Mars Lander Robot Recharger
Deliverable
#1 – Needs Assessment
FAMU-FSU College of Engineering
Department of Electrical and Computer Engineering
Department of Mechanical Engineering
Team Members:
Itiel Agramonte
Dean Gonzalez
Lucas Kratofil
Tyler Norkus
James Whaley
Table of Contents
NASA has invested heavily in the exploration of Martian surfaces. This has created a drive for more efficient means of operation. To achieve these higher efficiencies by consuming less energy NASA has decided that such a mission to Mars would One of the greatest constraints on extraterrestrial missions is mass. The largest drivers of mass on such missions are charging and energy storage systems. This creates a large drive for more efficient and lighter charging and storage. NASA has an existing Martian Lander with several technologies on the deck. The Lander will generate power via a hydrogen fuel cell. This power needs to be transferred to excavators on the surface to charge batteries aboard excavators.
The purpose of this project is to design a system which will charge Martian rover batteries from a stationary Martian lander base.
There are many components of the system which we will be designing. These components will be subjected to a variety of conditions in transport to, landing on, and remaining on the Martian surface. The components will need to be reliable in both terrestrial testing and extraterrestrial use.
2.1 Forces
The forces exerted on a structural member, such as the desired umbilical arm depend primarily on the acceleration due to gravity. Whatever design is decided upon must be able to function properly in the Martian atmosphere as well as withstand the forces exerted during launch (3g on manned missions and can be higher on unmanned missions). Because the Martian gravitational acceleration is 37.8% that of earth, the umbilical arm will most likely be able to withstand forces acting on it if it can survive exiting earth orbit.
Gravitational forces are not expected to have much of an impact on the electrical system, unless a PCB or connector is damaged upon launch or landing. The electrical connections themselves, should function properly, given the proper function of the umbilical arm.
2.2 Temperature
Temperature is a very important criterion to consider when dealing with electronics. Most electronic components have a maximum temperature allowable during storage and/or use. These maximum temperatures should not be a limiting factor in our design because the heat shield available on the rocket/shuttle should dissipate enough heat to protect circuitry.
The minimum operating temperature is a much more limiting condition for our design. During transit to Mars, temperatures can approach absolute zero, and temperatures on the Martian surface can reach as low as -100°C. Many general purpose integrated circuits, such as BJTs and MOSFETs have minimum operating temperatures between -70°C and -50°C. This necessitates the use of a heating system, much like what NASA has used on other missions.
2.3 Atmospheric Conditions
Pressure on the Martian surface is 600Pa (about 0.6% that of earth). The atmosphere is about 95% CO2. Operation of any components using air as a dielectric, such as some capacitors, will need to be verified under these conditions. Due to the low pressure and temperature found on Mars, this high concentration of carbon dioxide frequently created frost on the surface at night and evaporates during the day, producing near 100% humidity. The recharging station will need to ensure that its components are protected from any possible rust, or corrosion associated with this high level of humidity. Similar protection to that currently used on Martian rovers can be used.
2.4 Power Source/Conditioning
Ripple currents at the power conditioning stage can shorten fuel-cell life span, therefore this characteristic will need to be minimized.
The most common fuel cell used by the United States space program is the alkaline fuel cell (AFC). It is used to produce energy as well as help process water onboard spacecraft. These fuel cells use a solution of potassium hydroxide in water as an electrolyte and use a variety of non-precious metals as catalysts at the anode and cathode. The demonstrated efficiency in space applications is as high as 60%, among the highest efficiency rates in fuel cells.
One problem with using an AFC on the Martian surface is that the smallest amount of CO2 can have an impact on operation, so there will probably need to be a protective casing utilized in our design to protect the fuel cells.
The primary objective for our project is to recharge the batteries onboard extraterrestrial excavators. The primary power source will be hydrogen fuel cells and the recharging station will function for the duration of the mission.
The design will be broken into mechanical and electrical subsystems. The electrical subsystems will be the primary responsibility of the electrical engineers on the team, while the mechanical subsystem will be the primary responsibility of the mechanical engineers on the team.
The electrical power transfer system can be divided into the power supply, power reception, power consumption, and safety devices. The mechanical system can be divided into the active side umbilical arm, passive side umbilical arm, motion control, and heat transfer in transport.
Analysis will need to be done to calculate the power storage capacity, efficiency, power supplied, heat transfer requirements, stress, and strain. Since these calculations cover a variety of topics and are specific to the design used, full analysis will be unable to be completed until contact has been made with the sponsor.
We are expected to develop an umbilical arm, both the active and passive sides, which would allow a Martian excavator to drive to the Lander, connect the sides of the umbilical and recharge the mobility base batteries. The passive side umbilical is to be integrated onto the existing Red Rover mobility base.
Time: It will be very difficult to design, fabricate, and test our recharging station prior to the end of the school year. The lack of communication from our sponsor adds additional pressure in this regard due to the limited number of weeks in the school year.
Budget: Currently our budget is tentatively set at $2,000.00. Until more information is received from our sponsor, it will be difficult, if not impossible to determine if this is sufficient to complete the project as expected.
Team Size: Our team has five members from two different departments at the College of Engineering. Since our team is so large and diverse, it is difficult to find meeting times which are adequate for the entire team to meet. Our team’s size also makes it necessary for all team members to listen effectively when the rest of the team is offering an opinion about the project direction or any idea.
Physical Constraints: Although we have not yet received any specific details from our sponsor, we know that we have certain physical constraints which must be met by our project. These physical constraints include, but are not limited to, volume, mass, reliability, and resilience. Any failure to meet these physical constraints could cause failure of the mission, resulting in costs of millions, or even billions, of dollars to NASA and therefore the American people.
Power Constraints: We have been told that we are to use Hydrogen fuel cells as the power source for our project. This causes difficulty in that there are certain power and connection requirements which must be met by both the active and passive side umbilical arms, or the project will not function as desired.
Redundancy: Since the Excavator Recharger for Lander is designed to be used in NASA missions on Mars, the system must be redundant; otherwise, any small malfunction could cost NASA millions, if not billions, of dollars. Redundancy adds reliability to our system as a whole.
System: The Excavator Recharger must be integrated into the current Red Rover mobility system. This significantly reduces the freedom allowed in producing this recharging station.
Our team has attempted to contact the sponsor four times. Two communications have been by e-mail and two have been by telephone call. As of right now, no communication has been received in return from Mr. Townsend, the technical point of contact with NASA. The team has been in constant communication with each other and has contacted Dr. Shih with help in communicating with Mr. Townsend. All design requirements listed below are from the limited information received upon receiving the project assignment.
1. Of sufficiently small mass and volume to be sent to Mars.
2. Be capable of charging at least one Excavator an indefinite number of times.
3. Stationary on the planet in question.
4. 1.2 m height above the planetary surface.
5. Integrated into the current Red Rover mobility system.
[1] http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html
[2] http://www.afcenergy.com/technology/advantages_of_alkali_fuel_cells.aspx
[3] http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/pdfs/fc_comparison_chart.pdf
[4] http://en.wikipedia.org/wiki/Atmosphere_of_Mars
[5] http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1554624&tag=1
[6] http://www.jameco.com/Jameco/Products/ProdDS/178597.pdf
[7] http://www.space.com/16907-what-is-the-temperature-of-mars.html
[8] http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/What_Is_the_ Temperature.html
[9] http://quest.nasa.gov/aero/planetary/mars.html
[10] http://www.jpl.nasa.gov/news/press_kits/MSLLaunch.pdf