There's a Mars 2020 update from March here:http://mepag.nasa.gov/meeting/2016-03/21_MEPAG_160303_FINAL%20v2.pdfThey are scheduled to go into Phase C (Design and Development) in April/May, so presumably they are about to do that any time now. Considering that they already have a lot of hardware in hand, they should move through this faster than MSL/Curiosity did.
They have a good variety to chose from, although I hope consideration for MSR will be considered.
Quote from: redliox on 05/15/2016 02:04 amThey have a good variety to chose from, although I hope consideration for MSR will be considered.Sample return is going to drive landing site selection. It is the primary reason they are doing this mission.
Quote from: Blackstar on 05/14/2016 09:23 pmThere's a Mars 2020 update from March here:http://mepag.nasa.gov/meeting/2016-03/21_MEPAG_160303_FINAL%20v2.pdfThey are scheduled to go into Phase C (Design and Development) in April/May, so presumably they are about to do that any time now. Considering that they already have a lot of hardware in hand, they should move through this faster than MSL/Curiosity did.Hmm...so not as much detail on how the samples will be processed although it says adaptive cache is baselined. It's also interesting to see they're still considering the helicopter idea, more imaging in general EDL, and microphones. Inversely, cubsats and a ring parachute are off the list; both make sense if they're trying to duplicate Curiosity as much as possible.It appears that they've divided the landing sites into fluvial versus hydrothermal sites. I'm tempted to lean more towards the hydrothermal group because it includes Columbia Hills i.e. Gusev Crater, which has the advantage of better study, along with prominently considered Nili Fossae. They have a good variety to chose from, although I hope consideration for MSR will be considered.
Like the helicopter I hope the microphones do fly as well. Vision is all very well but sound is also an important part of how we interpret things.
Another reason for doing this is that while the rover has a design life of 2 years the expected life is more like 10-20 years.
Quote from: Blackstar on 05/15/2016 02:54 amQuote from: redliox on 05/15/2016 02:04 amThey have a good variety to chose from, although I hope consideration for MSR will be considered.Sample return is going to drive landing site selection. It is the primary reason they are doing this mission.Would you say the launch needs of a future MAV be part of that? If so I am assuming some leeway is being considered beyond a strictly equatorial site.
Quote from: Don2 on 05/20/2016 12:46 amAnother reason for doing this is that while the rover has a design life of 2 years the expected life is more like 10-20 years. Where do you get that latter figure?What is the available Pu-238 energy level at 10 years?
There's a couple of ways of looking at that. Half-life of Pu-238 is 88 years, so heat production drops off very slowly. Power conversion components inside the RTG also degrade. Several sources state a minimum lifetime of 14 years for a MMRTG, but many spacecraft have exceeded that. If the RTG is manufactured 3 years before launch and the journey to Mars takes 1 year, then the RTG should last at least 10 years on the surface. Wikipedia claims 125W when new, and 100W after 14 years.
Orbiter experience is similar. Mars Global Surveyor failed at 10 yr, but MRO (11 yr), Mars Express (12 yr) and Odyssey (15yr) are still going strong.
RTG also provides ample heat, eliminating or minimizing the need for electric heaters.
Mars Global Surveyor failed at 10 yr
The mission loss was attributed to a High Gain Antenna (HGA) positioning command sent by the spacecraft operations team five months earlier that, in the process of updating several parameters, created a bad memory load...
Quote from: vjkane on 05/20/2016 09:24 pmRTG also provides ample heat, eliminating or minimizing the need for electric heaters. The RTG on MSL can only heat the internal electronics via a fluid loop; all of the external actuators and instruments still have to be electrically heated to use them and this requires a fair amount of battery power. See, e.g., https://ttu-ir.tdl.org/ttu-ir/bitstream/handle/2346/59520/ICES-2014-295.pdf?sequence=1
Another issue is battery life. The RTG actually powers the battery, which is used for the bulk of Curiosity's operations. (RTG also provides ample heat, eliminating or minimizing the need for electric heaters). Curiosity's long life suggests that the Energizer bunny is alive and well on Mars.
Quote from: Don2 on 05/20/2016 08:49 pmMars Global Surveyor failed at 10 yrThe root cause of the MGS failure was errors in ground commanding, not a hardware failure.See http://llis.nasa.gov/lesson/1805
I've been digging into the battery issue a little. With lithium-ion, if you discharge them all the way, that is called a deep cycle, and it wears out the batteries quickly. A consumer battery might be killed by 400 deep cycles. If you only discharge them 10%, you can extend the life of the same battery by a factor of 10 to 4000 cycles or so. What do they mean by 'dead'? This seems to be defined as a 30% loss of capacity rather than a complete failure. So it might still be usable up to a point.NASA did a test of the batteries used on the Mars rover and found they could cope with 12000 cycles at 40% depth of discharge. 20 years on Mars would be 7105 cycles, so the batteries might not be life limiting if they are not deeply discharged on a regular basis.
What about the RTG? 20 years after manufacture that should still be producing 72% of its original power if it ages in the same way that the Viking ones did. Heat output should be 85% of new.