FLEX

NASA/James Blair. Public domain (NASA / US government work).

Overview

FLEX, Flexible Logistics and Exploration, is an unpressurized four-wheeled lunar rover built by Venturi Astrolab of Hawthorne, California. It carries two suited crew, accepts modular payloads at three quick-disconnect interfaces, and can be driven by an onboard crew, teleoperated from Earth, or run under supervised autonomy [4], [6]. A full-scale terrestrial prototype was built and field tested before the flight design was frozen. The flight configuration selected by NASA in May 2026 is designated CLV-1 and is derived from the FLEX architecture [5].

Astrolab is the prime. Venturi Space supplies the wheels, batteries and battery management system; Axiom Space, Interlune and Odyssey Space Research are named team members [5].

Almost every vehicle figure below comes from manufacturer documentation [4], [5], [6], [7], [9] rather than a reviewed publication, and the source column says which. The NASA papers cited [1], [2], [3] describe the government reference LTV design or the LTV requirement set, not the Astrolab vehicle.

Specifications

Parameter	Value	Source
Crew	2 suited astronauts	manufacturer [4]
Maximum vehicle mass, CLV-1	950 kg	manufacturer [5]
Stowed envelope	2.0 x 2.3 x 2.2 m
Deployed envelope	4.0 x 2.3 x 2.6 m to antenna top
Top speed, level ground	10 km/h
Locomotion	four wheels on articulating limbs	manufacturer [6]
Wheel diameter	930 mm	manufacturer [7]
Wheel life specification	at least 1000 km
Wheel temperature specification	-240 to +130 degrees C
Total payload capacity	2000 kg over three interfaces	manufacturer [4]
Cargo delivery capacity	1600 kg, 3 cubic meters
Solar array area	3 square meters
Robotic arm	6 DOF, 25 kg (250 N) at 2 m radius	manufacturer [6]
Payload bus, regulated	24 V DC, 100 W per standard payload
Payload bus, unregulated	60 to 80 V DC, 750 W per standard payload
Payload data interface	Gigabit Ethernet
Night survival	yes, by heated battery enclosure	manufacturer [9]

The 2000 kg total payload capacity is the current manufacturer figure [4]. The 2022 Payload Interface Guide gave 1000 kg for volumes in excess of 3 cubic meters and stated that mass limits for the lunar vehicle were still being specified [6]. Structural limits in that document are for the terrestrial prototype, and the document says lunar limits were expected to be comparable in load and higher in mass.

Mission profile

The following describe the flight assignments, not the vehicle.

Parameter	Value	Source
Contract	Lunar Terrain Vehicle Services, Phase 1 High Achievability Mission task order	[5], [8]
Task order value	approximately $219 million
Parent IDIQ	up to $4.6 billion, awarded 2024, 13 years plus 2	[5]
Surface arrival	no earlier than 2028	[5], [8]
Landing site class	lunar south pole	[8]
Precursor flight	FLIP on Astrobotic Griffin-1, Nobile region	[9], [10]

NASA awarded LTVS Phase 1 task orders to Astrolab at approximately $219 million and to Lunar Outpost at approximately $220 million, with delivery to the surface anticipated by 2028 [8]. The stated near-term plan is that over 18 months the providers finalize rover designs, conduct crewed evaluations, and qualify flight units. The NASA release restates CLV-1 as having a mass of about 2000 pounds and the ability to exceed 6 mph on level terrain, consistent with the 950 kg and 10 km/h given by Astrolab [5].

FLIP, the FLEX Lunar Innovation Platform, is a smaller vehicle of approximately 450 kg carrying up to 30 kg of payload, manifested on Astrobotic’s Griffin-1 lander to the Nobile region of the south pole [10]. It flies full-size FLEX batteries, tires, avionics, sensors and software, so its purpose is subsystem qualification for FLEX rather than an independent program [9].

Requirements the vehicle is built against

The LTV requirement set is published in NASA papers even though the Astrolab design against it is not. The 2021 request for information asked for a vehicle that survives an extended lunar night of at least 85 hours and 125 hours if achievable, fits a CLPS-class lander, accommodates a driver and a passenger in EVA suits, carries a total payload mass of at least 800 kg for as much as 20 km without recharging, is available at least 8 hours per Earth day outside night periods, survives south polar and permanently shadowed region temperatures of 50 K, has an operational life of at least ten years, and can be operated remotely [3]. Two numbered system requirements appear in the teleoperation study: LTV-SYS-071 sets 6 km as threshold and 8 km as goal for distance covered in one 24 hour period under remote operation, and LTV-SYS-029 requires no less than 20 km without stopping to recharge [1]. A separate NASA thermal analysis states a required top speed of at least 15 km/h [2], which the manufacturer figure of 10 km/h for CLV-1 does not meet [5]; the two documents describe different design generations and no source reconciles them.

Mobility

FLEX uses a wheel-on-limb architecture in which each of the four wheels is carried on an articulated limb. The limbs raise and lower chassis ground clearance, adapt to terrain while holding the chassis attitude, lower attached instruments to the ground, and let the vehicle collect and deposit modular payloads without a separate lifting mechanism [6]. The same mechanism is what allows multiple rovers to cooperate on payloads too large for one vehicle, including lander relocation.

The wheel is a Venturi Space design, 930 mm in diameter, built from 192 cables acting as spokes, an outer rim carrying springs, and a flexible tread of a material developed for the application [7]. It is specified for at least 1000 km of travel and for surface temperatures between -240 and +130 degrees C on a vehicle traveling at 15 km/h. The wheel was presented publicly in June 2023.

Wheel thermal behavior on a lunar rover is dominated by radiation rather than by contact with the regolith. In the NASA government reference LTV analysis, wheel temperatures over a full summer day at a highly illuminated Connecting Ridge site ranged from 240 K to 420 K against a maximum far-field regolith surface temperature near 114 K, and the temperature profile was insensitive to the assumed wheel-to-regolith conductance because the low conductivity of the regolith itself is the choke point [2]. Peak conducted heat loss was 12 W from a single wheel and 37 W from all four. Sinkage for that reference design was computed at 1.1 cm, against 1.3 cm measured in the Apollo 15 LRV tracks [2]. The exception is a traverse into a permanently shadowed region, where the rolling contact patch continually meets fresh 25 K regolith: over a 2 hour traverse at maximum speed the predicted mean wheel temperature ranged from 264 K at an assumed contact conductance of 0.1 W/K down to near 25 K at 100 W/K, with total energy transfer asymptotic to about 12,000 kJ above 10 W/K [2]. That paper states no test-verified method exists to derive the conductance analytically and that a thermal vacuum measurement against rotation speed, loading and temperature is required. Aluminum 7075 in the reference wheel carcass gains yield strength at cryogenic temperature and loses fracture toughness [2]. The Venturi cable-and-spring wheel is a compliant structure of the class that paper flags as hard to model, because conduction between contacting non-welded strands in vacuum depends on contact pressure and area, and radiating area must be reduced for the gaps. No published measurement of the Venturi wheel against these effects was located.

Power and energy

Generation is a deployable solar array of 3 square meters that tops up internal batteries [4]. Battery capacity in watt-hours is not published. Batteries and the battery management system come from Venturi Space [5]. The batteries sit in an enclosure built to hold them inside their operating range across the surface temperature swing, and it is that enclosure that the manufacturer identifies as the enabler of lunar night survival [9].

Battery minimum operating temperature is the sizing parameter for heater power on a vehicle of this class. The NASA thermal design study defines the critical component as the one with the highest minimum operating temperature, states that this is usually the battery, and takes 0 or -10 degrees C as the assumed limit from which worst-case cold heater power follows [3]. Cells qualified to operate colder reduce thermal management mass directly, because both battery size and heater count fall.

Thermal

Surviving the night is the dominant thermal case. Lunar surface temperature at the south pole reaches 300 K in daylight and 50 K at night, most nights at a given site last about 36 hours, and NASA analysis indicates a vehicle would see at least two extended nights of at least 85 hours per year, extending to 125 hours if stationary [3]. Radioisotope heater units were considered for the reference design and were constrained by Department of Energy material control, by units not being in production, and by CLPS launch licensing that has no precedent for radioisotope payloads.

Astrolab publishes no thermal architecture for FLEX beyond the battery enclosure [4], [9]. The payload interface supplies thermal management services to attached payloads through the blind-mate umbilicals, so the vehicle carries capacity beyond its own needs [6].

Compute and avionics

Astrolab describes the primary flight software as an architecture with flight heritage on multiple NASA missions, providing a portable, reusable and modular base, and does not name the framework [6]. The processor is not published. The autonomy stack runs as a separate process joined to the core flight software through a bridge, which is the mechanism by which individual autonomous functions can be moved to ground assets. Verification is stated as unit testing, physics-based simulation in the loop, hardware in the loop, and full system integration testing. FLIP carries flight avionics, sensors and software for surface qualification [9].

Autonomy

The published autonomy level is supervised: onboard hazard avoidance and navigation to operator-selected waypoints, with an operator in the loop selecting the waypoints [6]. The API is designed to let a payload take as much or as little control of the vehicle as its objectives require. Sensors for hazard avoidance are stated to exist but are not enumerated [4].

Teleoperation performance under lunar communication latency has been measured by NASA on a government reference LTV in simulation. Average speed across all operators and terrain scenarios fell monotonically with delay [1]:

One-way communication delay	Average speed	Time to cover 20 km
0 s	3.24 km/h	6 h 10 min
4 s	2.56 km/h	7 h 49 min
6 s	2.03 km/h	9 h 51 min
8 s	1.76 km/h	11 h 22 min

Values from [1]. Operators braked more frequently under latency, and subjective workload rose against the zero-delay case with mental demand, frustration and performance as the contributing factors. Driving strategy was uniform across operators at zero delay and diverged into three distinct strategies at 4 s [1]. Operators received about 30 minutes of familiarization before each run, and the simulation provided an operator-selected rate limiter on the hand controller and a predictive circle. Teleoperated average speeds of 1.76 to 3.24 km/h are a fraction of the 10 km/h vehicle top speed [5], so the binding constraint on remote traverse rate is the operator and the link rather than the drivetrain.

Communications

A gimballing high-gain antenna provides direct-to-Earth communication [4]. Bands, data rates and relay arrangements are not published. Payloads are given Gigabit Ethernet at the vehicle interface [6], which is a payload-to-vehicle link and not a downlink rate.

Payload interfaces

The payload interface is the part of FLEX with a published specification. Three quick-disconnect interfaces exist, two on the top deck and one underslung, each with blind-mate umbilicals carrying regulated power, data and thermal services [6]. The vehicle docks to payloads robotically at each of the three, so payloads can be picked up at a lander, carried, and set down elsewhere.

Interface	Payload mass limit	Limit load per hook	Forward/aft	Lateral
Top deck	460 kg	13.5 kN	27 kN	18 kN
Underslung	375 kg	6.3 kN	22 kN	15 kN

Values are terrestrial prototype design limits from [6]; the top deck also takes a pure moment about the lateral axis of 2200 N-m.

Standard underslung cargo containers come in three sizes, 1.5 x 1.0 x 1.0 m, 1.5 x 1.5 x 1.0 m and 1.5 x 2.0 x 1.0 m; the top-deck design envelope is 1.5 x 0.75 x 2.5 m [6]. A payload may span both.

The 6 DOF arm handles more than 25 kg, equivalently 250 N, within a 2 m radius workspace [6]. Its interface limits are 250 N pure axial, 250 N pure lateral root-sum-square, 120 N-m about the rotational axis for a torque-reacting mount and 56 N-m for a static mount, and 42.5 N-m root-sum-square bending about the interface plane. Arm payload envelopes are 236 x 236 x 340.5 mm for torque-transmitting and 236 x 340.5 mm for static mounting, a modular storage rack holds up to 15 end effectors or payloads as large as a 12U cubesat form factor, and per-payload power at the arm interface is 25 W regulated and 100 W unregulated, against 100 W and 750 W at the deck interfaces [6].

Modes of operation

Three driving modes are published: crew driving from the onboard crew station, remote teleoperation from Earth, and supervised autonomous navigation to operator-selected waypoints [4], [6]. The crew station is itself a removable top-deck payload, so the crewed and uncrewed configurations differ by a payload exchange rather than by vehicle build. Survive-the-night is a distinct state in which the vehicle is dormant with the battery enclosure held above its minimum operating temperature [9].

Ground operations

No operations concept, control center or planning cycle has been published for FLEX. The NASA teleoperation studies establish the operator-side envelope the ground system has to work within: single-operator remote driving is viable through 8 s of one-way delay with a rate limiter and a predictive circle in the display, at the cost of speed and workload [1]. Crewed evaluations of the vehicle have been run at NASA JSC with suited subjects working the crew station, stowage drawers and payload handling [8].

Technologies developed

Two products of the program are separable from the vehicle. The first is the intermodal payload standard: a published mechanical and electrical interface with downloadable schematics and off-the-shelf adapter plates and brackets, intended so that landers, rovers and payloads from different vendors interoperate the way containerized freight does [6]. The second is the Venturi hyper-deformable wheel, a cable-and-spring compliant wheel specified for 1000 km and for a 370 degree C temperature span, which is a component rather than a vehicle subsystem and is being flown on FLIP ahead of FLEX [7], [9].