Mars Pathfinder & Mars '96 Lander Science Opportunities (AO 96-OSS-01)

Freqently Asked Questions and Answers

How will the pre-surface mission test and training activities be scheduled?

MISSION OPERATIONS

Key Schedule Items

We expect 3-4 meetings during cruise taking a total of about 3 weeks at JPL will be required to organize and train the science team as well as perform Operational Readiness Tests.

The first meeting will be of all selected and existing Pathfinder scientists in early February 1997 to organize themselves into effective Science Operations Groups. This meeting will take 3-5 days and will provide an introduction to the mission and the operations plans and scenarios. Scientists will discuss the investigations being planned to allow organization into Science Operations Groups. During and following this meeting the operations plans will be revised to ensure that data necessary for their investigation will be obtained and downlinked. (A subset of the science group may meet following this to certify the surface operations plans and scenarios.)A second meeting will focus on training science team members to operate and analyze data returned from the instruments and spacecraft. The particular training sessions and the amount of training required will vary according to the role of each investigator. Proposers should anticipate spending approximately about one week at JPL for training activities sometime in March 1996. A final meeting will involve actual operation of the instruments and spacecraft in a series of Operational Readiness Tests to be performed in April 1996. These tests will simulate the actual landed operations, including science data planning and analysis for the first few sols. These tests will take about one week.

Was the IMP calibrated for polarization (self-polarization)? What is the magnitude of the polarization and which polarization characteristics were measured (e.g., polarization and direction, Stokes vectors or other)?

Answer:

No polarization measurements were performed on the flight IMP or the prototype or engineering models; thus its polarization characteristics are unknown.

What is the planned azimuth with respect to north of the entry velocity vector?

Answer: 252.9°

What is the subspacecraft latitude and longitude at the time of entry?

Answer: 23.0°N, 338.4°E

What is the expected angle of attack (angle between axis of vehicle and velocity vector) of the vehicle during entry?

Answer: Nominally, 0°, should be less than 5° throughout nearly all of entry

What are the drag (Cd) and lift (Cl) coefficients of the entry vehicle? These coefficients will vary somewhat with velocity so approximate values would be fine.

Answer: Cd = 1.68, Cl = -0.05

Does the 10 page limit for description of proposed research include Figures and Tables?

Answer: Yes

How long should Participating Scientists expect to be in residence at JPL during the primary and extended mission?

Answer:

There is no prescribed time that scientists are required to reside at JPL. The proposed residence for each scientist should be driven by the amount of time required to accomplish the proposed tasks.

The MPF landing takes place in the early a.m. of Sol 1. Is the last day of the lander's Primary Mission refered to as "Sol 30" or is it "Sol 31"?

Answer: The last day of the prime mission is Sol 30.

What is the energy resolution of the APXS instrument? Can it distinguish between any isotopes of elements? Are there any plans at present for atmospheric analyses using this instrument?

Answer:

The energy resolution of the APXS depends on the definition of the term: The resolution of the alpha mode is such that it starts having problems separating individual elements beyond Si. Proton mode can see only some light elements. The X-ray mode is concerned only with the atomic structure of the matter and therefore can not distinquish isotopes. The best resolution the instrument will likely get on Mars is between 230 to 250 eV FWHM at 5.9 keV line. This is good enough to separate most of the elements except the Na, Mg, Al lines. For these elements, the abundances are determined from the shape of the lines and the best model fit and best chi-square. The instrument can not measure isotopes of elements. It is likely that the first APXS spectra will be of the atmosphere.

How far out from the main body of the lander will the airbags reach and how much of the surface will be disrupted by their retraction? How well will the airbag material be retracted and how much will be exposed after opening of the lander?

Answer:

Prior to airbag retraction and petal opening the airbags may extend up to 1-2 m from the lander. After airbag retraction and petal opening the lander will occupy a smaller footprint within this zone. Airbag retraction and lander opening tests show that airbag retraction drags small rocks (creating small furrows) and can overturn and dislodge larger rocks. After full retraction and opening, little airbag material will extend beyond the lander footprint (less than 0.2 m), exceptions may extend up to 0.8 m from the edge of the lander.

Is the final flight aft-camera of the Rover in color or like the forward ones?

Answer:

The flight aft-camera is a color camera. This camera is essentially a lens and CCD system in which selected pixels of the CCD are color sensitive. In a 4x4 array of pixels, 2 are red, 2 are infrared and the remainder are green.

What is the relation between (a) torque and motor currents for the wheel and steering motors and (b) how does (a) vary with temperature?

Answer:

As measured at -80degC, torque vs current varies almost linearly. From 0 to 55in-lb requires 100mA to 200mA. Stall occurs at nearly 110in-lb with a current draw of 255mA. Motors are generally operated at 15.5V. As a means of comparison, at 0degC over the same torque range, current ranges from 13mA to 140mA.

What do you expect the wheel motor-current resolutions to be on Mars after telemetry?

Answer:

Motor currents are collected in telemetry as unsigned 8 bit values, 1.48mA per count. During traverses, current from each motor is measured at the highest frequency of one sample every 2 seconds. During soil mechanics experiments, current from the motor under test (i.e., motor of wheel being spun during the experiment) is measured one sample every 0.1 seconds. A sample in each case is determined from 10 readings of the current sensor : the highest and lowest readings are removed and the remaining 8 readings are averaged.

Will there be test-bed facilities for Rover tests at JPL before and after landing and can Scientists participate in the tests and suggest other tests?

Answer:

The SIM vehicle is at JPL and represents a test-bed for experiment, evaluation and training in a variety of indoor and outdoor simulated martian surfaces. Access and participation in tests can be negotiated.

How is data acquired by the spacecraft stored in the central computer and prioritized for return to Earth?

Answer:

All Pathfinder downlink data are packetized and assigned to APID ("Application Process IDentifier") queues, from which data is downlinked in FIFO (first in first out) order. The packetization and assignment takes place immediately as a result of execution of commands which acquire data -- separate commands to packetize and enqueue the data are not used. APIDs can be configured as rings, where old data is overlayed, or as queues, where new data is rejected if the size limit is exceeded. APIDs are identified by both name and number (0-42). Specific data formats are permanently assigned to specific classes of queues. For instance, one queue is for rover health data, and only data of that format can be assigned to it. There are multiple queues for IMP image data. Any IMP image can be assigned to any of these IMP queues, and within limits, the assignment is negotiable.

Within a single downlink session, APIDs are prioritized according to a two-dimensional priority matrix called a DPT ("Downlink Priority Table"). The DPT structure is used to make sure the most important data gets in the front of the downlink stream, regardless of when it is acquired, with the proviso that downlink from individual queues is FIFO. In the DPT, APIDs can be assigned to completely override others in priority (ie, completely prevent other APIDs from getting any downlink so long as any data is left in the higher priority APID), or they can be assigned to share a priority level on a percentage-of-bits basis.

Different downlink sessions can be governed by different DPTs, and within limits, the DPT organization is negotiable.

It is not possible to reorder packets within the queue, nor is it possible to move data packets between queues. Data packets can be deleted from the front of the queue up to a commanded time (the time when they were acquired) or by specific packet number at any point in the queue. It is not currently possible to delete specific data reliably from the center of a queue, but further study could mitigate this problem.

Can you summarize preliminary spacecraft and rover data acquisition, downlink and storage plans for the first 2-sols?

Answer:

The project is in the preliminary stages of defining the data acquisition, downlink and storage plans for the prime mission. The first 2 sols have received the most attention because of their criticality for mission success. On sol 1 roughly 20 Mbits of data are expected to be returned through 3 high-gain and 1 low-gain antenna downlinks. The most important activities are to drive the rover off the solar panel; to return entry, descent and landing engineering and science data; and obtain and downlink IMP images of the martian surface prior to deployment of the IMP mast at the end of the day. To safely drive the rover off the lander requires images (rover deployment mosaics - lossy, compressed mosaics in stereo of the rover and the area where the ramps will unfurl) be taken before and after ramp deployment. A mission success panorama is also taken (a lossy mono color mosaic of the rover and the surface of Mars). Within this panorama is a lossless strip from the spacecraft to the horizon in a variety of filters. A full lossy panorama in the red filter is taken and downlinked as are: lossy airbag assessment and Sun-Earth horizon panoramas; opacity measurements; and images of the magnetic targets. Also returned are all lander and rover engineering health data, all meteorology and atmospheric structure data, all APXS calibration data, and rover navigation images. Also taken on sol 1, but stored on board for later return are: (1) a full lossless panorama in the infrared filter, (2) full lossless stereo multispectral pans of the areas closest to the lander, (3) a rear rover color image of the lander, (4) dark current and radiometric calibration data. Finally, a series of full lossless panoramas in a variety of filters are taken, but erased if the IMP is operational after it is deployed to its full height.

On sol 2 total downlink is estimated at about 15 Mbits. A lossy stereo panorama is taken from the deployed configuration for planning rover traverses. In addition, multispectral data of small spots are taken and returned as are opacity measurements, magnetic target images, and wind sock images. The first APXS measurement of soil taken the night before is returned as are subframed multispectral images of the APXS site. Meteorology measurements taken the night before and the morning of the second sol are also returned as are all lander and rover engineering health data. The rover returns a variety of soil mechanics, wheel abrasion, and material adherence data. A handful of rover forward and rear images are planned on sol 2 to support the soils mechanics and APXS measurements. IMP navigation images of the rover will also be returned.

Does the IMP have the capability to square-root compress images by converting 12-bit images to 8-bit format?

Answer: Yes

According to the ASI/MET PIP, a flexible duct is proposed to link external flow to the TC sensor. What is the ratio of internal to external flow with this duct?

Answer:

The flexible duct was not implemented on the spacecraft.

Where are these six rover temperature sensors located?

Answer:

The 6 external temperature sensors are located as follows: - One is assembled within each camera housing for a total of 3 sensors - One is assembled with each front wheel motor for a total of 2 sensors - One is located on the solar panel as part of the Material Adherence Experiment (MAE).

What type of temperature sensor is used (PRT? thermistor, thermocouple)?

Answer: Each of the 6 external temperature sensors is a PRT.

How often are these temperature sensors read out during the day and night?

Answer:

Temperature sensor readings are collected as part of any rover health check. Health check data is collected approximately once every 10min while the rover is powered-up during the day. Health checks are performed approximately once each hour during the night. Health checks can also be commanded.

In addition, selected external temperature sensor measurements are taken as part of commanded rover activities. The relevant camera temperature sensor measurement is taken when the rover takes an image. The front wheel temperature measurement is taken during a soil mechanics experiment when a front wheel is under test. The front wheel temperatures are taken during traverses. Finally, the solar panel temperature measurement is included with the data taken when a MAE experiment is performed.

Images from each camera are taken once each day, normally at the conclusion of the rover's traverses for that day. Soil mechanics experiments are expected to be performed every other day during the nominal rover mission. Traverses are performed every day. MAE experiments are conducted nominally twice each day, once at local noon and then again at 2:00pm LST.

What is the sampling range (8, 12, 14-bit) and resolution (degrees C per bit) of these temperature sensors?

Answer:

When temperatures are measured for health checks, 8bit measurements are taken. As part of imaging, a 16bit measurement is taken from the camera temperature sensor (for the camera doing the imaging). During the soil mechanics experiment, a 16bit temperature measurement is taken from the front wheel temperature sensor (for the front wheel under test). As part of the MAE experiment, a 16bit temperature measurement is taken from the solar panel temperature sensor. Lastly, as part of traverse data reporting, 8bit temperature measurements are taken from the front wheel temperature sensors.

A temperature measurement in every case results from a set of samples collected from the sensor. A measurement is determined from 10 readings of the sensor: the highest and lowest readings are removed and the remaining 8 readings are averaged.

Temperature is a non-linear function of resistance measurement.

• 1109 ohms = -110 degrees C; 2609 ohms = 75 degrees C.
• Bridge resistance = 1859 + (reading * 0.381) ohms (16bit value).
• Bridge resistance = 1859 + (reading * 6.1) ohms (8bit value).

The temperature is nearly linear in the region of interest:

• Degrees C = 2.4855 * (ohms/20) - 248.16
• For 16bit values: Degrees C = (raw reading/21.1199) - 17.1328
• For 8bit values: Degrees C = (0.7581 * raw reading) - 17.1328

  [raw reading = measurement reported by telemetry]

Answer:

This is not a single number. The PSF has been graphed at wavelengths of 440 nm, 670 nm, and 965 nm. A model is being developed to predict it in the other filters, but the model does not yet exist. It is a function of filter. The approximate full and half widths at the three wavelengths are:

Wavelength	Half power, full width	Full width at zero
440	15 µm	40 µm
670	24 µm	80 µm
965	35 µm	120 µm

The tails get very wide due to electronic cross-talk as the wavelength increases.

How many electrons per DN?

Answer: 29.8

What is the read noise and digitization noise?

Answer:

Depending upon the assumptions used, many quatization noise estimates are possible. Using a rule-of-thumb of 0.33 DN, it would be 10 electrons.

The read noise is 14.79 electrons.

How large is the uncertainty in point source radiometry due to the presence of anti-blooming gates on the CCD?

Answer:

The radiometric calibration is based upon measurements made with CCD in its flight operational configuration, including the anti-blooming gates. No separation of the gate contribution has been made, since the camera can only be operated in one way. The linearity over the entire range of quantization levels is better than 1%.

This page was last updated on: 18 October, 1996