Shuttle_guy questions....

[drwayne]

And this:<br /><br />http://www.tsgc.utexas.edu/archive/subsystems/thermal.pdf<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[mrmorris]

SG -- on a thread -- long ago (possibly before the crash) -- there was a discussion about the cost of maintaining the shuttle TPS between flights. In it I made a reference to the high expense of individual shuttle tiles, and you had replied indicating the tiles themselves are very inexpensive, and that the expense came in the labor to shape them to fit them to the orbiter.<br /><br />In designing Gemini-X3 -- I've been doing a great deal of research on Thermal Protection Systems, and have been making the assumption that the shuttle tiles would be a very good option if the blunt end of G-X3 was designed to maximize TPS panel commonality. However -- during my research I found a doc from KSC that indicated the tiles cost about $2000 apiece, and the context indicates this is not due to labor issues in shaping them to the orbiter (it's in a section on spinoffs):<br /><br /><i>"Spinoffs<br /><br />There are numerous and far-ranging possibilities for spinoffs or commercial applications of Thermal Protection System materials. For example, tiles can be ideal as a jeweler’s soldering base because they absorb so little heat from a torch, do not contaminate precious metals, and are soft enough to hold items to be soldered. Because of their purity, tiles can be an excellent high-temperature filter for liquid metals. Carbon-carbon pistons have been shown to be lighter than aluminum pistons and increase the mechanical and thermal efficiencies of internal combustion engines. High costs at this time are a deterrent to widespread application of the techniques and materials of the Thermal Protection System. A single coated tile can cost as much as $2,000. But technological advances may make these pure, lightweight thermal materials the new insulators of the future."</i><br /><br />The document is from 1997, so the costs of tile production may have dropped considerably since then. Or I suppose it could be in

 

[mrmorris]

<font color="yellow">"For the blunt heat shield I believe that you will need RCC since the RCC can withstand a higher heat load which is produced by the blunt shape. "</font><br /><br />Based on everything I can find -- that shouldn't be the case. In particular -- from patent 5,064,151 for an Assured crew return vehicle filed by NASA employees -- the stagnation temperature on a similar re-entry capsule was estimated at ~2800 degrees F. This is within the capabilities of LI-2200 or AETB-8, as well as several metallic TPS concepts developed for various RLV programs. The most complete list I've seen is in NASA/TM-2000-210289 'Parametric Weight Comparison of Advanced Metallic, Ceramic Tile, and Ceramic Blanket Thermal Protection Systems". That document, BTW, is also a great cure for insomnia.<br /><br />The max heat analysis from the ACRV patent follows:<br /><br /><i>"The thermal protection system (TPS) for the return vehicle was selected based on the expected heating environment witnessed in trajectory simulations. A nominal atmospheric entry velocity of approximately 26,000 fps and flight path angle of -1.3 deg produced a maximum stagnation point convective heating rate of 61 British thermal units (Btu)/ft2/sec. This was based on a fully catalytic cold wall assumption, a nose radius of 3.5 ft, and the Detra, Kemp, and Riddell correlation formula for a blunt body of revolution in hypersonic flow. The corresponding radiation equilibrium temperature of the stagnation point was a maximum of 3050.degree. F. These values of heating rate and temperature would be slightly less if actual wall catalycity and non-equilibrium, considerations were taken into account. Therefore, the current best estimated peak temperature on the vehicle is expected to be approximately 2800.degree. F. "</i>

 

[mrmorris]

Ayup -- it's certainly close. That would be the temp at the stagnation point. Might require a circle of RCC at the center of the shield, with LI-2200/AETB tiles in concentric rings around that. <br /><br />Failing that -- an ablative shield is possible, albeit heavier. The suggested design already stipulates that the main heat shield be removable from the main craft for easier manufacturing, maintenance, and improved turnaround speeds. A new ablative shield for each flight may well be cheaper than tiles in any event.

 

[najab]

><i>A new ablative shield for each flight may well be cheaper than tiles in any event.</i><p>I've no figures to back me up, but I strongly believe this to be true.</p>