The Largest Launch Vehicles in Service - 1957 to the Present

With the successful launch of NASA’s Artemis I test flight, we now have a new holder of the title “the largest launch vehicle in service”: the Space Launch System (SLS) Block 1 super heavy-lift launch vehicle. With a low Earth orbit (LEO) payload capability of 95,000 kilograms, it easily displaced the Falcon Heavy, with its 63,800-kilogram maximum payload, which held the title since its first launch on February 6, 2018. While SLS is the uncontested largest launch vehicle in currently in service (as measured by LEO payload capability), there has been a long list of past holders of this title stretching back almost two thirds of a century to the very beginning of the Space Age.

 

The Soviet Union’s R-7 Rocket Family

The first rocket to hold the title of “the largest launch vehicle in service” was the 8K71PS which launched the first satellite, Sputnik, on October 4, 1957 (see “Sputnik: The Launch of the Space Age”). Designed and built by OKB-1 (Experimental Design Bureau 1) headed by the legendary Chief Designer Sergei Korolev, this launch vehicle was based on the R-7 ICBM also known as the 8K71. This unique rocket used a parallel staging concept where all of the engines of the Blok A core and its four tapered boosters (called Blok B, V, G and D) ignited at liftoff to produce 3,904 kilonewtons of thrust. This was done to avoid the then-untried procedure of igniting large rocket engines at altitude during flight. The four boosters would drop away after they had exhausted their kerosene and liquid oxygen (LOX) propellants leaving the Blok A core to continue for the rest of the ascent. In its role as an ICBM, the R-7 could hurl a 5,400-kilogram warhead with a yield of five megatons over a range of 8,000 kilometers.

Originally, Korolev and his team had planned to launch their first satellite using a purpose-built variant of their ICBM designated the 8A91. Delays in its development prompted a decision to strip all nonessential systems from an 8K71 and modify it to become the 8K71PS satellite launch vehicle in order to orbit a small test satellite as soon as possible. While the 83-kilogram mass of Sputnik was far greater than the approximately ten-kilogram payload capability of America’s first satellite launch vehicles (see “Vanguard TV-3: America’s First Satellite Launch Attempt” and “Explorer 1: America’s First Satellite”), this mass hardly pushed the limits of the 8K71PS design. On November 3, 1957 the second 8K71PS launched Sputnik 2 with a mass of 508 kilograms into orbit carrying a dog (see “Sputnik 2: The First Animal in Orbit”). With the more capable 8A91 finally ready in early 1958, Korolev and his team were able to orbit the 1,327 kilogram Sputnik 3 on their second (and last) launch of their purpose-built satellite launch vehicle on May 15, 1958 (see “Sputnik 3: The First Orbiting Geophysical Laboratory“).

With the limits of the basic two-stage R-7 design reached with the 8A91, a new approach was needed to increase the usable orbital payload. The 8K71 Blok A core was adapted to carry a small upper stage designated Blok E which would ignite at altitude after core burnout. Called the 8K72, the first mission of this rocket was to launch the 170-kilogram E-1 lunar probes on a direct ascent trajectory to impact the Moon. With a liftoff thrust now increased to 3,998 kilonewtons, the first launch of the 8K72 on August 18, 1958 was unsuccessful as were the following three launch attempts (see “The First Race to the Moon: Getting Off the Ground“). The first fully successful launch of the 8K72 was on January 2, 1959 when Luna 1 was sent to the Moon (see “The First Race to the Moon: Reaching our Neighbor“).

With its greatly enhanced performance compared to the two-stage variants of the R-7, the 8K72 was quickly adapted to launch payloads of up to about 4,700 kilograms into low Earth orbit. The first orbital mission of the 8K72 launched a prototype of the Vostok manned spacecraft called Korabl Sputnik 1 on May 15, 1960 (see “Korabl Sputnik & The Origin of the Vosotok Program“). Additional upgrades to the rocket resulted in the 8K72K (better known as the “Vostok”) which had its first successful launch on March 9, 1961 when it sent Korabl Sputnik 4 into orbit. The 8K72K was later used to launch the Soviet’s crewed Vostok missions through 1963.

In parallel with the development of the 8K72K, Korolev and his team at OKB-1 were busy working on still more powerful variants of the R-7 designed to launch probes to the planets. Engineers started with an improved version of their R-7 ICBM called the R-7A (or 8K74) whose core and four strap on boosters now produced 4,020 kilonewtons at launch. To this they added a new third stage called Blok I which was a significantly enlarged version of the second stage of the R-9A (or 8K75) ICBM also being developed at OKB-1. The first three stages of this new rocket, called 8K78, were designed to place an escape stage, known as Blok L, and its payload into a temporary parking orbit before the stage would ignite to send its payload to the Moon or planets.

The first launch attempts of the 8K78 on October 10 and 14, 1960 failed to reach orbit with their Mars-bound 1M spacecraft (see “The First Mars Mission Attempts”). The third launch of the 8K78 on February 4, 1961 managed to place the Blok L escape stage with its 1VA Venus probe into orbit. With a total mass of 6,483 kilograms, this was the heaviest object ever launched into LEO up to this time. Although the Blok L escape stage failed to operate on this flight, the launch of Venera 1 on February 12 was completely successful (see “Venera 1: The First Venus Mission Attempt”). The 8K78 would continue to be improved over the following years and eventually be named “Molniya” after the series of Soviet communications satellites which regularly used this launch vehicle.

While the four-stage 8K78 was designed specifically to launch payloads beyond LEO, it was not long before a three-stage variant was required for LEO payloads which were too heavy for the 8K72K and its successors to carry. Called the 11A57, the new rocket was designed from the start at OKB-1 to be a “unified launcher” that could orbit a range of different unmanned and manned payloads with masses of up to 6,000 kilograms and more. The configuration of the 11A57 was similar to the first three stages of the 8K78 and borrowed heavily from the technology being incorporated into the improved 8K78M. While the 11A57, with a liftoff thrust of 4,054 kilonewtons, had a superficial resemblance to the 8K78, it employed many new systems which were designed and built to a set of strict requirements known as the “3KA Regulations” so that the launch vehicle was man-rated from the start.

The first launch of the 11A57 orbited a prototype of the Vostok-based Zenit-4 photoreconnaissance satellite called Kosmos 22 on November 16, 1963 (see “Vostok’s Legacy”). Later the 11A57 was used to launch the first manned Voskhod mission on October 12, 1964 (see “The Mission of Voskhod 1”) earning the rocket its informal name of “Voskhod”. The 11A57 would eventually evolve into the 11A511 which was used to launch the first Soyuz missions into Earth orbit (see “The Avoidable Tragedy of Soyuz 1”). This first incarnation of the Soyuz rocket would continue to be incrementally improved over the next half a century eventually becoming the 14A14 “Soyuz-2” launch vehicle still used today to launch crews to the International Space Station (ISS).

 

The United States Takes the Lead

While the family of launch vehicles based on the R-7 ICBM gave the Soviet Union an early lead in payload capability to LEO and beyond, the US was quick to develop its own heavy lift capabilities to support increasingly ambitious national goals in space. Among the earliest American programs to produce heavy lift rockets was started in 1957 by German-American rocket pioneer Wernher von Braun and his team at what would become NASA’s Marshall Space Flight Center (MSFC). The family of proposed launch vehicles, called Saturn, would support a large range of NASA’s heavy lift requirements culminating in the Apollo lunar landing missions by the end of the 1960s.

The first of these new rockets to be developed at MSFC was designated the Saturn I. Like Korolev and his team at OKB-1, von Braun and his team relied on the cluster concept to produce a large launch vehicle quickly by incorporating as much proven technology as possible. The first stage structure of the Saturn I employed clusters of tanks originally used on Redstone and Jupiter missiles which had been developed in the 1950s by von Braun and his team when they were part of the Army Ballistic Missile Agency. While the availability of high-thrust engines was still some years off, the Saturn I used a cluster of eight H-1 engines which were improved versions of the earlier S-3D engine flown on the Jupiter IRBM. This gave the Saturn I an impressive liftoff thrust that eventually reached 6,690 kilonewtons.

The first stage of the Saturn I was flown successfully on four suborbital test flights with dummy upper stages between October 1961 and March 1963. With the flightworthiness of the Saturn I first stage and its cluster concept verified, it was ready for orbital test flights using a live second stage. Unlike the first stage which burned RP-1 grade kerosene and LOX, the second stage of the Saturn I (and subsequent Saturn rockets) used the high energy cryogenic combination of liquid hydrogen and LOX which produced half again as much thrust as a like mass of more conventional propellants. Using a cluster of six RL-10 engines of the sort first flown on NASA’s Centaur upper stage (see “The Launch of Atlas-Centaur 5”), the two-stage Saturn I was capable of placing 9,000 kilograms into LEO. This capability was tested for the first time on January 29, 1964 when Saturn SA-5 placed its spent upper stage and a load of sand ballast into LEO (see “The Coolest Rocket Ever”). The subsequent five flights of the Saturn I over the next year and a half launched boilerplate models of Apollo hardware to gather vital flight test data to support that program (see “The First Apollo Orbital Test Flight”). After completing this series of test flights, the uprated Saturn I (known as the Saturn IB) would be called into service for orbital test flights for the Apollo program.

Before the improved Saturn IB would fly for the first time, a competing family of rockets would seize the title for the largest launch vehicle in service from NASA. But instead of coming from the Soviet Union, this rocket was built for the US Air Force (USAF). During the late 1950s and early 1960s, the USAF performed a series of studies on the feasibility of adapting its Titan II ICBM for use as a satellite launch vehicle. One of the fruits of this effort was NASA’s selection of the Titan II as the Gemini Launch Vehicle (GLV) in October 1961 for their follow on to the Mercury program (see “The Launch of Gemini 1”). The eventual result of these studies into USAF launch needs was the Titan III family of rockets.

The Titan III launch vehicle concept was based on a modular approach that could lift payloads into a variety of orbits and included a heavy lift capability that was, for political reasons, independent of NASA’s Saturn family of launch vehicles. Literally at the core of all versions of the Titan III was a modified two-stage Titan II ICBM that was structurally reinforced to handle heavier payloads and extra stages. The initial heavy-lift version of this rocket, known as the Titan IIIC, strapped a pair of three-meter in diameter solid rocket motors to the sides of the core. Consisting of five-segments each that were assembled near the launch pad, this pair of solid rocket motors made up “Stage 0” of the Titan IIIC and generated a total of 10,500 kilonewtons of thrust at lift off making the Titan IIIC the most powerful rocket flown at the time. Topping the core of the Titan IIIC was an upper stage known as the Transtage. Capable of multiple restarts, the Transtage could deliver payloads into a range of Earth orbits or even beyond.

Although the USAF would typically use the Titan IIIC to place more modest sized payloads into medium to high Earth orbits, on paper it was capable of lifting up to 13,000 kilograms into LEO. This capability was tested on the maiden flight of the Titan IIIC launched on June 18, 1965 when it placed 9,700 kilogram of ballast in LEO – the heaviest payload ever orbited up to this time (see “The First Missions of the Titan IIIC”). While future variants of the Titan III were planned to have improved payload capabilities to LEO and beyond, NASA would launch still larger rockets before them in support of their Apollo program.

The next holder of the largest launch vehicle in service title went to NASA’s improved Saturn IB. Based on lessons learned from the Saturn I, the uprated first stage was lighter and employed eight uprated versions of the H-1 which initially produced a total of 7,100 kilonewtons of thrust at launch. A new, significantly enlarged second stage nearly identical to the third stage of the still larger Saturn V moon rocket boosted the LEO payload capability of the initial batch of five Saturn IB rockets to 17,000 kilograms – sufficient to launch either an Apollo Command-Service Module (CSM) or Lunar Module (LM) into LEO for initial test flights of this hardware.

The first flight of the Saturn IB was as part of the Apollo AS-201 mission which launched an Apollo CSM on an unmanned suborbital test flight on February 26, 1966 (see “The First Flight of the Apollo-Saturn IB”). The first orbital flight of the Saturn IB was the AS-203 mission launched on July 5, 1966. Since the objective of this mission was to test design features of its second stage, it did not carry a payload save for instrumentation and over eight metric tons of residual liquid hydrogen in its fuel tank (see “AS-203: NASA’s Odd Apollo Mission”). The first Saturn IB to orbit an actual spacecraft was the unmanned Apollo 5 mission launched on January 22, 1968 to test the first 14,300-kilogram LM flight article in LEO (see “Apollo 5: The First Flight of the Lunar Module”).

 

The Moon Rockets

As the initial batch of Saturn IB rockets were making their first flights, the title for the largest launch vehicle in service briefly went back to the Soviet Union. But unlike the R-7-based launch vehicles developed at OKB-1 (whose named changed to TsKBEM in March 1966 – the Russian acronym for “Central Construction Bureau of Experimental Machine Building”), this time a rival Soviet design bureau took the lead. TsKBM (Central Design Bureau for Machine Building, known as OKB-52 before 1965) under Vladimir Chelomei actively competed with Korolev’s OKB-1 in the development of ballistic missiles and spacecraft during the early years of the Space Age. One of the larger members of their family of modular “universal rockets” was the UR-500 which originally had been proposed as a super-heavy ICBM. This two-stage rocket would have been capable of hurling a thermonuclear warhead with a mass of about 12 metric tons and a yield of 100 megatons over a range of about 12,000 kilometers.

Although the UR-500 was never adopted by the Soviet government for use as an ICBM, Chelomei did secure approval to develop this rocket as the basis for a heavy lift satellite launch vehicle. The first launch of the UR-500 on July 16, 1965 orbited the 12,200 kilogram Proton 1 cosmic ray observatory. Although the Titan IIIC theoretically had better performance (especially just beyond LEO), Proton 1 took the record for the most massive usable payload launched into orbit up until that time (as opposed to inert ballast or publicly released in-orbit mass totals inflated by the inclusion of a spent upper stage). Although the rocket was originally to be named “Hercules”, instead the name “Proton” was adopted for the family of launch vehicles based on the UR-500.

Even though the UR-500 was a capable launch vehicle, it was retired after only a year following four launches (of which three succeeded) in favor of a more capable design known as the UR-500K (or 8K82K) to launch heavy payloads into LEO as well as Chelomei’s proposed LK-1 manned circumlunar ship. The Proton-K, as it is popularly called today, retained the first stage of the UR-500 with its six RD-253 engines producing 10,500 kilonewtons of thrust at lift off. The UR-500K now sported an enlarged second stage and included a new third stage to boost its initial LEO payload capability to 19,000 kilograms – slightly more than the first batch of Saturn IB rockets which flew from 1966 to 1968.

While the Proton-K would eventually be used to launch the first Soviet space stations and other manned spacecraft prototypes into LEO, its first use was for launching circumlunar spacecraft which would make a simple loop around the Moon and return to Earth. Much to Chelomei’s disappointment, the Proton-K would not launch his proposed circumlunar ship but the 7K-L1 originally designed by Korolev. Korolev’s circumlunar spacecraft consisted of a stripped down 7K-OK Soyuz without an orbital module and added a Blok D escape stage borrowed from the N-1 Moon rocket being developed by OKB-1/TsKBEM. The design of the 19,000 kilogram payload was tailored specifically for the Proton-K. The first launch of the Proton-K lifted the 7K-L1P/Blok D prototype known as Kosmos 146 into LEO on March 10, 1967. While Kosmos 146 met its mission objectives after the Blok D boosted the spacecraft into an elongated orbit, problems with this upper stage during the subsequent Kosmos 154 flight launched on April 8 doomed the flight and foreshadowed the many problems the Proton-K/D would experience in the years to come as the hurriedly developed rocket experienced numerous growing pains.

The ultimate heavy launch vehicle of the early years of the Space Age was NASA’s Saturn V. Developed by von Braun and his team at MSFC, the Saturn V was designed from the start to send the 44,000-kilogram Apollo CSM/LM to the Moon – a mass that exceeded even the LEO capabilities of all earlier rockets. Like the previous Saturn rockets, the first stage of the Saturn V burned RP-1 and LOX. But with the use of five huge F-1 engines, the liftoff thrust of the Saturn V was an unparalleled 33,950 kilonewtons. The upper two stages used the high energy propellants liquid hydrogen and LOX for a set of five J-2 engines in the second stage and a single J-2 for the third (which had already been flown as the second stage of the Saturn IB).

During an Apollo lunar mission, the first two stages and a short burn of the third stage would place the last stage and the Apollo into a temporary LEO. After reaching the proper position, the third stage would reignite to send the Apollo CSM/LM to the Moon. Used instead to launch a payload into LEO, the Saturn V could orbit about 118,000 kilograms. The first launch of the Saturn V took place on November 9, 1967 for the highly successful unmanned Apollo 4 mission (see “Apollo 4: The First Flight of the Saturn V”). Although some problems were encountered with the Saturn V during the unmanned Apollo 6 mission launched on April 4, 1968 (see “Apollo 6: The Saturn V That Almost Failed“), the Saturn V went on to chalk up a string of successes during the actual manned Apollo lunar missions leading to the first manned lunar landing on July 20, 1969 and beyond.

In order to increase the payload capability to the Moon to almost 47,000 kilograms to support the more capable (and heavier) J-series missions starting with Apollo 15 launched on July 26, 1971, a number of improvements were made to the Saturn V. The stages were lighted by removing unneeded equipment and improved engines were used which increased the liftoff thrust to 35,445 kilonewtons. After the completion of the final Apollo lunar mission in December 1972, a two-stage version of the Saturn V was used to launch the 77,000 kilogram Skylab space station on May 14, 1973 (see “Rockets Falling from Orbit: The Saturn V That Launched NASA’s Skylab“). This would prove to be the final flight of the Saturn V as NASA turned its attention to the development of the Space Shuttle to support future heavy-lift requirements.

 

The Post-Apollo Era

After the retirement of the Saturn V, the title of the largest launch vehicle in service fell back to NASA’s Saturn IB. Improvements made to the second batch of this rocket, which made it first flight launching Skylab’s SL-2 mission on May 28, 1973, boosted the lift off thrust to 7,285 kilonewtons (see “SA-206: The Odyssey of a Saturn IB“). With a LEO payload capability now pushed up to 21,000 kilograms, it now just outperformed the Soviet Proton-K launch vehicle. But with the final launch of the Saturn IB in support of the Apollo-Soyuz Test Project (ASTP) on July 15, 1975, the last member of the Saturn family had been retired. As NASA waited for the availability of the Space Shuttle, they relied on the USAF Titan III family to meet its heavy lift requirements.

With the last of NASA’s Saturn rockets phased out of service, the world’s largest launch vehicle still flying once again became the Soviet Proton-K. Although it was used to launch an increasing range of heavy payloads into LEO and beyond, the Proton-K continued to experience a fair number of failures as problems were encountered and resolved. It was not until its 60^th launch on September 29, 1977 when a Proton-K orbited the 19,800-kilogram Salyut 6 space station that this rocket officially completed its state trails and was deemed to be as reliable as other launch vehicles around the world. The Proton-K would be incrementally improved over the years and decades to come and continues to be used to orbit payloads including Russian elements of the ISS.

With the long-delayed introduction of NASA’s Space Shuttle, the US would once again take the lead in LEO payload capability. Approved for development in 1972, the Space Shuttle was the first element of the Space Transportation System which promised to make missions to LEO and beyond more affordable and routine. The Space Shuttle consisted of a reusable, 80,000 kilogram space plane or Orbiter with a large cargo bay which could deploy payloads (and any additional rocket stages it needed) into LEO as well as retrieve payloads for return to Earth. The Orbiter included a trio of high-performance, reusable Space Shuttle Main Engines (SSME but now known today as the RS-25) which together generated a nominal thrust of about 5,000 kilonewtons at sea level. The liquid hydrogen and LOX propellants for these engines was supplied by a large external tank (ET) attached to the underside of the Shuttle during launch and ascent. Unlike the other elements of the Space Shuttle, it was decided not to recover the ET for practical reasons.

While the RS-25 engines of the Space Shuttle supplied most of the energy to reach orbit, they had insufficient performance to lift the orbiter and its fully loaded ET off of the ground. Attached to either side of the ET were a pair of Solid Rocket Boosters (SRBs) which generated 14,680 kilonewtons of thrust each at lift off. After about two minutes of flight, the SRBs were jettisoned and descended to the ocean below on parachutes where they would be recovered, refurbished and reused. Combined with the Orbiter’s RS-25 engines, the typical liftoff thrust of the Space Shuttle with all of its propulsion systems throttled up was 34,677 kilonewtons.

While theoretically the Space Shuttle could lift as much as 29,500 kilograms of payload into LEO, practical considerations meant that this figure would not be reached in actual applications. The first spaceworthy Orbiter, OV-102 better known as Columbia which made its maiden STS-1 flight on April 12, 1981, was capable of launching 21,104 kilograms of payload into a 204-kilometer orbit with an inclination of 28.5° assuming a five person crew. Each additional kilometer of altitude reduced this total by 25 kilograms while each additional crew member cut 230 kilograms. With the introduction of four more orbiters over the next decade which included improvements in structures and systems to decrease mass and improve performance, this LEO capability eventually climbed to 24,950 kilograms.

The original intent was for the Space Shuttle to replace all of America’s expendable launch vehicles (ELVs) in the belief that it would save launch costs and improve reliability. In the end this proved to be an unwise policy as it became apparent that the Space Shuttle was more expensive and took more effort to refurbish for reuse than had been originally anticipated. The loss of OV-099 Challenger along with its crew of seven and payload during the launch of the STS-51L mission on January 28, 1986 resulted in a 32-month stand down of the program as the causes of the accident were investigated and changes to the Shuttle design were made. In the wake of this tragedy, national launch policy was also officially changed with renewed efforts made to expand and update America’s families of ELVs. After a backlog of Shuttle-specific payloads were launched following the resumption of flights in September 1988, all other government and commercial satellites were transitioned back to ELVs. As time wore on, Orbiters and crews would only be risked on missions which could make use of the Shuttle’s unique capabilities to meet the nation’s space objectives.

During this time, Soviet design bureaus were busy developing their own heavy lift capabilities to compete with the STS. After the failure of their program to develop the Soviet N-1 Moon rocket, the successor of TsKBEM called RKK Energia commenced the development of a new launch vehicle family in 1976 to meet future heavy lift needs for the Soviet Union. Originally designated 11K25 but better known by the name “Energia”, this new Soviet rocket would be the first to use the high energy cryogenic propellants, liquid hydrogen and LOX. The large core stage of the Energia employed four RD-0102 engines to produce about 5,800 kilonewtons of thrust at sea level. In the baseline Energia design, four boosters using kerosene and LOX for propellants were strapped to the sides of the core. Each booster used a four-chamber RD-170 engine to produce about 7,250 kilonewtons at sea level. Combined with the core, whose engines would also ignite at launch, the Energia had a total liftoff thrust of 34,800 kilonewtons. Although an additional propulsive maneuver (from an extra stage or the payload) was needed to reach orbit, this baseline Energia design was capable of placing on the order of 100,000 kilograms into LEO.

The first test flight of the Energia came on May 15, 1987. While the new launch vehicle successfully completed its task, a guidance software error in the 80,000-kilogram Polyus spacecraft prevented the payload from reaching orbit. Energia’s second launch on November 15, 1988 was likewise successful orbiting the new Soviet Buran space shuttle on its first (and only) unmanned test flight in space. The 105,000-kilogram Buran OK-1K1 successfully completed two orbits before returning to an automated landing at the Baikonur Cosmodrome where it was launched 3½ hours earlier.

Although Energia had much promise, the declining economic and political situation in the Soviet Union prevented development of payloads and further launches. While there was some hope after the dissolution of the Soviet Union at the end of 1991 that Energia would fly again perhaps in a modified form, there were simply no resources available in Russia to continue the program. Energia’s strap on boosters, however, would serve as the basis of the Zenit family of Soviet (now Ukrainian) launch vehicles and its propulsion technology would be adapted into the two-chamber RD-180 used in the current incarnation of the American Atlas launch vehicle (see “A History of American Rocket Engine Development”). With Energia quietly retired, the US Space Shuttle once again held the mantle of the largest launch vehicle in service.

 

A New Century

After a change in American launch policy following the Challenger accident, American aerospace companies embarked on a program to revive ELV production and new development of the Titan, Atlas and Delta families of rockets. Among these were new heavy lift variants that would equal or exceed the payload capabilities of the Space Shuttle which was no longer available to most customers. The ultimate example of this effort was the Delta IV Heavy.

Since its introduction in 1960, the Delta family of launch vehicles slowly evolved over time to include larger stages and increasing numbers of larger strap on solid rocket motors to increase its payload performance significantly over the decades. The Delta IV series was a completely new design using a two-stage core employing liquid hydrogen and LOX as propellants. The first stage, known as the Common Booster Core (CBC), has a RS-68 engine to produce 3,140 kilonewtons of thrust at lift off. Although not quite as efficient as the RS-25 used on the Space Shuttle, the RS-68 is a simpler design which produces higher thrust for much less cost. The upper stage of the Delta IV core uses a single RL-10B-2 engine whose design is based on the RL-10 engines used decades earlier starting with the Centaur and Saturn I second stage.

This basic core, known as the Delta IV Medium, can lift about 11,500 kilograms into LEO. With the addition of various strap on boosters, the payload capability of the Delta IV can be increased to meet various customer needs. The first Delta IV flight, using a variant known as the Delta IV Medium+(4,2) which sported a pair of GEM-60 strap on solid rocket motors to increase liftoff thrust, was launched from Cape Canaveral on November 20, 2002.

The largest member of this family, known as the Delta IV Heavy, uses the basic core with two RS-68-powered CBCs strapped to its sides. With a liftoff thrust of 9,420 kilonewtons, the Delta IV Heavy is capable of placing up to 28,800 kilograms into LEO from Cape Canaveral – somewhat more than the Space Shuttle which was retired in July 2011. The first launch of the Delta IV Heavy was on December 21, 2004 but bubbles in the LOX lines resulted in the early shutdown of the CBC strap ons and core preventing the test payloads from reaching orbit. The first fully successful Delta IV Heavy launch came on November 11, 2007 when it orbited the USAF DSP-23 early warning satellite. Since then, the Delta IV has been used primarily to launch heavy defense payloads from Cape Canaveral and Vandenberg Air Force Base as well as the first test flight of NASA’s Orion spacecraft on December 5, 2014 (see “From Apollo to Orion: Space Launch Complex 37”) and the Parker Solar Probe on August 12, 2018. The Delta IV Heavy is scheduled to be retired in 2024 after its 16^th launch.

Long before the retirement of the Delta IV Heavy, it lost its title as the largest launch vehicle in service to a new competitor, the Falcon Heavy. Developed and built by aerospace upstart SpaceX founded in 2002 by entrepreneur Elon Musk, the development of the Falcon Heavy was announced in 2011. At the core of the Falcon Heavy is a modified two-stage Falcon 9 launch vehicle which made its first flight on June 4, 2010. The current FT Block 5 version of the Falcon 9, which has been in use since 2018, sports a cluster of 9 Merlin 1D+ engines burning RP-1 and LOX to generate 7,600 kilonewtons of thrust at liftoff. With an LEO payload capability of up to 22,800 kilograms, this medium-lift launch vehicle has been used to launch payloads ranging from communication satellites to the Crew Dragon spacecraft (also developed by SpaceX) used to ferry crews to the International Space Station. The Falcon 9 has revolutionized the launch industry by offering launches for $67 million – just a fraction of the price of earlier legacy launch providers. SpaceX has been able to achieve these low costs, in part, by making the first stage of the Falcon 9 recoverable and reusable.

In the Falcon Heavy configuration, a pair of Falcon 9 first stages were added to the sides of the Falcon 9 core much as was done with the Delta IV Heavy. Using a total of 27 Merlin 1D+ engines, the Falcon 9 Heavy generates 22,800 kilonewtons of thrust at liftoff and is capable of delivering up to 63,800 kilograms of payload into LEO. With its first test flight on February 6, 2018, the Falcon Heavy became the new titleholder of the largest launch vehicle in service. Because of its launch cost of as low as $97 million, with the reuse of its boosters, the SpaceX Falcon Heavy is making significant inroads into the heavy-lift launch market with missions for commercial customers as well as NASA and the US Department of Defense.

 

The Return of the Moon Rockets

By the turn of the century, the world’s various spacefaring powers started setting their sights on crewed missions to the Moon and beyond. As had happened in the 1960s, there was a need to develop much larger launch vehicles with LEO payload capabilities of 100 metric tons and greater – far beyond the lift capabilities of existing launch vehicles. In the United States, studies were performed between 2005 and 2010 for the Constellation program which would use hardware derived from the Saturn V and soon-to-be-ended Space Shuttle program to support missions to the ISS, the Moon, Mars, and even near Earth asteroids. In 2010, Constellation was cancelled due to being over budget, behind schedule, and lacking in innovation. It was subsequently replaced in 2011 by what would eventually become today’s Artemis program.

One of the key components of this new program was the Space Launch System (SLS). Based on decades of various studies on the use of Space Shuttle technology to build a new super heavy-lift launch vehicle capability, including work done on the Ares V rocket for the Constellation program, the SLS would borrow heavily from Space Shuttle hardware. The core stage structure was derived from the Space Shuttle’s External Tank to supply liquid hydrogen and LOX to a quartet of modified RS-25D engines originally used on the Space Shuttle Orbiters. With a total thrust of 9,124 kilonewtons, these high performance engines do not provide enough thrust to lift the SLS off the launch pad, as was the case with the Space Shuttle. Strapped to the sides of the SLS core stage are a pair of five-segment solid rocket boosters derived from the four-segment design used on the Space Shuttle. With all four RS-25D engines and the pair of boosters, the total liftoff thrust of the initial version of the SLS is 39,000 kilonewtons.

The initial version of the SLS, like the one launched on November 16, 2022 for the Artemis I mission, is a Block 1 design using an Interim Cryogenic Propulsion Stage (ICPS) powered by a single RL10B-2 engine as an upper stage. In this configuration, the SLS Block 1 can lift 95,000 kilograms into LEO. The Block 1B design, using the larger Exploration Upper Stage (EUS), will be able to lift 105,000 kilograms into LEO and is expected to be first used on the Artemis 4 mission currently scheduled for launch in 2026. The SLS Block 2 will incorporate a number of upgrades which will eventually boost the LEO payload capability to 130,000 kilograms to support more ambitious Artemis missions.

But before the more advanced versions of the SLS will have a chance to fly, it will likely lose its title of the largest launch vehicle in service to a competitor. SpaceX is making its final preparations to launch its Starship launch vehicle on its first orbital test. Using a cluster of 33 Raptor engines burning liquid methane and LOX to produce 72,000 kilonewtons of thrust at liftoff, the Starship is designed to lift over 100,000 kilograms into LEO to support Elon Musk’s ambitious plans to reach the Moon and Mars. If SpaceX is able to deliver on its advertised $10 per kilogram to LEO cost goal, Starship promises to further revolutionize the space industry. Further into the future, the Chinese are developing a new rocket in the Long March series of launch vehicles to support their crewed lunar mission ambitions in the 2030s. The CZ-9 super heavy-lift rocket, with its first flight expected before the end of this decade, will have an LEO payload capability of up to 150,000 kilograms. With so much activity, it is only a matter of time before there is a new holder of the title of the largest launch vehicle in service.

 

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Detailed articles on these and other rockets can be found on the Drew Ex Machina Rockets & Propulsion page.