Linear Energy Transfer Spectrometer (LETS)¶
Peregrine Mission Two · 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'. A LETS flew on Peregrine Mission One toward the same region but never landed. Peregrine Mission Three carries another LETS to the same region.
PI: Not named for this unit. Edward Semones (NASA Johnson) was PI for the Peregrine Mission One 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), which built the Peregrine Mission One LETS. Astrobotic's June 2026 release calls it 'NASA's' LETS and names no builder. (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. This unit lands on the near side, near the Gruithuisen Domes. Peregrine Mission Three carries another LETS to the same region, so the two add one surface region and two transits to NASA's network, not two regions. Measured at different times, they could still show how the surface environment changes (the study's reading). How long LETS will measure on the surface is not stated: JSC planned about one lunar day on Peregrine Mission One, and CS-8 pays a bonus to landers that survive the night. 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 and flew on Peregrine Mission One. 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; Astrobotic won two, $297.9 million for both. Voyager, which bought Astrobotic, ties its award to the CS-8 procurement, which NASA's naming makes an SMD-led science delivery.; 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 Mission One); selected 2019 (NPLP); 2026-06-30 (named for the four late-2028 landings); launch 2028 (Astrobotic); no earlier than Q4 2028 (SCALPSS team poster); 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"payload is a radiation monitor derived from heritage hardware flown on Orion Exploration Flight Test-1 in 2014"
— NASA Sending Five Payloads to Moon on Astrobotic’s Peregrine Lander - NASA
- ISS or MISSE: International Space Station: REM2, Miniaturized Particle Telescope, ISS-HERA, and BioSentinel's ISS control experiment with its Timepix LET spectrometer; the HERA Artemis 2 flight spare, 2017-2021. Operational Timepix monitors in low Earth orbit, including the BioSentinel LET board that LETS uses. 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"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, on the top deck of the same lander type, aimed at Sinus Viscositatis near the Gruithuisen Domes, 2024-01-08 (launch); did not land. The LETS design itself, in space, on a Peregrine. Peregrine lost propellant and could not land. LETS was powered on soon after the anomaly 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 word 'flight-proven' for LETS.
"Small, single Timepix instrument on the top deck of the Astrobotic Peregrine (unmanned) lander"
— NTRS 20230008902, page 48 (LETS on Astrobotic Peregrine)"two NASA payloads, Linear Energy Transfer Spectrometer (LETS) and Neutron Spectrometer System (NSS), were powered on for operational checkouts and data collection"
— Peregrine: Mission 1, August 2024 Post-Mission Report (Astrobotic), Astrobotic post-mission report, Aug 2024"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"collected publishable scientific"
— Peregrine: Mission 1, August 2024 Post-Mission Report (Astrobotic), p. 17 (LETS, NSS and DLR's M-42)"Destination: Sinus Viscositatis (Bay of Stickiness) located near the Gruithuisen Domes"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…
Heritage hardware¶
- design heritage (BioSentinel board) and Peregrine interface: LETS uses the BioSentinel LET board design in its own housing (17.9 x 15.2 x 4.6 cm), with the lander's power and data interface. For Peregrine, JSC added a 28 V interface, thermal isolation and redundant heaters, and tuned the Timepix for stable work up to 80 C, because lunar noon was the main thermal concern. That Peregrine interface has flown once, so this unit returns to a lander JSC has already designed for (the study's reading; whether Peregrine-2's interface is unchanged is not stated).
"LETS integrates a Biosentinel board"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…"Peregrine Lander Design Updates"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, then: 28V DC interface, thermal isolation, redundant heaters"Increased thermal environment required active heating and better passive thermal management"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…"Optimized Timepix for stable operation up to 80C ambient."
— NTRS 20230008902, page 49"17.9 cm X 15.2 cm X 4.6 cm"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…
- spare unit: JSC had a second LETS 'ready for delivery' in July 2023 and listed it for a possible Beresheet 2 flight. Whether the four late-2028 units are new builds or include it is not stated.
"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"LETS(2) 2024/5 Berensheet 2"
— NTRS 20230008902, page 3 (marked '*Evaluating mission possibility')
- 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"Derived from heritage hardware, this radiation monitor uses a tiny, advanced silicon detector"
— NASA Awards More Moon Base Science, Previews New Opportunities - NASA
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). It 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)"RadWorks transitioned from a single project to multiple projects in Sept 2024."
— TechPort project 10581, outcomes
- SMD NASA-Provided Lunar Payloads (2019), which selected LETS and paid for the CLPS version flown on Peregrine Mission One. 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"NPLP LETS payload proposal required minimal design"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…
- 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. No USAspending contract names LETS, a 'linear energy transfer spectrometer' or Timepix (NASA, FY2019 on), and no SBIR award names them. (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,…"One of ten NPLPs selected for NASA’s Commercial Lunar Payload Services (CLPS) TO2 –AB, Astrobotic Peregrine1 Mission"
— 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"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"CS-3 is a CLPS Science delivery, the 3rd led by Science Mission Directorate (SMD)."
— Commercial Lunar Payload Services (CLPS) Deliveries - NASA Science, note on CLPS naming
On the Moon¶
Manifested on Peregrine Mission Two for late 2028, near the Gruithuisen Domes. LETS is also manifested on the other three late-2028 landings (Peregrine Mission Three, IM-6 and Blue Ghost Mission 5).
"(LETS), which will monitor the lunar radiation environment to support future human exploration under the Artemis campaign"
— Astrobotic Awarded 2 NASA Contracts for CLPS Moon Base Missions
FO's role¶
Grade: none. No FO flight of LETS, its Timepix predecessors or its JSC team was found; no FO project, report or page names LETS, Timepix or the PIs. 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 Mission One. The study's earlier traceback grade for the Peregrine Mission One 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 Mission One, Jan 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"Among the mission payloads is NASA’s Linear Energy Transfer Spectrometer (LETS)"
— Astrobotic Awarded 2 NASA Contracts for CLPS Moon Base Missions, 30 Jun 2026
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"will deliver three NASA-sponsored payloads on Peregrine to a landing site near the Gruithuisen Domes"
— Astrobotic Awarded 2 NASA Contracts for CLPS Moon Base Missions"Surface Ops: ~1 Lunar day"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, Peregrine Mission One plan"NASA has included a performance bonus for contractors who successfully demonstrate “survive the night” capabilities"
— Ignition - NASA, CS-8 Task Order"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.
- Is this unit a new build, or 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.
- What did LETS measure on Peregrine Mission One? NASA and Astrobotic say it returned data, and JSC planned PDS release about six months after the mission; no published analysis was found.
- Does Peregrine-2 aim for the CS-8 'survive the night' bonus, which would let LETS measure beyond one lunar day? Not in public sources.
- Does Peregrine-2 keep the 28 V interface and deck mount that JSC designed for Peregrine Mission One? Not in public sources.