5
$\begingroup$

My answer to Do exploration spacecraft enter Mars atmosphere against Mars rotation, or on the same direction? lauds the use of ablative heat shields for minimizing radiative heating of a spacecraft by the super-hot plasma sheath during atmospheric entry at Mars.

It then mentions that I think that the SpaceX Starship will use ceramic tiles for thermal shielding when landing on Mars rather than an ablative coating. I'm not 100% sure of that but it's not a premise of my question.

Question: Has there ever been an attempt or serious consideration for spacecraft to land on Mars without an ablative-type heat shield?

$\endgroup$
8
  • 5
    $\begingroup$ I would be surprised if any have--ablative shields are cheaper and just as good for a single use. $\endgroup$ Feb 17, 2021 at 3:49
  • 1
    $\begingroup$ From nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1971-045D it says for Soviet's Mars 2: Temperature control was maintained through thermal insulation and a system of radiators. Can't seem to find more details to confirm if that means no ablation. $\endgroup$
    – eps
    Feb 20, 2021 at 21:21
  • $\begingroup$ @eps cool, thanks! I've just asked What were Mars 2's conical aerodynamic braking shield and “gunpowder” engines? $\endgroup$
    – uhoh
    Feb 21, 2021 at 0:26
  • 2
    $\begingroup$ @eps I suspect that's talking about thermal management for the landed lander, not the reentry vehicle. $\endgroup$ Jun 18, 2021 at 5:29
  • 1
    $\begingroup$ It's hard to answer "no" a "has there ever" type of question without infinite knowledge. Perhaps if you asked, "Is there a reentry speed beyond which, in practice, an ablative thermal protection system (TPS) is a better design choice than a non-ablative TPS?" $\endgroup$
    – phil1008
    Mar 21 at 10:07

1 Answer 1

4
+100
$\begingroup$

All successful and attempted landings on Mars to date have used ablative heat shields. NASA shields have all been variants of phenolic impregnated carbon, sometimes with and oxide coating. The ESA missions have also used ablative heat shields although their composition is not publicly available. It's hard to find the details of Russian missions to Mars. Russian Soyuz Earth reentry capsules - the most widely used of all human flight vehicles - use an ablative glass-phenolic composite heat shield. It seems likely Russian Mars landing missions used the the same or similar materials.

The advantage of ablative heat shield is that it is cheap. The disadvantage is that it can be used only once.Non-ablative heat shields are desirable for spacecraft that are to be used more than once.The ceramic tiles on the Space Shuttle and Starship are examples.Carbon-carbon composites have been used on parts of the Space Shuttle that experienced less heating. Other refractory materials including metals are possible in principle, although they would not protect the cargo from heating and would likely require some spacing or insulating layer.

Non-ablative landing vehicles use entry descent and landing (EDL) techniques. A classic example was NASA's lunar landers, where the absence of an atmosphere on the Moon meant atmospheric breaking was impossible. For moon landings a spacecraft first used rocket propulsion to enter orbit. Subsequently a lander used propulsion to land on the Moon.

It's quite likely that (some) future Mars missions will use a similar approach, given the risk of direct atmospheric entry at high speed and the substantial deceleration involved, which would likely injure astronauts. A spacecraft will first use rockets to "brake" into Mars orbit and then a lander or the entire spacecraft will use EDL techniques to land on Mars. In these situations no heat shield is required, let alone an ablative one. In particular Robert Zubrin's Mars Direct mission proposals use this approach for EDL. https://en.wikipedia.org/wiki/Mars_Direct

In contrast, SpaceX appears to be designing a direct entry and landing mission involving aerobraking as well as retropropulsion. Such an approach would see a variant of Starship, likely with non-ablative reusable shields, land on Mars. The same vehicle will be required to return the astronauts to Earth, hence the heat shields must be reusable.

$\endgroup$
11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.