During the late 20th Century, rockets were largely considered expendable. But since the turn of the Century, as private space launch providers started entering the arena, the importance of cost & reusability became obvious.
Currently, orbital rockets are only partially reusable, with the first-stage boosters, payload fairings, and solid boosters the only sections that are successfully recovered and reused. The primary method for recovering is via a controlled descent and touchdown via parachute or a landing burn.
Imagine a major airline had to discard and replace each of its aircraft after it had flown only once. You don’t have to be an aviation expert or economist to know that any such airline will not exist for long. However, this is exactly what happens with most orbital rockets.
Apart from less than a handful of launch providers, the vast majority of orbital launch vehicles, costing hundreds of millions of dollars, are used only once and are either left as space debris in orbit around Earth or return and burn up in the planet’s atmosphere.
Nations around the world only started taking a serious look at spaceflight and initiated programs to develop orbital launch facilities and vehicles that could reach Space, enter Low Earth Orbit, and go beyond shortly after World War II.
The United States Of America and the former Soviet Union employed German scientists who worked on the country’s rocket program during the war & used them to advance their own space programs.
In 1955, the United States announced its intention to put a satellite in orbit, to which the Soviet Union responded by being the nation to launch the world’s first satellite into orbit in 1957, signaling the start of the Space Race between the two nations.
During this period, all attention was focused on the development of vehicles that could push the boundaries of the technology of the day, and all the rockets and spacecraft used during the period were considered expendable.
It was only with the development of the Space Shuttle in the 1970s, also known as the Space Transport System (STS), that the idea of a partially reusable launch system became a reality.
The first shuttle, Columbia, launched from Kennedy Space Center on 12 April 1981. The program operated from 1981 – 2012 but proved to be too costly with slower than required turnaround times. Two shuttles also suffered catastrophic failures, with 14 lives lost in total.
However, during the early 2000s, private space companies like SpaceX entered the arena. As private companies, these corporations didn’t have the “unlimited” financial resources the big government-funded space agencies enjoyed during the 1960s and 70s.
Saving costs is a huge priority for these private agencies with more limited resources and funding than the large “state actors” in the industry. Reusability plays a huge role in their strategy and has already yielded significant results, as the following section illustrates.
How Rockets Are Recovered And Reused
Compared to other developments in spaceflight, reusability is still in its infancy. However, that’s not to say it was never previously considered or paid attention to. Compared to the rapid development of new technology of the day, it simply wasn’t as high a priority.
The Space Shuttle, a concept that was already proposed during the 1950s and developed during the 1970s, can be considered the first true partially reusable launch vehicle. As previously mentioned, the first shuttle, Columbia, launched on 12 April 1981.
Today, we mostly think of the spectacular landings of SpaceX’s Falcon 9 first stages when we think of reusability. The extensive live coverage of atmospheric re-entries and dramatic landings almost makes one forget about other means of recovering a rocket for reuse.
However, this is not the only means of recovering and reusing launch vehicles. To get the full picture of the different methods in which orbital rockets (or sections of them) are recovered and reused, one needs to look at all previous, current, and new techniques utilized:
- Parachute Deployment
- Glider Type Landing
- Powered Soft Landing
- Inflatable Heat Shield
Whenever a spacecraft returns to the Earth’s surface, it travels at speeds of 28 000 km/h (17 500 mph) when re-entering the atmosphere. Hitting our dense atmosphere at these high speeds will cause it to burn up without the assistance of extensive protection.
Heat shields made of strong heat-resistant materials like silica tiles, as well as ablative materials (to carry the heat away from the vehicle’s surface), are used on space capsules to return crews and cargo back to Earth. It was also extensively used by the Space Shuttle.
However, once in the atmosphere, other means of safely reaching the surface must be used to protect and preserve a spacecraft or rocket to prevent it from falling to the ground and being destroyed on impact.
By taking a closer look at each of the four methods used for safely returning a craft back to the surface for future reuse, one will get a better understanding of how each method works:
1) Parachute Deployment
One of the earliest methods used to safely return crewed and uncrewed vehicles back to the planet’s surface, which is still widely used today, is the use of parachutes.
This method was also used to return the solid rocket boosters of the Space Shuttle back to the surface for refurbishment and reuse. Since they were still in the atmosphere at a height of 45 km (28 miles) when separating from the orbiter, they didn’t require thermal protection.
However, at this point, they were still traveling too fast to deploy their main parachutes safely. As a result, drogue parachutes were used to slow the craft down to a safe speed, at which point the main parachutes were deployed.
The main parachutes allowed the solid rocket boosters to descend safely and make a splashdown in the ocean. They were retrieved by a specially equipped ship and towed back to shore before returning to the manufacturing facility for refurbishment and later reuse.
(Solid rockets were reused several times for shuttle missions, but the corrosion caused by seawater and the fact that the rocket casing had to be refilled with solid rocket propellant made refurbishment so extensive and expensive that any cost saving was negligible.)
Parachutes are also used to safely return and reuse the first-stage boosters of smaller launch vehicles. At the time of writing, private space launch provider Rocket Lab has already used this technique to retrieve & reuse one of the first-stage boosters of its Electron rocket.
2) Glider Type Landing
Although the program was canceled in 2012 and the fleet of shuttles retired, the Space Shuttle is the most well-known and, to date, only launch vehicle to use this method to reuse a spacecraft multiple times successfully.
It had the shape of an aircraft with wings and a tailfin which allowed it to maneuver like a conventional aircraft when operating within the Earth’s atmosphere after re-entry.
Although the space shuttle was fitted with three hydrogen-fueled rocket boosters, it was mainly used during liftoff, assisted by two solid rocket boosters, to launch the vehicle into orbit. It lifted off vertically like a rocket, with the two solid boosters flanking the vehicle.
The solid rocket boosters were ejected away from the vehicle approximately 2 minutes into flight while the orbiter (shuttle) continued to orbit on top of the external propellant tank. After around 8 minutes, the shuttle’s external tank also separated from the vehicle.
Post-launch, and after the vehicle established its intended orbit, the vehicle’s three main engines were not used again. Upon re-entry, only the OMS (orbital maneuvering system) thrusters fired to orientate the vehicle and slow it down.
During re-entry, the shuttle entered the atmosphere with its nose forward, tilted up at an angle of 40° so that the heat shield below the vehicle absorbed the majority of heat experienced during this process.
After this critical part of re-entry, the shuttle pitched its nose down and started following its flight path to the designated runway, using its airplane-like structure to glide to the airstrip and make a landing like a conventional aircraft.
After landing, the shuttle was returned to the appropriate facilities for servicing, cleaning, and any refurbishing that was needed before being prepared for the next launch.
In 1988, the now former Soviet Union successfully launched a similar orbiter, called the Buran, on top of an Energia rocket and safely returned it to the planet’s surface, also landing in a horizontal fashion like a conventional aircraft.
However, the Buran only flew once and was never reused. It was also uncrewed during its first and only flight. It was essentially just a glider since it wasn’t powered like the Space Shuttle and only had smaller thrusters for its OMS (orbital maneuvering system).
Although no launch vehicle currently uses this method for returning to the surface anymore, and no plans are currently being developed for a similar vehicle, the concept has been proven as workable, leaving the path open for possible future developments.
3) Powered Soft Landing
As previously mentioned, when thinking about rocket usability, the first-stage landings of SpaceX’s Falcon 9 rockets immediately spring to mind. This method of safely bringing a rocket section back to the ground has more advantages than simply keeping it intact.
By using landing legs and performing a landing burn, the rocket can perform a soft touch-down without the first stage booster section touching a hard or any other surface, which protects the engine and nozzles from damage upon contact.
Landing on land or a barge at sea also prevents the rocket from splashing down in the ocean. Saltwater is highly corrosive to rocket engines, requiring extensive refurbishment. Preventing any contact with it makes it much cheaper to clean & prepare for future reuse.
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.
(This landing procedure is an excerpt taken from another article on this site focussing on the various ways in which spacecraft return to Earth’s surface. To learn more, you can read the full in-depth article here.)
4) Inflatable Heat Shield
Using a heat shield or performing a powered soft landing is not the only way to safely bring sections of a launch vehicle back to the planet’s surface for reuse at a later stage.
Sometimes, a combination of the two or a hybrid option can be a good practical solution. And this is exactly what the United Launch Alliance (ULA) are developing to reuse their BE-4 first-stage boosters on their upcoming Vulcan rocket.
ULA plans to capture and reuse the Vulcan’s first-stage thrusters by using a revolutionary yet unproven technique, which includes an inflatable heat shield, a parafoil, and a helicopter. The technology is known as SMART (Sensible, Modular, Autonomous Return Technology).
In theory, 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 clears 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 was already 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.
On 10 November 2022, NASA also successfully tested a six-meter wide inflatable heat shield by releasing it from the Centaur upper stage of an Atlas V rocket. It survived re-entry and safely landed in the ocean after parachutes were deployed to slow down its descent.
Orbital Rockets Successfully Reused And Reusable Rockets In Development
Currently, there are literally less than a handful of orbital rockets that were and are currently partially reused. No launch vehicle has been recovered and reused in its entirety yet. As already mentioned, the launch vehicle that has been successfully reused to date are:
- Space Shuttle
- SpaceX Falcon 9
- Rocket Lab Electron
This does not mean that things are not changing. At the time of writing, multiple new orbital launch vehicles are in development that will have some kind of reusable technology. The three most prominent vehicles that fall within this category are:
- ULA Vulcan
- Blue Origin Blue Glenn
- SpaceX Starship
The technology the United Launch Alliance (ULA) is planning to use on its upcoming Vulcan rocket has already been highlighted. SpaceX’s Starship and Blue Origin’s Blue Glenn will use the same type of “powered soft landing” currently used by the Falcon 9 rocket’s first stage.
As this article clearly illustrated, reusability in spaceflight hasn’t been a priority in the early years of space exploration, when all parties involved were primarily focused on developing launch vehicles as fast as possible to reach space, orbit the planet, and travel to the Moon.
Since the turn of the century and the growing involvement of private companies, reusability has come to the foreground, and one will be hard-pressed to find a new orbital rocket in development that doesn’t feature some kind of technology that will make it at least partially reusable.
This article was originally published on headedforspace.com. If it is now published on any other site, it was done without permission from the copyright owner.