# Frontier Radio

The Frontier Radio is a family of software-defined radios developed by the Johns Hopkins University Applied Physics Laboratory (or APL). Four variants have been developed: the Frontier Radio (FR), the Frontier Radio Lite (FR Lite), and the Frontier Radio Multi Lingual (FR ML), and the Next-Gen Frontier Radio. In addition, the Frontier-S and Frontier-X are licensed derivatives manufactured by commercial aerospace company Rocket Lab.

## History
### Parents and predecessors

The creation of the FR family was predated by the transceivers built for the New Horizons, TIMED, and CONTOUR spacecraft, all of which required lightweight transceivers with low power consumption. These efforts were successful; for example, the transceiver for New Horizons managed to save 12 W from total mission power and ended up being a mission-enabler. Based on results from these missions, APL sought an opportunity to build a general-purpose radio with even lower SWaP (Size, Weight, and Power) as a software-defined radio (SDR) platform usable by any aerospace organization. The SDR platform would accommodate transceivers with higher data-rate return link capabilities and better radiation tolerance than previous radios. APL brought the idea before NASA, who approved further research.

### Frontier Radio history

The first iteration of the Frontier Radio (FR) to fly was on the near space Van Allen Probes (VAP) mission. It was used because of its high radiation tolerance, low SWaP, and long lifetime. A deep space version of the FR flew on the Parker Solar Probe (PSP) mission in 2018. This version was modified for the PSP mission with updates such as software enhancements to improve downlink frame rates, RF hardware to operate at the higher frequency X and Ka bands, and hardware enhancements to increase processing capacity. The FR also flew on NASA's Double Asteroid Redirection Test (DART) missions, where it featured improvements such as support for higher data rates at X-Band.
Other missions needed radios with less size, mass, and power consumption, and did not require the full robustness of FR. This led to the development of Frontier Radio Lite, a much smaller radio for resource-constrained missions. The biggest change was a reduction in the maximum data rates and the signal sensitivity, allowing a lower power consumption, while some radiation tolerance was sacrificed to achieve better size, weight, and power. Next came the Frontier Radio Virtual Radio, intermediate between the FR and the FR Lite. It combines the robust nature and processing power of the original radio with a reprogrammable design and more modern architecture used by the FR Lite.

## Versions
### Heritage Frontier Radio

Following the launch of the New Horizons mission and its low SWaP radio, NASA funded more research into other small, highly reliable radio products for future missions by APL, this time utilizing software-defined platforms. The grant led to the creation of the heritage Frontier Radio (FR), built for near and deep space applications.

#### Types

The heritage FR has two main versions: a near space radio that operates at S-band, as used on the VAP mission, and a deep space version that operates at X/Ka-band, as used on the PSP mission. Both versions use the same core infrastructure with some improvements over the first version that flew on VAP. These include reduction of SWaP, improved robustness, lower noise, higher speed signal conversion and processing, and better signal acquisition and tracking.

#### Key features

The FR has a separate interface board so that the hardware can be customized to each mission without having to build a brand new radio. Certain features can also be reconfigured in flight, like in-band channel assignment, bit rate, loop bandwidths, and coding formats, and modulation schemes. Its circuits are designed to be highly reliable and fault tolerant, taking into account vacuum, high radiation, and extreme temperature environments. It can withstand total ionizing doses (TID) of up to 100 krad (1 kGy) and has single event latch-up (SEL, or a latch-up caused by a single event upset) immunity of 85 MeV-cm2/mg of linear energy transfer (LET).

#### Limitations

The FR is not reprogrammable. It is also the physically largest radio in the family.

### Frontier Radio Lite

The Frontier Radio Lite is the smaller version of its sibling, the Frontier Radio, fitting all of its systems onto a single card. Originally an S-band radio, FR Lite was the first in the family to be reprogrammable, and is designed for missions with high risk tolerance and quick schedules. It is the lowest SWaP radio in the Frontier family, making it ideal for small-sat and cube-sat missions.

#### Types

Two versions of FR Lite have been designed and built. The first is a two-way radio operating at S-band, and the second is a L-band receiver for GPS L1 & L2, renamed the Extensible Global Navigation System (EGNS). The S-band version of this radio has been transferred to industry and can be purchased from Rocket Lab under the name Frontier-S.

#### Key features

The FR Lite uses a reprogrammable field-programmable gate array (FPGA) instead of a dedicated Application Specific Integrated Circuit (ASIC), greatly decreasing development cost and allowing increased flexibility. Its mass and volume are less than 25% of the FR's, and its receive and transmit modes use less than 30% of the total FR power. These improvements were accomplished by moving a number of analog hardware sections into firmware, sharing components of the circuit for the up and down conversions of frequencies, improved power regulation design, and a number of smaller changes.

#### Limitations

The FR Lite sacrifices some of its radiation tolerance and SEL immunity in order to achieve its low SWaP; it can only withstand TID of 40 krads and has a 20% reduction in SEL immunity compared to the FR.

### Frontier Radio Multi Lingual

The Frontier Radio Multi Lingual (FR ML) is the newest addition to the FR family, and the first specifically targeting high throughput applications. With receive and transmit throughputs greater than 1 GBPs, FR ML was developed at the direction of NASA's Space Communications and Navigation Program, meant as a first step to replace the aging Tracking and Data Relay Satellite System (TDRSS) constellation. The radio is designed to operate in commercial, military, and science allocated Ka-bands, hence the multi-lingual nature of the design.

#### Types

The FR ML currently comes in one version, with Ka up- and down-conversion.

#### Key features

The FR ML features a more advanced FPGA than previous FR variants, allowing support for DBV-S2, OFDMA, and CCSDS waveforms. Improvements in processing power, predistortion, and RF front end linearity enable support of uplink and downlink data rates in excess of 1 GBps. The radio is tolerant to 100 krad TID and single event effect immunity to 72 MeV-cm2/mg. A supervisor co-processor also enables complete in-flight reportability, of not just software but firmware as well.

#### Limitations

High power consumption limits FR ML usage on some small-sat missions.

### Next Generation Frontier Radio

The Next Generation Frontier Radio is currently under development and aims to create the next generation deep space and near earth SDR platform. This platform seeks to combine the high reliability of the heritage FR with the low SWaP of FR Lite and the high performance of FR ML. This is accomplished via novel configurability of a deep space radio platform. Featuring both a high performance FPGA and co-processor, these computing capabilities can be scaled through component level variants to support both high performance FR ML applications and low power deep space applications on the same underlying architecture. This means that the same hardware, with component reconfigurations, can support GBps links in one mission, and sub-1W receive links in another. Like FR ML, the radio is tolerant to 100 krad TID and single event effect immunity to 72 MeV-cm2/mg.
Support for swappable and multiple RF front ends is also a key enabler of flexibility of NG-FR. RF front ends supporting this next-gen architecture at C/X/Ku and well as Ka bands have been developed. Future work on L/S-bands, VHF/UHF, and a low power NASA Deep Space Network front end are all in development as of May 2023. The first mission slated to fly this new architecture is NASA's DAVINCI mission to Venus.

### Frontier-S and Frontier-X

The Frontier-S and Frontier-X are a variants of the Frontier Radio Lite manufactured by United States-based aerospace company Rocket Lab, who licensed the design in 2021 for commercial use. Currently, the Frontier-S has flown on Rocket Lab's Photon Pathstone spacecraft, launched in March 2021, on the Photon spacecraft used for the CAPSTONE mission in March 2022 as well as a private mission to Venus. Rocket Lab also produces a "deep-space" variant with additional features.
The Frontier-X is an X-band version of the FR Lite, designed and licensed specifically for Rocket Lab. It will be first flown on the upcoming NASA SIMPLEx mission to Mars EscaPADE

### Comparison

| Parameter | Frontier Radio | FR Lite | FR ML | Next-Gen FR | Unit |
| Frequency Band | S / X / Ka | Ka | VHF/UHF/L/S/C/X/Ku/Ka | S | |
| Volume | 2050 | 320* | 960* | 790 | cubic centimeters (cc) |
| Mass | 2.1 | 0.4* | 1.0* | 0.59 | kilograms (kg) |
| Temperature | -35 to +60 | -35 to +60 | -35 to +60 | -35 to +70 | Celsius (C) |
| Voltage | +28 | +22-42 | +28 | 22–42 | Volts (V) |
| Power, Rx Only† | 6 | 1.5 (0.35 Standby) | 5-25 | 2-6 | Watts (W) |
| Power, Full Duplex† | 9.7 (X-band) | 2 w/ on-board 1-W SSPA (S-band) | 10-35 | 5-15 | Watts (W) |
| Rx / Tx Channels | 2 / 2 | 1 / 1 | 2 / 2‡ | 3/3 | - |
| Receive Rate | 1–1 M | 10 M | 10-1000 M | 1-1000 M | samples per second (sps) |
| Transmit Rate | 10–150 M | 10–100 M | 10–1000 M | 10-1000 M | sps |
| Rx Sensitivity | -160 | -145 | -140 (est.) | -155 | dBm |
| Noise Figure (Integrated LNA) | 2.5 | 5.5 | 2.0 | 3.0 (VHF/UHF) 2.0 (L/X/C/X/Ku/Ka) | decibels (dB) |
| FPGA Device | RTAX4000 | ProASIC3E 3000 | PolarFire | PolarFire | - |
| Reprogrammable | No | Yes | Yes | Yes | - |
| Interfaces | SpaceWire | SpaceWire | SpaceWire | SpaceWire, LVDS | - |
| Non-Volatile Memory Storage | 2 | 2 | 8 | | megabyte (MB) |
| SRAM | 1 | 0.5 to 2 | 2048 | 2048 | MB |
| Radiation (TID) | 100 | 40 | 100 | 100 | krad |
| Radiation (SEL for LET) | >85 | >68 | >72 | >72 | MeV-cm$^2$/mg |
*Bare slices only; total volume/mass depends on packaging.
†Frontier Radio & FR VR numbers include an ovenized oscillator and +28V bus power converter unit with ~1.4-W quiescent draw and ~80% efficiency vs. a lower-power TCXO and lower-voltage 6-12V bus power on FR Lite.
‡Two transmit channels switchable but not simultaneous.

## Current and future missions

FR radios have flown on various Cubesat missions. An L-band version of FR Lite (EGNS) flew on a Cubesat mission in 2019. Also, a version of the FR VR with S-band receive and transmit (with L-band receive as well) was scheduled to fly on a JHU/APL Cubesat mission in 2022.
The Emirates Mars Mission HOPE uses a FR transponder.
The Europa Clipper mission will use an FR transponder both for communication and gravity science.
Another mission that may use a member of the FR family is the proposed Europa Lander. In order to determine if Europa, one of Jupiter's smaller moons, is holding a liquid ocean beneath a layer of ice and could support life, NASA is investigating sending a lander to the surface of the moon. The current plan for the radio is for the Europa Lander and its Carrier and Relay Stage (CRS) to use a version of the heritage FR with added X-band functionality for cross-band uplink and downlink. The FR will also fly on NASA's Interstellar Mapping and Acceleration Probe to study to heliosphere as well as the NASA New Frontiers Dragonfly (Titan space probe) mission set to launch in 2027.