SLS finally flies….sending Artemis I’s Orion spacecraft on its way to the Moon…as SpaceX gets another lunar lander order

by | Nov 16, 2022 | exploration, Launches, NASA, Seradata News, SLS

After a series of delays, including one caused by Hurricane Nicole, Artemis I’s Orion spacecraft finally lifted off from Pad 39B at the Kennedy Space Center (KSC) in Florida, USA. The SLS (Space Launch System) rocket was launched at 0647 GMT on 16 November with its crackling rumble reportedly being felt for miles around.

The 98 m tall SLS Block 1 rocket was carrying the Orion Crew Module (CM) and its Service Module (SM) – a spacecraft destined for later Artemis human missions – in an uncrewed condition on the Artemis I test flight to the Moon.

The powerful first stage is believed to have achieved its projected unstable 1,806 x 30 km orbit on the initial burn (its very low perigee ensured a safe re-entry of the core stage over the Pacific). This was followed by a short burn by the SLS ICPS upper stage to put the assembly into a stable low Earth parking orbit. Another burn of the upper stage achieved Trans Lunar Injection (TLI) into its transfer orbit towards the Moon at T+1 hour 55 minutes. Ten minutes later the Artemis I/Orion spacecraft was finally deployed by the ICPS upper-stage 1. The mission is planned to last 26 days.

Lift-off took place 40 minutes into the launch window after extended holds during countdown related to a launch site “ethernet switch” issue and further evaluation of the loose RTV insulation on the exterior of the spacecraft, which had been damaged by Hurricane Nicole.

SLS launches Artemis I mission in night time launch. Courtesy: NASA/Bill Ingalls

Under current plans, the mission will deploy ten CubeSat satellites during this transfer and then, after a course correction, Orion will make a burn to enter a Distant Retrograde Orbit (DRO) around the Moon for six days. After that, it will re-enter the Earth’s atmosphere and splash down in the Pacific Ocean. On Day 11 of the mission, Artemis I’s Orion will take the human-rated spacecraft record for the longest distance travelled from the previous holder, Apollo 13.

Artemis I Flight Plan Courtesy: NASA

Slingshot Aerospace’s telescopes and other detection systems will be attempting to track the Artemis I mission as it plies its way around the Moon.

If this flight is successful, Artemis II is due to fly in 2024. That crewed Orion spacecraft mission will perform a lunar flyby test and return to Earth. A landing attempt with two crew – probably including the first female astronaut to land on the lunar surface – will be made in 2025 on Artemis III, with Artemis IV confirmed as having a human landing attempt in 2027. Later, larger-scale operations will involve the construction of the planned lunar Gateway orbiting space station followed by the building of a lunar surface base/village, although NASA does not want this later construction to delay its plan to land humans on Mars.

Earth as seen from the departing Artemis I Orion spacecraft. Courtesy: NASA TV

The History of the SLS

The first flight of NASA’s SLS heavy-lift rocket has been long awaited and its success will come as a relief. The rocket’s cost and design have been controversial since the programme began, so it must prove itself if that huge investment is to be deemed worthwhile. SLS will play a key part in returning humans to the Moon, over half a century after the original Apollo landings.

The forced conception 

After the Augustine Commission’s findings in 2008 ended Project Constellation in 2010, NASA found itself needing a different large rocket. This would be for crewed exploration of an asteroid (later revised to the Moon) and then of Mars as part of a “flexible path” approach. However, while NASA, along with the Obama Administration, wanted a new heavy-lift vehicle (HLV), this was only after it had fixed commercial low Earth orbit (LEO) spaceflight. In the meantime, it planned to spend US$3.1 billion on the development of commercial heavy-lift technologies, even if this was not actually guaranteed to yield a rocket.

NASA’s hand was forced into building a real one after criticism from former Apollo astronauts including the first and last men on the Moon. The late Neil Armstrong (Apollo 11) and Gene Cernan (Apollo 17) were concerned about the vagueness of the plan. They argued that without an HLV, a lunar and Mars exploration programme would get nowhere.

The US Senate supported this, especially given certain Senators’ political self-interest in defending space jobs in their states. So, it was decided that a new HLV should be built using technology based on the Space Shuttle programme – notably its RS-25 first stage engines and solid rocket boosters. While this “old technology” design drew criticism from industry experts and rocket engineers, there was some logic in using available technology to help contain costs.

The initial design, as stipulated by the US Senate, was that it had to be able to carry payloads of 70 metric tons to LEO with later variants carrying 130 metric tons. This Senate-led specification caused the SLS to be dubbed the “Senate Launch System”.

Some argued that NASA did not need an HLV since commercial heavy-lifters and in-orbit fuel depots might one day become available even without the agency’s help. NASA’s leadership was not prepared to gamble on either. Instead, it took the logical decision – at the time – to develop an inline HLV.

Remember, propellant depot and transfer technologies had yet to be developed (and still are not). Meanwhile, a commercial HLV able to carry more than 100 metric tons to orbit was just a twinkle in Elon Musk’s eye. While the Falcon Heavy was on the drawing board, its payload capability – later confirmed to be 64 metric tons to LEO – was still somewhat less than was needed (although if it had been fitted with a cryogenic upper stage, it may well have reached the 70 metric ton minimum).

NASA originally favoured a much cheaper, if less capable, design called the Shuttle-Derived Heavy Lift Launch Vehicle, but more commonly known as the “Sidemount HLV”. This derivative of the Shuttle-C concept of a Space Shuttle without wings would have made use of most of the Shuttle’s hardware and launch infrastructure. As a result, its development cost was estimated to be only US$6-8 billion – about half of the cost of inline alternatives. As such, Sidemount might have provided an ideal interim HLV that could have flown by December 2016 – the originally mandated start date of the new heavy-lift design. NASA’s own studies showed that it could have mounted some basic two-astronaut lunar landing expeditions using a two-launch mission architecture.

The one that got away: Sidemount. Courtesy: NASA

However, after comparing different configurations, NASA chose instead the much more expensive inline SLS design. It based this decision on the logic that SLS had greater development potential in terms of payload mass. While Sidemount would be able to make the initial 70 metric ton minimum, it was unlikely ever to achieve more than about 90 metric tons. A secondary argument, deployed by in-line supporters, was that Sidemount’s rocket-powered emergency crew escapes were a lot more hazardous, but this was disproven by simulations

And so SLS came into being.

The trick that the administration needed to pull off was to produce an effective inline HLV as cheaply as possible. While SLS has now achieved lift-off, from a cost perspective NASA has failed.

Gestation and delays…adding to the cost

For a time, things went well. The Critical Design Review (CDR) was achieved five months ahead of schedule, but it did point out some of the system’s weaknesses. For example, modelling discovered a reflected acoustics issue with the solid rocket boosters, and so the capability to perform a fly-away manoeuvre had to be scrapped. This meant that SLS would be limited to a launch crosswind of 25 knots rather than the originally envisaged 35 knots – a particular limitation given Florida’s stormy weather.

While such minor design and development setbacks were to be expected, there were several other delays in the actual construction ranging from problems with tank friction welding, to dropping and damaging tank parts, and even discovering a twist in the launch tower. More recently came main engine test failures. As a consequence, SLS is now long overdue: its original maiden launch target was December 2016.

There have even been delays during the pad testing, including wet dress rehearsal hold-ups in April due to leaky valves. As SLS finally approached launch, the first two attempts, in late August and September, were stymied by leaking hydrogen systems. Then Hurricane Ian delayed its maiden flight until mid-November. Even this attempt was delayed by a few days by Hurricane Nicole, which caused some very minor insulation damage to Orion.

Launch director Madison Tuttle who presided over the launch looks at the SLS roll past her window on its way to the pad before an earlier attempt. Courtesy: NASA/JoelKowsky

Likewise, the programme has proved very expensive. Development costs at circa US$24 billion are more than double NASA’s original estimate of US$10 billion, once later flights and infrastructure changes are included. The design of the Orion spacecraft and its service module has seen a similar dramatic rise in its originally projected US$6 billion cost.

For both SLS and Orion designs, NASA appears to have spent about US$20 billion more than was necessary for what is increasingly looking like an interim HLV and crew capsule. Worse still, budget and time constraints meant that NASA could only afford to build SLS but not a lunar lander. Thus, SLS began to look like a “rocket to nowhere”.

In fact, NASA always knew that its launch cadence would be slow, allowing – at best – two launches a year although a single launch was more likely given the construction constraints of its Michoud facility.

SLS launches were officially estimated to cost US$500 million each. However, if development costs are fully considered, this rises to about US$4 billion per flight across five Artemis flights. If the Orion costs are included, that adds another billion making these launches easily the most expensive ever.

Perhaps it is unfair to allocate development costs in this way, but even if only the annual SLS operational expenses are attributed to these launches, the bill is still likely to breach US$1 billion a pop.

Hindsight is a wonderful thing. However, at least NASA now has a human-rated working HLV to kick off its human exploration of the Moon. And it intends to make the most of it.

The SLS design: the core uses former Space Shuttle engines

The core of the SLS rocket uses the highly efficient propellant combination of liquid hydrogen and liquid oxygen (LOx). Following trade-off studies to compare first-stage engines, NASA settled on using four Space Shuttle Main Engine RS-25 rocket engines.

Exploded view diagram of key elements of SLS Block I rocket. Courtesy: NASA

The aluminium core first stage is 65 m long and 8.4 m in diameter. There is no longer an external fuel tank. Instead, all the propellants are held inside tanks within the core first stage. The propellant tanks are to be pressurised via autogenous pressurisation from heated tapped-off gaseous propellants.

Boeing is the prime contractor for the SLS core stages, including its avionics. The core stages are built at NASA’s Michoud facility in New Orleans using techniques such as friction welding.

Although reusability was never truly economic (it required too much maintenance between flights), the RS-25 engine is a highly admired design as it offers a very high specific impulse in a vacuum of 450 s (a measure of its propulsive efficiency).

The first four SLS (and Artemis) flights will each use four of the remaining 16 reusable RS-25D engines. These will be flown for a final time as expendable engines, albeit with modernised engine controllers and higher throttle limits. They also have extra insulation to cope with the high temperatures induced by the proximity of the solid rocket boosters.

The RS-25D engines carried by the first SLS flight had long histories. Courtesy: Aerojet-Rocketdyne

Later flights will switch to an RS-25E variant specially manufactured and optimised for expendable use. The thrust of each RS-25D engine has been increased from 492,000 lbf (2,188 kN), as on the Space Shuttle, to 513,000 lbf (2,281 kN) on the 16 modernised engines. The RS-25E will further increase per-engine thrust to 522,000 lbf (2,321 kN). The RS-25 engines are steered via hydraulic actuators.

SLS solid rocket boosters

While the RS-25 engines of the Main Propulsion System (MPS) are efficient, they need a thrust boost from a pair of Space Shuttle-derived solid rocket boosters to get the rocket off the ground. These are attached to the core stage.

The early Block 1 and 1B versions of the SLS will employ a five-segment solid rocket booster, using casing segments flown on the Space Shuttle’s four segment boosters with an additional central segment added. These are designed to be used expendably and fall into the ocean. They have new avionics and lighter insulation. The solid propellant is aluminium powder and ammonium perchlorate in a polybutadiene acrylonitrile (PBAN) binder.

Only eight SLS flights will use these boosters. A more powerful, booster design is being worked on under the Booster Obsolescence and Life Extension programme by Northrop Grumman space systems for later flights of the SLS Block 2. At one stage it was also mooted that a liquid propellant booster, using kerosene/LOx burning engines as in the original Saturn V’s F1 engine, might be used.

SLS upper stages: ICPS and then EUS

SLS will be equipped with two upper stage types. The early Artemis flights (I, II and III) will use the Interim Cryogenic Propulsion Stage (ICPS) which is, in effect, a stretched and human-rated Delta Cryogenic Second Stage powered by a single liquid hydrogen/Lox-burning RL10 engine.

The Artemis I flight’s ICPS will have an RL10B-2 engine, while Artemis II and III will use an RL10C-2. With these, the SLS Block 1 can launch up to 95 metric tons to LEO. A later burn will help achieve Trans Lunar Injection.

From Artemis IV onwards, a new upper stage – dubbed the Exploration Upper Stage (EUS) – will be used on the SLS Block 1 variant. The EUS carries four RL10C-3 engines and will eventually have RL10C-X engines.

Orion

The late Neil Armstrong once joked that as Project Constellation was deemed “non-executable” by the Augustine commission, this meant that it could not be killed. Well one part that did survive was the Orion capsule, which was deemed by most to be a good design and worth saving.

Artist’s impression of Orion separating from its ICPS after being Trans Lunar Injected. Courtesy: NASA

Good as the Orion was, the 5.02 m diameter, 3.3 m long conic aluminium-lithium crew module, which will eventually carry a crew of four to the Moon, still lacked a service module. Lockheed Martin began designing one, but as costs mushroomed, the European Space Agency and Airbus Defence and Space stepped in with one based on the ATV. It did this in lieu of payments owed for its share of the International Space Station launch and infrastructure costs. Hence, the “Mickey Mouse lookalike” circular solar arrays of the original design were replaced with an ATV X-configuration.

Although it granted NASA a significant cost saving, employing the European ATV as a baseline has resulted in a service module that is less than ideal on performance, meaning that Orion operations in low lunar orbit are effectively off the table. By the way, the lack of enough propellant on the Orion service module to reach Distant Retrograde Orbit is the real reason for the fancy gravity assist lunar flyby on the Artemis I mission.

A single AJ10 engine, using hydrazine and nitrogen tetroxide as the oxidiser, provides the spacecraft’s primary propulsion. Eight R-4D-1 engines and six pods of customised reaction control system engines, developed by Airbus, provide the spacecraft’s secondary propulsion. Orion is covered by a payload shroud for the initial launch phase and has an attached escape rocket on top should things go wrong.

Only the reusable landing module (LM) returns to Earth for re-entry (it is protected by the Apollo-style Avcoat ablative thermal protection system) and a parachute assisted splashdown.

Image of Artemis I Orion capsule taken on its way to the Moon with one of its own cameras. Courtesy: NASA

Human Landing System…but not on this flight

While NASA had SLS and Orion for early Artemis landing missions (Artemis III and IV), it also needed a landing craft – dubbed the Human Landing System (HLS). NASA eschewed a simpler storable propellant type, like that of the Apollo Lunar Module, and opted instead for a much more powerful version using cryogenic propellants even though the boil-off reduction and transfer technologies were not yet proven.

This has been partly driven by the relatively low performance of Orion’s service module, which cannot easily move to and from a low lunar orbit. Dockings with a lander will be made further out, including at the planned distant retrograde lunar orbit location of the Gateway space station.

A large lunar lander is also needed to provide sufficient cargo capacity to create lunar infrastructure on the Moon.

While NASA originally began a competition, with a Blue Origin-led team, Dynetics, and SpaceX on the short list, in the end a sole supply contract was awarded to SpaceX. It would use the Starship as the basis of the HLS, with a second lander to be selected later. SpaceX was chosen mainly because of the advanced stage of its Starship programme.

The initial Artemis mission, Artemis I, will test out the SLS/Orion combination in uncrewed condition, while no lander will be used until Artemis III.

Comment: Good Luck to Artemis I and well done to SLS

View of Earth and the far side of the Moon from Artemis I Orion. Courtesy: NASA

Artemis I has to be successful to make all of the above happen. We at Seradata and Slingshot wish Artemis I Godspeed and hope that this first flight is a success. We also congratulate all those who have worked on SLS’s successful maiden flight. That said, we doubt whether SLS will have a long-term future. With SpaceX’s much cheaper to operate Super Heavy/Starship combination now almost ready to fly, SLS is increasingly looking like an interim rocket. Interestingly, China, having once looked like copying the expendable SLS with its core-plus-boosters’ architecture for the planned Long March 9 HLV, now seems set on replicating the booster-less Super Heavy/Starship reusable design.

Of course, SpaceX’s offering has yet to prove itself, so it is just as well that NASA now has an operational SLS in its back pocket.

A live steaming video from Artemis i Orion is available below:

NASA Artemis I LIVE (ibm.com)

Post script: NASA originally placed a US$2.9 billion order with SpaceX in April 2021 for the HLS which will fly on Artemis III. Since then NASA has exercised “Option B” on the contract and awarded SpaceX a further US$1.15 billion to develop an upgraded version of its Starship lunar lander and fly the second crewed mission, Artemis IV.

Update on 21 November: At 1244 GMT on 21 November, Orion made a two-and-a-half-minute burn behind the moon at a 130 km altitude from the lunar surface to achieve its swing-by towards lunar DRO.

Update on 23 November: Some of the released CubeSats have had serious issues (Sources: NASA, Jonathan McDowell).

LunarHMap did not enter orbit around the Moon after it failed to fire its thrusters in time. It made a 1300 km flyby and carried out some scientific measurements as it did so on 21 November. Japan’s Omotenashi did not complete sun acquisition and failed to stabilise, with the result that power generation and communication were not ready in time to make its diversion for a planned lunar landing. The spacecraft was forced to make a lunar flyby instead, effectively losing 90 per cent of its mission. Both the NEAScout solar sail and the Team Miles CubeSat failed to establish communications with Earth. The infra-red imaging spacecraft LunIR is suffering from low signal strength in its communications.

The remaining satellites: Biosentinel, EQUUELEUS, ArgoMoon, CuSP and Lunar IceCube are believed to be operational.

Update on 28 November: At 0954 GMT on 25 November, Orion fired its OMS-E engine for 88 seconds to brake itself into DRO.


 

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