First, for those who don’t know (troll face):
Passive Cooling: Using Heat tiles or a heat shield such as on a capsule or the Shuttle. Heat-resistant materials are applied in tiles or as a large shield to cover the reentering surface. Sometimes ablative.
Pros: no complex plumbing, often lighter, cheaper (short term)
Cons: less reusable, more maintenance required, more fragile
Active Cooling: Using a heat-resistant or semi-heat-resistant materials are applied with plumbing inside it, pumping liquid (often water, methane, oxygen or hydrogen) through the pipes, cooling the material from the inside.
Pros: more reusable, less maintenance required, can be integrated with the engines’ active cooling, less fragile
Cons: plumbing, sometimes heavier, often more expensive (short term)
Asking this because on some rockets, which I am working on but have not been released (Titan, which some may know as Neptune) have used passive metallic tiles in the past, made of a TaTi alloy (Tantalum-Titanium), which can withstand roughly double the heat of reentry, while some (Nexus & the soon-to-be-released mega-rocket Artemis) use active cooling. Nexus’ upper stage pumps LH2 through the engine bell and skirt, reentering engine-first. Logically, if the engine can handle the ~3200K of combustion, it can handle the ~1800K of reentry (I use Kelvin for combustion and reentry, as well as cryo prop temps. If you don’t know what Kelvin is, it’s just Celsius, but it counts from absolute zero, -273C. Very useful to say LH2 is at 20K instead of -253C. Pretty sure Rankine is the same, but for Fahrenheit, but you couldn’t pay me to use Fahrenheit, sorry ‘Muricans). Artemis’ upper stage reenters like Stoke’s Nova, with the engines around an actively cooled dome heatshield, with LH2 pumped through both the engines and heat shield on reentry (and while the engines are firing, duh). It’s lighter than a passive heat shield, in Artemis’ case, because you only have to shield the underside, instead of the whole belly of the craft.
Just wanted everyone’s thoughts on diff types of cooling, personally, I think active cooling with a metallic heat shield is the best overall, but you need diff types of heat shields for diff applications, of course.
@LeMagicBaguette @Zenithspeed nice idea, I suppose that’ what I (somewhat unknowingly) did with my Ta-Ti-Cu (Tantalum-Titanium-Copper) Heatshield on Titan (might also do on Artemis, the mega-rocket and the Vector Spaceplane). Tantalum has like a 4200 Kelvin melting point, Titanium reduces that a bit but decreases mass by a lot and Copper has high thermal conductivity. In case the LH2 doesn’t pump, the Ta-Ti-Cu Heatshield will be a good backup! Thanks :)