A one-metre, modular radio telescope built to make hands-on astronomy more accessible. Explore the design, the construction, and what the first field test taught us.
ASTRA 100 · Prototype design and field evaluation
Eight replaceable dish segments, a pyramidal feedhorn, and a mount refined through repeated prototypes.
The prototype adapts the SatNOGS Rotator v3 design. Credit to the SatNOGS contributors for the original rotator design. Two NEMA 17 stepper motors drive a belt-and-worm-gear system with a total reduction of 54:1.
The team replaced slipping set-screw connections with M8 bolts and refined the tripod through eight design iterations. Motorised pointing is a design capability, but the first field test encountered power and mechanical failures.
| Reflector | 1 m diameter, eight sections |
| Focal ratio | f/D = 0.4 |
| Printed material | ABS for main printed components |
| Feed | Pyramidal horn with adjustable mount |
| Rotator | Modified SatNOGS v3 |
| Gear reduction | 54:1, combined stages |
| Mount controller | Makerbase SBASE V1.3 |
| Measured status | Single prototype; validation ongoing |
Select a photograph to inspect it. Construction imagery comes from the supplied report and presentation.
The receiving chain links the feed to an amplifier and filter, a software-defined radio, and a computer.
The GNU Radio flowgraph transforms the incoming samples into power spectra and saves data in HDF5 files. Hot/cold calibration was attempted, but the report notes that the output remained in relative units and the calibration was not fully validated.
A Python interface sends GRBL G-code commands over USB serial to the SBASE controller. Calibration relates motor steps to the physical azimuth and elevation angles of the telescope.
Signal issue identified, corrective work in progress. The original FC0013-based receiver did not cover the 1420.4 MHz target. The project presentation records ordering an RTL-SDR V4. We’re addressing receiver compatibility and calibration before repeating the observations. Read the recovery plan ↓
The first field test demonstrated that the telescope could be transported, assembled, and used to collect spectra. It also exposed problems with motor power, mechanical rigidity, and calibration.
The team assembled the instrument in the field and obtained HDF5 recordings and plotted spectra.
The dish, tripod, and feed survived, but the rotator system required improvements after gear and mounting failures.
No statistically significant feature near 1420.4 MHz was confirmed in the first test. The peak at 1421 MHz was classified as an instrumental DC spike. Fixing the receiver and validating the signal chain is now a priority.
The next stage builds on ASTRA 100 with paired telescopes, synchronised recordings, and signal correlation.
The first test gave us a problem to solve and a clear next step.
The initial spectra did not confirm astronomical hydrogen. Our follow-up investigation identified a receiver that could not cover the intended frequency. We’re addressing that limitation and improving the measurement process so the next observations can be tested properly.
Use a suitable receiver for the 1420.4 MHz band. The RTL-SDR V4 replacement was ordered in the documented project update.
Verify the receiver, amplifier, filter, connections, and power, then improve the hot/cold calibration procedure.
Look for a repeatable feature that can be distinguished from instrumental spikes and local interference, and document the results.
Receiver and calibration work is ongoing, with repeat observations planned to validate the improvements and support the future network.
The first worm-gear system failed under load. The report identifies brittle material, loose nuts, and inadequate mounting rigidity as issues. Other planned improvements include a feed counterweight and a simpler clip-on assembly mechanism.
The original project video, showing the build and later improvements.
Project improvements · original video from the presentation.
Video supplied by the project team.
The original tally totalled S$300.71, below the team’s S$400 target. It includes shipping and a miscellaneous allowance.
| Component | Quantity used | Recorded cost (RMB) |
|---|---|---|
| ABS printing filament | 7 kg | 420.00 |
| SBASE driver + controller | 1 | 269.00 |
| Original RTL-SDR V2 | 1 | 99.00 |
| LNA + bandpass filter | 1 | 60.00 |
| NEMA 17 stepper motors | 2 | 56.18 |
| Aluminium tube | 3 metres | 60.00 |
| 30 × 30 mm aluminium profiles | 6 | 52.26 |
| Shipping | Entire order | 200.00 |
| Miscellaneous allowance | — | 100.00 |
| Full reported tally, including other parts | All components | 1,582.96 |
Reported total: S$300.71
This is a selection, not the complete purchasing list. Prices and conversion are those in the report’s 3 August tally. The original SDR is documented for provenance; the slides identify it as unsuitable for the intended hydrogen-line frequency.
Read the prototype’s technical record, or download the full component list separately.
Design, construction, electronics, calibration, field-test findings, and the next development steps, with hardware photographs and source notes.
The complete 43-row prototype tally, including purchase and usage quantities, recorded prices, missing information, and the reconciled total.
The bill of materials records the original prototype. Check the documented receiver limitation and unspecified entries before using it for a new build.
The technical report brings together the design rationale, hardware photographs, calibration notes, and field-test analysis. The separate bill of materials preserves the complete original cost tally. Later receiver findings from the presentation are identified in both documents.
The report describes a modular design. The ASTRA forum is a planned space for future build discussions and shared resources. No standalone CAD or firmware archive was included with these materials. The technical report and separate materials list are available above, and a future ASTRA design library can host versioned files when they are ready.
We’re actively addressing the signal issue, beginning with receiver compatibility and calibration. Reliable power, stronger rotator components, and feed counterbalancing remain part of the development plan. The next milestone is a repeatable astronomical detection. See the recovery plan ↓
Interferometry remains a development goal. The report documents only one constructed node. Additional instruments, suitable timing and clocks, raw I/Q preservation, and correlation would need to be implemented and tested.
The design, initial costs, field-test outcomes, and spectrum analysis come from the written report. The later SDR diagnosis, revised electronics photos, and main project video come from the presentation. Neither source establishes a successful hydrogen-line detection.
A more capable instrument, and a platform where builders can learn and observe together.
Resolve the receiver issue, improve calibration, and repeat the observations. Publish the outcome so other builders can use what we learn.
Follow the recovery planCreate accounts, post build journals and observations, ask questions, reply to other builders, and share files, modifications, and solutions.
Register an ASTRA station, describe its hardware and capabilities, and choose what to share. A station directory could help builders find collaborators and arrange joint observing sessions.
Start with two compatible telescopes. Develop precise timing, synchronised raw I/Q recordings, and correlation tools to test whether their signals can be combined into a shared observation.
The forum and connection tools are planned features. Interferometry also needs suitable hardware, stable clocks, and successful tests with multiple instruments. These capabilities are not live yet.
Explore the future platformDiscover the open ecosystem behind the instrument.