Some learnings from mission of Perseverance Rover Landing on Mars...

It's exciting times, when one hand,  we are launching a next gen space telescope (James Webb Telescope) into space, on the other hand we are looking at Artemis 1 & 2 missions & then on another we are gearing towards Mar's landing. 

As we near the landing date for the Mars Perseverance Rover, let's talk about the journey & challenges and understand what we can learn from it. 

The Mars Perseverance Rover was launched from Cape Canaveral, Florida on July 30, 2020 on a ULA Atlas 5 rocket & is expected to touch down on Feb 18, 2021 on Mars, after traveling a distance of 300 million miles in space. 

Why is this landing different? - As mentioned by JPL, it can be summarized as 7 minutes of terror. The primary difference being that earlier missions used - air bag landing demonstrated in 1996 by sojourner or sky crane maneuver & tethered landing - these systems were mainly targeted to land on specific landing locations with less challenging surfaces & with minimal decisioning. The Perseverance however is different. 

Before we talk about that let's take 2 steps back - the steps in the guidance system to align the space craft in the direction of the planet start much early in the process, around 250 million miles before - the injection burns - like the trans mars injection burn is triggered. 

Guidance data provided by the craft during the course of the journey helps to identify if there is a need for further correction burns. Before the space craft  approaches near the planet - there is a series of 5 opportunities, including 1 contingency & 1 backup burn to making sure the trajectory is still on target.

The learning here is --- understanding how many opportunities we have is essential to getting our ducks in a row for the main event.

In the Entry Descent & Landing - EDL - phase, this sets up the space craft in the direction of target landing.

Okay now that is covered, let's look at the challenge of the - 'what' & 'how' of this difference of landing.

The landing siteSo, is Jezero Crater - which was supposed to be an ancient river delta earlier. It's different as it has a terrain which is composed of many groves and ridges, it has cracks in polygonal patterns which makes it difficult to land a piece of equipment carrying research instruments via a direct drop, also since the optimal site might vary - it's important to make the landing decisional. So here comes the difference - the TRN - or terrain relative navigation system is being used for the first time to allow craft to take decisions on the best site for touchdown.  The reason why Jeserzo was chosen is because it has a lot. of minerals which might hold the key to ancient life if it existed on mars.

Now, let's delve a bit deeper in to the landing mechanics of whole system & some of the critical decisioning areas.

This landing is one shot one opportunity situation - so if the craft has to land, it needs to on Feb 18, so it needs to be done right. 

From a Mars weather prediction perspective - weather accuracy is at most upto one day as of this time.

The craft has a heat shield, back shell and rover jetpack plus there are antennas &  a small helicopter Ingenuity.

Learning : Identify the main players for a critical mission.

The craft will be traveling at 50,000 miles per hour when it hits the thin atmosphere of mars. This is another challenge - as the atmosphere being thinner doesn't slow down the craft as a thick one would.

Post cruise & 10 minutes before entry, the craft separates. In 80 secs the craft reaches peak heating with 1300 degrees Celsius of temperature & whatever comms were there are also now not available, system is completely autonomous. The best part it will use the old Apollo era guided entry technique to stay on target during this phase.

Mission is to slow down to 1000 miles per hour from 50,000 miles per hour & then deploy the 21 meters diameter supersonic parachute at mach 1.75 and approximately 7 miles high in altitude from the surface of Mars. The speed would drop to 940 miles per hour, post which the heat shield is jettisoned at around mach 0.7. Now this will uncover the radar which is used to start searching for the ground to land.

Learning : Some parts are critically essential to slow down the pushback effect of a new environment and once they are used they must be removed.

Rover jetpack drops out of the back shield with a divert manouver which then reduces the velocity to 0.75 meters/sec and about 7000 feet over the surface. This will then execute sky crane maneuver which was a part of curiosity, which then separates the descent stage and fly it to the position of landing. The essential element here being the TRN which has already kicked in by now.

Terrain Relative Navigation - as mentioned in my earlier post is basically a navigation system which uses descioning autonomously to land the rover to a safe location by comparing the terrain with built in maps, learning and deciding which location suits the best to land the craft. It's an important concept which would be also helpful in future missions. Once landed the craft antennas are functional and heartbeat is sent back.

Since the communication to Mars takes 11minutes to reach back, there is no idea if the craft landing safely or not. The above sequence of events are happening in the 7 minute duration and once everything is complete correctly the crew can expect a confirmation. The signal travels back via the Deep Space Network and communication satellites & locations on earth.

Learning : Making sure that all the steps are defined, in order & correctly tested to execute in the same way as planned. This was done by rehearsing flight software and hardware choreography over and over again before the main mission.

So, it's an exciting event and most important are the bundle of scientific experiments like MOXIE which would carry an experiment to generate oxygen on surface of Mars. 

We will explore a bit about Artemis & why landing on Moon & moon base is essential in the next blog. 

Reference source: https://www.nasa.gov, talk by Chloe Sackier.