LISTER

NASA/Firefly Aerospace. Public domain (NASA / US government work).

Overview

LISTER is a pneumatic drill and heat flow probe built by Honeybee Robotics for a Texas Tech University investigation, flown as one of ten NASA payloads on Firefly Aerospace’s Blue Ghost Mission 1 to Mare Crisium [15], [18], [19]. It measures regolith temperature and thermal conductivity at a series of depths; heat flow is the product of the thermal gradient and the conductivity over the interval penetrated. Before this flight, lunar heat flow had been measured in situ only by the Apollo 15 and 17 crews with a handheld drill, emplacing probes by hand to about 1.6 and 2.3 m and reading a combined heat flow that the Apollo 17 report and later revisions treated as anomalously low against models of a radiogenically heated Moon [1], [2], [3]. Every synthesis since has carried those two numbers forward as the only ground truth for lunar heat flow [4].

It reaches depth without a rotating auger. A stainless steel tube is spooled off a reel and yielded straight on the way out, becoming a stiff boom; nitrogen fed through the tube leaves a nozzle at its leading end and blows regolith out of the way as the boom advances [15], [17]. The hole this produces is typically 6 cm across or wider against a 6.4 mm tube [18].

The instrument was mounted below the lander platform, which was a thermal decision rather than a packaging one: at an 18.5 N landing site, direct solar heating of the instrument housing had to be avoided [18].

Most lunar subsurface access to date has been rotary or rotary-percussive: an auger or corer turned, and sometimes hammered, into the regolith, a design lineage surveyed across Apollo, Luna, Chang’e-5 and the drills built for Mars and asteroid missions [5], [6]. That family’s own literature treats percussion as the main lever for lunar depth: bench comparisons find percussive assistance cuts the force needed for a given penetration rate several times over against rotation alone, and models of auger and corer loads built from bench data trace the rest of that force to rock content and to the pile of cuttings a plain rotary tool has to lift clear of the hole [7], [8], [9], [12]. Piezoelectric percussive drills pursued the same lever without a full rotary drivetrain, at the cost of two decades of field development to make the actuator survive planetary duty cycles [10]. A cryogenic testbed built around one volatiles-bearing lunar auger design found that frozen, icy regolith raises drilling loads and heat generation well past the dry case an Earth-bench test would show, and a thermal simulation of that same cryogenic condition traces the extra heat to friction at the drill-soil interface rather than to the ice itself [11], [13]. A 2022 survey of the whole lineage argues that every rotary or rotary-percussive lunar coring effort to date, Apollo through Chang’e-5, is bounded by the same cutting-element physics regardless of how the rotation or percussion is delivered [14]. LISTER’s pneumatic boom sits outside that lineage: it carries no rotating or percussive element to bind against the load that limit describes, and its own limit is a different one, the lift capacity of a gas jet against clasts the boom cannot blow clear of the hole.

Specifications

Parameter	Value	Source
Mechanism mass	under 9 kg, against a 15 kg instrument allocation	[17]
Mechanism envelope	32 x 33 x 43 cm
Coiled tubing	stainless steel, 6.4 mm diameter	[15], [17]
Excavated hole diameter	typically 6 cm or larger	[18]
Needle sensor	28 mm long, 2.8 mm diameter, platinum resistance thermometers	[16], [17]
Average power, quiescent	33 W	[17]
Average power, drilling	88 W
Heat flux accuracy requirement	10 percent
Depth requirement	at least three measurements between 1 and 2 m
Design depth	2 m threshold, 3 m objective
Working gas	nitrogen	[15]
Monitoring	two below-deck cameras	[18]

Mission profile

Parameter	Value	Source
Landing	2 March 2025, Mare Crisium	[15]
Operations start	two Earth days after landing
Depth after two further days	0.96 m, seven measurement depths
Progress slowed	at 0.94 m
Operations suspended	spacecraft heating under the midday Sun
Operations resumed	seven Earth days later
Final depth	0.98 m, one additional measurement set
Depths measured	8	[16]
Endogenic heat flow, early result	13 to 14 mW/m2	[15]

The preflight plan called for measurements at 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 m, with descent between depths expected to take a few tens of seconds unless rocks too large to be blown out were encountered [18]. That is what stopped the drill. Below 0.94 m, downward progress slowed as clasts and pebbles too large or heavy to be lofted accumulated in the bottom of the hole; the obstruction is inferred from the penetration rate rather than observed [15].

Ground test against flight

The instrument was qualified in a vacuum chamber against simulant beds whose rock content was deliberately set high, about 33 percent by volume, so that rock encounters would be frequent rather than avoided by luck [17]. Conservatism was added because the size and frequency of rocks in the real subsurface could not be predicted from available data, and because drilling performance cannot be analyzed in high fidelity and has to be verified empirically.

Condition	Depth reached	Source
Fines-only simulant, vacuum chamber, 1 g	2.2 m	[17]
Rocky simulant, about 33 percent rocks by volume, vacuum chamber, 1 g	1.35 m
Mare Crisium regolith	0.98 m	[15]

The flight result falls below the conservative ground case as well as the optimistic one. Against 1.35 m in the rocky simulant and the 2 m threshold requirement [17], the instrument stopped at 0.98 m [15], halted by an obstruction of exactly the kind the rocky test was designed to represent.

Approach

At each target depth the gas jet stops and the needle sensor is pushed into unexcavated regolith at the bottom of the hole, so the material it measures has not been disturbed by the excavation that reached it [17]. The sequence at each depth takes two hours: an hour of passive equilibration, 30 minutes of constant-power heating, and 30 minutes of cooling [16]. Equilibrium regolith temperature comes from extrapolating the first hour’s trend to infinite time by the Bullard method; conductivity comes from fitting a finite-element heat transfer model to the heating and cooling curve.

A rock small enough to move is dealt with by dithering, an oscillatory motion of the boom that pushes it aside, demonstrated in ground testing and carried into the flight concept of operations [17], [18].

Mobility

None beyond the boom’s own advance.

Power and energy

Average power is a requirement rather than a measurement: 33 W quiescent, 88 W during drilling, within a 15 kg, lander-agnostic package [17]. Neither the gas quantity carried nor the energy consumed per meter is published.

Thermal

The mounting below the lander platform exists to keep the instrumentation housing thermally stable at a low-latitude site by keeping it out of direct sunlight [18]. Deployment was timed to begin only once the Sun had risen high enough for the lander to cast a shadow on the regolith beneath it. Even so, the lander heating up at midday is what suspended science operations for seven Earth days [15].

The measurement itself is defeated by thermal noise near the surface. The uppermost half meter or so fluctuates with the diurnal and annual insolation cycles, and the 2 m threshold depth was set to escape those waves [16], [17]. A model driven by site ephemeris and Diviner surface temperature history places the depth below which annual fluctuation falls under 0.1 K at 0.6 m, and the modulation of that annual wave by the Moon’s 18.6-year precession happened to be at its minimum during the mission, which is what makes a heat flow value recoverable from measurements that stopped at 0.98 m [15].

Compute and avionics

Not published. Platinum resistance thermometers in the needle sensor are the only electronics described.

Autonomy

None. The drill descends one depth at a time under ground control: after each set of measurements, data and camera images are downlinked, the operations team has 90 minutes to assess instrument state and data quality, and only then is the next descent commanded [18].

Communications

Through the lander.

Payload and instruments

The needle sensor is the instrument: a 28 mm long, 2.8 mm diameter probe carrying platinum resistance thermometers, mounted at the gas nozzle [16], [17]. Two cameras below the lander deck monitor the excavation [18].

Modes of operation

Excavation, with gas flowing and the boom advancing; measurement, with the gas off and the probe pressed into undisturbed bottom-hole regolith; and dithering, an oscillatory motion used to displace small rocks [17], [18]. The suspension across the lunar midday was a response to spacecraft thermal conditions rather than a designed mode [15].

Ground operations

Run by the LISTER surface operation team, which reviews each depth’s data and imagery inside a 90-minute window before authorizing the next descent [18].

Technologies developed

Pneumatic excavation was used to penetrate a planetary subsurface for the first time, and LISTER became the first robotically operated device to actively excavate lunar regolith and the first to take science measurements in situ at multiple subsurface depths on the Moon [15]. The technique’s advantage is speed and the absence of a rotating cutting element; its demonstrated limit is that it moves only what the gas jet can lift, so a bed of coarse clasts ends the hole.

The measurement result is an early endogenic heat flow of 13 to 14 mW per square meter at Mare Crisium, obtained by inverting eight depth measurements against a thermal model [15]. The authors describe it as preliminary, with a fuller inversion and an uncertainty estimate outstanding, and the separation of endogenic flow from insolation transients rests on that model rather than on measurements taken below the thermal skin depth.

What is not established

The heat flow number is explicitly early: the team that produced it still has a fuller inversion and an uncertainty estimate outstanding, so it should not be read as a settled measurement, and it comes from one site, one deployment, one lander [15], [17]. The final depth of 0.98 m falls inside the band the 2 m threshold was set to escape, so separating endogenic heat flow from insolation transients rests on the site thermal model rather than on measurement taken below the thermal skin depth [16], [17]. The obstruction that stopped the drill is inferred from the slowing penetration rate, not observed directly or identified by composition [15]. The preflight plan and the ground qualification campaign were both built on simulant beds and analysis, not lunar regolith, and their own authors note that the size and frequency of rock encounters in the real subsurface could not be predicted from the data available before flight; the flight result, at 0.98 m, fell short of the rocky as well as the fines-only ground case [18].

References