JWST, the most powerful and important telescope ever made, will allow us to reach out into the universe as never before possible for mankind. Today we speak with Alejandro Rivera (born in Gijón and nationalized American), NASA Aerospace and Mechanical Engineer at the NASA Goddard Space Flight Center since 2000 and dynamic analysis engineer of the deployable structures and space mechanisms of the James Web Space Telescope .
Sarah Romero: After being successfully launched on Christmas Day 2021 and having passed the most risky stage of the mission, the unfolding of hundreds of processes, of individual implementations, until having a fully deployed telescope, Webb is heading towards the Lagrange point L2 what is the next step when I get there at the end of January? (will it reach that point on the 24th?)
Alejandro Rivera: JWST’s insertion into its final orbit had long been planned for approximately 29 days after launch. It was recently decided that on Monday the 24th at 2pm (US time) Webb’s thrusters will be fired to insert the space telescope into orbit around the Sun while simultaneously orbiting the second Lagrange point, or L2, its intended destination. 1.5 million km from Earth.
SR: Why is the Lagrange point L2 chosen as the destination of the telescope so important? What is special about L2 and why has this been selected instead of the rest of the hover points as L5?
AR: Lagrange points are equilibrium points for small mass objects that are under the influence of two massive orbiting bodies such as the Sun and the Earth. At Lagrange points, the gravitational attraction of two large masses is exactly equal to the centripetal force required for a small object to move with them. Due to this the objects that are sent to these points tend to remain stable. This is something that is used for space astronomy and observation missions because the amount of fuel needed to stay in orbit around it is very small. In other words, they are like “parking spaces” in space that are ideal for “parking satellites” and making scientific observations.
Of the five Lagrange points, three are unstable and two are stable. The unstable Lagrange points, L1, L2, and L3, lie along the line connecting the Earth and the Sun. The stable Lagrange points, called L4 and L5 , form the vertex of two equilateral triangles that have large masses at their vertices. L4 leads the orbit of the earth and L5 follows.
The L2 point of the Earth-Sun system was the home of the WMAP spacecraft, the current home of Planck, and the new home of the James Webb Space Telescope . L2 is ideal for astronomy because JWST will be close enough to communicate easily with Earth, yet can keep the Sun, Earth, and Moon behind it by blocking all sunlight through the sunshade , which is necessary since JWST is an infrared telescope. L2 also provides Webb with an unobstructed view of deep space 24 hours a day. By comparison, Hubble, which is in an orbit around the earth at an altitude of about 559 km, enters and leaves the earth’s shadow every 90 minutes. For its part, Webb’s orbit around L2 has a period of about 6 months and keeps the telescope out of the shadows of the Earth and the Moon. As the L1 and L2 points are unstable over a period of approximately 23 days, satellites orbiting these positions are required to have periodic course and position corrections and this is something that JWST will have to do in order to stay in the precise orbit around L2.
The L4 and L5 points host stable orbits as long as the mass ratio between the two large celestial objects is greater than 25. This condition is met for the Earth-Sun and Earth-Moon systems, and for many other pairs of bodies in the system. solar. Because of this, asteroids called ‘ Trojans ‘ are often found at these Lagrange points. For example, the Sun-Earth points L4 and L5 contain interplanetary particles and at least two of these asteroids.
SR: What other practical applications do Lagrange points have?
AR: In addition to the L2 point I just described, the L1 point of the Earth-Sun system offers an uninterrupted view of the Sun. This is really convenient for solar and heliospheric observatories like the SOHO satellite which is currently located at L1.
A satellite or space vehicle in orbit near the Sun-Earth Lagrange point L3 would not be very useful in principle, since this point is always hidden behind the sun. It could perhaps be used to provide solar storm predictions for manned missions to Mars and near-Earth asteroids. Due to their stability, the L4 and L5 points have been proposed in the past as possible candidates for space stations and colonies as part of what is known as “Lagrangian space colonization”.
The L1 Lagrangian point in the Earth-Moon system allows comparatively easy access to lunar and Earth orbits with minimal change in velocity . In the future, a habitable space station could be located here to help transport cargo and personnel to the Moon and back. The L2 point in the Earth-Moon system has been used with the Chinese satellite ‘Queqiao’ , launched in 2018 and observing the far side of the Moon and used for communications relay between Earth and a small Chinese robotic vehicle exploring this side of the Moon, something that would not otherwise be possible.
SR: It is a large telescope with state-of-the-art technology. Many may be wondering, how much power does Webb need to run?
AR: The Webb telescope has a solar panel located on the bus or control module, and under the sunshield. The solar panel provides approximately 2,000 watts of electrical power that are necessary for the operation of the telescope. Webb also has a propulsion system to maintain the observatory’s orbit and orientation around L2 with enough fuel on board for at least 10 years of science operations.
SR: Tell us, what is your day-to-day like at this great milestone in the launching of the most important scientific instrument for space science in history into orbit? What is your routine?
AR: I was on console in the mission operations center from launch day and for the next two weeks during which we did the deployments during the so-called “two weeks of terror”. Needless to say, it was the most amazing yet stressful two weeks of my life . After successfully overcoming this phase, things are now a bit calmer. I am analyzing the telemetry of the deployments that I was responsible for on behalf of NASA to compare it with my predictions. I also have to analyze the telemetry of the telescope separation of the upper stage of the Ariane 5 rocket, which was a dynamic analysis that I also did for NASA.
SR: We know that Webb will operate in infrared. Why in infrared? What peculiarities does this wave present, unlike others such as visible light, for example?
AR: The universe is expanding, and so the farther out we look, the faster objects are moving away from us, shifting light into the infrared. This means that light that is emitted as ultraviolet light or visible light is increasingly shifting toward the near and mid-infrared wavelengths of the electromagnetic spectrum. Therefore, to study the formation of the youngest stars and galaxies in the universe, we have to observe infrared light and use a telescope and instruments optimized for this light. On the other hand, the formation of stars and planets in the universe takes place in the center of dense, dusty clouds, obscured from our eyes at normal visible wavelengths. Near-infrared light, with its longer wavelength, is less hampered by small dust particles, allowing near-infrared light to escape dust clouds. By looking at the emitted near-infrared light, we can see the glow of the processes that lead to the formation of stars and planets. Finally, objects of about Earth temperature emit most of their radiation in mid-infrared wavelengths.
(You have reached the end of the first part of the interview with Alejandro Rivera, NASA engineer)
