EggFinder to 80,000' plus altitude

[High Desert Rocketry]

Last week a friend of mine asked if I could help with the launch and recovery of a HAB. I called another friend of mine doing the Sugar Shot to Space project with me and asked if he was available so we could test the EggFinder we have been using in our small scale 75mm Sugar Shot sustainer. It has continued to transmit gps up to our 30,000' flights and this would be a great opportunity to test just how high up we could still receive the signal.

Both the transmitter and receiver have the optional 2-3 db gain antennas on them. Because we were going as a 'ride-a-long' payload we would have to keep our weight below 79 grams. While the stock EggFinder weighs in at under 20 grams, the 2s Lipo battery and the optional antenna would add additional weight and that didn't include the insulating styrofoam 'brick' I needed to fashion for thermal protection and the string used to hang it below the primary scientific payload that was being launched.

The balloon was prepped pre-dawn for an early launch from a parking lot in the Southern California desert city of El Centro. Normally I've flown HABs using APRS/GPS but on this we would be using the EggFinder LCD Receiver with Bluetooth to track our our cell phone. The balloon had been in the air for over an hour when shortly above 80,000' we lost contact as the balloon was directly high above us. We continued visually watching the balloon from that location until we saw it burst at around 100,000'...you actually just see the small white dot in the sky vanish.

Sometime later we began receiving the signal at about 60,000' as it slowly came down on parachute. We continued monitoring as we drove below its position until somewhere around 5,000' we visually spotted the chute and watched it land a few hundred feet away in an alfalfa field.

Possible reasons for losing contact at 80,000':
1) We had been using Rocket Locator and were directly under the balloon when we lost contact...the antenna were now vertically aligned.
2) Even though I put the EggFinder in a styrofoam 'brick', it had been up in the subzero temperatures for over an hour.
3) At 80,000', it was too high up for the 3db gain antenna
and maybe
4) To save weight, we used our smallest 2s lipo battery we had since we were doing a ride along with a much larger experimental payload.

I believe if we were using a panel antenna and not directly below the EggFinder we could have tracked it all the way to 100,000'.

Rick

Photos: Prep, High above Salton Sea, Chris trying to regain reception at 80,000', me holding the red styrofoam 'brick'

 

[Cl(VII)]

That is amazing. Thanks for sharing this.

 

[watheyak]

Very cool. The Salton Sea pic is great.

 

[ksaves2]

I forgot about the patch antenna thing. That wouldn't deal with the cold soaking though. Could you toss in a chemical hand warmer? With good insulation that might keep the lipo warm enough at altitude due to the poorer heat conduction to the outside in the thin atmosphere. If the presumed battery situation is remedied, perhaps 100mW isn't cutting it but if you could see the balloon I'd expect you'd be able to aim a patch or Yagi antenna at it. Kurt

 

[High Desert Rocketry]

Could you toss in a chemical hand warmer? With good insulation that might keep the lipo warm enough at altitude due to the poorer heat conduction to the outside in the thin atmosphere. If the presumed battery situation is remedied, perhaps 100mW isn't cutting it but if you could see the balloon I'd expect you'd be able to aim a patch or Yagi antenna at it. Kurt

Some chemical hand warmers work with the reaction of oxygen in the air that don't work in this air so you need to pick the right type.

We constructed the styrofoam brick to help insulate the battery and EggFinder and hoped that the heat generated from their operation would keep things warm. We've done that on previous HAB flights and it seemed to work for flights lasting > 2 hours.

Use of a 8-10 db panel patch antenna vs the 2-3 db for the one we used should get us easily to 100,000'. A yagi would work great for a slow moving balloon that you can visually see would work great but for a rocket that you could not see at high altitude, the patch antenna on the ground receiver would be preferred.

 

[ksaves2]

Yeah, can't aim a yagi with a narrow beam width for a rocket so a patch is preferred. I found the yagi is doable once a rocket is on the ground. While proceeding to a downed rocket, I've used a yagi and once I started receiving decodable positions, I unscrewed the cable and put the 3db vertical back on. The signal disappeared. Put the yagi cable back on and it was easily reacquired. It will increase the ground footprint of the tracker. That may or may not matter depending on the nature of the flight.
What I found really neat was you were able to see the balloon at altitude. I've only read about that occasionally. Am told you need a nice clear sky and a fair sized balloon although the balloon expands at altitude and gets physically larger. Even then some folks tell me they need to use binoculars or a telescope to see it. Only the "eagle" eyed could spot it in some cases. Kurt

 

[High Desert Rocketry]

I use a Yagi when I only have a RF beacon in the rocket.

What I found really neat was you were able to see the balloon at altitude. I've only read about that occasionally. Am told you need a nice clear sky and a fair sized balloon although the balloon expands at altitude and gets physically larger. Even then some folks tell me they need to use binoculars or a telescope to see it. Only the "eagle" eyed could spot it in some cases. Kurt

When the HAB is directly overhead they are easy to see against the blue sky. When the wind carries them off into the less than blue sky towards the horizon they become hard to see. When we looked up at the Red Bull Stratos at 95,000' from below, it looked like a plastic grocery store bag had gotten carried up in a dust devil. It looked about the same size when Felix jumped at 124,000' because it was max expanded.

 

[watermelonman]

Awesome! Great work.

 

[ksaves2]

Cool shots. The accounts I read were from hobby balloonists. The Red Bull attempt was with a pretty large balloon for the man carrying task. Kurt

 

[bobkrech]

You should consider a patch antenna for the base station. https://www.l-com.com/wireless-antenna-900-mhz-patch-antennas are typical 900 Mhz patch antennas.

For a rocket flight or balloon flight simple put it on a cheap photo tripod parallel with the ground. The 3 db points of this type of antenna is ~70 degrees so since rockets and balloons initially go straight up, you should be able to track the object for a fair amount of time before you have to adjust the tripod. If you are doing real time tracking, you should be able to know how far the object is from you and the vector towards it. Simply tilting and rotating the antenna slightly will peak up the signal when required, but the adjustments are really not that critical.

The nice thing about patch antennas are in addition to gain, they can be made for linear or circular polarization. And they are rugged and not very expensive.

Also if you lost the GPS at 60 kft on the way up and regained it at 60 kft on the way down, the GPS hit the ITAR limit...

 

[cerving]

They lost it at 80K going up... no way the velocity of a balloon is gonna hit ITAR.

 

[ksaves2]

They lost it at 80K going up... no way the velocity of a balloon is gonna hit ITAR.

Yeah but some chipsets will cut out if they hit the altitude limit anyways. I thought 60k was the limit so if they lost it at 80k I'd suspect a technical issue perhaps. Kurt

 

[cerving]

Probably the radio's limit. They take a bit more signal to reacquire data once they've cut out in a fringe area, at least that's been my observation. That would explain why it locked until 80K but didn't pick back up until 60K. It could also be that the GPS' antenna moved in relation to the sky, too... who know what kind of thrashing is going on up there. I don't... I'm not that familiar with balloons (unless they have water in them or say "Happy Birthday").

 

[Wayco]

OK, I guess I will have to stop saying we haven't found the limit of an Eggfinder yet... DANG!

 

[John Beans]

Interesting that you flew an antenna with gain (versus a 0dB model that is omnidirectional) and oriented it vertically. Kinda worst case mounting, right? Since you spent extra sensitivity sideways, instead of up and down where your null was pointed. Whereas if you oriented it sideways, the gain would have worked a little more in your favor, "lobing" toward the ground.

 

[cerving]

OK, I guess I will have to stop saying we haven't found the limit of an Eggfinder yet... DANG!

So Wayco, you got your rocket for 80K yet?

 

[Wayco]

So Wayco, you got your rocket for 80K yet?

I'm collecting parts for it, but we aren't ready for a BALLS launch yet..... I think with the right antennas, oriented correctly, it might be doable.
Just put a TRS in the nosecone coupler of a 3" Punisher, with no all thread, what a pain!

 

[ksaves2]

Interesting that you flew an antenna with gain (versus a 0dB model that is omnidirectional) and oriented it vertically. Kinda worst case mounting, right? Since you spent extra sensitivity sideways, instead of up and down where your null was pointed. Whereas if you oriented it sideways, the gain would have worked a little more in your favor, "lobing" toward the ground.

I think maybe a horizontal dipole underneath the package or I believe the around the world picosat balloon fellow used a vertical ground plane antenna on the M0XER balloon. https://leobodnar.com/balloons/B-64/index.html Click on the links: B-64 envelope
B-64 envelope Payload Launch on that page for pictures. Used a 70cm transmitter and vertical element as facing down with a ground plane. Hard to do on a rocket but a dipole might be doable with nulls off the ends Kurt

 

[SpaceManMat]

How about simply using a collinear dipole on the RX to get a few more db?

https://store.rfdesign.com.au/antenna-900mhz-5dbi-collinear-dipole-rpsma/

 

[High Desert Rocketry]

You should consider a patch antenna for the base station...
For a rocket flight or balloon flight simple put it on a cheap photo tripod parallel with the ground.

We have a patch and use it for our rockets. On a balloon, normally they are off both horizontally and vertically; just happen to have driven under the balloon when it reached 80,000' on it's way up to 103,000' as tracked with the primary 1 watt gps.

 

[High Desert Rocketry]

OK, I guess I will have to stop saying we haven't found the limit of an Eggfinder yet... DANG!

Two years ago on a space launch I asked the day before if I could throw in my Eggfinder to test but was told there wasn't enough time to determine if it would cause interference with the avionics already in the rocket. Turns out their gps stopped working on launch and took a month before the payload was found...oh well.

We are getting ready to do another space launch this year and if successful, I'll try to get an Eggfinder aboard another flight as we are planning several.

 

[High Desert Rocketry]

Interesting that you flew an antenna with gain (versus a 0dB model that is omnidirectional) and oriented it vertically. Kinda worst case mounting, right? Since you spent extra sensitivity sideways, instead of up and down where your null was pointed. Whereas if you oriented it sideways, the gain would have worked a little more in your favor, "lobing" toward the ground.

Normally we are up wind of the balloon and not under it. Sometimes the balloon is 100 miles or more horizontally from us. On the Red Bull flight our ground station was 70 miles away still receiving video while we were underneath 'chasing' it. We've had them occasionally caught in 100+ knot jet stream winds between 30 and 40,000'.

Funny, after our balloon touched down we stopped to watch Felix jump and the Red Bull recovery team picked up our balloon landing across the street from them. "Hey, did we drop something with a blue parachute?" when they saw it coming down.