The incredible challenge of landing heavy payloads on Mars

Too bad, Mars is such an interesting place because it is one of the most difficult places to visit in the solar system, especially if you want to bring a lot of luggage. This planet is a mission graveyard that has not quite succeeded.

As our ambitions grow and we plan to explore Mars with humans – perhaps even future settlers – we will have to solve one of the biggest problems in space exploration.

It is very difficult to successfully land on the surface of Mars heavy payloads.

There is a whole series of problems with Mars, including the lack of protective magnetosphere and the lower surface gravity. But one of the most important is its fine atmosphere of carbon dioxide.

If you were on the surface of Mars without a spacesuit, you would die of cold by suffocating for lack of oxygen. But you would also have less than 1% atmospheric pressure on Earth.

And it turns out that this thin atmosphere makes it extremely difficult to route large payloads to the surface of the red planet. In fact, only 53% of Mars missions went well.

So let's talk about how Mars missions have worked in the past and I'll show you the problem.

Landing on Mars is the worst

Historically, missions to Mars are launched from Earth during flight windows that open approximately every two years as Earth and Mars get closer. ExoMars flew in 2016, InSight in 2018 and the March 2020 rover will fly until 2020.

Artist's view of the InSight lander beginning his phase of entry, descent and landing (EDL) towards Mars. Credit: NASA
Artist's view of the InSight Lander beginning its phase of entry, descent and landing on Mars. Credit: NASA

Missions follow an interplanetary transfer path designed to achieve this as quickly or with as little fuel as possible.

When the spacecraft enters the atmosphere of Mars, it travels tens of thousands of kilometers per hour. It must somehow lose all this speed before landing softly on the surface of the red planet.

Here on Earth, you can use the thick atmosphere of Earthican to slow down your descent, bleeding your speed with a heat shield. The space shuttle tiles were designed to absorb the heat of re-entry, with the 77-tonne orbiter having gone from 28,000 km / h to zero.

A similar technique could be used on Venus or Titan, where they have a thick atmosphere.

The moon, without any atmosphere, is relatively easy to land as well. Without any atmosphere, no heat shield is necessary, you only need to use a propulsion to slow down your orbit and land on the surface. As long as you bring enough thruster, you can stick the landing.

Back on Mars, with a spacecraft moving in its thin atmosphere to more than 20 000 kilometers at the hour.

Curiosity is the limit

Traditionally, the missions began their descent with an aerosol to remove some of the speed of the spacecraft. The heaviest mission ever sent to Mars was Curiosity, which weighed 1 metric ton, or 2,200 pounds.

When he entered the Martian atmosphere, he was traveling 5.9 kilometers per second, or 22,000 kilometers at the hour.

Curiosity passing in the Martian atmosphere. Credit: NASA / JPL
Curiosity passing in the Martian atmosphere. Credit: NASA / JPL

Curiosity had the largest airbrush ever sent to Mars, measuring 4.5 meters in diameter. This huge airbrush was tilted at an angle, which allowed the spacecraft to maneuver when it struck the thin atmosphere of Mars, aiming for a specific landing zone.

At approximately 131 km altitude, the spacecraft would begin launching thrusters to perfectly fine-tune the trajectory as the surface of Mars approaches.

About 80 seconds of flying in the atmosphere, the temperature on the heat shield has reached 2100 degrees Celsius. In order not to melt, the heat shield used a special material called Phenolic Impregnated Carbon Ablator, or PICA. The same material that SpaceX uses for its Dragon Capsules, by the way.

Once its speed had been reduced below Mach 2.2, the spacecraft deployed the largest parachute ever built for a mission on Mars – 16 meters in diameter. This parachute could generate 29,000 kilograms of drag strength, slowing it even further.

The suspensions consisted of Technora and Kevlar, which are the most resistant and heat resistant materials.

He then dropped his parachute and used rocket engines to slow down his descent even further. When it was close enough, Curiosity deployed a carrier that gently lowered the vehicle to the surface.

This is the fast version. If you want a complete overview of what Curiosity suffered while landing on Mars, I highly recommend you check out Emily Lakdawalla's "The Design and Engineering of Curiosity".

Illustration of the Curiosity skycrane, placing it gently on Mars. Credit: NASA / JPL
Illustration of the Curiosity skycrane, placing it gently on Mars. Credit: NASA / JPL

Curiosity only weighed a ton.

Go heavier does not have scale

Want to do the same thing with heavier payloads? I'm sure you can imagine bigger aeroshells, bigger parachutes, bigger skycranes.

In theory, the SpaceX Starship will send 100 tons of settlers and their equipment to the surface of Mars.

SpaceX Starship artist illustration. Credit: SpaceX
Illustration of the SpaceX Starship artist. Credit: SpaceX

Here is the problem. Deceleration methods in the Martian atmosphere are not very effective.

Let's start with the parachutes. To be honest, at 1 ton, Curiosity is about as heavy as you can get with a parachute. The heaviest and most versatile material engineers can withstand the deceleration load.

A few months ago, NASA engineers celebrated the success of the advanced research experiment on the inflation of supersonic parachutes, or ASPIRE. This is the parachute that will be used for the Mars 2020 robot mission.

The ASPIRE payload separates from its booster. Credit: NASA / JPL / Caltech
The ASPIRE payload separates from its booster. Credit: NASA / JPL / Caltech

They placed the parachute in advanced composite materials, such as nylon, Technora and Kevlar, on a rocket and launched it at an altitude of 37 km, reproducing the conditions in which the spacecraft will be confronted when It will arrive in March.

The parachute deployed in a fraction of a second and fully inflated sustained a force of 32,000 kilograms. If you were on board at that time, you will feel 3.6 times more powerful than hitting a wall at 100 km / h with your seatbelt. In other words, you would not survive.

If the spacecraft was heavier, it would have to be made with impossible composite fabrics. And forget the passengers.

NASA has tried different ideas to land more than 3 tons of payloads on Mars.

Illustration of the artist of the low density supersonic decelerator. Credit: NASA

An idea is called the low density supersonic decelerator, or LDSD. The idea is to use a much larger aerodynamic decelerator that would inflate around the spacecraft, like an inflatable castle when it would enter Martian gravity.

In 2015, NASA actually tested this technology, carrying a prototype vehicle on a balloon at an altitude of 36 kilometers. The vehicle then fired its solid rocket, bringing it to 55 km altitude.

While it was skyrocketing, it inflated its Supersonic inflatable aerodynamic decelerator to a diameter of 6 meters (or 20 feet), which then slowed it down to Mach 2.4 again. . Unfortunately, his parachute was not able to deploy properly. It has crashed in the Pacific Ocean.

It's a progress. If they can actually work on engineering and physics, we could someday see a 3-ton spacecraft land on the surface of Mars. Three whole tons.

More propulsion, less freight

The next idea to increase a landing on Mars is to use more propulsion. In theory, you can simply carry more fuel, fire your rockets when you arrive on Mars and cancel all that speed. The problem, of course, is that the more mass you have to support to slow down, the less you can land on the surface of Mars.

SpaceX Starship illustration landing on Mars. Credit: SpaceX
Illustration of the SpaceX spacecraft landing on Mars. Credit: SpaceX

The SpaceX Starship is expected to use a propulsive landing to send 100 tons to the surface of Mars. Because it takes a more direct and faster trajectory, the ship will reach the Martian atmosphere at a speed greater than 8.5 km / s, then it will use aerodynamic forces to slow down its entry.

You do not have to go that fast, of course. The spacecraft could use aerobraking, passing several times in the upper atmosphere to lose its speed. In fact, this is the method that orbital spacecraft going to Mars are using.

But then, passengers on board should spend weeks slowing down and getting into orbit around Mars and then going down into the atmosphere.

According to Elon Musk, his delightfully unintuitive strategy to handle all this heat is to build the stainless steel spacecraft, then tiny holes in the hull will purge methane from the fuel to keep the windward side of the ship cold.

Once the speed is sufficiently reduced, he will turn around, light his Raptor engines and land softly on the surface of Mars.

Aim the ground, go back to the last minute

Every kilogram of fuel used by the spacecraft to slow its descent to the surface of Mars is a kilogram of freight that it can not carry to the surface.

I'm not sure that there is a viable strategy that will easily put heavy payloads on the surface of Mars. People who are smarter than me think it's almost impossible without using huge amounts of propellant.

That said, Elon Musk thinks there is a way. And before coming back to his ideas, let's watch the rocket propellers Falcon Heavy land to perfection.

And do not pay attention to what happened to the central reminder.

A new study from the Aerospace Department of the University of Illinois at Urbana-Champaign suggests that missions to Mars could take advantage of the thicker atmosphere that is closer to the surface of Mars.

In their article "Entry Path Options for High Ballistic Vehicles on Mars", the researchers propose that space vehicles heading to Mars do not need to be in such a hurry to get rid of their speed.

As the spacecraft roars in the atmosphere, it will still be able to generate a lot of aerodynamic lift, which could be used to direct it into the atmosphere.

They did the calculations and discovered that the ideal angle was simply to steer the spacecraft down and dive to the surface. Then, at the last moment, lift yourself up using aerodynamic lift to fly sideways into the thickest part of the atmosphere.

This increases drag and allows you to get rid of as much speed as possible before turning on your downhill engines and completing your motorized landing.

It looks funny.

If humanity wants to build a viable future on the surface of Mars, we will have to solve this problem. We will have to develop a series of technologies and techniques that make landing on Mars more reliable and safer.

I guess it will be a lot harder than people expect, but I look forward to the ideas that will be tested in the years to come.

A big thank you to Nancy Atkinson who has covered this topic here on Universe Today more than a decade ago, and inspired me to work on this video.

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