Holes in the space mission
Forget Bush's short hop to the Moon - it's time to boldly go to Mars.
Two remotely controlled roving vehicles are now on the Martian surface. The first, Spirit, managed to sneak past the ‘great galactic ghoul’ (thought by superstitious mission controllers to be guarding all approach paths to the planet) at the beginning of January 2004 and make a successful landing on Mars’ cold and arid surface. The second mission, Opportunity, followed a few weeks later.
Like many, I anxiously awaited the first images: I was there peering at web pages in the weak grey light of Sunday morning. But looking at the beautiful, high-resolution pictures as they arrived, I have to admit that I was just slightly disappointed. The images showed a broad, featureless plain, not the sort of place you’d want to find yourself without a lot of reading material.
In terms of exciting vistas, this landing site was a bust. The only large surface feature visible in those first images was a mesa around 20 kilometers (km) away: other than that, Spirit is in the centre of a broad rocky plain stretching to the horizon. Spirit’s twin is inside a small crater – the horizon is a few short metres away.
The images relayed from the Pathfinder probe in 1997 were not much more exciting – some low hills and surface depressions. This wasn’t the Mars we’d read about – the Mars that has the solar system’s largest volcano, Olympus Mons, measuring 600km at its base and 25km high, or the Valles Marineris trench, 500km wide, around 6km deep and 5000km long – about as long as the continental USA. This Mars would look like a flat stretch of terrestrial desert, were it not for the strange lighting.
Of course, there is a very good reason why the vistas seen from these probes are so unappealing. In selecting the landing site, one of the primary concerns for the mission planners is the safety of the lander. Given the extreme difficulty of landing a probe on the Martian surface, this is without question a prudent strategy. The delivery system has to decelerate the probe from interplanetary cruise velocity and land on the Martian surface in around six minutes. Mission design is a direct consequence of planning decisions taken in the framework of available technology – such as the amount of mass that can be delivered to the surface of Mars by today’s rocket motors.
It’s worth noting that the total mass of Spirit, on the Martian surface, is around half a metric tonne – approximately the same as the Viking landers that arrived there almost 30 years ago. In the intervening three decades, rocket technology had made no significant advances: we still have almost the same total mass budget as before. The spectacular advances with respect to previous missions are almost entirely due to Moore’s law – the doubling in component density of microelectronic devices every 18 months – rather than the development of a revolutionary new propulsive technology. This means that the kinds of places we can visit with the delivery system we have today is very limited.
If we decide that we want to go to Mars to search for life, we probably won’t find it with an airbag-assisted delivery system. If there are living organisms on Mars they are almost certainly not going to be on the broad, exposed Martian surface, which is inimical to life but is the safe place to land. Life is going to be deep underground, in the valley floors and deep caves, far from the surface. It’s going to be in the kinds of places only accessible to human explorers. Robotic probes will only be able to act as our imperfect proxies, incapable as they are of independent thought and intuitive action. They are indeed a poor substitute for going there. But given that no major advances have been made in the process of hefting mass from the surface of Earth to orbit over the past 30 years, sending humans to Mars will not be a trivial undertaking.
Thinking these thoughts, I was of course interested to hear of President George W Bush’s new space exploration initiative, which features a return to the Moon and possibly a manned exploration of Mars after that. Of course, it is not the first time a Bush has promised such a thing: his father did the same before him, on the steps of the Air and Space museum in 1989. Those particular proposals quietly disappeared after it was realised how much they would actually cost. This time around, Bush Junior is being a little more cautious: around one billion extra dollars have been allocated. I won’t begin to speculate on the motives for the latest announcement, but I would like to imagine that perhaps now the long pause in our exploration of space of the past 30 years is now over. Could everything change with this one speech?
It was clear that the Space Shuttle program and the International Space Station (ISS) had been in trouble for a long time, even before the fatal accidents that destroyed one shuttle as it left the Earth and another as it returned. The Space Shuttle and the Station both existed to support the other– and not interesting to anyone. The Shuttle no longer carried out most of the functions it had been designed for, and the International Space Station was too small and under-staffed to perform any useful scientific tasks, other than educating and training people how to live on the International Space Station.
For me, as an astronomer, the unquestioned highlight of the Shuttle program has been the repair and successive servicing missions of the Hubble Space Telescope, but it is telling that Hubble’s successor, the James Webb Space Telescope (named after a NASA administrator, of all people, and much to the consternation of non-American astronomers) will be in an orbit where it cannot be serviced.
Even worse, it has now emerged that the fourth servicing mission to the Hubble, which would have installed two new instruments and significantly enhanced and extended Hubble’s scientific output, has now been cancelled.
Without this servicing mission, it is probable that the telescope will continue functioning for around two or three years before a fatal component failure renders it unusable. NASA administration officials insisted that the mission had not been scrubbed because of cost concerns. No, it turned out, the reason why the servicing mission had been abandoned is because it would have been too dangerous. The only place the Shuttle will now be allowed to visit is the ISS (which will take another 25 to 30 missions to complete).
In Bush’s speech the focus on first returning to the Moon seems truly bizarre: maintaining a human base on the Moon would be a costly and unrewarding activity. There is no reason why a mission to Mars could not bypass the Moon altogether. Several such schemes have been proposed over the past decade or so (schemes in part inspired by the profligate and expensive Mars missions proposed by Bush senior). Unlike Mars, there is no compelling scientific reason to visit the Moon: the old dream of lunar observatories dates from an epoch before we had the know-how to construct orbiting satellites. Most importantly, the Moon, unlike Mars, has precious little local resources (perhaps aside from some water ice) and it is hard to imagine a sustained human presence there without heavy financial support from Earth.
It’s hard to believe that we’ve escaped from our current impasse, and that manned exploration of Mars will start anytime soon. We have a 30-year gap in rocket technology to make up (it is worth noting in passing that one promising idea, nuclear-powered propulsion, has been more or less shelved indefinitely due to safety concerns and the unfashionable nature of nuclear energy). Ultimately, how can we contemplate a manned expedition to Mars when we’re not willing to risk a trip to low Earth orbit for a servicing mission to the Hubble Space Telescope? There is no place worth visiting in the solar system that is safe enough.
When gazing for the first time upon a mountain or lake or inlet or harbour, human explorers have long responded to their feeling of the unexplored and unknown by giving names to these new features. Of course, it was a way to make the unknowable knowable, to make the unfamiliar familiar. Here in the twenty-first century, names have now been given to both American Martian landing sites – and in both cases, the names chosen commemorate astronauts killed in tragic accidents. Suddenly, they are no longer landers but ‘memorial stations’. The nearby hills around the Spirit lander have been named after the Apollo One astronauts who perished in a launch pad fire 37 years ago.
We are expanding into the solar system, for sure, but our robotic explorers are really tombstones in disguise. In another less cautious age perhaps we wouldn’t be staring back so fixedly in this particular direction – perhaps instead we’d be looking towards that mile-deep trench, towards that distant mountain just visible there on the horizon?
Henry Joy McCracken is an astronomer at Paris observatory.
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