Aerial Mobility and MPPG Strategy
The Mars Concepts workshop was a feast for those interested in
exploring the Red Planet.There were numerous suggestions for ways to get around
on Mars. In today’s post, I will focus on one sector - aerial mobility.
Balloons and airplanes were once touted as a way to obtain very
detailed visual images. However, proposals such as the MAGIC
ultra-high-resolution camera (1) promise to produce images from a Mars
orbiter that would make those systems obsolete. Multi-spectral imaging systems
with much higher resolution than the CRISM spectrometer onboard the MRO are
also being planned. Therefore, those who propose aerial systems have found new
uses for them.
One suitable task for an aerial platform would be to visit, up-close,
more sites than could a rover.Another advantage of aerial vehicles is the
ability to get to sites that are inaccessible to rovers, such as recurrent
gullies on crater rims. High-resolution, non-visual, non-infrared, remote
sensing is yet another. This would include searching for underground ice or
methane seeps, or high-resolution mapping of remanent magnetism in Mars'
ancient crust. In addition, with NASA now seeking synergy between manned and
unmanned Mars programs, the proposals often make a nod toward their usefulness
in obtaining precursor data.
There were proposals for balloons and airplanes at this meeting.However,
this worksop also featured presentations for aerial systems that are quite
innovative. Let's begin with a few of those concepts.
The first category includes Mars hoppers. This concept envisions a
lander that is able to make substantial hops from place to place on Mars. This
allows rover-class investigations to be conducted at widely separated
locations. One hopper proposal, by Moeller (2), could travel
approximately 70 km per hop. It would use radioisotope energy to run an in-situ
resource unit (ISRU) device to generate CO2 and O2. The CO2 is then
"burned" as rocket fuel for its thrusters. It takes a hop about every
200 days.A rather able, yet complex design.
Also in this category are hoppers that use compressed CO2. One of
these is Robert Zubrin's Gashopper vehicle (3). This design is
simplicity itself, as far as its fuel supply. It would use compressed Martian
air (essentially pure CO2) and use it as thruster "propellant." Elegant
in design, with no combustion chamber required. The Gashopper's fuel supply
would be unlimited - the atmosphere of Mars. The CO2 is stored as a liquid at
10 Bar pressure, with no cryogenic storage and handling required. As Zubrin
pointed out, CO2 is a poor rocket propellant, but it is readily available. To
produce thrust, the CO2 is passed over a 1,000K pellet bed. At 80 lb. of thrust
each, the thrusters can propel the Gashopper to a distance of 20 miles, if it
is a simple lander. However, with wings, each "hop" can be up to
several hundred kilometers. In this concept, the Hopper could carry a
mini-rover which would investigate each landing site for about a month, while
the Hopper was replenishing its CO2 supply. The Hopper itself could carry a
Ground Penetrating Radar, GPR, to search for underground ice deposits. (Figure 1)
Figure 1
Another example is the ASRG Geyser Hopper (4) which uses
hydrazine pulsed thrusters. The advantage in this concept is the use of proven
technology. This model of thruster was thoroughly tested for the Phoenix
lander, and performed splendidly.
The next proposal in this category was a combination mission - hopper
and entomopter (5). The hopper in this proposal mimics the jump
mechanics of a frog. It will have 4 legs, with the knee joints powered by a
pneumatic artificial muscle system. The muscles will use compressed CO2 drawn
from the Martian atmosphere. A typical jump will travel 300 meters
horizontally, with a maximum altitude of 150 meters. A proposed mission for
this hopper would investigate the Arsia Mons system of lava tubes/skylights in
the Tharsis region of Mars. (Figure 2) The hopper would position itself
close to one of the skylights, then launch an entomopter to investigate the interior.
An example of one of these bug-like robots was covered in my earlier post.
Figure 2
There were several balloon proposals. Their advantages include being
able to conduct aerial reconnaissance for weeks/months (as opposed to
short-duration planes), and needing no power to generate lift. These vehicles
can perform remote-sensing with higher fidelity than an orbiter. One example
was the PICCARD Discovery proposal. It had a 2-kg. payload, including
magnetometer and camera, and used an 11.5-meter diameter balloon. A beef-upped
version of this mission would include a 10-kg. high-resolution subsurface radar
mapper
One of the more interesting entries in this category was a hybrid
balloon/kite (6). The LArK mission would be targeted to investigate the skylights
in the Tharsis volcanic province. Figure 3. The LArK system would
include a science module that could be winched down to investigate a skylight
and/or lava tube, as the kite structure hovered overhead. Figure 4. One
advantage of this mission is that it makes this volcanic region accessible to
researchers. The Tharsis plateau is at an average altitude of 5 km., and is
thus is off-limits to currently developed technologies for landing on Mars
which need lower elevations for the parachutes to slow the lander sufficiently.
Figure 3
Figure 4
The gullies on Mars have generated a lot of interest, but like the
lava tube skylights, they are inherently difficult to investigate. One approach
to reaching them would be to use an electric helicopter. This proposal (7)
would target the gullies, or RSL's (Recurring Slope Lineae), that extend for
many meters down the slopes of Martian crater rims. Their origin is mysterious,
perhaps caused by liquid water, or other mechanisms, such as dry flow, as has
been seen on the Moon by the LRO. They are accessible from air, but could be
impossible for a rover to reach. This helicopter would hop from safe spot to
safe spot until it was within reach of an RSL.The NRL's (Naval Research
Laboratory) SPIDER electric unmanned helicopter can be considered to be a
prototype.
One of the more unusual entries in the aerial mobility theme is the
Mars Cannon Assisted Flying Exploration, or CAFE mission (8) would
launch small aircraft to swarm over a specific region, such as a canyon. Figure
5. The aircraft are packaged in ballistic shells that are launched using
compressed CO2. Here is yet another use of this simple ISRU method.
Figure 5
Regarding overall strategy, the Mars Program Planning Group, MPPG, has
issued an update that is fascinating and revealing. Reading the tea leaves of
this report (9), I am guessing that a likely scenario would see Mars
Sample Return take place at a reduced tempo. In fact, one exploration pathway
option in this report would see samples cached and placed into Mars orbit by
the late 2020's or early 2030's. The report states that samples orbiting Mars,
No Later Than 2033, for return to Earth by humans and/or robotic missions, is a
point of possible convergence for the parties involved. It is fascinating to
see how NASA's manned sector may now dovetail with the decades-long effort to
return samples from Mars.If this becomes the adopted exploration roadmap, then
NASA's unmanned science directorate need only worry about caching samples and
getting them as far as Mars orbit. The astronauts will take care of the rest. This
could be a major budget relief for NASA's solar system exploration program.
This document indicates that
NASA's budget cannot support a Rover mission in 2018. It seems that an orbiter
for that launch window is preferred for several reasons. There is the budget
restriction, but also a dire need for an orbital relay for present, and future,
surface missions. As the recent extended safe-mode for the 2001 Mars Orbiter
shows, existing orbital assets are aging. In addition, even though the MAVEN
Mars Orbiter will carry a relay radio link, its elliptical orbit will mean that
it will be within range of landed missions on a limited basis. Rover missions
require daily relay links in order to conduct a useful mission. Assuming a
MER-like lifetime, the MSL Rover should still be operating in 2018. In
addition, the ESA/Roscosmos Exomars rover should land that year, and may need
orbital relay services. Beyond that are any future NASA rovers or other surface
missions. This document indicates that the budget may support a rover mission
in 2020.
This report lists various "drivers" for future Mars
missions. Science is the top priority. However, another top priority is the
degree to which the program advances knowledge and capabilities required for
manned flight in the 2030's. This "marriage" may benefit both
programs. The unmanned missions, being tied to a long-range goal of human
exploration of Mars, may have access to a larger pool of funds. At the same
time, the manned program will have the data that it needs to realistically plan
missions. Also, with samples of Mars rocks waiting in orbit, there is an added
incentive to get astronauts out to the red planet.
Philip Horzempa
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REFERENCES
1. "Mars Geoscience Imaging at Centimeter-Scale (MAGIC) from
Orbit"
by Malin Space Science Systems
2. "Mars Hopper for LongRange Mobility, Regional Surface and
Lower Atmospheric Investigations, and In-Situ Resource Utilization" by
Moeller et al
3."The Mars Gashopper" by R. Zubrin
4. "ASRG Mars Geyser Hopper" by G. Landis et al
5. "Hopper/Entomopter Tandem System for Surface and Subsurface
Exploration of Mars"
by Gemmer et al
6. "Mars Aerial and Subsurface Exploration Using the LArK
(Lighter Than Air Kite) Concept"
by L.E. Edwin et al.
7. "Vertical Takeoff and Landing UAV's for Exploration of
Recurring Hyrological Events"
by Lemke et al
8. "Mars Cannon Assisted Flying Exploration (CAFE)
by J.D. Denhar et al
9. NRC Committee on Astrobiology and Planetary Sciences (CAPS) Report
of May 23, 2012
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