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)
No comments:
Post a Comment