Intuitive Machines (IM)

Intuitive Machines expects to commission Odysseus several minutes after LVSEP autonomously. During autonomous commissioning, the lander’s GNC activates the cold-gas helium Reaction Control System (RCS) to control the vehicle attitude.

At this point, Odysseus does not know where it’s pointed, but it can stop its spin motion, much like a person spinning in a chair with closed eyes can control the spin without knowing where it stops.

After controlling the spin rate, special cameras known as star trackers autonomously match images of the distant star field and provide Odysseus with its orientation. Software onboard takes the star tracker measurements and processes them through an algorithm known as the Kalman filter to correct the onboard orientation, known as attitude, and then estimates and rejects bad measurements.

Once the GNC system has autonomously determined its attitude relative to the star field, it uses a reference position from the nominal launch vector to determine the approximate location of the sun. GNC then commands RCS jets to maneuver the lander’s top deck toward the sun with a slight angle to illuminate the top deck and side solar arrays to generate maximum power.

Odysseus holds this approximate attitude within +/- 15 degrees for the entire mission other than when flight controllers in Nova Control are executing maneuvers or pointing the lunar lander’s High Gain Antenna (HGA) used for communications back to Earth.

When Odysseus’ top deck is pointed toward the sun, this is known as max power attitude, which also helps flight controllers in Houston, Texas, manage the lander’s thermal state on the vehicle by keeping other systems in the shade of the top deck and side deck solar arrays. Each step in the commissioning process is expected to happen autonomously because flight controllers in Houston do not have communications with Odysseus yet.

When autonomous commissioning is complete and max power attitude is established, Odysseus turns on its communication radios and makes first contact with flight controllers in Nova Control.

After autonomous commissioning, flight controllers in Nova Control prepare for the engine commissioning maneuver using Odysseus’ state-of-the-art cryogenic propulsion system. The engine commissioning maneuver allows flight controllers to verify engine performance and adjust the lander’s first trajectory. 

Odysseus is moving on a Trans Lunar Orbit (TLO) after LVSEP on its way to the Moon before Engine Commissioning. Flight controllers on the trajectory team (TRAJ) use the signal from the lander’s communication systems to perform Orbit Determination (OD) and fire arcs of this signal data to update how fast it is moving. Minor corrections are expected to stay on course, like a car driver making minor adjustments with the steering wheel along a straight stretch of road.

Intuitive Machines’ Flight Dynamics Officer (FDO) uses this update to calculate a direction to execute the engine Commissioning Maneuver (CM) for the best improvement in Odysseus’ trajectory to intercept the Moon. With the CM direction set by FDO, Intuitive Machines’ Flight Manager (FM) and Communications Officer (COMM) command the vehicle to rotate from max power attitude to burn attitude. Now, CM transitions control to Intuitive Machines’ Propulsion Operations (PROP) lead to begin the main engine burn.

There are multiple steps to performing a main engine burn. The first is to flow cryogenic methane and oxygen down the lander’s feed lines to the engine to condition the propulsion system temperature; we call this chillin the engine. PROP monitors several automated valve and temperature readings in this process to ensure everything is progressing within the expected parameter ranges.

The onboard AFM is monitoring the Time of Ignition (TIG) for the CM to begin. A few seconds before TIG, the RCS system fires jets to settle their tanks’ liquid methane and oxygen. Then, the main engine igniter comes on, much like a pilot light in a gas oven, to ignite methane and oxygen, which have been mixed in the combustion chamber by a carefully orchestrated opening of main throttle valves. The engine start-up sequence is something that Intuitive Machines has tested thousands of times to validate safety and reliability.

During CM, the vehicle holds a constant attitude by adjusting the angles of the main engine inside a two-axis gimbal ring designed by the Intuitive Machines team. The automated CM sequence also throttles the main engine to give the PROP team data to make necessary adjustments across the engine’s power range. At the same time, Odysseus continues to coast toward the Moon

After CM, TRAJ collects data from another OD update. FDO evaluates this update and calculates how far Odysseus might be from hitting its orbit target around the Moon. FDO uses a particular coordinate system called the B-Plane, which is the mission design equivalent of the square on the backboard in basketball. If a basketball player hits the backboard square with a shot, the ball is likelier to go in the hoop. Similarly, if Odysseus hits its target on the B-Plane, it is in the right spot to be captured into lunar orbit.

The expected mission scenario is that each Trajectory Correction Maneuver (TCM) will be smaller than the previous one as flight controllers dial in the lander’s B-Plane target. TCM 3 is the most critical maneuver because it is the last chance flight controllers in Houston have to correct Odysseus’ trajectory before it is captured into lunar orbit.

For each TCM, FDO evaluates the maneuver size needed to keep the B-Plane target in the lander’s path. If the TCM is less than the ability of Odysseus’ main engine to execute, the flight controllers may choose not to perform that TCM and make any corrections during the next opportunity.

The Nova-C class lunar lander’s three TCM burns are executed at maximum throttle, where the engine is most efficient. After each TCM, Intuitive Machines flight controllers point the lander’s HGA back to Earth for communication to Nova Control. Following TCM 3, the TRAJ team collaborates with FDO to finalize the OD solution crucial for updating the Lunar Orbit Insertion (LOI) maneuver.

Concurrently, Odysseus’ top deck maximizes solar energy capture post-TCM 3, adopting the maximum power attitude. As LOI approaches, Odysseus uses its RCS to orient retrograde, directing the engine towards the Moon for optimal positioning ahead of the maneuver. 

After flight controllers load the final LOI maneuver solution on Odysseus, Intuitive Machines expects about four hours of watching systems prepare for this maneuver. For IM-1, LOI is performed in the blind on the far side of the Moon. Flight controllers are not receiving real-time updates because there is no lineof-sight communication back to Earth.

The Nova Control team counts down to LOI TIG and waits for the lander to perform its largest maneuver, between 800 and 900 meters per second, to capture into a 100 km circular Low Lunar Orbit (LLO). This maneuver is approximately one-third of the total capability of Odysseus’ propulsion system.

After a successful LOI, the Nova Control team starts a cadence of activities to check the lander’s status and its systems in LLO to prepare for landing. This includes calibrating Odysseus’ navigation optical cameras for lunar illumination conditions. 

For each lunar orbit, Intuitive Machines expects to have about 75 minutes of communication followed by 45 minutes where the Moon blocks Odysseus’ direct line-of-sight radio link between the lander and Intuitive Machines’ ground stations. When flight controllers lose communications and are in a communications blackout, we call it Loss of Signal (LOS). When flight controllers regain communication and are within line-of-sight, we call it Acquisition of Signal (AOS). Odysseus will orbit the Moon approximately 12 times before descending to the surface.

For Intuitive Machines, LLO environment is more complex than the deep space environment Odysseus experienced during transit. The Moon’s harsh environments are actively at play. When the lander is on the sunward side of the orbit, the sun heats the lander on one side, but the Moon also bakes the other side of the spacecraft with reflected infrared radiation, so Odysseus is very warm. Then, the lander passes into the lunar shadow, and the vehicle plunges into a deep cold regime and requires heater power drawn from batteries to keep systems warm.

Intuitive Machines designed Odysseus’ trajectory to fly to the Intended Landing Site (ILS) on the Moon. Once the Nova-C class lunar lander is getting closer to its ILS, the onboard software selects a safe Designated Landing Site (DLS) with the slightest slope, free from hazards, with the range of the lander.

Odysseus’ systems are intended to match lunar gravity to fly toward the DLS. During this time, the main engine is continually throttling down, lowering the engine power to compensate for the lander getting lighter and lighter with spend propellants spent leaving the spacecraft’s mass.

At this point, Odysseus uses inertial measurements only. No cameras or lasers are guiding the spacecraft to the lunar surface because they would read lunar dust kicking up from the lander’s engine. Odysseus’ Inertial Measurement Unit (IMU) senses acceleration like a human’s inner ears, which feel rotation and acceleration.

Terminal descent is like walking towards a door and closing your eyes the last three feet. You know you’re close enough, but your inner ear must lead you through the door.