Friday, 1 March 2013

To Mars in a nutshell

O God, I could be bounded in a nutshell and count myself a king of infinite space…

Hamlet was not alluding to space travel, but he might as well have been. An audacious proposal announced by American millionaire Dennis Tito calls for a man and woman to make a 501-day round trip to Mars in a spacecraft half the size of a camper van. There will be no landing – the spacecraft will simply make a fly-by, skimming past the Red Planet at a minimum altitude of 100 miles. The crew are likely to be a middle-aged married couple.

Dennis Tito first made the headlines in 2001, when over the objections of NASA he paid for a seat on the Russian Soyuz TM-32 mission to the International Space Station. He was subsequently described as the first ‘space tourist’, a rather unfortunate label in my view. Tito, now 72, shares the frustration of all space enthusiasts at the complete lack of progress with the manned exploration of space since Project Apollo. It is now four decades since Cernan and Schmitt blasted off from the surface of the Moon. Nobody has been back; no manned spacecraft has left Earth orbit since.

There have been innumerable proposals for an expedition to Mars, but none have got off the ground even metaphorically. It is of course much harder to mount an expedition to Mars than it is to the Moon. The most obvious problem is that Mars is very much further away than the Moon. The Apollo missions typically lasted under ten days; the duration of Tito’s mission will be fifty times longer. The next problem is that Mars, though small in comparison to Earth, is still much larger than the Moon. Furthermore, unlike the Moon, it has a significant atmosphere. To land on Mars and take off again, you need a craft that is not only built for re-entry, but is also able to escape the higher Martian gravity on take-off. This means a craft that is considerably larger and more complex than the Apollo lunar module. The fuel requirements for the mission are immense. Assuming an Apollo-type lander-orbiter configuration, you need sufficient fuel for 1) the spacecraft to launch and leave Earth orbit, 2) achieve Martian orbit, 3) the lander to land and take-off, 4) the orbiter to leave Martian orbit, 5) make any required mid-course alterations.

The crucial difference between a manned expedition and the innumerable unmanned landers and rovers sent to Mars since the 1970s is that the latter don’t have to return to Earth. To date, no unmanned sample return mission to Mars has ever been attempted, and even attempts to return samples from its moons have failed. To get round the problem, some have suggested a one-way trip to Mars. Unlike the Moon, there are sufficient raw materials on Mars to allow colonists to keep themselves alive indefinitely. 

The Tito proposal involves a fly-by rather than a one-way trip. There’s no landing, but the crew don’t have to spend the rest of their lives on Mars. The spacecraft will be launched on a so-called free return trajectory, which will return it to Earth without the expenditure of fuel. Very little fuel will be needed after leaving Earth orbit. The result is a far simpler mission profile, though this term is relative. Unlike the International Space Station, which is periodically resupplied from Earth, the spacecraft will need to carry oxygen and supplies for the whole of the 501 day round trip. Even items such as toilet paper will amount to 28kg (62 lb.) in the supplies manifest. A major complication is that the spacecraft will be travelling at 51,000 km per hour (32,000 mph) when it returns to Earth. No manned spacecraft has ever attempted re-entry at such speed. It is likely that the spacecraft will have to slow down by aerobraking in the Earth’s outer atmosphere. The technique has been used for twenty years to slow unmanned space probes, but has never been attempted with a manned craft.

Another factor is radiation from the Sun and from interstellar space. A vehicle in Low Earth Orbit, such as the International Space Station or a shuttle, is largely protected by the Earth’s magnetic field. On a short-duration mission beyond Earth orbit – such as Apollo – the dosage is not large enough to be a problem. The possible effects of exposure on a long-duration mission include sterility and an elevated risk of developing cancer in later life. That is the reason for selecting a middle-aged crew. It is further assumed that a married couple could better endure the psychological stresses of long-term confinement.

There is also the risk of a coronal mass ejection from the Sun – a massive burst of radiation occurring during a solar flare. The proposed mission will take place during a period of low solar activity, but the risk isn’t entirely absent. The radiation could seriously harm or even kill the crew. Unfortunately, there is very little that can be done with present-day technology to shield a spacecraft against radiation. Finally, there is the stark reality that if something goes wrong with the spacecraft or if there is a medical emergency on-board, there will be absolutely nothing that can be done to abort the mission.

No concrete proposals yet exist for the mission. A possible configuration would involve a Dragon spacecraft from the private US space company Space X. The Dragon is a re-usable capsule-type craft that has already carried out an unmanned resupply mission to the International Space Station. The Dragon would be coupled to an inflatable habitat module of the type under development by Bigelow Aerospace, another private US space company. The mission would be launched with a Space X Falcon heavy-lift launch vehicle. First launch of the Falcon Heavy is expected either late this year or early next year.

The next launch window for the 501-day flight occurs in January 2018. After that, Mars will not be in the right position again until 2031. This gives Tito 5 years to get his mission off the ground. At the glacial speeds which NASA has operated since Apollo, this might not seem possible. However, it should be remembered that little over eight years passed from Alan Shepard’s sub-orbital spaceflight in 1961 to the late Neil Armstrong’s ‘giant leap for mankind’. The entire history of powered flight from Kittyhawk to the Sea of Tranquillity took place within the lifetime of many, including my grandparents.

The cost of the mission has been estimated at between $1 to 2 billion (£660 – 1200 million). This might sound like a lot of money, but it is actually less than Russian oligarch Roman Abramovich is alleged to have spent on Chelsea FC over the last decade. In space terms, it’s peanuts. In terms of actual Mars science, the value of the mission will be far less than can be achieved with unmanned orbiters and rovers. The scientific value of the mission will be in terms of what can be learned about the physiological and psychological effects of long-term spaceflight beyond Earth orbit.

The real worth of the mission, however, will be in its inspirational rather than scientific value. Nobody much under the age of 50 can remember the Moon landings. The current President of the United States was a few days short of his eighth birthday when Armstrong and Aldrin landed on the Moon; UK Prime Minister David Cameron was a 2 ½ year-old toddler. I think we’ve been waiting long enough for mankind’s next giant leap.

© Christopher Seddon 2013

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