NSSDCA ID: DEEPSP2 -01
Mission Name: Deep Space 2The evolved water experiment is designed to detect subsurface water by collecting a sample from the soil adjacent to the forebody penetrator and examining it for the presence of water, giving information on the water ice and water-bearing minerals within the sample. The objectives of the experiment are to demonstrate a sample collection strategy for use on future missions and to return information on the presence of water-ice at the landing sites to be applied to models of climate and water inventory on Mars.
The instrument is situated in the upper portion of the forebody and consists of a small sample collecting drill, a collection chamber, a heater, a laser, a detector, and the attendant electronics. The water detection apparatus has a mass of less than a gram and takes up about 0.3 cubic centimeters. The sample collection chamber is a small cup with a central thermally insulating (torlon) post with four 0.05 cm holes. A resistive heater consisting of nichrome wire windings is mounted around the chamber. Two silicon diode temperature sensors are inside the cup, one on the side wall and one on the central post. A tunable diode laser projects light through a lens focused on a channel which contains water vapor driven off by heating the sample. The light passes through the channel to a mirror, which reflects the light to a detector. The laser is centered at a wavelength (1.37 microns) which is absorbed by water. The magnitude of the laser light which reaches the detector is a function of how much water vapor is present in the sample channel to absorb the light. The 0.9 W electric drill is powered by a small cylindrical motor which is positioned in the center of the forebody. The sample collection system is about 11 cubic centimeters with a mass of less than 50 grams and the instrument electronics take up 4.8 cubic cm with a mass of less than 10 grams. The peak power used during operation is 1.5 W.
Immediately after impact the condition of the instruments is assessed, and 2 to 6 hours later an in situ calibration of the instrument thermal properties and laser performance is conducted. The calibration consists of heating the empty sample chamber and letting it cool, measuring the temperature change inside the chamber for comparison with measurements made when the chamber is heated with a sample inside. The laser signals are also recorded at different temperatures for calibration.
After cooldown the drill is driven out of the side of the upper forebody. The drill has an auger and sample collection bit and is pushed into the surrounding soil by two springs. Over roughly 5 minutes of operation it brings back approximately 0.1 grams of sample and deposits it into a sample collection chamber. The chamber is sealed by firing a pyro which closes a titanium lid. The sample is slowly heated to a maximum of -10 degrees C. The temperature sensors control the sample heating rate and also provide data for analysis of the thermal properties of the sample. The energy required to heat the sample is also recorded. As the sample is heated, any water vapor and other gases driven off are vented through the holes in the central post to the spectral analysis chamber below the sample chamber. The gases are spectroscopically analyzed in the chamber by a laser and are then condensed onto a cold trap. The laser data are collected in uncompressed form prior to heating, at the peak temperature, and after 20 and 40 degrees C of cooling, and are collected as scans centered around the peak at other times every 5 seconds.
This sequence is followed by a second heating of the sample up to +10 C as measured by the inner temperature sensor. Temperatures will be recorded every second. Uncompressed laser data will be collected every 25 seconds and every 10 seconds when the temperature is between -3 and +5 degrees C. Laser data centered around the peak will be collected every 10 seconds throughout the experiment. The temperature will be maintained at +10 C for approximately 4 minutes followed by a 2 minute cooldown. The temperature and laser spectroscopic data should be sufficient to determine the presence and quantity of water ice in the sample. Data will be stored on board and then transmitted to the Mars Global Surveyor spacecraft and relayed to Earth.
Mass: 0.06 kg
Power (avg): 1.5 W
Questions and comments about this experiment can be directed to: Dr. David R. Williams
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. Suzanne E. Smrekar | General Contact | NASA Jet Propulsion Laboratory | ssmrekar@mail1.jpl.nasa.gov |
Dr. Bruce C. Murray | Team Member | California Institute of Technology | |
Dr. Aaron P. Zent | Team Member | NASA Ames Research Center | azent@mail.arc.nasa.gov |
Dr. Albert S. Yen | Team Member | NASA Jet Propulsion Laboratory | albert.s.yen@jpl.nasa.gov |
Science team selected (NASA Press Release, 08 April 1998)