Challenger's replacement, Endeavour, finally took to the skies in May 1992 with the STS-49 mission. Its aim was the most ambitious satellite repair yet attempted - servicing an enormous Intelsat communications satellite that had been stranded when the upper stage of its Titan rocket failed back in 1990. The successful mission provided valuable experience that helped in planning an even more ambitious mission to the Hubble Space Telescope in 1993 (see panel, right).
Throughout the early 1990s, NASA's four Shuttles carried out a successful and varied series of missions. Satellite and spaceprobe deployments continued, along with the release and retrieval of short-term independent satellites, or free fliers, developed with the European and Japanese space agencies. There were also further Spacelab missions - the experiments carried in the mid-deck storage lockers inside the spacecraft were supplemented by the commercially built Spacehab module, which fitted behind the main cabin while leaving most of the cargo bay empty, and contained additional experiment lockers for paying customers.
Alongside a programme of joint missions with the Russian space station Mir (see p.217), a number of missions of the early and mid-1990s also developed techniques for construction of the International Space
REPLACING HUBBLE'S SOLAR PANELS
Mission specialist Kathryn Thornton fixes replacement solar arrays to the Hubble Space Telescope during STS-61. Spacewalk activities are listed in the checklist on her right cuff.
Astronaut Story Musgrave rides to the top of the HST aboard Endeavour's robot arm, preparing to fit covers to some instruments during the last of STS-61's five spacewalks. Jeffrey Hoffman works below him in the pay load bay.
Station (ISS). Spacewalking astronauts practised building structures that might be used in a space station, including long truss sections and frameworks (see p.l 86). There were even opportunities to test rather more speculative ideas - Atlantis carried an experimental trolley-car for astronaut transport in its cargo bay in April 1991, while two other missions unwound a tethered satellite that generated electricity as its 1km- (2A-mile-) long tether sliced through the Earth's magnetic field.
Shortly after the Hubble Space Telescope's much-delayed deployment, NASA was highly embarrassed ij at the discovery that its great orbital observatory was delivering out-of-focus images (see p.252) - a major flaw in the mirror design had not been spotted before launch, and the telescope was crippled. Fortunately, the HST was designed with orbital servicing in mind - and each of its major instruments could be removed and replaced with relative ease. Engineers on the ground soon devised a system of corrective optics that could fit into one of the instrument bays and bring Hubble's vision into focus for the remaining instruments. The capture and repair of the HST by Endeavour in 1993 ultimately took five spacewalks, but it resurrected the HST. Further maintenance missions took place in 1997, 1999, and 2002, and a final one is planned for 2008.
Discovery launches on the first Space Shuttle mission since 1986. A decision to simplify the mission codes sees Discovery's flight named STS-26. However, schedule delays will frequently lead to later missions launching out of order.
4 May 1989
Atlantis deploys the Venus-bound Magellan spaceprobe.
18 October 1989
Atlantis launches the Galileo probe to Jupiter.
25 April 1990
Discovery deploys the Hubble Space Telescope.
6 October 1990
The Ulysses solar probe is launched from Discovery.
21 June 1993
Endeavour's STS-57 is the first mission to carry the Spacehab experimental module.
2 December 1993
Endeavour launches on its epic STS-61 mission to repair the HST.
3 February 1995
The launch of Discovery on STS-63 marks the beginning of the Shuttle-Mir programme.
The Shuttle upper deck is a maze of instrumentation that clearly shows its origins in the 1970s. From their seats, Commander and Pilot can control every aspect of the Space Shuttle's flight.
19 February 1986
The empty Mir core module is launched from Baikonur Cosmodrome into an orbit 390km (242 miles) above the Earth.
13 March 1986
The first crew of two cosmonauts is launched on an 18-week mission to both Mir and Salyut 7.
5 February 1987
After a seven-month hiatus caused by delays to Kvant-1, Mir's second crew is launched aboard Soyuz-TM 2.
9 April 1987
Kvant-1 docks with Mir.
22 July 1987
Soyuz-TM 3 brings a crew including Mohammad Faris, the first Syrian astronaut, to Mir. During the visit, the first in-orbit crew exchange is made.
21 December 1988
Cosmonauts Musa Manarov and Vladimir Titov return to Earth after spending 366 days in orbit.
6 December 1989
Kvant-2 is added to the Mir core.
10 June 1990
The Kristall materials science module docks with Mir.
Less than a month after the American space programme had suffered the loss of Challenger, the Soviet Union launched what turned out to be its last great space project - the space station Mir.
Development work on a more complex modular space station - one that would have more than two docking points, allowing the attachment of extra individual elements to the basic core - began in the mid-1970s. The station's design and construction was undertaken at NPO Energia (the former OKB-1) under Valentin Glushko, and initially it was supposed to use only the relatively lightweight, Soyuz-derived elements of the bureau's own Salyut stations. But the cancellation of Vladimir Chelomei's military Almaz programme (see p.179) led to a decision that the station should also accommodate much heavier modules developed from Chelomei's TKS space ferry. Development progressed throughout the early 1980s but was sidetracked by the pressure of other spacecraft programmes, such as the Progress cargo ferry (see panel, right) and Buran (see p.214). It only took priority once the bureau was given a launch deadline of spring 1986 - to coincide with the 27th Communist Party Congress.
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