History UsefulNotes / RocketsAndPropulsionMethods

[[https://en.wikipedia.org/wiki/Virgin_Orbit Virgin Orbit]] operates the [[https://en.wikipedia.org/wiki/LauncherOne LauncherOne]] air-launched rocket, the only such active rocket in the world as of 2022. (Pegasus, operated by Northrop Grumman, is technically still active but hasn't flown since 2021 and has no scheduled flights.) [=LauncherOne=] first reached orbit in 2021.

Soyuz is infamous for its longevity and has had high overall reliability, but there have been some notable failures. Most recently, the MS-10 mission to the ISS failed when a booster didn't detach from the core properly. The crew survived thanks to the Soyuz capsule's launch escape system.

The Japanese Aerospace Exploration Agency (UsefulNotes/{{JAXA}}) operates the H-II and H3 rocket families, built by Mitsubish Heavy Industries. The [[https://en.wikipedia.org/wiki/H-IIA H-IIA]] is currently in service, the [[https://en.wikipedia.org/wiki/H-IIB H-IIB]] made its last flight in 2020, and the [[https://en.wikipedia.org/wiki/H3_(rocket) H3]] is planned to go into service on February 12th, 2023.

The [[https://en.wikipedia.org/wiki/Saturn_V Saturn V]] rocket to this day retains the title of the largest and most powerful orbital rocket ever built and operated successfully by humans. Standing at 110.6 meters tall and capable of delivering over 7.5 million pounds (33 MN) of thrust, it was flown 13 times between 1967 and 1973 with a perfect operational record. (An engine shut down prematurely on Apollo 13 of all flights, but did not affect its performance.) Saturn V is of course best known for its role in the Apollo program, delivering U.S. astronauts to the Moon: the only humans to leave Earth orbit prior to the planned launch of Artemis II in 2024.

There are also political considerations around reusable rockets. State-sponsored space programs insulate themselves from politics to some extent by spreading their supply chains over many districts to engage as many constituents as possible and guarantee high-quality jobs. Every rocket reused is a rocket not built and potential money not being earned by voters.

One way to keep your margins high enough for landing is not to go to orbit at all. Such is the case with suborbital spacecraft, which don't need the high performance of orbital rockets because they use much less energy. Suborbital rockets (also known as sounding rockets) have their uses: monitoring weather, delivering experiments that need brief periods of free-fall, point to point transportation, and and space tourism.

To date, no nuclear pulse spacecraft has flown and international treaties against the deployment of nuclear arms in space may restrict the development of such a spacecraft for a long time to come (a lot of countries may get pretty nervous that a geopolitical rival gets a bunch of nuclear bombs in orbit). There's also the understandable problem that you wouldn't want to use it to get ''to'' space, or even in low Earth orbit, given the "minor" problems associated with setting off nuclear explosions in or near the atmosphere. Such a drive system would also require the construction of hundreds or thousands of times more nuclear bombs than currently exist today, with understandable political ramifications. Getting even a prototype working would require the agreement of the USA, China, Russia, France, Great Britain, India, Pakistan (and maybe Israel and North Korea), some of which are ''not'' on speaking terms. In addition the UN and the International Atomic Energy Agency would also need to be on-board, and several industrialized but non-nuclear countries (Canada, South Korea, Germany, Japan, Spain, Australia, New Zealand, etc...) would likely also have to be involved for resources and expertise. In other words, good luck.

A [[https://en.wikipedia.org/wiki/Solar_sail solar sail]] is designed to capture the flow of high-energy particles from the solar wind. A light sail is designed to capture the photons emitted by the Sun. A laser sail takes a light sail a step further by using a directed laser beam from a planet or satellite to generate thrust.

While solar and light sails have extremely low thrust and are impractical for human spaceflight, laser sails (powered by gigawatt laser arrays) have the potential to send our first relativistic spacecraft to other stars, being able to achieve velocities up to 10 percent of the speed of light, all without carrying or expending a drop of fuel, since their propulsion comes from an external source.

The best-known solar sail project to date is the [[https://en.wikipedia.org/wiki/Solar_sail#Planetary_Society_LightSail_Projects Planetary Society's LightSail]] spacecraft. [[https://en.wikipedia.org/wiki/LightSail#LightSail-2 LightSail-2]] was launched on a Falcon Heavy rocket in June 2019 and successfully demonstrated photonic propulsion in low Earth orbit.

While ion engines can have fuel efficiency many times that of chemical rocket engines, they have very low thrust, making them suitable only for maneuvering once a spacecraft has reached orbit. For this reason, they are also unsuitable for crewed spacecraft as their thrust is so low that it would take a long time to get anywhere. It is possible that future technology will improve ion engines to the point where they are practical for human interplanetary travel, but they will probably never be used to get off a planet into space.

* RP-1 or rocket-grade kerosene. This is essentially a highly refined jet fuel and is extremely common and cheap. It is liquid at room temperature, requiring no special storage, and so a fueled rocket can remain on the pad for days if necessary. It is more efficient than hypergolics but less than methane or hydrogen. The main problem with kerosene is its tendency to "coke", or generate long polymer chains that stick to the insides of engines and gum them up. This makes reuse of kerosene engines difficult. Rocket grade gasoline or diesel fuel could in theory be used, but would perform about the same as kerosene so there is no point in developing them.

However, you need something to turn the pumps, and that something has to be powerful. There are two primary kinds of pumps: [[https://en.wikipedia.org/wiki/Turbopump turbopumps,]] which work by burning some of the fuel and oxidizer to make what is in effect a miniature rocket, the force from which turns the turbines that power the pumps; and [[https://en.wikipedia.org/wiki/Electric-pump-fed_engine electric pumps,]] which are driven by motors that are in turn powered by batteries. Batteries are heavy, and unlike propellants don't lose mass as they discharge, [[note]]Well, they do lose a ''little'' thanks to mass-energy equivalence, but it's small enough not to count here.[[/note]] so they are only suitable for smaller rockets.

There are examples of solid fuel rockets everywhere, from the [[https://en.wikipedia.org/wiki/AJ-60A AJ-60A motors]] on the [[https://en.wikipedia.org/wiki/Atlas_V Atlas V rocket]] to the [[https://en.wikipedia.org/wiki/Solid_rocket_booster solid rocket boosters ([=SRBs=])]] on the [[https://www.nasa.gov/mission_pages/shuttle/main/index.html Space Shuttle]] to the [[https://en.wikipedia.org/wiki/Minotaur_IV Minotaur IV,]] which is a rocket with four solid fuel stages. Solid fuel rockets have extremely high thrust-to-weight ratios and are thus ideal for accelerating extremely rapidly. However, they don't generate chemical energy as efficiently as liquid fuels, meaning they can get to orbit but not much more. Solid fuels have the advantage of being easy to store; there are usable solid rocket boosters dating back decades in the U.S. inventory.

** '''Delta-V''': This is a measurement of how much total change in velocity a rocket can achieve. A rocket with 8 km/s of delta-V can speed up (or slow down) by a ''total'' of eight kilometers per second with its available propellant. If that's not enough to get where you want to go, you're hosed.

** '''Thrust-to-weight ratio (TWR)''': The ratio of a rocket's thrust to its weight, typically measured at liftoff. If this value is less than one, the rocket cannot get off the ground. Rockets with a liftoff TWR of less than one (and sometimes even more than one) will use detachable solid rocket boosters ([=SRBs=]) for an initial kick to the point where their main engines can take over. TWR increases as a rocket burns off its propellant supply.

** The RS-68 engine on the Delta IV uses ablative cooling, making its exhaust slightly orange in color when it would otherwise be mostly blue, as it it is composed almost entirely of water vapor.

To date, no nuclear pulse spacecraft has flown and international treaties against the deployment of nuclear arms in space may restrict the development of such a spacecraft for a long time to come. There's also the understandable problem that you wouldn't want to use it to get ''to'' space, or even in low Earth orbit, given the "minor" problems associated with setting off nuclear explosions in or near the atmosphere. Such a drive system would also require the construction of hundreds or thousands of times more nuclear bombs than currently exist today, with understandable political ramifications.

The Orion drive is the only method of getting to another solar system within a human lifetime that we could potentially achieve with current technology.

The [[https://en.wikipedia.org/wiki/Saturn_V Saturn V]] rocket to this day retains the title of the largest and most powerful orbital rocket ever built and operated successfully by humans. Standing at 110.6 meters tall and capable of delivering over 7.5 million pounds (33 MN) of thrust, it was flown 13 times between 1967 and 1973 with a perfect operational record. (An engine shut down prematurely on one flight, but did not affect its performance.) Saturn V is of course best known for its role in the Apollo program, delivering U.S. astronauts to the Moon: the only humans to leave Earth orbit prior to the planned launch of Artemis II in 2024.

Its safety record notwithstanding, the biggest problem with the Shuttle was its cost. Nominally around 500 million USD per launch, the total price tag over its lifetime averaged out to nearly 1.6 billion per launch, and it never met its goal of rapid reuse, flying no more than nine missions per year even with four operational orbiters. Simply put, it cost far more to refurbish each Shuttle than was originally promised, and safety issues plagued the program throughout its lifetime. Every incident led to more time and money spent on refurbishment and inspection, and as the existing orbiters reached the end of their lifespans, no new ones were built to replace them.

[[https://en.wikipedia.org/wiki/Ariane_5 Ariane 5]] is a heavy-lift vehicle designed primarily for geostationary launches. Using two solid rocket boosters and a hydrolox main stage equipped with a Vulcain 2 engine, it can lift over 20,000 kg to LEO and 10,865 kg to GTO. The second stage can be either a hydrazine (hypergolic) or hydrolox version. The first-ever Ariane 5 launch failed mid-flight due to a software bug, becoming one of the most costly programming errors in history. It is expected to be retired in favor of the upcoming Ariane 6.

[[https://en.wikipedia.org/wiki/Antares_(rocket) Antares,]] built by Northrop Grumman, is a medium-lift rocket mainly used for [[https://en.wikipedia.org/wiki/Cygnus_spacecraft Cygnus]] resupply launches to the International Space Station. Its maximum payload to LEO is 8,000 kg. The first stage is powered by two RD-181 kerolox engines and the second stage uses a Castor 30B solid fuel motor. It has optional third stages as well. Antares previously used [=AJ26=] engines adapted from Russian NK-33s, but when one of these failed catastrophically in-flight in 2016, they were replaced with the RD-181. In 2021, geopolitical tensions with Russia forced the RD-181 into retirement, causing Northrop to redesign Antares almost from scratch with the help of Firefly Aerospace.

[[https://en.wikipedia.org/wiki/Atlas_V Atlas V,]] built by United Launch Alliance (ULA), is the final iteration of the Atlas family of rockets, which dates all the way back to the 1950s. The current version is powered by a single, twin-nozzle RD-180 kerolox engine, with a Centaur upper stage powered by an RL-10 hydrolox engine and optional solid rocket boosters for additional thrust at liftoff. It has a wide variety of configurations supporting payloads of up to 20,520 kg to LEO and is capable of interplanetary missions. Atlas V has a perfect operational record over more than 80 missions. It is the second most used active commercial rocket in the U.S.. Atlas V will be replaced by Vulcan-Centaur (see below).

In 2016, [=SpaceX=] achieved the first ever propulsive landing of an orbital rocket booster, and now routinely lands and reuses them, with the goal of 10 flights per booster before extensive refurbishment. It also achieved the first recovery and reuse of a rocket fairing. The second stage is not recoverable. Falcon 9 became the first commercial rocket to lift humans to orbit on May 30, 2020, on the [[https://en.wikipedia.org/wiki/Crew_Dragon_Demo-2 Demo-2 mission.]]

The SLS program has faced criticism over its handling and practicality. The rocket alone costs 1.5 billion USD and more than 20 billion will have been spent on its development by the time it launches. In combination with all other components of the Artemis program (the Orion capsule and the Human Landing System), each Moon mission will initially cost a more than 4 billion USD before dropping to 2 billion USD when the total price is averaged out. This is less than Apollo, which cost close to 10 billion USD when adjusted for 2020, but even so is seen by many as unsustainable.

[[https://en.wikipedia.org/wiki/Falcon_Heavy Falcon Heavy]] is a variant of Falcon 9 intended for high orbit and interplanetary missions, consisting of three Falcon 9 first-stage cores strapped together. Falcon Heavy is the most powerful operational rocket as of 2022 (second only to the Saturn V on the all-time scoreboard, although SLS will retake the crown when Artemis I launches), able to carry about 30,000 kg to LEO in fully recoverable mode, and up to 63,800 kg in fully expendable mode. It has flown three times as of 2020, all successfully. The side boosters detach first and perform a return to launch site maneuver, with a perfect landing record (so far). The center core flies farther and has landed in only one of three attempts.

Falcon Heavy is expected to be extensively involved in supporting NASA's Artemis program, including launching supply craft to the Lunar Gateway as well as components of the Gateway itself.

Blue Origin, owned and operated by Jeff Bezos, is developing two orbital rockets. The first of these is named [[https://en.wikipedia.org/wiki/New_Glenn New Glenn,]] a heavy-lift vehicle planned to enter service in 2023. New Glenn is expected to have a payload of 45,000 kg to LEO and will be partially reusable. Its first stage booster will land propulsively on an ocean platform in much the same way as Falcon 9. The second stage is expendable, although Blue Origin is developing a reusable version. New Glenn's first stage will be powered by seven BE-4 engines using methalox, and the second stage will be powered by two BE-3U engines burning hydrolox.

Additional criticism targets its cadence, as it will be capable of no more than one flight per year, though production capacity to allow for 1.5/2 SLS’s per year is in the works. The SLS is also not very ambitious, reusing significant amounts of technology from the Space Shuttle program. It is a "safe choice", but faced with upcoming competition from commercial rockets such as [=SpaceX=]'s Starship, it may be obsolete before it ever gets to the Moon. Time will tell which approach will be successful.

[[https://en.wikipedia.org/wiki/SpaceX_Starship Starship,]] under development by [=SpaceX=], is a super-heavy-lift launch vehicle that is intended for full reuse. Its first stage is the Superheavy booster, powered by 31 Raptor engines burning methalox, and its second stage is the Starship vehicle, powered by six Raptor engines burning methalox. Several suborbital prototypes have flown, and the first orbital launch is expected in late 2022 or early 2023.

Starship's designed payload capacity is at least 100,000 kg and potentially up to 158,000 kg to LEO, and if its orbital refueling program succeeds, it will be able to transport that same payload anywhere in the Solar System. When operational, the full Starship/Superheavy stack will be the largest and most powerful rocket ever built, with nearly twice the thrust at liftoff of the Saturn V.

In contrast to SLS, which is expendable, meant for dedicated NASA missions, and will fly no more than once per year, Starship is designed for mass production and full and rapid reuse. Each booster will carry its Starship to space, return to land at its launch site, be refueled, and launch again, up to eight times per day. Each Starship will ascend to orbit and await one or more tanker missions that will dock, refuel it, then return to land. The Starship will then go to the Moon, Mars, or other destinations.

There will also be a version of Starship designed for suborbital, point-to-point flight on Earth, completing intercontinental trips in under an hour that could take 12 to 24 hours by commercial jet.

This rapid reuse is expected to reduce the cost of access to space by at least an order of magnitude, if it works, which is not guaranteed at this point. It would, if successful, be a revolutionary vehicle.

Vulcan Centaur will replace Atlas V in ULA's lineup, and will have a Heavy variant that is expected to replace Delta IV Heavy, used for high orbit and interplanetary missions.