Science

Space Observatories

by Duncan Lunan

From an early stage in planning space exploration, the benefits for astronomy were obvious.  As I explained in ‘Choosing a Telescope’  (ON May 9th 2021)  atmospheric conditions very often limit the magnification which can be used on a ground-based telescope, and as astronomers in Scotland know all too well, clouds frequently block the view altogether. 

Fig 1. The electromagnetic spectrum

Children visiting observatories on cloudy nights often ask ‘Can I not just look through it anyway?’, not realising that there will be nothing at all to see.  Advances in technology such as adaptive optics and image stacking have removed many of the problems caused by turbulence, for amateur observers as well as high-altitude observatories, but there remains the fundamental problem that for most of the electromagnetic spectrum the atmosphere is opaque  (Fig. 1).  Fortunate as that has been for the evolution of life, it means that from the ground we can see the Universe through only two ‘windows’ – the optical one to which most eyesight is adapted, and the radio one which began to be appreciated only in the 1930s  (Fig. 2).  All the rest is screened off  (Fig. 3), and the information which it carries didn’t begin to be recognised until high-altitude rockets became available in the late 1940s.

As far as I know, the first depiction of an orbiting observatory was an open-framework structure, in the classic endpapers by Chesley Bonestell for Across the Space Frontier, by Wernher von Braun, Willy Ley, Fred L. Whipple et al  (Sidgwick & Jackson, 1952).  It and the versions in the Daily Express ‘Jeff Hawke’ strip were man-tended from a wheel-type space station nearby, and accessed by space taxi  (Fig. 4).  The 1957 Soviet film Blazing a Trail to the Stars had cosmonauts using a conventional telescope on the stationary axis of a rotating space wheel  (Fig. 5), and despite the practical difficulties, supposedly they had obtained the best-ever photographs of Mars.  The 1967-68 Hawke story ‘The Venusian Club’ had a much larger one, with a crew compartment for use in testing;  and China has now announced that its space telescope, as large as the Hubble, will be placed alongside their Tiangong-3 space station for easier maintenance.    

Fig. 4. Space wheel with space observatory, Space Gen 1, Junior Express 1954
Fig. 5. Telescope on Soviet space station, ‘Blazing a Trail to the Stars’, 1960

Not waiting for manned observatories, astronomers have been launching unmanned ones since the 1960s.  The Orbiting Astronomical Observatories were intended to be served by Space Shuttle  (Fig. 6), and the very first in 1966 could have done with that, arriving on orbit with a disabling fault which any engineer could have repaired with a screwdriver.  Later ones like the ultraviolet observer ‘Copernicus’, were more successful  (Fig. 7), and they were soon followed by specialist versions such as the Orbiting Solar Observatories. 

The science fiction writer Alfred Bester worked on that programme and described it in an award-winning book, The Life and Death of a Satellite, and dramatised his experiences in a prizewinning short story, ‘Something Up There Likes Me’, (in Star Light, Star Bright, Vol. 2 of The Great Short Fiction of Alfred Bester, Gollancz, 1976).  The success of the OAO series was followed up with the High Energy Astronomical Observatories, with HEAO-1 for x-rays  (Fig.8)  and HEAO-2 for ultraviolet  (Fig. 9).

Gamma-ray astronomy had an unintended start in the 1970s with the discovery of Gamma-ray Bursters, out near the edge of the visible Universe, by the Vela satellites which were orbited to look for covert tests of nuclear weapons  (Fig. 10). 

Fig. 10. Vela deployment

There are persistent reports that the Velas actually did detect two covert nuclear tests  (probably Israeli)  near a South African fleet on manoeuvres, under cover of storms in the South Atlantic, in December 1980 and fifteen months earlier, apparently confirmed by ionosphere measurements conducted by the giant radiotelescope at Arecibo.  (Hugh Davies, ‘”A-Blast” Seen Off S. Africa’, The Daily Telegraph, 19th Feb. 1981).  But the GRBs were far too frequent to be nuclear tests, and were confirmed to be extraterrestrial in 1974 when the Mariner 10 space probe, on its way to Mercury, found that they were located all over the sky  (Fig. 11).  Early follow-up came with Europe’s COS-B gamma-ray telescope the following year  (Fig. 12).

Two particularly successful space telescopes were IRAS, the Infra-Red Astronomy Satellite, and IUE, the International Ultraviolet Observatory.  IRAS was launched in 1983  (Fig. 13)  and gave us the first view of the Galactic Centre, through the dust clouds which hide it from us, discovered ‘galactic cirrus’ of dust high above the plane of the Milky Way, observed multiple supernova shockwaves in Orion, and discovered the protoplanetary discs surrounding stars such as Fomalhaut, Vega and Beta Pictoris. 

Fig. 13. IRAS 1983

Its huge catalogue of infrared point and extended sources is still being followed up to this day.  IUE was launched in 1978 into an unusual ‘tundra’ orbit, with a 24-hour period but inclined to the equator, which brought it over the participating nations in turn, eliminating the need for onboard tape recorders  (Fig. 14).  IUE compiled an all-sky catalogue of ultraviolet sources comparable to IRAS’s infrared ones, but had to be turned off in 1996 for lack of funds, when it was still fully operational.

Fig. 14. International Ultraviolet Explorer, tundra orbit, 24 hrs inclined, Jan 1978

The history of the Solar Maximum Mission was equally frustrating.  Launched in 1980 to observe the Sun in the most active part of its 11-year sunspot cycle, the telescope developed problems and was repaired by Shuttle astronauts in 1984  (Fig.15).  It remained operational through the low years of the solar cycle and fell out of orbit in December 1989, shortly before the next 11-year peak.  It could have been saved again, but priority was given to the Shuttle launch of an electronic spy satellite.  I wrote a fairly strong article at the time called ‘Shame about Solar Max’.  

Fig. 15. Solar Max repair, Shuttle mission STS-41C

It’s not always realised that the Hubble Space Telescope was planned as one of four Great Observatories  (Fig. 16), along with the Compton Gamma-Ray Observatory  (1991-2000), the Space Infrared Telescope Facility  (SIRTF), 2003-2020, named Spitzer, after Lyman Spitzer of Princeton University, one of the first scientists to advocate the use of satellites in scientific research;  and the Advanced X-ray Astrophysics Facility (Chandra), which is still operational.  Separately and together  (Fig. 17), they have contributed a vast amount to our knowledge.  A new generation of unmanned observatories has included Herschel, Planck, WISE, Fermi, XMM and Swift, operating at a variety of wavelengths, and the astrometric  (position-finding)  Hipparcos and Gaia, all highly successful. 

The Soviet Salyut stations had telescopes fitted  (mostly for Earth observation including espionage)  and the US Skylab had the Apollo Telescope Mount, very sophisticated and used primarily for solar observations  (Fig. 18).  NASA’s original plan for the Large Space Telescope envisaged it as a manned observatory to be launched by the Saturn Five booster, which was intended to be the workhorse of the US space programme for the rest of the 20th century.  With its cancellation the LST had to be drastically scaled down, becoming the Hubble Space Telescope.  Its launch was delayed by the loss of the Space Shuttle Challenger, but took place on the Discovery in 1990 – only for it to be realised that the main mirror had been wrongly figured and a major alteration would be necessary.  NASA’s protests that the mistake could not have been found before launch were the laughing stock of amateur telescope makers:  the test for the figure of a parabolic mirror goes back so far that older books describe how to do it with a candle.

Fig. 18. Great Observatories Galactic Centre

In the early Hawke stories, spaceships had no attitude control jets and were oriented only by gyroscopes.  The Hubble Telescope has no attitude control jets in case they contaminate the optics.   For the same reason the scientific view was that the Hubble Telescope should be in an orbit away from other manned spaceflight operations, to minimise contamination and collision hazards, and both decisions subsequently backfired.  Moving parts on spacecraft are always vulnerable, and gyroscopes and tape recorders usually fail first.  A minimum three of the HST’s six gyroscopes are required to keep the Telescope operational, and by the time of the first repair mission, one by one they were failing.

Nevertheless, there was strong opposition to the repair.  The rescue of Solar Max had been opposed by segments of the scientific community with the extraordinary argument that they’d rather have it unusable than broken by the astronauts, and the argument was only strengthened when the Shuttle’s remote arm failed to capture the telescope and the astronauts manhandled it into the cargo bay.  Although the Solar Max repair was a complete success, there remained strong views that it should not have been attempted. 

One of the strongest opponents of the Hubble repair was a distinguished Scottish astronomer, who  insisted that the astronauts should be kept away from it despite the problem with the mirror, which was preventing his own project to look for spiral galaxies associated with distant quasars.  “The greatest threat to the Hubble Space Telescope is the machismo of the astronauts”, he declared in a lecture to the Astronomical Society of Glasgow, and at a meeting of the Scottish Astronomers Group, he referred off-mic to the astronauts as “chimpanzees”.  In the event, the repair and maintenance missions have been complete successes, including the replacement of the solar panels which are Britain’s contribution to the Hubble.  But after the loss of the Columbia, NASA decided that there would be no more Shuttle missions to orbits from which it couldn’t reach the Space Station, and consequently, that the fifth servicing mission to the Hubble Space Telescope would have to be abandoned.  The cancellation of the servicing mission aroused so much international protest that the head of the Columbia enquiry, Admiral Howard Gehman, was asked to review possible options for saving the Hubble, and in the end the mission was reinstated.  The Endeavour was assigned to the mission, with the Atlantis on standby in case a problem like Columbia’s prevented the crew’s safe return.

The delay proved fortunate because shortly before launch the primary computer on the HST also failed.  The backup came on successfully, but the mission was postponed to find a replacement for the primary one – there aren’t so many space-hardened IBM 386s around these days.   In giving the HST another ten years of life, the mission replaced the last of the original instruments;  all the newer ones have corrections for the mirror fault, so the ‘spider’ of corrective lenses installed in the first repair was removed and brought back to an honoured place in the Smithsonian Air and Space Museum. 

Fig. 19. STS-125 final Hubble Telescope repair, 2009

The final irony came on that last repair flight to the STS, in 2009  (Fig. 19).  One of the urgent repairs was to the Space Telescope Imaging Spectroscope, or STIS.  The instrument had been installed during the second  refurbishing mission, and failed in 2004, frustrating 30% of the Hubble’s scientific workload.  No replacement was available, and repairing it on-orbit was near-impossible, needing over 100 dedicated tools to be made specially.  Just one stage of the operation required the removal of 111 small screws, each with a washer and a cap of glue which had to be captured, not to contaminate the interior of the instrument.  The task fell to Mike Massimino, a veteran of the first repair mission, who had already saved another vital piece of equipment with an unrehearsed, tethered flying leap, as it floated away. 

If the STIS had been removed and replaced as a unit, he would have pulled it out using a handrail which now had to be removed, and at that stage, one of its retaining screws became stripped.  After trying a multitude of possible solutions, Mission Control told him that the only remaining option was to snap the screw and yank the handrail off – unrehearsed, and with the next decade of Hubble operations at stake.  Having done it, and saddled for the rest of his life with the nickname of ‘the man who broke into the Hubble Space Telescope’, Massimino wrote, “I felt like I’d been given a reprieve by God, like I’d been resurrected from the dead”  (Spaceman, An astronaut’s Unlike Journey to Unlock the Secrets of the Universe, Simon & Schuster, 2016).  What the critics of astronaut repairs thought about it is seemingly not on record.

Fig. 20. Hubble improvements and JWST

Still, it’s a sobering thought that the mission was intended to give the Hubble ten more years of life, and that was in 2009.  The James Webb Space Telescope has only just been commissioned, with a possible lifetime of 20 years, and they’re supposed to be working in tandem  (Fig. 20), and are already doing so, very successfully.  But only three gyroscopes are still working, though these are a newer type intended to last longer, and the HST can be operated in two-gyro or even one-gyro modes, though less effectively.  Refurbishing the telescope and raising the orbit will be difficult with smaller spacecraft, but several options have been studied and in September 2022, NASA formally asked SpaceX to study doing it with a Crew Dragon capsule, possibly giving the HST another 20 years of life.

Fig. 21. Sun-Earth Lagrange points

The James Webb Space Telescope is stationed in orbit around the Sun-Earth L2 point  (Fig. 21).  Over 1 million miles away, it’s beyond the reach of any currently possible repair team, though Elon Musk’s Starship may change that eventually.  The JWST does have a docking port, in case anybody becomes able to reach it.  Meanwhile, a minor problem of friction in the gears of the MIRI instrument has been tracked down and bypassed.  More seriously, in May 2022 the C3 mirror segment was hit by a meteoroid, larger and sooner than expected  (but that’s statistics for you).  It raises the possibility that the meteor flux at L2 may be larger than anticipated, and although the JWST can operate in a variety of modes while keeping its mirrors out of sunlight  (Fig. 22), for the moment it will restricted to those which face away from the likely direction of incoming dust.

Fig. 22. Webb possible orientations, thermal test begun May 2022

All of this time, there has been a backup mirror for the HST, without the flaw in the first one, which has been waiting for a spacecraft to fly on.  At last its WFIRST telescope is scheduled to fly, in 2027, and has been renamed the Nancy Grace Roman Space Telescope, after NASA’s first Chief Astronomer, ‘The Mother of Hubble’.  It will work in the infrared and take much wider-field images than any of the previous instruments  (Fig. 23).  Beyond that, there are even larger instruments on the drawing board, including the Athena 5-ton x-ray telescope, the Advanced Technology Large Aperture Space Telescope  (ATLAST), possibly for 2029, and the Large Ultraviolet Optical Surveyor  (LUVOIR) a 15 metre telescope, provisionally scheduled for 2039.  And then there’s astronomy outside the electromagnetic spectrum:  the three satellites of LISA, the Laser Interferometry Space Antenna, would constitute the first gravitational wave telescope, able to pinpoint sources and to look at frequencies inaccessible from the ground  (Fig. 24).  LISA isn’t funded at present, but the prototype LISA Pathfinder experiment outperformed expectations and raised hopes for the future.

There are even bigger plans for the future.  Even LUVOIR should be able to map the Universe at 100 kiloparsec resolution, but years ago now, Soviet astronomers proposed to put two telescopes at the Sun-Saturn L4 and L5 points.  Using laser interferometry, in theory they could map the entire Universe in three dimensions, at much higher resolution.  Very long-wave radio astronomy has been the poor relation in the field for a long time, but there are plans for huge arrays in space, like gigantic sea creatures, which might be where we find evidence of extraterrestrial life, as Arthur C. Clarke suggested in his novel Imperial Earth.  FOCAL is a proposal to use the Sun’s gravitational focus, far beyond the Solar System, to map exoplanets at 1-km resolution;  and in his novella Empress of Starlight, Dr. Gerald Nordley suggested that his version of the Dyson Sphere concept would allow exoplanets to be mapped at resolutions of only a few metres  (Fig. 25).  There’s clearly a lot still to play for.

Fig. 25. Dyson array resolving power from theta Circini, 276 ly (G. David Nordley)

G. David Nordley’s novella. Empress of Starlight, was published in Analog Nov/Dec 2018, and reprinted in G. David Nordley, Around Alien Stars, Brief Candle Press, 2019.