It’s really easy to lose a high-power rocket. Sending a rocket thousands of feet up into the atmosphere in only a few seconds means and you can:
- Loose visual track of the rocket as it ascends into the sky due to cloud cover or it simply moving too fast
- Loose visual track of the rocket as it descends and not know where it landed
- Have the rocket severely weathercock (turn into the wind) and arc towards the horizon
- Deploy a parachute that provides a safe descent rate at apogee, or another high altitude, either on purpose, or due to a dual-deploy malfunction, and have it be carried off by prevailing winds
- Have everything work perfectly but still need to walk several miles to recover it
There are ways to mitigate each of these occurrences but having a tracking device of some kind helps lend peace of mind. No one wants to lose a rocket. They are expensive: components, all the time you spent getting things just right, avionics, reloadable motor hardware, etc. And, the whole point of flying a rocket is to get it back and do it again.
In the late 90s and early aughts I used two methods of tracking:
- A 440MHz beacon made by Adept (now out of business; the beacon also required a HAM radio license, scanner, and directional gain antenna)
- GPS telemetry
Things Have Changed
Some of the biggest advancements in hobby rocketry in the past 20 years have been in electronics. They have gotten dramatically smaller, more sophisticated, and cheaper (at least in some cases). This is due, in part, to a proliferation of:
- Tiny, cheap GPS modules driven my demand to put GPS receivers in smartphones and other consumer electronic devices
- New license-free radio standards like Zigbee and LoRa
Because electronics vendors for hobby rocketry are themselves hobbyists or small businesses there is a lot of turn-over. Virtually all the vendors I bought electronics from 20 years ago are out of business. Some are even zombies–I’ve come across several websites that appear to have products for sale but links are broken or pages haven’t been updated in years. You can still use electronics after the vendor has closed its doors but the control software (if there is any) will gradually become incompatible with modern computers.
Between 2001 and now, independent of hobby rocketry, smartphones have gone from not existing to being our de facto computing devices. I would prefer not to have to lug a laptop out to the launch site and have it set up next to an effectively immobile1 ground station when I have a smartphone in my pocket. Despite this, most rocketry electronics either assume you will use them with a PC or they implement functionally that could be provided by a smartphone app in a proprietary way.
Commercially Available GPS Trackers for Rocketry
John Coker has a good write-up of GPS trackers c2015 it goes into a lot of technical detail. Start there for a good overview and an excellent discussion of antenna gain mechanics. However, it only covers a few products from 3 vendors–there are a lot more options out there. Here is a survey of what I could find from scouring the Internet:
- Multitronix TelemetryPro has two variants of sophisticated trackers & receivers with a 100-mile range ~$2000(!)
- Apogee Simple GPS tracker is a one-piece custom-built ground station and small tracker ~$430 (a smartphone app would be a preferable alternative to custom, hand-held ground station)
- Featherweight Altimiters has LoRa GPS Tracker that can be purchased with a small Bluetooth ground station (iOS app; Android planned but not available) ~$350 (sale price)
- BigRedBee has several VHF/UHF GPS APRS transmitter offerings that operate on 70cm and 2m HAM radio bands ~$260-$360 for only a transmitter, ground station equipment not included.
- Altus Metrum has several GPS-enabled products that use a 70cm HAM band and pair with their Bluetooth ground station, TeleBT ~$170, which needs to be connected to a directional antenna like a 70cm Arrow Antenna ~$60:
- Eggtimer Rocketry has several 900MHz & 70cm GPS transmitters and they keep costs low by only offering the electronic kits you have to solder yourself. Their “starter sets” start at ~$90 for a pair of RX and TX modules.
- ENTACore Electronics AIM XTRA GPS flight computer is a full-on flight computer (barometric sensor, 3-axis accelerometer, hi-G linear accelerometer) with pyro channels and USB connectivity that transmits live telemetry on the 432-434 MHz band ~$420 for flight computer and ground station.
- Missle Works has several RTx/GPS Systems (~$260-$290) that use standard Zigbee modules to transmit data to a ground station with Bluetooth (~$15), USB/PC (~$25), or onboard LCD (~$40) display options. The RTx system can also stream data from their RRC3 altimeter (~$70-$80). I think their T3 (~$155-$190) tracker is a more interesting product as it is cheaper, smaller, lighter, and specifically meant for using a smartphone as part of your ground station (they only recommend Android apps but I bet there are iOS apps out there that could work).
- FlightSketch is working on a “Super Simple Tracker”, a 900MHz LoRa/GPS unit. No information yet on pricing or availability yet but their other products are very reasonable and they have an app-first approach for delivering features via your phone.
Another alternative is to get a cheap/used Android phone and use the Insane Rockets app to beam back telemetry information via a cellular data connection. (Phones are only suitable payloads for large rockets.) This also assumes there will be cell service at your launch site–most fields big enough for rocketry are in rural areas which can have poor network coverage.
There are trackers in the consumer electronics market that could be repurposed for rocketry like this LoRa/GPS from Seed Studio, a GSM/GPS units from Trackimo, or even an LTE-M/WiFi/GPS dog collar from fi. These have design goals that line up with their intended uses so they usually make one or more of the following trade-offs that make them less than ideal for rocketry:
- Larger packages that weigh more
- Non-removable batteries
- Not be ruggedized for the forces of flight and (worst case) impact
- Lose satellite fix under high speeds
- Have low GPS polling rates to save battery life
These aren’t deal breakers, but I haven’t found any consumer products that are dramatically cheaper for a whole system: transmitter, receiver, phone interface and makes good design trade-offs. A possible exception are GPS trackers meant for falconry (yes really) like those from Marshall Radio but a full GPS system can easily add up to north of $1500.
For my needs (small, light, works with a phone as a ground station), the best options are:
- Missile Works T3 (RPSMA version with 4.7” rigid 1/2 wave dipole antenna), ~$170
- GPS tracker by Featherweight Altimeters, ~$350 (the only problem is I don’t have an iPhone)
- FlightSketch SST–only an announced product, not yet available
State of Android Apps
I spent a lot of time trying to find Android apps that would work with the Missile Works T32. Ideally, the app would do three things:
- Track the GPS location of the transmitter (received via Bluetooth)
- Track your current position based on the built-in phone GPS
- Plot the heading and report the distance between your position and the beacon’s position
Of the three apps recommended by MissileWorks, only RocketLocator is still available in the Google Play Store and it appears to meet the functional criteria. It is built around the BluetoothGPS4Droid (SourceForge) (Github mirror) library for interacting with Bluetooth GPS modules. That library hasn’t been updated since 2013 and uses a backport of a deprecated Bluetooth API to work with modern versions of Android. This isn’t great but if it works, it works. The app itself was updated in 2019 with compatibility fixes–so that’s a good sign–but it looks dated and is a bit rough around the edges.
The next best option is to split the tasks up across multiple apps.
Android does not have native support for Bluetooth GPS devices–you need to rely on a third-party app. I found several apps that claim to support this but by far the most common recommendation is Bluetooth GPS (Garmin even recommends it for use with their Glow 2 Bluetooth GPS). Unfortunately, the app hasn’t been updated since 2015 and appears to be completely unsupported–it’s starting to become incompatible with recent versions of Android. That doesn’t look good.
GPS Status is an excellent tracking app.
- It is a modern app (supports Dark Mode, etc) and recently updated (2019-09).
- Its pro mode removes adds for $1.99. I paid for this immediately.
- In “Radar” mode it supports tracking one or more locations at GPS coordinates you specify.
- It supports “picture in picture” mode so it could be run “over top” of a transmitter tracking app (or anything else).
I mean, you could drive it around in a car if you wanted. Assuming you have at least a driver and someone to monitor the ground station. Also, you would need to be able to drive where you needed to go, which is frequently not the case when chasing rockets through farm fields, etc. ↩
I’m trying to get the app situation sorted before I buy it or recommend that others do the same. ↩
There are lots of apps that make the GPS on your phone available over Bluetooth for other devices. You can still get tablets without built-in GPS but apparently, the market for apps that consume GPS-over-Bluetooth isn’t big enough to attract a lot of app developers. ↩
Most Bluetooth GPS devices don’t work out-of-the-box with Windows either. It seems pretty common for Bluetooth-enabled GPS modules to simply treat the Bluetooth connection as if it were a serial data connection. The data feed needs to be parsed and translated into something that the location services part of the operating system can understand what is going on. ↩