Mars on a Shoestring

A novel method to transport humans to Mars based on a pair of tethered Space Shuttle orbiters

A thought paper by Eric Knight.

Copyright İ 2009 Eric Knight. All rights reserved.


On the return flight from a meeting at NASA headquarters a couple of years ago, my mind was reflecting upon the Space Shuttle program...its milestones...its tragedies...and its soon-to-be fleet retirement. (As of this writing, the Space Shuttle fleet is slated for retirement by September 30, 2010.)

While gazing out over the clouds through the airplane window, a number of thoughts swirled in my head:

Instead of retiring the Space Shuttle, and simply moth-balling the orbiters at museums and "rocket parks" around the country, could we give the fleet a heroic assignment? A grand mission commensurate with their thirty years of service? Something that would be truly historic -- even through the lens of time a millennium from now?

My Lifetime Fascination with Space

In 1968, when I was in third grade, I wrote my first "book" of sorts. It was entitled Outer Space -- and, to this day, it is one of my most cherished childhood possessions. (Here's a scan of the front cover.) I've had a passion for space since my parents propped me up in front of the TV to witness Alan Shepard's space flight on May 5, 1961.

It's my love of space and space travel that are the foundation for my various aerospace endeavors over the years.

For instance, my company (Remarkable Technologies, Inc. -- helped finance and provide technical support to the Civilian Space eXploration Team "CSXT" -- the entity that conducted the world's first successful amateur space launch.

In the spring of 2003, my company and I conceived of, founded, funded, and "launched" UP Aerospace -- the aerospace firm that, as a free-standing entity in 2007, launched into space the cremated remains of Star Trek's "Scotty" James Doohan and NASA astronaut and pioneer L. Gordon Cooper.  Here's a photo my company's public unveiling UP Aerospace at NASA's National Space Grant Conference in 2003.  And here's a  SpaceChannel.TV interview of me at the New England Air Museum.

In all, as some have said, out-worldly thinking is apparently in my DNA.

A Twist on a Marvelous Idea

In the mid 90s I read -- with absolute fascination -- futurist Robert Zubrin's "Mars Direct" concept, particularly his idea to launch two tethered modules to Mars:


"One of the payloads is an unmanned fuel factory/ERV...the other is a habitation module containing a crew of four, a mixture of whole food and dehydrated provisions sufficient for three years, and a pressurized methane/oxygen driven ground rover. On the way out to Mars, artificial gravity can be provided to the crew by extending a tether between the habitat and the burnt out booster upper stage, and spinning the assembly."

The idea of linked modules, speeding their way to Mars, stuck in my mind all these years. And on that airplane flight from NASA, soaring over the clouds, a new concept was born.

My Concept

•  Fly two Space Shuttle orbiters into earth orbit.

•  Rendezvous and connect the two orbiters together -- top to top -- by a truss.

•  The ends of the truss are anchored to the bases of the orbiters' payload bays.

•  At the center of the truss, dock a sufficiently sized propulsion stage.

•  Install a "crew-transfer conduit" -- a pressurized, accordion-style inflatable system that connects the airlock hatches of the two orbiters so that the crew could freely move between the two spacecrafts.

•  Once the propulsion stage has accelerated this entire system on its trek to Mars, the truss is detached from the two orbiters and the truss-propulsion assembly is jettisoned.

•  The two orbiters then separate to a distance of a few hundred feet, but remain connected -- top to top -- by a tether cable that is spooled out.

•  During the separation, the accordion-style inflatable crew-transfer conduit equally elongates.

•  Once the orbiters are at their maximum fixed distance apart, they would simultaneously fire their reaction control systems to set the pair into an elegant pirouette -- creating a comfortable level of artificial gravity for the crew's voyage to the red planet.

A Few Questions -- and a Few Answers

What would comprise the propulsion stage?

How about an enhanced Earth Departure Stage being developed by NASA for the Constellation Program? Or perhaps a pair of these stages, side by side?

If we don't want to wait until the Earth Departure Stage is developed, there are other propulsion options. Since a mission to Mars would likely be an internationally cooperative event (at least that is my hope), we should consider all possibilities from the world's space-faring nations.  For instance, perhaps we could explore creative cryogenic refueling of a retrofitted upper stage of an existing propulsion system. 

Cryogenic refueling?

In my third-grade book Outer Space, I illustrated on page 11 my concept of in-space cryogenic refueling -- albeit from the perspective of an eight-year-old child.

Forty years later my research has taken a more scientific approach. For instance, here's an excellent white paper on in-space cryogenic refueling: "A Practical, Affordable Cryogenic Propellant Depot Based on ULA's Flight Experience."

What would be used for life support (oxygen, water, provisions, etc.) for the multi-month trip? And then once the crew is on the surface of Mars?

The orbiters would provide ample space to establish a near-closed-loop biosphere for the crew.

A pair of orbiters would give the astronauts over 5,000 cubic feet of shirt-sleeve living space. And, if each orbiter flies a SPACEHAB, Inc. "Research Double Module" (RDM) in its payload bay, the amount of overall space would be quadrupled [information from page four of SPACEHAB's public document].

Each RDM has a cargo capacity of up to 10,000 pounds, and includes heating, ventilation, and lighting systems. The RDMs could be upgraded for long-term astronaut life support, for both during the flight to Mars and once the crew is on the surface of the planet.

During the STS-126 Space Shuttle mission, the astronauts successfully tested on the International Space Station (ISS) state-of-the-art fluid recycling technology: the system efficiently processes urine and evaporating sweat back into drinking water.

The ISS crew also continues to test other Russian- and U.S.-made regenerative life-support systems, including electrolysis systems that split liquid water into oxygen and hydrogen (the latter could be used as a fuel and heat source). These sorts of regenerative systems could be built into the RDMs of both orbiters.

Food is, of course, a critical factor on long-duration space missions and for Mars habitation. Inside the SPACEHAB's RDMs, I envision hydroponics gardens for both growing food and as part of the mission's life-support system. Not only would the hydroponics system provide for nutritional needs, but also help convert carbon dioxide into oxygen for the crew.

The hydroponics and mechanical-regenerative systems, working together, could provide a long-term bioregenerative life-support system for the Mars mission.

Assuming we can get the orbiter pair to Mars, how would the crew descend to the surface of the planet?

The atmosphere of Mars is, of course, much too thin to support a fly-in descent. The Martian atmosphere is only one percent of earth's atmosphere density.

What I propose is the development of a very large parachute system that would be stowed in each of the orbiter's payload bays. The orbiters would detach from the tether and crew-transfer conduit.  Each orbiter would then enter the Mars atmosphere and descend ballistically (like Apollo and Soyuz capsules), deploy its parachute system, and land wheels down with surely a pretty good thump -- even with the planet's gravity just 38% of Earth's.

The vehicle's airfoil surfaces and orbital-maneuvering and reaction-control thrusters would provide only a small degree of assistance during the descent; however, the subtle assistance could be helpful during the final few thousand feet in nudging each craft to the clearest landing location.

For reference to very-large-scale parachute systems, visit "World's Largest Rocket Stage Recovery Parachute Test" and "Para-Flite Successfully Flies World's Largest Parachute."

How do the astronauts get home?

I believe there would be many thousands of qualified volunteers (astronauts, scientists, researchers, etc.) with the desire to be the first permanent settlers of the red planet.  History is replete with adventurers and explorers crossing seas and endless terrains to points unknown.  I believe it is an indelible part of the human spirit.

However, I think society may be squeamish to support a one-way trip. A more likely scenario would thus be an "extended stay" mission, in which the first explorers of Mars would reside on the planet for a couple of years until a replacement crew arrives. The return-trip system could be based upon the "Mars Direct" approach proposed by Robert Zubrin.

I encourage everyone to read an excerpt of Robert Zubrin's extraordinary book The Promise of Mars that was published in Ad Astra in May / June 1996. Here's the link again:

Final Notes

This thought paper is certainly not meant to be the technical be all, end all on the topic -- but merely a springboard to new thought.

The science and topics touched on herein are superficial; the concepts are simply provided to fuel the imagination and promote discussion.

I continue to be fascinated with Robert Zubrin's visionary "Mars Direct" approach. My thought paper leverages his vision by proposing to repurpose the Space Shuttle fleet for the mission.

In all, I hope that my thought paper provides a catalyst for additional thinking as we ponder our place in the universe -- and the methods to transport us to new frontiers.

Copyright İ 2009 Eric Knight. All rights reserved.

Eric Knight is a futurist, inventor, entrepreneur, and business pioneer.  He is the president of Remarkable Technologies, Inc.   As an inventor, Eric Knight has appeared on numerous television programs and networks (such as CNN, The Discovery Channel, and the BBC) as well a variety of talks shows, including a guest appearance on the Late Show with David Letterman.