Payload Concept Proposal
Mercury Lander Mission
Spring 2012
West Point High School
Team 3
1.0 Introduction
Team J.E.D.I. is a high school team under the InSPIRESS project. If selected, the team’s payload will go to Mercury aboard a lander designed by the UAHuntsville IPT team. Its goal, as described in detail later in this paper, will be to measure the composition of Mercury’s soil.
2.0 Science Objective and Instrumentation
For the objective to be completed, the payload will determine the chemical and mineralogical structure of collected soil samples. The current plan for this is to use an XRF scanner, similar to the Niton XL3t GOLDD+, modified to interface with the payload's circuitry. Specialized probes, with designs similar to the CHOMIK or the KRET designs (originally intended for the Phobos-Grunt Mission), will be launched from the main payload to collect soil samples. These probes will then follow one of two alternative concepts described further below.
Table 1. Science Traceability Matrix
Science Objective / Measurement Objective / Measurement Requirement / Instrument SelectedComposition of Mercury’s Soil / Chemical Composition / Short burst operation, power supply, etc. / XRF Scanner
“ / Mineral Composition / “ / XRF Scanner
Table 2. Instrument Required Resources
Instrument / Mass (kg) / Power (W) / Dimensions (cm) / Data Rate (bps)XRF / ~0.8 / ~1+ / Unknown* / Not Yet Verified*
*The companies we contacted were non-cooperative in giving us specifications on the parts that will be necessary. All we have is the outer dimensions of their entire product, which would be a gross overestimate of what we’d need because it includes large amounts of plastic casing and human interface. We assume that the device can be modified to fit within our probe design for our final project.
3.0 Alternative Concepts
Both of the concepts will deploy via a pneumatic helium powered launcher. The primary concept for the science objective is to keep the scanning and data measurement equipment safely stored on the lander, while sending out tethered probes to collect samples and bring them back for analysis.
The secondary concept is to send out smart probes as projectiles in various directions that will take data and radio it back to the main payload, where it will be transmitted back to Earth. This secondary design has the advantage of not being tethered and thus being able to travel farther from lander. However, it requires a radio device that will add its own difficulties to the project, including possible electromagnetic interference from the sun.
Figure 1. Group 1 Concept
Table 3. Mass and Power Budget for Group 1 Concept
Component / Number / Mass (kg) / Power (W) / Total Mass (kg) / Total Power(W)XRF / 1 / ~1.3 / ~2+ / ~1.3 / (~2+)
Tether Line / X / Undetermined / N/A / Undetermined / N/A
Figure 2. Group 2 Concept
Table 4. Mass and Power Budget for Group 2 Concept
Component / Number / Mass (kg) / Power (W) / Total Mass (kg) / Total Power (W)XRF / X / ~1.3 / ~2 / ~1.3X / (2+)X
Radio Transmitter / X / Unknown / Unknown / Unknown / Unknown
********ALL DATA IN THE TABLES REFLECTS WHEN THE IDEA WAS CONSIDERED, NOT REVISED.********
4.0 Decision Analysis
We completed a decision analysis via a F.O.M. (Factor of Merit) approach. We defined a weighting number (1, 3, or 9) for each factor that is important in our decision. We then assigned a number (same options) for each concept, with 1 being the Least Preferable and 9 being Most Preferable for each category. We then multiplied the number for each concept by its corresponding weighting, added the results for each concept, and declared the chosen concept to be the one with the greatest total. As seen in the table on the next page, the tethered design is the chosen concept. We also made alterations to this design; details are stated in the appropriate section.
Table 5. Payload Decision Analysis
Figure of Merit / Weight / Group 1 Concept / Group 2 ConceptPower / 3 / 9 / 1
Data Rate / 3 / 9 / 3
Reliability / 9 / 9 / 3
Deployment Efficiency / 3 / 3 / 9
Mechanical Failure / 3 / 9 / 3
Number of Probes / 1 / 1 / 9
Total:172 / Total:84
5.0 Payload Concept of Operations
Our payload will be transported via the UAH IPT team’s lander to Mercury’s surface, there, the main payload (launcher turret) will launch the probe outside of the lander’s “splash zone” of contamination. The probe will then collect data via an XRF scanner and transfer it back through a tether line to the lander’s communications. The probe will then be reeled back to the turret via a motorized system (included in budget for our turret design), where it will repeat this process for more data. If the first probe should fail, there will be a second one as a back-up attached to a secondary barrel.
6.0 Engineering Analysis
Assumptions:
• Ideal gas behavior (Should be approximately correct because of Helium’s nature);
• Adiabatic expansions/compressions (no heat transfer to environment, either insulated or too rapid);
• No gas leaks during the process;
• Friction is negligible;
Barrel has constant cross-sectional area across its length.
If all of these assumptions hold, then:
P1V1y=PVy→PV=P1(V1V)y (Rule of Adiabatic processes for ideal gases)
Fx=APx=AP1x1xy (From P=F/A)
Where x sub 1 is the length of the pressure chamber and x is any arbitrary length from x sub 1 to the end of the barrel.
Now, by the definition of work, and by the work-kinetic energy theorem:
W=x1lFxdx=x1lAP1x1xydx=AP1x1y1-yl1-y-x11-y=KE (Definition of work and the work-kinetic energy theorem)
P1=1-yKEAx1yl(1-y)-x1(1-y)=1-yKEAx1yl(1-y)-x1 (Solving for P sub 1)
This gives the starting pressure needed for any set conditions.
Now, taking a derivative with respect to pressure chamber length, holding all other values constant, and setting it equal to zero to find an x sub 1 that gives an extreme value.
dP1dx1=-1-yKEAyx1y-1l1-y-1x1yl1-y-x12=0→yx1y-1l1-y-1=0
x1=1yl1-y1y-1=y-1y-1l (Approx. 0.47*0.44 = 0.21 m)
This yields the optimal pressure chamber length relative to the total barrel.
7.0 Final Design
Because our scanner can scan at a small range, and we have a tether for power, we no longer plan to use the mole designs mentioned earlier. Instead, we plan to design our own housing for the probe that will suspend the scanner at an appropriate height and scan the ground’s surface directly. This probe will be shaped like a rectangular box with rounded edges, so it will only stabilize on one of two faces. Both faces will have an opening for the scanner, and the scanner will be free to rotate to either face so it can scan the ground.
This probe will be launched by a helium powered pneumatic launcher-turret. The scanner on the probe will determine the composition of the surface of mercury via x-ray fluorescence and transmit this data back to the Earth through the UAH IPT team’s communications by a tether line.
Figure 4. Payload Final Design
Table 6. Mass and Power Budget for Final Design
Component / # / Mass (kg) / Power (W)* / Total Mass (kg) / Total Power(W) / Data Rate(bps)
XRF / 2 / ~0.8 / ~1+ / ~1.6 / (only one active at a time) / **
Tether Line / 2 / ~0.0298 / N/A / ~0.0596 / N/A / N/A
Arduino UNO R2 Micro-controller / 2 / 0.0239 / 0.2-2.8 / 0.0478 / (only one active at a time) / Arbitrary (set by a program)
DE-ACCM Accelerometer / 2 / 0.0009 / 0.006 to 0.01 / 0.0018 / (only one active at a time) / N/A
Turret Design (our own) / 1 / ~3*** / ~5*** / ~3 / ~5 / N/A
Probe Casing / 2 / ~0.0015*** / N/A (just shell) / ~0.0030 / N/A / N/A
Total Mass of all equipment:~4.7kg
*All powers are only while the device is running. Many of the devices will not be on at the same time all together.
**Data rate could not be determined due to lack of resources. We assume that it can sync with the micro-controller.
***These are the roughest estimates you’ll probably see. We tried to estimate high, however, so even if the estimates are wrong we should still fall under budget if we were on the right track.
Page - 2