by Duncan Lunan

“To Mars!” was the watchword of the Russian rocket pioneer Friedrich Tsander, and it was resurrected by the author and editor Ben Bova, as a toast when he was our guest at the Annual Dinner of ASTRA, then Scotland’s national space society, in 1993.  But how soon we can get there, with human beings as against unmanned probes, is very much anyone’s guess.

The first detailed study of a Mars mission that I know of was Das Marsprojekt, by Wernher von Braun, published in 1953, and the subject of the late Prof. Archie Roy’s first lecture to the society in February 1954.  It envisaged a massive ten-ship, seventy-person mission, and helped to inspire the second of the BBC Light Programme’s Journey into Space serials, although the ships in that were smaller.  Von Braun, Willy Ley and Chesley Bonestell afterwards collaborated on The Exploration of Mars  (Sidgwick & Jackson, 1956), portraying a much smaller expedition of two ships and twelve people, with a departure mass from Earth orbit of nearly four thousand tons, requiring a whole fleet of shuttles to deliver and assemble.

One ship was a winged lander and the other, without streamlining, was to bring both crews home.  Confusingly, there was a British paperback edition called Project Mars, and still more confusingly the George Pal movie based on The Exploration of Mars was called The Conquest of Space, after a previous book by Ley and Bonestell, which was in part the basis of Pal and Bonestell’s previous movie, Destination Moon.  The film Conquest of Space suffers from terrible dialogue and a plot which makes absolutely no sense, but the effects by Bonestell were spectacular and the design of the Mars landing craft was actually superior to the one in the book.  Most remarkably the film showed Mars as rocky and cratered, very unlike the dune-covered world of the book but quite like its true self, with at least one giant volcano.  The final takeoff from Mars showed an overhead view of which the late John Braithwaite remarked, “If you took out the rocket plume, you could put that still in the Cambridge Photographic Atlas of the Planets and nobody would think it was unusual.”  Yet it’s followed by a shot which seems to be from a different movie, never made – in which the rocket is climbing away from Percival Lowell’s Mars, from an ‘oasis’ at the junction of three canals.

The ships in The Exploration of Mars were to be fuelled by nitric acid and hydrazine, which are hypergolic – i.e. they ignite on contact, burning with a spectacular bright red flame – and also have the virtue of being ‘space-storable’, i.e. requiring no refrigeration.  Their disadvantage is that they’re not the most energetic of propellants;  they have a relatively low specific impulse, which measures the thrust per unit mass of propellant consumed.   Considerably higher I_sp‘s can be obtained with cryogenic fuels, and the combination of liquid hydrogen  (LH₂) with liquid oxygen  (‘lox’ or LO₂)  is currently the top of the chemical propellant range.  A cryogenically fuelled Mars mission could be flown with a mass of two thousand tons, but one difficulty with them is that the fuels have to be kept at very low temperatures for the duration of the mission, and that needs a lot of power.  With chemically fuelled missions, there’s not much chance of improving on minimum-energy trajectories, giving a round-trip time to Mars of two and a half years.

One way to generate that cooling would be with a nuclear reactor, but as they tend to be very massive, if you were taking one to Mars you’d want to use it for propulsion and go for higher I_sp ranges altogether.  One way to achieve that is with ion-drive, which generates very low but continuous thrust and would overtake a chemically fuelled Mars mission, getting there several months earlier.  Von Braun designed an ion-drive, nuclear-powered Mars fleet for the Walt Disney movie Mars and Beyond, shown at one of ASTRA’s meetings in 1962.  An ion-drive fleet also featured in Chesley Bonestell’s artwork for Mars by Robert S. Richardson in 1965, and even better versions appeared on several covers of Fantasy & Science Fiction.  Incorporating the results of the Mariner 4 mission, the book showed vertical landings, by parachute and retro-rocket, now it was known that the air was too thin for winged landers.

The disadvantage of ion-drive is the very low acceleration and the long time the ships would take to pull away from Earth.  If the heat of the nuclear reaction can be applied directly to the reaction mass  (ideally, liquid hydrogen), a high specific impulse can be obtained with relatively brief acceleration times, allowing return trips to Mars taking little over a year.

  In the 1960s NASA developed a solid-core nuclear rocket called NERVA, and detailed plans were drawn up for a manned Mars flyby in 1980, with landings in 1986 by two six-person teams.  The Mars ships would use space station modules and nuclear tugs from the post-Apollo programme, predicated on use and continuing development of the Saturn V booster.   A minimum payload of 100 tons is needed to orbit a nuclear reactor, and even in its initial version Saturn V could loft 150 tons.  The total mass of the Mars mission at launch would be 1000 tons, and with the abandonment of the Apollo programme the whole programme became impracticable and the NERVA project was shut down.  Although the payload of the Space Shuttle was doubled, to make it capable of launching spy satellites, it was wholly inadequate for the segments of an interplanetary mission.

Dr. Krafft Ehricke, whose paper ‘A Strategic Approach to the Solar System’ we drew on heavily in ASTRA’s Man and the Planets project, had been highly critical of NERVA.  For all the improvement over chemical propulsion, NERVA lacked long-term growth potential and could only be used for small scientific mission to Mars and Venus.  Dr. Ehricke conducted a detailed comparison of NERVA’s merits with ion-drive, gas-core nuclear reactors  (which would yield higher I_sp, but have yet to be demonstrated), nuclear fusion  (ditto), or the Orion concept, advocated by Prof. Freeman Dyson.  That would use small hydrogen bombs to propel the ship, ‘giving a very good reason for going off in the opposite direction’, but would allow transfers with continuous acceleration as high as 0.1 g, reaching Mars in only two weeks.   Orion ships would be physically big as well as massive, however, so Saturn V-class launchers would still be needed, and we no longer have them.

In 1986, I was in Houston at the time when the USA would have been on its way to Mars, which was then at its closest to Earth for fifteen years.  I was a guest of space expert Jim Oberg, and we walked by starlight along the side of one of the last two Saturn V’s, in the static display park.  Mars was directly over the nose of the rocket, and when we reached the second stage, Jim picked up a stone from the gravel and threw it at one of the engines.  A great chorus of hooting arose, and a huge owl came out and flapped across the Milky Way.   “They’re nesting in the engines,” said Jim.  “They have a right to it:  they know how to make use of it, which is more than we did.”

In the late 1970’s, however, it had come to seem that others might be going.  The USSR began launching mystery vehicles, designated only by numbers in the catch-all ‘Cosmos’ series, which were very big, had solar panels, and returned telemetry on two wavebands normally used by the manned Soyuz spacecraft and Salyut space stations.  The occasional interruption of signals indicated that these were actually coming from two different antennae, and on some missions the segments separated.  The first three of these made only a couple of orbits, but Cosmos 929 stayed in orbit for months and performed a strange series of manoeuvres, raising and lowering its orbit, until finally it had demonstrated 10% of the velocity change needed for a minimum-energy return from Mars.

I suggested that these were trials of a prototype Mars ship and lander.  It later emerged that the Soviets developed an alternative military space station, as a counterpart to the Salyut programme, with a large return-to-Earth unmanned module, but it never became operational;  instead, several of the Salyuts were specifically military espionage missions.  The vehicle was later used to carry large cargoes to the Salyuts and Mir, but in the meantime, it had become clear that a Mars mission was in preparation.  Long-stay missions on the Soviet space stations pushed up endurance times to six months, then to over a year, and eventually it was admitted that this was in preparation for missions to the red planet.  For a while journalists, and I, treated that as a joke, but eventually I realised that the Soviets took the Red Flag very seriously.  If Mars had been the Stars and Stripes planet, the Americans wouldn’t have given up on reaching it first anything like so easily – and China still flies the Red Flag today.

But the Soviets had abandoned the Lenin booster which they created for their own lunar programme, and the biggest booster they had was the Proton.  Without cryogenic technology, it wasn’t at all obvious how a Mars mission could be staged:  a hypergolically fuelled one would need 200 Proton launches to assemble.  The whole picture changed radically in the late 1980’s with the appearance of the Energia booster, with which the Soviets entered the cryogenic field at the top of the range.  The basic Energia had a payload to Low Earth Orbit of 100 tons, but with extra clip-on boosters and upper stages it could carry 250 tons.

Gerry Webb of the British Space Company discovered that the Russian Mars mission was to be assembled from four Energia payloads, and that changed the picture radically once again.   Either the Soviets were about to reveal a similar breakthrough in nuclear rocketry, or the 1000-ton mass was inadequate even for a cryogenically fuelled mission.  For a hypergolically fuelled one, however, it would be adequate for the outward journey, and that revealed the strategy:  if the moons of Mars turned out to be water-rich carbonaceous chondrite asteroids, as there was then strong reason to believe, then hypergolic propellants could be manufactured on-site.  If you don’t have to carry the fuel for the return on the way out, then the initial launch mass can be reduced by three-quarters, though it would take a certain amount of nerve to set off for Mars knowing you had to manufacture fuel there in order to get back.  But sure enough, the next move was the launch of the Phobus missions with the declared purpose of analysing the surface chemistry of the Martian moons.  Unfortunately, Phobus 1 was accidentally switched off on the way to Mars and Phobus 2 failed in Mars orbit.

With the collapse of the Soviet Union, the Energia programme was mothballed, and remained on ice for years in hopes that some arrangement could be found to enable the West to bail it out.  This proved to be a vain hope.  Nothing more was heard of the announcement that the World Bank was financing a bulk launch of Russian communications satellites on Energia;  there were pleas from Western experts that Energia launches could save billions on the Space Station programme and relieve the strain of construction flights on the Space Shuttle fleet, but they went unheeded.  In 1995 the Russians conceded that they were at the end of the road:  the mothballed Energia hardware was removed from storage and the teams were disbanded.  On 12^th May 2002, the remaining Energia boosters and the only completed Buran space shuttle were destroyed when the storage building collapsed during inspection, with loss of life.  For believers in the human future in space it was a profoundly depressing development, the second time that we’d had the launch capability to take us to the stars and thrown it away.   As a potentially space-faring civilisation, how many chances do we get?

In 1986, President Reagan’s National Commission on Space produced the report Pioneering the Space Frontier, covering the next fifty years in space.  For Mars the recommendation was to establish ‘swing stations’, space stations orbiting cyclically between Earth and Mars, with a transfer station at the Earth-Moon L1 point.  Unmanned, nuclear-powered ion-drive cargo freighters would back up the manned exploration of the planet.  There was no sign of any initiative to bring it all about, however, and in 1987 the astronaut Sally Ride produced another study.  On my visit to Houston in ’86 I attended a briefing that set forth the plan she endorsed, which would use liquid oxygen manufactured on the Moon for cryogenically fuelled missions.   Still nothing happened, and in 1989 President Bush set up the ‘Synthesis Group’ under astronaut Tom Stafford, to formulate the ‘Space Exploration Initiative’.  This recommended a return to nuclear propulsion for Mars missions, in the report America at the Threshold.   The proposal met with no support in Senate or Congress, and that was the end of that – until now.

Meanwhile, other players have at least considered joining the game.  In 1992 the European Space Agency drew up a detailed plan for manned missions to Mars, to be assembled in orbit using Ariane 5 boosters, beginning in 2020.  Prof. Max Vasile of Strathclyde University, who was a member of the study group, confessed to us that they had to make special assumptions and cut some significant corners to make it work, even on paper!  Subsequently the target date moved back to 2030 in ESA’s Aurora programme, bu that’s still a long way from progressing to manned missions.  In 1997, the Japanese space agency NASDA intended to begin Mars exploration in 2001 with unmanned probes, achieving manned missions by 2010 and establishing a self-sufficient colony by 2057.  In the longer term, Japanese engineers have conducted detailed studies on plans to make the whole planet habitable;  but again, little headway has been made.

In the excitement of the 1996 news about possible signs of life in Martian meteorites, President Clinton announced that a major conference would be held in 1997 to consider options for the exploration of Mars.  It came in  the context of moves to make space exploration quicker, simpler and cheaper, breaking away from the massive programmes of the past, which are generally agreed not to have been successful.  There were two major challenges to established thinking on Mars missions, as regards the construction of Mars ships and the fuel question.   On structure, the Lawrence Livermore Laboratory was pushing the concept of ‘inflatables’, which would allow relatively small ships to be launched, expanding their living quarters for the coast phase and packing them away again for powered manoeuvres on the approach to Mars.

As regards fuel, for some years Robert Zubrin had been enthusiastically promoting the concept of ‘Mars Direct’.  In this scenario, an automated factory would be landed on Mars to manufacture rocket fuel from the atmosphere during the ‘waiting period’ between one opposition  (when Mars is overtaken by the Earth in its orbit)  and the next. Two and a half years later, the manned vessel would then go out with fuel for a one-way trip, as the Russians planned to do, but with the big difference that the fuel for the return would already be manufactured and waiting.  There is now an international Mars Society which backs Robert Zubrin’s plan, to the extent that they’ve built experimental bases, one in a meteorite crater on Devon Island in the Arctic, the other in the desert in Utah.

One possible advantage of the plan is that there’s a commitment to returning each time to the same site on Mars, building up resources for a more permanent presence – especially if the crew stays on Mars till the next opposition, or brings the return stage of the first ship back.  The disadvantage, of course, could be that the first location proved to be unsuitable, or other sites might prove to be scientifically more important.  In my book Man and the Planets  (Ashgrove Press, 1983), the ASTRA scenario was to explore Mars from orbiting bases with considerably larger, two-stage ships, leaving each descent stage to be a shelter for future use.   A cluster of four such landers could be used as the nucleus of a more permanent settlement.

(To be continued).