Linear Energy Transfer Spectrometer (LETS)

Peregrine Mission One · failed to land · NASA payload

A small radiation monitor built around one Timepix silicon pixel detector (256 x 256 pixels, 2 square cm). It records each charged particle that crosses the sensor and its linear energy transfer, to measure the radiation dose and spectrum on the lunar surface, and in transit and lunar orbit when the lander allows.

PI: Edward Semones (NASA Johnson); the 2023 team slides also list Dan Fry and Stuart George as PIs
Built by: NASA Johnson Space Center, Space Radiation Analysis Group (SRAG) (NASA center)

Technology	radiation monitor (Timepix detector)
Moon Base need	DN-012 L (The study's reading. NASA does not tie the Peregrine LETS to a data gap. The knowledge base pairs the later LETS units (the June 2026 Moon Base landings) with DN-012 L, and grades the fit partial: DN-012 L asks for long-term South Pole measurements, including neutrons up to 100 MeV, which a Timepix charged-particle sensor does not cover. Peregrine aimed at a near-side mare site, not the South Pole.)
Route onto CLPS	NPLP; NASA-Provided Lunar Payloads: SMD's request to NASA centers, selected 21 February 2019. Manifested on Astrobotic's first delivery (task order TO2-AB, awarded May 2019); listed with the Peregrine payloads in NASA's January 2020 announcement. It stayed on Peregrine when NASA moved five other payloads off in April 2023.; 2019-02-21
Timeline	first funding FY2012 (RadWorks, the Timepix line); 2019 (NPLP, LETS itself); first flight test 2012 (Timepix REM on the ISS); selected 2019-02-21 (NPLP); on the Peregrine manifest by January 2020; launch 2024-01-08; landing not in public sources
On the Moon	partly operated
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: dose rate and particle tracks in low Earth orbit. Same sensor technology and team as LETS, not the 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 Orion EFT-1 (Exploration Flight Test-1)"
— NASA press kit, Commercial Lunar Payload Services Initiative: Astrobotic's Peregrine Mission One…

• ISS or MISSE: International Space Station: REM2 network, Miniaturized Particle Telescope (MPT) and ISS-HERA (Timepix instruments), 2017-2018. Operational Timepix monitors in low Earth orbit, including the HERA system that shares LETS' core technology.

"REM2 2018 ISS LEO Ops ISS 7 MPT 2017 ISS LEO Science ISS 2"
— NTRS 20230008902, page 3, list of NASA Timepix flight hardware

"ISS-HERA 2018 ISS LEO Demo ISS 3"
— NTRS 20230008902, page 3

• ISS or MISSE: International Space Station: BioSentinel ISS Control Experiment, with its Timepix LET spectrometer, 2020 (planned for SpX-21). The BioSentinel LET spectrometer board, the board design LETS uses, on the ISS. NASA calls these LETS units.

"This dosimeter or linear energy transfer (LET) spectrometer is based on TimePix chip technology."
— NTRS 20205003485, BioSentinel ISS investigation summary

"Biosentinel 2020 ISS LEO Science ISS 1"
— NTRS 20230008902, page 3

"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 a solar orbit, 2022-11-16. A LET spectrometer in deep space, past the Moon. It recorded solar events, including coronal mass ejections in February 2023, before Peregrine's launch.

"Launch and Deployment: November 16, 2022"
— NTRS 20230011375, slide 6 (BioSentinel, SmallSat 2023)

"Has captured solar events including coronal mass ejections"
— NTRS 20230011375, slide 16

• Earth orbit or deep space: Orion on Artemis I: Hybrid Electronic Radiation Assessor (HERA), 2022-11-16. The Timepix system that shares LETS' core technology, flown around the Moon as a flight test objective.

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

"LETS uses the same core technology as the HERA (Hybrid Electronic Radiation Assessor) system"
— NASA press kit, Commercial Lunar Payload Services Initiative: Astrobotic's Peregrine Mission One…

Heritage hardware

• design heritage (BioSentinel board): LETS uses the BioSentinel LET board design in a new housing with the lander's power and data interface and modified software. For Peregrine the team added a 28 V interface, heaters and thermal isolation. A JPL-led 2019 proposal calls LETS a flight spare built for BioSentinel; the sources do not say whether the Peregrine unit is that spare.

"LETS integrates a Biosentinel board design"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, slide 5

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

"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,…, slide 6

• design heritage (Timepix, from CERN): The Timepix sensor comes from the Medipix collaboration at CERN. JSC has flown it since 2012: more than 23 Timepix units in space by mid-2023, by the team's count.

"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

• NASA Science Mission Directorate, NASA-Provided Lunar Payloads (NPLP), as a CLPS TO2-AB payload. The NPLP proposal asked for minimal design work. (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,…, slide 5

• 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. The PI, Edward Semones, was RadWorks' project manager. (NASA AES / ESDMD (RadWorks); FY2012-FY2024): amount not in public sources

"RadWorks donated resources"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, slide 5

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

"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; contacts list Edward J Semones as Project Manager

• SMD's DALI program: 'Lunar CubeSat Mass Spectrometer with LETS Radiation Sensor' (TechPort 96501, Caltech/JPL lead, JSC supporting, 2019-2022). A different payload: JPL's mass spectrometer paired with a LETS sensor, for a later commercial lander. The sources do not say it paid for the Peregrine unit. (SMD DALI; 2019-10 to 2022-09): amount not in public sources

"JSC's Linear Energy Transfer Spectrometer (LETS) will make the first radiation measurements on the Lunar Surface"
— TechPort project 96501, description

How it got onto CLPS

"The Linear Energy Transfer Spectrometer will measure the lunar surface radiation environment."
— NASA Selects Experiments for Possible Lunar Flights in 2019 - NASA, release of 21 Feb 2019

"LETS is one of original 13 science and technology payloads selected as part of the NASA Provided Lunar Payloads (NPLP) program in 2019"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, slide 3

"The LETS radiation sensor will collect information about the lunar radiation environment and relies on flight-proven hardware"
— First Commercial Moon Delivery Assignments to Advance Artemis - NASA, 22 Jan 2020, under Astrobotic Payloads

"Linear Energy Transfer Spectrometer (LETS) - Johnson Space Center (JSC), Dr. Edward Semones"
— TO2-AB Science Payloads - NASA Science, updated manifest, 6 Apr 2023

On the Moon

Peregrine had a propulsion failure soon after launch and could not land; it burned up over the South Pacific on 18 January 2024. LETS powered on and measured the radiation environment in space around the Earth and the Moon, alongside NSS. NASA says the preliminary data showed the instruments worked as expected, and Astrobotic counts LETS among the three payloads that collected publishable scientific data. It made no lunar surface measurements, its primary objective. A published analysis of the LETS flight data was not found.

"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

"a positive sign that the instruments survived the harsh conditions of space and are functioning as expected"
— NASA Science, Astrobotic’s Peregrine Lunar Lander Mission to Conclude - NASA

"Four out five NASA payloads on Peregrine successfully powered on and collected data while in flight"
— NASA Science, Astrobotic Peregrine Mission One Concludes - 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)

FO's role

Grade: none. No FO flight of LETS, its Timepix predecessors or its JSC team was found in FO's TechPort records, reports or pages. FO flew other radiation monitors, such as Space Environment Technologies' ARMAS, which also measures linear energy transfer; that is the same topic, not the same team or instrument. LETS' flights before Peregrine were all on the ISS, Orion and BioSentinel. The study's earlier traceback grade (none found) stands.

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

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

"PIs: Eddie Semones, Dan Fry, Stuart George"
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, slide 2 (JSC SRAG, WRMISS, July 2023)

Moon Base need

"Measure the radiation environment on the lunar surface at the south pole."
— Moon to Mars knowledge base: DN-012 L: In situ lunar surface radiation environment measurements and space weather monitoring, Description

"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

"The primary mission objective is to obtain radiation data on the lunar surface."
— The Linear Energy Transfer Spectrometer (LETS) Payload on NASA's CLPS TO2 Peregrine-1 (M. Ecord,…, slide 3

Open questions

• LETS' development cost: not in public sources (NPLP amounts and RadWorks' share are not published).
• Is the Peregrine LETS the BioSentinel flight spare named in TechPort 96501, or a new unit built on the BioSentinel board design?
• What did LETS measure in transit? JSC planned to post the data in NASA's Planetary Data System about six months after the mission; no published analysis was found.
• When was LETS delivered to Astrobotic and integrated on Peregrine? Not in public sources.
• A second LETS was 'ready for delivery' in July 2023 for a non-CLPS lunar mission (JSC slides); which mission, and is it one of the LETS units on the June 2026 Moon Base landings?