The Week in Space and Physics #30
On repairing Hubble, a scandal in superconductivity, asteroid deflection and the graveyard of the Milky Way
After thirty-two years in space, Hubble should, by rights, be little more than space junk. Yet it is not. The telescope continues to produce stunning images and vast amounts of scientific data, year after year. That - an extraordinary success for NASA - is down to a series of five servicing missions, each of which repaired, enhanced and boosted the telescope.
Yet the last of these missions took place over a decade ago, in 2009. It, like all the others, relied on the Space Shuttle, a vehicle that was able to manoeuvre around the telescope and grab it with a robotic arm. With the retirement of the Shuttle, in 2011, those capabilities were lost. The prospects for a sixth mission looked remote.
That, however, means the telescope is now operating with thirteen years of wear and tear. Engineers are most worried about Hubble’s gyroscopes: a set of six instruments that control its orientation and rotation. Three of them have failed; a fourth failure – which could happen at any point – would severely restrict the operations of Hubble.
A second issue concerns the height of its orbit, which is gradually dropping. Even if the gyros hold out, this will eventually doom Hubble. In a decade or two, at current rates, Hubble will hit thicker layers of the atmosphere and begin a sharp and fiery descent back to Earth.
Fortunately, NASA is now considering a plan to repair Hubble once again. The idea was raised by SpaceX, who asked NASA if a private mission to Hubble might be feasible. Though few details have been announced, it appears the mission would be part of the Polaris Program: a series of missions funded by billionaire Jared Isaacman.
SpaceX is proposing to use their Dragon capsule to dock with Hubble. Its engines could then boost Hubble, pushing it to a higher orbit. That would postpone re-entry, giving Hubble at least another decade in orbit. Yet repair of the gyroscopes is more complicated. In the past, NASA astronauts carried out spacewalks to physically access similar components.
No private spacewalk has ever been conducted, and NASA has previously been reluctant to consider the idea. Spacewalks are among the most dangerous activities done by astronauts, and need extensive preparation. That, along with the specialist training needed to work on Hubble, is likely out of reach of paying tourists.
The proposal is perhaps better understood as an attempt to find a more useful purpose for space tourists. Axiom-1, a private mission to the Space Station earlier this year, drew some criticism for the disturbances introduced by the visiting crew. Yet it is not clear here, either, whether space tourists can actually contribute much of value.
A simple operation to boost the altitude of Hubble could be done robotically, for far less cost. A proper servicing of the telescope will need professional astronauts, if only to lower the risk of damaging Hubble. Fixing Hubble would be nice, but either way the tourists will just be along for the ride.
A Scandal in Superconductivity
The quantum world, as Schrödinger aptly demonstrated with his quantum cat, is a bizarre place. Particles can appear in multiple places at once, tunnel through seemingly impenetrable walls, or vanish, only to reappear moments later. This unsettling behaviour is normally invisible to us, occurring only at the subatomic scale.
Yet a few quantum effects leak into the larger world. Some of these are already widely used. Lasers, for example, would be impossible without quantum physics; as would be the tiny transistors that power computers and smartphones. Yet one effect so far little used is superconductivity: a strange phenomenon that allows us to transmit electricity with almost no resistance at all.
In the classical, non-quantum, world, electric currents must flow through a conductor of some kind, like an electrical cable. This inevitably involves resistance. As electrons move through the conductor they crash into atoms, thus wasting some of the electrical energy as heat. A decent fraction of the electrical energy we generate, therefore, is lost as we move it around.
Yet quantum physics allows something known as a superconductor: a material that offers no resistance to electricity at all. That raises the prospect of ultra-efficient energy transfer, allowing engineers to create almost magical new ways of storing, moving and using electricity.
Yet there is a catch. Though researchers have made superconductors in the lab, they only work at temperatures far below zero. That, of course, makes them rather impractical for use in the real world. Nothing, in theory at least, seems to forbid superconductivity at room temperature; it’s just that for a long time, we knew of no material that did allow it.
Excitement followed, then, when researchers announced they’d stumbled across such a material in 2020. Reports hailed it as a landmark breakthrough: a big step towards a technological wonderland. Yet last week those claims spectacularly fell apart.
After the publication of the original paper, rival scientists soon found problems with the approach it took. Graphs in the paper were questioned, and some asked whether the raw data showed any sign of superconductivity at all. After an investigation, Nature last week retracted the paper, putting an end to the claims of room temperature superconductivity.
Whether this was a deliberate effort to publish misleading data or merely an accidental slip is so far unclear. But the incident is sadly reminiscent of other disproven breakthroughs, such as that of cold fusion in 1989, or of cloning in 2004. Those incidents badly damaged the research areas in which they took place. One can only hope superconductivity – with all its promise - is spared the same fate.
DART Smashes into an Asteroid
It sounds like a terrible accident; the kind often encountered by Hollywood astronauts as they intrepidly explore the solar system. Yet when NASA’s probe DART smashed into an asteroid last week, it was no accident. The collision, indeed, had been carefully planned years in advance, as part of a test of our ability to redirect an incoming asteroid.
DART targeted Dimorphos, a small asteroid orbiting Didymos, a bigger asteroid. The collision, NASA is hoping, will have changed that orbit slightly, pushing Dimorphos to circle Didymos at a faster rate. If so, this would prove that we can move an asteroid and that we could, if we ever find one heading towards Earth, take action to push it onto a safer path.
The collision was watched by telescopes across the Solar System. From Earth the ATLAS observatory captured a stunning sequence of images: showing the asteroid suddenly brighten as DART hit it, followed by a vast plume of debris billowing out. Hubble and the James Webb were also watching; both capturing images of that plume.
Over the next few weeks and months NASA will monitor the orbit of Dimorphos to find out how much it has changed. A follow up probe, HERA, will visit the asteroid later this decade. This, currently being built by the European Space Agency, will image the crater left by DART and study the aftermath of the impact.
The Underworld of the Milky Way
The tombstones of dead stars litter the Milky Way, according to a recent study published in the Monthly Notices of the Royal Astronomical Study. Many of these tombstones are hard to spot. They take the form of small black holes, dense neutron stars or quietly fading dwarf stars. Yet all were once stars; ones that burned for millions or billions of years before their eventual deaths.
The new study sought to understand where these tombstones lie today. Many, they found, have probably been thrown out of the galaxy entirely, discarded in the wasteland of intergalactic space. But many remain in the Milky Way, either in a broad disk overlapping its spiral arms, or in a vast halo stretching far above and below the galaxy.
This distribution is, for now, largely theoretical, based on what we know about the birth and death of stars. Yet new telescopes should soon start to pick out many of these tombstones, especially those lying closer to Earth. That should allow us to chart the history of the galaxy more accurately, and reveal the location of dozens of small but nearby black holes.