A small but loud group continues to lobby for the manned exploration of Mars. A tremendous amount of research, planning, experimentation, and time devoted to conferences has engaged, and continues to engage, many scientists and engineers (and politicians). It may be unfair to gather up this widespread effort under a single acronym but, for convenience, I will try to get away with it: In this essay, it is called the Mars Manned Mission (MMM). 

     Most of what follows is based on gems provided by the Scientific American in its issue of March 2000. The issue presents a group of articles concerned with almost every aspect of the MMM [1],[2],[3]. 

     Based on information in the articles, I estimate that the bill will eventually come to $60 billion. With all of the trillions bandied about nowadays without batting an eye, do we have to concern ourselves with a “mere” $60 billion? Manned exploration of the Moon put an appreciable dent into our national budget, but it added a glorious chapter to the history of mankind’s greatest achievements. Is the glorious chapter that may be written by MMM worth $60 billion? This is a controversial matter. The manned exploration of Mars, however, is several orders of magnitude more complicated and expensive than that of the Moon. Society should be concerned, in my opinion, because the “dent” will appreciably and adversely affect medical research and health care. 

     We have been previously assured by NASA that, based on a probability assessment, the risk of failure is very low. Nevertheless, in view of horrible past fatalities, the Congress may be reluctant to support an MMM. Are we prepared to face further loss of life, equipment, scientific data, and so forth? With regard to this, the following, presented as a headline-grabber 26 years from now, is my “imagination run riot” (it is followed by pertinent technical information):

     WASHINGTON DC, 1 MAY 2029 -- In a speech that is certain to go down in history, the President declared today that “Enough is enough,” and vetoed the $30 billion (that is, $30,000,000,000) Emergency Martian Rescue Appropriation Bill (commonly known as EMRAB). Because Congress, as usual, is almost evenly divided on the issue, a veto override is not expected. 

     Outside the White House, small groups of angry demonstrators clashed with security police and with each other. Some of the placards declared “Heartless Harry: Bring My Son Back,” and “Congress: You Are An Immoral Bunch of Sinners.” On the other hand, an equal number of placards urged “Let the Adventurers Rot,” and “$60 Billion Went To Feed 4 Martians While One Billion Children Are Starving On Earth.”

     The President’s veto is certain to doom further manned exploration of Mars, especially since the cause of the Mars Ascent Vehicle (MAV) explosion on 19 April is not known. The “black boxes” were apparently blown away, and cannot be retrieved by the four astronauts. Furthermore, the deep-Mars samples that were gathered, despite the extreme hardships, during their 500-day sojourn, have to be subjected to electron microscopic examination on Earth. NASA is preparing a plan whereby the bodies of the crew, as well as their precious cargo, can be retrieved by means of robots. 

     The crew is receiving instructions on how to painlessly end the mission. Out of concern for their families, the end will not be aired on public television. In his speech, the President pledged that the astronauts will receive dignified burials on Earth, and he will propose generous compensation for their survivors. 

     NASA officials explained that the $60 billion total cost of the Mars Manned Mission (MMM) is an example of a chain reaction. The decision to send four astronauts who would spend 260 days getting to Mars, and 531 surface days living and exploring, plus a return trip of 260 days, all in hermetically-sealed vehicles, prompted every effort to ensure the safety of the crew. (Mars has a cold, thin atmosphere, 95% carbon dioxide.) This, plus the huge amount of fuel needed for the mission, added up to the astronomical total. 

     The MMM has received two severe blows. One was, of course, the terrible explosion of 19 April. But before that, on 19 May 2027, the discovery of pre-DNA-cells (PDCs) in deep-earth goo was announced. The goo was brought to the surface in an insulated, sealed container that preserved temperature, pressure, and so forth. In a completely sealed laboratory environment, analysis of the goo with an electron microscope revealed individual PDCs that, if stimulated with a modest impulse of energy, proceeded to combine with some of the ambient material, and grow larger. In fact, several different PDC “species” were found, some quite complex and apparently evolving towards a DNA architecture. This was unexpected since all previous attempts failed because the PDCs were eaten by endogenous bacteria. Furthermore, exactly a year later, on 19 May 2028, a PDC was synthesized in a Polytechnic University (Brooklyn, New York) chemistry lab. Since then, many other species have been synthesized, and the Cloning Foundation is offering a $500,000 prize to the laboratory that ends up with the minimum number of atoms in a PDC that can evolve into a DNA helix (entry deadline is 19 May 2031). 

     The PDC findings are highly controversial, but the scientific world, at least, is satisfied that this is the way in which life began, continues to begin, and continues to evolve. Furthermore, the same process is taking place in billions of goo pockets throughout the universe, and right here, on Earth, underneath oil wells and/or in the sea. These conclusions largely destroyed the raison d’etre of the MMM. However, because the astronauts were already well on their way during the PDC discovery on 19 May 2027, NASA decided to leave the mission unaltered. 

     As a service to our readers, the events leading up to today’s veto are briefly reviewed: 

     We have witnessed years of heated debate, and costly research and development. Because of the huge cost, our international partners pulled out one-by-one (although they agreed to sell components for the MMM as needed). The financial support of international corporations similarly faded when it was realized that it would be difficult to organize advertising slots. (Because of the tremendous distances involved, round-trip communication between Earth and Mars can take anywhere from 9 to 80 minutes, depending on the configuration.) But the nation agreed with NASA that “Man does not live by bread alone.” The two goals: Finding life on Mars, and national pride in a putative successful mission, led to the historic launch. 

     Well before that spectacular event, out of thousands of eager applicants, a four-man crew was assembled and trained -- an engineer, a physicist, a medical doctor, and a psychologist. Despite strong objections from the Association for Women in Science (AWIS), it was an all-male crew.

     Today’s tragic Presidential decision comes just 30 days before the crew was scheduled to blast off for the return trip, on 1 June 2029. They were expected to rendezvous with the CTV, which would reach Earth, followed by splash down, on 17 February 2030.

     May they rest in peace.
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     In the remainder of this essay, I give some the technical information surrounding the MMM, which  is very interesting and useful even if MMM never gets off the ground.

     The article by G. Musser and M. Alpert [2] includes a discussion of propulsion systems. These are presented in Table 1 and briefly considered as follows:

     A space vehicle has nothing to push against in the vacuum outside the earth’s atmosphere. A terrestrial vehicle, such as a propeller-driven airplane, pushes against the air to accelerate and maintain constant speed. It cannot fly above the atmosphere. A jet airplane is in a special category because it relies on the atmosphere to provide oxygen to burn its fuel. A space vehicle has to push against its own high-speed exhaust jet that is generated from the fuel that it carries. The simple equation that governs this is that the change in speed of the vehicle, multiplied by its mass, is equal to the speed of the exhaust jet, multiplied by its mass. In other words, impulse change = impulse change. 

     Table 1 shows that many different propulsion systems, and many different fuels, are possible. In order to fairly compare competing systems, the table is based on a 25-metric-ton (25,000 kilograms = 55,000 pounds) vehicle. Most of the entries are paper designs, or scaled up from a small experimental model. 

     The important propulsion information is given in the 3rd to 5th column of Table 1. Column 3 gives the force, in newtons, exerted backward on the vehicle to, of course, propel it forward. Column 4 tells how long the force acts, the “burn time.” Remember that it has to get the 2.5-ton vehicle to go from a relatively slow low-earth orbital velocity to a final “escape” velocity. Here, a simplification is possible: The vehicle starts out in low-earth orbit, at an altitude of 500 km, say, with the earth’s gravitational pull balanced by the orbital centrifugal force. Then, very approximately, 

Change in Velocity (column 5) = Force (column 3) X Burn Time (column 4) ÷ 25,000 kg. 
     Column 6, the jet exhaust speed relative to the vehicle, is also of interest.
     Comments with regard to each row of Table 1 follow:

1. Chemical This is the usual system, in which liquid hydrogen reacts with liquid oxygen.
2. Nuclear Thermal A nuclear reactor heats hydrogen to over 2500°C.
3. Variable Specific Impulse Magnetoplasma (1) Hydrogen is first ionized, then heated by a radio-frequency field to 10 million°C.
4. Magnetoplasmadynamic The fuel is first ionized, then heated by a magnetic field.
5. Variable Specific Impulse Magnetoplasma (2) In the system of row 3, a choke is used to reduce the thrust while increasing the jet exhaust speed.
6. Solar Sails Sunlight exerts a pressure of 9 newtons/sq km. By using a huge 4-square-kilometer sail, one can get a force of 36 newtons.
7. Ion The fuel is first ionized, then accelerated by an electric field.
8. Hall Effect The fuel is first ionized, then accelerated using the “Hall” effect.          
9. Pulsed Inductive The fuel is first ionized, then accelerated using a pulsed capacitive-inductive circuit.

     Finally, let’s consider the sequence of events that are planned for the MMM. This is an 1840-day (over 5-year) mission. I’ve broken it down into six rows in Fig. 1, which provides a time line that links the “day” starting with zero and the dates in the above 1 May 2029 “newspaper story.” The six significant steps of Fig. 1 are also depicted in the six rows of Fig. 2, which assume that the mission will be successfully completed:

     On Day Zero In the first row, Day Zero, one should not take the “zero” too literally and think that everything is accomplished in one day. On the left, in Fig. 2, on Earth, four 65-ton (143,000 pounds) unmanned half-vehicles are launched into low-earth orbit. Two of them are then assembled, via docking maneuvers controlled from the ground, to form the Cargo Lander; the remaining two are assembled to form the Habitat Lander. The half-vehicle tactics allow low-earth orbits from “Magnum” launch vehicles (yet to be constructed) that can handle 65 tons. After assembly, each 130-ton Lander blasts off towards Mars, as indicated in Fig. 2. 

Fig. 1- Time line for the Mars Manned Mission (MMM). The dates on the right correspond to the dates given in the 1 May 2029 “newspaper story.”

Fig. 2- The six significant steps of the MMM. E = Earth, M = Mars. See the text for the action taking place in each row.

     In this short essay, it is not appropriate for me to go into the restrictions on launch periods and travel times that are based on suitable conjunctions between Earth and Mars; this information is also available in the review by Musser and Alpert [2]. 

     On Day 260 The Cargo and Habitat Landers reach Mars. The Cargo vehicle successfully lands with the aid of parachutes and retrorockets, while the Habitat Lander is placed into a circular orbit around Mars.  

     Because “landings” are probably the most critical challenges in the MMM, a few additional words of explanation are given via the four stages of Table 2. Although the atmosphere of Mars is very thin, the situation is similar to that of a vehicle that first hits the thin atmosphere of Earth: Kinetic energy is converted into heat energy, so the vehicle has to be  protected with heat shields.  

1. Retrorockets fire. The Lander slows down.
2. Atmospheric entry. Heat shields absorb energy. The vehicle is maneuvered toward its landing site.
3. Heat shields are jettisoned; parachutes are deployed.    
4. Retrorockets fire to bring the vehicle to near-zero velocity relative to the landing site.

     On Day 790 Finally, the four-man crew is launched in a Crew Transfer Vehicle. (The Earth and Mars are only in a suitable configuration for launch, from one to the other, around once every 26 months, or 790 days.) 

     On Day 1050 The Crew Transfer Vehicle reaches Mars and briefly goes into a circular orbit. The crew transfers to the Habitat Lander. The latter successfully lands close by the Cargo Lander. The crew disembarks and begins a 500-day exploration for life on Mars. 

     On Day 1580 The crew blasts off for the return trip in an Ascent Vehicle. They rendezvous with and transfer to the Crew Transfer Vehicle, which has been orbiting Mars. Then they head for Earth. According to the version shown in Fig. 2, they leave behind the Ascent Vehicle (which may be outfitted as an orbiting Space Station).  

     On Day 1840 The Crew Transfer Vehicle reaches Earth, and splashes down near a rescue ship. It is difficult to imagine the tumultuous welcome that the crew will receive. 

     After reading the above narrative, I come away with two conclusions: First, the MMM is so complex, with Cargo Lander, Habitat Lander, Crew Transfer Vehicle, Ascent Vehicle, hermetically-sealed living quarters and supplies for a four-man crew for 1050 days, and so forth, that it is easy to believe that the mission can eat up $60 billion; second, because of its complexity, it is difficult to believe that it can be a successful venture.

     From Force = mass X acceleration we get, for a constant force,

where F = force, newtons,
            t = the time during which it acts, seconds,
           m = mass of the vehicle, kilograms,
           Δv = change in velocity, meters/second.
Then Δv = Ft/m. In general, one must include gravitational and centrifugal forces in F.

References
     [1] Glenn Zorpette, “Why Go To Mars?,” Scientific American, March 2000.
     [2] George Musser & Mark Alpert, “How To Go To Mars,” Scientific American, March 2000.
     [3] Robert Zubrin, “The Mars Direct Plan,” Scientific American, March 2000.