Making the Case for a Mission to the Martian Moon Phobos
From
where did Phobos arise or arrive? The Inner or Outer Solar System? Is
it dry or wet? Should we flyby or sample & return? Or should it be
Boots or Bots? In the illustration, space probes (L-R) Phobos-Grunt 2,
JPL/SAR, ARC PADME. Also, Stardust’s return capsule, Phobos above Mars,
the Solar Nebula and the MRO HiRISE photo of Phobos. (Photos: NASA,
Illustration:T.Reyes)
Ask any space enthusiast, and almost anyone will say humankind’s
ultimate destination is Mars. But NASA is currently gearing up to go to
an asteroid. While the space agency says its Asteroid Initiative will
help in the eventual goal of putting people on Mars, what if instead of
going to an asteroid, we went to Mars’ moon Phobos?
Three prominent planetary scientists have joined forces in
a new paper in the Journal Planetary and Space Science to explain the case for a mission to the moons of Mars, particularly Phobos.
“Phobos occupies a unique position physically, scientifically, and
programmatically on the road to exploration of the solar system,” say
the scientists. In addition, the moons may possibly be a source of in
situ resources that could support future human exploration in
circum-Mars space or on the Martian surface. But a sample return mission
first could provide details on the moons’ origins and makeup.
The Martian moons are
riddles, wrapped in a mystery, inside an enigma. Phobos and its sibling Deimos
seem like just two asteroids which were captured by the planet Mars,
and they remain the last objects of the inner solar system not yet
studied with a dedicated mission. But should the moons be explored with
flybys or sample-return? Should we consider “boots or bots”?
The publications and mission concepts for Phobos and Deimos are
numerous and go back decades. The authors of “The Value of a Phobos
Sample Return,” Murchie, Britt and Pieters, explore the full breadth of
questions of why and how to explore Phobos and Deimos.
Dr. Murchie is the principal investigator of the Mars Reconnaissance Orbiter’s
CRISM instrument, a visible/infrared imaging spectrometer. He is a planetary scientist from John Hopkins’ Applied Physics Lab (
APL)
which has been at the forefront of efforts to develop a Phobos mission.
Likewise, authors Dr. Britt, from the University of Central Florida and
Dr. Pieters from Brown University have partnered with APL and JPL in
Phobos/Deimos mission proposals.
A
MRO HiRise image of the Martian moon Phobos. Taken on March 23, 2008.
Phobos has dimensions of 27 × 22 × 18 km, while Deimos is 15 × 12.2 × 11
km. Both were discovered in 1877 at the US Naval Observatory in
Washington, D.C. (Photo: NASA/MRO/HiRISE)
APL scientists are not the only ones interested in Phobos or Deimos.
The Jet Propulsion Laboratory, Ames Research Center and the
SETI Institute have also proposed several missions to the small moons. Every NASA center has been involved at some level.
But the only mission to actually get off the ground is the Russian Space Agency’s Phobos-GRUNT[
ref].
The Russian mission was launched November 9, 2011 and two months later
took a bath in the Pacific Ocean. The propulsion system failed to
execute the burns necessary to escape the Earth’s gravity and instead,
its orbit decayed despite weeks of attempts to activate the spacecraft.
But that’s a whole other story.
The
Russian-led mission Phobos-Grunt did not end well; under Pacific swells
to be exact. Undaunted Russian scientists are pressing for Phobos-Grunt
2 (illus.), an improved lander with sample-return. Proposed
for 202os (Credit: CNES)
“The Value of a Phobos Sample Return” first discusses the origins of
the moons of Mars. There is no certainty. There is a strong consensus
that Earth’s Moon was born from the collision of a Mars-sized object
and Earth not long after Earth’s formation. This is just one possibility
for the Martian moons. Murchie explains that the impacts that created
the large basins and craters on Mars could have spawned Phobos and
Deimos: ejecta that achieved orbit, formed a ring and then coalesced
into the small bodies. Alternative theories claim that the moons were
captured by Mars from either the inner or outer solar system. Or they
could have co-accreted with Mars from the
Solar Nebula.
Murchie and the co-authors describe the difficulties and implications
of each scenario. For example, if captured by Mars, then it is difficult
to explain how their orbits came to be “near-circular and
near-equatorial with synchronous rotational periods.”
To answer the question of origins, the paper turns to the questions
of their nature. Murchie explains that the limited compositional
knowledge leaves several possibilities for their origins. They seem
like
D-type asteroids
of the outer asteroid belt. However, the moons of Mars are very dry,
void of water, at least on their surfaces as the paper discusses in
detail. The flybys of Phobos and Deimos by NASA and ESA spacecraft is
simply insufficient for drawing any clear picture of their composition
or structure, let alone their origins, Murchie and co-authors explain.
If the moons were captured then they have compositions different from
Mars; however if they accreted with or from Mars, then they share
similar compositions, with the early Mars when forming or from Martian
crustal material, respectively.
The paper describes in some detail the problem that billions of years
of Martian dust accumulation presents. Every time Mars has been hit by a
large asteroid, a cloud of debris is launched into space. Some falls
back to the planet but much ends up in orbit. each time, some of
the debris collided with Phobos and Deimos; Murchie uses the term
“Witness plate” to describe what the two moons are to Mars. There is an
accumulation of Martian material and also material from the impactors
covering the surfaces of the moons. Flyby images of Phobos show a
reddish surface similar to Mars and numerous tracks along the surface as
if passing objects struck, plowed or rolled along. However, the reddish
hue could be weathering from Solar flux over billions of years.
The paper continues with questions of the composition and how
rendezvous missions could go further to understanding the moons makeup
and origins, however, it is sample return that would deliver, the pay
dirt. Despite how well NASA and ESA engineers have worked to shrink and
lighten the instruments that fly, orbit and land on Mars, returning a
sample of Phobos to labs on Earth would permit far more detailed
analysis.
SpaceX
and Elon Musk claim that they will mount human flight to Mars before
2030. Many others remain less optimistic with hopes to human flights
before 2040. (Illustrations: Total Recall, 1990, early artist
illustration c.1950s )
Science Fiction writers and mission designers have imagined Phobos,
in particular, as a starting point for the human exploration and
colonization of Mars. A notable contemporary work is “Red Mars” by Kim
Stanley Robinson; however, the story line is dated due to the retirement
of Space Shuttle and the external tanks Robinson clustered to form the
colonization vessel. While this paper by Murchie et al. is purely
scientific, fiction writers have used the understanding that Phobos is
far easier to reach from Earth than is the surface of Mars (see Delta-V
chart below).
A
diagram showing the stair-step energy needed to travel to places beyond
the Earth. Delta-V is the speed in km/sec required to reach a
destination. As shown, the Delta-Vs are accumulative. Note that it takes
an extra 5 km/sec beyond Phobos to reach the Martian surface; a prime
reason for making the journey to the moons of Mars. (Credit: Wikipedia,
Delta-V)
Phobos, orbiting at 9,400 kilometers (5,840 miles) and Deimos at
23,500 km (14,600 miles) above Mars avoids the need for the 7-odd
minutes of EDL terror – Entry, Descent and Landing — and pulling oneself
out of the Martian gravity well to return to Earth. Furthermore, there
is the interest in using Phobos as a material resource – water, material
for rocket fuel or building materials. “The Value of a Phobos Sample
Return” discusses the potential of Phobos as a resource for space
travelers – “In Situ Resource Utilization” (ISRU), in the context of its
composition, how the solar flux may have purged the moons of water or
how Martian impact debris covers materials of greater interest and value
to explorers.
With so many questions and interests, what missions have been
proposed and explored? The Murchie paper describes a half dozen missions
but there are several others that have been conceived and proposed to
some level over several decades.
At present, there is at least one mission actively pursuing funds.
The SETI and Ames proposed “Phobos and Deimos & Mars Environment” (
PADME) mission led by Dr. Pascal Lee is competing for
Discovery program funding.
Such projects must limit cost to $425 million or less and be capable of
launching in less than 3 years. They are proposing a launch date of
2018 on a
SpaceX Falcon 9. The PADME mission design would reuse Ames
LADEE hardware
and expertise, however, it does not go so far as what Murchie and
co-authors argue – returning a sample from Phobos. PADME would maintain a
synchronized orbit with Phobos and then Deimos fore repeated flybys.
The mission is likely to cost in the range of $300 million.
Stardust,
a relevant mission due to its sample return capsule, launched in 1999
and had costs which likely reached a similar level by end of mission in
2012.
The Russian Space Agency is attempting to gain funding for
Phobos-Grunt 2 but possible launch dates continue to be moved back –
2020, 2022 and now possibly 2024.
Return
of the Stardust sample inside the Lockheed-Martin developed
sample-return capsule. Seen here upon successful landing in the Utah
desert. (Credit: NASA/Stardust)
Additionally, each of this papers’ authors have mission proposals described. Dr. Pieters, JPL and
Lockheed-Martin proposed the
Aladdin mission and Dr. Britt at APL also with Lockheed-Martin proposed the mission
Gulliver;
both would re-use the Stardust sample-return capsule (photo, above).
Dr. Murchie also describes his APL/JPL mission concept called
MERLIN (Mars–Moon Exploration,Reconnaissance and Landed Investigation).
Phobos and Deimos are the last two of what one would call major
objects of the inner Solar System that have not had dedicated missions
of exploration. Several bodies of the Asteroid Belt have been targeted
with flybys and
Dawn is nearing its second target, the largest of the Asteroids, Ceres.
So sooner rather than later, a spacecraft from some nation (not
necessarily the United States) will target the moons of Mars. Targeted
Phobos/Deimos missions are also likely to include both flyby missions
and one or more sample-return missions. A US-led mission with
sample-return in the Discovery program will be strained to meet both
criteria – $425 million cost cap and 3 year development period.
Those utilizing the Lockheed-Martin (LM) Stardust design have a
proven return capsule and spacecraft buses (structure, mechanisms and
avionics) for re-use for cost and time savings. This includes five
generations of the LM flight software that holds an incredible legacy of
mission successes starting with Mars Odyssey/Genesis/Spitzer to now
Maven.
All three proposals by this paper’s authors could be re-vamped and
proposed again and compete against each other. All three could use
Lockheed-Martin past designs. Cooperation in writing this paper may be
an indicator that they will join forces, combine concepts and share
investigator positions on a single NASA-led project. The struggle for
federal dollars remains a tough tight battle and with the human
spaceflight program struggling to gain a new footing after Space
Shuttle, dollars for inter-planetary missions are likely to remain very
competitive. However, it appears a Phobos-Deimos mission is likely
within the next ten years.
From an altitude of more than 135,000 feet (41,148
meters), Alan Eustace had a view of the curvature of Earth against the
blackness of space.
Alan Eustace was carried into the stratosphere with a high-altitude scientific balloon.
China’s lunar sample program involves upcoming re-entry
capsule test to evaluate high-speed plunge into Earth’s atmosphere.
Long March booster being readied to support China's
next mooncraft takeoff this month, dedicated to testing technology for
future lunar sample-return mission. 
The 4M mission is dedicated to Manfred Fuchs who died early this year. 4M stands for the Manfred Memorial Moon Mission.
LuxSpace launch preparation team in China has
successfully completed the system functional tests and health checks of
its 4M probe before integration with China's Long March 3C. 
