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Linear Energy Transfer Spectrometer (LETS)

IM-6 · manifested · NASA payload

A small radiation monitor built around a Timepix silicon pixel detector. It records each charged particle that crosses the sensor and the energy it deposits (its linear energy transfer), giving the dose and the kind of radiation in transit and on the surface. NASA flies LETS on all four late-2028 landings to compare transit paths and surface sites, 'akin to having weather stations'.

PI: Not named for IM-6. Edward Semones (NASA Johnson) was PI for the Peregrine LETS; JSC's 2023 slides list Eddie Semones, Dan Fry and Stuart George as PIs.
Built by: NASA Johnson Space Center, Space Radiation Analysis Group (SRAG) (NASA center)
Technology radiation monitor (Timepix charged-particle spectrometer)
Moon Base need DN-012 L (The knowledge base's own matching, not NASA's: for the four late-2028 landings it pairs LETS with DN-012 L and grades the fit partial. Same subject, but DN-012 L asks for long-term measurements at the South Pole, including neutron spectra to at least 100 MeV, which a Timepix charged-particle sensor does not give. Four landings at different sites add spatial coverage. A late-2028 landing falls in Phase 1 ('Now through 2028'), the study's reading.)
Route onto CLPS other NASA; No payload call for this flight. LETS was first selected in 2019 as one of SMD's NASA-Provided Lunar Payloads (it flew on Peregrine). In June 2026 NASA's Moon Base Program named the same three 'flight-proven' payloads (SCALPSS, LRA, LETS) for each of four late-2028 landings; Intuitive Machines' share is IM-6 ($148.3 million). Voyager names the procurement CS-8, an SMD-led science delivery by NASA's naming; that IM-6 is a CS-8 order is the study's reading.; 2026-06-30
Timeline first funding FY2012 (RadWorks, the Timepix line); 2019 (NPLP, LETS itself); first flight test 2012 (Timepix REM on the ISS); 2024-01-08 (LETS on Peregrine); selected 2019-02-21 (NPLP); 2026-06-30 (named for the four late-2028 landings); launch no earlier than Q4 2028 (SCALPSS team poster); Intuitive Machines: lander to the Moon no later than 2028; landing late 2028 (NASA, target)
On the Moon not yet flown
FO none

Flights before the Moon

  • ISS or MISSE: International Space Station: Radiation Environment Monitor (REM), five Timepix units on station laptops (RadWorks), 2012. The first flights of JSC's Timepix detectors, in low Earth orbit. Same sensor technology and team, not a LETS unit.

"In 2012 the first set of 5 REM detectors (IEAP Minipix) flew to ISS"
— NTRS 20230008902, page 19

  • Earth orbit or deep space: Orion Exploration Flight Test-1: Battery-operated Independent Radiation Detector (BIRD), 2014-12. A second-generation Timepix detector through the Van Allen belts. NASA says LETS is derived from this hardware.

"The second generation of this TimePix technology, the BIRD (Battery-operated Independent Radiation Detector), was flown on the NASA EFT-1 flight in December 2014."
— NTRS 20150021957, RadWorks poster, 2015

"derived from heritage hardware flown on"
— NASA press kit, Commercial Lunar Payload Services Initiative: Astrobotic's Peregrine Mission One…, continues: 'Orion EFT-1'

  • ISS or MISSE: International Space Station: REM2 network, Miniaturized Particle Telescope, ISS-HERA, BioSentinel's ISS control experiment with its Timepix LET spectrometer, and the HERA Artemis 2 flight spare, 2017-2021. Operational Timepix monitors in low Earth orbit, including the BioSentinel LET board that LETS uses and the HERA system that shares LETS' core technology. NASA calls the BioSentinel instruments LETS units.

"This dosimeter or linear energy transfer (LET) spectrometer is based on TimePix chip technology."
— NTRS 20205003485, BioSentinel ISS investigation; planned launch on SpX-21

"The HERA Artemis 2 flight spare is currently on ISS and has been successfully collecting data of the ISS environment since April 2021."
— TechPort project 10581, description

"LETS units also were flown as BioSentinel payloads aboard Artemis I and aboard the International Space Station."
— NASA Sending Five Payloads to Moon on Astrobotic’s Peregrine Lander - NASA

  • Earth orbit or deep space: BioSentinel CubeSat (launched on Artemis I into solar orbit), with its LET spectrometer; and HERA on Orion, Artemis I, 2022-11-16. A LET spectrometer in deep space beyond the Moon, which recorded coronal mass ejections in February 2023; and HERA on Orion around the Moon.

"Has captured solar events including coronal mass ejections"
— NTRS 20230011375, BioSentinel, SmallSat 2023

"HERA successfully turned on at 50,000 ft as planned"
— NTRS 20230008902, page 46 (Artemis I)

  • Earth orbit or deep space: Astrobotic's Peregrine Mission One: the first CLPS LETS, 2024-01-08 (launch); did not land. The LETS design itself, in space. Peregrine lost propellant and could not land; LETS powered on and measured radiation in space near the Earth and the Moon. Astrobotic counts it among three payloads that returned publishable data. No surface data. This is the flight behind NASA's 'flight-proven'.

"The NSS and LETS experiments gathered measurements of the radiation environment in interplanetary space around the Earth and the Moon."
— NASA Science, Astrobotic’s Peregrine Lunar Lander Mission to Conclude - NASA

"Two NASA payloads, Linear Energy Transfer Spectrometer (LETS) and Neutron Spectrometer System (NSS), and one commercial payload, The German Aerospace Center (DLR)’s M-42 Radiation Detector, collected publishable scientific data"
— Peregrine: Mission 1, August 2024 Post-Mission Report (Astrobotic), p. 17, (Astrobotic post-mission report, Aug 2024)

  • Earth orbit or deep space: Orion on Artemis II (HERA, the Timepix system that shares LETS' core technology), 2026-04. The study's reading: HERA units were delivered for Artemis 2 onward, and Artemis II flew around the Moon in April 2026. No source read here reports HERA's data from that flight. Related technology, not LETS.

"multiple units have been delivered to the Orion program to be flown on Artemis 2 through Artemis 11 missions"
— TechPort project 10581, description

"In April 2026, Artemis II launched on a nearly 10-day voyage around the Moon"
— Moon to Mars

Heritage hardware

  • design heritage (BioSentinel board): LETS uses the BioSentinel LET board design in its own housing, with the lander's power and data interface; for Peregrine the team added a 28 V interface, heaters and thermal isolation. JSC had a second LETS 'ready for delivery' in July 2023; whether the four late-2028 units are new builds or include it is not stated.

"LETS integrates a Biosentinel board"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…

"Additionally, a 2nd LETS is ready for delivery to NPLP"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, July 2023

"Derived from heritage hardware, this radiation monitor uses a tiny, advanced silicon detector"
— NASA Awards More Moon Base Science, Previews New Opportunities - NASA

  • design heritage (Timepix, from CERN): The Timepix sensor comes from the Medipix collaboration at CERN; JSC had flown more than 23 Timepix units in space by mid-2023.

"Highly successful technology transfer from CERN, powering NASA missions for the last 10 years"
— NTRS 20230008902, page 3

"> 23 Timepix in Space to date"
— NTRS 20230008902, page 3

Funding before the lunar flight

  • RadWorks, JSC's radiation-monitoring technology project (TechPort 10581, FY2012-FY2024; NASA Advanced Exploration Systems, now listed under ESDMD's Mars Campaign Office), which built the Timepix line (ISS REM, BIRD, HERA) and gave resources to LETS. In September 2024 RadWorks was split into five projects, none named for LETS. No amount in TechPort. (NASA AES / ESDMD (RadWorks); FY2012-FY2024): amount not in public sources

"Since its inception in FY12, the RadWorks project has had as its overarching objective to mature and demonstrate affordable, enabling solutions"
— TechPort project 10581, description

"RadWorks donated resources"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…

"This work has been supported by NASA Advanced Exploration Systems."
— NTRS 20230008902, page 5, Funding (10 Years of Timepix in Space)

  • SMD NASA-Provided Lunar Payloads (2019), which selected LETS and paid for the CLPS version flown on Peregrine. The NPLP proposal asked for minimal design work. No amount public. (SMD NPLP; from 2019): amount not in public sources

"NASA's Science Mission Directorate (SMD) initiated the request for proposals leading to these selections"
— NASA Selects Experiments for Possible Lunar Flights in 2019 - NASA

  • SMD DALI: 'Lunar CubeSat Mass Spectrometer with LETS Radiation Sensor' (TechPort 96501, Caltech/JPL lead with JSC, 2019-2022). It paired a LETS sensor (a BioSentinel flight spare) with JPL's mass spectrometer for a later lander. The sources do not say it paid for any CLPS LETS unit. (SMD DALI; 2019-10 to 2022-09): amount not in public sources

"LETS is a flight spare radiation sensor built by JSC for NASA's BioSentinel CubeSat"
— TechPort project 96501, description

  • The money for the four late-2028 LETS units is not in public sources. (not in public sources; 2026-2028): amount not in public sources

How it got onto CLPS

"LETS is one of original 13 science and technology payloads selected as part of the NASA Provided Lunar"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…

"Each delivery will carry three NASA payloads to the lunar surface:"
— NASA Awards More Moon Base Science, Previews New Opportunities - NASA

"These three payloads are flight-proven and their data is critical to supporting safe human exploration of the lunar surface."
— NASA Awards More Moon Base Science, Previews New Opportunities - NASA

"a Linear Energy Transfer Spectrometer (LETS) radiation monitor to gather critical environmental safety data"
— Intuitive Machines wins NASA CLPS contract up to $148.3M, Intuitive Machines, 30 Jun 2026

"including the CS-8 competitive procurement under the existing Commercial Lunar Payload Services (CLPS) indefinite delivery/indefinite-quantity framework"
— Voyager Awarded $298M NASA Contract Under Completed Astrobotic Acquisition

On the Moon

Manifested on IM-6, a production Nova-C, for late 2028; the site is not in the sources. LETS is also manifested on the other three late-2028 landings (two Astrobotic, one Firefly).

"Among the mission payloads is NASA’s Linear Energy Transfer Spectrometer (LETS)"
— Astrobotic Awarded 2 NASA Contracts for CLPS Moon Base Missions, Astrobotic, 30 Jun 2026

FO's role

Grade: none. No FO flight of LETS, its Timepix predecessors or its JSC team was found. FO flew other radiation monitors, such as Space Environment Technologies' ARMAS, whose balloon system includes linear energy transfer spectroscopy (TechPort 106715); that is the same topic, not the same team or instrument. LETS' flights before the Moon were on the ISS, Orion, BioSentinel and Peregrine. The study's earlier traceback grade for the Peregrine LETS (none found) stands.

"No FO project, report or page names LETS or its Johnson team."
— earlier finding of this study (not a public source)

"ARMAS Dual Monitor Pre-Operations Mission Demonstration"
— TechPort project 106715, title (FO; Space Environment Technologies)

Who built it

"Payload principal investigator: Dr. Edward Semones, NASA’s Johnson Space Center"
— NASA Sending Five Payloads to Moon on Astrobotic’s Peregrine Lander - NASA, Peregrine, 2024

"PIs: Eddie Semones, Dan Fry, Stuart George"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, JSC SRAG, WRMISS, July 2023

Moon Base need

"Partial. Same subject, but DN-012 L asks for long-term measurements at the South Pole, including neutron spectra to at least 100 MeV"
— Moon to Mars knowledge base: Architecture data gaps: all 25, June 2026 landings table, LETS row

"Helps to better understand the radiation environment from a variety of lunar transit approaches and at different locations on the lunar surface."
— NASA Awards More Moon Base Science, Previews New Opportunities - NASA

"It’s akin to having weather stations in different locations on Earth."
— NASA Awards More Moon Base Science, Previews New Opportunities - NASA

"Phase 1 "Now through 2028""
— Moon to Mars knowledge base: Moon Base phases

Open questions

  • Who is LETS' PI for the late-2028 units? Not named in the June 2026 sources.
  • Are the four late-2028 LETS units new builds, or does one include the second LETS that was 'ready for delivery' in July 2023? Not in public sources.
  • What do the four units cost, and which project pays for them now that RadWorks has been split? Not in public sources. A February 2024 NASA purchase of 'sensors' from ADVACAM, a Timepix maker (80NSSC24PA025, $132,200), does not say which project it serves.
  • What did LETS measure on Peregrine, and did HERA return data on Artemis II? No published analysis was found.