Cut-Down Timer

What happens if your balloon doesn’t reach altitude and pop in a timely manner?  Well, you end up with a very long chase.  It can happen, especially if the balloon is not filled with an adequate volume of helium.  So, a prudent strategy is to include a cut-down circuit – a device set up to separate the balloon from the lower stages -- the parachute and payload.

REUK's Super Timer 3 Mini

A common approach to creating a cut-down circuit is to apply power to a nichrome wire wrapped around the mainline – that is to say, the connection between the balloon to the parachute.  A few seconds of current heats the wire to near red-hot and slices through nylon cord like butter. Descent begins immediately. Of course this means that there must be some trigger event to heat the wire. One solution is to use a smart timer.

REUK, a United Kingdom (UK) company (www. reuk.co.uk) sells a timer that seems ideal.  Their Super Timer 3 Mini has the ability to be programmed to apply power to a circuit at two separate and highly different intervals ranging from 99 hours to 1 second (see chart). For example, upon launching the balloon, the timer would be started. Its program period ‘A’ can be set to run for 2 hours - an adequate time for a balloon to reach altitude; then switch to period ‘B’ and apply power to the cut-down nichrome wire for 10 seconds, and then shut itself off (see mode 4).

There are some details to make this work in the real application. The location of the power to energize the nichrome wire cannot be too distant as long wire runs add too much resistance.  A localized payload box containing the cut-down circuitry and power must be located just below the parachute. A locater beeper circuit could also be started by the cut-down timer event, and so this would be incorporated too.

Consideration must be given to the expected case of the balloon popping at altitude and before the circuit timer sends power to the nichrome wire.  It is then likely a hot nichrome wire could be laying across the parachute, causing it damage.  A heat resistant shield is necessary to block the nichrome wire from touching the parachute.

Consideration too should be given to the case of the balloon making touchdown before the timer sends the 10 seconds of energy. The nichrome wire shield must be smartly designed to protect the heat from any any ignition source.

The 10 Fundamentals of Unmanned Balloon Flight

Are you really excited about the possibilities of this hobby, but are trying to figure out the big picture elements to be successful? Here is an outline of ten core operating elements to be mastered:

 (1) Image Capture: Of course you want your very own pictures and video from the edge of space. Establishing a robust, yet lightweight approach to photography is core to the project!

(2) In-Flight Beaconing: You want to be able to see the cool pictures you shot, right? This means installing beaconing / radio system to transmit GPS location data from the time of launch to the point of touchdown so you can retrieve your equipment.

(3) Payload and Flight System Integration: An overall plan is needed for housing the photography equipment, the tracking equipment, and any other scientific experiments; this plan needs to be sure to properly link together with the parachute and the balloon; all while following a strict weight budget!

(4) Accent and Descent: The balloon size, gas type, and gas fill-volume must be carefully determined. The aim is successful payload lift into the stratosphere in under a couple of hours to avoid a long chase or worse - unintentionally causing the balloon to become a “floater." This element includes selecting the right parachute for a quick, but gentle descent for safe recovery.

(5) Compliance with the FAA Regulations:  Understanding the regulations and providing the required launch information is absolutely fundamental to achieving a safe mission.

(6) Flight Path Prediction: Where will the balloon travel? Where should launch site be to provide the greatest aviation safety and best chance of recovery? Using Flight Predictions tools will guide in answering these questions.

(7) Ground Tracking, Chase, Payload Recovery: Selection of tools to track the balloon in real-time, while traveling in a vehicle requires planning. What specific methods and tools will be used to track and recover the payload while chasing at highway speeds?

(8) Science / Technology: Besides taking cool pictures, what other science or technology experiments will be part of the payload to learn from?

(9) Operations Check Lists: Development of through check lists to ensure all steps are taken to minimize mistakes that would cause an expensive and disappointing mission.

(10) Relationship Building: Perhaps the most important element of all is the opportunity a balloon project offers is building relationships with family and friends.  Lifetime memories come from setting and achieving shared goals and having joyful experiences.  Who is going to help you make this happen?

The Chase – Four Mobile Dash Boards for Payload Recovery

Who is ready for a chase?  Perhaps the best part of balloon flight operations is the pursuit to recover the payload! The mystery of all the planning and preparation unfolds as the providence of God reveals the true journey undertaken by the balloon. Everyone wonders, “How close to the predicted touchdown point will it land?;” “Will it be caught-up in a tree or take a dunk in a lake?;” “Will it meet it a disastrous fate like landing on a road and crushed by a passing car?;” “Or will we get the outcome of being able enjoy seeing near-space from our own camera?”

Of course to know the answers, the balloon must be chased and found! Here are four software / hardware tools that can be run in the chase vehicle to provide near real-time tracking of data – altitude, latitude, longitude, speed, direction – updated every few minutes – that will greatly increase the likelihood of recovering your payload:

 

APRS.FI Screen Shot of a Balloon Flight

Key Chase Vehicle Tools:

(1) APRS.FI Display [Available online for FREE] – You will want a dedicated computer to display your balloon's location from data transmitted by the payload ham radio and received on the APRS network. A mobile Internet connection can be achieved using a cellphone enabled hot spot -- but of course presumes there is good cellphone coverage in the chase area.

        Computer App <--- TNC <--- Ham Radio <--- Antenna 

(2)  APRSpoint Display [Commercial Software and Hardware]– If forced to pick a single method to ensure receiving location data from the payload -- this is it.  Configure a dedicated computer to a Terminal Node Controller (TNC) (e.g., Tiny Tracker) that in turn is linked to a ham radio tuned to the payload signal.  APRSpoint will show on detailed maps the balloon's altitude, longitude, latitude, speed and direction.  As long as the  chase vechile can stay within a  few hundred miles of the balloon, this system will provide the most robust method of staying connected with the balloon, removing the peril of lost Internet connection from poor cellphone signals in remote areas.

(3) SPOT App Display [FREE with SPOT purchase/rental] – The backup to the on-board ham transmitter is the SPOT tracker. The SPOT broadcasts location data to a network of commercial satellites, that in turn relay the data to the Internet enabling location data on a web browser. SPOT is the backup system as it has some limitations -- e.g. limited to working below 25,000 feet --  but it will provide information when needed the most - the last few thousand feet of the flight. The on-the-road display app is displays on a smartphone.

(4)  Flight Prediction Tools Touchdown Zone [Five Tools Available FREE] – Be mentally prepared ahead of the chase by reviewing and having at the ready the flight prediction touchdown zone plotted on Google maps. (See separate post for specifics). An Internet link is necessary to make the last set of prediction runs just before launch, and are great to maintain during the chase to find the closest rural roads that lead to the landing spot.

Table of Perfect Horizon Distance by Altitude

One of the concerns in tracking a balloon is the distance that a on-board transmitter needs to reach a listening (APRS) station. The table that follows shows the line-of-sight distance to the horizon based on balloon altitude - assuming perfect conditions.  The formula is: distance (miles) = 1.22 x SQRT (height in feet). A radio signal from a balloon payload should be able to reach an APRS repeating station over 90 miles away at a height of 7,000 feet; and at 110,000 feet, an on-board transmitter has a line-of-sight of over 385 miles!

On the return trip down, a payload's radio signal should reach out as far as 29 miles at just 700 feet up, giving a reasonable approximation of the touchdown location right up to landing!

Line of Sight Radio Distance / Altitude

Altitude in Feet	Miles to Horizon	Square Miles Area	Altitude in Feet	Miles to Horizon	Square Miles Area
120,000	422.6	561,113	600	27.1	2,300
110,000	404.6	514,354	500	24.7	1,916
100,000	385.8	467,594	400	22.1	1,533
90,000	366.0	420,835	300	19.1	1,150
80,000	345.1	374,075	200	15.6	767
70,000	322.8	327,316	100	11.0	383
60,000	298.8	280,557	90	10.5	345
50,000	272.8	233,797	80	9.9	307
40,000	244.0	187,038	70	9.2	268
30,000	211.3	140,278	60	8.6	230
20,000	172.5	93,519	50	7.8	192
10,000	122.0	46,759	40	7.0	153
9,000	104.8	34,495	30	6.0	115
8,000	98.8	30,662	20	4.9	77
7,000	92.4	26,829	10	3.5	38
6,000	85.6	22,996	9	3.3	34
5,000	78.1	19,164	8	3.1	31
4,000	69.9	15,331	7	2.9	27
3,000	60.5	11,498	6	2.7	23
2,000	49.4	7,665	5	2.5	19
1,000	34.9	3,833	4	2.2	15
900	33.1	3,449	3	1.9	11
800	31.2	3,066	2	1.6	8
700	29.2	2,683	1	1.1	4