The Mars Microprobe Project is paying approximately $2.8 million for the ride to Mars. Not requiring a dedicated launch vehicle for this mission has saved taxpayer's tens of millions of dollars (an order of magnitude of savings).
To simplify cruise operations and the probes interface with the lander, there are no electrical interfaces between them. The probes are powered off during cruise, thus, there are no communications with them from installation on the launch pad until after impact with the Martian surface.
By not commanding the probes during cruise, the Mars Microprobe Project is saving taxpayer dollars.
The prime landing site is located at the northern most boundary of the PLT deposits near 73 degrees south latitude and 210 degrees west longitude. The high latitude landing site will provide unique opportunities for the 1998 Mars Surveyor Lander to study the distribution and behavior of Martian volatiles, as well as aspects of the climate history of Mars. The microprobes may impact anywhere from 50 to 100 kilometers from the Lander.
Just prior to atmospheric entry, the 1998 Mars Lander will separate from its cruise ring. The force of separation will initiate mechanical pyro devices, which in turn will separate the microprobes from the cruise ring approximately 18 seconds later.
The microprobe entry, descent, and impact (EDI) system is single stage from atmospheric entry until impact. The non-erosive aeroshell uses an advanced ablative material, which can withstand temperatures associated with heating rates up to 300 W/cm2. This material provides a significant mass advantage over traditional aeroshell designs, and maintains a constant aerodynamic shape. The aeroshell will be carried to the surface, and will shatter upon impact leaving the penetrator aftbody clear for communications with the Mars Global Surveyor spacecraft.
The microprobes are expected to hit the surface with an impact velocity of 160 to 200 m/s, an impact incidence angle < 25°, and an angle of attack < 12°. Upon impact, each penetrator will separate into a fore and an aftbody that are connected via a cable system. The forebody is expected to penetrate to a depth of 0.3 to 2 m for soil types that vary from frozen-soil to very loose fine-grained soil, respectively. The forebody must also withstand a peak rigid body shock of up to 30,000 G's. The aftbody is designed to stay on the surface, and withstand a peak rigid body shock of < 80,000 G's.
Upon impact, an accelerometers will measure the deceleration of the forebody before it comes to rest in the martian soil. This data may provide clues to climate history if geological stratification or an ice layer is detected below the surface. Accelerometer data will also provide information on the depth of probe penetration.
Within minutes of impact, a micromotor will drive a small drill out the side wall of the penetrator. Soil tailings from the drill be pulled into the water experiment sample cup. Collection of a subsurface soil sample is one of the probe's key technological demonstrations, as it is considered very important for future missions and the search for life on Mars.
The water experiment is designed to detect the presence of subsurface ice if present. Power permitting, it will also characterize subsurface soil composition by measuring the temperature at which water is released. This is accomplished several hours after impact by gradually heating the 100 mg subsurface soil sample in 10° C increments, and measuring the water vapor released.
The probe will also collect temperature, pressure, and sun detection measurements every hour for at least the first two martian days (A Martian day-or sol-is 24 hours, 37 minutes long), and will continue until the probe battery is depleted (approximately 20 additional sols). The pressure sensor will measure the martian atmospheric pressure which is less than 1% of Earth's. The two temperature sensors will measure the soil conductivity and will supply information on the operating status of the probes while the sun detector will verify that the aftbody has remained on the surface.
Science and engineering data collected during the mission will be temporarily stored in the probes' microcontrollers until it is transmitted to earth via the Mars Global Surveyor (MGS) spacecraft. MGS, which was launched in November 1996, is currently on its way to Mars, and will be in a near-polar orbit when the microprobes arrive at the red planet in December 1999. There will be four opportunities in the first 2 sols to send data, at 7 kilobits per second, to the MGS spacecraft as it passes over the probe landing site. MGS will then relay the microprobe data to NASA's Deep Space Network on Earth.