Many people think of the James Webb Space Telescope as a kind of Hubble 2. They understand that the Hubble Space Telescope (HST) has served us well, but is now old and overdue for a replacement. NASA seems to agree, as it has not sent a maintenance mission in over fifteen years and is already preparing to cease operations. But a recent paper argues that this is a mistake. Despite its age, HST still performs brilliantly and continues to deliver an avalanche of valuable scientific results. And since JWST was never designed to replace HST (it is an infrared (IR) telescope), it would be best for us to operate both telescopes in tandem to maximize coverage of all observations.
Let's face it: the Hubble Space Telescope (HST) is old and will eventually fall back to Earth. Although it was designed to be repairable and upgradeable, there have been no maintenance missions since 2009. These missions relied on the Space Shuttle, which could capture the telescope and provide a working base for astronauts. Servicing missions could last weeks, and only the space shuttle could transport the six astronauts to the telescope and house them for the duration of the mission.
Without these maintenance interventions, faulty components can no longer be replaced and the overall condition of the HST will continue to deteriorate. If nothing is done, HST will eventually stop working altogether. To prevent it from becoming another piece of space junk, plans are already being developed to deorbit it and crash it into the Pacific Ocean. But that's no reason to forego it. The view of the cosmos is still as clear as ever, and mission scientists are doing an excellent job of troubleshooting technical problems as they arise.
The James Webb Space Telescope was launched on Christmas Day 2021. Its system of folding hexagonal mirrors gives it an effective diameter about 2.7 times larger than that of the HST, and it is designed to see into the mid-infrared. Within months of its launch, it had already seen things that contradicted existing models of the origins of the universe, causing a mini-crisis in some areas and prompting unscrupulous news editors to write headlines asking whether the ” Big Bang Theory” is in danger!
This image from NASA's Hubble Space Telescope was taken on May 19, 2009, after deployment during Servicing Mission 4. NASA
The reason JWST was able to capture such ancient galaxies is because it is primarily an IR telescope: as the universe expands, photons from distant objects are redshifted to stars that originally glowed in visible light , can only be seen in IR. But these IR views also prove extremely valuable in scientific areas other than cosmology. In fact, many of the most striking images released by JWST's press team are IR images of well-known objects, revealing hidden complexities that have not been seen before.
This is a key difference between the two telescopes: While HST's range slightly overlaps that of JWST, it can see into the ultraviolet (UV) wavelength range. HST was founded in 1990, seven years late and billions of dollars over budget. Its 2.4-meter-long primary element had to be one of the most precisely ground mirrors ever made because it was supposed to be diffraction limited at UV wavelengths. It is known that avoidable problems in the testing process resulted in the lens being very precisely molded into a slightly incorrect shape, resulting in spherical aberration that prevented sharp focusing.
Fortunately, the telescope was designed to be operational from the start and was even returned to Earth by the Space Shuttle for repairs when necessary. In the end, however, NASA opticians were able to design and build a series of corrective optics to solve the problem, and the COSTAR system was installed by astronauts on the first servicing mission. Over the years, NASA sent three additional maintenance missions to upgrade or repair components and install new instruments.
Illustration of NASA's James Webb Space Telescope. Photo credit: NASA
HST could be one of the most successful scientific instruments ever built. Since 1990, it has been the subject of approximately 1,200 scientific press releases, each of which has been read more than 400 million times. The more than 46,000 scientific papers written using HST data have been cited more than 900,000 times! And even in its current dilapidated state, it still provided data for 1,435 articles in 2023 alone.
JWST also exceeded time and budget, but was used far more successfully. Despite a much larger mirror with more than six times the collecting area of HST, the entire observatory weighs only half as much as HST. Because of its greater sensitivity and the fact that it can see ancient light redshifted in IR wavelengths, it can see much deeper into the universe than HST. It was these observations of galaxies forming when the universe was very young (100-180 million years) that caused so much excitement shortly after deployment.
As valuable as these telescopes are, they won't last forever. JWST is located deep in space, about 1.5 million kilometers from Earth, near the L2 Lagrange point. When it finally fails, it becomes another piece of solar system debris orbiting the sun in the vast void of the solar system. However, HST is in low Earth orbit (LEO) and suffers from very low drag from the weak outer reaches of the atmosphere. Over time, it gradually loses speed and drifts downward until it enters the atmosphere proper and crashes to Earth. Due to its size, it does not burn completely and large pieces shatter on the surface.
Since it is impossible to predict where exactly it will re-enter, the mission planners always planned to capture it with the space shuttle and bring it back to Earth. His final resting place was supposed to be displayed in a museum, but unfortunately the shuttle program was canceled. The current plan is to send up an unmanned rocket to dock with the telescope (a special attachment was installed for this purpose on the last servicing mission) and deorbit it in a controlled manner to ensure that its parts land safely in the ocean .
The original paper can be found at https://arxiv.org/abs/2410.01187
Like this:
Load…
Comments are closed.