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ProductSpec.doc
1. Product Specification Document
Venus Atmospheric Explorer
Version 1.0 – Revised 3/20/2016
Authors:
Sinem Ergen
Efrain Ortiz
Julius Chua
Christopher Bill
2. 1
Executive summary
The Venus atmospheric explorer will be an unmanned blimp probe on the atmosphere of
Venus. It will be a technology demonstrator of feasibility of long-duration flight on Venus. The
Venus Probe will be flying at an altitude of 57-65km above the surface of Venus. The reason
being is that on this region of Venus is similar to Earth’s atmospheric condition and is theorize
that it could be habitable. The probe will also fly at a latitude of 750 because power dynamic drag
is an issue with wind speeds greater than 40m/s, especially at solar efficiency of only 12%.
The total mass of the probe will be 267 kg, and the envelope by itself will have a total
mass of 157kg. The envelope will have a length of approximately 26m and its diameter will be
approximately 8m. This envelope will have a factor of safety of 3 and an optimum thickness of
Dyneema of 25 micro-meters and it will also consist of Mylar, Kapton, adhesives, and solar
panels. The Envelope will also have internal structure, which are septums and ballonets. The
septum safety factor is 4.6 and it will be made of dyneema. Once the envelope is packaged, it
had a dimension of 1.2m x5.3m x0.1m.
The solar array will have an efficiency of 10%, an area of 289.5 square meters, will be
able to produce 64.1 kW, and a total weight of 51.5 kg. The propellers will be three bladed, have
an efficiency of 80%, a diameter of 3.4 meters, and the motors will have a power density of 5.9
kW/kg, produce 78.4 kN/m of torque, and will weigh 3.4 kg each. Avionics will be able to measure
velocities of up to 40 m/s, pressures of up to 20 kPa, and temperatures up to 260 K. Dimensions
of the instruments are: the IMU will be 46 x 21 mm, the magnetometer will be 2 x 2 x 0.8 mm, the
anemometer will be .38 x .04 x .46 m, and the pH sensor will be 19 mm long.
The capsule holding the blimp will be a 4m diameter re-entry vehicle for which a front
cover with an SLA-561 ablative is implemented to combat the heating entry loads. The aft cover
will be composed of a similar ablative material but since the heating loads on the aft cover are
significantly less the material for that part is . Within the capsule a support structure is attached to
the front cover of the heat shield and the gondola so that the thermal loads and entry load of 108
g’s would not affect the payload. The parachutes for this mission compose of a drogue and main
parachute of Disk Gap Band style of decelerators. The release for both parachutes will be using
the mortar technique, which employs the use of a charge or gas to release the parachute from the
packaging canister. The drogue will deploy connected to the aft cover at an altitude of 135 km at
a velocity of Mach 2 slowing down the payload and release the front cover to be prepared to
release the payload into the environment. The main parachute will be mounted to the gondola
and will be deployed at an altitude of 128 km and will take thirteen minutes to reach the target
altitude of 57 km. Under the main parachute the inflation will begin for which a six in diameter
outlet inside the envelope will inflate the blimp in a time of 10 minutes. With a margin of 3 min the
envelope will adjust course and begin operation as per requirements.
The team is looking to make a contract with NASA for 56 million dollars with this project.
5. 4
Scope
1.1. Identification
The purpose of this project is split into two main objectives:
a. To acquaint the scientific community with the feasibility of extended operation of
unmanned systems in the Venusian atmospheric environment.
b. To acquaint the scientific community of the atmospheric conditions in the altitude
range of 50-65 km by collecting continuous data with varying scientific
equipment.
1.2. System Requirement
Mission cruise duration: 6 months
Altitude flight range: 55-65 km
Latitude flight: 750
Blimp System mass: 267 kg
Other Characteristics: Solar Powered
Payload Mass: 20kg
Cruise Wind speed: 40 m/s
1.3. System Overview
The whole system will encompass the entry system as well as the blimp. The
capsule will safely house the blimp as it enters the Venusian atmosphere. The blimp will
then be deployed and cruise for a period of 6 months while relaying data back into earth.
1.4. Document overview
The document will consist of the system specifications including the entry system
as well as the explorer system. It will provide specification and other ideal characteristics
of both systems, assumptions, as well as other important data. An update from PDR
numbers will also be included.
The business case and manufacturing specifications will also be included. This
will include assumptions made during the business case, as well as how the blimp, and
heat shields of the capsule will be manufactured.
2. Applicable documents
2.1. Government documents
CODE OF FEDERAL REGULATIONS
Title 14 → Chapter III → Subchapter C → Part 417 →Subpart B1
417.105 Launch personnel qualifications and certification.
Title 14 → Chapter V → Part 1216
1216.102 Policy.
1
6. 5
1216.305 Actions requiring environmental assessments.
1216.306 Actions normally requiring an EIS.
1216.310 Classified actions.
3. System
3.1. Definitions
3.2. Characteristics
3.2.1. Performance
Summary of System Level characteristics
Parameter Value
Total mass 267
Envelope Length 26.2
Envelope Diameter 8.2
Cruise velocity (m/s) 40
Cruise Altitude (km) 57
Finess Ratio 3.2
Zero lift drag 0.024
Mission Duration
(months)
6
Prop. Efficiency (%) 80
Solar Power Eff (%) 12
Latitude 75
Payload Mass (kg) 20
7. 6
3.2.2. External interface characteristics
Experimental Data collection tools:
Sensors and Flight Data:
The Venus UAV flight data collection sensors will include various devices. Here is a list of flight
sensor data collection devices:
● Pitot Tube
● pH meter (Operating temp: 268 - 393K)
● Anemometer (Operating temp: 233 - 338K)
● Temp/Humidity meter (Op Temp: 273 - 323K)
● IMU: Accelerometer, Gyroscope
● Magnetometer (Operating temp: 233 - 358K)
● Heater (total: 113.24 watt)
3.2.3. Physical characteristics
8. 7
Table 1. System mass distribution
Mass Tracking
Basic Mass
Growth
Allowance Predicted
Required
(SRD) Margin
Propulsion/PWR 26.04 7.812 33.852 35 1.148
Structure 157 15.7 172.7 140 -32.7
Communication 11.8 1.77 13.57 10 -3.57
Thermal Reg. 0 0 10 10
Entry/Deploy 500 50 550 600 50
Total Allocated 694.84 75.282 770.122 795 24.878
System Level
Margin 35
Total Allocated 694.84 75.282 770.122 830 24.878
Though the communication system and structure is overweight by approximately 36 kg
total, the system is still within the system level allocated.
9. 8
3.3. Design
The design process was the same compared to our PDR and CoDR. There were two
main concepts looked into, an aircraft and an airship. From those two concepts, there were 3
concepts within them. The main parameters that drove our design selections were power,
generation, weight, wind speeds, and other Venusian atmospheric conditions, for example, CO2
and sulfuric acid.
3.3.1. Design approach
Power and weight were the biggest concern for our blimp project, and nothing
else affects both of these parameters more than the envelope of the blimp, therefore
most of the design approach was concentrated here. There were already general
calculations about the size, and surface area of the blimp from the PDR, but a more
detailed analysis had to be done.
Envelope:
There were a few small modifications on the blimp envelope from PDR since the
mission latitude is now specifically determined. The things that changed were effected
were the mass of the envelope, safety factor, thickness of the Dyneema, as well as the
volume of the envelope. Here are the updated numbers for each:
Mass: 157 kg
Dyneema Thickness: 25e-6 m
Safety Factor: 3
Volume: 289 m3
3.3.2. Analysis tools
Many of our tools did not change from PDR. There were exception though. Some
of these exceptions are our inflation rate formulae where it was derived from the
equation of mass flow rate and Bernoulli's equation. Packing efficiency, heat rate,
propulsion power, propeller diameter and efficiencies, torque and RPM are some of the
other exceptions. But for most cases, see PDR.
3.3.3. Trade studies and selection
See structure/envelope subsystem.
3.4. Integration
Envelope/Gondola/Fins
The envelope and the gondola will have an interface in between, which will be
the mount. The mount will be bolted unto itself through some of the excess flaps of the
envelope itself. The excess flap will be made of the same material as the envelope, and
the mount and gondola will be made of a hexagonal shaped composite. after the mount
is attached to the envelope, the gondola will be attached to the mount using screws and
fasteners. The design of the fins will be inflatable as well and it will be made of the same
material as the envelope.
The Gondola will be a composite fiber structure and it is what will contain the
payload and will be the integrating structure for the blimp envelope. It also serves to
protect the sensors housed within. As auxiliary the motors and antenna are mounted as
well for operational requirements.
10. 9
Propulsion/Gondola
The motors will be mounted onto the gondola by means of support columns that
will be 5 meters in length, and that will contain the power lines from the solar array, as
well as the communication lines from the avionics main computer. The support columns
will be made from the same composite fiber material as the gondola.
Heat Shields-
The heat shields are designed with a thickness of 1.5 cm of ablative material for
a material of SLA-561V over a 4 diameter front cover of the re- entry vehicle. For
structure support of the cover a layer of fiberglass and honeycomb structure will be
sandwiched between the ablative material and the carbon fiber structure.
Payload Integration- The payload adapter is meant to withstand the peak deceleration of
108 g’s the re-entry vehicle experiences when entering the Venusian atmosphere.
In addition, it will serve to reduce the heat flux from the heat shield to the gondola.
3.5. Qualification
At the next phase of design, both the capsule and blimp will undergo a testing
procedure to verify intended performance characteristics. The power system shall be
measured again and will be compared to initial calculations to verify flights on intended
latitude and altitude will suffice. Also, structural integrity for both the blimp and capsule
shall be verified using FEAD lab or solidworks simulation or any other verification tool to
validate calculations.
3.6. Cost
Envelope materials
Each material’s mass is known. Therefore, cost per mass of each were found using
various references, and an estimate were found for each.
Dyneema: $955
Mylar: $1180
Kapton: $810
Adhesive: $271
Total: $3216
Structure-
Total for whole Capsule: $10 million
Communication System
Communication system (high gain): $2000
Propulsion System
Propulsion system: $2100
Avionics
Total: $291
Manufacturing/equipment
11. 10
A venue that is similar to the size that we need was found and used to approximate the
venue cost per year. For our case, our 33 x 88 m facility was comparable to a building
with 2860 ft2
therefore this was the number used for it.
Venue: $8.5 million per year.
Sewing machine: $5000
Renting 2 lifts: $16800 per year.
Workers
Assumed to have 45 workers (technicians and engineers) with 65k average salary with
40% overhead.
Workers: $40 million per year
Misc.
Miscellaneous: $3000
Cost Summary Approximate. Cost ($) MSL
Envelope 3.2 K -
Manufact/Equipment 900 K -
Propulsion 2.1 K -
Avionics 300 -
Comm. 20 K -
Capsule 10 M -
Workers (40% overhead) 40 M -
Total 51 M 1.4B
10% profit 56 M -
3.7. Floor plans / manufacturing tools and equipment
This is the team’s general plans for the plans for the manufacturing equipment and floor
plans for the blimp.
Venue:
● 33m x80m flat space
● All space will be in a clean room
Manufacturing Tools/equipment:
● Tarps: 40.5m x 12.5m
● Heating nip pressure roller
○ Max Temp: 500F
○ 2.5 m in length
● Nip pressure reader: 2m
● 4 home Irons
● Materials needed for envelope
○ Dyneema: 35 kg
○ Mylar: 95.4 kg
○ Kapton: 32.4 kg
12. 11
○ Dupont 68070: 23.5 kg, or 8 gallons
● Mechanical Compressor
● Carbon Fiber
● Industrial grade sewing machine
● Lifters
○ 2 scissor lifts
○ 2 reach forks
○ 2 boom lifts
● ropes and dollies
● misc items e.g.: scissors, protractors, etc.
4. “Propulsion & Power
This section and the following ones are similar in structure to Sect. 3, but each addresses a
particular subsystem and thus, has its scope restricted to the particular subsystem in question.
The subsystem description (Sect. x.1.1) starts at the subsystem level (Level 2) and proceed to
the component level (Level 3). Additional levels may be added if necessary to reach part level
(Level 4). A few differences between system and subsystem description are outlined below.
13. 12
4.1. Definitions
The propulsion and power subsystem includes the propellers, motors, solar arrays, and
avionics. The propellers and motors must be able to produce the thrust required to fly at
the chosen altitude and velocity, while the solar arrays need to produce the power
required by the motors, avionics, communication subsystem, and the payload
electronics. The avionics need to collect flight data, create commands for the propulsion,
and transmit data to the orbiting satellite via the communication subsystem.
4.2. Characteristics
4.2.1. Performance
The solar panels will have an efficiency of 10%, and will be able to
produce 64.1 kW of electricity. The propellers will be three-bladed with an
efficiency of 80%, and will operate at 2700 RPM to produce 40 kW of
thrust. The motors will have a power density of 5.9 kW/kg, and will
produce 78.4 kN/m of torque. The avionics instruments will be able to
measure velocities of up to 40 m/s, pressures of up to 20 kPa, and
temperatures up to 260 K.
4.2.2. External interface characteristics
The solar panels will be glued directly onto the envelope and are of a
flexible design so that they may be folded with the envelope while it is
inside the entry capsule. The motors with be mounted onto the gondola,
and the propellers will have folding blades so that they can be easily fitted
into the entry capsule. All avionics instruments will be mounted on or in
the gondola, with the processing computer within the gondola structure.
4.2.3. Physical characteristics
The solar array will have an area of 289.5 square meters, and a total
weight of 51.5 kg. The propellers will have a diameter of 3.4 meters, and
the motors will weigh 3.4 kg each. For avionics: the IMU will be 46 x 21
mm, the magnetometer will be 2 x 2 x 0.8 mm, the anemometer will be
.38 x .04 x .46 m, and the pH sensor will be 19 mm long.
4.3. Design
4.3.1. Design approach
To design the solar array, we looked at available flexible designs and
chose the one that fit both our environmental requirements (sulfuric acid)
and had the best solar cell efficiency. Due to the reflective nature of the
clouds on Venus, we are able to utilize the entire surface area of the
envelope, that is not covered by the gondola, to produce power.
For the propulsion, we used the drag induced by the envelope, and an
assumed propeller efficiency of 80% to calculate the propulsive power
required to fly at our desired velocity, then we sized the propeller
diameter. From there, we were able to find an optimal RPM, and calculate
the torque required from the motors and select the motors.
14. 13
4.3.2. Analysis tools
In order to size both the propulsion and the solar array, we needed to
calculate the propulsive power required to fly at our desired conditions. To
do this we used the drag generated off of our envelope:
(Nicolai)
Where the V2/3
is the volume to the two-thirds power. And use it to
calculate our power required using the following equation from Raymer’s
book:
From here can can calculate the minimum size of the solar array using
the sizing equation from Brown:
By adding the power required by the payload and avionics and
substituting that for the EEOL, we can then compare the solar array area
required to the total surface area of the envelope to ensure that we will be
producing enough power to meet demand.
For the propellers, we take the propulsive power required and convert it to
horsepower, which we then plug into the propeller diameter equation from
Raymer’s book:
And then we find the diameters for the two blade setups. Due to space
restrictions in the entry capsule, we select the design with the smallest
diameter, which is the three blade design. We then take the horsepower
and use it to find torque required from the motor, using the following
equation:
Where the RPM is obtained from engine data. Using this we are able to
size the motor, as electric motors create more torque depending on their
length.
4.3.3. Trade studies
Our main trade studies were to test three different flight paths, which
varied in maximum velocity, altitude, and angle to the sun. The original
altitude we had selected during PDR was 60 km above the surface of
Venus, which we had to lower to 57 km due to atmospheric density being
much too small for the propulsion to combat the wind velocity. Through
our calculations we determined that a flight path at a latitude of 75° with a
maximum velocity of 40 m/s.
15. 14
4.4. Construction
The solar array will be attached after the envelope has been assembled, and will
be glued onto the envelope using Dupont 68070. The gluing will be done with the
envelope fully inflated, and will have hot irons run over it to ensure curing of the
adhesive. To test for adhesion, the envelope will be deflated after curing, and the
solar array will be examined for delamination. Avionics instruments will be COTS,
and will be mounted onto and into the gondola using hand tools. The motors will
also be COTS and are to be mounted onto the support columns attached to the
gondola, then the propellers are to be attached onto the motor drive shafts.
5. “Communication & Orbits”
5.1. Definitions
5.2. Characteristics
5.2.1. Performance
5.2.2. External interface characteristics
5.2.3. Physical characteristics
5.2.4. Other characteristics
5.3. Design
5.3.1. Design approach
5.3.2. Analysis tools
5.3.3. Trade studies
5.4. Construction
5.5. Qualification
5.6. Cost
6. Blimp Structure Subsystem
6.1. Definitions
The envelope will be responsible for most, if not all of lift that will be generated
during the mission. It is the main structure of the explorer. This includes Gondola mount,
Gondola, and fins.
6.2. Characteristics
6.2.1. Performance
The biggest difference in pressure for the envelope is at the top of the blimp and
that has a value of 7300 Pascals. Using this value, the safety factor of the envelope
flying at 40 m/s is approximately 3. The envelope itself will only have 157 kg in mass.
The envelope will have a Cd of .024. Reynolds number is 8.6e5 which is relatively low.
6.2.2. External interface characteristics
The whole structure will interact with the Venusian atmosphere all the time.
Therefore, the whole thing has to be impervious to the Venusian atmosphere. Everything
will be coated with Kapton, because Kapton is non-sensitive to anything Venus can give
to it, may it be heat, radiation, sulfuric acid, and carbon dioxide.
16. 15
6.2.3. Physical characteristics
This section includes Assembly drawings for Category I projects or Detail drawings for Category II
projects. Detailed mass table for the subsystem in included here as well.
The septum radius was assumed to have a 7mm radius and with this to have a
suggested safety factor of 1.5 more than the envelope, which in this case is 4.6, then
there had to be at least 20 septums running across the top of the envelope. The fins
were also determined, except in our case, because of packaging complications, the fins
there will only be 3 fins, the bottom vertical fin will have 2x the surface area compared to
the other 2. The fins will have a surface area of approximately 10 m2
and 5m2
respectively. The fins will also have no moving parts and will be made of the same
material as our envelope, that being said, it will also be inflatable. The envelope will have
a length of 26.25m and diameter of 8.2m, volume of 289m3, and surface area of
551m2.
17. 16
6.2.4. Other characteristics
Ballonets has a volume of 86.8 m3
, radius of 2.7 m, and surface area of 94.8 m2
. The
volume of the ballonets is assumed to be 30% of the volume of the envelope.
6.3. Design
6.3.1. Design approach
18. 17
6.3.2. Analysis tools
Some assumptions were made within a reasonable scope. The pressure and
atmospheric density were assumed to be accurate according to a few different
references ranging from scholarly articles, as well as past NASA Venus mission online
websites. Some tools that were used were the basic ellipse equations for finding
volumes and surface areas. Ellipsoid volume was found using V = 4*pi*a*b*c, being that
a, b, c given finesse ratios of the envelope itself.
Some were a bit more complicated, and it was in the Nicoli's book. These formulae were
variations and manipulation of the original Bernoulli's equations. Some other tools to find
pressure differences were from the Bernoulli’s equation and as well as the fundamental
equations describing flow over a spherical ball. Dynamic pressure and total pressures
were found using Bernoulli's equation, and from here, pressure differences were found
using the equations describing flow over a sphere.
Bernoulli's equation is:
where the first term is the data acquired from references and the velocity is the indicated
velocity of Venusian atmosphere.
Theoretical airflow describing flow over a sphere are:
And this was taken from the Fundamentals of aerodynamics book.
After the theoretical differences of pressure were found, safety factors can be found here
using the most likely place where the envelope will tear. For our situation, that is in the
top part of our blimp. Reynolds number were also taken into account for the type of flow
that was on the envelope at any given time. Especially at the ends of the blimp, where
the separation of flow occurs.
Here is the equation of Reynolds number used:
Our Reynold’s number came out to be approximately 8.56e5. This is expected
and desired because the blimp will be traveling at relatively low speed at 40 m/s at 75
degrees’ north latitude. Low Reynold’s number is also desired because flow separation
and flow behavior is somewhat predictable.
19. 18
Since most of the weight will be from the envelope itself, the team had somewhat
of idea of how much the blimp will weigh approximately. Since the type of material are
known, and dimensions of the blimp as well as what is inside it are known, weights can
be approximated. Some approximations did come from the Nicoli's book regarding
septum weights and ballonets.
Leak rates were also calculated using Venusian atmospheric conditions. Tools
used for this part of the project are your standard ideal gas laws and leak rate formula,
which are:
PV = nRT
and
LR = 10 K * A * dP / D
The first formula is your basic ideal gas law where P, V, n, R, T are the basic
pressure, volume, molar mass, gas constant, and lastly temperature respectively.
For the leak rate formula, K was a material characteristic gotten from ref[ ] for Mylar and
Kapton. A is the surface area, dP is pressure difference of inside and outside of
envelope, and D is the thicknesses of the material between the two fluids. Of course this
formula was for the British units, therefore there had to be some tampering for this to
work in the SI units.
6.3.3. Trade studies
The main trade study that was conducted for the blimp was the envelope. The
trade study that was conducted were a balance of thickness of the main stress holding
material, in this case, Dyneema, safety factor, altitude, latitude, and weight. Power was
not much of a concern since there was plenty of power on our initial calculations. This
was then verified that the power needed were not in deficient after the trade study of the
envelope. The chosen mission design are as follows:
Altitude(km) 57 t(Dyneema)(m) weight(kg) F.S.
Dens(kg/m^3) 0.96 0.000025 157 3
pressure(pa) 20000
6.4. Construction
6.4.1. Envelope
1) 2 Sheets of 65m x 29m sheets of materials of each of the
materials will be needed: Dyneema, Kapton, Mylar, as well as 8
gallons of Dupont 68070.
2) The Sheets will be cut into 8 strips of 65m x 1.8125m each. A total
of 16 for both sheets when cut up.
3) Lay Dyneema flat first. Then coat it with 1 mil thickness of the
adhesive.
4) Then lay the Kapton on top of the adhesive. Again, coat the
Kapton on top with the adhesive.
20. 19
5) Then lay the Mylar on top. Therefore, the strip should look
something like this:
6) The Strips will be rolled through a rolling heat press:
a) Temperature: 408 - 477K
b) Nip Pressure: 8 - 175 N/cm
7) An angle of 22.5 degrees will be cut from the ends of the strips so
the 16 pieces should fit together accumulating to 360 degrees
when fitted together.
8) 2 strips should have excess flaps e.g. width should be bigger than
1.8125m. These pieces will be placed on the bottom of the
envelope because this is where the mount should be integrated.
9) 4 circular patch of the same kind of material will also be made and
this will be sown on the inside and outside into the front and the
ends of the 16 strip connection point. Radius won’t play a big role,
therefore for convenience, it will be of radius 1.
10) Ballonets will be made of the same material and has a mass of 3.3
kg except it will have Mylar on the inside (inside envelope still). A
small pump should be installed at the ends of the ballonets.
11) Stringers/septum will be made of just the Dyneema and this will be
stitched onto the Dyneema inside the envelope. The stringers
should have a 1.5 safety factor compared to the original 2.6 safety
factor.
12) The stitching should occur from the inside of the envelope first,
then should work itself outward.
6.4.2. Fins
1) 3 fins will be constructed, 2 of the same size, 1 with twice the
surface area.
2) The fins will be made the same material as the envelope.
3) Same steps will be done like the envelope (see envelope
construction).
4) Stitch together fin and envelope.
21. 20
5) Do the earlier steps for all 3 fins.
6.4.3. Gondola
1) Gondola will be made of light weight composites and it will house
the payload and other flight equipment and devices.
2) Because of the geometry of the gondola the composite work will
be done using a mold method or hand lay-up.
3) the mount will be bolted into the excess flaps of the envelope
4) then the gondola will be attached to the mount using fasteners
and bolts.
7. Capsule & Heat Shield
7.1. Definitions
The capsule system consists of the front shield, aft cover, support structure, gondola and
parachutes. The main requirement for this system was to protect the payload and deploy
it successfully in its required operational conditions.
7.2. Characteristics
7.2.1. Performance
Capable of withstanding an estimated heat flux of 300 J/cm^2 and flight
loads up to 109 g’s.
7.2.2. Physical characteristics
7.3. Design
7.3.1. Design
approach
As a requirement the blimp has to be inflated
and operational by the target altitude of 57 km.
Using the max pressure allowable for a
type four composite tank with Helium and a
atmospheric pressure of the envelope, the mass
flow rate with relation to the outlet diameter was
refined to give an inflation time that was manageable for the parachute sizing. Given a
10-minute inflation time, the drogue and main parachute diameters were chosen to give
22. 21
a velocity profile that would not exceed current parachutes on the market. In addition to
having a total flight time of 13 minutes, giving the blimp three extra minutes under a
parachute to fully inflate and operate.
7.3.2. Analysis tools
Heat-shield-
To conduct the heating rates and ablation thickness several equations were used. The
equations derived by gave an estimation of the total heating rate experienced based on
several parameters of the re-entry vehicle and environment such as the mass, drag
coefficient, surface area and skin friction coefficient. These body parameters gave an
expected heating rate of 300 W/cm^2. After conducting an analysis of the radiative and
convective heating at the stagnation point, it was concluded that the heating rate would
result to 250 W/cm^2 on the heath shield putting our values in a reasonable range.
Equations: This equation related the heating rate as a function of some capsule
parameters, entry velocity and mass of system. This equation also took into
consideration the skin friction coefficient which is used as a fudge factor to make up for
the fact that we assumed that the relation for heat and momentum transfer are similar.
(Allen & Eggers)
A similar equation was found to estimate the convective heat transfer to the front cover
but was a function of the entry velocity and the density of Venus. (Detra & Hidalgo)
Inflation-
The tool used to calculate the time of inflation and the corresponding mass flow rate is
modelled after the Arian FL40 flow computer. Their equation for mass flow rate related
the Helium tank’s measurements to an outlet diameter pipe. Reiterating the process
gave us a diameter that was needed for inflation under the main parachute. Using the
total volume of the envelope and the specific volume of helium a total of 12 kg would be
needed. The total mass of helium divided by the mass flow rate gave us an inflation time
of ten minutes.
Assumptions: For this analysis, thermo-dynamic energy conservation and turbulent flow
is not considered. In addition, helium and hydrogen are the two molecules that heat up
upon the expansion of gas through and outlet. This phenomenon is described by the
Joule-Thomson effect also known as a throttling process.
Equation:
23. 22
Parachutes-
The parachute sizing was done following a technical report by Airborne Systems and the
Air Force, “Recovery System Design Guide” ( AFFDL-TR-78-151).The parachute sizing
considered the radius, coefficient of drag, system mass and pressure at deployment to
calculate the shock the system would experience. For the drogue a shock of 2 g’s would
be taken by the aft cover adapter while the gondola would experience a 4 g shock when
the main parachute inflates. Using Newton’s second law of motion a relationship
between the force and velocity was derived to produce a velocity profile of the two
parachutes. The design guide gave a relation of disk, gap and band area based on the
nominal area of the parachute in consideration. The length of the lines was part of this
relation with a predicted 7 and 11-meter length for drogue and main parachute.
Assumptions: It is assumed that the gondola and aft cover doesn't interrupt the free
stream flow while opening of the parachute occurs.
24. 23
Equations:
The opening shock is a function of the mass of the system, which is related by the finite
mass opening shock factor given by this equation:
This value is used to calculate the opening shock of the decelerator along with the
coefficient of drag, area of parachute and pressure at deployment.
FdD=Rm*CmD*Sd*PdD
Using Newtons Second Law of Motion the following equation was derived to obtain the
velocity of the system while on parachute.
7.3.3. Trade studies
In the preliminary design report we looked at the trade-offs between angles of
attack, entry velocity and packing configurations with respect to the heating rates
expected. In this stage of the project we looked at the diameter size of a outlet to give a
desired time of inflation for the helium envelope using documentation of a flow regulator.
We wanted a time of inflation that would be less than the time the payload was under the
main parachute in order to proceed to nominal operational conditions. In conjunction,
the sizing of the parachutes was done using a technical report for recovery systems to
provide a decent rate that was low enough to deploy the blimp in adequate conditions.
The gondola’s orientation in PDR within the capsule was confirmed and support
structures as well as deployment mechanisms were established to provide a simplified
deployment.
7.4. Construction
The integration of the heat shield will consist of producing several layers or skeleton,
honeycomb and ablative layers that will be connected together through fasteners,
adhesives and possibly welding. The skeleton would be composed of a carbon fiber
structure with optimized fiber angles to handle some of the flight loads experienced.
While the carbon fiber structure will be of support, most of the 109 g load predicted will
be handled by the layer of reinforced honeycomb material. Different methods will be
looked at for applying the ablative material. Among the ones considered will be mounted
on pads injected with the ablative material, sprayed on or molded pads that are
integrated to complete the whole heat shield. The aft cover similarly will be either a light
wight material sprayed on with the ablative material.
25. 24
The payload support adapter material will be decided upon thermal analysis. This
subsystem will be manufactured from a a different size billets and joined together by
welding.
Manufacturing site- NASA’s Michoud Assembly in New Orleans
Testing site- Plum Brooke Station , Ohio
7.5. Qualification
Qualification for this system would compose of placing model in a simulation within
SolidWorks to check the displacements of the front shield cover would endure due to the
flight and thermal loads. A fluid simulation will be looked at to validate the heat flux
predicted by empirical formulae.
7.6. Cost
The estimated cost for manufacturing and material was estimated at over 2 million but
the qualification and testing would compose of another 8 million for a total of 10 million
development cost for the re- entry capsule.
8. Appendices
Individual contribution
Efrain Ortiz
Leadership and Teamwork: Would work closely with Julius to ensure that the integration
between blimp and envelope matched with his results and requirements. Would track the
progress on the capsule, gondola and parachutes on the task list. Consulted team mates
when problems arose in the development of the project.
Technical: Conducted the analysis for the heat shield ablation, parachute times and
opening shocks, calculated time of inflation, led the deployment baseline and CADed the
capsule, gondola and blimp.
Christopher Bill
Leadership and Teamwork: Lead on the propulsion and power subsystem. Managed
task list, and set due dates for individual assignments. Updated mass and power
tracking tables. Provided assistance with structure design, and assisted with inflation
and deployment mechanism designs.
Technical: Established system break down, and subsystem categories. Performed
calculations for solar array sizing, propeller design and sizing, and motor requirements.
Selected avionics instruments based off of flight and environmental conditions, and
created block system diagram for the avionics system.
Julius Chua
Leadership and Teamwork: Worked closely with Efrain Ortiz to find the right dimensions
for the capsule because of how the blimp was going to be packaged. Kept close tabs on
all three team members. Followed given assignments. Help set assignments to direct
team members. Collaborated with team members to help mitigate work load.
Technical: Helped outline CDR, and product specification sheet. Proofread and fix spec
document. Inserted flowcharts/tables on product spec sheet. Re-orient Product spec
sheet. Had a major role into writing system level segment on product sheet and
executive summary. Wrote the subsystem: “structure” segment on the product sheet.
Reference page. Did extensive research on manufacturing; tools needed, floor plans,
steps on how to construct envelope. Calculated/researched fin dimensions.
26. 25
Calculated/researched internal structure i.e. septums/ballonets. Calculated/researched
fold dimensions. Did calculations/research on business case. Researched COTS flight
components and sensors.
Sinem Ergen
Leadership and Teamwork:
Technical:
27. 26
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