EOSS Handbook Chapter 4 - Part A

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  • 4.1. Flight subsystem
  • 4.1.1. Balloons
  • 4.1.1.1. Small balloons
  • 4.1.1.2. Extensible balloons
  • 4.1.1.3. Zero pressure balloons
  • 4.1.1.4. Super pressure balloons
  • 4.1.2. Cut-down system
  • 4.1.2.1. Requirements
  • 4.1.2.2. Current system
  • 4.1.3. Parachutes
  • 4.2. Shuttle
  • 4.2.1. Payload box construction
  • 4.2.1.1. Type I
  • 4.2.1.2. Type II
  • 4.2.1.3. Type III
  • 4.2.1.4. Type IV
  • 4.2.2. Control computer
  • 4.2.2.1. Description
  • 4.2.2.2. Present features
  • 4.2.2.3. Parameter updating
  • 4.2.2.4. Altimeter
  • 4.2.2.5. The temperature sensors
  • 4.2.2.6. LORAN-C navigation
  • 4.2.3. Beacon
  • 4.2.3.1. Transmitter
  • 4.2.3.2. ID'er
  • 4.2.3.3. Packaging
  • 4.2.3.4. Antenna
  • 4.2.3.5. Battery
  • 4.2.4. Command & telemetry
  • 4.2.4.1. Background
  • 4.2.4.2. Hardware
  • 4.2.4.3. Transceiver control
  • 4.2.4.4. Commanding
  • 4.2.4.5. Typical commands
  • 4.2.4.6. Range
  • 4.2.4.7. Telemetry

Chapter 4 Part B


4. Flight components

4.1. Flight subsystem

4.1.1. Balloons

4.1.1.1. Small balloons

<<Merle McCaslin>> Small balloons are manufactured of either an extensible material, such as natural or synthetic rubber, or a non-extensible material such as various types of plastic films.

4.1.1.2. Extensible balloons

Two sizes of balloons have been used for EOSS flights. They are manufactured by Kaysam of Totowa, New Jersey. These are designed for collection of meteorological data. The balloon increases in size as it rises and the atmospheric pressure decreases. The balloon bursts as it expands beyond it limits and the ascent is terminated. The weather services do not care if the balloon bursts while the payload is attached because they are not as concerned about recovery of the payload. At EOSS we are concerned about the balloon fouling the parachute and impairing its operation. We use a radio command release that is a nichrome wire to cut the string prior to burst. These are the two sizes of balloon we have used of this design: 105G at 1200 GRAMS, and 100G at 1000 GRAMS.

4.1.1.3. Zero pressure balloons

These are the balloons EOSS has used on the Humble flights. They were manufactured by Raven of Sioux Falls S.D. These balloons are designed to float at a predetermined altitude. They are designed to be cut loose from the payload and also must be deflated in some manner. We used the rip panel method to deflate the balloon which uses the payload weight to pull a panel out of the top of the balloon. Humble-I used a 19,000 cubic ft. volume balloon, and Humble-II used a 54,000 cubic ft. volume balloon.

4.1.1.4. Super pressure balloons

This is the type used by Utah State for the attempted launch from Reno, it has a volume of 260,000 cubic ft. and is manufactured by Winzen International, Inc. This type of balloon can float for months under the right conditions.

4.1.2. Cut-down system

4.1.2.1. Requirements

FAA

<<Jack Crabtree>> Part 101 of the Federal Aviation Regulations require that balloon systems with payload weights exceeding six pounds be equipped with at least two payload cut-down systems or devices that operate independently of each other. The use of these devices allow a controlled separation of the payload and parachute system from the balloon. This could occur at the end of the mission or during an emergency situation where it was necessary to terminate the flight.

For Small Payloads

A controlled separation is also often desired with smaller payloads using weather type balloons that burst at altitude. After bursting, remnants of the balloon and the attachment cord can become tangled in the parachute system. A controlled separation before balloon burst will prevent this from occurring. Of course, the balloon operator is now faced with the decision of where to initiate the separation. The operator often wants maximum altitude or flight time before separation. Careful planning and experience is required to formulate the final separation plan.

For Large Payloads

Cut-down systems are also used with zero pressure balloons to help terminate the flight of the balloon when the payload drops a distance of 10-20 feet and yanks on a cord that attaches to the balloon rip panel. Once the panel is ripped open, the balloon quickly deflates and descends. An additional cut-down device is often used to then separate the rip cord (and thus the balloon) from the parachute and payload to preclude entanglement.

4.1.2.2. Current system

EOSS has developed a cut-down system that uses a nichrome wire that when heated by current flowing through it, burns through the nylon cord between the parachute and the balloon. Because several Amperes of current are required, and to minimize the size of wire required between the payload and the parachute, a localized current source is installed at the top of the parachute. This consists of a small lithium 6 VDC battery with at least 1 amp-hour of capacity, and a small relay that switches the battery across the nichrome wire. The nichrome wire is approximately one and a half inches long and is wrapped several times around the nylon cord leading up to the balloon. Wraps must not touch each other. A much smaller 2-conductor wire can then be used between the payload and the separation device because of the low current requirements of the relay. One conductor is connected to +12 VDC and the other to a commandable, open-collector transistor output on the payload controller.

Other separation devices are under study by EOSS and experiments have been conducted with small pyrotechnic devices. Due to safety considerations however, the nichrome wire device has been adopted as the EOSS standard.

4.1.3. Parachutes

<<Merle McCaslin>> For our first flights we used a weather service type parachute. They are not made for the loads we fly and they came down too fast and one was torn. We are now making the parachutes out of a bright orange ripstop material. This material is heavier than we would like, but it has been doing the job. We have used the same angle of parachute as the small paper ones, just increased the length.

The illustration shown is a calculator that can be used to determine the parachute diameter required for a given descent rate and a given payload weight.

Formulas for use in design of parachute follow some variable definitions:

A = Angle, B = Side Length, D = Diameter of Circle.

A / 360 * 4 * B = D

Example: 112.5 / 360 * 4 * 56 = 70 Diameter

D * 90 / A = B

Example: 70 * 90 / 112.5 = 56 inches Side Length.

4.2. Shuttle

4.2.1. Payload box construction

EOSS has flown four types of payload packaging on the 12 flights.

4.2.1.1. Type I

A round foam box 15 inch diameter; 4 inches deep, with half inch wall thickness. This package flew in a vertical position. It had a little wheel ATV antenna mounted above the main package.

4.2.1.2. Type II

Constructed of a rectangular foam box flown in a horizontal position. It's size was approximately 15 x 4 x 10 inches with half inch walls. The printed circuit boards were laid in the box covered with insulation material. This type was flown in a horizontal position. EOSS experimented with various 2 meter and ATV antenna's on various flights.

4.2.1.3. Type III

This construction is used on the beacon and cross band repeater. A more solid block of foam approximately 6 inches square and 15 to 18 inches long. This type had a much thicker wall of foam, two to three inches.

4.2.1.4. Type IV

This is the foam core construction. The box can be custom built to size required, the sheets of foam are cut to size and hot glued together. This works very well in area's such as the mounting of the mirror. In this construction the electronic equipment is hard mounted to the box giving a more solid and reliable construction.

4.2.2. Control computer

4.2.2.1. Description

<<Bob Schellhorn>> This controller is comprised of a Z80-based microcontroller which has 32K of ROM, 32K of RAM, two PIO's ( parallel I/O chips ), a Real Time Clock chip, a DTMF decoder chip, an Exar tone encoder chip used for generating packets, a National voltage to frequency converter for translating the minute voltages from the pressure sensor at high altitudes into values the CPU can handle, and a National 8 input, 8 bit analog-to-digital converter used to measure different temperatures. The CPU is kept at 1 MHz clock speed to hold down any interference to receivers on board.

4.2.2.2. Present features

  • A two meter beacon transmitter which identifies the balloon in CW including the present altitude in thousands of feet (long form CW mode only).
  • Following the CW ID, a packet message is transmitted telling the status of the balloon which includes:
  • Present altitude in thousands of feet.
  • Present temperature of the inside the payload.
  • Present temperature of the outside of the payload.
  • Local time and date.
  • Position of a movable TV camera positioned from the ground to any vertical angle from straight up to straight down.
  • Status of a balloon release device commandable from the ground which allows for the payload to be detached before it is damaged by the exploding balloon.
  • Status of a command receiver to accept commands from designated ground control stations.
  • Status of a confirmation packet message is sent following any commands to indicate if the command was completed or no good. This also is a time stamped log of any and all commands used.
  • A general information packet message sent on command which tells all stations the nature of the mission and where to send any confirmations of receiving the balloon signals.

4.2.2.3. Parameter updating

A terminal can be plugged into the payload prior to launch time to allow for updating parameters. These include:

  • Setting the present time and date.
  • Changing to a different CW speed.
  • Entering a different Call for the ID.
  • Entering a selected password used in commanding.
  • Changing to a different general information message.
  • Check-out other functions such as the release device.

4.2.2.4. Altimeter

The sensor is a Motorola device which gives an output voltage from 5.0 to 0 volts for a given air pressure and is very linear.

The difference in pressure per thousand foot is much greater at the lower altitudes but at near 100,000 feet, the difference in the output of the sensor for each 1000 feet will be only a few millivolts. Since this is too big a job for our 8-bit A/D converter, a voltage-to-frequency converter was used.

The sensor is connected directly to the LM331 with its output running about 4.0 MHz. This output is then divided by 256 and run into a bit on one of the I/O ports. The program detects when the signal changes state and starts a counter which steps until the signal changes again. This number is then used with a lookup table to determine the present altitude.

4.2.2.5. The temperature sensors

These are National LM335's. We tried using LM34's and LM35's which read temperature directly in Fahrenheit and centigrade, but since the temperature range we encounter goes to about -50 degrees Fahrenheit, it was difficult to use sensors that go minus. The LM335's give a linear output of 10 millivolts per degree Kelvin, which never goes minus. We convert the output read by the A/D converter, to degrees Fahrenheit via a lookup table which is inserted into the packet status message to read out from -59 to 179 degrees.

4.2.2.6. LORAN-C navigation

TBW (Bob 'ORE)

4.2.3. Beacon

4.2.3.1. Transmitter

<<Bob Ragain>> The EOSS beacon transmitter is crystal controlled (18.5 MHz range) with 5 stages. The final is a 2N3553. The voltage requirement was reduced from the original 16 vdc down to 6 vdc. Present output frequency is 147.555 MHz with the power output tuned to 200 mW. The two watt transmitter strip was originally used for naval sono-buoy telemetry operations.

4.2.3.2. ID'er

The ID'er is a design developed by WN0EHE and is EPROM based. A one bit "channel" of the 8 bit byte is checked as either high or low state. A "high" state enables an audio output tone produced by a '555 oscillator. The sequence of highs and lows is selected to produce a Morse code message. The '555 oscillator output is subdivided to create a clock pulse for strobing the EPROM to output byte by byte. Any of the 8 "bit channels" can be chosen by DIP switch and each channel can have a different message. Voltage regulation for the TTL chips is via an LM-7805.

4.2.3.3. Packaging

The packaging material is closed cell Styrofoam and is in 3 layers. The two electronics boards and the battery are attached to a 2 inch thick central layer. Two 1 inch thick cover layers "sandwich" the middle layer and are attached with tape, tying the package together. The beacon is suspended by nylon cord from the package(s) above. A loop of "Weed-eater"(R) cord through the middle layer provides an attachment point on top and an antenna support on the bottom and prevents any tensional force on the styrofoam. The electronics boards are inside vented plastic bags. The entire package is draped in another plastic bag for flight.

4.2.3.4. Antenna

The 2 meter antenna is an upside-down quarter wave with ground plane suspended below the beacon package. The radiating element is about 19 inches of stainless steel wire tuned for best SWR. 25 dB of return loss was achieved at 147.555 MHz. The ground plane is four elements at 90 degree spacing with a support ring of about 12 inch diameter. The outer ends of the ground plane elements are bent in such a way to make the antenna flip to a vertical position and skid along the ground as the package is dragged after landing. The antenna is attached to the beacon package by about 2 feet of RG-58 coax to allow the antenna to move independently of the beacon package.

4.2.3.5. Battery

The battery pack is 3 lithium cells in series to provide about 9 vdc at 4 ampere hours capacity. Battery life is calculated at 20 hours at full output but current requirements decrease as battery voltage drops with temperature. Battery life has been tested to more than 30 hours under cold "flight" conditions. The beacon will operate down to 6 vdc.

4.2.4. Command & telemetry

4.2.4.1. Background

<<Tom Isenberg>> Command and telemetry data (information being sent to and from the Shuttle computer, respectively), enables EOSS to control the different devices on board, as well as collect data. All data that we collect has some importance during the flight. Sample telemetry may look similar to the following: W6OAL>CQ: EOSS Balloon Status 09/28/91 09:37:37 AM Altitude; 5000 feet. Temperatures; Inside 88, Outside 72. This information is given every 30 seconds. During the time ground control is sending the computer commands, normal telemetry output will be interrupted and command information will be displayed. Payload altitude is given in a rounded format so you may see two consecutive altitudes the same. If the altitude remains the same repeatedly, then the balloon is not ascending. The temperature inside the Shuttle tells us if the electronics on board is keeping warm. If the temperature drops inside, we know that maybe some damage to the Shuttle may have occurred. The outside temperature is used for comparison. A third temperature sensor tells us that the on-board heater is working. There may be other information contained in the telemetry to indicate more to the ground control station.

4.2.4.2. Hardware

<<Mike Manes>> Two-way radio communications is maintained with the Shuttle and experiment in-flight. Control commands are "uplinked" to the Shuttle from the ground control station. Shuttle status information is "downlinked" from the Shuttle to the ground control station. The downlink data stream is known as "telemetry." Command and telemetry communications use the 2-meter amateur radio band on 144.34 MHz simplex and 3 KHz deviation frequency modulation (FM). The Shuttle radio is a stripped-down Midland LMR 70-150B commercial hand-held transceiver. Transmit and receive frequencies are crystal-controlled. The transmitter operates at about 1 watt (W) RF output power, and the receiver will respond to signals down to 0.25 microvolt (uV). The internal transmit/receive (T/R) antenna switch is connected to a 1/4 wavelength (about 19") vertical whip antenna mounted atop the Shuttle package.

4.2.4.3. Transceiver control

This transceiver is controlled entirely by the Shuttle Control Computer. Transmitted audio is audio-frequency-shift-keyed (AFSK) 1200 baud digital data formatted per AX.25 as Unproto Information (UI) frames. This signal can be decoded by ordinary amateur radio packet terminal node controllers (TNCs) in the monitor mode. Packet bursts with telemetry data are transmitted in 2 second bursts every 30 seconds, except while ground commands are being processed. In addition, AFSK CW (Morse code) is transmitted for FCC identification every 9 minutes, and the CW mode may be invoked during the flight by ground command; this mode leaves the transmitter on for most of the 30 second telemetry cycle.

4.2.4.4. Commanding

When the transmitter is off, the receiver is listening for commands from the ground station. Commands are transmitted as a series of standard touch-tone (DTMF) signals, and may be issued by any appropriately equipped 2 meter FM transmitter. To avoid accidental or malicious operation, each command contains an embedded password which is programmed into the Shuttle Controller just prior to launch. Once command decoding is initiated, the Shuttle Controller will delay transmit activation for at least 5 seconds or until a complete command string is received; it will then issue an acknowledgment response on packet.

4.2.4.5. Typical commands

Standard commands include: (1) ATV on/off, (2) ATV camera elevation control,(3) CW Mode on/off, (4) Send special packet message programmed prior to launch, and (5) Balloon release. See Section on Electrical Connections, (4.3.4) regarding additional commands and telemetry specific to the experiment interface.

4.2.4.6. Range

Despite the modest on-board power and antenna, the command and telemetry link to the launch site has been successfully maintained to ranges over 200 miles. This is primarily due to the unobstructed line of sight path to the balloon's lofty height. After touchdown, the link range is typically reduced to less than one mile.

4.2.4.7. Telemetry

Standard telemetry includes:

  • (1) date and time
  • (2) altitude - derived from a pressure transducer
  • (3) location in latitude and longitude, plus range and bearing to launch site - via on-board Loran C navigation receiver,
  • (4) Shuttle internal, outside air and experiment temperatures in Fahrenheit, and
  • (5) Shuttle battery voltage.

Go to Chapter 4 (part b)