Landing Sequences

Examples of different sequences and technologies used to deploy probes on the surface of celestial bodies: EDL (Entry, Descent & Landing) for atmospheric probes and SDL (Separation, Descent & Landing) on airless environments such as the Moon, asteroids and comets. Note that some techniques do not shed any equipment while others use various systems to secure a soft landing.

Full red arrows point out the deployed or discarded hardware, hollow ones show modules that were returned to Earth, and red-boxed names identify the main probes.

Luna 9 & 13 (The Moon) – 75 km from the surface, the Cruise Bus main engine was ignited to slow the stack down and both the Radio-Altimeter and Astro-Navigation modules were jettisoned. Meanwhile, a Surface Contact rod was deployed and the probe’s airbags were inflated, ripping off the Thermal Shroud. At touchdown, the Surface Contact Rod triggered the probe’s ejection, which hit and rolled on the surface. Once stopped, the two hemispheric airbags were seperated to let the probe deploy its petals and intruments – Credit: Roscosmos,
Surveyor 1 to 7 (The Moon) – At about 75 km from the surface the Main Descent Engine was fired, expeling the Radar Antenna housed into the nozzle. Once depleted, the engine was discarded at the 10 km mark and the probe soft-landed using small Vernier Engines – Credit: NASA,
Second Generation Lunas (The Moon) – At about 15 km from the surface, the Cruise Bus/Lander released two side ‘Backpacks’ containing two propellant tanks and an avionics bay each. Once on the Moon and depending on the mission type, a Rover (Lunokhod, right) was deployed or an Ascent Module lifted-off after a soil sample was fetched and placed in a Return Capsule (left). In the latter case, the Ascent Module was lost at reentry while the Capsule was recovered and displayed in a Museum – Credit: Roscosmos,
Apollo (The Moon) – The Lunar Module didn’t shed off any equipement during the landing sequence, however the astronauts deployed a lot of harware on the surface. Later on, once the crew back and safe aboard the Command Module, the LM Ascent Stage was intentionally crashed on the Moon. The Command Module was recovered and displayed in a Museum while the Service Module was incinerated in the Earth’s atmosphere at reentry. Additionally, Apollo 15 and 16 deployed each a small Subsatellite which also ended on the Moon after several weeks of orbital operations – Credit: NASA,
Chang’e 3 (The Moon) – Similar to the Surveyor program, minimal design is used for small Lunar Landers: a single module is used for coasting, orbital insertion and landing and nothing is discarded. Beresheet and Hakuto-R M1 did it that way too, although unsuccessfully – Credit: CNSA, CASC,
Chang’e 5 (The Moon) – After orbital insertion, the Landing Module separated from the Orbiter and proceeded to a direct touchdown. Meanwhile the Adapter Cone from the Orbiter was discarded in preparation for the Rendez-Vous with the Ascent Stage later on. Once the Lunar samples safe aboard the Return Capsule, the Ascent Stage was jettisoned along with the Docking Interface. The Return Capsule is now back on Earth while the Orbiter made another trip to Lunar orbit where it still remains. Apart from the Moon launch and the Earth Return Capsule, Chang’e 4 and both Chandrayaan spacecraft followed a similar landing profile involving an orbiter – Credit: CNSA, CASC,
Omotenashi (The Moon) – Even small 10 × 20 × 30 cm cubesats can soft-land on the Moon: delivered on a Moon-impact trajectory by the Artemis-1 ICPS, the Orbital Module was supposed to maneuver into an optimal attitude for landing. At about 400 meters above the surface, the Airbag was to be inflated, the Orbital Module ejected and the Retro-rocket ignited for a few seconds. The Surface Module would have then free-fell the remaining 100 meters and hit the surface protected by the Airbag. Unfortunately the probe was lost soon after the ICPS release due to the solar cells failing to generate power and is probably now wandering in Cislunar space – Credit: JAXA,
SLIM (The Moon) – **NOTE: this is an ongoing mission, the probe is on its way to the Moon** If everything goes to plan, at about a 1.8 meter from the surface, the probe will release two small Rovers and a protective cover. A thruster will then make the probe tip-over to the side to set it firmly on the uneven ground – Credit: JAXA,
Venera 3 to 8 (Venus) – Cruise Buses from the first generation Venera probes released the landers minutes before burning up into the atmosphere. Venera 3 used three parachutes while Venera 4 to 6 used two of them and the last probes only one in order to soup up the descent into the dense atmosphere that crushed all four first probes. Apart for the Pilot Chute, Backshell and some probable mortar elements, nothing else was discarded during the descent (the Heatshield for instance was part of the pressure hull, and the Main Chute remained fixed to the probe). Note that Venera 8 dropped a Secondary Antenna to improve communication with the Earth – Credit: Roscosmos,
Venera 9 to 14 (Venus) – The first two second generation Venera probes used six parachutes and this number was brought down to three for the remaining four probes, still to reduce the descent time. The Main Chutes were released at about 50 km in altitude and the probe free-falled the remaining distance using a dish-like brake. In addition to the Backshell and probable mortar elements, the probe released a Heatshield and, once on the surface, two Camera Covers (although on some missions they didn’t pop-up). Orbiters from Venera 10 and 11 are probably still orbiting the planet while all other ones were sent into Solar orbit – Credit: Roscosmos,
Pioneer 13 (Venus) – 23 days before reaching Venus, the Cruise Bus released the ‘Large’ Probe and the remaining three small probes four days later. While the large probe followed a classic Venera-style EDL scheme using two parachutes, a Backshell, a Heatshield and a free-fall, all three small probes plummeted to the surface using only a Heatshield, the dense atmosphere and their light weight smoothing their impact. However pressure and heat made them quit before reaching the surface, except for the ‘Day’ probe who returned surface data for an hour– Credit: NASA,
Vega missions (Venus) – Vega probes were modified second generation Veneras using two parachutes only and were loaded with an atmospheric balloon experiment: two additionnal parachutes, an inflation system, a ballast and the balloon itself holding the instrument laden gondola. Both Orbiters ended up in Solar orbit – Credit: Roscosmos,
Mars 3 & 6 (Mars) – An expendable propulsion ring was used to spin the probe before atmospheric entry, and a rocket was used to extract the Drogue Chute and Backshell, another one to move away the Main Parachute and a third one to soft-land the probe as a Skycrane. A Heatshield and a foam Cap were also discarded in the process and a tethered rover was supposed to be deployed on the surface, but contact was lost with both probes while landing. The Mars 3 Main Bus is probably still orbiting the planet while that of Mars 6 is wandering around the Sun – Credit: Roscosmos,
Viking 1 & 2 (Mars) – The landing sequence seems relatively simple with only three discarded equipement: a Heatshield, a Backshell/Parachute combination which was released at 1.5 km altitude when small Vernier engines ignited to soft-land the probe. However there are also mortar elements, the probe’s robotic arm Sampler Head Cap and the Orbiter/Lander adapter, also known as the Bioshield Upper Cap (the lower one was released in Solar orbit while coasting to Mars). Both Orbiters are believed to be still orbiting the planet, however they won’t last long anymore – Credit: NASA, JPL,
Pathfinder, Spirit & Opportunity (Mars) – A mix of Luna, Venera and Mars probes EDL technologies were adopted: minutes before burning up into the atmosphere, the Cruise Buses released the probes and Landing Rockets were used to skycrane the lander protected by a ball of airbags. The rockets also moved away the Backshell/Main Chute stack and a Heatshield was discarded earlier in the process. Pathfinder’s Landing Platform was used for the Earth to communicate with the Sojourner Rover while those from Spirit and Opportunity were inert and abandoned – Credit: NASA, JPL,
Mars Polar Lander (Mars) – The Cruise Bus released three probes before burning up into the atmosphere, among which the twin Deep Space 2 impactors similar to the Pioneer 13 small probes: they stroke the surface without any EDL equipment except for the Heatshield and shattered at impact to let their penetrators study the Martian soil subsurface composition up to a meter deep. Meanwhile the main lander followed a rather standard Viking-style EDL with one chute, a Backshell, a Heatshield and Vernier retro-rockets to soften the landing. All three probes were lost, probably due to an underestimated impact velocity for the Deep Space 2 probes and faulty sensors aboard MPL – Credit: NASA, JPL,
Beagle 2 (Mars) – This Pathfinder-style EDL was modified by adding a Pilot Chute and by releasing the Backshell before the Heatshield. Unfortunately and despite the Airbags this specific approach didn’t secure a soft enough landing to the probe – Credit: National Space Center, ESA,
Phoenix & Insight (Mars) – Apart from an expendable Cruise Bus, the sisterships used a standard Viking-type EDL technique, discarding a Heatshield and a Backshell/Main chute stack before using Vernier retro-rockets to soft-land – Credit: NASA, JPL,
Curiosity & Perseverance (Mars) – An improved Spirit/Opportunity-like EDL was developed for the more massive Curiosity-class rovers. A pair Cruise Mass Balances were dropped to shift the probe’s center of gravity during atmospheric entry and six other ones to put it back into position before the single Parachute deployment. The airbags were deleted and more powerful Landing Rockets skycraned the rover onto the surface. Perseverance also delivered a small Helicopter Drone, Ingenuity – Credit: NASA, JPL,
Tianwen-1 (Mars) – Viking-style EDLs are also used to commission rovers on the surface of the Red Planet. The Zhurong Rover landing platform is now inert and the Rover communicates with the Earth via the Orbiter. Three wireless cameras were also deployed during the mission: the first one in Solar orbit while cruising to Mars, the second one on the surface to shoot the landing hardware and the last in orbit to picture the Orbiter – Credit: CNSA,
Galileo Atmospheric Entry Probe (Jupiter) – This rather standard EDL profile is unique as every single piece of hardware was crushed and melted into the very deep atmosphere, and it is highly probable that no remains -if any- has achieved the ‘L’ that stands for landing – Credit: NASA,
Huygens (Titan) – The probe was released by the Cassini Saturn Orbiter while flying-by the Moon. The landing sequence was standard with mortar elements, a Backshell, three Parachutes and a Heatshield. A couple of instrument dust caps were also released before touchdown. The Stabilizer Chute remains fixed to the Lander – Credit: ESA,
Philae (Comet 67P/Churyumov–Gerasimenko) – Landing on a very low gravity field implies using specific methods to prevent any rebound: upward-firing thruster to stick the spacecraft on the surface, harpoons and screw-equipped footpads to anchor it – Credit: ESA, J.-P. Bibring et al.,
Hayabusa2 (Asteroid 162173 Ryugu) – The probe has released at least fourteen objects on the surface: four small Rovers (Hibou, Owl, Mascot and Minerva2) and their protective covers, four target markers to help sampling the surface, two bullets that were fired at the surface to stir up material and a wireless free-flying camera (DCAM-3) that shot the SCI impact. Note that unlike Philae the Rovers weren’t equipped with any landing aids, that the cannon was destroyed when firing the impactor and its debris sent to Solar orbit, and that the DCAM-3 camera is presumed to have fallen on the asteroid since then. The Hayabusa probe has delivered the sample capsule to the Earth in December 2020 and is now back wandering in Solar orbit – Credit: JAXA,