Relativity overachieves Terran 1 debut objectives

by Anthony Iemole

Relativity Space conducted the first flight of its Terran 1 rocket Wednesday. The Good Luck, Have Fun (GLHF) mission lifted off at 11:25 PM EDT (03:25 UTC on Thursday) from Launch Complex 16 (LC-16) at the Cape Canaveral Space Force Station. While the mission failed early into second stage flight, Relativity successfully flew through max-q per the main objective.

A first launch attempt on March 8 was scrubbed due to out-of-bounds propellant thermal conditions on the upper stage. During the second day of attempts on March 11, the countdown was aborted twice, first due to a stage separation automation issue at T- 0.5 seconds, then again due to low stage two fuel pressure.

Relativity and Terran 1

California-based Relativity Space was founded in 2016 by Tim Ellis and Jordan Noone. The company’s Terran 1 rocket is a two-stage fully expendable small-lift launch vehicle capable of delivering a maximum payload of up to 1,250 kg to low Earth orbit (LEO), and up to 900 kg of payload to a Sun-synchronous orbit (SSO).

The entire vehicle stands 33.5 meters tall, with a diameter of 2.28 meters and a dry mass of 9,280 kg. Terran 1 is unique compared to other launch vehicles as it is predominantly 3D printed – and was aiming to be the first vehicle of its type to reach orbit. The vehicle used for the GLHF mission was 85% 3D printed by mass with Relativity hoping to increase that proportion to 95% in the future.

Both of Terran 1’s stages use the same propellant: liquid methane (CH4) and liquid oxygen (LOX). This allows the design to be kept simple, eliminating the need for the rocket itself and the ground support equipment (GSE) to handle additional types of propellant. With this launch, Terran 1 is also aiming to become the first methane-fueled rocket to reach orbit — China’s Zhuque-2 rocket having suffered a failure during its first launch in December.

The first stage is propelled by nine Aeon 1 engines, built in-house at Relativity. Similar to SpaceX’s Falcon 9 rocket, the engines are arranged in an octagonal configuration, with eight of the engines clustered around the ninth, center, engine at the base of the vehicle.

Aeon 1 is the first engine to have been developed by Relativity and was designed for use on Terran 1. It uses a gas generator cycle and produces approximately 100 kilonewtons of thrust at sea level, increasing to 113 kN in a vacuum. Like Terran 1 itself, Aeon 1 is almost entirely 3D printed. This vastly simplifies the design and manufacturing of the engine compared to traditional methods, as complex assemblies can be printed as single parts, greatly reducing the number of individual components needed to make up an engine.

Terran 1’s second stage supports a single vacuum-optimized Aeon Vac engine, which is also 3D printed.

Relativity is currently developing the more powerful Aeon R engine for its upcoming Terran R launch vehicle, but after development is complete this is also expected to be used on Terran 1. A planned block upgrade to Terran 1 will see the nine Aeon 1 engines on the first stage replaced with a single Aeon R.

Good Luck, Have Fun mission

Since the Good Luck, Have Fun mission was Relativity’s first attempt to reach orbit, Terran 1 was not carrying a functioning payload. Instead, a small 16.5-centimeter, 1.49-kilogram aluminum alloy ring was aboard the rocket. This ring was one of the first metal 3D prints the company made using its first generation of Stargate 3D printers.

The 16.5 cm, 1.49 kg aluminum ring being flown on the GLHF mission. (Credit: Relativity Space)

For its maiden flight, Terran 1 also flew without a deployable payload fairing. Instead, it used a smaller fixed nosecone, which remained attached to the second stage.

The launch took place from the Cape Canaveral Space Force Station’s Launch Complex 16 (LC-16), a launch pad formerly used to test Titan, and later Pershing, missiles.

Shortly before liftoff, Terran 1 ignited its nine Aeon 1 engines, with a command sent by the onboard flight computers to release the vehicle for flight. After climbing vertically for the first 12 seconds of flight, the vehicle began its gravity turn by slowly pitching downrange.

Terran 1 passed through the area of maximum aerodynamic pressure (max-q) at T+1 minute and 20 seconds. Max-q is the period of flight where the rocket will experience the greatest amount of aerodynamic forces as it climbs through the atmosphere.

Relativity stated that passing this point of the flight during this launch would be a big inflection point, as it proved the structural integrity of the 3D-printed rocket under the most extreme conditions it is expected to encounter in flight.

Having passed max-q, the nine first-stage engines continued to fire for another 80 seconds until the next major flight event – main engine cutoff (MECO) – was reached. At this point in the flight, the first stage shut down its engines, with the separation of the first and second stages taking place approximately five seconds later.

Launch timeline of the Good Luck Have Fun (GLHF) mission. (Credit: Relativity Space)

Terran 1’s second stage was to coast for six seconds after separation before igniting its single Aeon Vac engine at two minutes and 51 seconds mission elapsed time. However, despite visual indications that the engine was attempting to ignite, no amount of useful thrust was produced and the anomaly ended the mission.

Terran R

While Relativity was preparing for its first launch with Terran 1, the company was also already making progress on its much larger next-generation launch vehicle: Terran R. This is expected to be a fully-reusable launch system with an anticipated payload capacity of 20,000 kg to LEO.

Like Terran 1, Terran R will be a two-stage rocket, which will be almost entirely 3D-printed and use the same propellant combination of liquid methane and liquid oxygen. It will fly with seven Aeon R engines powering its first stage, with a single vacuum-optimized Aeon R on its second stage.

Using lessons learned from the development of Terran 1, as well as from the GLHF mission, Terran R’s first launch is currently slated to occur no earlier than 2024. While this goal may be optimistic, Relativity has seemingly been making rapid progress on the engine that will power its next-generation launcher.

An Aeon R engine undergoes a hot-fire test. (Credit: Relativity Space)

Testing of the Aeon R engines has proceeded rapidly with development engines recently achieving full thrust – around 1,148 kilonewtons – on the test stand. This came just shortly after the engine’s first full-scale hot-fire test in December 2022, where the engine successfully reached 35% of its maximum power level on the stand.

Once operational, Terran R will begin working through a backlog of launches worth more than $1.2 billion from multiple customers, including a multi-year, multi-launch launch services agreement (LSA) with communications company OneWeb.

Another customer for Terran R is space transportation startup Impulse Space, which has partnered with Relativity to conduct the first commercial mission to Mars. Relativity will use its Terran R rocket to send a lander built by Impulse Space toward the red planet. This is currently slated to be the payload for Terran R’s maiden flight.

(Lead image: Terran 1 launches from LC-16. Credit: Julia Bergeron for NSF)

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