Positioning Sensors The Inertial Measurement Unit (IMU) for the Icebreaker mission could be a similar unit to those supplied by Litton and Honeywell for the Clementine mission. The Litton IMU consisted of a three axis fiber optic gryoscope and silicon accelerometer. The specifications of the Litton IMU provided to the Clementine mission are the following: Litton Model No.: LN-200 Size: 3.5" diameter x 3.2" height Weight: 0.71 kg Power: 10 W Run (+/- 5, +/- 15 V.D.C.) Performance ( 1 sigma): Gyro 1 deg/hr bias Accelerometer 500 microGs bias Environment: Temp -54 C to 71 C Vibration 15 Grms (20 Hz to 2000 Hz) Shock 1500 G's Hermetic sealed I/O: Flexible data rates and scaling, anti-alias filters, RS-422 output. The Honeywell IMU consists of three ring laser gyroscopes (RLGs) and 3 accelerometers. The specifications of the Honeywell IMU provide to the Clementine mission are the following: Honeywell Model No.: GG1308 Size: 3.9" diameter x 3.36" height Weight: 0.465 kg Power: < 13 W Performance ( 1 sigma): Gyro < 1 deg/hr bias Accelerometer < 100 microGs bias Environment: Temp -20 C to +55 C Vibration 3 axis random for 30 minutes total at 7.5 Grms Shock 1500 G's Hermetic sealed I/O: Rate: 400 Hz at 2 Mbit/sec. Data Latency: 350 micro sec. RS-422 Both IMUs were not originally designed for a radiation environment, but through minor electronic component changes, they were able to function in a radiation environment. One issue affecting the design of the IMU that is unique to this mission is the fact that the IMU will be required to function within both a flying and driving vehicle. The dynamics of the flight spacecraft will certainly be different than the dynamics present in the surface traversal application. This could present a range or resolution difference required when reporting angular rates. For instance, in the Clementine mission, the Honeywell IMU was altered to report rates of +/- 360 deg/sec. The vehicle dynamics on the lunar surface need to be analyzed to determine if the same range and resolution will suffice in this case. Star Tracker Camera A Star Tracker Camera such as the two flown on the Clementine mission could be used to provide an inertial reference for the spacecraft by comparison of star field with an on-board star map. Specifications: Mass: 0.29 kg Size: 12 x 12 x 14 cm Power: 4.5 W Field of View: 29 x 43 degrees Pixel Format: 384 x 576 Environmental: Structural Requirements for Clementine mission were listed as: steady-state 100 g's each axis , no testing for this analysis only random vibration, 14 g rms, 60 s, tested a qualification unit to 19.8 g rms, 60 sec. pyro-shock 84 g's, peak accel, no testing done, analysis only Temperature Limits: operating and non-operating min max CCD -15.8 C 27.1 C lens -26.1 C 30.8 C Voltage, steady-state + 15 (+/- 0.25), - 15 (+/- 0.25), +5 (+0.25/-0.15), -5 (+/- 0.25) Direct Sun Viewing: Brief exposures ok, but this is not recommended The Clementine Star Tracker ran Stellar Compass software on it's R3000 processor for star matching and quaternion generation. The measured rotation (quaternion) accuracy ( 1 sigma) is 80 microRad x 80 microRad x 400 microRad. Using an assumption that this angular accuracy can be converted to an accuracy in meters on the lunar surface by using the product of the lunar radius and the angle. 80 microRad * 1738 km = 139 meters 400 microRad * 1738 km = 695 meters If this calculation is correct, then this will not give particularly accurate fixes on the lunar surface. This will not allow complete position-based navigation over long periods of time and navigation will require using other sources of information. The Star Tracker system will be similar to using single-ended CA code GPS on earth. Remote Ice Detection Our team has not pursued the problem of remote ice detection, therefore no sensor has been identified. The type of sensor that might possibly be used if it could be proven that ice could be detected by passively sensing a particular wavelength of the EM spectrum is a camera similar to the UV-Visible Camera used on the Clementine mission. This camera used silicon CCD technology and operated in the near ultraviolet and visible region of the spectrum. A six position spectral filter wheel allowed the camera to be used for remote sensing applications. In this mission a different focal length would be required for close imaging on the lunar surface. A pan and tilt, or at least a tilt capability, would be required since the spacecraft's attitude can't be adjusted as with an orbital spacecraft. The specifications for this sensor for Clementine: Mass: 0.41 kg Size: 10.5 x 12 x 16 cm Avg. Power: 4.5 W Wavelength: 0.3 - 1 micron depending on position of the filter wheel Field of View: 4.2 x 5.6 degrees Pixel Format: 384 x 288