The Vanguard is a 6-wheeled vehicle of a rocker bogie design which allows the traverse of obstacles a wheel diameter (13cm) in size. Each wheel is independently actuated and geared providing superior climbing capability in soft sand. The front and rear wheels are independently steerable, providing the capability for the vehicle to turn in place. The vehicle has a top speed of 0.9 m/min.

The design methodology used for this vehicle started with determining the overall system requirements for the Vanguard. It was determined that the main deliverable of the system is imagery of the moon, and the vehicle was designed to provide that as reliably and with as much availability as possible.

The Vanguard subsystem consists of many different components. These components include a sensor system, communications system, thermal system, power system and drive/steering system. All components are needed in order for Vanguard to function properly on the moon. The figure below illustrates how each system will interact within the rover.

Fig. Vanguard System Block Diagram

 

Structure / Material

            Due to the unpredictable lunar terrain, the Vanguard is designed to be flexible for the proposed mission. The flexible design considered allows Vanguard to navigate most terrain it is likely to encounter and still be relatively small.
            The frame is divided into three different sections allowing the frame to flex. Torsional springs are used at the hinges as a supplemented damping system. Each wheel has an independent suspension attaching it to the frame of Vanguard, acting as the primary damping system. This independent suspension acts as a mechanism to compact Vanguard for storage on the lander.
            The main body of Vanguard is completely sealed from the elements. This allows protection from Lunar dust. A cooling system is implemented to channel the heat away from the sensitive components.

Fig. Predecisional Concept Drawing of the Vanguard

 

Drive / Steering

            Each wheel has its own independent drive motor. This assures that Vanguard keeps in contact with the ground even on rough terrain as well as simplifies drivetrain design. Steering mechanisms are placed on the front and the rear sections to work in conjunction with variable speed motors. The wheels are constructed of a rigid metal strip attached to the hub by eight thin spokes. This design adequately supports the Vanguard and its cargo while maintaining traction and conserving mass.

Motor selected:

 

 

Thermal System Design

            As the mission takes place entirely during the lunar day, the ambient temperatures are going to be extremely high. Thus, Vanguard is mirrored on the outside in order to reflect radiant energy. This highly reflective coating along with the cooling system will prevent overheating and protect the sensitive components. A barrier of Aerogel is placed between the outer and the inner shell for insulation purposes.

Aerogels
Aerogels are extremely lightweight insulating materials made by evacuating the fluid components from regular gel materials without collapsing the solid support structure of the gel. Aerogels have been fabricated with densities as low as 5 kg/m3 and thermal conductivities of 0.02 W/m/K in vacuum at room temperature. The development of carbon aerogels increases the insulating capability of aerogels. These carbon aerogels are opaque and greatly reduce radiative heat transfer and can also insulate effectively while withstanding temperatures up to 1000 K.

 

Power System

The Vanguard is powered by a 0.25m2 solar panel comprised of 2 strings of 7, 5.5mil Spectrolab Ultra Triple Junction GaInP2/GaAs/Ge cells each. These are the same solar cells used on the lander.  The power system is battery backed by 4 Saft VL8P Li-ion batteries, providing up to 100Wh each and 7.5Ah.  This PV-battery system allows the microrover to draw up to 112W of peak power while the peak panel production is 20W. The normal driving power requirement for the Vanguard is 10W.

 

	Full Operation Mode (in watts)	Hard Terrain Mode (in watts)	Idle (in watts)
Locomotion	30	45	0
Thermal Control	10	10	10
Communications	0.05	0.05	0.005
Computing	8	10	2
Imagery	15	7	0
Compression	12	5	0
Total	75.05	77.05	12.005

 

“Full Operation Mode” in which the Vanguard operates with average locomotion power and full video panorama transmitted during the lunar day. “Hard Terrain Mode” in which the Vanguard operates at peak locomotion draw with single camera transmission only.

 

Sensor System

 

Communication System

The Vanguard uses the following antennas for communication with the lander/base station.

1 0.65 meter omni directional antenna at 405 MHz.
1 0.65 meter omni directional antenna at 450 MHz.

Click here to see the link budget analysis

 

Control System

 

Mass Estimates

 

Design Constraints

The design of the Vanguard system was impacted by many factors. The primary design drivers, after the imagery subsystem payload was accounted for, were the Vanguard's operating environment.