When it comes to landing spacecraft on planets, or moons, or back here on earth – Mars sucks.
There’s a lower success rate landing on Mars than on Venus, the moon, the earth, even
Saturn’s moon Titan.
And in large part, this is because Mars’s atmosphere is in the perfect goldilocks zone
of being a total headache.
On the moon (or an asteroid) you can use lightweight spacecraft made essentially out of tinfoil
because there’s no air to cause drag or pressure or heat.
Essentially, you save weight not having heat shields or thick walls, but need to use rockets
to land in what’s called a “powered descent.”
On earth, or Venus, or Titan, there’s enough air that you can land largely unpowered, first
by slowing down with a heat shield and atmospheric drag, and then with parachutes.
So you use a lot of weight for heat shields and walls and parachutes, but don’t need
big rockets or lots of fuel to land.
However, the air on Mars is literally the worst of both worlds – thick enough that
you actually have to deal with it with heat shields and walls, but thin enough that it
doesn’t help you slow down much and you also need to use rockets.
Mars is simply a challenging place to land a spacecraft, which is why we’ve tried so
many different and crazy techniques for landing there: we’ve landed landers and rovers using
retrorockets, in inflatable bouncy airbags, by being lowered from a hovering sky crane
– all of which ALSO used heat shields and parachutes and rocket powered descent before
the last stage of landing.
And space agencies are testing other crazy things like giant supersonic parachutes and
inflatable innertubes around landers to increase their surface area and help them slow down
more in the thin air before landing (probably still with rockets, or sky cranes).
Yes, you heard that right – it’s possible that when the first humans land on Mars, we
may do so in an inflatable donut.
Or we’ll just skim at a really low angle past the tops of mountains for a really long
time to slow down enough...