Link : https://youtu.be/pUK0KIZAa9E?si=DOLViBgWnkv-SxK2

INTRO

Since the birth of astronomy and the discovery of other planets in space, mankind has always wondered what it would be like to actually land on these celestial bodies. After all, exploring such an alien environment would not only teach us a lot about these harsh worlds, it would also increase the chances securing a much more brighter future for humanity as a whole. But before we dream such magnificent dreams, how do we even land on another planet in the first place? This is the question which has perplexed most scientists to a major degree. Even in the case of our most closest celestial relative, Mars. However the scientists in space X have made a multi step game plan in order to make this fantasy a reality. So join us as we talk about how space X will pull of the landing on our red neighbour, Mars.

GRAVITY AND HOW IT WORKS

Now you probably know that in order to fly into space a huge amount of upthrust is required to escape Earth’s gravity. Well then, what really is gravity and how does the concept of gravity help us understand space travel? In simple terms, gravity is explained as the force which attracts objects towards the centre of the earth, or any other physical body which has large a amount of mass. Albert Einstein explains gravity beautifully. In his theory of gravity, it is explained that space itself is like a stretched sheet of fabric. Now any object placed on this sheet of fabric leaves a dent on it. If a heavier object, meaning object with greater mass is placed on that sheet, the dent formed by it would be much deeper. Similarly an object with lesser mass will have a much more shallow dent. This can simply be done at your home as well, go ahead and try it with any two spherical objects! Now objects with huge amount of mass, like planets and the sun leave such a huge dent on the fabric that this forms what we call a gravity well. Here any object that comes within the range of this gravity well, gets sucked closer towards that planet. Understood? Great! This concept of gravity will be essential in order to understand taking off and especially landing.

DELTA V

Now keeping in mind the concept of the gravity well, let’s discuss another factor called delta V. It does not take a rocket scientist to understand the fact that our earth is constantly orbiting around the sun. And just like earth, so is Mars. The orbital speed of the Earth is 30km/s and the only thing which holds us from dropping even deeper into the massive gravity well of the sun is this orbital speed. Now similarly Mars is also orbiting with a fixed speed, which is 24km/s. The reason why it is stable with a much lesser speed is because it is much higher than earth in the gravity well of our sun. Now in order to escape the surface of our home planet earth, we would need a huge amount of upthrust, but that would not be the only problem. You See, after leaving the gravitational force of our blue home, we would become just another object stuck in the gravity well of our sun. And if our orbital speed decreases below 30km/s, well then we would be hurtling towards the sun, forcefully being pulled into it’s gravity well. In order to escape such a gruesome fate, we would need to speed up our spaceship more than 30km/s, slowly climbing up towards our planned destination, Mars. So in order to travel through space, the key component we need to understand is this change in our velocity relative to our starting position. This change in velocity is called Delta V. Now as we discussed this earlier, we are moving at the speed of 30km/s on our blue planet, but if we were to travel in a rocket ship at the speed of 31km/s, this would mean we are moving with a delta V of one. Similarly, if we were to travel at a speed of 29km/s, this would still mean we are moving with a delta V of one, because it refers to the change in velocity

LAUNCH OF STARSHIP

I hope you’ve got a good understanding of the concept of delta V, because you’re going to need it here. Now let’s talk about how space X plans to launch their starship from earth. Taking into consideration the natural forces such as atmospheric drag and gravity, the amount of delta V needed would be 9.4km/s. This monumental amount of force required to push through and reach low earth orbit is why it is extremely difficult to take off in the first place. This much amount of acceleration would need just as much amount of fuel and muscle from the rockets, and this is why the upthrust of our super heavy booster would be absolutely essential. Once up in earth’s orbit, starship would need to stop for refuelling, as a lot more muscle power, meaning propulsion would be needed for much greater delta V. Now from this set point in our orbit, we would need another 9.5km/s of delta V in order to reach the surface of our destination planet, Mars.

OVERARCHING CONCEPT

Okay so we have completed phase one, the launch of starship, let’s take a little detour and consider how it would travel towards our intended goal, and land on the surface of mars. Now a full starship in lower Earth orbit is considered to have enough thrust for somewhere between 6-7 km/s of delta v, so we have reached a problem here. This would be much lesser than our desired amount which we discussed earlier at 9.5 km/s. You might be asking, in that case how would we even reach the planet Mars? It’s simple, remember the forces we talked about earlier, which made it so excruciatingly hard for us to escape Earth? We are going to use those exact forces in our favour at this time. This means that we just need enough delta V to come in contact with the gravitational field of Mars and let those natural forces do the work for us, therefore increasingly the delta V potential of our starship.

DEPARTURE FROM EARTH

Okay so left off when our starship was orbiting around the Earth. Here the only thing which is holding us up in the lower earth orbit is the velocity of our starship. Remember the concept of gravity well that we talked about earlier? It applies here as well. If we are to decelerate then we might fall back onto the surface of the earth, and on the opposite end of this scenario, if we are to accelerate then we would rise much higher from surface of earth. Now since we are still very close to the surface of earth, we would need a lot more delta V in order to effectively escape Earth’s gravity. From the low earth orbit, we would need around 3km/s of delta V in order to reach lunar altitude orbit, meaning the height of the moon. Here we would finally be at the edge of earth’s gravity well. Now all we would need is an increase of 0.09km/s in delta V and we would be completely free from earth’s gravitational forces, and completely space bound. Here far away from earth and the moon, we would need only 0.39m/s of delta V to successfully reach the transfer velocity needed to travel from earth to Mars, through the vast emptiness of space. The departure from Earth as well as travelling through space to reach planet Mars has used up around 3.6km/s of the total delta V, which is half the amount of delta V a fully fuelled starship has, as we discussed earlier. So do we even have enough fuel left in our starship to land on the surface of mars? Well let’s discuss that further.

THE LANDING PRINCIPLE

Now that we are entering the proximity of Mars, we have a much bigger problem at hand. Here the issue isn’t that we might be too slow, but in fact the opposite. We started off with the orbital speed of the earth, which was 30km/s, and after speeding up even more we need to slow down to the orbital speed of Mars at around 24km/s. If this manoeuvre is not executed correctly, we will end up missing mars entirely and shoot past it into the asteroid belt. Let’s understand the principle of landing on Mars and the problems accompanying it. After several months of travel, we need to start the process of deceleration. Our first deceleration burn starts off as we begin to come close to the gravity well of Mars. Now the starship must flip itself over and align the engines perpendicular to the landing surface and begin to decelerate. Here we must cut off 0.67km/s of delta V so we could get pulled into the gravity well of Mars. After being successfully caught by the gravitational forces of Mars, we must now burn off 0.34km/s more of our delta V to reach the moon, Deimos. 0.4km/s more and we move to the inner moon of mars, Phobos. And this is the point where we run into another problem. You see by now we have used up around 5km/s of our delta V, meaning we are only left with one or two more in the tank. Where as, the amount necessary to make a soft landing on Mars at this point is around 4 and a half km/s of delta V. However this does not mean that landing on Mars would be impossible. We still can achieve that, but we have to be extremely strategic regarding fuel conservation.

TOUCHDOWN ON MARS

Now this is the most logistically possible way of landing on Mars. I do have to remind you that this is all purely theoretical. In order to save as much fuel as possible, we must use as much external forces available in order to slow the velocity of our starship and land safely on the surface of Mars. Hypothetically speaking, lowering our spaceship in a circular motion onto the surface of Mars will consume tons of our precious fuel, but what if we use an elliptical orbit instead? Here we can conserve a good amount of fuel. The orbit around the planet Mars would be in an oval shape, with it’s low spot or perigee near the planet and a high spot apogee far away into space. Using this specific manoeuvre, we might be able to use the aerodynamic drag as well as the gravitational force of Mars instead of our precious delta V to make a soft touchdown. Now the idea is that, although the atmosphere of Mars is very thin, it would supply us with some atmospheric drag and decrease the velocity by a small amount, before we get flung out to the apogee. Here, the gravity of Mars would hopefully pull us back, if executed properly, to repeat this process until we have decreased our velocity enough. However this can not be continued over and over again. We do have to transition from these dips into the atmosphere into a full on dive onto the surface of Mars. Here, on it’s final approach, starship will enter the atmosphere of Mars upside, with it’s nose towards the surface. This way the lift created would be helpful in slowing down the spaceship. Next we would see the traditional belly flop manoeuvre as seen on earth. All of these actions taken will make sure we have maximum amount of drag, but this will only be helpful until we hit terminal velocity. Due to the much thinner atmosphere on mars, the terminal velocity would be five times faster than earth, meaning it would still require a lot more engine power on Mars to land softly than it is required on earth. And on the moment of touchdown, hopefully we would have enough fuel left in the tank to provide us with the right amount of delta V to decelerate more land safely. That is a long list of events that absolutely need to be perfectly executed in order to successfully reach the surface.

OUTRO

Now this task seems extremely difficult if not impossible, but space X is currently working harder to make their spaceships much lighter as well as making them much more fuel efficient. The overarching plan made by Elon musk is just as grand, which is building a self sustaining community on Mars made up of 1 million individuals. And in order to pull that off they certainly will need a gigantic ship, which translates to even higher efficiency of their raptor engines to account for that much increase in mass. As we have seen time and time again, failure is just the gateway towards success, and seeing how committed space X has been after their failures before, it might be only a matter of time before we can turn this vision into a reality.

This is why landing on mars will be a huge achievement for space X