Thursday, July 5, 2012

Mars Concepts and Approaches - Aerial Concepts

If you are an ecologist, as I am, summer is likely to be your busy season.  Phil Horzempa, who wrote the last post also, is kindly helping to fill the gap.  With this post, Phil continues to look at the ideas presented at the Mars Concepts and Approaches Workshop with an emphasis on concepts for aerial missions.  - VRK

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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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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