Modifications from Falcon 9 v1.0
The original Falcon 9 flew five successful orbital launches in 2010–2013, all carrying the Dragon spacecraft or a test version of the spacecraft.
The Falcon 9 v1.1 ELV was a 60 percent heavier rocket with 60 percent more thrust than the v1.0 version of the Falcon 9. It includes realigned first-stage engines[12] and 60 percent longer fuel tanks, making it more susceptible to bending during flight.[13] The engines were upgraded from the Merlin 1C to the more powerful Merlin 1D engines. These improvements increased the payload capability to LEO from 10454 kg[14] to 13150 kg. The stage separation system was redesigned and reduced the number of attachment points from twelve to three,[13] and the vehicle had upgraded avionics and software as well.[13]
The v1.1 booster version arranged the engines in a structural form SpaceX called Octaweb, with eight engines arranged in a circular pattern around a single center engine. The v1.0 used a rectangular pattern of engines. The Octaweb pattern was aimed at streamlining the manufacturing process.[15] Later v1.1 vehicles include four extensible landing legs,[16] used in the controlled-descent test program.
Following the first launch of the Falcon 9 v1.1 in September 2013, which experienced a post-mission second-stage engine restart failure, the second-stage igniter propellant lines were insulated to better support in-space restart following long coast phases for orbital trajectory maneuvers. Falcon 9 Flight 6 was the first launch of the Falcon 9 configured with a jettisonable payload fairing.
First stage
The Falcon 9 v1.1 uses a first stage powered by nine Merlin 1D engines.[17][18] Development testing of the v1.1 Falcon 9 first stage was completed in July 2013.[19][20]
The v1.1 first stage has a total sea-level thrust at liftoff of 5885 kN, with the nine engines burning for a nominal 180 seconds, while stage thrust rises to 6672 kN as the booster climbs out of the atmosphere.[21] The nine first-stage engines are arranged in a structural form SpaceX calls Octaweb. This change from the v1.0 Falcon 9's square arrangement is aimed at streamlining the manufacturing process.[15]
Second stage
The upper stage is powered by a single Merlin 1D engine modified for vacuum operation.[27]
The interstage, which connects the upper and lower stage for Falcon 9, is a carbon fiber aluminum core composite structure.[28] Separation collets and a pneumatic pusher system separate the stages.[29] The Falcon 9 tank walls and domes are made from aluminium-lithium alloy.[30] SpaceX uses an all-friction stir welded tank, a technique which minimizes manufacturing defects and reduces cost, according to a NASA spokesperson.[31] The second-stage tank of Falcon 9 is simply a shorter version of the first-stage tank and uses most of the same tooling, material and manufacturing techniques.
Payload fairing
The fairing design was completed by SpaceX, with production of the 43 ft-long, 17 ft-diameter payload fairing in Hawthorne, California.[32]
Testing of the new fairing design was completed at NASA's Plum Brook Station facility in spring 2013 where acoustic shock, mechanical vibration, and electromagnetic electrostatic discharge conditions were simulated. Tests were done on a full-size test article in vacuum chamber. SpaceX paid NASA US$581300 to lease test time in the $150M NASA simulation chamber facility.[33]
The first flight of a Falcon 9 v1.1 (CASSIOPE, September 2013) was the first launch of the Falcon 9 v1.1 as well as the Falcon 9 family configured with a payload fairing. The fairing separated without incident during the launch of CASSIOPE as well as the two subsequent GTO insertion missions.[33] In Dragon missions, the capsule protects any small satellites, negating the need for a fairing.[34]
Control
SpaceX uses multiple redundant flight computers in a fault-tolerant design. Each Merlin engine is controlled by three voting computers, each of which has two physical processors that constantly check each other. The software runs on Linux and is written in C++.
For flexibility, commercial off-the-shelf parts and system-wide "radiation-tolerant" design are used instead of rad-hardened parts.[35] Falcon 9 v1.1 continues to utilize the triple redundant flight computers and inertial navigation—with GPS overlay for additional orbit insertion accuracy—that were originally used in the Falcon 9 v1.0.
