Gateway to Space ASEN/ASTR 2500 Fall 2007
Colorado Space Grant Consortium
GATEWAY TO SPACE
FALL 2007
DESIGN DOCUMENT
Team Icarus
“Wings Cast Toward the Sun…”
Written By:
Edgar Alejandro Flores
Vicky Wei Hsu
Filip Maksimovic
Brandon Scott Bosomworth
Jonathan Taylor
Scott Randolph
10/4/07
Revision B
Revision Log
Revision Description Date
A Conceptual Design Review 10/04/07
B Preliminary Design Review 10/16/07
C Critical Design Review 11/08/07
D Analysis and Final Report 11/29/07
Table of Contents
1.0 Mission Overview...... 4
2.0 Requirements Flow Down……..……………………………………………………5
3.0 Design ...... 6-9
4.0 Management ...... 10-12
5.0 Budget ...... 13
Mission Overview
1.0 Mission Overview
Mission Statement:
The BalloonSat Aquintus shall ascend to an altitude of approximately 30,000 meters to carry out scientific experiments that will measure the tilt of the satellite, forces acting upon it, wind speed, and solar energy to better understand the conditions in which high altitude observatories would be in.
Experiments:
1) Solar Panel Experiment
This experiment tests whether solar panels are more efficient at higher altitudes. However, the experiment is not as simple as measuring the voltage and the current from the solar panel and recording the data. On the contrary, a value called ‘peak power’ will be measured. Peak power is when the product of the voltage and the current is at a maximum value. This can be measured by using the following circuit:
Ampmeter
Capacitor
Transistor
Voltmeter
The capacitor will charge, and due to the nature of a capacitor, the voltage of the circuit will decrease. As voltage decreases, current increases, and the data logger will log values for current and voltage. The purpose of the transistor (connected to the BASIC data stamp) is so that when the capacitor charges, it will not discharge across the solar panels, and will instead discharge across a resistor. The data will be collected so quickly that even if clouds obscure the sun’s rays, the voltage and current data will still be collected.
Hopefully with this experiment our team will discover that solar panels are more efficient at high altitudes due the fact that there are less particles and clouds, thus showing that they are an effective way to power a high altitude observatory.
Some pitfalls of the experiment are that there is a chance that a larger capacitor will be needed if the HOBO data logger has a slow sampling rate.
Due to last minute insurmountable technical difficulties, we have been force to redesign this experiment. We will only measure solar power in function of altitude. In order to do this we have adapted a circuit to the solar panels so that the voltage measured by the HOBO does not exceed 2.5 V. After the data has been recovered we will be able to determine, taking into account a graph of altitude with respect to time, how much more or less energy is can be produced depending on the altitude
2) Accelerometer
Aquintus contains two experiments concerning the accelerometer. One is tilt, and the other is force.
The tilt aspect of the accelerometer shall be used for two reasons. One is to see whether a high-altitude observatory will be spinning and changing orientation quickly and at a constant rate. The other is to see (in the analysis process) if data from our other experiments, the solar panel experiment and the wind speed experiment, were affected by spinning.
The accelerometer aspect shall be used to see if there are extreme forces on the satellite during ascent and while the BalloonSat is floating at approximately 30,000 feet. This experiment shall be done to see whether fragile equipment could be damaged before the observing process even begins. A pitfall in this experiment is that inexpensive accelerometers can only measure between –3 and 3 G.
Hopefully, our team will discover that there are not extreme forces on a high altitude observatory while it is observing or ascending to its observation altitude. If this experiment proceeds successfully, it could show that equipment cannot be damaged, and that conditions at 100,000 feet are stable for observing the cosmos.
3) Wind Speed Experiment
It has come to our attention that trying to measure wind speed by utilizing a fan would not be an effective method at high altitudes. Due to low atmospheric pressure at near space altitudes the fan would not turn thus we would be unable to determine wind speed. There are however several other ways of measuring wind speed in low-pressure environments. The first method that we found was to use a pitot static tube. The problem with this kind of sensor is that it needs calibrating and is over budget. Another option, which seems the most promising albeit technical difficulties it presents, that we are considering in our trade study comes from Mars. The exploration vehicles that have been sent to the Red planet have faced the same challenge we are facing. How to measure wind speed in a low atmospheric pressure environment?
The answer derives from one of the simplest methods man has used to determine speed and direction of the wind. By wetting our finger and sticking them out in the wind we can determine the speed and the direction. Actually, we do not determine we feel these conditions. Now the question we must ask ourselves is: How do we feel speed and direction of the wind. The answer lies in heat transfer. As the wind goes over a wet finger it cools it. So could we use this same principle to design a system capable of determining the speed of the wind?
The wind sensor has several hot wire resistance thermometer (temperature sensors that exploit the predicable change in electrical resistance of some material with changing temperature) that are spaced around a cylinder of dimensions TBD. Each of those wires will get hot when run a low electrical current through them in the order of mA . With wind blowing past the cylinder, some of the wires are going to be in front of it, as it sees the wind, and some will be behind it. The wires in front of the cylinder will get cooler than the wires behind it because the wires in front will have a faster wind going over them.
This is the first step for measuring the wind speed. The second part of this method is determining the relationship between the temperature of the wires and the speed of the wind. Not because we know the temperature range of the wire does it mean that we it will immediately give us the speed is. We would have to calibrate our sensor by testing in a low pressure environment (as similar as we can to near space) different known wind speeds, different known temperatures and the establishing the relationship between the temperature of the wires and the speed of the wind. Once this we have this calibration we would be able to extrapolate the wind speed at high altitude from the recorded temperature of the wires. The temperature itself will not be recorded but rather the variation in voltage going through each one of the wires. The data would be recorded in the HOBO data logger for it’s later extraction on the ground.
After looking over the advantages and disadvantages of measuring current or voltage, we came to the conclusion that it would be best to measure voltage. The main reason for this is that the HOBO can record voltages ranging from 0-2.5 V thus we would not have to spend any money on sensors for measuring current. There is however an inconvenient to measuring voltage. The HOBOs have an internal resistance of 10k ohms. Hence, it is necessary to amplify the voltage signal coming from the thermistor. In order to solve this problem we must add an operational amplifier (circuit LN358) to boost that signal. Each thermistor will have its own operational amplifier that will then be hooked up to the HOBO.
Resistance
Thermistor
Operational amplifier (LN358)
The overall objective of our experiments is to provide essential data for the future design of an airborne telescope observatory. We believe that one of the only reliable and efficient sources of power at that altitude would be solar panels. This is the reason why we intend to measure how much electrical power can be harnessed depending on the altitude. We think this is an important factor because maybe better quality images can be taking at a higher altitude but what if you can not harness enough power at that altitude with respect to say 5000 feet below.
Other scientific measurements that we believe to be paramount for the design of a telescope observatory mounted on a balloon are tilt, temperature and humidity. If we can determine how much the satellite tilts during flight then future telescopes can be designed with the adequate equipment to compensate or dampen such variations in position.
The last experiment, which we intend to carry out and that be also, consider of the utmost importance for the construction of airborne telescopes is wind peed. One of the objectives of such a telescope would be to be able to stare at a fixed object for a reasonable amount of time. Hence, wind speed factors must be taking into account when designing the systems that will compensate for the possible instability created by such winds.
We expect to discover the ambient conditions (wind speed, temperature and humidity) as well abundance of energy at near space in the hope of helping to improve the design future airborne telescope observatories.
Requirements Flow Down
(Nomenclature: Requirement # (Requirement from which it orginated)
(0: Objectives / S# : system requirement / SS#: Subsystem requirement)
Level (0) Mission objectives (come from Mission statement)
(O1) Construct BalloonSat to improve understanding of environmental conditions at 30,000 meters for under $200 dollars by November 10th 2007.
(O2) Measure tilt in z axis (perpendicular to surface) and G forces within a range of -3 to 3 Gs a function of altitude in the range of 30,000 meters.
(O3) Measure wind speed perpendicular to any of the faces that are parallel to the balloon cord of the BalloonSat as well as solar energy as a function of altitude.
Level (1) System requirements
S1 (O1/O2) The BalloonSat system shall ascend to a near space altitude.
S2 (O2/O3) The BalloonSat system shall carry out scientific experiments of relevance for the future design of airborne telescope observatories
S3 (O2/O3) The BalloonSat system shall store the data from the measurements for later recovery on the ground.
S4 (O1) The BalloonSat system shall not exceed the dimension limitations of weight and volume
S5 (O1) The BalloonSat system shall not be a one-time flight design but shall be ready for another launch after a week from recovery from the first mission.
S6 The BalloonSat system shall comply with FAA regulations.(O1)
Level (2)
Structural subsystem
SS1 S1 The BalloonSat structural subsystem shall remain attached to the balloon cord for the duration of the mission.
SS2 S2 The BalloonSat structural subsystem shall provide openings for the temperature sensor, camera lens and switches.
SS3 S5 The BalloonSat structural subsystem shall bare the American flag on the outside of the satellite.
SS4 S2 The BalloonSat structural subsystem shall keep the components from shifting for the duration of the mission.
SS5 S4 The BalloonSat structural subsystem shall be constructed from one piece of foam core.
SS6 S1 The BalloonSat structural subsystem shall allow for the balloon cord to go through the middle of the satellite.
SS7 S1 The BalloonSat structural subsystem shall be submitted to structural tests prior to launch.
SS8 S1 The BalloonSat structural subsystem shall withstand the physical stress conditions of t he ascend, descend and landing.
SS9 S4 The BalloonSat structural subsystem shall not exceed a volume of 1500 cm3.
SS10 S1 The BalloonSat structural subsystem shall have only on removable cover.
Science subsystem
SS11 S2 The BalloonSat science subsystem shall measure ambient temperature and humidity.
SS12 S2 The BalloonSat science subsystem shall measure tilt and acceleration of the satellite.
SS13 S2 The BalloonSat science subsystem shall measure wind speed and electrical power derived from solar energy at high altitudes.
The BalloonSat science subsystem shall not provide energy for the other systems through the solar panels.
SS14 S2 The BalloonSat science subsystem shall require that the wind speed sensor be calibrated on the surface in a low-pressure environment.
SS15 S3 The 4 channel HOBO loggers will record at a rate of 10 seconds
Thermal subsystem
SS16 S2 The BalloonSat thermal subsystem shall maintain the interior temperature of the satellite within the functional temperature range of the components for the duration of the missions.
Power subsystem
SS17 S2/ S3 The BalloonSat power subsystem shall provide energy to all the electronic components aboard.
SS18 S4 The BalloonSat power subsystem shall be composed solely of a number of batteries TBD.
Design
Our design requires no less than 1500 cm3 of volume. From the Solidworks models we have seen that the components will be somewhat tightly packed with this precise volume. Another requirement needed for the design of our satellite is a cylindrical structure mounted at the top around which the thermistors for the wind speed sensor will be mounted.