Nasa announces new rover mission to Mars in 2020 |
Nasa announces new rover mission to Mars in 2020 |
Dec 11 2012, 08:40 PM
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#61
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Senior Member Group: Members Posts: 4256 Joined: 17-January 05 Member No.: 152 |
He says "a 2020 launch would be favorable", but he doesn't say with respect to what. That's the crucial question. The 2018/20 opportunities should be compared with the
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Dec 11 2012, 08:58 PM
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#62
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Senior Member Group: Members Posts: 2173 Joined: 28-December 04 From: Florida, USA Member No.: 132 |
...The 2018/20 opportunities should be compared with the 2010 flight. That would be an interesting comparison, but the payload of a future rover is dependent only on the 2018 vs 2020 dates.From the same article I linked in my previous post: John Grunsfeld, NASA's science chief... however, cautioned that "2020 is ambitious, and a lot of it has to do with the science instrument development. ... It might be possible to do it in 2018, but it would be a push. What it might do is exclude certain science investigations that might be possible if we had the extra two years. That's something downstream." I don't know what use extra payload would be at the expense of "certain science investigations", especially if a geochronometer is a possibility in 2020 but not in 2018. |
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Dec 11 2012, 09:02 PM
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#63
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
You could add approx 100kg to the mass of MSL within the current architecture - but it's not coming from the ballast. http://trs-new.jpl.nasa.gov/dspace/bitstre...2011_216988.pdf is an interesting study of potential improvements to MSL; one of the options discusssed is replacing the entry balance masses with an actively-controlled trim tab. Of course it's not clear how many changes to the MSL architecture are going to be possible for cost and schedule reasons. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Dec 11 2012, 09:06 PM
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#64
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
The distance between Earth and Mars will reach a local minimum in the 2018 opposition, and will grow in each successive opposition through 2027 then decrease again before reaching the next local minimum in 2035.
2020, however, is only slightly farther than 2018. Then there's a steep climb with each successive opposition. The Earth-Mars opposition distance isn't quite the same thing as trajectory energy for the launch opportunity, but I think they correlate very well. |
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Dec 11 2012, 09:17 PM
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#65
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
2020, however, is only slightly farther than 2018. Here's the C3 in km2/sec2 for the opportunities from 2009 to 2022. You can clearly see that 2020 is much higher (worse) than 2018. Source: table 2 in Interplanetary Mission Design Handbook: Earth-to-Mars Mission Opportunities and Mars-to-Earth Return Opportunities 2009–2024, NASA/TM—1998–208533. 2009: 10.27 2011: 8.95 2013: 8.78 2016: 7.99 2018: 7.74 2020: 13.17 2022: 13.79 -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Dec 11 2012, 09:24 PM
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#66
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Senior Member Group: Members Posts: 2173 Joined: 28-December 04 From: Florida, USA Member No.: 132 |
At least it's good to see that a mission planned for 2020 won't be much affected by a launch in 2022. On the other hand, a mission design based on a 2018 launch could run into big trouble with a slip of launch date.
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Dec 11 2012, 09:32 PM
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#67
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
I certainly stand corrected. It looks like there's a phase shift in the relationship between opposition distance and energy with the shift being about one launch opportunity.
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Dec 11 2012, 09:33 PM
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#68
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
one of the options discusssed is replacing the entry balance masses with an actively-controlled trim tab. Yeah - that (and others) were even looked at earlier in MSL development (my favorite was using tanks of mercury that could be pumped around the backshell) - but they were dumped just to keep the architecture simple. Mass wasn't a problem - complexity, reliability and schedule were - so they went with the simplest option. To be honest, I'd expect them to do the same this time around. |
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Dec 11 2012, 10:09 PM
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#69
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Senior Member Group: Members Posts: 4256 Joined: 17-January 05 Member No.: 152 |
2009: 10.27 2011: 8.95 2013: 8.78 2016: 7.99 2018: 7.74 2020: 13.17 2022: 13.79 So getting back to my question, this shows that 2020 is worse than 2011 in terms of delta v^2, so all else being the same a 2020 MSL2 could carry less payload than the current MSL. How easily can this delta v^2 difference be translated into a payload mass difference? 2018, on the other hand, is a bit better than 2011. |
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Dec 11 2012, 10:26 PM
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#70
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
So getting back to my question, this shows that 2020 is worse than 2011 in terms of delta v^2, so all else being the same a 2020 MSL2 could carry less payload than the current MSL. Not a foregone conclusion, since MSL probably wasn't using all of the C3 available. In general I think C3 scales as the square of injected mass, but I haven't seen a detailed analysis of the 2020 opportunity. For 2018 there is a detailed breakdown in http://www.nap.edu/reports/13117/App%20G%2...gy-Explorer.pdf -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Dec 11 2012, 10:54 PM
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#71
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Junior Member Group: Members Posts: 63 Joined: 20-April 05 Member No.: 312 |
http://trs-new.jpl.nasa.gov/dspace/bitstre...2011_216988.pdf is an interesting study of potential improvements to MSL; one of the options discusssed is replacing the entry balance masses with an actively-controlled trim tab. Of course it's not clear how many changes to the MSL architecture are going to be possible for cost and schedule reasons. Why not replace the entry balance masses with something useful such as Penetrators or Micro-probes http://www.planetaryprobe.eu/IPPW7/proceed...ion7B/pr401.pdf |
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Dec 11 2012, 11:07 PM
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#72
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
Why not replace the entry balance masses with something useful such as Penetrators or Micro-probes The usual reasons: cost, complexity, increased mission risk. Volumetrically it's impossible to get a microprobe to weigh as much as a piece of tungsten. At some point it just wouldn't fit in the available space. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Dec 11 2012, 11:27 PM
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#73
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Senior Member Group: Members Posts: 2106 Joined: 13-February 10 From: Ontario Member No.: 5221 |
And they wouldn't be balanced very well either, which is the whole point of a ballast mass. Penetrators and others would need a dedicated mission of their own.
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Dec 12 2012, 12:45 AM
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#74
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Senior Member Group: Members Posts: 1591 Joined: 14-October 05 From: Vermont Member No.: 530 |
It would be neat happenstance if there happened to be a seismometer relatively near the impacts of those ballast masses.
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Dec 12 2012, 12:47 AM
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#75
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Forum Contributor Group: Members Posts: 1374 Joined: 8-February 04 From: North East Florida, USA. Member No.: 11 |
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