Picture yourself driving along an unfamiliar country road at night, miles from anywhere. The engine keeps making funny noises which you pretend you aren't hearing, but suddenly it grinds to a halt. What do you do? No problem. Out comes the mobile phone, call in a tow truck and gaze at the stars while you wait for the rescue.
Motor trouble is quite a bit different 240 miles above the earth in the Mir space station. Help could be sent up but it would take days or weeks to arrive. Even if you don't mind the wait, don't step outside for a smoke. You would probably be unconscious in 10 seconds and soon after your blood would begin to "boil" in the absence of air pressure.
Mir is also quite a bit more complicated than the typical car. It weighs in at about 140 tonnes. It has dozens of systems controlling the things we don't even think about on the ground like the supply of air and water, power, light, temperature and humidity.
It carries computer systems, communications systems and a battery of warning systems that watch over all of these systems just in case something goes wrong. And it also packs a small university's worth of experimental equipment to study the earth below and the stars above, the reason why people want to be in orbit in the first place.
The world's longest serving and only space station - now in its 11th year - is having a rough go of it in recent times however. A series of major and minor failures have kept it in the news for months, but in particular since June 25th when a collision with an unmanned Progress supply ship depressurised Spektr, one of its key modules, in the process knocking out half of Mir's electrical power.
Since then there has been a catalogue of errors as system components shut down and over-tired cosmonauts under severe pressure were forced into mistakes such as accidentally disconnecting the main computer.
The world has watched in fascination as the very real drama unfolds unseen above our heads, culminating in yesterday's potentially dangerous mission to replace damaged power cables inside the depressurised Spektr module.
Questions have been asked, however, about whether continued occupation of the Mir station represents an unacceptable risk to the lives of those billeted there, currently two cosmonauts and a British-born visiting astronaut from the US National Aeronautics and Space Administration (NASA).
The first crew members reached Mir in March 1986 and the station was expected then to have a five or six-year working life. The technological achievement of putting the station into orbit and keeping it in constant use was a source of pride for the then Soviet Union.
That was then, this is now. Mir is well past its sell-by date and in the meantime, the country which designed, built and launched it is no more. Funding and support for Mir is now left to Russia alone, which is struggling to convert its old collective system to a free market economy.
This has left Mir's controllers having to make do with old technology and clapped out computers as budgets dry up. But fly it must because Mir has also become something of a cash cow for the Russian space programme.
It is the world's only working space station and as such has attracted crew, scientists and funding from NASA and the European Space Agency (ESA). It is the only show in town if you want to study long-term effects of microgravity on humans, for example. And while the US space shuttle enjoys greater reliability, flights are typically only one or two weeks long.
Andre Balogh, professor of space physics at Imperial College, London, estimates that Mir is worth tens of millions of dollars a year to the Russians. So breakdowns or not, Mir must be kept in orbit.
He argues however that Mir is now a danger and at this stage should be taken out of service. "They are taking risks and my feeling is the risks outweigh the advantages of keeping Mir in space. There are real people up there," he says. "Mir is really kept in place by the participation of NASA and the European Space Agency."
He is strongly of the view that unmanned spacecraft, such as the recent highly successful Pathfinder mission which landed on Mars in July, are a cheaper and safer alternative to manned flights. "We should distinguish between space science and science that can be done on a space station. Most of the science we want to do in space can be done unmanned.
"I am not saying man should not go into space but this is not the same thing as doing effective science in space," he argues. He also notes the advantages of manned flights as a way to keep the taxpayer who funds the whole thing on-side.
"Astronauts do matter and public awareness is tied to the presence of astronauts. Manned space travel has its public relations value."
In the case of the struggling Mir however, onboard science is no longer an option, he believes. The crew are too involved simply in keeping it up in space to do any credible science. And even if power delivered by solar panels attached to the Spektr module are reconnected, this key scientific module will remain depressurised and so off-limits to crew.
"It is no longer useful," he says. The Mir crew and flight controllers are still learning he believes. "Yes they are learning, they are learning crisis management."
BUT what is it actually like to be on board Mir? German scientist and ESA astronaut, Dr Ulf Merbold (56) had little bad to say about his monthlong visit to Mir - despite getting quite a rough ride.
"There is always something that doesn't work," he says, whether it is the US shuttle or Mir. Even so, he was on board in October 1994 when Mir experienced a major system failure during which all electric power was lost. Crew were left in the dark with no life support systems and no navigation. They scrambled to right things in 45-minute periods of sunlight as Mir orbited the earth.
He nonetheless remained confident about Mir and its systems, "otherwise I would not have flown. The Russian design and the way it is built is very sound and solid". The crew is not in a life threatening situation at any stage, he believes, because there is always a Soyuz capsule ready for a quick departure. "In the worst case you would go to the Soyuz and go home."
He has flown in space shuttles twice and once on Mir, but says they can't be compared. "Mir is the only real space station. The shuttle is a transportation system." While the shuttle is better organised with stowage and a place for absolutely everything, he makes Mir sound almost homely.
"It is fun to be there," he says. "It is a big station and it has a funny architecture. There were six people there when I visited, but everyone finds his own little corner. It is not cramped."
Mir operates on Moscow time and the day starts at 7 a.m. Each crew member is given a list of activities for the day and, says Merbold, "You do these things in a disciplined way." Everyone tends to muck in and share chores such as getting the breakfast coffee ready and clearing up, but short stay "guests" tend to be saved from these tasks, he says. "I was a guest so most of the time I was busy with scientific work."
Over the years, belongings such as tapes and videos have been left behind by cosmonauts and visitors and the lack of stowage means they are always about the place. While the "permanent" hands on six-month flights might watch a video, read or listen to a tape or CD, the "visitors" from NASA or ESA use their free time in other ways.
"The best is to watch the wall or spend some time at the windows," he says. The scenery changes all of the time as the earth revolves beneath the orbiting Mir. "It is absolutely spectacular. You can have a day, sunset, night and then sunrise every 90 minutes," - the time it takes to complete an orbit.
At 240 miles, Mir has a clear view of the northern and the southern lights near the polar regions and night-time thunderstorms can be dazzling, he says. If the earth becomes tiresome, there is always the opposite view with a window on the stars and planets unobscured by any atmosphere.
Communication can be a problem, he says, unless your Russian is very good. "The most difficult part of the whole training was the Russian," he says.
The scientific work that can be achieved on board Mir is only available on such a facility he says, dismissing arguments that unmanned flights are better value as "too dogmatic". "It is foolish to make statements that one is better than another," he says. "You have to look into the particular scientific question to see if you should used manned or unmanned.
"Automated systems are good when the thing being studied is already understood. In other situations, a human being with five senses and the ability to learn from mistakes gives the better option for solving the question."
Mir has been used to grow successive generations of plants to establish whether microgravity affects reproduction. Crystals and drug compounds formed without the tug of gravity are different from those which form on earth. And the bone demineralisation that happens to crew on long-term flights on Mir provides a useful source of information that may be applicable to patients suffering mineral loss caused by osteoporosis, Dr Merbold says.
Mir's days may be numbered for reasons other than system failures. NASA, ESA, the Russians and the Japanese are all committed to a co-operative venture to put the International Space Station into orbit. The first module is due for launch by the Russians in June 1998, with modules two and three following in July and December of that year. The first crew are scheduled to occupy the new station during 1999.
The space agencies will then be able to choose between ageing Mir and the new station and it should be a fairly safe bet where the flight crew will be sent. If no other use has been found for this old workhorse, it will be allowed to drift back towards earth, eventually to burn up in a firey re-entry that will close a chapter on human endeavour in space.