Demystifying Mars: Landing the manned missions on Mars.
Here’s the thing — I’m no scientist or a physicist or a researcher, to write about this. However, that’s a great thing, because I think most of the people would be able to relate to my take on this seemingly esoteric topic. So, sometime back, I happened to come across this quote by Elon Musk:
I would like to die on Mars. Just not on impact — Elon Musk
This made me think, as to what’s the big deal about (impact) landing on Mars. Given humans have already successfully landed on Moon, I had safely presumed that landing missions on Mars wouldn’t be the most prominent challenge. As I realised later, this wasn’t really the case.
As I read more about this topic, the first thing I learnt was: rocket science is NO rocket science. At the root of it, the concepts that power rockets are pretty simple. And once you realise this, everything becomes approachable and starts making perfect sense.
The approach I’ve taken to learn more about this topic was pretty straight forward — and inspired by the the one employed by folks at WaitbutWhy.
The way I approach a post is I’ll start with the surface of the topic and ask myself what I don’t fully get — I look for those foggy spots in the story where when someone mentions it or it comes up in an article I’m reading, my mind kind of glazes over with a combination of “ugh it’s that icky term again nah go away” and “ew the adults are saying that adult thing again and I’m seven so I don’t actually understand what they’re talking about.” Then I’ll get reading about those foggy spots — but as I clear away fog from the surface, I often find more fog underneath. So then I research that new fog, and again, often come across other fog even further down. My perfectionism kicks in and I end up refusing to stop going down the rabbit hole until I hit the floor.
So, coming back to the our basic question: What’s the BIG deal about landing manned missions on Mars ?
Entry descent & landing of large payloads on Mars
Ever wondered why most of the asteroids/comets gets burned down while entering the earth ? Yes, it’s because of the atmosphere, which acts as protective shield for the earth.
“The great thing about Earth is the atmosphere. Returning to Earth and entering the atmosphere at speeds between 7–10 kms per second, the proposed Crew Exploration Vehicle (CEV) will all decelerate to less than Mach 1 at about twenty kms above the ground just by skimming through Earth’s luxuriously thick atmosphere and using a heat shield.” — Universe Today. com
However, Mars has very thin atmosphere, being just about 1% (as compared to that of earth). So what that means is that there is no air-drag to slow down the objects entering the Mars atmosphere. It’s something like facing an impact force after jumping from the aircraft, without a parachute. This makes for a great challenge wherein any mission to mars has to slow down considerably (from about Mach 5 to touchdown in just a few seconds) by itself before landing onto its surface.
Now, to tackle this, here are the few options that we have:
- Airbags, and parachutes
This seems an obvious choice because that’s how the earlier successful Mars missions (Spirit and Opportunity) landed. But, the problems now are:
a. The non-manned exploration vehicles were (relatively) small to use airbags, and parachutes for landing. One calculation shows that missions > 1 metric tons won’t be able to use the same techniques for landing. And the approx. weight of manned mission to Mars would be approx. 60 metric tons.
b. There is a huge amount of impact force (somewhere between 10–20G) that the rover suffers as it falls onto ground using airbags. Now, the robotic missions can withstand such an impact but the humans won’t.
The below video illustrates the process of landing using airbags and parachutes.
Both of these factors clearly rule our use of airbags or parachutes for landing manned missions. Now, one other method that we have is the Sky Crane.
2. Sky Crane
Sky Crane method of landing was tried successfully in case of Mars Science Laboratory rover (or Curiosity); when it landed on Mars in 2012. Sky crane uses a combination of heat shield, parachutes and then thrusters to make a landing. Here’s a video of how it works:
However, this method is also not scalable enough to land manned missions. Thus, leaving with us the only possibility to invent a whole new way to land, which is Low Density Supersonic Decelerator.
3. Low Density Supersonic Decelerator (LDSD): Though this technique was experimented a while back by NASA engineers, it wasn’t put into actual use because it wasn’t really needed for the payloads that we have been sending to Mars until now. For smaller payloads, parachutes or Sky Crane seemed to be sufficient enough. However, as we plan to land manned missions on Mars, LDSD seems to be the most preferred way to make landings possible.
The concept it’s made of is very similar to parachutes; the main difference in LDSD’s case being, the drag is provided by inflatable membranes attached right next to the mission. The video below illustrates the workings of LDSD.
So, with the landing problem solved; we’ll move on to the other challenges that we’ll face to put humans on the Mars in the subsequent posts.
You can reach out to me on twitter: @smilesikand
