Power for Mars Mission?

[green_meklar]

<blockquote><font class="small">In reply to:</font><hr /><p>Two things: <br /><br />1. The final format for the MSL power supply hasn't been chosen, so designing fins for it would be premature. At this time, they don't even know if it will be a standard RTG generator using thermocouples, or one use a Stirling engine to improve efficiency. That choice will *radically* change the size & placement of radiative needs. <br /><br />2. In general RTGs have been used in orbiters/probes rather than landers. Since they operate in vacuum, they would require much larger radiative space than a Mars Lander. Ergo -- MSL would have smaller fins than that of an RTG designed for vacuum operation.<p><hr /></p></p></blockquote><br />1. Really? Then why have we already seen some pictures of it? Are they just concepet sketches or artwork or what?<br /><br />2. True, but I thought we were comparing it to that other land vehicle in the link rather than our various nuclear spaceships. <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>

 

[willpittenger]

If you look at JPL's page on the rover proper, you will see that they have not gotten very far on the rover's design. The other major components (like Cruise and Descent) appear to be ready. But not the rover. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[bpfeifer]

Since mass is the limiting factor in most launch and landing designs, I'm curious about the reletive mass per kwatt for RTGs and photovoltaics. Since we've eliminated wind power for Mars, and no-one has a good nuclear reactor yet for these missions, it looks like nuclear batteries and solar cells are the way to go.<br /><br />mrmorris, any chance you could pull some numbers out of your hat? Any idea about the mass difference between an RTG using thermocouples v.s a sterling engine? Thanks. <div class="Discussion_UserSignature"> Brian J. Pfeifer http://sabletower.wordpress.com<br /> The Dogsoldier Codex http://www.lulu.com/sabletower<br /> </div>

 

[scottb50]

The thread originally focused on a manned mission and meeting the power requirements and has become a discussion about rovers. I have to agree RTG's and photovoltics are pretty much the only credible options with RTG's having advantages if operations are conducted in higher latitudes. I would also think the reliability of thermocouples compared to the complexity of mechanical Sterling Engines would make them the best long-term power source, especially considering the life span of an RTG.<br /><br />Back to the original theme of the post I think my proposal using water from the surface to LEO and water and Solar power in LEO would offer the most reliable, cheapest, and safest method of meeting multiple requirements. <br /><br />Meeting the requirements of internal power, propullsion, life support, as well as long term shielding to protect crew and passengers with a single system has numerous advantages. Overall mass could be reduced dramatically compared to Nuclear options and redundancy could be increased by using multiple small scale hydrolysers and fuel cells as well as Solar arrays that combine the output of multiple panels, or sections of panels. Another advantage would be safer and more efficient storage of propellant, producing just the amount needed rather than tankering volatile or cryogenic materials in large quantities. Used for the environmental system water could be infinitely recycled through a closed loop for consumption then purified through the power production system for re-use.<br /><br />With the abundant electrical power it would even be possible to break-down CO2 and recover the Oxygen, the same way Zubrin planned it on Mars so the only waste outputted would be Carbon. <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

For a 4-man semi-direct mission, you can do all of that for under 30 kW.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[mrmorris]

<font color="yellow">"Are they just concepet sketches..."</font><br /><br />Yes -- best guesses.<br /><br /><font color="yellow">" I thought we were comparing it to that other land vehicle in the link..."</font><br /><br />As JonClarke said -- the picture of the Marsokhod likely did not *have* an RTG because it didn't have cooling fins. You replied that the picture of MSL didn't have cooling fins, and I was responding to that. If this were an Excel spreadsheet -- there would be an error message about a circular reference right now...

 

[mrmorris]

<font color="yellow">"it looks like nuclear batteries..."</font><br /><br />Dunno what you mean by nuclear batteries. <br /><br /><font color="yellow">" Any idea about the mass difference between an RTG using thermocouples v.s a sterling engine?"</font><br /><br />To my knowledge, no RTG with Stirling engines has reached the stage where someone would put mass figures anywhere I could get to. Anything I could come up with would be a figment of my estimation.<br /><br />From what I've read, the key benefit for Stirling vs. thermocouple is making the maximum use of the Plutonium used rather than a mass/kW issue. In similar fashion -- the argument for nuclear vs. solar isn't a mass/kW issue so much as it is a power availability one. MSL with an RTG can operate round the clock from the time it hits dirt until the point at which something critical fails. By contrast, the MER rovers operate 11.5 hours a day (or so) and take winter vacations.

 

[green_meklar]

<blockquote><font class="small">In reply to:</font><hr /><p>As JonClarke said -- the picture of the Marsokhod likely did not *have* an RTG because it didn't have cooling fins.<p><hr /></p></p></blockquote><br />Whoops, maybe I missed a post or got mixed up. I thought the first post regarding cooling fins was in reference to the MSL. <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>

 

[docm]

<blockquote><font class="small">In reply to:</font><hr /><p>mrmorris said;<br /><br />Dunno what you mean by nuclear batteries. <p><hr /></p></p></blockquote><br />Other than RTG (nuclear thermal) there are also reciprocating electromechanical, betavoltaic and optoelectric. <br /><br />Reciprocating electromechanical works by beta flux deforming a piezoelectric cantilever, which in turn produces voltage. Good for high temperature environments.<br /><br />Betavoltaics use beta emitters and a silicon pickup, acting in a similar manner to photovoltaic cells.<br /><br />Optoelectric uses beta emitters, but to stimulate an excimer cell whose light drives a high efficiency photovoltaic array.<br /><br /> <div class="Discussion_UserSignature"> </div>