Destination Mars: An Astronaut's Perspective
Scott Parazynski, M.D.
NASA Johnson Space Center
The recent discovery of possible fossilized life forms within a Martian
meteorite has rekindled interest in human exploration of the planet. While
the global scientific community must carefully study this physical evidence
as well as await the results of 4 space probes to Mars in the coming
years, others are looking ahead to the next logical step of sending humans
to the planet. Such a feat, while a tremendous scientific undertaking, is
nearly within the grasp of current technology.
The travel distance involved and the harsh Martian environment itself
impose great challenges to human physiology as well as to spacecraft
design. Mission planners face challenges from the long-duration
microgravity environment, complex life-support systems, interplanetary
radiation, and the psychological stressors involved in such an endeavor.
While the human body readily adapts to weightlessness, significant
deconditioning of the musculoskeletal and cardiovascular systems occur
that could preclude safe landing and operations under the 1/3 G
environment of Mars. Further, the long-term effects of microgravity
are poorly studied, although a Russian cosmonaut colleague has spent
438 consecutive days on-orbit and has returned to normal daily
activities here on Earth. This re-adaptation was due to his intensive
exercise regime, including both resistive and aerobic training every
day of his flight. Space travel longer than this might require "artificial
gravity," but these systems might be prohibitively complex and
expensive. Studies from the soon-to-be-built International Space Station
will address the problem of decondtioning in-depth, and help define
Interplanetary space places astronauts at significant risk of
irradiation from solar particle events (SPEs) as well as low-level
galactic cosmic rays. Moreover, even extravehicular activity (EVA) on
the planet's surface is not without risk, since Mars has essentially
no magnetic field to shield the spacewalking astronaut. SPE forecasting
from Earth, as well as "space weather" instrumentation onboard the
spacecraft will be essential during the expedition. Enroute to Mars, EVA
should be minimized, and the spacecraft will need to be designed for
maximum shielding from radiation.
Crew selection and compatibility is a key consideration for
travel to Mars. Not only must the crew have a wide skill base
(scientific, engineering, medical) to enable self-reliance, but also they
will need extensive compatibility screening preflight and considerable
psychological support inflight. Notably, a busy training and science
schedule in-transit and frequent communications with family and friends
back on Earth will be a formula for success. Results from long duration
space crews, submariners, Antarctic scientists and Biospherians support
a team approach with a well-defined command structure.
Until recently, planned Mars trajectories have involved hundreds of
days in interplanetary space and have relied on conventional rocket
technologies. A developmental tunable exhaust plasma rocket, utilizing
nuclear electric propulsion, reduces the transit time to the order of
90 days each way. Additionally, system redundancy and the power
capabilities of such a vehicle would allow a powered abort capability
for return to Earth.
A "split-sprint" mission is favored, the first spacecraft being
a payload tugboat (instrumentation, supplies, fuel, etc.) that would
establish the Martian outpost and potentially generate supplies needed
for the return home. Once the outpost is fully established
robotically, a human-operated speedboat will transfer the crew from
low-earth orbit to Mars. Depending on phasing, Martian stays could range
from 30 days to 2 years.
Assembly of the craft including the nuclear reactors will occur
in low earth orbit for safety. The vehicle will be comprised of at least
3 redundant plasma rocket engines and 3 redundant nuclear reactors due to
their criticality as well as the propulsion and power needed for such a
mission. Other critical life-support systems, including environmental
control and rendezvous systems must be designed to be highly
reliable, modular, and fault-tolerant.
Shielding from SPEs and other sources of radiation will be
provided by liquid hydrogen fuel tanks surrounding the crew modules, as
well as an induced magnetic field from the plasma rockets themselves.
Due to the short transit times enabled with the tunable exhaust
plasma rocket, complex countermeasure systems like artificial gravity
will not be required. Daily exercise en route to preserve musculoskeletal
and cardiovascular health will be necessary, as well as to preserve
neuromuscular coordination once the crew arrives on Mars.
In the not-too-distant future, the global scientific community may
require human investigation of the planet Mars. Lessons learned from
Skylab, the Space Shuttle Program, Mir, and the planned International
Space Station, as well as technological advancements in rocketry, will
take us there.
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Last updated Feb-11-1997