We've just about finished up all the technical details we can alone, and are beginning to work on outreach. As the blog is a truly horrible way to make details accessible, we're working on a MarMoSat website! It is very much a work in progress, but new information is being added all the time.
This means the blog will now function as a blog! Posts will be rare for the foreseeable future, but when they do come, they'll be broader and more stand-alone, talking about all sorts of Phobos-related stuff.
We are officially shifting out focus onto our orbiter-only concept, as it appears far more achievable. We are hoping that regardless of what happens with MarMoSat, we can use our experience with PALADIN to get involved with a secondary payload for JAXA's MMX mission to the Martian moons in 2024.
Thanks for staying with us!
-Daniel
Wednesday, June 7, 2017
Wednesday, April 19, 2017
Mobility update
A brief update on PALADIN's mobility system:
The above is an early animation of the deployment of PALADIN's wheels. Details are available at our earlier post on Mobility.
We are currently looking at motors for PALADIN. There are a number of options we're looking at, with the following criteria (including gearhead):
Runs on less than 1W (up to 1.5 W acceptable)
Output step size at most half a degree - preferably smaller
Output rotational speed at least 2 rpm - preferably higher
Mass under 25 g per motor - preferably ~10 g
Diameter under 30 mm - preferably ~10 mm
Length under 50 mm - preferably ~30 mmMinimizing step size allows careful positioning and keeps the rover in contact with the surface.
Maximizing rotational speed allows a higher maximum speed for longer traverses.
We are reaching out to space advocacy organizations and aerospace companies for support.
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| Phobos postcards! Thanks to Vistaprint. |
Coming up next, a lengthy post on why we want to explore the Martian moons!
-Daniel
Friday, April 7, 2017
Focus On: Power Subsystem
A brief note on MarMoSet's power:
Mars will be near aphelion, its furthest point from the Sun, when MarMoSet arrives. Being 1.6 times further from the Sun than the Earth is, solar panels would provide only 36% of the power they would in Low Earth Orbit.
Our propulsion system, the ConstantQ hybrid electrostatic thruster, requires about 22 watts to operate. The thrusters would have to fire for extended periods due to their low thrust, so solar arrays must provide at least this much power. For this reason, we plan to use MMA Design's eHaWK array, which is the largest off-the-shelf CubeSat solar array.
With two wings, each with three 20 x 30 cm panels, the eHaWK provides 26 watts of power even at Mars. The arrays are gimbaled, so they can track the Sun as MarMoSet orbits, ensuring consistent power.
Such large arrays pose challenges for PALADIN, the mission architecture that includes roving on Phobos's surface. Even if the arrays are strong enough not to be broken or mangled during landing, they could easily get caught on the terrain, prematurely ending PALADIN's mission. For this reason, the two large wings will detach from the spacecraft during its final approach of Phobos (confirmed feasible by MMA). Once landed, the nanorover no longer requires enough power to operate its thrusters, which in any case would not be capable of lifting it off Phobos's surface.
PALADIN (and possibly the orbiter-only architecture, DELPHI) would therefore also have a body-mounted solar panel on its upper 6U face. Depending on the model, this array would provide at least 4.3 - 7.2 watts at solar noon.
MarMoSet will also carry batteries to provide the spacecraft with power during nights on Phobos. We are still deciding how much storage is necessary, but are currently planning to store 40 Wh, enough to fire the thrusters at full power for nearly two hours and to provide PALADIN with power for a full Phobos day.
Depending on orbital planning and volume available, we may increase energy storage capacity. Two 10 Wh batteries would likely fit on either side of the NAC's optical tube..
That's all for now! We're currently working on flight computers, Mars capture, and nanorover motors, posts on each likely coming soon!
-Daniel
Mars will be near aphelion, its furthest point from the Sun, when MarMoSet arrives. Being 1.6 times further from the Sun than the Earth is, solar panels would provide only 36% of the power they would in Low Earth Orbit.
Our propulsion system, the ConstantQ hybrid electrostatic thruster, requires about 22 watts to operate. The thrusters would have to fire for extended periods due to their low thrust, so solar arrays must provide at least this much power. For this reason, we plan to use MMA Design's eHaWK array, which is the largest off-the-shelf CubeSat solar array.
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| Credit: MMA Design |
With two wings, each with three 20 x 30 cm panels, the eHaWK provides 26 watts of power even at Mars. The arrays are gimbaled, so they can track the Sun as MarMoSet orbits, ensuring consistent power.
Such large arrays pose challenges for PALADIN, the mission architecture that includes roving on Phobos's surface. Even if the arrays are strong enough not to be broken or mangled during landing, they could easily get caught on the terrain, prematurely ending PALADIN's mission. For this reason, the two large wings will detach from the spacecraft during its final approach of Phobos (confirmed feasible by MMA). Once landed, the nanorover no longer requires enough power to operate its thrusters, which in any case would not be capable of lifting it off Phobos's surface.
PALADIN (and possibly the orbiter-only architecture, DELPHI) would therefore also have a body-mounted solar panel on its upper 6U face. Depending on the model, this array would provide at least 4.3 - 7.2 watts at solar noon.
MarMoSet will also carry batteries to provide the spacecraft with power during nights on Phobos. We are still deciding how much storage is necessary, but are currently planning to store 40 Wh, enough to fire the thrusters at full power for nearly two hours and to provide PALADIN with power for a full Phobos day.
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| Credit: Clyde Space |
That's all for now! We're currently working on flight computers, Mars capture, and nanorover motors, posts on each likely coming soon!
-Daniel
Monday, March 20, 2017
Targets of Interest
Both moons are covered in a thick layer of dust. Due to their proximity, Mars, Deimos, and Phobos exchange this dust as ejecta when one body is impacted. The amount of dust exchanged is not known, but a careful investigation of Phobos's regolith may reveal information about Mars's history that cannot be found even at Mars. Phobos's trailing face receives large amounts of dust from Deimos. Due to the moons' small orbits, most ejecta thrown off a moon will return to it, although usually on the opposite side of the moon, spreading it rather evenly.
Very few surface features of Deimos are known, both because it is smoother due to a thicker layer of dust, and because fewer missions have taken pictures of it. The only remarkable feature is a large concavity in its south hemisphere. Only two craters, Voltaire and Swift, are named.
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| Credit: NASA |
Phobos is pretty cool. Both moons have a layer of light dust at least a few meters thick, but Phobos's layer is thinner, so craters and other features are not "muted" as those on Deimos are. It is also closer to Mars, so it is in a more dynamic environment, taking more impacts from ejecta thrown off of Mars and undergoing larger tidal stresses.
Phobos's most obvious surface feature is Stickney Crater. Stickney Crater is massive, about nine kilometers in diameter. Keep in mind, Phobos itself is only two to three times wider! Learning more about Stickney is crucial to learning more about Phobos, as the Stickney impact event shaped Phobos as we see it today. The impact nearly shattered the moon, and sent it spinning for about 14,000 years. In fact, there is evidence that Phobos's original orientation was opposite its current orientation - the impact flipped Phobos! The impact also coated all of Phobos with a layer of ejecta over a meter thick. There is some debate over the age of Stickney crater, as different methods suggest drastically different ages, and more information is needed to determine its true age.
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| Credit: NASA |
Stickney Crater is a promising site for future exploration, including crewed missions, as it would shield crews from radiation*.
Stickney's northwestern rim displays landslide features, which are an obvious dynamic process that can teach us about Phobos's development, and unearth fresher regolith that would ordinarily be buried. These landslides may also be hazards that need to be investigated before a crewed mission, as the severity and extend of landslides is unknown.
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| Credit: NASA |
Both moons are very dark, about as reflective as asphalt. However, in the near infrared spectrum, colors can be discerned. The moons' dust layer is largely reddish, but a region within and east of Stickney crater known as the "bluish" unit is, significantly less red. This region is likely excavated regolith, and investigating the interaction between the color units may help clarify Phobos's interior composition; whether Phobos is primarily "blue", with a thin layer of "red" on the surface, or a mix of "blue" and "red" blocks.
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| Credit: Brown University |
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| Credit: Journal of Geophysical Research |
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| Credit: Brown University |
Phobos is strewn with large boulders called ejecta blocks, most of which are thought to have been thrown up by the Stickney impact. Investigating the weathering of these ejecta blocks can teach us about Phobos's history and environment. More importantly, while the dust that makes up Phobos's surface layer is definitely weathered by long-term exposure to solar radiation, and is at least partially comprised of ejecta from Mars or Deimos, ejecta blocks are likely representative of Phobos's interior.
The most prominent ejecta block is the Phobos Monolith, an 85 meter boulder. This monolith is our primary target due to its proximity to the Sub-Mars point. As any single solid ejecta block can be called a monolith, we unofficially call this the "Reynolds Monolith" after Alastair Reynolds, who, in addition to being a magnificent science fiction writer, had the Phobos Monolith play a critical role in his "Blue Remembered Earth" universe.
Other ejecta blocks are scattered across Phobos, and can be sampled opportunistically. One other notable block is what seems to be a pile of ejecta, which we unofficially call "The Cairn". While not composed of a single block, it appears to be considerably larger than the Reynolds Monolith.
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| The Reynolds Monolith. Credit: NASA |
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| The Cairn, a pile of ejecta blocks. Credit: NASA |
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| An ejecta block on the Moon. Credit: NASA |
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| Map of ejecta blocks. Credit: Journal of Geophysical Research |
Finally, Phobos is covered in unique grooves. There are many different theories as to the grooves' origins, including crater chains, paths of rolling boulders, and dust draining into fractures formed by outgassing, impacts, or tidal stresses. Any of these have strong implications for all of Phobos. Likely more than one cause is responsible for the grooves, as at least three different types of grooves exist, and most theories do not explain all grooves. High-resolution imagery of grooves will reveal subtle characteristics that will provide scientists with a lot more data to go off of, and could settle the debate entirely. The trailing face of Phobos has a region largely devoid of grooves, though it is possible that this is because it receives dust from Deimos that could bury grooves. This is my personal theory, and has not, to my knowledge, been acknowledged, but the rather high exchange rate means it is possible, depending on how and when grooves formed. Subsurface sounding may reveal these, or other hidden features!
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| Credit: NASA and ESA |
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| Credit: Brown University |
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| Alignment of grooves with tidal stress. Source: Brown University |
That's it for now, thanks for reading another long post!
-Daniel
*DIFP
Thursday, March 16, 2017
PALADIN instrument orientation
What effect will our fixed-wheel design have on the nanorover's design?
A brief detail - our non-roving design is called DELPHI, for Deimos Exploration; Landing and PHobos Investigation. Our nanorover design, which will be detailed in this post, is called PALADIN, for Phobos Automotive Lander And Deimos INvestigation.
Most rovers that are equipped with an Alpha Proton X-ray Spectrometer have it on the end of an arm, so that it can be held against a specific target. MUSES-CN did not, but it was able to turn its body to press against a target. PALADIN, however, has a fixed AXS, held within the body at the proper distance from the surface. This is fine for measuring the composition of the surface regolith, but how will we measure the composition of ejecta blocks*, such as the Phobos Monolith, our primary target?
First, we have an optical spectrometer mounted on the front of the nanorover. By pointing the nanorover towards a boulder, we can take its spectra. An oversized momentum wheel allows the entire nanorover to be tilted up or down as required, pointing the spectrometer any desired target.
Second, on Eros, "ponds" were spotted around boulders (source). These ponds seem to be eroded boulder material, probably due primarily to the expansion and contraction of the boulder between day-night cycles. This seems to suggest that the upper layer of the regolith next to an ejecta block would closely match the composition of the block itself. Thus, by getting close to a block and taking the composition of the surface adjacent to it, the composition of the block can at least be inferred.
The NAC will point forward on the same axis as the optical spectrometer, and will be pointed in the same manner. LiDAR will, if possible, also point forwards, allowing distance measurements and mapping. The microscope will point directly downwards and will be located near the AXS. WAC angles have yet to be decided; one will point forward to provide context for the NAC, and other WACs may be included to provide multiple fields of view.
-Daniel
*DIFP
A brief detail - our non-roving design is called DELPHI, for Deimos Exploration; Landing and PHobos Investigation. Our nanorover design, which will be detailed in this post, is called PALADIN, for Phobos Automotive Lander And Deimos INvestigation.
Most rovers that are equipped with an Alpha Proton X-ray Spectrometer have it on the end of an arm, so that it can be held against a specific target. MUSES-CN did not, but it was able to turn its body to press against a target. PALADIN, however, has a fixed AXS, held within the body at the proper distance from the surface. This is fine for measuring the composition of the surface regolith, but how will we measure the composition of ejecta blocks*, such as the Phobos Monolith, our primary target?
First, we have an optical spectrometer mounted on the front of the nanorover. By pointing the nanorover towards a boulder, we can take its spectra. An oversized momentum wheel allows the entire nanorover to be tilted up or down as required, pointing the spectrometer any desired target.
Second, on Eros, "ponds" were spotted around boulders (source). These ponds seem to be eroded boulder material, probably due primarily to the expansion and contraction of the boulder between day-night cycles. This seems to suggest that the upper layer of the regolith next to an ejecta block would closely match the composition of the block itself. Thus, by getting close to a block and taking the composition of the surface adjacent to it, the composition of the block can at least be inferred.
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| Credit: Icarus |
The NAC will point forward on the same axis as the optical spectrometer, and will be pointed in the same manner. LiDAR will, if possible, also point forwards, allowing distance measurements and mapping. The microscope will point directly downwards and will be located near the AXS. WAC angles have yet to be decided; one will point forward to provide context for the NAC, and other WACs may be included to provide multiple fields of view.
-Daniel
*DIFP
Monday, March 13, 2017
Focus On: Orbits
A quick post about the different kinds of orbits our mission uses!
QSO is used for mapping and reconnaissance from a safe, stable vantage point. This type of orbit allows for quick mapping of a moon and is stable over long periods, requiring very little stationkeeping. However, in order to remain stable, the craft must remain far enough away from the moon that the moon's gravity does not perturb its orbit. This means a craft in QSO of Phobos must remain about 30 km away. QSOs of Deimos may be slightly closer due to its lower mass.
Transitions between these orbits will be detailed when I actually understand them.
QSO
Because of the moons' low mass and proximity to Mars, actually orbiting them is nearly impossible. However, it is possible to enter a "Quasi-Synchronous Orbit" (QSO) where the craft is actually orbiting Mars in a slightly eccentric orbit in such a way that it circles the moon.
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| Credit: Instituto Superior Técnico |
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| Credit: Instituto Superior Técnico |
QSO is used for mapping and reconnaissance from a safe, stable vantage point. This type of orbit allows for quick mapping of a moon and is stable over long periods, requiring very little stationkeeping. However, in order to remain stable, the craft must remain far enough away from the moon that the moon's gravity does not perturb its orbit. This means a craft in QSO of Phobos must remain about 30 km away. QSOs of Deimos may be slightly closer due to its lower mass.
LPO
Because of the moons' low mass and their proximity to Mars, Phobos's Lagrange point, where the gravity of Mars and Phobos cancel each other out (in this context), is 2-3 km from Phobos's surface. This allows for proximity investigation of Phobos's surface, over a hundred times closer than Earth-based CubeSats ever get to their targets, and over ten times closer than the closest Phobos flyby to date.
A spacecraft at a Lagrange point is like a marble on top of a hill - while it takes relatively little energy to keep it there, without correction it will slowly drift off. A craft in an LPO can take very accurate measurements and extremely high-resolution images of Phobos, but the stationkeeping required to keep it there is rather difficult, especially without the use of ground-based radio telescopes. Most likely the spacecraft will spend a relatively short time in LPO before safely flying out or landing. Thankfully, an LPO can stretch across a large region around the Lagrange point, and can pass over many objects of interest, such as the Phobos Monolith, Stickney Crater, and a number of grooves *.
Artificial LPO
Because of the moons' low mass and their proximity to Mars, Phobos's Lagrange point, where the gravity of Mars and Phobos cancel each other out (in this context), is 2-3 km from Phobos's surface. This allows for proximity investigation of Phobos's surface, over a hundred times closer than Earth-based CubeSats ever get to their targets, and over ten times closer than the closest Phobos flyby to date.
A spacecraft at a Lagrange point is like a marble on top of a hill - while it takes relatively little energy to keep it there, without correction it will slowly drift off. A craft in an LPO can take very accurate measurements and extremely high-resolution images of Phobos, but the stationkeeping required to keep it there is rather difficult, especially without the use of ground-based radio telescopes. Most likely the spacecraft will spend a relatively short time in LPO before safely flying out or landing. Thankfully, an LPO can stretch across a large region around the Lagrange point, and can pass over many objects of interest, such as the Phobos Monolith, Stickney Crater, and a number of grooves *.
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| Credit: Mattia Zamaro |
Artificial LPO
By applying constant thrust in one direction, the stability of an LPO can be significantly increased and orbits can be moved closer to the surface. While propellant-intensive, such an orbit can be used to facilitate a very low-velocity landing*.
Transitions between these orbits will be detailed when I actually understand them.
For more details on orbits of the Martian moons, read Mattia Zamaro's thesis.
-Daniel
*DIFP
Friday, March 10, 2017
Focus On: Instruments
What do we want to do once we get to the moons? What instruments will we be carrying?
Orbital instruments
The most important instrument is a Narrow-Angle Camera! This camera gives us high-resolution imagery of both moons. Current CubeSat imagers are more than powerful enough, as we can get far closer to the moons than CubeSats can ever get to the Earth's surface. Our first choice right now is GOMspace's NanoCam C1U (datasheet).
With a 70 mm lens, it masses about 277 grams and takes up most of 1U ( = 10 x 10 x 10 cm), although the space next to the lens may be used for flat components such as batteries. At a range of 30 km, which is our mapping distance for both moons*, we get a resolution of about 132 cm/pixel, four times better than the current best images. At a distance of 2.5 km, which is our proximity imaging distance*, we get a resolution of about 11 cm/pixel, which is amazing. However, this is a narrow-angle camera, and so has a limited field of view, with a swath of about 2 km at mapping, and 200 m at proximity.
Our second choice for a NAC is the SCS Gecko (brochure), which has about half the resolution, significantly shorter, and about twice as heavy.
A smaller, wide-angle camera (WAC) is also important to give context to high-resolution imagery and to allow navigation via craters. We may include multiple WACs pointing in different directions. There are a number of options we are considering, and these cameras are rather common among CubeSats. The model we are currently planning to use is the Crystalspace CAM1U (datasheet).
A laser altimeter is necessary for stationkeeping and landing, but ideally we would want a LiDAR which would let us map Phobos (We may be keeping our distance from Deimos, so likely wouldn't get close enough for LiDAR to work*). Since most CubeSats remain in LEO, where LiDAR isn't especially easy or useful, not a lot of work has been done, except for development of short-range LiDARs for rendezvous and formation flying. SPEC was working on a 0.5 U LiDAR (proposal) in 2014 that had a range of 8 km, a 30 degree field of view, and an integrated camera. Georgia Tech is currently working on a LiDAR CubeSat that is accurate to a few centimeters over ranges of tens of kilometers.
Although both moons' spectra has been taken in the past, a spectrometer working together with the NAC or with imaging capabilities would be able to find the spectra of specific targets and map the different regions of the moons. We are currently looking into a hyperspectral imager developed in Finland (presentation), which would take pictures at different wavelengths, returning a "data cube" with the spectra of each pixel.
However, this imager is still in early stages of development, and may require significant modification to work for our mission, so it may not be feasible. We also plan to include the Argus 1000 IR spectrometer (datasheet) which takes a much higher-resolution spectra of a single point. This smaller instrument is 45 x 50 x 80 mm and masses 215 grams. The spectrometer has a spectral range of 900 nm to 1700 nm, with an extended version reaching 2400 nm. It will point along the axis of the NAC, so we can see exactly what the spectrometer measures.
Landed instruments
If we opt for a simplified mission plan*, most of the following instruments will not be included, although some may be, as a landing would still be attempted towards the end of the mission. In this case, it is possible that orbital instruments will be expanded, depending on the volume available.
One reason so little is known of Phobos and Deimos's composition is that they both have very ambiguous spectra. An Alpha-X-ray Spectrometer, however, is able to directly measure the elemental composition of all elements (except hydrogen and helium). An AXS built for the MUSES-CN mission fits within 65 cubic centimeters, masses only 95 grams, and takes 30 minutes to three hours to take a measurement. This instrument was built nearly 20 years ago, and Dr. Economou, the primary investigator for the AXS, is working on an updated version of the AXS with significantly higher accuracy, smaller size, and shorter accumulation time.
A lander is uniquely capable of taking extremely high-resolution images of regolith. In a pinch, a WAC with special optics will do, but ideally we would wish to include a microscope. We initially planned to have a MicrOmega imaging spectroscope (details), which would allow the spectra of each dust particle to be measured, but despite its obvious value, MicrOmega is slightly too large to feasibly include without redesigning it and removing other instruments.
The microscope built for the failed Beagle 2 mission is similar in resolution and significantly smaller, although not able to take spectra. It masses about 245 grams and measures 111 x 52 x 22 mm and takes images about 4 x 4 mm, with a resolution of 4 microns per pixel. This would have to be reduced slightly in size to be shorter than 100 mm, and would need to have a longer focal length to work with a rover*. Some loss in performance is likely to be expected, since minimizing cost and size is more important than reaching some specific resolution.
Some less-likely instruments include a muograph (paper) and a radio sounding instrument (paper) which would allow mapping Phobos's interior to a depth of a few hundred meters; dust adhesion/electrical rejection and regolith compression and cohesion experiments to investigate regolith properties; a thermal infrared imager, thermal radiometer, or temperature probe to investigate heat flow; or dedicated gravitometers or magnetometers to measure the gravitational and magnetic environment.
Thermometers, magnetometers, and accelerometers on the flight computer can give rough measurements without any dedicated instruments.
Sorry for another lengthy post, I'm trying to get all the mission details into the public domain. The next few will be shorter, I promise! Coming up next- Considerations for a fixed-wheel rover.
-Daniel
*Detailed In Future Post (DIFP)
Orbital instruments
The most important instrument is a Narrow-Angle Camera! This camera gives us high-resolution imagery of both moons. Current CubeSat imagers are more than powerful enough, as we can get far closer to the moons than CubeSats can ever get to the Earth's surface. Our first choice right now is GOMspace's NanoCam C1U (datasheet).
 |
Credit: GOMspace
|
With a 70 mm lens, it masses about 277 grams and takes up most of 1U ( = 10 x 10 x 10 cm), although the space next to the lens may be used for flat components such as batteries. At a range of 30 km, which is our mapping distance for both moons*, we get a resolution of about 132 cm/pixel, four times better than the current best images. At a distance of 2.5 km, which is our proximity imaging distance*, we get a resolution of about 11 cm/pixel, which is amazing. However, this is a narrow-angle camera, and so has a limited field of view, with a swath of about 2 km at mapping, and 200 m at proximity.
Our second choice for a NAC is the SCS Gecko (brochure), which has about half the resolution, significantly shorter, and about twice as heavy.
A smaller, wide-angle camera (WAC) is also important to give context to high-resolution imagery and to allow navigation via craters. We may include multiple WACs pointing in different directions. There are a number of options we are considering, and these cameras are rather common among CubeSats. The model we are currently planning to use is the Crystalspace CAM1U (datasheet).
A laser altimeter is necessary for stationkeeping and landing, but ideally we would want a LiDAR which would let us map Phobos (We may be keeping our distance from Deimos, so likely wouldn't get close enough for LiDAR to work*). Since most CubeSats remain in LEO, where LiDAR isn't especially easy or useful, not a lot of work has been done, except for development of short-range LiDARs for rendezvous and formation flying. SPEC was working on a 0.5 U LiDAR (proposal) in 2014 that had a range of 8 km, a 30 degree field of view, and an integrated camera. Georgia Tech is currently working on a LiDAR CubeSat that is accurate to a few centimeters over ranges of tens of kilometers.
Although both moons' spectra has been taken in the past, a spectrometer working together with the NAC or with imaging capabilities would be able to find the spectra of specific targets and map the different regions of the moons. We are currently looking into a hyperspectral imager developed in Finland (presentation), which would take pictures at different wavelengths, returning a "data cube" with the spectra of each pixel.
 |
| Credit: VTT |
However, this imager is still in early stages of development, and may require significant modification to work for our mission, so it may not be feasible. We also plan to include the Argus 1000 IR spectrometer (datasheet) which takes a much higher-resolution spectra of a single point. This smaller instrument is 45 x 50 x 80 mm and masses 215 grams. The spectrometer has a spectral range of 900 nm to 1700 nm, with an extended version reaching 2400 nm. It will point along the axis of the NAC, so we can see exactly what the spectrometer measures.
 |
| Credit: Thoth Technology |
Landed instruments
If we opt for a simplified mission plan*, most of the following instruments will not be included, although some may be, as a landing would still be attempted towards the end of the mission. In this case, it is possible that orbital instruments will be expanded, depending on the volume available.
One reason so little is known of Phobos and Deimos's composition is that they both have very ambiguous spectra. An Alpha-X-ray Spectrometer, however, is able to directly measure the elemental composition of all elements (except hydrogen and helium). An AXS built for the MUSES-CN mission fits within 65 cubic centimeters, masses only 95 grams, and takes 30 minutes to three hours to take a measurement. This instrument was built nearly 20 years ago, and Dr. Economou, the primary investigator for the AXS, is working on an updated version of the AXS with significantly higher accuracy, smaller size, and shorter accumulation time.
 |
| Credit: University of Chicago |
A lander is uniquely capable of taking extremely high-resolution images of regolith. In a pinch, a WAC with special optics will do, but ideally we would wish to include a microscope. We initially planned to have a MicrOmega imaging spectroscope (details), which would allow the spectra of each dust particle to be measured, but despite its obvious value, MicrOmega is slightly too large to feasibly include without redesigning it and removing other instruments.
 |
| Credit: CNES |
The microscope built for the failed Beagle 2 mission is similar in resolution and significantly smaller, although not able to take spectra. It masses about 245 grams and measures 111 x 52 x 22 mm and takes images about 4 x 4 mm, with a resolution of 4 microns per pixel. This would have to be reduced slightly in size to be shorter than 100 mm, and would need to have a longer focal length to work with a rover*. Some loss in performance is likely to be expected, since minimizing cost and size is more important than reaching some specific resolution.
 |
| Credit: Beagle 2 |
Some less-likely instruments include a muograph (paper) and a radio sounding instrument (paper) which would allow mapping Phobos's interior to a depth of a few hundred meters; dust adhesion/electrical rejection and regolith compression and cohesion experiments to investigate regolith properties; a thermal infrared imager, thermal radiometer, or temperature probe to investigate heat flow; or dedicated gravitometers or magnetometers to measure the gravitational and magnetic environment.
Thermometers, magnetometers, and accelerometers on the flight computer can give rough measurements without any dedicated instruments.
Sorry for another lengthy post, I'm trying to get all the mission details into the public domain. The next few will be shorter, I promise! Coming up next- Considerations for a fixed-wheel rover.
-Daniel
*Detailed In Future Post (DIFP)
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