IPT2003 White Paper Template

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Team 02E

IPT 2008 White Paper

The Attached Document is Competition Sensitive until May 2, 2008

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Dr. Robert A. Frederick, Jr.

IPT Project Director

Office: 256-824-7203

Cell: 256-503-4909

Alternate Concepts White Paper

IPT 02E

Submitted By:

[1]

Team Eclipse

February 21, 2008

Submitted To:

Dr. P.J. Benfield and Dr. Matthew Turner

Department of Mechanical and Aerospace Engineering

The University of Alabama in Huntsville

[Matt1]

Abstract

This Whitepaper seeks to establish[Matt2] team roles, develop two alternative designs, and select one of them as the final concept to take into Phase 3 of the design process. The Viking Lander serves as the baseline design for this project and is compared to the alternatives developed by the team. The two alternative concepts that Team E[Matt3] is proposing and analyzing during this phase are a Lander on Wheels and a Lander with a Single Rover. At the beginning of Phase 2, the team broke [Matt4]into specified disciplines and began analyzing the advantages and disadvantages of each alternative design with respect to their particular subsystems. Descriptions and concept drawings are created based on the ideas and discussions of the team and are outlined in this document. Through pros and cons[Matt5] of each concept[Matt6] as well as weighting and utilization of the Weighted Factor Analysis and Concept Evaluation Matrix a final concept is chosen. The results of this process can be seen in the following sections[Matt7].

Technical Description

1.0 Overview of Phase 2

For Phase 2, the individual Integrated Product Teams have worked independently to produce three alternative configurations to a Baseline Design. The deliverables for Phase 2 are a White Paper and an Oral Presentation. The White Paper compares the Baseline Concept, named the Viking Mars Lander 02BL with two alternative concepts. This White Paper summarizes a strategy for selecting alternative systems, qualitative and quantitative information to evaluate each idea, and a logical rationale for down selecting one concept from among the three presented.

1.1Specification Summary

The customer has provided several level 1 requirements and design constraints for the Lunar Exploration Transportation System (LETS). The subsequent paragraphs describe, in detail, these requirements.

The entire system is to be housed within an Atlas V-401 extended payload fairing (EPF) shroud and have a total landed mass allocation of 997.4 kg. Of this mass, the propulsion system dry mass is to consume 64.6 kg, having two propellant tanks at 10.2 kg, two helium tanks at 10.4 kg, helium weighing 2 kg, two main engines totaling 15.8 kg, 12 ACS thrusters totaling 6.0 kg, a component weight of 14.1 kg, and a contingency weight of 6.1 kg. The given propulsion system is designed to carry 159.6 kg of the liquid propellant hydrazine (N2H4) and 2.0 kg of helium to provide pressurization of the fuel. Both the propellant and the helium gas are to be contained in two spherical propellant tanks each – with a propellant tank diameter of 0.55 m, and a helium tank diameter of 0.4 m. Much like the Viking Landers terminal descent engines, the LETS propulsion system will also be designed for two MR-80B monopropellant liquid rocket engines. For control, the LETS will utilize the help of 12 MR-106 attitude-control thrusters.

Having a launch date of no later than September 30, 2012, the LETS shall be designed to survive for a time period of one year upon landing on the lunar surface. While on the moon, several requirements are to be met. The first mission of the lander is to operate at a polar region, however maintaining the capability of landing at other locations and also landing at a maximum slope of 12 degrees (between the highest elevated leg of landing gear and the lowest elevated leg). Given a predicted landing area, the landing precision should be ± 100m 3σ of that location. Guidance, navigation, and control should be incorporated into the LETS during the terminal descent phase (approx. 5 km from the lunar surface), however, hazard avoidance will not be an issue. Upon landing, the LETS should be able to at least withstand the g-loads that were present at anytime between launch and terminal descent, primarily with respect to stiffness only. The LETS will not be concerned with frequency responses/loads. Not only must the design successfully land on the moon, but it must also have the capability of maneuvering and the fortitude to endure the proposed concept of operations as well as meet both the Science Mission Directorate (SMD) and the Exploration Systems Mission Directorate (ESMD[Matt8]).

1.2Team Eclipse Approach to Phase 2

For Phase 2 of the design process, Team Eclipse looked at both the baseline presentation and the customer briefing from Phase 1 in greater detail as shown in Figure 1. The team focused specifically on the Figures of Merit (FOMs) section from the CDD and the mobility trade space from the customer briefing. Upon reviewing all the suggested alternatives from the customer briefing, the team decided to look at both the Lander on Wheels concept and the Lander Single Rover concept in more detail. A team member from each discipline analyzed the two designs and prepared key concerns about each of the alternatives and the affect it would have on their design. At this point in the process, a team meeting was held where the lead of each discipline voiced these key concerns to the team lead and systems engineer. After hearing all the issues pertaining to each alternative concept, the team decided as a group to rank each of the FOMs on a scale of 1 to 3, with 3 being the most important and 1 being the least important. Once the scale was established, a concept matrix was created and both of the design concepts plus the Viking baseline design were rated on each of the FOMs and how close they were to meeting or exceeding the customer’s mission goals[Matt9]. Values of zero, five, and ten were assigned to each of the designs for a particular FOM based on how close they came to meeting or exceeding the accomplished goal. A value of zero was assigned if the design failed to meet any of the stated goals. A value of five was assigned if the design was able to met the objectives of the specific FOM. Finally, if the team believed one of the particular concepts was able to exceed the goals of a particular FOM a value of 10 was assigned. After values were assigned to each of the designs, each value was multiplied by the corresponding weighing factor. Once this was complete, the numbers generated for each FOM were summed to obtain a mission total. The design with the highest total was selected to move on towards Phase 3. This is where Team Eclipse currently stands in the design process.

Figure 1 – Outline of the Design Methodology

2.0 Description of Concepts

Concepts for the Lunar Exploration Transportation System (LETS)[Matt10] were identified based on the various rover and lander configurations possible. These configurations include a Lander on Wheels (Concept 1), a single lander plus single rover (Concept 2), and a single lander plus multiple rovers (Concept 3). Initially, Team Eclipse discussed and summarized the three concepts by creating a list of pros and cons[Matt11] for each of the configurations. These pros and cons were later given importance and weighting before utilizing the Weighted Factor Analysis and Concept Evaluation Matrix.

Concept 3 was eliminated early on since it was determined that the team was only required to have two concepts.[Matt12] The Viking Lander was established as the baseline for this project. This configuration plus[Matt13] the two remaining concepts were the ones[Matt14] compared before narrowing the choices down to one final concept. Table 1 - Boost[Matt15] Matrix for Project 02 summarizes these three final configurations and details several categories that include power, thermal, structures, operations, GN&C,[Matt16] and payload.

The baseline Viking Lander includes various subsystems which add specific attributes to this design. The structural subsystem consists of legs equipped with crush pads that allow the lander to rest on a maximum slope of six degrees while supporting the rest of the lander. The thermal subsystem of this design includes both a passive and an active system. The passive system consists of things such as insulation and shielding while the active system is made up of variable thermal switches and electric heaters. Communications subsystems of the lander include both UHF [Matt17]and S-band transmitters and receivers. The GN&C of the design is the most complex subsystem and consists of gyros and accelerometers as well as radar altimeters and Doppler radar. All of these devices are used to control the engine thrust, roll, pitch, and yaw. The final subsystem of the Viking Lander is the power subsystem. Two RTGs [Matt18]and four nickel-cadmium batteries provide the power for the lander.[Matt19]The RTGs are the main power source while the batteries provide necessary backup power in the event of peak loads[Matt20].

Concept 1 and Concept 2 share common power, thermal, structure, operations, GN&C, and payload options. These attributes only differ in that the arrangement and number of subsystems may differ depending on which concept is chosen.[Matt21] For example, both concepts can use the same heating system, Concept 2 would require two heating subsystems, one for the lander and one for the rover. Since the same attributes are available for each of these concepts, these are not extremely important in determining a final concept.[Matt22]

The differences in the concepts that allowed Team Eclipse to decide between the two come from the pros and cons [Matt23]lists outlined early in the process. Concept 1 allows the design to be more efficient, have a larger payload, and only one set of subsystems; however it also has drawbacks including higher risk[Matt24] and greater mass to move. Concept 2 also has advantages such as more ability to multitask and less risk[Matt25], and disadvantages that include smaller payload and two sets of subsystems. The Figures of Merit outlined in the CDD were weighted and Ratio of Off the Shelf to New Technology along with ConOps were determined to be the most important for this project followed by Surface Objectives Comleted, Percent Payload, SMD to ESMD Ratio, and Percent Power System[Matt26]. The analysis of these attributes in comparison to the Figures of Merit are seen in Table 3 – Concept Evaluation Matrix and allowed the team to arrive at the conclusion that Concept 1, a lunar lander and rover combination, was the best configuration for the given project.

Table 1– BOOST Matrix for Project 02 (LETS)

2.1Baseline Concept: “Viking ”[02-BL]

The Viking Lander was chosen as the baseline for the 2008 IPT Lunar Lander due to the availability of information for the lander and its similarities in mission objectives. The Viking consisted of several subsystems including the following: structural, thermal, guidance, navigation, control, power, and communications.

The structural subsystem consisted of the majority[Matt27] of the craft. This subsystem included the landing legs which were designed to accommodate a landing site with a maximum of six degrees slope. Attached to the bottom of the landing legs were crush pads to absorb some of the energy from landing. Also included in the structures was the supporting structure that held all of the other subsystems. The structures subsystem of the Viking Lander consisted of many components which will not be needed on the lunar lander because there is no atmosphere. These include the parachute, bioshield, and aerodecelerator.

The thermal subsystem of the Viking lander consisted of a passive and active system. The passive system included thermal insulation, wind covers, and radiation shields to protect the lander from the harsh Martian environment. The active system provided heat to the lander through variable thermal switches and electric heaters. When the craft became too cold, the thermal switches would close and provide power to the electric heaters.

The communications subsystem consisted of UHF and S-band transmitters and receivers. The UHF system was the primary communications system, and the S-band was a redundant system. This communication required direct line of sight to the receiver on earth.

The guidance, navigation and controls subsystem was the most complex subsystem on the Viking Lander. This subsystem was responsible for all guidance and control from the time the craft separated from the launch vehicle until it successfully landed on the Martian surface. It used gyros and accelerometers on three primary axis with a redundant gyro and accelerometer on the x-axis. Also, it used redundant radar altimeters to provide altitude feedback to the navigation computer and Doppler radar to measure the crafts velocity relative to the surface. Using this feedback information, the guidance and control computers managed engine thrust, roll, pitch, and yaw.

The final subsystem of importance to the Viking lander was the power subsystem. The Viking utilized two RTGs and four nickel-cadmium batteries to provide power to the lander. The RTGs provided the main power to the lander, and the batteries stored energy in the event of peak loads which the RTGs could not provide adequate power[Matt28].[2][Matt29]

2.2 Alternative 1 Concept: “Lander on Wheels” [02E – ALT1]

Team Eclipse has found the Lander on Wheels (LOW) configuration to be a strong possibility at this point of the design process. The team is analyzing the LOW configuration due to its ability to eliminate the need for more than one system. Since the LOW would have only one system, it also reduces the need for power as well as multiple power sources. The LOW reduces the need for two heating and cooling systems as our design would use the main power source (two RTGs) for heating the system and the moon’s environment as a cooling system.

The LOW will be able to accomplish all mission objectives. The LOW will have 6 wheels (as shown in Figure 3) which will allow for it to travel to and from different sites as well as help to negotiate slopes of12 degrees. Much like the design of Sojourner, our design will utilize the rocker bogie suspension system. This will ultimately allow for each wheel to act independent of the other wheels to allow for a more versatile design. The LOW will be capable of landing at a polar location and possess the ability to move to other predetermined lunar locations. The LOW will also send all data collected to the LRO (Lunar Reconnaissance Orbiter) and to Earth when in direct line of sight.

The LOW will possess the ability to accomplish all the specified scientific objectives. By having the lander act as the rover, this will allow more payload space to be allotted for more complex scientific equipment. Data samples will be picked off the lunar surface with the use of a robotic arm. Having a mobile base creates the opportunity to perform extended research at a given site. Upon gathering data from a site, the LOW will be able to transfer data to the LRO or Earth (with Direct LOS) while moving on the lunar surface, being limited only by the time the LRO or Earth is visible by direct LOS. Upon completion of all twenty (20) sites and all other mission/scientific objectives, the Lander on Wheels has the capability to launch the SRV with the scientific payload from its present location.

With regards to power, the LOW will rely solely off of two RTGs[3], which has a combined weight of 30.8kgs (as mentioned in Table 2). As previously discussed, the RTGs will play a role in heating the scientific instruments carried on the lander, as it has a heat output of 1400 Watts. The Sample Return Vehicle (SRV), designed by ESTACA, which will be attached to the lander, will have its own separate power system. The SRV will run off of a Lithium Ion battery, which will be charged and kept warm by the RTGs heat output. The team decided on a Lithium Ion Battery as opposed to a Nickel Cadmium Battery knowing that a Lithium Ion Battery is significantly lighter.