To Mars -- in three easy steps

Since the Apollo landings nearly a half- century ago, NASA has been adrift in interplanetary space in search of an overarching goal.  Mars is the obvious choice -- both for science and for public impact.

Now, of course, "easy" is a relative term.  I visualize three initial steps of increasing technical difficulty in the human exploration of Mars.  Landing on the planet is not one of these; too difficult and risky; too costly; and perhaps not worth it at this stage.  I know that this strategy won't be acceptable to "space cadets," who plan to colonize Mars without delay -- but we need initial steps before sending astronauts to the surface of Mars.

Why Mars?

Mars holds the promise of fundamental scientific discoveries -- plus a wealth of data about a neighboring planet that will benefit understanding how our own planet works.  Mars is Earth-like in some ways -- yet obviously very different -- an ideal way to test our theories about the Earth, oceans and atmosphere.  These days we hear much talk about modifying the climate and other schemes of "geo-engineering."  Wouldn't it be wise to experiment with Mars rather than Earth?

The scientific returns from studying another planet like Mars would be immense: its climate history and current meteorology; its composition, both surface and interior; the fate of past atmospheres, oceans, and planetary magnetism.  A major question for decades has been the origin of the Martian moons; a solution to that puzzle could tell us much about the formation of the terrestrial planets: Mercury, Venus, Earth, and Mars.

But the holy grail of Martian exploration has always been the development of life beyond Earth, the discovery of ancient (paleo) life, or perhaps even of hidden (krypto) life.  The key question is whether life developed in ways similar to Earth or whether our planet is unique.  No such life is likely to exist on other targets of space missions -- neither on the Moon, nor on asteroids, and certainly not at libration points. 

Mars presents our only hope to discover facts that will not only advance life science but also impact on philosophy and even theology.

Three technical features put all these possibilities within reach within the next few years:

1.  Trajectory manipulation can keep the duration of the mission to less than roughly 500 days -- from take-off from Low Earth Orbit (LEO) until eventual re-entry to Earth.  If the mission were to last much longer, one would run into difficult problems of life support: prolonged exposure to space radiation; absence of gravity for an extended period; and the need for complete recycling, including also solid waste.  Based on experience from the International Space Station (ISS), all of this problem can be avoided by keeping mission duration below about 18 months.

2.  Chemical propulsion is really amazingly cheap -probably less than 5% of the total mission cost -- with almost all of that cost spent on lifting propellants into LEO.   There is no point therefore to stint on using propulsion for reducing mission duration and for addressing re-entry into the Earth's atmosphere.  An additional bonus; propellants of low atomic weight make excellent shields against space radiation, particularly heavy ions in the Galactic Cosmic Radiation (GCR),  We judge that 100 tons of propellants would be sufficient to protect the crew during transit to Mars -- with further protection from additional propellants on the return leg.

Since conventional chemical propulsion is not a problem, there is no need for special, exotic propulsion technologies to achieve the initial Mars missions discussed below.

3.  By not landing on Mars, one avoids the need for high-thrust rockets.  All maneuvers, including take-off from LEO, can then be accomplished with a medium-thrust engine; to achieve more change in velocity (delta-Vee), one just increases the burn time.


The Slingshot Missions

If launched from LEO towards Mars at just the right time, the spacecraft is turned around by Mars' gravity and sent back to Earth on a coasting unpowered trajectory -- sort of like a boomerang.  But such opportunities occur only infrequently; the next one is in 2018.  4The world's first "space tourist" Dennis Tito has proposed sending two astronauts on such a 'free-return' roundtrip.  But there is little chance that this plan can be accomplished so soon.  On the other hand, it may be feasible to launch an unmanned slingshot in 2018 and delay the Tito mission by a few years.

I therefore visualize the following Step #1:  An unmanned slingshot mission to check out trajectory and propulsion maneuvers, including safe re-entry into Earth's atmosphere.  Duration would be less than 500 days, if launched in 2018.  To add some planetary science to this engineering mission, one could include autonomous rovers to retrieve samples from the Martian moons.  Step #1 has lowest cost; yet also modest scientific returns.

Step #2 would be the Tito mission -- the manned slingshot (with two astronauts) to check out habitat, life support systems, radiation shielding, etc.  Again, autonomous rovers would return samples from Phobos and Deimos to the spacecraft.  Other science tasks can be added at little extra cost.  Missing the 2018 opportunity, this mission requires some studies on how to keep its duration to less than 500 days.

Ph-D Mission
Step #3 would be the Phobos-Deimos mission (5 astronauts, ~500 days), with a Deimos base, fully equipped geological laboratory, and a nuclear reactor power supply.  It would include a full complement of rovers, with sample returns to the Deimos lab from Mars' surface and subsurface.  It might even include a manned sortie to Phobos and to Mars.  Altogether --major scientific returns, yet moderate cost.

The basic architecture of the Ph-D mission is as follows:
It is divided into two parts -- both starting in LEO.  The first part starts with (say) 200 tons of propellants and a medium-sized rocket engine, plus about 24 rovers (equipped for sample return from Mars to Deimos), a number of (instrumented) Mars 'penetrators' (to be launched against Mars at close range), a fully equipped laboratory, and a passive nuclear reactor.  All of this is prepositioned on Deimos -- and then left behind for a future mission.

The second (manned) part of the Ph-D mission contains about 100 tons of propellants, a habitat, and instrumentation for planetary studies.  The power supply during transit to Mars is solar and/or RTG (a space-project-tested energy source, based on radioactivity).

The crucial parameter for the design of the mission is the total mission time spent in space away from LEO.  We should be willing to use more propellants -- particularly on the return trip, to shorten the transit time and to aid re-entry into Earth's atmosphere.  A tradeoff study is necessary to learn how much propellant is needed to reduce the total mission time significantly.  The resulting savings should be weighed against the cost of the extra propellants.

We visualize a crew consisting of five astronauts, including one medical person, one computer specialist, and two geologists with experience in mineralogy and chemistry to operate the laboratory.

Deimos is the preferred destination: It is easier to reach than Phobos, in terms of propulsion.  It has a near-synchronous orbit, allowing one to control a rover directly for up to 40 hours.  Also, from Deimos one can see the polar regions of Mars.

During transit to Deimos data can be obtained from interplanetary observations, from a possible Venus fly-by, and from the penetrators launched to Mars.  These can investigate subsurface conditions, especially water, and detect seismic waves from subsequent experiments. 

After landing on Deimos, one needs to set up the nuclear reactor in a nearby crater to provide shielding and sufficient distance.  The reactor will be remotely controlled, with power carried by cables to the habitat and laboratory.  Rovers will then be sent to different parts of Mars -- with examination of the returned samples in the laboratory, followed by additional sample returns from the more interesting locations, depending on results from the laboratory.  With a large number of rovers available, loss of a few is of little consequence.

Deimos also provides shielding against 50% of galactic cosmic rays -- and nearly all high-energy particles from solar flares and meteor streams (by moving the habitat to the opposite site).

In addition to studying Deimos surface and interior, a sortie to Phobos (and even to Mars itself) by two astronauts, using solar/RTG power, can explore this larger moon and bring back samples for examination in the Deimos laboratory.  These may help answer questions about the puzzling origin of the moons: Are they made of the same stuff? They do look very different; but this may be due to the regolith layer covering their surfaces.  We suspect that Phobos, with a (deduced) average density less than solid rock, is a rubble pile; what about Deimos?

To do all this, may require a stay on Deimos of about three weeks.  On returning, we leave behind the reactor and laboratory but return all samples for further studies in terrestrial laboratories.

Manned Base on Mars

Landing on Mars and take-off present severe engineering problems that jeopardize safety and raise mission cost by a large factor.  In addition -- and contrary to many expectations -- humans operating on the planet's surface are extremely limited in what they can do -- while remaining exposed to many hazards.

Since their mobility is quite limited and travel in the more interesting locations is dangerous, astronauts must tele-operate robotic rovers via a satellite communication network.  Returning samples to the base also presents problems.  Further, operating a laboratory on Mars is more difficult than on Deimos, where a vacuum (required by most instruments) is freely available.  Also, Deimos has fewer environmental hazards: no winds, no dust storms, no precipitation.

Ad Ares!

S. Fred Singer is professor emeritus at the University of Virginia and director of the Science & Environmental Policy Project.  His specialty is atmospheric and space physics.   An expert in remote sensing and satellites, he served as the founding director of the US Weather Satellite Service.  The Ph-D mission proposal is based on a 1978 study performed for NASA under Order No. H-27272B and H-343115B.  For recent writings see and also Google Scholar.

Note: If we take the specifications of the Falcon booster, the cost for providing 300 tons of propellants at LEO is only $1.2 billion, about 4% of the likely cost of a Ph-D mission.  [We use: Cost of Falcon -- $54 million; payload -- 13 tons]