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Posted by: pioneer Dec 5 2018, 08:29 PM

Is there any chance we can get a Cubesat in orbit around Mars or would that take too much propellant?

Posted by: djellison Dec 5 2018, 09:25 PM

A spacecraft would probably need something over 10x the ammount of delta-V that the MarCO spacecraft had to enter orbit. I can’t imaging a 6U cubesat being able to pull that off.

Once could imagine a scenario where a ‘parent’ larger orbiter delivered one or more Cubesats into Mars orbit after having put itself into orbit, however.

Posted by: nprev Dec 5 2018, 09:33 PM

I wonder about the longevity of CubeSats for such applications. We obviously need to maintain a comm relay capability for surface missions now & in the future, and to date that's not been addressed as a core requirement for most orbiters so far as I'm aware. A flotilla of cubes dedicated to this would be a most appealing and presumably cost-effective alternative if they could last for a sufficient amount of time.

Posted by: djellison Dec 5 2018, 10:21 PM

Well - NASA's committed to not sending any orbiter without Electra UHF radios for relay....so even though MAVEN's orbit isn't great for relay - it still has one (and it performs well). That said - a dedicated relay orbiter fleet is clearly a must-have before humans head that way.

The problem with Cubesats for relay is power and downlink capacity. The MarCO cubesats top out at 8kbps - and can only do a few hours of downlink per day (using the rest of the time to recharge). The power situation would be worse in Mars orbit due to occultation/shadowing etc. A modest MRO UHF pass with Curiosity might be 250 megabits - and that would take almost 9 hours to downlink via a MarCO like spacecraft. Even an order of magnitude improvement over what MarCO can do would be significantly worse than Mars Odyssey is capable of. I think MarCO is generating around 15W at 1.5 AU. When Earth and Mars are at their most distant, they'll probably be down to 1kbps or worse for downlink.

That said - there's huge scope for spacecraft like MarCo to have a use out beyond LEO. Exploring Phobos and Deimos, for example.

We've been slowly pulling down the best of the images MarCO B took during its flyby - each little 752 x 480 image takes around 10 minutes. It was more like 20 before we asked the gumstix camera board to start GZipping them before downlink

Posted by: mcaplinger Dec 5 2018, 10:45 PM

12U cubesat: https://en.wikipedia.org/wiki/Mars_Micro_Orbiter

wikipedia is a little out of date, mission wasn't funded for launch in 2020.

Posted by: nprev Dec 6 2018, 01:23 AM

Yeah, that bitrate ain't gonna cut it for sure. Thanks!

Posted by: mcaplinger Dec 6 2018, 02:39 AM

MMO would have gotten something like a peak of 80 kbits/sec at closest Mars range using Ka-band. https://www.hou.usra.edu/meetings/smallsat2018/pdf/20_Malin.pdf

Posted by: djellison Dec 6 2018, 02:50 AM

OK - Wow - that's pretty epic for a the Ka band in 12 U. Has anything like that flown yet? MarCO had the benefit of the investment in the IRIS Xband package developed for INSPIRE (which, ironically, is still on a shelf)

Posted by: pioneer Dec 6 2018, 03:51 AM

Thanks for the answers.

Posted by: HSchirmer Dec 6 2018, 05:48 AM

Actually, you'd probably send several, IIRC 64 satellites is the current record-
You'd want about 30-40 of the smallest cubesats with solar sails to start establishing a Mars GPS systme (MPS?)
leaving space for 4-5 larger cube sats - so still workable.

Posted by: vjkane Dec 6 2018, 02:27 PM

There's a fairly detailed presentation on the Mars Micro Orbiter proposal here: https://www.hou.usra.edu/meetings/smallsat2018/pdf/20_Malin.pdf

According to statements made by NASA managers at meetings, technical review boards gave the proposal a strong thumbs up. I have not seen any statement on why it wasn't ultimately funded; finding funding for it would seem to be one obvious reason.