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 © 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. --
www.remarkable.com) 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
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
"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.
• Fly two Space Shuttle orbiters into earth orbit.
• Rendezvous and connect the two orbiters together -- top to top -- by a
• The ends of the truss are anchored to the bases of the orbiters'
• 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
• 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
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
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
Forty years later my research has taken a more scientific approach. For
instance, here's an excellent white paper on in-space cryogenic refueling:
Practical, Affordable Cryogenic Propellant Depot Based on ULA's Flight
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
processes urine and evaporating sweat back into drinking
The ISS crew also continues to test other Russian- and U.S.-made
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
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
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
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
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:
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"
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
Copyright © 2009 Eric Knight. All rights reserved.
Eric Knight is a futurist, inventor, entrepreneur, and business pioneer.
He is the president of Remarkable Technologies, Inc.
www.remarkable.com 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
Show with David Letterman.