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Despite only being founded in 2002, SpaceX is now the world’s foremost provider of space launch services. SpaceX has been responsible for dramatically decreasing the cost of access to space and is aiming to land people on Mars. They’re also behind the Starlink constellation of communications satellites. Part one of two by Dr David Maddison VK3DSM Starship’s seventh test flight Image source: SpaceX / <at> Space_Time3 via X (Twitter). 14 Silicon Chip A size comparison of common rockets from the last few decades. Unlike SpaceX’s, Australia's electronics magazine siliconchip.com.au most are not reusable (exceptions include the Space Shuttle & New Glenn). Sources: Blue Origin, FloraFallenrose (Wikimedia) & public domain sources O f the many achievements of SpaceX, their ability to vertically land and reuse a rocket is particularly notable. Never routinely done before they made it normal, it has enabled a great decrease in space launch costs. Their satellite constellation, Starlink, provides global internet services at a price not too much different from regular wired or wireless services. SpaceX’s Falcon 9 rocket has regular weekly launches (sometimes more frequent) and is usually reused. It can carry a larger payload if its boosters are not reused. It has become a workhorse of the industry for delivering crew and cargo into space. At the time of writing, Falcon 9 rockets have launched 453 times. SpaceX’s competitors like Arianespace (the world’s first commercial launch service), Roscosmos (a Russian stateowned corporation) and ULA (United Launch Alliance, a joint venture of Lockheed Martin and Boeing) cannot currently compete with SpaceX on cost or delivery schedule. As a result, SpaceX dominates the launch services market. According to Space Insider, in the fourth quarter of 2023, SpaceX launched 382,020kg of cargo into space, which was 318 times more than ULA. China’s stateowned launch service, CASC delivered, 40,810kg in the same period. Note that dates provided in this article refer to the local time at the event location, not Australian time. Also, any images that are uncredited are publicity images provided by SpaceX or in the public domain (eg, from NASA). The objectives of SpaceX The chief objectives of SpaceX are stated as: 1. Developing affordable access to space 2. Developing and launching Starlink for global internet access 3. Sending humans back to the Moon 4. Establishing a colony on Mars Successes and failures Like any space agency, SpaceX has had a few failures, especially with its early rockets. Antares Ariane 5 Soyuz Space Shuttle Failure is not treated by SpaceX with despair, but rather as a learning experience. Failures are to be expected, after all; they are pushing the limits of technology and are trying things that have never been done before. Notable events in SpaceX history are: 14th of May 2002 SpaceX was founded. 28th of September 2008 SpaceX’s first rocket launch to reach orbit, the Falcon 1, which was also the first privately developed liquid­fuelled launch vehicle to reach orbit. 8th of December 2010 The first launch, orbit and recovery of a privately developed spacecraft, SpaceX’s Dragon. 25th of May 2012 Dragon was the first commercial spacecraft to dock with the International Space Station (ISS). 3rd of December 201 The SES-8 communications satellite was launched on a Falcon 9. This was the first SpaceX mission to place a spacecraft in a geostationary transfer orbit. 22nd of December 2015 SpaceX achieved the first orbital rocket propulsive landing. 8th of April 2016 The first propulsive landing on an autonomous drone ship. 27th of September 2016 SpaceX’s Interplanetary Transport System was unveiled, comprising the most powerful rocket ever built, to carry 100 passengers to Mars with a view to establishing a self-sustaining Martian colony by 2050. 30th of March 2017 The first re-flight of an orbital rocket (Falcon 9 B1021 was first flown on the 8th of April 2016). It was recovered after its second flight. 3rd of June 2017 A previously used Dragon spacecraft was launched to resupply the ISS. This was the first time Dragon was reused. It was reused a third time, landing on the 7th of June 2020. 6th of September 2017 Starship was announced, then known as Big Falcon Rocket (BFR). It is the largest rocket seriously conceived. 6th of February 2018 Falcon Heavy was launched into solar orbit. 24rd of May 2019 The first 60 operational Starlink satellites were launched. 30th of May 2020 The first launch of the Crew Dragon spacecraft, Demo-2, on a Falcon 9 rocket. The astronauts onboard were transferred to the ISS. It was the first crewed orbital flight conducted by the United States since the cessation of the Space Shuttle program in 2011. 24th of October 2020 The 100th SpaceX rocket was launched, carrying Starlink satellites. 16th of November 2020 The first fully operational flight of Crew Dragon, Crew-1, to the ISS. It was also the first of the Commercial Crew Program flights to the ISS under contract to NASA. 16th of September 2021 The first private fundraising flight on Crew Dragon by Jared Isaacman, founder of the Polaris program, on a Falcon 9 rocket. This was also the first orbital spaceflight with all private citizens. Known as Inspiration4, Energia Atlas Falcon Falcon Delta IV Yenisei New Long Ares I SLS New V Vulcan 9 Heavy Heavy Glenn March 9 Block 1 Glenn 2-Stage 3-Stage N1 Ares V Saturn V SLS Starship Block 2 Cargo the flight obtained an orbital altitude of 585km, the fifth-highest ever orbit for human spaceflight. The mission lasted just under three days. 8th of April 2022 The Axiom Ax-1 mission to the ISS carried four private astronauts, one a professional astronaut and three “space tourists” aboard a Crew Dragon launched by a Falcon 9. This was the first time private citizens visited the ISS as tourists, although they conducted some experiments. The tourists paid US$55 million per seat. 20th of April 2023 The first flight test of Starship atop a Super Heavy booster as an integrated assembly. It became the most powerful rocket ever flown. A lot of damage was done to the launch pad due to the enormous power of the engines. Problems were encountered several minutes into the flight, and the autonomous flight termination system activated to destroy the rocket. 18th of November 2023 The second test flight of Starship. Both the booster and Starship were lost. 15th of February 2024 A Falcon 9 delivered the first American spacecraft to land on the Moon since 1972, the Odysseus lander by Intuitive Machines. of America due to a loss of comms at the landing site caused by damage to an antenna during launch. Starship performed a controlled splashdown in the Indian Ocean as planned. 16th of January 2025 The seventh test flight of Starship. Super Heavy landed successfully but Starship was destroyed. 2nd of March 2025 Blue Ghost Mission 1 by Firefly Aerospace landed on the Moon. It was the first fully successful commercial lunar landing. It was launched on a SpaceX Falcon 9 rocket. 6th of March 2025 The eighth test of Starship. Super Heavy landed successfully but Starship was destroyed. This was the last Starship launch at the time of writing. 6th of March 2025 The PRIME-1 mission landed on the Moon, launched using a Falcon 9. 4th of April 2025 The private space mission Fram2 splashed down. This was the first time astronauts have been in polar orbit. They were in a Dragon capsule, and an Australian was on board. SpaceX’s engines Among the many reasons for the success of SpaceX is the innovative design of its engines and the relatively low cost of their manufacture due to simplicity of design and the extensive use of metal 3D printing to minimise fabrication cost. SpaceX currently uses two families of engine for its boosters: the Merlin and the Raptor. The Merlin is an ‘open cycle’ engine, while the Raptor is ‘closed cycle’. SpaceX also uses two other types of engine for manoeuvring and launch abort, the Draco and the SuperDraco, which are hypergolic engines. Rocket engines contain two propellant components: fuel and oxidiser. Those like the SpaceX Merlin and Raptor engines require turbopumps (similar to jet engines but pumping liquid rather than air) to bring the fuel components together in the combustion chamber (see Fig.1). Hypergolic engines, also used by SpaceX, require no turbopumps; the two fuel components come from pressurised tanks and spontaneously combust when they are brought into contact with each other. They are much simpler than the engines requiring turbopumps (however, some larger hypergolic engines use turbopumps). The pressurising medium is usually helium. 14th of March 2024 The third test of Starship. It completed the second stage burn but broke up during re-entry. The Super Heavy booster was destroyed before landing. 6th of June 2024 The fourth test flight of Starship. Both Starship and Super Heavy successfully performed re-entry and simulated a vertical landing over the ocean (with no recovery tower). 13th of October 2024 The fifth test flight of Starship. The Super Heavy booster landed successfully, while Starship performed a suborbital flight with a soft water landing as planned (it was never intended to be recovered). 19th of November 2024 The sixth test flight of Starship. Super Heavy was planned to land at Starbase, but had to land on water in the Gulf 16 Silicon Chip Fig.1: the Merlin engine is open cycle, while Raptor is closed cycle. Source: https://woosterphysicists.scotblogs.wooster.edu/2022/01/01/merlin-raptor/ Australia's electronics magazine siliconchip.com.au In an open-cycle rocket engine such as the Merlin (Fig.1, left side), some fuel and oxidiser are burned to create gas to run the turbopump and the exhaust from this process is dumped overboard. In closed-cycle rocket engines such as the Raptor (also known as staged combustion engines), the gases from driving the turbine are routed into the combustion chamber, where they contribute to thrust. A closed-cycle engine is more fuel efficient than an open-cycle engine although its design is more complex (see the right side of Fig.1). The Merlin engine The Merlin engine was used on the defunct Falcon 1 and the present Falcon 9 and Falcon Heavy boosters. These engines run on liquid oxygen and RP-1 kerosene fuels. The current versions of the Merlin engine in use is the 1D+, with nine on the Falcon 9 first stage, and 27 on the Falcon Heavy first stage, which is essentially three Falcon 9 boosters joined together. The second stage of the Falcon 9 and the Falcon Heavy both use one Merlin 1C vacuum engine, which is optimised for operation in a vacuum rather than at sea level, with a larger exhaust nozzle. The Raptor engine Fundamental to SpaceX’s desire for high rates of reusability and RAPTOR 1 turnaround of rocket engines is the innovative liquid methane/liquid oxygen fuelled Raptor engine. This engine is so innovative that it has been described as a reinvention of the rocket engine. The fuel comprising liquid methane and liquid oxygen is known as methalox, and it has a higher specific impulse than RP-1 kerosene and liquid oxygen. Specific impulse is a measure of rocket efficiency with units of seconds; it indicates the amount of thrust generated for each unit of fuel used. The higher the number, the more efficient the engine. This means the Raptor can provide more thrust for the same mass of fuel as the Merlin. Methane is commonly available; it is the main constituent of natural gas. Methalox also does not leave much residue in the engines, unlike kerosene. This means the engines don’t have to be cleaned or rebuilt between uses. Thus, they are amenable to reuse and quick turnaround, like aircraft engines, which can be reused immediately after refuelling. Although methalox has a lower specific impulse than liquid hydrogen/liquid oxygen, that fuel is difficult and expensive to use for many reasons. It was used on the 1960s to early 1970s Saturn V Moon rocket for the second RAPTOR 2 Fig.2: 33 Raptor engines power Super Heavy on the IFT-5 test. and third stages, and is used in the first and second stages of NASA’s Space Launch System (SLS) today. The Raptor engine is used on the Starship and Super Heavy booster, for missions to Earth orbit, the Moon and eventually, Mars. The Super Heavy booster has 33 engines; 20 are fixed, while the inner 13 can be gimballed for steering (see Fig.2). Starship has six engines: three regular Raptors and three vacuum variants. The vacuum-­ optimised Raptor variant is named RVac. The Raptor engine has been in a development cycle of constant improvement, simplification and weight and cost reduction; see Fig.3 RAPTOR 3 Fig.3: the Raptor 3 is the current model of the engine. As the development progressed, they were simplified, yet the performance increased. Source: https://x.com/SpaceX/status/1819772716339339664/photo/1 siliconchip.com.au Australia's electronics magazine July 2025  17 and Table 1. For more details on how Merlin and Raptor engines work, see the video at https://youtu.be/ nP9OaYUjvdE The Draco engine The Draco engine is a small rocket thruster used on the Crew Dragon and Cargo Dragon capsule for manoeuvring and attitude control. Each Dragon spacecraft has 16 Dracos. The fuel used is a hypergolic mixture: monomethyl hydrazine and nitrogen tetroxide. Each thruster generates 400N of thrust, or about 40.7kg-force. It is comparable to the Marquardt R-4D thrusters (490N thrust) used on the Apollo Service and Lunar modules, modernised versions of which are still in use today (but which use hydrazine instead of monomethyl hydrazine). Fig.4 shows a Draco operating as the capsule autonomously docks with the ISS. For a video from the same mission of the Dragon later undocking using the Draco thrusters, see https://youtube. com/shorts/AadTz2eqGq4 The SuperDraco engine The SuperDraco (Fig.6) was originally intended for propulsive landing of the Dragon spacecraft as well as being part of the Launch Abort System (LAS), but it was only used on Crew Dragon for emergency escape during a launch – see Fig.5. The Dragons land on water using parachutes for descent, but in the Fig.4: Cargo Dragon firing a Draco thruster (the orange flame) while docking with the ISS. Fig.5: a demonstration of the Crew Dragon launch escape capability using the SuperDraco engine. unlikely event of a complete parachute failure, Crew Dragon can, per a recent enhancement, be propulsively landed using the SuperDracos. There are eight SuperDracos in four pairs on each Crew Dragon. Cargo Dragon does not need this safety feature, so it is deleted to save weight. Each SuperDraco has a thrust of 71kN (7240kg-force), a burn time of 25s and a chamber pressure of 6.9MPa (69 bar). special measures are taken. There is very little written about how SpaceX solves this for the Draco thrusters. Methods that can be used include keeping the fuel in a bladder with the outside of the bladder pressurised; a sliding diaphragm in the tank; the use of surface tension effects to keep a quantity of fuel in place near the tank outlet; a small auxiliary header tank full of fuel; or a small engine with pressurised gas for an ‘ullage’ burn to accelerate the spacecraft and to deposit the fuel at the tank outlet. Only a small amount of acceleration is needed to relocate the fuel, then pumps or pressurisation will push the fuel into the engine. Starting a rocket engine in weightlessness Starting or restarting a rocket engine in the weightlessness of space is difficult, as the fuel in the tanks floats freely and does not settle at the outlet unless Fig.6: SuperDraco engines on Crew Dragon for the launch escape system. 18 Silicon Chip Australia's electronics magazine Fig.7: a Falcon 9 launch. siliconchip.com.au Fig.8: Falcon 9’s first stage landing. Fig.11: the Falcon 9 fairing. Fig.9: the Falcon 9 interstage. Source: Teslarati Fig.10: a Falcon 9 rocket with the Dragon capsule, Trunk and crew access arm. We suspect that Draco and SuperDraco use the bladder method. Both Starship and Super Heavy use residual gas in the tanks for attitude control during descent; Falcon 9 uses nitrogen gas. SpaceX’s rockets SpaceX has three main launch platforms in use: Falcon 9, Falcon Heavy and Super Heavy. Falcon 1 was SpaceX’s first rocket. It made five launches, three being unsuccessful and one with a commercial payload. It was the first privately funded rocket to reach orbit. It operated from 2006 to 2009, but SpaceX decided it was not an economical proposition and started work on Falcon 9. They then rebooked satellite launches from Falcon 1 to Falcon 9. Falcon 9 is SpaceX’s current workhorse rocket for commercial launches (see Fig.7). It first flew on the 4th of June 2010. In 2020, it became the first commercial launch vehicle to put humans into orbit. It is the most launched rocket in US history that has an orbital capability. Falcon 9’s cost per launch in 2024 was US$69.75 million (about $115 million). The total fuelled mass of the FT version is 549,054kg (about 549 tonnes) and it is approximately 70m tall and 3.7m in diameter. A Falcon 9 rocket comprises the first stage (booster), interstage, second stage, payload and fairing. The first stage or booster stage (Fig.8) is the most expensive stage, and is usually recovered. If the booster is optionally not recovered, it allows a higher launch payload, although at greater expense. The first stage has nine Merlin engines. The interstage (Fig.9) is a section connecting the first and second stages. It contains equipment to separate the two stages and the grid fins. The second stage (Fig.12) contains one Merlin vacuum engine and is impractical to recover. The payload is contained within a fairing, which is recovered. It is 13.1m long and 5.2m in diameter (Fig.11). If Dragon or Crew Dragon is launched atop a Falcon 9 rocket, no fairing is necessary (see Fig.10). The FT version of the rocket can launch 22,800kg into low Earth orbit (LEO) if the rocket is expended, or 17,500kg if it is to land. For geosynchronous transfer orbit (GTO), its payload capacity is 8300kg if the rocket is expended, 5500kg if it lands on a drone ship, or 3500kg if the rocket returns to the launch site. Falcon 9 is certified for human spaceflight. Its payload deliverable to Mars is 4020kg. It lands on four legs when it is recovered, and uses its grid fins for guidance. When it is not to be recovered, the legs and grid fins are deleted to save weight and cost. A user guide for the Falcon 9 and Falcon Heavy, intended for mission planning rather than payload design, is available at www.spacex.com/media/ falcon-users-­guide-2021-09.pdf Falcon Heavy comprises a strengthened Falcon 9 core with two Falcon 9 first stages attached as boosters on Table 1 – Raptor engine specifications (sea level variants) Raptor 1 Raptor 2 Raptor 3 Thrust force 185t 230t 280t Specific impulse 350s 347s 350s Engine mass 2080kg 1630kg 1525kg Engine+accessories mass 3630kg 2875kg 1720kg Chamber pressure 250bar 300bar 370bar siliconchip.com.au Australia's electronics magazine Fig.12: an illustration of the Falcon 9’s second stage separating. July 2025  19 Fig.13: the Falcon Heavy rocket. Source: https:// w.wiki/ DkQg Fig.14: grid fins are deployed during re-entry for booster guidance. Fig.16: the simultaneous landing of two boosters from a Falcon Heavy. Fig.15: a Falcon 9 lands on a drone ship off the coast of the Bahamas. either side (see Fig.13). The boosters and the core each have 9 Merlin 1D engines for a total of 27 engines. The core carries a standard Falcon 9 second stage, with the payload attached inside a fairing. It is powered by a single Merlin 1D engine. Apart from carrying cargo, Falcon Heavy was designed to carry humans into space, and has structural safety margins 40% above flight loads compared to 25% on other human-rated rockets. It is capable of taking crewed missions to the Moon or Mars. Its propellant is liquid oxygen/RP-1 (a highly refined kerosene). The first stage burns for 187 seconds and the second stage for 397 seconds. The first flight of the Falcon Heavy was on the 6th of February 2018. Both the boosters and core can be optionally recovered, but if they are, the payload is reduced due to the extra fuel that needs to be carried to power the engines for the descent stage of the flight. The options are to recover boosters and core, just the boosters or none at all. Recovering the boosters and core reduces the cost of the launch. The rocket is 70m tall, while each booster and the core has a diameter of 3.7m for a maximum total width of 12.2m. The mass of the rocket without payload is 1,420,000kg (1420 tonnes). It can carry a payload of up to 63,800kg into low Earth orbit when both the core and boosters are not recovered, or less than 50,000kg when both the core and boosters are recovered. It can carry a payload of 26,700kg into GTO, 16,800kg to Mars or 3,500kg to Pluto if the boosters and core are expended. If the boosters are recovered, the payload to GTO is 16,000kg and if the core is also recovered, the payload to GTO is 8,000kg. The Falcon Heavy has the fourth-­ largest payload capacity of any rocket to ever reach orbit, after NASA’s SLS, the obsolete Soviet Energia (which made two flights) and the US Saturn V, which made 13 flights. Thus, of current rocket systems, it has the second-­highest payload capacity after the SLS. Super Heavy is the booster (first stage) for the Starship spacecraft, which together are the largest rocket ever made, with a combined mass of approximately 5,000,000kg (5000 tonnes) or perhaps more. Both vehicles, Super Heavy and Starship, are designed to be reusable. Fig.17: capturing the Super Heavy booster on the 6th of March 2025. Source: SpaceX & Steve Jurvetson 20 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.18: recovering the payload fairing by parachute. Fig.19: the Dragon capsule (uc.edu). The booster is 71m tall. With the 9m diameter ‘vented interstage”, it has an empty mass of 275,000kg (275 tonnes) and a gross mass, when fuelled, of 3,675,000kg (3675 tonnes). It is powered by 33 Raptor engines with a total thrust of 73,500kN/7,490,000kgforce (Block 1), 80,800kN (Block 2) or 98,100.1kN (Block 3). Block 1 rockets have a burn time of 166 seconds and use methalox propellant. When Starship separates from Super Heavy, the Starship engines ignite while the booster is still attached, thus ‘pushing off’ from Super Heavy. This is the reason for the vented interstage connector; the ‘hot staging’ provides extra thrust. It was stated that this allows for up to 10% more payload to LEO. The payload capacity of Super Heavy into LEO is 100-150 tonnes when the rocket is recovered. The payload might be Starship carrying satellites, up to 100 people going to Mars, cargo, fuel, passengers to the Moon or point-to-point transport on Earth. For an image of Super Heavy landing and being captured by Mechazilla (more on that later), see Fig.17. The Saturn V was the world’s most powerful, successful rocket until the Super Heavy came along. Falcon & Super Heavy re-entry When the Falcon 9 or Falcon Heavy first stage boosters perform re-entry, the engines first slow the booster(s), then the grid fins (Fig.14) help to orientate and guide the booster(s) for a landing on either a drone ship (see Fig.15) or the landing zone on land LZ1 or LZ2 (Fig.16). A landing of Falcon or the side boosters of a Falcon Heavy usually occurs at LZ1 and LZ2, while the core booster lands on a drone ship if it is a full recovery mission. The fairing siliconchip.com.au used to protect the payload is also recovered by parachute and reused where possible (see Fig.18). The second stage is not recovered because it is travelling too fast (27,000km/h) and would require too much fuel to slow down and re-­ enter, unlike the first stage, which is moving much slower. The first stage would eventually fall back to Earth in any case. Grid fins On Falcon 9, Falcon Heavy and Super Heavy, grid fins are used and guide the booster to a landing (Fig.14). For Super Heavy, the landing is in the “Mechazilla” structure. The boosters have four grid fins each. Those on Falcon 9 and Falcon Heavy are made of titanium and measure 2 × 1.2m. They are folded during ascent. On Super Heavy, they remain extended to simplify the design and save weight. In this case, each measures 7 × 3m, is made of stainless steel and weighs three tonnes. When the boosters re-enter, they return enginefirst; the heat-resistant engines act as a de facto heat shield. Super Heavy vs the N1 and Saturn V On the 20th of April 2023, the Super Heavy rocket broke the record for the most powerful rocket. For the 50 years before that, the record was held by the Soviet N1, a competitor to the United States’ Saturn V Moon rocket. However, the N1 never achieved orbit after four attempts. Similar to Super Heavy with 33 engines generating 73,500kN of thrust, the N1 had 30 engines and produced 45,400kN of thrust. The US Saturn V with five engines generated 34,500kN of thrust and successfully took astronauts to the Moon. Australia's electronics magazine Spacecraft SpaceX’s main spacecraft in use or under development now are variants of Dragon and Starship. The Dragon spacecraft are primarily designed for crew and cargo transport to the ISS and Earth orbit. Starship is designed for heavy lifting of crew, cargo and fuel to locations on the Earth’s surface, Earth orbit, the Moon, Mars and elsewhere. Starhopper was a test vehicle built for the purpose of landing and control algorithms for Starship and flown four times in 2019. It used methalox fuel. Dragon 1 flew 23 cargo missions to the ISS from 2010 to 2020. It was not designed to carry astronauts and was the first private spacecraft to dock with the ISS. Dragon 2 (Fig.19) was introduced in 2019, with both Crew Dragon and Cargo Dragon variants. The Crew Dragon carries astronauts to and from the ISS under NASA’s Commercial Resupply Services (CRS) program and also on orbital missions such as the recent Fram2 (Fig.20). Fig.20: recovery of the Fram2 mission Crew Dragon capsule. Note the scorch marks from re-entry. July 2025  21 Fig.21: note how (relatively) spacious the interior of the Crew Dragon capsule is. These are the SpaceX Crew-8 astronauts. The Crew Dragon usually carries four astronauts, but it can be configured to carry seven. The interior is relatively spacious (see Fig.21). Both types of Dragon spacecraft are fully autonomous, but astronauts or Mission Control can take control of Crew Dragon if necessary. Like Dragon 1, Dragon 2s (which are now called Crew Dragon or Cargo Dragon) are reusable. Also see Figs.22, 23 & 24. The Dragon 2 capsules are 8.1m tall, 4m in diameter, with a volume of 9.3m3 and a launch mass of 6,000kg (six tonnes). The return mass is 3,000kg (three tonnes). For landing, Dragon is designed to re-enter the Earth’s atmosphere, where it is initially slowed by its heat shield. Drogue parachutes are then released, Fig.22: The Trunk section at the back of the Dragon 2 capsule is discarded after launch. followed by four main parachutes. Crew Dragon can land safely even if only one of the four parachutes deploy (see https://youtu.be/YDFgFnEVn_o). After landing in the ocean, the main parachutes are disconnected to stop the capsule being dragged by the wind. The capsule is designed to float by itself, but if necessary, extra flotation devices can be deployed in an emergency to prevent the capsule sinking. The Dragon capsules were originally intended to land propulsively using SuperDraco engines, but this idea was abandoned in favour of ocean splashdowns. The Crew Dragon also has SuperDraco engines in case of a launch failure, to remove the capsule from the rocket and move it to safety for a parachute landing (shown earlier in Fig.5). The Cargo Dragon does not need this safety feature, so it does not have the SuperDraco engines installed. In the unlikely event of a total parachute failure, Crew Dragon now has the ability to use the SuperDraco engines to land propulsively. The reason the original plans for Crew Dragon to land propulsively were abandoned was partly due to NASA’s requirement for a parachute landing on water. But now propulsive landing has been reinstated as an emergency measure. The Dragon carries a Trunk module with a 37m3 volume, which is unpressurised and can carry cargo. It is half-covered in solar panels to generate power for the capsule while in flight or docked at the ISS. The other half is covered with a thermal radiator system. Active Vent Valves Emergency Ventilation Fan Dehumidifier Vacuum Isolation Valves Fig.23: a cutaway of Dragon capsule, from the same source as Fig.24. Toilet Dehumidifier Vacuum Lines Fire Extinguisher Valve Panel Cabin Fans Dehumidifier Waste Locker Active LiOH Cartridge Valve Panel Waste Fans Urine Tank Fig.24: some of Dragon’s plumbing and thermal controls. Source: www.uc.edu/content/dam/ refresh/cont-ed-62/olli/fall-23-class-handouts/ SpaceX%205Dragon%20Capsules.pdf 22 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.26: a rendering of the USDV designed for deorbiting the ISS. It is a modified Dragon. Source: https://x.com/ SpaceX/status/1813632705281818671/photo/1 Fig.25: under the skin of the Dragon capsule (uc.edu). The Trunk module is jettisoned before re-entry and is meant to burn up in the atmosphere, but parts of it occasionally survive re-entry. The Trunk provides the mechanical and electrical interface to the Falcon 9. The Trunk also has fins to stabilise the Dragon and Trunk in the event of an aborted launch. Electrical and fluid connections are provided inside the trunk to accommodate various payloads, including small satellites. The Trunk space is almost ‘free’ and represents the utilisation of an area that would otherwise be unused. Fig.25 shows the inner structure of the Dragon, which is made of aluminium, while the outer shell is carbon fibre. Section A is the pressure vessel, which contains the crew couches, while section B contains equipment. The primary heat shield at the bottom is made from PICA-X (more on that later). Dragon 2 communicates by several methods. It connects to satellites via NASA’s Tracking and Data Relay Satellite System; it can communicate with ground stations with a 300kbps Command Uplink and 300Mbps+ telemetry and data downlink. Payloads can be connected to the vehicle via Ethernet, RS-422 and MIL-STD-1553. There are redundant communications systems via telemetry and video transmitters on S-Band and, as of Fram2, connectivity with Starlink via laser. There was once a Red Dragon proposal to propulsively land an uncrewed Dragon capsule on Mars to deliver equipment and a sample return rover. Propulsive landing would be ideal siliconchip.com.au on Mars since the thin atmosphere makes parachute landings difficult. Red Dragon was abandoned when Starship became the focus for trips to Mars. Dragon XL is a planned variant that will be used to supply NASA’s Lunar Gateway, a planned space station in lunar orbit. It will carry cargo and experiments, keeping up to 5,000kg (five tonnes) of supplies in lunar orbit with the Gateway for 6–12 months. The XL is not required to return to Earth; after use, it will be parked in a heliocentric orbit (ie, orbiting the sun). When the ISS is finally deorbited, as planned in the early 2030s, a modified Dragon called the US Deorbit Vehicle (USDV; Fig.26) will dock with the ISS and use 46 Draco engines attached to a larger-than-usual trunk section to guide and push it into the atmosphere at an appropriate place. This will ensure that the structure burns up over the Pacific Ocean and any small remaining debris will fall into the empty ocean after shipping has been cleared from the area. The USDV will have six times the propellant and four times the power of a regular Dragon. It will be a sad ending for the ISS but is necessary for reasons explained in the video at https://youtu. be/cohVHaVMBl8 Starship Starship and its variants (Fig.27) will be a highly versatile workhorse of the future SpaceX fleet, delivering Fig.27: Starship ready for launch. One of the thermal protection tiles has been removed for testing purposes. Australia's electronics magazine July 2025  23 people, cargo and fuel to other locations anywhere on Earth in less than one hour or into Earth orbit, the Moon, Mars and beyond. Starship is the second stage of the Super Heavy booster. Perhaps confusingly, the ‘stacked’ (combined) Super Heavy booster and Starship second stage might also be called Starship together. The depot version of Starship will remain in orbit and so does not require heat shields or control surfaces. The HLS version, which will shuttle between Earth and Moon and will not land on Earth, is similar. Propellant tankers, which can land, can also refuel other Starships. When stacked with Super Heavy and fuelled (Fig.28), Starship has a total mass of approximately 4975 tonnes (Block 1) or 5260 tonnes (Block 2) and a height of 121–123m depending on the version. It is the largest and most powerful rocket ever built and the heaviest object ever flown. Starship can deliver 100–150 tonnes of cargo if reused, or 250 tonnes if the booster is expended. Versions of Starship for landing on the Moon or Mars will have landing legs. One possible use of Starship is for rapid delivery of supplies for military missions or natural disasters on Earth. It will be able to reach anywhere on Earth within one hour. For landing on Earth, Starship will use four flaps for guidance, two forward and two aft, as well as grid fins. It will be caught in the arms of a Mechazilla structure, like Super Heavy. Heat shields protect it during re-entry. The Starship second stage has a height of about 50m (Block 1) or 52m (Block 2), a diameter of 9m, an empty mass of about 85,000kg (85 tonnes) and a fully fuelled mass of 1,500,000kg (1500 tonnes). Starship uses methalox fuel, with three Raptor engines and three Raptor vacuum engines. The versions of Starship optimised for lunar landing will have legs, and possibly engines that are mounted higher up, to avoid kicking up lunar dust. Such versions will shuttle between the Moon and Earth orbit, where they will be refuelled and will not land on Earth. It is estimated that eight Starship launches will be required to get enough fuel into orbit for one refuelling. Why use so many engines? Compared with the Space Shuttle, the Saturn V and other rockets that use relatively few engines, SpaceX rockets use many (see Fig.29). This Fig.28: Starship & Super Heavy booster for Starship’s 8th flight test. 24 Silicon Chip relates to propulsive landing. Large rocket engines have a limited range of thrust in which they will work, and cannot be throttled back to the relatively low thrust levels required for a landing (other rocket designs can’t land this way). Note that while all engines are used for launch, only some are reignited for landing. Smaller engines that can work within the required thrust range are needed. However, because their thrust is relatively low compared to large engines, more are needed for launches. Having many engines also makes the failure of one more tolerable. Another advantage is that standardising on a few engine designs for multiple rocket designs enables greater economies of scale of mass production. SpaceX wants to have a fleet of hundreds or thousands of rockets running continuous missions into Earth orbit and beyond. Next month There is more to this story, but that’s all we can fit in this issue. In the second and final part next month, we will have details of SpaceX’s proposed Mars missions using Starship, more on the rocket recovery methods, their launch sites and some notable missions SpaceX has undertaken. We’ll also have some brief updates on two of their main competitors, Blue Origin and Virgin Galactic. Along with SpaceX, they were both mentioned in our October 2018 article on Reusable Rockets (siliconchip.au/ Article/11257), but much has changed since then. Fig.29: Falcon 9 has nine engines in its first stage, Falcon Heavy has 27, while Starship has 33! This gives redundancy and better control for landing. Australia's electronics magazine siliconchip.com.au Elon Musk: a controversial figure Elon has been somewhat divisive since he became one of the world’s richest people. These days, “controversial” is putting it mildly! Still, as the founder of and visionary behind SpaceX, we can’t tell the story of the company without mentioning him. Whether you love him, hate him, or are totally indifferent, he has been a driving force behind several major technology companies, including PayPal, SpaceX, Twitter/X, OpenAI and Neuralink, among others. Elon Musk’s engineering philosophy These are the distinguishing characteristics of his businesses, as opposed to traditional, more conservatively run ones. He emphasises excellence, high-quality engineering and simplicity of design, as quoted in Walter Isaacson’s biography of Musk: A humourous AI-generated image of Elon Musk and Optimus with Starship on Mars (one wonders how he is breathing with his helmet removed). 1) Question every requirement. Each should come with the name of the person who made it. You should never accept that a requirement came from a department, such as from “the legal department” or “the safety department.” You need to know the name of the real person who made that requirement. Then you should question it, no matter how smart that person is. Requirements from smart people are the most dangerous, because people are less likely to question them. Always do so, even if the requirement came from me. Then make the requirements less dumb. 2) Delete any part or process you can. You may have to add them back later. In fact, if you do not end up adding back at least 10% of them, then you didn’t delete enough. 3) Simplify and optimize. This should come after step two. Common mistake is to simplify and optimize a part or a process that should not exist. 4) Accelerate cycle time. Every process can be speeded up. But only do this after you have followed the first three steps. In the Tesla factory, I mistakenly spent a lot of time accelerating processes that I later realized should have been deleted. 5) Automate. That comes last. The big mistake in Nevada and at Fremont was that I began by trying to automate every step. We should have waited until all the requirements had been questioned, parts and processes deleted, and the bugs were shaken out. Elon is quoted as saying, “the best part is no part”. Another aspect of Musk’s philosophy is that he sees patents as “stifling” and, in 2019, he made Tesla’s entire patent portfolio available under Creative Commons licensing for non-­ commercial purposes. With regards to SpaceX, he said, “If things are not failing you’re not innovating enough.” He wants to see rocket launches become as routine as airline flights, and nearly as cheap, with a similar turnaround time between flights. He wants to ‘democratise space’ and making it accessible to as many people as possible. Musk has said that with SpaceX, he spends more time on government paperwork than rocket development. On the 15th of March 2025, Elon Musk announced on X that “Starship departs for Mars at the end of next year, carrying Optimus. If those landings go well, then human landings may start as soon as 2029, although 2031 is more likely.” (https://x.com/elonmusk/status/1900774290682683612). Optimus is the humanoid robot designed by Tesla. As for the continuing development of Starlink, Elon Musk Tweeted on the 15th of October 2024 that, “The next generation Starlink satellites, which are so big that only Starship can launch them, will allow for a 10X increase in bandwidth and, with the reduced altitude, faster latency” (https://x.com/elonmusk/ status/1845884681050276333). SC siliconchip.com.au Australia's electronics magazine The current Starlink constellation. Source: satellitemap.space July 2025  25