Mars landings

Comparison of Mars Landers

Multiple countries or organisations have performed Mars missions. The first hard and soft landing were performed by the soviet union with Mars 2 and Mars 3 missions in 1971. The first long term successful mission was the US Viking mission in 1975. ESA became the third organisation to reach Mars with Beagle 2 and Schiaparelli both failing during landing.

The MARS program was a soviet union space program to reach the red planet. The first launch occurred in 1960 with the Mars 1M spacecraft. The first successful hard landing was the Soviet Mars 2 landing on the 19th of May 1971, followed by the first soft landing of Mars 3 ten days later. Both Mars 2 and 3 missions used the Mars 4M spacecraft.  Mars 3, unfortunately, operated only shortly and did not provide scientific data. Mars 2/3 also carried the first Mars rovers, both never deployed. The Mars 4M spacecraft used parachutes for deceleration followed by a propulsive landing. A second set of rocket motors were used to push the parachute away from the lander to ensure it did not cover the lander. 

No other Soviet Mars landers landed successfully. Below is an overview of the Mars spacecraft with the number of launches and the mission designations. 

Several soviet missions were never flown. The first are were the Mars 4NM and 5NM landers which would launch onboard the N1 booster. The 4NM mission would deploy heavier Mars landers or Marsokhod rovers. And the 5NM mission would perform a Martian sample return. The capsule would be about 20 tons and would send a 13 kg capsule back to earth. To help decelerate the capsule would deeply a deployable heat shield of 30 panels. This increased the diameter of the capsule from 6.5m to 11m. The final landing would be done using a propulsive landing system. The missions were never flown as the N1 rocket system failed to reach orbit.

The last Mars mission was the Mars 5M, which was redesigning the Mars 4NM and 5NM landers using the more reliable Proton rockets. Two Protons would carry an 8500 kg lander to Mars and a third would carry the sample return vehicle. The sample return capsule would crash on earth without a parachute system to keep the design as simple as possible. 

NASA Viking program aimed at launching 4 spacecraft to Mars in the 1970s. They consisted of 2 identical spacecraft, each with one orbiter and one lander. These would become the first successful landings on Mars in 1976. note the Russian Mars 2 did successfully land on Mars but failed shortly after landing. Viking thus became the first successful Mars science mission. Originally NASA proposed a different mission for the first Mars landings, derived from the Apollo modules launched on top of the Saturn V rocket. This project was called Voyager and was later modified into the successful Voyager deep space missions. After concluding that Mars’ atmosphere is very tenuous, this idea was scrapped and ultimately replaced by the Viking program.

Both spacecraft were launched a month apart in 1975 on top a Titan IIIE-Centaur and reached Mars a similar period apart almost a year later. The orbiter sections of the full spacecraft were initially tasked with photographing the surface to find a suitable landing spot. Once this was selected the spacecrafts separated, with the lander initiating its EDL sequence with a de-orbit burn. Once it bled off enough velocity to the aerodynamic friction the parachute deployed around 6 kilometres above the surface and with a velocity of around 900 kilometers per hour. This was swiftly followed by the jettison of the aeroshell and the deployment of the landing legs.

The parachute alone was not enough to slow down the lander inside the thin atmosphere to a safe touch down velocity. The terminal velocity underneath the parachute was around 60m/s, too high to be considered a soft landing. About 1,5 kilometres of the surface the lander fired its retrorockets and detached from the parachute. The retrorockets allowed for a slow and soft landing, around 2,4m/s, on the surface of Mars both for Viking 1 and Viking 2.

Realizing that the atmosphere at Mars is much thinner than Earth, the EDL engineers had to develop a new parachute that could handle these never-before-seen conditions. Since the density of Mars’ atmosphere is only around 1% compared to Earth, aerodynamic deceleration would be considerably less and thus the lander’s velocity is much higher at parachute deployment. It would in fact be so high that engineers had to figure out what kind of parachute could survive supersonic deployment conditions. What they ended up with was a 16m diameter, 204 square meter, Disk-Gap-Band parachute, a type that would fly on every single Mars lander since then. In August 1972 NASA tested this new concept at the New Mexico’s White Sands Missile Range, by dropping a test vehicle from a balloon, accelerating it to supersonic conditions and deploying the parachute [see figure]. This test confirmed the parachute can function up to the desired conditions needed for a Mars landing and this design was thus successfully implemented in not only the Viking program but every NASA Mars lander since.

The Mars 96 mission was based on the Phobos 1 and 2 probes. Unfortunately, the Mars 96 mission failed in LEO and never reached Mars. If successful the mission would mostly still be one of the most ambitious missions to date. The program consisted of an orbiter, two surface stations and two penetrators. The surface stations would decelerate through the atmosphere and deploy a parachute at an altitude of 19.1 km altitude. Then at 17.9km, the airbags would inflate. The penetrators would be spun up for stability and use a solid rocket motor to enter the atmosphere. A small inflatable braking device would be deployed ensuring only part of the penetrator would enter the surface. The remainder remains on the surface to help with communication with the orbiter. 

After the two successful Viking spacecraft, Mars Pathfinder was the second lander mission from the US that was sent to Mars. Launched in 1996 the vehicle successfully landed on Mars in July 1997, consisting of the lander part and Sojourner, the first rover on Mars. Its predecessor used multiple systems in succession to ensure a safe landing on Mars, namely an aeroshell, supersonic parachute and retrorockets. Pathfinder used these systems too, but added an airbag system for the final leg of the flight.

After it entered the Mars atmosphere from a hyperbolic trajectory, it used the aeroshell to bleed off its velocity from 6.1km/s to just 0.37km/s. From this point, the supersonic disk-gap band was deployed to slow down the lander to around 70m/s.  The parachute was 12.7m in diameter and consisted of 32 gores, making it smaller than the Viking parachutes. Viking followed a similar profile up to point and used retrorockets to slow down it until touchdown, Pathfinder had an additional airbag system attached to the lander. This airbag pack deployed while it was suspended from the backshell, where the retro thrusters were located.

The spacecraft was brought to a stop around 20 meter above the surface. At this point the lander detached from the backshell, which flew away and crashed, and used its airbags to come to a safe landing on the surface. The drop from the backshell led to an impact of 18G upon contact and the airbags continued to bounce along the surface for at least 15 bounces. Whereas the most recent Mars landings experience about 7 minutes of EDL activities, from re-entry to touchdown, Pathfinder completed this in just 4 minutes.

The Mars Polar Lander (MPL) was the fourth lander designed by NASA to fly to Mars and the first one to fail the entry, descent and landing phase. As the name suggests the spacecraft was supposed to touchdown on Mars’ Polar region, more specifically the South Pole.

The EDL profile for this mission started with an entry velocity of 6.9 km/s at 125 km above the surface. The first part of the re-entry would use its heat shield to slow down. This was an ablative heatshield measuring 2.4 m in diameter and was used to bleed off the majority of the speed. Roughly 9 km above the surface the main parachute was fired from a mortar while the spacecraft travelled about 500 m/s. This parachute was only used for a minute to slow down to 80 m/s after which the Mars Polar Lander would separate from the backshell and parachute, about 1.3 km above the surface. The last stage of EDL was a powered descent phase using thrusters to slow the vehicle down to a complete stop about 12 meters above the ground. At this point, the engines were cut off and the vehicle would fall the remainder of the way.

Before re-entry began, the lander separated from the cruise stage, which cut-off direct communication with the lander and was not planned to reconnect until after a successful landing around 6 hours later. When contact with the lander was unsuccessful, the Mars Polar Lander was declared crashed and lost. Despite decades of footage from orbiters around Mars taking detailed images of every corner of the planet, the exact whereabouts of this lander is still unknown. No debris or EDL subsystems have been able to be located on images despite some promising leads over the years. The investigation into the failure did produce a likely scenario about the lost lander. The most probable failure was the premature shutdown of the thrusters in the last stage of EDL. This shutdown would have been triggered by a software error that mistakenly identified vibrations as a signal for a touchdown, therefore shutting down its engines much earlier and much higher above the surface, leading to a high-speed impact, above the design limitations of the lander.   

The deep space 2 mission was a piggyback mission on the ill-fated Mars Polar Lander. The mission had no parachute and would impact the surface of Mars. After impact, a part of the lander would shoot into the surface to analyse the Martian Subsurface. There were two probes, named Scott and Amundsen for redundancy reasons. It is somewhat unknown what happened to the mission. From the records, it can be seen that is separated successfully from MPL, but no contact was established afterwards. It could be that the probes did not survive impact landed wrongly and could not establish contact or that the landing site was too rocky. 

Beagle 2 was a British-made Mars lander that was transported by the European Space agency’s Mars Express orbiter in 2003. Once detached from the orbiter craft descended into the Martian atmosphere. Once the vehicle had completed its initial deceleration a mortar is used to deploy a disc-gap-band drogue parachute which decelerated the vehicle from roughly Mach 1.5  to between Mach 0.4 and 0.6 at an altitude of 2.6km above the Martian surface. At this point the rear aeroshell is jettisoned and pulled away from the vehicle by the drogue parachute. The main parachute was stored within the aeroshell and thus as it was pulled away the main parachute was deployed. The front heat shield was subsequently jettisoned and radar used to determine the vehicles altitude. At a height of 280m above the terrain two airbags were inflated to cushion the landing.

The Mars Exploration Rovers Spirit and Opportunity were two small rovers delivered on Mars in 2003. The identical rovers were launched on top of a Delta II rocket. The landers used a combination of parachutes and airbags to bounce to a safe landing. The rovers had a planned operational life of 90 days but lasted much longer. Spirit lasted for more than 6.5 years where Opportunity lasted for more than 15 years.

The landing system of the MER missions used a 14.1-meter disk gap band parachute to decelerate the vehicle to subsonic velocities. After this, the rover was lowered, the airbags inflated and the break rockets fired. The four large solid motors delivered about 10 kN of thrust and burned about 4 seconds.  The Vectran airbags were the same type as used on the Mars Pathfinder lander. There was an offset in the centre of mass of the lander,  increasing the odds of an upright landing. If the rover would land unside down, the computer would detect this and the sides of the vehicle would push it upright. 

The story of the Phoenix lander starts before it was named the Phoenix lander. The lander started as the 2001 Mars Surveyor lander. But after the Mars polar lander failed, there would not be enough time to perform the failure analysis before the launch of the Mars Surveyor lander. Therefore the Mars surveyor lander was cancelled and shelved. In 2003 a new Mars polar lander program was started, and the shelved Mars Surveyor lander was repurposed. The scientific instruments were changed, along with some small changes in the communication and radar system. Also aptly is was renamed Phoenix[78,79,80].

After the successful landing on Spirit and Opportunity in 2004, NASA was looking into landing a much larger rover. Where the MER rovers were about 300 kg, the new one would be about 1000 kg. This required a significantly different EDL system. The increase in mass means an increase in parachute diameter, but also put more requirements on the landing system. Where the other landers would use an airbag system, this would be too heavy for the Mars Science laboratory. Alternatively, a pallet style landing system using a crushable structure and a rocket motor would be an option. This would also be too heavy or the decelerations upon impact would be too high.

The final configuration chosen was the now-famous Sky crane. This meant that the lander would hover at a stable altitude while ropes would lower the rover. At first instance, this seems like a crazy concept that should never have been chosen. However, at a deeper glance, the sky crane has several major advantages.

• The sky crane only has two parts attached to each other instead of three as with earlier landers
• There is no cratering of a rocket motor during landing
• The propulsive flight allows for more control over the landing reducing the landing ellipse

The Schiaparelli Entry, Descent and Landing demonstrator module (EDM) was a mission designed to test the technology required to perform a soft landing on the Martian surface as part of the European space agency’s ExoMars project. The vehicle was carried to Mars by the ExoMars Trace Gas Orbiter. Given that the vehicles primary aim was to test Entry, Descent and Landing technology the vehicle carried limited instrumentation that was primarily aimed at characterising and performing measurements on Mars’s atmosphere.

The vehicle was intended to decelerate initially using the body drag of the vehicle before deploying a 12m disc-gap-band parachute at an altitude of 11km above the surface. This parachute was intended to decelerate the vehicle from 470m/s to around 70m/s which point the heat shield would detach followed shortly after by the back cover of the aeroshell with the parachute attached. The vehicle would then use three sets of hydrazine thrusters to decelerate the vehicle for the final 1.2km of its descent. At a radar altitude of 2m above the ground, the engines would be cut allowing the vehicle to freefall using crust structures to absorb the remaining energy.

Insight was a small lander inspired by the Phoenix structure. The main goal of the mission was to study the inside of the red planet and provide insight into the internal structure.  The resemblance to the Phoenix lander can be seen in both the aeroshell and the parachute, which are both identical in size. Over the mission, time InSight measured several Marsquakes and took sound recordings of the Martian wind. 

After the successful landing on curiosity, NASA JPL attempted to do the same thing with a new rover that resembled Curiosity quite a bit. The new rover, Perseverance, was slightly heavier but about the same size. This meant that the parachute would be slightly bigger, but the same sky crane design would be kept. However, this time the sky crane would incorporate a terrain relative navigation system. This allowed the lander to avoid hazards such as rocks during the landing. Something earlier rovers could not do. Perseverance also used a range tricker over a velocity trigger for the parachute deployment. Where Curiosity deployed the parachute when it was going a certain preprogrammed velocity, Perseverance deployed the parachute at a certain location, decreasing the landing ellipse.  

Perseverance was also the first Mars mission with a camera set focussing on the landing. Several cameras were pointed at the parachute inflation and on the sky crane lowering the rover to the surface.  This marked the first time images of a Martian parachute in flight were taken. 

The European/Russian ExoMars mission was originally planned for 2018 but postponed due to several reasons. The lander weighs about 1100 kg making it heavier than the Schiaparelli EDM mission launched in 2016. The lander consists of the Russian Kazachok surface platform and the European Rosalind Franklin rover. The parachute system, designed in Europe consists of four parachutes. A supersonic disk gap band with a supersonic pilot chute and a large subsonic main parachute with a dedicated pilot chute. After the parachute phase, the lander decouples from the parachutes and flies to the landing location using retrorockets. When the whole combination is close to the ground an airbag is deployed for the final landing. This entire EDL system is significantly more complex than other Mars landers such as Perseverance. The mission is currently on hold and uncertain after ESA cancelled the cooperation after the invasion of Ukraine. 

The Mars Sample Return mission has a lot of phases. First, the sample needs to be collected and then launched into space from the Martian surface. It needs to travel between two planets, and finally, when it has reached Earth, the sample needs to re-entre and land. This last phase is performed with the Earth Entry Vehicle (EEV).

Where usually, entry vehicles are complicated systems with multiple deceleration systems and deployment systems, which increase the mass and complexity of a system. For the EEV, the goal was to make things as reliable as possible to avoid possible contamination of the sample. So to achieve this reliability, all active systems were removed from the “normal” entry system [95,96]. That means no parachutes, no control system, no thrusters, not even electronics. Everything is done passively [95].

The design that follows from this is a 16cm diameter spherical sample container to hold 0.5 kg of Mars samples [95]. The sphere sits in a 0.9m diameter blunt body that acts as a heat shield and a separate debris/meteoroid shield around the entire vehicle [95,96]. The whole vehicle would weigh only 44kg [95]. The shape it has makes sure that even if the EEV would start upside down, with an angle of attack of 180 degrees, it would right itself before the entry heat pulse. The EEV would be expected to start entry at 12km/s and land with a terminal velocity of 41 m/s [95,96]. The maximum deceleration that is expected during the flight is 130g during entry [95].

Because the entire system is launched from Mars in order to avoid any Martian dust sticking to the side of the EEV when entering Earth, the whole craft is sterilized during entry. This means all surfaces must reach a temperature of at least 500C [95]. The landing system, if you can call it that, consists of an energy-absorbing structure at the bottom of the vehicle. It is resin-impregnated Kevlar and carbon walls braced by carbon foam. This would limit the impact deceleration below 2500g-3500g.