Onwards to Mars

Looking beyond its return to the Moon scheduled for 2020, NASA is turning its attention to a far more ambitious Mars mission. By then, a small army of new probes will have assessed the conditions that await human visitors.

EXOMARS ROVER

Europe's next Mors mission, planned for the mid-201 Os, will put a robotic field biologist on Mars. The roving laboratory will search for signs of past and current life, but also investigate the nature of the Martian soil to assist future monned missions.

EXOMARS ROVER

Europe's next Mors mission, planned for the mid-201 Os, will put a robotic field biologist on Mars. The roving laboratory will search for signs of past and current life, but also investigate the nature of the Martian soil to assist future monned missions.

A trip to Mars is the next obvious step in human exploration of the Solar System, but huge new challenges will have to be overcome. Nevertheless, NASA's new Vision for Space Exploration has probably the best chance since the Apollo era of actually putting a man on Mars.

To date, the agency has not officially endorsed even a basic mission profile, but there are several independent proposals and, with some knowledge of the difficulties, we can at least get a glimpse of what may be involved in a manned Mars mission.

Assuming it is designed to take advantage of the periodic close approaches between Mars and Earth, a round trip to Mars would be a roughly three-year mission. The real dangers of such a long spaceflight will lie in the continuous exposure to radiation and the dangerous first steps on Mars after months of muscle deterioration in zero gravity (for even though the spacecraft will be moving at high speed, its astronauts will be weightless as soon as it stops accelerating). For these and other reasons, some form of radiation shielding around the spacecraft will certainly be needed, and if possible the design should generate artificial gravity (see panel, below).

Another major challenge of a manned mission is the sheer amount of fuel it requires: the spacecraft must break free of Earth's gravity, accelerating enough to reach Mars in a reasonable time, and then decelerating to drop into orbit. Getting to and

Zero Gravity Radiation Protection

PHOENIX LANDER

NASA's next Mars mission, due to touch down in 2008, has fan-like circular solar arrays. It will target the Martian north pole, hopefully with more success than 1999's Mars Polar Lander (see p.273).

PHOENIX LANDER

NASA's next Mars mission, due to touch down in 2008, has fan-like circular solar arrays. It will target the Martian north pole, hopefully with more success than 1999's Mars Polar Lander (see p.273).

VISION OF MARS

(Right) A NASA artist's impression shows the crew of a future Martian manned mission setting up equipment during exploration of the Martian poles.

from the Martian surface will require even more fuel, as will the journey back to Earth.

Shielding, artificial gravity, and a heavy fuel load will all increase the size and mass of a Mars spacecraft at the start of its long mission, and any all-in-one mission will be far too large to launch directly from Earth - instead it will probably be assembled in Earth orbit from separately launched components.

Direct to Mars

One ingenious solution to the many problems with such a mission was developed in the 1990s by the American Robert Zubrin, founder of the Mars Society. Zubrin's Mars Direct mission involves sending an automated Earth Return Vehicle (ERV) to land on Mars ahead of the main mission's departure. The ERV would contain equipment and chemicals to manufacture at least 96,000kg (211,0001b) of oxygen and methane propellants using carbon dioxide extracted from the Martian atmosphere.

Once the ERV had generated sufficient fuel, a second craft called the Mars Habitation Unit (MHU) would set out, carrying a crew of four and generating

FUTURE SPACESUIT

Astronaut Andrew Feustel rehearses a 10km (6 mile) low-gravity walk in a prototype hard-shelled spacesuit. Similar suits will be needed for both the Project Constellotion lunar loadings and the future exploration of Mars.

FUTURE SPACESUIT

Astronaut Andrew Feustel rehearses a 10km (6 mile) low-gravity walk in a prototype hard-shelled spacesuit. Similar suits will be needed for both the Project Constellotion lunar loadings and the future exploration of Mars.

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ARTIFICIAL GRAVITY

The easiest way of creating artificial gravity is simply to set a spacecraft spinning. The centrifugal force this generates will produce an effect equivalent to gravity, with objects pushed away from the spacecraft's centre of mass, as seen in countless science-fiction films. However, this is not ideal in a small spacecraft, since all the walls effectively become floors. One way to produce artificial gravity in a consistent direction is to move the centre of mass outside the spacecraft, and this can be done by tethering it to a similar mass and setting the entire assembly spinning. The crew of Gemini 11 briefly managed to do this in 1966 (see p.110). In the Mars Direct proposal, artificial gravity is generated during the journey to Mars by tethering the Mars Habitation Unit to its spent upper rocket stage, while on the return it is done using the exhausted engine of the Earth Return Vehicle as a counterweight.

PHOENIX IN WINTER

The Phoenix Lander is a strictly short-term mission to investigate subsurface ice and signs of life around the Martian North Pole. Because Mors has a similar tilt to Earth, the polar regions are dark for port of the year. Robbed of sunlight and covered in winter frosts, the probe will soon cease to function when winter sets in.

HISTORY FOCUS

REHEARSALS FOR MARS

the need for a huge new launcher. Based on the specification for the Ares launchers and the profile for the Constellation lunar missions, it seems likely that any NASA Mars mission will indeed feature some orbital construction. The agency also originally wanted methane engines on its LSAM lunar lander, suggesting it likes the idea of on-site Martian fuel production (although the idea had to be abandoned due to reasons of time and cost). It will doubtless be some time before the various discussions and arguments crystallize into a single coherent plan.

Robot explorers

In the meantime, NASA is concentrating on laying the foundations. A new wave of Mars probes, begun by the Mars Reconnaissance Orbiter and continued with the Phoenix Lander and ExoMars, will travel to the planet and investigate the burning scientific questions of water and life, while scouting out potential sites for manned landings. Elsewhere, spacecraft and rover designs suitable for the surface of Mars are being tested in hostile desert conditions, and scientists conducting biomedical experiments are searching for volunteers to spend months on simulated space missions (see panel, above).

Soviet Mars Rover

Early Martian astronauts will be on the planet for a long time - the shifting positions of Earth and Mars in their orbits ensure that close approaches suitable for the journey between planets happen only every couple of years. Assuming they have enough supplies, how will the astronauts fare physically and psychologically? To answer this question, several experiments have been carried out - most famously, the establishment of Biosphere 2, a self-contained colony in the Arizona desert, where eight people lived for two years in the early 1990s. A Russian experiment, Mars 500, w'" short|y cor|duct a similar

BBIBSMMni^^w isolation study of how to provide for the wellbeing 8If SSfeof crews during its own artificial gravity. Reaching Mars in about six months, the MHU would slow itself by aerobraking and land close to the waiting ERV. At the end of the surface expedition, the astronauts would use the ERV to launch themselves on the trip back to Earth.

The ERV proposal dramatically reduces the weight of a Mars spacecraft and also gets around the potential risks of landing a fuel-laden rocket on the planet. Disadvantages of the original Mars Direct scheme included the need for a Saturn V-dass launcher to send the ERV direct from Earth and reliance on its onboard chemical plant for the return journey. A NASA-developed variation from 1997 would put a fully fuelled ERV in Mars orbit, land a Mars Ascent Vehicle (MAV), fuel plant, habitat, and other equipment on the Martian surface, and then send a small descent vehicle along with the crew.

Other suggestions involve assembling the various elements of the Mars mission in Earth orbit (perhaps using the ISS as a construction base) to avoid

New horizons

Over the next decade, new spaceprobes are scheduled to explore the extremes of the Solar System, from baking Mercury to the frozen outer worlds beyond Neptune.

Plans for future unmanned spaceprobes are notoriously prone to change - priorities alter, budgets spiral out of control, and of course things go wrong. Even if a probe survives launch and reaches its target, computers can develop bugs, or physical apparatus can jam or break: the history of unmanned space exploration is littered with examples. However, some future plans are more certain than others - and barring accidents, at least a handful of probes currently in the late stages of development or already on the way to their destinations should be surprising us with new discoveries before long.

MESSENGER to Mercury

The Mercury Surface, Space Environment, Geochemistry and Ranging mission (fortunately known by the acronym MESSENGER) embarked on a lengthy journey to the innermost planet on 3 August 2004. Despite Mercury's proximity to Earth, the probe must fly through a complex series of gravity-assist manoeuvres in order to pick up speed and gain enough energy to match Mercury's orbit. This convoluted route is needed because, unlike the

MESSENGER FROM EARTH

After flying past Earth one year after launch, MESSENGER'S route takes it twice past Venus to speed it up and direct it Sunwards. Three flybys of Mercury and a series of engine burns will gradually adjust the probe's path until finally it will rendezvous with Mercury in the correct trajectory to slip into orbit.

ENCAPSULATING MESSENGER

Workers at the Astrotech Space Operations facility near Kennedy Space Center carry out final tests on MESSENGER (far right) before the finished probe is unveiled to the world's media on 14 September 2004 (right).

Mariner 10 probe that first visited

Mercury in the 1970s, MESSENGER ^H^Ljp3*

will go into orbit around the planet.

After its arrival in March 2011, MESSENGER'S instruments will go to work, gathering data for at least a year. As well as cameras, the probe carries spectrometers for analyzing minerals and gases, a laser HISBSSmI

altimeter for measuring the height of the surface, and instruments to map Mercury's gravitational and magnetic fields.

For such a nearby planet, we know surprisingly little about Mercury, and we have seen less than half of its surface. MESSENGER should change all this, turning the mysterious little ball of rock into a fascinating new world in its own right.

Into the frozen deep

Since the planets were officially re-classified in 2006, NASA can claim to have sent probes to all the major worlds of the Solar System, but what of the former ninth planet, Pluto? Astronomers now know that it is really a dwarf planet, part of the Kuiper Belt,

a ring of icy objects beyond Neptune. The belt was proposed by Gerard Kuiper (see panel, below) in 1951, but it took four decades for modern telescopes to bring it into view.

In January 2000, NASA launched a probe that is now hurtling towards this mysterious region in a race against time. New Horizons was the fastest spacecraft ever to leave Earth, and a boost at Jupiter will send it across the realm of the outer planets in just eight years, passing Pluto in 2015, before continuing into the cold depths of the Kuiper Belt.

The reason for this blistering pace is that Pluto is a changing world. It follows a 248-year elliptical orbit that, between 1979 and 1999, brought it closer

BIOGRAPHY

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Soviet Union Mars Photo

to the Sun than Neptune. During this "perihelion Dawn is a certainty - a NASA mission to be launched passage", ice on Pluto's surface evaporated to form a in 2007 which, if all goes well, will fly past and thin atmosphere, and NASA hopes that New Horizons investigate the two largest denizens of the asteroid will arrive in time to study the gas around Pluto belt, Vesta and Ceres, in 2011 and 2015 respectively, before it freezes again, probably in the late 2010s. Powered by an ion drive similar to that used on Deep

Space 1 (see p.282), it will be the first spacecraft ever

Grand plans to go into orbit around two separate alien worlds. Over the next decade, a dozen or more new Further afield, ESA and JAXA plan to follow spaceprobes are sure to be launched. Most will go to MESSENGER with their own Mercury orbiter, the Moon and Mars as preparation for new manned BepiColombo, and after the cancellation of NASA's missions gather pace, but which other plans will plans for a Jupiter Icy Moons Orbiter, ESA hopes to fill make it off the drawing board? the gap with a mission to investigate Europa.

IN THE LAB

The New Horizons spacecraft is seen here under construction at Johns Hopkins University Applied Physics Laboratory in Maryland. In order to fly at high speed to the outer Solar System, the probe's weight had to be kept to 479kg (1,0541b), including propellant for in-flight manoeuvres.

TO PLUTO AND BEYOND

New Horizons had to take off in a narrow launch window if it was to take advantage of a gravity-assist from Jupiter. If it had missed the window, it would have had to spend three more years crossing space.

REX: to analyze Pluto's atmosphere

PEPSSI:

particle detection experiment

February-March 2007

The spacecraft flies past Jupiter at 21km (13 miles) per second

14 July 2015

New Horizons passes within 9,700km (6,000 miles) of Pluto and its giant moon Charon, with just a day to gather most of its data. It then continues into the Kuiper Belt.

SWAP: particle instrument for measuring solar wind

19 January 2006

New Horizons launches: by the time upper stage shuts down, the probe is travelling at more than 16km (10 miles) per second

Alice: ultra-violet imaging spectrometer

LORRI: high- X resolution optical telescope and camera

Ralph: optical/infrared imaging equipment to make colour maps of Pluto and Charon dust counter

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