L2.
In the coming month, the James Webb Space Telescope will travel to Lagrangian point 2, aka L2, some 4 times the moon’s distance away. L2 is a gravitationally stable point in the Earth-sun system. A spacecraft at that point orbits the sun while “hovering” in place with respect to Earth. Image via ESA.

Bottom line: The James Webb Space Telescope will take about a month to unfurl as it travels to L2. Some are calling this nail-biting time interval Webb’s 30 days of terror.

Via Inverse

Via ESA

Via NASA

Posted 
December 28, 2021
 in 
Space

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