The spectacular display orbital rockets put up when firing their thrusters to launch into space always remains awe-inspiring. But if astronauts or a spacecraft need to return to Earth, how do they get back and land safely?
A rocket’s crew or cargo module typically returns to Earth by firing its thrusters to deorbit. Once in the atmosphere, parachutes deploy to land the craft. The first stages of modern rockets like the Falcon 9 use their thrusters to slow the vehicle down and deploy landing legs for the touchdown.
The iconic images of the Apollo spacecraft’s command module deploying its three massive parachutes and drifting through the atmosphere before touching down in the ocean are probably the way most people envision astronauts and spacecraft returning to Earth.
More than 50 years after Apollo 11 first landed humans on the moon & returned them safely to Earth’s surface, crewed spacecraft still use parachutes to bring astronauts & cosmonauts back to Earth. SpaceX’s Crew Dragon and Russia’s Soyuz capsule are two modern examples.
However, in recent years, advancements in rocket technology now allow an increasing amount of rocket sections to return and land on the planet’s surface for reuse in upcoming launches. This is largely due to private companies getting involved in the space industry.
During the late 20th and early 21st Century, the Space Shuttle Program ushered in a new era of space travel where a launch vehicle lifts off like a rocket but return from space and lands like a conventional aircraft.
The different means by which rockets and other spacecraft return from space and land back on Earth, past and present, can be categorized into five distinct sections:
- Conventional Spacecraft Landing With Parachutes
- Space Shuttle Landing
- SpaceX Falcon 9 First Stage Landing
- ULA Vulcan’s Inflatable Heat Shield With Helicopter Recovery
- Rocket Lab’s Electron First Stage Capture With Helicopter
Most of these recovery methods are tried and tested procedures, but as will be explained in the upcoming sections, at least two of the landing procedures are in the development phase and haven’t been proven yet.
The landing/recovery procedures have a lot in common and follow the same principles but differ substantially in their approach and the technologies they use. By looking at each in more detail, one will get a better understanding of how each system works:
1) How Conventional Spacecraft Land With Parachutes
The method used by most crewed and uncrewed space capsules to return to Earth is by deploying large parachutes to slow it down sufficiently to perform a safe landing either on land or in the ocean.
The most modern application of this landing procedure is SpaceX’s Crew Dragon (and Cargo Dragon), which performs splashdown in the ocean. Russia’s Soyuz Capsule usually lands in Kazakstan’s open plains while China’s Shenzhou capsule touches down in the Gobi desert.
However, the most famous example of this method for returning spacecraft to Earth is the well-documented splashdowns performed by the command modules during the Apollo missions in the 1960s and 70s (by implementing the principles still used today).
The re-entry and landing procedure of a typical Appolo command module looked as follows:
- Before the Apollo command module can re-enter the Earth’s atmosphere, it first needs to separate from the service module. (The command module is the only part of the original Saturn V rocket that returns to Earth.)
- After separation, the command module must approach the atmosphere at an inclination of 5.3 – 7.7 degrees. A steeper angle will cause spacecraft to burn up in the atmosphere, while a shallower angle will cause the capsule to skip off the atmosphere back into space.
- The command module must also re-orientate itself so that the base of the craft covered with heat shields points forward. The wedge shape of the base will also allow it to slow down.
- After re-entering the atmosphere, the speed of the craft pushing against the dense atmospheric air will cause the ablative heat shield to absorb temperatures of up to 2 760° Celsius (5 000° Fahrenheit).
- While still in the upper atmosphere, two ribbon drogue parachutes are deployed to slow the capsule down and help to stabilize it.
- After reducing enough speed, the capsule releases three pilot parachutes that are responsible for extracting the three ringsail main parachutes, which will slow the spacecraft sufficiently down to perform a safe splashdown in the ocean.
- After splashdown, a helicopter with navy divers will secure the craft before it is airlifted to a nearby naval ship.
Although modern capsules like SpaceX’s Crew Dragon use vastly improved materials and technology, the basic procedures and approach for re-entry and landing remain almost identical to that of the Apollo spacecraft implemented more than 50 years ago.
2) How The Space Shuttle Landed
The Space Shuttle (Columbia) first flew on 12 April 1981, and the last flight took place on 8 July 2011. It revolutionized the way humans travel to space and back by launching an orbiter like a rocket and returning it to the Earth by landing like a conventional aircraft.
NASA’s aim with the Shuttle Program was to operate a reusable spacecraft with quick turnaround times between launches to save costs and allow for more frequent missions. Unfortunately, the program proved too costly and was canceled in 2011.
The technology and approach still remain revolutionary and many of the lessons learned and equipment developed during this period are being implemented in current and future space vehicle designs.
The re-entry and landing procedure of a Space Shuttle looked as follows:
- Once the cargo doors are closed, and everything is secured inside the craft, the space shuttle is flipped around with its RCS (Orbital Control System) so that its tail is facing forward.
- With the tail facing forward, the OMS (Orbital Maneuvering System) thrusters are fired to slow the craft down and allow it to start falling out of orbit.
- As soon as the orbiter reaches the upper atmosphere, it pitches around again with its nose facing forward and its belly, which contains the heat shields, facing down.
- As the space shuttle re-enters the atmosphere at speeds of around 28 000 km/h (17 300 mph), the heat shields have to absorb and withstand temperatures of up to 1 650° Celsius (3 000° Fahrenheit).
- The orbiter is now essentially a giant heavy glider, and after slowing down to subsonic speeds about 40 kilometers (25 miles) before the landing site, it starts to align itself to the runway.
- After a steep dive, the nose is raised in preparation for the landing, and the landing gear is lowered 15 seconds before touchdown, after which the space shuttle performs a landing in almost an identical fashion to a conventional aircraft.
Although the space shuttle fleet is not operational anymore, many of its components and technology are used by NASA’s Artemis program, which will return humans to the moon on its Space Launch System (SLS).
3) SpaceX Falcon 9 First Stage Landing
On 21 December 2015, a privately owned company called SpaceX made history by becoming the first rocket manufacturer to successfully land a fully reusable first stage of a rocket.
It landed the rocket in the true sense of the word by firing its thrusters, extending its landing legs, and performing a soft touchdown. SpaceX (by now a household name) used its two-stage Falcon 9 rocket, of which the second stage continued into orbit with its payload.
This recovery method brings down the cost of a rocket launch since a rocket’s first stage, which is the most expensive part of a launch vehicle, can be refurbished and reused multiple times. Blue Origin’s New Shephard rocket uses the same technique.
The re-entry and landing procedure of a Falcon 9 First Stage looks as follows:
- After launch, the rocket continues on its planned trajectory for the first 162 seconds, after which the first-stage engines cut out (a process called MECO) and the first stage separate from the second stage.
- After separation, the second stage continues into orbit while the first stage continues to its apogee of approximately 120 kilometers (74.5 miles) before returning to the planet’s surface.
- Shortly before reaching its apogee, the rocket’s smaller cold thrusters flip the vehicle around to allow its main thrusters to face forward.
- At this point, the main thrusters fire to align the vehicle’s trajectory towards the landing site.
- As the vehicle starts reentering the atmosphere, the first stage’s grid fins are deployed to guide and steer the rocket.
- Upon reentry, the rocket fires its main engines again to slow the vehicle down.
- The rocket’s grid fins guide the vehicle throughout the rest of the descent.
- Seconds before touchdown, the vehicle fires its main thrusters one final time while deploying its landing legs to perform a soft landing on either an automated drone ship or landing site on land.
A similar technique will be deployed on SpaceX’s upcoming Starship Super Heavy launch vehicle to land the massive first-stage rocket. (SpaceX is also recovering its Falcon 9 payload fairings with the assistance of a parachute and recovery ship fitted with a net.)
(This method is one of several techniques currently used to retrieve a rocket for future reuse. Learn more about the importance of reusability and the various techniques currently used and in development to recover launch vehicles for future reuse in this in-depth article.)
4) How Vulcan’s Inflatable Heat Shield With Helicopter Recovery Works
United Launch Alliance (ULA) is in the process of phasing out its Atlas V and Delta IV Heavy launch vehicles and will replace them with the Vulcan Centaur rocket, currently in development at the company’s manufacturing facility in Decatur, Alabama (USA).
Unlike its predecessors, ULA plans to capture and reuse the Vulcan’s two BE-4 first-stage thrusters by using a revolutionary but yet unproven technique, which includes an inflatable heat shield, a parafoil, and a helicopter.
In practice, capturing and recovering the Vulcan’s first-stage thrusters will look as follows:
- When the rocket’s first stage separates from its second stage, an inflatable heat shield is deployed to protect the thrusters from the heat generated as the vehicle passes through the upper atmospheric air at hypersonic speeds.
- At a height of approximately 30 kilometers (100 000 feet), after the vehicle cleared the part of the atmosphere where it experienced the most friction and heat buildup, the heat shield is ejected from the rest of the craft.
- Shortly afterward, a small ring parachute is released that will help to slow the craft down before the main parafoil deploys to allow it to steer and slow down even further.
- As soon as the first-stage thrusters and parachute are low enough in the atmosphere, a helicopter on location is dispatched with a fixed pole and hook to grab the parachute and its payload.
- The helicopter flies the payload to a barge located nearby, where it is secured and returned to land to be refurbished for future launches.
This method may seem like an outlandish idea, but the principle has already been proven decades ago when the United States Air Force implemented this principle to retrieve high-resolution film from space.
In the 1960s (long before the age of digital photography), high-resolution film, captured by spacecraft, was housed in capsules that could survive atmospheric re-entry. After deploying its parachute, the capsule was intercepted by a passing aircraft equipped with a hook.
This capturing and retrieving technique formed part of the United States Air Force and Central Intelligence Agency’s (CIA) Corona Program.
It consisted of a series of reconnaissance satellites that flew over and performed photographic surveillance of the former Soviet Union and China. The high-resolution images were recovered by making use of this innovative capturing method.
5) Rocket Lab’s Electron First Stage Capture With Helicopter
Rocket Lab, operating out of New Zealand, is having tremendous success with its small satellite launch vehicle, the Electron. Although not originally designed to be reusable, the company is experimenting with recovering its first-stage booster for reuse.
With more than 20 launches and multiple first-stage recoveries from the ocean under its belt, Rocket Lab is optimistic that its first-stage booster is tough enough to survive reentry with the assistance of a heat shield at its base.
The capture and recovery method of the Electron rocket looks almost identical to that of ULA’s Vulcan rocket, but without the need for a large complex inflatable heat shield. The procedure will look as follows:
- After 2½ minutes into the flight at approximately 80 kilometers (50 miles), the first stage separates from the second stage and commences its return to the planet’s surface.
- After the vehicle slowed down to below Mach 2, a drogue parachute is deployed to slow it down even further and stabilize the craft.
- When the first-stage booster slowed down enough, the main parachute is deployed for the final part of the descent and prepares the assembly for capturing and recovery.
- At this point, a helicopter is dispatched from a recovery ship that will “catch” the parachute with a hook and cable (similar to the recovery procedure of the Vulcan rocket).
- The first-stage booster is returned to and secured on the recovery ship, which will take it back to land for refurbishment.
At the time of writing, Rocket Lab had already recovered several first-stage boosters from the ocean for damage assessment and analysis. It also performed a simulated drop test where a helicopter successfully caught a rocket booster dropped from a higher altitude.
Although it is clear that no rocket that successfully made it to orbit and beyond has yet been able to return to Earth and land in its entirety, a lot of progress has been made over the last half-century.
From returning only the small command module of the 110 meters tall Saturn V rocket in the 1960s to SpaceX landing its entire first-stage boosters and catching its payload fairings, the future of rockets returning and landing safely on the planet’s surface looks promising.
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