# NASA and Sunpower free-piston Stirling references (public domain) and design numbers

> Where are the NASA free-piston Stirling engine design reports and what are the key numbers?

- Category: Stirling engines › Guide
- Kind: List / guide
- Basis: NASA Technical Reports Server (NTRS): US Government works are public domain. Headline numbers from the published convertor papers (ASRG, GPHS-ESP, TDC, RE-1000, Sunpower EE-35 / Microgen); hobby-scale rules from Urieli / Berchowitz
- Page: https://xemstudio.com/objects/nasa-fpse-references/ · JSON: https://xemstudio.com/api/geometry?object=nasa-fpse-references · Plain text: https://xemstudio.com/objects/nasa-fpse-references/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- Where the real designs are: NTRS (ntrs.nasa.gov) hosts decades of free-piston Stirling work: the Sunpower RE-1000 test engine (1 kW, 1980s, the best-documented FPSE: dimensions, pressures, strokes, phase angles all published), the Stirling Technology Co. 55 W TDC, the Sunpower ASC/ASRG convertors (80 We class, 102 Hz, helium at 3.5 MPa, 850 °C hot end, flexure suspended, 14+ years on test), Glenn's flexure fatigue and life-test reports, and the thermoacoustic (TASHE) work. Search NTRS for 'free-piston Stirling', 'ASRG', 'RE-1000', 'flexure bearing', 'linear alternator'.
- Representative numbers: RE-1000: 57 mm bore, 1 kW, 30 Hz, 7 MPa helium, displacer on a gas spring, piston on a gas spring + dashpot load. ASC-E2: ~80 We, 102 Hz, 3.5 MPa He, piston stroke ~5 mm, hot end 850 °C, cold 90 °C, 38% convertor efficiency, flexure-suspended displacer and piston. GPHS-ESP / SRG110: 55 We, 80 Hz. Microgen (Sunpower-derived) domestic CHP: 1 kWe, 50 Hz, helium.
- Why it matters at hobby scale: the same physics scales down (resonance, clearance seals, flexures, linear alternator), only the pressure and frequency drop: air at 1 bar, 10–20 Hz, 0.1–2 W. The parts on this shelf (flexures, alternator kit, free-piston core, regenerator media, tri-clamp vessel) are the hobby-scale translation of the ASRG parts list.
- Open design tools: Urieli's Stirling cycle machine analysis (ideal adiabatic + simple models, free online); Sage (commercial, used by NASA); Berchowitz & Urieli 'Stirling Cycle Engine Analysis' (1984) is the standard text; Walker 'Stirling Engines' (1980); Senft 'An Introduction to Low Temperature Differential Stirling Engines' for the can-engine end.
- Nothing here is NASA's CAD (none is public); the dimensions quoted are from the papers.

## Sizes

| machine | power | freq_hz | pressure | hot_c | suspension | ntrs_search |
|---|---|---|---|---|---|---|
| Sunpower RE-1000 | 1 kW | 30 | 7 MPa He | 600 | gas springs | RE-1000 free-piston |
| STC 55 W TDC | 55 We | 80 | 2.5 MPa He | 650 | flexures | Technology Demonstration Convertor |
| Sunpower ASC-E2 (ASRG) | 80 We | 102 | 3.5 MPa He | 850 | flexures | Advanced Stirling Convertor |
| Microgen (Sunpower) | 1 kWe | 50 | He | 500 | flexures | Microgen Stirling |
| LES hobby free-piston | 0.1–2 W | 10–20 | 1 bar air | 150 | printed/steel flexures | — |

## Where the files are

- NASA (NTRS, public domain): [Advanced Stirling Convertor (ASC) development (2010)](https://ntrs.nasa.gov/search?q=Advanced Stirling Convertor) — PDF — US Government work, public domain
- NASA (NTRS, public domain): [RE-1000 free-piston Stirling engine sensitivity test results (1986)](https://ntrs.nasa.gov/search?q=RE-1000) — PDF — US Government work, public domain
- NASA (NTRS, public domain): [Stirling convertor flexure fatigue testing (2008)](https://ntrs.nasa.gov/search?q=flexure fatigue Stirling) — PDF — US Government work, public domain
- NASA (NTRS, public domain): [Thermoacoustic Stirling heat engine (TASHE) for space power (2004)](https://ntrs.nasa.gov/search?q=thermoacoustic Stirling) — PDF — US Government work, public domain
- Wikipedia: [Advanced Stirling radioisotope generator](https://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope_generator) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Stirling radioisotope generator](https://en.wikipedia.org/wiki/Stirling_radioisotope_generator) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Questions

**Are NASA's Stirling engine designs public?**

The reports are (US Government work, public domain, on NTRS): dimensions, operating points, test data and analysis for RE-1000, TDC, ASC/ASRG. The CAD and the Sunpower-proprietary details are not.

**What frequency and pressure do NASA Stirling convertors run at?**

ASC/ASRG: about 102 Hz on helium at 3.5 MPa with an 850 °C hot end; RE-1000: 30 Hz at 7 MPa; the 55 W TDC: 80 Hz at 2.5 MPa.

**Can I build a free-piston Stirling engine at home?**

Yes at air pressure and 10–20 Hz: the physics is the same, the output is 0.1–2 W. The hard parts are the clearance seal (lap or use glass/graphite) and tuning the two resonances; everything else is on this shelf.

## Fits with

- [Free-piston Stirling core: displacer, power piston, liner, gas spring, stops, clearance-seal and tuning tables](https://xemstudio.com/objects/free-piston-core/)
- [Planar spiral flexure bearings (Sunpower / NASA free-piston style): Ø40–120, DXF + STEP](https://xemstudio.com/objects/spiral-flexure-bearings/)
- [Moving-magnet linear alternator kit (free-piston Stirling power take-off)](https://xemstudio.com/objects/linear-alternator-kit/)
- [Regenerator and heat materials: stainless mesh counts, steel wool, scrubbers, mica, fiberglass, ceramic, firebrick](https://xemstudio.com/objects/regenerator-and-heat-materials/)
- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/)