User:Chessrat/Interplanetary Transport System (2016 proposal)



The Interplanetary Transport System was a 2016 design for a privately-funded orbital launch vehicle and spaceship to be developed by SpaceX. The initial design objective of the vehicle was to launch a variety of SpaceX Interplanetary Transport System missions to Mars and other destinations in the beyond-Earth-orbit portion of the Solar System. Design work on the vehicle began in 2012 and first launch was not expected before the 2020s. In the event, the vehicle was not developed as planned in 2016.

The ITS launch vehicle was to be operated as a somewhat unusual two-stage rocket. Its first stage was to have been powered by 42 Raptor rocket engines—designed and manufactured by SpaceX—operating on densified methane/oxygen, propellants that have not been widely used as rocket propellants in the past. Like the Falcon 9 orbital launch vehicle that preceded it, the ITS launch vehicle's first stage design was intended to be reusable, following a return to the launch site and vertical landing following each launch. When announced, is was also designed to have a new feature for SpaceX launch vehicles: full reusability of even the second-stage and orbital spacecraft as well. The large payload capacity of the launch vehicle placed it into the super-heavy lift class, with the ability to place 300 tonnes into low Earth orbit in reusable configuration and 550 tonnes in expendable mode.

The second stage of the Earth launch vehicle was to have been one of two spacecraft that would be used on the launch vehicle. Both spacecraft, unusually, would also serve as upper stages during the launch. Both were to be powered by six vacuum-optimized Raptor rocket engines with three additional sea-level-nozzle Raptor engines for maneuvering. Thus, the element of the launch vehicle that provides second-stage acceleration to orbital velocity on all launches from Earth would also be used—in much longer-duration roles—as on-orbit spacecraft. The two model options were the ITS tanker, a transport carrier of propellant cargo to Earth orbit; and the Interplanetary spaceship, a very long-duration carrier of both passengers and space cargo to interplanetary destinations, and which would also serve as both a descent and ascent vehicle at Mars.

The high-level specifications for the vehicle were publicly announced in September 2016, but by July 2017, SpaceX had stated they would not build the super-heavy vehicles as previously planned, but would instead build a "still large" but much smaller launch vehicle first - that would be revealed as the BFR.

Description and technical specifications
The ITS launch vehicle stack was to be composed of two stages. The first stage would always have been an interplanetary booster while the second stage may have been either an interplanetary spaceship (for beyond-Earth-orbit missions) or an ITS tanker (for on-orbit propellant transfer operations).

Both stages of the ITS launch vehicle would have been powered by Raptor bipropellant liquid rocket engines utilizing the full flow staged combustion cycle with liquid methane fuel and liquid oxygen oxidizer. Both propellants would have been fully in the gas phase before entering the Raptor combustion chamber. Both stages would have utilized a bleed-off of the high-pressure gas for autogenous pressurization of the propellant tanks, eliminating the problematic high-pressure helium pressurization system used in the Falcon 9 launch vehicle. The self-pressurization gas system is a critical part of SpaceX strategy to reduce launch vehicle fluids from five in their legacy Falcon 9 vehicle family to just two, eliminating not only the helium tank pressurant but all hypergolic propellants as well as nitrogen for cold-gas reaction-control thrusters.

The overall launch vehicle height, first stage and the integrated second-stage/spacecraft, will be 122 m. Both stages of the ITS LV will be constructed of lightweight-yet-strong carbon fiber, even the deep-cryogenic propellant tanks, a major change from the aluminum-lithium alloy tank and structure material used in SpaceX Falcon 9 family of launch vehicles. Both stages are fully reusable and will land vertically, technology initially developed on the Falcon 9 launch vehicle first stages in 2012–2016. Gross liftoff mass is 10500 t at a lift-off thrust of 128 MN. ITS LV would be able to carry a payload to low-Earth orbit of 550 tonne in expendable-mode and 300 tonne in reusable mode.

ITS booster
The first-stage ITS booster, or Interplanetary booster—is a 12 m-diameter, 77.5 m-high, reusable rocket powered by 42 sea-level rated Raptor engines producing over 3024 kN of thrust in each engine. Total booster thrust is approximately 29000000 lbf, several times the 8000000 lbf thrust of the Saturn V Moon mission launch vehicle.

The engine configuration will include 21 engines in the outer ring and 14 in the inner ring, with these 35 engines fixed in place. The center cluster of seven engines are gimbaled for directional control, although some directional control to the rocket is also available by utilizing differential thrust on the fixed engines. Design thrust on each engine is variable between 20 and 100 percent of rated thrust.

Methane/oxygen will also be used to power the control thrusters, as gas thrusters rather than the subcooled liquid used to power the main engines. The methalox control thrusters will be used to control booster orientation in space, as well as to help provide additional accuracy in landing once the velocity of the descending booster has slowed.

The design is intended to use about seven percent of the total propellant load at launch in order to support the reusable aspect and bring the booster back to the launch pad for a vertical landing, assessment, and relaunch, assuming a separation velocity of approximately 8650 km/h.

During atmospheric reentry, once the atmosphere is sufficiently dense, grid fins will be used to control the attitude of the rocket and fine tune the landing location. The booster return flights are expected to encounter loads that are lower than those experienced on the Falcon 9 rentries, principally because it will have both a lower mass ratio and a lower density than Falcon 9. The booster will be designed for 20 G nominal loads, and possibly as high as 30–40 G's without breaking up.

In contrast to the landing approach used on SpaceX mid-2010s reusable rocket first stages—either a large, flat concrete pad or downrange floating landing platform used with Falcon 9—the ITS booster will be designed to land on the launch mount itself, where it may then be refilled with propellant and checked out for follow-on flights.

Spacecraft that operate briefly as upper stages during launch
The ITS launch vehicle does not have a dedicated and single-function second stage in the way most launch vehicles have had. Instead, the upper stage function of gaining sufficient velocity to place a payload into Earth orbit is provided as a relatively short term role by a spacecraft that has all the requisite systems for long-duration spaceflight. This is not a role that most upper stages have had in launch vehicle designs through the 2010s, as typical upper stage on-orbit life is measured in hours. Previous exceptions to this norm exist, for example the Space Shuttle orbiter provided part of the boost energy and all of the second stage energy for lofting itself into low-Earth orbit. Differences also exist: the Space Shuttle expended its propellant tank and primary launch vehicle structure on ascent, whereas the ITS first- and second-stage options are designed to be fully reusable.

In the 2016 design, SpaceX had identified two spacecraft that would also play the upper stage role on each Earth-away launch: the interplanetary spaceship and the ITS tanker. Both spacecraft are the same physical external dimensions: 49.5 m-long and 12 m-diameter (17 m across at the widest point. Both designs were powered by six vacuum-optimized Raptor engines, each producing 3.5 MN thrust, and were to have had three lower-expansion-ratio Raptor engines for in-space maneuvering as well as during descent and landing to allow for reuse on future launches.

Interplanetary spaceship
The Interplanetary spaceship was a large passenger-carrying spacecraft design proposed by SpaceX as part of their ITS launch vehicle in September 2016. The ship would operate as a second-stage of the orbital launch vehicle on Earth-ascents—and would also be the interplanetary transport vehicle for both cargo and passengers— capable of transporting up to 450 tonne of cargo per trip to Mars following propellant-refill in Earth orbit.



In addition to use during maneuvering, descent and landing, the three lower-expansion-ratio Raptor engines were also to have been used for initial ascent from the surface of Mars. In 2016, the first test launch of a spaceship was not expected until 2020 or later, and the first flight of the ITS booster was expected to follow a year or more later.

Early Mars flights—in the mid-2020s or later—were expected to carry mostly equipment and few people.

ITS tanker
The ITS tanker is a propellant tanker variant of the ITS second stage spacecraft. This spacecraft design was to be used exclusively for launch and short-term holding of propellants to be transported to low-Earth orbit. Once on orbit, a rendezvous operation was to have been effected with one of the interplanetary spaceships, plumbing connections made, while a maximum of 380 tonne of liquid methane and liquid oxygen propellants would be transferred in one load to the spaceship. To fully fuel an interplanetary spaceship for a long-duration interplanetary flight, it was expected that up to five tankers would be required to launch from Earth, carrying and transferring a total of nearly 1900 tonne of propellant to fully load the spaceship for the journey.

Following completion of the on-orbit propellant offloading, the reusable tanker was to reenter the Earth's atmosphere, land, and be prepared for another tanker flight.

Reusability
Both stages were designed by SpaceX to be fully reusable and were to land vertically, using a set of technologies previously developed by SpaceX and tested in 2013–2016 on a variety of Falcon 9 test vehicles as well as actual Falcon 9 launch vehicles.

Importantly, the "fully and rapidly reusable" aspect of the ITS launch vehicle and spacecraft design was the largest factor in the SpaceX analysis for bringing down the currently huge cost of transporting mass to space, in general, and to interplanetary destinations, in particular. While the transport system under development in 2016-2017 relied on a combination of several elements to make long-duration beyond Earth orbit (BEO) spaceflights possible by reducing the cost per ton delivered to Mars, the reusability aspect of the launch and spacecraft vehicles alone was expected by SpaceX to reduce that cost by approximately 2 1/2 orders of magnitude over what NASA had previously achieved on similar missions. Musk stated that this is over half of the total 4 1/2 orders of magnitude reduction that he believes is needed to enable a sustainable settlement off Earth to emerge.

Launch location
As of September 2016, the planned location for initial launches of the ITS launch vehicle was LC-39A, at SpaceX's leased pad at Launch pad 39A on the Florida coast, the same launchpad where Apollo 11 launched in 1969 to the Moon and from where subsequent Apollo Missions were also launched.

Operations concept
The concept of operations for ITS launches envisions the fully loaded second-stage reaching orbit with only minimal propellant remaining in the interplanetary spaceship vehicle's tanks. At this time, while the spaceship remains in Earth orbit, three to five cargo second stages—called ITS tankers—would be launched from Earth carrying additional methane fuel and liquid oxygen oxidizer to rendezvous with, and transfer propellant to, the outgoing spaceship. Once refueled, the spaceship would perform a trans-Mars injection burn, departing Earth orbit for the interplanetary portion of the journey.

Outer planet concepts
The overview presentation on the Interplanetary Transport System architecture given by Musk in September 2016 included concept slides outlining missions to the Saturnian moon Enceladus, the Jovian moon Europa, Kuiper belt objects, a fuel depot on Pluto and even the uses to take payloads to the Oort Cloud. "Musk said ... the system can open up the entire Solar System to people. If fuel depots based on this design were put on asteroids or other areas around the Solar System, people could go anywhere they wanted just by planet or moon hopping. 'The goal of SpaceX is to build the transport system ... Once that transport system is built, then there is a tremendous opportunity for anyone that wants to go to Mars to create something new or build a new planet.'" Outer planet trips would likely require propellant refills at Mars, and perhaps other locations in the outer Solar System. This emphasis was totally missing in the update one year later when the smaller BFR launch vehicle and spacecraft were introduced.

Funding
The development and manufacture of the new two-stage launch vehicle has been to date (through 2016), and is being, privately funded by SpaceX. The entire project is even possible only as a result of SpaceX multi-faceted approach focusing on the reduction of launch costs.

The full build-out of the Mars colonialization plans will likely be funded by both private and public funds, according to Musk in September 2016. The speed of commercially available Mars transport for both cargo and humans will be driven, in large part, by market demand as well as constrained by the technology development and development funding.

Elon Musk has said that there is no expectation of receiving NASA contracts for any of the ITS system work. He also indicated that such contracts, if received, would be good.

Competition for the American super-heavy-lift market
In August 2014, media sources noted that the US launch market may have two competitive launch vehicles available in the 2020s to launch payloads of 100 tonnes or more to low Earth orbit. The US government is currently developing the Space Launch System (SLS), a super heavy-lift launch vehicle designed to propel very large payloads of 70 to 130 tonnes to low Earth orbit.

Blue Origin's New Glenn rocket, announced in September 2016, is also expected to compete in the super-heavy lift class. In March 2017, New Glenn's reusable payload capacity was announced as 45 tonnes to LEO and 13 tonnes to GTO.